Jamming of hard spheres in a 2D hopper: Reconstructing empirical results using simple agent-based rules

Abstract

We study the jamming of the flow of hard spheres in a 2D hopper and we reconstruct numerically some anomalous as well as expected results by adjusting simple agent-based rules. Jamming of brass and acrylic spheres with pure (all-large) and mixed (large and small) configurations were investigated. In the pure case, both acrylic and brass spheres exhibited the same step function for the jamming probability, which is consistent with our previously reported results. Moreover, the number of jamming events for acrylic spheres had a steeper slope than brass spheres. For the mixed case, an anomalous decrease in the number of jams is observed after the peak. Also, the number of jamming events for the acrylic spheres had a steeper slope than brass spheres. To understand both the expected and the anomalous results for the mixed and the pure cases, we simulated the counting of the number of contacts of the spheres on a particular cell during jamming. We observe an increase in the number of contacts as the number of spheres is increased. Beyond the peak, the number of contacts fluctuates at a constant value, reminiscent of the pure case results. The threshold behavior observed in the jamming incidents for the pure configuration and number of contact suggest that jamming is a threshold process.