Validation Of Discrete Element Method Research Articles

Experimental validation of DEM in rotating drums using Positron Emission Particle Tracking

Despite the widespread use of the Discrete Element Method (DEM) to simulate industrial rotating drum flows, comparatively little work has been done to evaluate its accuracy. To bridge this gap, Positron Emission Particle Tracking (PEPT) was employed to benchmark tuned DEM simulations. Two granular mixtures of mono-sized glass beads (31% filling), run at 60 and 75% of critical speed, were used. To ensure an equitable comparison, both DEM and PEPT data were coarse grained. The comparisons include the free surface (average RMS error = 2.6 mm), equilibrium surface (average RMS error = 3.3 mm), bin-by-bin comparisons of the solids fraction (15% relative error) and velocity (10% relative error), and equivalent comparisons along slices drawn orthogonal to the free surface that produced complete statistical agreement between PEPT and DEM. The results suggest a strong statistical agreement between the tuned DEM and coarse grained PEPT data.

Simulation model of loading bin bottom by bulk material

The trend of modern times is to use the increasingly more advanced technology of design, research and validation of transport, handling, storage and treatment processes using simulation methods. Programs used take advantage of computational algorithms that determine a large variety of different parameters. To extend the applicability of these programs, collaborative plug-ins (systems) are created that allow two or more simulations, analytical programs and methods to work together. In this study the cooperative plug-ins are utilised in an application dealing with the issues caused by Janssen forces/pressures of bulk material and deformation effects acting on the bottom of a bin. An examination of such issues includes observing a change in the position of a measuring plate due to the deformation of a force sensor placed at an outlet of an innovative prototype for measuring deformation effects. The experiment was evaluated and validation of discrete element method (DEM) simulation created; the force effects acting on the bottom of the bin were then transferred to a finite element method (FEM) analysis. This was followed by strength analysis of the force sensor deformation located under the outlet of the bin. A comparison was made between a real experiment and simulations that consisted of filling the bin with bulk material. Force reactions occurring at the bottom of the bin and the change of the position of the measuring plate due to the deformation of the force sensor were observed. The results show a low percentage deviation of the simulation from the real experiment. The maximum percentage deviation of the simulation from the real measurement expressed by the change of the measuring plate position due to the deformation of the force sensor is 3.70% and 0.23% when the forces acting on the measuring plate are compared using DEM. The results confirmed the assumption that the coupled DEM and FEM simulation is suitable for this type of engineering tasks. Application of the above mentioned DEM simulation and FEM analysis appears to be a universal tool for designing, modifying or upgrading of equipment for transporting, treatment and storing bulk material and includes equipment where the active member comes into contact with bulk material.

Characterization of additive manufactured particles for DEM validation studies

Discrete element method (DEM) simulations are often validated using physical laboratory tests on analogue soils to confirm the macro-scale response. These analogue soils have typically consisted of steel ball bearings or glass beads, thus limiting the shapes to spherical particles. Additive Manufacturing (AM) technologies can be used to create 3D objects of any shape layer-by-layer. Using these AM particles as analogue soils allows for DEM validations to be performed using a wide range of shapes, more realistically replicating natural sands and gravels. In order to use these AM particles, however, characterization of the AM material is essential to ensure its suitability for laboratory testing and to determine the intrinsic material properties input into the DEM models. This paper describes a study in which material properties and surface characteristics of two different additively manufactured materials are determined. A gypsum-epoxy composite material and a photopolymer material were tested to determine properties such as Young’s modulus, Poisson’s ratio, shape, surface roughness, and inter-particle friction angle. In comparison to the commonly used steel ball bearings and alkaline glass beads, the AM particles exhibited improved circularity. The hardness and Young’s modulus values were measured directly and then a fitting procedure was used to assess the Hertzian behavior of the spheres under uniaxial compression. While the inter-particle friction angle and the surface roughness were higher for the AM particles in comparison to the steel ball bearings and glass beads, the ability to control particle shape for the AM particles proves advantageous for manipulation of shape parameters for DEM validation.

