Dynamics and pattern transition in a two-dimensional vibrofluidized granular bed*

Experiments are conducted in a two-dimensional monolayer vibrofluidized bed of glass beads, with an aim to study the dynamics and the transition scenario in different patterned states. At small shaking accelerations ($\Gamma=A\omega^2/g<1$, where $A$ and $\omega= 2\pi f $ are the amplitude and angular frequency of shaking and $g$ is the gravitational acceleration), the particles remain attached to the base of the vibrating container; this is known as the solid bed (SB). With increasing $\Gamma$ (at large enough shaking amplitude $A/d$) and/or with increasing $A/d$ (at large enough $\Gamma$), the sequence of transitions/bifurcations unfolds as follows: SB (“solid bed”) to BB (“bouncing bed”) to LS (“Leidenfrost state”) to “2-roll convection” to “1-roll convection” and finally to a gas-like state. For a given length of the container, the coarsening of multiple convection rolls leading to the genesis of a “single-roll” structure (dubbed the "multiroll transition") and its subsequent transition to a granular gas are two findings of this work. We show that the critical shaking intensity $\Gamma_{BB}^{LS}$ for the $BB \rightarrow LS$ transition has a power-law dependence on the particle loading ($F$) and the shaking amplitude ($A/d$).