Abstract
This work is concerned with the characteristics of very low frequency sound propagation (VLF, ≤100 Hz) in the shallow marine environment. Under these conditions, the classical hypothesis of considering the sea bottom as a fluid environment is no longer appropriate, and the sound propagation characteristics at the sea bottom should be also considered. Hence, based on the finite element method (FEM), and setting the sea bottom as an elastic medium, a proposed model which unifies the sea water and sea bottom is established, and the propagation characteristics in full waveguides of shallow water can be synchronously discussed. Using this model, the effects of the sea bottom topography and the various geoacoustic parameters on VLF sound propagation and its corresponding mechanisms are investigated through numerical examples and acoustic theory. The simulation results demonstrate the adaptability of the proposed model to complex shallow water waveguides and the accuracy of the calculated acoustic field. For the sea bottom topography, the greater the inclination angle of an up-sloping sea bottom, the stronger the leak of acoustic energy to the sea bottom, and the more rapid the attenuation of the acoustic energy in sea water. The effect of a down-sloping sea bottom on acoustic energy is the opposite. Moreover, the greater the pressure wave (P-wave) speed in the sea bottom, the more acoustic energy remains in the water rather than leaking into the bottom; the influence laws of the density and the shear wave (S-wave) speed in the sea bottom are opposite.
Highlights
This paper demonstrates the power of finite element method (FEM) for handling VLF sound propagation in a full waveguide of shallow water
This paper demonstrates the power of FEM for handling VLF sound propagation in a rameters on the characteristics of VLF sound propagation and its corresponding mechafull waveguide of shallowthrough water. numerical
VLF sound propagation andwater, its corresponding mechabe used to develop new sensors and equipment which unify underwater acoustic signals nisms are investigated through numerical simulation and acoustic theory
Summary
The sea bottom should be considered as a range-dependent elastic medium when studying the characteristics of VLF sound propagation in shallow water In this type of sea environment model, the strong penetrability of VLF acoustic signals could cause substantial acoustic energy to leak into the sea bottom, generating seismic acoustic signals that propagate through the sea bottom or bottom surface [8,9,10]. A number of acoustic field calculation methods, such as the normal mode method, ray method, parabolic equation method, fast field method, and their derivatives, have been established to study sound propagation in shallow water These methods are based on limiting assumptions and approximations of the wave equation and sea environment, restricting their universality, especially for the calculation of sound propagation at VLF in range-dependent shallow water with an elastic bottom [14].
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