| Summary: | 碩士 === 國立中山大學 === 海下技術研究所 === 95 === The aim of this research is to establish a measurement system to acquire 2-D sound scattering field by an underwater target. In the system, A 3-DOF (degree of freedom) block is remotely orientated by Borland C++ Builder programming language and the batch-processing for signals is used to estimate strength by programing language, Matlab. The process of experiment is simplified by standard operating procedure and the safty of facilities is controled by monitor. Based on the improvements above-mentioned, we can develop an more automatical system to save time effectively, better work conditions, reduce personnel cost, and acquire more objective outcomes. We set up experiment in an water tank of dimension 4mx3.5mx2 m, located in National Sun Yat-sen University, and choose a copper sphere of diameter 60 mm as target. The projector and receiver both are iTP-192k transducer with directivity and frequency response at 192k Hz. In order to measure the 2-D scattering field at 1 m from target without strong boundary interference, projector transmits 64 sine waves at 3.8 Hz and receiver changes direction by block and rotating mechanisms. The effects of direct signal in forward scattering field can be reduced by modified signal process according to Ding (JASA, 101(6), pp.3398-3404, 1997). The difference between actual and theoretical magnitude, based on Hickling (JASA, 34(10), pp.1582-1592, 1962), is 2~3 dB in most of backward scattering region and parts of forward scattering region (30°~60° and 300°~330°), and 5~10 dB in else forward scttering range. Generally speaking, that experimental result displays symmetrical distribution corresponds with theory and indicates the design of mechanism, software and procedure in this study practicable and useful for further research in the future.
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