Variation in Cutoff Effect and Sound Field Caused by Geometrical Structures near the Coast

Abstract

The mysterious mass stranding of whales often arises in specific areas in the world. Moreover, vibrational noise, suspected to originate from large-scale construction in coastal areas, is problem. These problems could be considered to be related to sound propagation near coastal areas with a special geometrical structure and an ambient noise environment. We set up a propagation model in a coastal area, and simulated low-frequency sound propagation near the coast using the parabolic equation method (PE method) and the normal mode method. It has been shown that low-frequency sound cannot propagate from the ocean to the coast owing to the cutoff effect of shallow water that occurs when there is a water layer with a basement half space. However, when the water layer has a sediment layer, mode coupling occurs between the water layer and the sediment layer and propagation attenuation rapidly decreases. Sound can propagate to the coast in this case.

Modeling of the hydroacoustic signal and tsunami wave generated by seafloor motion including a porous seabed

“…The propagation of hydroacoustic waves outward from the generation area, with frequencies lower than the proper frequency of the water layer is affected by the porous sedimentary layer: the resulting behavior, in fact, is different from that expected in the case of an elastic basement, where there is a propagation cutoff, due to the waveguide formed by the water‐free surface and elastic seafloor [ Tolstoy , 1963]. As shown by Naoi et al [2006], if the effect of a sediment layer is considered, then the attenuation of the low‐frequency acoustic waves, propagating toward shallower water, is not as strong as in the case of an elastic seafloor, due to the coupling between the water layer and the sediment.…”

“…Furthermore, the porous sediment acts as a natural low‐pass filter for hydroacoustic waves. Some doubts are raised about the effectiveness of the Tolstoy cutoff mechanism in the presence of porous sediments [see also Naoi et al , 2006], thus allowing the possibility of propagation of the hydroacoustic waves, upslope and at a considerable distance from the source area. The model also shows that some remarkable characteristics can be extracted from the acoustic signal generated in the water layer by seafloor motion.…”

Performances of Various Types of Constrained Interpolation Profile Method for Two-Dimensional Numerical Acoustic Simulation

“…Numerical analysis in a time domain has been investigated for sound wave propagation. [1][2][3][4][5][6] The development of accurate numerical schemes has become an important technical issue. [7][8][9][10][11][12] In this study, we simulate the propagation of acoustic waves using several constrained interpolation profile (CIP) methods.…”