共查询到20条相似文献，搜索用时 125 毫秒
1.
用三维梁-颗粒模型BPM3D(beam-particlemodelinthreedimensions)对岩石类非均质脆性材料的力学性质和破坏过程进行了数值模拟。梁-颗粒模型是在离散单元法基础上,结合有限单元法中的网格模型提出的用于模拟岩石类材料损伤破坏过程的数值模型。在模型中,材料在细观层次上被离散为颗粒单元集合体,相邻颗粒单元由有限单元法中的弹脆性梁单元联结。梁单元的力学性质均按韦伯(Weibull)分布随机赋值,以模拟岩石类材料力学参数的空间变异性。材料内部裂纹通过断开梁单元来模拟。通过自动生成的非均质材料模型对岩石类材料的破坏机理进行研究。岩石类非均质脆性材料在单轴压缩状态下破坏过程细观数值模拟结果显示,岩石材料宏观破坏是由于其内部细观裂纹产生、扩展、贯通的结果。通过数值模拟结果之间的对比分析,揭示出岩石试样宏观破坏模式随细观层次上韦伯分布参数的变化而不同。与实际矿柱破坏形态的对比分析表明了模型的适用性。根据数值模拟结果对岩石类非均质材料的破坏机理进行了探讨。 相似文献
2.
颗粒材料的表面粗糙度在很大程度上影响颗粒集合体的力学特性,传统离散元方法中对颗粒具有光滑表面的假设,使得其无法准确描述真实颗粒材料的接触行为,因此有必要发展可以定量考虑颗粒表面粗糙度的随机离散元方法。在介绍经典粗糙表面接触模型Greenwood-Williamson(简称G-W)模型的基础上,分析了G-W模型应用于离散元模拟的缺陷,提出了分别考虑颗粒重叠光滑部分和粗糙部分的改进模型,并推导出了相应的无量纲形式,对比了经典G-W模型与改进模型计算得到的粗糙颗粒接触时压力分布、变形分布、总接触力等结果。结果表明,改进的接触模型能够更直观地反映颗粒表面粗糙度对颗粒接触的影响。基于改进的接触模型,采用两步曲线拟合手段,得到了可以直接应用于离散元模拟的随机法向接触定律。将该定律通过开发用户自定义接触模型引入到颗粒离散元程序PFC~(3D)中。通过数值试验观察了表面粗糙度在不同加载路径下对颗粒集合体力学特性的影响。 相似文献
3.
为充分利用石质弃渣,填石路堤已经成为山区高等级公路较普遍的路堤形式,为确保填石路堤的稳定性,急需开展弃渣碎石材料性质的研究。为研究颗粒粗糙度对样本性质的影响,本文以雅泸路某隧道废弃碎石的室内大三轴试验数据为基础,开展离散元法模拟级配碎石材料大三轴试验的颗粒粗糙度效应研究。论文详细介绍了样本颗粒形态及粗糙度的模拟原理、级配碎石数值样本的生成过程。分析数值试验过程及结果表明:团粒形态样本可以更真实地模拟碎石材料的骨架-孔隙结构,样本加载前有着合理、均匀的接触力分布形式; 团粒间的镶嵌结构可以极大的提高样本强度,变形过程中体现出不规则颗粒间的咬合、滑动特征; 样本强度与颗粒粗糙度(即D4值)有着线性正比关系; 样本初始平均接触数是决定样本内摩擦角的决定性因素; 团粒形态样本平均接触数随轴向变形发展的变化规律再现了颗粒材料弹性变形的微观力学机制。 相似文献
4.
弹丸侵彻无钢筋混凝土的数值模拟 总被引：1，自引：0，他引：1
采用二维梁-颗粒模型BPM2D（beam-particle model in two dimensions）模拟了刚性弹丸侵彻无钢筋混凝土的过程。离散元法（DEM）和有限元法（FEM）等数值计算方法各有其优势,同时也都存在不足之处：离散元法适于处理由连续介质向非连续介质转化的破坏问题,但对于连续体计算结果精度不高;有限元法适于预测材料破坏的区域,但难以直接用于计算脆性材料破坏过程,因此将两种方法结合可以形成一种较好的混合模型。梁-颗粒模型BPM2D是基于离散元法,结合有限元法开发的二维数值计算模型,采用3种类型梁单元形成混凝土数值试样,每种类型梁单元的力学性质均按韦伯（Weibull）分布随机赋值,以模拟混凝土细观结构的非均匀性,同时梁单元的强度随应变率不同而变化。利用此模型分析了弹丸侵彻下混凝土的破坏过程,并给出侵彻过程弹丸减速度-时间历程曲线。比较计算结果与试验数据表明梁-颗粒模型可有效应用于计算和模拟脆性材料动态破坏问题。 相似文献
5.
