Eng. Mech. Discipline, Open Univ., Milton Keynes MK7 6AA, England
The Open University
A numerical procedure for computing sound propagation from a point source in an environment consisting of a stratified fluid half-space above a layered poro-elastic ground is described. The wave amplitudes are computed from depth-separated wave equation by forming a system of linear equations arising from the boundary conditions at each and every interface between layers and solving the resulting global matrix. The inverse Hankel transform is then performed by fast Fourier method (FFP) to obtain the pressure and particle velocity at any elevation as a function of range. Wave propagation within the porous elastic layers is calculated according to the modified Biot--Stoll theory which predicts two compressional and one shear wave types in the medium. Six boundary conditions are therefore required at each ground intefaces and four at the fluid--ground interface, while only two are needed at the fluid--fluid interfaces. Using this code the role of the ground elasticity on above-ground propagation and in acoustically induced seismic excitation are explored. It is predicted that on certain ground types, characterized by a thin layer with small compressional and shear velocities, and at frequencies that coincide with a peak in the seimic-to-acoustic coupling ratio spectrum there is an extra sound attenuation.