Authors

Abstract

Accurate discrete element method (DEM) parameters are essential for simulating key operations in jujube postharvest processing, such as pneumatic cleaning during mechanical harvesting. The fundamental physical properties of Yimeng Mountain jujubes were systematically measured. A jujube particle template was constructed using the multi-sphere method, and the Hertz–Mindlin (no slip) contact model was adopted. The jujube simulation model was generated by filling the particle template with multiple spheres of different diameters. The static friction coefficient between jujubes ranged from 0.41 to 0.69, while that between jujubes and a steel plate ranged from 0.40 to 0.54. The rolling friction coefficient between jujubes ranged from 0.16 to 0.30, whereas that between jujubes and a steel plate ranged from 0.11 to 0.24. The coefficient of restitution between Yimeng Mountain jujubes, determined using a high-speed camera, ranged from 0.41 to 0.54, while that between jujubes and a steel plate ranged from 0.46 to 0.61. A Plackett–Burman screening design was conducted, and the results showed that the Poisson’s ratio of jujube, the static friction coefficient between jujubes, and the static friction coefficient between jujubes and the steel plate were the three dominant factors. The steepest ascent method was then used to narrow the ranges of these significant parameters. Subsequently, a Box–Behnken design was employed to establish a quadratic regression model relating the angle of repose to the three significant factors. Using the experimentally measured angle of repose of 28.08° as the optimization target, the optimal simulation parameters were determined as follows: a Poisson’s ratio of 0.32, a jujube–jujube static friction coefficient of 0.52, and a jujube–steel static friction coefficient of 0.47. The relative error between the simulated and experimentally measured angles of repose was 2.17%, further confirming the accuracy and reliability of the calibrated simulation parameters.

Abstract in Chinese

为沂蒙山红枣风选机械化采收等关键环节的仿真提供准确的离散元模型参数，本文通过物理试验精准测定红枣的物性参数，构建具备尺寸特征和形态特征的三维模型，采用斜面仪测得沂蒙山红枣之间的静摩擦系数为0.41-0.69，沂蒙山红枣与钢板之间的静摩擦系数为0.40-0.54。沂蒙山红枣之间的动摩擦系数为0.16-0.30，沂蒙山红枣与钢板之间的动摩擦系数为0.11-0.24。采用高速摄像机测得沂蒙山红枣与沂蒙山红枣的恢复系数为0.41-0.54，沂蒙山红枣与钢板的碰撞恢复系数0.46-0.61。开展Plackett-Burman试验筛选出对堆积角有显著影响的参数为：红枣泊松比、红枣-红枣静摩擦系数和红枣-钢静摩擦系数，进一步通过最陡爬坡试验确定显著性参数最优范围区间。通过Box-Behnken 试验，建立堆积角与显著性参数的二阶回归模型，并以物理试验得到最优堆积角目标值进行优化求解，得到最优仿真参数：红枣泊松比为0.32、红枣-红枣静摩擦系数为0.52、红枣-钢静摩擦系数为0.47。仿真堆积角与物理堆积角的相对误差为2.17%。进一步验证了仿真试验和标定后仿真参数的真实性和可靠性。