Journal of Fluid Mechanics

Monopole emission of sound by asymmetric bubble oscillations. Part 2. An initial-value problem

Michael S.  Longuet-Higgins a1p1
a1 Center for Studies of Nonlinear Dynamics, La Jolla Institute, 7855 Fay Ave., La Jolla, CA 92037, USA

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In Part 1 it was shown that an asymmetric, normal-mode bubble oscillation will emit monopole radiation at second order. Here we show that a general initial distortion of the bubble, with no initial volume change, can be resolved into normal modes each of which radiates independently. The zero-order ‘breathing mode’ is stimulated also.

Because of the peculiar damping characteristics, and the possibility of a resonance between the distortion modes and the breathing mode, the pulse of sound produced by the initial distortion will appear to have approximately the fequency of the breathing mode.

The conclusions are borne out in some detail by a comparison with the experiments of Fitzpatrick & Strasberg (1957) on the underwater sound generated by bubbles breaking away from a nozzle. A similar mechanism may contribute significantly to the generation of sound at the sea surface.

(Published Online April 26 2006)
(Received June 16 1988)
(Revised September 30 1988)

p1 Permanent address: Department of Applied Mathematics and Theoretical Physics, Silver Street, Cambridge CB3 9EW, UK.