Simulation analysis and experiment of drag reduction effect of convex blade subsoiler based on discrete element method

Abstract: Due to long-term shallow ploughing, rotary tillage and tractor wheel rolling, a hard and compact Plow pan layer is formed between the tillage layer and the subsoil layer. The presence of plow pan layer can inhibit roots growing and prevent material transfer between tillage layer and the susoil layer, thus reducing crop yield. The subsoiling can improve the soil water storage, improve soil water retention capacity, promote roots growth, and effectively improve crop yield effectively, but the resistance and energy consumption of subsoiling is high. The convex blade subsoiler was designed to reduce the subsoiling resistance in the paper. The convex blade subsoiler was mainly composed of subsoiler handle, subsoiler tip and convex edge, in the process of subsoiling, the convex edge on the subsoiler tip slip cutting the soil on the upper surface of the subsoiler tip, which reducing the pressure of the soil on the upper surface of the subsoiler tip, thereby reducing the subsoiling resistance. Firstly, the curve expression of convex blade edge was calculated based on the sliding cutting condition. And then, the convex blade subsoiler with convex blade and stander subsoiler were selected as the study object by EDEM simulation and field experiment, which used to verify the drag reduction effect of convex blade and the accuracy of soil simulation model. Taking North China Plain as the research object, the physical parameters of soil particle was determined, and the soil geometry model which consists of tillage layer, the subsoil layer and plow pan layer was constructed by 3D graphics software NVENTOR. In order to improve the accuracy of the soil model, the Edinburgh Elasto-Plastic Adhesion Model was used as soil contact model to simulate the tillage resistance of subsoiler. The EDEM software was employed to analyze the drag reduction effect of convex blade subsoiler at different tillage depths and forward speeds, which had been compared with the stander subsoiler. The experiment results showed that convex blade subsoiler had a drag reduction effect compared with stander subsoiler, and the average drag reduction was 7.56%. In addition, the EDEM_Addin plug-in was used to introduce the contact force of the soil with convex blade subsoiler into ANSYS WORKBENCH 17.0 for finite element analysis, and the results of finite element analysis showed that the convex blade subsoiler stress was mainly concentrated in the fixed position of the subsoiler handle, the maximum stress value was 123.36 MPa and the maximum deformation variable was 8.68 mm at the tip of the subsoiler, which meetting the design requirements. In order to verify the rationality of the designed convex blade subsoiler and judge the rationality of the constructed soil model, the field experiments were carried out according to the tillage depth and the working speed of the simulation. The field experiments proved that the convex blade subsoiler had dragged reduction effect compared with stander subsoiler, and the average drag reduction was 10.24%, and compared with the simulation results, the numerical error was 3%-10%. the tillage depth and forward speed could have an appreciable impact on tillage resistance and the tillage resistance increased with the tillage depth and forward velocity. The results of simulation and experiment showed that the proposed soil model basically matched the soil mechanical properties in North China Plain and could approximating substitute the real soil environment. The study proved that it was feasible to analyze the tillage resistance of the subsoiler by using the DEM and it was of great significance to further optimize the structure of subsoiler.