采用细观数值模拟方法研究散粒体的锚固效应,基于随机模拟技术生成三维多面体颗粒及其在空间中的分布,在随机散粒体不连续变形模型的基础上将砾石锚固试验进行数值实现,分析加锚散粒体材料的宏观与细观力学性能,研究加锚密度及其与颗粒粒径的关系对散粒体力学性质的影响,并探讨锚杆在散粒体材料中的作用机制。分别建立不同锚杆间距和不同颗粒粒径的数值试样,数值模拟结果表明：散粒体锚固数值试验能够较好地反映不同加锚散粒体结构的变形规律与锚固效应;散粒体材料的宏观特性与其细观组构的演化密切相关;锚杆加固散粒体的作用机制为加锚散粒体内形成压缩区,挤压加固作用提高了散粒体间的接触作用力,散粒体结构的整体性得到加强并能承受一定荷载;不考虑锚杆长度的情况下,当锚杆间距小于3倍的散粒体平均粒径时,锚杆能够有效地加固散粒体形成稳定结构。 相似文献
6.
围绕堆石料单粒强度尺寸效应的颗粒流模拟方法展开研究。首先,基于FISH二次开发建立了堆石料的随机不规则单粒模型,充分考虑堆石料的形状特征和破碎现象;然后,建立了堆石料单粒强度尺寸效应的等效模拟方法,以单粒强度随其粒径的变化规律为基础,推导了堆石料模型中细观黏结强度与堆石料等效粒径的负指数经验公式;其次,基于建立的数值模型对堆石料的室内单粒压缩试验进行仿真模拟,验证数值模型的正确性和合理性,并对较大粒径堆石料的单粒强度进行模拟预测,突出数值试验的优势;最后,基于建立的数值模型对相同粒径不同形状特征堆石料的单粒强度分布特征进行模拟研究。研究结果表明：（1）堆石料内部缺陷含量和尺寸随粒径增加对其单粒强度所产生的尺寸效应,可通过堆石料模型中细观强度参数随粒径折减进行等效模拟;（2）形状特征对堆石料的破裂机制具有重要影响,方形颗粒为压剪破裂,单粒强度较高,而随机不规则颗粒和圆形颗粒为拉剪或劈裂,单粒强度相对较低;（3）拉剪或劈裂条件下,堆石料形状越不规则,其单粒强度的离散程度越高,反之则离散程度越低。相关研究成果可为进一步研究荷载作用下堆石体内各粒径段堆石料的破碎量奠定基础,从而更加真实地反映堆石体的级配演化规律。 相似文献
7.
基于MatDEM的砂土侧限压缩试验离散元模拟研究 总被引：2，自引：2，他引：0
离散元法基于非连续介质力学理论,尤其适用于砂土等离散介质体的数值模拟研究。利用岩土体离散元模拟软件MatDEM的二次开发功能,研发了砂土侧限压缩试验三维离散元模拟器。对三个不同级配砂土试样进行了侧限压缩试验,并且进行了与之相对应的数值模拟,通过分析对比试验结果与数值模拟结果验证了所开发模拟器的有效性。模拟结果表明:离散元法可以很好地反应砂土压缩过程中的配位数变化;每个模拟样品中,粒径较小的单元受到较大的平均压力,导致平均位移较大;数值计算结果的主要误差是由离散元颗粒自身的泊松比引起的。研究突破了常规土力学研究方法的局限性,为今后岩土工程离散元模拟研究提供了参考。 相似文献
8.
