Discrete Element Simulation Of Vertical Dynamics Of A Horizontally-oscillating Disk In A 2D Granular System

On the basis of the hiding behavior in sand of the sand lizard,using the discrete element model?DEM?,we have systemically studied the dynamics of a self-energized object,modeled as a disc,oscillating horizontally within a two-dimensional bed of denser and smaller particles.To get the high efficient simulation parameters of the system,we firstly analyzed the different vertical behaviors of a horizontally dragged disc by using different parameters in the simulation.Based on this analysis,we find that,for given material parameters,the immersed disc may rise,sink or not change depth,depending on the oscillation amplitude and frequency,and construct a phase diagram of this behavior in the oscillation frequency and velocity amplitude variable space.We explain the observed rich behavior by two competing effects:climbing on particles,which fill voids opening under the disc,and sinking due to bed fluidization.In view of the competing effects,we present a cavity model that allows us to derive analytically general results,which can half-quantitatively explain the mechanism of the vertical movement of the horizontally-oscillating disc.The specific analytic results are the following:derivation of a critical frequency,f_c,according the idealized cavity model,above which the disc cannot float up against gravity in the simulation;derivation of a minimal amplitude,A_min,according the critical condition of the cavity existing,only above which the disc can descend down;derivation of a critical value of the disc's acceleration amplitude,g_c,according to get the bed particles under the cavity fluidized,which is the boundary of rising and sinking in the phase diagram and giving a computing method of the local driving force,which makes a bed particle attain critical point of solid-liquid phase transition.