Pick-up your nametag, tickets and program overview guide at the registration desk (see map) from 12:00-20:00 on Sunday and 07:30-19:00 on Monday, and 8:00-19:00 on Tues.-Thur.;
Invited Persons: IIAV Officers and Directors, Observers, & Other Guests Making Presentations
Agenda: 1) Welcome. Eleonora Carletti, President
2) Adoption of Agenda. Eleonora Carletti, President
3) Approval of Minutes of Last Meeting. Eleonora Carletti, President
4) Report on Election of Officers and Directors. Eleonora Carletti, President
5) Report on New IIAV Honorary Fellow. Eleonora Carletti, President
6) Treasurer’s Report. Zhuang Li, Treasurer
7) Report on IJAV and ICSV’s Papers Abstracting & Indexing. Jorge Arenas, IJAV Editor-in-Chief
8) Report on Society Relations. Marek Pawelczyk, Vice President for Professional Relations
9) Report on IIAV Committee Activities. Eleonora Carletti, President
10) The activities of the Bylaws Revision Committee Eleonora Carletti, President
11) Honours and Awards Committee. The Sir James Lighthill award winner(s). Special awards for scientific achievements. Eleonora Carletti, on behalf of Len Gelman (Chair)
12) Nomination of Dr. Jiri Naprstek for IIAV Honorary Fellow, Marek Pawelczyk, Vice President for Professional Relations
13) Publications Committee Report. Adrian Brown, Chair
As a little (ICSV26 accountant would say otherwise) token of appreciation for their hard work and dedication, the local organizing committee of ICSV26 is offering a fine reception and dinner to all its Theme Area Chair, Sessions Chairs, Keynote speakers, and Local Organizing Committee members as well as to IIAV Executives and Directors, their guests and observers, and their accompanying persons.
NOTE: Tickets for that event are included within delegate's nametag, when applicable
ICSV26 has arranged to have Speaker Ready Rooms in room "Outremont 1" (see map) to allow presenters the opportunity to view their presentations and to obtain any technical support they might require prior to their scheduled sessions. Technicians will be present in the Speaker Ready Rooms to assist.
Even if you have uploaded your presentation in our online system, you are still required to check into the Speaker Ready Room to review your presentation with the technician.
Pick-up your nametag, tickets and program overview guide at the registration desk (see map) from 12:00-20:00 on Sunday and 07:30-19:00 on Monday, and 8:00-19:00 on Tues.-Thur.;
An extensive exhibition (see floor map) of sound and vibration measurement instrumentation, equipment and noise and vibration control technologies is featured in St-Laurent 1&2 rooms Monday-Wednesday 8:30-17:00. Lunch desserts and coffee breaks will be served in that exhibition area.
1. Welcome to ICSV26 – 10 min Prof Jérémie Voix, ICSV26 General Chair Dr. Franck Sgard, ICSV26 Scientific Chair The numbers, the hard work and the satisfaction.
2. 25 years since ICSV03! - 8 min Prof. Malcolm Crocker, Executive Director IIAV The story of a quarter-century journey
3. IIAV Welcome Speech - 5 min Prof Eleonora Carletti, President IIAV
4. IRSST Welcome Note – 5 min Mrs Marie Larue, IRSST Director What is IRSST. Its involvment in ICSV26. The recognition it gained (Prix ambassadeurs, etc.)
5. CAA Welcome Note – 5 min Prof. Umberto Berardi, Editor in Chief What is CAA.
6. Housekeeping and Keynote introduction – 5 min Prof Jérémie Voix, ICSV26 General Chair Dr. Franck Sgard, ICSV26 Scientific Chair The rest of your 1st day. Our keynote.
Porous materials everywhere in the Universe! At the Planck length scale (10e-33 cm), physicists describe space as a quantum foam. At the cosmic scale (> 10e26 cm), galaxies are distributed according to the structure of a cosmic foam. Closer to the human scale, natural porous media are formed (honeycomb, soil, rock, bone). This omnipresence and the remarkable properties of these media have long fascinated the engineers who have inspired them to create porous materials adapted to different applications of mechanical engineering: sound absorption and insulation, cooling of electronic components, implants and substitute bones, light structures, absorption of impacts, porous electrodes for fuel cells, filtration and purification of water. After an introduction of the porous media at these different scales, this presentation gives an overview of the porous materials used in noise control. This overview presents conventional and unconventional porous materials. Man manufactures conventional porous materials based on conventional chemical and physical processes and the mimicry of natural porous media. However, it seems that these materials have reached the physical limits of sound absorption and sound insulation. Moreover, their use becomes an important issue in terms of sustainable development. To obtain acoustic properties that go beyond those of conventional materials, and materials more in line with sustainable development, man must intervene by structuring the material and choosing materials safer for the environment. Metamaterials and materials designed using an ascending or a multiscale approach belong to the family of unconventional materials. Similarly, materials based on natural fibers and recycled materials belong to this family. The presentation mainly focuses on this family of materials and the underlying design methods, while presenting examples of applications and comparisons to conventional materials. In parallel, what makes a porous material a good acoustic absorber will be discussed and analyzed.
Raymond Panneton is a professor-researcher in the Department of Mechanical Engineering at the Université de Sherbrooke since 1998. His research program focuses on the modeling, characterization and optimization of porous acoustic media. More specifically, he explores the relationships... Read More →
Buried piping systems play a very important role in modern societies, especially in transporting fluids and gases for everyday use. Within these systems, plastic pipes have been widely used in recent decades because of their relatively low failure rates compared against other type of pipes in service. Unfortunately, the records of these underground utilities are often inaccurate and incomplete. Problems associated with inaccurate location of buried pipes are exacerbated in the presence of rapid development of urbanization, which increases both the difficulty and economic costs of excavation work. In response to this, trenchless technologies have been developed and shown effective in locating buried piping systems. In particular, acoustic detection method is considerably promising in locating plastic pipes. By applying acoustic excitation on one part of the pipe and analyzing the ground surface vibration, the location of the buried pipe can be determined. Whilst there are existing studies relating to plastic water pipes in this field, limited research has been carried out on buried gas pipes detection. Based on the model of buried fluid-filled pipe, an analytical model of buried plastic gas pipe will be studied in this paper. The analytical solution and numerical simulation results of the mode waves will be presented and their characteristics will be analyzed. Moreover, in our proposed model, the ground surface vibration directly above the pipe will be expressed as the result of radiated conical waves resulted from the propagation of the specific mode wave inside the pipe. Hence, there is no need to approximate conical waves as plane waves, which will make our analytical solution more accurate. This work can provide theoretical insight to acoustic detection techniques used for locating buried pipes.
RESEARCH ON TRANSIENT TORSIONAL VIBRATION OF PROPULSION SHAFT WITH PARALLELING ENGINE UNDER TORQUE IMPACT, School of Energy and Power Engineering, Wuhan University of Technology, Wuhan, China
In order to design the exterior sporty warning sound for EVs without annoying the drivers and passengers, a phonating solution coupling acoustical vehicle alert system (AVAS) and active noise control (ANC) is proposed. Considering the relevant standards of warning sound, the frequency range of cancellation and the sound quality inside and outside the vehicle, a phonation strategy of the strengthened warning sound is designed, which combines multiple low-frequency characteristic sounds with the high-frequency sound required by the regulations. Meanwhile, the active noise control is carried out for low order noise within 300Hz. The test results demonstrate that the exterior warning sound not only meets the requirements of sound pressure level, but also resembles the booming of sports car. Owing to the active noise control, the interior booming issue caused by the exterior warning sound is solved simultaneously so that the subjective assessment of the interior sound is improved greatly.
The blades of wind turbine are the most critical parts of the wind turbine system, which con-tribute to noise generated by wind turbine due to excitation from air streams across them. In this study, the effect of various design factors for both horizontal and vertical wind turbines is simulated and analysed in order to determine the most critical design factors. The knowledge of such information is important to control and reduce the noise level from wind turbine. The simulation results show that the pitch angle, which is the summation of angle of attack and twist angle, along with the height of air foil section have the most significant effect on the overall sound pressure level. The results also reveal that the overall sound pressure level is least sensitive to the size of the blade and shell thickness.
Age has been demonstrated to alter auditory processing, as well as having an interaction effect with (urban) environmental perception. And yet, age is not systematically considered when designing and evaluating urban soundscapes. The present study used an on-site questionnaire to measure the perceived quality of two different newly designed urban spaces (N = 103 and 438, respectively), which was analyzed as a function of participants' age. Participants were asked to rate the soundscape in terms of eight well-known soundscape indicators (SSQP) including pleasant, chaotic, and vibrant, along with reporting the perceived loudness and soundscape appropriateness, their noise sensitivity, and age. The fraction of participants younger than 30 was 60~% at site 1, and 51~% at site 2, however, age distribution did not differ significantly between the two sites. In terms of the sound environment, site 1 was more shielded from road traffic while site 2 was next to a relatively busy city road; mean pleasantness across all participants was rated as 4.5! and 3.1!, respectively, on a 5-point scale. For both sites, and in line with the literature, noise sensitivity increased significantly with age. At site 1, only monotonous decreased with increasing age. For site 2, however, increasing age had a stronger effect, such that people rated the soundscape significantly louder, more chaotic, less calm, and less appropriate. It could be hypothesized that especially in poorer soundscapes, age becomes a more important factor in perceived quality. Conversely, for a younger population, a quiet area could be too quiet. From this comparison, no hard conclusions can be drawn because different participants have been questioned at each site and there might be other underlying confounders steering these results. Nevertheless, further research should clearly take age into account, and collapsing soundscape evaluations across age groups is certainly not supported by these findings.
This paper deals with dynamic behavior analysis of construction materials subjected to technological actions in order to obtain a suitable compaction degree. Direct interaction between working body and materials both at the input point and at overall domain that acquire dynamic changes, frames the main objective of this study. We present a basic approach regarding nonlinear models intended for computational dynamics of vibratory compaction process in order to evaluate the consolidation level, taking into account the complex rheology of terrains and the relative variable dynamic load in time for each point inside the working area. Numerical simulations have developed for two nonlinear models that contain conservative and complex dissipative rheological elements representing the cohesive and non-cohesive ground. The results put into evidence the cumulative effect of the successive passes and the consolidation in depth all over the monitored area.
Mohammad Rafiee received his Ph.D. degree in Mechanical Engineering from the University of Ottawa in 2018. Currently, he is a Postdoctoral Fellow at Polytechnique Montreal in Canada. His research interests are primarily focused on the development of advanced composite materials, smart... Read More →
The ship propulsion shafting with paralleling engine withstands various kinds of torque im-pact during different operation conditions. The traditional frequency domain calculation method cannot calculate the shafting response under the torque impact load. In order to obtain the dynamic response of the propulsion shafting, a multi-mass point model for the calculation of transient torsional vibration of the propulsion shafting is established by the classical lumped parameter method. In order to obtain an accurate calculation model, damping and ex-citation are specifically studied in the paper. Based on the Newmark-β method, the time-domain torsional vibration calculation process of the propulsion shafting is proposed, and the dynamic response of the shafting during the impact is obtained. Taking the electric propulsion system with two paralleling motors as an example, the transient torsional vibration simulation is carried out. The influence of phase angle between different loads on the dynamic response is discussed, which provides a reference for calculating the transient torsional vibration of the propulsion shafting of the combined power plant.
The relatively efficient and accurate Adomian modified decomposition method (AMDM) is used in this paper to investigate the free vibrations of Euler-Bernoulli beams, with a single section discontinuity present, and resting on a two-parameter elastic foundation. The discontinuity can stem from a geometric change in the beam cross-section, a sudden material change within the beam or a sudden change in foundation material properties. The proposed AMDM is used to analyze the vibration of beams using a recursive approach. The solution is obtained by solving a set of algebraic equations with only three unknown parameters, and the method can easily be extended to obtain approximate solutions to vibration problems for any type of non-uniform beam. This work develops a fast and accurate method of calculation, with the ability to change boundary conditions easily. Analytical calculations are presented for natural frequencies and associated mode shapes, which are compared with experimental and calculated results found by experimental and other calculation methods reported in the literature.
Associate Professor, Rose-Hulman Institute of Technology
Professional interests include undergraduate engineering education, finite element modeling, ground-borne vibrations, vibrations of musical instruments, and dynamics of toys.
An acoustic waveguide consisting of a cylindrical tube with fitted thin rigid rings whose inner radius decreases appropriately causes incident acoustic waves to slow down, resulting in considerable absorption in the cavities between the rings. The absorption becomes greater towards the end of the waveguide, where the wave speed becomes very small and the waves are spatially concentrated. Such a system demonstrates the so-called 'Acoustic Black Hole' effect. In this paper, the reflection coefficient of an acoustic waveguide whose ring inner radius has either a linear or a quadratic profile is calculated, using a Transfer Function method. A Transmission Line model is also used, which forms a low-frequency approximation to the Transfer Function method. Different geometrical assumptions for the cavity between two consecutive rings and for the core of the waveguide are considered for both methods. The results are compared with experimental ones from the literature. The numerical results predict the general characteristics of the reflection coefficient. For the linear case, the fluctuations of the reflection coefficient are also predicted over part of the spectrum.
The optimization of stealth (response to an active sonar) and discretion (noise radiated from the vehicule) performance for underwater vehicules at very low frequencies is currently an important research topic in underwater acoustics. One classical way to improve acoustic performance is to cover the hull with specific acoustic coatings. This talk focuses on another approach, which is to introduce slight modifications of the hull internal structure. The results that are presented have been obtained in the frame of a project with the ANR French agency, supported by the french DGA. Classically, in order to withstand hydrostatic pressure, the hulls of underwater vehicles support periodically distributed rib stiffeners, which give rise to typical phenomena of acoustic diffraction at low frequencies and thus allow the detection and identification of these vehicles (Bloch-Floquet waves and Bragg diffractions). To overcome these problems, we propose to attach to a part of the stiffeners resonant systems whose characteristics vary randomly from one stiffener to the next. The frequency signature created by the network of stiffeners equipped with resonators is thus jammed and attenuated, improving stealth at low and very low frequencies This paper first presents analytical, numerical and experimental results obtained on a plate equipped with simple rib stiffeners, associated or not with resonators. Stealth performance diagrams highlight the usefulness of the proposed rib attachments. Then, optimization algorithms are used to choose the parameters of the resonators and their distribution in order to minimize a given objective function. The extension of this concept to the discretion problem is finally discussed.
The operational transfer path analysis methodology is applied on a side-by-side recreational type vehicle to rank vibro-acoustical sources contributions to the overall sound pressure level at driver's ears. The truncated singular value decomposition technique (TSVD) is used to establish the transmissibility matrix and to reduce measurement noise and cross-talk influence. The influence of post-processing parameters such as frequency resolution, overlap and TSVD threshold on the synthesized acoustic response is investigated. The usefulness of the methodology is demonstrated by validating noise reduction solutions resulting from modifications to either the dominant sources or weakest identified transmissibility paths.
Attiko Metro S.A., in view of the further development of the Athens Metro network, has fully initiated the new extension of 7.6 km, for line 3 "Haidari to Piraeus Dimotiko Theatre" towards "University of Piraeus" (forestation), connecting the major Piraeus Port with "Eleftherios Venizelos" International Airport. During the operation of this major urban subway rail transit system, vibrations are expected to be generated when transmitted through the soil and cause vibrations in nearby buildings. In urban areas, these vibrations are a consequence of the vehicle forces acting from the wheels onto the track in local defects. The transmission of ground-borne vibrations from a subway urban rail transit systems inside adjacent buildings is mainly governed by the transfer function (TF) of vibration diffusion from the tunnel wall or invert towards the soil surface in the façade and the interior of two sensitive neo classic buildings of great aesthetic and historical value e.g. the Municipal theatre of Piraeus and the building. During the construction of the extension of Athens Metro to Piraeus in both areas a methodology was proposed using as source of vibration : (a) the TBM operation (considered as linear source), and (b) a point source based on an impact force at the tunnel invert. Both set ups were tested in the above sites in order to determine the necessary TF of the rail vibration diffusion inside the given geological media demonstrating the vibration attenuation values in 1/3 octave band analysis. The proposed metrological approach aims to ensure a high accurate estimation of the expected vibration and ground borne noise levels in each receptor, during operation, and assess possible negative effects on local communities from the metropolitan railway–induced ground vibrations.
The propagation of acoustic waves in an air-filled pipe system with periodic membrane-type Helm-holtz resonators is studied theoretically. And the band structure of infinite periodic cells and trans-mission loss of periodic cells are calculated by the finite element method. Finally, we find that the band and transmission loss can be tunable significantly by adjust the tension. It is useful to obtain a low-frequency and broadband gap in piping systems.
In the study of acoustic properties of porous metal materials at higher temperatures, the mechanism of sound absorption inside or outside of porous materials may involve physical fields' couplings such as acoustic, and temperature fields. The results obtained here are mainly related to the design of an improved experimental test system at high temperatures and essential acoustic parameters of porous materials - porosity, static or dynamic flow resistance, kinetic viscosity, and so forth - also including physical properties of free air. In the light of special requirement for the sizes of a developed test bench in authors' laboratory, a two-dimensional (2D) geometric model with scale of 1: 1 was established by employing software COMSOL. Some different simulation models are presented by applying sound absorption models embedded in COMSOL for porous media. After that the sound absorption properties of several porous metals are evaluated and compared with tested data. The work in this paper will provide a guide to the establishment of more complicated three-dimensional (3D) acoustic models, and also give an important reference for the improvement of existing experimental test system.
Starting from the application of Alberich anechoic layers, the cavity structure has been widely stud-ied and applied in the field of underwater sound absorption. The sound absorption performance of the structure is closely related to structural parameters such as cavity radius and height. The struc-ture with large cavity radius has good low-frequency performance but narrow frequency band, and performs poorly in high-frequency band; and the structure with small cavity radius is just opposite. This makes it difficult to combine low-frequency and broadband sound absorption performance simultaneously with a single-scale cavity structure. To solve this problem, a multi-scale cavity structure was designed based on the sound absorption characteristics and mechanism of cylindrical cavity. For cavities with different radius, the sound absorption bands are different. Designed with appropriate structure and parameters, different cavities could be combined together to achieve high-efficiency sound absorption in a wide frequency band. The finite element method was used to cal-culate theoretically and simulate the structure. With parallel models of multi-scale cavities con-structed, the influence of the spatial arrangement of the cavities and the structural parameters on the sound absorption performance were studied. The results show that the multi-scale cavity model de-signed in this paper owns broader band compared with single cylindrical cavity structure.
Porous materials (PMs) are known to have been used since the development of powder metallurgy. The main fields of PM include: filtering, node sealing, cooling, vibration and sound suppression. In particular, PMs are used to muffle the exhaust of technological equipment. PM samples are manufactured by melting, pressing, and also by chemical means, while the structure is difficult to be reproduced again with a high degree of accuracy. Such a 3D printing method as selective laser melting (SLM) allows obtaining samples with a low deviation of the structure (up to 13%) in a wide range of porosity P=0.3...0.7. The increase in sound absorption factor and expansion of the frequency range can be achieved by selecting the effective porosity and pores tortuosity coefficient. The high coefficient of normal sound absorption and high manufacturability determine the popularity of application of samples obtained by 3D printing methods in noise suppression designs
This paper focuses on the problem of be unable to have both high frequency and low frequency sound absorption performance for ordinary honeycomb sandwich structure, the honeycomb sandwich structure of adjustable absorption frequency with internally installed micro perforated plate is designed in this study. In order to improve the sound absorption performance of honeycomb sandwich panel structure, a micro-perforated panel was installed inside the honeycomb sandwich panel structure. Some micro-perforated plates which can change the perforation rate are arranged periodically to achieve the purpose of changing the sound absorption performance of honeycomb structure. The numerical simulation shows that the structural design idea of honeycomb sandwich structure with adjustable absorption frequency is feasible.
Thermal reduction by enhancing heat-carrying phonon scattering can improve thermoelectric performance. In this paper, the phonon transport in two-dimensional nanoscale thermoelectric phononic crystals is investigated by frequency-dependent Monte Carlo simulations. The dispersion curves of thermal wave propagating in phononic crystals are calculated based on a nonlinear regression model. And the influence of geometric parameters on dispersion curves and phonon transport is discussed in detail. The results indicate that the pore configuration and porosity have remarkable influence on the phonon transport. In addition, the dispersion curves are primarily controlled by the pore placement and temperature. This study offers useful suggestions for fabricating these materials with heat isolation and reduction.
Lamb wave propagations in a semi-infinite plate and scatterings by free edges have important practical applications, such as non-destructive inspections in aircraft wings and underwater submarine hulls, and damping of unwanted vibrations, etc.. Real or complex resonances and associated localized modes occur when free edges are pr sent. The reflections and (resonant) scatterings at and near these resonant frequencies might play important roles in the aforementioned applications. In this work, we study the absorption of the edge in a homogeneous, isotropic semi-infinite visco-elastic plate when the symmetric S0 mode is incident. Using critical coupling, we show that by adding a small part of the loss in the elastic plate, total absorption by the free edge can be realized.
The thickness of the micro-perforated plate (MPP) used in sound absorption usually does not exceed 1.5mm due to the difficulty of punching. A dense honeycomb core is presented to replace the micro-perforated plate to improve the sound absorbing performance in low frequency. The perforation ratio of the honeycomb is controlled by punching large holes in a thin face plate which is fixed to the honeycomb core. This structure is named low frequency honeycomb sound absorber (LFHSA) in this article. The sound absorbing performance of LFHSA is measured in an impedance tube. The LFHSA and back space in a limited 100mm depth show a good sound absorbing performance in frequency range 100-300Hz.
Interior noise of A battery electric vehicle in high speed is studied in this paper. From the per-spective of practical engineering application, the interior sound pressure level (SPL) of the electric vehicle under the working condition of 30m/s is analyzed based on the Corcos model, the Diffuse Acoustic Field (DAF) model, the boundary element method(BEM) and the statisti-cal energy analysis(SEA) method. The accuracy of the methods was verified by comparison with the experiment. The influence of different thickness of side window glass on the SPL of the driver's head cavity is analyzed, which can guide the design of body material parameters and sound package.
