177 research outputs found
Space-time domain decomposition for advection-diffusion problems in mixed formulations
This paper is concerned with the numerical solution of porous-media flow and
transport problems , i. e. heterogeneous, advection-diffusion problems. Its aim
is to investigate numerical schemes for these problems in which different time
steps can be used in different parts of the domain. Global-in-time,
non-overlapping domain-decomposition methods are coupled with operator
splitting making possible the different treatment of the advection and
diffusion terms. Two domain-decomposition methods are considered: one uses the
time-dependent Steklov--Poincar{\'e} operator and the other uses optimized
Schwarz waveform relaxation (OSWR) based on Robin transmission conditions. For
each method, a mixed formulation of an interface problem on the space-time
interface is derived, and different time grids are employed to adapt to
different time scales in the subdomains. A generalized Neumann-Neumann
preconditioner is proposed for the first method. To illustrate the two methods
numerical results for two-dimensional problems with strong heterogeneities are
presented. These include both academic problems and more realistic prototypes
for simulations for the underground storage of nuclear waste
Postprocessing of Non-Conservative Flux for Compatibility with Transport in Heterogeneous Media
A conservative flux postprocessing algorithm is presented for both
steady-state and dynamic flow models. The postprocessed flux is shown to have
the same convergence order as the original flux. An arbitrary flux
approximation is projected into a conservative subspace by adding a piecewise
constant correction that is minimized in a weighted norm. The application
of a weighted norm appears to yield better results for heterogeneous media than
the standard norm which has been considered in earlier works. We also
study the effect of different flux calculations on the domain boundary. In
particular we consider the continuous Galerkin finite element method for
solving Darcy flow and couple it with a discontinuous Galerkin finite element
method for an advective transport problem.Comment: 34 pages, 17 figures, 11 table
Modeling fractures as interfaces with nonmatching grids
We consider a model for fluid flow in a porous medium with a fracture. In this model, the fracture is represented as an interface between subdomains, where specific equations have to be solved. In this article we analyse the discrete problem, assuming that the fracture mesh and the subdomain meshes are completely independent, but that the geometry of the fracture is respected. We show that despite this non-conformity, first order convergence is preserved with the lowest order Raviart-Thomas(-Nedelec) mixed finite elements. Numerical simulations confirm this result.Nous étudions un modèle d'écoulement dans milieu poreux contenant une fracture. Dans ce modèle, la fracture est représentée comme une interface entre sous-domaines, au sein de laquelle des équations spécifiques doivent être résolues. Dans le présent article, nous analysons le problème discret, en faisant l'hypothèse que le maillage de la fracture et les maillages des sous-domaines sont complètement indépendants, mais respectent toutefois la géométrie de la fracture. Nous montrons que malgré cette non-conformité, le premier ordre de convergence est conservé pour les éléments finis mixtes de Raviart-Thomas(-Nedelec) de plus bas degré. Des simulations numériques confiment ce résultat
Robin Schwarz algorithm for the NICEM Method: the Pq finite element case
In Gander et al. [2004] we proposed a new non-conforming domain decomposition
paradigm, the New Interface Cement Equilibrated Mortar (NICEM) method, based on
Schwarz type methods that allows for the use of Robin interface conditions on
non-conforming grids. The error analysis was done for P1 finite elements, in 2D
and 3D. In this paper, we provide new numerical analysis results that allow to
extend this error analysis in 2D for piecewise polynomials of higher order and
also prove the convergence of the iterative algorithm in all these cases.Comment: arXiv admin note: substantial text overlap with arXiv:0705.028
Robust a posteriori error control and adaptivity for multiscale, multinumerics, and mortar coupling
International audienceWe consider discretizations of a model elliptic problem by means of different numerical methods applied separately in different subdomains, termed multinumerics, coupled using the mortar technique. The grids need not match along the interfaces. We are also interested in the multiscale setting, where the subdomains are partitioned by a mesh of size h , whereas the interfaces are partitioned by a mesh of much coarser size H , and where lower-order polynomials are used in the subdomains and higher-order polynomials are used on the mortar interface mesh. We derive several fully computable a posteriori error estimates which deliver a guaranteed upper bound on the error measured in the energy norm. Our estimates are also locally efficient and one of them is robust with respect to the ratio H/h under an assumption of sufficient regularity of the weak solution. The present approach allows bounding separately and comparing mutually the subdomain and interface errors. A subdomain/interface adaptive refinement strategy is proposed and numerically tested
- …