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Effects of loading waveforms on rock damage using particle simulation method

Journal of Central South University 2018年第7期25卷 1755-1765页

作者： XIA Ming GONG Feng-qiang Hunan Key Laboratory of Geomechanics and Engineering Safety Xiangtan UniversityXiangtan 411105China College of Civil Engineering and Mechanics Xiangtan UniversityXiangtan 411105China School of Resources and Safety Engineering Central South UniversityChangsha 410083China

The particle simulation method is used to study the effects of loading waveforms （i.e. square, sinusoidal and triangle waveforms） on rock damage at mesoscopic scale. Then some influencing factors on rock damage at the mesoscopic scale, such as loading frequency, stress amplitude, mean stress, confining pressure and loading sequence, are also investigated with sinusoidal waveform in detail. The related numerical results have demonstrated that： 1） the loading waveform has a certain effect on rock failure processes. The square waveform has the most damage within these waveforms, while the triangle waveform has less damage than sinusoidal waveform. In each cycle, the number of microscopic cracks increases in the loading stage, while it keeps nearly constant in the unloading stage. 2） The loading frequency, stress amplitude, mean stress, confining pressure and loading sequence have considerable effects on rock damage subjected to cyclic loading. The higher the loading frequency, stress amplitude and mean stress, the greater the damage the rock accumulated; in contrast, the lower the confining pressure, the greater the damage the rock has accumulated. 3） There is a threshold value of mean stress and stress amplitude, below which no further damage accumulated after the first few cycle loadings. 4） The high-to-low loading sequence has more damage than the low-to-high loading sequence, suggesting that the rock damage is loading-path dependent.

关键词： rock damage failure process crack initiation and propagation loading waveform cycle loading particle simulation method

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simulation of Rock Mechanical Behavior Under Cyclic Loading Using Clump Parallel-Bond Models

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GEOTECHNICAL AND GEOLOGICAL ENGINEERING 2019年第4期37卷 2325-2333页

作者： Xia, Ming Xiangtan Univ Hunan Key Lab Geomech & Engn Safety Xiangtan 411105 Peoples R China Xiangtan Univ Coll Civil Engn & Mech Xiangtan 411105 Peoples R China

In order to investigate rock mechanical behavior under cyclic loading and unloading conditions, the clump parallel-bond model (CPBM) combined with the newly-proposed loading procedure was used in numerical simulations and the simulated results were compared with those of the experiment. Then the intact rock under different confining pressures and pre-cracked rock with different flaw inclination angles are also investigated in detail. The related numerical results have demonstrated that: (1) the CPBM, combined with the use of the newly-proposed loading procedure, can be used to modelling the intact rock and pre-cracked rock mechanical behavior under cycle loading and unloading conditions. The simulated results are in good agreement with the experimental results;(2) the number of microscopic cracks increases with the cycle increases during the loading process, while few microscopic cracks are generated during the unloading process. The higher the confining pressure, the less damage the rock has accumulated during the cyclic loading process;(3) the inclination of the pre-existing flaw has a significant effect on the macroscopic fracture pattern.

关键词： particle simulation method Clump parallel-bond model Cyclic loading and unloading Loading procedure Rock mechanical behavior

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Thermo-mechanical coupling particle simulation of three-dimensional large-scale non-isothermal problems A comprehensive upscale theory

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ENGINEERING COMPUTATIONS 2017年第5期34卷 1551-1571页

作者： Xia, Ming Xiangtan Univ Hunan Key Lab Geomech & Engn Safety Xiangtan Peoples R China Xiangtan Univ Coll Civil Engn & Mech Xiangtan Peoples R China

