Granular avalanches in a two-dimensional rotating drum with imposed vertical vibration

Abstract

We present statistics on granular avalanches in a rotating drum with and without imposed vertical vibration. The experiment consists of a quasi-two-dimensional, vertical drum containing pentagonal particles and rotated at a constant angular velocity. The drum rests on an electromagnetic shaker to allow vibration of the assembly as it rotates. We measure time series of the slope of the interface and find that the critical angle for slope failure θ(c) and the resulting angle of repose θ(r) are broadly distributed with an approximate power-law distribution of avalanches θ(c)-θ(r) for large avalanches. The faceted pentagonal grains used lead to significant interlocking with critical and repose angles (θ(c)≈45° and θ(r)≈39°) larger than experiments using spherical grains, even with vibration, and avalanche magnitudes correlated with the prior build-up and anti-correlated with the prior avalanche. We find that the stability of the assembly increases with small vibrations and is destabilized at vibration amplitudes above a dimensionless acceleration (peak acceleration divided by acceleration due to gravity) of Γ=0.2. We also study history dependence of the avalanches by periodically oscillating the drum to compare the initial avalanche upon reversal of shear to steady-state distributions for avalanches during continuous rotation. We observe history dependence as an initial decrease in critical angle upon reversal of the drum rotation direction, indicating that a texture is induced to resist continued shear such that the surface is weaker to reversals in shear direction. Memory of this history is removed by sufficient external vibration (Γ≥0.8), which leads to compaction and relaxation of the surface layer grains responsible for avalanching dynamics, as initial and steady-state avalanche distributions become indistinguishable.

Spatiotemporal chaotic unjamming and jamming in granular avalanches

“…Let's suppose that after time t 0 , the existence of some perturbations makes the real trajectory diverge from the “ideal” one, where the system would reach the maximum angle of repose under zero perturbations. We assume that the existence of perturbations makes the avalanche happen in advance, which is consistent with the experimental observation that the critical angle of repose has a wide range of about 10 degrees 22 . Since the duration of the avalanche is short, typically 1 to 2 seconds, and the rotation speed is slow, i.e.…”

“…Jamming transition in amorphous materials has become an active research field recently .The inverse processthe unjamming transition, where a system may suddenly lose rigidity and flow like a liquid, is of crucial importance in studying natural disasters such as snow avalanches, landslides and earthquakes. The continuous tilting of a pile of cohesionless grains will eventually create an avalanche [22][23][24][25][26], which can be viewed as a dual-process of both the unjamming transition, i.e. when the surface-layer particles lose rigidity and start flowing, and the jamming transition, i.e.…”

Laboratory experiment and discrete-element-method simulation of granular-heap flows under vertical vibration

“…A dense surface flow, which is also called a heap flow, is one of the avalanche types that we frequently encounter in daily life. The steady state of heap flows can be observed mainly in two situations: when granular media are continuously supplied onto the top of a static pile [1][2][3][4][5][6] or filled in a rotating drum [3,[7][8][9][10][11][12][13]. In most of the experimental observations, the typical fluidized layer consists of 10 0 − 10 1 grain diameters, which is spontaneously determined by the system itself.…”

Origin of magnetic flux-jumps in Nb films subject to mechanical vibrations and corresponding magnetic perturbations

“…Moreover, avalanche dynamics in sand considers a certain response to mechanical vibration. Horizontal or vertical vibrations of a pile imposes additional alternating forces acting on grains, which effectively assist to "depin" and propagate grains decreasing the critical slope of the pile [44][45][46][47][48][49]. The critical slope is progressively decreased with the larger amplitude and/or frequency of the mechanical vibrations.…”