Agarwal Shashank, Karsai Andras, Goldman Daniel I, Kamrin Ken
Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Department of Physics, Georgia Institute of Technology, Atlanta, GA 30332, USA.
Sci Adv. 2021 Apr 23;7(17). doi: 10.1126/sciadv.abe0631. Print 2021 Apr.
Granular intrusions, such as dynamic impact or wheel locomotion, are complex multiphase phenomena where the grains exhibit solid-like and fluid-like characteristics together with an ejected gas-like phase. Despite decades of modeling efforts, a unified description of the physics in such intrusions is as yet unknown. Here, we show that a continuum model based on the simple notions of frictional flow and tension-free separation describes complex granular intrusions near free surfaces. This model captures dynamics in a variety of experiments including wheel locomotion, plate intrusions, and running legged robots. The model reveals that one static and two dynamic effects primarily give rise to intrusion forces in such scenarios. We merge these effects into a further reduced-order technique (dynamic resistive force theory) for rapid modeling of granular locomotion of arbitrarily shaped intruders. The continuum-motivated strategy we propose for identifying physical mechanisms and corresponding reduced-order relations has potential use for a variety of other materials.
颗粒侵入，如动态冲击或轮式移动，是复杂的多相现象，其中颗粒同时表现出类似固体和类似流体的特性以及喷射的类似气体的相。尽管经过了数十年的建模努力，但对于此类侵入中物理现象的统一描述仍然未知。在这里，我们表明，基于摩擦流和无张力分离的简单概念的连续介质模型描述了自由表面附近复杂的颗粒侵入。该模型捕捉了包括轮式移动、平板侵入和有腿奔跑机器人在内的各种实验中的动力学。该模型表明，在这种情况下，一种静态效应和两种动态效应主要产生侵入力。我们将这些效应合并到一种进一步降阶的技术（动态阻力理论）中，用于对任意形状侵入体的颗粒移动进行快速建模。我们提出的用于识别物理机制和相应降阶关系的基于连续介质的策略对各种其他材料具有潜在用途。