地下水流数值模型不仅是认识深部水动力场形成演化机制的有效工具,也是建立核素迁移数值模型的基础,因而是高放废物处置场选址和安全评价中重要的技术手段。高放废物深地质处置地下水流数值模拟方法较多,如何选择适当的方法也是值得关注的问题。针对高放废物深地质处置地下水流数值模拟技术展开研究,通过阅读大量国内外文献,文章系统阐述了目前常用的4 类地下水流数值模拟方法的研究进展、适用条件和实例应用;综述了深地质处置中常用的模型不确定性分析方法及研究成果,列表给出了适用于放射性废物地质处置的地下水流数值模拟软件及其在废物处置选择和安全评价中的应用。研究结果表明:等效连续介质模型适用于大区域、长序列、裂隙发育程度较高或较均匀的地区,该类模型方法成熟、所需的数据和参数易于获得,但是不能精确刻画裂隙介质中地下水的流动特征。离散裂隙网络模型适合解决处置场地、储罐尺度等需要精细刻画的地下水流问题,但由于需要大量裂隙及其连通性数据、相关参数等,该方法存在着工作量大、耗时多的缺点。双重介质模型主要用于解决区域尺度裂隙水流问题,但并不能表现出裂隙介质的各向异性、不连续性等特征,因而适用范围存在一定的限制。等效-离散耦合模型可以通过区域分解法对裂隙密度大的区域采用等效连续介质模型,对于裂隙密度较小的地区采用离散裂隙网络模型,从而更符合一般地质条件下裂隙渗流的特征,但也存在交换量难以确定、模型耦合技术问题。通过灵敏度分析,将不同敏感因子对模型敏感指标的影响程度进行排序,提高模型精度、减少参数不确定性分析的工作量。蒙特卡罗法是目前常用的一种模型不确定性方法,原理简单、易于实现。文章展望了数值模型在仿真性、不确定性分析、预测和多介质耦合等方面的研究前景。 相似文献
9.
《岩土力学》2017,(Z1):70-78
针对岩体中随机结构面存在粗糙特性的特点,开展了粗糙离散节理网络(roughness discrete fractures network,RDFN)模型研究。采用数字图像处理技术,开发了生成RDFN模型的算法,并基于Matlab方法建立了与颗粒流离散元PFC方法的接口。采用颗粒流PFC方法研究粗糙度对RDFN模型单轴压缩下的弹性、强度和破坏模式的影响规律,并与直线型DFN模型进行对比。结果表明,RDFN模型的弹性模量低于DFN模型,而峰值强度较高,残余强度较低;DFN模型中微裂纹沿节理方向贯通,局部存在基岩内部裂纹扩展;RDFN模型由破坏模式相对复杂,达到峰值强度后基岩发生显著破坏。 相似文献
10.
结合现有对结构性土的认识及边坡稳定性方面的研究,分别对有限元和离散元数值模拟方法在研究结构性土坡稳定性方面的适用性进行了分析。通过在数值模拟过程中对土体强度变化、边坡失稳特征等多个因素的分析比对,得出了以PFC2D为代表的离散元软件更能有效模拟出结构性土强度的非线性变化以及结构性土坡全程失稳规律的结论。对结构性土坡失稳破坏的全程PFC2D模拟观察到结构性土坡具有失稳突然、灾前位移变形较小的破坏特点。同时,离散元分析方法更能直观地反映出土颗粒微观结构的改变对结构性土坡失稳特征的影响。 相似文献
11.
12.
In this paper, steady-state conditions for ideal monodisperse dry granular materials are both theoretically and numerically analysed. A series of discrete element (DEM) numerical simulations have been performed on a periodic cell by imposing stress paths characterized by different Lode angles, pressures, and deviatoric strain rates. The dependence of the material response on both inertial number and loading path has been discussed in terms of void ratio, fabric, and granular temperature. DEM numerical results have been finally compared with the prediction of an already conceived model based on both kinetic and critical state theories, here suitably modified to account for three-dimensional conditions. 相似文献
13.
