共查询到20条相似文献，搜索用时 31 毫秒
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为了研究颗粒棱角对颗粒材料力学行为的影响,建立了具有不同棱角度的对称多面体颗粒,采用了一种简单并适合任意颗粒形状的接触本构模型,对三维离散元开源程序YADE进行了修改,研究了颗粒棱角度在模拟直剪试验中的影响以及接触力各向异性在剪切过程中的演化规律。研究结果表明,颗粒棱角度越小,颗粒间相互咬合自锁的作用越小,颗粒受剪更易转动,致使颗粒体系的剪切强度和剪胀性下降;竖向加载力越大,颗粒棱角度的影响越明显;法向接触力的各向异性在剪切过程中表现为先增后减最后趋向稳定的趋势;法向接触力的各向异性变化程度随颗粒棱角度的增大而增大。 相似文献
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Creep tests on asphalt mixtures have been undertaken under four stress levels in the laboratory while the discrete element model (DEM) has been used to simulate the laboratory tests. A modified Burger’s model has been used to represent the time-dependent behaviour of an asphalt mixture by adding time-dependent moment and torsional resistance at contacts. Parameters were chosen to give the correct stress-strain response for constant strain rate tests in Cai et al. (2013). The stress-strain response for the laboratory creep tests and the simulations were recorded. The DEM results show reasonable agreement with the experiments. The creep simulation results proved to be dependent on both bond strength variability and positions of the particles. Bond breakage was recorded during the simulations and used to investigate the micro-mechanical deformation behaviour of the asphalt mixtures. An approach based on dimensional analysis is also presented in this paper to reduce the computational time during the creep simulation, and this analysis is also a new contribution. 相似文献
4.
Wave propagation in granular materials is numerically studied using discrete element simulation. Primary interest is concerned with linking material microstructure with wave propagational behaviors for materials composed of elliptical particles. The discrete element (DEM) scheme uses a nonlinear hysteretic contact law which accounts for differences related to the radius of curvature at the interparticle point of contact. Modeling results yield information on wave speed and amplitude attenuation on two-dimensional, meso-domain model systems of both regular and random assemblies. Particulate models were numerically generated using a biasing scheme whereby partial control of particular fabric measures could be achieved. Three specific fabric measures which were used to characterize the granular material models include branch, contact normal and orienation vectors. DEM simulation results indicated that wave speed and attenuation generally correlated with vector distributions of these fabric variables. A power law relation was proposed between wave speed/attenuation and three averaged projected fabric variables based on orientation, contact normal and branch vectors. Predictions from this specific relation correlated reasonably well with DEM results. 相似文献
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A homogenization strategy for granular materials is presented and applied to a three-dimensional discrete element method (DEM), that uses superellipsoids as particles. Macroscopic quantities are derived from the microscopic quantities resulting from a DEM simulation by averaging over representative volume elements (RVEs). The implementation of an RVE is described in detail regarding the definition and discretization of the RVE boundary. The homogenization strategy is validated by DEM simulations of compression and shear tests of cohesionless granular assemblies. Finally, an elasto-plastic material model is fitted to the resulting stress–strain curves. 相似文献
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In this paper, numerical simulation of 3-dimensional assemblies of 1000 polydisperse sphere particles using Discrete Element
Method (DEM) is used to study the liquefaction behaviour of granular materials. Numerical simulations of cyclic triaxial shear
tests under undrained conditions are performed at different confining pressures under constant strain amplitude. Results obtained
in these numerical simulations indicate that with increase in confining pressure there is an increase in liquefaction resistance. 相似文献
7.
