流体动力剪切颗粒床运动的开始和停止
Onset and cessation of motion in hydrodynamically sheared granular beds
摘要：
我们进行了分子动力学模拟的颗粒床驱动的模型流体动力学剪切流，以阐明一般颗粒尺度的机制，确定泥沙输运的开始和停止。通过改变希尔兹数（在床的顶部的无量纲剪切应力）和颗粒雷诺数（颗粒惯性粘性阻尼的比率），我们探讨了流体流速，颗粒惯性和流体粘度的变化如何影响床运动的开始和停止。对于低到中等颗粒雷诺数，临界边界分离的移动和静态。当从上面和下面接近这个边界时，这些状态之间的过渡时间会有所不同。在高颗粒雷诺数下，惯性效应占主导地位，并且颗粒运动可以维持在远低于发生静态床移动的流速下。我们还发现，床运动的发病（低和高颗粒雷诺数）描述的威布尔最弱环节的统计，因此是至关重要的依赖于颗粒床的填充结构，甚至深的表面下。
英文摘要：
We performed molecular dynamics simulations of granular beds driven by a model hydrodynamic shear flow to elucidate general grain-scale mechanisms that determine the onset and cessation of sediment transport. By varying the Shields number (the nondimensional shear stress at the top of the bed) and particle Reynolds number (the ratio of particle inertia to viscous damping), we explore how variations of the fluid flow rate, particle inertia, and fluid viscosity affect the onset and cessation of bed motion. For low to moderate particle Reynolds numbers, a critical boundary separates mobile and static states. Transition times between these states diverge as this boundary is approached both from above and below. At high particle Reynolds number, inertial effects become dominant, and particle motion can be sustained well below flow rates at which mobilization of a static bed occurs. We also find that the onset of bed motion (for both low and high particle Reynolds numbers) is described by Weibullian weakest-link statistics, and thus is crucially dependent on the packing structure of the granular bed, even deep beneath the surface.
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