An Investigation On Sound Transmission Characteristic In Water Due To A Bubbly Curtain

Biological organism, wind weather and mechanical engine will generate a lot of bubbles in the ocean. Transparent bubbles are easy to deform, divide and integrate, the acoustic characteristics of underwater bubbles are very different from pure water. Since the bubbles group is strong scattering in the water, it has a strong influence on the sound transmission by attenuation and scattering. When underwater bubbles group is resonant, it causes obvious attenuation on the resonant frequency of acoustic wave then usual. With the continuous development of underwater combat technology, the Navy has developed the vessel noise suppressing, the naval air wake rejecting, the bubble-shell and other new technologies owing to the acoustic characteristics of underwater bubbles, which have been applied in the field of naval equipment. Therefore, it is important to study the acoustic characteristics of underwater bubbles since it has important scientific significance and application prospects.We mainly study the sound transmission loss characteristics due to a bubbly curtain.According to the acoustic scattering effect of bubble interaction model and the bubble small amplitude vibration model, we derive the theoretical relationship between the bubble-structure parameters and sound pressure transmission coefficient through the bubble screen. In order to measure bubble size and bubble concentration by optical method, we use porous ceramic tube to deflate underwater bubbles curtain, then we use function fitting method to get particle size distribution function of bubbles curtain. At different concentrations,we investigate bubble size distribution separately so as to get particle size distribution function of the bubble curtain. In addition, we utilize the insertion loss to measure the sound pressure amplitude changes through the bubble curtain. During the experiment, we change the transmission frequency, transmission power and the deflation flow in order to measure insertion loss change under different experimental conditions. The structural parameters of the bubble curtain will be fed into the calculation formula of sound transmission coefficient of bubble curtain, the calculation agrees well with the values measured experimentally, but the deviation is a little big.On the basis of classical theory, considering the effect of bubble resonance sound absorption, we put the resonance peaks corresponding to the generation of air bubbles into the classical theory of model by virtue of the double-peaks structural feature in the bubble size distribution. So we put forward an improved theoretical method for calculating sound pressure transmission coefficient. The experimental results show that the proposed method is more effective than the original. The method can also be used to calculate sound transmission due to the multi peaks particle size distribution of bubble curtain for reference.