The control of rumbling noise is one of the major strategic targets of interior sound quality inside the cabin of a passenger car. To effectively control rumbling noise in a passenger car, the transfer path of the rumbling noise should be initially identified. It is known that the major source of this noiseis the combustion force of an engine. The combustion force excites the engine and induces vibrations of the powertrain. These vibrations are then transferred to the body of the vehicle via its structural transfer path. Moreover, the vibrations of the vehicle's body emit internal vibro-acoustic noise. This noise is often referred to as the rumbling noise due to the structural borne path. If there are structural resonances among the structural paths such as the engine, transmission, mount bracket, suspension, and the vehicle's body, the rumbling noise could be amplified. To identify the major resonances of the structural transfer path, classical transfer path analysis (CTPA) has been traditionally utilized. The method has a significant limitation in that it is necessary to decouple the substructures to obtain the contact force between individual components and to identify the transfer path of the structure-borne sound. Recently, blocked force transfer path analysis (BF-TPA) was introduced and this approach does not require the decoupling of the substructures. In this study, we identify the structure-borne path of rumbling sound based on blocked force transfer path analysis (BF-TPA) in a passenger car. In addition to identification, the passive control method for rumbling sound is presented.
This study deals with the magnetically levitated capsule train running through the sub-vacuum. Due to the low air resistance and friction between capsule and tube, the capsule train can theoretically reach over 1,000km/h speed. As levitation, the superconducting electrodynamic suspension(EDS) technique is used in the capsule train. Since EDS levitation inherently has very small electromagnetic damping and non-linear magnetic stiffness, the vibration caused from outer disturbance such as guideway irregularity should be carefully investigated and then reduced by using additional devices for ride comfort improvement. In this study, firstly the capsule train model is introduced and the dynamic analysis including non-linear magnetic stiffness is conducted. Then, as ride comfort improvement method, the semi-active suspension between carbody and bogie is applied and the effectiveness is examined. Lastly, through the hardware-in-the-loop simulation(HILS) system composed with the capsule train dynamic model and the real actuator as semi-active suspension, performances is experimentally examined.
Noise and vibrations from an engine form important benchmarks from customer satisfaction view while choosing an automotive car. There are several sources of noise and vibrations emissions from an engine installed in a car. Some of these sources include: combustion noise, exhaust flow noise, aero dynamic noise as well as noise due to mechanical motion of parts etc. Each of these sources of noise depends on some factors which includes fuel injection parameters, design of engine, lubrication regime, operational parameters like speed and load. Motion of piston skirt form a major source of noise and vibrations in an automotive car. Apart from normal reciprocating motion of skirt, there can be secondary motion along the lateral direction. This motion is known as piston slapping motion. There are several factors that affect this lateral motion of skirt which includes the design of piston, type of lubrication as well as the speed of engine. In the present work a numerical model of lateral motion of skirt has been proposed. The proposed model was applied for a dual cylinder water cooled diesel engine. Effects of various design parameters like piston-liner clearance, skirt length, mass of skirt, and location of piston pin has been analyzed. The proposed methodology can be used to optimize the design of skirt in order to reduce the noise and vibration emissions arising due to lateral striking motion of skirt with liner.
Friction-induced vibrations and noise are an issue of increasing relevance in the automotive sector as interior sound levels have diminished in recent years. Especially, stick-slip vibrations between surfaces in relative tangential motion is a topic of high interest. We present a meth-odology for measuring and evaluating the displacements between two component surfaces at relevant contact locations in vehicles with piezoelectric acceleration sensors. The method is exemplified for the automotive door and side frame relative motion in the ceiling area. By means of a comparison with laser triangulation sensors we show that the displacements are in the sub-millimeter range in this area. Based on the knowledge on the actual relative displace-ments at the door sealing system the relative motions are reproducibly simulated on a laboratory test setup. Level-scaling and spectral filtering are used to examine their influence on fric-tion-induced vibrations of a characteristic component pair. It is shown that downscaling of the displacement level and, therefore, lower relative velocity between the components, leads to more stick-slip vibrations and louder noise.
The European Organization for Nuclear Research is an organization that operates the largest particle physics laboratory in the world. CERN's main function is to provide the particle accelerators and other infrastructure needed for high-energy physics research – as a result, numerous experiments have been constructed at CERN through international collaborations. Many activities at CERN currently involve operating the Large Hadron Collider (LHC) and the experiments for it which most of them are situated in the 27 km circumference circular tunnel around 100m under the ground. One of the main reasons for this location is requirement of stability for the beam. This means that vibration conditions must be taken into account. Additionally, the High Luminosity upgrade of the LHC (HL-LHC) will require unprecedented orbit stability and the effect of seismic noise might become a relevant source of luminosity loss. Many studies have been conducted in the past to characterise the actual ground motion in the LHC tunnel, and recently a few geophones have been installed to permanently monitor the ground stability in two LHC locations. The CERN seismic network, equipped with both broadband and strong-motion seismometers, allows now for continuous monitoring of vibratory conditions. Moreover, in the past, due to transfer function approach the impact of heavy machinery work on the induced oscillation of the magnetic centre was calculated. Currently, additional two surface monitoring stations were placed at the sites where new shafts are being excavated. This allow for constant monitoring of civil engineering works and impact of specific machinery on vibration levels in the tunnel and connect specific events to the machinery working on the site. Full characterisation of the equipment impact will allow to foreseen future vibration problems for LHC and its upgrades depending on the activity on the surface.
This paper presents a study inspired from the research project on the Active Control of Trolleybus Current Collection System (ACTCCS) in Loughborough University (UK). The goal of the study is to address a fundamental issue of varied static stiffness of spring under pre-load. The derivation of varied static stiffness is based on conservation of energy law. A special parameter of Jing-Ar Stiffness (ratio of pre-load to excitation) is introduced into the dynamic model and simulation. As an example, the modelling and simulating of a quarter two-axle railway vehicle are carried out during the vehicle going through regular joint gaps of railway track. The comparison of the simulation results between the varied static stiffness and existing static stiffness is exhibited in conclusion of the paper.
The subsonic Capsule Train adopts the non-contact magnetic levitation system with SCM. In order to investigate the effect of the subsonic Capsule Train on the driving dynamic characteristics and ride quality of the vehicle, we investigated the dynamic characteristics of the Capsule Train according to the traveling speed based on the initial concept of the subsonic Capsule Train. Simulation was performed by deriving an equation consisting of a dynamic model with 15 degrees of freedom for vertical, lateral, roll, pitch, and yaw direc-tions for a Capsule Train consisting of one body and two bogies. In this study, only the vi-bration in the vertical direction was addressed. The side EDS (Electrodynamic Suspension) magnetic levitation trains system, which has a similar concept in the case of Capsule Train levitation stiffness and guidance stiffness, was applied. The simulation was carried out for the speed range from 210km/h to 1080km/h. Based on the simulation results, the change of the vertical displacement in the time domain was confirmed, and the frequency analysis were performed. The results of frequency analysis showed that the dominant frequency components were 0.9Hz, 14.5Hz and 15.01 Hz in front/rear bogie and 1.1 Hz and 1.64Hz in carbody.
The mitigation of vibrations accompanying the running urban rail transport must be done effectively using the patented Vibration Energy Harvesting Dampers designed to provide dual results: reduction of harsh vibrations and producing the additional electrical power. The proposed technology is the implementation of Vibration Energy Harvesters combined with re-tuning mass damper. The device could be successfully introduced in rail supports (crossties), vehicle bogies and other vibrating components of urban rail transport. The approximate estimates for crossties show that the installations of vibration energy harvesters allows get around 25 kW per one running Toronto TTC Subway train, Paris Metro train or 20 kW per one running Calgary C-train. It is necessary to highlight that these kilowatts now are known as lost energy and never used. The analysis of dynamical performance of patented devices is presented in application to components of the vehicle bogies and rail supports. The experiments illustrate the compliance with theoretical predictions and efficiency of proposed Vibration Energy Harvester Damper operating mainly in low frequency interval.
Diseases occurring near the vocal cords, such as laryngeal cancer, often cause voice disturbance as an initial symptom. As an acoustic diagnostic method for such diseases, the GRBAS (grade, roughness, breathiness, asthenia, strain) scale is widely used, but its objectivity is not well estab-lished. Instead, more accurate diagnosis may be possible by capturing the waveform of the volume velocity at the vocal cords (the vocal sound-source waveform). The aim of this study is to enable diagnosis of diseases near the vocal cords by identifying the sound-source waveform from voice measurements. In the proposed method, an analytical model of the vocal tract is used to identify the sound source. The air inside the vocal tract is modeled as concentrated masses connected by linear springs and dampers. The vocal tract shape is identified by making the natural frequencies of the analytical model correspond to the measured formant frequencies. The sound-source wave-form is calculated from the analytical model by applying the measured voice (sound pressure) to the lip position of the identified vocal tract. To assess the validity of the proposed method, an ex-perimental device was made to simulate the human voice mechanism. The device is equipped with artificial vocal cords made of a urethane elastomer that are self-excited by air flow. The sound pressure equivalent to the voice was measured using a microphone set at the lip position of the experimental device, and the flow velocity at the artificial vocal cords was measured using a laser Doppler velocimeter (LDV). To assess the model's validity, the sound-source waveform iden-tified from the measured sound pressure was compared with the waveform measured using the LDV.
In this paper different cost functions are studied for the optimization of FIR filters as minimum variance controllers in active noise cancelling headphones. The resulting controllers are implemented in a headphones prototype and their attenuation performances are measured using a dummy-head. The measurements are then compared and evaluated in terms of psychoacoustic objective metrics, in order to establish which one of the cost functions relates more closely to the human perception of noise.
The issue of noise pollution caused by wind turbines is an important part of the implementation of the Energy transition. In Germany, the number of wind turbine installations has continuously increased over the last years. In 2017, there were 28.675 wind turbines with an installed wind power capacity of 50.777 MW. Therefore, it is particularly important to have clear legal regulations for noise protection by wind turbines. In order to prevent harmful effects on human beings and the environment, various industrial and commercial installations are subject to licensing in Germany. This includes wind turbines with a height of more than 50 m. The legal basis is the German Federal Immission Control Act and the "Technical Instructions on Noise Abatement, TI Noise". Principally, installations subject to licensing shall be established and operated in such a way that this does not involve harmful effects on the environment or other hazards, considerable disadvantages and considerable nuisance to the general public and neighbourhood. In this paper the German regulations for the protection against noise from wind turbines are presented and discussed.
In previous work an experimental evaluation of the acoustic efficiency of the fan combined noise reduction system was performed at the model test facilities. Typically, an acoustic lining is installed in the engine intake and in the bypass duct downstream the outlet guide vanes. In model tests the combined liner reduced the fan noise by 2-3 dB more than the double-layer honeycomb liner of the same length at fan operation modes corresponding to rotational speeds in certification points. In current work the experimental study of the combined liner lattice design parameters was completed in the conditions of model duct with the flow and high SPL. The length of the combined liner was equal to three calibers consisted of 2-caliber double honeycomb liner and the lattice of half-caliber installed upstream and downstream the double honeycomb liner. The distance between lattice plates varied in the range from 5 - 20 mm, the installation angle of the plates varied from 0 to 60 degrees. It is shown that the lattice space changing within 5-10 mm results in additional PWL reduction by 3-5 dB for tonal noise and 2-2.5 dB for broadband noise due to the lattice element. If the lattice spacing is equal to 20 mm the benefit the lattice element installation is less. When the lattice plates installation angle changes from 0 up to 60 degrees relative to axis of model duct the benefit of the lattice element almost monotonously decreases. The maximum difference in the efficiency of the lattice element in this case reaches 2 dB. As a result of the experimental work it could be stated that the best configuration of the studied lattice element turned out to be a lattice of 5-10 mm spacing and 0 degrees of installation angle.
The Environmental Noise Directive requires the member states of the European Union to determine the noise exposure of the population. In addition, the noise action plans should contain appropriate measures to reduce high noise exposure. The noise maps for Germany show high exposure to traffic noise, especially road traffic noise. Therefore, the focus of the noise action plans is on measures like speed reductions, noise barriers, low-noise road surfaces and traffic management. The Directive also require wide public participation in the development of action plans. The competent authorities have therefore taken into account the requests of the public, the legal framework for such measures, the financial framework and the technical requirements. Moreover, the competent authorities for the action plans and the authorities for the implementation of the measures are often not the same. Close coordination between all authorities is therefore necessary for successful noise action planning.
The basic feature of hearing protection devices considered for years is the noise reduction. The noise reduction is main parameter to be taken into account during selection of the proper hearing protection device for a specific noise. This is also valid in the case of impulse noise, which is especially hazardous to hearing. Due to the nature of the impulse noise, measurements of noise reduction of hearing protection devices, are not carried out with the participation of subjects, but with the use of an acoustic test fixture. The numerical calculations may also be used to assess the effectiveness of impulse noise reduction. However, for hearing protection device user it is often necessary to hear important sounds. For safety reasons, it may be especially important to correctly recognise the direction of the auditory danger signal and/or understand speech. The paper presents the aspects of hearing protection and the perception of useful sounds when using hearing protectors. Our studies have shown that depending on the model of hearing protection devices, using level-dependent mode instead of passive mode, may be insignificant or may impair the ability to correctly recognize the direction of warning signal. Individual hearing protection devices are varied, e.g. due to the number of cases of correct indications of the direction from which the auditory danger signal is coming Thus, the choice of a specific model of hearing protection device in addition to noise reduction should also include aspects related to hearing important sounds.
Materials and structures absorbing shock energy are crucial for diverse engineering applications. Conventional materials or structures absorb energy through material destruction or viscoelastic effect, resulting in systems that can be used only once or strongly rate-dependent. Very recently, mechanical metamaterials have been designed in novel geometrics to achieve recoverable energy absorption in elastic systems, opening new avenue for mechanical dissipation of energy. However, numerical modeling of impact response of this mechanical materials is really scarce. Here we build a finite element method (FEM) model of a mechanical metamaterial with negative stiffness elements to simulate the quasi-static and low velocity impact behavior. Quasi-static simulation results agree well with experimental results reported in literature, and low velocity impact results indicate this mechanical metamaterial with multistable negative stiffness elements is ideal for impact energy absorption. The methods and results are helpful for analyzing, designing, and manufacturing of mechanical metamaterials for energy absorption.
Mohammad Rafiee received his Ph.D. degree in Mechanical Engineering from the University of Ottawa in 2018. Currently, he is a Postdoctoral Fellow at Polytechnique Montreal in Canada. His research interests are primarily focused on the development of advanced composite materials, smart... Read More →
In this paper, a labyrinth seal calculation model of the dynamic characteristic coefficient is established, the influence of rotor rotating speed and pressure on the dynamic characteristic of labyrinth seal are numerically analyzed. The calculation results show that the cross stiffness and main damping are important factors affecting the stability of the seal-rotor system; the increase of speed and pressure between inlet and outlet are not conducive to the stability of the system.On the basis of numerical analysis, a research device for air flow excitation test is set up to study the influence of rotor speed ,pressure and other parameters on the vibration characteristics of the rotating subsystem. The experimental results show that the flow induced force increases the deformation of the flexible rotor, makes the stiffness of the rotor system change and changes the critical speed of the system. The flow of gas promotes the whirling of the rotor and makes the running track of the rotor more chaotic.
Vibrational characteristics of layered truncated conical shells are studied. The method of collo-cation with Chebyshev polynomial approximation is applied for solving the problem. The for-mulation of the problem is based on an extension of Love's first approximation theory. The governing equations of motion are obtained in terms of the reference surface displacements. The equations are coupled in the longitudinal, circumferential and transverse displacement functions. Assumption of the solution in separable form leads to the ordinary differential equa-tions in the assumed displacement functions, which are functions of only a meridional coordi-nate. These equations are still coupled and have to be solved only numerically, in their general form. The displacements are assumed in series of Chebyshev polynomials. Collocation leads to a set of homogeneous equations in the unknown coefficients in the series assumed and become as a generalised eigenvalue problem solving which the frequency parameter values and the cor-responding mode shapes of vibration are obtained. Parametric studies are made to find the in-fluence of the many geometric and material parameters available on the frequencies. The effect of layering and that of neglecting the coupling between extensional and flexural displacements are studied, in particular. The results are presented in terms of graphs and are discussed
Associate Professor, Rose-Hulman Institute of Technology
Professional interests include undergraduate engineering education, finite element modeling, ground-borne vibrations, vibrations of musical instruments, and dynamics of toys.
A transfer matrix approach that combines finite element calculation to characterize homogeneous and non-homogeneous acoustic absorbing materials with in-plane periodicity is proposed. The approach is similar to the three-microphone two-load method and based on plane wave propagation assumption in a waveguide like a stationary wave tube. This approach allows one to model multilayers acoustic metamaterials that are non-homogeneous and periodic where each layer is represented by an equivalent transfer matrix. The results of the normal incidence sound transmission loss predicted by the present method are compared with finite element results. Good agreements are obtained.
Raymond Panneton is a professor-researcher in the Department of Mechanical Engineering at the Université de Sherbrooke since 1998. His research program focuses on the modeling, characterization and optimization of porous acoustic media. More specifically, he explores the relationships... Read More →
The bladder type water muffler is a new type of liquid pipe muffler, by which the pulsating pressure and the acoustic noise of the fluid can be well absorbed. The theory here is the changed pressure generated by the built-in airbag when it meets the pulsating liquid. Howev-er, the performance of the muffler depends enormously on the relationship between the infla-tion pressure of the airbag within the muffler and the pressure of the piping system. In this paper we aim to design a test bench with continuously variable pressure of the piping system to approve their relevance to the performance of the muffler. In the experiment, the optimal state of the muffler is found by adjusting the inflation pressure of the muffler airbag and the pressure of the system pipeline. Meanwhile, the relevance of the inflating pressure in the bladder and working pressure of the pipe system to the performance of the muffler is further verified, which provides a useful guide for the application of the muffler on ships and submarines.
A detailed measurement and analysis study has been carried out to determine both the variability of noise from high speed trainsets when in operation in respect of SEL and Lmax data. The aim of the study was to demonstrate the extent to which the variabilty of train noise occurs in actual operating conditions and whether it is appropriate to rely on future predictions of train noise from new railway lines without describing an uncertainty budget or confidence level.
Partial coherent excitations make the transfer path analysis (TPA) of road noise more complicated than the TPA of engine noise. In this research, a backward-multiple reference strategy is used to solve this partial coherent problem. First, the decoupling of multiple references is achieved by principal component analysis (PCA). Then, several backward-single reference TPAs referring to the principal components are performed to obtain the contribution of each path in the principal component space. At last, the total contribution of each path is obtained in the form of energy summation. This backward-multiple reference TPA is used to analyze the road noise of a prototype vehicle and the advantage of this method is presented in details. This method can not only be used to diagnose road noise problem, for example drumming noise, but also be used to lay down an excitation force standard.
Bolted joint is a basic form of connection which is widely used in engineering. The stress concentration near the distributed bolts in connection structure is possible to cause structural damage. The failure of the joint may lead to serious accidents. The acoustic emission (AE) wave generated by the structural damage can be used to localize the damage source. In this paper, a localization method of bolted joints damage with two AE sensors is developed based on arrival time difference (ATD) database. Firstly, the finite element model with the double-row bolt connection structure is established to obtain the damage signals at difference posi-tions, and the localizing method of bolted joints damage with only two AE sensors is pro-posed with ATD database. Secondly, the optimal method of sensors' positions is explored, which is relative to the layout of two sensors. Finally, the feasibility of presented localization method of bolted joints damage with two AE sensors is verified by experiments. The results show that the presented bolted joints damage localization method based on two AE sensors has good applicability and high success rate.
Experimental modal analysis is a tool for measuring the dynamic properties of structures under vibration excitation. In order to improve the understanding of the structural dynamic behavior of complex structures, modal parameters, such as eigenfrequencies, damping ratios, and mode shapes are of high importance. Furthermore, based on the mode shapes, the structural integrity of a component can be assessed and monitored. EMA results are also used in research and development for the validation and optimization of numerical models. The advantage of a non-contact measurement of the vibration patterns is that there is no damage or contamination of the material surface. In addition, the modal quantities are not contaminated by the additional weight of vibration transducers, so that the dynamic response of the system is not influenced by the measurement itself. In contrast to other non-contact methods (e.g. laser vibrometers), the use of a suitable microphone array allows the simultaneous detection of the entire surface vibration covered by the array. Time-consuming, selective measurements of individual measuring points and the merging to point clouds are therefore no longer necessary. The modal analysis method is demonstrated in experiments on application-oriented, large-area structures. The parameter of interest, the mode shapes, are determined by measuring the pressure fluctuations in the near field of the structure. A commercial 120-channel microphone array with an integrated optical camera (Fibonacci120 AC Pro, gfai tech GmbH) is used for this purpose. The integrated optical camera allows to assign the measured system response to the corresponding surface section. The entire surface of the examined structures is covered by the planar microphone array, which has a diameter of 0.5 m. Measurements with a laser vibrometer are used to validate the data obtained from the microphone measurements. The modal assurance criterion (MAC) is used to compare the mode shapes determined by both methods.
Noise radiation through the blade pump is the focus of noise control in the power systems of ships, while low-frequency line spectral vibration with high energy need to be further suppressed. An Active Vibration Control (AVC) system adapted to blade pump is designed to attenuate low-frequency line spectral vibration. This system is made up of the secondary source, controller, power amplifier, sensor etc. The system uses a frequency tracking algorithm to estimate the frequencies of vibration, and a complex LMS algorithm to design the controller. A pump water circulation system is implemented to validate the control system's performance in vibration reduction through experiments. Active control experiments on vibration of the pump with fixed frequency and multi-frequency are carried out respectively. The results show that the control system can track frequencies automatically, and effectively reduce the vibration transferring from the pump to the foundation in cases of fixed frequency and multi-frequency. The AVC system can achieve vibration attenuation of over 5 dB at multi-frequencies and has good robustness. This provides a possible solution for the control of low-frequency line spectral vibration of the pumps onboard ships.
