Fluidization Mechanism of a Granular Material Containing Fluid

1. 粒状物质在外部振荡作用下的图案形成；研究了流体流动引起的颗粒材料边界的变形和移动。在前者中，我们对颗粒容器在垂直振动下组成颗粒的对流或混合进行了实验和数值研究。我们发现了层的“拉伸和折叠”，这是混沌产生的机制之一。我们还发现，在这一层的表面有波纹，当这一层的深度减少到不到十层时，这些波纹就会变成陡峭的驻波。高速摄像机对引力波的进一步观察显示，引力波的振荡频率是外部施加的振荡频率的一半或四分之一。我们进一步得到了波长与外强迫频率和振幅、颗粒尺寸和层深等的关系。在横向薄颗粒层中，随着振荡幅度的增加，我们发现了正方形、条纹、三角形/六边形和准晶体平面图案。在后一种情况下，我们分析了在无界颗粒材料中均匀流动时空隙空间的影响，并与实验进行了比较。当存在圆柱形圆形空腔时，空洞中心的速度是没有空腔时的3倍，而进入该区域的体积是没有空腔时的2倍（而在球形空洞情况下，它们分别是6倍和3倍）。靠近空洞表面的流动的增加导致边界的坍塌。在多孔洞的情况下，它们相互作用形成一个相连的孔洞，或水道网络。最后的观测结果表明，由于大雨落在地面上，导致了山体滑坡或雪崩的基本过程。

1. Pattern formation of granular materials under external oscillation, and2. deformation and movement of the boundary of granular materials due to fluid flow are investigated. In the former, we made both experimental and numerical approaches to the convection or mixing of the constituent grains under vertical vibration of the container filled with granules. We found "stretching and folding" of the layer, which is one of the chaos-producing mechanisms. We also found ripples on the surface of the layer, which grow into steep standing waves as the layer depth is reduced to less than about ten layers. Closer observation of the waves by a high-speed video camera revealed that they oscillated with a frequency one half or one fourth of the externally applied oscillation. We further obtained the dependence of the wave-length on the frequency and amplitude of the external forcing, granule size and layer depth, etc. In the horizontally thin granular layer, we found squares, stripes, triangle/hexagonal, and quasi-crystal planar patterns as the magnitude of oscillation was increased. In the latter case, we analyzed the effect of the void space in an otherwise uniform flow in an unbounded granular material, which was compared with experiment. When cylindrical circular cavity are present, the velocity at the center of the void becomes three times, while the volume flow into that region amounts to twice larger (on the other hand in the spherical void case, they become, respectively, six times and three times larger) than those without the hole. The increment of the flow near the void surface leads to the collapse of the boundary. In the multi-void case, they interact each other to form a linked voids, or waterway network. The last observation suggests a fundamental process of landslides or avalanche due to heavy rain fall on the ground.