基于概率接触算法的椭球离散元及料仓试验研究

该文提出一种基于概率接触算法,并嵌入到球形颗粒离散元程序中,在保持原有颗粒接触检索效率的基础上,实现了非球形颗粒模拟。以椭球颗粒为例给出了算法推导过程,进行了球形西米、椭球形绿豆和长米的料仓卸料过程模拟,对颗粒体系的流态和流量进行了研究,并开展了相应的试验加以验证。结果表明:基于概率接触算法的非球形颗粒离散元法适用于在椭球颗粒流动特性方面的研究,可以较精确的模拟卸料过程,且计算效率较高。     

粉粒体斜面慢速流的三维颗粒流程序仿真

为了研究粉粒体斜面慢速流的机理,在分析粉体流动性影响因素的基础上,应用颗粒离散元法三维颗粒流程序建立斜槽仿真模型并进行三维流动过程模拟,观察颗粒在斜槽内的流动情况及单个颗粒在流动过程中的受力、位移和速度,测量颗粒内部力场和颗粒速度场变化。结果表明,随着斜槽倾角的增大,粉粒流的速度呈连续、不均匀增大,堆积颗粒之间的接触力与不平衡力显著增大,并对流速产生一定的影响。     

粒子法和离散元法在管土耦合分析中的应用

为克服管土耦合分析中土体分层、压缩、运移、流变等大变形问题,传统有限元分析技术需借助新的土体模拟及耦合方法。其中,基于纯拉格朗日的粒子法(PM)和细观离散单元理论的离散元法(DEM),因其在土体大变形领域的独特优势而得到广泛关注。针对管道沿线最常见的地质灾害和第三方扰动行为,利用光滑粒子流体动力学(SPH)分析土质滑坡大变形、黏性泥石流冲刷下管道的受力变形特征,获取管道受土中近场爆炸冲击下的动态响应规律,精确模拟了爆炸土中成腔、土体层裂、压缩等现象,联合离散元法中的颗粒流软件(PFC)与三维有限差分程序(FLAC 3D)再现挖机多铲掘进下土体的运移过程,得到管体的载荷累积效应。多次实践表明：以SPH为代表的粒子法和以PFC为代表的离散元法均能较好解决管土耦合分析中土体的非线性大变形问题,引入流体动力学手段,达到了土体变形研究方法多元化的目的,为进一步研究土中多物理场耦合响应机理奠定了基础。     

基于计算接触力学的粗颗粒土体材料细观性质模拟

采用离散元等数值模拟方法研究粗颗粒土体材料的细观力学行为,是近年来岩土力学的热点研究课题。提出了一种基于计算接触力学的粗颗粒土体材料细观力学行为模拟分析新方法。该法将土体颗粒剖分成一定数量的单元,通过计算接触力学方法模拟颗粒间的多体接触行为,是一种基于有限元变分原理的隐式数值求解方法,具有严格的理论基础。和离散元法方法相比,该方法在描述颗粒本身的力学特性方面具有优势,可以计算得到颗粒内部的应力分布情况,从而为颗粒破碎等细观行为的模拟计算提供依据。利用所发展的粗颗粒土体多体接触有限元计算程序,进行了不同围压的常规三轴数值试验,模拟计算结果符合粗颗粒土体材料三轴试验的一般规律,初步验证了所提出的计算方法的适用性。     

拆除爆破研究中数值分析方法的比较与选择

概述了数值分析法的分类。介绍了平面杆系有限元法、离散元法、数值流形法和不连续变形分析等几种数值分析方法。简单地讨论了平面杆系有限元法的分析步骤以及在拆除爆破中适于解决的问题 ;同时叙述了流形分析中采用的有限覆盖技术。通过分析和比较这几种方法在拆除爆破研究中的应用 ,作者认为 ,当前应用传统的有限元法进行爆破理论研究或拆除爆破模拟存在一些困难 ;离散元法用于拆除爆破理论的研究是可行的 ;不连续变形分析法对于拆除爆破模拟研究是一种具有良好前景的数值方法     

拆除爆破研究中数值分析方法的比较与选择

概述了数值分析法的分类。介绍了平面杆系有限元法、离散元法、数值流形法和不连续变形分析等几种数值分析方法。简单地讨论了平面杆系有限元法的分析步骤以及在拆除爆破中适于解决的问题 ;同时叙述了流形分析中采用的有限覆盖技术。通过分析和比较这几种方法在拆除爆破研究中的应用 ,作者认为 ,当前应用传统的有限元法进行爆破理论研究或拆除爆破模拟存在一些困难 ;离散元法用于拆除爆破理论的研究是可行的 ;不连续变形分析法对于拆除爆破模拟研究是一种具有良好前景的数值方法     

