Discrete Element Simulations Research Articles

Optimization Design and Experimentation of a Soil Covering Device for a Tree Planting Machine

In an effort to improve the soil covering effect of tree planting machines and reduce the lodging rate of seedlings, this paper analyzes the soil covering process and working principle of the soil covering device of tree planting machines and designs a soil covering device with adjustable soil covering width. With the help of the discrete element simulation software EDEM, the orthogonal test was designed with the width of the covering soil and the inclination angle as the test factors and the soil backfill rate as the response index. The regression analysis of the test results was carried out by Design-expert, and the optimal parameter combination of the covering soil device was determined as follows: the width of the covering soil: 600 mm, the forward angle: 45°, and the depth of the soil: 20 mm. The prototype verification test was carried out under the optimal parameters, and the soil backfill rate was 88.4%, which was basically consistent with the optimized parameters. The soil covering device with adjustable width designed in this study is of great significance to improve the soil covering rate of tree planting machines and reduce the lodging rate of seedlings.

Evaluation of Mixing Effects and Particle Breakage on a Cross Flow Turbine with DEM

AbstractVarious effects during conveying and storage processes lead to size segregation of bulk material, but many applications require a mostly constant particle size distribution. Especially during bunker filling, segregation effects are noticed, which are further intensified by possible core flow effects. In order to reduce segregation effects during bunker filling, a cross flow turbine is installed at a bunker used for storage of blast furnace sinter. In this contribution, discrete element simulations were performed to analyze mixing effects and possible particle breakage due to the cross flow turbine. Significant mixing effects during bunker filling are noticed due to the cross flow turbine. The results show a more evenly distributed bunker outflow in terms of particle size.Particle breakage is analyzed by means of a newly developed breakage model for the Discrete Element Method (DEM). The model is based on a probabilistic particle replacement with voronoi-tessellated fragments. The validated breakage model allows high accuracy in prediction of fragment size distribution. Fragments are further breakable, which allows simulation of processes with several damaging effects. The breakage model was calibrated with a specially developed automated single particle impact tester for rapid analysis of breakage characteristics of bulk materials.

Simulation Analysis and Optimization Design of Paddy Field Mud Spreader Blades for Uniform Dispersion

To improve the distribution of mud particles collected in the tray during the operation of paddy field mud spreader blades, the optimal combination of parameters for the blades that results in the best uniformity of mud dispersion needs to be identified. In this study, a thorough force analysis was conducted on the spreading process, and computational equations were formulated to describe the motion of mud particles. By utilizing the discrete element simulation technique, a simulation model was developed to accurately represent the intricate interaction between the blades and mud particles. Through the single-factor simulation experiments, the ranges of key parameters such as the rotation radius, bending angle, sub-blade tilt angle, forward velocity, and rotational speed of the blade were determined. A secondary orthogonal rotational combination design was employed to establish a regression prediction model between the non-uniformity of mud dispersion and the key blade parameters. Subsequently, a multivariate single-objective optimization method was used to develop an optimization model for the non-uniformity of mud dispersion. The results indicate that the hierarchical order of factors influencing the non-uniformity of mud dispersion is as follows: rotation radius > rotation speed > bending angle > forward velocity > sub-blade tilt angle. To achieve a minimum spreading non-uniformity of 29.63%, a specific configuration is required, which includes a blade rotation radius of 188 mm, a bending angle of 121°, a sub-blade tilt angle of 30°, a forward velocity of 400 mm/s, and a rotation speed of 191 r/min. Finally, the accuracy of the optimization results was verified by means of bench tests. The research results provide a crucial reference for enhancing the uniformity of mud dispersion in paddy field mud spreader blades.

Dual-scale 3DEC-GBM Discrete Element Simulation On Mechanical Behavior and Anisotropic Fracture Evolution Mechanism of Rock Induced by True Three-dimensional Stress

Dual-scale 3DEC-GBM Discrete Element Simulation On Mechanical Behavior and Anisotropic Fracture Evolution Mechanism of Rock Induced by True Three-dimensional Stress

How Fast are Elastic Domino Waves?

