Discrete Element Method Solver Research Articles

A parallel coupling framework for DEM-MBD: Model verification and application

Bulk material handling equipment can be numerically studied using the DEM-MBD method, where the particulate dynamics are solved by DEM (Discrete Element Method) and the motion characteristics of the mechanical components are modeled by MBD (Multi-Body Dynamics). In this work, a two-way coupling framework is proposed for the co-simulation of our self-developed DEM solver (DEMSLab) with the commercial MBD software (RecurDyn) using a parallel staggered coupling approach. To verify the proposed coupling method, the simulation result of a torsional spring damper system is compared with the corresponding analytical solution. After that, to assess the feasibility of this method in industrial-scale applications, a series of simulations involving a wheel loader is carried out. Different simulation conditions are adopted to reveal their impact on computational efficiency and simulation accuracy. These conditions include the mesh representation of the equipment geometry, the MBD time step size, and the coupling interval. An improved mesh simplification algorithm is proposed and used to reasonably simplify the surface mesh of the wheel loader, thus lowering the computational intensity of particle-wall interactions in DEM. The comparison results indicate that the computational time can be largely saved while the simulation accuracy remains considerably high. The MBD step size and coupling interval are crucial for numerical stability and should be selected carefully.

An Automatized Simulation Workflow for Powder Pressing Simulations Using SimStack

Automated computational workflows are a powerful concept that can improve the usability and reproducibility of simulation and data processing approaches. Although used very successfully in bioinformatics, workflow environments in materials science are currently commonly applied in the field of atomistic simulations. This work showcases the integration of a discrete element method (DEM) simulation of powder pressing in the convenient SimStack workflow environment. For this purpose, a Workflow active Node (WaNo) was developed to generate input scripts for the DEM solver using LIGGGHTS Open Source Discrete Element Method Particle Simulation code. Combining different WaNos in the SimStack framework makes it possible to build workflows and loop over different simulation or evaluation conditions. The functionality of the workflows is explained, and the added user value is discussed. The procedure presented here is an example and template for many other simulation methods and issues in materials science and engineering.

Multiscale modeling of granular dynamics on flowslide triggering and runout

AbstractA hierarchical multiscale modeling framework is proposed to simulate flowslide triggering and runout. It couples a system‐scale sliding‐consolidation model (SCM) resolving hydro‐mechanical feedbacks within a flowslide with a local‐scale solver based on the discrete element method (DEM) replicating the sand deformation response in the liquefied regime. This coupling allows for the simulation of a seamless transition from solid‐ to fluid‐like behavior following liquefaction, which is controlled by the grain‐scale dynamics. To investigate the role of grain‐scale interactions, the DEM simulations replace the constitutive model within the SCM framework, enabling the capture of the emergent rate‐dependent behavior of the sand during the inertial regime of motion. For this purpose, a novel algorithm is proposed to ensure the accurate passage of the strain rate from the global analysis to the local DEM solver under both quasi‐static (pre‐triggering) and dynamic (post‐triggering) regimes of motion. Our findings demonstrate that the specifics of the coupling algorithm do not bear significant consequences to the triggering analysis, in that the grain‐scale dynamics is negligible. By contrast, major differences between the results obtained with traditional algorithms and the proposed algorithm are found for the post‐triggering stage. Specifically, the existing algorithms suffer from loss of convergence and require proper numerical treatment to capture the micro‐inertial effects arising from the post‐liquefaction particle agitation responsible for viscous‐like effects that spontaneously regulate the flowslide velocity. These findings emphasize the important role of rate‐dependent feedback for the analysis of natural hazards involving granular materials, especially for post‐failure propagation analysis.

CFD-DEM coupled simulation of fluidized beds with improved lumped formulation for heat transfer