Purpose -The main purpose of this paper is to present a comprehensive upscale theory of the thermo-mechanical coupling particle simulation for three-dimensional (3D) large-scale non-isothermal problems, so that a small 3D length-scale particle model can exactly reproduce the same mechanical and thermal results with that of a large 3D length-scale one. Design/methodology/approach -The objective is achieved by following the scaling methodology proposed by Feng and Owen (2014). Findings -After four basic physical quantities and their similarity-ratios are chosen, the derived quantities and its similarity-ratios can be derived from its dimensions. As the proposed comprehensive 3D upscale theory contains five similarity criteria, it reveals the intrinsic relationship between the particle-simulation solution obtained from a small 3D length-scale (e.g. a laboratory length-scale) model and that obtained from a large 3D length-scale (e.g. a geological length-scale) one. The scale invariance of the 3D interaction law in the thermo-mechanical coupled particle model is examined. The proposed 3D upscale theory is tested through two typical examples. Finally, a practical application example of 3D transient heat flow in a solid with constant heat flux is given to illustrate the performance of the proposed 3D upscale theory in the thermo-mechanical coupling particle simulation of 3D large-scale non-isothermal problems. Both the benchmark tests and application example are provided to demonstrate the correctness and usefulness of the proposed 3D upscale theory for simulating 3D non-isothermal problems using the particle simulation method. Originality/value -The paper provides some important theoretical guidance to modeling 3D large-scale non-isothermal problems at both the engineering length-scale (i.e. the meter-scale) and the geological lengthscale (i.e. the kilometer-scale) using the particle simulation method directly.

关键词： particle simulation method Upscale theory 3D non-isothermal problems Scaling methodology Thermo-mechanical coupling

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Thermo-mechanical coupled particle model for rock

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Transactions of Nonferrous Metals Society of China 2015年第7期25卷 2367-2379页

作者：夏明中南大学计算地球科学研究中心长沙410083

A thermo-mechanical coupled particle model for simulation of thermally-induced rock damage based on the particle simulation method was *** simulation results of three verification examples,for which the analytical solutions are available,demonstrate the correctness and usefulness of the thermo-mechanical coupled particle *** model is applied to simulating an application example with two cases：one is temperature-independent elastic modulus and strength,while the other is temperature-dependent elastic modulus and *** related simulation results demonstrate that microscopic crack initiation and propagation process with consideration of temperature-independent and temperature-dependent elastic modulus and strength are different and therefore,the corresponding macroscopic failure patterns of rock are also *** the contrary,considering the temperature-dependent elastic modulus and strength has no or little effect on the heating conduction *** results,which are obtained by using the proposed model with temperature-dependent elastic modulus and strength,agree well with the experimental *** also reveals that the rock subjected to heating experiences much more cracking than the rock subjected to cooling.

关键词： particle simulation method micromechanics rock fracture thermo-mechanical coupled model

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particle simulation of thermally-induced rock damage with consideration of temperature-dependent elastic modulus and strength

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COMPUTERS AND GEOTECHNICS 2014年 55卷 461-473页

作者： Xia, Ming Zhao, Chongbin Hobbs, B. E. Cent S Univ Computat Geosci Res Ctr Changsha 410083 Hunan Peoples R China CSIRO Div Earth Sci & Resource Engn Bentley WA 6102 Australia

Based on the particle simulation method, a thermo-mechanical coupling particle model is proposed for simulating thermally-induced rock damage. In this model, rock material is simulated as an assembly of particles, which are connected to each other through their bonds, in the case of simulating mechanical deformation, but connected to each other through thermal pipes in the case of simulating heat conduction. The main advantages of using this model are that: (1) microscopic parameters of this model can be directly determined from the related macroscopic ones;(2) the temperature-dependent elastic modulus and strength are considered in an explicit manner, so that thermally-induced rock damage can be realistically simulated in a thermo-mechanical coupling problem. The related simulation results from an application example have demonstrated that: (1) the proposed model can produce similar behaviors to those observed in experiments;(2) the final failure is initiated from the outer surface of the testing sample and propagates toward the borehole;(3) microscopic crack initiation and propagation processes can be reasonably simulated at the cooling stage. (C) 2013 Elsevier Ltd. All rights reserved.

