Discrete Element Method Numerical Simulation Research Articles

Numerical Simulation of Torque Variation During Paste Mixing and Kneading

In the production process of aluminum electrolytic carbon anode, the kneading process is to fully mix asphalt and powder to obtain the best paste, because the kneading process is completed in a high-temperature kneading machine, there is no suitable automatic real-time judgment method for the uniformity of paste. Real-time online monitoring based on the viscoelastic change of paste during kneading is a potential method to judge the uniformity of paste. In this paper, the Discrete Element Method numerical simulation is used to study the variation law of stirring torque in the mixing and kneading wet mixing process, mainly examining the effect of viscosity on stirring torque. The results showed that the mixing and kneading torque varied periodically and the total torque of the stirrer was positively correlated with the viscosity.

Using discrete element numerical simulation to determine effect of persistent fracture morphology on permeability stress sensitivity

AbstractThe stress sensitivity of coal seams with different fracture structures affects gas migration characteristics in the fracture zone. In this study, permeability stress experiments for intact and persistent fracture coal samples are carried out. A discrete element method numerical simulation that adopts the changing joint stiffness method is proposed. Based on the experimental data, the corresponding parameters of persistent fractures and elastic joints for fluid–solid coupling simulations are determined. Subsequently, the internal influence mechanisms of fracture morphology on axial and confining stress sensitivities are determined. The simulation results show that sectional fractures with different dip angles in the persistent fracture control the sensitivity to axial and confining stresses. The horizontal segment fracture aperture decreases with an increase in axial stress, which reduces its flow capacity. This results in a decrease in the flow rates in the persistent fracture. When the confining stress increases, the vertical fracture aperture is significantly reduced, considerably reducing the flow rate in the persistent fracture.

Failure Process of Modeled Recycled Aggregate Concrete under Uniaxial Compression.

This paper investigates the failure processes of recycled aggregate concrete by a model test and numerical simulations. A micromechanical numerical modeling approach to simulate the progressive cracking behavior of the modeled recycled aggregate concrete, considering its actual meso-structures, is established based on the discrete element method (DEM). The determination procedure of contact microparameters is analyzed, and a series of microscopic contact parameters for different components of modeled recycled aggregate concrete (MRAC) is calibrated using nanoindentation test results. The complete stress–strain curves, cracking process, and failure pattern of the numerical model are verified by the experimental results, proving their accuracy and validation. The initiation, growth, interaction, coalescence of microcracks, and subsequent macroscopic failure of the MRAC specimen are captured through DEM numerical simulations and compared with digital image correlation (DIC) results. The typical cracking modes controlled by meso-structures of MRAC are concluded according to numerical observations. A parameter study indicates the dominant influence of the macroscopic mechanical behaviors from the shear strength of the interfacial transition zones (ITZs).

Rocking Blocks Stability under Critical Pulses from Near-Fault Earthquakes Using a Novel Energy Based Approach

Following the seminal work of Housner, a novel energy based critical pulse theoretical model is derived to assess the seismic stability of rocking rigid blocks under single pulses from near-fault earthquakes. It is shown that overturning is conditional on the availability of sufficient kinetic energy in the exciting pulse and on the inception of rocking. The theoretical model is shown to be in good agreement with discrete element method numerical simulations for similar blocks of sizes 0.5, 1, and 20 m. Similitude rules are established to scale between block sizes and pulse types and tested successfully. The results agree with available experimental data. The proposed stability chart approach provides a practical and simple alternative to the presentation and study of the stability and overturning of blocks published by others in the frequency spectrum domain. For any given rigid block or inverted pendulum structure the model or normalized stability charts provide a method to determine the characteristic period and peak acceleration required for overturning and by extension to identify the critical content of the dominant pulse of a given earthquake signal. Alternatively, the approach could be used in archaeoseismology to identify the characteristics of the dominant pulse content of past earthquakes based on their impacts on various historical and heritage structures.

