Carvalho Douglas D, Lima Nicolao C, Franklin Erick M
School of Mechanical Engineering, University of Campinas, Rua Mendeleyev 200, Campinas, São Paulo, Brazil.
Phys Rev E. 2022 Mar;105(3-1):034903. doi: 10.1103/PhysRevE.105.034903.
We investigate numerically how the motion of an intruder within a two-dimensional granular system affects its structure and produces drag on the intruder. We made use of discrete numerical simulations in which a larger disk (intruder) is driven at constant speed amid smaller disks confined in a rectangular cell. By varying the intruder's velocity and the basal friction, we obtained the resultant force on the intruder and the instantaneous network of contact forces, which we analyze at both the cell and grain scales. We found that there is a bearing network that percolates forces from the intruder toward the walls, being responsible for jammed regions and high values of the drag force, and a dissipative network that percolates small forces within the grains, in agreement with previous experiments on compressed granular systems. In addition, we found the anisotropy levels of the contact network for different force magnitudes and regions, that the force network can reach regions far downstream of the intruder by the end of the intruder's motion, that the extent of the force network decreases with decreasing the basal friction, and that the void region (cavity) that appears downstream of the intruder tends to disappear for lower values of the basal friction. Interestingly, our results show that grains within the bearing chains creep while the chains break, revealing the mechanism by which bearing chains collapse.
我们通过数值模拟研究了二维颗粒系统中入侵者的运动如何影响其结构以及如何对入侵者产生阻力。我们利用离散数值模拟，其中一个较大的圆盘（入侵者）在限制于矩形单元内的较小圆盘中间以恒定速度驱动。通过改变入侵者的速度和基底摩擦力，我们获得了作用在入侵者上的合力以及接触力的瞬时网络，并在单元和颗粒尺度上对其进行分析。我们发现存在一个承载网络，它将力从入侵者向壁面渗透，导致堵塞区域和高阻力值，还有一个耗散网络，它在颗粒内部渗透小的力，这与之前关于压缩颗粒系统的实验结果一致。此外，我们发现了不同力大小和区域的接触网络的各向异性水平，力网络在入侵者运动结束时可以到达入侵者下游很远的区域，力网络的范围随着基底摩擦力的减小而减小，并且入侵者下游出现的空隙区域（空洞）在较低的基底摩擦力值下趋于消失。有趣的是，我们的结果表明，承载链中的颗粒在链断裂时会蠕变，揭示了承载链坍塌的机制。
