Wheat Mill Stream Properties for Discrete Element Method Modeling

Material characterization and inter/intra-particle validation for DEM simulation of urea coating process

The discrete element method (DEM) is an effective tool for obtaining qualitative and quantitative information on particle motion, which aids in the design and optimization of agricultural equipment structures. The accuracy of the DEM simulation parameters significantly impacts the simulation results. This study employed a combination of high-speed camera measurement, DEM simulation, and validation tests to determine the material and interaction property parameters for fertilizer particles. The basic parameters (triaxial size, bulk density, density, and coefficient of static friction) and coefficients of restitution between fertilizer and material were measured for three fertilizer varieties. There was a significant difference in the angle of repose between various material plates and fertilizer particles. The calibration values of coefficients of restitution and coefficients of rolling friction between fertilizer particles were optimized using the Box–Behnken method. The angle of repose was significantly affected by the coefficient of static friction and the coefficient of rolling friction between the fertilizer particles. The determined values for the coefficient of restitution, coefficient of static friction, and coefficient of rolling friction between the fertilizer particles were 0.323, 0.381, and 0.173, respectively. The error in the angle of the repose test was less than 3.0%, and the variation coefficient for each row consistency was less than 1.68 percentage points under the optimal simulation parameters. DEM simulations of the angle of repose and each row consistency variation coefficient test using the measured parameters can accurately predict the experimental results. The findings of this paper provide a theoretical basis for the DEM study of fertilizer particles.

In this paper, the mesocalibration test was used to measure the contact parameters (restitution coefficient, rolling friction coefficient, static friction coefficient, and surface energy) between coarse aggregate particles and mortar particles in Discrete Element Method (DEM) model of concrete. Then, the DEM model of concrete slump was established according to the coarse aggregate gradation to study the flow behavior of coarse aggregate in fresh concrete. The slump test result was compared with the output of the slump DEM model with high consistent, indicating the promising reliability of the mesocalibration test. Finally, based on the mesocalibration test results, the DEM model of pumping concrete was established. It was obtained that the pumping pressure calculated by the numerical model was similar to that of the pumping test with satisfactory accuracy better than the concrete pumping pressure calculated according to the rheological test results of concrete and lubricating layer. On this basis, the movement trajectory of coarse aggregate in the pump pipe was analyzed and the influence of coarse aggregate on the pumping performance of concrete was revealed.

Evaluation of particle models of corn kernels for discrete element method simulation of shelled corn mass flow

To address the lack of contact and breakage parameters in the discrete element method (DEM) simulation of potato seed cutting and sorting processes, this study took the ‘Atlantic’ potato seed as the research object and constructed a crushable potato model using EDEM. Through physical experiments, the mean average diameter, moisture content, density, Poisson’s ratio, and elastic modulus were measured. The coefficients of collision restitution, static friction, and rolling friction between the potato seed and the Q235 steel plate were determined as 0.576, 0.559, and 0.073, respectively. Using the actual repose angle of 22.89° as the response target, and combining the steepest ascent test with the Box–Behnken design, the non-cohesive contact parameters between potato seed particles were calibrated. The resulting coefficients of collision restitution, static friction, and rolling friction between particles were determined as 0.404, 0.412, and 0.0156, respectively. Finally, based on physical shear tests (maximum shear force 23.56 N), significant influencing factors were identified through Plackett–Burman screening as the bonding radius ratio r and the normal stiffness per unit area Kn. Using the steepest ascent test and the Box–Behnken response surface method, the key bonding parameters of the Bonding V2 model were calibrated as follows: r = 1.098, Kn = 8.597 × 107 N·mm−3, tangential stiffness per unit area Kt = 3.250 × 106 N·mm−3, critical compressive stress σn = 5.500 × 105 Pa, and shear strength τt = 3.000 × 104 Pa. The relative error between the simulated and actual maximum shear forces was 0.89%, which is small. The calibrated flexible model accurately represents the physical characteristics of potato seeds and provides a reliable reference for the design of mechanized potato seed cutting and sorting equipment.

