Development and Validation of a Discrete Element Simulation Model for Pressing Holes in Sowing Substrates

To conduct DEM simulation research on the collision characteristics between seeds and pressed substrate holes, a discrete element model of mechanically pressed holes in sowing substrates was developed in this study. The geometric DEM models of sowing substrate particles were established based on the sieve test, and the Hertz–Mindlin with JKR contact model was utilized for simulating of the fine, moist, and cohesive substrate particles. The angle of repose measured by the funnel method was served as the target, Plackett–Burman experiments were conducted to screen significant contact mechanical parameters, while steepest ascent and Box–Behnken experiments were employed to define their value ranges. A neural network model for predicting the angle of repose was constructed, and a genetic algorithm was applied to optimize the significant contact mechanical parameters. The cross-sectional profiles of the pressing hole were obtained through image profile feature extraction in simulation and 3D scanning projection methods in the experiment. The calibrated inter-particle dynamic friction coefficient, inter-particle coefficient of restitution, dynamic friction coefficient between particles and stainless steel, and JKR surface energy of the substrate were 0.0349, 0.5448, 0.0233, and 0.4279, respectively. The deviation of the simulated angle of repose utilizing the optimized contact parameters was 0.4°. The shapes of the pressed holes obtained from simulation and experiment showed good consistency. The pressing speed had no significant effect on the mean depth of all sampling points, suggesting that a higher pressing speed should be set to improve the operation efficiency. The pressing depth has a highly significant effect on the mean depth of all sampled points, but no significant effect on the deviation between the simulated and experimental mean depths. The maximum difference in the mean depth deviation between simulated and experimental sampled points is 1.308 mm. It demonstrates that the established discrete element model can efficiently and accurately simulate the deformation of the pressing hole in sowing substrate. It provides an applicable simulation model for fast optimization design of the pressing hole and sowing equipment.