Calibration of discrete element parameters of farmland model after rotary tillage

Soil contact parameters are different due to different factors such as soil moisture content, composition, and particle size. In order to improve the accuracy of the trenching and soil covering operation of a new high-density shrub seedling transplanter, this study conducted a discrete element parameter calibration experiment on farmland soil after spring cultivation in northern China. Through a combination of physical and simulation experiments, the Hertz-Mindlin（no slip） contact model was used to calibrate the parameters with the soil-soil response angle and the soil-steel sliding friction angle as the response values, and the recovery coefficient, static friction coefficient, and rolling friction coefficient as the target values. Firstly, the Box-Behenken response surface analysis method was applied to the target value to conduct a three factor and three level orthogonal rotation test, so as to obtain a second-order regression model. Secondly, taking the actual stacking angle and sliding friction angle as the response values, the optimal parameter combinations were obtained through the Design-Expert optimization module as follows: soil-soil recovery coefficient was 0. 4, soil-soil static friction coefficient was 0. 8, and soil-soil rolling friction coefficient was 0. 39. Soil-steel recovery coefficient was 0. 27, soil steel static friction coefficient was 0. 53, and soil steel rolling friction coefficient was 0. 16. A comparison between physical experiments and simulation experiments was also conducted, and the results showed that the errors of the two methods were 0. 68% and 1. 34%, respectively, which were within an acceptable range, and had a good reliability and certain engineering guiding significance.