月壤的钻取采样离散元动态行为研究

月壤为离散介质,其力学行为不仅受外部因素影响,而且受月壤颗粒形状之间相互作用和约束因素影响,一般连续介质力学难以模拟其力学特性,而离散元法作为一种分析离散介质的数值方法,可用来模拟器具与月壤相互作用的力学行为.基于前苏联Luna-24月面钻取采样过程力学机理分析,首先对钻取运动过程进行分析,然后应用PFC3D离散元软件,构建离散元月壤模型,通过赋予颗粒接触刚度、摩擦系数、粘结系数等定义月壤本构模型,仿真钻取过程,对比钻取消耗能量和钻进阻力.计算结果表明螺距和转速对钻取消耗能量和钻进阻力影响较大,螺距越大,转速越高,钻取消耗能量和钻进阻力越大,且与螺距和转速呈线性关系.研究结果可为月表采样机构的设计与优化提供借鉴.     

基于离散单元法的群楼拆除爆破仿真模拟

基于青岛开发区一商场爆破工程,利用颗粒离散元法建立离散元网格实体模型,用多面体离散元法模拟分析拆除爆破中建筑物的倒塌过程。研发的网格实体模型详细模拟了建筑物从结构局部失稳到整体完全倒塌的整个过程,确定了爆堆轮廓线和爆堆尺寸,直观给出了爆破设计的效果。触地振动、冲击力变化分析结果表明:所给出的爆破方案可达到预期拆除爆破的效果,触地振动符合《爆破安全规程》要求;该模型可优化爆破设计,指导爆破施工,为建筑物拆除爆破的灾害预测与安全评估提供理论依据。     

基于离散单元法的群楼拆除爆破仿真模拟

基于青岛开发区一商场爆破工程,利用颗粒离散元法建立离散元网格实体模型,用多面体离散元法模拟分析拆除爆破中建筑物的倒塌过程。研发的网格实体模型详细模拟了建筑物从结构局部失稳到整体完全倒塌的整个过程,确定了爆堆轮廓线和爆堆尺寸,直观给出了爆破设计的效果。触地振动、冲击力变化分析结果表明:所给出的爆破方案可达到预期拆除爆破的效果,触地振动符合《爆破安全规程》要求;该模型可优化爆破设计,指导爆破施工,为建筑物拆除爆破的灾害预测与安全评估提供理论依据。     

浅谈非阻塞性颗粒阻尼的离散元法（DEM）

提出了一种研究颗粒阻尼减振特性的离散元算法,建立了离散元法（DEM）数学模型。通过分析颗粒间以及颗粒与容器壁间的相互作用规律,能较准确地预测颗粒阻尼的减振特性。与实验结果进行了比较,验证了该离散元数学模裂的正确性。利用离散元数学模型来研究颗粒阻尼结构属性的改变对其阻尼减振特性的影响,结果表明,质量比和材料密度都对颗粒阻尼的减振特性有影响。     

颗粒间摩擦对颗粒流润滑影响的力学机制

颗粒流润滑是一种可用于苛刻工况环境的新型润滑方式,颗粒间摩擦对颗粒流润滑影响的规律和特性是阐明颗粒流润滑理论的关键科学问题,也可以为极端工况环境下颗粒流润滑轴承的设计和参数选择提供技术支持。为了分析颗粒间摩擦对颗粒流润滑系统宏、微观特性以及下摩擦副与颗粒润滑介质间摩擦的影响规律,构建了颗粒流润滑离散元数值模型,并对该问题进行了分析和研究。研究结果表明:颗粒间摩擦对颗粒流润滑系统的减摩润滑特性具有显著影响,下摩擦副和颗粒润滑介质之间的平均摩擦系数会随着颗粒间摩擦的增大而增大;颗粒流润滑系统内的微观配位数和滑动率均随着颗粒间摩擦系数的减小而增大;颗粒润滑介质在摩擦副间隙的宏观流动行为具有明显的分层特性,且宏观流动速度随着颗粒间摩擦的增大而减小,进一步的分析结果表明:颗粒润滑介质的波动速度是直接反映其宏观流动速度快慢的关键性参数。     

