Formation and Collapse of Cavity Network in a Granular Material due to Viscous Flow and Vibration

在均匀颗粒材料中，空穴区域的存在对空穴周围的局部流场有很大的影响。我们已经表明，与没有空腔的情况相比，圆柱形（球形）空腔的体积流率和中心处的速度分别达到两（三）倍和三（六）倍。同时，增强了孔洞边界处的局部应力，导致孔洞的坍塌。我们还定性地表明，这些影响增加了在存在许多腔与某些配置。为了定量地检验这些发现，我们进行了新的实验和数值模拟。1.由于粘性流引起的空腔塌陷的实验：我们观察了两个相互作用的空腔塌陷的变化率和临界速度。通过改变两个腔的中心距和方向，我们阐明了 ...更多信息 的基本过程的日期，以及崩溃的配置发生在低于临界崩溃速度的单腔的情况下。这些结果可应用于暴雨时滑坡的预测，并为预测地下水流中污染物通过空洞网络的快速对流提供了一种新的技术。2.空洞网络形成的数学模型：基于元胞自动机模型，对粘性流作用下多个空洞之间的相互作用进行了数值模拟。该模型可以解释空穴的运动、伸长和合并，并最终形成大规模的空穴区域网络或流体化。3.颗粒表面变形实验：观察到规则间隔的波纹和Barhan沙丘，这取决于颗粒材料表面粘性流的剪切速率。这些结果可用于沙漠区扩展的预测和海湾地区海底水位的控制。4.颗粒表面涡环碰撞实验：产生了典型的边缘呈波浪形或有凸起的环形陨坑，这可以解释火星上唯一观测到的Rampart陨坑。这一观测结果表明，在火星早期环境中存在流体流动，并揭示了这种陨石坑形成的机制。5.垂直振动颗粒层图案形成的实验：将薄层颗粒材料垂直振动，显示出波纹和起伏。我们阐明了这些图案的形成机制，并在同一时间得到的临界层数，显示集体运动像在连续介质中观察到的。我们的研究工作将填补颗粒材料微观碰撞过程与宏观流体运动之间的差距，并在四个主要的国际会议和国内会议上发表。少

The presence of cavity regions in an otherwise uniform granular material makes great influence on the local flow field around that cavity. We have already shown that the volume flow rate and the velocity at the center of the latter attains as large as two (three) times and three (six) times for a cylindrical (spherical) cavity, respectively, in comparison to the case without a cavity. At the same time, the local stress at the boundary of the cavity is enhanced, and the collapse of the latter is induced. We have also shown qualitatively that these effects are increased in the presence of many cavities with certain configurations. In order to examine these findings quantitatively, we performed new experiments and numerical simulations.1.Experiments on the collapse of cavities due to viscous flow : We observed the rate of change and the critical velocity of the collapse of two interacting cavities. By changing the center-to-center distance and the orientation of the two cavities, we eluci … More dated the fundamental process of the collapse of cavities, as well as the configurations in which the collapse occurs below the critical velocity of collapse for a single cavity case. These results can be applied to the prediction of landslides at the time of heavy rainfall and a new technique to predict anomalously fast convection of contaminants in underground water flow through cavity networks.2.Mathematical models of cavity network formation : We performed numerical simulation of the interaction of many cavities exposed to viscous flow, on the basis of cellular-automaton type model. Our model can explain the movement, elongation and merging of cavities, depending on the stiffness of the medium and the applied velocity, which eventually forms large-scale network of cavity regions or fluidization.3.Experiments on the deformation of granular surface : We observed regularly spaced ripples and Barchan dunes depending on the shear rate of viscous flow over the surface of the granular material. These results are applicable to the prediction of spread of desert area and the control of seabed level in the bay area.4.Experiments on the collision of vortex ring on the granular surface : Typical ring-like crater with a wavy edge or a lobe was generated, that can explain the Rampart crater observed only on Mars. This observation suggests the presence of fluid flow at the earlier time of Mars' environment as well as the mechanism of this crater formation.5.Experiments on the pattern formation of vertically vibrating granular layer : Thin layer of granular materials were vertically vibrated, which revealed ripples and undulations. We elucidated the mechanism of the formation of these patterns, and at the same time obtained the critical layer number that showed collective motion like those observed in continuum media. The behavior was partially explained by the buckling and bending motion of thin elastic layer.All our studies are expected to bridge the gap between microscopic collision process and macroscopic fluid motion of the granular material, and our works are presented at four major international conferences and domestic meetings. Less