Implementation of a computational model for random directional seas and underwater acoustics

Bayindir, Cihan
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University of Delaware
Acoustic wave propagation in the ocean is an old and interesting problem. In the literature the problem of interaction of acoustic waves with the ocean surface has drawn the attention of many researchers. This interaction problem is a very complicated problem due to many physical processes involved. Some of the important factors on the ocean surface which affects underwater communications are presence of waves, turbulence generated by wind input, wave breaking, white capping, bubbles and density, salinity and temperature effects. In this thesis, the effect of linear and nonlinear surface gravity waves on high frequency acoustic propagation is discussed. Realistic models of linear and nonlinear surface gravity waves, which solve the exact governing equations, are created, and these models are coupled with an acoustic Gaussian beam tracing program called Bellhop. Since Bellhop is not capable of accounting for out of plane scattering of acoustic rays, coupling is done only for two spatial dimensions, one horizontal and one vertical. The wave model provides velocity components in the normal direction to the surface. These velocity components are used in the Doppler frequency shift calculations of acoustic rays generated by Bellhop. Data from an acoustic experiment are taken as experimental results and coupled wave-acoustic model has been run with the same conditions and same geometric layout of experiments. Comparisons between experimental results and coupled wave-acoustic model results are presented and the limits of model validity are discussed.