A parametric study based on the analytical predictions of tonal and broadband noise for a generic turbulent boundary layer interacting with the rotor of an ultra high bypass ratio fan is presented. The approach and take-off conditions are considered. To classify the importance of ingestion noise, the rotor-stator interaction noise of the fan stage is also evaluated analytically based on computational fluid dynamic simulations. The implemented analytical boundary layer model provides the axial mean velocity profile and also the axial and transversal turbulent quantities. This allows to consider the turbulence within the boundary layer as anisotropic. The acoustic response of the rotor blades is predicted by using a modified theory for the acoustic radiation from an airfoil. The predicted tonal sound power levels are similar for the ingestion noise and the rotor-stator wake interaction noise at take-off conditions. For approach conditions the tonal boundary layer interaction noise is dominated by the rotor-stator wake interaction noise. The influence of the boundary layer thickness and the a shape factor, linked to the axial pressure gradient, on tonal noise is discussed. Concerning broadband noise the results indicate that the boundary layer interaction noise has the potential to dominate the low to mid frequency range compared to rotor-stator interaction noise. The predicted sound power levels show that the ingestion noise increases with boundary layer thickness and shape factor.
Noise emissions from wind turbines are one of the main issues that the wind energy industry must deal with nowadays. Strict noise regulations often prevent wind turbines to operate at maximum power conditions, causing large losses of power production and, hence, of revenue. Several noise reduction measures have been proposed so far, but the use of trailing-edge serrations and permeable inserts seem to be the two most promising approaches, showing broadband noise reductions of several decibels. This paper considers the noise reductions (with respect to the baseline blade) observed in previous wind–tunnel measurements featuring these two measures, and scales and synthetically applies them to an experimental recording of a full–scale Vestas V90-2.0 MW wind turbine in operational conditions. The calculated results are then auralized for the observer location used for noise certification in the IEC 61400-11 standard. State–of–the–art sound quality metrics (loudness, tonality, sharpness, roughness and fluctuating strength) are then applied to these simulated sound signals to better understand the achieved reduction in noise annoyance experienced by humans. Reductions in the maximum A-weighted sound pressure level (Lp,A,max) of about 2.4 and 1.2 dBA are observed for the serrations and permeable inserts, respectively. In general, trailing-edge serrations seem to reduce the calculated annoyance experienced (17% lower than the baseline) more efficiently than the permeable inserts (just 2% lower).
It is well known that the European Noise Directive 2002/49/EC (END), proposes the incorpo-ration of quiet areas (QAs) as one of the objects of analysis. The data generated by this anal-ysis should define, among other things, if for the declaration of these QAs, the municipalities should take some measures, such as including noise mitigation measures in the action plans, or other urban planning measures to favor the use of them. However, the conditions neces-sary to carry out the best identification of QAs of the city are not specified nor harmonized, resulting in a collection of non-homogeneous data. In these circumstances, the EU Member States have the autonomy to establish their own criteria for the delimitation and planning of the QAs. The main objective of this study focuses on the possibility for developing a system of identification and ranking of QUA candidates inside agglomeration (or quiet urban areas) based on GIS. The criteria applied, seek a degree of flexibility that allows them to adapt to the specificities of medium-sized cities (between 50,000 and 250,000 inhabitants) located in Andalusia (a region situated in southern Spain). For this, three cities have been chosen as a case study, two of them have their strategic noise map. On-site surveys have been designed and carried out in a stratified way, describing the predilections of citizens for rest and leisure areas in the city. There have been more than 400 surveys per municipality from which a ranking of areas was drawn. To conclude, the results of the surveys are contrasted with the methods based on GIS applied in other European regions and extracted from the literature, with the idea of analyzing their suitability to be applied in Andalusia
This work addresses a simplified model for simulating the dynamic behavior of electric motors, more specifically the acoustic response of stators. Targeting this application, both structural and acoustic responses are calculated by Finite Element (FE) and Boundary Element (BE) methods, respectively. The FE model consists in a geometry simplification which represents the stator by curved and straight beam elements (body and teeth), and concentrated mass elements (wiring representation). An emulation of the dynamic forces acting on the stator teeth was also taken into consideration, however the forces magnitudes were arbitrarily chosen since this is not the focus of this document. The structural representation was validated by using a commercial software, achieving satisfactory results. Later on, the acoustic part was modeled by the Direct BE Method, using values for areas, normals, coordinates and velocities from the previously described FE part. Therefore, this algorithm was built to obtain both sound pressure level and radiated sound power (calculated by ISO 3744), with respect to the FE model and the forces of arbitrary magnitude prescribed on the stator teeth. Finally, this acoustic part also was validated by comparing the calculated sound pressure level with a commercial software which uses Acoustic FE as solution method. The observed results supports the idea that this simplified model is suitable for a limited range of frequency up to 3.8 kHz, and reduced the time of this analysis type by approximately 60x.
Military Operators (MOs) are exposed to a broad range of impulse noise that can vary greatly in terms of level, temporal and spectral characteristics. The accurate characterization of the performance of hearing protectors is required, to mitigate the hearing damage risk for the MOs working under such conditions. Presently, the accepted method to characterize Hearing Protection Devices (HPDs) performance is based on the measurement of the Impulse Peak Insertion Loss (IPIL); however, this measurement doesn't provide the peak Insertion Loss (IL) per Octave Band (OB). A method for measuring the peak IL per OB for HPDs was developed and is presented in this paper. The concept of an Octave Band Impulse Peak Insertion Loss (OBIPIL) is introduced to account for the HPD peak attenuation at each OB. Using a modified version of the ANSI/ASA S12.42-2010 test setup, the impulse noise signals for a 5.56 mm caliber weapon were recorded. The IPIL and the OBIPIL values of the tested HPDs were computed and are presented for comparison. Moreover, an OBIPIL comparison versus the Bone Conduction (BC) attenuation limits is provided to gauge the attenuation capabilities of each HPD at each OB. A performance behavior for each HPD is presented in the time domain and per OB. Finally, remarks, conclusions, pros and cons of the proposed methodology as well as future work are discussed.
The circular mesh antenna is designed as a lightweight and flexible structure in the orbit and use mainly metal meshes as a reflecting surface. This paper analyzes frequencies and modal shapes of the circular mesh antenna by using the finite element method, and the nonlinear resonant responses of the circular mesh antenna are studied based on a circular cylindrical shell equivalent model clamped along a generatrix and with membranes at both ends. Firstly, we establish the finite element model of the circular mesh antenna considering the influences of meshes on the vibration characteristics of the circular mesh antenna. It is found that there exist the 1:3 internal resonance under a certain mesh stiffness between the first-order and the fourth-order vibrations of the circular mesh antenna, and we give the comparison of the first six orders vibration modal shapes under the different mesh stiffness cases to study the influences of mesh stiffness on the vibration modal shapes of the circular mesh antenna. Then, we obtain the four-dimensional nonlinear averaged equation based on the two degrees of freedom non-autonomous nonlinear equations of the circular mesh antenna equivalent model considering this case of 1:3 internal resonance. At last, we compute the curves of equilibria in order to study the nonlinear resonant responses of the equivalent circular mesh antenna model. The amplitude-frequency response curves and the parametric excitation amplitude curves of the system on the state-parameter space are obtained, meanwhile, jump points and Antronov-Hopf points are detected and located on these resonance response curves. Furthermore, the effects of temperature excitation on amplitude-frequency response curves of the equivalent circular mesh antenna model are investigated.
Mohammad Rafiee received his Ph.D. degree in Mechanical Engineering from the University of Ottawa in 2018. Currently, he is a Postdoctoral Fellow at Polytechnique Montreal in Canada. His research interests are primarily focused on the development of advanced composite materials, smart... Read More →
Water-lubricated journal bearings have been widely applied in the ships rotor-bearings system and often operate at low speed and heavy load condition. The traditional method to investigate the characteristics of water-lubricated journal bearing is to solve Reynolds equation or N-S equation. However, as the poor operating conditions make the water film thickness very thin at mesoscopic scale and the water-lubricated journal bearings work under boundary lubrication condition, the traditional method is not suitable. In order to overcome the shortcoming of traditional method, a full scale method named lattice Boltzmann method is applied to study the characteristics of the water-lubricated journal bearing. In the present paper, basic principle of the lattice Boltzmann method, modeling process and how to deal with boundary conditions are presented in detail. The results of infinitely long water-lubricated journal bearing are obtained, including velocity, film pressure and stiffness coefficient. Using the stiffness coefficient, the shaft system natural frequency and the response to the exciting force are simulated.
A dynamic stiffness method is proposed for bending vibrations of completely free plates derived from improved Gorman superposition method. Instead of decomposing vibration modes into symmetry and anti-symmetry scenarios, only two building blocks are utilized to construct the general solutions for the dynamic responses of plates. The ensuing dynamic stiffness formulations are established by use of projection method. Natural frequencies and dynamic responses can be obtained by the proposed method and validated against the results available in the literature and the finite element analysis. It can be found that the proposed method possesses high efficiency and accurate performance.
Associate Professor, Rose-Hulman Institute of Technology
Professional interests include undergraduate engineering education, finite element modeling, ground-borne vibrations, vibrations of musical instruments, and dynamics of toys.
Metamaterials can be engineered for noise and vibration control through the design of their internal structure. For example, a periodic arrangement of resonant inclusions in a rubber medium applied as a viscoelastic coating on the outer hull of a marine vessel can help improving its stealth. In order to study the properties of a metamaterial, the material parameters of an equivalent homogeneous medium are commonly derived. Retrieval methods are techniques leading to such effective properties using scattering coefficients. In this work, two retrieval methods are applied on a 2D periodic medium with rigid inclusions in an elastic matrix to obtain the effective properties of the constituent unit cell, based on scattering coefficients calculated from numerical simulations (finite element method). Effective wavenumbers and effective impedances are presented along with the displacement fields for the resonance frequencies. Homogenization issues are highlighted, related to the strong hypotheses implied in the different retrieval methods. It is shown that, to predict more accurately the reflection and transmission coefficients for metamaterial samples of given thicknesses, it can be beneficial to combine effective parameters coming from different methods.
Reading is a typical task in everyday life of employees. Many employees have to get information or instructions from written material in the frame of their occupation. Reading was therefore chosen as the main task in a resarch project on noise effects on cognitive performance at the work place. In order to get valid results on the possible effects, it is important to use a task that is sensitive to noise, and that is evaluated with regard to training effects and also to the equivalence of different test versions, when more than one version is used. The project has several work packages. Currently an experimental study with 51 participants has been finished, where the participants worked on a reading task that was developed by this author. The task has two different versions. Participants were asked to find mistakes in sentences that were presented on a computer screen. Since the focus of this study was mainly on the task itself, participants worked on the task either twice in a silent condition (group 1) or twice in a condition with speech as background sound (group 2). Each person worked once on test version A and once on test version B. The main questions in this study were: (1) Is there a difference between the mean results in the first and the second run, and if so, is this different for group 1 and group 2? (2) Are there differences in the performance between both test versions? The results are presented and discussed in this contribution. They will finally be used to optimise the reading task and the design of the test runs, in order to get a solid basis for a prospected work package in which the effects of different typical sounds from the work place will be investigated.
The distribution of underwater acoustic field is traditionally measured by a scanning hydrophone or a hydrophone array, which would both perturb the acoustic field. Optical technique provides an alternative way to measure underwater acoustic noninvasive. As such, an optical measurement system for underwater acoustic field is implemented in an anechoic water tank. This system is based on the so-called acousto-optic interaction between an optical beam and the acoustic field, and it uses a laser Doppler vibrometer (LDV) to measure the rate of change of optical path length caused by the presence of the acoustic field. Then processed by a tomographic technique, the underwater acoustic field could be reconstructed without perturbation. Three piston transducers covering the frequency range 100 to 500 kHz are utilized to validate the optical measurement system. The reconstructed acoustic distributions obtained by the LDV are also compared with the scanning results of a hydrophone at the same plane, and good agreements are observed in the frequency range of interest.
The efficiency of vibro-acoustics analysis has been a major concern in dealing with large-scale vibro-acoustic systems such as a passenger car, owing to that its finite element model usually contains a huge amount of degrees of freedoms (DOFs) because of its geometrical complexity. To speed up the analyses while keeping desired computational accuracy, this paper develops a modified component mode synthesis method which emphasizes on the coupling techniques of non-conforming structural-acoustic interfaces. The non-conforming interfaces are introduced intentionally by considering that acoustic cavities are usually not necessary to be discretized as finely as structures to deliver equally accurate results. A radial basis function-based, master-slave interpolation formulation is developed to connect the physical field variables across the boundaries of substructures, while the left internal DOFs in each substructure are condensed to fewer modal variables. The computational perfor-mances of the proposed method are verified through a passenger car model.
Reducing noise from rail freight has been identified by the European rail sector itself as a key objective. The regulations by the European Union - Physical Directive 2003/10 (Block, 2005) were adopted and the main implication of these regulations is to reduce the noise level in the cabin of the train by 5 dB and the noise for the average train speed of 160 km/h would be about 4 dB lower. Railway operational noise originates from several sources, such as: rolling (wheel-rail interaction), traction (locomotive engine, fans and gears), aerodynamic effects (pantograph, body turbulence) and so on. The dominant contributor, over the widest speed range (from around 50km/h to around 180km/h) is wheel-rail rolling noise, engine and powertrain noise. In order to reduce the different noise sources and study the noise propagation around the trains, the manufacturing companies and their suppliers have to come up with innovative solutions to predict the emitted noise level. The train pass-by-noise regulation aims to characterize the overall acoustic signature of a vehicle and it requires experimental measurement in its operational condition – as it passes over stationary microphones. In the development process of new and innovative trains, the pass-by-noise tests are the last step in the standardization process. Non-compliance or critical issues could be arise so new methods and numerical models must investigate solutions to control the acoustic propagation around the vehicle arises. This paper deals with an engineering method for predicting a vehicle pass-by noise based on a FEM/ BEM exterior acoustic calculation in the frequency domain. The researchers simulate, in a virtual environment, the experimental outdoor pass-by noise measurement. The simulated pass-by noise campaign is synthesized from multiple acoustic transfer functions between a line of virtual microphones located 7.5m on the side of the vehicle and each noise source. A numerical FEM/BEM train bogie acoustic model is created within the MSC ACTRAN and Coustyx commercial software. Wheel-rail rolling noise, engine and powertrain noise acoustic source are implemented and positioned inside the FEM and BEM model to demonstrate the validity of the proposed methods. The contribution from noise sources, expressed both in terms of sound pressure level and overall value, to the pass-by noise is evaluated up to 5 kHz. The virtual pass-by-noise assessment has been then validated by experimental measurement of the complete four coaches train with respect to 80 and 160 Km/h speed regimes.
In order to research the influence of rotor slot type on electromagnetic excitation and vibration characteristics of induction motor, a 22kW asynchronous motor of Y2-200L2-6 is taken as an example. We established an experimental platform for physical separation of stator and rotor, the rotor of straight slot, skewed slot and dual skewed slot are combined with the same stator. The influence of different slot type on the vibration characteristics is analyzed through the analysis and test. It shows that the rotor slot type does not change frequency of electromagnetic excitation, but has a great influence on the frequency amplitude. The study can provide some reference for low vibration motor design.
The article deals with the design of a metadevice able to trap acoustic waves in a duct. The aim is to limit the outgoing acoustic power and confine the perturbation inside the duct exploiting the unconventional reflection of the optimized metasurface. The target engineering application is related to the improvement of the efficiency of standard acoustic liners in the ultra-high-bypass-ration engines, where the ratio between diameter and length of the nacelle inlet increases significantly. The metabehaviour is modeled by means of the generalized Snell's law for reflection from acoustically rigid surfaces. The realization of the device relies on a modular concept, which building set is made of eight elementary cells, able to induce a reflected field suitably phase-delayed with respect to the incident wave. The acoustic perturbation is produced by a source placed inside the duct. The set spans the whole 0-2$pi$ phase delay range, and the anomalous reflection is obtained by the tailored design of the phase delay gradient profile on the metasurface. The cells are designed through numerical optimisation in order to extend the effective frequency range of the device, keeping the overall thickness of the metadevice smaller than a quarter of the nominal wavelength. The duct and the source are considered co--moving within the fluid at rest. The numerical analysis is performed in the frequency domain in a frame of reference rigidly connected to the duct, and considering several values for the Mach number. Preliminary numerical results show thatr the phase-delay profile can be effectively tailored to achieve the required reflection steering.
In order to explain human evaluation strategies in complex sound environments, not only the interaction and nature of present individual sounds have to be considered. How an environment is perceived, strongly depends on contextual factors and cognitive processes guiding the listener's focus of attention. The contributions of these various influencing factors to subjective overall assessments have been subject to research for many years. However, no reliable model exists yet, to predict human evaluation of sound quality in an acoustic environment with multiple sound sources. With the aim to investigate the relationships between individual environmental sounds and overall assessments in detail, a series of listening experiments was conducted at Hochschule Düsseldorf – University of Applied Sciences. In the course of soundwalks in the city center of Düsseldorf, the participants experienced and evaluated the sound quality of four different locations (pedestrian zone, square, urban park, traffic road). 360° videos and 3D audio recordings were taken at each location, and were later implemented in a laboratory setting with video screens and a 6-channel loudspeaker setup. The soundwalk participants conducted a second evaluation of the four urban locations in the laboratory setup. In a short concluding interview, they provided a comparison of both test experiences. The ratings from the soundwalks and the laboratory experiment were compared in terms of overall sound evaluation, the number and type of individual sounds mentioned and further non-acoustic factors. To assess the effect of local experience on the sound evaluations, a second group of test persons, who had not participated in the soundwalks before, conducted the laboratory experiment as control group. The judgements of both groups were juxtaposed as well. The results showed remarkable similarity in overall evaluation of the four urban locations, despite of the different experimental conditions.
Valves are used in industrial sites where flows (gas, liquid or diphasic) are in action — for example, industries of energy, oil and gas, water cycle or chemistry. The damage or the maladjustment of valves in operation cause leak flows which induce financial costs, environmental problems and safety hazards. Thus, an accurate live evaluation of operating valves would limit these risks by adjusting them or by performing less expensive maintenances. Hence, we instrumented during for nine months a valve on a nuclear power plant which is closed in normal operating condition. The aim was to measure the Acoustic Emissions AE, produced by leak or passing flows, propagate in valve. There was water vapor in ducts: 64 bar / 280°C at the upstream and 8 bar / 175°C at the downstream. A measurement system of AE, composed of three piezoelectric sensors, was developed to operate at high temperature. Our system acquired continuously and simultaneously data from four measurement channels at a sampling frequency of 1 MHz. The pressure at the downstream — which evolves as a function of operating phases of the industrial facility and, especially here, of the valve opening — was also measured. We correlated pressure measurements with acoustic emissions measurements to identify frequencies excited by AE generated by leak or passing flow in the studied valve. In addition, a data processing analysis to denoise AE signals, contaminated by industrial noises, was developed and validated by our experimental data. From the evolution of AE statistical parameters (like the root mean square or the spectral average characteristic to the acoustic intensity), which are correlated to the rate flow, we detected the apparition of valve opening, damage or maladjustment in an industrial environment.
The human earcanal remains mostly an unchartered territory: earcanal shapes and dimensions are unique to each individual and despite recent advances in 3D scanning, the capture of the earcanal's exact geometry remains challenging. Nevertheless, the proper selection of an intra-aural hearing protector often requires that the earcanal size be estimated. Therefore, several tools -such as earcanal and concha gages- have been developed over the years to quickly and approximately assess one's earcanal dimensions and recommend the appropriately matching earplug size. In this anthropometric study, sparked by the lexical similarity in French between the noun for the little finger (auriculaire) and the adjective related to aural parts (auriculaire), we explore whether Nature did not provide a suitable earcanal sizing tool... at the tip of our fingers. The methodology is based on the calculation of correlation coefficient matrix obtained by comparison between characteristic geometric features - such as volumes, sections, diameters, and lengths- of both the ear canal and the little finger. The results from a recent pilot study will be presented together with possible field applications for hearing protectors and a selection of in-ear wearables.
The in-plane vibration of elastic thin plates is becoming increasingly important in the transmission of high-frequency vibration since lightweight plate structures have been widely used in many engineering applications. Although the free in-plane vibration of rectangular and circular plates has been extensively investigated and the free out-of-plane vibration of elliptic plates has widely investigated, comparatively limited publications dealing with the free in-plane vibration of elliptic plates are available. To investigate the free in-plane vibration of elliptic plates with clamped edge, a general semi-analytic method is proposed. In such a method, the conformal mapping method is utilized to overcome the mathematical treatment difficulty in describing the complex boundary conditions of elliptic plates. By using conformal mapping method a boundary-value problem on a unit circle is obtained. Numerical examples of elliptic plates with different aspect ratios have been analysed and the results agreed well with those available in published literature and those calculated by ANSYS.
Associate Professor, Rose-Hulman Institute of Technology
Professional interests include undergraduate engineering education, finite element modeling, ground-borne vibrations, vibrations of musical instruments, and dynamics of toys.
This paper investigates the dynamic behaviour of a rotordynamic system incorporating stiffness nonlinearity in the supporting bearings. The system model comprises a horizontal Jeffcott rotor mounted on symmetrically located ball bearings. The nonlinear radial stiffness of the bearing is estimated based on the Hertzian contact theory. The harmonic balance approximations and the time-marching method are applied to solve the governing equations and to determine the steady-state dynamic response. The results show that a small nonlinear bearing stiffness provides benefits for the suppression of response in the high frequency range. A large damping coefficient in the bearing can reduce the peak response amplitude. A combination of a small bearing stiffness and a large bearing damping can assist in effective vibration suppression from rotor in a broad excitation frequency range. These results lead to a better understanding of the effects of stiffness nonlineari-ty and damping property of the bearing on vibration behaviour and hence benefit enhanced de-signs with desirable dynamic characteristics.
