Discrete Element Method Algorithm Research Articles

Simulation of an anti-sloshing technique using floating foams based on the moving particle semi-implicit method—The discrete element method algorithm

Simulation of an anti-sloshing technique using floating foams based on the moving particle semi-implicit method—The discrete element method algorithm

Multi-objective optimization of concrete pumping S-pipe based on DEM and NSGA-II algorithm

In the process of fresh concrete pumping, the S-pipe plays a crucial role in the pumping system. The impact and scratching of concrete aggregate on the wall of S-pipe will cause the wear of the wall and lessen its service life. The structural design of the pumping S-pipe typically relies on experience, and the cost for experiments is too expensive. In addition, the influence mechanism of structural parameters on S-pipe wear is still unclear. In view of this, to reduce the wear of S-pipe and investigate the influence of structural parameters on the wear of S-pipe, the structural parameters of S-pipe (curvature radius r1 and r2, horizontal dimension l3, and inclination angle θ) were optimised through discrete element numerical simulation combined with the non-dominated sorting genetic algorithm-II (NSGA-II) in this paper. Firstly, the wear coefficient was determined by friction and wear test. The discrete element method (DEM) model of pumping suction unit was simplified, and the S-pipe was parameterised. Secondly, sample points and their exact values of the optimization objectives were obtained by Latin hypercube sampling (LHS) plan and DEM simulations, respectively. From these, a Kriging surrogate model was constructed. Taking the average wear rate and the maximum wear of the S-pipe as the optimization objectives, a multi-objective optimization design was performed based on the NSGA-II and the Kriging models. After optimization, a series of Pareto optimal S-pipe models were obtained. Comparing the optimised model with the original model, the average wear rate and maximum wear amount of the S-pipe were reduced by 9% and 26%, respectively.

Multi-GPUs DEM algorithm and its application in the simulation of granular materials

The Discrete Element Method (DEM) is one of the most common numerical approach for modeling the physical and mechanical properties of granular materials. However, its computational efficiency can be a major bottleneck, which significantly hinders its application in engineering fields. To overcome this challenge, a multi-GPU framework with OpenMP has been developed. In this framework, the DEM particles in 3D space and their corresponding contact information are sorted in a given direction in the simulation, and each GPU device handles a subdomain of particles and relative contacts. Additionally, the contact information is densely arranged to minimize memory usage. To further enhance efficiency, sorting and packing algorithms for the contact information have been introduced. During calculating loop, the number of contacts on each device is monitored, and the spatial division of devices is adjusted to balance memory distribution. The efficacy of the multi-GPU algorithm is verified through a chute flow test. Using numerical results, the segregation process and mechanics of granular materials during sliding have been studied in detail. Furthermore, the simulations demonstrate that the developed multi-GPU algorithm greatly enhances computational efficiency and reduces memory usage per device.

Numerical Comparison of Contact Force Models in the Discrete Element Method

The discrete element method (DEM) is usually applied in analyzing the scientifical origin/evolution of the asteroids and the landing/sampling of the regolith. In order to manage the contact between the non-spherical granules, the Polygonal Contact Model (PCM) has been introduced into the DEM method. This paper applies four different contact force models in the newly-proposed DEM algorithm to analyze their difference and implication. The four contact force models include one linear model and three nonlinear models derived from the complete Mindlin–Deresiewicz equations. By considering the macroscopical results and calculation efficiency, the single-collision and multiple-collision cases are analyzed by comparing the four contact models. Specifically, the restitution coefficient, the angular velocity, the rebound angle, and the kinetic energy are applied as indicators for the single collision. The multiple-collision case is studied under the Brazil nut effect with ellipsoidal granules. Additionally, the softening feasibility is also discussed by decreasing the Young’s modulus of the material, mainly analyzing the outgoing results and the calculation efficiency.

