The glutenite reservoir is strongly heterogeneous due to the random distribution of gravels,making it challenging to perform hydraulic fracturing effectively.To solve this issue,it is essential to study inter-action b...The glutenite reservoir is strongly heterogeneous due to the random distribution of gravels,making it challenging to perform hydraulic fracturing effectively.To solve this issue,it is essential to study inter-action behavior between hydraulic fractures(HFs)and gravels.A coupled hydro-mechanical model is proposed for HF propagation in glutenite using a grain-based discrete element method.This paper first investigates the dynamic evolution of HFs in glutenite,then analyzes the influences of various factors such as horizontal stress difference(D_(s)),minimum horizontal stress(s_(h)),gravel content(V_(g)),gravel size(d_(g)),and stiffness ratio of gravel to matrix(R_(s))on HF propagation geometries.Results show that pene-trating the gravel is the primary HF-gravel interaction behavior,which follows sequential and staggered initiation modes.Bypassing the gravel is the secondary behavior,which obeys the sequential initiation mode and occurs when the orientation of the gravel boundary is inclined to the maximum horizontal stress(s_(H)).An offset along the gravel boundary is usually formed while penetrating gravels,and the offsets may cause fracture widths to decrease by 37.8%-84.4%.Even if stress dominates the direction of HF propagation,HFs still tend to deflect within gravels.The deviation angle from sH decreases with rising D_(s) and increases with the increase of d_(g) and R_(s).Additionally,intra-gravel shear HFs(IGS-HFs)are prone to be generated in coarse-grained glutenite under high D_(s),while more gravel-bypassing shear HFs(GBS-HFs)tend to be created in argillaceous glutenite with high R_(s) than in sandy glutenite with low R_(s).The findings above prompt the emergence of a novel HF propagation pattern in glutenite,which helps to understand the real HF geometries and to provide theoretical guidance for treatments in the field.展开更多
In polar regions, floating ice exhibits distinct characteristics across a range of spatial scales. It is well recognized that the irregular geometry of these ice formations markedly influences their dynamic behavior. ...In polar regions, floating ice exhibits distinct characteristics across a range of spatial scales. It is well recognized that the irregular geometry of these ice formations markedly influences their dynamic behavior. This study introduces a polyhedral Discrete Element Method (DEM) tailored for polar ice, incorporating the Gilbert-Johnson-Keerthi (GJK) and Expanding Polytope Algorithm (EPA) for contact detection. This approach facilitates the simulation of the drift and collision processes of floating ice, effectively capturing its freezing and fragmentation. Subsequently, the stability and reli ability of this model are validated by uniaxial compression on level ice fields, focusing specifically on the influence of compression strength on deformation resistance. Additionally, clusters of ice floes nav igating through narrow channels are simulated. These studies have qualitatively assessed the effects of Floe Size Distribution (FSD), initial concentration, and circularity on their flow dynamics. The higher power-law exponent values in the FSD, increased circularity, and decreased concentration are each as sociated with accelerated flow in ice floe fields. The simulation results distinctly demonstrate the con siderable impact of sea ice geometry on the movement of clusters, offering valuable insights into the complexities of polar ice dynamics.展开更多
Although conventional coal mine designs are conservative regarding pillar strength,local failures such as roof-falls and pillar bursts still affect mine safety and operations.Previous studies have identified that disc...Although conventional coal mine designs are conservative regarding pillar strength,local failures such as roof-falls and pillar bursts still affect mine safety and operations.Previous studies have identified that discontinuous,layered roof materials have some self-supporting capacity.This research is a preliminary step towards understanding these mechanics in coal-measure rocks.Although others have considered broad conceptual models and simplified analogs for mine roof