Reconstruction of transient acoustic radiation from a thin disk

Abstract

The HELS method [Wu, J. Acoust. Soc. Am. 107, 2511–2522 (2000)] is extended to reconstruction of transient acoustic radiation from a highly nonspherical structure. The test object is a thin disk subject to an impulsive acceleration in an unbounded fluid medium. Since the HELS method allows piecewise reconstruction of acoustic quantities on the source surface, it is possible to focus on one side of the disk at a time. Also, since the origin of coordinates is arbitrary, one can set the spherical coordinates in such a way that the spherical surface looks almost flat locally. This treatment legitimizes the Rayleigh hypothesis and facilitates reconstruction of the normal surface velocity on the disk front surface. Reconstruction of normal surface velocity on the opposite side of the disk can be done in a similar manner. The input acoustic pressure signals are collected using an array of microphones in front of the disk and reconstructed acoustic quantities are compared with the analytic results [Wu, J. Acoust. Soc. Am. 94, 542–553 (1993)]. Results show that the accuracy of reconstruction depends on that of input signals, and convergence of the reconstructed normal surface velocity improves with an increase in the cutoff frequency of input data. [Work supported by NSF.]