基于离散元的玉米种子颗粒模型种间接触参数标定

由于EDEM(离散元法)中建立的玉米种子颗粒模型与实际玉米种子在外形、表面粗糙度等方面存在差异,若直接将实际测量的物性参数引入EDEM中进行仿真,会出现仿真失真的情况。针对此问题,该文提出一种建立数学回归模型主动寻找目标参数的方法,简化标定过程,将仿真试验和真实试验相结合,对玉米种子颗粒模型的种间静摩擦系数和滚动摩擦系数两个关键参数进行标定,使其在EDEM中建立的玉米种子颗粒重新获得与真实颗粒相近的物理特性。利用两种接触材料(有机玻璃板与铝质圆筒)进行玉米种子堆积角仿真试验,建立两个自变量为种间静摩擦系数、种间滚动摩擦系数的二元回归方程。以实际测量种群堆积角作为已知目标量进行数值求解,求得EDEM中玉米种间静摩擦系数和滚动摩擦系数这两个目标参数:玉米种间静摩擦系数为0.0338,玉米种间滚动摩擦系数为0.0021。将标定的玉米种子物性参数输入EDEM中进行仿真试验,通过提取关键特征尺寸和图像边界将试验结果与实际试验结果进行对比,结果表明:关键特征尺寸数值差异在4.70%以内,标定后的玉米种子堆积角边界与实际情况更接近,提高了仿真结果的可靠性。

Calibration method of contact characteristic parameters for corn seeds based on EDEM

Abstract: The pneumatic metering device has the advantages of high qualified index, less mechanical damage to seeds and good adaptability for high-speed operation. But traditional calculation method is not capable of analyzing the law of seeds motion because of the complex stress state. Discrete element method (DEM) is the key method to solve the above problem. However, physical characteristics parameters of particles, mainly consisting of static friction coefficient and rolling friction coefficient between corn seeds, are key factors for reliable simulation results in the DEM. Due to the difference between corn seeds and simulation particles in surface shape and size, the actual physical parameters of corn seeds are not suitable for the EDEM (enhanced discrete element method). Particles models established in the EDEM are rougher than corn seeds, which leads to the distortion of simulation results. Therefore calibration works for particle parameters are essential. In this paper, a new method was proposed for actively seeking the target parameters based on regression analysis. It was estimated that repose angle was commonly influenced by static friction coefficient and rolling friction coefficient between corn seeds. All factors simulation experiments were conducted to obtain the regression equations, of which the tangent value of repose angle at different contact material was separately taken as the dependent variables, and the static friction coefficient and rolling friction coefficient between corn seeds were taken as independent variables. In order to decrease the measuring error, MATLAB software was used for images acquisition and analysis. The variance analysis showed that the static friction coefficient and rolling friction coefficient between corn seeds had significant influence on the repose angle and natural heaping angle separately at significance level of 5%. The tangent value of repose angle had an increase trend with the increase of static friction coefficient and rolling friction coefficient between corn seeds. For the first test with organic plate, it had a bigger increase when the static friction coefficient was at 0-0.2 and then increased slowly, at this time which was mainly influenced by the rolling friction coefficient. For the second test with aluminum plate, it also increased with the increase of static friction coefficient and rolling friction coefficient between corn seeds in a consistent state. By the simulation tests, 2 regression equations were obtained. For solving the independent variables, the actual tangent values of repose angle with different contact material were measured by the actual tests and taken as the dependent variables. By this way, the static friction coefficient of 0.0338 and the rolling friction coefficient of 0.0021 between corn seeds were obtained. Verification tests with calibrated physical parameters were carried out. Results showed that the tangent values of repose angle were consistent with the actual tests. The simulation model of corn seeds was composed of multiple small spherical particles. There were sunk areas between adjacent seeds, so the contact area between corn seeds increased and meanwhile the friction force was increased. Corresponding relation between actual seeds and simulation model was found by this calibration method. The boundary of repose angle was extracted to compare the simulation and actual test results, which verified that the calibrated physical parameters were applicable for the EDEM and the method was feasible.