Determination of contact parameters for discrete element method simulations of granular systems

Both linear-spring-dashpot （LSD） and non-linear Hertzian-spring-dashpot （HSD） contact models are commonly used for the calculation of contact forces in Discrete Element Method （DEM） simulations of granular systems. Despite the popularity of these models, determination of suitable values for the contact parameters of the simulated particles such as stiffness, damping coefficient, coefficient of restitution, and simulation time step, is not altogether obvious. In this work the relationships between these contact parameters for a model system where a particle impacts on a flat base are examined. Recommendations are made concerning the determination of these contact parameters for use in DEM simulations.

Calibration and test of the contact parameters for chopped cotton stems based on discrete element method

In view of the fact that the existing cotton stem simulation models are simplified and have a large discrepancy from the actual appearance and the contact parameters have not been calibrated.In this study,the simulation model and numerical simulation were established using the discrete element software EDEM.Then a second-order response model between contact parameters and repose angle had been constructed.The test result showed that the static friction coefficient,rolling friction coefficient,and coefficient of restitution between cotton stems were crucial factors affecting the repose angle.The determination coefficient corrected determination coefficient and p-value of the second-order response model were R^(2)=0.959,R^(2)_(adj)=0.921,and p<0.0001 respectively.The error values of the comparison between the simulation test results and the corresponding physical test values were all less than 10%,which showed that the model was reliable and had high interpretation and predictability,this study can provide a certain theoretical basis and data support for the setting of contact parameters in the data simulation of cotton stem harvesting and processing,mechanically-harvested film residue crushing and film stem separation,etc.

DEM investigation of weathered rocks using a novel bond contact model

The distinct element method（DEM） incorporated with a novel bond contact model was applied in this paper to shed light on the microscopic physical origin of macroscopic behaviors of weathered rock, and to achieve the changing laws of microscopic parameters from observed decaying properties of rocks during weathering. The changing laws of macroscopic mechanical properties of typical rocks were summarized based on the existing research achievements. Parametric simulations were then conducted to analyze the relationships between macroscopic and microscopic parameters, and to derive the changing laws of microscopic parameters for the DEM model. Equipped with the microscopic weathering laws, a series of DEM simulations of basic laboratory tests on weathered rock samples was performed in comparison with analytical solutions. The results reveal that the relationships between macroscopic and microscopic parameters of rocks against the weathering period can be successfully attained by parametric simulations. In addition, weathering has a significant impact on both stressestrain relationship and failure pattern of rocks.

Influence of Structure Parameters on Performance of the Thermoelectric Module

A numerical model of thermoelectric module （TEM） is created by academic analysis,and the impacts of the resistance ratio and thermoelement size on the output power and thermoelectric efficiency of the TEM are analyzed by the MATLAB numerical calculation.The numerical model is validated by the ANSYS thermal,electrical,and structural coupling simulation.The effects of the variable physical property parameters and contact effect on the output power and thermoelectric efficiency are evaluated,and the concept of aspect ratio optimal domain is proposed,which provides a new design approach for the TEM.

Determination and analysis of basic physical and contact mechanics parameters of quinoa seeds by DEM

Quinoa is an ancient crop that is nutritious,balanced,and suitable for most people.However,it has not been known and sought by the public until modern times.In recent years,quinoa has been intensively known and widely grown in China.Quinoa mechanized production machines have also been developed.With the help of DEM,we design and optimize the quinoa combined seeder,improving seeding efficiency and quality.In this paper,the basic physical and contact mechanics parameters required for the Hertz-Mindlin(no slip)of quinoa seeds in EDEM software were determined.The coefficient of rolling friction of quinoa seeds was calibrated on DEM,and which of Long Quinoa 4 is 0.043,and that of Meng Quinoa 4 was 0.016.Meanwhile,we can find that the coefficient of rolling friction strengthens the shape to restrict rolling and weakens the shape to increase rolling.The above research provides simulation parameters for the design and optimization of quinoa seed seeding machinery.

Discrete element modeling and verification of the simulation parameters for chopped hybrid Broussonetia papyrifera stems

In this study,the discrete element software EDEM was applied to establish a simulation model of non-uniform-sized particle units for Broussonetia papyrifera stalks,which aimed to address the low utilization rate of existing Broussonetia papyrifera harvesting machinery,the significant variation between the simulated model of Broussonetia papyrifera stalks and their actual appearance,as well as the absence of contact parameter calibration.Through a combination of the free-fall collision method,inclined plane sliding method,and inclined plane rolling method,numerical simulation was conducted to analyze the pattern of variations in contact parameters between Broussonetia papyrifera stalks and the steel material of the machinery.Accordingly,these parameters were calibrated.The results showed that the coefficient of restitution between Broussonetia papyrifera stalks and steel materials was 0.321,the static friction factor was 0.589,and the rolling friction factor was 0.078.With the parameters of contact between Broussonetia papyrifera stalks as variables and the experimentally measured pile angle as the objective of optimization,the steepest ascent experiment and the three-factor five-level rotation combination experiment were conducted.In this way,a second-order response model was constructed to analyze the relationship between the contact parameters and the pile angle.Through the optimization analysis of experimental data,it was determined that the coefficient of restitution between Broussonetia papyrifera stalks was 0.21,the static friction factor was 0.24,and the rolling friction factor was 0.03.Furthermore,the calibration results were validated through experimentation to show that the relative error between the obtained pile angle under the context of optimal parameter combination and the actual one was 4.11%.In addition,the relative error of mass flow rate in spiral transport was within a reasonable range,this study lays a foundation both theoretically and statistically for the simulation of contact parameters for Broussonetia papyrifera stalk harvesting processing,mechanical harvesting,and so on.

