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Monday, July 8 • 11:40 - 12:00

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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.


Lars Håkansson

professor, Linnaeus University


Monday July 8, 2019 11:40 - 12:00 EDT
Westmount 2
  T01 Ac. meas. & instrum., RS01 Ac imag & ac detection