Micromechanical Modelling of Granular Materials: Effect of Particle Size and Gradation 总被引：4，自引：0，他引：4
In this paper the effects of maximum particle size, particle gradation/sorting and fabric on bulk mechanical behaviour of granular materials such as coarse grained soils and rockfills are investigated" from micromechanical considerations starting from the grain scale level, using numerical" simulations based on Discrete Element Modelling (DEM). Hydrostatic compaction and biaxial tests on 2-dimensional assemblies of discs with varying particle sizes and gradations were modelled using DEM. An examination of the constitutive behaviour of granular media considering" the particulate nature of the medium has been attempted to explain the effect of particle size and gradation. Simulation results on perfectly parallel graded assemblies indicate that with increase in the size of the particles, a marginal increase (or no increase) in the angle of internal friction is observed during biaxial loading conditions. A change to a wider gradation (keeping the minimum grain size the same) results in a decrease in the angle of internal friction and an increase in volumetric strain to a considerable extent. Based on micromechanical force and fabric parameters, the basis for the physical behaviour was established. This helps in understanding the physics of parallel gradation techniques. 相似文献
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Natural loess is a kind of under-consolidated and unsaturated loose granulates (silts) with its microstructure characterized with large voids and inter-particle cementation. This paper presents a distinct element method (DEM) to investigate its macro- and micro-mechanical behaviour (compression and collapse behaviour) under one-dimensional (1D) compression condition. A relationship between bond strength in DEM model and initial water content is used to develop a bond contact model for loess. Then, DEM structural loess samples are prepared by the multi-layer under-compaction method, and cemented with the bond contact model. The effect of water content and void ratio on compression and collapse behaviour of loess is numerically investigated by simulating 1D compression and wetting tests on the DEM material. The DEM results agree qualitatively with available experimental observations in literatures. The wetting-induced deformation is independent of the sequence of wetting and loading under 1D compression condition. The macroscopic yielding and collapse behaviours are associated with bond breakage on microscopic scale. Moreover, bonds break in one of the two failure types in the simulations, i.e. tensile failure and shear failure (compression-shear failure and tension-shear failure), with bonds broken firstly mainly due to tension followed by shear when the samples are compressed, while mainly due to shear when the samples are wetted under a certain pressure. In addition, the contact orientations and deviator fabrics of contacts under 1D compression and wetting were also investigated. 相似文献
9.
Geogrids are commonly used in railway construction for reinforcement and stabilisation. When railway ballast becomes fouled due to ballast breakage, infiltration of coal fines, dust and subgrade soil pumping, the reinforcement effect of geogrids decreases significantly. This paper presents results obtained from Discrete Element Method (DEM) to study the interface behaviour of coal-fouled ballast reinforced by geogrid subjected to direct shear testing. In this study, irregularly-shaped aggregates (ballast) were modelled by clumping together 10–20 spheres in appropriate sizes and positions. The geogrid was modelled by bonding a large number of small spheres together to form the desired grid geometry and apertures. Fouled ballast with 40% Void Contaminant Index (VCI) was modelled by injecting a predetermined number of miniature spheres into the voids of fresh ballast. A series of direct shear tests for fresh and fouled ballast reinforced by the geogrid subjected to normal shear stresses varying from 15 kPa to 75 kPa were then simulated in the DEM. The numerical results showed a good agreement the laboratory data, indicating that the DEM model is able to capture the behaviour of both fresh and coal-fouled ballast reinforced by the geogrid. The advantages of the proposed DEM model in terms of capturing the correct stress–displacement and volumetric behaviour of ballast, as well as the contact forces and strains developed in the geogrids are discussed. 相似文献
10.
针对离散元中圆形颗粒模拟出的内摩擦角小于真实砂土内摩擦角的缺陷,将已有NS2D离散元程序中的圆形颗粒参量改进为椭圆形颗粒参量,形成改进的NS2D程序。介绍了改进后NS2D程序的基本力学模型,详细推导了程序中椭圆颗粒间以及椭圆颗粒与墙之间接触点的力-位移关系。利用改进后的离散元程序分别模拟了恒定围压下长短轴比例分别为1.1:1、1.4:1,孔隙比均为0.19的椭圆颗粒堆积体的双轴试验,所得的内摩擦角在真实砂土的内摩擦角范围之内,且其应力特征与已有成果吻合良好,证明了改进后的NS2D离散元程序能够模拟分析真实砂土的力学性能 相似文献
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In the present work, a methodology for setting up virgin stress conditions in discrete element models is proposed. The developed algorithm is applicable to discrete or coupled discrete/continuum modeling of underground excavation employing the discrete element method (DEM). Since the DEM works with contact forces rather than stresses there is a need for the conversion of pre-excavation stresses to contact forces for the DEM model. Different possibilities of setting up virgin stress conditions in the DEM model are reviewed and critically assessed. Finally, a new method to obtain a discrete element model with contact forces equivalent to given macroscopic virgin stresses is proposed. The test examples presented show that good results may be obtained regardless of the shape of the DEM domain. 相似文献
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This paper introduces a new generator algorithm and computer program for 3-D numerical simulation of packing configuration in a granular assemblies composed of ellipsoidal particles of different a/b aspect ratios. Each ellipsoidal particle is approximated by the revolution of an ellipse, formed by four connected arcs, about the major axis passing through its centroid. The centroid co-ordinates, major axis direction and lengths of the major and minor axes are the essential data for the packing generation and associated contact detection. The domain to be filled with particles can be a polyhedron of any shape. The packing program was coded based on a newly proposed scheme which obeys the no interpenetration kinematics of solid bodies. New contact detection algorithms for any two ellipsoids in the packing space were developed. Though simple, these algorithms effectively determine the contact condition and contact point without solving the simultaneous equations of the two ellipsoidal surfaces. Each particle's packing location, contact-point co-ordinates, and three-dimensional graphs can be created using the packing domain given boundaries, along with numbers, and geometrical information of particles to be generated. Simulation results show that this new algorithm provides an effective packing model as a required initial input for analysing the mechanics of granular material. This generation scheme potentially can explore the complex 3-D behaviours of material composed of discrete particles. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
14.
