A study for sound wave scattering by corrugated ground with complex trench structures

Abstract

Several trench structures in corrugated ground are investigated for the possibility of mitigating gun blast noise by numerical simulations. The blast noise usually includes large explosive energy with nonlinearity in the near field and exhibits a very low-frequency spectrum. In this study, the linearity approximation for the noise is taken because the nonlinearity of the wave reaching the scatterer is not serious for many proved guns and the low-frequency characteristic is concentrated. The structures are designed based on the surface impedance design approach proposed in our previous work and arbitrary three-dimensional (3D) geometries within a truncated ground are now assumed. The acoustic characteristic of the structures is evaluated by using a fast numerical solver. The solver employs the multilevel fast multipole algorithm (MLFMA) as an accelerator and can solve very large acoustic wave scattering problems with millions of unknowns on workstations within several days. This tool allows us to truncate the ground as large as needed for accurate modeling. Four structures are mainly considered in the design, namely, concentric trenches, sectorial trapezoidal trenches, interlaced arc trenches and parabolic reflectors. Some of them may have a sloped inner wall or tilted surface as a means of adjustment. Numerical simulations show that the concentric trench design has a very good mitigation behavior for linear and continuous noise sources and the structure is further studied for mitigating real-world gun blast noise.