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Revisiting rolling and sliding in two-dimensional discrete element models

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Particuology 2015年第1期13卷 35-41页

作者： yucang wang Fernando Alonso-Marroquin Sheng Xue Jun Xie School of Engineering and Technology.Central Queensland University Earth Science and Resource Engineering The Commonwealth Scientific and Industrial Research Organisation(CSIRO) School of Civil Engineering The University of Sydney

It has long been recognized that the rotation of single particles plays a very important role in simulations of granular flow using the discrete element method （DEM）. Many researchers have also pointed out that the effect of rolling resistance at the contact points should be taken into account in DEM simulations. However, even for the simplest case involving two-dimensional circular particles, there is no agreement on the best way to define roiling and sliding, and different definitions and calculations of rolling and sliding have been proposed. It has even been suggested that a unique rolling and sliding definition is not possible. In this paper we assess results from previous studies on rolling and sliding in discrete element models and find that some researchers have overlooked the effect of particles of different sizes. After considering the particle radius in the derivation of rolling velocity, all results reach the same outcome： a unique solution. We also present a clear and simple derivation and validate our result using cases of rolling. Such a decomposition of relative motion is objective, or independent of the reference frame in which the relative motion is measured.

关键词： Discrete element method Rolling Sliding

Lattice Solid/Boltzmann Microscopic Model to Simulate Solid/Fluid Systems——A Tool to Study Creation of Fluid Flow Networks for Viable Deep Geothermal Energy

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Journal of Earth Science 2015年第1期26卷 11-19页

作者： Peter Mora yucang wang Fernando Alonso-Marroquin MCM Global ToowongBrisbaneAustralia Earth Science and Resource Engineering CSIROKenmore Qld 4069BrisbaneAustralia School of Civil Engineering The University of SydneySydney NSW 2006Australia

SUMMARY： Realizing the potential of geothermal energy as a cheap, green, sustainable resource to provide for the planet＇s future energy demands that a key geophysical problem be solved first： how to develop and maintain a network of multiple fluid flow pathways for the time required to deplete the heat within a given region. We present the key components for micro-scale particle-based numerical modeling of hydraulic fracture, and fluid and heat flow in geothermal reservoirs. They are based on the latest developments of ESyS-Particle--the coupling of the lattice sofid model （LSM） to simulate the nonlinear dynamics of complex solids with the lattice Boltzmann method （LBM） applied to the nonlinear dynamics of coupled fluid and heat flow in the complex solid-fluid system. The coupled LSM/LBM can be used to simulate development of fracture systems in discontinuous media, elastic stress release, fluid injection and the consequent slip at joint surfaces, and hydraulic fractur- ing; heat exchange between hot rocks and water within flow pathways created through hydraulic fracturing; and fluid flow through complex, narrow, compact and gouge- or powder-f＇flled fracture and joint systems. We demonstrate the coupled LSM/LBM to simulate the fundamental processes listed above, which are all components for the generation and sustainability of the hot-fractured rock geothermal energy fracture systems required to exploit this new green-energy resource.

关键词： lattice Boltzmann particle-fluid interaction geothermal energy coupled lattice solid/lattice Boitzmann model discrete element method lattice solid model.

Numerical Modeling of Porous Flow in Fractured Rock and Its Applications in Geothermal Energy Extraction

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Journal of Earth Science 2015年第1期26卷 20-27页

作者： yucang wang Shimin wang Sheng Xue Deepak Adhikary Earth Science and Resource Engineering CSIROKenmore Qld 4069BrisbaneAustralia Key Laboratory of Computational Geodynamics University of Chinese Academy of Sciences

Understanding the characteristics of hydraulic fracture, porous flow and heat transfer in fractured rock is critical for geothermal power generation applications, and numerical simulation can provide a powerful approach for systematically and thoroughly investigating these problems. In this paper, we present a fully coupled solid-fluid code using discrete element method （DEM） and lattice Boltzmann method （LBM）. The DEM with bonded particles is used to model the deformation and fracture in solid, while the LBM is used to model the fluid flow. The two methods are two-way coupled, i.e., the solid part provides a moving boundary condition and transfers momentum to fluid, while the fluid exerts a dragging force to the solid. Two widely used open source codes, the ESyS Particle and the OpenLB, are integrated into one code and paralleled with Message Passing Interface （MPI） library. Some preliminary 2D simulations, including particles moving in a fluid and hydraulic fracturing induced by injection of fluid into a borehole, are carried out to validate the integrated code. The preliminary results indicate that the new code is capable of reproducing the basic features of hydraulic fracture and thus offers a promising tool for multiscale simulation of porous flow and heat transfer in fractured rock.

