DETERMINATION OF INTRINSIC PARAMETERS AND DEM PARAMETER CALIBRATION OF MULTI-COMPONENT PARTICLES IN MILLET THRESHING MIXTURES

The millet threshing mixture is the primary material processed during post-combine cleaning operations and mainly comprises components such as seeds, millet panicle clusters, and short stalks. These components exhibit significant differences in material properties, which consequently affect cleaning efficiency. In this study, the morphological dimensions and mechanical parameters of each component in Longgu 31 millet threshing mixtures were systematically measured, including Poisson’s ratio, elastic modulus, shear modulus, angle of repose, static and dynamic friction coefficients, and the coefficient of restitution. The discrete element method (DEM) was employed to establish particle models for millet seeds, millet panicle clusters, and short stalks. Key contact parameters—namely static and dynamic friction coefficients and the coefficient of restitution—were calibrated using the Plackett–Burman design, the steepest ascent method, and the Box–Behnken response surface methodology. The results reveal substantial differences in the physical parameters among the components. The calibrated simulation values of the angle of repose show high consistency with experimental results, with an average error of less than 5%, thereby validating the reliability of the model and parameter system. The robust model and key parameters obtained in this study provide a solid data foundation for elucidating the mechanism of material motion during millet cleaning and for optimizing the design of cleaning and screening equipment. The findings also provide valuable references for simulation studies on the cleaning of small-particle-size minor grains.