Analysis of the Brinkman-Forchheimer equations with slip boundary conditions

In this work, we study the Brinkman–Forchheimer equations driven under slip boundary conditions of friction type. We prove the existence and uniqueness of weak solutions by means of regularization combined with the Faedo-Galerkin approach. Next, we discuss the continuity of the solution with respect to Brinkman’s and Forchheimer’s coefficients. Finally, we show that the weak solution of the corresponding stationary problem is stable.     

Continuous dependence for the convective Brinkman–Forchheimer equations

In this article, we have considered the convective Brinkman–Forchheimer equations with Dirichlet's boundary conditions. The continuous dependence of solutions on the Forchheimer coefficient in H ¹ norm is proved.     

Approximation of the incompressible convective Brinkman–Forchheimer equations

This paper studies the approximation of solutions for the incompressible convective Brinkman–Forchheimer (CBF) equations via the artificial compressibility method. We first introduce a family of perturbed compressible CBF equations that approximate the incompressible CBF equations. Then, we prove the existence and convergence of solutions for the compressible CBF equations to the solutions of the incompressible CBF equations.     

Convergence and Continuous Dependence for the Brinkman–Forchheimer Equations

The Brinkman–Forchheimer equations for non-slow flow in a saturated porous medium are analyzed. It is shown that the solution depends continuously on changes in the Forchheimer coefficient, and convergence of the solution of the Brinkman–Forchheimer equations to that of the Brinkman equations is deduced, as the Forchheimer coefficient tends to zero. The next result establishes continuous dependence on changes in the Brinkman coefficient. Following this, a result is proved establishing convergence of a solution of the Brinkman–Forchheimer equations to a solution of the Darcy–Forchheimer equations, as the Brinkman coefficient (effective viscosity) tends to zero. Finally, upper and lower bounds are derived for the energy decay rate which establish that the energy decays exponentially, but not faster than this.     

Approximation of the unsteady Brinkman‐Forchheimer equations by the pressure stabilization method

In this work, we propose and analyze the pressure stabilization method for the unsteady incompressible Brinkman‐Forchheimer equations. We present a time discretization scheme which can be used with any consistent finite element space approximation. Second‐order error estimate is proven. Some numerical results are also given.© 2017 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 33: 1949–1965, 2017     

Numerical analysis for generalized Forchheimer flows of slightly compressible fluids

In this article, we will consider the generalized Forchheimer flows for slightly compressible fluids. Using Muskat's and Ward's general form of Forchheimer equations, we describe the fluid dynamics by a nonlinear degenerate parabolic equation for density. The long‐time numerical approximation of the nonlinear degenerate parabolic equation with time dependent boundary conditions is studied. The stability for all time is established in a continuous time scheme and a discrete backward Euler scheme. A Gronwall's inequality‐type is used to study the asymptotic behavior of the solution. Error estimates for the solution are derived for both continuous and discrete time procedures. Numerical experiments confirm the theoretical analysis regarding convergence rates.     

Modelling boundary and nonlinear effects in porous media flow

We consider the problem of employing a Brinkman–Forchheimer system to model flow in a porous medium when Newton cooling conditions are appropriate at the boundary of the body. Specifically it is shown that the solution depends continuously on the Forchheimer coefficient and on the coefficient in the Newton cooling law at the boundary. Since we are dealing with non-slow flow rates and a porosity which is close to one we employ the Brinkman–Forchheimer equations and this leads to a second order differential inequality in the analysis as opposed to the first order one often found.     

Convergence and continuous dependence for the Brinkman–Forchheimer equations

This paper investigates the flow of fluid in a porous medium which is described in the Brinkman–Forchheimer equations and obtains the structural stability results for the coefficients.     

A Vanka-based parameter-robust multigrid relaxation for the Stokes–Darcy Brinkman problems

We consider a block-structured multigrid method based on Braess–Sarazin relaxation for solving the Stokes–Darcy Brinkman equations discretized by the marker and cell scheme. In the relaxation scheme, an element-based additive Vanka operator is used to approximate the inverse of the corresponding shifted Laplacian operator involved in the discrete Stokes–Darcy Brinkman system. Using local Fourier analysis, we present the stencil for the additive Vanka smoother and derive an optimal smoothing factor for Vanka-based Braess–Sarazin relaxation for the Stokes–Darcy Brinkman equations. Although the optimal damping parameter is dependent on meshsize and physical parameter, it is very close to one. In practice, we find that using three sweeps of Jacobi relaxation on the Schur complement system is sufficient. Numerical results of two-grid and V(1,1)-cycle are presented, which show high efficiency of the proposed relaxation scheme and its robustness to physical parameters and the meshsize. Using a damping parameter equal to one gives almost the same convergence results as these for the optimal damping parameter.     

Existence of global attractors for the three‐dimensional Brinkman–Forchheimer equation

In this paper, we investigate the asymptotic behavior of solutions of the three‐dimensional Brinkman–Forchheimer equation. We first prove the existence and uniqueness of solutions of the equation in L², and then show that the equation has a global attractor in H² when the external forcing term belongs to L². Copyright © 2008 John Wiley & Sons, Ltd.     

A systematic approximation for the equations governing convection–diffusion in a porous medium

In order to take into account thermal effects in flows through porous media, one makes ad hoc modifications to Darcy’s equation by appending a term that is similar to the one that is obtained in the Oberbeck–Boussinesq approximation for a fluid. In this short paper we outline a systematic procedure for obtaining an Oberbeck–Boussinesq type of approximation for the flow of a fluid through a porous medium. In addition to establishing the appropriate equation for a flow governed by Darcy’s equation, we proceed to obtain the approximations for flows governed by equations due to Forchheimer and Brinkman.     

