Discrete Element Model Simulations Research Articles

A multiscale bifurcation analysis using micromechanical-based constitutive tensor for granular material

The current study presents a multiscale approach that investigates material instability and localization phenomena in plastic granular materials and the discrete-continuum duality. A bifurcation and stability analysis in continuum mechanics usually requires the material’s tangent (stiffness) operator, the computation of which in a micromechanical approach such as Discrete Element Modeling (DEM) requires specific treatment. To bridge the discrete and continuum worlds, a new computational approach incorporating strain probing is proposed to reconstruct the elastoplastic constitutive tensor and its spectral characteristics from DEM simulations. The probing technique permits the computation of the tangent operator that inherits microstructural information from the discrete world to analyze bifurcation in elastoplasticity at the macro level. An incrementally linear constitutive tensor is computed, distinct for each of the ensemble of probing directions belonging to a particular tensorial zone or sector of incremental stress or strain space, thus making it directionally non-linear. Following such an approach, material instability can be evaluated from the spectral characteristics of the tangent constitutive tensor deduced from DEM probing calculations belonging to an identified tensorial zone. A meso-scale analysis is finally offered to detect shear band localization through the well-known Rice’s criterion as a continuum-based concept extended to a micromechanical discrete modeling framework. These new numerical results show that the multiscale proposed approach, which allows access to microstructural information, is consistent with a continuum one such as when predicting the localization angle during shear banding in a granular specimen in DEM.

Multi‐scale study of fluidized bed‐chemical vapour deposition process in nuclear fuel coated particle fabrication for high‐temperature gas‐cooled reactor: A review

AbstractFluidized bed‐chemical vapour deposition (FB‐CVD) is a kind of key technology used widely in many application fields, such as semiconductors, nuclear energy, energy storage, and catalysts. In recent years, it has drawn much attention in the preparation of nuclear fuel coated particles (CP). It also has long played a crucial role in the preparation of high‐temperature gas‐cooled reactor (HTGR) fuel pebbles. The multi‐scale study of FB‐CVD technology has paid attention to the industrial fabrication of nuclear fuel particles at a large scale. In this paper, the recent FB‐CVD studies of different application fields are summarized first. Then, the recent works of our group in the field of FB‐CVD process in nuclear fuel particle fabrication are summarized. The FB‐CVD process in nuclear fuel particle fabrication and the multi‐scale study of the FB‐CVD process are overviewed in detail. Molecular dynamics (MD) simulation is used to study the CVD process of preparing the coating layer at the micro‐scale. Computational fluid dynamics–discrete element model (CFD‐DEM) simulation is used to study the high‐density particle fluidization, mixing particle fluidization, and particle coating process at the particle scale. Process simulation is used to study the entire FB‐CVD production line at the macro scale. Finally, the great application potential of the multi‐scale coupling study of the FB‐CVD process in the industrial fabrication of nuclear fuel particles is revealed. This paper is helpful to develop the academic research field of fluidized beds. It also has inspiration and reference significance for the expansion of other industrial applications of FB‐CVD.

小区小麦联合收获机割台清理离散元仿真参数标定

The analysis of the clearing process of the cutting deck of a small plot wheat combine harvester requires the use of discrete element simulation methods. However, the current simulation test lacks the contact parameters such as wheat stalk and stalk-seed. In this paper, the wheat stalks and seeds at harvest time were taken as the research objects, and the calibration study of the discrete element simulation model parameters of stalks and stalk-seeds was carried out by means of mechanical test determination and EDEM software simulation. The stiffness coefficients of wheat stalks were determined by mechanical tests; the average values of wheat stalk stacking angle of 39.22° and wheat stalk-seed stacking angle of 44.41° were obtained by stacking angle tests. By the steepest climb test and binary regression test, the stalk normal stiffness coefficient was determined to be 5e+08N/m2 and tangential stiffness was determined to be 6.35e+08N/m2; the stalk-stalk collision recovery coefficient was obtained to be 0.551, static friction coefficient was obtained to be 0.797, and rolling friction coefficient was obtained to be 0.079 by the two-level analytical factorization test, the steepest climb test, and the three-factor response surface test. Based on this, the average value of wheat stalk-seed stacking angle was obtained to be 39.22° and the average value of wheat stalk-seed stacking angle was obtained to be 44.41° by the stacking angle test. On this basis, the coefficient of recovery of stalk-stalk collision was 0.434, the coefficient of static friction was 0.884, and the coefficient of rolling friction was 0.339 obtained by the three-factor response surface test. Three validation experiments were carried out by substituting the obtained parameters into the simulation test, and the error values were close to the error value %0.255 in the model, which proved that the experimental data were reliable.