关键词： particle simulation method Thermo-mechanical coupling Temperature-dependent elastic modulus and strength Crack initiation and propagation Rock damage

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simulation of rock deformation and mechanical characteristics using clump parallel-bond models

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Journal of Central South University 2014年第7期21卷 2885-2893页

作者：夏明赵崇斌 Computational Geosciences Research Centre Central South University

To properly simulate hard rock with a high ratio of the uniaxial compressive strength to tensile strength(UCS/TS) and realistic strength-failure envelope,the rock deformation and mechanical characteristics were discussed in detail when the particle simulation method with the clump parallel-bond model(CPBM) was used to conduct a series of numerical experiments at the specimen ***,the effects of the loading procedure and crack density on the mechanical behavior of a specimen,which was modeled by the particle simulation method with the CPBM,were *** related numerical results have demonstrated that:1) The uniaxial compressive strength(UCS),tensile strength(TS) and elastic modulus are overestimated when the conventional loading procedure is used in the particle simulation method with the CPBM; 2) The elastic modulus,strength and UCS/TS decrease,while Poisson ratio increases with the increase of the crack density in the particle simulation method with the CPBM; 3) The particle simulation method with the CPBM can be used to reproduce a high value of UCS/TS(>10),as well as a high friction angle and reasonable cohesion strength; 4) As the confining pressure increases,both the peak strength of the simulated specimen and the number of microscopic cracks increase,but the ratio of tensile cracks number to shear cracks number decreases in the particle simulation method with the CPBM; 5) Compared with the conventional parallel-bond model,the CPBM can be used to reproduce more accurate results for simulating the rock deformation and mechanical characteristics.

关键词： particle simulation method clump parallel-bond model crack density loading procedure rock mechanical behavior

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OPTIMAL DESIGN AND EXPERIMENTAL VALIDATION OF A TURGO MODEL HYDRO TURBINE

OPTIMAL DESIGN AND EXPERIMENTAL VALIDATION OF A TURGO MODEL ...

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11th ASME Biennial Conference on Engineering Systems Design and Analysis, (ESDA 2012)

作者： Anagnostopoulos, John S. Koukouvinis, Phoevos K. Stamatelos, Fotis G. Papantonis, Dimitris E. Natl Tech Univ Athens Sch Mech Engn GR-10682 Athens Greece

ISBN: (纸本)9780791844854

This work presents the development and application of a new optimal design methodology for Turgo impulse hydro turbines. The numerical modelling of the complex, unsteady, free surface flow evolved during the jet-runner interaction is carried out by a new Lagrangian particle method, which tracks a number of representative flow elements and accounts for the various hydraulic losses and pressure effects through special adjustable terms introduced in the particle motion equations. In this way, the simulation of a full periodic interval of the flow field in the runner is completed in negligible computer time compared to the corresponding needs of modern CFD software. Consequently, the numerical design optimization of runner geometry becomes feasible even in a personal computer and affordable by small and local manufacturers. The bucket shape of a 70 kW Turgo model is properly parameterized and numerically optimized using a stochastic optimization software to maximize the hydraulic efficiency of the runner. The optimal runner and the rest turbine parts are then manufactured and installed in the Lab for testing. Detailed performance measurements are conducted and the results show satisfactory agreement with the numerical predictions, thus validating the reliability and effectiveness of the new methodology.

关键词： Turgo impulse turbine particle simulation method Bucket parameterization Design optimization Performance measurements

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Phenomenological modelling of crack generation in brittle crustal rocks using the particle simulation method

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JOURNAL OF STRUCTURAL GEOLOGY 2007年第6期29卷 1034-1048页

作者： Zhao, Chongbin Hobbs, B. E. Ord, A. Robert, P. A. Hornby, P. Peng, Shenglin Cent S Univ Computat Geosci Res Ctr Changsha 410083 Peoples R China CSIRO Div Explorat & Min Bentley WA 6102 Australia

The particle simulation method is used in this paper to explicitly simulate spontaneous crack generation in brittle crustal rocks. Although the method was previously used to simulate crack generation in small-scale laboratory specimens and mining sites, it has seldom been used to simulate spontaneous crack generation in large-scale geological systems. If a geological system can be treated as a quasi-static one, the mechanical response of the system should be independent of the loading rate. Based on this understanding, we have compared the commonly-used continuous loading procedure with a newly-proposed discontinuous loading procedure, which is independent of the loading rate within the elastic range of a particle system. The use of the discontinuous loading procedure enables the macroscopic elastic modulus of a two-dimensional particle system to be directly evaluated from the particle stiffness. However, the particle-size sensitivity analysis of at least two different models needs to be conducted for dealing with the particle size-dependent issue when the particle simulation method is applied to solve crack generation problems in geological systems. Through the phenomenological modeling of spontaneous crack generation problems, it has been demonstrated that the particle simulation method is useful for simulating spontaneous crack generation phenomena at geological length scales. (c) 2007 Elsevier Ltd. All rights reserved.