Discrete Element Method–Based Investigations of Granular Flow in a Pebble Bed Reactor

In a pebble bed reactor (PBR) core, nuclear fuel in the form of pebbles moves slowly under the influence of gravity. Due to the dynamic nature of the core, a thorough understanding about slow and dense granular flow of pebbles is required from both a reactor safety point of view and a performance evaluation point of view. In the current study, validation of discrete element method (DEM)–based simulation for the pebble flow in a PBR was carried out. Validation of DEM-based simulations necessitates validation of the employed numerical method of simulating packed structure. Hence, a parametric sensitivity study of packing interaction properties was initially conducted and also validation of the numerical method simulating packed structure at first. The parametric sensitivity analysis suggests that static friction characteristics play an important role from a packed/pebble bed structural characterization point of view. In addition, the simulated packed structure approach has shown a good agreement with the available benchmark data. Afterward, the effect of two different half-cone angles of 30 deg and 60 deg on pebble flow field in a PBR was studied by EDEMTM-based simulations. Results of streamlines, velocity radial profiles, and direct observation of discharge indicated a plug-type flow in the upper cylindrical region, whereas results indicated converging-type flow near the bottom conical region. EDEMTM results of granular flow were validated against experimental benchmark data and show a fair agreement in terms of Lagrangian trajectories and velocity profile. Therefore, this validated EDEMTM-based simulation can be used to obtain reliable results of pebble dynamics in a PBR and to enhance understanding of this phenomenon in a PBR. However, additional experimental investigations are recommended to be carried out for different sizes of test reactors, different bottom cone angles, and different sizes of pebbles to further assess DEM simulation results before using them for full-scale reactor simulations.

Validation of discrete element method by simulating a 2D assembly of randomly packed elliptical rods

This paper aims at establishing the predictive capability of the discrete element method (DEM) by validating the simulated responses of granular systems against experimental observations at both the macroscale and the microscale. A previously published biaxial shearing test on a 2D assembly of randomly packed elliptical rods was chosen as the benchmark test. In carrying out the corresponding DEM simulations herein, the contact model was derived and then validated using finite element analysis; the associated parameters were calibrated experimentally. The flexible (membrane) boundary was modeled by a bonded-particle string with experimentally calibrated parameters. An iteration procedure was implemented to replicate the initial packing and also to satisfy the boundary conditions in the experiment. Overall, the DEM simulation is found effective in reproducing the stress–strain–volumetric response, the statistical observation on the fabric anisotropy and the strain localization. Furthermore, the closer the numerical packing is to the experimental one, the closer the response is reproduced, demonstrating the significance of the initial packing reconstruction. Still, there are some minor differences between the experiment and simulation, reflecting the limitations associated with the particle number and the measurement resolution used in the experiment when reproducing the initial packing.

Discrete element modelling and experimental validation for the falling process of dry granular steps

Abstract This paper presents an experimental validation of discrete element method (DEM) simulation for falling process of dry granular steps. Three chute slopes were considered in the study. The corresponding physical experiments were carried out in our previous study. The DEM simulations matched well with the experimental results regarding the external flow characteristics such as flow regimes, surface profiles, final deposit angles, velocity profiles at the sidewall, receding upper granular surfaces and flow rates. Subsequently, the DEM simulations were used to explore the internal flow patterns of the granular collapse, including translational velocity profiles and angular velocity profiles inside the granular assembly. According to the DEM simulation results, a mixed velocity profile (an upper convex and lower concave profile) appears in the central part of the chute, whilst the velocity profile follows a sidewall-stabilized heap (SSH) rheology (a concave profile) near the sidewall. The chute inclination facilitates the transformation from the SSH rheology to the mixed velocity profile in a narrow channel. The DEM simulations not only verify the experimental observation but also enhance the understanding of flow patterns induced by the collapse of dry granular steps.

