[SY-M4] Time dependent interaction between intruders in granular media
In this presentation, we will discuss the interactions between two intruders in two dimensional granular environment from DEM (discrete element method) simulation and phenomenological theory. Through the DEM simulation, we found that the interaction is repulsive if there exists a steady flow or the amplitude of an external oscillation is small enough, but the interaction becomes attractive if the amplitude of the oscillation is large. Such an attractive interaction is known as depletion effect or Casimir effect nearly equilibrium environments, but it is interesting that both attractive and repulsive interactions can be observed in out-of-equilibrium systems such as granular media. We also develop a phenomenology based on an analogous equation to Boltzmann-Enskog equation. The phenomelogy can explain the drag force acting on one intruder in granular environment and the repulsive interaction between two intruders under a steady flow, but is still far away to describe the attractive interaction between two intruders in highly oscillated situations.