| Summary: | 碩士 === 國立臺灣海洋大學 === 輪機工程學系 === 104 === In this thesis, we use finite element method (FEM)/boundary element method (BEM) to predict the noise of the submerged structure. Recently, it is very popular issue for controlling radiation and scattering noise from the submerged structure especially in the ocean engineering. In this thesis how to correct predict the energy and radiation pattern scattering form the submerged structure is the primary aim. Because the under water structural acoustics includes the coupling of the responses of structure and fulid, it is very difficult to solving. For overcoming this problems, to obtained the response of the submerged structure need at the same time to solve the structural equation and acoustic equation. Solving both equations, the structural equation is formulated by FEM, whereas the acoustic equation is either by BEM or FEM, referring as FEM/BEM and FEM/FEM. Because FEM/BEM solved the coupled equation is better than FEM/FEM in the low frequency. Therefore, in this thesis we used FEM/BEM solving for low frequency domain, and applied the vibration natural modes (VNM) for the displacement expansions and coupling with BEM to compute the submerged structural responses. In order to verfied the numerical accuracy and stability, we compared numercial solutions with analytical solutions. The results are shown that the present methods have good computational efficiency and high accuracy.
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