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Comparison of Three Dimensional and Axisymmetric Software for Predicting Acoustic Target Strength

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Technical Report

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Defence Research Establishment Atlantic Dartmouth, Nova Scotia Canada

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Recent work at the Defence Research Establishment Atlantic DREA has led to the development of software for predicting the target strength of underwater objects. This capability is incorporated into the general acoustic radiation prediction software tool, AVAST. While AVAST has been successfully validated against a limited set of theoretical data, it has not been fully validated against experimental data or other numerical codes. In that report, AVAST predictions are compared to those made by an axisymmetric-based code ASBIEMdeveloped at SACLANTCEN for a small cylinder with e1ther flat or hemispherical end caps. The results were compared at three frequencies for either the full monostatic case or the bistatic case with three different source locations. For the bistatic case, there was generally good agreement between AVAST, ASBIEM, and theoretical results for the specific source locations selected The results from the cylinder with hemispherical end caps showed slightly better agreement than those from the flat end cylinder For the monostat1c analyses, the AVAST and ASBIEM codes showed very good agreement at the lower frequencies for both cylinder models. At the lowest frequency, AVAST seemed to show a slightly better agreement with the theoretical results At the highest frequency, however, AVAST, while correctly matching the broadside and end fire results and the general level, appears to contain some anomalous side lobes and nulls. In general, the comparisons showed that AVAST gave comparable results when used to predicting target strength The ASBIEM code runs on the order of one magnitude faster than the AVAST code, but cannot be used to model structures which are not axisymmetric.

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