Acoustic Properties of Toroidal Bubbles and Construction of a Large Apparatus
NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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When a burst of air is produced in water, the result can be a toroidal bubble. This thesis is concerned with experimental investigations of three acoustical properties of toroidal bubbles i propagation through high-intensity noise, ii emission, and iii scattering. In i, an attempt to observe a recent prediction of the acoustic drag on a bubble is described, which is analogous to the Einstein-Hopf effect for an oscillating electric dipole in a fluctuating electromagnetic field. No effect was observed, which may be due to insufficient amplitude of the noise. In ii, observations of acoustic emissions of volume oscillations of toroidal bubbles are reported. Surprisingly, the emission occurs primarily during the formation of a bubble, and is weak in the case of very smooth toroidal bubbles. In iii, we describe an experiment to observe the effect of a toroidal bubble on an incident sound field. In addition to the acoustical investigations, we describe the construction of a large hallway apparatus for further investigations and for hands-on use by the public. The tank has cross section 2 feet by 2 feet and height 6 feet, and the parameters of reservoir pressure and time between air bursts are adjustable by the observer.