Coupling Discrete Element Method Research Articles

Simulation of grain growth and sintering process by combined phase-field/discrete-element method

A combination of the phase-field method (PFM) and the discrete-element method (DEM) is proposed to simulate simultaneously the movement of particles and the grain growth behavior in powder compacts during sintering. To take the mutual interaction into consideration, a precise way of coupling PFM and DEM is developed based on a sintering model. The sintering forces and the contact areas in linked particles are evaluated from the phase field variables, computed in PFM and introduced into the calculation of the rigid motion of particles in DEM. Before treating actual problems as the application, the sintering process of two particles is simulated first for fundamental verification, including the case with different particle sizes. It is confirmed that the changes in the neck size and the center-to-center distance between particles are reproduced well using the proposed method. Secondly, the simulation of microstructural evolution during sintering is implemented for some small clusters of particles. The internal spatial structure and the outer shape of the clusters vary with the shrinkage deformation as well as the grain boundary migration in sintering. The proposed method of simulating the microstructural evolution in sintering bodies may be effective in the computer-aided design of microscale components or thin films produced by powder processing.

Three-Dimensional Modeling of Gas–Solid Motion in a Slot-Rectangular Spouted Bed with the Parallel Framework of the Computational Fluid Dynamics–Discrete Element Method Coupling Approach

The gas–solid flow in a three-dimensional slot-rectangular spouted bed is numerically investigated under the parallel framework of the computational fluid dynamics–discrete element method coupling approach. The fluid phase is solved with the k–ε turbulence model at the computational grid level, while the solid phase is tracked individually with the discrete element method at the particle scale. Millions of particles are calculated using a total number of 112 CPUs in a cluster. The predicted pressure drop profiles and the minimum spouting velocities of the calculations under different bed heights agree well with the experimental data. The startup procedure and the solid flow pattern are identified. Then, wall effects on the distribution properties of the gas–solid hydrodynamics are explored. Moreover, the interaction between spout and annulus and the effects of the superficial velocity and bed height on the bed hydrodynamics are discussed. The results show that a larger pressure drop appears in the system with a higher bed height. A bubble with its shape influenced by the slot geometry is formed in the startup procedure. Moreover, the bed hydrodynamics show a strong 3-D behavior along the depth direction. Large vertical solid flux mainly concentrates in the central region of the spout. The spout–annulus interface is dramatically influenced by the slot shape and shows different evolutionary tendencies in the different directions, and this influence becomes weaker along the bed height. The larger the superficial velocity is, the higher the bed height and the larger the spouting height appear. Besides, solid flow patterns under different bed heights with the superficial velocity the same ratio to the corresponding minimum spouting velocity show a similar behavior.

Numerical simulation of 3D sloshing in a liquid–solid mixture using particle methods

SUMMARYSloshing of liquid–solid particle mixtures is an important issue in industrial settings and research fields. In numerical simulations, difficulties are encountered in capturing or tracking the interface between different phases and calculating the interactions between particles, as well as considering hydrodynamic effects between liquid and particles. The finite volume particle (FVP) method, which is based on the Lagrangian framework, does not require applying extra techniques to capture the dynamics at the interface. Moreover, the hydrodynamic behavior between liquid phase and solid particles can be solved implicitly. The discrete element method (DEM) is a useful computational tool, which can explicitly calculate the interaction forces acting on particles and exactly describe their transient trajectories. Owing to the same particle assumption and Lagrangian description, the approach coupling FVP and DEM is more straightforward than the Euler–Lagrange approach. In this study, the applicability of the coupled FVP/DEM method is investigated by simulating sloshing in liquid–solid particle mixtures. A comparison of simulation and experimental results shows good agreement and demonstrates the accuracy of the method. It is hoped that the FVP/DEM method can provide an effective 3D means for a quantitative comparison and validation of more complicated multiphase flows with a variety of particles. Copyright © 2013 John Wiley & Sons, Ltd.

Simulation of particles and sediment behaviour in centrifugal field by coupling CFD and DEM

Centrifugal separation systems, such as solid bowl centrifuges, are used to effectively separate fine particles from industrial fluids. Knowledge of the streams and sediment behaviour inside such solid bowl centrifuges is required to determine the geometry and the process parameters that lead to an optimal performance. The multiphase flow of water, air and particles is calculated numerically in a cylindrical solid bowl centrifuge using a Computational Fluid Dynamics (CFD) software coupled with a Discrete Element Method (DEM) software. The CFD software calculates the flow of water and air and transfers the hydrodynamic forces to the DEM software in order to calculate the particle positions adding the hydrodynamic effect to the contact forces. Afterwards, the influence of the particles on the flow is considered. Thus, an unsteady and coupled simulation calculates flow and particles alternatively. Different sediment forms and solid volume concentrations are obtained when varying the geometry, operating conditions, particle size and contact model parameters such as the friction coefficient.

