The antlions dig a conical simple pit in sand to catch ants.The funnel shape of the trap is deliberate with a critical angle of repose and is steep and shallow enough to trigger avalanches and cause struggling prey to...The antlions dig a conical simple pit in sand to catch ants.The funnel shape of the trap is deliberate with a critical angle of repose and is steep and shallow enough to trigger avalanches and cause struggling prey to fall into the funnel.The trap should be designed by optimizing pit morphology according to natural selection.In the current study,antlion behavior and pit morphology in the sand samples with different particle shapes and particle size distributions were studied.The small larvae build in fine sand and silty sand,while larger ones prefer fine to medium sands.However,there is no preference for sands with different particle shapes.Further,the static and dynamic angles of repose for the sand samples were measured,and the slope of the pits was compared with the repose angles.The angle of the heap slope oscillated between an upper angle or angle of sliding(the angle that triggers a landslide)and a lower angle named repose angle.展开更多
Heshan, a city in Southwest China, has been built over an old coal mining area. Due to low level of reclamation, coal gangue had been stacked in large heaps and caused geological environ- mental problems. To facilitat...Heshan, a city in Southwest China, has been built over an old coal mining area. Due to low level of reclamation, coal gangue had been stacked in large heaps and caused geological environ- mental problems. To facilitate designing management project of coal gangue, we made an investigation of the largest coal gangue heap in Dongkuang Mine of Heshan. Firstly, the grain composition of coal gangue was estimated through the sieving method, then the representative grading curve was drawn through the statistics method of coarse grain content, and lastly the relationship between the repose an- gle and grain grading was studied by piling up coal gangue with different mix proportion. The result indicates that there is a wider range of grain size in the upper part of coal gangue heap, and the repre- sentative grain grading is well graded and easy to be compacted as filling materials. Besides, the wavy relationship curve of repose angle and coarse grain content shows that the content of 70% is the infiec- tion point of ascent stage and 85% the inflection point of descent stage of the repose angle. What＇s more, the repose angle corresponding to the representative grading of coal gangue is approximately 38.4° and this has guiding significance for management project of coal gangue.展开更多
The repose angle is one of the most significant macroscopic parameters in describing the behavior of granular materials. Under a static condition, the repose angle is the steepest angle at which sediment particles can...The repose angle is one of the most significant macroscopic parameters in describing the behavior of granular materials. Under a static condition, the repose angle is the steepest angle at which sediment particles can rest without motion. In this paper, we use existing data and aeolian physics to analyze the main factors that influence the repose angle of sand dunes, and we investigate different repose angles involving various states and types of materials. We have determined that different factors have differential influence on the magnitude of the repose angle. Our results show that for powdery （〈400-μm diameter） desert sands, the main influential factor on the magnitude of repose angle is the molecular force among particles. Particle size does not influence the repose angle of desert sands directly, but has an indirect impact by affecting the grit sphericity and surface roughness, of which the grit sphericity acts as a major factor. Even at the same average particle size, the repose angle differs with different grain compositions. Furthermore, with increasing unevenness in grain composition, the repose angle increases correspondingly. Sand texture also has a direct influence on the repose angle of desert sands. In two sand samples having the same grain composition but different textures, the repose angles may be different. Water content has a stronger influence on the repose angle than any other factor. However, the relationship between the repose angle and water content is not a simple direct proportion. In fact, with increasing water content, the repose angle first increases and then decreases. These research results will be useful for understanding the mechanisms of dune transport, variations of dune morphology, and the stability and fluidity of dune sands.展开更多
