Monotone difference schemes for weakly coupled elliptic and parabolic systems

The present paper is devoted to the development of the theory of monotone difference schemes, approximating the so-called weakly coupled system of linear elliptic and quasilinear parabolic equations. Similarly to the scalar case, the canonical form of the vector-difference schemes is introduced and the definition of its monotonicity is given. This definition is closely associated with the property of non-negativity of the solution. Under the fulfillment of the positivity condition of the coefficients, two-side estimates of the approximate solution of these vector-difference equations are established and the important a priori estimate in the uniform norm C is given

МОНОТОННЫЕ РАЗНОСТНЫЕ СХЕМЫ ДЛЯ СИСТЕМ ЭЛЛИПТИЧЕСКИХ И ПАРАБОЛИЧЕСКИХ УРАВНЕНИЙ

In this article, for the canonical form of vector-difference schemes under the positivity conditions of matrix coefficients the two-sided estimates for an approximate solution at the arbitrary non sign- constant input data of the problem are obtained. The obtained results are used for deriving two-swided estimates and a priori estimates in the norm C of monotone vector-difference schemes that approximate the weakly coupled systems of elliptic and parabolic equations with the Dirichlet foundary conditions.В настоящей работе для канонической формы векторно-разностных схем общего вида при условиях положительности матричных коэффициентов получены двусторонние оценки сеточного решения при произвольных незнакопостоянных входных данных задачи. Полученные результаты применяются для получения двусторонних оценок и априорных оценок в норме С конкретных монотонных векторно-разностных схем, аппроксимирующих слабо связанные системы эллиптических и параболических уравнений с граничными условиями Дирихле

Numerical analysis of a robust free energy diminishing Finite Volume scheme for parabolic equations with gradient structure

We present a numerical method for approximating the solutions of degenerate parabolic equations with a formal gradient flow structure. The numerical method we propose preserves at the discrete level the formal gradient flow structure, allowing the use of some nonlinear test functions in the analysis. The existence of a solution to and the convergence of the scheme are proved under very general assumptions on the continuous problem (nonlinearities, anisotropy, heterogeneity) and on the mesh. Moreover, we provide numerical evidences of the efficiency and of the robustness of our approach

Robust Numerical Methods for Singularly Perturbed Differential Equations--Supplements

The second edition of the book "Roos, Stynes, Tobiska -- Robust Numerical Methods for Singularly Perturbed Differential Equations" appeared many years ago and was for many years a reliable guide into the world of numerical methods for singularly perturbed problems. Since then many new results came into the game, we present some selected ones and the related sources.Comment: arXiv admin note: text overlap with arXiv:1909.0827

Unsaturated subsurface flow with surface water and nonlinear in- and outflow conditions

We analytically and numerically analyze groundwater flow in a homogeneous soil described by the Richards equation, coupled to surface water represented by a set of ordinary differential equations (ODE's) on parts of the domain boundary, and with nonlinear outflow conditions of Signorini's type. The coupling of the partial differential equation (PDE) and the ODE's is given by nonlinear Robin boundary conditions. This article provides two major new contributions regarding these infiltration conditions. First, an existence result for the continuous coupled problem is established with the help of a regularization technique. Second, we analyze and validate a solver-friendly discretization of the coupled problem based on an implicit-explicit time discretization and on finite elements in space. The discretized PDE leads to convex spatial minimization problems which can be solved efficiently by monotone multigrid. Numerical experiments are provided using the DUNE numerics framework.Comment: 34 pages, 5 figure