A nonlocal multiscale discrete‐continuum model for predicting mechanical behavior of granular materials

A three‐dimensional nonlocal multiscale discrete‐continuum model has been developed for modeling mechanical behavior of granular materials. In the proposed multiscale scheme, we establish an information‐passing coupling between the discrete element method, which explicitly replicates granular motion of individual particles, and a finite element continuum model, which captures nonlocal overall responses of the granular assemblies. The resulting multiscale discrete‐continuum coupling method retains the simplicity and efficiency of a continuum‐based finite element model, while circumventing mesh pathology in the post‐bifurcation regime by means of staggered nonlocal operator. We demonstrate that the multiscale coupling scheme is able to capture the plastic dilatancy and pressure‐sensitive frictional responses commonly observed inside dilatant shear bands, without employing a phenomenological plasticity model at a macroscopic level. In addition, internal variables, such as plastic dilatancy and plastic flow direction, are now inferred directly from granular physics, without introducing unnecessary empirical relations and phenomenology. The simple shear and the biaxial compression tests are used to analyze the onset and evolution of shear bands in granular materials and sensitivity to mesh density. The robustness and the accuracy of the proposed multiscale model are verified in comparisons with single‐scale benchmark discrete element method simulations. Copyright © 2015 John Wiley & Sons, Ltd.     

颗粒流动模型研究进展

颗粒流动在自然界中和各种工业过程中广泛存在,但人们对于其机理认识的还不深入。描述颗粒运动的模型有很多,连续介质模型应用简单但准确性比较低,离散微粒学模型是近来人们研究的一个热点,以每个颗粒为考察对象,能够更准确地反应颗粒系统的性质。本文介绍了描述颗粒流动的模型,概述了各模型的理论和应用,通过对多种模型的比较可以看到,每个模型都有一定的使用范围,要更准确、更方便地描述颗粒系统的运动,还要进行深入地研究。     

基于颗粒流离散元模型的弹丸侵彻细观混凝土数值模拟方法研究

利用颗粒离散单元法,研究弹丸侵彻细观混凝土模型中弹丸受到介质的阻应力与侵彻速度的关系。采用蒙特卡罗法随机生成并投放混凝土骨料且骨料的粒径分布满足级配曲线。通过对混凝土颗粒离散元细观力学模型进行单轴压缩实验、巴西劈裂实验和双轴压缩实验的参数反演,确定细观模型参数,能使细观混凝土模型具有和一般混凝土等效的力学性能。分析了骨料、过渡层和砂浆三相材料各细观参数对混凝土单轴压缩应力应变关系影响以及锥形弹和平头弹弹丸直径对侵彻阻应力的影响。将颗粒离散元细观力学模型方法计算的弹丸阻应力与空腔膨胀理论计算模型相比较,表明计算离散元方法具有良好的精度和实用性。     

A coupled SDPH–FVM method for gas‐particle multiphase flow: Methodology

This paper describes a novel methodology that combines smoothed discrete particle hydrodynamics (SDPH) and finite volume method (FVM) to enhance the effective performance in solving the problems of gas‐particle multiphase flow. To describe the collision and fluctuation of particles, this method also increases a new parameter, namely, granular temperature, according to the kinetic theory of granular flow. The coupled framework of SDPH–FVM has been established, in which the drag force and pressure gradient act on the SDPH particles and the momentum sources of drag force are added back onto the FVM mesh. The proposed technique is a coupled discrete‐continuum method based on the two‐fluid model. To compute for the discrete phase, its SDPH is developed from smoothed particle hydrodynamics (SPH), in which the properties of SPH are redefined with some new physical quantities added into the traditional SPH parameters, so that it is more beneficial for SDPH in representing the particle characteristics. For the continuum phase, FVM is employed to discretize the continuum flow field on a stationary grid by capturing fluid characteristics. The coupled method exhibits strong efficiency and accuracy in several two‐dimensional numerical simulations. Copyright © 2016 John Wiley & Sons, Ltd.     