Influence of cavity partition on the damping performance of additively manufactured particle dampers

Additively manufactured particle dampers (AMPDs) are innovative particle dampers created by intentionally preserving unfused powder within a structure during laser powder bed fusion. One of their distinct advantages is the ease of fabricating structures with multiple cavities. This study focused on exploring the influence of cavity partitioning on the damping capacity of AMPDs at five different frequencies (200, 500, 1000, 1500, and 2000 Hz) and an acceleration range of 50–250 m/s2. Five AMPDs were designed to have similar cavity ratios while differing in cavity size. A complex power experiment and discrete element model simulation analysis were carried out. Notably, a consistently larger clearance between the ceiling of the wall and the powder bed was observed in the AMPDs with larger cavity sizes. Furthermore, dividing a larger cavity of AMPD into several smaller cavities emerged as an effective approach to maintain the damping performance at higher frequencies.

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.

On the friction dependency of the stress Lode angle

AbstractThe shape of the failure locus of a material is significant for its strength predictions. Even when constitutive models include the same critical stress surface, different critical stress ratios can be predicted for an identical applied isochoric strain path. In this article, we investigate critical stress predictions of different constitutive models, which include the surface according to Matsuoka–Nakai (MN). We perform analytical investigations, true triaxial test simulations with hypoplasticity and barodesy, and discrete element modelling (DEM) simulations to investigate the friction dependency of the stress Lode angle. Our results demonstrate that in hypoplasticity, the direction of the deviatoric stress state at critical state depends solely on the direction of the applied deviatoric strain path. In contrast, in barodesy, the predictions are also dependent on the friction angle of the material. In addition, we compare these results with those obtained with a standard elastoplastic MN model. To validate this friction dependency on the stress Lode angle, we conduct DEM simulations. The DEM results qualitatively support the predictions of barodesy and suggest that a higher friction results in a higher Lode angle at critical stress state.

A numerical study on the multi-cycle self-burrowing of a dual-anchor probe in shallow coarse-grained soils of varying density

Development of self-burrowing probes that can penetrate soils without the aid of external reaction force from drill rigs and trucks would facilitate site characterization activities and deployment of sensors underneath existing structures and in locations with limited access (e.g., toe of dams, extraterrestrial bodies). Successful deployment of self-burrowing probes in the field will require several cycles of expansion, penetration, and contraction motions due to the geometric constraints and the increase in soil strength with depth. This study explores the multi-cycle performance of a dual-anchor self-burrowing probe in granular assemblies of varying density using discrete element modeling simulations. The simulated probe consists of an expandable top shaft, expandable bottom shaft, and a conical tip. The expansion of the shafts are force-controlled, the shaft contraction and tip advancement are displacement-controlled, and the horizontal tip oscillation is employed to reduce the penetration resistance. The performance of the self-burrowing probe in terms of self-burrowing distance is greater in the medium dense specimen than in the dense and loose specimens due to the high magnitude of anchorage force in comparison with penetration resistance. For all three soil densities, most of the mechanical work is done by tip oscillation; however, this accounts for a greater percentage of the total work in the denser specimen. Additionally, while tip oscillation aids in enabling self-burrowing to greater depths, it also produces a greater work demand. The results presented here can help evaluate the effects of soil density on probe prototypes and estimate the work requited for self-burrowing.

Direct numerical simulation of fluid/solid particles flow inside a channel

The modeling of moving solid particles in fluid flow has been the focus of many studies and has succeeded to attract significant attention from researchers. However, commonly used modeling approaches such as discrete element modeling (DEM) and direct numerical simulations (DNS) lack simplicity and have been computationally intensive. The aim of this paper is to develop a new approach to simulate solid transport in an incompressible Newtonian fluid flow. This method is based on the Finite element method with penalization of the deformation tensor. The fluid behavior is governed by the Navier-Stokes equations within the investigation domain. To take into account collisions, we present an algorithm which allows us to handle contacts between rigid particles. In this paper, 2D fluid/particles flow simulations are performed; the results are validated by comparison with results from other methods. We attempt to simulate the conveying of solid particles behavior of circular particles in a fluid flow inside a pipe. The numerical tests show that the present method provides a very efficient approach to directly simulate the solid transport inside the channels.

