Effects of Material Properties on Granular Flow in a Silo Using DEM Simulation

In order to test the effect of material properties on flowability of particulate materials, discharge procedures of spherical particles within a flat-bottomed model silo with three sets of material properties, i.e., soft and hard without adhesion and adhesive hard, were simulated using the Discrete Element Method. For each system, three particles on the center line were selected and their instant vertical velocity components were traced. In addition, both discharge and the rate were recorded throughout the procedure. The predicted results show that, for both the systems without adhesion, though the soft has a material modulus only 1/1000 of the hard, there are no significant differences in f low pattern and discharge rate. This suggests that a soft system can be used to predict the behavior of a hard one to save CPU time in a gravity-driven granular flow. On the other hand, comparison between both hard systems shows that adhesion can significantly reduce the flowability in granular flow. By analyzing the velocity plot for the traced particles, free fall was clearly detected above the decompression zone, indicating the motion of a particle in a granular flow can be resolved as free fall together with the movement due to particle collision. In addition, select dynamic behavior related to the kinetic fluctuations affecting flow was observed. discrete element method silo granule flow particulate material     

DFT的装配车间生产物流策略仿真与研究

针对某汽车部件的实际装配生产,运用离散事件仿真的方法对基于需求流动技术(DFT)的装配生产物流策略进行了研究.在分析该汽车部件装配生产流程的基础上,确定eM-Plant仿真软件中的建模对象与装配生产系统中实体对象的对应关系,使用面向对象的方法建立了相应的离散事件仿真模型.在模型中分别实施基于推式生产方式的物流策略和基于DFT的物流策略,以该汽车部件的平均日产量为绩效指标,比较了两种物流策略对装配生产的影响.     

Discrete Element Simulation of Granular Lost Circulation Material Plugging a Fracture

Granular lost circulation material (LCM) is the most commonly used material to reduce drilling fluid loss in drilling industry. Although, the plugging role of granular LCM in fracture is widely accepted by drilling engineers, the control and optimization are still limited due to the lack of the fundamental understanding of the LCM plugging process. This article presents a numerical study of the granular LCM plugging behavior at a particle scale by means of discrete element method (DEM). The effects of the particle shape, size distribution, and concentration on the fracture-plugging performance are studied by a series of controlled numerical experiments. The results are analyzed in terms of plugging depth and time spent before plugging. They are useful to the development of a better understanding and the control of granular LCM plugging process in fractures.     

筒仓内散体静态屈服的研究

认为仓贮散体为服从Mohr—Coulomb屈服准则的理想弹塑性材料 ,散体与仓壁之间的摩擦属于Coulomb摩擦接触问题。就刚性筒仓讨论研究了静态时影响散体进入屈服状态的有关因素 ,提出了一种由散体临界内摩擦角来判断静态散体是否进入屈服状态的方法 ,并用有限元法做了数值模拟     

粉粒体斜面慢速流的三维颗粒流程序仿真

为了研究粉粒体斜面慢速流的机理,在分析粉体流动性影响因素的基础上,应用颗粒离散元法三维颗粒流程序建立斜槽仿真模型并进行三维流动过程模拟,观察颗粒在斜槽内的流动情况及单个颗粒在流动过程中的受力、位移和速度,测量颗粒内部力场和颗粒速度场变化。结果表明,随着斜槽倾角的增大,粉粒流的速度呈连续、不均匀增大,堆积颗粒之间的接触力与不平衡力显著增大,并对流速产生一定的影响。     

粘结颗粒材料双轴试验的数值模拟研究

利用离散元法数值模拟了5组试件的双轴试验,得到了粒径对弹性模量、泊松比、强度和裂缝初始应力的影响,分析了20MPa围压条件下粒径与弹性模量、泊松比、强度和裂缝初始应力的关系,以及6种围压与裂缝初始应力的关系,给出了5组试件荷载作用后颗粒间的接触力和颗粒位移矢量,从细观角度阐释了荷载作用下颗粒的运动模式。模拟结果表明,随着粒径的增大,弹性模量、强度和裂缝初始应力均呈减小的趋势;随着围压的增大,各粒径范围试件的裂缝初始应力呈增加的趋势,并且粒径越大的试件最大接触力和最大位移越大。     

