DEM Simulations Research Articles

Fully Coupled CFD–DEM Simulation of Oil Well Hole Cleaning: Effect of Mud Hydrodynamics on Cuttings Transport

This paper presents a coupled computational fluid dynamics–discrete element method (CFD–DEM) simulation to predict cuttings transport by the drilling fluid (mud) in different oil well drilling conditions. The mud rheology is expressed by the Herschel–Bulkley behaviour and modelled in a Eulerian framework (CFD), while the cuttings are modelled using the Lagrangian approach (DEM). In this work, the effects of drill string rotation, inclination angle, cutting size, mud rheology, and annular velocity on cleaning efficiency are investigated. It is found that increasing the well deviation from vertical to horizontal leads to a higher cuttings concentration. However, at low annular velocity, the cuttings concentration for the inclined (45-degree) annulus is found to be higher than the horizontal one due to the sliding motion of cuttings on the lower section of the annulus. Overall, the drill pipe rotation has little effect on decreasing the cuttings concentration, but the effect is more pronounced at low annular velocity.

Construction of Maize Threshing Model by DEM Simulation

This paper proposes a modeling method of maize in threshing. The static friction coefficient and rolling resistance coefficient of the maize grain were measured using the slope method. The maize grain stacking angle test was designed using the central composite design response surface test. A regression model was established based on the simulation results to find the best combination. The results suggested that the modeling method proposed in this paper was effective in improving the accuracy of maize grain simulation compared with previous methods. Furthermore, this paper presents a method to verify the feasibility and reliability of the maize grain cob discrete element model using the distribution of grain in the granary and the final removal rate as the verification method. The results of the actually simulated threshing test were analyzed using a Wilcoxon signed-rank test, heat map analysis, and the Spearman’s rank correlation coefficient. It was found that the DEM model of maize cob is suitable for simulating the maize threshing process. This can aid in further research on the subject.

Wear at an incipient ploughing–cutting transition

Ductile wear is highly desirable in manufacturing and machining operations to achieve a high quality of finish. In a ductile regime of operation, a characteristic transition from ploughing to cutting is often observed in materials with different mechanical properties. We unveil the origin of this transition through a plastic, debris-free model of a tip causing wearing of a flat surface. The abraded volume depends on the equilibrium depth which is reached once the normal force is balanced by the lifting force during scratching. We show that the dependence of the equilibrium depth on the lifting force is highly non-linear and diverges above a threshold force that depends on the hardness, friction force and geometry of the tip. The threshold corresponds to a characteristic depth marking the ploughing–cutting transition. When this characteristic depth is below the ductile–brittle depth of cut, ploughing, cutting and brittle modes of operation are all possible. These abrasive wear modes are summarised in a unified mechanism map. The findings of this model, derived from theoretical considerations, are validated by DEM simulations and literature data from experiments.

Scale-up of dry impregnation processes for porous spherical catalyst particles in a rotating drum: experiments and simulations

Catalyst impregnation is the first step and one of the most crucial steps for preparing industrial catalysts. The process is typically performed in rotating vessels with a spray-nozzle to distribute the liquid onto porous catalyst supports until the pore volume is reached. The inter-particle variability of the impregnated liquid inside the particles significantly affects the activity and selectivity of the resulting catalyst. Current scale-up practices lead to poor fluid distribution and inhomogeneity in the liquid content. The aim of this work is to understand the dynamic behavior of the particles under the spray nozzle, which is essential for desired content uniformity, and to develop a scale-up model for the dry impregnation process. In this work, we considered four dimensionless numbers in the scaling analysis. The scale-up rules require that the dimensionless numbers are kept constant for different scales. Both DEM simulations and matching experiments of dry impregnation inside the porous particles were performed for different vessel sizes. The water content of the particles was compared for different times and locations, and the relative standard deviation is calculated from the axial water content. Simulation and experimental results show that particles achieve similar content uniformity at the end of impregnation, confirming that the scale-up rules are applicable to all vessel sizes. The dimensionless numbers give very good scale-up performance since curves collapse indicating similarity in the processes. In addition, the scale-up method is validated for different particle sizes in simulations.Graphical abstract

A study of membrane correction accounting for both curvature and tension in DEM simulations of triaxial tests of sand and ballast with two alternative flexible membrane models

