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Search Results: 1 - 10 of 15399 matches for " 离散元(dem) "
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三维模态变形体离散元方法
张冲,金峰
岩石工程学报 , 2007,
Abstract: 本文针对小应变、大位移和大转动的块体系统建立了三维模态变形体离散元数值模型(3mdem)。首先推导了包含块体刚体运动和变形的整体运动和变形方程,同时提出了在小变形条件下,变形块体的运动可以分解为块体刚体运动和变形的叠加,从而分别推导出刚体平移、转动和变形的方程,并用变形模态分解块体的变形模式。和一般的离散元方法相同,本文模型也采用了显式的时步步进求解格式,适用于求解非连续、大变形及动力问题。该模型克服了三维变形体离散元(3dem)需要对块体内部细分网格导致计算量急剧上升的缺点,具有高效、仿真和可变形的特点。一系列算例表明:本文模型在小变形以及连续介质力学领域可以给出和有限元相媲美的应力和位移结果,而在大变形、大位移的强非线性领域可以给出与3dem相媲美的计算结果,并具有良好的数值稳定性。
考虑简化胶结模型的深海能源土宏观力学性质离散元数值模拟分析
肖俞,蒋明镜,孙渝刚
岩土力学 , 2011,
Abstract: 根据蒋明镜等所提出天然结构性砂土微观胶结模型[1–2]及微观胶结试验结果[3–5],将该模型引入离散元商业软件pfc2d,进行能源土双轴试验离散元数值模拟分析,并同masui等[6]能源土三轴试验结果进行对比分析,结果表明,蒋明镜等所提出胶结模型能够较好的模拟水合物的微观胶结力学行为,水合物胶结的存在对能源土强度具有一定的贡献。
基于局部单元劈裂的fem/dem自适应分析方法
严成增,孙冠华,郑宏,葛修润
岩土力学 , 2014,
Abstract: 为了模拟岩体中裂纹的萌生、扩展,munjiza提出了有限元法/离散元法(fem/dem)耦合分析方法。因为裂纹是沿单元边界进行扩展的,亦即裂纹扩展具有网格依赖性,为获得较好的裂纹扩展形态,需要划分密集的初始网格。为解决上述难题,基于fem/dem耦合分析方法,提出了基于局部单元动态劈裂的fem/dem自适应分析方法,以克服裂纹扩展形态对网格的依赖性。该方法在最初建模时无需划分很密的初始网格,随着荷载的施加,对裂纹尖端附近的局部单元进行动态劈裂,为裂纹的后续扩展提供了更多可能的扩展方向,使得裂纹扩展不必沿着初始网格的单元边界扩展,即可以沿着单元内部进行扩展,裂纹扩展形态更为平滑,与实际情况更为接近。同时相对原fem/dem耦合分析方法一开始就划分很密的网格而言,新方法可以划分较为稀疏的初始网格,计算成本降低。最后,通过巴西劈裂算例与原fem/dem耦合分析方法对比,分析表明,新方法在一定程度上克服了裂纹扩展形态对初始网格的依赖性。
粗糙颗粒的随机离散元模拟——随机法向接触定律(英文)
Stochastic discrete element modelling of rough particles-a random normal interaction law

