Unidentified enegy conversions in an oscillating bubble

Acoustic radiation of freely oscillating bubbles has been studied experimentally. The oscillating bubbles have been generated by underwater spark discharges. Recorded pressure waves made it possible to determine the acoustic energy radiated by the oscillating bubbles and potential energy of the bubbles when attaining the first and second maximum volumes. Comparison of the potential and acoustic energies revealed that about 70% of the potential energy of the bubble available at the first maximum volume has been converted into an unidentified energy. A possible candidate for the energy conversion mechanism seems to be internal converging shock wave in the bubble interior. The presence of this wave can be observed indirectly in a radiated pressure wave. The measured energies are compared with energies computed using a suitable model. This comparison shows that the theoretical values agree with experimental data until the bubble attains the first minimum volume. However, at later times discrepancies are observed.