Researches On Acoustic Scattering Of Elastic Target On Finite Element Methods

With the development of computer technology,the computational technique of Finite Element Methods(FEM),as its advanced arithmetic,intuitive modeling and accurate computation,has been widely applied to the study of underwater acoustic scattering by more and more researchers.Whereas,as its particular self-arithmetic requirement,the huge mesh quantity will result in enormous computational quantity while the calculated frequency is relatively high.In this paper,through studying the fundamental theory of FEM,one kind of 2D(two-dimension)FEM numerical calculation modeling aim to deal with underwater axisymmetric target acoustic scattering issues is put forward.This method,through turning the 3D space problem into 2D surface problem,improves the computational efficiency and frequency of FEM greatly,and has great practical significance and research values for the study of underwater acoustic scattering.Firstly,by means of COMSOL Multiphysics software,the 3D FE model of underwater targets with simple geometry shapes were built,whose echo characteristics were also calculated and compared with theoretical solutions.The numerical results showed that despite the 3D FE numerical method can reach high computational accuracy,the computational cost are usually high and cannot accomplish high frequency computation.On the basis of studying the weak form solution of the FEM and its mathematical method intensively,for the axisymmetric target,the volume integral of 3D space weak form can be turned into 2D surface integral.Via the built-in computational module function of COMSOL Multiphysics,and putting obtained weak form into the self-owned computational module,the computational model aim to deal with underwater axisymmetric target acoustic scattering issues was built.Finally,through building 2D FE numerical calculated model,the acoustic scattering characteristics of spherical target,half spherical-short cylindrical target and different cylindrical targets were researched,and the underwater acoustic scattering experiment of double stiffened cylindrical shell target was also carried out.Through comparing the calculated results of spherical targets with normal series solutions,the applicability and validity of 2D FE numerical computational model were testified.Compared with the computational efficiency and frequency band of 3D FE modeling,the computational accuracy of 2D FE modeling keeps high,and its computational efficiency is also higher than that of 3D FE modeling.Taking advantage of 2D FE numerical computational model,the scattering characteristics of shell target filled with solid filler and underwater multi-layer structural target were researched.The study shows that the solid filler has an attenuation effect on the vibration of shell and affects the target scattering characteristics together with shell.For the acoustic scattering of underwater multi-layer elastic structural target,its inner multi-layer elastic structure and outer structure vibrate together and have effects on the scatted wave.