This paper describes a three-dimensional random network model to evaluate the thermal conductivity of particulate materials. The model is applied to numerical assemblies of poly-dispersed spheres generated using the discrete element method (DEM). The grain size distribution of Ottawa 20–30 sand is modeled using a logistic function in the DEM assemblies to closely reproduce the gradation of physical specimens. The packing density and inter-particle contact areas controlled by confining stress are explored as variables to underscore the effects of micro- and macro-scales on the effective thermal conductivity in particulate materials. It is assumed that skeletal structure of 3D granular system consists of the web of particle bodies interconnected by thermal resistor at contacts. The inter-particle contact condition (e.g., the degree of particle separation or overlap) and the particle radii determine the thermal conductance between adjacent particles. The Gauss–Seidel method allows evaluation of the evolution of temperature variation in the linear system. Laboratory measurements of thermal conductivity of Ottawa 20–30 sand corroborate the calculated results using the proposed network model. The model is extended to explore the evolution of thermal conduction depending on the nucleation habits of secondary solid phase as an anomalous material in the pore space. The proposed network model highlights that the coordination number, packing density and the inter-particle contact condition are integrated together to dominate the heat transfer characteristics in particulate materials, and allows fundamental understanding of particle-scale mechanism in macro-scale manifestation. 相似文献
15.
The discrete element method (DEM) is frequently used in numerical simulation of the behaviour of discontinuum often encountered in granular flow, soil or rock mechanics or powder compaction. The DEM requires an assemblage of elements that need to fill the domain geometry. Generation of such arrangement of elements, such as disks in 2D DEM simulation is not a trivial task. The available methods to create the arrangements of disks can either take considerable time, have limited control over the final outcome of the disk generation or exhibit difficulty in generating a tight arrangement of disk with varying radii. This paper presents an algorithm employing principles of computational geometry to efficiently generate a tight packing of disks while addressing the common problems of disk generation. The algorithm’s performance is linear with respect to time and scales well. As a demonstration of the algorithm’s capabilities, a DEM model of an ore pass is presented. 相似文献
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Ling Jiang Mingwei Zhao Tianxiang Yue Na Zhao Chun Wang Jinglu Sun 《Earth Science Informatics》2018,11(3):423-431
In many spatial interpolation fields, high accuracy surface modeling (HASM) has yielded better accuracy than classical interpolation methods. The Gaussian equation is the core of the HASM algorithm; The current version of the HASM method builds the Gaussian equation in Cartesian coordinates and, computes the two partial derivatives of the surface in the horizontal and vertical directions for each grid. In this paper, a modified HASM method is proposed that integrates flow paths to improve the original HASM methodology. The modified HASM approach involves two steps. The first step generates an initial DEM, which is used to compute the flow path. Then, the second step is conducted based on scatter points and the flow direction. The output from this step is better than the initial DEM. First, we used a theoretical mathematical surface to validate the correctness of the modified model. Then, we chose a small study area where the topography is affected by hydrological erosion for analysis. The test results showed that the modified HASM method constructed a DEM with low MAE and RMSE values compared to those of traditional methods, and it more accurately characterized topographic features. Finally, a relatively gently sloping area was selected to validate that the applicability of the new method in other areas. 相似文献
17.