Calibration and validation of a large scale abrasive wear model by coupling DEM-FEM: Local failure prediction from abrasive wear of tipper bodies during unloading of granular material

Handling of granular materials like rocks, pebbles and sand can expose equipment to abrasive wear that can result in local failure. In some cases this can have far reaching economic significance such as the costs of replacement, the costs from machine downtime and lost production. Models for predicting wear can be found from lab scale tests, but are difficult to apply in large scale applications. An important property is the flow behaviour of granular material during its transportation in a granular material handling system. In order to effectively predict abrasive wear in large scale applications, models for solid structure, granular material flow and wear behaviour have to be coupled. In this work; the finite element method is used to model the structure of the tipper body and the discrete element method is used to model the granular material. To couple the structure response to granular flow behaviour a contact model is used. A calibration of the wear constant in Archard's wear law is obtained from measurement data of rotating drum tests, using the representative material combination used in a tipper unloading case. This wear model is then used in a full scale tipper body simulation to predict the absolute wear and validated against field measurement. A good agreement between numerical calculation and field measurement regarding the spatial position and size of wear areas were found. This combination of numerical methods gives new possibilities to understand the wear process and is one step towards more physically correct models for large scale predictions between tipper bodies and granular material. Numerical tools can give future opportunities to optimise material selections and geometry with the intension to increase functionality, life of large scale wear applications and avoid local failure.     

Particle finite element analysis of the granular column collapse problem

The problem of granular column collapse is investigated by means of an axisymmetric version of the particle finite element method (PFEM). The granular medium is represented by a simple rate-independent plasticity model and the frictional contact between the granular flow and its rigid basal surface is accounted for. In the version of the PFEM developed for this study, the governing equations of the boundary value problem are cast in terms of an optimization problem and solved using mathematical programming tools. The agreement between model and experiment is generally satisfactory, quantitatively as well as qualitatively. However, the friction angle of the granular material, as well as the exact interface conditions between the base and granular material, are shown to have a relatively significant influence on the results.     

On the influence of inter-particle friction and dilatancy in granular materials: a numerical analysis

Mechanical behavior of granular soils is a classic research realm but still yet not completely understood as it can be influenced by a large number of factors, including confining pressure, soil density, loading conditions, and anisotropy of soil etc. Traditionally granular materials are macroscopically regarded as continua and their particulate and discrete nature has not been thoroughly considered although many researches indicate the macro mechanical behavior closely depends on the micro-scale characteristics of particles. This paper presents a DEM (discrete element method)-based micromechanical investigation of inter-particle friction effects on the behavior of granular materials. In this study, biaxial DEM simulations are carried out under both ‘drained’ and ‘undrained’ (constant volume) conditions. The numerical experiments employ samples having similar initial isotropic fabric and density, and the same confining pressure, but with different inter-particle friction coefficient. Test results show that the inter-particle friction has a substantial effect on the stress-strain curve, peak strength and dilatancy characteristics of the granular assembly. Clearly, it is noted that apart from the inter-particle friction, the shear resistance is also contributed to the dilation and the particle packing and arrangements. The corresponding microstructure evolutions and variations in contact properties in the particulate level are also elaborated, to interpret the origin of the different macro-scale response due to variations in the inter-particle friction.     

Discrete modelling results of a direct shear test for granular materials versus FE results

The intention of this paper is to present a comparison of the results of discrete element and finite element simulations of a simple shear test for medium dense cohesionless sand. Such a comparison may provide useful information on the limitations and possible advantages of micro-polar continuum models for granular media as compared with discrete element models. To simulate the discrete nature of sand at the micro-level during shearing, the 3D discrete open-source model YADE developed at Grenoble University was used. Contact moments at spheres were assumed to capture the influence of force eccentricities due to grain roughness. Attention was paid to some micro-structural events (such as vortices, force chains, vortex structures, local void ratio fluctuations) appearing in a shear zone and kinetic, elastic and dissipated energies in granular specimen. The results of the discrete element simulations were compared with the corresponding finite element (FE) solutions based on a micro-polar hypoplastic constitutive model for granular material. A satisfactory agreement between discrete and FE results was achieved. Advantages and disadvantages of both approaches are outlined.     

Experimental and numerical study of granular medium-rough wall interface friction

Wall roughness plays a crucial role in granular medium - rough wall interface friction. In this study, an experimental device has been designed to study the influence of boundary conditions, more specifically wall roughness, on the behavior of sheared granular medium. The study is based on use of an analog model, and consists of simulating roughness by means of notches and grains in the medium by monodisperse beads and on use of a numerical model based on the discrete element method. The test protocol entails displacing at fixed speed notched rods under confined granular medium. Movement of the beads layer near the rods as well as friction of the beads against the rods are both studied herein. Results indicate that the parameter controlling friction at the granular medium - rough wall interface is primarily the depth of beads embedment in surface asperities. The objective of the associated numerical modeling is to supplement the experimental results.