窄振动颗粒床中的运动模式

实验研究了竖直振动情况下,窄容器中颗粒的运动模式.发现运动模式与颗粒床厚度及振动加速度有很强的依赖关系.实验表明横向尺寸较小的容器可以抑制对流卷及拱起现象.对于足够厚的颗粒床,即使振动加速度很大,颗粒床下部仍然存在着颗粒聚集态.出现聚集态时,颗粒床对容器底的冲击力是倍周期分岔的.实验表明倍周期分岔点与颗粒床厚度无关.对于较薄的颗粒床,颗粒可以是聚集态或对流卷,视颗粒尺寸而定.如果使用尺寸分布非常窄的球形颗粒,可以观察到颗粒的有序排列.出现同心的圆筒形“壳”结构,每个“壳”上的颗粒是二维六角密排列的. 关键词： 颗粒物质 倍周期分岔 颗粒聚集态 球堆积

Motion modes of granular particles in a vibrating narrow tube

Experiments are performed to investigate the motion modes of granular particles contained in a vibrating narrow tube. It is found that the motion modes strongly depend on the bed thickness and vibration acceleration. Experiments show that in a container with small lateral size, convection rolls and arching of the particles can be confined. For the bed with sufficient thickness, a condensed state of particles always exists in the lower part of the bed, even when strong vibration is applied. Once a condensed state is formed, subharmonic bifurcations of the impact of granular particles at the container bottom can be observed. Experiments reveal that the bifurcation points are independent on the bed thickness. For shallow beds, the particles may be in condensed states or in convections, depending on the particle size.For spherical particles with a narrow size distribution, an ordered packing of the particles is observed. The packing consists of a concentric array of cylindrical “shells" of particles.In the “shell”, the particles are arrayed hexagonally.