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.
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