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1、1971年，CUNDALL提出的一种处理非连续介质问题的数值模拟方法，离散元方法（Discrete Element Method,简称DEM），理论基础是结合不同本构关系（应力-应变关系）的牛顿第二定律。随后，这种方法被越来越广泛的应用于涉及颗粒系统地各个领域。通过求解系统中每个颗粒的受力（碰撞力及场力），不断地更新位 置和速度信息，从而描述整个颗粒系统。CFDDEM耦合方法的基本思路是：通过CFD技术求解流场，使用DEM方法计算颗粒系统的运动受力情况，二者以一定的模型进行质量、动量和能量等的 传递，实现耦合。该方法的优势在于，无论流体还是颗粒，都可以采用更适合自身特点的数值方法 进行模拟，将
2、颗粒的形状、材料属性、粒径分布等都考虑进来，更准确地描述颗粒 的运动情况及其与流场的相互影响。大多为气固(Gas-Solid Fluid)两相流(PFC)1. 北京海基.流体一颗粒系统数值模拟的FLUENT-EDEM解决方案，2。92. Coupled particle and fluid flow modeling of fracture and slurry injection in weakly consolidated granular mediaWe have investigatethe use of coupled fluid flow and particle flow mod
3、els to simulate fracture and dilation processes during waste injection.3. GRANULAR FLOWS AND NUMERICAL MODELLING OF LANDSLIDESA granular material is an assembly of a large number of discrete solid components that are dispersed in one or more fluids. The granular flow may behave like a solid or a flu
4、id showing very different behaviour and features both during and after movement. Dispersed single-phase flows4. Physically Representative Micro-Mechanical Models of Fluid-FilledGranular Media5. Mocro-mechanical Simulation of Water Flowthrough Granular Soils6. DEM simulation of impact force exerted b
5、y granular flow on rigid structures(Springer-Verlag 20117. Yasuhiko Okada， Shear behaviour in numerical triaxial compression tests by 3Dfluid-coupled DEM: a fundamental study on mechanisms of landslide initiation (2011)2. 郑建祥.粘附性颗粒动理学及气固两相流体动力特性的研究.工学博士学 位论文,2008模拟方法：大涡模拟（LES）基于Chapman和Cowling的稠密气体动
6、理学方法，建立了粘附性颗粒动理学理论，提出了颗粒相本构方程3. Tatemoto运用DEM方法数值模拟粘附性颗粒在振动流化床内流动2011 12.29 （博士论文阅读采取点）振动压实对道路材料空间组构及其力学性能演化的离散元模拟1. 颗粒之间只是在接触时，才有力的作用，颗粒之间存在压应力和剪应力， 但其规律性比固态物质复杂的多，具有对边界面产生压力的性质，难以抵 抗拉力，抗剪强度取决于围压的大小，无围压时，理想的颗粒系统无抗剪 强度，具有压硬性、剪胀性。2. 单个颗粒的尺寸、形状、物理性质以及颗粒分布决定了固体骨架的细观力 学性质。固体、液体、气体三个组成部分之间的比例关系和相互作用决定 了道
7、路材料的宏观力学性质。由试验分析确定各种材料的力学计算参数， 只能根据试验试件整体表现出的力学性能参数为依据，难以考虑材料自身 微观的差异，同时试验误差引起的数据离散程度大，导致材料参数的可靠 度下降。3. 一般是由于颗粒系统自身具有的特点（离散性，耗散性，形态的多样性等 而造成，使得研究者们不能用传统的理论揭示颗粒系统的普遍规律。4. 这是困为离散元理论的计算单元和我们研究的真实材料之存在很多而又难于控制的因素，这些因素之间的非线性是非常显著的，而且相互之间的 影响又是很明显的。比如与材料强度有关的细观参数就与颗粒之刚的接触 模量、平行粘结模量、法向平行粘结强度和切向平行粘结强度有关，如果
8、同时变化多个细观参数柬得lB材料宏观强度的变化规律是很难控制，而且 是不太可能的。5. 主要基于混台物多孔介质理论建立三相体数值模型。采用杨松岩教授提出 的“多孔介质的车构描述”的理论为离散元时步差分控制简化方程唧J， 研究湿颗粒（考虑固、液、气三项体）振动压实下的瞬态响应6. 由于数值模拟软件将基本颗粒假定为刚性体，在模拟中水被简化为流体域 上的体力7. 颗粒与颗粒间的动摩擦转化为颗粒与水的动摩擦8. 由固体颗粒和填隙流体形成的一种多孔介质材料气固两相流技术发展状况2012.2.12复杂两相流动中颗粒碰撞的DEMLES/DNS耦合模拟研究一、a)欧拉欧拉方法(Eulerian- Euleri
9、an approach),即将连续相和颗粒相都看作可进入的连续流质和拟连续流质，用连续介质力 学的连续性方程、动量方程和能量方程来分别描述两相的性质和运 动。b)欧拉 拉格朗日方法(Eulerian- Lagrangian approach)，即 对离散相采用跟踪计算颗粒的运动轨迹，用直接模拟或者随机模型的 方法计算颗粒-颗粒相互作用等。这两种途径都需要考虑流体-颗粒两相的相互作用，欧拉-欧拉 方法最典型的即使双流体模型(Two-Fluid Model, TFM)，而欧拉- 拉格朗日方法典型的即是离散颗粒模型(Discrete Particle Model， DPM)。此外，对分散相的描述又分
10、随机性方法(stachastic way ) 和确定性方法。DEM方法在颗粒体系混合现象的理论研究和实际应用进行了 综述和讨论，包括连续模型和离散模型、DEM的验证、非球形因素和 粘结性因素的考虑等，同时他们指出了DEM模型在实际应用上受计算时间和颗粒数目的限制，在解决此限制方面，可采取的途径将CFD计 算和DEM耦合起来，如采用有限元方法计算群体速度，同时考虑每个 组分的浓度导出积分型输运方程等。采用两维的硬圆碟无弹性碰撞模 型模拟了稳态重力驱动颗粒流。在计算机技术和离散颗粒模型的快速发展的基础上，颗粒尺度的 颗粒-颗粒、颗粒-流体、颗粒-壁面之间的相互作用的研究工作在近 期得到了快速发展。
