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

1.进行了实验研究，发现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影响。孔洞边界处的应力局部增强，导致孔洞坍塌。我们开发了一个数值模拟，可以令人满意地解释我们的实验结果。此外，我们还扩展了数值模拟，以处理三维空腔。这些结果可以应用于暴雨时滑坡的预测，以及预测地下水中污染物通过空洞网络的异常快速对流以及人体肝脏肿瘤细胞周围的血管生成的新技术。我们研究了颗粒材料表面粘性流动产生的波纹和巴坎沙丘。这些结果适用于荒漠区扩展的预测和湾区海床水位的控制。对涡环撞击颗粒表面进行了实验研究。我们考察了撞击时颗粒层上留下的刻痕图案对涡环强度的依赖关系。薄层颗粒状物质垂直振动，呈现规则的多边形波纹和起伏。我们解释了这些图案的形成机制，同时得到了与连续介质中观察到的集体运动类似的临界层数。弹性薄层的屈曲和弯曲运动部分解释了这一行为。这些研究有望在颗粒材料的微观碰撞过程和宏观流体运动之间架起一座桥梁，我们的工作在主要的国际会议和国内会议上发表。

1. We performed experiments and found that the presence of cavity regions in an otherwise uniform granular material gives great influence on the local flow field around that cavity. The stress at the boundary of the cavity is locally enhanced, and the collapse of the latter is induced. We have developed a numerical simulation that can satisfactorily explain our experimental findings. Furthermore we extend our numerical simulation so as to deal with three-dimensional cavities. 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, as well as angiogenesis around tumor cells in the human liver.2. We studied the generation of ripples and Barchan dunes due to 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.3. Experiments on the collision of a vortex ring on the granular surface were made. We examined the dependence of the strength of the vortex ring on the engraved patterns left on the granular layer at the impingement.4. Thin layer of granular materials were vertically vibrated, which revealed regular polygonal ripple patterns 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. These 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 major international conferences and domestic meetings.