Fluidization Mechanism of a Granular Material Containing Fluid

1.颗粒材料在外加振动作用下的花纹形成；研究了流体流动作用下颗粒材料边界的变形和运动。在前者中，我们对装满颗粒的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模拟。我们发现了这一层的“拉伸和折叠”，这是产生混乱的机制之一。我们还在表层发现了涟漪，当表层深度减少到10层以下时，这些涟漪就会成长为陡峭的驻波。用高速摄像机对这些波进行更仔细的观察，发现它们的振荡频率是外部振荡的一半或四分之一。我们进一步得到了波长与外力的频率和幅度、颗粒大小和层深等的关系。在水平薄的颗粒层中，随着振荡强度的增加，我们发现了正方形、条纹状、三角形/六边形和准晶面图案。在后一种情况下，我们分析了无界颗粒材料中均匀流动中空隙空间的影响，并与实验进行了比较。当存在圆柱形空腔时，空洞中心的速度是无空洞时的三倍，而流入该区域的体积则是无空洞时的两倍(而在球形空洞情况下，则分别是无空洞时的六倍和三倍)。空心面附近流动的增加会导致边界的坍塌。在多孔洞的情况下，它们相互作用，形成一个链接的孔洞，或水路网络。最后一次观测表明，地面上的暴雨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.