Calibration and testing of discrete element simulation parameters for spinach seeds

The accuracy of simulation parameters for spinach sowing process was enhanced by establishing the seed simulation model based on the intrinsic parameters of spinach seeds using the Hertz–Mindlin model. Calibration of simulation parameters between spinach seeds and contact materials (ABS resins and stainless steel) was performed using free-fall collision method, inclined plane sliding method, and inclined plane rolling method. The results indicated: coefficients of restitution, static friction coefficients, and rolling friction coefficients between spinach and ABS resins were 0.310, 0.467 and 0.045, respectively. Coefficients of restitution, static friction coefficients and rolling friction coefficients between spinach and stainless steel were 0.346, 0.505 and 0.047, respectively. Considering inter-seed contact parameters, a study was conducted using the relative error between measured repose angle and simulated repose angle as the indicator. This involved steepest ascent experiment and three-factor five-level rotational combined design experiment with the optimisation goal of minimising relative error. Through optimal analysis of test data, the following results were obtained: coefficients of restitution, static friction coefficients, and rolling friction coefficients between spinach seeds were found to be 0.47, 0.37 and 0.04, respectively. Calibration results were validated through sowing verification experiments, demonstrating that the qualified rate, multiple rate and missing rate of both simulation and actual tests were less than 5.8%, verifying the reliability of the calibration results. The research findings can serve as a theoretical reference for the design and simulation optimisation of spinach sowing devices.