Finite Element Modeling of Acoustic Scattering from Fluid and Elastic Rough Interfaces for Ocean Acoustics Applications

date September 6, 2013
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Friday, September 6, 2013 4:00 p.m. in ETC 4.150

Dr. Marcia J. Isakson
Applied Research Laboratories
The University of Texas at Austin

Quantifying acoustic scattering from rough interfaces is critical for ocean acoustic applications, especially in shallow water waveguides.  In this scenario, the sound has many interactions with both the air/water interface and the sediment/water interface.  Scattering from these interfaces both reduces the coherent reflected component of the sound as well as produces reverberation.   The air/water interface is often modeled as pressure release while the sediment/water interface must be modeled as penetrable.  Depending on the sediment, it can be modeled as a fluid, visco-elastic solid or poro-elastic solid.  This study concentrates on the sediment/water interface by modeling both a fluid-like sediment and a visco-elastic solid.  Historically, scattering is quantified by approximations to the Helmholtz/Kirchhoff integral.  The two main approximations used are the Kirchhoff approximation and perturbation theory.  The Kirchhoff approximation considers scattering as reflections from planes tangent to the facets of the surface.  Perturbation theory expands the scattered pressure in a Taylor series with respect to the relief of the surface and truncates the series.  Although these approximations are used extensively, there has not been a systematic study of validity especially for realistic rough surfaces.  In this study, the finite element model results for scattering from fluid and visco-elastic solids with rough interfaces will be compared to the approximate methods.  The results illustrate the role of the waves excited at the interface in the scattering process.