Jacques Desrues Albert Argilaga Denis Caillerie Gaël Combe Trung Kiên Nguyen Vincent Richefeu Stefano Dal Pont 《国际地质力学数值与分析法杂志》2019,43(5):919-955
Double-scale numerical methods constitute an effective tool for simultaneously representing the complex nature of geomaterials and treating real-scale engineering problems such as a tunnel excavation or a pressuremetre at a reasonable numerical cost. This paper presents an approach coupling discrete elements (DEM) at the microscale with finite elements (FEM) at the macroscale. In this approach, a DEM-based numerical constitutive law is embedded into a standard FEM formulation. In this regard, an exhaustive discussion is presented on how a 2D/3D granular assembly can be used to generate, step by step along the overall computation process, a consistent Numerically Homogenised Law. The paper also focuses on some recent developments including a comprehensive discussion of the efficiency of Newton-like operators, the introduction of a regularisation technique at the macroscale by means of a second gradient framework, and the development of parallelisation techniques to alleviate the computational cost of the proposed approach. Some real-scale problems taking into account the material spatial variability are illustrated, proving the numerical efficiency of the proposed approach and the benefit of a particle-based strategy. 相似文献
14.
粒状土的微观结构和微观力学被认为是其宏观力学和体积特性的内在根本因素,近年来得到越来越多的关注和研究。离散单元法作为一种研究颗粒材料的数值模拟计算方法,比试验方法快捷、简便、经济,而且能够容易得到在实验室试验中很难或无法得到的更多重要的微观结构和微观力学的信息,近年来得到越来越多应用。本文介绍了离散单元法对土的微观特性研究的一些最新方法和进展,对数值建模中的一些重要方面如比重(质量)放大、树脂薄膜模拟等方面进行了阐述,对离散单元法在土的微观结构分析(如颗粒旋转、颗粒位移、中尺度孔隙率分布)的一些最新研究作了分析和介绍。分析表明,离散单元法是研究粒状土的微观特性的一个有力工具,可以对土的宏观特性从微观角度得到更好的解释和认识。 相似文献
15.
As we transition into an era of data generation and collection, empirical summaries in the classical continuum modeling of granular materials cannot take full advantage of the increasingly larger data sets. This work presents a data-driven model for modeling granular materials, with the material data being extracted from discrete element method (DEM) simulations. A long short-term memory (LSTM) network is then employed to learn the mechanical behaviors of granular materials from the material dataset. Particular emphasis is placed on three elements: modification of LSTM unit cell, phase space sampling, and material history parameterization. The LSTM unit cell is modified so that the initial hidden state can be specified as the initial states of granular materials. Massive DEM simulations are performed to consider the effects of particle size distribution, initial density, confining pressure, and loading path on the mechanical behaviors of granular materials. The history-dependency of the granular materials is well represented by the architecture of the LSTM network and internal variable-based history parameterization. We compare the model predictions against DEM simulations to assess the performance of the proposed data-driven model. The results demonstrate that the model can predict the material behaviors of granular materials with different microstructures and initial states and reproduce the material responses under complex nonmonotonic loading paths. This data-driven model exhibits good generalization ability and high prediction accuracy in various situations.
相似文献16.
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
17.
Internal erosion by suffusion can change dramatically the constitutive behavior of granular materials by modifying the fabric of granular materials. In this study, the effect of an internal fluid flow on granular materials is investigated at the material point scale using the numerical coupling between a discrete element method (DEM) and a pore-scale finite volume (PFV) coupling scheme. The influence of the stress state and the hydraulic loading (direction and intensity) on the occurrence of grain transport in dense widely graded granular samples is thus investigated and interpreted in terms of micromechanics. In particular, it is shown that grain transport is increased when the macroscopic flow direction is aligned with the privileged force chain orientation. The stress-induced microstructure modifications are shown to influence the transport distances by controlling the number of rattlers. 相似文献
18.
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
19.
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
20.
The paper presents a numerical study on the side resistance of a drilled shaft in granular materials. The numerical result is used to develop new design equations for the side resistance of drilled shafts in granular soils. The Discrete Element Method (DEM) is used to model a drilled shaft in granular material. The granular material is represented as assemblies of ellipsoidal particles. Nominal side resistance is represented as the product of a parameter (β) and vertical stress. The numerical result shows that the relationship between β and void ratio can be described by a hyperbolic function for a given vertical stress. DEM result is also compared with three design equations. Although these design equations capture the decrease of β with depth, deviation is observed between the DEM results and the design equations. Finally, new design equations based on state parameter are proposed. 相似文献