Discrete Element Simulation Calibration and Flowability Study of Organic Manure with Different Moisture Contents

This study calibrated discrete element parameters for organic fertilizer (OF) and compost fertilizer (CF) to support spreading equipment design. Using the Hertz–Mindlin with JKR model, DEM simulations were integrated with physical angle of repose measurements. Parameters were systematically optimized via Plackett–Burman screening, steepest ascent, and Box–Behnken response surface methodology. Results indicated distinct moisture-sensitive behaviors: OF exhibited monotonic increases in dynamic friction coefficient (0.223–0.362) and JKR surface energy (0.064–0.166 J/m2), whereas CF showed nonlinear friction trends with surface energy rising from 0.209 to 0.326 J/m2. A predictive model directly linking moisture content to DEM parameters was established using the cylinder-lifting method. Validation confirmed model accuracy, with angle of repose errors of 2.57% (OF) and 4.05% (CF). Simulated spreading widths closely matched field data, showing relative errors below 8%. The calibrated DEM framework provides a reliable basis for optimizing organic manure spreader performance.