scholarly journals PRECONDITIONED ITERATIVE METHOD FOR REACTIVE TRANSPORT WITH SORPTION IN POROUS MEDIA

2020 ◽  
Vol 25 (4) ◽  
pp. 546-568
Author(s):  
Michel Kern ◽  
Abdelaziz Taakili ◽  
Mohamed M. Zarrouk
Keyword(s):  
Porous Media ◽  
Reactive Transport ◽  
Mixed Finite Element ◽  
Operator Splitting ◽  
Splitting Method ◽  
Mesh Size ◽  
Mixed Finite Element Method ◽  
Alternative Formulation ◽  
Preconditioning Techniques ◽  
Newton Step

This work deals with the numerical solution of a nonlinear degenerate parabolic equation arising in a model of reactive solute transport in porous media, including equilibrium sorption. The model is a simplified, yet representative, version of multicomponents reactive transport models. The numerical scheme is based on an operator splitting method, the advection and diffusion operators are solved separately using the upwind finite volume method and the mixed finite element method (MFEM) respectively. The discrete nonlinear system is solved by the Newton–Krylov method, where the linear system at each Newton step is itself solved by a Krylov type method, avoiding the storage of the full Jacobian matrix. A critical aspect of the method is an efficient matrix-free preconditioner. Our aim is, on the one hand to analyze the convergence of fixed-point algorithms. On the other hand we introduce preconditioning techniques for this system, respecting its block structure then we propose an alternative formulation based on the elimination of one of the unknowns. In both cases, we prove that the eigenvalues of the preconditioned Jacobian matrices are bounded independently of the mesh size, so that the number of outer Newton iterations, as well as the number of inner GMRES iterations, are independent of the mesh size. These results are illustrated by some numerical experiments comparing the performance of the methods.

scholarly journals A Numerical Method for Compressible Model of Contamination from Nuclear Waste in Porous Media

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Zhifeng Wang
Keyword(s):  
Porous Media ◽  
Method Of Characteristics ◽  
Mixed Finite Element ◽  
Grid Method ◽  
Thermal Conditions ◽  
Mixed Finite Element Method ◽  
Fine Grid ◽  
Modified Method ◽  
Optimal Accuracy ◽  
Modified Method Of Characteristics

This paper studies and analyzes a model describing the flow of contaminated brines through the porous media under severe thermal conditions caused by the radioactive contaminants. The problem is approximated based on combining the mixed finite element method with the modified method of characteristics. In order to solve the resulting algebraic nonlinear equations efficiently, a two-grid method is presented and discussed in this paper. This approach includes a small nonlinear system on a coarse grid with size H and a linear system on a fine grid with size h . It follows from error estimates that asymptotically optimal accuracy can be obtained as long as the mesh sizes satisfy H = O h 1 / 3 .

A fully-mixed finite element method for the Navier–Stokes/Darcy coupled problem with nonlinear viscosity

2017 ◽  
Vol 25 (2) ◽  
Author(s):  
Sergio Caucao ◽  
Gabriel N. Gatica ◽  
Ricardo Oyarzúa ◽  
Ivana Šebestová
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Porous Media ◽  
Stokes Equations ◽  
Mixed Finite Element ◽  
Mixed Finite Element Method ◽  
Transmission Conditions ◽  
Navier Stokes ◽  
Porous Media Flow ◽  
Element Method

AbstractWe propose and analyze an augmented mixed finite element method for the coupling of fluid flow with porous media flow. The flows are governed by a class of nonlinear Navier–Stokes and linear Darcy equations, respectively, and the transmission conditions are given by mass conservation, balance of normal forces, and the Beavers–Joseph–Saffman law. We apply dual-mixed formulations in both domains, and the nonlinearity involved in the Navier–Stokes region is handled by setting the strain and vorticity tensors as auxiliary unknowns. In turn, since the transmission conditions become essential, they are imposed weakly, which yields the introduction of the traces of the porous media pressure and the fluid velocity as the associated Lagrange multipliers. Furthermore, since the convective term in the fluid forces the velocity to live in a smaller space than usual, we augment the variational formulation with suitable Galerkin type terms arising from the constitutive and equilibrium equations of the Navier–Stokes equations, and the relation defining the strain and vorticity tensors. The resulting augmented scheme is then written equivalently as a fixed point equation, so that the well-known Schauder and Banach theorems, combined with classical results on bijective monotone operators, are applied to prove the unique solvability of the continuous and discrete systems. In particular, given an integer

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