Micromechanical Exploration of the Lade–Duncan Yield Surface by the Discrete Element Method

The Lade–Duncan yield surface has long been known to outperform other yield criteria (e.g., Mohr–Coulomb, Drucker–Prager) for predicting macro-scale failure in non-cohesive granular (pressure-dependent) materials. Such yield criteria are critical for a wide variety of civil and infrastructure engineering applications, including the design and analysis of foundations and retaining walls for architectural, highway, and railway support structures. The Lade–Duncan yield surface has been repeatedly validated, not only by numerous experimental studies, but also by three-dimensional discrete element method numerical simulations performed on mono- and poly-disperse assemblies of spheres. However, a fully satisfying micromechanical explanation for the empirically-motivated Lade–Duncan yield criterion has never been offered. In particular, the increase in the macro-scale friction angle $$\phi$$ relative to the Mohr–Coulomb yield surface that occurs as the Lode angle of deviatoric stress moves from simple compression toward simple extension on the $$\varPi$$ -plane in principal stress space, which is characteristic of the Lade–Duncan yield surface, has never been given a rigorous micromechanics-based explanation. In this paper, we attempt to fill this “gap”, by presenting a simple yet rigorous analysis of micro-scale inter-particle force-equilibrium, which, when combined with detailed 3D-DEM data obtained from simulations of cubical true-triaxial tests performed on mono- and poly-disperse spheres with a variety of micro-scale or inter-particle friction coefficients $$\mu$$ , provides a meaningful micromechanics-based explanation for the shape of the Lade–Duncan yield surface. In particular, we hypothesize that the Lade–Duncan yield criterion can be motivated directly from the continuum-mechanics-based spatially mobilized plane or Matsuoka–Nakai criterion in terms of the ratio of shear stress to normal stress on the spatially mobilized plane if the magnitude of the shear stress on the SMP is increased to account for deviations in the paths of sliding particles on the SMP.

Process of particles flow across staggered tubes in moving bed

Moving beds with staggered tubes are widely used in industrial applications to heat or cool solid particles. The heat transfer process is complicated and involves heat transfer amongst particles and between particles and tubes. Furthermore, the heat transfer mechanism is directly determined by the flow characteristics of particles across the outer surfaces of tubes because particles are the main heat carriers of particle flow. However, the particle flow across tubes is a kind of non-continuum flow, which is substantially different from Newtonian fluids, and the continuum theory is inappropriate for predicting particle flow in moving bed. In addition, little attention has been focused on this process. Thus, it is necessary to study the flow patterns of particles across tubes before studying the corresponding heat transfer mechanism. To describe this process, this work establishes a quasi-funnel flow (QFF) model, which can be used to calculate parameters, such as velocity field and residence time, by analyzing particle flow characteristics. The discrete element method (DEM) is used for a numerical simulation of three-dimensional particle flow across staggered tubes. The flow patterns, velocity field, typical particle trajectories and particle flow of local areas are obtained. Meanwhile, a moving bed experimental system is constructed, and the obtained results are used to verify the DEM numerical simulation results. Lastly, the results of the QFF model and that of the validated DEM numerical simulation are compared and found to be consistent. The ranges of the parameters required to describe the particle flow across tubes and the applicable range of the QFF model are also determined.

Discrete-element numerical modelling method for studying mechanical response of methane-hydrate-bearing specimens

It is important to understand the deformation mechanism of methane-hydrate specimens (MHSs) to avoid deforming the seabed during methane-hydrate production. For this purpose, discrete-element method (DEM) modelling is advantageous because it requires much less cost and effort compared to artificial specimens and in situ sediments. In this study, a method for generating DEM numerical simulation models of MHSs is proposed to study the deformation mechanism of MHSs. First, numerical models that consider the saturation of methane hydrate (SMH), following which the bi-axial compression of these models is simulated. The mechanisms controlling the shear strength of MHSs are verified and modified by investigating the stress–strain response behavior, crack-development process, and evolution of the void change rate (Echange) of MHSs. The increases of the peak strength and secant elastic modulus of the MHS with the increment of confining pressure follow parabolic relationships. Under different loading rates, the peak strength tends to increase parabolically with the increment of loading rate, while the relationship between the secant elastic modulus and loading rate is linear. Based on the testing results, empirical formulas of peak stress and elastic modulus are proposed for different confining-pressure and strain-rate conditions.

