Acoustic color of viscoelastic objects in two-fluid environments: High-fidelity, high-speed, three-dimensional finite-element modeling.

Abstract

NSWC PCD has developed a computer simulation system for modeling the acoustic color (target strength versus frequency and aspect angle) of realistic three dimensional (3-D) objects that are near to or straddling the interfaces between different fluids. It employs high-fidelity (fully 3-D physics throughout object and environment), finite-element (FE) modeling of acoustic scattering from viscoelastic objects. It is implemented in a scalable-architecture, multiblade rack system that automatically runs hundreds of thousands of FE models, changing the mesh resolution and outer fluid boundaries of the models as they sweep over frequency. This frequency-dependent modeling yields a frequency-independent modeling error for the acoustic color response. This, in turn, yields higher accuracy for subsequent signal processing of the acoustic color data. The first part of this paper will present a brief overview of the theoretical, numerical, and software issues. The second part will present verification and validation of the system: (1) ultra-high-precision correlation with T-matrix simulations for four canonical target/environment configurations and (2) experimental validation for objects in free space and straddling the interface between two different fluids. [Work supported by ONR and SERDP.]