The effect of vertical vibration waveform on wall friction induced Brazil nut effect

Abstract

When binary mixtures of granular materials are subjected to vibration, larger particles (intruders) tend to rise to the surface, regardless of whether they are lighter or heavier than the smaller particles. This phenomenon is called the Brazil-nut effect (BNE). During BNE, granular convection currents are generated, and this induces rising movement of particles in the center of the container and descending movement of those near the container wall. Previous studies generally suggest that the intruder’s rising speed can be boosted by increasing the vibration amplitude and frequency. In this study, the rising speed is increased by changing the waveform without altering the amplitude or frequency. The waveform was modified by adjusting the fall/rise time ratio and the amplitude ratio. Using the discrete element method (DEM), we simulated granular motion under different waveform conditions. Our results show that, when the specific energy transferred from the container to the particles over one vibration cycle is held constant, different waveforms yield nearly identical rising speeds, confirming that specific energy is the primary governing factor. Furthermore, the rising speed increases linearly with specific energy. These findings support the implementation of waveform manipulation to control particle behavior as desired.