In DEM simulations of triaxial tests, modelling a flexible lateral membrane is crucial and challenging. It is essential for the correct application of a uniform lateral pressure and for an accurate measurement of sample volume. Here, we introduce a membrane made of triangular facets, and model it as a continuum; we then compare this approach with a well-established method that uses a layer of bonded spheres. With either method, it is also possible to assess the additional stress applied by the membrane as it deforms, i.e. the difference between the stress applied at the boundary and the actual stress within the sample. It is shown that this difference has two origins: the tension developed in the membrane, as it deforms; and the curvature of the membrane, since this causes a vertical component of the confining pressure which can be significant. These findings may be used to inform and improve the membrane correction commonly used in experiments, where similar effects occur.Graphic abstract

Image-Based Tool Characterization and DEM Simulation of Abrasive Brushing Processes

Brushing with bonded abrasives is a finishing process used for deburring, edge rounding, and roughness reduction. However, due to the complex motion, chipping, and wear behavior of abrasive filaments, industrial brushing processes have historically relied on empirical knowledge. To gain a better understanding of filament interactions, a physical model based on the discrete element method was developed to simulate process forces and contact areas. Filament patterns of round brushes were determined through the use of laser line triangulation and image processing. These filament patterns showed interlocked filaments and yielded more accurate results when used in brushing simulations than the oversimplified square patterns, which were used in previous research. Simulation confirms the occurrence of filament interactions, distinguishes between sweeping and striking filament motions, and reveals dynamic behavior at high brushing velocities that may increase undesirable tool wear.

Representation of the microstructure of pearlitic steels for DEM simulations of fatigue

The fatigue behavior of pearlitic steels in wheel-rails is correlated to the microstructure. However, existing models do barely take this correlation into account. In this work, we propose a hierarchical meshing to describe the microstructure of pearlitic steels. The mesh includes grain and block/colony boundaries, lamellae orientations, and orientation perpendicular to lamellae. We use the Voronoi Tessellation method to generate elements with the specific area fraction distribution for pearlite colony areas. The colony and block information is obtained from SEM and EBSD measurements of R260 steel to construct the mesh that represents the microstructure. Finally, we obtained the deformed microstructure via simple geometrical shearing. This meshing method is the first step for modeling fatigue crack growth anisotropy due to plastic deformation.

Investigation of Suffusion in Soil with Arching Based on CFD–DEM Simulation

Investigation of Suffusion in Soil with Arching Based on CFD–DEM Simulation

Investigating Soil Arching in Pile-Supported Embankments through Physical Experiments and DEM Simulations

Investigating Soil Arching in Pile-Supported Embankments through Physical Experiments and DEM Simulations

An improved characterization model of liquefaction resistance by shear wave velocity for binary mixtures with consideration of coarse content

This paper aims to develop an improved CRR-Vs1 characterization model for soil liquefaction evaluation for binary mixtures via a series of DEM simulations of drained monotonic tests, undrained cyclic tests and shear wave velocity measurements. The contributions of different contact types to the mean effective stress of binary mixtures depend mainly on the coarse content and to a negligible extent on the confining pressure and particle size ratio. The threshold coarse content, denoting the mechanical behavior transition of binary mixtures, can be identified either by the macroscopic evolutions of critical state lines or the distributions of microscopic contact forces. The skeleton reinforcement factor m decreases approximately linearly with the increase of coarse content, while the skeleton supporting factor b exhibits a nonlinear decrease relationship with coarse content, both of which are influenced by particle size ratio. Under the condition of the same equivalent skeleton void ratio, a Vs-correction function and a CRR-correction function are introduced to consistently describe the nonlinear coarse content effects on the shear wave velocities and liquefaction resistances of binary mixtures. The improved CRR-Vs1 characterization model with consideration of coarse content is established by relating the shear wave velocity and liquefaction resistance of binary mixtures to those of the base fine or coarse matrix using the concept of equivalent skeleton void ratio. Application of the proposed characterization model to real geotechnical materials requires laboratory element tests to determine the Vs-correction function and the CRR-correction function, together with the CRR-Vs1 benchmark curve of the base fine or coarse matrix.

CFD–DEM Simulation of Heat Transfer and Reaction Characteristics of Pyrolysis Process of MSW Heated by High-Temperature Flue Gas

Pyrolysis is a promising disposal method for municipal solid waste (MSW) due to the high-value utilization of the organic components of MSW. Traditional indirect heating has low heat transfer efficiency and requires an increase in the heat exchange area. In this study, a refined numerical simulation model for the pyrolysis of four typical MSW components with high-temperature flue gas was established to study the influence of flue gas on the heat transfer and reaction characteristics of MSW. The temperature distribution and particle size change in different components were obtained, and the effects of flue gas temperature and velocity on the pyrolysis process were analyzed. It was found that the temperature difference of the four components along the bed height direction was about 1.36–1.81 K/mm, and the energy efficiency was about 55–61%. When the four components were uniformly mixed, the temperature increase rates of each component were similar during the pyrolysis process. As the flue gas temperature increased, the amount of gas consumption decreased and the energy efficiency increased. When the flue gas velocity increased, the flue gas consumption increased and the energy efficiency decreased. The research results are of great significance for the promotion and application of pyrolysis technology to MSW with high-temperature flue gas.