颗粒流的离散元法模拟及其进展

颗粒流问题是众多工农业生产领域中的常见问题,然而人们至今对颗粒流机理认识不深。目前一种基于离散元的数值模拟方法被用以模拟和分析颗粒流问题,研究实践表明该方法是散体力学分析的一种有效的工具。本文介绍了颗粒流研究的背景以及离散元法的发展过程,概述了颗粒流动力学研究的动理论模型和摩擦塑性模型,综述了离散元法的理论和各种颗粒作用模型及其在粉体工程领域的应用,讨论了颗粒流研究的主要困难和离散元法发展中亟待解决的问题。     

Effect of Passive Inserts on the Granular Flow from Silos Using Numerical Solutions

Experimental investigations indicate that placing a passive insert in a silo is a method for influencing the discharging flow pattern. These inserts have consisted of an inverted cone, a cone-in-cone, and a double cone. However, providing unequivocal guidelines on where those inserts should be placed for an optimum effect has not been possible experimentally. A numerical approach was therefore developed to predict material flow in the presence of such inserts in silos. Simulation results showed that all these inserts could make a funnel-flow silo perform in mass flow under certain circumstances if positioned correctly. The inserts should be installed at higher levels close to the transition rather than at lower positions close to the outlet, especially with the cone-in-cone insert and the inverted inserts; the maximum diameter of the inverted cone and the double cone should, however, be below the transition of the silo. Among the three inserts investigated, the double cone appeared to be the best, although even with this insert mass flow could not always be obtained if the hopper had an inclination angle as large as 45°. In such a situation, more simulations revealed that the extension of the lower part of the double cone had the potential to improve the flow pattern in the hopper. This potential could be utilized by a combination of extending the lower cone of the double cone insert and reducing the friction between the material and the hopper wall. To ensure improvement, further simulations illustrated that a ratio of 2:7 between the maximum diameter of the insert and the diameter of the silo was also crucial for the best effect.     

Effect of Passive Inserts on the Granular Flow from Silos Using Numerical Solutions

Experimental investigations indicate that placing a passive insert in a silo is a method for influencing the discharging flow pattern. These inserts have consisted of an inverted cone, a cone-in-cone, and a double cone. However, providing unequivocal guidelines on where those inserts should be placed for an optimum effect has not been possible experimentally. A numerical approach was therefore developed to predict material flow in the presence of such inserts in silos. Simulation results showed that all these inserts could make a funnel-flow silo perform in mass flow under certain circumstances if positioned correctly. The inserts should be installed at higher levels close to the transition rather than at lower positions close to the outlet, especially with the cone-in-cone insert and the inverted inserts; the maximum diameter of the inverted cone and the double cone should, however, be below the transition of the silo. Among the three inserts investigated, the double cone appeared to be the best, although even with this insert mass flow could not always be obtained if the hopper had an inclination angle as large as 45°. In such a situation, more simulations revealed that the extension of the lower part of the double cone had the potential to improve the flow pattern in the hopper. This potential could be utilized by a combination of extending the lower cone of the double cone insert and reducing the friction between the material and the hopper wall. To ensure improvement, further simulations illustrated that a ratio of 2:7 between the maximum diameter of the insert and the diameter of the silo was also crucial for the best effect.     

Development of Load on a Hopper During Filling with Granular Material

A finite element analysis using ABAQUS was carried out to investigate the loads on a hopper during filling. Simple geometries were chosen, and meshes were designed to represent the granular material and the hopper. An interaction between the contacting surfaces of the granular material and the hopper wall was modeled through a constitutive model of Coulomb friction. In order to simulate a filling process, the meshes representing the granular material and the interaction between the granular material and the wall of the hopper were suspended at the beginning of the analysis. They were then incrementally reactivated in a designed sequence. Such an operation of reactivation of meshes and interactions after initial suspension was assumed to represent the filling process. With this assumption, the development of loads exerted from the granular material on the hopper wall was investigated. Several material constitutive laws widely used for granular materials were adopted and implemented in parallel analyses. An analysis of the so-called "switch-on" filling was carried out as well. It was found that the maximum load was not at the outlet, even from the very beginning of the filling. The maximum load increased and moved upwards along the hopper wall with the development of filling and was located at a position around two-fifths of the length of the hopper wall from the outlet when the filling was finished. It was also shown that the different material models did not have obvious effects on the trend and magnitude of loads under the current investigation conditions. The switch-on filling method reduced the magnitude of the loads on the lower part of the hopper wall and increased it in the upper part. The maximum load using the switch-on filling method was smaller than that when filling layer by layer and was slightly shifted upwards.     