Shape has an undeniable impact on particle behaviour,and the shapes of naturally occurring granular matter are typically irregular.Computational studies of irregularly shaped particles are challenging but necessary to...Shape has an undeniable impact on particle behaviour,and the shapes of naturally occurring granular matter are typically irregular.Computational studies of irregularly shaped particles are challenging but necessary to gain a better understanding of the flow of particulate matter.This study focuses on the behaviour of irregular sinter particles and applies the discrete element method to examine the effects of static and rolling friction coefficients and particle shape on the angle of repose and porosity of sinter piles.A three-dimensional model of an irregular sinter particle reconstructed by close-range photogrammetry served as the template for generating multi-sphere particles with varying numbers of sub-spheres(1,3,7,22,and 135)and sphericity ranging from 1 to 0.69.Simulations of particle piles were conducted for a range of values of the coefficients of static and rolling friction.The results indicate that the angle of repose increases with static friction and also increases with rolling friction coefficient when it is lower than the static coefficient.The angle of repose shows clear dependence on particle shape,particularly for lower rolling friction coefficients.The friction coefficients for particles of five different shapes were individually determined through bulk calibration,and irregularly shaped particles in DEM were found to require lower friction coefficients.Porosity was marginally affected by the static and rolling friction coefficients for spherical particles,while non-spherical particles showed porosity increasing with the rolling friction coefficient.The relationship between particle sphericity and porosity was nonlinear:as sphericity decreases from 1.00 to 0.69,the porosity first decreases to a minimum and then increases.The findings confirmed that both friction and particle shape have a significant influence on the structure of sinter piles,with implications for material handling and processing in industrial applications.展开更多
针对烟草包衣种子播种过程离散元仿真中因种粒与播种部件接触参数缺失导致仿真模型准确性差、可靠性低的核心问题,以云烟87烟草包衣种子为研究对象,采用离散元法(Discrete Element Method,DEM)开展数值模拟与接触参数标定研究。首先,通...针对烟草包衣种子播种过程离散元仿真中因种粒与播种部件接触参数缺失导致仿真模型准确性差、可靠性低的核心问题,以云烟87烟草包衣种子为研究对象,采用离散元法(Discrete Element Method,DEM)开展数值模拟与接触参数标定研究。首先,通过物理特性测试与力学性能试验系统测定种子关键物理参数;然后,采用斜面法与跌落试验分别标定种子-种子、种子-ABS板的静摩擦因数、动摩擦因数等核心接触参数;接着,开展种子堆积物理试验,测得种子实际堆积角为23.81°;最后,构建烟草包衣种子离散元仿真模型,经Plackett-Burman试验和最陡爬坡试验筛选对堆积角影响显著的关键因素,缩小参数寻优区间,并通过响应面法完成接触参数的精准寻优。研究结果表明:种粒间静摩擦因数与动摩擦因数的最优组合为0.504、0.022,对应的仿真堆积角为23.87°,与实际堆积角的相对误差仅为0.25%。所构建的烟草包衣种子离散元模型与标定的接触参数具备良好的准确性与可靠性,可为播种过程的离散元仿真分析与精量排种器的结构优化设计提供重要理论依据与技术参考。展开更多
The numerical effort of discrete element method (DEM) simulations results in a general idealisation of DEM models that makes the calibration crucial to obtaining realistic simulation results. The angle of repose test ...The numerical effort of discrete element method (DEM) simulations results in a general idealisation of DEM models that makes the calibration crucial to obtaining realistic simulation results. The angle of repose test has become a standard test for the calibration of DEM parameters of cohesionless bulk materials and is extensively discussed in the literature. One of the most used test methods is the pull-up test of a hollow cylinder filled with bulk material. This paper presents how this basic pull-up test can also be used for the calibration of DEM parameters of cohesive materials by changing the analysis criteria. In contrast to analysing the static angle of repose, the focus lies on the macroscopic flow behaviour during the lifting of the cylinder. Reproducible phases of flow are identified in experiments: the build-up of a stable bulk material column, the convex bending of the column, and the beginning of collapse of the column. Furthermore, the phases are independent of the size and lifting velocity. The convex bending of the bulk-material column combined with the moment of first collapse are introduced as new measurable calibration criteria. These experimental results of wet sand are used for the calibration of related DEM parameters using a simplified JKR cohesion model. The DEM calibration including an analysis algorithm that fits the experimental flow behaviour and the final selection of the relevant parameters (i.e., sliding friction coefficient, rolling friction coefficient, and cohesion energy density) is presented in detail.展开更多
A conception of exposure degree is used in this article to account for the hiding and exposure mechanism of nonuniform sediment transport. The force arms of particles on the bed slope are assumed to be a function of t...A conception of exposure degree is used in this article to account for the hiding and exposure mechanism of nonuniform sediment transport. The force arms of particles on the bed slope are assumed to be a function of the exposure degree, which is stochastically related to the size and gradation of bed materials. Based on this conception, the formula for the angle of repose of nonuniform sediment is developed. The angle of repose of nonuniform sediment is experimentally investigated in rotation drum at the rolling motion of sediment particles. The nonuniform sediment is gotten from the mixture of two kinds of uniform sediment with different weight ratios and two experimental plans that one for changing the weight ratio of two kinds of uniform sediment from 1：9 to 9：1 and the other changing the uniform sediment size and weight ratio are used. The effect of the rotation speed and the filling degree on the angle of repose is investigated, too. Finally, the formula has been tested against a wide range of laboratory data, the prediction by the newly proposed formulas is very good.展开更多
