Resonance-induced acceleration of the RBNE-BNE segregation inversion of granular mixtures

TL;DR

This study investigates how resonance effects accelerate the inversion of segregation states in granular mixtures, showing that container shape influences the speed and location of segregation transitions through standing-wave resonances.

Contribution

It reveals the role of container geometry and standing-wave resonances in speeding up segregation inversion in granular mixtures, supported by experiments, simulations, and theoretical analysis.

Findings

Circular-bottom containers accelerate segregation inversion compared to flat-bottom ones.

Standing-wave resonant spots of granular temperature facilitate faster segregation transitions.

Heavier grains sink at resonant spots with higher granular temperature due to buoyancy effects.

Abstract

This paper presents the experiments and simulations on the resonance-induced acceleration of the reverse Brazil nut effect (RBNE)-Brazil nut effect (BNE) segregation inversion of binary mixtures in flat-bottom and circular-bottom containers. Both experimental and simulation results indicate that the starting location of the sinkage of heavier grains at the top layer is triggered with certain randomness in the flat-bottom container, whereas it first occurs at either of the lateral edges of the bottom in the circular-bottom container. The quantified segregation factors in simulations show that the transition from the RBNE segregation state to the BNE segregation state happens faster in the circular-bottom container than that in the flat-bottom container. The occurrence of standing-wave resonant spots of higher and lower granular temperature accelerates the RBNE-BNE segregation inversion. From the elastic collision model of single grain, the bottom with a larger angle leads to more energy transfer from the vertical direction to the horizontal direction. The theoretical predictions are confirmed by the simulations of a monodisperse granular bed. The flat-bottom container has a uniform distribution with a standing-wave period of granular temperature and packing density, whereas the circular-bottom container possesses a higher granular temperature in the horizontal direction and a lower packing density at the lateral edges of the circular bottom. Owing to the buoyancy effect, heavier grains easily sink first at the resonant spots with higher temperature.