Frequency Methods Applied to the Characterization of the Thermophysical Properties of a Granular Material with a Cylindrical Probe

In many fields, such as in the agri-food industry or in the building industry, it is important to be able to monitor the thermophysical properties of granular materials. Regular thermal probes allow for the determination of one or several thermophysical factors. The success of the method used depends in part on the nature of the signal sent, on the type of physical model applied and eventually on the type of probe used and its implantation in the material. Although efficacious for most applications, regular thermal probes do present some limitations. It is the case, for example, when one has to know precisely the thermal contact resistance or the nature of the signal sent. In this article is presented a characterization method based on thermal impedance formalism. This method allows for the determination of the thermal conductivity, the thermal diffusivity, and the contact thermal resistance in one single test. The application of this method requires the use of a specific probe developed to enable measurement of heat flux and temperature at the interface of the probe and the studied material. Its practical application is presented for dry sand.     

Development of Load on a Hopper During Filling with Granular Material

A finite element analysis using ABAQUS was carried out to investigate the loads on a hopper during filling. Simple geometries were chosen, and meshes were designed to represent the granular material and the hopper. An interaction between the contacting surfaces of the granular material and the hopper wall was modeled through a constitutive model of Coulomb friction. In order to simulate a filling process, the meshes representing the granular material and the interaction between the granular material and the wall of the hopper were suspended at the beginning of the analysis. They were then incrementally reactivated in a designed sequence. Such an operation of reactivation of meshes and interactions after initial suspension was assumed to represent the filling process. With this assumption, the development of loads exerted from the granular material on the hopper wall was investigated. Several material constitutive laws widely used for granular materials were adopted and implemented in parallel analyses. An analysis of the so-called "switch-on" filling was carried out as well. It was found that the maximum load was not at the outlet, even from the very beginning of the filling. The maximum load increased and moved upwards along the hopper wall with the development of filling and was located at a position around two-fifths of the length of the hopper wall from the outlet when the filling was finished. It was also shown that the different material models did not have obvious effects on the trend and magnitude of loads under the current investigation conditions. The switch-on filling method reduced the magnitude of the loads on the lower part of the hopper wall and increased it in the upper part. The maximum load using the switch-on filling method was smaller than that when filling layer by layer and was slightly shifted upwards.     

基于遗传算法的材料特性参数的辨识

为了得到一个相对精确的材料特性参数,引入遗传算法(GA)到有限元模型更新的应用中,以一个简单的转轴模型为例,以模态实验得到的固有频率数据和模型输出数据之间的误差建立遗传算法的目标函数,以材料的特性参数为更新参数,对该转轴的有限元模型进行了修正,辨识出了材料的特性参数.然后通过比较由修正后的模型计算得到的频率响应函数(FRF)和模态实验得到的FRF,检验了基于GA辨识的有效性.最后比较了模型计算得到的固有频率、FRF和模态实验,结果表明吻合性非常好.     

A General Simulation Programme for Material Flow in Batch Chemical Plants

Techniques for the simulation of material flow through multi-stage full-scale batch chemical plants are described and the need for general computer programmes is argued. An outline is given of a general simulation programme written in ‘Mercury’ auto-code, which is based on the reduction of interstage pipe networks to a small number of “common mains.”     

筒仓卸料时超压与变形分析

针对筒仓卸料时侧压增大对仓壁变形的影响,运用离散元法模拟煤炭颗粒在筒仓中的静储和卸料过程,导出的离散元仿真数据结合筒仓模型进行有限元分析;根据离散元分析可以得出卸料时筒仓侧压及增压比的变化规律,从有限元计算结果得到卸料时径向变形及位移比的分布。结果表明:卸料时增压比与径向位移比变化基本一致,增压比与料仓内颗粒流动速度存在一定的线性关系;静、动态时侧压峰值出现在直筒壁与漏斗壁过渡处靠近直筒壁一侧,侧压增压比在筒仓中上部达到最大值,必须强化过渡处和筒仓上部的结构设计。     

On the Choking of a Gas Flow by a Granular Bed

Journal of Engineering Physics and Thermophysics - A study has been made of the effect of choking of a gas flow by isothermal and heat-releasing granular beds under the conditions of a...     

拓扑互锁复合材料在过水面防护中的试验研究

从拓扑互锁的理论出发,设计了玻璃钢拓扑互锁复合材料。为了验证材料的抗冲刷及整体性能,设计的冲刷试验,在10m/s的流速作用下,对其进行了抗冲试验,试验结果表明,设计的玻璃钢拓扑互锁复合材料在抗冲及整体连接方面具有较好的性能,满足目前的抗冲要求,该材料的优点是可以拆卸重组,重复使用。