Construction of Discrete Element Model for Individual Sugarcane Roots and Calibration of Contact Parameters

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.

HighlightsThe relationship between the angle of repose and compound fertilizer particle size distribution and sphericity was revealed.The range of the rolling friction coefficient obtained by different modeling was calibrated by the golden section method.Scanning modeling required 80% of the rolling friction coefficient of spherical modeling to reflect actual motion.The relative error of scanning modeling (7.91%) was better than that of spherical modeling (30.84%).Abstract. The discrete element method (DEM) is widely used to simulate the behavior of granular materials. The accurate establishment of the particle model has a great influence on the accuracy of the simulation. Most of the existing discrete element simulations of granular compound fertilizers use spherical modeling without considering the shape or particle size distribution. To compare the simulation accuracy of spherical modeling (spherical particles with equivalent diameters) and scanning modeling (a three-dimensional model of fertilizers was obtained by a scanner and then automatically filled by EDEM2020 software) on compound fertilizer discharge, three kinds of granular compound fertilizers (Changqingshu, Xinshidai, and Munvhong) were selected as the research objects. The characterization parameters of fertilizer shape and fluidity were measured. Principal component analysis and Pearson correlation analysis were used to analyze the influence of the compound fertilizer characterization parameters on the angle of repose. The results showed that the particle shape and particle size distribution of compound fertilizer were the main factors affecting its angle of repose. Through the golden section method and a single-factor experiment, the rolling friction coefficients of the three granular fertilizers under the two granular modeling methods for spherical modeling and scanning modeling were determined. The results showed that the rolling friction coefficient when using scanning modeling to approximate the actual angle of repose was approximately 80% of that when using the spherical modeling method. The influence of different modeling methods on the total rotational kinetic energy and the formation of the angle of repose was discussed. For the same fertilizer, the total rotational kinetic energy was greater in spherical modeling than in scanning modeling, and the formation time of the angle of repose was longer in scanning modeling than in spherical modeling. The results of an external tank wheel fertilization simulation and bench test showed that considering the scanning modeling of fertilizer shape and particle size distribution, the fertilization variation coefficient obtained from the simulation test was closer to that of the bench test. This research helps to better understand the influence of particle shape and particle size distribution on DEM simulations and provides references for discrete element modeling of other granular fertilizers. Keywords: Compound fertilizer, Modeling method, Shape, Simulated flow characteristics, Size distribution.

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.

HighlightsSoil particle shapes were statistically analyzed, and four representative particles were obtained.A particle model was established using three-dimensional non-contact surface topography.This study used a response surface design method to calibrate significant soil parameters.The simulation parameters were verified by rotary tiller experiment.Abstract. The discrete element method (DEM) has broad prospects for application in soil-tool simulations. To ensure the reliability of simulations, appropriate simulation parameters and particle modeling are essential. Therefore, in this article, a method combining simulation and actual tests is proposed to calibrate the critical soil parameters. First, the effect of soil particle shape on particle contact was considered. Soil particle shapes were statistically analyzed using an improved GrabCut algorithm and k-means algorithm. Four representative soil particles were obtained. Second, a soil particle model was established by microscope and three-dimensional non-contact surface topography. Finally, taking the angle of repose as the response value, the three parameters with significant effects on the angle of repose, i.e., soil shear modulus, Hertz-Mindlin with Johnson-Kendall-Roberts contact model (JKR), and soil-soil restitution coefficient, were obtained via a Plackett-Burman experiment. The optimal value intervals of the significant parameters were determined by the steepest climbing test. A polynomial regression model between the angle of repose and the three significant parameters was established with a Box-Behnken experiment using three factors and three levels. The interactions between the three significant parameters were not significant, as revealed by response surface analysis. The optimal values of the significant parameters were obtained by taking the actual angle of repose as the target and resulted in a soil shear module of 9.8 MPa, JKR of 0.063, and soil-soil restitution coefficient of 0.478. To verify the reliability of the calibrated parameters, the soil angles of repose from the simulation and from actual tests were compared and analyzed. For a simulated angle of repose of 38.5°, the actual angle of repose was 38.6°, and the relative error was 0.26%. DEM was also used to simulate a rotary tiller with the calibrated parameters. The maximum error of the simulated soil throwing angle was less than 10% when compared with the actual throwing angle. The experimental results showed that the calibrated parameters were accurate and can provide a reference for the selection of soil discrete element parameters. Keywords: Angle of repose, Numerical simulation, Parameter calibration, Shape survey, Soil.

