Index of content:
Volume 115, Issue 3, March 2004
- NONLINEAR ACOUSTICS 
115(2004); http://dx.doi.org/10.1121/1.1646398View Description Hide Description
The motion of an interface in acoustic field is modeled as a nonlinear relaxator driven by sound wave. The nonlinearity is due to nonlinear dependence of an interaction force between the surfaces composing the interface on their separation distance. The theory describes hysteresis in the response of the interface to continuously varying acoustic loading: with increasing acoustic field a strongly unharmonic variation of a characteristicinterface width starts under some circumstances at higher amplitudes of external action than those at which it later stops with decreasing acoustic field. This dynamic hysteresis phenomenon is found to be dispersive in a sense that it depends on the relative values of the acoustic frequency and characteristic relaxation frequencies of the interface. These theoretical predictions might be also relevant to some recent experimental observations of hysteresis phenomena in the interaction of powerful ultrasonic fields with cracks.
115(2004); http://dx.doi.org/10.1121/1.1646402View Description Hide Description
The sound produced by the collapse of discrete cavitationbubbles was examined. Laser-generated cavitationbubbles were produced in both a quiescent and a vortical flow. The sound produced by the collapse of the cavitationbubbles was recorded, and its spectral content was determined. It was found that the risetime of the sound pulse produced by the collapse of single, spherical cavitationbubbles in quiescent fluid exceeded that of the slew rate of the hydrophone, which is consistent with previously published results. It was found that, as collapsing bubbles were deformed by the vortical flow, the acoustic impulse of the bubbles was reduced. Collapsing nonspherical bubbles often created a sound pulse with a risetime that exceeded that of the hydrophone slew rate, although the acoustic impulse created by the bubbles was influenced largely by the degree to which the bubbles became nonspherical before collapse. The noise produced by the slow growth of cavitationbubbles in the vortex core was not detectable. These results have implications for the interpretation of hydrodynamiccavitationnoise produced by vortexcavitation.