### ASA 124th Meeting New Orleans 1992 October

## 5pPA5. Coupling finite element and boundary element methods for the
analysis of the acoustic scattering by elastic structures.

**Antoine Lavie
**

**
Bertrand Dubus
**

**
**
*Dept. d'Acoust. I.E.M.N., U.M.R. C.N.R.S. 9929, Inst. Superieur
d'Electron. du Nord, 41 boulevard Vauban, 59046 Lille Cedex, France
*

*
*
Considerable interest has been expressed recently in the scattering of a
plane acoustic wave by an elastic structure. In this paper, a method that
couples the finite element method and a boundary element method is proposed. A
finite element code (ATILA) is used to model the elastic structure and a
boundary element code (EQI) to describe the propagating waves in the infinite
fluid medium surrounding the body. The analysis is performed in three steps for
each frequency: (i) the effect of the fluid is characterized by a nodal
impedance matrix using BEM, (ii) the analysis of the structure using FEM
including fluid effects via the impedance matrix provides the displacement
field, (iii) from these displacements, the near-field and far-field pressures
are obtained using BEM. The method is successfully applied to the scattering by
spherical shells of various thicknesses for ka varying from 0 to 15 (k is the
acoustic wave number in the fluid and a is the external radius of the sphere).
The advantages of the method (analysis of complex geometries with various
materials, direct knowledge of the displacement field, exact description of
Sommerfeld's radiation condition) and its drawbacks (irregular frequencies
associated with BEM, limitation to medium values of ka) are discussed. [Work
supported by D.R.E.T. Paris.]