The paper is concerned with the problem of toppling propagation velocity in elastic, domino-like mechanical systems. We build on the work of Efthimiou and Johnson, who developed the theory of perfectly elastic collisions of thin rigid dominoes on a frictional foundation. This theory has been criticised for the lack of correspondence with the experimental observations, in particular, prediction of infinite propagation velocity for zero spacing between dominoes, as well as the inability to represent the collective nature of collisions in real domino systems. In our work we consider a more realistic scenario of dominoes of finite stiffness and obtain a theory of fast elastic domino waves, taking into account a limit velocity of the perturbation propagation in the system of dominoes. Moreover, finite collision time allows to extract dynamic quantities of collisions and establish upper and lower borders for domino separations where the theory could still be applied. Our discrete element simulations support our theoretical findings and shed light on the nature of collective interactions in the nearly-elastic domino chains.Graphical abstract

Simulation and Identification of Multiscale Falling Morphology of Fresh Tea Leaves at Different Transport Speeds Based on Discrete Element Method

To explore the falling morphology of multiscale fresh tea leaves at different speeds, this study evaluated the multiscale fresh tea leaves (one bud with two leaves, one bud with one leaf, single leaf, and damaged leaf) at different heights (0.7 m, 0.5 m, 0.3 m, and 0.1 m from the ground) during the process of dropping on the conveyor belt at different speeds (0.6 m/s and 1.2 m/s). The motion morphology of fresh tea leaves on multiple scales was analyzed by discrete element simulation, the results showed that the movement patterns of multiscale fresh tea leaves at different positions from the ground were different when the conveyor was dropping at different speeds, and that the multiscale fresh tea leaves all rotated around the long axis, short axis, and root of the fresh tea leaves. When the conveying speed of the conveyor belt was 0.6 m/s, the movement patterns of one bud with two leaves and of one bud with one leaf of fresh tea were near the ground, and the movement patterns of the fresh tea leaves were mostly oriented toward the ground. The leaf tips of the fresh tea leaves were mostly on the side near the ground, the damaged leaves were near the ground, and the movement patterns of the fresh tea leaves were mostly parallel to the ground. When the conveyor belt throwing speed was 1.2 m/s, the roots of one bud with two leaves moved toward the ground when they were close to the ground. When one bud with one leaf was close to the ground, the leaf tip moved toward the ground, and the single leaf and damaged leaf rotated around the root because of the inertia of the conveyor belt throwing.

A Review of Contact Models’ Properties for Discrete Element Simulation in Agricultural Engineering

In agricultural engineering, the discrete element simulation of the operational structure, object of movement, and force has become a standard method of modern agricultural equipment design. The selection and development of an appropriate contact model are critical factors affecting the accuracy of the process of the simulation calculation of the movement and force. Understanding how to choose or establish suitable contact models according to different research fields, objects, and purposes has become the focus of present research. This paper gives an overview of contact models for discrete element simulation, summarizes and analyzes the simulation calculation basis of different contact models, and focuses on the application status and scenarios of different models at this stage. It analyzes and summarizes the selection basis and application fields of contact models. The next direction in the development of discrete element simulation contact models should be the hybrid application of multicontact models and the precise development of specialized contact models. It is necessary to establish a standardized parameter-calibration process for different contact models to guarantee the accuracy of the models, to improve the application of computer arithmetic, and to establish an efficient and accurate simulation contact model selection and application in the field of agricultural engineering. Efficient and accurate simulation contact model selection, design theory, and calculation processes will improve the efficiency of modern agricultural machinery design.