关键词： discrete element method lattice Boltzmann method hydraulic fracturing geothermalenergy extraction multiscale modelling.

Rolling and sliding in 3-D discrete element models

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Particuology 2015年第6期13卷 49-55页

作者： yucang wang Fernando Alonso-Marroquin William W. Guo School of Engineering and Technology Central Queensland University Australia School of Civil Engineering The University of Sydney Australia

Rolling and sliding play fundamental roles in the deformation of granular materials. In simulations of granular flow using the discrete element method （DEM）, the effect of rolling resistance at contacts should be taken into account. However, even for the simplest case involving spherical particles, there is no agreement on what is the best way to define rolling and sliding; various versions of definitions and calculations of rolling and sliding were proposed. Some even suggest that a unique definition for rolling and sliding is not possible. We re-check previous studies on rolling and sliding in DEMs and find that some researchers made a conceptual mistake when dealing with pure sliding between particles of different sizes. After considering the particle radius in the derivation of rolling velocity, the results yield a unique solution. Starting with clear and unique definitions of pure rolling and sliding, we present the detailed derivation and validate our results by checking two special cases of rolling. The decomposition of the relative motion is objective; that is, independent of the reference frame in which the relative motion is measured.

关键词： Discrete element method Roiling Sliding

Characters of variation of LURR during the earthquake sequence of Xinjiang

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Chinese Science Bulletin 1998年第20期43卷 1752-1755页

作者： Haitao wang Keyin Peng Yongxian Zhang yucang wang Xiangchu Yin Xinjiang Seismol Bur Urumqi 830011 Peoples R China State Seismol Bur Ctr Analyt & Predict Beijing 100036 Peoples R China State Seismol Bur Inst Geophys Beijing 100081 Peoples R China Chinese Acad Sci Inst Mech Lab Nonlinear Mech Beijing 100080 Peoples R China

The theory of the loading/unloading response ratio (LURR) was applied to the Jiashi earthquake sequence which occurred at the beginning of 1997 in Xinjiang, and found that, before the earthquakes with relatively high magnitudes in the sequence, the ratio showed anomalies of high values. That is to say, the LURR theory can be applied to the short_term earthquake prediction in some cases, especially in the early period after a strong earthquake, such as the forecasts for some strong earthquakes in the Jiashi sequence.

关键词： Jiashi earthquake sequence theory of loading/unloading response ratio (LURR) earthquake sequence.

Gas diffusion in a cylindrical coal sample – A general solution,approximation and error analyses

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International Journal of Mining Science and Technology 2014年第1期24卷 69-73页

作者： Li Yaobin Xue Sheng wang Junfeng wang yucang Xie Jun Key Laboratory of Integrated Coal Exploitation and Gas Extraction Anhui University of Science and Technology School of Energy and Safety Anhui University of Science and Technology CSIRO Earth Science and Resource Engineering School of Mining Engineering Taiyuan University of Science and Technology

The analytical mathematical solutions of gas concentration and fractional gas loss for the diffusion of gas in a cylindrical coal sample were given with detailed mathematical derivations by assuming that the diffusion of gas through the coal matrix is concentration gradient-driven and obeys the Fick’s Second Law of *** analytical solutions were approximated in case of small values of time and the error analyses associated with the approximation were also *** results indicate that the square root relationship of gas release in the early stage of desorption,which is widely used to provide a simple and fast estimation of the lost gas,is the first term of the approximation,and care must be taken in using the square root relationship as a significant error might be introduced with increase in the lost time and decrease in effective diameter of a cylindrical coal sample.

