Study of the Interaction of Two Acoustical Fields and One FRP Structure with FEM—BEM Coupling Analysis

Abstract

A numerical scheme is applied in the study of an acoustic—structure interaction of sound and a vibratory composite structure by finite element method and boundary element method (FEM—BEM) coupling analysis. The composite structure, as described by the finite element model, is made of a fiber-reinforced plastic (FRP) shell of a torpedo head. The purpose of this report is to evaluate sound insulation of a FRP shell and to learn how to predict the amount of noise reduction from a sound source to a sonar detector. Two acoustical fields were applied to the FEP torpedo head for numerical calculations. The fields were simulated using BEM, and field calculations were performed inside and outside of the shell structure. The FRP shell was modeled using FEM. The two acoustical fields and the vibratory structure are then coupled at the interface. Various laminated shells with different fiber orientation are investigated. The frequency domain of the BEM—FEM coupling algorithm was applied to analyze the noise reduction of a FRP shell submerged in the selected fluids. Based on the results, we found the fiber arrangement of FRP layer does not obviously affect the results of noise reduction. The influence of fiber arrangement on the vibrating modes is obvious in the noise reduction. Furthermore, a hemisphere-shaped shell that possesses transverse isotropy on the surface seems to produce small levels of sound insulation. It was also found that glycerin is more suitable than water for the interior fluid of the hemisphere, even though the glycerin corresponds to a sound constructive interference at high frequencies. Furthermore, small arched-shaped FRP shells appear to possess a higher noise reduction.