Chaotic Dynamics in a Slowly Rotating Drum
Recent computational work (Banigan et al., Nat. Phys. 9, 288 (2013)) has demonstrated that jamming and unjamming in a shear cell can be described in terms of chaotic dynamics. Experimental work (Wang et al., Sci. Rep. 5, 8128 (2015)) found that avalanches in a rotating drum behave consistently with this description. We employ computer simulations to examine the chaotic dynamics accompanying granular avalanches in the rotating-drum system. These simulations directly evolve imposed perturbations and provide access to the largest short-time Lyapunov exponent. We find that the local chaotic properties of the system and its dynamics are indeed coupled; the system becomes chaotic as avalanches develop, and returns to a non-chaotic state as avalanches decay. Interestingly, the transition between chaotic and non-chaotic regimes lags behind the change in avalanche state. This contrasts with prior work on the shear cell, where the same force model yielded dynamics that becomes chaotic leading up to, rather than lagging behind, local reorganizations of disks.