An improved numerical method for lunar dust transport during electric curtain-traveling wave removal in the lunar environment

The law of dust removal by electric curtain in the lunar environment is considerably different from that in Earth's environment. This paper proposes an improved calculation method, which successfully simulates the kinematics of lunar dust transport during removal by electric curtain-traveling waves in the lunar environment. The numerical formula of the dielectrophoretic force component is derived based on a six-node triangular (T6) finite element method (FEM) in electromagnetics. A discrete element method (DEM) based on the Johnson–Kendall–Roberts soft-sphere model is chosen to simulate lunar dust particle transport under the action of the electric curtain dust removal system in the lunar environment. The validity, accuracy, and reliability of the present DEM algorithm are verified by comparing the experimental and numerical results. The final dust removal rate is positively correlated with frequency when the surface energy between the particles and insulating film is γf≥0.0075 J/m2. The final dust removal rate is negatively related to the surface energy between the particles and the film but positively related to the applied voltage and the charge of the particles. This research is of great significance to the mitigation of the lunar dust pollution problem that the crewed lunar exploration project will face in the future.

Algorithm design and the development of a discrete element method for simulating particulate flow and heat transfer

AbstractAn algorithm using the discrete element method (DEM) for simulating the particulate behaviour of flow and heat transfer is developed and described, the reasonable hypothesis and the ingenious design of which have been presented in detail. The organizational structure of the developed algorithm contains an efficient method for determining particle collisions, the status analysis for each particle and the particulate-kinematics analysis during the time step. The reasonability and correctness of the developed DEM algorithm are validated by laboratory experiments: the discharge process of glass beads from a silo; and heating of metal alloy particles in a calciner. Afterwards, a group of validated mechanics parameter values for coal and sand have been tested and verified in the article, preparing for the simulation of the pyrolysis process in a downer or screw reactor in subsequent research projects.

The very hard and the very soft: Modeling bio-inspired scaled skins using the discrete element method

Natural protective systems are attracting an increasing amount of attention for their ability to provide simultaneous flexibility and puncture resistance by combining hard and soft materials in mechanically efficient ways. In typical flexible natural armors, a continuous layer of soft material is either covered or embedded with segmented hard scales. The interaction between the hard scales and the softer surrounding materials give rise to unusual and attractive mechanisms which are not fully understood to this day. Here we propose and validate the discrete-element method (DEM) to capture the mechanics of stiff scales on soft substrates including scale-substrate elastic deformations, scale-scale interaction through the substrate, and direct scale-scale interaction by contact. We considered two configurations: (i) hard scales on soft substrates to capture scale tilting and penetration resistance, and (ii) hard scales on soft membranes to study flexural compliance. The computational efficiency of the DEM algorithm allowed for large parametric studies with many combinations of aspect ratio, slant angle, and gap size to identify the best designs in terms of resistance to unstable tilting, coverage, penetration resistance, and flexural compliance. DEM is a promising tool for the design and optimization of fish-skin-like protective structures, also providing new insights into the synergistic role of the hard scales and the soft substrate.

Fast GPU simulation of reinforced concrete at the scale of reinforcement ribs by the discrete element method

The paper presents the development of the GPU-based discrete element method (DEM) code for simulating damage and fracture of cohesive solids with application to reinforced concrete at the scale of reinforcement ribs. The solid volume of concrete and steel is modelled by bonded spherical particles. Very fine discretization, containing more than million particles, is applied to describe the 3D reinforcement bar geometry at the scale of ribs and to investigate cracking behaviour of concrete near the reinforcement bar. The numerical model is validated by using experimental results of the double pull-out test. Influence of the discretization scale to the numerical solution is evaluated by using the reinforcement strain profiles and the cracking patterns. The developed GPU-based DEM algorithm efficiently handles interaction of particles, does not require any atomic operation and allows performing fast damage and fracture simulations with large number of particles. The performance measured on GPU is compared with that attained on different CPUs for varying number of particles. The high value of the Cundall number (particle number multiplied by time steps computed per second) equal to 4.3E+07 is measured on NVIDIA® Tesla™ P100 GPU in the case of 1858560 particles.