This study aims to investigate the impacts of acoustic environment on the relationship be-tween job characteristics and job satisfaction. Acoustic measurements and questionnaire sur-veys were conducted in open-plan offices in the UK and Korea. Background noise levels were recorded for 8 hours in each office and speech transmission index (STI) and sound pressure levels were measured for quantifying the single number quantities in ISO 3382-3. A total of 324 employees from 12 offices completed a questionnaire survey. The questionnaire included questions assessing noise disturbances and speech privacy, as well as job satisfaction and job characteristics. The result confirmed the strong impacts of job characteristics on self-rated job satisfaction. Background noise levels during working hours and reverberation time were negatively associated with job satisfaction; however, there were little influences of speech privacy and noise disturbance on job satisfaction. It was also observed that speech privacy, noise disturbance, background noise level, and cultural difference (Korea and UK) had moderating effects on the relationship between job characteristics and job satisfaction. In particular, greater speech privacy and lower background noise level increased the impacts of job characteristics on job satisfaction.
After cavitation, the noise of propeller will become the main component of ship radiation noise. It is necessary to detect propeller cavitation in real time to reflect a ship's acoustic performance. In order to detect propeller cavitation accurately, various characteristics of cavitation noise are inves-tigated. In this research, propeller noise under different rotating speeds of a trial ship is collected by a hydrophone fixed at the aft hull. The original noise signal is processed by wavelet packet re-construction to obtain cavitation characteristic signal. The envelope of cavitation characteristic signal is demodulated and its features changes in time domain and frequency domain are analyzed. The results indicate that the structure of DEMON spectrum changes and the modulation degree of cavitation characteristic signal increases with the development of cavitation. In addition, it is more effective to detect propeller cavitation by monitoring the amplitude of modulation frequency line spectrum in DEMON spectrum than sound pressure level of noise signal.
In recent years the European automotive market has seen the introduction of an increasing number of battery electric vehicles, i.e. vehicles powered by a purely electric powertrain without an internal combustion engine. Although electric powertrains give rise to a different set of vehicle noise problems which need to be better investigated and understood in general, that has been hardly possible until recently due to their limited availability on the market. Nowadays the situation has improved and a reasonable number of battery electric vehicles from several different car makers are available. Based on experimental investigation of the current European market sample, this paper presents a first picture of the state of the art for what concerns the NVH package trends and the acoustic performance in the interior passenger compartment of those vehicles.
Lunch breaks are strategically scheduled within each conference session and last typically 60 minutes. You are encouraged to stick to your assigned timing (see your folded paper guide) and designated lunch room (either "Salon Ville-Marie" or "Salon Bonaventure" on the top floor) to minimize your waiting time and maximize your interaction with your colleagues within your session.
Lunch is served as a buffet. Desserts are served in the Exhibition Hall (on lower floor, refer to this map if needed). Seating is limited and priority should be given to people needing a seat (other are invited to seize that moment to stand tall and/or stretch, as recommended by the Canadian Center for Occupational Health and Safety).
Measuring characteristics of gas bubbles in a fluid is among important and challenging tasks in many industrial settings. Such measurements can be carried out more efficiently and accurately by using a Wave Phase Conjugation (WPC) device due to its useful relevant properties such as signal retro-focusing and compensation for phase distortions. In the present work, this technique is explored via numerical modelling in application to bubble size measurements. A modified version of the high-order Nodal Discontinuous Galerkin (NDG) method, which is based on the non-collocated solution and flux bases, is implemented for modelling of the acoustic wave propagation in the WPC conjugator and the surrounding fluid. Additional volume-averaged terms are added to the model to account for the presence of bubbles in the fluid. The modified Keller-Miksis model is employed to simulate vibrations of bubbles exposed to acoustic waves. After the verification and validation of the numerical model, the interaction of bubble dynamics with the WPC process is examined. The results demonstrate that the WPC-based technique is an adequate tool to be used for measuring bubble dimensions via stimulation of the bubble natural frequency.
The low-frequency pulsation of the marine hydraulic system is transmitted along the pipe, which can create structural vibration. For the low-frequency pulsation which is difficult to control by passive style, a by-pass secondary source is designed and pulsation control re-search by active style is carried out. The designed by-pass secondary source is driven by pie-zoelectric ceramics, which is compact. The active control system of the hydraulic system is built with two secondary sources and the FxLMS adaptive algorithm is used to control the pul-sation. The experimental result shows that the by-pass secondary source can effectively at-tenuate the low-frequency pulsation at multi-frequencies and reduce the vibration energy transmitted with the fluid.
The objective of the work described in this paper is to set up and validate an adjoint based method for blade shape optimisation aiming at propeller noise reduction. As a first step toward a comprehensive propeller noise optimisation, the present study focuses on the loading noise of a single propeller isolated and without incidence. In this respect, an acoustic objective function is derived, based on the Hanson-Léwy steady loading noise formulation. After defining this function, the first step is to derive its sensitivities to mesh and aerodynamic field parameters. Once implemented in the ONERA adjoint based optimisation procedure, the acoustic function predictions are compared to a classical Ffowcs Williams and Hawkings approach, and the sensitivities are validated by comparison with the finite differences method.
Acoustic emission (AE) technique has been investigation for identification and location of osteoarthritis in knee joint. Although, AE technique has widely been used for years as a NDT tool in damage monitoring and condition inspection of industrial and structural materials, similar applications of AE technique has been considered in integrity analysis of knee joint as well. Of course, integrity analysis of knee joint involves a detail study of several anatomical parts of knee joint like bones, cartilage, tendons etc. However, the interest of the present investigation has been confined to knee osteoarthritis which is considered to be caused due to the degeneration of knee cartilage. The incidence of this widely manifested knee disease increases in aging society. The major concern of this disease is its incurability at its matured stage. However, early detection for adopting appropriate measures can reduce the risk of this disease. The present investigation focuses on the dynamical behavioral characterization of knee joint for its integrity analysis with acoustic emission characterizing parametric features of AE signals. Data has been collected from the participants with different age groups without any knee problems as well as with knee problems (OA). All data have been clarified for identifying the technique as a clinical tool in monitoring knee condition effectively.
People exposed to loud industrial, military or other noise need to be protected by suitable Hearing Protection Devices. The best solution is to use individually fit earplugs. However, it is difficult to know the real (in site) performance of such devices, as it depends on the morphology of the user's ear canal as well as on the way it is put in place by the user. Different types of earplugs (foam, pre-molded and moldable) are available in different sizes. All these parameters make it difficult for the user to choose a well-adapted earplug for his ear. It is therefore important to find a robust, fast, and easy method helping the user to choose correctly the earplug adapted to the morphology of his ear. The proposed method uses a prototype of an instrumented earplug (loudspeaker and microphone) allowing different types of tips to be fixed. As in the range of very low-frequency (below 90 Hz) the frequency response of the loudspeaker depends strongly on the proper sealing (airtightness) of the earplug in the ear canal, and therefore it may be used as a measurement for the earplug's fitting. If there is a leak, the frequency response will drop in the low-frequency domain. The method using these properties has been implemented in a DSP coupled with the instrumented earplug. A single measurements takes less than one minute and the developed prototype indicates the result with a color code: Red LED - leak; Green LED - airtight. REAT (Real-Ear Attenuation at Threshold) measurements using 3 sizes of existing earplugs have been realized and show a strong correlation between the airtightness (no acoustic leak) measured by the system and the performance of the earplug.
Curved beams are frequently used structural elements in traditional and emerging fields of civil and mechanical engineering with usual requirements of vibration and deformation analyses utilizing the beam theory and numerical methods. There are challenges in such analyses due to complex equations with the curved beam segment and numerical methods in case the analytical solutions are no longer available. In this study, curved Timoshenko beams with commonly encountered arc types are studied with the Rayleigh-Ritz method using polynomial functions as the deformation for calculations of strain and kinetic energies, and accurate frequencies and mode shapes are obtained from convergent and verified solutions. It is the objective of this study that the method will be extended to a short, curved, and periodic beam for its free vibrations for in-depth understanding of such unusual but widely encountered structures from recent technological advances. It is found that for the sinusoidal-shaped beams, we need the deformation in since series up to the 25th order, showing a large size equation for the eigenvalue extraction. It is worth to try other types of deformation functions to improve the computing efficiency for curved beams. Eventually, the study will be merged with current methods for analyses of beams of various types for unified approach and results with further extension to composite structures of combinations of periodic beams with shorter unit cells from the 3D-printing technology showing up with wide applications today. Additional considerations of higher-order theories and couplings of modes can also be included for more practical and robust analyses of beam elements.
Associate Professor, Rose-Hulman Institute of Technology
Professional interests include undergraduate engineering education, finite element modeling, ground-borne vibrations, vibrations of musical instruments, and dynamics of toys.
The inter-shaft bearing could simplify the supporting structure of a dual-rotor system, so it is widely used in rotating machinery like gas turbine engine. When monitoring the vibration of an inter-shaft bearing, sensors usually could not be installed inside the engine because of the compact structure, then will be installed on the casing. The vibration of the inter-shaft bearing will be transmitted though both the two rotors to the supporting bearings then to the casing, and both the inner and outer ring rotate, making the condition monitoring much more difficult than normal bearings. In this paper, a dual-rotor system dynamic model with the rotor-bearing-casing structure is built to simulate the vibration of an inter-shaft bearing. The rotors and the casing are modeled using finite element method and the bearings are modeled using a nonlinear multi-body dynamic model. The normal state of the inter-shaft bearing is simulated, then the bearing fault states with localized defects on the inner race, the outer race and one of the rolling elements are simulated. Signal processing methods are utilized to extract bearing fault features from the casing vibration acceleration signal. Besides the fixed rotating speed condition, rotors under variable speeds are also simulated, then the vibration signal and fault feature become more complex and the signal analysis becomes a bigger challenge.
Awareness about large energy consumption and global warming risks has encouraged many initiatives for sustainability and energy consumption reduction. As buildings account for large portion of energy consumption worldwide many initiatives address the issue of the sustainability of buildings. There is an increasing trend toward "green" buildings among building industry in general. This is led mostly by third party non-governmental initiatives such as the US Green Building Council and its LEED green building which has become one of the leading green building third-party initiatives worldwide. Green building rating schemes require buildings to be environmentally friendly, resource and energy efficient and healthy places to live and work. Yet the quality of the buildings certified according to commercially available green building schemes is sometimes questioned. Many studies have found discrepancies between green building ratings and the actual performance of the certified buildings. Furthermore, acoustic performance is one of the aspects quite often overlooked by the schemes. In the buildings, acoustics sometimes represents conflicting situations with other aspects of buildings performance such as thermal, or indoor air quality, or even lighting. Therefore it is very important to include the examination of acoustic performance alongside other aspects for a high quality green building. While providing an overview of the common problems reported on the acoustics of green buildings, this paper compares the results of a post-occupancy evaluation of a number of "green" and conventional buildings.
Propeller cavitation can produce strong noise, and serious cavitation will also lead to the damage of propeller blades. Therefore, it is necessary to conduct real-time detection of propeller cavitation. Acoustic method is the main research orientation of propeller cavitation detection. In this study, an experiment is carried out in cavitation tunnel to obtain noise of a propeller model under differ-ent cavitation states. A number of typical parameters related to energy intensity, pulse character-istics, spectrum structure of the noise signal are calculated and their changes with the develop-ment of cavitation are analyzed. The effective parameters are chosen to comprise feature vectors, and a classify based on support vector machine (SVM) is designed to identify the propeller cavita-tion state. The result shows that the method is effective, and the recognition rate of the classifier reaches 95.8% using 240 test samples.
Ride comfort of the driver/occupant of a vehicle has been usually analyzed by multibody biodynamic models of human beings. Accurate modeling of critical segments of the human body, e.g. the spine requires these models to have a very high number of segments. The resultant increase in degrees of freedom makes these models difficult to analyze and not able to provide certain details such as seat pressure distribution, the effect of cushion shapes, material, etc. This work presents a finite element based model of a human being seated in a vehicle in which the spine has been modelled in 3-D. It consists of cervical to coccyx vertebrae, ligaments, and discs and has been validated against modal frequencies reported in the literature. It was then subjected to sinusoidal vertical RMS acceleration of 0.1 g for mimicking road induced vibration. The dynamic characteristics of the human body were studied in terms of the seat to head transmissibility and intervertebral disc pressure. The effect of the seat pan angle on these parameters was studied and it was established that the optimum angle should lie between 15 and 19 degrees. This work is expected to be followed up by more simulations of this nature to study other human body comfort and seat design related parameters leading to optimized seat designs for various ride conditions.
Directional sound fields can be generated by arrays of multiple sound sources, with the most common and straightforward method being an array of loudspeaker drivers. Although such a system, when appropriately designed, is capable of high levels of directivity control over a broad bandwidth and with good audio quality, it can be prohibitively expensive and too fragile in certain applications. This work presents and investigates the idea of using an array of actuators mounted to a structure to generate a directional sound field. Structural actuators have previously been used as an affordable and robust alternative to conventional loudspeakers, particularly in applications where the actuators can be used to drive a structure that would already be in place to radiate the desired sound field and where the required audio quality is lower. By distributing a number of actuators on a structure, and controlling the relative amplitudes and phases with which they are driven, it is possible to manipulate the structural vibration such that it generates a controlled directional sound field, similar to that resulting from an array of individual sound sources. In this work, an analytical model is first formulated of a rectangular panel excited by an array of structural actuators, which are approximated as point forces acting perpendicularly to the surface of the panel. This model is used to perform a simulation based parametric study, which provides insights into the design trade-offs for a structural actuator array based system. In particular, this considers how the number of actuators, their geometry and the dimensions of the structure influence the directivity control and achievable bandwidth. Based on this parametric study, a structural actuator array is assembled using a rectangular aluminium panel and six actuators. The system is tested and evaluated through measurements in an anechoic chamber.
Background: Over the past two decades, the increasing and unregulated production of infrasound and low frequency noise (ILFN, ≤200 Hz) has led to a considerable rise in associated noise complaints and health-related issues. The most recent of such ILFN sources are industrial wind turbines (IWT). Acoustical field-data was collected within a home located in the vicinity of IWT, to which the AUC Rule 012 and its requirements were applied. In Ontario, IWT noise complaints were gathered under the Freedom of Information legislation. Goal: To explore the usefulness of current noise control rules when protecting human populations against ILFN generated by IWT.
Graphene nanoplatelet (GPL) is a two-dimensional single layer of carbon atoms with extraordinary mechanical, thermal and electrical properties, and can provide excellent reinforcement effects on the matrix when it disperses at a low concentration. Mechanical behaviors of graphene reinforced nanocomposites structures have attracted tremendous interests due to their potential applications in engineering fields. Nonlinear free vibration behaviors of novel functionally graded nanocomposite spinning cylindrical shells reinforced with GPLs are studied where the weight fraction of GPLs varies through the thickness direction. Three different GPL distribution patterns are considered. The modified Halpin-Tsai micromechanical model and the extend rule of mixture are employed to determine effective values of position-dependent elastic moduli, mass density and Poisson's ratio. Based on the Donnell's nonlinear shell theory, the nonlinear partial differential equations of motion for the cylindrical shell are formulated by using the Hamilton's principle with the effects of centrifugal and Coriolis forces as well as the spin-induced initial hoop tension taken into account. A set of nonlinear ordinary differential equations are derived by employing the Galerkin approach. Parametric studies of weight fractions, geometrical sizes and distribution patterns of GPLs, spinning speeds and travelling wave numbers on the linear and nonlinear natural frequencies for the nanocomposite cylindrical shell are conducted. Results show that the effective stiffness of the cylindrical shell can be significantly increased by adding small amounts of graphene into the metal matrix. GPLs with a larger surface area but less single graphene layers are preferred nanofillers as they offer the best structural performance of the nanocomposite cylindrical shell.
Associate Professor, Rose-Hulman Institute of Technology
Professional interests include undergraduate engineering education, finite element modeling, ground-borne vibrations, vibrations of musical instruments, and dynamics of toys.
In this study, the subjective experiment was carried out using the description terms of the quality of the different classes in ISO/WD TS 19488 on low-frequency rubber ball impact sound standardized in the ISO as the heavy/soft standard impact source. Experimental condition of 3 times experiments consisted of different background noise and task conditions. In addition, a questionnaire survey on the noise sensitivity and opinion of neighbours of each subject was conducted. The response differ-ence became larger when the presented rubber ball impact sounds more loudly. When subjects carried out internet surfing in high background noise condition, the level differences between groups were decreased in both cases. These results mean that noise sensitivity of subjects influence more in the low background noise condition and the influence became smaller when background noise increasing and concentration on the presented sound interfered by carrying out a task. Noise sensitivity was influencing when subjects hear clearly the presented sound, but when subjects were interfered con-centrating on the presented sound by an external condition such as background noise or other tasks the effect of noise sensitivity can be decreased clearly.
Despite the cost of noise reduction is growing every year, excessive noise is one of the most pressing problems in the workplace and in community. There is a growing number of complaints about the negative impacts of noise is registered. Noise barriers are widely used for transport and occupational noise reduction. Main noise barrier parameters are studied in order to increase barrier insertion loss. In situ noise reduction and sound absorption are investigated and discussed. Experimental results of noise barriers insertion loss are also presented. Durability of noise barriers made from different materials are discussed.
We demonstrate a high-efficiency sound-absorbing metasurface operating at low frequency. The metasurface absorber is based on acoustic porous layer embedded two identical but oppositely oriented split tube resonators. A high absorption (>50%) is obtained in a frequency range from 170 Hz to 750 Hz and over 90% absorption exhibits from 285 Hz to 340 Hz, while the thickness of the absorber is only 1/6 of the relevant wavelength at 500 Hz. The broadband and high absorption performances are due to the coupling of the resonance modes and the trapped mode. Furthermore, the high-efficiency low-frequency absorption of the metasurface is robust under oblique incidence even at large angles. The absorber is ease of fabrication, subwavelength thickness, and robust high-efficiency. Therefore, it has high potential applications in noise control and architectural acoustics.
A near-perfect and near-broadband sound absorption at low frequencies is achieved by using hybrid resonance in an acoustic metasurface. The metasurface for perfect absorption at N frequencies con-sists of two-dimensional periodic array of unit cells, which are composed of 2N meta-atoms. Each meta-atom is designed to acquire hybrid resonance at a target frequency by using two Helmholtz resonators of sub-wavelength scale whose cavities are coiled up. We design a metasurface exhibit-ing perfect sound-absorption at four different frequencies by using optimization based on a theoret-ical model. The proposed metasurface is fabricated by using 3D printing. The experimental results show near-perfect and near-broadband sound absorption in that the absorption coefficient is 0.91 on average over a broad frequency range between 360Hz to 540Hz. The normalized bandwidth of 80% absorption to the centre frequency is 0.44 since the experimental results show greater absorption coefficients than 0.8 over the frequency range from 360Hz to 540Hz.
Metamaterial-based micro-perforated panels (MMPPs) were proposed by adding local resonators (LRs) upon one face of a conventional flexible micro-perforated panel (FMPP). Mass-cantilever resonant structures are adopted as LRs here, and they are separated on a sub-wavelength scale. Through theoretical and numerical analyzing, MMPPs are proved able to enhance sound absorption in the stop bands caused by local resonances. Specifically, the theoretical model is developed based on effective medium method, as the distance between the LRs is much smaller than the structural wavelength in the host panel (i.e. FMPP) in the considered frequency range. The full-size simulation model is conducted by utilizing the commercial software COMSOL, considering all the multi-physical couplings among the fluid and solid domains. Good agreement is achieved between the theoretical predictions and the simulation results, for both the FMPPs and MMPPs. Physically, the theoretical and numerical models reveal that the sound absorption enhancement mechanism stems from the resulted additional phase shift, and the enlarged divergence between the average velocity of the air particles inside the perforations and that of the panel attached with LRs. The proposed MMPPs possess great potential in noise reduction industry.
Gears have recently been aggressively adopted in large aircraft engines because they improve turbine and fan blade efficiency by better matching the optimal speeds of the associated shafts. The high operating speeds and extreme focus on weight reduction lead to gear vibration behaviors that are distinct from conventional gears. High speeds give high excitation frequencies, and lightweight, thin-walled gears have lower natural frequencies. This combination triggers resonance, gyroscopic effects, nonlinearity, vibration of the gears as elastically compliant bodies, and parametric instability. These behaviors are driving development of new models and analysis tools different than what is typical for conventional gears. This presentation will start with industrial examples motivating the work. Next, we describe modeling and analysis of gear vibration using analytical and finite element/contact mechanics methods, with special attention to planetary gears because they are the de facto standard in aerospace applications and because of their interesting dynamics arising from cyclic symmetry. These models, and their experimental validations, will be used to illustrate and explain, without emphasis on mathematical details, the unique vibration behaviors that occur and how the analytical/computational findings have powerful practical implications.
NOTE: The live recording of this keynote is now available on YouTube.
From 2012 Prof. Parker is the L. S. Randolph Professor in the Department of Mechanical Engineering at Virginia Tech, where he also served as Department Head. Previously he was a University Distinguished Professor and the Executive Dean at the University of Michigan-Shanghai Jiao Tong... Read More →
With a certified guide from Guidatour, explore the old Montreal, including the visit of Cathédrale Notre-Dame (this one did not burn yet and hosted the famous wedding of Céline Dion years ago). Built between 1824 and 1829, the Basilica is the first Gothic Revival church in Canada. It is renowned for its splendid interior and ornamentation. Don't miss the Casavant organ, one of the largest in North America, the remarkably carved high altar, the pulpit and the Our Lady of the Sacred Heart Chapel.
NOTE: This tour is for accompanying person registered in the accompanying program. Meeting time is 13h45 from ICSV26 registration desk.
