Sound Radiation And Transmission Characteristics Calculation Of Submerged Structures

Sound radiation and transmission characteristics of submerged structures have always been a focus to ship designers. Presently the prediction methods mainly include analytical method, numerical method and experimental method, etc. Analytical method is applicable to simple structures, and experimental method costs a lot. The numerical method has been the most widely used because of its flexibility and efficiency. Acoustic radiation of submerged structures is typical fluid-structure interaction problems that needs to build structure and fluid model respectively. Sound radiation characteristics of submerged thin shell were calculated using coupled FEM and BEM in this paper. The main contents are as follows:Firstly, based on the Mindlin plate theory, this paper gave the plate and shell structure as research object and derived the finite element equations. And then a FEM program with four node quadrilateral isoparametric element was compiled to solve this problem. The subspace iteration method has also been used to calculate the natural frequency and vibration mode of the structure. With calculating the modal of a cantilever plate and a free edge plate, the validity of the program has been proved.Based on the Helmholtz equations, the boundary integral equation is derived using the weight function method. The four node quadrilateral isoparametric element is adopted to discrete boundary. With coordinate transformation method to eliminate the singularity of integral function and CHIEF method to solve the non-uniqueness of characteristic frequency. Subsequently, a DBEM program was compiled to calculate the acoustic radiation. The numerical example of a pulse ball was set to verify the program's validity..According to the continuity conditions on the boundary, coupled equation based on FEM/BEM is established. The influence of fluid is simplified to added mass when solving structural vibration characteristics. By solving the coupling equation, sound pressure in the fluid domain were calculated. A submerged spherical shell excited by a harmonic pressure on the inner surface was calculated to verify the validity of the compiled program.Finally, Sound transmission through submerged thin shell due to acoustic excitation was studied. Both of the inner and exterior domains satisfy the Helmholtz integral equation. The coupled equations for the two acoustic domains were then derived by continuity condition of interface velocity. Radiation characteristics of a submerged spherical shell excited by a point sound source located at the center of the sphere was calculated. Comparison of the numerical solution with the analytical solutions shows the validity of the program.