受振颗粒“毛细”系统中的对流与有序化

将球形颗粒倒入内径较窄的管状容器时,管壁的曲率会对颗粒的堆积结构产生影响,存在壁效应. 实验表明通过连续的竖直方向的振动,壁效应可以被强化,颗粒可以经由对流由无序排列转变为稳定的同轴筒形“壳层”结构. 每一壳层内,颗粒是二维的六角密堆积, 在这一转变过程中,颗粒堆积率的径向分布由初始的衰减振荡转变为等幅振荡. 分析了堆积率的不均匀性及空气在对流中的作用,以及形成“壳层”结构的动力学过程,对“壳层”结构的稳定性亦进行了讨论. 关键词： 颗粒物质 对流 有序化 毛细

Convection and crystallization in vertically vibrated granular' capillary' systems

The packing structure of identical spheres poured into a narrow cylindrical container will be influenced by the curvature of the container wall. This has been known as the wall effect. Our experiments reveal that under the action of vertical vibration, the wall effect can be enhanced, that the spheres, initially in a random packed state, can be organized through convection into a stable ordered packing consisting of a concentric array of cylindrical "shells" of spheres. In each shell the spheres are hexagonally arrayed. During such a structure transition, the packing density distribution, initially with a damped oscillatory variation along the radial direction, turns into an undamped one. The effects of interstitial air and inhomogeneity in the packing on the convection of particles, and thereby on the dynamics for the formation of "shell" structure, are analyzed. In addition, some discussions on the stability of the "shell" structure are made.