PurposeThis paper aims to present a novel approach for computing particle temperatures in simulations coupling computational fluid dynamics (CFD) and discrete element method (DEM) to predict flow and heat transfer in fluidized beds of thermally thick spherical particles.Design/methodology/approachAn improved lumped formulation based on Hermite-type approximations for integrals to relate surface temperature to average temperature and surface heat flux is used to overcome the limitations of classical lumped models. The model is validated through comparisons with analytical solutions for a convectively cooled sphere and experimental data for a fixed particle bed. The coupled CFD-DEM model is then applied to simulate a Geldart D bubbling fluidized bed, comparing the results to those obtained using the classical lumped model.FindingsThe validation cases demonstrate that ignoring internal thermal resistance can significantly impact the temperature in cases where the Biot number is greater than 0.1. The results for the fixed bed case clearly demonstrate that the proposed method yields significantly improved outcomes compared to the classical model. The fluidized bed results show that surface temperature can deviate considerably from the average temperature, underscoring the importance of accurately accounting for surface temperature in convective heat transfer predictions and surface processes.Originality/valueThe proposed approach offers a physically more consistent simulation without imposing a significant increase in computational cost. The improved lumped formulation can be easily and inexpensively integrated into a typical DEM solver workflow to predict heat transfer for spherical particles, with important implications for various industrial applications.

Numerical assessment of recellularization conditions to vessel occlusion.

To ensure the functional properties of an organ generated by the process of decellularization and recellularization, the initial density and distribution of seeding cells in the parenchymal space should be maximized. However, achieving a uniform distribution of cells across the entire organ is not straightforward because of vessel occlusion. This study assessed vessel occlusion during recellularization under different conditions. A combination of the electrical analog permeability (EPA) model, computational fluid dynamics (CFD), and discrete element method (DEM) was employed to describe the vessel occlusion phenomenon. In particular, realistic flow distributions in vascular trees of the decellularized organ were indicated by the EPA model. The cell suspension flow was modeled by a coupled CFD-DEM model, whereby living cells were presented as a discrete phase (solved by the DEM solver), and the culture medium was modeled as the fluid phase (solved by CFD solver). The cell suspension velocity was reduced up to 47% after decellularization, which directly affected cell movement. Simulation results also indicate that the occurrence of vessel occlusion was promoted by gravity direction in the asymmetric bifurcation and increased as the cell concentration increased. The assessment of vessel occlusion under different conditions was quantitatively investigated. The model provides insights into the dynamics of cells in the vessel compartment, allowing for the selection of optimum seeding parameters for the recellularization process.

Parametric Study on Strength Characteristics of Two-Dimensional Ice Beam Using Discrete Element Method

Strength characteristics of a two-dimensional ice beam were studied using a discrete element method (DEM). The DEM solver was implemented by the open-source discrete element method libraries. Three-point bending and uniaxial compressive tests of the ice beam were simulated. The ice beam consisted of an assembly of disk-shaped particles with a particular thickness. The connection of the ice particles was modelled using a cuboid element, which represents a bond. If the stress acting on the bond exceeded the bond strength criterion, the bond started to break, explaining the cracking of the ice beam. To find out the effect of the local parameters of the contact and bond models on the ice fracture, we performed numerical simulations for various bond Young‘s modulus of the particles, the bond strength, and the relative particle size ratio.

Assessment of bi-disperse solid particles mixing in a horizontal paddle mixer through experiments and DEM

In the current study, the mixing of bi-disperse particles in a horizontal paddle mixer was investigated through the sampling experimental technique and discrete element method (DEM). LIGGGHTS software was employed as the DEM solver. A close agreement between the simulation and experimental data was observed. Using the calibrated DEM model, the influence of some operating parameters such as impeller rotational speed, vessel fill level, particle number ratio (rn) and particle loading arrangement on the mixing quality was analyzed. A detailed analysis of this specific type of mixer comprising bi-disperse particles has not been reported in literature. It was found that rn had the most significant effect on the mixing performance. It was also found that the diffusion mechanism was dominant over the convection mechanism and in the cases in which the values of the diffusion coefficients of 5 mm and 3 mm particles were close, the best mixing performance was achieved.

Application of a new method for experimental validation of polydispersed DEM simulation of silo discharge

There are numerous experimentally validated simulations for mono-dispersed systems in the literature based on discrete element method (DEM). In practice, however, most of granular systems consist of polydispersed assemblies of particles. Few studies have considered the effect of polydispersity, and yet fewer have experimentally validated the results. In this study, application of a new experimental method for granular flow analysis is presented, capable of validating the results of an in-house developed GPU-based DEM solver in both monodispersed and polydispersed assemblies. Silo discharge is chosen as the case study in which discharge time, flow pattern and more importantly, the outlet composition variation with time (for polydispersed configurations) have been experimentally evaluated and validated with numerical results. The outlet composition, which is the ratio of fine to coarse particles in the outlet stream, is an essential measure of segregation in polydispersed silos, and its numerical prediction can be correct only if the interactions between fine and coarse particles within the silo are modelled precisely. Measuring this parameter is not possible using conventional experimental methods established in silo discharge studies such as high speed photographing or high-frequency weight measurement of the bed. A new apparatus has been developed which can measure this parameter. The device is a compartmented wheel rotating with a motor which gathers the outlet stream of the silo into different compartments. Due to practical limitations, design and function of the apparatus are not ideal. Forward mixing, distribution of particles with the same resident time in different compartments, is the most critical problem. Non-idealities must be compensated by means of post-processing codes so that comparable results are obtained from experiment and simulation.

