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 lowfrequency 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.

Study on Three-Dimensional Dynamic Stability of Open-Pit High Slope under Blasting Vibration

“…The rock mass parameters are used in theoretical analysis and calculation as shown in Table 2. In our study, using geotechnical analysis modeling software and some self-compiled preprocessing programs, a threedimensional model of the topographic contour of the Jianshan open-pit was established [45,46]. Affected by the difference of terrain, lithology, blasting distance, and maximum charge, the acceleration transmitted by the blast wave will change irregularly.…”

Homogenization of thin-structured surfaces for acoustics in the presence of a two-dimensional low Mach potential flow

“…The best known are micro-perforated absorbers and liners for acoustic noise reduction in vehicles or airplanes or for optimal acoustics in conference or lecture halls [1,2]. For surfaces consisting of rectangular grooves, approximate effective impedance models [3] have been derived and as detailed in [4] roughness can be used to modify effective impedances to enhance the surface transport noise reduction [5,6] mechanism is the creation of surface waves by roughness near grazing incidence [7]: the energy reaching a receiver can then be reduced by transferring the incident sound energy into these surface waves [8].…”

Approximate impedance models for point-to-point sound propagation over acoustically-hard ground containing rectangular grooves

“…[1][2][3][4] The surface structure may be manipulated such that the resulting energy reaching the receiver can be reduced at certain frequencies and for a given source-receiver geometry by the transfer of incident sound energy into surface waves and diffraction modes. 5 Under certain circumstances it has been found that grating structures can be represented as having an effective impedance similar to that of a porous hard-backed layer. 3 In an air-filled medium having slit-like pores with widths smaller than the incident wavelength, viscous friction and thermal exchange at the internal surfaces contribute to the surface impedance.…”