Experiments with the Underwater Bubble Low Frequency Sound Resonator

Abstract

An infra-sound source with a resonator in the form of an underwater bubble made from an elastic material is a simple engineering solution. The elastic membrane supports high volume displacement and a large radiation aperture. The Rayleigh-Plesset equation defines the dynamics of a spherical bubble including surface tension and viscous effects. The shape of a large bubble deforms due to gravitational effects. Its internal pressure oscillations are comparable with the difference of gravity pressure and these effects are part of its dynamics. The real Q-factor of a practical bubble is smaller than theoretical. The underwater bubble resonator was studied experimentally in the pool and at the Woods Hole Oceanographic Institution’s dock. The research includes the 3D finite-element analysis and its comparison with the experimental data. The study gave the real values for the Q-factor, resonance frequencies and sound pressure levels. The experimental resonator has good performance with a maximum SPL 190 dB at the resonance frequency 6-12 Hz. It was shown that a cylindrical resonator can be towed with a speed of 8 knots. The research proved that this is a practical approach for a coherent low frequency sound source, which can find applications in a marine seismic survey.An infra-sound source with a resonator in the form of an underwater bubble made from an elastic material is a simple engineering solution. The elastic membrane supports high volume displacement and a large radiation aperture. The Rayleigh-Plesset equation defines the dynamics of a spherical bubble including surface tension and viscous effects. The shape of a large bubble deforms due to gravitational effects. Its internal pressure oscillations are comparable with the difference of gravity pressure and these effects are part of its dynamics. The real Q-factor of a practical bubble is smaller than theoretical. The underwater bubble resonator was studied experimentally in the pool and at the Woods Hole Oceanographic Institution’s dock. The research includes the 3D finite-element analysis and its comparison with the experimental data. The study gave the real values for the Q-factor, resonance frequencies and sound pressure levels. The experimental resonator has good performance with a maximum SPL 190 dB at the...