冯云田,赵婷婷,加藤淳,周伟
- , 2016, DOI: 10.7511/jslx201604032
Abstract: 真实颗粒的力学性质会受到其随机粗糙表面的影响,然而在传统离散元模拟中通常假设颗粒具有光滑表面,因此有必要在定量考虑颗粒表面粗糙度的基础上改进离散元的接触模型。本文基于经典Greenwood-Williamson(GW)模型通过理论分析和数值模拟提出了一种可以考虑颗粒表面粗糙度的法向接触定律;开发了基于Newton-Raphson迭代的数值计算方法,通过输入颗粒重叠量和一系列表面粗糙系数计算总接触力;讨论了改进计算方法效率和准确性的相关问题。相对于GW模型中接触关系的复杂积分表示,拟合得到新随机接触定律的表达式具有类似Hertz定律的简单结构,只包含一个表征颗粒表面粗糙度标准偏差的新增参数,σ,可以方便的引入当前离散元模拟程序中进行计算。
Particles are assumed smooth in classical discrete element modelling,but real particles have random rough surfaces which may influence their mechanical properties.It is necessary therefore to quantitatively improve the conventional discrete element model particles by taking their surface roughness into consideration.In this work,a new random normal contact law is established for particles that have random rough surfaces.The contact law,based on the classic Greenwood and Williamson (GW) model,is derived by both theoretical derivation and numerical simulation.A Newton-Raphson based numerical solution procedure is proposed to obtain the total contact force for a given overlap and a set of rough surface parameters.Some related computational issues key to improve computational efficiency and accuracy are addressed.Instead of a complicated integral expression involved in the GW model,the curve fitted empirical formula of the random contact law retains the closed form and simplicity of the Hertz model,with only one added parameter, σ, the standard deviation of the surface roughness,and therefore can be readily incorporated into the current discrete element modelling framework.
基于离散元法的干湿颗粒系统仿真
A discrete element method-based simulation platform for dry and wet particulate systems

邱流潮,张之豪,袁林娟
- , 2015, DOI: 10.7511/jslx201505017
Abstract: 介绍了基于离散元法的干湿颗粒系统仿真软件DEMSIM。对于干颗粒系统,DEMSIM可以分析二维和三维颗粒系统的弹性和塑性接触碰撞过程;对于湿颗粒系统,DEMSIM采用传统的液桥模型;对于颗粒-流体系统,DEMSIM采用CFD-DEM细观耦合模型模拟。一系列典型算例的模拟分析,验证了干湿颗粒系统仿真软件DEMSIM的精度和有效性。
A discrete element method-based simulation platform for dry and wet particulate systems,DEMSIM,is introduced in this paper.In the case of dry particulate systems,DEMSIM has the ability to model the elastic and plastic contact of granular systems in two and three dimensions.For particulate system with few liquid,a liquid bridge model is applied in this simulation platform.In addition,a numerical method coupling discrete element method (DEM) with computational fluid dynamics (CFD) is developed to simulate particle-liquid flow in DEMSIM.The liquid motion was considered as a weakly compressible flow solved using CFD solvers while the discrete particle motion is solved using DEM in which the particle-particle interaction are based on theoretical contact mechanics thereby enabling particles to be directly specified using realistic material properties such as friction and elasticity.Several numerical examples are presented to verify the simulation platform by comparing the numerical results with theoretic solution and experimental data in the literature.The results demonstrate the ability to simulate the dynamics of the dry and wet particulate systems.
The DEM simulation for two-dimension granular system with point defects
带有点缺陷的二维颗粒系统离散元模拟

Yi Chen-Hong,Mu Qing-Sun,Miao Tian-De,
宜晨虹
,慕青松,苗天德

物理学报 , 2008,
Abstract: In this article, the discrete element method is used to research the force distribution of two-dimensional granular system under the condition of isotropic compression and pure shear. The simulation results are compared with the experimental results under the same conditions. Then we simulate the force distribution of two-dimensional granular system with point defects under the condition of isotropic compression and pure shear and compare the results with the results without point defects. The affects of point defects to granular system are found.
胶粘道床横向阻力特性试验和离散元分析
Experiment and DEM Analysis of Lateral Resistance of Glued Ballast