To establish a fundamental property database for discrete elements targeting long-fiber materials and address the issue of response surface methodology (RSM) being prone to local optima in high-dimensional nonlinear optimization, this study conducted parameter calibration experiments and validated the calibrated parameters through a combined approach of simulation and physical testing. The Plackett–Burman design and steepest ascent test were employed to screen significant factors. Using the angle of repose (42.3°) obtained from physical experiments as the response value, response surface methodology (RSM) and a particle swarm optimization–back propagation (PSO-BP) neural network model were independently applied to optimize and compare the critical parameters. The results demonstrated that the dynamic friction coefficient between wheat straw particles, the static friction coefficient between wheat straw and steel plate, and the JKR surface energy were the most influential factors on the simulated angle of repose. The PSO-BP model exhibited superior optimization performance compared to RSM, yielding an optimal parameter combination of 0.17, 0.46, and 0.03. The simulated repose angle under these conditions was 41.67°, exhibiting a relative error of only 1.5% compared to the physical experiment. These findings provide a robust theoretical foundation for discrete element simulations of wheat straw feedstock.

To obtain the contact parameters of the moist bulk of shotcrete accurately and quickly, this study calibrated the contact parameters of the moist bulk of shotcrete by physical stacking test and simulation method. Based on the Hertz–Mindlin with JKR (Johnon–Kendall–Roberts) model, the discrete element simulation is carried out. Using P-BD to screen seven initial parameters, it is found that JKR surface energy, rolling friction coefficient between particles and restitution coefficient of particle impact have significant effects on the angle of repose of the moist bulk of shotcrete. According to B-BD, the second-order regression model of angle of repose and significance parameters was established. Three significant parameters were obtained: JKR surface energy 0.418 J/m2, rolling friction coefficient 0.06 and static friction coefficient 1. The angle of repose obtained by simulation is compared with the physical test value, and the relative error is 1.88%. The results show that the calibration method proposed in this study can accurately simulate the physical stacking test, and can provide a reference for the calibration of contact parameters of the moist bulk of shotcrete.

The discrete element method (DEM) has been widely employed to model processes in different industries, such as mining, agriculture, pharmaceuticals, and food. One of the main lines of research, and in which different authors propose several approaches, is the calibration of parameters. Bulk calibration (BCA) is a common approach used that does not necessarily represent the individual behavior of each particle. On the other hand, direct measurement (DMA) is another approach employed in some cases. This work presents a comparison between calibration of DEM model parameters with non-cohesive spherical and polyhedral particles using a combination of direct measurement and bulk calibration. BCA is employed to calibrate friction parameters and DMA to characterize shape of the particles and coefficient of restitution of the contact between particles. Experimental data from Draw Down Tests are used to calibrate the friction parameters. Numerical optimization of the parameters is conducted by altering the coefficients of friction regarding the objective variables of mass flow, final mass, shear angle, and angle of repose. Quartz, granite, and coal are calibrated, obtaining good agreement with the experimental results. The influence of particle shape is tested, proving that more complex particles obtain better results for the analyzed case.

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.

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.

In view of the large difference in moisture content of cotton stalk in autumn in Xinjiang, the existing process of obtaining discrete element simulation parameters of cotton stalk is low in accuracy and complicated in operation, leading to the problems of poor universality and low accuracy in regard to the discrete element simulation parameter-calibration method in the process of mechanized transportation, throwing and returning to the field. Therefore, the experimental study on cotton stalk with different moisture content was carried out with the accumulation angle as the response value, so as to construct a parameter model that can quickly and accurately calibrate cotton stalk with different levels of moisture content. The model has high applicability and flexibility, and it can be widely used in the simulation test of various cotton field-operation machinery, such as a residual film-recycling machine, cotton picker, crushing and returning machine and other equipment. The water content–accumulation angle model was established by the cylinder-lifting method, and the correlation coefficient of the model was 0.9993. Based on EDEM 2020 software, the Hertz–Mindlin model was used to simulate the stacking angle of cotton stalk, and the rolling friction coefficient, static friction coefficient and collision recovery coefficient between cotton stalk and cotton stalk–steel were obtained. Through the Plackett–Burman test, climbing test and Box–Behnken test, three significant parameters, namely the rolling friction coefficient, static friction coefficient and static friction coefficient between cotton stalk and steel, were selected from discrete element simulation parameters to characterize the moisture content of cotton stalk, and the accumulation angle–discrete element parameter model was established. The p-value of the model was less than 0.0001, and the relative error was only 2.67%. Based on the moisture content–stacking angle model and the stacking angle–discrete element parameter model, the moisture content–discrete element parameter model was constructed. The model was verified by the cylinder-lifting method and the plate-drawing method, and the relative error was only 2.79%. Finally, the model was further verified by comparing the effect of the throwing uniformity between the mechanical simulation test and field test, and the relative error was only 4.75%. The test proves that the moisture content–discrete element parameter model is accurate and reliable, not only providing the design basis and support for the mechanization research of cotton stalk conveying and returning to the field in Xinjiang but also providing ideas for the calibration of discrete element simulation parameters of other crop straws.

