Calibration and experiment of the discrete element simulation parameters of rape threshing mixture in combine harvester

Existing gas-solid coupling simulation analysis of rape combined harvesting and cleaning device still has the challenge to obtain the accurate and reliable basic parameters that are necessary for discrete element simulation. As a solution, the contact parameters of the components of the rape threshing mixture were calibrated based on EDEM. As the main components of rape threshing mixture, rapeseed, Rape stalk, and rapeseed pod were taken from the rape plant that was ripe and benefitted for the combine harvesting. The radial elastic coefficients and characteristic parameters such as Poisson's ratio and elastic modulus of rape stalks were measured and analyzed by radial global compression test. Furthermore, the static friction coefficient and collision restitution coefficient among rapeseed, Rape stalk, rapeseed pod, and steel plate were measured by the inclined plane method and free-fall piezocone test, as well as the range of contact parameters of the particle model. By taking the relate error of stalk repose angle between its values of simulation and physical test, Plackett-Burman experiment was conducted to screen out the parameters that had significant influence on stalk repose angle and the optimal ranges of those parameters was further determined by the steepest climbing test based on EDEM. The regression relationship between the repose angle and the parameters that had appreciate impact on the angle was figured out, and the optimal combination of the contact parameters was obtained. The results indicated that the parameters that had significant effects on the stalk repose angle were the static friction coefficient between rape stalks, the rolling friction coefficient between rape stalks, the rolling friction coefficient between steel plate and rape stalk, while the optimal combination of those parameters were 0.707, 0.015, and 0.012, respectively. Under the optimal condition, the relative error of stalk repose angle was 0.54%. To further validating the calibrated parameters, the numerical simulation of cyclone separation cleaning device was carried out based on DEM-CFD method. The bench experiment to compare the performance of the cleaning device with that illustrated by the simulation was conducted based on the test-bench. The results of the simulation showed that the cleaning ratio and loss ratio of the cleaning device was 94.42% and 3.96%, respectively, while the relative error, compared with that obtained in the bench experiment, was 2.81% and 7.48%, respectively. It could validate the reliability of the calibrated parameters. This research could provide the basic discrete element parameters for the simulation analysis for rapeseed combine harvesting.