Evolution Characteristics of Plastic Zone in Jointed Rock Mass of High-Temperature Hydraulic Tunnel

The evolution characteristics and the extent of the plastic zone in rock mass can reflect the failure characteristics and destruction degree of a hydraulic tunnel. In this research, we derived the equation of a plastic zone range based on a gateway-like structure high-temperature tunnel through a theoretical analysis. On-site monitoring and discrete element model simulation were combined to analyze the temperature field law and plastic zone evolution characteristics of the jointed rock mass at high temperatures. The results show that the joints affect the temperature field variation in rock mass, and the vertical and horizontal joint groups pose significantly greater influence than the inclined joint group on temperature field. The sensitivity of the joint internal friction angle and thermal expansion coefficient to the range of the plastic zone is relatively small. Under various joint spacings, the influence of horizontal and inclined joint groups on the plastic zone morphology decreases, while the vertical joint group exhibits an incremental influence on the plastic zone morphology. Similar to the influence of the temperature field, the vertical and horizontal joint groups have a significantly greater influence on the plastic zone range than the inclined joint group. Under various rock mass temperatures, the plastic zone in rock mass results in the occurrence of uneven expansions along the direction of the joint dip angle, which changes the potential failure direction of rock mass and increases the potential destruction degree of rock mass, whereas it exhibits a smaller uniform expansion perpendicular to the joint dip angle, and the boundary of the plastic zone coincides with the joint surface, relatively hindering the potential destruction degree of rock mass. The research results of this study have certain reference values for the stability control of jointed rock mass in high-temperature hydraulic tunnels.

Understanding the behaviour of a new robotic device for next-generation site investigation: A 3D DEM Exploration

Accelerating advancements in robotic engineering provide an opportunity for developing economical and efficient site characterisation devices, particularly for critical offshore applications. A new intelligent robotic device, ROBOCONE (Figure 1), is being developed for site characterisation and design of offshore structures, which would be capable of mimicking the load histories of the soil inside the ground at a desired depth [1]. The obtained soil constitutive properties would support an efficient design of offshore structures, considering “whole life” stress-strain histories. ROBOCONE could apply lateral, shear, and torsional modes (Figure 1(a)) of loading on the surrounding soil, operated remotely from the ground. In the pursuit of developing such a device, a prior understanding of its behaviour is essential. The lateral loading static and cyclic responses of offshore foundations are critical aspects of their design. The present work highlights the lateral module (P-Y Module) behaviour of the ROBOCONE device (Figure 1(a)) under various stresses, using 3D Discrete Element Modelling (DEM). The P-Y module moves horizontally at a desired depth in the ground and this lateral motion is numerically simulated using commercial DEM software, Particle Flow Code (PFC3D) [2].
 The proposed dimensions of the P-Y module are 200mm long and 54mm diameter (DRC). Present DEM model uses rigid walls as P-Y module placed in a rigid monodisperse 3D granular assembly with grain diameter of around 1/3rd DRC [3]. The Hertz contact model micro-parameters for grain-grain (E50 value of 27.4±2.2MPa) and grain-wall contacts are shown in Table 1. A 10 times higher shear modulus of grain-wall contact than the grain-grain contacts is sufficient to have stiffer response. The servo mechanism in PFC enables the model to reach desired average stresses. The primary objective of this work is to understand the ROBOCONE P-Y module behaviour and thus the lateral soil reaction curves without the influence of boundary. For the current testing mode, where the module moves laterally in the soil, the ratio of the moving object to soil bed dimensions for no boundary effects is unprecedented. A simple and innovative method of using periodic boundaries is proposed in the present study. Conventionally, periodic boundaries replicate the representative volume element infinitely at the boundaries. Due to the presence of ROBOCONE in the centre of the model, the required extent reduces to half in X and Y directions, as schematically shown in Figure 1b. This paper discusses the model side to ROBOCONE diameter, L/DRC, (e.g., 9, 18, 30) influence on the P-Y curves (at a given stress level). The effects of random particle generations for different models in PFC software can be minimized using same central core zone of contacts with ROBOCONE for each simulation, while the extent of model side is increased. ROBOCONE wished-in-place rather than driving/jacking in the model reduces the DEM computation costs. Limited amount of lateral displacement of the ROBOCONE (around 2.5mm) is sufficient to establish the effectiveness of the proposed modelling. Optimum loading rate (the lateral velocity of P-Y module) of around 0.8mm/s, which can maintain the inertial number lower than the threshold value of 7.9x10-5[4] further helps the computational efficiency.
 Once the optimum L/DRC value is obtained, the quantitative outcomes from these simulations are the lateral soil reaction curves at different stress levels and also the bending moments on the ROBOCONE P-Y Module. Though the ROBOCONE model in these simulations is a rigid wall and doesn’t mobilize in bending, the moments calculated from the magnitude and locations of each contact force on the P-Y module provide an estimate of bending stresses generated on the module. These results provide a basis for developing an understanding of the physical capacity of the robotic device in sustaining the lateral forces. Figure 1(c) shows preliminary results of soil reaction curve from the P-Y module at 500kPa stress level for L/DRC value of 9. The changes in the contact forces during the P-Y module motion can be qualitatively assessed through the changes in the force chain network (Figure 1(d)). Figure 1(e) shows a representative plot of bending moments calculated at different lateral movement stages of the P-Y module, and the maximum value at a desired displacement of the P-Y module suggests the physical design requirements of the ROBOCONE. The results from these DEM simulations would directly inform the design of the robotic device for ground investigation and hence improve the economical offshore foundation designs.

