1. A system comprising a computer programmed to: create a finite element model of a structural response to an acoustic field with decay, the model including a surface partitioned into a plurality of subdivisions, and cross-correlation loading terms for the subdivisions; and reduce the cross-correlation loading terms by eliminating those terms for each subdivision that exceeds a computed spatial distance from adjacent subdivisions, where the computed distance indicates how far apart a subdivision can be without being influenced by cross-correlation loading of the adjacent subdivisions, where the spatial distance is a function of a minimum scale density factor over frequency range of the analysis.