In automotive field, vehicle vibrations induce movement on hundreds of connectors which are located near the engine or inside the vehicle compartment. These vibrations produce induced-frictions between male and female parts in contact inside the connector (named pin and clip respectively) and generate electrical failure due to the well-known fretting-corrosion phenomenon. A relative displacement of 5 micrometers between the pin and the clip is sufficient to generate debris at the contact zone and lead to an intermittent conduction at this interface which represents 60 % of electrical failure within a car. Connectors are made of a substrate of copper alloy plated with a tin layer. Tin is used to coat and protect the copper substrate. The oxygen reacts with the soft tin and formed a hard and brittle layer of tin debris and cause high degradations. This third-body layer is composed of insulated (oxide) and conductive debris (non-oxides). The electrical conduction could be disturbed through this granular layer. The displacement and evacuation of oxidized debris is not so well understand. For our study, an automotive connector was submitted to vibration tests. The used bench is composed of a piezo-electric actuator which provides a controlled movement between the clip and the pin. A generator provides a stable current through the connector and the measurement were performed with a voltmeter, a temperature controller and an oscilloscope for real-time analysis. The bench is mounted on an anti-vibration table in order to avoid external vibrations. The measurement of electrical behavior was undertaken under two atmospheres: air and nitrogen gas. The use of air atmosphere shows a typical augmentation of the amplitude of the contact voltage whereas the use of nitrogen gas induces a contact voltage decrease. The measurement of these electrical characteristics provides new information to understand the fretting-corrosion phenomena.
The vehicle suspension system considering time delay is taken as the research object, and the combination methods of theory and experiment is used to study the vibration characteristics of vehicle suspension system. Firstly, a matrix inequality for system asymptotic stability is derived by using the Lyapunov-Krasovskii functional and free-weighting matrix method. Based on the matrix inequality, a H∞ controller is designed for the system with known maximum time delay. Then, the proposed control strategy is used to solve the control problem of the active suspension system. Numerical simulation and experimental methods are used to verify the time-delay control strategy. The results show that the control law in this paper can effectively suppress the sprung mass acceleration. Finally, the relationship between the time delay and the RMS value of the sprung mass acceleration under different gains is analyzed. It's found that a better control effect could be obtained when the difference between d and τ is small.
Parallel barriers are widely adopted to control environmental noise, but their performance may be inferior to that of a single barrier owing to the formation of multiple reflection waves between the parallel barriers. To improve the performance of parallel barriers, single or multiple Helmholtz resonators (HRs) are proposed to be mounted on the barrier surface. An acoustic interaction occurs between the HR and open cavity formed by the rigid ground and a pair of barriers, whereby the acoustic modal response within the open cavity is significantly suppressed and the diffraction wave at the barrier top edge is reduced. A semi-analytical model for dealing with acoustic coupling between the open cavity and HRs in a two-dimensional configuration is established in order to understand the sound suppression mechanism within the shadow zone. With the optimal position of a single HR, the insertion loss of about 10 dB around the target frequency can be controlled, while less influence is exerted on the off-target frequency.
Poroelastic materials are well known to possess exclusive properties for sound absorption. However, tuning their properties for achieving the better acoustic performance is not an easy experimental tasks which can be significantly improved by mathematical modelling. In this work we exploit the homogenization procedure to determine the effective properties of an air-saturated material with microstructure. These properties are then used to solve an acoustic problem with the final objective of finding the optimal design microstructural parameters for the highest acoustic absorption. The microstructure of a material is formed by the translation of a unit cell. We study certain topologies of a unit cell to verify their effects on the optimization results. Moreover, we consider different types of a skeleton material (perfectly rigid, stiff and soft frames) and demonstrate the influence of the material properties on the optimal design parameters. Particularly, the effective elastic properties experience different patterns for the stiff and soft matrix materials. It leads to the distinct behavior of the absorption coefficient. Additionally, the optimal design parameters for a poroelastic material with a stiff and rigid frames become identical with the high values of optimal porosity whereas for a material with soft frame the optimal porosity remains low. The developed procedure can be adopted for the studies of related problems, such as optimal acoustic absorption of sandwich panels.
When measuring the insertion loss of a hearing protection device (HPD) with an acoustical test fixture (ATF), the measured insertion loss can be limited by the self-insertion loss (SIL) of the ATF. The SIL is impacted by any pathways that allow acoustic energy to reach the ATF ear simulator microphones via a route other than through the HPD being measured. Standards that specify the use of an ATF for HPD measurements (such as ANSI/ASA S12.42 or ISO 4869-3) include minimum requirements for the SIL of the ATF, as one component in ensuring the validity of insertion loss measurements made on HPD samples. Traditionally, SIL has been measured with any artificial flesh simulations removed from the ATF and with the ear simulator microphones blocked by metal plugs or isolation caps. Such measurements may not be representative of the SIL obtainable when the ATF is configured for HPD measurements. We propose a method for measuring the ATF SIL with all flesh simulations in place and as configured for HPD measurements and present data measured on several commercially-available ATFs. We also propose insertion loss limits to be met by ATFs when measured with this method, in the hopes that such limits will be useful to future revisions to HPD measurement standards using ATFs.
The analysis of defects in compressor rotor blades in the development and operation of aircraft gas-turbine engines implies the aerodynamic nature of rotor blade vibrations (in most cases). Flutter is a very dangerous phenomenon, that is why it is necessary to outline the conditions of its occurrence in engine development. This is especially true of modern engine compressor rotor blades with a high aspect ratio and integral joint connection with the blade wheel disk. Despite many existing methods for determination of the conditions of flutter initiation, its prediction at the stage of engine design remains a topical issue. This paper will focus on basic concepts of the express assessment of the dynamic stability limit of gas-turbine compressor blade assemblies to prevent subsonic flutter, as well as the examples of its application.
Mohammad Rafiee received his Ph.D. degree in Mechanical Engineering from the University of Ottawa in 2018. Currently, he is a Postdoctoral Fellow at Polytechnique Montreal in Canada. His research interests are primarily focused on the development of advanced composite materials, smart... Read More →
Centrifuge is wildly utilized in civil engineering and environment experiments et al. The power system drives the rotor shaft and arms to produce centrifugal field for experiments, it is a typical rotor system. Some previous work has focused on modal frequency to investigate the dynamic characteristics of centrifuge, and estimated the structural design by strength instead of stability. With the increased requirement for higher load and faster rotational speed, the Coriolis effect of spinning could not be ignored. This work develops the analysis approach of rotor dynamics for typical centrifuge with arms, based on considering the Coriolis effect and the principle of rotor dynamics. Also, the stress strengthen effect induced by the high centrifugal force has been considered. The numerical results is verified by data from the experiment. Next, a new centrifuge is modeled by the above approach and its critical speed is studied with the influence of different parameter including the stiffness of the bearings. The state of unbalance force is also analyzed and the dynamic stability of the centrifuge is assessed according to the standards of rotor machines. The assessment method for dynamic stability of centrifuge is established by deformation of the shaft instead of the stresses, which could supply reference for this class of rotor systems.
Designing a thin sound absorber having the wide bandwidth in the low-frequency range has been a challenging problem, but recently, researches on the metamaterials or the metasurfaces are actively investigated. In this study, we propose an acoustic metasurface that absorbs sound energy perfectly at target frequencies based on hybrid resonance using an array of mul-tiple-type Helmholtz resonators of subwavelength scale. Based on a theoretical model, we op-timally design a unit cell of the proposed metasurface for perfect sound absorption at a target frequency. Since oblique incidence of the sound should be considered for a practical applica-tion of the proposed metasurface, we fabricate samples of periodic array of multiple unit cells for large area and the absorption of the sample in diffuse field are measured in a reverbera-tion room. The present work is expected to open a possibility for potential applications of the proposed metasurface in room acoustics and architectural acoustics.
The exterior sound emission of a vehicle is an increasingly important criterion for the homologation of road vehicles. Until recently, it has been measured outdoors, but can now be evaluated in a laboratory environment using a linear microphone array and a stationary vehicle on a rolling bench. Within this procedure, the tyre noise contribution, as well as the various noise source contributions, can be individually estimated and analysed by further using a near field microphone array in close proximity to the tyre to characterise the tyre source. This work assumes a low frequency tyre model which predicts the structural behaviour of a tyre up to 1 kHz. A microphone array in the far field is used to estimate the far field pressure spectrum of the source. The tyre is then embedded into an inverse method model, where near field pressure observations are used to estimate a simplified equivalent radial velocity distribution on the tyre. The equivalent source distribution and the far field microphone array are then utilised to synthesise the far field spectrum of the equivalent source and comparison is made between the original and synthesised pressure directivity. A number of p-norm regularisation techniques are also introduced to improve the accuracy of the equivalent source and synthesised pressure estimates by optimising the number and position of the equivalent sources. Corresponding measured results are also shown to highlight the validity of the method.
With the continuous development of high-speed train technology in China, many high-speed train lines have been incorporated into the national plan, and high-speed railway stations have gradually become the indispensable center of urban economic and cultural development. As the main part of high-speed railway station, waiting hall plays an important role in passenger diversion waiting. Because the high-speed railway station belongs to the super-large space in acoustics, there is little research data on its acoustical characteristics. At present, China has not formulated the acoustical design specifications for high-speed railway station, so there is no reference for the acoustic design parameters of waiting hall. For this kind of huge public space, how to hear public broadcasting clearly is the primary problem of acoustic design. In this paper, the main acoustic parameters (STI, STIPA and RT) related to speech intelligibility are selected to simulate and analyze the acoustic characteristics of the waiting hall of Chengdu Railway Station. The analysis results show that the reverberation time of the waiting hall with a volume of 1.2 million cubic meters can be shortened to 6.2seconds and the average speech transmission index of the waiting hall can reach 0.4 by using perforated aluminum panels with acoustic tissue applied on the back in the ceiling. After reasonable electroacoustic design, the average speech transmission index of public broadcasting in waiting area can be increased to 0.5 by using strong directional loudspeaker array with large horizontal coverage angle and small vertical coverage angle to cover passenger seats evenly. According to IEC 60268-16 standard, STIPA results are in the fair level (0.45-0.60).
In the automotive industry, the silence and ride comfort of the car body have been markedly improved by the development of the hybrid vehicles and fuel cell vehicles. However, the complicated frictional vibration is caused in brake system by the pursuit of a high brake performance. In high-speed areas of highways and roads with steep descents, the heat in car disc brakes sometimes causes a vibration problem. This phenomenon, called hot judder, is generated by hot spots on the surface of the disc. The generation mechanism of hot judder has not yet been clarified. In this study, hot judder is modeled as self-excited vibration due to the time delay caused by heat deformation of the disc, and the fundamental generation mechanism of hot judder is analyzed by a simple three degree-of-freedom system. In the analysis, the temperature of the disc is calculated by the equation of heat conduction. Then, the relations between disc temperature and the expansion due to heat and the shrinkage due to cooling is examined. Furthermore, the effects of disc surface wear are considered in the vibration analysis model because it has been known that the quantities of the surface wear is large at the position where the hot spot has occurred. It was found that (1) hot judder is an unstable vibration due to the time delay of the fluctuation of brake disc thickness caused by thermal deformation, (2) the number of hot spots is related to the natural frequency of the system, and (3) the wear increases in proportion to the quantities of expansion. Moreover, (4) when the vehicle speed changes, the number of hot spots also changes.
It is intended to present dynamic model of the drilling system consists of drillstring and drilling fluid. The drillstring is a sequence of Euler-Bernoulli beam elements with some constraints and loads. Its dynamic model is established by using the absolute nodal coordinate formulas (ANCF). The drilling fluid is composed of three sequences of one-dimensional compressible fluid elements. The three sequences representinternal, annulus and under-bit fluid each. The drilling fluid is modeled by using the Arbitrary Lagrangian-Eulerian (ALE) description, where the force of the drillstring acting on the drilling fluid is introduced through the drilling fluid transport motion, meanwhile, the reaction force acting on the drillstring is taken as an external load. The model also considers the boundary conditions in usual drilling engineering at the bit, at the top, at the connection and at the inner surface of the wellbore.Using this model, the coupled vibration of the drillstring and the effects of the drilling fluid are investigated through several examples.
Recently, the study of topological phase transitions and edge states for acoustic wave systems has become a research hotspot. However, most current studies on topological edge states are based on Bragg scattering, which is not practical to apply in situations involving low-frequency sound because of the large structural dimensions. Therefore, we construct in this study a graphene-like structure based on a sub-wavelength resonant unit Helmholtz resonator and adjust the acoustic capacitance diameter of adjacent units to change the local resonance frequency, and thereby impose the degeneracy of the Dirac cone and topological spin states, which is characterized by valley Chern numbers of opposite sign. We also check topological valley edge states at zigzag and armchair interfaces and find that gapless topological valley edge states only appear at zigzag interfaces, whereas armchair interfaces host gap edge states. Moreover, the results show that the transmission properties of edge states in a zigzag rectangular waveguide are immune to backscattering and defects.
A pipeline is often considered as the most convenient, efficient and economical mode of transporting liquids likes petroleum, natural gas, and water etc. Damages to this pipeline can cause loss of resources and the contents can also be harmful to the environment. In order to minimise the damages brought to the environment and the loss of resources, rapid non-destructive detection of pipeline leakage is indispensable. In previous works, acoustic wave propagation based methods were used in leakage detection in a pipe without flow. In this study, the acoustic wave method and a modal frequency technique are used to detect leakage in a pipeline system in the presence of mean flow velocity. Computational fluid dynamics (CFD) analysis was employed to simulate acoustic wave propagation in air-filled pipes with leakage in the presence of mean flow velocity. Furthermore, experimental testing was conducted to validate some of the numerical results. The experiment performed consisted of the measurement of acoustic wave propagation in a straight air-filled pipe with leakage. The CFD analysis of fluid-filled pipe can be used to simulate the acoustic wave propagation and acoustic wave reflectometry of a fluid-filled pipe with leakage of different sizes in the presence of flow. Also, the measured signal of acoustic wave propagation in the pipeline from the experiment can be decomposed and de-noised to identify and locate leakages of different sizes.
Focused transducers with a central hole are widely used in high-intensity focused ultrasound applications. The spatial averaging effects of hydrophones when characterizing the field characterization of such transducers should be reckoned. The analytical model derived based on Fresnel approximation will end up with multiple integrals, which is very time consuming to be computed. In this research, a fast estimation method for spatial averaging correction of hydrophones when characterizing such transducers based on multi-Gaussian beam model is developed, the computer optimization is used to evaluate the coefficients. Generally, the spatial averaging effects will result in an underestimation of the absolute acoustic pressure amplitudes. The results derived based on the multi-Gaussian beam model are compared with the Fresnel approximation, which agreed well with each other.
We propose a design to realize a one-dimensional two-way unidirectional acoustic filter in the linear regime for the first time. This is down by combining the concept of functionally graded phononics and the free vibration characteristic of a finite-sized phononic structure. The key to this design is to locate a natural frequency precisely in a band gap, and we show theoretically here that this frequency should be associated with an edge mode. The efficiency of the acoustic diode is also discussed and optimized. Further, by making use of soft materials, we are able to realize a tunable acoustic filter through stretch.
Acoustic levitation is a non-linear effect under the high sound intensity condition. The principle is that the vertical levitation force is generated by the interaction between acoustic standing wave and object to overcome the weight of small object, and the horizontal positioning force is generated to fix the object at the node of sound wave. The standing wave field is very sensitive to the distance between resonantor and difficult to manipulate particles. In the paper a non-resonant standing wave field is used for acoustic levitation to manipuated particle in air. A series of experiments are investigated and discussed.
Mufflers are widely used in automotive, aerospace, military and other traditional industries, as well as compressor and pipeline systems in household appliances. Based on the transfer ma-trix method, this paper studies noise elimination mechanism of single-sided inlet or outlet mufflers. In this paper, the four-pole parameters of the side inlet and outlet muffler are de-rived. The sensitivity analysis of the four-pole parameters of the muffler is carried out, and the key parameters affecting the transmission loss performance of the muffler are determined. Furthermore, the influence of key parameters on the performance of muffler is analysed, and the performance optimization method of side inlet and outlet muffler is finally obtained.
Dirac cones of an acoustic system are the foundation of most topological phase transitions and topological states, and have recently become a research hotspot. Although the Dirac cones, Dirac-like cones, double Dirac cones and semi-Dirac points are all skillfully designed, it is still indispensable to realize a tunable Dirac cone in a novel acoustic structure. We propose two-dimensional acoustic metamaterials with matryoshka structure to achieve tunable Dirac cones and topological spin states. Dirac points can be obtained on the dispersion curves owing to the high symmetry. The concentric circular scattering units of the matryoshka structure are arranged in honeycomb lattices. By a rotating-scatterer mechanism to break the symmetry, the Dirac cone at K (K') is split and the topological spin states appear at the band valley. The existence of a topological transition with opposite Chern numbers as the rotating angle varies is also verified, and chair edge states are obtained along the interfaces separating the topologically opposite spin states insulators. Moreover, the frequency of the Dirac cone is tuned by rotating the inner structure in a double-layer matryoshka structure.
This works presents a methodology to obtain, numerically, the transfer matrix (TM) of a pipeline component with fluid-structure interaction (FSI), supported by experimental model verification and compared with well-known analytical solutions.This is achieved by extending the two-load method used to obtain the TM of a purely acoustic component to a four-load method, applied to a FEM model with FSI. Analytical models are available for singular pipeline components, but when it comes to complex shaped components, numerical and/or experimental analysis have to be performed in order to obtain a representative model of the system. One way of achieving this is by modelling the overall system in a TM method (used to describe the acoustic behaviour of a fluid contained in a pipe), which relates the state vector at two different locations of the circuit. This method can be used in a substructure fashion, where each component can be described/characterized independently by a transfer matrix. An approach exists to obtain these properties numerically from a FEM model, via the two-load method, used for a purely acoustic model, in which state vector contains two generalized quantities: velocity and pressure of the fluid. Further analysis show that neglecting FSI in some cases leads to wrong results. In this case, the state vector containing four generalized quantities, relating not only the pressure and velocity of the fluid in the inlet and outlet, but also the stress and velocity of the pipe wall is needed. A combination computational approaches with experimental verification are used to perform the characterization of such components.
The current riveting process to assemble components in the aerospace industry involves either manual riveting or the use of riveting robots. The manual riveting process requires pneumatic rivet hammers and bucking bars. This operation creates a hazardous environment for operators, as it produces significant noise and vibration levels. Prolonged exposure to noise has adverse impacts on the human hearing system and also contributes to other physiological concerns. Similarly, vibrations transferred to their hands during operation, puts them at risk for developing musculoskeletal disorders leading to injuries. Despite advances in additive manufacturing, composites, and robotics, human operated riveting will likely remain a large component of aerospace and other manufacturing. Alternative kinds of bucking bars, intended to reduce vibration-related stress on the operator, have been proposed and tested with mildly positive results, including spring-dampened bars. This study explores the feasibility and effectiveness of a novel kind of bucking bar, which will incorporate an active control system to reduce the vibration transmitted to the operator. The incorporation of an active element makes this problem analogous to the comparison of active and passive suspensions in motor vehicles. Various active-control bucking bar (ACBB) designs will be discussed, some of which will be selected for development into prototypes. A mathematical model of the selected ACBBs will be developed and a neural network algorithm will be used to evaluate an optimization metric based on ISO 5349-1. The optimal control parameters to best reduce the vibration felt at the bucking bar handle are then selected to minimize the metric. These results will be compared with mathematical models of the current state-of-the-art standard and passive damping bucking bars.
Despite the wearing of hearing protection, the number of acute acoustic trauma remains important. Machine guns, artillery, explosives and all kind of weapon systems used by soldiers especially during training exercises frequently induce hearing damage. French Army counts more than one thousand acute acoustic trauma every year. Nowadays, passive earplugs with nonlinear attenuation (level dependent) are increasingly used in Armies: they protect against impulsive noise while keeping contact with the useful sound environment. Nevertheless when they are in "open position" they do not protect against continuous noise. However, to reduce the number of acute acoustic trauma, it is obvious that noise attenuation should be maximized by taking care of the well-fitting of earplugs. This is the reason why ISL and the French Company Cotral Laboratory, specialized in high quality custom molded earplugs initiated a partnership to realize 30 prototypes of an intelligent earplug for assessment in military environment. This study is financially supported by French government (DGA) in a project named BANG (Bouchon Auriculaire de Nouvelle Génération). The intelligence of both the processing and diffusion algorithms for input and output sound signals is connected in one way to the ear via a custom molded earplug and to the communication equipment of the soldier in other way. Main functionalities of BANG are: i) high-quality passive protection, ii) active noise reduction, iii) reproduction of the sound environment at a controlled level, iv) check-up of the correct insertion of the protection during switch-on procedure, v) sound recording directly within the ear canal. Another capability is to realize in situ dosimetry during professional activities. In the near future, one important capability of BANG will be to use the microphones inserted in the custom molded earplugs (doublet right/Left ears) to improve acoustic detection of noises in the battlefield.
Pumping systems are used for transmission of fluids in various technological processes. Quite frequently the pumping unit in the pumping process is of a displacement type. Using the same type of pump in different systems results in pressure pulsations, which become the cause of increased vibroacoustic loading and failure of a unit components. Therefore, it is important to know the pressure pulsations in the fluid power system at the design stage. We have applied the theory of electrodynamic analogy and the equations of an acoustic quadrupole to propose a method for calculating pressure pulsations in fluid power systems based on models of dynamic primitive geometries such as "capacitance", "pipe" and "resistance". The proposed method allows to estimate the dynamic characteristics of the fluid power system at the design stage, and also allows to select the geometric parameters of the system ensuring minimal pressure pulsations
Noise in hospitals is known to hinder communication among staff, causing annoyance, irrita-tion and fatigue, and detrimentally impact the quality and safety of healthcare. High noise levels and noise-induced stress impact negatively on staff performance and wellbeing. The paper presents the results of the assessment of working conditions at workstations in selected hospital rooms in Poland. Environmental measurements were conducted in the rooms of a second referral level hospital in Warsaw. Measurements of quantities characterising noise, were carried out at selected workstations in the rooms occupied by the Radiodiagnostics Unit, Operating Suite, Central Sterilisation, Endoscopic Examinations Unit, Analytical Laboratory and Water Treatment Station. In order to assess the exposure to noise at workstations, the measured quantities of noise characteristics were compared to the exposure limit values. The test results showed that the exposure limit values and exposure action values are not exceeded.