We explore the effect of particle shape on the angle of repose (AoR) in granular packing using a three-dimensional discrete element method.Non-spherical particles were modeled using super-ellipsoids characterized by a...We explore the effect of particle shape on the angle of repose (AoR) in granular packing using a three-dimensional discrete element method.Non-spherical particles were modeled using super-ellipsoids characterized by aspect ratio and blockiness.The relationship between AoR and particle shape was examined,followed by a series of analyses on the origin of AoR from a microscopic perspective.Results show that,with blockiness deviating from unity,AoR has an approximate "M" shape that exhibits a strong to weak trend with aspect ratio,matching results of previous reports.Another finding suggests a parabolic relationship between normalized AoR and normalized coordination number,AoR increases with anisotropy related more with the anisotropy of particle orientation than with the anisotropy of contact normal.Particle shape is more likely to affect AoR by affecting the tangential force than the normal contact force.An analysis based on traction indicates that dips in stress associated with the tangential force (compared with the normal force) and non-spherical particles (compared with spheres) are more significant.For various particle shapes,AoR is positively correlated with friction mobilization but is negatively correlated with friction mobilization for various coefficient of friction.展开更多
Corn kernel shape is an important feature to improve the accuracy of simulation results,also the repose angle is often used to calibrate model parameters in simulation.In this study,the effects of the corn kernel shap...Corn kernel shape is an important feature to improve the accuracy of simulation results,also the repose angle is often used to calibrate model parameters in simulation.In this study,the effects of the corn kernel shapes on the behavior during corn kernels accumulation were investigated in detail.Firstly,the DEM models of three typical shapes of corn kernels were developed.Secondly,the influences of the corn kernel shapes on the process of forming repose angle were investigated,such as corn kernels distance change,energy conversion,and the contact number between corn kernels.Results show that the corn kernel shape has a significant effect on the repose angle formation.The irregular shape of corn kernels limit their rolling when adding the corn kernel length in one or two directions.In addition,the irregular shapes of corn kernels increase the contact number and extend simulation time.Regular shape corn kernels need to be mixed with irregular shape corn kernels to improve their flowability.Finally,observation of the trajectory of corn kernel repose angles indicates that spherical corn kernels contact the bottom plate early,and forming small cone first,then the cone becomes bigger to change the direction of other corn kernels from top to bottom.展开更多
Discrete element modelling(DEM)is a numerical method for examining the dynamic behavior of granular media.In order to build an accurate simulation model and provide more comprehensive soil characteristic parameters fo...Discrete element modelling(DEM)is a numerical method for examining the dynamic behavior of granular media.In order to build an accurate simulation model and provide more comprehensive soil characteristic parameters for the design and optimization of various soil contact machinery,in this paper,the discrete element simulation method(EDEM)combined with experimental approach is used to investigate the soil contact characteristic parameters in East Asia.In this study,Hertze-Mindlin(no slip)was used as a particle contact model by taking particle contact parameters and soil JKR(Johnson-Kendall-Roberts)surface energy as determinants,and repose angle,internal friction angle,and cohesive force as evaluation indexes.The method of Plackett-Burman,Stepest ascent,and Box-Behnken were used to gradually reduce the range of parameters needed for simulation until the most accurate value was determined.The results show that the restitution coefficient,static friction coefficient,and rolling friction coefficient between soil particles have significant effects on the DEM model,and their value of them are 0.596,0.725,and 0.16,respectively.Based on these parameters used for the repose angle test and direct shear stress test,the value of repose angle is 31.97°,the internal friction angle is 27.61°,and the cohesive force is 33.06 kPa.The relative errors with the actual measured values are 9.54%,1.87%,and 2.31%,respectively.In order to further test whether the simulation parameters of soil obtained by repose angle test and direct shear stress test are consistent with the real soil,comparison test between field test and discrete element simulation was used.The results show that the error in height of ridge between the simulated soil and the actual soil is 4.06%,which is within the acceptable range.It also indicates that the calibrated and optimized soil simulation model can accurately represent the real soil.The research provides theoretical basis and technical support for the study of soil contact parts by using the discrete element method,combined with repose angle test and direct shear stress test.展开更多
