Parameter Calibration of Xinjiang Paperbark Walnut Kernels by Discrete Element Simulation

Abstract

To solve the problem of the lack of an accurate model for mechanized transportation and grading of walnut kernels, this paper took the shelled walnut kernels as the research object and calibrated the parameters of the discrete element model of walnut cracking kernels with the discrete element simulation software EDEM. The physical parameters of cracking kernels were measured by experiments, and the Hertz–Mindlin model was used to simulate the repose angle of cracking kernels. The contact parameters, such as the particle collision recovery coefficient, the static friction coefficient, and the rolling friction coefficient, were determined by the two-level factor test, steepest ascent test, and response surface test, respectively. Subsequently, the Hertz–Mindlin model with bonding contact was exploited to conduct the simulation of cracking kernels bending test based on the calibrated contact parameters. Finally, the normal contact stiffness, tangential contact stiffness, critical tangential force, and normal force of cracking kernels were determined by response surface analysis. It was shown that the relative error between the simulated values and the experiment results was 3.00 ± 1.31%. These results indicated that the calibrated parameter values are reliable, and could be used for the mechanized transportation and grading of walnut kernels.