Numerical Computation of Steady State Scattered Sound External to Submerged Infinite Cylinders by Combining Finite Element and Integral Equation Methods

Abstract : In a previously reported investigation, scattered sound pressures and velocity distributions on the surfaces of submerged infinite cylinders ensonified by steady-state plane waves were calculated. The numerical method used for these calculations was based on a finite element formulation of the coupled fluid-structure interaction problem and implemented using the NASTRAN computer program. In the present investigation, these pressure and velocity data are used as the basis for numerical calculations of the scattered sound pressures generated in the exterior fields of the cylinders. The method consists of replacing an infinite cylinder by a finite cylinder whose external sound field, in three dimensions, converges to the required two-dimensional (2-D) field as the cylinder length increases. The field pressures are obtained by numerical quadrature of the HELMHOLTZ integral formulation which relates external field pressures to pressures and normal velocities at the structural surface. Calculated 2-D pressure fields, obtained for rigid and elastic cylinders, are in excellent agreement with analytical results. (Author)