Discharge behavior of spherical and rock chip mucks by screw conveyors in TBM: Physical model experiments and DEM simulations

The discharge of muck through a screw conveyor system plays a crucial role in ensuring safe and cost-effective tunneling with earth pressure balance tunnel boring machines (EPB-TBM). However, the discharge mechanism of chip-type rocky mucks through a screw conveyor has not been well examined. Therefore, this study investigates the discharge behavior of rock chips through a screw conveyor by using a 3D discrete element model (DEM). Numerical simulations are conducted with rock chip particles of various sizes, as well as spherical particles, while varying the inclination angle, screw pitch length, and rotational speed of the screw conveyor. The simulation results show that the relative size between the muck particles and pitch has a significant effect on the discharge rate, and an optimal ratio of pitch to flight diameter is suggested. The particle-level analysis reveals distinctive particle discharge paths and a velocity distribution of muck particles along the screw axis. The study proposes the ratio of the screw pitch to the maximum particle size as the primary design parameter to predict the discharge rate. This is because large particles play a critical role in determining the discharge rate. The study highlights the usefulness of 3D DEM-based simulation as a tool to investigate discharge behavior of particulate materials through a screw conveyor. Moreover, it advances our understanding of rock chip-type muck discharge behavior during TBM excavation, providing guidance for screw conveyor design and feedback during TBM operation.

Discrete element modelling of granular materials incorporating realistic particle shapes

This paper proposes an approach to generate realistic particle shapes considering the major plane of orientation of particles in discrete element modelling (DEM). The particle generation framework includes capturing high-quality scanning electron microscope (SEM) images, followed by image processing and generation of clumps using a commonly used multi-sphere (MS) approach in particle flow code (PFC3D). A set of experimental direct shear tests (DST) and subsequent DEM simulations were performed by incorporating realistic particle shapes. The simulation results show a good agreement with those obtained in the laboratory. In addition, the normal stress showed a significant effect on the structural anisotropy of the granular materials.

Joint Geophysical and Numerical Insights of the Coupled Thermal‐Hydro‐Mechanical Processes During Heating in Salt

AbstractSalt offers an optimal medium for the permanent isolation of heat‐producing radioactive waste due to its impermeability, high thermal conductivity, and ability to close fractures through creep. A thorough understanding of the thermal‐hydrological‐mechanical (THM) processes, encompassing brine migration, is fundamental for secure radioactive waste disposal within salt formations. At the Waste Isolation Pilot Plant (WIPP), we conducted joint in situ geophysical monitoring experiments during active heating to investigate brine migration near excavations. This experiment incorporated electrical resistivity tomography (ERT) alongside high‐resolution fiber‐optic‐based distributed temperature sensing within a controlled heating experiment. Additionally, discrete element model (DEM) based numerical simulations were conducted to simulate THM processes during heating, providing a more mechanistic understanding of the coupled processes leading to the observed changes in geophysical measurements. During heating, resistivity shifts near the heater were reasonably explained by temperature effects. However, in more distant, cooler regions, the resistivity decrease exceeded predictions based solely on temperature. DEM simulations highlighted brine migration, propelled by pore pressure gradients, as the likely primary factor contributing to the additional resistivity decline beyond temperature effects. The comparison between the predicted ERT responses and observations was much improved when considering the effects of brine migration based on the DEM simulations. These geophysical and simulation findings shed light on brine migration in response to salt heating, enhancing our understanding of the coupled THM processes in salt for safe radioactive waste disposal.