A methodology for calibration of DEM input parameters in simulation of segregation of powder mixtures, a special focus on adhesion

Conducting a numerical simulation for cohesive granular mixtures that is well comparable with experiments has always been a challenge. In this study, a systematic methodology is proposed for increasing the fidelity of Discrete Element Method (DEM) simulations of cohesive powder mixtures. Segregation of granules during heap formation of a ternary powder mixture is simulated as a proof of concept. The mixture contains three model particles, one of which is an enzyme placebo granule (EP), in order to simulate the segregation of the actual enzyme granules used in detergent formulations. These granules are at a low content level (~2 wt%) and are highly prone to segregation. In this study, the segregation tendency of the EP granules is mitigated by coating them with Polyethylene Glycol 400 (PEG 400). The resulting adhesion is expressed in terms of equivalent interfacial energy for the DEM numerical simulations and is tuned by careful calibration using the concept of the angle of repose. The Cohesion number is used to scale material stiffness or changing the particle size for faster simulation. The particles shapes in DEM are modelled as clumped spheres based on the X-ray tomograms of the real particles. The rest of the DEM input parameters are also selected and tuned based on the particles physical and mechanical properties. Considerable reduction in segregation tendency of the low-level ingredient granules is observed as a result of coating its surfaces by PEG400. Following the proposed calibration strategy, the DEM simulations have predicted the experimental trends closely and a reasonable agreement is achieved. It is observed that using the Cohesion number for scaling the interfacial energy can significantly reduce the number of calibration trials.

An equivalent discontinuous modeling method of jointed rock masses for DEM simulation of mining-induced rock movements

The Discrete Element Method (DEM) is of obvious and inherent advantages in simulating large displacements and discontinuous deformations of rock masses, and thus is suitable to simulate the mining-induced rock movements. However, when the region of the DEM calculation model is large, for example, when both the length and width of the research area are larger than several hundreds of meters, the rock mass in the model range often contains a large number of actual joints. If the calculation model is built according to the distribution of the actual joints, the calculation model of DEM will consist of a large number of blocks, which would lead to the impossibility of numerical calculations. To address this problem, an Equivalent Discontinuous Modeling Method (EDMM) of jointed rock masses for DEM simulation of mining-induced rock movements is proposed in this paper. In this method, an actual geological body with a complex joint system will be simplified into an Equivalent Discontinuous Model (EDM), which is a DEM calculation model with a simple hypothesis joint system. The approach for determining the mechanical parameters, i.e., the cohesive strength (C), the internal friction angle (ϕ), the joint normal stiffness (JKN), and the joint shear stiffness (JKS), of the hypothetical joints of the EDM is the core of the proposed EDMM. The main procedure of the proposed EDMM is composed of: (1) for each subarea of an EDM, building a group of Equivalent Discontinuous Cube Models (EDCMs) that are of different joint spacings; (2) determining the joint mechanical parameters of each EDCM based on the mechanical properties of the actual rock masses of the subarea; (3) establishing the relationships between the joint spacings and joint mechanical parameters for each subarea of EDM; and (4) determining the mechanical parameters of the hypothesis joints in each subarea of the EDM according to these relationships. By exploiting the EDM, the DEM numerical simulation is performed to simulate the mining-induced rock movements and failures. To demonstrate the applicability, the proposed EDMM was employed to simulate the rock movements and failures triggered by mining under the western open-pit final slope of Yanqianshan iron mine.

The influence of particle shape on screening: case studies regarding DEM simulations

PurposeThe purpose of this study is to explore how particle shape influences the screening, including screening efficiency per unit time, and the relationship between vibration parameters and screening efficiency per unit time in discrete element method (DEM) numerical simulations.Design/methodology/approachIn this paper, a three-dimensional discrete element model of vibrating screen with composite vibration form of swing and translation was proposed to simulate the screening process. In total, 11 kinds of non-spherical particles whose shapes changed in a continuous regularity gradual process were established using a multi-sphere method. In the DEM simulations, vibration parameters, including vibration frequency, vibration amplitude and stroke angle, and swing parameters, including swing frequency and swing angle, were changed to perform parametric studies.FindingsIt shows that the effect of particle shape on screening efficiency is quantitative actually. However, the trends of different shape particles’ screening efficiency per unit time are mainly consistent.Originality/valueSome simple particle shapes can be expected to be explored to do screening simulation studies reasonably with modification of the simulation data in DEM numerical simulations. That may improve the computational efficiency of numerical simulations and provide guidance to the study of the screening process.