Improving the analysis of heat transfer in packed beds: A comparative study between DEM simulations and existing literature models

The heat transfer within particle beds is of significant importance in various industrial applications; however, its comprehension remains limited. The investigation of packed beds involves employing the use of effective thermal conductivity, a widely employed approach that is constrained by the need for extensive experimental work and the presence of heterogeneities. Discrete Element Method (DEM) simulations are widely recognized as a valuable tool for enhancing comprehension of complex systems. Nevertheless, the extensive computational time required for these simulations poses a significant limitation on their widespread implementation. The present study encompassed the integration of particle-particle and particle-wall heat transfer models into the MUSEN framework. The models were employed to simulate scenarios involving stationary packed particle beds. The proposed models were validated by data obtained from existing literature. A favorable agreement was achieved for all examined instances, with notable reductions in simulation times, comparable to those observed in simulations employing the continuum approach. The simulations were compared with established models in the literature, and the simulations exhibited higher accuracy in predicting experimental values. This highlights the potential of the proposed methodology to be utilized in heat transfer analysis while maintaining efficient simulation times, without the need for continuum approach simulations, and providing additional understanding of the underlying micro mechanisms.

Development of a novel perforated type precision metering device for efficient and cleaner production of maize

This research presents a filling method that strips the kernels from the seed group to address the poor performance and energy efficiency of the mechanical maize metering devices at high-speed operating conditions. In addition, it advances the design of a novel perforated type precision seed-metering device. The quantity and posture of seed filling are restricted by the perforated ring, which creates a dispersed particle flow, thus enhancing the filling effect of the seeding plate and reducing energy consumption. The structural design of critical components is completed, and the principle of improving performance and energy efficiency is analyzed. The DEM simulation and bench experiment assisted in analyzing the effects of operating parameters on seed dynamic characteristics, seeding plate's filling performance, and operational energy consumption. Finally, the optimal parameter combination is determined. The result demonstrates that the number of teeth in the perforated ring was 21, accompanied by an improved seed-filling effect and lower energy consumption. The metering performance was optimal when the tooth length of the perforated ring was 8.65 mm, the center angle of the teeth was 8°, and the operating speed was 13.55 km/h. Moreover, the qualified rate was 94.5%, the multiple rate was 2.7%, and the leakage rate was 2.8%. The operating speed was in the range of 8–14 km/h, the qualified rate of the perforated seed-metering device was higher than 92.7 %, the leakage rate was lower than 5.4 %, the multiple rate was lower than 3.5 %, and the coefficient of performance was more than 9.2. Its energy efficiency was significantly better than that of the picker finger seed-metering device and the air-suction seed-metering device, thus satisfying the demands for an efficient and cleaner production of maize.

DEM simulation of a single screw granulator: The effect of liquid binder on granule properties

The Caleva UK single-screw Variable Density Extruder (VDE) is a continuous powder processing equipment known for spheronization and extrusion. Its suitability for granulation remains uncertain, a common challenge in powder processing industries that deal with granules, pellets, and tablets. This study investigates the VDE's potential for granulation, using 65 µm CaCO3 powder and PEG 4000 as a liquid binder. In order to replicate several experimental setups with varying binder concentrations and liquid-to-solid ratios (L/S) of 0.1 and 0.15, eight DEM simulations were run. Our results indicate that higher binder concentrations yield more consistent products with fewer fines, while lower concentrations result in inconsistent products with increased fines. Low L/S ratios produce fragile, fine-sized products with a broad particle size distribution (PSD). DEM simulations reveal a direct relationship between liquid binder content and contact forces. Analysis of bonds formed, and particle counts in simulations corroborates experimental observations of fines production. Additionally, granule strength appears to be directly proportional to contact force.

