| 1. |
- Chen, Y., et al.
(author)
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Numerical model for fully coupled THM processes with multiphase flow and code validation
- 2009
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In: Chinese Journal of Rock Mechanics and Engineering. - 1000-6915. ; 28:4, s. 649-665
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Journal article (peer-reviewed)abstract
- A numerical model for fully coupled THM processes with multiphase flow in porous media was developed based on the momentum, mass and energy conservation laws of the continuum mechanics and the averaging approach of the mixture theory over a solid-liquid-gas three-phase system. To characterize multiphase THM coupling and to make the governing equations closed, complete and compatible, six processes and their coupling effects were considered, including stress-strain, water flow, gas flow, vapor flow, heat transport and porosity evolution processes. The physical phenomena such as phase transition, gas solubility in liquid, thermo-osmosis, moisture transfer and moisture swelling were modeled. As a result, the relative humidity of pore gas was defined on a sounder physical basis, avoiding the traditional definition as a negative exponential function of suction and absolute temperature. By selecting displacements, pore water pressure, pore gas pressure, pore vapor pressure, temperature and porosity as basic unknown variables, a finite element formulation was then established, and a three-dimensional computer code, THYME3D, was developed, with each node of 8 degrees of freedom. The bentonite THM Mock-up experiments performed by CEA were employed to validate the mathematical model and the software. The main coupling mechanisms involved in the experiments were satisfactorily simulated in the validation, and the effects of the governing equations, the constitutive relations and the parameters on the coupled THM processes were understood. The work developed enabled further in-depth research on fully coupled THM or THMC processes in porous media.
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| 2. |
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| 3. |
- Liu, Chang, et al.
(author)
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Effect of Porosity on Soil-Water Retention Curves : Theoretical and Experimental Aspects
- 2020
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In: Geofluids. - : Hindawi Limited. - 1468-8115 .- 1468-8123. ; 2020
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Journal article (peer-reviewed)abstract
- Porosity change is a common characteristic of natural soils in fluid-solid interaction problems, which can lead to an obvious change of the soil-water retention curve (SWRC). The influence of porosity on soil water retention phenomena is investigated by a theoretical model and an experimental test in this study. A model expressing the change in suction with porosity and effective saturation is put forward theoretically. The model is based on an idealization of three-phase porous materials, the pore structures of which are homogeneous and isotropic. It accounts for the porosity effect on soil water retention, using four parameters with clear physical meanings. The presented model can obtain the SWRC at any porosity, which will reduce the test number required in characterizing the hydraulic behavior of soil. A laboratory experiment for loamy sand with different porosities is performed. The test results show that suction has a significant variation with changes in porosity and decreases with the increase of porosity. The formulation is verified by both the test data and the literature data for FEBEX bentonite and Boom clay. The very good agreements between measured and predicted results show that the SWRC model is reliable and feasible for various soils.
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| 4. |
- Tong, Fuguo, et al.
(author)
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A 3D FEM simulation of the buffer and buffer-rock interfacebehaviour of the Canister Retrieval Test (CRT) at Äspö HRL : 29 Sep-01Oct 2009, Luxembourg. European Commission
- 2009
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In: Proceedings Conference of impact of THMC processes on thesafety of underground radioactive waste repositories.
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Conference paper (peer-reviewed)abstract
- This paper presents a 3D FEM model for simulating the coupled THM behaviour of the buffer and buffer-rock interface behaviour of the Canister Retrieval Test conducted at the Äspö Hard Rock Laboratory, Sweden. The effect of the interface between the canister and buffer was also included. New numerical techniques were developed for more efficient FEM formulation and equation solution, and for modeling saturated or partially saturated water flow, gas flow and heat transfer in buffer and interfaces. The numerical results compare well with the measured data, and the reasonably good agreement between simulated and measured results indicates that the coupled THM processes of buffer material can be accurately predicted by the newly developed THM model and computer code.
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| 5. |
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| 6. |
- Tong, Fuguo, et al.
(author)
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A fully-coupled finite element code for modeling thermo-hydro-mechanical processes in porous geological media
- 2009
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In: 43rd U.S. Rock Mechanics Symposium and 4th U.S.-Canada Rock Mechanics Symposium. - : American Rock Mechanics Association (ARMA). - 9781615674312
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Conference paper (peer-reviewed)abstract
- This paper describes a new FEM code for modeling coupled thermo-hydro-mechanical processes in porous geological media. For three-dimensional problems, six governing equations, which are based on the conservation equations of momentum, mass, and energy, are presented to describe the coupled THM processes. The three displacement components, the temperature, the pore fluid pressure and the porosity are chosen as the six primary variables. The governing continuum equations are discretized in space by using the Galerkin finite element formulation, and are discretized in time by one-dimensional finite difference scheme. This leads to a large non-symmetric matrix equation that has many small entries along its diagonal, and is therefore ill-conditioned. For efficient equation solution, some special numerical techniques are used in the code in order to deal with the problem of a large non-symmetric ill-conditioned matrix equation. The code was validated against several classical analytical solutions to problems in poroelasticity and thermoelasticity, and tested against a benchmark laboratory experiment that was performed in the Polytechnic University of Catalonia (UPC), Spain.
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| 7. |
- Tong, Fuguo, et al.
