Collaborative behavior of intruders moving amid grains

TL;DR

This study uses numerical simulations to explore how groups of intruders move within granular materials, revealing cooperative behaviors, force interactions, and optimal spacing for minimal drag, with implications for ground-stirring devices.

Contribution

The paper uncovers the cooperative dynamics of intruders in granular media, highlighting contact chains, medium deformation, and optimal spacing, which are novel insights into granular intruder interactions.

Findings

Intruders cooperate over large distances.

Contact chains link intruders and influence dynamics.

An optimal distance minimizes drag force.

Abstract

We investigate the motion of groups of intruders in a two-dimensional granular system by using discrete numerical simulations. By imposing either a constant velocity or a thrusting force on larger disks (intruders) that move within smaller ones (grains), we obtained instantaneous positions and components of forces for each intruder and grain. We found that (i) intruders cooperate even when at relatively large distances from each other; (ii) the cooperative dynamics is the result of contact chains linking the intruders as well as compaction and expansion of the granular medium in front and behind, respectively, each intruder; (iii) the collaborative behavior depends on the initial arrangement of intruders; and (iv) for some initial arrangements, the same spatial configuration is eventually reached. Finally, we show the existence of an optimal distance for minimum drag for a given set of intruders, which can prove useful for devices stirring the ground or other granular surfaces.