Heavy Fluid Loading Research Articles

A Reverberant Chamber Facility for Sound Power Measurements in Air or Water

A reverberant chamber for use with both air and water media is described. The chamber is used to investigate the acoustic coupling of simple vibrating structures under conditions of light or of heavy fluid loading. Calibration was effected by measuring 60-dB reverberation times in 13-oct bands; decay times of 2 sec in air and 0.2 sec in water were observed. These broad-band results were cross checked in water by measuring the spectrum of acoustic pressure in the chamber generated by a calibrated hydrophone source. Sound pressure levels measured in narrow (50-Hz) bands varied ±3 dB spatially in the air-filled chamber and ±5 dB spatially in the water-filled chamber.

Force and moment admittance of plates under arbitrary fluid loading

Exact closed form expressions are given for the line force and moment admittances of an infinite thin elastic plate immersed in compressible fluid. Very simple approximations to the admittances are found in the heavy fluid loading limit. The approximations are shown to completely cover the low-frequency range which has previously not been dealt with, even by the numerical computations of Nayak [1]. The plate response throughout the near-field of the line of excitation is also obtained in simple form.

Influence of Fluid Loading on the Radiation from Infinite Plates below the Critical Frequency

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 occurs 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)].

Acoustic Radiation from Locally Driven Infinite Plates with Fluid Loading

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.]