An experimental study on the angle of repose （AoR） of pulverized coal with different particle sizes and different moisture contents （MC） was conducted. Three different measurement methods, free-base piling, fixed-...An experimental study on the angle of repose （AoR） of pulverized coal with different particle sizes and different moisture contents （MC） was conducted. Three different measurement methods, free-base piling, fixed-base piling and sliding, were used. The data were analyzed by one-way and two-way analysis of variance. The results showed that the AoRs of pulverized coal with particle sizes smaller than 150 μm were in the range of 30-50°. The characterization of the flowability of pulverized coal was some cohesiveness or true cohesiveness. The increase of MC will increase AoR and thus decrease the flowability of the powder. However, the particle size effect is bifurcated. Below a critical size, the decrease of particle size decreases the flowability; while above the critical size, the decrease of particle size increases the flowability. It was found that the value of the critical size strongly depends on the powder density. Moreover, the AoR dependence on particle size could be linked with the Geldart＇s particle classification. The critical size at the turning point is on the boundary between Group A and Group B in Geldart＇s classification diagram. Based on the experimental results, there is no significant cross interaction between particle size and MC. The AoRs measured by free-base method and fixed-base method are close, but both remarkably smaller than that measured by the sliding method.展开更多
The coefficient of static friction(SF),the coefficient of rolling friction(RF)for particles are two key parameters affecting the repose angle formation and flow characteristics.In this paper,the interaction effects of...The coefficient of static friction(SF),the coefficient of rolling friction(RF)for particles are two key parameters affecting the repose angle formation and flow characteristics.In this paper,the interaction effects of SF and RF on the formation process of corn repose angle was investigated by the discrete element method.Firstly,five shape kinds of corn models(horse tooth,spherical cone,spheroid,oblate,and irregular shape)were established.Secondly,aluminum cylinder and organic glass box were used to conduct the simulation experiments with taking SF and RF as independent factors and seeing the repose angle as dependent value.Based on simulation results the regression equations were established.Simulation results showed the relation between two factors and the rotational kinetic energy is not nonlinear,and SF does not significantly restrict the flow of corn models after increasing the flow direction,and the effect of SF on the contact number between corns and the bottom plate is remarkable,while the effect of RF on the contact number is not remarkable.Finally,the interaction effect of two factors on the repose angle was analyzed by variance analysis and results showed SF and RF all have a significant impact on the repose angle.Moreover,their interaction effect has an impact on the repose angle.展开更多
文摘The antlions dig a conical simple pit in sand to catch ants.The funnel shape of the trap is deliberate with a critical angle of repose and is steep and shallow enough to trigger avalanches and cause struggling prey to fall into the funnel.The trap should be designed by optimizing pit morphology according to natural selection.In the current study,antlion behavior and pit morphology in the sand samples with different particle shapes and particle size distributions were studied.The small larvae build in fine sand and silty sand,while larger ones prefer fine to medium sands.However,there is no preference for sands with different particle shapes.Further,the static and dynamic angles of repose for the sand samples were measured,and the slope of the pits was compared with the repose angles.The angle of the heap slope oscillated between an upper angle or angle of sliding(the angle that triggers a landslide)and a lower angle named repose angle.
文摘Heshan, a city in Southwest China, has been built over an old coal mining area. Due to low level of reclamation, coal gangue had been stacked in large heaps and caused geological environ- mental problems. To facilitate designing management project of coal gangue, we made an investigation of the largest coal gangue heap in Dongkuang Mine of Heshan. Firstly, the grain composition of coal gangue was estimated through the sieving method, then the representative grading curve was drawn through the statistics method of coarse grain content, and lastly the relationship between the repose an- gle and grain grading was studied by piling up coal gangue with different mix proportion. The result indicates that there is a wider range of grain size in the upper part of coal gangue heap, and the repre- sentative grain grading is well graded and easy to be compacted as filling materials. Besides, the wavy relationship curve of repose angle and coarse grain content shows that the content of 70% is the infiec- tion point of ascent stage and 85% the inflection point of descent stage of the repose angle. What＇s more, the repose angle corresponding to the representative grading of coal gangue is approximately 38.4° and this has guiding significance for management project of coal gangue.
