Mingliang Xie

OpenGeoSys: an open-source initiative for numerical simulation of thermo-hydro-mechanical/chemical (THM/C) processes in porous media

In this paper we describe the OpenGeoSys (OGS) project, which is a scientific open-source initiative for numerical simulation of thermo-hydro-mechanical-chemical processes in porous media. The basic concept is to provide a flexible numerical framework (using primarily the Finite Element Method (FEM)) for solving multifield problems in porous and fractured media for applications in geoscience and hydrology. To this purpose OGS is based on an object-oriented FEM concept including a broad spectrum of interfaces for pre- and postprocessing. The OGS idea has been in development since the mid-eighties. We provide a short historical note about the continuous process of concept and software development having evolved through Fortran, C, and C++ implementations. The idea behind OGS is to provide an open platform to the community, outfitted with professional software-engineering tools such as platform-independent compiling and automated benchmarking. A comprehensive benchmarking book has been prepared for publication. Benchmarking has been proven to be a valuable tool for cooperation between different developer teams, for example, for code comparison and validation purposes (DEVOVALEX and CO2 BENCH projects). On one hand, object-orientation (OO) provides a suitable framework for distributed code development; however, the parallelization of OO codes still lacks efficiency. High-performance-computing efficiency of OO codes is subject to future research.

Numerical Implementation of Thermally and Hydraulically Coupled Processes in Non-Isothermal Porous Media

Abstract To better understand the coupling of thermal (T), hydraulic (H) and mechanical (M) processes (T-H-M processes) and their influence on the system behaviour, models allowing T-H-M coupling are developed. These models allow simulations in the near-field of the system. Such a model has been developed within the simulator RockFlow/RockMech. This paper concentrates on the thermal and hydraulic processes. For those processes, the material parameters and state variables are highly non-linear and mostly functions of temperature, saturation and pressure. This paper shows how these dependencies are formulated mathematically and are implemented into RockFlow/RockMech. The implementation allows phase changes between the fluid phases (gas and liquid) to occur explicitly. The model allows the simulation of very low permeability clays with high capillary pressures. An example for code validation is shown, where low permeability clay is desaturated, lastly, current work on the calculations performed in the near field study (BMT1) of the DECOVALEX III project is outlined.

Geochemical Effects on Swelling Pressure of Highly Compacted Bentonite: Experiments and Model Analysis

Bentonite is widely selected to to be used as buffer material for highlevel nuclear waste (HLW) repositories owing to its favorite hydrogeological and geochemical properties. This is because mainly of its moisture swelling effect. Experimental and theoretical evidences indicate that the swelling characteristic is largely influenced by the porewater chemistry. A chemical swelling model for constrained condition is developed on the basis of diffuse double layer (DDL) theory and related the microscopic theory to the macroscopic swelling pressure. Experiments with purified clay fraction (< 2 μm) of MX‐80 bentonite were undertaken. The fine bentonite was compacted to a dry density of 1600 kg/m3 with initial liquid saturation of 35.7% and then installed into a rigid container for swelling pressure experiment. The unsaturated bentonite sample was then flushed with NaCl solutions in different concentrations. With the increase of the ionic strength, the measured swelling pressure decreases. The experimental swelling pressure values agree well with the modelled results using the chemical swelling model.

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.

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.