CFD-DEM and PR-DNS studies of low-temperature densely packed beds

Over the past few decades, granular media is gaining attention as a viable option for heat transfer fluids (HTFs). Several research efforts are studying the use of particle-based heat transfer fluids in a wide variety of applications. With this motivation, the current work focusses on analyzing the different heat transfer mechanisms in low-temperature mono-sized densely packed granular media. To study the heat transfer behavior of granular media at different scales, the current work employs a two-way coupled computational strategy. The motion of particles is solved using the Discrete Element Method (DEM) and the interstitial air is solved using a Finite-Volume (CFD) approach. The Open-Source library CFDEM Coupling® is used in the current study to join the Finite Volume PISO solver of OpenFOAM® and the DEM solver of LIGGGHTS®. Typically, particle-particle contact conduction and particle-air convection are the most popular closure models. But recent research identified a different heat transfer phenomenon in packed beds that cannot be identified by conduction or convection models. Though closure models were developed to implement this on a CFD-DEM framework, they did not capture the effect of intra-particulate thermal gradients on this phenomenon. Hence the current work also employs Particle-Resolved Direct Numerical Simulations (PR-DNS) to gain valuable insights allowing for the modification of existing models. A new closure model is then proposed here and is implemented in the CFD-DEM framework. This model provides key insights into the different heat transfer mechanism of packed beds.

Discrete element simulation of damage evolution in coatings

This paper aims to use discrete element method (DEM) to investigate the cracking and interfacial delamination in ceramic coatings under uniaxial substrate tension. In DEM, the domain of the problem is discretized with a set of dense packing random arrangement of particles bonded together with springs or beam elements. In this method, partial damages can be well described which gives new insights into the qualitative description of damages in ceramic coating/substrate structures. A DEM solver code and dense particle packing generator has been developed by the authors. Yttria-stabilized zirconia is considered as an example of ceramic coatings which is usually used as a thermal insulator for superalloy substrates. A unit cell of ceramic coating/substrate structure was considered with three coating thicknesses and the effect of coating thickness was investigated on damage initiation and propagation. The results showed that the coating thickness affects the damage initiation mechanism. In addition, the structures with thick coatings are more susceptible to interfacial delamination.

A DEM modeling of biomass fast pyrolysis in a double auger reactor

Thermochemical conversion of biomass via fast pyrolysis is a proven pathway to product low-carbon crude bio-oils. In this research, an extended discrete element method (DEM) is proposed for simulating biomass fast pyrolysis reacting granular flows in a double auger reactor, in which particle hydrodynamics and interparticle heat transfer processes are involved and coupled with chemical reactions in solid particles. An adaptive time step algorithm is proposed to achieve a stable coupling between the integration of reaction ordinary differential equations and the DEM solver, and the algorithm is proven computationally efficient. A multi-component fast pyrolysis kinetics is adopted and its modeling accuracy is assessed by carrying out simulations of benchmark biomass pyrolysis experiments and comparing the prediction results with experimental data. The predicted product yields of bio-oil, char and non-condensable gas from the simulation of the biomass fast pyrolysis in the auger reactor are in satisfactory agreement with experimental measurements. The decomposition rates of biomass components in the reactor are revealed from the simulation and the pyrolysis number Py is calculated from the decomposition rate of biomass and the heat transfer coefficient. The Py number illustrates that the biomass fast pyrolysis process is limited by the heat transfer process at particle size of 2 mm.