胶结颗粒接触力学特性测试装置研制 总被引：5，自引：2，他引：3
为验证天然结构性砂土离散元模拟中接触模型及其参数的合理性,设计了一套用于理想胶结颗粒成型及实现不同加载条件下接触力学特性测试装置。通过胶结颗粒成型装置在两大小相同的铝棒间形成具有特定几何尺寸的胶结物,随后,采用一系列辅助加载装置实现简单及复杂加载条件下胶结颗粒接触力学特性的测试。试验结果表明：该装置可用于胶结颗粒在不同加载条件下接触力学特性的测试,实测胶结颗粒接触力学响应与天然砂土离散元中接触模型基本相符,且其抗剪和抗扭强度均随着法向压力的增大而增大,在三维应力空间中胶结颗粒强度包线呈椭圆抛物面状。 相似文献
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考虑到颗粒形状对粗粒料的力学特性有重大影响,提出了一种新的表征颗粒形状的方法,即在椭圆上随机选取一系列点连接成多边形颗粒,表征狭长扁平的颗粒。新方法较圆上取点的方法能代表更多类型的颗粒形状,适用范围更广。提出了一种新的粗粒料投放算法,即先缩小颗粒,然采用随机算法将缩小的颗粒投放至给定区域,对颗粒划分好网格后,将颗粒放大到原来的大小,然后采用有限元-离散元(FEM/DEM)方法计算稳定后即生成了相应的试样。通过将上述颗粒生成及投放算法与FEM/DEM结合,应用于粗粒料的数值模拟。分析表明,FEM/DEM是研究粗粒料力学性质的较好方法,对复杂的颗粒形状也可简单建模,且因在颗粒内部划分了有限元网格,复杂的接触判断及接触力计算转化为标准统一的三角形和三角形之间的接触判断及接触力计算,所有的计算均可标准化、统一化。同时因为颗粒是可以变形的,依然保留了连续介质力学中应力和应变的概念,无须像PFC那样需通过测量圆来间接表示某点的应力、应变。最后,通过粗粒料的侧限压缩试验的数值模拟,展现了文中提出的一整套解决方案在模拟粗粒料方面的巨大潜力。 相似文献
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Pirnia Pouyan Duhaime François Ethier Yannic Dubé Jean-Sébastien 《Acta Geotechnica》2020,15(10):2877-2889
This paper presents a coupled finite and discrete-element model (FEM and DEM) to simulate internal erosion. The model is based on ICY, an interface between COMSOL, an FEM engine, and YADE, a DEM code. With this model, smaller DEM subdomains are generated to simulate particle displacements at the grain scale. Particles in these small subdomains are subjected to buoyancy, gravity, drag and contact forces for short time steps (0.1 s). The DEM subdomains provide the macroscale (continuum) model with a particle flux distribution. Through a mass conservation equation, the flux distribution allows changes in porosity, hydraulic conductivity and hydraulic gradient to be evaluated for the same time steps at a larger, continuum scale. The updated hydraulic gradients from the continuum model provide the DEM subdomains with updated hydrodynamic forces based on a coarse-grid method. The number of particles in the DEM subdomains is also updated based on the new porosity distribution. The hierarchical multiscale model (HMM) was validated with the simulation of suffusion. Results for the proposed HMM algorithm are consistent with results based on a DEM model incorporating the full sample and simulation duration. The proposed HMM algorithm could enable the modelling of internal erosion for soil volumes that are too large to be modelled with a single DEM subdomain.
相似文献20.
Exploring the influence of interparticle friction on critical state behaviour using DEM 总被引：1，自引：0，他引：1
Understanding the extent to which discrete element method (DEM) simulations can capture the critical state characteristics of granular materials is important to legitimize the use of DEM in geomechanics. This paper documents a DEM study that considered the sensitivity of the critical state response characteristics to the coefficient of interparticle friction (μ) using samples with gradings that are representative of a real soil. Most of the features that are typically associated with sand behaviour at the critical state were seen to emerge from the DEM simulation data. An important deviation occurs when high μ values (μ ≥ 0.5) are used, as has been the case in a number of prior DEM studies. While there is a systematic variation in the critical state behaviour with μ for μ < 0.5, when μ ≥ 0.5, the behaviour at the critical state seems to be insensitive to further increases in μ. In contrast to observations of conventional soil response, when μ ≥ 0.5, the void ratio at the critical state initially increases with increasing mean effective stress (p′). Analysis of the DEM data and use of simple models of isolated force chains enabled some key observations. When ‘floating’ particles that do not transmit stress are eliminated from the void ratio calculation, the void ratio at the critical state decreases consistently with increasing p′. There is a transition from sliding to rolling behaviour at the contact points as μ increases. Beyond a limiting value of μ, further increases in μ do not increase the buckling resistance of individual strong force chains. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献