11、研究发现当恢复系数为07和0.9、颗粒摩擦系数为0.3和0.6、 壁面摩擦系数为0和0.3时模拟结果和放射性颗粒跟踪实验测量结果 非常接近。对于颗粒流的数值研究，也可分为拟连续介质描述和拉格朗日 离散颗粒描述两大类，其中连续介质描述用于弹性颗粒快速颗粒流 （rapid granular flow ），因为此时颗粒流行为与流体流动行为十 分相似。由于DEM方法是基于颗粒尺度行为的基本物理定律和材料物 理特性的，碾磨过程中的功耗、转矩、装载、速度等重要参数以及碰 击能、力传输链、壁面应力等关键力学量都可通过DEM模拟来预测和 评估。这两天你突击把看过的考虑粘性和流体作用的文献和我上面给你提的建议
12、（考虑粘性或流体作用的离散单元法方面的文献（尤其是看是否有用PFC的），主 要关注粘性或流体作用如何加入到离散元模型中以及做的哪些具体的问题等）的 文献总结整理一下，这周五我们讨论一下。考虑粘性和流体作用的散体介质静、动力学行为分析粘性 viscosity,作用 1.动词affect 2.名词影响effect 3.名词活动action散体物质：Discrete Material静、动力学行为：the behavior of still and dynamics Force;散体物质：属于软物质范畴，是自然界和工程界最为普遍的一种物质类型，具有 多学科内涵和丰富的力学行为以及广泛的应用背景。散体
13、物质的多尺度特性更多的体现在不同层面上具有明显不同的物理本质和率 相关性方面。（a）微观尺度（特质颗粒层面）上颗粒间的挤压与摩擦在细管尺 度上形成分布不均匀且可以承受外部载荷的力链。（b）宏观尺度上又可能表现 出变形或流动等特征。散体物质力学行为不仅受到其颗粒的形状、尺寸、孔隙度、颗粒表面的粗糙度、 颗粒的排列方式和接触形态等内部因素的影响，也受到加载条件和环境等外部因 素的影响，包含了多个事件和空间尺度的相互耦合。对于散体物质这种由大量颗粒组成的复杂系统，仅仅通过求解单一颗粒的运动方 程来实现对宏观系统的定量描述是不现实的，因此我们必须探讨新的范式来包括 跨尺度耦合的过程。统计处理和分析可能
14、是不可或缺的，这是应为系统中的大量 颗粒会表现出相应的统计规律，而且由此得到的统计规律可能是问题解决过程中 的一个重要输入量。2012.2.19滑坡：landslide泥石流：Debris flow润滑的；喝醉了的：Lubricated隔离，分离；种族隔离：SegregationWet granular materials in sheared flowsWen-Lung Yang 略，Shu-San Hsiau * 曜Department of Mechanical Engineering, NalionaJ Central University, Chung-U, 32054 Tarran
15、, ROCReceived 13 December 2OT4. Reused 3 February 2005. Accepted 1 March 2005. A/afeible onlne 26 Apr! 2005.http:/dx.do.arg/10.101 ces.2005.D3.001. Howto Cite or Link Using DOIPermissions & ReprintsAbstractThe transport properties cf wet granular materials in a shear cell apparatus have been studied
16、. If the particles are wet? the flaw becomes more viscous forming liquid bridges betw&en particles. The dynamic liquid bridge forces are considered as the cohesive forces between particles to restrict their movements. The cohesive ft)rce& make the particles stick tighter with each other and hamper t
17、he movement cf particles. The mixing and transport properties are influenced sericusly by the amcunt cf moisture added in the flow. This paper discusses a &erie& cf experiments performed in a shear cell device with five different moisture contents using 3-m m glass sp h eres asthegranular m ateri al
18、s. Th e mcti cn cf g ran ular m aterials was record ed by a high speed camera. Using the image processing technology and particle tracking method, the average and fluctuaticn velocities in the streamwise and transverse directions could be measured. The selWilTusicn coefficient could be found from th
19、e history cf the particle displacements. TheselWiffusion coefTicients andfluctuations in the streamwi&e directicn were much larger than those in the transverse direction. Three bi- directicnal stress gages were installed to the upper wall to measure the normal and shear stresses cf the granular mate
20、rials along the upper wall. For wetter granular material flows, the fluctuaticn velocities and the selWiffusicn coetTi cients were sm al I er.KeywordsMoisture content; Cohesive; Granular flows; Shear cell; SelMiffusion coefficient; Stress gage1. IntroductionGranular materials are col I ecti c ns of
