![]() The second important effect is that surface roughness also causes scattering and attenuation of sound in the bright zone before it reaches the shadow zone. The first effect is that surface roughness leads to the formation of a "boundary wave" in the fluid in a layer above the surface that channels more sound into the shadow zone behind the curved surface in the form of a "creeping boundary wave". 79(3) 657-665 (1986)), which is valid for densely packed, steep-sloped elements and at grazing sound incidence, describes qualitatively the two major effects associated with the diffraction and scattering of sound by a curved rough surface. For the second problem, experiments show that the Biot-Tolstoy-Medwin model for flat rough surfaces (H. Experiments carried out with a transient acoustic spark source confirm that: (1) in the region where there are no reflected waves, diffracted waves combine with the diffracted-reflected waves to produce a smooth transition (2) the acoustic field around the step discontinuity can be highly directional due to the interference of the direct, the reflected, the diffracted, and the diffracted-reflected waves and (3) the acoustic field is essentially unchanged if the step discontinuity is replaced with a smooth edged step discontinuity whose radius of curvature is less than the characteristic wavelength of the incident sound. 69(4) 1060-1064 (1981)) can be used to predict the acoustic field around the step discontinuity directly in the time domain. For the first problem, it is shown that the Biot -Tolstoy-Medwin model for a rigid 90^circ wedge (H. ![]() Two canonical problems of outdoor sound propagation have been studied in detail: (1) the propagation of sound over a rigid surface with a step discontinuity in height with the step height comparable to an acoustic wavelength and (2) the propagation of sound over a curved rough surface with a radius of curvature much greater than the acoustic wavelength and with a roughness scale smaller than the acoustic wavelength. ![]()
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