Parameter Identification Based on Force-Displacement Curves for a Bolted Joint Finite Element Model

In order to identify the uncertain parameters of a bolted joint finite element model,a simple and applicable way of parameter identification is introduced.By utilizing numerical simulation with the Abaqus software and experimental investigation with the MTS material testing system,the tangential force-displacement curves that reflect the characteristics of the bolted joint were acquired.On the basis of this,by employing the response surface methodology（RSM）and genetic algorithms（GAs）,parameters in the FEM model were identified.The force-displacement curves by both virtual and experimental approaches are well correlated at the end.This phenomenon-based parameter identification method may help facilitate precise prediction of complex jointed connection structures.

Calibration of the simulation parameters of the particulate materials in film mixed materials

In order to obtain accurate contact parameters of a particulate material in residual film mixture collected by cotton field machine in Xinjiang,the angle of repose test and inclined plane test were carried out.In the tests,the angles of repose of the particulate material with the water content of(6.26±1.5)%and(14.1±2.1)%were measured respectively,as well as the static sliding friction angle between the particulate material and the residual film.At the same time,the EDEM software was used to calibrate the coefficient of restitution,static friction coefficient and dynamic friction coefficient between the material and the film.Then,the second-order response model between contact parameters and the angle of repose and static sliding friction angle was constructed.In addition,the optimal contact parameters between the granular materials and the mulch were obtained by fitting the physical test data.The results indicated that the errors between the physical test results and the numerical simulation results are small.It was proved that the second-order response model could predict the repose angle of granular materials and the static sliding friction angle between granular materials and farmland film.This study could provide theoretical support for the subsequent model construction of the residual film mixture collected by the cotton field machine.

Contact parameter analysis and calibration in discrete element simulation of rice straw

Discrete element method was used to study and analyze the interaction between rice straws and between rice straw and agricultural machinery parts,thereby providing a scientific basis for post-harvest paddy field processing.Calibrations of rice straw-rice straw,rice straw-agricultural machinery part contact parameters(collision recovery coefficient,static friction coefficient and rolling friction coefficient)constitute an important prerequisite for the discrete element research process.In this study,the collision recovery coefficients of rice straw-steel and rice straw-rice straw were 0.230 and 0.357,respectively,which were calibrated by the collision method.The static friction coefficient and rolling friction coefficient of rice straw-steel were 0.363 and 0.208 respectively,which were calibrated by the inclined plate method and the slope method.The static friction coefficient and rolling friction coefficient of rice straw-rice straw were 0.44 and 0.07,respectively,which were calibrated by the split cylinder method.The paired t-test showed insignificant differences between calibration parameter simulation results and the physical test values(p>0.05).Taking the angle of repose that reflecting rice straw flow and friction characteristics as the evaluation index,the verification tests of the above calibration values indicated that the simulated angle of repose has no significant difference from the physical test value(p>0.05).The side plate lifting test on rice straw of different lengths showed no significant difference between the simulated angle of repose and the physical test value(p>0.05).This study can provide a basis for contact parameters choice in discrete element simulation analysis with rice straw-rice straw and rice straw-agricultural machinery parts as the research object.The calibration method can provide a reference for the contact parameter calibration of other crop straws.

Calibration of the simulation parameters of jujubes in dwarfing and closer cultivation in Xinjiang during harvest period

order to obtain accurate contact parameters of jujubes in dwarfing and closer cultivation in Xinjiang during the harvest period,based on the Hertz-Mindlin(no-slip)contact model in EDEM,the contact parameters,including the coefficient of restitution,static friction,and rolling friction,between jujube and machine components have been calibrated through physical and simulation test.The coefficient of restitution,static friction,and rolling friction between the jujubes and steel(jujube-steel)were calculated as 0.33,0.46,and 0.04,respectively.The coefficient of restitution,static friction,and rolling friction between the jujubes and polyvinyl chloride(PVC)(jujube-PVC)were calculated as 0.39,0.61,and 0.06,respectively.The optimum contact parameters among jujubes(inter-jujubes)were 0.23,0.33,and 0.04.The accumulation test was applied for comparing the simulation and testing values of jujube’s repose angle.In the results,the relative error was 1.27%which means the discrete element model and the contact parameters of jujube can be used for the discrete element simulation test.In addition,the results can be adequately used to simulate particle scale mechanics(grain commingling,flow/motion,forces,etc.)of jujube in harvest as well as the design and working mechanism study of post-harvest processing machinery and devices.

Nano inhomogeneity effects on small Ag/n-Si Schottky diode parameters at high temperature

Schottky diodes with an Ag/n-Si/W/Cu structure and 100μm in diameter were studied.Analyzing the silver metal surface coating on the n-Si substrate using a scanning probe microscopy（SPM） device showed a large number of nano patches in the surface with dimensions of 0 to 100 nm.The potential distribution of the patches revealed that the potential of each patch with the neighboring patches was different.The electrical characteristics of the devices were studied between temperature ranges of 300 and 380 K.When the temperature ideality factor approximately increases,the potential barrier height decreases.The potential barrier height was calculated separately from theⅠ-Ⅴand C-V characteristics.The main reasons for the significant difference between room temperature and higher temperatures were the differences in patch distribution,the different potentials of each patch,and the interactions between them.The effective potential barrier height depended on the degree of inhomogeneity,and thus the operating potential barrier height in the contact surface was smaller than the average value,and the ideality factor was more than unitary.With the increase in the potential value,the ideality factor becomes close to unitary, and with increasing temperatures,the ideality factor is increased.In this case,the maximum potential barrier height accrues at a greater distance from the metal contact.For this reason,at high temperatures the average value of the potential barrier height is smaller.Moreover,with increasing temperature,the ideality factor is increased.