Research On Vibration And Acoustic Radiation Of Thin-walled Ship Structure Based On FEM/BEM

Prediction and Reduction of vibration and acoustic radiation of marine structures has been an important issue, because it involves kinds of performance of ships and submarines. In the early stages of ship design, how to quickly and accurately predict the vibration and noise characteristics has become an important task. This dissertation addresses a study on numerical analysis of vibration and acoustic radiation based on FEM/BEM. The major contents of the dissertation are as follows.Main methods related to vibration and acoustic radiation problems are introduced. The research status about vibration and acoustic radiation of thin-walled beam and cylindrical shell are discussed.To predict vibration and acoustic radiation of marine structures, a coupled finite element-boundary element method is presented. The basic theory of the finite element and boundary element method is introduced. Based on Benscoter theory and Timoshenko beam theory, a one-dimensional thin-walled beam element is used to model the structure and the two-dimensional acoustics boundary element method is employed to account for the acoustic load. Modal analysis and response analysis are studied. Then the structural acoustic radiation is easy to get using the three-dimensional boundary element method. The Fortran programs of the infinite domain and half infinite domain are developed. To validate the present method, the numerical results are verified by comparing with the results obtained with ANSYS analysis and SYSNOISE analysis. The comparison of the results indicates feasibility of the proposed method.Elastic cylindrical shell is the typical structure of submarines. So its vibration and acoustic radiation characteristics are important in engineering. The basic theory of cylindrical shell is introduced. The research object is the closed cylindrical shell with free boundary. The finite element and boundary element model are building. The finite element software (ANSYS) is used to model the structure and calculate the vibration response, which is used as the boundary conditions of the boundary element software (SYSNOISE). Then the structural acoustic radiation is easy to get using SYSNOISE. The influences of the different incentive points, adding ring ribs and the longitudinal ribs for the acoustic radiation properties are studied. The radiation directivity of cylindrical shell is analyzed.