A NUMERICAL TECHNIQUE TO DESCRIBE ACOUSTICAL SCATTERING AND PROPAGATION FROM AN OBJECT IN A WAVE-GUIDE

The treatment of scattering from submerged objects in an unbounded environment is of considerable interest to both the academic and technological communities. Several approaches have yielded results for different classes of problems and have proven manageable for the free-environment case. Scattering in a confined environment is difficult to express in a form useful for calculation because the effects from the scattered object couple with the boundary effects. The purpose of this work is to propose a numerical scheme that will adequately describe scattering from realistic objects in a confined environment. Some realistic objects of interest are elongated spheroids and cylinders with rounded end caps. Boundary conditions of interest range from those associated with rigid objects to those associated with elastic shells. The object in a waveguide problem is examined in approximate numerical schemes rather than with attempts at exact solutions. The starting point will be the solution of the incident field in terms of normal modes. Next, transition matrix is used that relates the incident field to the scattered field. The transition matrix, which is obtained from Waterman's extended boundary condition method, does not account for boundaries other than that of the object. The solution is then coupled with a waveguide solution to satisfy all boundary conditions. The method, an application of Huygens' principle, couples the solutions and leads to a manageable solution of the problem. This method also satisfies all appropriate boundary conditions and yields a continuous solution throughout space. Details and examples of this method are presented.