Acoustic Diffraction from a Semi-Infinite Elastic Plate Under Arbitrary Fluid Loading with Application to Scattering from Arctic Ice Leads.

摘要

The problem of a low-frequency acoustic plane wave incident upon a free surface coupled to a semi-infinite elastic plate surface, is solved using an analytic approach based on the Wiener-Hopf method. By low-frequency it is meant that the elastic properties of the plate are adequately described by the thin plate equation. The diffraction problem relates to issues in long range sound propagation through partially ice-covered Arctic waters, where open leads on the surface represent features from which acoustic energy can be diffracted or scattered. This work focusses on ice as the material for the elastic plate surface, and the results and conclusions are directed toward the ice lead diffraction process. An exact solution to a canonical problem is derived first: a plane wave incident upon a free surface (Dirichlet boundary condition) coupled to a perfectly rigid surface (Neumann boundary condition). Ice material properties are addressed using the locally reacting approximation for the input impedance of an ice plate. This is followed by use of the thin plate equation to describe the input impedance which incorporates elements of elastic wave propagation. An important issue in working with the thin plate equation is the fluid loading pertaining to sea ice and low-frequency acoustics, using an approximation to the exact kernel of the Wiener-Hopf functional equation allows one to proceed to a complete and readily interpretable solution for the far field diffracted pressure.