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1.
离散单元法的计算参数和求解方法选择   总被引:8,自引:0,他引:8  
本文对离散单元法的一些基本问题进行了研究,给出了刚度计算公式,提出了两种新的用于求解静态问题的自适应阻尼,并以自由落体运动为例,探讨了中心差分法、  相似文献
2.
对花岗石进行了单颗粒金刚石磨削试验.通过测量磨削力对单颗金刚石磨粒所承受的平均法向力和切向力进行了研究,讨论了主轴转速和单颗磨粒最大切削厚度与磨削力的关系.利用离散单元方法(DEM)构造了2种不同的花岗石数字模型,在此基础上对单颗磨粒磨削进行了模拟分析,分析结果与试验结果基本吻合.  相似文献
3.
Micro-scale behavior of granular materials during cyclic loading   总被引:1,自引:0,他引:1  
This study presents the micro-scale behavior of granular materials under biaxial cyclic loading for differ- ent confining pressures using the two-dimensional (2D) discrete element method (DEM). Initially, 8450 ovals were generated in a rectangular frame without any overlap. Four dense samples having confining pressures of 15, 25, 50, and 100 kPa were prepared from the initially generated sparse sample. Numeri- cal simulations were performed under biaxial cyclic loading using these isotropically compressed dense samples. The numerical results depict stress-strain-dilatancy behavior that was similar to that observed in experimental studies. The relationship between the stress ratio and dilatancy rate is almost indepen- dent of confining pressures during loading but significantly dependent on the confining pressures during unloading. The evolution of the coordination number, effective coordination number and slip coordina- tion number depends on both the confining pressures and cyclic loading. The cyclic loading significantly affects the microtopology of the granular assembly. The contact fabric and the fabric-related anisotropy are reported, as well. A strong correlation between the stress ratio and the fabric related to contact normals is observed during cyclic loading, irrespective of confining pressures.  相似文献
4.
ROTATIONAL RESISTANCE AND SHEAR-INDUCED ANISOTROPY IN GRANULAR MEDIA   总被引:1,自引:0,他引:1  
This paper presents a micromechanical study on the behavior of granular materials under confined shear using a three-dimensional Discrete Element Method (DEM). We consider rotational resistance among spherical particles in the DEM code as an approximate way to account for the effect of particle shape. Under undrained shear, it is found rotational resistance may help to increase the shear strength of a granular system and to enhance its resistance to liquefaction. The evolution of internal structure and anisotropy in granular systems with different initial conditions depict a clear bimodal character which distinguishes two contact subnetworks. In the presence of rotational resistance, a good correlation is found between an analytical stress-force-fabric relation and the DEM results, in which the normal force anisotropy plays a dominant role. The unique properties of critical state and liquefaction state in relation to granular anisotropy are also explored and discussed.  相似文献
5.
三方程线性弹性-阻尼DEM模型及碰撞参数确定   总被引:1,自引:1,他引:0       下载免费PDF全文
建立了一种考虑法向接触力、切向接触力(含静滑动摩擦力及动滑动摩擦力)和力矩(含由切向力产生的力矩及静滚动摩擦力矩和动滚动摩擦力矩)的三方程线性弹性-阻尼离散单元模型,并将该模型应用到颗粒物料的三维数值模拟中,讨论了模型中几个重要碰撞参数--刚性系数、阻尼系数及摩擦系数的选择及其对计算结果的影响,同时也探讨了时间步长等计算参数对模拟结果的影响.为了验证算法和参数选择的正确性,本文对几个有代表性的颗粒系统进行了数值试验研究,并对计算结果进行了细致的分析,验证了新模型和参数选择的正确性.  相似文献
6.
Investigation of grain mass flow in a mixed flow dryer   总被引:1,自引:0,他引:1  
The numerical modeling of grain drying is a topic of great relevance to post-harvest engineering. The required type of drying process depends on the quantity of grain to be dried and the required quality of the grain. The choice of the drying system depends on the operating parameters of the drying process. The granular flow pattern of the material exerts a significant influence on the drying process. Post-harvest drying of grain is essential for better storage, handling, and processing. Therefore, it is important to know the material behavior that controls the particle flow patterns of grain in the drying equipment to guarantee the product quality and to optimize the drying process conditions. The discrete element method (DEM) was applied to investigate the particle flow pattern of wheat through a mixed-flow dryer (MFD) without airflow, and the findings were compared with experimental results in this work. The investigations were performed using dry wheat with 14 wb% moisture content.  相似文献
7.
The production of biomass pellets and briquettes from agroforestry residues has increased rapidly in recent years. The design of machines, equipment and the infrastructure necessary for the handling, trans port and storage of these products has been an engineering challenge since, when moving, biomass does not usually flow as easily as other granular materials. The discrete element method (DEM) provides a means of studying the handling and silo discharge behaviour of granular solids as well as the distribution of the pressures exerted by such materials in silos. However, the development of such models requires certain properties of the particles in question to be known. The present work experimentally determines the true density, Young's modulus of elasticity (axial and radial), the particleparticle restitution coeffi cient and the particlewall friction coefficientall variables that must be known in the construction of DEM modelsfor briquettes made from maize stalk, maize stalk plus pine wood chips, rice husk, vine shoots, raoe straw, cereal straw and sawdust olus cereal straw.  相似文献
8.
The discrete element method (DEM), developed by Cundall and 5track to solve geomecnamcai problems, is used to simulate the mechanical behavior of granules. According to the DEM, an individ ual granule can be modeled as a realistic mechanical system consisting of primary particles bonded by interaction forces. Cranulometric properties of the model material, zeolite 4A, have been measured to determine their macro properties. To investigate the compression behavior, a compression test was performed using a strength tester on single granules between two pistons. A modeled granule consisting of more than 22,000 primary particles was generated. The micro properties of the modeled granule have been precisely set to allow its macro properties to be equivalent to the macro properties of zeolite 4A granules. To calibrate the mechanical properties, diametrical compression was simulated using two rigid walls stressed at a constant stressing velocity, The force-displacement curve of the modeled granule at compression has been calibrated by the experimental curve of zeolite 4A.  相似文献
9.
Axial segreganon or a bidisperse mixture of particles in a long rotating drum is studied using the discrete element method. Simulation results show that particle interaction is responsible for axial segregation, the patterns of which are influenced by the end wall effect. Axial segregation patterns transform under competing influences of the end walls and the particle interaction forces. The two influential factors vary with various rotational speeds and end wall friction levels. The result is the transition of different axial segregation patterns: two large-particle bands at both ends, two small-particle bands at both ends, or a random segregation pattern where either a large-particle band or small-particle band may appear at either end.  相似文献
10.
Discrete element method (DEM) has been used to investigate the effects of particle elastic modulus and coefficient of inter-particle sliding friction on milling of mineral particles. An autogeneous mill of 600 mm diameter and 320 mm length with 14,500 particles has been selected for the simulation. Various mill performance parameters, for example, particle trajectories, collision frequency, collision energy and mill power have been evaluated to understand the effects of particle elastic modulus and inter-particle sliding friction during milling of particles. For the given model, it has been concluded that at high energy range, as the elastic modulus and particle sliding friction increase the energy dissipated among the particles increases. The collision frequency increases with the increase in elastic modulus, however, this trend is not clearly observed with increasing inter-particle sliding friction. The power draw of the mill increases with the increase in fraction of mill critical speed.  相似文献
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