关键词： Gas content Lost gas Gas diffusion Cylindrical coal sample Approximation Error analysis

A coupled DEM and LBM model for simulation of outbursts of coal and gas

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International Journal of Coal Science & Technology 2015年第1期2卷 22-29页

作者： Sheng Xue Liang Yuan Junfeng wang yucang wang Jun Xie CSIRO Energy P.O. Box 833 Kenmore QLD 4069Australia Taiyuan University of Technology Taiyuan 030024 China National Engineering Research Centre for Coal Mine Gas Control Huainan 232001 China Central Queensland University Rockhampton QLD 4702Australia Shandong University of Science & Technology Qingdao 266590 China

An outburst of coal and gas is a major hazard in underground coal mining. It is generally accepted that an outburst occurs when certain conditions of stress, coal gassiness and physical-mechanical properties of coal are met. Outbursting is recognized as a two-step process, i.e., initiation and development. In this paper, we present a fully-coupled solid and fluid code to model the entire process of an outburst. The deformation, failure and fracture of solid （coal） are modeled with the discrete element method, and the flow of fluid （gas and water） such as free flow and Darcy flow are modeled with the lattice Boltzmann method. These two methods are coupled in a two-way process, i.e., the solid part provides a moving boundary condition and transfers momentum to the fluid, while the fluid exerts a dragging force upon the solid. Gas desorption from coal occurs at the solid-fluid boundary, and gas diffusion is implemented in the solid code where particles are assumed to be porous. A simple 2D example to simulate the process of an outburst with the model is also presented in this paper to demonstrate the capability of the coupled model.

关键词： Coal and gas outburst Discrete element method Lattice Boltzmann method Solid-fluid coupling

A general solution and approximation for the diffusion of gas in a spherical coal sample

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International Journal of Mining Science and Technology 2014年第3期24卷 345-348页

作者： wang yucang Xue Sheng Xie Jun CSIRO Earth Science and Resource Engineering Kenmore QLD 4069 Australia

The square root relationship of gas release in the early stage of desorption is widely used to provide a simple and fast estimation of the lost gas in coal mines. However, questions arise as to how the relationship was theoretically derived, what are the assumptions and applicable conditions and how large the error will be. In this paper, the analytical solutions of gas concentration and fractional gas loss for the diffusion of gas in a spherical coal sample were given with detailed mathematical derivations based on the diffusion equation. The analytical solutions were approximated in case of small values of time and the error analyses associated with the approximation were also undertaken. The results indicate that the square root relationship of gas release is the first term of the approximation, and care must be taken in using the square root relationship as a significant error might be introduced with increase in the lost time and decrease in effective diameter of a spherical coal sample.

关键词： Coal content Lost gas Spherical coal sample Gas diffusion Approximation Error analysis

Advances in gas content based on outburst control technology in Huainan, China

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International Journal of Mining Science and Technology 2014年第3期24卷 385-389页

作者： Xue Sheng Yuan Liang Xie Juna wang yucang CSIRO Earth Science and Resource Engineering Kenmore QLD 4069 Australia Key Laboratory of Integrated Coal Exploitation and Gas Extraction Anhui University of Science and Technology School of Mining Engineering Taiyuan University of Science and Technology National Engineering Research Centre for Coal Mine Gas Control

The sudden and violent nature of coal and gas outbursts continues to pose a serious threat to coal mine safety in China. One of the key issues is to predict the occurrence of outbursts. Current methods that are used for predicting the outbursts in China are considered to be inadequate, inappropriate or impractical in some seam conditions. In recent years, Huainan Mining Industry Group(Huainan) in China and the Commonwealth Scientific and Industrial Research Organisation(CSIRO) in Australia have been jointly developing technology based on gas content in coal seams to predict the occurrence of outbursts in Huainan. Significant progresses in the technology development have been made, including the development of a more rapid and accurate system in determining gas content in coal seams, the invention of a sampling-while-drilling unit for fast and pointed coal sampling, and the coupling of DEM and LBM codes for advanced numerical simulation of outburst initiation and propagation. These advances are described in this paper.

关键词： Coal mining Outburst Outburst prediction Gas content Numerical model ing