关键词： crack generation brittle rocks loading procedure particle simulation method discrete block mechanics

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Critical contact stiffness concept and simulation of crack generation in particle models of large length-scales

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COMPUTERS AND GEOTECHNICS 2009年第1-2期36卷 81-92页

作者： Zhao, Chongbin Hobbs, B. E. Ord, A. Peng, Shenglin Cent S Univ Computat Geosci Res Ctr Changsha 410083 Hunan Peoples R China CSIRO Div Explorat & Min Bentley WA 6102 Australia

When the particle simulation method is used to simulate large length-scale problems, such as crustal length-scale problems in the field of geology, it is necessary to include gravity effect into the particle model. To consider gravity effect appropriately, there is a minimum value requirement for the contact stiffness of a particle so that unexpected particle overlap can be avoided. This minimum value is called the critical contact stiffness of a particle due to gravity effect. Using the vertical force equilibrium condition of a particle at the bottom of a two-dimensional particle model, a theoretical formula has been successfully derived for determining the critical contact stiffness of the particle in this paper. For the two-dimensional particle model consisting of circular particles of unit thickness, there is a relationship between the critical contact stiffness of a particle and the critical elastic modulus of the particle material when a linear-elastic-con tact model between any two particles is used. Since the elastic moduli of most crustal rocks are greater than the corresponding critical elastic modulus of the particle material, it has been theoretically demonstrated that the particle simulation method, which is based on the linear-elastic-contact model between any two particles, is suitable for simulating gravity effect within the particle model of a large length-scale. The related simulation results have demonstrated the usefulness of the particle simulation method for simulating spontaneous crack generation patterns within brittle crustal rocks. (C) 2008 Elsevier Ltd. All rights reserved.

关键词： Gravity effect Critical contact stiffness Large length-scale Crack generation Brittle rocks particle simulation method

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particle simulation of spontaneous crack generation associated with the laccolithic type of magma intrusion processes

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INTERNATIONAL JOURNAL FOR NUMERICAL methodS IN ENGINEERING 2008年第10期75卷 1172-1193页

作者： Zhao, Chongbin Hobbs, B. E. Ord, A. Peng, Shenglin Cent S Univ Computat Geosci Res Ctr Changsha 410083 Peoples R China CSIRO Div Explorat & Min Bentley WA 6102 Australia

The main purpose of this paper is to extend the particle simulation method for simulating the spontaneous crack generation problem associated with the laccolithic type of magma intrusion and emplacement within the crust of the Earth. As the mechanical behavior of the intruded magma is different from that of its surrounding rocks, the intruded magma is simulated using fluid particles of relatively less compressibility. whereas the surrounding rock of the intruded magma is simulated using conventional solid particles. Using the proposed particle simulation method, it is possible to simulate some magma-intrusion-induced important phenomena, such is hydraulic fracturing associated with the creation of a magma chamber. complicated moving boundaries associated with the growing magma chamber and spontaneous crack initiation in the surrounding rocks when magma pressure is propagating from the magma chamber into the Surrounding rocks. The related particle simulation results have demonstrated that (1) the proposal particle simulation method is useful and applicable for simulating spontaneous crack generation problems associated with the laccolithic type of magma intrusion process within the crust of the Earth: (2) the generated cracks are highly concentrated on the narrow region that is just above the intruded magma chamber;and (3) the layer-stiffness ratio has a significant effect oil the spontaneously generated crack patterns within the upper crust of the Earth. Copyright (C) 2005 John Wiley & Sons, Ltd.

关键词： spontaneous crack generation brittle rocks magma intrusion particle simulation method geological systems

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