Vibration And Sound Radiation Analysis Of Submerged Structure Based On FEM/BEM

The prediction of vibration and noise of the submerged structure has been researched by many scholars. The analysis in this field is necessary for structural design, as the natural frequency of structure can be avoided of the frequency of the excitation. Therefore, through this method, resonance can be avoided. The vibration and noise control of structure need to know the natural frequency and vibration mode, so the computation of natural frequency and mode is also an important basis of the vibration and noise control. The numerical calculation of vibration and noise of the submerged structure by finite element method (FEM) is not always satisfactory, especially when this method is used to calculate the infinite and half-infinite fluid domain, and simulate the fluid boundary conditions. FEM is only applied to the finite fluid domain and low frequency of the excitation. For the above problems, vibration and sound radiation analysis of submerged structure based on FEM/BEM is researched in this paper, this method can be applied to the low and middle frequency of the excitation. The characteristics of FEM/BEM are shown as:it can be used for the infinite fluid domain, the convergence rate is moderate and accuracy of derivative is high. The computational accuracy is high and also converged quickly.The stiffness matrix and mass matrix of the Mindlin shell element and space beam element are deduced, FEM can be applied to calculate the vibration and sound radiation of plate and stiffened plate. The dynamic equation is numerically discrete, the mode and the response of the structure are calculated by subspace iteration method or Lanczos method. From the Helmholtz differential equation, the fundamental solution is deduced and the sound pressure of arbitrary field point is expressed by Green function. The singular integral is eliminated by coordinate transformation method, the non-uniqueness difficulty is solved by choosing proper CHIEF point. The added mass matrix is deduced by BEM, meanwhile combining the FEM, the mode of the structure can be obtained. The numerical algorithm of coupled equation is studied and the coupled equation which the sound pressure is regarded as unknown variables is solved. The theory and numerical algorithm are examined by corresponding numerical analysis.