Numerical quantification of the bivalve presence in granular sediments on coastal seabeds

Abstract

[Abstract]: A seabed environment has been numerically studied by computing the hydroacoustic scattered field, enabling the seabed classification and quantifying the bivalves buried within the seabed. The echosounder has been represented as an end-fire array with an axis-symmetric directivity pattern. The seabed domain has been modelled as a poroelastic medium using the Biot-Stoll model, which quantifies the energy dissipation caused by the sediment grains but written in a simplified displacementbased formulation, where only the compressional waves with the lowest absorption rates have taken into account. Since the underwater coupled problem involves a bilayer unbounded configuration (seawater and granular seabed), a displacement-based Finite Element Method combined with a Perfectly Matched Layer technique has been used to compute the time-harmonic solutions where the bivalves are enclosed in a localized narrow spatial domain, which reduces the computational cost of the numerical simulations. Assuming, additionally, that the coupling interface between the fluid and granular media is planar, the scattering field in the seawater has been evaluated at the far field using a Green’s representation formula utilizing the explicit evaluation of the fundamental solution of the Helmholtz equation in bilayer media.