肖宏, 令行
XIAO Hong
, LING Xing

- , 2017, DOI: 10.3969/j.issn.0258-2724.2017.06.002
Abstract: 为揭示胶粘道床横向阻力的工作机理,在高速铁路胶粘道床路段进行了横向阻力现场试验.分析了胶粘道床横向阻力的变化特征;利用离散元软件PFC3D(particle flow code in 3 dimensions)建立了胶粘道床三维模型,对胶粘道床内部接触力、应力进行了统计分析.研究结果表明:用胶状态下胶粘道床横向阻力值是有砟道床规范值的4.6倍,横向阻力提升显著;胶粘道床在提升横向阻力的同时,轨枕-道砟接触点压力值最大为1.2 KN,平均值为112.48 N,道砟仍处于良好的受力状态;道床全断面粘结时应保证枕下26 cm范围道砟胶喷涂的充分和均匀,以确保道床粘结效果的发挥;胶粘道床不同位置对横向阻力的分担比相对于有砟道床变化明显,胶粘道床枕侧承担63%、枕底承担24%、砟肩承担13%.
:Lateral resistance data were obtained through a field experiment in a high-speed railway to reveal the working mechanism of the lateral resistance of glued ballast. The change characteristics of the lateral resistance of the glued ballast were analysed. Moreover, a three-dimensional discrete element model was established by PFC3D. The contact force and stress of the glued ballast were also statistically analysed. The results show that the lateral resistance of the glued ballast is significantly improved, and its value is 4.6 times of the standard value of the ballast bed. The ballast can maintain a good force state under its high-lateral resistance state. The maximum value of the contact force between the sleeper and the ballast is 1.2 KN, and the average value is 112.48 N. When the whole section is bonded, a depth range of 26 cm must be ensured to be fully and uniformly bonded to ensure the bonding effect. Compared with the ballast bed, the sharing ratio of the lateral resistance significantly varies in different glued ballast positions. Furthermore, the lateral resistance of the glued ballast is mainly shared by the sleeper side, followed by the sleeper bottom and the shoulder with a sharing ratio of approximately 63%, 24%, and 13%, respectively
IDENTIFICATION OF DEM PARAMETERS FOR ROCKFALL SIMULATION ANALYSIS
滚石离散元数值模拟的参数反演

JIANG Jingcai,YOKINO Kazuyoshi,YAMAGAMI Takuo,
蒋景彩
,能野一美,山上拓男

岩石力学与工程学报 , 2008,
Abstract: Distinct element method(DEM) provides a powerful analytical tool for modeling rockfall behaviors,i.e. trajectories,velocities and energies of falling rocks. Better DEM prediction of the motion of the falling rock requires realistic input parameter values used for the analysis. A methodology is developed in which the DEM parameters are determined from back analysis of a rockfall trajectory observed in field rockfall experiments or traced by site investigation of natural rockfall events. A number of techniques and strategies are proposed to ensure the efficiency and robustness of the solution procedure. The method is also extended into non-homogeneous slope cases,by applying repeatedly the presented procedure to each of the homogeneous segments along a given rockfall trajectory. Laboratory rockfall experiments on small model slopes are carried out to verify the proposed method. Case studies on well-documented rockfall records are also presented to show good performance of the method for both homogeneous and non-homogeneous slopes.
INFLUENCES OF HYDRAULIC UPLIFT PRESSURES ON STABILITY OF GRAVITY DAM
坝底水浮力对重力坝稳定性的影响分析

UTILI Stefano,UTILI Stefano,YIN Zhenyu,JIANG Mingjing,
UTILI Stefano
,尹振宇,蒋明镜

岩石力学与工程学报 , 2008,
Abstract: 着重研究一个典型的混凝土重力坝的坝底水浮力对大坝稳定性的影响,此大坝位于意大利的Cumbidanovu岛.大坝的基础由含有高度开裂的岩石所构成.首先,通过把大坝视为自由体的平衡分析法来评价大坝破坏前的最大水压力和有效排水系统对大坝稳定性的影响.然后,使用离散元方法来进一步评价开裂基岩中的水流状态,得到该水流产生的浮托力的分布,最终得到此水浮力对大坝稳定性的影响.对设计而言,上述分析考虑了岩基渗透,运用离散元方法进行模拟.研究结果表面,相比保守的平衡分析法,此模型可以得到更大的水浮力荷载.
MODELLING OF GROUNDWATER AND ROCK BOLTS IN 3-D DEM
三维离散元法中地下水及锚杆的模拟

Jiao Yuyong,Ge Xiurun,Gu xianrong,
焦玉勇
,葛修润,谷先荣

岩石力学与工程学报 , 1999,
Abstract: Based on three dimensional discrete element method which uses dynamic relaxation, a three dimentional method is proposed to analyse underground water and bolts, the corresponding algorithm and formulas are given, and two examples are computed.
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