VIE proposal for the groundwater code ESTEL

Details

Published on Wednesday, 31 July 2013 16:15

Development of numerical methods in the groundwater flows and pollutant transfer code ESTEL within the open-source framework openTELEMAC-MASCARET

 - EDF R&D / LNHE and STFC Daresbury.

Context

The openTELEMAC-MASCARET system is an integrated suite of modules used to simulate free-surface flows involving flooding, wetting and drying as well as discharge of pollutants and release of freshwater. It also includes the 3D code ESTEL, which is a groundwater model for contaminant transfer in variably saturated flows. ESTEL has mainly been applied to study nuclear waste disposal safety assessments. Possible future applications of ESTEL deal with hydrogeological studies for safety assessment of industrial facilities, coupling surface and subsurface or watershed influence analysis. However, for this purpose, numerical developments in ESTEL are required, especially for large scale modeling with accurate precision.

Objectives

This proposal is divided in two main parts, which are all related to the development of numerical methods in ESTEL.

Parallel multigrid solver

Hierarchical solvers, such as algebraic multigrid methods, are known to be well suited for groundwater flows when heterogeneities decrease the performance of classical iterative solvers, such as Conjugate Gradients, and when direct methods cannot be applied due to the very large computational domain (millions of degrees of unknowns). A multigrid solver has already been developed by EDF R&D and has been successfully tested in ESTEL in comparison to the other solvers currently available in openTELEMAC-MASCARET. A gain of a factor 10 to 300 in terms of CPU time has been regularly obtained. Both implementation and parallelization of the prototype within the ESTEL code is then asked.

Prism-based discretization

The aim of this task is to adapt the existing code (based on a full unstructured grid of tetrahedra) to a full prism-based discretization, similar to the one used in the TELEMAC-3D module. Most of the prism-based mathematical tools have already been developed and have successfully been used in TELEMAC-3D. A substantial gain in both memory and CPU time is expected. As the surface of the prismatic mesh is made of triangles, coupling between TELEMAC-2D and ESTEL-3D will not be affected.

The VIE proposal is organized into three main tasks

1. 1st task: Implementation of the multigrid solver. The existing prototype of algebraic multigrid solver, developed by SINETICS, must be transferred into ESTEL. More precisely, the structure of the solver has to be modified to function in the openTELEMAC-MASCARET system. The two major steps will be to adapt the solver to the matrix storage used in ESTEL and to create a dynamic storage strategy that will be able to manage the different grids.
2. 2nd task: Prismatic discretization. The first step will be to modify both Input (mesh) and Output (results) subroutines used in ESTEL to support the prismatic discretization. Second, the existing flow module (Richards equation) and the transport module (convection, dispersion, diffusion and decay) of ESTEL must also be adapted to the use of prisms, similarly to the discretization used in TELEMAC-3D. The validation step will be carried out on test cases available in the ESTEL database.
3. 3rd task : Parallelism. Parallelism in ESTEL is performed by Message Passing Interface between sub-meshes. The different partitions of the original mesh are distributed over the processors of the cluster. A special attention will be paid to the impacts of the multigrid solver and the prismatic discretization on the performance of the ESTEL parallelism. A special focus will be given on the efficiency of the partitioning method for meshes based on prisms.

The work will be also supervised by the ESTEL development team and monthly progress meetings (phone, mails, in-situ) will be held.

Required competences

A scientific background in applied mathematics and/or fluids mechanics is required as well as programming skills, autonomy and interests in geosciences.

Duration

The expected duration is at least one year at STFC Daresbury Laboratory, UK. However, the VIE will be preceded by a training month on ESTEL with the developers team in Chatou, France.

Conditions of eligibility

The VIE is reserved exclusively to French nationals and to nationals from the European Economic Area (the EU + Iceland, Monaco, Norway and Lichtenstein). More information is available on civiweb.com.

Corresponding contacts

ESTEL Team
Vincent STOBIAC, Elsa VITORGE
Tel: 01-30-87-75-29
E-mail : This email address is being protected from spambots. You need JavaScript enabled to view it.
EDF R&D, LNHE
6, quai Watier, 78400 CHATOU, FR

MULTIGRID solver
Frank Hülsemann
EDF R&D, SINETICS
CLAMART, FR

HPC and openTELEMAC researcher
C. Moulinec, D. R. Emerson
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
STFC Daresbury Laboratory
WARRINGTON, UK