On dense granular flows

Midi, G. D. R.

doi:10.1140/epje/i2003-10153-0

Cited by 1,644 publications

(545 citation statements)

References 92 publications

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“…Jain et al [5] in rotating tumblers). The streamwise velocity profiles resemble those in unbounded heap flow [1,8,49,50,52] or rotating tumbler flow [4,5,53]. However, in bounded heap flow, the streamwise velocity at constant depth decreases in the streamwise direction.…”

Section: Results (A) Free Surface Dynamic Repose Angle and Rise Velomentioning

confidence: 82%

“…Throughout most of the flowing layer (|z/δ| < 1), the scaled velocity u/u s decreases rapidly from 1 at the free surface. Deeper in the flowing layer, u/u s decreases approximately exponentially, similar to unbounded heap flow or rotating tumbler flow [1,8,55,58]. This exponential tail can be seen more clearly in figure 7b, where u/u s is plotted on a log scale.…”

Section: (Iii) Streamwise and Normal Velocity Scalingmentioning

confidence: 76%

“…In the first method, similar to the earlier studies [8,54,55], the velocity profile at each streamwise location is fit to u(x, z) = u o (x)exp(z/z o ), where u o is the nominal surface velocity at each x and z o is a characteristic depth, to which z bottom is proportional. In the second method, the bottom of the flowing layer is determined by extrapolating the approximately linear part of the velocity profile to zero [1]. In the third method, a cutoff value u c , proportional to u s at each x (e.g.…”

Section: Results (A) Free Surface Dynamic Repose Angle and Rise Velomentioning

confidence: 99%

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Kinematics of monodisperse and bidisperse granular flows in quasi-two-dimensional bounded heaps

et al. 2013

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Quasi-two-dimensional bounded heap flow is a useful model for many granular flows in industry and nature. It belongs to a family of free surface flows—inclined chute flow, rotating tumbler flow and unbounded heap flow—but differs from the others in that uniform deposition of particles onto the static bed results in the uniform rise of the heap. The kinematics, however, are only partially understood. We performed discrete element method simulations to study granular flows in quasi-two-dimensional bounded heaps. The experimentally validated computational results show a universal functional form for the streamwise velocity profile for both monodisperse and bidisperse systems when velocities and coordinates are scaled by the local surface velocity and the local flowing layer thickness. This holds true regardless of streamwise location, feed rate, particle size distribution and, most surprisingly, the local particle concentration for bidisperse flows. The local surface velocity decreases linearly in the streamwise direction, while the flowing layer thickness remains nearly constant; both quantities depending only on local flow rate and local mean particle diameter. Additionally, the velocity profile normal to the overall flow, which is important in understanding segregation, can be predicted analytically from the streamwise velocity and matches the simulation results.

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Section: Results (A) Free Surface Dynamic Repose Angle and Rise Velomentioning

confidence: 82%

Section: (Iii) Streamwise and Normal Velocity Scalingmentioning

confidence: 76%

Section: Results (A) Free Surface Dynamic Repose Angle and Rise Velomentioning

confidence: 99%

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Kinematics of monodisperse and bidisperse granular flows in quasi-two-dimensional bounded heaps

et al. 2013

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“…Full details are given in Luding [15]. rate, however, is not a priori a governing quantity, so we choose to control the piston rate via the inertial number, I, which is defined as I =γ d m / P/ρ p , which is the ratio of inertial to imposed stresses, where P is a typical pressure andγ is a typical shear strain rate [17]. Takingγ = u/D, and P = ρ p gD, gives…”

Section: Methodsmentioning

confidence: 99%

Compaction of granular material inside confined geometries

et al. 2015

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In both nature and engineering, loosely packed granular materials are often compacted inside confined geometries. Here, we explore such behavior in a quasi-two dimensional geometry, where parallel rigid walls provide the confinement. We use the discrete element method to investigate the stress distribution developed within the granular packing as a result of compaction due to the displacement of a rigid piston. We observe that the stress within the packing increases exponentially with the length of accumulated grains, and show an extension to current analytic models which fits the measured stress. The micromechanical behavior is studied for a range of system parameters, and the limitations of existing analytic models are described. In particular, we show the smallest sized systems which can be treated using existing models. Additionally, the effects of increasing piston rate, and variations of the initial packing fraction, are described.

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“…[45] The shear strength of dense granular flows has been a matter of study for many years, using a great variety of devices and loading conditions [Groupement de Recherche Milieux Divises, 2004]. Experimental and theoretical results show that the coefficient of friction of a sheared granular material varies with the mean ''agitation'' of its particles.…”

Section: Rheology Of Dense Granular Flowsmentioning

confidence: 99%

Rock‐and‐soil avalanches: Theory and simulation

Taboada

Estrada

2009

J. Geophys. Res.

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[1] We present a 2-D Contact Dynamics discrete element model for simulating initiation and motion of rock avalanches, integrating hillslope geometry, Mohr-Coulomb rock behavior, pore pressure before avalanche triggering, and avalanche trigger. Avalanche motion is modeled as a dense granular flow of dry frictional and cohesive particles. On the basis of granular physics and shear experiments, we review some of the theories for the unexpectedly long runout of rock avalanches. Different causes are evoked, according to the strength (strong or weak) of the slip surface relative to the bulk. ''Mechanical fluidization'' and ''acoustic fluidization'' theories state that agitation of rock particles reduces frictional strength, increasing runout. Conversely, granular mechanics suggests that, as ''shear-strain'' rate increases, granular material becomes more agitated, more dissipative, and more resistant. Another theory states that dynamic fragmentation of clasts creates an isotropic pressure that drives longer runout. In contrast, granular mechanics suggests that fragmentation may induce fluidization and strengthening of the granular material, while particle size reduction (among others) induces weakening of the granular flow and enhances long runout. Runout is also enhanced for column-like rock masses collapsing from steep hillslopes. Long runout may also be linked to thermal weakening mechanisms at the slip surface (e.g., thermal pressurization, and shear melting), which may lower drastically the shear strength. The model is illustrated with a hypothetical example of a rain-triggered avalanche, mobilizing shallowly dipping layers. Several phases are identified, including slope failure, avalanche triggering resulting from slip weakening, and avalanche motion in which rocks are folded and sheared.

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On dense granular flows

Cited by 1,644 publications

References 92 publications

Kinematics of monodisperse and bidisperse granular flows in quasi-two-dimensional bounded heaps

Kinematics of monodisperse and bidisperse granular flows in quasi-two-dimensional bounded heaps

Compaction of granular material inside confined geometries

Rock‐and‐soil avalanches: Theory and simulation

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