新疆棉田耕后土壤模型离散元参数标定

为提高耕后分层施肥开沟覆土过程离散元仿真模拟的准确性，采用EDEM离散元软件对分层施肥作业土壤的堆积和滑落过程进行仿真模拟，来标定土壤接触参数。通过通用旋转中心组合试验，采用 Design-Expert 软件对试验数据进行回归分析，以实测土壤休止角、土壤与65 Mn钢滑动摩擦角为优化目标，获得最优的离散元接触参数组合为：土壤间恢复系数0.48、土壤间滚动摩擦系数0.56、土壤间静摩擦系数0.24、土壤与65 Mn钢间恢复系数0.5、土壤与65 Mn钢间滚动摩擦系数0.1、土壤与65 Mn钢间静摩擦系数0.31。为验证标定优化的离散元模型参数的准确性，对土壤堆积试验和滑落试验进行仿真试验与实际试验对比，两者相对误差分别为1.7%和2.5%；并在最优标定参数组合条件下，采用离散法仿真模拟分层施肥装置的开沟覆土过程，获得分层施肥装置5、6和7 km/h作业速度下，仿真试验和田间试验的工作阻力相对误差分别为10.2%、7.95%、7.04%，误差在可接受范围内。仿真试验和田间试验开沟覆土效果基本一致，验证了土壤参数标定的准确可靠，可为后期分层施肥装置减阻研究提供理论基础和技术支持。

Calibration of the discrete element parameters for the soil model of cotton field after plowing in Xinjiang of China

Abstract: A multi-layer fertilization has been considered as an efficient way to meet the needs of fertilizers at different growth stages of crops. A layered fertilization device is usually used for the process of ditching and covering soil after ploughing. In this case, the movement of soil particles is very complicated. In this study, an EDEM discrete element software was used to simulate the process of soil accumulation and sliding in the layered fertilization area, in order to calibrate soil contact parameters. A Hertz-Mindlin non-slip model was selected to simulate the contact surface of soil-soil and soil-layered fertilization device (65 Mn steel), according to the soil characteristics of cotton fields after ploughing. Three common shapes of soil particles were represented by Dual Surface, Square Four, and Straight Four. The calibration parameters were also selected to determine the ranges. Specifically, the static friction coefficient, rolling friction coefficient, and collision recovery coefficient between soil-soil and soil-65 Mn steel were used as test factors, while the soil angle of repose, and sliding friction angle of soil-Mn steel were used as evaluation indicators. The universal rotation center combination test was conducted to verify the model. The Design-Expert software was then utilized to perform the regression on the test data. The results showed that the coefficient of recovery from the collision of soil-soil and soil-65 Mn steel presented no significant effect on the angle of repose and sliding friction of soil. Taking the measured soil angle of repose and the sliding friction angle between the soil and 65 Mn steel as the optimization objectives, an optimal combination of discrete element contact parameters was obtained: the coefficient of restoration between soils was 0.48, the coefficient of rolling friction between soils was 0.56, the coefficient of static friction between soils was 0.24, the coefficient of restitution between the soil and 65 Mn steel was 0.5, the coefficient of rolling friction between soil and 65 Mn steel was 0.1, and the coefficient of static friction between soil and 65 Mn steel was 0.31. A soil accumulation test and the sliding test were also compared with the actual test, in order to verify the accuracy of the optimized parameters. The relative errors of the two tests were 1.7% and 2.5%, respectively, under the optimal combination of calibration parameters. Consequently, the discrete elements can be expected to simulate the ditching and soil covering process of the layered fertilization device. The relative errors of simulation and field test were 10.2%, and 7.95%, respectively, at the operating speed of 5, 6,, and 7 km/h of layered fertilization device. Among them, the error of 7.04% was within the acceptable range. Consequently, the simulation and field test presented basically the same effect of ditching and covering soil, indicating the high accuracy and reliability for the calibration of soil contact parameters. The finding can provide strong theoretical and technical support for the later research on drag reduction of layered fertilization devices.