Finite-element technique for multi-fluid 3-D two-way propagation in ocean waveguides

Abstract

A finite-element technique is presented which makes it possible to treat 3-D forward- and backward scattering in underwater waveguides with inhomogeneous layers of fluid and sediment of arbitrary geometry. The finite-element multi-fluid scattering model was derived from the linear wave equation via the Galerkin residual formulation. From the numerical model, software was developed by customizing an hp-adaptive finite-element package developed by COMCO/Altair Engineering in Austin, Texas. Based on automatic error estimation, it is possible to adapt the user-supplied inhomogeneous computational mesh by making the element size smaller, so-called h-refinement, and/or by increasing the order of the approximating polynomials, so-called p-enrichment, in selected regions of the domain. This process is repeated until a desired level of accuracy in the numerical solution is eventually achieved. The code is validated against a coupled normal-mode model for two-dimensional geometries, and results for shallow-water two-way propagation and scattering with strongly three-dimensional features are presented. The finite-element software is particularly useful for the prediction of scattering from geometries with high local complexity, and as a benchmarking tool for possible future three-dimensional underwater-propagation models.