Research On Vibration And Radiation Characteristics Of Submerged Structures Based On FEM/IBEM

Coupled Finite Element method/Indirect Boundary Element Method is implemented for calculating the vibration and acoustic radiation problems of general submerged structure. The numerical method has an import significance for the prediction of vibration and noise of structure and it could be referred for reduction of vibration and noise.Finite element method for calculating the structure vibration problem is presented and illustrated, including the derivation of element stiffness matrix and mass matrix of3-node triangular element based on Mindlin plate theory. The generalized eigenvalue problem is solved by subspace iteration method and the shift method is used to solved the singularity or illness of stiffness matrix problem. Model analysis is done for the free rectangular plate. Indirect Boundary Element Method is implemented for the acoustic radiation problem, including a new numerical algorithm for the singularity problem, and the solution of open structure acoustic is described in the paper. By writing the relevant programs by FORTRAN, solution for typical pulsating sphere show the reliability of method.Coupled problems are divided into weak coupling problem and strong coupling problem depending on the property of fluid. For the weak coupling problem, the coupling effect could be ignored, structure equation and fluid equation should be established and be solved independently. Considering the impact of material, thickness of plate and excitation places, solution of a simply supported plate in the air indicate avoiding resonance is an effective method to reduce acoustic. While the coupling effect must be taken into account for the strong coupling problem, the coupled structure equation and fluid equation should be established and solved. The coupled FEM/IBEM is an effect method to solve the problem.At the low frequencies, the fluid effect on the structure could be considered as the added mass effect, the added mass matrix could be calculated by Indirect Boundary Element Method, and the frequency in calculating the added mass has little impact on the structural vibration characteristics, the results of modal identification experiment for the free submerged plate indicate the reliability of the method, the results also show fluid compressibility has little effect on the structure vibration characteristics, considering the fluid as compressible fluid is reasonable while calculating the submerged structures vibration characteristics.