Authors

Abstract

To further optimize the simulation process of grass seed pellet coating, it is essential to construct an accurate geometric model of the seed particles. In this study, the discrete element method (DEM) was employed to model and analyze the particles with high precision, thereby improving the modeling efficiency and simulation accuracy for forage seeds. Ice grass seeds were selected as the research subject. A three-dimensional geometric model of the particles was constructed based on the hyperquadratic surface (hyperellipsoid) equation, which was then used as the mesh-generation domain for the DEM model. Subsequently, a standardized filling-sphere method tailored for ellipsoid-like particle geometries was proposed. Treating the ice grass seed as an axisymmetric ellipsoid, a maximum filling sphere with a diameter of 1.2 mm was placed at its center. Three multi-sphere models—17-sphere, 9-sphere, and 5-sphere—were developed using 0.25×, 0.5×, and 0.75× of the maximum filling sphere diameter, respectively. The diameter of each filling sphere corresponded to the largest inscribed sphere tangent to the ellipsoid surface. Through simulation experiments, a second-order regression equation for the static angle of repose was obtained. Based on the target static angle of repose (30.54°), parameter optimization was performed, yielding the optimal simulation parameters: a shear modulus of 1.9×10^7 Pa, a seed-to-seed coefficient of restitution of 0.5, and a maximum packing sphere diameter ratio of 0.35. The average simulated static angle of repose was 30.67°, with a relative error of 0.43%. Finally, a rotating drum test was conducted to calibrate the dynamic angle of repose. The drum was filled to 40% of its volume and rotated at 58 r/min. The physical experiment produced a dynamic angle of 38.46°, while the corresponding 10-second simulation yielded a dynamic angle of 38.12°, resulting in a relative error of 0.88% compared with the physical test. These results provide a reference for establishing discrete element models of ellipsoidal particles and support accurate simulations of seed pellet coating processes.

Abstract in Chinese

本研究为优化草种丸粒化包衣的离散元模拟，基于超椭球方程构建了冰草种子的三维几何模型，并提出适用于类椭球颗粒的标准化填充球建模方法。以种子中心最大内切球为基准，构建了5球、9球和17球三种组合球模型，并通过休止角仿真获得相应的二阶回归方程。依据目标休止角30.54°优化得到最佳参数组合：剪切模量1.9×10^7 Pa、种子间恢复系数0.5、最大填充球直径倍数0.35，使静态休止角仿真误差仅0.43%。进一步通过旋转鼓试验完成动态休止角标定，仿真值与实测值相对误差为0.88%。研究结果为类椭球颗粒的离散元建模提供了有效参考。