Simulations of Rapid Bimodal Granular Flows

Nakagawa, Masami; Imaizumi, Taku

doi:10.1016/b978-0-444-89213-3.50020-1

Cited by 3 publications

(3 citation statements)

References 5 publications

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“…Such concentrations are typical of sand‐laden fluids [ Bagnold , ; Hanes , ] in a dilute flow rather than a grain collisional regime. In dilute flows, fine grains such as silts and clays behave as the fluid phase and produce minimal values of shear stresses on any surfaces [ Anderson , ; Nakagawa and Imaizumi , ; Laity and Bridges , ]. Therefore, only the high concentrations of suspended load of sand in the unmeasured near‐bed parts of the tidal flows (Figure ) and any bed load transport should be responsible for abrading the yardangs.…”

Section: Discussionmentioning

confidence: 99%

“…As saltation is replaced by suspension dynamics at higher levels, the concentration profile and the average size of the constituent grains will reduce further ( S < <1) such that abrasion should decrease with increased height. In water, as in air, finer sediment has less abrasive power, even in the faster flows higher in the velocity profile [ Nakagawa and Imaizumi , ; Laity and Bridges , ]. It might be expected therefore that the vertical distribution of the kinetic energy flux imposed on the bedrock surface of a pedestal and prow will exhibit a peak in the region of collisional forces.…”

Section: Discussionmentioning

confidence: 99%

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Subaqueous “yardangs”: Analogs for aeolian yardang evolution

Carling

2013

JGR Earth Surface

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[1] Landforms, morphologically similar to aeolian yardangs but formed by erosion of bedrock by currents on an estuarine rock platform, are described for the first time. The geometries of the "yardangs" are described and related to semi-lemniscate shapes that minimize hydraulic drag. The processes of bedrock erosion by the reversing sedimentladen tidal currents are described, and a semi-quantitative model for landform evolution is proposed. The model casts doubt on the "simple" role of the maximum in the twodimensional vertical suspended sediment flux distribution and the consequent distribution of potential kinetic energy flux in the process of shaping the rock wall facing the ebb flow. Rather, although the kinetic energy flux increases away from the bed, the sediment becomes finer and abrasion likely is insignificant compared with coarse sand abrasion lower in the profile. In addition, the vertical distribution of sediment flux is mediated by topographic forcing which raises the elevation at which bed load intersects the yardang prow. Consequent erosion leads to ebb-facing caprock collapse and yardang shortening. In contrast, the role of ebb-flow separation is paramount in mediating the abrasion process that molds the rock surface facing the flood flow. The length of yardangs is the least conservative dimension, reducing through time more rapidly than the height and width. Width is the more conservative dimension which implies that once the caprock is destroyed, scour over the obstacle is significant in reducing body height, more so than scour of the flanks which reduces width. The importance of vertical fissures in instigating the final breakdown of smaller yardangs and their extinction is noted. Similarities to aeolian yardang geometries and formation principles and processes are noted, as are the differences. The model has implications for aeolian yardang models generally.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Subaqueous “yardangs”: Analogs for aeolian yardang evolution

Carling

2013

JGR Earth Surface

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“…Discrete-element method (DEM), molecular-dynamics type, or particle dynamics modelling approaches are all synonymous names of event-driven simulations where discrete particles interact through the laws of hard or soft elastic collisions. Hard collisions [13,14] occur when they are instantaneous and the post-collision velocities are not dependent on the particle deformations, whereas soft collisions [15,16] take into account the deformation or overlap of particles. DEM simulations of the Couette or simple shear flows have been conducted for soft, smooth, and elastic hard discs as binary mixtures in rapid shear flow [17], for soft binary-size particles in dense (high solid fraction) two-dimensional gravity-free cells [15], for hard, rough, elastic discs [14], for hard, smooth, and rapid grains of uniform size [18], and for soft dense and rapid granular flows in rough cells [7].…”

Section: Introductionmentioning

confidence: 99%

An evaluation of the explicit finite-element method approach for modelling dense flows of discrete grains in a Couette shear cell

Kabir

Jasti

Higgs

et al. 2008

Proceedings of the Institution of Mechanical Engineers, Part J:

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Granular flows are complex materials that are composed of discrete solid particles that can display gaseous, liquid, and/or solid behaviour under various conditions. Consequently, tribologists have studied them for their ability to carry loads and/or accommodate sliding surface velocities. Because of the highly non-linear behaviour of granular materials, their behaviour is difficult to predict. One new modelling approach that holds promise in simulating the behaviour of these particulate materials is the explicit finite-element method (FEM). The explicit FEM is a computational modelling approach capable of capturing dynamic, transient events, such as collisions and particle-particle interactions of grains in granular flows. This paper presents an explicit FEM simulation of a dense flow of steel particles in a rough gravity-free Couette shear cell with no externally applied load. Parametric tests of this cell are also carried out by varying the height of the shear cell and the types of known granular materials sheared in the cell. Subsequently, a final evaluation of the explicit FEM approach is conducted by simulating a dense flow of sheared titanium oxide (TiO 2 ) powder in the shear cell and comparing it to a similar simulation done using the discrete-element method (DEM) approach. In this comparison, the velocity of the flow in the DEM cell is larger, whereas the FEM and DEM solid fraction distributions are almost identical in the core regions of the shear cells. The merits of the FEM and DEM approaches are presented in light of the results shown in this work.

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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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Simulations of Rapid Bimodal Granular Flows

Cited by 3 publications

References 5 publications

Subaqueous “yardangs”: Analogs for aeolian yardang evolution

Subaqueous “yardangs”: Analogs for aeolian yardang evolution

An evaluation of the explicit finite-element method approach for modelling dense flows of discrete grains in a Couette shear cell

Density waves in gravity-driven granular flow through a channel

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