Abstract
The effective density fluid model (EDFM) was developed to approximate the behavior of sediments governed by Biots theory of poroelasticity. Previously, it has been shown that the EDFM predicts reflection coefficients and backscattering strengths that are in close agreement with those of the full Biot model for the case of a homogeneous poroelastic half-space. However, it has not yet been determined to what extent the EDFM can be used in place of the full Biot-Stoll model for other cases. Using the finite element method, the flat-interface reflection and rough-interface backscattering predictions of the Biot-Stoll model and the EDFM are compared for the case of a poroelastic layer overlying an elastic substrate. It is shown that considerable differences between the predictions of the two models can exist when the layer is very thin and has a thickness comparable to the wavelength of the shear wave supported by the layer, with a particularly strong disparity under the conditions of a shear wave resonance. For thicker layers, the predictions of the two models are found to be in closer agreement, approaching nearly exact agreement as the layer thickness increases.
Highlights
Biot’s theory of poroelasticity, which models a given porous material as a skeletal elastic frame coupled to a fluid which completely fills its pores, was first introduced in a series of classic papers.[1,2] Biot theory has since been applied to the modeling of unconsolidated marine sediments by Stoll.[3,4] For sandy sediments, it has been shown that the Biot-Stoll model provides a better fit with measured reflection[5] and backscattering[6] data than models that assume the sediment to behave either as a fluid or as a viscoelastic solid.Despite this success, the Biot-Stoll model can be cumbersome to implement and requires 13 material parameters as inputs, many of which being difficult to measure
IV A are implemented in the commercial finite element method (FEM) code COMSOL Multiphysics, which is used for all meshing and solving.[26]
Unlike the case of sediment modeled as a poroelastic half-space, the bottom loss and backscattering strength predictions of the effective density fluid model (EDFM) can differ substantially from those of the full Biot-Stoll model
Summary
Biot’s theory of poroelasticity, which models a given porous material as a skeletal elastic frame coupled to a fluid which completely fills its pores, was first introduced in a series of classic papers.[1,2] Biot theory has since been applied to the modeling of unconsolidated marine sediments by Stoll.[3,4] For sandy sediments, it has been shown that the Biot-Stoll model provides a better fit with measured reflection[5] and backscattering[6] data than models that assume the sediment to behave either as a fluid or as a viscoelastic solid Despite this success, the Biot-Stoll model can be cumbersome to implement and requires 13 material parameters as inputs, many of which being difficult to measure.
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