花生种子颗粒离散元仿真参数标定与试验

由于花生排种装置在优化设计过程中缺乏准确的仿真模型参数，从而造成仿真与理论计算结果存在较大误差，一定程度上制约了花生排种装置的发展。该研究系统测定了花生种子的三轴尺寸、颗粒密度、弹性模量、泊松比等本征参数及其静摩擦因数、滚动摩擦因数、恢复系数。通过开展花生种子颗粒堆积试验，标定得到花生种间静摩擦因数为0.213，种间滚动摩擦因数为0.035。为检验标定参数的可靠性，开展了花生堆积角仿真与物理试验对比。结果表明花生物理堆积角和仿真堆积角相对误差为0.22%。通过开展机械式花生精量排种器的仿真与台架排种性能的对比试验，得到排种性能中漏播指数、重播指数相对误差分别为8.24%、5.12%，结果表明花生标定参数具有可靠性。本研究结果可为排种装置的优化设计与仿真研究提供理论参考。

Calibration and experiments for discrete element simulation parameters of peanut seed particles

In order to obtain the parameters required for the discrete element simulation between the peanut seed and the seed-metering device, the basic physical parameters of peanut seeds, such as the grain density, the dimension feature, Poisson''s ratio, elastic modulus, static friction coefficient and recovery coefficient, were determined by experimental method. The average density was 1.04×103 kg/m3, the average moisture content was 12.95%, and the bulk density was 0.69×103 kg/m3 of peanut seed were used. 200 peanut seeds were randomly selected from the peanut seeds with good quality, and the characteristic size of the peanut was measured by a digital vernier caliper. The results showed that the long average of peanut seeds was 13.44 mm, the width was 8.37 mm, and the thickness was 8.02 mm. Since the shape of peanut seeds was similar to an ellipsoid, the volume of the peanut seed was calculated by the ellipsoid volume formula. The volume distribution of peanut seeds was basically normal distribution. With the pressure deformation experiment of peanut seeds was carried out by universal materials testing machine, and Poisson''s ratio of peanut seeds was calculated by measuring the deformation of length and width before and after loading seeds, and the result was 0.362. The elastic modulus of peanut seeds measured by Hertz contact stress method was 5.06×107 Pa. Using the self-made measuring apparatus of peanut seed static friction coefficient, the static friction coefficients between peanut seed and other material including photosensitive resin and PMMA were measured, and these were respectively 0.441 and 0.293. By the combination of seed-free fall and high-speed camera image acquisition and processing, the collision recovery coefficient between peanut seed and material including peanut seed, photosensitive resin and PMMA was determined, and the collision recovery coefficient was 0.505, 0.515 and 0.519, respectively. Since the current rolling friction coefficient measurement method is not yet mature, the rolling friction coefficient between peanut seeds and the above two materials was measured by the inclined surface method and high-speed photography method. The results showed that the rolling friction coefficients between the peanut seeds and the two materials determined by the inclined surface method were 0.126 and 0.099, respectively, and the results determined by the high-speed photography method respectively were 0.121 and 0.095. Therefore, the results obtained by the two methods were similar, and the average value (0.124, 0.097) was taken as the calibration value. Due to the difference between peanut seeds and simulation particles in shape, the particle models established by the discrete element method are rougher than peanut seeds, which leads to the distortion of simulation test results. Therefore, a discrete element simulation model of peanut seeds was established by the slicing method, the coefficient of static friction and the coefficient of rolling friction between peanut seeds were used as variables, and the angle of repose of peanut is used as the response value to establish a regression model. Predicted values are 0.213 and 0.035 respectively, when peanut angle of repose is 22.97°. Finally, angle of repose simulation experiments were carried out using the calibrated parameters, and compared with the physical test value, the relative error between the two test values of the angle of repose was 0.22%. Through the simulation and bench comparison test of the designed pneumatic-mechanical combined precision metering device for peanut. The results showed that the relative errors of the miss seeding index and replay seeding index of the discrete element simulation test and bench test of the seed-metering device were 8.24% and 5.12%, respectively, which satisfies the standard JB/T 10293-2001 Specifications of single seed drill (precision drill). The above verification test showed that the calibrated parameters were accurate and reliable, and the obtained optimized parameter combination can provide a reference for the discrete element simulation of the peanut metering device.