An efficient multi-field dynamic model for 3D wave propagation in saturated anisotropic porous media

An efficient multi-field coupled dynamic model for saturated anisotropic porous materials is proposed here. The mathematical formulation of the dynamic deformation-diffusion problem is developed starting from the mixture theory and the definition of the effective stress for anisotropic poro-elasticity, taking into account also the fluid phase compressibility and anisotropic permeability. The effective stress principle is properly extended through the Biot tensor to predict the coupling between the shear stress of the solid skeleton and the pore fluid pressure. Numerical solution of the coupled problem is obtained by inf-sup stable Finite Element spaces. A fundamental issue for the computational efficiency of the coupled model is the numerical solution of the resulting large-size and non-symmetric discrete problem. In this work, we develop a fully implicit monolithic solver based on the Bi-Conjugate Gradient Stabilized (BiCGStab) algorithm accelerated via an ad-hoc Multi-Physics Reduction (MPR) preconditioning technique. The proposed advances are implemented in the 3D GeoMatFem research code and several numerical analyses are performed to test the potential and computational efficiency of the proposed tool. In particular, we focus on 3D wave propagation applications in fully saturated single and multi-layered anisotropic media. Numerical results show that our implementation is able to identify the shear wave splitting phenomenon due to the different degree of material symmetry between the solid phase and the whole porous material.