The running all-terrain amphibian vehicles are subjected to intensive vibrations of all parts of a vehicle, and mainly of its powertrain and chassis. Newly patented Vibration Energy Harvesting Damper (VEHD) is designed to provide dual results: reduction of severe vibrations and producing the additional electrical power. The perspective feature of proposed VEHD is the ability of effective vibration damping combined to energy harvesting in broad range of frequencies. The mathematical analysis based on parameters of the selected all-terrain amphibian vehicle powertrain (specifically engine) and chassis is developed. The arranged tests on recently designed all-terrain amphibian vehicle demonstrate the satisfactory compliance with theoretical forecasts.
I am now developing the new sound localization method, the Double Near-field Acoustic Holography (DNAH) method. This method can localize the location of low frequency sound source precisely. In this method, the measurement plane of NAH method is doubled. To measure the sound information on the doubled measurement plane, two microphones which move vertically and horizontally are used. In former research, the distance between two microphones, the distance between two measurement planes is 0.2m. In this paper, the experiments are carried out with variable distance. As the result, it is verified that the DNAH method is also effective in the case that the distance between two microphones is short, several cm. Therefore, it is proved that the intensity probes can be used for measurement of DNAH method.
Recent years, rather than the noise measures, the noise gives us the impression especially accelerating sound for cars. That is, the control method of the engine sound is shifted from the noise reduction to sound design. Therefore, we proposed a method to design the engine sound using Active Quality Control of Sound based on Active Noise Control. We confirmed that the engine specific order components can be amplified and reduced like an equalizer with the proposed algorithm. And, auditory impressions of engine sound controlled by proposed method were investigated using psychoacoustic measurements. The scale values of preference for each stimulus were obtained by Scheffe's paired comparison tests. When the reduction-level increased, the preference was decreased or increased from the reference sound. Also when the amplification-level increased, the preference was decreased from the reference sound. As the reason, it seems that reference sound pressure is felt to be sufficiently large. These results indicated that the control corresponding to the individual is important for improvements in auditory impressions. To solve these problems, our method was developed to adjust to individual preferences. The individual preferences of sound were connected to each driver's driving pattern. Thus, we developed our system, which enables the automatic generation of individual sound preferences.
Turbulent boundary layer trailing edge noise is the dominant noise in airfoil self-noise. This noise generated by the trailing edge can be minimized by different edge treatments. Varying the acoustic impedance of the trailing edge acoustic radiation can be varied. A NACA0012 symmetric airfoil with 0.3 mm thick solid and perforated plate fitted at the trailing edge is used for this study. Experiments were carried out in an anechoic facility at different velocity varying from 20 to 45 m/s and geometric angles of attack of 0o. Solid trailing edge extension and perforated trailing edge extensions enhance the noise reduction in the low frequency range. As compared to solid extensions perforated extensions provide greater noise reduction. Maximum noise reduction of approximate 6.5 dB in the low frequency range is obtained for the perforate plate attachment at zero angle of attack. At higher velocities an increase in the high frequency noise is observed due to the roughness offered by the perforated extension plate. OASPL analysis shows the strong dependency of the trailing edge with the jet velocity.
The advent of low-cost acoustic sensor networks in cities allows the development of innovative approaches such as sound environment recognition, sound source detection, and more. Such tools are capable of improving the quality of the monitoring of the acoustic quality of cities. In order to improve the context of road traffic noise mapping, the use of Non-negative Matrix Factorization (NMF) techniques, as a source separation method to estimate the urban road traffic sound levels from measurements, has proved to be a successful approach. In order to gain knowledge about the robustness of those techniques, this paper studies their behaviors of the initialized thresholded NMF on a corpus composed of urban sound scenes mixing traffic and specific interfering components with calibrated sound. The results reveal the different performances of this approach to estimate the road traffic sound level, depending on the noise levels of the interfering sources, their proximity to the urban traffic spectrum and the choice of the threshold value.
We consider acoustic wave propagation in periodic scaffolds saturated by Newtonian slightly compressible fluids. The wave-induced fluctuations are superimposed to the steady incompressible flow. To analyze the wave dispersion, two approaches are examined: the periodic homogenization (PH) and the Floquet-Bloch wave decomposition (FB). Pursuing the first approach, the homogenization of the Navier-Stokes equations in the rigid skeleton provides the dynamic permeability of the effective porous medium which captures the wave propagation for wave lengths significantly larger than the characteristic porosity size corresponding to the one period of the lattice. The dispersion phenomenon is remarkable for low frequencies, whereas constant phase velocity characterizes the asymptotic behaviour for larger wave numbers. Using the second approach, the FB decomposition enables to capture the wave response for wave numbers within the whole first Brillouin zone. We derive the equations of the cell problems describing the local fluctuations of the wave polarization. Several models are considered. For the inviscid static fluid, the pressure, or velocity formulations are derived. The computational analysis for scaffolds of different types and with variable porosity was performed, showing the band gap between the two lowest frequency modes. Further, using the FB wave decomposition ansatz, we derived a model of viscous fluids in the scaffolds, respecting effect of the fluid convection flow at a steady state upon which perturbations induced by the wave propagation are superimposed. Differences in the wave dispersion between the inviscid and viscous fluid are reported. Dispersion effects influenced by the fluid advection are illustrated for different fluids. Numerical illustration are given.
Auditory discomfort induced by hearing protection devices (HPD) which is related to the value of the sound pressure at the eardrum is one reason that reduces their efficiency. Numerical models prove to be efficient tools to better predict this pressure since they allow for integrating all geometrical and structural complexities of the head-ear-HPD system and go beyond the practical and ethical limits of experiments on living humans. The ultimate goal of this research is to elaborate a finite element (FE) model of a head-ear-HPD system and an associated anatomical phantom to investigate both the air-conducted and bone-conducted sound transmission through ears occluded or not by HPD of earplug type. This paper focuses on the development of the FE head model and its preliminary evaluation. The procedures of geometrical reconstruction and modeling of the head, including the brain, cerebrospinal fluid, skull, and soft tissues based on in-vivo magnetic resonance imaging and cone-beam computed tomography medical images are explained. As head resonances are related to bone-conducted sound, the eigenfrequencies and corresponding mode shapes of the system provide valuable information for interpreting its vibratory response and also for further understanding their impacts on hearing perception. Therefore, as a first step in the FE head model evaluation, a modal analysis and a study of the forced response are carried out using COMSOL Multiphysics 5.4 (COMSOL®, Sweden). Results are compared with available numerical and experimental data in the literature and discussed.
This investigation is about the motion of a cantilevered beam used in tapping mode atomic force microscopy (AFM) which can be utilized in scanning the topographical features of biological samples or "pliable" samples in general. These cantilevered beams can be used to modify samples by using high frequency oscillations to remove material or shape nano structures. A cantilever nanobeam with arbitrary boundary conditions is studied to investigate different configurations and the effects on the relevant parameters. The nano structure is modelled using the Euler-Bernoulli theory. Eringen's theory of non-local continuum is incorporated to simulate the dynamics of the system. This theory is effective at nano-scale because it takes into account the small-scale effects of the structure. The scanning process is achieved by tapping/contact with the sample surface to determine the topographical profile of the sample. The tapping contact force can also be used to deform the sample surface or remove material using high frequency oscillations. The fixed end is modelled as a torsional spring with zero transverse displacement instead of the "ideal" or clamped boundary condition. The torsional boundary condition can be tuned, by changing the torsional spring stiffness, such that the compliance of the system matches that of the sample to prevent mechanical damage of both the cantilever tip and the sample. The boundary condition at the free end is a tip-mass attached to a transverse linear spring which models a contact force. At nano scale, the surface area to bulk ratio increases and surface effects becomes a significant factor when determining the natural frequencies of the system. The motions of the tip of the beam and the tip-mass is investigated to frequency response and force. The tip response frequency includes information about the maximum displacement amplitude and therefore the sample penetration depth.
Mohammad Rafiee received his Ph.D. degree in Mechanical Engineering from the University of Ottawa in 2018. Currently, he is a Postdoctoral Fellow at Polytechnique Montreal in Canada. His research interests are primarily focused on the development of advanced composite materials, smart... Read More →
The importance and use of curvic coupling joints are garnering interest in many aero-engine rotordynamics applications thanks to their benefits such as lower stress, higher service life, reliable positioning, precise centering and strong loading capability. Their predominant application is in the assembly of the rotating elements such as shafts, impellers and turbine discs in order to mainly provide torque transmission in high-speed rotating machines. In order to predict rotor dynamic behavior of the rotor systems, specialized one dimensional (1D) finite element codes are generally preferred due to their computational efficiency. However, the effect of the curvic couplings is usually ignored in traditional rotor dynamics analysis due to their complex geometry. This approach may lead to inaccurate calculations especially at higher speeds. In this study we compare the dynamic characteristics of continuous and discontinuous curvic coupling joints on a single stage compressor-turbine rotor system with tie-bolt design. The first four lateral natural frequencies are calculated and compared for each case by using three dimensional (3D) finite element models considering the contact effect via modal analysis with linear perturbation method. Results show that curvic couplings reduce the natural frequencies of rotor system at all rotating speeds under preload and centrifugal forces. Finally, a sensitivity analysis under separation loading is examined in which higher frequency shifting and mode shape changes are observed.
A numerical optimization method is performed on a fictive but realistic porous material with a continuous through the thickness gradient of porosity. The porous material is made of ordered unit cell with parametric geometrical dimensions. The Johnson-Champoux-Allard-Lafarge parameters of any geometrical unit cell is computed by FEM method. These parameters are used as input for the prediction of the acoustic properties of the graded material. A conjugate gradient algorithm eventually creates the best micro-geometrical continuous gradient with the optimal acoustic absorption. The acoustic performances of the continuous graded material are discussed with respect to the optimized non-graded material. All the investigations are made on the same unit cells. The numerical results show a significant improvement of the targeted acoustic absorption when introducing the gradient of properties.
For the adverse effects of a large amount of background noise on the test results in the wind tunnel test, a noise separation method based on double arrays is proposed. Firstly, all back-ground noise is equivalent to an interference sound source, which is located on two planes re-spectively with the target sound source. Two planar arrays are inserted between the target sound source and the interference sound source. Next, by calculating the sound pressure measured on two arrays jointly, the data of the target sound source radiated to an array sur-face alone is obtained. Finally, the nearfield acoustic holography algorithm in moving fluid medium is used to reconstruct the target sound source, achieving the separation of the target sound source and background noise. In addition, a hologram pressure extrapolation technique using back propagation neural network is introduced to reduce the window effect by the finite aperture and the wraparound error due to the discrete microphone array. Compared with the traditional noise separation methods, the proposed method does not require a priori knowledge and is easy to use, yet of strong robustness and high accuracy. Numerical simulations further verify the feasibility and effectiveness of this method.
Comfort and wellbeing of an individual in a room depends largely on sound pressure level within the room and psychoacoustics. The importance of accurate prediction of acoustics parameters is vital during the initial room's design stage. Many researchers provide a detailed study on the interaction between the acoustics and psychoacoustics parameters. This paper develops a prediction model using different Neural Networks (NNs) such as Autoencoder, Support Vector Regression, Extreme Learning Machines, Deep Neural Network and others to predict the sound pressure level (SPL), Loudness and Sharpness. The results shown that the Deep Neural Network can predict the root mean square error of less than 2 dBA in SPL, 2 sone in Loudness and 3 acum in Sharpness.
In 2016, a standard describing the experimental procedure to measure the underwater sound from ships has been published (ISO17208-1). A second part has been written to correct the measured data from the reflection on the sea surface, effect known as the Lloyd's mirror effect (not published yet). For these procedures, deep waters are required, i.e. a minimum depth of 150 m or 1.5 times the overall ship length. In some maritime areas, this requirement can be difficult to fulfill and the measurements can only be done in shallow waters. It is well known that in a shallow water environment, it is difficult to assess the level of a sound source, because of the multiple reflections on the bottom and on the sea surface. The aim of this study is to understand which parameters influence the sound measured by a hydrophone array in such a configuration, assuming the source level is known. The sound level measured by the hydrophone array is simulated using open source underwater propagation models for propagation distances up to a few hundred meters. The influence of different parameters is successively investigated: source depth, water depth, source range, number of hydrophones, sea bottom properties, speed of sound profile. At low frequencies, the radiation of the source is similar to a dipole because of the Lloyd's mirror effect. At high frequencies, the third-octave bands level tends to a constant number with respect to frequency, which depends on the ratio of water depth to distance to source, and to the sea floor properties. Observations of the results show also that the gap between these two frequency domains is at a fixed value of the acoustic wavenumber multiplied by the source depth. Based on the simulations, empirical formulas are proposed to correct the effect of the shallow water environment.
DEPUTY HEAD/SENIOR RESEARCH FELLOW, ACOUSTIC RESEARCH LAB, NATIONAL UNIVERSITY OF SINGAPORE
A senior researcher with 30 years of experience in underwater acoustics research. Senior member of IEEE, Member of IIAV, ASA and Society of Acoustics Singapore. IEEE OES AdCom and JOAB member, General Chair for OCEANS 2020 Singapore and co-Chair for ICSV 28 Singapore. See my technical... Read More →
This study is the third iteration in a series of studies aimed to develop a system that allows driving blindfolded. We used a sonification approach, where the predicted angular error of the car 2 seconds into the future was translated into spatialized beeping sounds. In a driving simulator experiment, we tested with 20 participants whether a surround-sound feedback system that uses four speakers yields better lane-keeping performance than binary directional feedback produced by two speakers. We also examined whether adding a corner support system to the binary system improves lane-keeping performance. Compared to the two previous iterations, this study presents a more realistic experimental setting, as participants were unfamiliar with the feedback system and received the feedback without headphones. The results show that participants had poor lane-keeping performance. Furthermore, the driving task was perceived as demanding, especially in the case of the additional corner support. Our findings from the blind driving projects suggest that drivers benefit from simple auditory feedback; addition-al auditory stimuli (e.g., corner support) add workload without improving performance.
There are over 100 million of train journeys around the world every day. The dynamic interactions between vehicle and track impose vibrations and acoustic radiations and become moving vibro-acoustic sources along the railway corridor. Especially when there is imperfection of either wheel or rail, the dynamic amplification of loading conditions and reflected vibration effects on infrastructure and rolling stocks is significantly higher. In practice, imperfection of rail tracks can be classified into short wave length and long wave length defects. The short wavelength defects include high-frequency related rail surface defects such as dipped joint rails, rail squats, rolling contact fatigues (RCFs), rail gabs and crossing nose. The long wavelength defects are those associated with low frequency vibrations such as differential track settlement, mud pumping, bridge ends, stiffness transition zone, etc. Most previous studies into vehicle-track interactions are concerned only to a single one of the defect individually. This study is the world first to evaluate the coupling dynamic vehicle-track interactions over coupled multiple short and long wavelength rail defects. The vehicle model has adopted multi degrees of freedom coupling with a discrete supported track model using Herzian contact theory. This paper highlights the dynamic impact load factors experienced by railway track components due to wheel/rail contacts. The insight into the dynamic amplification will enable predictive track maintenance and risk-based track inspection planning to enhance public safety and reduce unplanned maintenance costs.
The paper describes a new class of a hybrid vehicle that uses piezoelectric devices for powering an electric motor while still using conventional fuels, such as gas, diesel, or oil. The installed piezoelectric devices can transform the mechanical energy of the moving pistons or crankshafts into electrical energy, which can be stored in the capacitor or the battery charger. Consequently, the stored electrical energy powers an electric motor, which can supplement the conventional gasoline or diesel engine or work independently. The solution to the problem can significantly reduce the consumption of the conventional fuel, diversify transportation fuel supply, and reduce the air pollution. Use of piezoelectric devices for powering a supplemental electric motor will lead to the development of a new generation of hybrid vehicles, where the mechanical energy of the existing conventional gasoline engine will be converted to electrical energy without significant changes in the design of the existing automobile engine and generator. Using piezoelectric elements for powering the motor can significantly increase the cost-effectiveness of the hybrid vehicles and simplify the currently used charging system of the electric vehicles. The principle of operation is based on the unique properties of piezoelectric materials, which are able to generate an electrical voltage when they are mechanically stressed. The preliminary experimental results demonstrate that a single piezoelectric element under transient dynamic mechanical load can generate a pulse of an electrical voltage in the range of tens or even hundreds of kilovolts. Keywords: power harvesting, piezoelectricity, hybrid vehicles
This work describes the application of a piezo-shunt absorber for robust vibration suppression on a cantilever beam with two piezoelectric patches. The cantilever beam is submitted to harmonic excitation forces containing several harmonic components. In particular, the implementation of the Resistance-Inductance-Capacitance circuit is employed for vibration absorption at the first four mode-shapes of the beam and, by using the Frequency Response Function of the arrangement, the modal parameters of such dominant mode-shapes can be used to synthesize an adaptive-like piezo-shunt absorber for damping injection at specific modes. Some experimental results are presented to validate the good dynamic performance of the piezo-shunt absorber for adaptive damping injection to the cantilever beam.
An experimental study on the effect of artificial hairy coating on the broadband trailing edge noise of a flat plate was conducted and presented in this paper. The study was inspired by the hairy feather structure of quiet-flying owls. The experiment was conducted at the HKUST low speed anechoic wind tunnel, UNITED, at chord-based Reynolds number ranging between 160,000 to 300,000 at zero angle of attack. Turbulent strips were applied at 12-20% of the chord to suppress the instability noise. Three different hairy coatings with varying lengths and diameters were tested. A 56-channel microphone array was used to acquire the induced noise, as well as to investigate the effect of hairy coating on the source distribution. It was observed that the presence of hairy coating significantly reduces the trailing edge noise above a critical chord-based Strouhal number, which depends on the hair length. However, the hairy coating also produces an apparent low frequency hump in the noise spectrum below that Strouhal number. Interestingly, at flow speed close to the owl's flight speed (below 10 m/s), the critical frequency corresponding to the critical Strouhal number is well below 2 kHz, which is the lower hearing bound of owls' prey.
According to the World Health Organization, environmental noise features among the top environ-mental risks to physical and mental health and well-being. Environmental noise includes noise produced by transport traffic, industrial activities, neighborhood and leisure activities. Among the leisure activi-ties which may cause hearing impairment and environmental noise annoyance include fireworks, shoot-ing ranges, car racing and outdoor music activities; this study focuses on the latter. The regulations of Australia, Belgium, France, United Kingdom and Canada (Montréal) are analysed in order to provide a comprehensive comparison. It is shown that regulations are not harmonized, many different indicators and values are used to protect attendees or residents living in noise sensitive areas.
A porous medium made with ceramics is set inside a resonator and the acoustic dissipation occurring in it is measured. Two conditions are tested. One is that the wall of the porous medium is wet by water, and the other is that it is dry. Measured results show that water does not affect dissipation caused by velocity oscillation; however, it affects the dissipation caused by pressure oscillation. Furthermore, it is found that the effect of water increases with the temperature of the working gas. A theory that can consider the effect of condensation and evaporation on sound propagation is used to investigate the result.
Acoustic test fixtures (ATFs) can be used to measure the insertion loss (IL) of earplugs. Reliable numerical modeling of the occluded artificial ear canal of the ATF could be helpful for optimizing the earplug performance during the design phase. This requires the simulation of the IEC 60318-4 occluded ear simulator which is usually based on the classical lumped parameter model (LPM) or complete 3D numerical model. Lumped models are generally accepted to have inherent frequency limitations and cannot properly deal with the thermal and viscous phenomena in certain areas of the simulator. 3D numerical models based on the finite element (FE) or boundary element method are capable of accurately describing the simulator behavior taking thermo-viscous effects into consideration but many dimensional details related to the published numerical models of the IEC 60318-4 simulator remain unspecified. This study proposes a transfer matrix (TM) model of the IEC 60318-4 simulator whose geometry is determined using Computed Tomography scan images. The specific acoustic impedance of certain elements in the simulator model is deduced using the low reduced frequency (LRF) model which has been proved satisfactory to account analytically for thermo-viscous energy losses. The TM model is validated using a 3D FE model of the simulator based on the same geometric dimensions. It is then coupled to a 2D axisymmetric FE model of an ATF ear canal occluded or not by a silicone earplug to simulate the earplug IL. The coupled FE/TM method is found to provide satisfactory IL prediction compared to a complete 3D FE model of the corresponding system. The proposed TM model is also shown to better capture the simulator behavior compared to the classical LPM.
Planetary gear with equally spaced planets is mostly used to achieve vibration and noise reduction. To investigate the internal mechanism of planet phasing, a time-varying mesh stiffness - static transmission error planet phasing model was proposed. The mesh stiffness and transmission error were expressed as Fourier series, and the mesh excitation of the central component was derived to reveal the relationship among mesh stiffness phasing term, transmission error phasing term and mesh excitation phasing term. Meanwhile, the mesh torque phasing theory of traditional planet phasing theory was modified by stating that vibration is suppressed when the mesh torque harmonic is zero. Numerical simulations were implemented to verify the modified planet phasing model. The results indicated that it agrees well to the traditional one except for the case that the mesh torque harmonic is zero. The proposed model incorporates the actual mesh stiffness and transmission error into planet meshing, which improves the compatibility between the study of planet phasing theory and the study of the internal mesh characteristics.