Characterization of artificial spherical particles for DEM validation studies

This paper describes a study in which advanced particle-scale characterization was carried out on spherical particles that can be used in experimental tests to validate discrete element method (DEM) simulations. Two types of particle, alkaline and borosilicate glass beads, made from two different materials, were considered. The particle shape, stiffness, contact friction properties and surface roughness were measured. The influences of hardness and roughness on the mechanical response of the particles were carefully considered. Compared to the alkaline beads, the borosilicate beads were more spherical and more uniform in size, and they exhibited mechanical characteristics closer to natural quartz sand. While only two material types were studied, the work has the broader implication as a methodology for selecting particles suitable for use in DEM studies and the key parameters that should be considered in the selection process are highlighted.

On the validation of DEM and FEM/DEM models in 2D and 3D

PurposeAs particulate systems evolve, sliding, rolling and collision contacts all produce forces that discrete element method (DEM) methods aim to predict. Verification of friction rarely takes high priority in validation studies even though friction plays a very important role in applications and in mathematical models for numerical simulation. The purpose of this paper is to address sliding friction in finite element method (FEM)/DEM and rolling friction in DEM.Design/methodology/approachAnalytical solutions for “block sliding” were used to verify the authors' tangential contact force implementation of 2D FEM/DEM. Inspired by the kinetic art work Liquid Reflections by Liliane Lijn, which consists of free balls responding within a rotating shallow dish, DEM was used to simulate rolling, sliding and state‐of‐rest of spherical particles relative to horizontal and inclined, concave and flat spinning platforms. Various material properties, initial and boundary conditions are set which produce different trajectory regimes.FindingsSimulation output is found to be in excellent agreement when compared with experimental results and analytical solutions.Originality/valueThe more widespread use of analytically solvable benchmark tests for DEM and FEM/DEM codes is recommended.

Experimental Analysis and Micromechanical Modelling of Dry Granular Flow and Impacts in Laboratory Flume Tests

The paper presents the results of a numerical analysis, carried out by using the Discrete Element Method (DEM) and aimed at reproducing a series of tests on a small-scale laboratory model of a slope. Particular attention is devoted to the validation of DEM when used for the prediction of the run-out distance and of the impact force on obstacles. The soil used for the small-scale model is a mono-granular medium sand, which revealed to be particularly suitable to simulate flows like debris or rock avalanches. The experimental set-up comprises a flume equipped with a system of differently sized instrumented obstacles. The numerical model of the granular flow has been calibrated on the basis of the displacement measurements, obtained through a photogrammetric technique.

The discrete element method (DEM) to simulate fruit impact damage during transport and handling: Model building and validation of DEM to predict bruise damage of apples

The validity of the discrete element method (DEM) as a tool to predict impact damage of fruit was investigated for ‘Jonagold’ apples. ‘Bruise damage’ was preferred over the ‘particle trajectory’ as the validation parameter. The bruise damage of apples in boxes shaken with a well defined acceleration signal on an electro-hydraulic shaker was compared with the bruise damage calculated from DEM simulations with the same initial conditions. The parameters for the contact force models, needed as input for the simulations, and the bruise prediction model were determined on the same batch of apples, utilized in the validation experiments. The validations indicated that DEM can predict in an acceptable way apple bruise damage (bruise depth). However, due to the lack of the possibility of saving the impact positions on the apple surface by means of a coordinate system no prediction of multi-impact bruise surface and volume could be obtained.

Discrete element method (DEM) modelling of evolving mill liner profiles due to wear. Part I: DEM validation

Since the early 1990s the discrete element method (DEM) gained considerable success in its ability to predict the power draw and the load behaviour in mills as affected by operating conditions. The DEM can also be used to design milling equipment and predict the breakage of particles. A detailed validation of this method is required in order to produce accurate results. In this paper, we assess the ability of the DEM to predict forces exerted by the mill charge on liners. Data obtained on an experimental two-dimensional mill designed in order to record the normal and tangential forces exerted on an instrumented lifter bar was available. The measured results are compared to the DEM simulated results. Good agreement has been found in terms of amplitude of forces and positions of shoulder and toe at low speed.