Influence of multiple detachments on structural vergence and evolution of the thin-skinned fold-and-thrust belt in the eastern Sichuan Basin: Insights from numerical modeling

The thin-skinned fold-and-thrust belt with multiple detachments in the eastern Sichuan Basin is characterized by a series of fault-detachment folds with a backward preferred structural vergence, which is rare in nature and can't be explained well by the classic critically taper theory. Here, three discrete element simulations were conducted to study the influence of multiple detachments on the structural vergence and evolution of the eastern Sichuan thin-skinned fold and thrust belt. The experimental results reveal that multiple detachment layers affected the bulk mechanical strength and facilitated a dually vergent thrust wedge with a backward preferred structural vergence. The addition of intermediate detachment layers influences structural vergence and fault activity of thrust wedges. With the increase in intermediate weak layers, the preferred structural vergence of these model results progressively moved from forward to nearly symmetric and eventually to backward. These results exhibit first-order structural similarities to the structural vergence and fault activity in the eastern Sichuan fold and thrust belt, which indicates that the influence of the internal distribution of weak layers within the eastern Sichuan Basin should not be ignored. The limited Cambrian evaporite layer and the widespread Silurian shale and Lower-Middle Triassic evaporite layers had significant impacts on the deformation of the fold-and-thrust belt in the eastern Sichuan basin. Consequently, we propose a kinematic model for the coupled geodynamic processes of the eastern Sichuan fold-and-thrust belt. The framework of the eastern Sichuan Basin with a number of backward fault-detachment folds was formed by Mesozoic northwestward propagation, and Cenozoic eastward propagation reactivated the folding and thrusting. The Huayingshan fault was affected by the limited Cambrian evaporite layer.

Parameter Calibration for Discrete Element Simulation of the Interaction between Loose Soil and Thrown Components after Ginseng Land Tillage

Given the lack of accurate and reliable discrete element simulation parameters to study the interactions between soft soil and soil casting components after ginseng land cultivation in Northeast China and the design of ginseng land-specific borders, this paper calibrates the relevant model parameters of ginseng soil using the Hertz–Mindlin with JKR contact model in EDEM to standardize the contact parameters between soil particles and between soil and Q235 steel in soft soil after cultivation in ginseng land. Taking the soil particle accumulation angle as the response value, a Box–Behnken design (BBD) was introduced to establish a regression model for the soil accumulation angle; the surface energy, static friction coefficient, rolling friction coefficient, and coefficient of restoration parameters were obtained, respectively, through the optimization of the model, at which time, the simulated value of the soil accumulation angle was 37°, which is a 4% relative error to the actual measured accumulation angle of 35.5°. Taking the sliding friction angle of the soil on the Q235 steel plate as the response value, the regression model of the soil sliding friction angle was obtained based on the BBD. The static friction factor, rolling friction factor, and coefficient of restitution between the soil particles and the Q235 steel were obtained, respectively. Based on the combination of these parameters, the simulated value of the sliding friction angle was 32.2°, which is a 2% relative error to the measured accumulation angle of 31.5°. To verify the accuracy of the optimized simulation parameters, field and simulation tests of soil-throwing components were conducted. The results show that the maximum relative error between the measured value and the simulation value is 5.6% and 3.4%. The error is within an acceptable range, and the simulation test and field test soil-throwing effects are the same, which verifies the accuracy and reliability of the reference soil parameter calibration. The results of the study can be used for discrete element simulation analysis of the interaction between ginseng loam and touchdown components and their structural optimization.

Calibration of Simulation Parameters for Fresh Tea Leaves Based on the Discrete Element Method

To address the problem of a lack of accurate parameters in the discrete element simulation study of the machine-picked fresh tea leaf mechanized-sorting process, this study used machine-picked fresh tea leaves as the research object, established discrete element models of different fresh tea leaf components in EDEM software version 7.0.0. based on the bonded particle model using three-dimensional scanning inverse-modeling technology, and calibrated the simulation parameters through physical tests and virtual simulation tests. Firstly, the intrinsic parameters of machine-picked tea leaves were measured using physical tests; the physical-stacking tea leaf test was conducted using the cylinder lifting method, the tea leaf repose angle being 32.62° as measured from the stacking images using CAD. With the physical repose angle as the target value, the Plackeet–Burman test, the steepest-ascent test and the Box–Behnken optimization test were conducted in turn, and the results showed that the static friction coefficient between tea leaves, the rolling friction coefficient between tea leaves and the static friction coefficient between tea leaves and PVC have a major effect on the repose angle, and the optimal combination of the three significant parameters was determined. Finally, five simulations were conducted using the optimal combination of parameters, the relative error between the repose angle measured by the simulation test and the physical repose angle being just 0.28%. Moreover, the t-test obtained p > 0.05, indicating that there was no significant difference between the simulation test results and the physical test results. The results showed that the calibrated discrete element simulation parameters obtained could provide a reference for the discrete element simulation study of fresh tea leaves.

