冰草种子物性参数测定与离散元仿真参数标定

Measurement and calibration of physical property parameters for Agropyron seeds in a discrete element simulation

为了提高冰草种子丸化包衣过程离散元仿真模拟试验所用参数的准确度,该研究通过物理试验和仿真试验相结合的方法对仿真参数进行标定。首先,采用物理试验的方法测定冰草种子的基本物性参数(外形尺寸、千粒重、密度、含水率、泊松比、弹性模量和剪切模量)和接触参数(静摩擦系数、滚动摩擦系数和碰撞恢复系数),参考物理试验测定结果选择仿真试验参数取值范围,采用Plackett-Burman试验对仿真参数进行显著性筛选,筛选试验结果表明:冰草种子-冰草种子静摩擦系数、滚动摩擦系数、碰撞恢复系数对仿真试验休止角有显著性影响。进一步通过最陡爬坡试验确定3个显著性参数最优取值范围,并根据Box-Behnken设计试验得到显著性参数与休止角的二阶回归模型,以物理试验实测的休止角30.54°为优化目标值获得最优参数组合为:冰草种子-冰草种子静摩擦系数0.57、滚动摩擦系数0.74、碰撞恢复系数0.54。最后对物理试验休止角和仿真试验休止角进行双样本T检验得出P>0.05,结果表明仿真得到的休止角与物理试验值无显著性差异,且最优参数组合下仿真试验休止角30.86°与物理试验休止角30.54°的相对误差为1.037%,进一步验证了仿真试验的可靠性。研究结果表明标定所得的最优参数可用于冰草种子丸化包衣过程的离散元仿真试验。

Agropyron,a perennial xerophytic grass of the gramineae,is one of the most widespread grass species in arid and semi-arid areas.In artificial grasslands on the dry land,Agropyron is also commonly used in the process of reseeding in grazing areas and spray sowing,due mainly to its drought resistance,as well as cold and grazing tolerance.In addition,the roots of wheatgrass are whisker-like,densely growing,and sand-gathering,particularly for the soil and water conservation,as well as wind-proof and sand-fixing.Therefore,the accuracy of physical parameters is highly demanding in the process of pelleting and coating on Agropyron seeds using a discrete element method.In this study,a novel approach combined physical and simulation test was proposed to calibrate the physical parameters used in an EDEM software.A physical test was conducted to determine the basic physical parameters of Agropyron seeds(dimensions,thousand-grain weight,density,moisture content,Poisson’s ratio,elastic modulus,and shear modulus),and the contact parameters(static friction coefficient,rolling friction coefficient,and collision restitution coefficient).The measurement values from the physical test indicated that:In the friction pair of Agropyron seed-Agropyron seed,the collision restitution coefficient ranged from 0.45 to 0.65,the static friction coefficient ranged from 0.5 to 0.7,and the rolling friction coefficient ranged from 0.6 to 0.9,whereas,in the Agropyron seed-steel plate,the collision restitution coefficient ranged from 0.4 to 0.6,the static friction coefficient ranged from 0.2 to 0.4,and the rolling friction coefficient ranged from 0.3 to 0.6.A Plackett-Burman design was carried out to select the physical parameters from the physical test for the later use in the simulation test.The results show that between the Agropyron seed-Agropyron seed,the static friction coefficient,the rolling friction coefficient,and the collision restitution coefficient have a significant effect on the angle of repose.A steepest climbing test was further used to determine the optimal ranges of three parameters.In the Box-Behnken test,the second-order regression equation of the repose angle,and the saliency parameter were established,where an optimal repose angle(30.54°)was used to optimize the model.The best simulation parameters were then achieved:The collision restitution coefficient of Agropyron seed-Agropyron seed was 0.54,the static friction coefficient of Agropyron seed-Agropyron seed was 0.57,and the rolling friction coefficient of Agropyron seed-Agropyron seed was 0.74.In the two-sample T test,there no significant difference in the repose angle from the physical and simulation test(P>0.05).The relative error of repose angle was 1.037%,where the simulation(30.86°)and physical test(30.54°)were under the optimal combination of parameters,indicating the reliability of the simulation test.As such,the optimized parameters that obtained by calibration can be used in the discrete element simulation for the pelletizing and coating process of Agropyron seeds.