Accuracy and convergence properties of the fixed-stress iterative solution of two-way coupled poromechanics

Abstract

The paper deals with the numerical solution of Biot's equations of coupled consolidation obtained by a mixed formulation combining continuous Galerkin finite-element and multipoint flux approximation finite-volume methods. The solution algorithm relies on the recently developed fixed-stress solution scheme, in which first the flow problem and then the mechanical one are addressed iteratively. We show that the algorithm can be interpreted as a particular block triangular preconditioning strategy applied within a Richardson iteration. The key component to the success of the preconditioner is the sparse approximation to the Schur complement based on a pressure space mass matrix scaled by a weighting factor that depends element-wise on the inverse of a suitable bulk modulus. The accuracy of the method is assessed, making use of well-known analytical solutions from the literature. Numerical results demonstrate robustness and low computational cost of the fixed-stress scheme in accurately capturing the two-way coupling between deformation and pressure.