Wenqing Wang

Solving coupled geoscience problems on high performance computing platforms

This paper describes a finite element geo-process modeling software, which is able to solve multiphysics problems in the area of geo science. It is one of the first applications providing complete thermal, two-phase-flow, inelastic deformation court within one framework. As a real-life example the FEBEX TH2M coupling problems are described. These kind of problems are very demanding in terms of CPU time and memory space which cannot be provided by single processor architecture. Therefore the exploitation of high performance architectures is required. Here we present the results of the vectorization of the existing serial code as a first step towards parallelization.

A process-oriented approach to compute THM problems in porous media - Part 1: Theoretical and informatics background

Object-oriented (OO) methods become more and more important in order to meet scientific computing challenges, such as the treatment of coupled non-linear multi-field problems with extremely high resolutions. This two-part paper introduces an object-oriented concept for numerical modelling multi-process systems in porous media (Part 1). The C++ implementation of the OO design for process objects (PCS) as a class is described and illustrated with several applications. Due to the importance of the encapsulation of processes as individual PCS objects we denote our concept as an processoriented approach. The presented examples (Part 2) are dealing with thermal (T), hydraulic (H), mechanical (M) and componental processes (C) in bentonite materials, which are used as buDer material for the isolation of hazardous waste in geologic barriers. In particular, we are interested in coupling phenomena such as thermally induced desaturation, non-isothermal consolidation, swelling/shrinking phenomena as well as in a better understanding of the coupled, non-linear THM system.

Hydraulic Characterisation of Clay Rock Under Consideration of Coupled THM Properties

Clay rock is being investigated in many countries as a potential host rock for nuclear waste repositories. Due to the state of over-consolidation and water saturation, characterisation of undisturbed rock with regard to its hydraulic and mechanical properties is a big challenge. Increased complexity is caused by temperature change in the repository of high-level waste. In situ measurement of single component, e.g. rock permeability, was conducted in the Mont Terri Rock Laboratory (CH) and the French Underground Research Laboratory Bure. Several so-called heater experiments are being carried out at different scale. The measured data including temperature, humidity, pore pressure, and deformation in various boreholes shows strong coupling effects. For interpretation of the experimental data, a numerical 3D code OpenGeoSys (OGS) was developed taking into account the strongly coupled thermal, hydraulic and mechanical processes. Because of the significant dependency of the thermal conductivity on the water saturation, the determination of the saturation state, which is again controlled by hydraulic permeability, is therefore important. The evaluated permeability from packer tests can be validated using numerical modelling. The state-dependency on the pressure, saturation and temperature is discussed.

Parallel Finite Element Analysis of THM Coupled Processes in Unsaturated Porous Media

Numerical analysis of thermo-hydro-mechanical (THM) coupled problems leads to an extremely high computational expense. This work is devoted to reduce such computational expense by parallel computing methods. To this purpose, parallelization is applied to the most time consuming portions of finite element simulations, i.e. assembly of linear equation systems (LES) and solving them. Since an iterative solver is adopted in the present study, the sub-structuring technique of domain decomposition plays an important role in both assembly and solving of LES. Three principles of the parallelization procedure are: (1) all processes of a coupled problem share a unique finite element mesh; (2) this mesh is discretized into sub-domains, each of them are established with mesh topology for both linear and quadratic interpolation, the assembly of linear equation systems is performed in sub-domains and is distributed to the involved processors (CPU-nodes); (3) matrix-vector multiplications, which are the basic computational operations in an iterative solver, are split to sub-domain level and are also performed by the involved processors concurrently. The parallel FEM is applied successfully to the solution of a THM coupled problem in partially saturated bentonite which are used as buffer material in geotechnical sealings.

A process-oriented approach to compute THM problems in porous media - Part 2: Numerical applications

Object-oriented (OO) methods become more and more important in order to meet scientific computing challenges, such as the treatment of coupled non-linear multi-field problems with extremely high resolutions. This two-part paper introduces an object-oriented concept for numerical modelling multi-process systems in porous media (Part 1). The C++ implementation of the OO design for process objects (PCS) as a class is described and illustrated with several applications. Due to the importance of the encapsulation of processes as individual PCS objects we denote our concept as an process-oriented approach.