Acoustic radiation from elastic structures in shallow water by finite element method combined with normal modes

Abstract

Acoustic radiation problem of elastic structures in shallow water has not been solved effectively. Finite Element Method (FEM) is not suitable for higher frequency and large range problems. In principle, the Combined Wave Superposition Method can deal with such problems. However, it is hard to optimize a large number of virtual sources. For low and middle frequency bands, we propose a new method combining FEM and normal modes. FEM is used to calculate the near range acoustic field of the structural source, then the eigen function expansion is performed on the field, and the coefficients of modes can be obtained by using the orthogonality of the eigen function. Therefore, we can calculate the acoustic field at any range. This method avoids the process of solving inverse matrix of a large complex matrix, which is an essential step in wave superposition method, and is very efficient to calculate the far field. To show the efficiency and accuracy of the method, the simulation results of various structural sources and waveguide models are compared with that of using FEM directly.