scholarly journals Multisphere Representation of Convex Polyhedral Particles for DEM Simulation

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Qiang Zhang ◽  
Chaojun Jia ◽  
Jun Yu ◽  
Jiawen Zhou
Keyword(s):  
Particle Surface ◽  
Good Representation ◽  
Dem Simulation ◽  
Convex Polyhedral ◽  
Polyhedral Particles ◽  
Complex Shapes ◽  
Mass Properties ◽  
Polyhedral Particle ◽  
A Current ◽  
2D To 3D

The representation of particles of complex shapes is one of the key challenges of numerical simulations based on the discrete element method (DEM). A novel algorithm has been developed by the authors to accurately represent 2D arbitrary particles for DEM modelling. In this paper, the algorithm is extended from 2D to 3D to model convex polyhedral particles based on multisphere methods, which includes three steps: the placement of spheres at the corners, along the edges, and on the facets in sequence. To give a good representation of a polyhedral particle, the spheres are placed tangent to the particle surface in each step. All spheres placed in the three steps are clumped together into a clump in DEM. In addition, the mass properties of the clump are determined based on the corresponding polyhedral particle to obtain accurate simulation results. Finally, an example is used to validate the robust and automatic performance of the algorithm in generating a sphere clump model for an assembly of polyhedral particles. A current FORTRAN version of the algorithm is available by contacting the authors.

scholarly journals CFD-DEM Simulation of Spouted Bed Dynamics under High Temperature with an Adhesive Model

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2276
Author(s):  
Zhao Chen ◽  
Lin Jiang ◽  
Mofan Qiu ◽  
Meng Chen ◽  
Rongzheng Liu ◽  
...  
Keyword(s):  
High Temperature ◽  
Particle Surface ◽  
Particle Collision ◽  
Gas Velocity ◽  
Spouted Bed ◽  
Dem Simulation ◽  
Linear Spring ◽  
Adhesion Model ◽  
Adhesive Model ◽  
Damping Model

Particle adhesion is of great importance to coating processes due to its effect on fluidization. Currently, Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) has become a powerful tool for the study of multiphase flows. Various contact force models have also been proposed. However, particle dynamics in high temperature will be changed with particle surface properties changing. In view of this, an adhesion model is developed based on approaching-loading-unloading-detaching idea and particle surface change under high temperature in this paper. Analyses of the adhesion model are given through two particle collision process and validated by experiment. Effects of inlet gas velocity and adhesion intensity on spouted bed dynamics are investigated. It is concluded that fluidization cycle will be accelerated by adhesion, and intensity of fluidization will be marginally enhanced by slight adhesion. Within a certain range, increasing inlet gas velocity will lead to strong intensity of particle motion. A parameter sensitivity comparison of linear spring-damping model and Hertz-Mindlin Model is given, which shows in case of small overlaps, forces calculated by both models have little distinction, diametrically opposed to that of large overlaps.

The Research on the DEM Simulation of the Railway Ballast Tamping Process

2013 ◽  
Vol 724-725 ◽  
pp. 1723-1726
Author(s):  
Xue Jun Wang ◽  
Bin Hua ◽  
Bin Hu ◽  
Yi Lin Chi ◽  
Yan Fang Ding
Keyword(s):  
High Speed ◽  
Retaining Wall ◽  
Sphere Packing ◽  
Contact Dynamics ◽  
Railway Ballast ◽  
Dem Simulation ◽  
Polyhedral Particles ◽  
Long Time ◽  
Ballast Track ◽  
Packing Method

Ballast degradation and unrecoverable deformation are emerged on the railway ballast track under the loads of high-speed and heavy loading locomotive. With the change of tamping frequency, a better understanding of the physics of compactness degree is important for long-time stability of ballast. This paper presented a numerical investigation of the bulk materials dynamics and the transient impaction of a system of irregular polyhedral particles confined with a rectangular box with a retaining wall subjected to cyclic tamping loading. Sphere packing method was being used in this study to simulate typical full-sized ballast particles. This paper aimed to establish firm-soft coupling particle-flow tamping operation simulation numerical model based on contact dynamics theory. This study checked the validity of the model while different tamping working conditions and out-loads was being implemented. The study shows that discrete element method (DEM) is an efficient method to reveal the rearrangement rule of railway ballast after the process of tamping operation.

scholarly journals DEM Simulation of Binary Blend Mixing of Cohesive Particles in a High Intensity Vibration System

2021 ◽  
Author(s):  
Kai Zheng ◽  
Kuriakose Kunnath ◽  
Rajesh Dave
Keyword(s):  
Surface Energy ◽  
High Intensity ◽  
Mixing Time ◽  
Particle Surface ◽  
Bond Number ◽  
Vibration System ◽  
Mixing Rate ◽  
Binary Blend ◽  
Dem Simulation ◽  
T Values

