A Mixed Finite Element Method for the Stationary Stokes Equations

1978 ◽  
Vol 15 (3) ◽  
pp. 534-555 ◽  
Author(s):  
V. Girault
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Stokes Equations ◽  
Mixed Finite Element ◽  
Mixed Finite Element Method ◽  
Element Method

A Banach spaces-based analysis of a new fully-mixed finite element method for the Boussinesq problem

2020 ◽  
Vol 54 (5) ◽  
pp. 1525-1568 ◽  
Author(s):  
Eligio Colmenares ◽  
Gabriel N. Gatica ◽  
Sebastián Moraga
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Banach Spaces ◽  
Stokes Equations ◽  
Mixed Finite Element ◽  
Mixed Finite Element Method ◽  
Small Data ◽  
Temperature Dependent Viscosity ◽  
Boussinesq Problem ◽  
Element Method

In this paper we propose and analyze, utilizing mainly tools and abstract results from Banach spaces rather than from Hilbert ones, a new fully-mixed finite element method for the stationary Boussinesq problem with temperature-dependent viscosity. More precisely, following an idea that has already been applied to the Navier–Stokes equations and to the fluid part only of our model of interest, we first incorporate the velocity gradient and the associated Bernoulli stress tensor as auxiliary unknowns. Additionally, and differently from earlier works in which either the primal or the classical dual-mixed method is employed for the heat equation, we consider here an analogue of the approach for the fluid, which consists of introducing as further variables the gradient of temperature and a vector version of the Bernoulli tensor. The resulting mixed variational formulation, which involves the aforementioned four unknowns together with the original variables given by the velocity and temperature of the fluid, is then reformulated as a fixed point equation. Next, we utilize the well-known Banach and Brouwer theorems, combined with the application of the Babuška-Brezzi theory to each independent equation, to prove, under suitable small data assumptions, the existence of a unique solution to the continuous scheme, and the existence of solution to the associated Galerkin system for a feasible choice of the corresponding finite element subspaces. Finally, we derive optimal a priori error estimates and provide several numerical results illustrating the performance of the fully-mixed scheme and confirming the theoretical rates of convergence.

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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