Fluidization Mechanism of a Granular Material Containing Fluid

1.颗粒状材料在外部振动下的斑图形成;研究了颗粒材料边界在流体流动作用下的变形和运动。在第一部分中，我们对装有颗粒的容器在垂直振动下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”，这是产生混沌的机制之一。我们还发现了层表面上的波纹，当层深度减少到不到10层时，波纹会变成陡峭的驻波。通过高速摄像机对波进行更近距离的观察发现，它们的振荡频率是外部施加振荡的一半或四分之一。我们进一步得到了波长对频率和振幅的外部强迫，颗粒大小和层深度等的依赖关系。在水平薄颗粒层，我们发现正方形，条纹，三角形/六边形，和准晶体平面图案的振荡幅度增加。在后一种情况下，我们分析了空隙空间的影响，否则均匀流在一个无界颗粒材料，这是与实验进行了比较。当存在圆柱形圆形空腔时，空隙中心处的速度变为三倍，而进入该区域的体积流量为没有孔的体积流量的两倍（另一方面，在球形空隙的情况下，它们分别变为六倍和三倍）。空泡表面附近流动的增加导致边界的崩溃。在多空隙的情况下，它们彼此相互作用以形成连接的空隙或水道网络。最后的观察表明，由于大雨落在地面上，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.