Acoustic Radiation from Locally Driven Infinite Plates with Fluid Loading

Abstract

Fluid loading influences the total acoustic power and the directivity of the radiation from a large flat plate driven by localized forces. The frequency range considered here is that below the “critical” frequency. In this range, the in vacuo speed of plate flexural waves is less than the speed of sound in the adjacent fluid medium. For a point force, the directivity of the radiation field is that of a monopole for light fluid loading, but changes to that of a dipole for heavy fluid loading. Analogous behavior occcurs in the case of a line force. An equivalent acoustic dipole source can be specified, and one can apply this equivalent source formalism to calculate the power radiated by point and line moment excitations under conditions of heavy fluid loading. The radiated power for a point moment excitation computed by this approach agrees with the earlier results of Thompson and Rattayya [J. Acoust. Soc. Am. 36, 1488–1490 (1964)]. [Work supported by the Ship Silencing Branch of the U.S.N. Bureau of Ships.]