Acoustical emissions from bubble clouds

Bubble clouds are believed to be responsible for producing acoustical frequencies much lower than the resonant frequencies of the inherent bubbles. Earlier models for determining the resonant frequencies of a cloud were based on a uniform void fraction throughout the cloud. In general, the void fraction in a bubble cloud may not be uniform, especially in oceanic bubble clouds - referred to as plumes. A new model is proposed that accounts for a variation in the void fraction as a function of position in the cloud. In this work, the cloud is modelled as a cylindrical resonant cavity with a void fraction that decreases with radius. Experimental results show good agreement with theory. This research provides further evidence that the source of these lower frequencies is due to the geometry and void fraction properties of the cloud.