Exact modeling of targets in littoral environments

The US Navy needs the capability to model acoustic propagation in complex ocean environments containing natural or man-made objects. Such accurate modeling requires the solution of the wave equation in the ocean containing scatterers. In the absence of the scatterer, the oceanic waveguide can be assumed to be axially symmetric. This allows certain types of physically valid approximations to be made, which are 2D in nature, but can accurately compute the acoustic field in a 3D ocean. The presence of the scatterer breaks this symmetry and forces one to model the ocean as fully 3D. Due the large size of the computational domain, the solution of the wave equation in an oceanic waveguide in the presence of scatterers is a daunting numerical task. In Phase I of this STTR we developed finite element models in the frequency and time domains to compute the acoustic field in a 2D, elastic, range-dependent waveguide in the presence of an elastic object. The objective of this Phase II effort is to develop the numerical capability to accurately solve the wave equation in a range-dependent elastic waveguide in the presence of a general, 3D elastic target to ranges of at least 10,000 acoustic wavelengths. To cope with the numerical complexities in 3D, we plan to accomplish this objective by developing numerical tools that implement a hybrid model composed of finite element and propagation models.