FD-TD MODELING OF ELECTRICALLY LARGE 3-D STRUCTURES WITH THE CRAY EMDS SOFTWARE PACKAGE

This paper describes the EMDS (ElectroMagnetic Design System) software package that we have developed in collaboration with Cray Research, Inc. EMDS implements conformal curved-surface FD-TD modeling of electromagnetic wave interactions with electrically large 3-D structures of complex shape. EMDS aims to minimize computational burdens by using an almost-completely-structured FD-TD mesh, with rectangular Yee cells everywhere except for the relatively few finite-volume stretched or cut cells adjacent to the target surface. It allows the user to rapidly specify complicated structures via the General Dynamics ACAD (Advanced Computer Aided Design) system, or import appropriate files from other CAD systems. And, using Cray's MPGS (MultiPurpose Graphics System,) it provides tools to visualize the dynamics of electromagnetic wave scattering and surface current flow via color animations.

A number of examples will be presented which provide validations of EMDS modeling for perfectly electrically conducting 3-D targets. These will include the double sphere (validated versus generalized multipole theory) and the NASA almond (validated versus measurements). EMDS results for a complete General Dynamics fighter aircraft prototype will be shown and compared to scale-model scattering measurements (if the latter are available in time for this symposium).

This paper will also discuss EMDS modeling of metal scatterers with thin, high-density dielectric layers and coatings. To avoid the numerical storage, running time and stability problems experienced in directly resolving these thin layers, a "smart-cell" strategy is used wherein a surface impedance boundary condition is applied at the finite-volume stretched or cut cells adjacent to the target surface. For this case, validations will be provided for canonical 2-D and 3-D curved target shapes.