Kinetic grain flow in a vertical channel

Hui, K. L.; Haff, P. K.

doi:10.1016/0301-9322(86)90031-5

Cited by 17 publications

(9 citation statements)

References 10 publications

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“…Particles that are not part of the flow proper because they travel individually and form, when at rest, the distal distribution are clearly discernible in front of the flow proper in the images of the numerical simulations (for example, at 0.7 s in Figure 4 and at 0.65 s in Figure 7). Figure 6 shows that the slopeparallel component of particle velocity decreases downward toward the subsurface as expected in flows that travel in contact with a boundary surface [Hui and Haff, 1986;Iverson, 1997;Cagnoli and Manga, 2004]. Figure 8 illustrates the μ A versus β data of the granular flows in the numerical simulations where the surfaces of accelerator and chute have the same friction coefficient.…”

Section: Resultsmentioning

confidence: 72%

Grain size and flow volume effects on granular flow mobility in numerical simulations: 3‐D discrete element modeling of flows of angular rock fragments

Cagnoli

Piersanti

2015

JGR Solid Earth

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The results of three-dimensional discrete element modeling presented in this paper confirm the grain size and flow volume effects on granular flow mobility that were observed in laboratory experiments where batches of granular material traveled down a curved chute. Our numerical simulations are able to predict the correct relative mobility of the granular flows because they take into account particle interactions and, thus, the energy dissipated by the flows. The results illustrated here are obtained without prior fine-tuning of the parameter values to get the desired output. The grain size and flow volume effects can be expressed by a linear relationship between scaling parameters where the finer the grain size or the smaller the flow volume, the more mobile the center of mass of the granular flows. The numerical simulations reveal also the effect of the initial compaction of the granular masses before release. The larger the initial compaction, the more mobile the center of mass of the granular flows. Both grain size effect and compaction effect are explained by different particle agitations per unit of flow mass that cause different energy dissipations per unit of travel distance. The volume effect is explained by the backward accretion of the deposits that occurs wherever there is a change of slope (either gradual or abrupt). Our results are relevant for the understanding of the travel and deposition mechanisms of geophysical flows such as rock avalanches and pyroclastic flows.

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Section: Resultsmentioning

confidence: 72%

Grain size and flow volume effects on granular flow mobility in numerical simulations: 3‐D discrete element modeling of flows of angular rock fragments

Cagnoli

Piersanti

2015

JGR Solid Earth

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“…Shearing, in turn, can modify the granular pressure gradient by influencing the local granular temperature, grain concentration, and possibly the pore-fluid pressure [cf. Hui and Haft, 1986;Johnson et al, 1991]. Thus Bagnold's results, obtained with fixed concentrations and shear rates, provide valuable insight but not a valid constitutive equation for debris flows.…”

Section: Usgs Flume Experiments Oddstad Debris Flowmentioning

confidence: 99%

“…Instead, granular temperature requires bulk deformation and depends on flow interaction with boundaries that impart external forces. Granular temperatures and boundary forces cannot be specified independently but must be determined hand in hand as part of rigorous mathematical models [Hui and Haft, 1986] An obvious possibility is that sediment consolidation produces high pore pressures in debris flows [cf. Hutchinson, 1986].…”

Section: Debris Flow Motionmentioning

confidence: 99%

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The physics of debris flows

Iverson¹

1997

Reviews of Geophysics

2,533

2,240

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Abstract. Recent advances in theory and experimentation motivate a thorough reassessment of the physics of debris flows. Analyses of flows of dry, granular solids and solid-fluid mixtures provide a foundation for a comprehensive debris flow theory, and experiments provide data that reveal the strengths and limitations of theoretical models. Both debris flow materials and dry granular materials can sustain shear stresses while remaining static; both can deform in a slow, tranquil mode characterized by enduring, frictional grain contacts; and both can flow in a more rapid, agitated mode characterized by brief, inelastic grain collisions. In debris flows, however, pore fluid that is highly viscous and nearly incompressible, composed of water with suspended silt and clay, can strongly mediate intergranular friction and collisions. Grain friction, grain collisions, and viscous fluid flow may transfer significant momentum simultaneously. Both the vibrational kinetic energy of solid grains (measured by a quantity termed the granular temperature) and the pressure of the intervening pore fluid facilitate motion of grains past one another, thereby enhancing debris flow mobility. Granular temperature arises from conversion of flow translational energy to grain vibrational energy, a process that depends on shear rates, grain properties, boundary conditions, and the ambient fluid viscosity and pressure. Pore fluid pressures that exceed static equilibrium pressures result from local or global debris contraction. Like larger, natural debris flows, experimental debris flows of --•10 m 3 of poorly sorted, water-saturated sediment invariably move as an unsteady surge or series of surges. Measurements at the base of experimental flows show that coarse-grained surge fronts have little or no pore fluid pressure. In contrast, finer-grained, thoroughly saturated debris behind surge fronts is nearly liquefied by high pore pressure, which persists owing to the great compressibility and moderate permeability of the debris. Realistic models of debris flows therefore require equations that simulate inertial motion of surges in which high-resistance fronts dominated by solid forces impede the motion of low-resistance tails more strongly influenced by fluid forces. Furthermore, because debris flows characteristically originate as nearly rigid sediment masses, transform at least partly to liquefied flows, and then transform again to nearly rigid deposits, acceptable models must simulate an evolution of material behavior without invoking preternatural changes in material properties. A simple model that satisfies most of these criteria uses depth-averaged equations of motion patterned after those of the Savage-Hutter theory for gravity-driven flow of dry granular masses but generalized to include the effects of viscous pore fluid with varying pressure. These equations can describe a spectrum of debris flow behav-

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“…Such work includes flow in shear cells, inclined chutes and vertical channels and various types of density waves have been observed in all of these systems. 3,[7][8][9][10][11][12][13][14] Density waves may affect the flow properties, heat transfer, and reaction rates of a process involving granular materials. 15 In addition, an understanding of the rapid flow of a granular material ties in directly with an understanding of many gas-particle flows.…”

Section: Introductionmentioning

confidence: 99%

Density waves in gravity-driven granular flow through a channel

2002

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A molecular-dynamic computer simulation is used to examine rapid granular flow in a vertical channel. A two-dimensional event driven algorithm is used with periodic boundary conditions in the flow direction and solid walls in the lateral direction. Flow in the channel leads to an inhomogeneous distribution of the particles and two distinct types of density waves are identified: An S-shaped wave and a clump. The density waves are further characterized by quantifying their temporal evolution using Fourier methods and examining local and global flow properties of the system, including velocities, mass fluxes, granular temperatures, and stresses. A parametric study is used to characterize the effect of the system parameters on the density waves. In particular we are able to show that the dynamics of large systems are often qualitatively and quantitatively different from those of small systems. Finally, the types of density waves and dominant Fourier modes observed in our work are compared to those that are predicted using a linear stability analysis of equations of motion for rapid granular flow.

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Kinetic grain flow in a vertical channel

Cited by 17 publications

References 10 publications

Grain size and flow volume effects on granular flow mobility in numerical simulations: 3‐D discrete element modeling of flows of angular rock fragments

Grain size and flow volume effects on granular flow mobility in numerical simulations: 3‐D discrete element modeling of flows of angular rock fragments

The physics of debris flows

Density waves in gravity-driven granular flow through a channel

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