Attenuation of low-frequency sound in water containing dense bubble clouds.

Abstract

Recently, the attenuation of sound propagating through a bubble cloud has been a subject of investigation due to its ability to mitigate low-frequency underwater noise from anthropogenic sources. The primary purpose of this work was to explore the use of bubbles to attenuate low-frequency underwater sound in a laboratory tank, when multiple scattering between bubbles is significant and the classic theory cannot be used. Bubbles of 1 mm radius were generated using a commercial fish tank air pump and air diffusers. The transfer function was measured at frequencies between 400 and 800 Hz. The insertion loss and extinction cross section were obtained through this experiment, and the results were compared with those from an existing predictive model [Feuillade, Nero, and Love, J. Acoust. Soc. Am. 99, 196-208 (1996)], which incorporates multiple scattering effects between bubbles. The effects of the enclosure on the sound propagation are incorporated through specular surface reflections. The comparison with theoretical models yielded satisfactory results in the forward field, with a normalized root mean squared error between 0.13 and 0.17. Computational modeling, experimental details, and a data/model comparison are presented.