behavior,this study presents a unique numerical model that more completely represents in-situ roof conditions.The discrete element method(DEM)is utilized to conduct a parametric analysis considering a range of in-situ stress ratios,material properties,and joint networks to determine the parameters controlling the stability of single-entries modeled in two-dimensions.Model results are compared to empirical observations of roof-support effectiveness(ARBS)in the context of the coal mine roof rating(CMRR)system.Results such as immediate roof displacement,overall stability,and statistical relationships between model parameters and outcomes are presented herein.Potential practical applications of this line of research include:(1)roof-support optimization for a range of coal-measure rocks,(2)establishment of a relationship between roof stability and pillar stress,and(3)determination of which parameters are most critical to roof stability and therefore require concentrated evaluation.展开更多
This study investigated the correlations between mechanical properties and mineralogy of granite using the digital image processing(DIP) and discrete element method(DEM). The results showed that the X-ray diffraction(...This study investigated the correlations between mechanical properties and mineralogy of granite using the digital image processing(DIP) and discrete element method(DEM). The results showed that the X-ray diffraction(XRD)-based DIP method effectively analyzed the mineral composition contents and spatial distributions of granite. During the particle flow code(PFC2D) model calibration phase, the numerical simulation exhibited that the uniaxial compressive strength(UCS) value, elastic modulus(E), and failure pattern of the granite specimen in the UCS test were comparable to the experiment. By establishing 351 sets of numerical models and exploring the impacts of mineral composition on the mechanical properties of granite, it indicated that there was no negative correlation between quartz and feldspar for UCS, tensile strength(σ_(t)), and E. In contrast, mica had a significant negative correlation for UCS, σ_(t), and E. The presence of quartz increased the brittleness of granite, whereas the presence of mica and feldspar increased its ductility in UCS and direct tensile strength(DTS) tests. Varying contents of major mineral compositions in granite showed minor influence on the number of cracks in both UCS and DTS tests.展开更多
The discrete ordinates(S N)method requires numerous angular unknowns to achieve the desired accu-racy for shielding calculations involving strong anisotropy.Our objective is to develop an angular adaptive algorithm in...The discrete ordinates(S N)method requires numerous angular unknowns to achieve the desired accu-racy for shielding calculations involving strong anisotropy.Our objective is to develop an angular adaptive algorithm in the S N method to automatically optimize the angular distribution and minimize angular discretization errors with lower expenses.The proposed method enables linear dis-continuous finite element quadrature sets over an icosahe-dron to vary their quadrature orders in a one-twentieth sphere so that fine resolutions can be applied to the angular domains that are important.An error estimation that operates in conjunction with the spherical harmonics method is developed to determine the locations where more refinement is required.The adaptive quadrature sets are applied to three duct problems,including the Kobayashi benchmarks and the IRI-TUB research reactor,which emphasize the ability of this method to resolve neutron streaming through ducts with voids.The results indicate that the performance of the adaptive method is more effi-cient than that of uniform quadrature sets for duct transport problems.Our adaptive method offers an appropriate placement of angular unknowns to accurately integrate angular fluxes while reducing the computational costs in terms of unknowns and run times.展开更多