Discrete element analysis of the mechanical properties of deep-sea methane hydrate-bearing soils considering interparticle bond thickness

Due to increasing global energy demands, research is being conducted on the mechanical properties of methane hydrate-bearing soils (MHBSs), from which methane hydrate (MH) will be explored. This paper presents a numerical approach to study the mechanical properties of MHBSs. The relationship between the level of MH saturation and the interparticle bond thickness is first obtained by analyzing the scanning electron microscope images of MHBS samples, in which is the bridge connecting the micromechanical behavior captured by the DEM with the macroscopic properties of MHBSs. A simplified thermal-hydromechanical (THM) bond model that considers the different bond thicknesses is then proposed to describe the contact behavior between the soil particles and those incorporated into the discrete element method (DEM). Finally, a series of biaxial compression tests are carried out with different MH saturations under different effective confining pressures to analyze the mechanical properties of deep-sea MHBSs. The results of the DEM numerical simulation are also compared with the findings from triaxial compression tests. The results show that the macromechanical properties of deep-sea MHBSs can be qualitatively captured by the proposed DEM. The shear strength, cohesion, and volumetric contraction of deep-sea MHBSs increase with increasing MH saturation, although its influence on the internal friction angle is obscure. The shear strength and volumetric contraction increase with increasing effective confining pressure. The peak shear strength and the dilation of MHBSs increase as the critical bond thickness increases, while the residual deviator stress largely remains the same at a larger axial strain. With increasing the axial strain, the percentage of broken bonds increases, along with the expansion of the shear band.

Study on the meso-structure development in direct shear tests of a granular material

Stress induced anisotropy phenomenon has been the main interest of many researches, especially in granular materials. Discrete element method (DEM) is one of the important methods for the study of meso-mechanics of granular materials. Based on previous studies, a 3D meso-fabric statistical method have been established, which can be used for quantitative analysis of 3D meso-fabric development in DEM numerical simulation of granular materials under external loads. Taking the direct shear test of sand as an example, the stress induced anisotropy of sand in 3D under the shearing loads has been studied systematically. According to the analysis results: the magnitude of anisotropy significantly develops during shear tests and gradually become steady after the peak, and the principal directions of anisotropy rotates consistent with the principal stress direction; the connectivity between the particles decreases and a series of particle skeletons are formed in the sample which undertake the main external loads. Furthermore, the stress state does also influence the evolution of anisotropy and force chain networks.

Random generation of the meso-structure of a soil-rock mixture and its application in the study of the mechanical behavior in a landslide dam

A discrete element method (DEM) numerical simulation is used as a tool to study the mechanical behavior of soil-rock mixtures (S-RM) in a landslide dam. A 2D random generation program (R-SRM2D) of the meso-structure of (S-RM) based on random polygonal rock blocks has been developed, and is used to generate the (S-RM) numerical model of the study area. A new multi-circle representation method of polygonal blocks has been developed, which can better model the mechanical properties and failure process of rock blocks. A DEM biaxial test method with a flexible confining stress boundary has also been developed, which can better model the side boundary conditions of the sample. The meso-parameters of the circular particles representing the soil and rock blocks of the (S-RM) have been obtained from laboratory tests and DEM numerical simulations of soil and rock samples. Based on the meso-parameters, a series of biaxial tests of (S-RM) sample have been conducted using the DEM numerical method. The shear strength, failure process and formation mechanism of shear zones in (S-RM) have been studied. With the increase of the confining stress, the rock blocks in or near the shear zones will be broken, changing the shape of the shear zones, and leads to the shear strength of the (S-RM) sample showing nonlinear characteristics. Furthermore, the strength envelope of (S-RM) sample can be fitted through a power law function in the p-q plane.

Discrete element modelling of a soil-rock mixture used in an embankment dam

The deformation and failure mechanism and the mechanical behavior of soil and soil-rock mixture used in an embankment dam was studied using numerical testing, based on a discrete element method (DEM). In this work, a 3D random meso-structure modelling system of soil-rock mixture is developed and used to generate a meso-structural model of soil-rock mixture. A non-overlapping combination method was used to model convex polyhedron rock blocks for the DEM numerical simulation. Based on the Voronoi cell, a method representing volume strain at particle scale is proposed. Results show that there is close contact between macro mechanical behavior and deformation localization of the sample. Rotation, occlusion, dilatation and a self-organizing force chains are remarkable phenomena of the localization band, and occur simultaneously with localization. Rock blocks influence localization characteristics and distribution of the force chains of the soil-rock mixture sample. Rotation and overcoming of the occlusion of the larger rock blocks in the localization band are more difficult than for small soil particles, which is the important reason for higher shear strength of soil-rock mixture than that of soil. The shearing process leads to anisotropy of the contact force, reaching its maximum at the start point of the plastic deformation, and then begins to decrease in the subsequent process.

