| Summary: | 博士 === 國立中興大學 === 物理學系所 === 97 === This report discusses the behavior of the intruded particles in a group of background particles which are agitated by external force. The intruded particles population is minority and have larger size than the background particles and also different in mass. The main researches for the last 30 years mostly focused on systems in which the vibrated direction is parallel to gravitational field. Some reports found the so called Brazil Nut Effect(BNE) [32] that the larger particles always accumulate on the top layer after agitation.And also the larger particles may sink to bottom (Reverse BNE) [41] if the size ratio and mass ratio are selected appropriately.
By the Molecular dynamics (MD) simulation, this report found the similar phenomenon of BNE in the 2 dimensional granular systems in the absence from gravitational field. The intruder in the system migrates either to the center or the edge of the cluster of the background particles. Since this system has negligible influence by gravity and the interstitial fluid, it may be an easier and important way to understand the mechanisms of particles segregation. Furthermore, it can be approximately realized by horizontal shaken experiment in gravitational field.
With the aids of simulation and experiment, this report suggests a mechanism for migration of an intruder in the shaking granular bed. The mechanism suggests that the migration of the intruder is due to the competition between the collision frequency and the inertia of the intruder. Since the collision frequency and the inertia is proportional to the size and the mass respectively, that explain why the size ratio and mass ratio become the main control parameters in particles migration. This mechanism also explains well the results in the system shaken in two dimensions.
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