Experimental Validation of Time-Domain Three-Dimensional Finite-Difference Techniques for Predicting Interior Coupling Responses

The finite-difference code G3DXL3 (generalized 3-dimensional expandable Lawrence Livermore National Laboratory) has been applied to the problem of interior coupling. The coupling test object was a 1-m-tall sheet aluminum cylinder, 0.2 m in diameter with an interior cavity of variable height coupled to the exterior via variable-size rectangular apertures. Inside the cavity, wires were run at different locations with a mix of short and open terminations. Cable current responses at the base of the wires were measured for several geometries and compared with the code predictions. Agreement was very good to excellent up to 3 GHz. In this case, a VAX 11/780 was used with a problem space of 32 × 32 × 88 cells (roughly equivalent to 503 cells) and cells 1.25 cm on all sides. In that many interior modes of the test object were predicted with excellent frequency agreement and typically very good amplitude agreement, the time-domain finite-difference technique should be considered an experimentally validated tool for interior response predictions of idealized interior coupling geometries when employed with the proper resources and necessary care in specifying the inputs and outputs.