基金supported by the National Natural Science Foundation of China (Grant No. 50879033)the National Science Fund for Fostering Talents in Basic Research of the National Natural Science Foundation of China (Grant No.J0730536)
文摘The repose angle is one of the most significant macroscopic parameters in describing the behavior of granular materials. Under a static condition, the repose angle is the steepest angle at which sediment particles can rest without motion. In this paper, we use existing data and aeolian physics to analyze the main factors that influence the repose angle of sand dunes, and we investigate different repose angles involving various states and types of materials. We have determined that different factors have differential influence on the magnitude of the repose angle. Our results show that for powdery （〈400-μm diameter） desert sands, the main influential factor on the magnitude of repose angle is the molecular force among particles. Particle size does not influence the repose angle of desert sands directly, but has an indirect impact by affecting the grit sphericity and surface roughness, of which the grit sphericity acts as a major factor. Even at the same average particle size, the repose angle differs with different grain compositions. Furthermore, with increasing unevenness in grain composition, the repose angle increases correspondingly. Sand texture also has a direct influence on the repose angle of desert sands. In two sand samples having the same grain composition but different textures, the repose angles may be different. Water content has a stronger influence on the repose angle than any other factor. However, the relationship between the repose angle and water content is not a simple direct proportion. In fact, with increasing water content, the repose angle first increases and then decreases. These research results will be useful for understanding the mechanisms of dune transport, variations of dune morphology, and the stability and fluidity of dune sands.
基金funded by China Scholarship Council(grant No.202106890009).
文摘Shape has an undeniable impact on particle behaviour,and the shapes of naturally occurring granular matter are typically irregular.Computational studies of irregularly shaped particles are challenging but necessary to gain a better understanding of the flow of particulate matter.This study focuses on the behaviour of irregular sinter particles and applies the discrete element method to examine the effects of static and rolling friction coefficients and particle shape on the angle of repose and porosity of sinter piles.A three-dimensional model of an irregular sinter particle reconstructed by close-range photogrammetry served as the template for generating multi-sphere particles with varying numbers of sub-spheres(1,3,7,22,and 135)and sphericity ranging from 1 to 0.69.Simulations of particle piles were conducted for a range of values of the coefficients of static and rolling friction.The results indicate that the angle of repose increases with static friction and also increases with rolling friction coefficient when it is lower than the static coefficient.The angle of repose shows clear dependence on particle shape,particularly for lower rolling friction coefficients.The friction coefficients for particles of five different shapes were individually determined through bulk calibration,and irregularly shaped particles in DEM were found to require lower friction coefficients.Porosity was marginally affected by the static and rolling friction coefficients for spherical particles,while non-spherical particles showed porosity increasing with the rolling friction coefficient.The relationship between particle sphericity and porosity was nonlinear:as sphericity decreases from 1.00 to 0.69,the porosity first decreases to a minimum and then increases.The findings confirmed that both friction and particle shape have a significant influence on the structure of sinter piles,with implications for material handling and processing in industrial applications.
文摘针对烟草包衣种子播种过程离散元仿真中因种粒与播种部件接触参数缺失导致仿真模型准确性差、可靠性低的核心问题,以云烟87烟草包衣种子为研究对象,采用离散元法(Discrete Element Method,DEM)开展数值模拟与接触参数标定研究。首先,通过物理特性测试与力学性能试验系统测定种子关键物理参数;然后,采用斜面法与跌落试验分别标定种子-种子、种子-ABS板的静摩擦因数、动摩擦因数等核心接触参数;接着,开展种子堆积物理试验,测得种子实际堆积角为23.81°;最后,构建烟草包衣种子离散元仿真模型,经Plackett-Burman试验和最陡爬坡试验筛选对堆积角影响显著的关键因素,缩小参数寻优区间,并通过响应面法完成接触参数的精准寻优。研究结果表明:种粒间静摩擦因数与动摩擦因数的最优组合为0.504、0.022,对应的仿真堆积角为23.87°,与实际堆积角的相对误差仅为0.25%。所构建的烟草包衣种子离散元模型与标定的接触参数具备良好的准确性与可靠性,可为播种过程的离散元仿真分析与精量排种器的结构优化设计提供重要理论依据与技术参考。
文摘The numerical effort of discrete element method (DEM) simulations results in a general idealisation of DEM models that makes the calibration crucial to obtaining realistic simulation results. The angle of repose test has become a standard test for the calibration of DEM parameters of cohesionless bulk materials and is extensively discussed in the literature. One of the most used test methods is the pull-up test of a hollow cylinder filled with bulk material. This paper presents how this basic pull-up test can also be used for the calibration of DEM parameters of cohesive materials by changing the analysis criteria. In contrast to analysing the static angle of repose, the focus lies on the macroscopic flow behaviour during the lifting of the cylinder. Reproducible phases of flow are identified in experiments: the build-up of a stable bulk material column, the convex bending of the column, and the beginning of collapse of the column. Furthermore, the phases are independent of the size and lifting velocity. The convex bending of the bulk-material column combined with the moment of first collapse are introduced as new measurable calibration criteria. These experimental results of wet sand are used for the calibration of related DEM parameters using a simplified JKR cohesion model. The DEM calibration including an analysis algorithm that fits the experimental flow behaviour and the final selection of the relevant parameters (i.e., sliding friction coefficient, rolling friction coefficient, and cohesion energy density) is presented in detail.