A series of accidents caused by crowds within the last decades evoked a lot of scientific interest in modeling the movement of pedestrian crowds. Based on the discrete element method, a granular dynamic model, in whic...A series of accidents caused by crowds within the last decades evoked a lot of scientific interest in modeling the movement of pedestrian crowds. Based on the discrete element method, a granular dynamic model, in which the human body is simplified as a self-driven sphere, is proposed to simulate the characteristics of crowd flow through an exit. In this model, the repulsive force among people is considered to have an anisotropic feature, and the physical contact force due to body deformation is quantified by the Hertz contact model. The movement of the human body is simulated by applying the second Newton＇s law. The crowd flow through an exit at different desired velocities is studied and simulation results indicated that crowd flow exhibits three distinct states, i.e., smooth state, transition state and phase separation state. In the simulation, the clogging phenomenon occurs more easily when the desired velocity is high and the exit may as a result be totally blocked at a desired velocity of 1.6 m/s or above, leading to faster-to-frozen effect.展开更多
Mine overburden dumps have posed significant safety issues in the operations of various unit operations of open pit min-ing especially the external dumps. The external dumps are composed of a mixture of fragmented roc...Mine overburden dumps have posed significant safety issues in the operations of various unit operations of open pit min-ing especially the external dumps. The external dumps are composed of a mixture of fragmented rocks and loose soil. Their charac-teristic is comparable to heavily discontinuous solid mass. The conventional approach of limit equilibrium methods provide safety factors for the slope but nothing about the stress-strain characteristics of the large dump mass. The designs of dump location and their respective geometry are integrated for the know-how of the stability characteristics of these dumps. The discrete element method uses a circular disk to represent the granular solid mass and their interactions are described by the Newton’s third law of motion. The displacement is described by the sliding of the circular disk. This work is focused on the modeling efficiency of the discrete element methods to represent the behaviour of mine dump masses with the specified joint plane for the limit equilibrium method. The advantage of the work lies on the ease of information retrieval at any point at the dump mass concerning the stress and strain histories, displacement, failures etc. which when integrated produces a better understanding of the stability of the dump masses.展开更多
To simulate ballast performance accurately and efficiently,the input in discrete element models should be carefully selected,including the contact model and applied particle shape.To study the effects of the contact m...To simulate ballast performance accurately and efficiently,the input in discrete element models should be carefully selected,including the contact model and applied particle shape.To study the effects of the contact model and applied particle shape on the ballast performance(shear strength and deformation),the direct shear test(DST)model and the large-scale process simulation test(LPST)model were developed on the basis of two types of contact models,namely the rolling resistance linear(RRL)model and the linear contact(LC)model.Particle shapes are differentiated by clumps.A clump is a sphere assembly for one ballast particle.The results show that compared with the typical LC model,the RRL method is more efficient and realistic to predict shear strength results of ballast assemblies in DSTs.In addition,the RRL contact model can also provide accurate vertical and lateral ballast deformation under the cyclic loading in LPSTs.展开更多
针对茶园耕作过程中因土壤板结粘滞特性导致的机具耕作阻力大、作业质量差等问题,基于鼹鼠爪趾生物力学特征创新设计了一款复合仿生耕作铲,通过四杆机构集成设计研制了新型茶园掘耕机。研究过程中,首先基于离散元法(Discrete element me...针对茶园耕作过程中因土壤板结粘滞特性导致的机具耕作阻力大、作业质量差等问题,基于鼹鼠爪趾生物力学特征创新设计了一款复合仿生耕作铲,通过四杆机构集成设计研制了新型茶园掘耕机。研究过程中,首先基于离散元法(Discrete element method,DEM)与多体动力学(Multi-body dynamics,MBD)耦合算法对仿生掘耕机的耕作过程进行动态模拟分析。同时借助Design-Expert 13试验设计软件,采用三因素三水平正交试验法(耕作铲入土角度、驱动臂转速、机具前进速度)开展整机工作参数优化研究,确定在耕作深度100 mm时,安装复合仿生耕作铲的茶园仿生掘耕机最佳工作参数组合为入土角度33.506°、驱动臂转速289.923 r·min^(-1)、机具行进速度0.2 m·s^(-1)。基于此优化参数,通过土壤颗粒运动速度分布特征进行耕作扰动对比仿真分析。最后开展田间验证试验,结果表明:相较于传统原型铲,装配复合仿生耕作铲的掘耕机减阻率为5.70%,碎土率提升至91.05%,其他作业评价指标均有所提升,工作性能能够满足茶园耕作的要求,验证了其仿生结构设计的有效性与工程实用性。展开更多