21、d iscrete sol i d particles dispersed in vacuum or in an interstitial fluid. The voids between particle& are filled with a fluid-like air or water. Therefore, the flow behavior cf granular material can be treated as a multiphase flow. Granular flows are widely found in nature, such as avalanche, soi
22、l liquefaction, landslides and river sedimentation. In industries, granular flaws include mixing and transport processes cf foodstuffs, coal, pellets, and metal mine. In chemical industry, more than 30% cf the products are formed as particles (Shamlou, 19SB). All granular flows are highly dissipativ
23、e. The energy supplied to a granular flow, through vibration, gravity, cr shearing is rapidly dissipated into heat. Thus, energy must be constantly supplied to the system to maintain a granular flow.The dominant mechanism effecting the flow behavior is the random motion cf particles resulted from th
24、e interactive collisicn between parti cl e& (Campbell, 1990). Since the random motion cf particles in a granular flow is analogcus to the motion cf molecules in a gas, the densegas kinetic theory (Savage and Jeffrey, 19S1, Jenkins and Savage, 19S3, Lun et al., 1984 and Jenkins and Richman, 1985) and
25、 molecular dynamic simulations (Campbell, 1939; Lan and Rosato, 1995) are utilized to analyze and model the granular flow behavicr. HOWever, the granular flow is not completely analogous to molecular dynamic theory. In this study, we use the densegas kinetic theory to analyze the granular fldw.The p
26、resence cf a small amcunt of interstitial fluid in the system introduces another degree cf complexity due to the cohesive fcrces between particles in addition to the core repulsive force and the force cf friction in adry granular matter. An increase in repose angle is the most well known effect cf t
27、he presence cf interstitial fluid in a granular system and has become a topic cf current interest (T&gzes et al., 1999 and Halsey and Levine, 199ST). The interstitial fluid also alters the percolation cf particles, and the particles tend to behave as clumps rather than individual grains. The researc
28、h about wet particles is mere important at present. When thi particles contain slight amount cf water, they would gather together and hinder the movements themselves. Ambient humidity, for instance, causes serie us disruptions ly creating clumps of particles tha are more cr less mobile. We know from
29、 common ex|erience that wet sands could be fairly cohesive whereas dry sands crumble apart readily. Due to the appearance cf the liquid bridge between particles, thi capillary force should be considered as an important force affecting the metien behaviors cf the granula system. Calculating the capil
30、lary force that keeps two wet spheres in contact is far from trivial. Severs methods have been proposed to avoid the difficulties associated with solving the Laplace-Young equatioi (Erie etal., 1971 and Lian etaL, 1993).The Couette granular flow is the simplest and suitable for fundamental research.