Optimal Design of and Experiment on a Dual-Spiral Ditcher for Orchards

This study aimed to design a counter-rotating dual-axis spiral ditcher to address the problems of the lack of ditching models, low ditching quality, and high power consumption in ditching operations in hilly and mountainous orchards. By establishing a discrete element simulation model of the interaction between the dual-spiral cutter and the soil, we analyzed the effects of different operating parameters on the ditching performance and power consumption to explore the mechanism of the interaction between the soil-engaging components and the soil; meanwhile, according to the simulation data, we took the forward speed, cutter speed, and ditching depth as the experimental influencing factors, and we took the ditching qualification rate and power consumption as the experimental indicators. Then, through a three-factor and three-level orthogonal experimental analysis, we obtained the optimal parameter combination. Based on the optimized simulation results, a prototype ditcher was fabricated, and the results of a soil trough test showed that the ditcher had a stable ditching performance, an average ditching qualification rate of 91.4%, an average soil crushing rate of 72%, and a ditching adjustment structure that could adjust the ditching depth and width within the ranges of 15–25 cm and 10–20 cm, respectively. The optimized ditcher had high efficiency, stability, and energy savings during its operation, and it was able to meet the agronomic requirements for ditching operations. This study provides a design basis and technical support for dual-spiral trial ditching operations.

Multi-scale soot formation simulation providing detailed particle morphology in a laminar coflow diffusion flame

The macroscopic simulation of soot production in flames by CFD approaches often assumes of spherical particles or considers ad-hoc formulas in order to take the particle fractal aggregates’ morphology into account. On the other hand, numerically simulated aggregates can be generated by Discrete Element Modeling (DEM) simulations at the nanoscopic scale. However, the change in thermodynamic conditions, surface growth, oxidation, and nucleation mechanisms are commonly neglected by this approach. This work combines these complementary approaches to investigate the detailed morphology of soot along 4 different particle trajectories in a diffusion flame. The proposed multi-scale approach shows remarkably larger and more compact aggregates near the wings of the flame as compared to the centerline, in agreement with previous experimental studies. This approach allows to analyse the particle polydispersity and morphological parameters beyond the fractal dimension, such as anisotropy coefficient and monomers overlapping coefficient. It becomes possible to reveal clear morphological signatures of soot formed along different streamlines in the flame. Finally, we have also observed a positive correlation between primary particle diameter and aggregate gyration diameter due to the predominance of surface reactions over aggregation. The proposed post-processing of CFD results based on DEM methods, bringing new information on soot morphology, is a proof of concept of a more accurate procedure for validating soot models used in CFD codes as compared to existing methods in the literature.

Parameter Calibration of Discrete Element Model for Cotton Rootstalk–Soil Mixture at Harvest Stage in Xinjiang Cotton Field

Due to the lack of accurate discrete element simulation model parameters in the design optimization process of key agricultural machinery components in the whole mechanization technology system of cotton generation, the optimization and improvement of the machine is restricted to a certain extent. Taking a cotton rootstalk–soil mixture at harvest stage in a Xinjiang cotton field as the research object, the discrete element simulation model of a cotton rootstalk–soil mixture was constructed, and the contact parameters of discrete element simulation were calibrated by combining simulation analysis with a physical test. The discrete element significant-influence parameters of cotton rootstalk–soil mixture were screened by Placket–Burman test, and the optimal range of significant-influence parameters was determined by the steepest climbing test. According to the principle of Box–Behnken test, the quadratic regression model of repose angle and significant parameters was established with repose angle as the response value. Taking the actual repose angle as the target, the Design-Expert software was used to optimize the parameters with significant influence and obtain the optimal combination of parameters. The optimal parameter combination was compared and verified by simulation experiments. The relative error between the simulated repose angle and the physical test was 2.36%. The results showed that the calibrated parameters were true and reliable, which could provide a theoretical reference for the discrete element simulation of cotton rootstalk–soil mixture in a Xinjiang cotton field.

