Huang C., Tien T.

Attenuation of sounds propagating through a bubble screen Ching-Jer Huang and Tsung-Mo Tien Department of Hydraulic and Ocean Engineering National Cheng Kung University Tainan, TAIWAN Tel: 886-6-2757575 ext. 63252 E-mail: cjhuang@mail.ncku.edu.tw ABSTRACT The attenuation of sounds propagating through a bubble screen was investigated both theoretically and experimentally in this study. By adding an additional virtual mass force into the momentum equation of the bubbly liquid, a modified Helmholtz equation valid for the sound propagation in the bubbly liquid at finite gas-volume fraction is reformulated. The transmission and reflection coefficients for the sound propagating through a bubble screen are derived. Experimental study was made to verify the accuracy of the theory. The experimental set-up consists of two parts. The first part is to measure the sound attenuation due to the presence of the bubble screen; while the second part is to measure the gas-volume fraction of the bubbly liquid contained in the screen. The bubble size was justified by taking bubble picture using a CCD camera. In the experiments the sound frequency was restricted to the range from 10 to 100 kHz due to the restriction of the facilities. At low gas-volume fraction, our theoretical results and experimental data coincide with those obtained from the classical theory. At higher gas-volume fraction, our theoretical results agree also with our experimental data very well. However, the transmission coefficients obtained from the classical theory showed a large deviation from the experimental data.