The discrete element method with deformable particles

SummaryThis work presents a new original formulation of the discrete element method (DEM) with deformable cylindrical particles. Uniform stress and strain fields are assumed to be induced in the particles under the action of contact forces. Particle deformation obtained by strain integration is taken into account in the evaluation of interparticle contact forces. The deformability of a particle yields a nonlocal contact model, it leads to the formation of new contacts, it changes the distribution of contact forces in the particle assembly, and it affects the macroscopic response of the particulate material. A numerical algorithm for the deformable DEM (DDEM) has been developed and implemented in the DEM program DEMPack. The new formulation implies only small modifications of the standard DEM algorithm. The DDEM algorithm has been verified on simple examples of an unconfined uniaxial compression of a rectangular specimen discretized with regularly spaced equal bonded particles and a square specimen represented with an irregular configuration of nonuniform‐sized bonded particles. The numerical results have been verified by a comparison with equivalent finite element method results and available analytical solutions. The micro‐macro relationships for elastic parameters have been obtained. The results have proved to have enhanced the modeling capabilities of the DDEM with respect to the standard DEM.

The effects of adhesive forces on the collision behavior of polyolefin particles

Abstract The collision behavior of particles in a polymerization reactor was simulated with the help of the Discrete Element Method (DEM). Analysis of the magnitudes of the potential forces acting on particles in a fluidized bed shows that the dominant role affecting the collision behavior of polymer particles is represented by adhesive forces causing the formation of liquid bridges and reflecting the entanglement of polymer chains. However, these forces do not act instantaneously. Therefore, the time duration of particle collisions was evaluated and subsequently compared to the characteristic times of liquid bridge formation and chain entanglement. This comparison implies that the collision lasts long enough for adhesive forces to apply. Two approaches are presented and compared which introduce these forces into the DEM algorithm. The first approach applies to any visco-elastic model (e.g. the Maxwell or Kelvin model) for force interactions between microelements from different particles; the second relies on special adhesive inter-particle connections, providing a gradual increase in adhesive force according to the corresponding dynamics. The decrease in kinetic energy of particles after collision can be evaluated by means of an experimentally measurable restitution coefficient relating the particle velocities before and after collision.

Parallel computing of discrete element method on multi-core processors

This paper describes parallel simulation techniques for the discrete element method (DEM) on multi-core processors. Recently, multi-core CPU and GPU processors have attracted much attention in accelerating computer simulations in various fields. We propose a new algorithm for multi-thread parallel computation of DEM, which makes effective use of the available memory and accelerates the computation. This study shows that memory usage is drastically reduced by using this algorithm. To show the practical use of DEM in industry, a large-scale powder system is simulated with a complicated drive unit. We compared the performance of the simulation between the latest GPU and CPU processors with optimized programs for each processor. The results show that the difference in performance is not substantial when using either GPUs or CPUs with a multi-thread parallel algorithm. In addition, DEM algorithm is shown to have high scalability in a multi-thread parallel computation on a CPU.

Applications of the discrete element method in mechanical engineering

Compared to other fields of engineering, in mechanical engineering, the Discrete Element Method (DEM) is not yet a well known method. Nevertheless, there is a variety of simulation problems where the method has obvious advantages due to its meshless nature. For problems where several free bodies can collide and break after having been largely deformed, the DEM is the method of choice. Neighborhood search and collision detection between bodies as well as the separation of large solids into smaller particles are naturally incorporated in the method. The main DEM algorithm consists of a relatively simple loop that basically contains the three substeps contact detection, force computation and integration. However, there exists a large variety of different algorithms to choose the substeps to compose the optimal method for a given problem. In this contribution, we describe the dynamics of particle systems together with appropriate numerical integration schemes and give an overview over different types of particle interactions that can be composed to adapt the method to fit to a given simulation problem. Surface triangulations are used to model complicated, non-convex bodies in contact with particle systems. The capabilities of the method are finally demonstrated by means of application examples.