The effects of processing intensity, time and particle surface energy on mixing of binary cohesive blends (size ratio 1:2, fine concentration at 10 %) in high intensity vibration system were investigated via DEM simulations. Results show that both increasing processing intensity from 50 to 100 Gs and reducing surface energy from 50 to 0.5 J/m2 lead to a faster mixing rate. Mixing Bond number (〖Bo〗_m) was introduced to capture the effective mixing rate, Rm; higher 〖Bo〗_m corresponding to lower mixing rate. The coefficient of variation, Cv, formed the basis for the mixing quality and Rm, while the mixing action is quantified by the product of Rm and mixing time (Pr,t). Simulation results show that Cv values drop initially, and then rise with Pr,t. Hence, low Pr,t indicates inadequate mixing intensity, while high Pr,t most likely indicates mixture segregation, and therefore too high or too low Pr,t values should be avoided.

scholarly journals CFD-DEM Simulation of Fluidization of Polyhedral Particles in a Fluidized Bed

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4939
Author(s):  
Zihan Liu ◽  
Huaqing Ma ◽  
Yongzhi Zhao
Keyword(s):  
Fluidized Bed ◽  
Chemical Engineering ◽  
Spherical Particles ◽  
Gas Velocity ◽  
Reasonable Accuracy ◽  
Dem Simulation ◽  
Polyhedral Particles ◽  
Common Process ◽  
Dem Model

Fluidization of non-spherical particles is a common process in energy industries and chemical engineering. Understanding the fluidization of non-spherical particles is important to guide relevant processes. There already have been numerous studies which investigate the behaviors of different non-spherical particles during fluidization, but the investigations of the fluidization of polyhedral particles do not receive much attention. In this study, the investigation of the fluidization of polyhedral particles described by the polyhedron approach is conducted with a numerical CFD-DEM method. Experiments of the fluidization of three kinds of polyhedral particles are conducted under the same condition with corresponding simulations to validate the accuracy of our CFD-DEM model. The results indicate that our CFD-DEM model with the polyhedron approach can predict the behaviors of polyhedral particles with reasonable accuracy. Fluidization behaviors of different polyhedral particles are also investigated in this study. Compared to spherical particles, the motion of polyhedral particles is stronger, and mixing degree is higher under the same fluidization gas velocity.

scholarly journals Pros and Cons of CAD

2006 ◽  
Vol 128 (09) ◽  
pp. 38-40
Author(s):  
Jean Thilmany
Keyword(s):  
Computer Aided Design ◽  
Digital Design ◽  
Design Engineers ◽  
Design Changes ◽  
Complex Shapes ◽  
Current Design ◽  
Pros And Cons ◽  
Aided Design ◽  
Straight Lines ◽  
A Current

This paper describes the pros and cons of computer-aided design (CAD). CAD packages lack features to easily make the intuitive, complex shapes so pervasive in modern products. It is much easier with CAD to create a part with square features and rectangles and straight lines and round things. Even in a current design project, engineers will sculpt the design in clay, scan it with a digitizer, bring it back into the CAD package, then change it into a solid model and refine that. One of the biggest criticisms of CAD systems is that digital design is slower than sketching and that inhibits the brainstorming process. Today’s systems are not equipped to let engineers play with a design. Engineers start with a basic design and they can change parameters as they draw, but cannot change complete concepts midstream or cut and paste ideas between designs. Most CAD packages include features that track design changes so engineers working collaboratively can see what's been changed, where, when, and why.

Transmission Electron Diffraction Analysis by Computer

1970 ◽  
Vol 28 ◽  
pp. 40-41
Author(s):  
R.A. Ploc ◽  
G.H. Keech
Keyword(s):  
Electron Diffraction ◽  
Input Data ◽  
Reciprocal Lattice ◽  
Computer Programme ◽  
Transmission Electron Diffraction ◽  
Usual Procedure ◽  
Transmission Electron ◽  
Complex Shapes ◽  
Computer Input ◽  
Diffraction Effects

An unambiguous analysis of transmission electron diffraction effects requires two samplings of the reciprocal lattice (RL). However, extracting definitive information from the patterns is difficult even for a general orthorhombic case. The usual procedure has been to deduce the approximate variables controlling the formation of the patterns from qualitative observations. Our present purpose is to illustrate two applications of a computer programme written for the analysis of transmission, selected area diffraction (SAD) patterns; the studies of RL spot shapes and epitaxy.When a specimen contains fine structure the RL spots become complex shapes with extensions in one or more directions. If the number and directions of these extensions can be estimated from an SAD pattern the exact spot shape can be determined by a series of refinements of the computer input data.

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