A new capillary force model implemented in micro-scale CFD–DEM coupling for wet granulation

A DNS (Direct Numerical Simulation) model for solid, liquid, and gas three-phase flow, mainly targeting to simulate the nucleation processes in wet granulation, is presented in this paper. A liquid–gas two-phase flow is solved by using the CIP (Constrained Interpolation Profile) method, which is one of the CFD multi-phase solvers, and a solid particle flow is solved by DEM (Discrete Element Method) separately. The interaction between fluid (liquid and gas) and solid phases is taken into account by coupling CFD and DEM. A new model is developed to account for the capillary force exerted on particles, i.e. the surface tension force which pulls a particle along with the solid–liquid–gas contact line, and the accuracy of the model is examined. Although the main focus in this study is to develop a CFD–DEM coupling and the capillary force models for wet granulation, some simulation results are also presented to see the droplet behaviour often encountered in a wet granulation process, i.e. the droplet penetration into a static particle bed as well as the droplet impingement onto a dynamic particle bed. The simulation results are compared with the experimental results in the literature and it shows a good agreement in terms of tendency.

Meshless numerical modeling of brittle–viscous deformation: first results on boudinage and hydrofracturing using a coupling of discrete element method (DEM) and smoothed particle hydrodynamics (SPH)

We have developed a new approach for the numerical modeling of deformation processes combining brittle fracture and viscous flow. The new approach is based on the combination of two meshless particle-based methods: the discrete element method (DEM) for the brittle part of the model and smooth particle hydrodynamics (SPH) for the viscous part. Both methods are well established in their respective application domains. The two methods are coupled at the particle scale, with two different coupling mechanisms explored: one is where DEM particles act as virtual SPH particles and one where SPH particles are treated like DEM particles when interacting with other DEM particles. The suitability of the combined approach is demonstrated by applying it to two geological processes, boudinage, and hydrofracturing, which involve the coupled deformation of a brittle solid and a viscous fluid. Initial results for those applications show that the new approach has strong potential for the numerical modeling of coupled brittle–viscous deformation processes.

Experimental and numerical investigation into the residence time distribution of granular particles on forward and reverse acting grates

Forward and reverse acting grates are widely employed in waste-to-energy plants. In order to predict the motion of solid granular particles and optimise the design of such systems, Discrete Element Method (DEM) is increasingly used. The objective of this paper is to predict the dynamics of granular particles on forward and reverse acting grates by applying DEM. The residence time distribution of solid particles is analysed by DEM and compared with experimental results in a pilot plant excluding combustion. The results indicate a very good consistency between DEM and experimental results, highlighting the promising capabilities of DEM in predicting the dynamics of granular particles in grate systems. Coupling DEM with computational fluid dynamics techniques can further advance the method to account for thermal conversion of solid fuels in future work.

Meso-scale coupling model of DEM and CIP for nucleation processes in wet granulation

This paper presents a coupling of Discrete Element Method (DEM) and Constrained Interpolation Profile (CIP) mainly designed for simulations of the nucleation process in wet granulation. The governing equations for fluid (liquid and gas) phases are the volume averaged form of the Navier–Stokes equation, continuity and colour function equations. These equations are solved by use of a meso-scale fixed Cartesian grid whose cell is larger than individual particles. The solid–liquid–gas interfacial effects on both fluid and particle phases are taken into account in the simulation. The surface tension effect on the fluid motion was modelled in three different ways depending on the relative position of the liquid–gas interfaces to powder beds: the models outside, inside, and on the surface of powder beds correspond to a free surface, capillary action and bed surface wetting. A new model for the surface tension effect on the solid (particle) motion, i.e. the capillary force effect, is proposed in this paper. This capillary force model is particularly useful when using a meso-scale fixed grid, and it can be used with various types of multi-fluid scheme such as CIP, Volume of Fluid (VoF) and Level Set methods. The proposed models are validated by comparing the simulation results with theoretical and experimental results. It is also revealed that the capillary force model is crucial to obtain reasonable simulation results for nucleation process.

Coupling of discrete-element method and smoothed particle hydrodynamics for liquid-solid flows

Particle based methods can be used for both the simulations of solid and fluid phases in multiphase medium, such as the discrete-element method for solid phase and the smoothed particle hydrodynamics for fluid phase. This paper presents a computational method combining these two methods for solid-liquid medium. The two phases are coupled by using an improved model from a reported Lagrangian-Eulerian method. The technique is verified by simulating liquid-solid flows in a two-dimensional lid-driven cavity.

Models, algorithms and validation for opensource DEM and CFD-DEM

We present a multi–purpose CFD–DEM framework to simulate coupled fluid–granular systems. The motion of the particles is resolved by means of the Discrete Element Method (DEM), and the Computational Fluid Dynamics (CFD) method is used to calculate the interstitial fluid flow. We first give a short overview over the DEM and CFD–DEM codes and implementations, followed by elaborating on the numerical schemes and implementation of the CFD–DEM coupling approach, which comprises two fundamentally different approaches, the unresolved CFD–DEM and the resolved CFD–DEM using an Immersed Boundary (IB) method. Both the DEM and the CFD–DEM approach are successfully tested against analytics as well as experimental data.