31、 Some examples cf thi related experimental studies include the investigations by Savage and Mckeown, 1933, Savage an： Sayed, 19S4, Hanes and Inman, 1985, Johnson and Jackson, 1987 and Wang and Campbell, 1992 an： Hsiau and Shieh (1399). Most earlier experiments measured only the average stresses from
32、 the transducer： and assumed th at the flew in the cell was a simple sheared flow. However, the assumption should not in a shear cell because cf the gravitational force as demonstrated in the study of Hsiau and Shieh (1399). Ii curearlier research (Hsiau and Yang, 2002 and Hsiau and Yang, 2005), we
33、started using the bi-directicns stress gages to measure the normal and shear stresses cf granular materials along the upper wall. Thi granular flews with different wall friction coefficients and solid fractions have been discussed in the earlie works. The selNiiffusicn coefTi ci ents cf g ran u I ar
34、 fl ows increase wi 比 th 已 increase in wall friction coefficients H owever, th ey decrease with the in crease in solid fractic n&. This paper focuses cn the effect cf the presen o cf moisture. We performed experiments in a shear cell device supplied by a constant extern al energy usin： granular mate
35、rials with five diffierent moi&ture contents. The present paper employed the imaging technclog; and particle tracking method to investigate the granular flow transport properties in the shear cell. Three bi directional stre&s gages were buried in the upper wall to measure the normal and shear stress
36、es cfgranula materials along the surface. The dependence of the measurements cn the moisture content will bi discussed.2. Experimental setupSoda lime beads with an average diameter, cf 3 mm (standard deviation of 0.04 mm and particle density 2Of 2490 kg/m )have been used as the experimental material
37、. Th ere are 5% identical red soda lime beads serving as tracer particles. The average solid fraction vet the test is calculated from the particle mass (1.5 kg in this paper) divided by the particle 汁巳%什 and th 日 test sectiqn volume. In th is study, we control the .0.c. Full-sizeimage(47K) L 4.avera
38、ge solid fractionv as 0.6285.A certaiL二出 testparticleswere weighed byanelectrcnic scale with an accuracy cf 0.001 g. The water and the particles were put into a sealed jar. The sealed jar was shaken to mix the water and particles. The wet particles were then put into the testsecticn cf the shear cel
39、l apparatus. We also measured the weight cf the sealed jar and the residual water, which coherences the sealed jar. The accurate values cf the masses cf water and particles, which were put in the shear cell, and the dimensionless liquid volume V could be calculated. The dimensionless liquid vclume,
40、V- ViV- IO, was used as a control parameter in th is study, where Kand * were the volumes cf water and the particles, respectively.The annular shear cell apparatus is schematically shown in Fig. 1. The experimental setup has a rotating bottom disk (cutside diameter: 45.00 cm; thickness cf 4.50 cm),
41、which is driven by a 3 hp AC-Motor. A tachometer was used to measure the rotation speed cf the bottom disk. In this study, the AC-Motor supplies a constant energy into the shear cell. The bottom disk is made cf plexiglass fcr visualization purposes. An annular treugh (inner diameter: 31.67 cm; cuter
42、 diameter: 4-2.02 cm) was cut in the bottom disk. The stationary upper disk was inserted into the trough after the wet granular materials were put in the test secticn. Adial indi cator is i n stalled in the apparatus to m easu re the adj ustabl e height Acf the test section.Three bi-directicnal stre
43、ss gages were installed along the upper wall to measure the normal and shear stresses, as shown in Fig. 1. The detecting surfaces cf the stress gages are in the same plane with the upper wall surface. The stress gage is based cn a simple ring dynamometric element, which is provided with semiconducto
44、r strain gages (Smid, 1980). The normal and shear stresses are realized by two different wiring systems cf the strain gages, and the normal and shear stresses can be measured simultaneously.The stress gage utilizes two different full bridge semiconductcr strain circuits to measure both stress compcn
45、ents simultaneously and independently. The diameter of the measuring surface cf the gage is 2.0 cm. The measuring surTace can be replaced with the same wall material as the upper surTace cf the test secticn. A stable voltage cf jp y is supplied to each stress gage by a DC power supply. When the stre
46、ss gages sense the normal and shear forces from the granular materialsn the vcItage signals are translated from the gage& to a personal computer through a data acquisition card (Advantech PCL-818HG). A series of calibration tests were carefully dene ale ng two directicns. The accuracy cf the pressur
47、e gages is over 99%. The normal and shear stresses are determined from the average signals obtained from the three stress gages 一In this study, the influence cf the moisture conditions cn the flow behavior is investigated. The friction coefficients between particles and walls, and among particles we
48、re measured by a commercial Jen ike shear tester. The detail method of operation is in the handbook of Jen ike (19&4). The Jenike shear tester could also measure the cohesion cf the wet particles. The researches Bilgili et al. (2Q04) had detail statement of the Jenike shear tester.The rotational spe
49、ed cf the bottom disk was controlled in a relatively value to reduce the centrifugal force so that the radial movements cf particles could be diminished. The granular flaw in the test section is assumed to be two-dimensional with streamwise (horizcntal) direction as the Jtaxisand transverse (vertical) direction as the yaxis
