Calibration and Experimental Validation of Discrete Element Parameters for Long-Grain Rice with Different Moisture Contents Based on Repose Angle

The accurate determination of discrete element parameters is crucial for ensuring reliable results in simulating the critical post-harvest stages of rice grain (processing, transportation, and storage) with different moisture contents. To determine the discrete element parameters, a physical model of rice grain was constructed by the multi-sphere (MS) modeling approach. Using the repose angle as the evaluation index, the discrete element parameters of rice grain were calibrated and optimized through the Plackett–Burman (PB) test, the steepest climbing test, and the Box–Behnken (BB) test using EDEM software. A moisture content–significance discrete element parameters model was further developed based on a moisture content–repose angle model (R2 = 0.992) and a repose angle–significance discrete element parameters model (R2 = 0.970). The calibration results showed that the relative error between the simulated and actual repose angle did not exceed 3.52%. Meanwhile, the cylinder lifting method and unloading mass flow rate verification were performed. And the results showed that the relative errors of the repose angle and mass flow rate of rice grain did not exceed 2.09% and 7.72%, respectively. The study provides a general and reliable method for determining the parameters of discrete element method simulation for rice grain with different moisture contents.