Process design for carbon black size and morphology

The structure (size and morphology) of carbon black (CB) largely determines its performance in tires, inks, batteries etc. Here, the impact of CB process synthesis variables, i.e. temperature, T, precursor (i.e. acetylene) flow rate, Q, and volume fraction, fv, on CB structure is elucidated by discrete element modeling (DEM) and compared to experimental data in the literature. The CB structure is quantified by the mobility, dm, and spherule or primary particle, dp, diameters, effective density, ρeff, and fractal dimension, Df. Decreasing Q or T enhances the CB yield, surface growth and agglomeration. This increases the mean dm and dp, consistent with experimental data from laminar flow ethylene pyrolysis reactors. The CB made at high Q or T is less compact than that made at low Q and T, having up to 50% smaller ρeff and 30% smaller Df, in excellent agreement with experimental data also. Increasing the fv (e.g. by increasing the precursor flow rate) results in CB aggregates (covalently-bonded CB primary particles) and increases the mean dm and dp, explaining commercial furnace black data. These CB aggregates are quite compact having up to 45% larger Df and larger ρeff than those of ethylene black. So process design diagrams generated by the present DEM simulations can be used to guide design and optimization of CB for various applications from first principles.

Effects of defects on the transverse mechanical response of unidirectional fibre-reinforced polymers: DEM simulation and deep learning prediction

The presence of defects in composite materials is hardly avoidable during the process of materials manufacturing, which may affect the mechanical behaviour of the material. This paper presents a Representative Volume Element (RVE) based Discrete Element model (DEM) for analysing the effects of defects on the transverse mechanical response of unidirectional (UD) fibre-reinforced polymer (FRP) laminae. Using the DEM model, crack initiation and propagation in defective RVEs with different fibre distributions are analysed and compared. In addition, the effects of the distribution of the defects on stress–strain responses are also investigated. The DEM model shows excellent capabilities in predicting the crack path at failure that is consistent with experimental tests. Based on a data set generated by 1000 DEM simulations, back-propagation deep neural network (DNN) models are developed for a fast determination of crack initiation and instantaneous critical load of the RVEs. The results show that both the initial crack and the critical stress of the laminae can be accurately and efficiently predicted by the data-driven DNN models with consideration of randomly distributed defects.

Particle size and shape effect of Crumbler® rotary shear-milled granular woody biomass on the performance of Acrison® screw feeder: A computational and experimental investigation

Physical experiments and discrete element model (DEM) simulations are conducted to evaluate particle characteristics and operation parameter effects on screw feeding performance for rotary shear-milled Douglas fir. Three performance metrics are used: mass flow rate, shaft driving torque, and specific energy consumption. The impact of particle size, particle size distribution (PSD), shaft rotational speed (rpm), and hopper dimensions on the performance are investigated. All employed performance metrics reveal the superior flowability of the 2-mm particles in contrast to the larger 6-mm counterpart. Remarkably, wider PSD results in poorer flowability than the two mono-sized particles, proving the flowability enhancement achieved by narrower PSD of the woody feedstock. More importantly, DEM simulations unveil PSD-induced degradation in flowability is attributed to mechanical interlocking and particle segregation effects. Furthermore, higher shaft rpm causes higher mass flow rate at the cost of higher specific energy consumption due to viscous dissipation and changes in flow pattern.

Parameter calibration of the discrete element simulation model for soaking paddy loam soil based on the slump test.

The discrete element computer simulation method is an effective tool that enables the study of the interaction mechanism between the pulping components and the paddy soil during the paddy field pulping process. The findings are valuable in optimizing the parameters of the paddy beating device to improve its working quality and efficiency. However, the lack of accurate soil models for paddy soil has limited the application and development of the discrete element method in paddy pulping research. This study selected the Hertz-Mindlin with Johnson-Kendall-Roberts discrete element model for the pre-pulping paddy loam soil and used the slump error as the test index to select nine parameters, including soil Poisson's ratio and surface energy, as test factors to calibrate the model parameters. The Plackett-Burman test identified soil shear modulus, surface energy, and soil-iron plate static friction coefficient as significant factors affecting the test index. The steepest ascent test results determined the test range of the above parameters. The Box-Behnken test obtained the regression model between the significant factors and the test index, and the regression model was optimized using the slump error as the target. The optimal combination of parameters was surface energy of 3.257 J/m2, soil shear modulus of 0.709 MPa, and static friction coefficient between soil and iron plate of 0.701. The slump simulation test using this combination of parameters yielded an average slump error of 2.04%. The collective results indicate the accuracy of the calibrated discrete element simulation parameters for paddy loam soil. These parameters can be used for discrete element simulation analysis of the paddy pulping process after paddy field soaking.