基金supported by the National Natural Science Foundation of China (Grant Nos.50739002,50979064)
文摘A conception of exposure degree is used in this article to account for the hiding and exposure mechanism of nonuniform sediment transport. The force arms of particles on the bed slope are assumed to be a function of the exposure degree, which is stochastically related to the size and gradation of bed materials. Based on this conception, the formula for the angle of repose of nonuniform sediment is developed. The angle of repose of nonuniform sediment is experimentally investigated in rotation drum at the rolling motion of sediment particles. The nonuniform sediment is gotten from the mixture of two kinds of uniform sediment with different weight ratios and two experimental plans that one for changing the weight ratio of two kinds of uniform sediment from 1：9 to 9：1 and the other changing the uniform sediment size and weight ratio are used. The effect of the rotation speed and the filling degree on the angle of repose is investigated, too. Finally, the formula has been tested against a wide range of laboratory data, the prediction by the newly proposed formulas is very good.
基金the Fundamental Research Funds for Central Universities,State Key Laboratory of Subtrop-ical Building Science(2017KA04)partially by Science and Technology Program of Guangzhou(201707020047)。
文摘We explore the effect of particle shape on the angle of repose (AoR) in granular packing using a three-dimensional discrete element method.Non-spherical particles were modeled using super-ellipsoids characterized by aspect ratio and blockiness.The relationship between AoR and particle shape was examined,followed by a series of analyses on the origin of AoR from a microscopic perspective.Results show that,with blockiness deviating from unity,AoR has an approximate "M" shape that exhibits a strong to weak trend with aspect ratio,matching results of previous reports.Another finding suggests a parabolic relationship between normalized AoR and normalized coordination number,AoR increases with anisotropy related more with the anisotropy of particle orientation than with the anisotropy of contact normal.Particle shape is more likely to affect AoR by affecting the tangential force than the normal contact force.An analysis based on traction indicates that dips in stress associated with the tangential force (compared with the normal force) and non-spherical particles (compared with spheres) are more significant.For various particle shapes,AoR is positively correlated with friction mobilization but is negatively correlated with friction mobilization for various coefficient of friction.
基金This work was supported by the Fostering Foundation for the Excellent Ph.D.Dissertation of Gansu Agricultural University(YB2020003)the Chinese Natural Science Foundation(52065004).
文摘Corn kernel shape is an important feature to improve the accuracy of simulation results,also the repose angle is often used to calibrate model parameters in simulation.In this study,the effects of the corn kernel shapes on the behavior during corn kernels accumulation were investigated in detail.Firstly,the DEM models of three typical shapes of corn kernels were developed.Secondly,the influences of the corn kernel shapes on the process of forming repose angle were investigated,such as corn kernels distance change,energy conversion,and the contact number between corn kernels.Results show that the corn kernel shape has a significant effect on the repose angle formation.The irregular shape of corn kernels limit their rolling when adding the corn kernel length in one or two directions.In addition,the irregular shapes of corn kernels increase the contact number and extend simulation time.Regular shape corn kernels need to be mixed with irregular shape corn kernels to improve their flowability.Finally,observation of the trajectory of corn kernel repose angles indicates that spherical corn kernels contact the bottom plate early,and forming small cone first,then the cone becomes bigger to change the direction of other corn kernels from top to bottom.