Simulation of Multiscale Time and Space in Fracture Process of Three-Point-Bending Concrete Beam with Offset Notch

In order to accurately analyze the dynamic damage process of three-point-bending concrete beam with offset notch, the multiscale numerical model of time and space by coupling Discrete Element Method (DEM) and Finite Element Method (FEM) of three-point-bending concrete beam with offset notch was established. Using the multiscale numerical model of three-point-bending concrete beam, the generating and the extending processes and rules of cracks in concrete beam under condition of different offset distances of notch were analyzed at macro- and meso-levels. The simulated results are in accordant with the experimental ones. Comparing the computation time of the multiscale model and that of the DEM model in the example of three-point-bending concrete beam, the former accomplished the heterogeneous mesoscopic simulations of the latter, at the same time, the former was much more efficient than the latter.

Coupling between finite and discrete element methods for the modelling of earth structures reinforced by geosynthetic

Due to the use of new technologies and innovative materials in civil engineering (reinforcement, recycled or natural materials), the design of geotechnical earth structures has become more complex, involving improvements to existing numerical models in order to consider the specific mechanical behaviours of each component in the structure. In this article, we focus on a new numerical model dedicated to earth structures reinforced with geosynthetic sheets, based on coupling the finite element method (FEM) and the discrete element method (DEM). The numerical model proposed takes the tensile and membrane behaviours of the geosynthetic into account by the FEM, and the interface friction between soil and geosynthetic and granular soil behaviour under large displacements by the DEM. The model used to describe the membrane and the tensile behaviours of the geosynthetic sheet is presented, and the basic assumptions of the discrete element method are then set out. Particular attention was paid to the description of the geometrical and micro-mechanical parameters of the discrete particle assemblies needed to reproduce realistic behaviour of granular soils. The aim of this article is to model the interaction between the geosynthetic sheet and the particles of soil, so the numerical coupling of FEM–DEM is described in detail; in particular, a specific contact law relating to the friction behaviour of the composite soil–geosynthetic is proposed. To show the interest of the numerical developments in modelling reinforced earth structures, an application is provided for embankments, reinforced at their base by a geosynthetic and built on areas subject to potential sinkholes. The numerical results of the FEM–DEM coupling are compared to those of true-scale instrumented experiments and of an analytical design method. The qualitative and quantitative comparisons of strains and tensile forces acting on the geosynthetic sheet make it possible to validate the numerical model suggested.

1414 高濃度粒子を含む流れ場の直接数値計算(OS14-3 分散系混相流のダイナミクス,オーガナイズドセッション)

The behavior of flows containing dense particles is very complex. Due to the particle-particle collision effect and hydrodynamic effect caused by the fluid existing in-between particles, particles make spontaneous structures. Flow characteristics are heavily depending on these internal structures and it is important to know why and what sort of structure is formed in the flow field. In the present study, internal flow structures of the flow containing dense particles are calculated by coupling Full-resolved DNS and DEM (Discrete Element Method).

Discrete particle simulation of particulate systems: Theoretical developments

Particle science and technology is a rapidly developing interdisciplinary research area with its core being the understanding of the relationships between micro- and macroscopic properties of particulate/granular matter—a state of matter that is widely encountered but poorly understood. The macroscopic behaviour of particulate matter is controlled by the interactions between individual particles as well as interactions with surrounding fluids. Understanding the microscopic mechanisms in terms of these interaction forces is therefore key to leading to truly interdisciplinary research into particulate matter and producing results that can be generally used. This aim can be effectively achieved via particle scale research based on detailed microdynamic information such as the forces acting on and trajectories of individual particles in a considered system. In recent years, such research has been rapidly developed worldwide, mainly as a result of the rapid development of discrete particle simulation technique and computer technology. This paper reviews the work in this area with special reference to the discrete element method and associated theoretical developments. It covers three important aspects: models for the calculation of the particle–particle and particle–fluid interaction forces, coupling of discrete element method with computational fluid dynamics to describe particle–fluid flow, and the theories for linking discrete to continuum modelling. Needs for future development are also discussed.

A Numerical Study of Heat Transfer Mechanisms in Gas–Solids Flows Through Pipes Using a Coupled CFD and DEM Model

A two dimensional numerical model has been developed to simulate heat transfer in gas–solids flows through pipes, in which the gas phase is modelled as a continuum using the Computational Fluid Dynamics (CFD) approach and the solids phase is modelled by the Discrete Element Method (DEM). This allows interactions between gas, particles, and pipe wall to be accounted at the scale of individual particles and convective and conductive heat transfers to be calculated using local gas and solids parameters. The predicted changes to the flow structures and the various heat transfer mechanisms due to the presence of particles were analyzed and compared with other workers' findings. This study has quantitatively demonstrated the crucial effect of particle transverse motion on heat transfers due firstly to the thermal energy transport by rebounding particles and secondly to the modification of the fluid thermal boundary layer characteristics.