关键词: 茎瘤芥种子, 离散元, 堆积角, 参数标定

Abstract: In order to solve the problem of lack of accurate simulation parameters in the discrete element simulation of stem mustard seed, the discrete element parameters of “Fuza 2” stem mustard seed were determined by direct measurement and virtual calibration method. First of all, the triaxial size, equivalent radius, thousandkernel weight and density of the stem mustard seeds were measured by using digital vernier caliper, electronic scale and other physical and mechanical property measuring tools. Crash ramp test, threepoint sliding test, and ramp test were conducted, and coefficient of restitution, coefficient of static friction and coefficient of rolling friction between seed and the polymethyl methacrylate (PMMA) were attained to be 0.561, 0.420, and 0.155, respectively. The dynamic repose angle and static repose angle of stem seeds were 35.235 2° and 14.483 0°, respectively through rotating drum test and the cylinder lifting test combining with MATLAB image processing techniques. Then, seedseed rolling friction coefficient and seedseed static friction coefficient were proved to be significant factors for both kinds of repose angle by a discrete element simulation test based on PlackettBurman design method. Therefore, taking seedseed rolling friction coefficient and seedseed static friction coefficient as control factors, and dynamic repose angle and static repose angle as evaluation index, a simulation test based on Central Composite Design (CCD) test method was carried out. Quadratic regression equations of dynamic repose angle and static repose angle with control factors were established respectively. The regression model was used to optimize the control factor combination, and two sets of optimal factor combinations were obtained as 0.666 1, 0.023 7 and 0.341 6, 0.036 0. In the end, the simulation test parameters were respectively set as two sets of optimal factor combinations to compare with actual values measured in physical test. The results indicate that the relative errors between the simulated values and measured values of dynamic repose angle and static repose angle are 0.477%, 3.590% and 1.820%、4.950%. The results show that when the seedseed static friction coefficient and the seedseed rolling friction coefficient are 0.666 1 and 0.023 7 in the simulation, the performance of the stem mustard seeds are more in line with the actual physical characteristics. This conclusion can provide a reference for the research of sowing process of stem mustard seed and the design of related devices.

Key words: stem mustard seed, discrete element method, repose angle, parameter calibration