Development and Experimentation of Intra-Row Weeding Device for Organic Rice

Weeds in paddy fields can seriously reduce rice yield. An intra-row weeding device with double-layer elastic rods was designed, considering the differences in mechanical properties between rice and weeds, which can press weeds into the soil and avoid damaging rice. The elastic force of the elastic rods can be adjusted by changing the position of the regulating mechanism to adapt to different weeding conditions. A measurement experiment was conducted to determine the variation rule of elastic force. The quadratic orthogonal rotation combination discrete element simulation experiment, which used weeding depth and weeding speed as experimental factors, and the amount of soil disturbance and the force of the inner and outer elastic rod in the horizontal and vertical directions as experimental indicators, was conducted to study the interaction between the weeding device and the soil. The optimal weeding parameters were obtained: the weeding depth was 15 mm, the weeding speed was 0.9 m/s. The field experiment, which used the various parameters of the weeding device as experimental factors and the weeding rate and damaging seedling rate as experimental indicators, was conducted to determine the weeding effect. The experimental results showed that the optimal position of the regulating mechanism was 270 mm, with a weeding rate of 80.65% and a damaging seedling rate of 3.36%. The weeding rate can be increased by at least 11.18% by adjusting the regulating mechanism to a suitable position under the same weeding conditions. This study can provide a reference for research on weeding machinery for organic rice.

Design and Experiment of Active Spiral Pushing Straw Row-Sorting Device

Aiming to solve the problems of excessive straw residue and large soil loss in the seeding belt of the straw row-sorting operation when the full volume of straw is crushed and returned to the field in the northeastern region of China, an active spiral pushing straw row-sorting device (ASPSRD) was designed in this paper. The straw on the surface of the land is collected and stirred by the high-speed rotating spiral-notched blades in the device and pushed to the non-seeding area for the purpose of cleaning the seeding belt. The parameters of key components were determined through theoretical analysis. The orthogonal combination test method of four factors and three levels was adopted. The EDEM discrete element simulation experiment was carried out by selecting the straw mulching quantity (SMQ), the rotating speed of the active rotating shaft (RSARS), the forward speed of the tractor (FST), and the notch width of the spiral notch blade (NWSNB) as the test factors, and the straw-cleaning rate (SCR) and soil loss rate (SLR) as the test indexes. Through range analysis, the parameters were optimized, and the optimal operation parameters of the straw row-sorting device were determined as follows: SMQ was 1.8 kg/m2, RSARS was 120 rpm, FST was 4 m/s, and NWSNB was 9 mm. The operational performance of the device was verified by field experiments. The results of the test showed that after the device was operated with the optimal combination of parameters, the SCR of the 20 cm wide seeding belt was 95.32%, and the SLR was 7.12%, which met the agronomic and technical requirements of corn no-tillage sowing operation in Northeast China. This study can provide a reference for the design of a straw row-sorting device of a no-tillage machine.

Calibration and Testing of Parameters for the Discrete Element Simulation of Soil Particles in Paddy Fields

