We discuss the use of the Discrete Element Method (DEM) to simulate the dynamics of granular systems made up of elements with nontrivial geometries. The DEM simulator is GPU accelerated and can handle elements whose shape is defined as the union with overlap of diverse sets of spheres with user-specified radii. The simulator can also handle complex materials since each sphere in an element can have its own Young's modulus $E$, Poisson ratio $\nu$, friction coefficient $\mu$, and coefficient of restitution CoR. To demonstrate the simulator, we produce a "digital simulant" (DS), a replica of the GRC-1 lunar simulant. The DS follows an element size distribution similar but not identical to that of GRC-1. We validate the predictive attributes of the simulator via several numerical experiments: repose angle, cone penetration, drawbar pull, and rover incline-climbing tests. Subsequently, we carry out a sensitivity analysis to gauge how the slope vs. slip curves change when the element shape, element size, and friction coefficient change. The paper concludes with a VIPER rover simulation that confirms a recently proposed granular scaling law. The simulation involves more than 11 million elements composed of more than 34 million spheres of different radii. The simulator works in the Chrono framework and utilizes two GPUs concurrently. The GPU code for the simulator and all numerical experiments discussed are open-source and available on GitHub for reproducibility studies and unfettered use and distribution.

翻译：本文讨论了利用离散元方法（DEM）模拟由具有复杂几何形状的单元组成的颗粒系统动力学过程。该DEM模拟器采用GPU加速，能够处理形状定义为多个用户指定半径球体重叠并集的单元。模拟器还可处理复杂材料，因为单元中的每个球体可独立设置杨氏模量$E$、泊松比$\nu$、摩擦系数$\mu$及恢复系数CoR。为展示模拟器性能，我们生成了GRC-1月球模拟物的数字孪生体（DS），其粒度分布与GRC-1相似但非完全相同。通过休止角、圆锥贯入、牵引力及爬坡测试等数值实验验证了模拟器的预测能力。随后进行敏感性分析，探究坡度-滑移曲线随单元形状、尺寸及摩擦系数变化的规律。本文以VIPER月球车模拟作为结论，验证了近期提出的颗粒尺度定律。该模拟涉及超过1100万个由3400余万个不同半径球体组成的单元。模拟器运行于Chrono框架，并联合使用两块GPU。模拟器代码及所有数值实验的GPU程序均已在GitHub开源，可供重复性研究及自由使用与分发。