结合有限元离散元方法(finite-discrete element method,FDEM),对计算流体力学(computational fluid dynamics,CFD)软件FLOW-3D进行二次开发,建立了基于CFD-DEM的流固耦合模型,模拟了多块石入水、沉降以及触底的动力过程,分析了不同块...结合有限元离散元方法(finite-discrete element method,FDEM),对计算流体力学(computational fluid dynamics,CFD)软件FLOW-3D进行二次开发,建立了基于CFD-DEM的流固耦合模型,模拟了多块石入水、沉降以及触底的动力过程,分析了不同块石等效直径、形状和入水速度对触底速度和反力的影响。研究发现,块石入水后速度迅速减小,并逐渐趋于定值,随后做动态平衡沉降运动,直至与底面发生碰撞。块石抛填的触底速度随等效直径的增大而增大,不同等效直径下球形块石触底速度绝对值最大,其次是纺锤形块石,最小为圆盘形块石。最大触底反力也随等效直径的增大而增大,成非线性关系,通过拟合得到了触底反力的经验公式。显著性分析结果表明,块石等效直径对触底反力影响最大,其次是块石形状,最小为入水速度。展开更多
With the application of Hammer integral formulas of a continuous function on a triangular element, the numerical integral formulas of some discrete functions on the element are derived by means of decomposition and re...With the application of Hammer integral formulas of a continuous function on a triangular element, the numerical integral formulas of some discrete functions on the element are derived by means of decomposition and recombination of base functions. Hammer integral formulas are the special examples of those of the paper.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.52304003)the Natural Science Foundation of Sichuan Province(Grant No.2024NSFSC0961)the Postdoctoral Fellowship Program of CPSF(Grant No.GZB20230090).
文摘The glutenite reservoir is strongly heterogeneous due to the random distribution of gravels,making it challenging to perform hydraulic fracturing effectively.To solve this issue,it is essential to study inter-action behavior between hydraulic fractures(HFs)and gravels.A coupled hydro-mechanical model is proposed for HF propagation in glutenite using a grain-based discrete element method.This paper first investigates the dynamic evolution of HFs in glutenite,then analyzes the influences of various factors such as horizontal stress difference(D_(s)),minimum horizontal stress(s_(h)),gravel content(V_(g)),gravel size(d_(g)),and stiffness ratio of gravel to matrix(R_(s))on HF propagation geometries.Results show that pene-trating the gravel is the primary HF-gravel interaction behavior,which follows sequential and staggered initiation modes.Bypassing the gravel is the secondary behavior,which obeys the sequential initiation mode and occurs when the orientation of the gravel boundary is inclined to the maximum horizontal stress(s_(H)).An offset along the gravel boundary is usually formed while penetrating gravels,and the offsets may cause fracture widths to decrease by 37.8%-84.4%.Even if stress dominates the direction of HF propagation,HFs still tend to deflect within gravels.The deviation angle from sH decreases with rising D_(s) and increases with the increase of d_(g) and R_(s).Additionally,intra-gravel shear HFs(IGS-HFs)are prone to be generated in coarse-grained glutenite under high D_(s),while more gravel-bypassing shear HFs(GBS-HFs)tend to be created in argillaceous glutenite with high R_(s) than in sandy glutenite with low R_(s).The findings above prompt the emergence of a novel HF propagation pattern in glutenite,which helps to understand the real HF geometries and to provide theoretical guidance for treatments in the field.
文摘In polar regions, floating ice exhibits distinct characteristics across a range of spatial scales. It is well recognized that the irregular geometry of these ice formations markedly influences their dynamic behavior. This study introduces a polyhedral Discrete Element Method (DEM) tailored for polar ice, incorporating the Gilbert-Johnson-Keerthi (GJK) and Expanding Polytope Algorithm (EPA) for contact detection. This approach facilitates the simulation of the drift and collision processes of floating ice, effectively capturing its freezing and fragmentation. Subsequently, the stability and reli ability of this model are validated by uniaxial compression on level ice fields, focusing specifically on the influence of compression strength on deformation resistance. Additionally, clusters of ice floes nav igating through narrow channels are simulated. These studies have qualitatively assessed the effects of Floe Size Distribution (FSD), initial concentration, and circularity on their flow dynamics. The higher power-law exponent values in the FSD, increased circularity, and decreased concentration are each as sociated with accelerated flow in ice floe fields. The simulation results distinctly demonstrate the con siderable impact of sea ice geometry on the movement of clusters, offering valuable insights into the complexities of polar ice dynamics.