Discussion on “Study on mechanical and fracture characteristics of rock-like specimens with rough non-persistent joints by YADE DEM simulation”

Discussion on “Study on mechanical and fracture characteristics of rock-like specimens with rough non-persistent joints by YADE DEM simulation”

Micro‐mechanism of stress‐dilatancy anisotropy in granular materials: Affine and nonaffine deformation

AbstractThe stress‐induced dilatancy anisotropy is an important kinematic response in granular materials and is very complex due to the stochastic motion of particles. In this study, the local stress‐dilatancy relationship is investigated referring to the local contact force and relative displacement in a certain contact direction. The micromechanism of this anisotropy is investigated from the view of affine and nonaffine approaches based on DEM simulation. Numerical results indicate that the local nonaffine dilatancy/contraction tendency is opposite with that of local affine deformation in macroscopic compression and extension direction, which mainly stems from the counteraction effect between the normal components of affine and nonaffine displacements. The local stress‐dilatancy of affine and nonaffine components is linear and orientation‐dependent, which results in the nonlinear character of macroscopic stress‐dilatancy. By establishing an analytical relation of stress‐dilatancy, the local affine/nonaffine dilatancy is decomposed into the component of stress‐induced dilatancy synchronized with the local stress anisotropy; and the component of stress‐induced dilatancy asynchronized with the local stress anisotropy. The former is related to the unchanged isotropic microstructure, and the latter attributes to the anisotropic microstructure. Besides, the contribution of nonsliding contacts to nonaffine dilatancy is larger than that of sliding contacts even for the case of relatively higher sliding ratio, which indicates that the heterogeneous deformation attributes not only to the friction dissipation, but to the blocked energy at micro contacts in granular materials.

Research on the propagation mechanisms and meso-mechanical responses of reflective cracking on the asphalt overlays on concrete airfield pavement by Fiber Bragg Grating sensing technology

This study evaluated the propagation mechanisms and dynamic meso-mechanical responses of reflective cracking on the asphalt overlays on concrete airfield pavement based on flexible Fiber Bragg Grating (FBG) sensors. The encapsulated FBG sensors were efficiently calibrated, possessing outstanding capability for the measurement of transverse expansion of lateral reflective cracking propagation. Virtual three-point bending test model was proposed and validated by macroscopic indoor experiments. The DEM model facilitated quantifying the proliferation of reflective cracks, unraveling the trajectory from micro-crack inception to visible macroscopic manifestation. Results indicated that the emergence and elongation of the composite structure experienced three phases: the initiation and accumulation of microcracks, the extension of reflective cracking, and the ultimate penetration. The DEM simulation and FBG sensors were recommended to establish a mutually reinforcing mechanism for nuanced validation of reflective crack formation on the composite structures of asphalt overlays on concrete airfield pavement.

Exploring the role of particle-form polydispersity in the fabric of granular packing: Insights from DEM simulations with ellipsoidal particle assemblies

Granular materials, such as sand, exhibit a wide range of particle sizes and shapes, known as polydispersity. This study aims to investigate the effects of particle-form (first-level approximation of particle shape) polydispersity on a fabric of granular packing using DEM simulations of ellipsoidal particle assemblies. A framework for DEM simulations is proposed to investigate the particle-form polydispersity, and an overall polydispersity index (OPI) is introduced to quantify its magnitude. Various parameters are employed to quantify the fabric, including packing density, coordination number, contact force, and fabric anisotropy. The results highlight that the particle-form polydispersity notably affects the packing density and mean coordination number of the granular packings. Furthermore, a prediction model for the packing density and mean coordination number of polydisperse packings is proposed based on the correlations fitted from the monodisperse packing data.

Strain localization in the standard triaxial tests of granular materials: Insights into meso‐ and macro‐scale behaviours

AbstractThe standard triaxial tests cease to be valid as material tests since the homogeneity of the granular mass is lost when localized failures such as shear bands occur requiring a different approach to interpreting and analyzing material responses at the meso scale from the macro behaviour. This study sheds light on the above issue by analyzing the standard triaxial tests of the granular specimens undergoing localized failure at different scales using DEM. For the first time, the behaviour of material inside and outside of the shear band as well as the entire sample are quantitatively quantified through DEM simulations. The results enable confirmation of various theoretical hypotheses and experimental observations on the localized failure in granular materials. For example, by quantifying the inter‐particle contact forces of materials inside and outside the shear band zone, it is confirmed that the material outside the localization band undergoes inelastic unloading beyond the bifurcation point, while those inside the localization band experience inelastic shearing to reach the critical state. Moreover, the analysis in this study suggests that if the volume of the localization zone can be precisely measured from the experiment, the mesoscale constitutive responses that truly represent the inelastic behaviour can be quantified. This gives rise to a more appropriate method to obtain inelastic constitutive responses of granular materials from specimens undergoing localized failure in triaxial tests.

Framework for incorporating multi-level morphology of particles in DEM simulations: independent control of polydisperse distributions of roundness and roughness while preserving form distributions in granular materials

Framework for incorporating multi-level morphology of particles in DEM simulations: independent control of polydisperse distributions of roundness and roughness while preserving form distributions in granular materials