Investigation on the effective parameters of through-the-width crack propagation in ceramic coatings due to substrate tension using discrete element method

This paper aims to simulate surface cracking and interfacial delamination in ceramic coatings due to their application in different industries. For this purpose, one of the most widely used ceramics, yttrium-stabilized zirconia, which is used as a thermal insulator for superalloy substrate is considered as a case study. Discrete element method was used, due to its great ability to capture the damages at the microscale, to investigate the effect of crack spacing and coating thickness on crack initiation and propagation. Discrete element method solver code is provided by the authors. To investigate damages, a unit cell of the structure between two successive surface cracks was considered. The length of the unit cell represents the crack density in the structure. In addition, for each unit cell length, three coating thicknesses were considered. The results of the current study were compared and validated with those experiments and numerical simulation results presented in the open literature. Good agreement was found. Finally, the effect of interface roughness on stress distribution and damage initiation was examined.

MOTION OF SOLID SPHERES UNDER SOLITARY WAVE ATTACK: PHYSICAL AND NUMERICAL MODELING

In this study, physical and numerical test are carried out focusing on the motion of two solid spheres under solitary wave attack. The numerical model CADMAS-SURF/3D-2F-DEM coupling a multiphase flow solver solving Reynolds Averaged Navier-Stokes Equations based on a porous body model and a discrete element method solver for Newton’s equations of motion is validated against the data of physical model experiments carried out in the wave flume of METU Ocean Engineering Research Center. Comparisons of the numerical simulations and physical model experiments show that the numerical model is capable of simulating the motion of solid spheres under solitary wave attack in a reasonably well accuracy.

Mixing assessment of non-cohesive particles in a paddle mixer through experiments and discrete element method (DEM)

In this study the mixing kinetics and flow patterns of non-cohesive, monodisperse, spherical particles in a horizontal paddle blender were investigated using experiments, statistical analysis and discrete element method (DEM). EDEM 2.7 commercial software was used as the DEM solver. The experiment and simulation results were found to be in a good agreement. The calibrated DEM model was then utilized to examine the effects of the impeller rotational speed, vessel fill level and particle loading arrangement on the overall mixing quality quantified by the relative standard deviation (RSD) mixing index. The simulation results revealed as the impeller rotational speed was increased from 10 RPM to 40 RPM, generally a better degree of mixing was reached for all particle loading arrangements and vessel fill levels. As the impeller rotational speed was increased further from 40 RPM to 70 RPM the mixing quality was affected, for a vessel fill level of 60% and irrespective of the particle loading arrangement. Increasing the vessel fill level from 40% to 60% enhanced the mixing performance when impeller rotational speed of 40 RPM and 70 RPM were used. However, the mixing quality was independent of vessel fill level for almost all simulation cases when 10 RPM was applied, regardless of the particle loading arrangement. Furthermore, it was concluded that the particle loading arrangement did not have a considerable effect on the mixing index. ANOVA showed that impeller rotational speed had the strongest influence on the mixing quality, followed by the quadratic effect of impeller rotational speed, and lastly the vessel fill level. The granular temperature data indicated that increasing the impeller rotational speed from 10 RPM to 70 RPM resulted in higher granular temperature values. By evaluating the diffusivity coefficient and Peclet number, it was concluded that the dominant mixing mechanism in the current mixing system was diffusion.

Local lubrication model for spherical particles within incompressible Navier-Stokes flows.

The lubrication forces are short-range hydrodynamic interactions essential to describe suspension of the particles. Usually, they are underestimated in direct numerical simulations of particle-laden flows. In this paper, we propose a lubrication model for a coupled volume penalization method and discrete element method solver that estimates the unresolved hydrodynamic forces and torques in an incompressible Navier-Stokes flow. Corrections are made locally on the surface of the interacting particles without any assumption on the global particle shape. The numerical model has been validated against experimental data and performs as well as existing numerical models that are limited to spherical particles.

Implementation and validation of a volume-of-fluid and discrete-element-method combined solver in OpenFOAM

Numerous gas–liquid–solid flows exist in chemical engineering and metallurgical processes. Numerical modeling is an important topic that can be used to improve the design and investigate the operating conditions of these processes. The complicated interphase interaction within such three-phase systems, which include free surfaces and discrete phases, poses challenges in the existing methods. We implemented a volume-of-fluid (VOF) and discrete-element-method (DEM) combined solver, which should be useful for modeling the gas–liquid–solid systems, within the OpenFOAM framework. The Du Plessis and Masliyah drag force, added mass force, and capillary force were considered for fluid–particle coupling. The VOF–DEM solver was tested in three different cases, namely, particles in pure gas, particle collision in water, and gas–liquid–solid three-phase dam break. The results were validated against previous experiments and good agreement was obtained between the simulations and the experiments, which indicates the accuracy and suitability of this VOF–DEM solver for gas–liquid–solid systems.