The parameters of the discrete element simulation model for rice field soils serve as valuable data references for investigating the dynamic characteristics of the walking wheel of high-speed precision seeding machinery in paddy fields. The research specifically targets clay loam soil from a paddy field in South China. Calibration of essential soil parameters was achieved using EDEM_2022 software (and subsequent versions) discrete element simulation software, employing the Edinburgh Elasto-Plastic Adhesion (EEPA) nonlinear elastic-plastic contact model. The tillage layer and plough sub-base layer underwent calibration through slump and uniaxial compression tests, respectively. Influential contact parameters affecting slump and axial pressure were identified through a Plackett–Burman test. The optimal contact parameter combinations for the discrete element model of the tillage layer and plough sub-base layer were determined via a quadratic rotational orthogonal test. The accuracy of the discrete element simulation model’s parameters for paddy field soils was further validated through a comparative analysis of the simulation test’s cone penetration and the field soil trench test. Results indicate that the Coefficient of Restitution, surface energy, Contact Plasticity Ratio, and Tensile Exp significantly influence slump (p < 0.05). Additionally, the Coefficient of Restitution, Contact Plasticity Ratio, coefficient of rolling friction, and Tangential Stiff Multiplier significantly impact axial pressure (p < 0.05). Optimal contact parameters for the plough layer were achieved with a particle recovery coefficient of 0.49, a surface energy of 18.52 J/m2, a plastic deformation ratio of 0.45, and a tensile strength of 3.74. For the plough subsoil layer, optimal contact parameters were a particle recovery coefficient of 0.47, a coefficient of interparticle kinetic friction of 0.32, a plastic deformation ratio of 0.49, and a tangential stiffness factor of 0.31. Results from the cone penetration test reveal no significant disparity in compactness between the actual experiment and the simulation test. The calibrated discrete element model’s contact parameters have been verified as accurate and reliable. The findings of this study offer valuable data references for understanding the dynamic characteristics of the walking wheel of the entire machinery in high-speed precision seeding in paddy fields.

Hydrodynamics of polydisperse gas-solid flows: Kinetic theory and multifluid simulation

Polydisperse gas-solid flows, which is notoriously difficult to model due to the complex gas-particle and particle-particle interactions, are widely encountered in industry. In this article, a refined kinetic theory for polydisperse flow is developed, which features single-parameter Chapman-Enskog expansion (the Knudsen number) and exact calculation of the integrations related to pair distribution function of particle velocity without any mathematical approximations. The Navier-Stokes order constitutive relations for multifluid modeling of polydisperse gas-solid flow are then obtained analytically, including the solid stress tensor, the solid-solid drag force, the granular heat flux and the energy dissipation rate. Finally, the model is preliminarily validated by comparing to the discrete element simulation data of one-dimensional granular shear flow and by showing that the hydrodynamic characteristics of gas-solid flows in a bubbling fluidized bed containing bidisperse particles can be successfully predicted.

A novel creep contact model for rock and its implement in discrete element simulation

The creep behavior of rocks significantly impacts projects' structural safety, including mining, tunneling, and hydraulic engineering. Numerous creep models used in numerical calculations incorporate basic elements, such as Burger's model. However, relying solely on series or parallel combinations of these basic components fails to account for the accelerated creep stage, prompting efforts toward developing enhanced creep models. Despite noted progress, a limited number of studies on the full-process simulation of graded creep loading and the consequent generation of cracks. To overcome this problem, an innovative creep model is proposed based on both the Parallel Bond and the Kelvin-Voigt contact models. This proposed creep model simulates the graded loading creep test of rocks under different load conditions and also conducts a parameter sensitivity analysis for the impact of the proportionate discrepancy between the two contact models. The results indicate that this new creep model could successfully simulate the comprehensive creep process, effectively capture crack progression, and represent ultimate failure modes during the creep process. Notably, to ensure the precision of simulations, it is recommended that the proportion of the Kelvin-Voigt contact model within the total contact is at most 25%.

Extended kinetic theory applied to pressure-controlled shear flows of frictionless spheres between rigid, bumpy planes.