Cell optimization for fast contact detection in the discrete element method algorithm

The objective of this paper is to find out a rule of cell optimization for fast contact detection in the discrete element method (DEM) algorithm. The contact detection process was executed by using the conventional cell model or distinct cell model (DCM) under several particle conditions having different particle size ratio and volume ratio, and its time was measured. The conventional cell model is suitable for the conditions that particle size ratio, d large/ d small, is small and its volume ratio, V small/ V 0, is also small. The optimum cell condition of the conventional cell model is that the mean number of particle in a cell is 1.0–5.0, regardless of the particle size ratio and its volume ratio. Contact detection using DCM, which has several grids for different sized particles, is much faster than that of the conventional model when particles have a large size ratio. The size of the larger cell does not affect the contact detection speed; however, the size of the smaller cell is important for the fast contact detection and its size is determined to be about 3.0 times the particle radius. Therefore, the optimum cell condition is estimated from the particle size ratio and its volume ratio, and a large-scale DEM will be possible.

DISCRETE ELEMENT METHOD AND ITS APPLICATION TO THE ANALYSIS OF PENETRATION INTO GRANULAR MEDIA

Application of discrete element method (DEM) to keel penetration in granular media is investigated. The basic relations for visco‐elastic granular media composed of spherical particles are presented, together with 5th order Gear predictor‐corrector scheme for time‐integration. The background version of DEM and numerical time integration algorithm are developed and implemented into DEMMAT code. The implementation of time‐integration algorithm is verified by simple tests concerning particle‐particle, particle‐wall interactions, for which analytical expressions exist. By limiting the size of the media domain, the three‐dimensional problem is reduced to particular case presented as two‐dimensional domain of spherical particles. The variation of keel reaction and distribution of the particle forces due to different material properties are investigated

Discrete element method and its application to the analysis of penetration into granular media

Application of discrete element method (DEM) to keel penetration in granular media is investigated. The basic relations for visco‐elastic granular media composed of spherical particles are presented, together with 5th order Gear predictor‐corrector scheme for time‐integration. The background version of DEM and numerical time integration algorithm are developed and implemented into DEMMAT code. The implementation of time‐integration algorithm is verified by simple tests concerning particle‐particle, particle‐wall interactions, for which analytical expressions exist. By limiting the size of the media domain, the three‐dimensional problem is reduced to particular case presented as two‐dimensional domain of spherical particles. The variation of keel reaction and distribution of the particle forces due to different material properties are investigated. First Published Online: 14 Oct 2010

Micro‐mechanical simulation of geotechnical problems using massively parallel computers

AbstractThis paper demonstrates that the architecture of a massively parallel computer can be adapted for micro‐mechanical simulations of a Geotechnical problem. The Discrete Element Method was used on a massively parallel supercomputer to simulate Geotechnical boundary value problems. For the demonstration, a triaxial test was simulated using an algorithm titled ‘TRUBAL for Parallel Machines (TPM)’ based on the discrete element method (DEM). In this trial demonstration, the inherent parallelism within DEM algorithm is shown. Then a comparison is made between the parallel algorithm (TPM) and the serial algorithm (TRUBAL) to show the benefits of this research. TPM showed substantial improvement in performance with increasing number of processors when compared with TRUBAL using single processor. Copyright © 2003 John Wiley & Sons, Ltd.

A robust algorithm for ellipse-based discrete element modelling of granular materials

With recent research indicating the importance of the rolling mechanism of deformation in granular systems consisting of perfectly round particles, it has become popular to use ellipse-shaped particles in the Discrete Element Method ( DEM) numerical model. Inherent in this technique is the need for accurately computing ellipse to ellipse intersection, in order to properly detect contact formation and compute relative contact velocities. However, the commonly used algorithms for computing ellipse-ellipse intersection are generally poorly conditioned and can be inaccurate. An alternate method for computing ellipse-ellipse intersection is developed and presented which results in a well-conditioned, stable and accurate contact detection method. These modification are incorporated into the general DEM algorithm.