Simulation of Temperature Effects on Near-field Acoustic Holography: Validation by SLDV Measurements

摘要

Near-field Acoustic Holography (NAH) is one of the most promising and interesting tool for the investigation of vibro-acoustic problems. This hybrid tool is based on array microphones pressure cross-spectra acquisitions from which the acoustic field on the 3D space can be calculated. The reconstruction procedure involves numerical computations where the effect of many uncertainty sources can be propagated. One of these is the temperature factor: if the vibrating object is undergoing a high temperature gradient, the wavelength of sound propagation will change within the surrounding space. The conventional instruments applying NAH do not take into account this effect since they are based on the hypothesis of constant sound speed along the reconstruction path. In order to appreciate the influence of noteworthy temperature gradients on NAH calculations, an algorithm has been developed for taking into consideration the fluctuation of the sound wavelength. Hence, the results accuracy have been checked by comparing them to the surface velocity measured in the vibrating source by means of Scanning Laser Doppler Vibrometry (SLDV). This research work has been performed within the European Growth Project "ACES" (Optimal Acoustic Equivalent Source Descriptors for Automotive Noise Problems) GRD1-1999-11202.