In many engineering fields, plates carrying added masses are present. For example, in a circuit board or a slab carrying machines at different locations, the solid components fixed on the surface can be simulated as concentrated masses due to their small dimensions compared to those of the plate. This may make the calculations of the natural frequencies and their associated mode shapes quite a laborious task, especially in the nonlinear regime. In this paper, a semi-analytical method is developed in order to investigate the linear and geometrically nonlinear vibrations of fully clamped rectangular plates carrying multiple masses at various locations. The theoretical model, based on Hamilton's principle and spectral analysis, used previously to examine the non-linear structural dynamic behavior of various beams, plates and shells, is adapted here. The non-linear formulation, involving a fourth order tensor due to the membrane forces induced by the large vibration amplitudes, has been used to analyze the geometrically non-linear case after the preformation of the necessary change of bases from the BFB (beam functions basis) to the MFB (modal functions basis) which is needed in the present case due to the distortion in the mode shapes caused by the presence of the added masses. The numerical results obtained are compared with the literature in different cases of an added mass at the central line of the plate. A focus is then made on the non-linear case in order to get a better qualitative understanding and quantitative evaluation of the effect of the added masses on the mode shapes and the corresponding backbone curves at large vibration amplitudes. Then, the single-mode approach is used to investigate the effects of the geometrical non-linearity on the forced response of fully clamped rectangular plates carrying one concentrated mass at its center under a harmonic distributed force.
Associate Professor, Rose-Hulman Institute of Technology
Professional interests include undergraduate engineering education, finite element modeling, ground-borne vibrations, vibrations of musical instruments, and dynamics of toys.
High cyclic fatigue (HCF) is by far the main source of failure of bladed disks in turbomachinery applications. In order to reduce the vibration amplitudes, dry friction damping has been widely used in the design of bladed disks in different forms such as; blade root joints, shrouds, solid dampers and etc. This will make the dynamic analysis of bladed disks more challenging due to presence of nonlinear interactions between contacting surfaces. The purpose of the current study is to develop an efficient and highly compact reduced order model (ROM) for nonlinear dynamics of bladed disks subjected to different sources of friction damping. The developed ROM consists of two steps: first, representing the kinematics of the contact nodes lying on adjacent friction interfaces in terms of relative displacements between the node pairs. Afterwards, performing the Craig-Bampton Component Mode Synthesis (CB-CMS) on the full-order model already transformed into relative coordinates. Implementation of relative coordinates not only reduces the computational time but also enhances the CB-CMS basis by incorporating the fully stuck modeshapes of the fundamental sector. Relative coordinates have been already used to reduce the size of the nonlinear problem, in case of contact surfaces located inside the bladed disk fundamental sector, while the proposed formulation in this paper extends their use to contact surfaces over the sector boundaries, where cyclic symmetry boundary conditions are applied. The proposed method was applied to a bladed disk with shroud and blade root friction damping. Numerical simulations revealed the efficiency and the accuracy of the proposed ROM for forced response analysis of bladed disks.
Mohammad Rafiee received his Ph.D. degree in Mechanical Engineering from the University of Ottawa in 2018. Currently, he is a Postdoctoral Fellow at Polytechnique Montreal in Canada. His research interests are primarily focused on the development of advanced composite materials, smart... Read More →
Fibrous absorbers, such as glass wool, are widely applied as thermo-acoustic insulation. The lightweightness and good fire-smoke-toxicity properties of glass wool makes this material a well proven insulation material, e.g. in aircraft cabins. However, since the sound absorption of fibrous materials is governed by viscous losses, their sound insulation performance is reduced at low frequencies. Acoustic metamaterials, on the other hand, have emerged in the recent years as new sound insulation materials with particular efficiency in the low-frequency regime. Due to the dispersive properties of most acoustic metamaterials, however, this efficiency typically is limited to relatively narrow frequency bands. Therefore, it seems to be reasonable to combine the strengths of both types of sound insulation materials in order to achieve good sound insulation characteristics at low and high frequencies with low additional weight and/or installation space. In this contribution, first results from investigations of how the low-frequency acoustic performance of glass wool can be improved by adding acoustic metamaterials are presented. The investigated concept employs a thin plate-type acoustic metamaterial (PAM), which exhibits tunable anti-resonance frequencies with transmission loss values much larger than the corresponding mass law. The PAM is combined with lightweight aircraft grade glass wool and attached to a plate in order to improve the sound transmission loss of the plate. An analytical model is used to predict the acoustic performance of this design. Finally, the concept is validated using a 1.2 m² test sample, which is experimentally characterized using sound intensity measurements in a laboratory.
Spherical microphone arrays allow sound field extrapolation using spherical harmonic expansion. Orthogonality of spherical harmonic functions is a key property to perform sound field extrapolation. When measuring the surface impedance of plane materials, it can be convenient to use a hemispherical array whose equatorial plane is set on the material of interest. In that case, spherical harmonics cannot be used, as orthogonality of the spherical basis does not hold on a half-space. When the hemispherical array of microphones is located above a surface with non-trivial boundary conditions (not Neumann or Dirichlet) a closed-form, orthogonal solution of the wave equation in spherical coordinates does not exist .This paper presents a revisited version of a classical numerical approach to derive orthogonal, hemispherical solutions of the wave equation for non-trivial boundary conditions on the equatorial plane. This theory derives such solutions as a combination of spherical harmonics in the restricted hemispherical range, leading to the so-called spherical Slepian functions. It will be shown that such a functional basis makes it possible to accurately extrapolate the sound field of a source at an arbitrary position in free field using a direct frequency independent matrix. It is shown that the high frequency limitations of the method are related to the spatial sampling of the hemisphere, while measurement noise impacts accuracy in low frequency. Finally, simulation results are presented for a hemispherical array above an acoustically absorbing plane material, with the objective of identifying the surface impedance of the material.
In this paper, the evaluation of source location was conducted by the elderly in different re-verberation times, different signal-to-noise ratios and different noise azimuths. The location ability on noise sources of the elderly was investigated through loudspeaker reproduction in the two real rooms and headphone reproduction after using artificial head recorded in two rooms. The result from the elderly was compared with those from the young adults. It showed that the ability of locating the noise source for the elderly were poorer than that for the young adults. There was a great difference in the location of non-front sound sources between the elderly and the elderly. The accuracy of location for the non-front sound source for the elder-ly and the young adults by using headphone reproduction was poorer than that by using loud-speaker reproduction.
According to the underwater radiation noise requirements of the Polar Scientific Icebreaker, the finite element and statistical energy models were established to calculate the low-frequency and medium-high frequency radiation noise. The prediction and evaluation of underwater radiation noise under the condition of 11 knots speed were carried out. The results show that the underwater noise level of the Polar Scientific Icebreaker is mainly determined by two sets of pod propulsion devices, and the contribution of other mechanical is relatively little. Due to the excessive underwater radiation noise of the pod propeller, the requirements of ICES 209 cannot be met in the frequency range of 90 Hz~600 Hz. For the prediction result, the suggestions to optimize the tip of propeller is given.
DEPUTY HEAD/SENIOR RESEARCH FELLOW, ACOUSTIC RESEARCH LAB, NATIONAL UNIVERSITY OF SINGAPORE
A senior researcher with 30 years of experience in underwater acoustics research. Senior member of IEEE, Member of IIAV, ASA and Society of Acoustics Singapore. IEEE OES AdCom and JOAB member, General Chair for OCEANS 2020 Singapore and co-Chair for ICSV 28 Singapore. See my technical... Read More →
With advancement of technology, methods to restrict concerns at source in automobiles at early stage has become standard. With certain knowledge base industry has been saturated with standard processes to be followed to achieve the required targets. The field of noise and vibration is dynamic and depends on perception of customer. Noise source annoying to one customer might not be same to other. Once we suppress predominant noise in the vehicle secondary noise source can be perceived and becomes irritant. Even with low level of these intermittent noises, annoyance level of customer can change and create bad perception about product. Noise source identification is crucial to implement the solution to achieve the set reduction. It is required to logically collect all the relatable data and use the correct processing techniques to distinguish major source. In commercial vehicle due to variation and multiple source it take big size of data to find the source. In this study, test based measurements for noise and vibration has been performed to find the contributing source of brake pneumatic compressor assembly noise of commercial vehicle run by engine with gear train system. Angle domain processing technique has been widely used to find the exact cause.
The fast movement associated with high speed trains can cause significant dynamic effects within the supporting railway track structure. The speed at which maximum dynamic re-sponse occurs is known as the 'critical velocity' and is undesirable because large rail vibra-tions are generated when travelling close to it. These vibrations can cause a safety concern, and also propagate to the free-field where they disturb nearby buildings. A method to mini-mise these vibrations is to stiffen the soil directly below the track either via soil replacement or soil improvement, however both options are expensive. Their cost can be reduced though if either the depth or stiffness magnitude of the replacement is optimised. Therefore this work develops a track-ground model using the thin-layer method, which is capable of as-sessing the effect of different combinations of soil improvement on track vibration levels. It is shown that if improvement is carefully designed, performance can be maximised for mini-mum cost. Similarly, if improvement is poorly chosen, it can result in marginal improvement, and in some cases even amplify track vibration.
Acoustic measurements of an architectural material in a free field or in-situ are influenced by diffraction from sample edges and reflections from other room boundaries. These undesired waves may cause a measurement error. Especially, a measurement at oblique incidence is quite difficult as the incident angle is larger or the sample size is smaller. In this study, a parametric loudspeaker, which is super-directive by utilizing the nonlinearity of ultrasound, is used to overcome the difficulty. The parametric loudspeaker can reduce the undesired waves by focusing the incident sound onto a small spatial range and will be used as a simple and accurate measurement method. However, the super strong ultrasound used as the source signal causes the nonlinear distortion called "pseudo sound" on the microphone surface and increases the measurement errors. In order to minimize such induced errors, two methods are investigated experimentally: acoustic filtering via phononic crystals and the phase-cancellation excitation of the ultrasound. In our previous work, acoustic impedance of a glass-wool board at oblique incidence is measured using these two methods in an anechoic chamber. The results show that the proposed method is effective at frequencies above 800 Hz in a free field. Based on this, in the presented study, in-situ measurements are conducted in a conference room. This investigation shows that the proposed method can efficiently estimate the acoustic impedance at oblique incidence in-situ at frequencies above 800 Hz.
Ventilation ducts are often lined with passive absorption material for both thermal insulation and noise and vibration reduction. However, the noise reduction performance is not significant at low frequencies. Active Noise Control (ANC) on the other hand can be used in controlling low frequency noise in ducts effectively. This paper presents the main results obtained from the development of an active noise control system for ventilation noise using two approaches. A comparison between the performance of an adaptive feedforward control algorithm and a regenerated reference adaptive algorithm shows that both algorithms provide good noise reduction. Experimental results in the laboratory show that adequate active noise reduction occurs in the frequency range between 100 Hz to 300Hz. The noise attenuation of 20 dB or more for tonal noise can be achieved. The system is also tested in an actual classroom where noise reduction from the ventilation duct is controlled. The results show that the tonal component can be attenuated successfully and a quiet zone achieved in the classroom with a single channel control system.
The trailing edge noise from a heaving wing with a constant NACA 0012 airfoil section was studied at a Reynolds number of 198000 using an anechoic wind tunnel. The airfoil was fixed at an incident angle of 0 degrees. The heaving frequency and amplitude were selected as 8Hz and 10mm, corresponding to a reduced frequency of 0.08 and a Strouhal number of 0.008 based on the chord length. A microphone array was utilized to detect the position and the strength of the noise source at different frequencies. For a stationary wing, the source strength of the broadband noise spreads evenly across the whole wing span while the source of the discrete tones appears as a pair of spanwise cells symmetrical about the spanwise centre. Short-time Fourier transform and a wavelet-based real-time beam-forming algorithm were used to analyse the time dependence of the sound spectra and the source strength in one heaving period, respectively. The sound pressure levels of the discrete tones increases while the wing passing over the mean phase position and experiencing the largest effective angle of attack, and it is attributed to the enhancement of the source strength at the corresponding time.
Transportation noise as an element of pollution of human environment is no longer to demonstrate. Road traffic noise induced annoyance is one of the most negative health impacts includes damage risk, sleep disturbance, increased blood pressure, heart rate, interference with task performance etc. In Africa, most of the time noise is not recognized as pollutant that can cause wide range of negative social impacts, this can be explained by the scarcity of studies in this sector, only very few are available. What is particularly important is the increase in the sound level year after year. This phenomenon is linked to various factors of increase including: demographic growth, the number of vehicles, distances traveled, urban peripheral displacements and semi-permanent secondary residences. Home building is deficient in the use of insulating materials and noise protection measures are almost non-existent. The results of social surveys focused on community response to road traffic noise in Africa are reviewed.
Here we analyze by means of the z-transform, a system of recursive relations for the stress terms, developed to study impact problems in Goupillaud-type layered elastic media. As a result, we are able to gain insight on the monotonic behavior and damped oscillations observed about the steady state values of the stress. The analytical expectations are confirmed for one- and two-layer targets, and demonstrated through various numerical experiments.
Occlusion effect is a known phenomenon affecting hearing protection device (HPD) wearers. Objectively, it is an amplification of low frequency sounds resulting from bone conduction that can be induced by different types of excitations internal or external to the human body. A common or standard occlusion effect indicator (OE) is defined as the difference between sound pressure levels (SPL) measured inside the occluded ear and the unoccluded ear. Two factors may cause this indicator to be sensitive to the type of excitation: (i) the repeatability of the excitation, because occluded and unoccluded noise levels are commonly measured at two different moments, (ii) the contribution of airborne noise emitted during the excitation process and mainly captured during unoccluded ear measurements. To investigate the impact of these factors, SPL are measured in the ears of 30 participants subjected to different excitations, namely physiological noises (chewing, breathing, heart beats), vocal effort and bone oscillator. Miniature microphones are placed outside and inside both ears using microphonic earpieces ensuring a constant positioning of the microphones for both ear conditions and for all the participants. Measurements are done in three ear configurations: (i) both ears unoccluded, (ii) one ear occluded and contralateral ear unoccluded, (iii) both ears occluded. This allows for the calculation of the aforementioned OE but also a new indicator called Real Time Occlusion Effect (RTOE) calculated as the difference between the SPL measured simultaneously in both ears, one being occluded and the other one unoccluded, for a given excitation. Results are presented and discussed to compare the OE induced by the three excitations and the OE and RTOE respectively.
The rotary drilling is performed with a long drillstring composed of an assembly of 9-10 m pipes screwed together and driven by a motor located at the surface. In the lower part, the drill-collar ensures the transmission of the rotation and the weight on the cutting tool. The mud is pumped down the pipes to the bit, back up into the annular drillstring-well space loaded with cutting debris, calories. Moreover, it provides the drillstring-well lubrication. During the drilling, the mass unbalances distributed along the drillstring, the mud pulsations, the Weight-on-Bit and Torque-on-Bit generated by the shapes of the rotating bit (RC, PDC, etc.) induce the drillstring vibrations combining axial, torsional, and bending motions corresponding with bit bouncing, stick-slip, forward-backward whirls. This set of vibratory phenomena may cause pipes wear, unscrewing, fatigue-cracking-rupture, etc. Consequently, the rate of penetration is slowed down and the mean time between failures reduced. Understanding, predicting and controlling drilling dynamic, a complicated rotordynamics problem, are required to ameliorate the drilling performance. The proposed beam element model predicts the drilling dynamics by taking into account the slender, rotating and pre-loaded drillstring immersed and deflected inside a 3D well. Consequently, this specific rotordynamics model combines in particular nonlinearities, couplings and parametric loads. The carried out numerical simulation concerns a 200 m drillstring in a 3D field borehole. First, its quasi-static equilibrium position is computed. Then, the Campbell diagram is considered for the modal analysis. Finally, the nonlinear mass unbalance response is studied. The conducted parametric analysis focuses on the interest of a Campbell diagram on the response prediction. This research is conducted by Drillab, a joint laboratory of DrillScan and LaMCoS, grant Labcom-SME program ANR 15-LCV4-0010-01. The authors are indebted to the Agence Nationale de la Recherche (ANR) for its financial support.
Liquid crystal elastomers (LCEs) are weakly crosslinked polymers with liquid crystal (LC) moiety. They combine the finite deformability of elastomers with the multi-functionality of LCs. Rather large spontaneous deformations can be produced by thermal, optical and electrical stimuli. They can be used as active soft materials in many applications. However, their mechanical behavior depends strongly on the physical properties of the LC molecules attached to the polymer backbones. We propose a continuum mechanical model that combines the finite elasticity theory with the liquid crystal dynamics. In addition to the mechanical equations, we obtain the governing equations for the LC alignment: the director and the order parameter. The stress-strain relation of LCEs is affected strongly by these internal variables. Thin films of LCEs can bend and vibrate under optical or electrical stimuli due to spontaneous deformations. However, the bending behavior can be quite different from purely elastic materials as the LC alignment can have strong effects on the transversal shear strains. A first order shear strain theory is proposed to model the spontaneous bending and vibration. Through proper design of the LC alignment, we can regulate and control the spontaneous bending and vibration behaviors.
Associate Professor, Rose-Hulman Institute of Technology
Professional interests include undergraduate engineering education, finite element modeling, ground-borne vibrations, vibrations of musical instruments, and dynamics of toys.
The load of the rapid maneuver aircraft is characterized by high accelerations, high jerks and multiple directions in space. The ground load simulation test of the aircraft is usually carried out on a triaxial centrifuge. In this paper, considering the three-axis centrifugal motion and elastic vibration of the beam, velocity and acceleration model of the beam are established by the method of motion synthesis and matrix rotation. The acceleration model of the beam is the basis of the load analysis and calculation of the dynamic responses. Dynamic equations of the beam in the three-axis centrifugal environment is established. Based on the dynamic equations, responses of the beam is calculated at the cases of different motion parameters. The influence of the accelerations and jerks on the responses is analyzed. The results show that both the accelerations and jerks can result deformation on the beam. Jerks can cause vibration of the beam and a sudden change of acceleration will induce a significant vibration of the beam. For the beam, a sudden change of acceleration just likes an impact force loading on the beam. The mechanical model and calculation method obtained in his paper can be used to simulate the flight responses of the aircraft with high accelerations and jerks.
Mohammad Rafiee received his Ph.D. degree in Mechanical Engineering from the University of Ottawa in 2018. Currently, he is a Postdoctoral Fellow at Polytechnique Montreal in Canada. His research interests are primarily focused on the development of advanced composite materials, smart... Read More →
An acoustic metamaterial sound-insulator by Helmholtz resonators combined with thin membranes is developed to realize extraordinary sound transmission loss (STL). Small Helmholtz resonators are embedded periodically within the sub-wavelength throughout the insulation plate that covers an elastic plate with an intermediate air layer to compose a double-wall system. The throats of the Helmholtz resonator open at the intermediate air layer, and the bottom faces of the back cavities are composed of thin membranes. This system has three resonances; One is a structural resonance of a mass and spring system where the insulation plate works as a mass and the intermediate air layer as a spring. Second one is an acoustic resonance of the Helmholtz resonator. The last one is an elastic resonance of the membrane at the bottom surface of the back cavity. This system exhibits extraordinary high STL compared with a conventional double-wall insulation system in the frequency range where these three resonances are excited. This frequency range can be controlled by designing the geometry of the Helmholtz resonators, the intermediate air layer, and the size and the stiffness of the thin membrane. The theoretical analysis gives the expression of the equivalent properties of the intermediate air layer and the insulation plate. Numerical calculations are also performed by using representative unit cell. To demonstrate the acoustic performance of the developed system, an elastic steel plate of 1 mm is covered with a plastic plate of 20 mm thick where the resonators that has a resonance around 1.6 kHz. Air layer of 5 mm between these two plates gives resonant transmission loss around 800 Hz, and the membrane of 0.1mm thickness gives an elastic resonance around 2.2 kHz. The finite element analysis utilizing COMSOL Multiphysics gives higher transmission loss than a conventional double-wall from 1 kHz to 2 kHz.
The generalized cross correlation (GCC) is a standard technique for estimating time delay between microphone signals. A prefiltering operation by a weighting function may be included to whiten the cross spectrum of the microphones signals. The expected result is a narrow cross correlation function and a more accurate estimation of the time delay. Among the classic weighting functions, the most known is the PHAse Transform (PHAT). The ability of the PHAT weighting function to whiten the cross spectrum of the microphone signals can be improved by adding an exponent or the minimum value of the coherence function to the denominator. Both approaches have shown promising results for time delay estimation. In this work, the aforementioned modifications of the PHAT weighting function are considered for performing acoustic imaging with the classic GCC and the GCC based on the geometric mean. Numerical and experimental measurements are carried out in the case of two acoustic sources in front of a regular microphones array.
By means of auralizations created by the ODEON software, the present study aims towards testing whether such auralizations are capable of revealing systematic subjective differences between two topologies of concert halls shapes (shoebox and arena). Anechoic multisource orchestra recordings were used as signal input in the auralization of Brahms music in 6 concert hall models and 27 subjects with and without musical background evaluated the halls with respect to general preference in paired comparisons tests. The paper discusses the results regarding the subjects' detection of differences in room shape.
In many instances, the ambient ocean noise is impulsive in nature. Classical channel estima-tion methods optimized for Gaussian noise suffer serious performance degradation even when the noise is slightly impulsive. This paper deals with the problem of sparse underwater acoustic (UWA) channel estimation under impulsive noise environments with non-Gaussian distribution. Channel estimation is realized based on the recursive least p-norm (RLP) algorithm which has been proved to be robust under impulsive noise environment. L10 or L20 norm is incorporated to the cost function to take advantage of the group sparse nature of UWA channel. Simulation results show that the proposed RLP can resist the influence of the impul-sive noise and L10-RLP and L20-RLP has better estimation performance regardless of Gaussian or non-Gaussian noise when group sparse channel encountered.
