Dynamics of an Intruder in Dense Granular Fluids

TL;DR

This paper studies how an intruder moves in a dense granular fluid, revealing the development of momentum fronts, effects of boundary reflections, and the impact of friction and force on intruder velocity through simulations.

Contribution

It introduces a method to incorporate frictional forces into event-driven simulations and explores the intruder's velocity dependence on force and packing fraction.

Findings

Momentum front propagates and reflects at boundaries.

Frictional forces significantly affect intruder dynamics.

Linear and nonlinear velocity regimes identified.

Abstract

We investigate the dynamics of an intruder pulled by a constant force in a dense two-dimensional granular fluid by means of event-driven molecular dynamics simulations. In a first step, we show how a propagating momentum front develops and compactifies the system when reflected by the boundaries. To be closer to recent experiments \cite{candelier2010journey,candelier2009creep}, we then add a frictional force acting on each particle, proportional to the particle's velocity. We show how to implement frictional motion in an event-driven simulation. This allows us to carry out extensive numerical simulations aiming at the dependence of the intruder's velocity on packing fraction and pulling force. We identify a linear relation for small and a nonlinear regime for high pulling forces and investigate the dependence of these regimes on granular temperature.