(author)
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A fully coupled thermo-hydro-mechanical model for simulating multiphase flow, deformation and heat transfer in buffer material and rock masses
- 2010
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In: International Journal of Rock Mechanics And Mining Sciences. - : Elsevier BV. - 1365-1609 .- 1873-4545. ; 47:2, s. 205-217
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Journal article (peer-reviewed)abstract
- This paper presents a numerical method for modeling coupled thermo-hydro-mechanical processes of geomaterials with multiphase fluid flow. A FEM code has been developed and validated for modeling the behavior of porous geological media, and is equally applicable for modeling coupled THM processes in rocks. The governing equations are based on the theory of mixtures applied to the multiphysics of porous media, considering solid phase deformation, multiphase fluid flow, and heat transport. New numerical techniques have been developed for more efficient FEM formulation and equation solution for modeling saturated or partially saturated water flow, gas flow and heat transfer indeformable porous media, as are commonly encountered in performance and safety assessment of underground radioactive repositories. The code has been validated against an experimental benchmark test, which involves bentonite under laboratory conditions, with good results. Several critical outstanding issues for modeling coupled processes of geomaterials are discussed indepth.
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| 8. |
- Tong, Fuguo, et al.
(author)
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A Numerical Model of Tracer Transport in a Non-isothermal Two-Phase Flow System for Geological Storage Characterization
- 2013
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In: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 98:1, s. 173-192
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Journal article (peer-reviewed)abstract
- For the purpose of characterizing geologically stored including its phase partitioning and migration in deep saline formations, different types of tracers are being developed. Such tracers can be injected with or water, and their partitioning and/or reactive transfer from one phase to another can give information on the interactions between the two fluid phases and the development of their interfacial area. Kinetic rock-water interactions and geochemical reactions during two-phase flow of and brine have been incorporated in numerical simulators (e.g., Xu et al., TOUGHREACT User's Guide: A Simulation Program for Non-isothermal Multiphase Reactive Geochemical Transport in Variably Saturated Geologic Media. LBNL Report 55460, V.1.2., Berkeley, CA, 2004). However, chemical equilibrium between the fluid phases is typically assumed, and multi-component, multiphase, non-isothermal codes for -brine systems that incorporate kinetic mass transfer of tracers between the two fluid phases are not readily available. New models or further developments of existing models are therefore needed to provide the capability for interpreting the signals of novel tracers, including tracers with kinetic/time-dependent interface transfer. This paper presents such new numerical model of tracer transport in a non-isothermal two-phase flow system. The model consists of five different governing equations describing liquid phase (aqueous) flow, gas ( flow, heat transport and the movement of the tracers within the two phases, as well as allowing kinetic transport of the tracers between the two phases. A finite element method is adopted for the spatial discretization and a finite difference approach is used for temporal discretization. Some special technologies and solution strategies are adopted for increasing the convergence, ensuring the numerical stability and eliminating non-physical oscillations. The new numerical model is validated against the code TOUGH2/ECO2N as well as some analytical/semi-analytical solutions. Good agreement between the simulated and analytical results indicates that the model has capability to simulate two-phase flow and tracer transport in a non-isothermal two-phase flow system with high confidence. Finally, the capability to model transport and kinetic mass transfer of tracers between the two fluid phases is demonstrated through examples.
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| 9. |
- Tong, Fuguo, et al.
(author)
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A Water Retention Curve Model for the Simulation of Coupled Thermo-Hydro-Mechanical Processes in Geological Porous Media
- 2012
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In: Transport in Porous Media. - : Springer Science and Business Media LLC. - 0169-3913 .- 1573-1634. ; 91:2, s. 509-530
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Journal article (peer-reviewed)abstract
- This paper presents a new water retention curve (WRC) model for the simulation of coupled thermo-hydro-mechanical processes in geological porous media. The model simultaneously considers the impact of porosity and temperature on suction, for both wetting processes and drying processes. The model is based on an idealization of porous geological media as having an isotropic and homogeneous microscopic pore structure. Suction is expressed as a function of degree of saturation, porosity, surface tension of the water-air interface, and the length of air bubble perimeter of the pores per unit area on a random 2D cross-section of the medium. The tension of water-air interface is written as a function of temperature, and the length of perimeter of the water-air interface of the pores becomes a function of porosity and degree of saturation. The final equation of the new WRC is a function of suction, effective degree of saturation, temperature, porosity, pore-gas pressure, and the rate of degree of saturation change with time for both wetting and drying processes. The model was used to fit experimental data of the FEBEX bentonite, with good agreements between measured and calculated results.
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| 10. |
- Tong, Fuguo, et al.
(author)
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An effective thermal conductivity model of geological porous media for coupled thermo-hydro-mechanical systems with multiphase flow
- 2009
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In: International Journal of Rock Mechanics And Mining Sciences. - : Elsevier BV. - 1365-1609 .- 1873-4545. ; 46:8, s. 1358-1369
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Journal article (peer-reviewed)abstract
- The objective of this paper is to present the development of an effective thermal conductivity model for simulation of thermo-hydro-mechanical processes of geological porous media. The Wiener bounds and Hashin-Shtrikman bounds for thermal conductivity of three-phase mixture are introduced first, followed by descriptions of thermal conductivities of gas, water and solid, respectively. The derivation of a new effective thermal conductivity model, in closed form, is then presented. The model considers the combined effects of solid mineral composition, temperature, liquid saturation degree, porosity and pressure on the effective thermal conductivity of porous media, when multiphase flow with phase change is involved. The model strictly obeys the Wiener bounds (for anisotropic media) and Hashin-Shtrikman bounds (for isotropic media) over wide ranges of porosities and saturations, and the predicted results agrees very well with the experimental data for MX80 bentonite, compared with Johansen's method. An experimental benchmark test problem under laboratory conditions for coupled thermo-hydro-mechanical processes of compacted FEBEX bentonite is simulated for validation of the model, and the results show that the model provides improved predictions of the evolution and distribution of temperature, with simpler forms of mathematical functions. (C) 2009 Elsevier Ltd. All rights reserved.
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