Granular flow in confined geometries: jamming, clogging, and instability

In this talk, we will discuss three small-scale granular experiments, all prepared in two dimension: (1) drag friction in a granular medium [1-3], (2) granular statics and dynamics in a certain hopper [4], and (3) meandering airflow in a granular medium (Fig. 1) [5]. For the drag friction, we highlight the divergence of the friction force towards the jamming transition and a simple physical explanation for it. For the hopper problem, we discuss the statics of an unstable state and the dynamics of bubbles and its connection to clogging, again in simple physical frameworks. For the meandering problem, we discuss the mechanism of its destabilization and stabilization, together with a quasi-static nature. In all cases, we derive scaling laws for the phenomena on physical grounds, which agree well with experiments.

[1] Yuka Takehara and Ko Okumura, Phys. Rev. Lett. 112 (2014) 148001.
[2] Yuka Takehara, Sachika Fujimoto and Ko Okumura, EPL (Europhys. Lett.) 92, 44003 (2010).
[3] Ko Okumura, Phil. Mag. 96, 828-841 (2016).
[4] Yui Yagisawa, Hui Zee Then, Ko Okumura, Sci. Rep. 6, 25065; doi: 10.1038/srep25065 (2016).
[5] Yuki Yoshimura, Yui Yagisawa, and Ko Okumura, Sci. Rep. 6, 38457 (2016); doi:10.1038/srep38457.