振动颗粒物质中倍周期运动对尺寸分离的影响

实验研究了竖直振动颗粒床中，倍周期运动对尺寸分离的影响.实验中，当振动加速度足够大时，系统中出现稳定的对称对流，进一步增大振动加速度到某个临界值时，还会出现倍周期运动.观察表明，背景颗粒的对流运动对分离过程起主导作用，对流速度决定着分离过程的快慢，而在2倍周期和4倍周期分岔之后，分离时间有所减慢.对引起对流运动的起因进行了分析，以此为基础分析了倍周期运动产生影响的物理机理，并对分离时间进行了定量计算，结果与实验值符合很好. 关键词： 颗粒物质 “巴西果”效应 倍周期分岔 对流

Effects of subharmonic motion on size segregation in vertically vibrated granular materials

Experiments have been performed to investigate the effect of subharmonic motion on size segregation in vertically vibrated granular beds. In our experimental systems, symmetric normal convection of granular particles is induced when vibration acceleration is sufficiently large, and subharmonic motion of the particles appears when vibration acceleration is above another larger critical value. Observations reveal that particle convection is the main mechanism leading to the segregation of larger intruder particles imbedded in smaller ones, the convection flux dominates the rising time of the intruder, and a distinct retardation of the segregation time is induced when the bed’s bulk motion undergoes period-doubling and period-quadrupling bifurcations. An analysis of the convection due to the effects of air is given. Then the mechanism leading to such retardation is discussed and simple expression for the segregation time is formulated. The obtained results agree well with experimental values.