基金sponsored by the Alpha Foundation for the Improvement of Mine Safety and Health, Inc. (Alpha Foundation)the funding provided for this project by the Alpha Foundationpartially funded by the National Institute of Occupational Health and Science (NIOSH) under Grant Number 200-2016-90154.
文摘Although conventional coal mine designs are conservative regarding pillar strength,local failures such as roof-falls and pillar bursts still affect mine safety and operations.Previous studies have identified that discontinuous,layered roof materials have some self-supporting capacity.This research is a preliminary step towards understanding these mechanics in coal-measure rocks.Although others have considered broad conceptual models and simplified analogs for mine roof behavior,this study presents a unique numerical model that more completely represents in-situ roof conditions.The discrete element method(DEM)is utilized to conduct a parametric analysis considering a range of in-situ stress ratios,material properties,and joint networks to determine the parameters controlling the stability of single-entries modeled in two-dimensions.Model results are compared to empirical observations of roof-support effectiveness(ARBS)in the context of the coal mine roof rating(CMRR)system.Results such as immediate roof displacement,overall stability,and statistical relationships between model parameters and outcomes are presented herein.Potential practical applications of this line of research include:(1)roof-support optimization for a range of coal-measure rocks,(2)establishment of a relationship between roof stability and pillar stress,and(3)determination of which parameters are most critical to roof stability and therefore require concentrated evaluation.
基金This research was supported by the Department of Mining Engineering at the University of Utah.In addition,the lead author wishes to acknowledge the financial support received from the Talent Introduction Project,part of the Elite Program of Shandong University of Science and Technology(No.0104060540171).
文摘This study investigated the correlations between mechanical properties and mineralogy of granite using the digital image processing(DIP) and discrete element method(DEM). The results showed that the X-ray diffraction(XRD)-based DIP method effectively analyzed the mineral composition contents and spatial distributions of granite. During the particle flow code(PFC2D) model calibration phase, the numerical simulation exhibited that the uniaxial compressive strength(UCS) value, elastic modulus(E), and failure pattern of the granite specimen in the UCS test were comparable to the experiment. By establishing 351 sets of numerical models and exploring the impacts of mineral composition on the mechanical properties of granite, it indicated that there was no negative correlation between quartz and feldspar for UCS, tensile strength(σ_(t)), and E. In contrast, mica had a significant negative correlation for UCS, σ_(t), and E. The presence of quartz increased the brittleness of granite, whereas the presence of mica and feldspar increased its ductility in UCS and direct tensile strength(DTS) tests. Varying contents of major mineral compositions in granite showed minor influence on the number of cracks in both UCS and DTS tests.
基金supported by the National Natural Science Foundation of China(No.11975097)the Fundamental Research Funds for the Central Universities(No.2019MS038).
文摘The discrete ordinates(S N)method requires numerous angular unknowns to achieve the desired accu-racy for shielding calculations involving strong anisotropy.Our objective is to develop an angular adaptive algorithm in the S N method to automatically optimize the angular distribution and minimize angular discretization errors with lower expenses.The proposed method enables linear dis-continuous finite element quadrature sets over an icosahe-dron to vary their quadrature orders in a one-twentieth sphere so that fine resolutions can be applied to the angular domains that are important.An error estimation that operates in conjunction with the spherical harmonics method is developed to determine the locations where more refinement is required.The adaptive quadrature sets are applied to three duct problems,including the Kobayashi benchmarks and the IRI-TUB research reactor,which emphasize the ability of this method to resolve neutron streaming through ducts with voids.The results indicate that the performance of the adaptive method is more effi-cient than that of uniform quadrature sets for duct transport problems.Our adaptive method offers an appropriate placement of angular unknowns to accurately integrate angular fluxes while reducing the computational costs in terms of unknowns and run times.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.71473207,51178445,and 71103148)the Research Grant Council,Government of Hong Kong,China(Grant No.City U119011)the Fundamental Research Funds for the Central Universities,China(Grant Nos.2682014CX103 and 2682014RC05)
文摘A series of accidents caused by crowds within the last decades evoked a lot of scientific interest in modeling the movement of pedestrian crowds. Based on the discrete element method, a granular dynamic model, in which the human body is simplified as a self-driven sphere, is proposed to simulate the characteristics of crowd flow through an exit. In this model, the repulsive force among people is considered to have an anisotropic feature, and the physical contact force due to body deformation is quantified by the Hertz contact model. The movement of the human body is simulated by applying the second Newton＇s law. The crowd flow through an exit at different desired velocities is studied and simulation results indicated that crowd flow exhibits three distinct states, i.e., smooth state, transition state and phase separation state. In the simulation, the clogging phenomenon occurs more easily when the desired velocity is high and the exit may as a result be totally blocked at a desired velocity of 1.6 m/s or above, leading to faster-to-frozen effect.
