Estimating the size and spatial distribution of bubble clouds in an underwater acoustic test tank.

Abstract

The AB Wood Underwater Acoustic test tank at ISVR, University of Southampton, UK is outfitted with a Venturi‐based apparatus for generating bubble clouds containing a large range of bubble sizes. Larger bubbles are allowed to rise out in a settling tank before the nearly opaque bubbly water is pumped into the acoustic test tank through a discharge manifold on the bottom. A series of acoustic attenuation measurements was made at AB Wood in July 2008 in order to estimate the size and spatial distribution of bubbles in the cloud. An acoustic projector transmitted 1‐ms pure tones from 25 to 100 kHz, which were received at a co‐linear three‐element horizontal array. The receive hydrophones were spaced 0.5 m apart, with the center hydrophone placed directly over the bubble discharge location. Measurements were taken on‐axis with the projector, and at three distances off‐axis, in 12‐in. increments. The attenuation measurements were used to estimate the size and spatial distribution of bubbles within the cloud. The bubble size data will be used to support a study of the effect of nearby bubbles on array performance degradation. [Work sponsored by the Office of Naval Research, Code 321.]