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dc.contributor.authorDietzen, Gregory C.
dc.date.accessioned2012-03-14T17:39:06Z
dc.date.available2012-03-14T17:39:06Z
dc.date.issued2008-09
dc.identifier.urihttp://hdl.handle.net/10945/3694
dc.descriptionCIVINS (Civilian Institutions) Thesis documenten_US
dc.description.abstractBenthic shells can contribute greatly to the scattering variability of the ocean bottom, particularly at low grazing angles. Among the effects of shell aggregates are increased scattering strength and potential subcritical angle penetration of the seafloor. Sand dollars (Dendraster excentricus) occur commonly in the ocean and have been shown to be significant scatters of sound. In order to understand more fully the scattering mechanisms of these organisms, the scattering from individual sand dollars was studied using several methods. Using an approximation to the Helmholtz-Kirchhoff integral, the Kirchhoff method gives an analytic integral expression to the backscattering from an object. This integral was first solved analytically for a disk and a spherical cap, two high aspect ratio oblate shapes which simplify the shape of an individual sand dollar. A method for solving the Kirchhoff integral numerically was then developed. An exact three dimensional model of a sand dollar test was created from computed tomography scans. The Kirchhoff integral was then solved numerically for this model of the sand dollar. The finite element method, a numerical technique for approximating the solutions to partial differential equations and integral equations, was used to model the scattering from an individual sand dollar as well. COMSOL Multiphysics was used for the implementation of the finite element method. Modeling results were compared with published laboratory experimental data from the free field scattering of both an aluminum disk and a sand dollar. Insight on the scattering mechanisms of individual sand dollar, including elastic behavior and diffraction effects, was gained from these comparisons.en_US
dc.description.urihttp://archive.org/details/acousticscatteri109453694
dc.format.extent160 p. : ill.en_US
dc.language.isoen_US
dc.publisherMonterey California. Naval Postgraduate Schoolen_US
dc.rightsThis publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.en_US
dc.subject.lcshShellfishen_US
dc.subject.lcshMathematical modelsen_US
dc.subject.lcshFinite element methoden_US
dc.subject.lcshBackscatteringen_US
dc.titleAcoustic scattering from sand dollars (dendraster excentricus) modeling as high aspect ratio oblate objects and comparison to experimenten_US
dc.typeThesisen_US
dc.contributor.corporateMassachusetts Institute of Technology
dc.description.funderCIVINSen_US
dc.description.serviceUS Navy (USN) author.en_US
dc.identifier.oclc662524825
etd.thesisdegree.grantorCambridge, Massachusetts : Massachusetts Institute of Technology (MIT)en_US
etd.thesisdegree.grantorWoods Hole Oceanographic Institutionen_US
etd.verifiednoen_US
dc.description.distributionstatementApproved for public release; distribution is unlimited.


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