文摘Mine overburden dumps have posed significant safety issues in the operations of various unit operations of open pit min-ing especially the external dumps. The external dumps are composed of a mixture of fragmented rocks and loose soil. Their charac-teristic is comparable to heavily discontinuous solid mass. The conventional approach of limit equilibrium methods provide safety factors for the slope but nothing about the stress-strain characteristics of the large dump mass. The designs of dump location and their respective geometry are integrated for the know-how of the stability characteristics of these dumps. The discrete element method uses a circular disk to represent the granular solid mass and their interactions are described by the Newton’s third law of motion. The displacement is described by the sliding of the circular disk. This work is focused on the modeling efficiency of the discrete element methods to represent the behaviour of mine dump masses with the specified joint plane for the limit equilibrium method. The advantage of the work lies on the ease of information retrieval at any point at the dump mass concerning the stress and strain histories, displacement, failures etc. which when integrated produces a better understanding of the stability of the dump masses.
基金by the China Scholarship Council and the Natural Science Foundation of China(Grant No.51578469)We also would like to acknowledge the support of the Chinese Program of Introducing Talents of Discipline to Universities(111 Project,Grant No.B16041)。
文摘To simulate ballast performance accurately and efficiently,the input in discrete element models should be carefully selected,including the contact model and applied particle shape.To study the effects of the contact model and applied particle shape on the ballast performance(shear strength and deformation),the direct shear test(DST)model and the large-scale process simulation test(LPST)model were developed on the basis of two types of contact models,namely the rolling resistance linear(RRL)model and the linear contact(LC)model.Particle shapes are differentiated by clumps.A clump is a sphere assembly for one ballast particle.The results show that compared with the typical LC model,the RRL method is more efficient and realistic to predict shear strength results of ballast assemblies in DSTs.In addition,the RRL contact model can also provide accurate vertical and lateral ballast deformation under the cyclic loading in LPSTs.
文摘结合有限元离散元方法(finite-discrete element method,FDEM),对计算流体力学(computational fluid dynamics,CFD)软件FLOW-3D进行二次开发,建立了基于CFD-DEM的流固耦合模型,模拟了多块石入水、沉降以及触底的动力过程,分析了不同块石等效直径、形状和入水速度对触底速度和反力的影响。研究发现,块石入水后速度迅速减小,并逐渐趋于定值,随后做动态平衡沉降运动,直至与底面发生碰撞。块石抛填的触底速度随等效直径的增大而增大,不同等效直径下球形块石触底速度绝对值最大,其次是纺锤形块石,最小为圆盘形块石。最大触底反力也随等效直径的增大而增大,成非线性关系,通过拟合得到了触底反力的经验公式。显著性分析结果表明,块石等效直径对触底反力影响最大,其次是块石形状,最小为入水速度。
文摘With the application of Hammer integral formulas of a continuous function on a triangular element, the numerical integral formulas of some discrete functions on the element are derived by means of decomposition and recombination of base functions. Hammer integral formulas are the special examples of those of the paper.
