Reduction of low frequency noise generated by devices is an important problem. Passive noise reduction methods require thick and heavy barriers to be effective for low frequencies. Active control of casing walls provides much higher low frequency noise reduction, and in such system, compared to classical Active Noise Control systems, a global noise reduction is possible. Active systems, however, require additional power and are quite expensive. Shunt systems offer another alternative. In the shunt system the controlled mechanical system is coupled with the electrical circuit, usually using piezoelectric effect, and a control law is implemented in an electrical circuit. The whole shunt system can be passive, semi-active or active. In this paper the passive shunt system will be investigated for application to a cubic casing with a rigid frame. The passive system is proposed due to simplicity in applications, and the fact that no additional power source is required. Synchronized switch damping on inductor (SSDI) control law is implemented using a simple electronic circuit. The performance of the resulting system is verified by simulations, and obtained results are presented.
The main issue of this contribution is the reduction of aircraft interior noise by means of actively controlled sidewall panels (linings). It was shown in prior work that considerable reductions of interior sound pressure level can be achieved using structural actuators on the lining and microphones distributed in the seat area in front of the linings. The use of microphones is undesirable for several reasons and it contradicts the aim of a fully integrated and autonomous lining module (smart lining). Therefore, the present contribution aims at the replacement of the error microphones by a number of structural sensors and an acoustic filter. This method is called the remote microphone technique for active control. Several steps are undertaken to define the smart lining with remote microphones. The whole work is based on experimental data of a double panel system mounted in a sound transmission loss facility. A multi-tonal acoustic excitation, typical for a counter rotation open rotor (CROR) engine, is used as the load case for the definition of the actuators and a broadband acoustic excitation, is used as the load case for the definition of structural sensors. 40 Accelerometers are mounted on the structures and 20 microphones are placed in front of the lining. All sensor signals are sampled simultaneously for deterministic and broadband load cases. The lining is equipped with two inertial mass actuators at fixed positions which are used for the active control. The measurement data is used for the derivation of an observer and for the simulation of a smart lining with remote microphones.
Adaptive exponential functional link network (AEFLN) is a recently developed linear-in-the-parameters nonlinear filter, which provides significantly better convergence performance over other traditional linear-in-the-parameters nonlinear filters. To further improve the convergence characteristics of AEFLN, a variable step-size AEFLN (VSS-AEFLN) is proposed in this paper. An adaptive exponential variable step-size least mean square (AEVSS-LMS) algorithm is developed, and the same is tested on modeling benchmark nonlinear plants. Following the above formulation, a VSS-AEFLN-based nonlinear active noise control (ANC) system is designed, and an adaptive exponential filtered-s variable step-size least mean square (AEFsVSS-LMS) algorithm is also developed for improved noise mitigation. Simulation results show that the convergence performance of the proposed algorithms, for system identification and ANC systems, is superior to the state-of-the-art linear-in-the-parameter nonlinear adaptive filters.
There is a desire in many situations to achieve a perfect acoustic cloak, which renders an object acoustically invisible. Although significant contributions have been made to realising passive acoustic cloaks, there is significant potential in the use of active control technologies for cloaking. However, this requires that an accurate estimate of the scattered pressure can be obtained in real-time to provide an error signal to the controller. This is non-trivial, since a standard pressure sensor would detect the contributions from both the incident and scattered fields. The measured pressure must, therefore, be decomposed into these two constituent parts, which has previously been achieved using a double layer of pressure sensors enclosing the scattering object. This paper proposes an alternative method of estimating the scattered component of the sound field, which does not require a double layer of sensors. The proposed virtual sensing method is based on an adaptation of the Remote Microphone Technique that has previously been used in active noise control applications. The proposed method filters the measured pressures using an optimally designed filter to estimate the scattered component of the sound field. The paper first formulates the proposed virtual sensing method for scattering detection and then presents an investigation into the accuracy of this estimation procedure using a series of measurements taken in an anechoic chamber. The effect of varying both the number of sources in the incident sound field, and the number of microphones used in the estimation is investigated. Finally, the practicability of designing an active control system using the estimated scattered field is discussed, and preliminary results from offline simulations of active control are presented.
Damping plays an important role in vibration control. To find the best control strategy for vi-bration isolation system using magneto rheological (Mr) damper, the existing relative speed damping control strategy and acceleration damper control strategy are analyzed. On this basis, the relative speed-acceleration joint damping control strategy and the optimal vibration isola-tion semi-active control algorithm based on full state feedback are designed. The simulation results show that semi-active control algorithm based on full state feedback has the best vibra-tion isolation effect among four situations.
The objective of active vibration control of plain bearings is to extend their operating speed range. The control is carried out by a proportional controller that controls the position of the bearing bushing according to the deviation of the bearing journal position. The piezo actuators are used for bearing bushing motion. Increasing the signal-to-noise ratio of the journal position measurement is achieved with the use of the bandpass filter of the second order in the feedback loop which is tuned to the instability frequency of the whirl type. The center frequency of the bandpass filter is tuned to the rotor rotational speed. At the end of the paper, the results of experiments showing the extension of the bearing rotational speed range without rotor position instability are presented.
Inertial actuators can be used with velocity feedback controllers to reduce structural vibration, however, their finite stroke length can affect the behaviour and stability of the control system. Stroke saturation not only limits the amount of force available from the actuator but also causes the proof mass to suddenly decelerate, causing impulse-like excitations that are trans-mitted to the structure and may result in damage. The shocks produced by these impacts are in phase with the velocity of the structure, leading to a reduction of the overall damping of the system, which eventually destabilises the system. This paper examines the implementation of a nonlinear feedback controller to avoid collisions of the proof mass with the actuator's end-stops, thus preventing this instability. A nonlinear feedback control strategy is then presented, which actively increases the internal damping of the actuator only when the proof mass ap-proaches the end-stops. The nonlinear control strategy is investigated both theoretically and experimentally for the control of a cantilever beam, and a comparison in terms of stability is made when both control loops or only the velocity feedback loop are present. Finally, a virtu-al sensing approach based on an extended Kalman filter algorithm is discussed for the real-time estimation of the proof mass states that are used to calculate the feedback signal of the nonlinear control law. It is shown that larger velocity feedback gains can be used without the system becoming unstable when the nonlinear feedback loop is adopted.
An adaptive method is presented for suppressing mechanical vibration of multiple harmonics. Online estimation of the plant model and the disturbance is combined with an output saturation alleviator to improve the convergence rate and performance of the adaptive algorithm. Tracking filters are used to extract harmonics of fluctuating frequencies and the anti-saturation unit works in series with the tracking filters to give constrained harmonic output. As a result, the controller is insensitive to saturation that would otherwise induce divergence in control. Experiments were conducted to verify the performance of the adaptive method. Excitation with multiple fluctuating frequencies was applied and the results demonstrated that the harmonics can be suppressed substantially.