On the time discretization for the globally modified three dimensional Navier-Stokes equations

In this work, we analyze the discrete in time 3D system for the globally modified Navier-Stokes equations introduced by Caraballo (2006) [1]. More precisely, we consider the backward implicit Euler scheme, and prove the existence of a sequence of solutions of the resulting equations by implementing the Galerkin method combined with Brouwer’s fixed point approach. Moreover, with the aid of discrete Gronwall’s lemmas we prove that for the time step small enough, and the initial velocity in the domain of the Stokes operator, the solution is H² uniformly stable in time, depends continuously on initial data, and is unique. Finally, we obtain the limiting behavior of the system as the parameter N is big enough.     

Galerkin finite element method for generalized Forchheimer equation of slightly compressible fluids in porous media

We consider the generalized Forchheimer flows for slightly compressible fluids. Using Muskat's and Ward's general form of Forchheimer equations, we describe the fluid dynamics by a nonlinear degenerate parabolic equation for the density. We study Galerkin finite elements method for the initial boundary value problem. The existence and uniqueness of the approximation are proved. A prior estimates for the solutions in , time derivative in and gradient in , with a∈(0,1) are established. Error estimates for the density variable are derived in several norms for both continuous and discrete time procedures. Numerical experiments using backward Euler scheme confirm the theoretical analysis regarding convergence rates. Copyright © 2017 John Wiley & Sons, Ltd.     

On generalized Stokes’ and Brinkman’s equations with a pressure- and shear-dependent viscosity and drag coefficient

We study generalizations of the Darcy, Forchheimer, Brinkman and Stokes problem in which the viscosity and the drag coefficient depend on the shear rate and the pressure. We focus on existence of weak solutions to the problem, with the chief aim to capture as wide a group of viscosities and drag coefficients as mathematically feasible and to provide a theory that holds under minimal, not very restrictive conditions. Even in the case of generalized Stokes system, the established result answers a question on existence of weak solutions that has been open so far.     

Numeric solution of advection–diffusion equations by a discrete time random walk scheme

Explicit numerical finite difference schemes for partial differential equations are well known to be easy to implement but they are particularly problematic for solving equations whose solutions admit shocks, blowups, and discontinuities. Here we present an explicit numerical scheme for solving nonlinear advection–diffusion equations admitting shock solutions that is both easy to implement and stable. The numerical scheme is obtained by considering the continuum limit of a discrete time and space stochastic process for nonlinear advection–diffusion. The stochastic process is well posed and this guarantees the stability of the scheme. Several examples are provided to highlight the importance of the formulation of the stochastic process in obtaining a stable and accurate numerical scheme.     

An alternating direction implicit scheme for discrete ordinate transport equations

This paper concerns a finite difference approximation of the discrete ordinate equations for the time-dependent linear transport equation posed in a multi-dimensional rectangular parallelepiped with partially reflecting walls. We present an unconditionally stable alternating direction implicit finite difference scheme, show how to solve the difference equations, and establish the following properties of the scheme.If a sequence of difference approximations is considered in which the time and space increments approach zero, then the corresponding sequence of solutions has a subsequence which converges continuously to a strong solution of the discrete ordinate equations. Provided that the time increment is sufficiently small, independently of the space and velocity increment sizes: the solution of the difference equations is bounded by an exponential function of time; in the subcritical case the coefficient of t in this exponential bound is zero or negative; and if the constituent functions are all nonnegative, then the solution of the difference equations will also be nonnegative. This last result implies a monotonicity principle for solutions of related difference problems.     

Approximation of the long‐term dynamics of the dynamical system generated by the multilayer quasigeostrophic equations of the ocean

In this article, we study the multilayer quasigeostrophic equations of the ocean. More precisely, we discretize these equations in time using the implicit Euler scheme and using the classical and uniform discrete Gronwall lemmas we prove that the approximate solution is uniformly bounded in H^?1, L² and H¹. Using the uniform stability of the scheme and the theory of the multivalued attractors, we then prove that the discrete attractors generated by the numerical scheme converge to the global attractor of the continuous system as the time‐step approaches zero. © 2015 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 32: 1041–1065, 2016     

A note on an NSFD scheme for a mathematical model of respiratory virus transmission

We construct a non-standard finite difference (NSFD) scheme for an SIRS mathematical model of respiratory virus transmission. This discretization is in full compliance with the NSFD methodology as formulated by Mickens. By use of an exact conservation law satisfied by the SIRS differential equations, we are able to determine the corresponding denominator function for the discrete first-order time derivatives. Our scheme is dynamically consistent with the SIRS differential equations, since the conservation laws are preserved. Furthermore, the scheme is shown to satisfy a positivity condition for its solutions for all values of the time step size.     

Optimal L ∞ error estimates for finite element Galerkin methods for nonlinear evolution equations

Finite element Galerkin solutions for three classes of nonlinear evolution equations are considered. The existence, uniqueness and convergence of the fully discrete Crank-Nicolson scheme are discussed. At last a linearized Galerkin approximation is presented, which is also second order accurate in time fully discrete scheme.     

Finite Element Solution of the Fundamental Equations of Semiconductor Devices II

In part I of the paper (see Zlamal [13]) finite element solutions of the nonstationary semiconductor equations were constructed. Two fully discrete schemes were proposed. One was nonlinear, the other partly linear. In this part of the paper we justify the nonlinear scheme. We consider the case of basic boundary conditions and of constant mobilities and prove that the scheme is unconditionally stable. Further, we show that the approximate solution, extended to the whole time interval as a piecewise linear function, converges in a strong norm to the weak solution of the semiconductor equations. These results represent an extended and corrected version of results announced without proof in Zlamal [14].