Heat transfer rates in wall bounded shear flows near the jamming point accompanied by fluid-particle heat exchange

We investigate the heat transfer rates through a contact network of a sheared granular material using the Discrete Element Method (DEM). The tool ParScale enables us to study intra-particle transport processes, and the DEM solver LIGGGHTS is used to carry out the simulations. A plethora of dimensionless parameters is investigated, in order to picture different phenomena occurring near the jamming point (e.g., solidification) of a sheared granular material. Thereby, the main outcome is the quantification of thermal fluxes which occur due to (i) conduction in case of particle-particle collisions, as well as (ii) convection due to random particle motion. Also, the transferred heat between the particles and the ambient fluid is analysed. In addition, we analyse the phenomenon of crystallization, and the effect on the thermal transport rate in the granular material. Furthermore, we demonstrate that the ordering process, and hence the heat transport rate, can be controlled by adjusting the coefficient of friction of the granular material. Again, measured thermal fluxes are exploited to decide whether a system is crystallized or not.

Heat transfer rates in sheared beds of inertial particles at high Biot numbers

We investigate heat conduction rates through the contact network of sheared granular materials that consist of particles with a density much larger than that of the ambient fluid. The tool ParScale, a finite difference solver for intra-particle transport processes, is coupled to the discrete element method solver LIGGGHTS to carry out the simulations. Heat transfer to the surrounding fluid is considered via a fixed heat transfer coefficient. We identify a combination of Biot and Peclet number as the key non-dimensional influence parameter to describe the non-dimensional heat flux through the particle bed and provide an analytical solution to calculate mean particle temperature profiles. Simulations over a wide range of particle volume fractions, Biot and Peclet numbers are then performed in order to develop a continuum model for the heat flux. We show that for Biot numbers below 10^{-3} our results agree with a simple model based on a uniform particle temperature. However, for Biot numbers above a certain threshold, the conductive heat flux decreases substantially depending on the flow situation, and temperature gradients within the particle should be considered in order to correctly predict the heat transfer rate to the surrounding fluid.

Investigation of screening performance of banana screens using LIGGGHTS DEM solver

Deeper understanding of screening performance of banana screens helps mineral processing engineers to control and optimize them. In this article, screening performance of banana screens using a DEM (Discrete Element Method) solver ‘LIGGGHTS’ is investigated. An industrial double-deck banana screen with five panels and two laboratory single-deck banana screens with three and five panels are simulated. Effects of design parameters including incline angle of each panel, vibration amplitude and vibration frequency on screening performance of both the industrial screen and laboratory screens are studied. Also, the effects of operational parameters including simulation time and feed particle size distribution on screening performance of the industrial screen are examined. Simulation results are expressed in terms of recognized and comprehensible quantities for engineers, i.e., screen efficiency and screening recovery. To validate simulation results, a parameter named partition number is defined. Comparison of the partition numbers of simulations related to the laboratory screens with those available in the literature demonstrates a good agreement which validates the DEM simulations and the used software. Also, the results indicate that the industrial and laboratory screens show a totally different behavior with respect to changes in design parameters.

Recent advances in the simulation of particle-laden flows

A substantial number of algorithms exists for the simulation of moving particles suspended in fluids. However, finding the best method to address a particular physical problem is often highly non-trivial and depends on the properties of the particles and the involved fluid(s) together. In this report, we provide a short overview on a number of existing simulation methods and provide two state of the art examples in more detail. In both cases, the particles are described using a Discrete Element Method (DEM). The DEM solver is usually coupled to a fluid-solver, which can be classified as grid-based or mesh-free (one example for each is given). Fluid solvers feature different resolutions relative to the particle size and separation. First, a multicomponent lattice Boltzmann algorithm (mesh-based and with rather fine resolution) is presented to study the behavior of particle stabilized fluid interfaces and second, a Smoothed Particle Hydrodynamics implementation (mesh-free, meso-scale resolution, similar to the particle size) is introduced to highlight a new player in the field, which is expected to be particularly suited for flows including free surfaces.