We numerically investigate, through discrete element simulations, the steady flow of identical, frictionless spheres sheared between two parallel, bumpy planes in the absence of gravity and under a fixed normal load. We measure the spatial distributions of solid volume fraction, mean velocity, intensity of agitation and stresses, and confirm previous results on the validity of the equation of state and the viscosity predicted by the kinetic theory of inelastic granular gases. We also directly measure the spatial distributions of the diffusivity and the rate of collisional dissipation of the fluctuation kinetic energy, and successfully test the associated constitutive relations of the extended kinetic theory, i.e., a kinetic theory which includes the role of velocity correlations. We then phrase and numerically integrate a system of differential equations governing the flow, with suitably modified boundary conditions. We show a remarkable qualitative and quantitative agreement with the results of the discrete simulations. In particular, we study the effect of (i) the coefficient of collisional restitution, (ii) the imposed load and (iii) the bumpiness of the planes on the profiles of the hydrodynamic fields, the ratio of shear stress-to-pressure and the gap between the bumpy planes. Finally, we predict the critical value of the imposed load above which crystallization occurs, based on the value of the solid volume fraction near the boundaries obtained from the numerical solution of the kinetic theory. This notably reproduces what we observe in the discrete simulations.

Shear zones in granular mixtures of hard and soft particles with high and low friction.

Granular materials show inhomogeneous flows characterized by strain localization. When strain is localized in a sheared granular material, rigid regions of a nearly undeformed state are separated by shear bands, where the material yields and flows. The characteristics of the shear bands are determined by the geometry of the system, the micromechanical material properties, and the kinematics at the particle level. For a split-bottom shear cell, recent experimental work has shown that mixtures of hard, frictional and soft, nearly frictionless particles exhibit wider shear zones than samples with only one of the two components. To explain this finding, we investigate the shear zone properties and the stress response of granular mixtures using discrete element simulations. We show that both interparticle friction and elastic modulus determine the shear-band properties and packing density of granular mixtures of various mixing ratios, but their stress response depends strongly on the interparticle friction. Our study provides a fundamental understanding of the micromechanics of shear band formation in granular mixtures.

Parameter calibration and experimental verification of discrete element simulation model for Protaetia brevitarsis larvae bioconversion mixture

Parameter calibration and experimental verification of discrete element simulation model for Protaetia brevitarsis larvae bioconversion mixture

Calibration and test of contact parameters for alfalfa stalk at primary florescence based on discrete element method.

In view of the lack of accurate models for discrete element simulation in the current research and development process of forage harvesting and crushing machinery, the contact parameters were calibrated based on Hertz-Mindlin (no slip) contact model by EDEM simulation software with alfalfa stalk at primary florescence as the research object. Based on the angle of repose, the restitution coefficient, static friction coefficient, rolling friction coefficient of alfalfa stalks were determined through the Placket-Burman test, steepest ascent test and Box-Behnken test. The simulation test of the repose angle was carried out with the determined contact parameters. The results showed that the relative error between the simulated repose angle and the physical test repose angle was 0.48%, which indicated that the calibrated contact parameters could truly reflect the physical characteristics of alfalfa stalks at the primary florescence. It provided a reliable model and parameter calibration method for the discrete element simulation in the research and development process of forage machinery, and also provided a reference for the research and optimization design of forage harvesting, crushing and processing machinery.

Particle clogging mechanisms in hyporheic exchange with coupled lattice Boltzmann discrete element simulations

The clogging of a stream bed has a significant impact on the exchange of water between a river and groundwater, known as hyporheic exchange. Clogging issues in orifices influenced by fluid flow have long been a concern, particularly in understanding clogging mechanisms and particle dynamics. This study focuses on investigating the behavior of poly-dispersed particle systems in the Shanghai soft soil using a coupled lattice Boltzmann method and a discrete element method (LBM-DEM). A particle-orifice model was developed based on LBM-DEM to study the clogging problem. Three different orifice diameters with the same particle size distribution were set at a microscopic scale. The simulation results indicate that the primary form of clogging is the formation of particle domes, exhibiting distinct characteristics depending on orifice size. As the orifice size increases, clogging becomes more challenging. Interestingly, the flow rate of fluid passing through clogged orifices is quite complex, as it does not decrease significantly. The formation process of the particle structure shows significant randomness, posing challenges for quantitative analysis and experimental validation. This study provides insights into the initial stages of clogging formation, leading to a better understanding of hyporheic exchange phenomena in stream bed ecosystems.