Magnetic liners can improve the performance of ball mills by increasing grinding efficiency, extending service life, and reducing maintenance costs. Despite their importance, the fundamental understanding and the quantitative investigation on the effects of the magnetic liners has not been addressed in the literature. This paper addresses this gap by studying charge motion, and how the use of a magnetic liner affects the breakage mechanism of the mill, using discrete element method (DEM) modeling and the Hertz-Mindlin contact model with relative velocity dependent (RVD) rolling friction. Charge motion was modeled under different mill speeds. Compared to conventional steel and rubber liners, the charge motion in the magnetic liner mill was predominantly cascading. Quantitative analysis of the energy dissipation within the mill was conducted to investigate mill breakage. Regardless of speed, over 50% of the total energy dissipation in the magnetic liner mill was in the form of abrasion and attrition. The results highlighted the appeal of magnetic liners in secondary and regrinding application, where abrasion and attrition are considered more efficient in the fine material breakage, and where impact is ideally minimized to reduce mill wear. A number of experiments were conducted to assess the effect of different model parameters on the performance of the magnetic liner mill. The highest abrasion/attrition intensity was observed with high values of the model parameters namely the restitution coefficient, static friction coefficient, and rolling friction coefficient.

The discrete element method (DEM) was used to establish the slump model and J-Ring model of concrete to describe the flow behavior in the slump test and J-Ring test. Then, the contact parameters of particle-particle and particle-geometry for the concrete DEM model, including restitution coefficient, rolling friction coefficient, static friction coefficient, and surface energy, were measured. In order to avoid the influence of the shape and size of the aggregate, this paper used high-precision glass spheres as the aggregate of the concrete for meso-calibration test, slump test, and J-Ring test. Comparing the simulation results of DEM model with slump test result, a very high agreement between the initial stage, the rapid flow stage, and the slow flow stage of the slump flow–time curve can be found as well as the final slump and slump flow. Moreover, similar to the slump DEM model, the DEM models of J-Ring test, V-funnel test, and U-channel test were established to study the passing ability and filling ability of concrete with outstanding accuracy. Therefore, the concrete DEM model with contact parameters and JKR model can be adopted to study the flow behavior of the fresh concrete.

Powder fluidity is one of the important factors affecting the smoothness of selective laser sintered parts and the mechanical properties of sintered parts. In this paper, the angle of repose (AOR) and angle of internal friction of nylon PA3200 powder were measured by a powder comprehensive tester and a direct shear tester to evaluate the flow properties of the powder particles. Based on the discrete element method (DEM), the rolling resistance contact model and the van der Waals force model were used to describe the interaction forces between the powder particles. The rolling resistance coefficient and friction coefficient within the contact model were calibrated by the results of the AOR experiments. Based on the orthogonal experimental method, the particle size and particle size distribution (PSD) (such as uniform distribution and Gaussian distribution) were selected as the influencing factors, and the effect of particle size and PSD on the fluidity of nylon PA3200 powder was studied by numerical simulation. The results show that the PSD has a stronger influence on the AOR than particle size, and the fluidity of uniform distribution is better than that of the Gaussian distribution.

Discrete element method study of effects of the impeller configuration and operating conditions on particle mixing in a cylindrical mixer

Determining the angle of repose of sand under low-gravity conditions using discrete element method

Discrete element method (DEM) is a numerical technique that models the material as a combination of discrete particles which interact with each other through the contacts springs. While modelling soil in finite element method (FEM), approximations are made which considers soil as a continuous material. Hence certain properties such as void ratio which are intrinsic properties of the soil cannot be directly modelled or monitored. FEM also requires the failure criteria to be defined to predict the post elastic behaviour of the soil. DEM overcomes such drawbacks and the particle contacts are the only parameters that has to be defined. In the present work the contact parameters for sand grains are estimated for the purpose of being modelled in DEM, using direct measurement approach. The parameters required for defining the contact springs between the particles are the young's modulus, coefficient of restitution, friction coefficient, Poisson's ratio and density. The estimated parameters from the experiments were used to model the soil behaviour in an oedometer test. The obtained results from the DEM modelling are compared with the experimental results to benchmark the parameters estimated for the sand grains.

There are approximately 36.7 million hectares of saline alkali land available in China. To enhance the comprehensive utilization value of coastal saline alkali land and boost crop yields in such areas, it is essential to conduct research on optimizing the operational performance of high-performance soil contact components in light of the soil characteristics of coastal saline alkali land. Discrete element simulation can be employed to investigate the operational mechanisms of various key components. Nevertheless, at present, there is a dearth of discrete element models for the key physical parameters and soil structure of coastal saline alkali land soil. In this article, typical coastal saline alkali field soil was sampled, and the physical properties of the saline alkali soil, including salt content, moisture content, particle size distribution, and particle size, as well as intrinsic parameters such as soil compaction, density, Poisson’s ratio, and shear modulus, were measured. The Hertz Mindlin with Bonding contact model was employed. Physical experiments on soil accumulation angles at different depths were carried out using the cylindrical lifting method. Subsequently, by means of the discrete element method and the BBD experimental design method, a response surface model was established, and an optimization analysis was performed on the optimal parameters for the soil–soil collision recovery coefficient, static friction coefficient, and dynamic friction coefficient at each depth. Test benches for measuring the collision recovery coefficient, static friction coefficient, and rolling friction coefficient of saline alkali soil at -65Mn were set up, calculation formulas for each parameter were derived, and the contact parameters between soil at different depths and 65Mn were obtained. The results of the sliding friction angle test on different depths of saline alkali soil at -65Mn were further verified using the discrete element method, with a maximum error of 3.11%, which falls within the allowable range. This suggests that the calibration results of the discrete element simulation parameters for the interaction between soil and contact components are reliable, providing data and model support for future research on enhancing the operational performance of high-performance contact components.

