验证N体代码Chrono用于减重力环境中的颗粒DEM模拟
Validating N-body code Chrono for granular DEM simulations in reduced-gravity environments
摘要：
离散单元法（DEM）经常被用来模拟复杂的颗粒系统，并增加我们通过理论，实验和现实世界的观察所获得的知识。数值模拟是研究小行星、彗星和小卫星表面风化物覆盖的一种特别强大的工具，在这些表面，重力降低的环境会产生不明确的流动行为。在这项工作中，我们提出了一种方法来验证软球DEM代码的陆地和小天体颗粒环境。开源代码Chrono首先通过一系列简单的两体碰撞测试进行修改和评估，然后通过一组打桩和打桩测试进行评估。在打桩测试中，我们改变滚动摩擦的滚动摩擦因数，以针对使用1 mm玻璃珠的实验校准模拟。然后，我们使用摩擦系数来模拟1 mm玻璃珠在旋转鼓中的流动，使用来自先前实验研究的鼓配置。我们测量了不同颗粒尺寸、接触力模型、滚动摩擦系数、内聚力水平、滚筒转速和重力水平下的动态休止角、流动层厚度和流动层速度。试验表明，相同的流动模式，可以观察到在地球和减少重力水平，如果鼓轮转速和重力水平设置根据无量纲参数称为弗劳德数。Chrono在不同重力和凝聚力水平下成功地验证了已知的流动行为，并将在未来的工作中用于研究小天体风化动力学。
英文摘要：
The Discrete Element Method (DEM) is frequently used to model complex granular systems and to augment the knowledge that we obtain through theory, experimentation, and real-world observations. Numerical simulations are a particularly powerful tool for studying the regolith-covered surfaces of asteroids, comets, and small moons, where reduced-gravity environments produce ill-defined flow behaviors. In this work, we present a method for validating soft-sphere DEM codes for both terrestrial and small-body granular environments. The open-source code Chrono is modified and evaluated first with a series of simple two-body-collision tests, and then, with a set of piling and tumbler tests. In the piling tests, we vary the coefficient of rolling friction to calibrate the simulations against experiments with 1 mm glass beads. Then, we use the friction coefficient to model the flow of 1 mm glass beads in a rotating drum, using a drum configuration from a previous experimental study. We measure the dynamic angle of repose, the flowing layer thickness, and the flowing layer velocity for tests with different particle sizes, contact force models, coefficients of rolling friction, cohesion levels, drum rotation speeds and gravity levels. The tests show that the same flow patterns can be observed at Earth and reduced-gravity levels if the drum rotation speed and the gravity-level are set according to the dimensionless parameter known as the Froude number. Chrono is successfully validated against known flow behaviors at different gravity and cohesion levels, and will be used to study small-body regolith dynamics in future works.
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