Using the discrete element method to simulate the interaction between growing media and machinery is an effective method to design seedling machinery and improve the precision of facility horticultural operations. In order to further improve the accuracy of the study on the interaction between seedling block-forming machines and growing media, the growing media used in the production of seedling nursery blocks was taken as the research object, and the Plackett–Burman screening test and Box–Behnken test were conducted based on the discrete element method using the EEPA model to conduct the calibration of discrete element parameters of the growing media. Optimization was conducted with an actual repose angle as the target value, and the optimal combination is as follows: the interparticle collision-recovery coefficient is 0.5066, the collision-recovery coefficient between particles and the geometric model is 0.714, the interparticle dynamic-friction coefficient is 0.381, and the tangential stiffness factor is 0.375. Finally, the soil uniaxial closed compression test was conducted with optimized calibration parameters. The relative error between the maximum axial load on the punch and the measured value in the simulation process was 4.23%, which verified the accuracy and reliability of parameter calibration of the growing media and provided support for the simulation of growing media and optimization of seedling nursery block-forming machine.

Aiming at predicting what happens in reality inside mills, the contact parameters of iron ore particles for discrete element method (DEM) simulations should be determined accurately. To allow the irregular shape to be accurately determined, the sphere clump method was employed in modelling the particle shape. The inter-particle contact parameters were systematically altered whilst the contact parameters between the particle and wall were arbitrarily assumed, in order to purely assess its impact on the angle of repose for the mono-sized iron ore particles. Results show that varying the restitution coefficient over the range considered does not lead to any obvious difference in the angle of repose, but the angle of repose has strong sensitivity to the rolling/static friction coefficient. The impacts of the rolling/static friction coefficient on the angle of repose are interrelated, and increasing the inter-particle rolling/static friction coefficient can evidently increase the angle of repose. However, the impact of the static friction coefficient is more profound than that of the rolling friction coefficient. Finally, a predictive equation is established and a very close agreement between the predicted and simulated angle of repose is attained. This predictive equation can enormously shorten the inter-particle contact parameters calibration time that can help in the implementation of DEM simulations.

The rolling friction coefficient was a fundamental parameter for particle modeling, but it was challenging to quantify for unevenly shaped corn seeds. If the rolling friction coefficients of corn with different guiding seeds and different shapes were not believed to be significantly different, direct simulation in EDEM would produce simulation distortion. This paper began by selecting three models with a relatively high proportion from five corn samples with various shapes (such as horse-tooth shape, spherical shape, oblate shape, and irregular shape, etc.) and modeling them according to the actual seeds. Due to the large disparity between seed models with different shapes, the study adopted the method of combining physical experiment and discrete element simulation, took the rolling friction coefficient as the independent variable and the angle of repose in the simulation test as the target value, and calibrated the rolling friction of various shapes of corn seed particles separately. Coated corn seeds' rolling friction coefficients were accurately predicted (0.0047 for horse tooth, 0.0058 for pyramid, and 0.049 for spherical shape). During the validation test, the calibrated simulation parameters were entered into EDEM for simulation, and the distribution of seeds on the seed platter was compared between the actual test and the simulation test. The results demonstrated that the difference in the sizes of key features was less than 5.60 percent, and the population boundary in the seed platter after calibration was closer to the actual situation, which improved the accuracy of the simulation.

To address the problem of poorly defined mechanical parameters in discrete element simulations of mechanized pepper harvesting, a discrete element model was developed to accurately represent the biomechanical characteristics of pepper stems. This research presents a parameter calibration and optimization approach using both Hertz-Mindlin and Hertz-Mindlin with bonding methods. The basic properties of the pepper stems were determined by mechanical property testing, while the stacking angle was assessed using the cylinder lift technique. The stacking angle and maximum bending damage force were used as evaluation indexes. Significant parameters influencing the model were identified using the Plackett-Burman test, followed by a steepest ascent test to define the central test group. The Central-Composite and Box-Behnken tests were then used to formulate quadratic regression equations and optimal parameter combinations for the significant factors were derived using an optimization solver to validate the accuracy of the model. The results showed that the relative errors between simulated and actual values for the two models under optimal conditions were 0.86% and 1.02%, respectively. The discrete element model of pepper stems closely approximates real-world conditions and reflects the mechanical behavior of pepper stems as they bend and break upon impact during harvesting. This research provides a basic framework for mechanistic analysis of the pepper harvesting process.

A way to equalize granular rockfill dumps at a sea or river bed is the use of a plough. A plough can be modeled as a set of straight blades in sequence. Several cutting models for dry and saturated sand are present in the literature. In cutting coarse material, the increase in pore water pressures caused by dilatancy of the grain structure play a minor role. This results in a different shape of the layer cut than for traditional cutting methods in fine soils. The layer cut has a limited surface slope resulting in grains rolling down under the angle of repose ?. Failure of the grain structure in coarse material depends mainly on the gravitational, shear and inertial forces between grains. This master thesis gives an analytical model for cutting rockfill larger than medium coarse sand with straight cutting blades (Chapter 4.2). A description is given of the important processes involved in equalizing with a plough and the different stages of filling. The analytical model is realized by use of models made by S.Miedema for cutting saturated sand and models for cutting dry sand by Hettiaratchi, and Reece (1966). The analytical model is verified by performing a physical scale model. The scale model is used to attempt to simulate the process in a discrete element computer model EDEM.