Accession Number : ADA309091
Title : Bubble Clouds and Surface Reverberation of Underwater Noise.
Descriptive Note : Final rept. 1 Mar 89-3 Jan 94,
Corporate Author : JOHNS HOPKINS UNIV BALTIMORE MD DEPT OF MECHANICAL ENGINEERING
Personal Author(s) : Prosperetti, Andrea
PDF Url : ADA309091
Report Date : 03 JAN 1994
Pagination or Media Count : 18
Abstract : In a paper presented in 1985 at the Nashville meeting of the Acoustical Society of America we suggested that bubble clouds could oscillate in collective modes that would have a significant effect on underwater sound. For example, bubble clouds form structures capable of oscillating at frequencies as low as a few tens of Hz, even though the constituent bubbles, in isolation, might have natural frequencies of tens of kHz or more. Similarly, the large contrast between the index of refraction of pure liquid and bubbly liquid gives rise to strong reflection and scattering processes that might well explain the unexpectedly large backscattering data at low grazing angles. The work carried out under this grant has developed these ideas with particular emphasis on the backscattering from bubble clouds. We have studied the acoustic excitation of bubble cloud as a whole by adapting tools developed for non-homogeneous media in which the bubbly liquid is treated, in an average sense, as a continuum and the individuality of the bubbles lost. The bubble cloud is modelled as a region filled of a complex fluid having a dispersion relation different from the one prevailing in the surrounding pure water. The Helmholtz equation is solved in the bubble region and in the pure water and the two solutions are matched by suitable boundary conditions. In this way it is possible to simulate noise emission as well as scattering processes. This mathematical model has been very precisely validated by comparison with laboratory experiments conducted with artificial bubble clouds. The results of the work are documented in a series of papers.
Descriptors : *BUBBLES, *UNDERWATER SOUND, CLOUDS, OCEAN SURFACE, ACOUSTIC WAVES, BACKSCATTERING, RESONANT FREQUENCY, ACOUSTIC SCATTERING, OSCILLATION, REVERBERATION, GRAZING ANGLES, HELMHOLTZ EQUATIONS.
Subject Categories : Acoustics
Distribution Statement : APPROVED FOR PUBLIC RELEASE