Discrete Element Method (DEM) is a numerical technique that uses particulate mechanics in simulating the discontinuous behavior of particulate materials. DEM presents the advantage of modelling thosematerials in a particulate level allowing specifications of particle geometry including how their contacts interact. However, identifying microparameters that can accurately simulate the behavior of particulate materials is challenging. This paper presents the calibration of the microparameters of materials used in an earthfill damthat experienced slope movements. The main components of the earthfill dam under study were clay, for the core and blanket, and rockfill materials, for the protective shell. Linear parallel-bond model (LPBM) was used to describe the interactions between clay particles. Microparameters involved with the LPBM were particle stiffness, friction coefficient, bond strength, and bond stiffness. A triaxial test DEM model was developed to calibrate the clay microparameters, and it was successful in simulating the measured macroscopic peak and critical state behavior of clay materials. Rolling resistance linear model was used to describe the interactions between rockfill particles. Microparameters associated with the rolling resistance linear model were particle stiffness, friction coefficient, and rolling resistance coefficient. Large-scale direct shear test was simulated to calibrate rockfill microparameters, and it was able to capture the measured macroscopic shear behavior of rockfill materials. Calibration methodologies performed were successful in identifying appropriate microparameters for both rockfill and clay materials. The calibrated microparameters are beneficial in the development of a DEM model that can analyze movements and landslides in the vicinity of the earthfill dam or other earthfill dams built with similar materials.

To improve the accuracy of contact parameters in discrete element simulations of seed metering devices and avoid errors arising during parameter measurement, this paper does not determine the values of each parameter in advance during parameter calibration. Instead, it directly uses the sliding friction angle, angle of repose, and rebound height as indicators, and employs regression analysis to calibrate the static friction coefficient, rolling friction coefficient, and restitution coefficient. The accuracy of the simulation parameters is verified through comparative experiments with the seed metering device. The results show that: the static friction coefficient is proportional to the sliding friction angle, and the correlation between the two is independent of material properties. The calibrated static friction coefficients between seeds, PMMA, and PLA are 0.39, 0.43, and 0.54, respectively; the rolling friction coefficient of seeds is exponentially related to the angle of repose, and the rolling friction coefficient between seeds is 0.029; the restitution coefficient is quadratically related to the rebound height in drop tests, and the calibrated restitution coefficients of seeds with PMMA and PLA are 0.33 and 0.32, respectively; the verification experiments demonstrate that the motion patterns of seed populations in simulation and physical experiments are similar, and the differences in seed filling rates between the two are not significant, proving the reliability of the calibrated simulation parameters.

Discrete element simulation on ballasted beds is an important method to study the service characteristics of ballasted tracks; an effective simulation should be based on proper ballast parameters. Ballast contact parameter, which exhibits a high discreteness affected by factors such as material, shape, and gradation, can effectively be calibrated by an angle of repose test. Based on the testing principles of a multi-parameter response surface method, the Box-Behnken method is adopted to design the angle of repose test under the influence of restitution, static friction, and rolling friction coefficients; laboratory-measured results are combined with the simulation; regression analyzed angle of repose is considered as the goal; parameters optimization and ballasted bed resistance simulations are verified for multiple parameters. The results demonstrate that Chinese special-grade ballasts exhibit an average laboratory-measured angle of repose of (39.78±1.27)°, and the optimal combination of parameters in this discrete element simulation based on the response surface method are as follows: the restitution coefficient is 0.72, the static friction coefficient is 0.56, and the rolling friction coefficient is 0.27. The results of the lateral resistance simulation are in accordance with the laboratory test, indicating that the optimal parameters are usable. The multi-parameter response surface method effectively helps calibrate the parameters of the discrete element simulation on ballasted beds.