基金This work was financially supported by the National Science and Technology Major Project of China(Grant No.2019YFD 1002502)the National Natural Science Foundation of China(Grant No.51675239)+2 种基金The Natural Science Fund Project of Colleges in Jiangsu Province of China(Grant No.19KJA430018)The Important Development Program of Ningxia Province of China(Grant No.2018BBF02020)The Research and Development Program of Zhenjiang Province of China(Grant No.NY2019015).
文摘Discrete element modelling(DEM)is a numerical method for examining the dynamic behavior of granular media.In order to build an accurate simulation model and provide more comprehensive soil characteristic parameters for the design and optimization of various soil contact machinery,in this paper,the discrete element simulation method(EDEM)combined with experimental approach is used to investigate the soil contact characteristic parameters in East Asia.In this study,Hertze-Mindlin(no slip)was used as a particle contact model by taking particle contact parameters and soil JKR(Johnson-Kendall-Roberts)surface energy as determinants,and repose angle,internal friction angle,and cohesive force as evaluation indexes.The method of Plackett-Burman,Stepest ascent,and Box-Behnken were used to gradually reduce the range of parameters needed for simulation until the most accurate value was determined.The results show that the restitution coefficient,static friction coefficient,and rolling friction coefficient between soil particles have significant effects on the DEM model,and their value of them are 0.596,0.725,and 0.16,respectively.Based on these parameters used for the repose angle test and direct shear stress test,the value of repose angle is 31.97°,the internal friction angle is 27.61°,and the cohesive force is 33.06 kPa.The relative errors with the actual measured values are 9.54%,1.87%,and 2.31%,respectively.In order to further test whether the simulation parameters of soil obtained by repose angle test and direct shear stress test are consistent with the real soil,comparison test between field test and discrete element simulation was used.The results show that the error in height of ridge between the simulated soil and the actual soil is 4.06%,which is within the acceptable range.It also indicates that the calibrated and optimized soil simulation model can accurately represent the real soil.The research provides theoretical basis and technical support for the study of soil contact parts by using the discrete element method,combined with repose angle test and direct shear stress test.
基金supports by National Basic Research Program of China(2010CB227006)National High-tech R&D Program(2009AA05Z216)
文摘An experimental study on the angle of repose （AoR） of pulverized coal with different particle sizes and different moisture contents （MC） was conducted. Three different measurement methods, free-base piling, fixed-base piling and sliding, were used. The data were analyzed by one-way and two-way analysis of variance. The results showed that the AoRs of pulverized coal with particle sizes smaller than 150 μm were in the range of 30-50°. The characterization of the flowability of pulverized coal was some cohesiveness or true cohesiveness. The increase of MC will increase AoR and thus decrease the flowability of the powder. However, the particle size effect is bifurcated. Below a critical size, the decrease of particle size decreases the flowability; while above the critical size, the decrease of particle size increases the flowability. It was found that the value of the critical size strongly depends on the powder density. Moreover, the AoR dependence on particle size could be linked with the Geldart＇s particle classification. The critical size at the turning point is on the boundary between Group A and Group B in Geldart＇s classification diagram. Based on the experimental results, there is no significant cross interaction between particle size and MC. The AoRs measured by free-base method and fixed-base method are close, but both remarkably smaller than that measured by the sliding method.
基金by the Excellent Ph.D.Dissertation of Gansu Agricultural University(YB2020003)the Chinese Natural Science Foundation(52065004).
文摘The coefficient of static friction(SF),the coefficient of rolling friction(RF)for particles are two key parameters affecting the repose angle formation and flow characteristics.In this paper,the interaction effects of SF and RF on the formation process of corn repose angle was investigated by the discrete element method.Firstly,five shape kinds of corn models(horse tooth,spherical cone,spheroid,oblate,and irregular shape)were established.Secondly,aluminum cylinder and organic glass box were used to conduct the simulation experiments with taking SF and RF as independent factors and seeing the repose angle as dependent value.Based on simulation results the regression equations were established.Simulation results showed the relation between two factors and the rotational kinetic energy is not nonlinear,and SF does not significantly restrict the flow of corn models after increasing the flow direction,and the effect of SF on the contact number between corns and the bottom plate is remarkable,while the effect of RF on the contact number is not remarkable.Finally,the interaction effect of two factors on the repose angle was analyzed by variance analysis and results showed SF and RF all have a significant impact on the repose angle.Moreover,their interaction effect has an impact on the repose angle.