Analysis of ballast direct shear tests by discrete element method under different normal stress

The discrete element method (DEM) was applied to simulate the direct shear tests of irregular ballast stones by constructing clump particles, where irregular clumped-particles have similar particle size distribution (PSD) with those of the real ballast stone. With these clumped particles, the interlock of ballast stones in the direct shear test is investigated. The nonlinear contact force model with Mohr–Coulomb is adopted to model the interaction of the clumped particles. With different normal loads, the simulated microscopic characteristics in the direct shear test were linked with that of tests. The results demonstrate that DEM numerical simulations can produce interrelated responses of the ballast behavior, including the critical state response and are in good agreement with experimental observations. The shear resistance value increases with the normal stress application, indicating that the lateral confinement of ballast bed leading to less vertical settlement and more track stability. In addition, the DEM can further provide details of the microstructure evolutions during shearing processes.

Thermal DEM–CFD modeling and simulation of heat transfer through packed bed

Abstract Heat transfer between particles takes place in a variety of industrial applications, but because of the stress and contact heterogeneities inherent to these applications, it is poorly understood, even in simple cases. Although particle–particle heat transfer is relatively weak compared with particle–fluid convection heat transfer, it may become very important in applications such as packed beds, where the fluid flow can be neglected or where fluid/particle stagnation areas can be observed. During our previous studies, CFD–DEM models and numerical simulations were developed to account for momentum and heat transfer between the fluid and the solid particles. The predictions of the simulations were validated with experimental data. In the present study, particle–particle and particle–wall heat transfer models were developed and integrated into our in-house unsteady three-dimensional discrete element method (DEM) software. Heat transfer simulations for predicting the effective thermal conductivity (ETC) of particulate beds under compression were conducted to validate these models with published experimental data. The results showed good agreement with the experimental data, and it was found that heat conduction through the bed's pores cannot be neglected even when particle thermal conductivity is much larger than that of the air. The influence of particle roughness on heat transfer through packed bed was examined. It was found that heat conduction through the packed bed pores cannot be neglected for rough particles.

DEM Numerical Simulation of Abrasive Wear Characteristics of a Bioinspired Ridged Surface

This paper presents numerical investigations into a ridged surface whose design is inspired by the geometry of a Farrer's scallop. The objective of the performed research is to assess if the proposed Bioinspired Ridged Surface (BRS) can potentially improve wear resistance of soil-engaging components used in agricultural machinery and to validate numerical simulations performed using software based on the Discrete Element Method (DEM). The wear performance of the BRS is experimentally determined and also compared with a conventional flat surface. Different size of soil particles and relative velocities between the abrasive sand and the testing surfaces are used. Comparative results show that the numerical simulations are in agreement with the experimental results and support the hypothesis that abrasive wear is greatly reduced by substituting a conventional flat surface with the BRS.

A discrete element method for the simulation of CFRP cutting

Orthogonal machining of unidirectional carbon fiber-reinforced polymer (UD-CFRP) composites is simulated using discrete element method (DEM). The objective of this work is to present a simple numerical model that allows the study the machining of unidirectional composites during orthogonal cutting. To control the physicochemical phenomena that occur during cutting, it is necessary to identify the parameters of contact, very difficult to measure experimentally. The DEM numerical simulation is presented then as an alternative to the problem. This tool has helped to recreate the physical mechanisms identified experimentally and to understand the origin of the abrasive wear of carbide tools. The observation of the chip formation using a high speed video camera made possible to validate qualitatively the results of numerical simulation by discrete elements. This tool can also determine the cutting forces quite close to reality.

Determining particulate–solid interphase strength using shear-induced anisotropy

The resistance to shear deformation developed by a granular material layer in contact with a topographically rough natural or manufactured solid material surface is critical to the stability of a variety of composite systems. By using discrete-element method numerical simulations, we show that evolution of fabric and contact force anisotropy at the boundary between the surface and the granular media controls shear behavior. Full mobilization of granular material strength occurs when the contact force anisotropy developed at the interface is equal to the maximum contact force anisotropy of the granular media.