DEPUTY HEAD/SENIOR RESEARCH FELLOW, ACOUSTIC RESEARCH LAB, NATIONAL UNIVERSITY OF SINGAPORE
A senior researcher with 30 years of experience in underwater acoustics research. Senior member of IEEE, Member of IIAV, ASA and Society of Acoustics Singapore. IEEE OES AdCom and JOAB member, General Chair for OCEANS 2020 Singapore and co-Chair for ICSV 28 Singapore. See my technical... Read More →
Recently, the instrumented sleeper has been developed to measure the sleeper response in-situ. An analytical model of the dynamics of railway sleepers has been developed to calculate rapidly the sleeper response under vertical wheel loads. However, lateral wheel loads are not taken into account in this model but would influence the sleeper response. This paper presents a new analytical model of the dynamics of railway sleepers under lateral wheel loads. In this model, the sleeper is considered as a Euler-Bernoulli's beam resting on a visco-elastic foundation. Thereafter, by combining the relation between the reaction forces and displacements of the periodically supported beam, the sleeper response can be calculated with help of the Green's function. Finally, the numerical application shows the influence of the laterals wheel load on the sleeper response.
The increasing demand for high performance recreational vehicles combined with more stringent noise regulations and customer expectations lead to intake and exhaust systems design challenges, namely in-creased mass flow rate, reduced pressure losses and reduced space available for silencing devices along with shortened development cycles. Design choices must be made carefully to reach the performance targets while having the desired attenuation on harmonic noise related to combustion cycles without in-ducing excessive pressure losses and flow noise levels. Usage of predictive tools in conjunction with vali-dation testing is becoming paramount to guide the design of such high-performance exhaust silencing de-vices. A discussion regarding the available simulation methodologies is presented with the associated pros and cons. All these approaches are widespread and well documented on four-stroke automotive engines, but additional challenges arise with high performance two-stroke engines, such as non-linear behavior of perforations due to grazing flow and high acoustic amplitude in addition to extended frequency range of noise predictions. Despite these new challenges, usage of simulation tools in product development al-lowed to identify the root cause of a problematic resonance in an exhaust silencer and to define 2 differ-ent strategies to mitigate it. One of the two design alternatives was finally selected and successfully im-plemented in a mass production consumer product.
Acoustic localization inside aircraft cabins is of increasing interest. It allows to identify issues through sound measurements in a tight schedule, especially in an industrial context. Moreover, in such environments, the reverberant nature of the acoustic field and the space constraints make it difficult to use conventional localization method. For instance, beamforming among other localization techniques, requires large microphone arrays for applications to low- and mid-frequency range. This study combines the development of an array geometry and the definition of a post-processing method adapted to applications within aircraft. The research originality lies in the considered post-processing method, consisting in a subtractive array based on high-order differential microphones and exploiting acoustic gradient properties. With such a method, the use of a compact microphone array with a strong directivity in low frequencies is proposed. Precisely, a fourth-order analytical model is established, driven by the desired directivity and the sensitivity to noise, especially at low frequencies. The study aims at developing a compact array, allowing mainly localization from 500Hz up to 1000Hz, taking into account the space limitations. The frequency band target is used to drive the simulations and the antenna geometry definition. An experimental proof of concept is tested in an anechoic room. Simulations and experimental results are compared to an analytical modeling. Good agreement between them is observed. The comparison highlights the method advantages as well as the experimental limitations of the designed linear array. Then, a first localization test is performed using the experimental database. Finally, a modification of the post-processing method is suggested, with an improvement of the achieved directivity in the targeted low-frequency band.
Acoustic black holes are structural features that are realised by tapering the thickness of a beam or plate, usually via a power law profile. Practical acoustic black holes have been shown to significantly reduce vibrations at high frequencies when combined with a thin layer of passive damping but, due to design constraints on the taper length and tip height, passive designs are somewhat limited at lower frequencies. In this paper, an active solution has been investigated to control the low frequency vibration of a beam with an acoustic black hole termination. Piezoelectric patch actuators have been attached to the taper and unconstrained feedforward control has been simulated to minimise the kinetic energy of the uniform beam section. The effect that this control strategy has on the structural response has been investigated through a series of numerical simulations and the potential performance of an active acoustic black hole has thus been demonstrated.
During lift-off, space launchers are submitted to high acoustic levels which can be dramatic for the payload inside the fairing. The present study aimed at improving the acoustic environment of VEGA (Vettore Europeo di Generazione Avanzata) launcher thanks to microphone array analysis. Two years ago, in 2015, a first analysis of this type has provided recommendations for launch pad evolutions in order to reduce the acoustic loads on the fairing. Based on these results, openings on the launch table were covered. We present here new measurement and analysis performed after this change. In Kourou, French Guyana, the time signals measured on a circular array during launcher lift-off are used to identify the acoustic sources on the launch pad, in terms of location and magnitude, thanks to deconvolution method. As for the first campaign, three source scanning plans are defined: two horizontal ones (at the level of the jet deflector and on the table) and a vertical one including the launcher. The overall results provide the evolution with time of acoustic sources on VEGA launch pad for all frequencies of interest. These are then used to extrapolate the acoustic levels to the fairing. Thanks to launch pad change, the acoustic levels are shown to be reduced by 2 dB, for the frequencies of interest and the source localization confirms strong reduction of the sources radiated from the table.
The Valero – Jean-Gaulin Refinery is the largest oil refinery in the province of Quebec and the second largest in Canada, operating for nearly 50 years. The refinery is located in the city of Lévis with access to St Lawrence river. Built in the late 60s on predominantly rural land, several residential and commercial properties were developed, and environmental issues brought light on the importance of industrial noise management. This presentation shows the sound survey program and model the sound control measures used. Different examples of sound-emitting operations are presented to demonstrate both application of sound survey program and the mitigation actions implemented. Also demonstrated is the processes of sound data management and the communication strategy in place to report the environmental performance and keep the community informed about all the efforts put in place to minimize the impact of operations in the neighborhood. All these initiatives contribute to maintaining a harmonious cohabitation of the refinery with the community.
Wave propagation in hexagonal lattices is characterised by a transition from isotropic to anisotropic regime as the frequency increases. This feature cannot be observed when the lattice material is modelled within the framework of classic Cauchy theory of elasticity, except when the real geometry of the microstructure is explicitly described. Homogenized equivalent continua can capture the onset of this anisotropy only if tensors involved in the constitutive law are at least of order six. This requirement is met in the case of Strain-Gradient Elasticity (SGE). In this work the SGE model is calibrated to quantitatively describe wave propagation within hexagonal lattices in a sufficiently large region of the dispersion diagram, by fitting the dispersion relations obtained from a Bloch-Floquet analysis on the unit cell. It is then shown that focussing and beam steering effects can be obtained by acting only on the local material orientation of the hexagonal lattice. This is achieved by computing the Poynting vector in the SGE model and optimising the distribution of material orientation.
The occlusion of the human earcanal is commonly associated with the so-called occlusion effect. This phenomenon is particularly uncomfortable at low frequency when wearing an intra-aural occlusion device in shallow insertion. In low frequency, the occlusion effect is objectively quantified as the acoustic pressure increase in the occluded earcanal compared to the open one. Fundamentally, the occlusion effect is governed by the change of earcanal acoustic impedance seen by its wall due to its occlusion. However, several factors influence the occlusion effect such as the occlusion device (e.g., type, fit, position in the earcanal), the stimulation (e.g., position and nature) and the earcanal anatomy (e.g., geometry and material properties of earcanal surrounding tissues). Compared to the first two aforementioned aspects, the latter has not been investigated yet because of experimental difficulty. However, it is important since the earcanal anatomy influences the earcanal wall vibration, which is the origin of the acoustic pressure generated in the earcanal. In this work, the influence of the earcanal surrounding tissues geometry on its vibration distribution is numerically studied. For this purpose, a full factorial design of experiment is conducted using a 2D axi-symmetric finite element model of an open and occluded outer ear. The occlusion is simplified to an infinite impedance defined at the earcanal entrance. The influence of the earcanal vibration distribution on the occlusion effect and its fundamental mechanism is then investigated. In conjunction, an eletro-acoustic model is proposed to explain in a simplified way the trend of the finite element model results.
The diesel engine transmission shaft includes a thrust shaft, an intermediate shaft and a tail shaft. In order to connect the shafts as a whole for power transmission and reduce torsional impact, a flexible coupling is required. The flexible coupling is actually a non-linear element whose stiffness changes with the vibration frequency as the torque ripple changes. Since the stiffness has a great influence on the inherent characteristics of the transmission shafting system and the vibration reduction effect, the influence of the stiffness nonlinearity cannot be ignored. In this paper, the transmission shaft with flexible coupling is taken as the research object. The finite element method is used to establish the nonlinear dynamic model of the transmission shaft, and the nonlinear torsional vibration response under random excitation is solved and the influence of the flexible coupling characteristic parameters on the shafting response and stability is obtained. The results show that the linear stiffness of the flexible coupling can avoid the generation of "resonance"; the nonlinear stiffness can reduce the amplitude, preferably using the soft nonlinear stiffness; increasing the damping of the flexible coupling can also achieve the damping effect.
Mohammad Rafiee received his Ph.D. degree in Mechanical Engineering from the University of Ottawa in 2018. Currently, he is a Postdoctoral Fellow at Polytechnique Montreal in Canada. His research interests are primarily focused on the development of advanced composite materials, smart... Read More →
High seed design of flywheel and motor rotor is preferred to get higher energy and power density for the flywheel energy storage system. The rotor dynamics model of a composite flywheel storing energy of 25MJ driven by permanent magnetic motor with power of 400kW supported by active magnetic bearings running speed of 12000-24000rpm was built to reveal the natural frequencies and modes of the rotor bearing system. The rotor bearing system exhibited some flexible rotor dynamics performances such as shaft bending, local flexural structure mode and axial mode. Some modal frequencies varied sharply with the increase of rotational speed. The frequencies crossing and modes mixing are observed and described. The parameters such as bearing stiffness, core shaft structure and flexibility of coupling were analyzed and chosen to obtain a reasonable distribution for critical speed.
Power and signal cables form an integral part of spacecraft and satellite structures which could weigh up to as high as 20% of the total structural mass. Accurate modeling of these cable-harnessed structures has received a lot of attention in the past two decades as the coupling of cable dynamics is observed to play an essential role in the vibration response of these structures. Previous studies have been primarily focused on cables attached to beam-like 1D structures. However, in practice, many of these host structures are better modeled as plate-like geometry. In the present work, we study the dynamics of cable harnessed plate structures using energy equivalence-based homogenization technique. The system consists of a rectangular plate harnessed with multiple parallel cables attached on the top surface in a periodic pattern. The cables are given a pre-tension and assumed to be under tension during vibrations. Strain and kinetic energy expressions are developed using linear displacement field and Green-Lagrange strain tensor. The governing partial differential equations are obtained for an undamped cable-harnessed plate system using Hamilton's principle. The natural frequencies are found for several boundary conditions and are compared with the pristine plate to show the importance of the proposed modeling technique.
Associate Professor, Rose-Hulman Institute of Technology
Professional interests include undergraduate engineering education, finite element modeling, ground-borne vibrations, vibrations of musical instruments, and dynamics of toys.
Multiple detection and Direction-of-arrival (DOA) estimation of bird sources have been studied for some years. In Hudson and Yao, we used the k-th suband of the cross-covariance matrix of H-frame of contiguous array of N sensors data to perform an eigen-decomposition . The ratios of the larger eigenvalues in Dk relative to the smallest eigenvalue provide a possible detection criterion for various sources and the corresponding eigenvectors can be used to estimate the DOA's of multiple sources. In Yu, et al, the phase differences among the sensors are used to analytically obtain the DOA without needing any optimization operations. In this manuscript, we combine the previous two techniques to obtain an efficient fast analytical DOA estimation of the sources based on the eigenvectors. Simulations of field measured array data are used to confirm the proposed scheme.
This paper discusses the design, realisation and acoustical performance of the newly modernised (2018) primary school (classes' I-VI) located in Warsaw, Poland. Four types of rooms are discussed: classrooms, corridors, canteen and a sports hall. Pre-modernisation acoustical measurements showed long reverberation times, high sound pressure levels and low speech intelligibility in all rooms, which confirmed complains from teachers, parents and pupils and resulted in a decision to retrofit sound absorbing elements in all rooms just 5 years after the school was commissioned (2012). Due to restrictions in possible reduction of classrooms height and area of retrofitted materials, acoustical and architectural designs were focused on minimising the thickness and required area of newly installed sound absorbing materials, while still achieving the required reverberation time (RT ≤ 0,6 s.) and Speech Transmission Index (STI ≥ 0,6). Use of measurements for proper calibration of computer models are described, followed by the acoustical performance and subjective evaluation of the finished rooms. Aspects deserving special mentioning were: the possible use of materials only on walls in sports hall; negative effect of parallel smooth painted walls in acoustically damped corridors causing flutter echoes; the effect of low thickness of sound absorbing material on it's performance in low frequencies; construction details of interior materials and technical installations.
Time-warping transform is often used in underwater acoustics to separate normal mode components of a broadband signal recorded by a single hydrophone. An important application of time warping is retrieval of modal dispersion curves for subsequent inversion of the measured mode dispersion for unknown geoacoustic parameters. The time-warping transform was developed for range-independent shallow-water waveguides. Physical parameters of the ocean are never quite constant in the horizontal plane, with bathymetry variations being typically responsible for the bulk of the waveguide's range dependence as well as horizontal refraction of sound in the coastal ocean. We use simple, exactly solvable models of shallow-water waveguides to illustrate the effects that the range dependence and horizontal refraction have on the performance of the warping transform and the inferred geoacoustic parameters. Horizontal refraction due to generic bathymetric variations is addressed in the adiabatic approximation using perturbation techniques. Theoretical predictions are verified using numerical simulations. It is found that moderate bottom slopes can lead to large errors in retrieved geoacoustic parameters and cause positive bias in bottom sound speed estimates if horizontal refraction is ignored.
DEPUTY HEAD/SENIOR RESEARCH FELLOW, ACOUSTIC RESEARCH LAB, NATIONAL UNIVERSITY OF SINGAPORE
A senior researcher with 30 years of experience in underwater acoustics research. Senior member of IEEE, Member of IIAV, ASA and Society of Acoustics Singapore. IEEE OES AdCom and JOAB member, General Chair for OCEANS 2020 Singapore and co-Chair for ICSV 28 Singapore. See my technical... Read More →
Structure-borne road noise in cars originates from vibrations generated at the tyre-road interface that propagate through the suspension into the car's body. Manufacturers require accurate tools to predict and therefore mitigate road noise in the cabin. However, the process is complicated by the presence of nonlinear components in the suspension. This paper presents an investigation into the dynamic behaviour of the damper and top mount, which constitute the most strongly nonlinear transmission path in a typical car suspension, for frequencies up to 500 Hz. Experiments have been conducted on the damper and top mount individually to quantify their nonlinear characteristics. When coupled together, the coherence of transmitted vibrations was observed to decrease at frequencies above 50 Hz, suggesting that nonlinear processes are significant in the vertical strut. Published physical models of each component have been fitted to experimental data and shown to perform well over the low audio frequency range. The models have been combined to form a nonlinear suspension strut model that predicts the interaction of the damper and top mount; results from the model are presented and compared with experimental measurements. The development of a nonlinear strut model, validated for low audio frequencies, is a novel contribution that represents a step towards a full suspension model suitable for structure-borne road noise analyses.
Based on an analytical model of the curved track, the effect on decay rates of some parameters of curved track are analyzed, including the stiffness, damping and spacing of fasteners, and the radius of curvature. The track is modelled as a curved Timoshenko beam, and the dynamic response of curved track subjected to a harmonic load can be obtained. The superposition of track modes and the periodic structure theory are applied to motion equations of curved track so that the dynamic response of track can be calculated efficiently in a reference cell. The track decay rates can be calculated based on the velocity mobility of the rail obtained through the model. Some conclusions are drawn as follows. The fastener stiffness affects the decay rates below 2000 Hz to some degree, and the decay rates become larger as the stiffness rises. The fastener damping has a significant influence on the decay rates above 100 Hz, which are enhanced greatly with increasing damping. Compared to other fastener spacing, the decay rates for 0.6 m fastener spacing are larger in most of the frequencies. The radius of curved track does not have effect on the decay rates for the tracks of railway and urban rail transit systems.
Locally resonant metamaterials have emerged as effective solutions for several types of NVH problems over the last few years, since they offer better performance of noise and vibration reduction than other NVH solutions. However, there have not been many cases that extend to the industrial applications, due to limitations which are often linked with design requirements, such as robustness, lightness and durability. In this paper, the authors propose a novel struc-tural design which is feasible for mass production of locally resonant metamaterial that im-proves the productivity for industrial application. The proposed structure is made of metal in-sert injection molding. It enables mass production with insert injection and effectively joins plastic with metal. The manufactured model is applied on a thin plate structure, and experi-mentally verified. It is observed that the proposed structure effectively reduces the noise and vibration at the target frequency band, and is relatively superior to other vibration treatments such as deadeners. So, the proposed structure of locally resonant metamaterial is expected to be applicable to various industrial fields such as automobiles and home appliances.
Due to the eutrophication phenomena in shallow waters, e.g. lakes and rivers, aquatic plants may grow rapidly and cause serious ecological problems. Therefore, the measurement and evaluation of the underwater plants are important for the environmental protection and ecological restoration of shallow waters. Ultrasonic sensors are widely used to detect underwater objects due to their ad-vantages of low cost and real-time monitoring. This paper develops an echo-location measurement system which includes the acoustic source, the propagation model of the water media and the sound absorption model of the aquatic plants and sediments. The proposed sound absorption models show the relationship between sound absorption coefficient and the amount of plant. Experiments are then carried out to measure and identify the sound absorption coefficients of the plant samples. Considering variations of different kind of plants, a deep learning method is employed to identify different plants and eliminate the differences in experiments. By using the model of plants, the identification and quantity estimation of aquatic plants with conventional ultrasonic sensors is realized.
DEPUTY HEAD/SENIOR RESEARCH FELLOW, ACOUSTIC RESEARCH LAB, NATIONAL UNIVERSITY OF SINGAPORE
A senior researcher with 30 years of experience in underwater acoustics research. Senior member of IEEE, Member of IIAV, ASA and Society of Acoustics Singapore. IEEE OES AdCom and JOAB member, General Chair for OCEANS 2020 Singapore and co-Chair for ICSV 28 Singapore. See my technical... Read More →
Acoustic comfort is a very important feature when designing a room used by many people such as a gymnasium, a concert hall, a conference room or an office. It is mainly related to reverberation time and other characteristics of the room. Building and construction stakeholders (architects, contractor, designers, developers, etc.) usually work with acoustic consultants to optimize room acoustics. However, they do not have a simple decision support tool, which provides both guidance and recommendations to make preliminary decisions regarding acoustics, therefore saving time and money. A smartphone application (ClapReverb) was designed to measure and compute reverberation time in the medium range frequency domain. The user needs to produce a few handclaps while following instructions on the screen. This method does not require additional hardware because the sound is recorded using the inboard microphone of the smartphone. The upcoming results provide the room's reverberation time and recommendations on acoustic comfort. Thus, two main concerns were addressed in this study: 1) defining the range of validity of the measurement through handclaps and the smartphone microphone, 2) developing an ergonomic application useful for building and construction stakeholders. A parametric study has been conducted to develop a robust process to measure reverberation time and to define the range of validity of the measurement in terms of frequency, reverberation time error, room volume, ambient noise, handclap type, etc. Measurements were compared to a reference method, which was wooden clapping device impulses recorded with a class-1 microphone and analyzed with a Scilab analysis program that complied with ISO-3382 Standard. Overall reverberation time results showed a mean absolute error of 0.09 s computed by ClapReverb (mean relative error of 6.0 %). ClapReverb provides reliable results with ambient noise up to 60 dBA, and is therefore a promising easy-to-use smartphone application which democratizes acoustics and helps stakeholders to optimize room acoustics.
Active-passive isolation technology is applied in ship equipment to achieve higher isola-tion efficiency both in broadband vibration and low-frequency harmonic vibration. A hy-brid vibration isolation system (HVIS) is designed with active-passive vibration isolators, which consist of electromagnetic actuator and air spring. In order to obtain expected effect for vibration line-spectra isolation, the air gap of actuator need maintain in a fairly small range. As low and nonlinear stiffness characteristics, the air gap is more susceptible to some disturbance, such as temperature variation and air spring pressure change. So how to control attitude of the isolation system to ensure air gap in appropriate range is a challenge for designers. In this paper, the factors affecting air gap are analyzed, and an attitude con-trol algorithm is designed to achieve high control precision and stability. The experiment results show the algorithm meet the air gap requirement for electromagnetic actuator.
This paper highlights three on-going projects conducted at HKUST towards the development of a noise assessment platform for multi-rotor flying vehicles. The first project outlines the development of a test rig for assessing the aerodynamic and aeroacoustic performance of small-scale UAV propellers. Generic propellers were developed so that the importance of key design parameters may be determined systematically. Additionally, these generic propellers were made of metal to minimize any aeroelastic effects. The second project focuses on full-scale drone experiments that were conducted within a large anechoic chamber, which overcomes any environmental or meteorological factor that may otherwise be present in outdoor field testing. The experiment consisted of microphone array measurements and simultaneous position tracking, which provided a complete characterization of drone noise under realistic flight conditions. The final project focuses on the development of an acoustic ray tracing code, to predict the noise impact of a hovering drone in complex urban environments. The noise source applied to this code was developed from the anechoic chamber tests.
Dynamic noise assessment and the development of common methodologies between different countries are the current trends in urban environmental noise studies. The development of common and precise methods will allow a better comparison of the acoustic situation of cities located in different countries. Dynamic noise assessment will provide more information on the trend and variability of noise levels. This information may be important in determining the effectiveness of corrective measures or in influencing negative health effects. These European trends are also being considered in the studies being carried out in Chile. The city of Valdivia is an example of the evolution of different urban noise assessment methodologies in recent decades. In 2002, the first noise map of Valdivia was made using the grid method. Subsequently, other urban noise assessment methodologies have been used based on the typology of urban roads and calculation methods. This study compiles the results obtained in the studies carried out from 2002 to the present with the aim of analyzing the temporal evolution of the acoustic situation of the city of Valdivia. The sound levels recorded in the main urban access and exit routes of the city (Category 1), did not present significant differences in the different years analyzed. However, in the rest of the types of urban roads, noise levels have decreased in recent years.
