Wall effects on granular heap stability

Pont, Sylvain Courrech du; Gondret, Philippe; Perrin, Bernard; Rabaud, Marc

doi:10.1209/epl/i2003-00156-5

Cited by 76 publications

(25 citation statements)

References 19 publications

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“…The effect of side walls on grains which are fully immersed in a liquid has been reported in Ref. [9]. The data in that case reaches the asymptotic value for a W of a few grain diameters because liquid bridges are absent.…”

Section: Lowermentioning

confidence: 62%

Maximum angle of stability of a wet granular pile

2005

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Anyone who has built a sandcastle recognizes that the addition of liquid to granular materials increases their stability. However, measurements of this increased stability often conflict with theory and with each other [1,2,3,4,5,6,7]. A friction-based Mohr-Coulomb model has been developed [3,8]. However, it distinguishes between granular friction and inter-particle friction, and uses the former without providing a physical mechanism. Albert, et al.[2] analyzed the geometric stability of grains on a pile's surface. The frictionless model for dry particles is in excellent agreement with experiment. But, their model for wet grains overestimates stability and predicts no dependence on system size. Using the frictionless model and performing stability analysis within the pile, we reproduce the dependence of the stability angle on system size, particle size, and surface tension observed in our experiments. Additionally, we account for past discrepancies in experimental reports by showing that sidewalls can significantly increase the stability of granular material.The experimental apparatus consists of a clear plexiglass drum which is rotated about an horizontal axis. We primarily use a drum with a diameter D of 28.5 cm and a width W which can be varied from 0 cm to 14.5 cm. A drum with D = 12.5 cm and W = 11.5 cm is also used to vary system size. The rotation rate ω is varied from 9.0×10 −4 rpm to 5.6×10 −1 rpm. Soda-lime glass spheres which have a density ρ of 2.4 g cm −3 , and with radius r = 0.25 mm, 0.3 mm, 0.5 mm, and 1.5 mm and size dispersity within 0.1 mm were used. The drum was 40% filled with grains premixed with a small amount of liquid. We report the amount of liquid added in terms of the volume fraction, V f , which is defined as the volume of the liquid divided by the volume occupied by the grains alone. The effect of surface tension of the liquid Γ was tested by using silicone oil and water which have Γ = 20 ± 1 dyne cm −1 and Γ = 70 ± 1 dyne cm −1 , respectively. Silicone oil with viscosity ν ranging from 5 cS to 1000 cS is used to study its impact on the measured inclination angles.The drum is back lit so that light could pass through a thin layer of grains that tends to accumulate on the sides of the drum, but is unable to pass through the bulk of the pile. Images were acquired with a mega-pixel resolution digital camera at a rate of three frames per second 100 50 time (s) (b) 32 30 28 26 Surface angle (deg.) 100 50 0 time (s) (a) FIG. 1: Avalanching regimes Glass spheres (radius r 0.5 mm) mixed with silicone oil in a rotating drum (width W 14.5 cm). (a) Stick-slip flow is observed for a rotation rate ω of 0.028 rpm and viscosity ν = 5 cS. (b) Continuous flow is observed for rotation rate of 0.28 rpm.and used to determine the surface slope with automated code. At this rate, the slope of the pile changed no more than 0.2 degrees between frames. This error in measurement is not significant given that the slope of the pile at the moment of avalanche was distributed over about two degrees in a given run....

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Section: Lowermentioning

confidence: 62%

Maximum angle of stability of a wet granular pile

2005

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“…͑16͒ enables the proposed model to predict hysteretic flow thresholds. [56][57][58] Equations ͑12a͒, ͑12b͒, ͑15͒, and ͑16͒ contain seven unknowns, i.e., u x , p K , p S , xy K , xy S , T, and , meanwhile, only six equations are available, including Eqs. ͑4͒ and ͑7͒ for determining xy K and p K , respectively.…”

Section: Governing Equationsmentioning

confidence: 99%

Model of sheared granular material and application to surface-driven granular flows under gravity

Lee

Huang

2010

Physics of Fluids

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This work presents a novel model of sheared granular materials that consist of two-dimensional, slightly inelastic, circular disks. To capture the static and kinetic features of the granular flow involving different regimes, both the shear stress and pressure are superimposed by a rate-independent component ͑representing the static contribution͒ and a rate-dependent component ͑representing the kinetic contribution͒, as determined using granular kinetic theory. The dilatancy law is adopted to close the set of equations, and the constraint that static pressure is non-negative is utilized to determine the transition between the dense regime and the inertial regime. The balance equation of granular temperature incorporates the works done by both the static and kinetic components of shear stress. This enabled the proposed model to predict the hysteretic flow thresholds and the shear bands. Additionally, a thick, surface-driven granular flow under gravity is investigated using the proposed model. The predicted velocity, volume fraction, granular temperature, and stress are consistent with results obtained using the molecular dynamic method. This finding demonstrates the ability of the proposed model to simulate granular flow in which the quasistatic, dense, and kinetic regimes coexist simultaneously.

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“…ω and u denote the rotation speed and flowing layer velocity, respectively, and β is the dynamic angle of repose of the free surface with respect to horizontal. and the rotational speed of the tumbler ω [21][22][23][24]. A simple model of 3D flow in a spherical tumbler [1,13,14] assumes that flow in each plane perpendicular to the axis of rotation is essentially that of a two-dimensional circular slice of the appropriate diameter, as shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

Slow axial drift in three-dimensional granular tumbler flow

et al. 2013

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Models of monodisperse particle flow in partially filled three-dimensional tumblers often assume that flow along the axis of rotation is negligible. We test this assumption, for spherical and double cone tumblers, using experiments and discrete element method simulations. Cross sections through the particle bed of a spherical tumbler show that, after a few rotations, a colored band of particles initially perpendicular to the axis of rotation deforms: particles near the surface drift toward the pole, while particles deeper in the flowing layer drift toward the equator. Tracking of mm-sized surface particles in tumblers with diameters of 814 cm shows particle axial displacements of one to two particle diameters, corresponding to axial drift that is 13% of the tumbler diameter, per pass through the flowing layer. The surface axial drift in both double cone and spherical tumblers is zero at the equator, increases moving away from the equator, and then decreases near the poles. Comparing results for the two tumbler geometries shows that wall slope causes axial drift, while drift speed increases with equatorial diameter. The dependence of axial drift on axial position for each tumbler geometry is similar when both are normalized by their respective maximum values PACS numbers: 45.70.Mg

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Wall effects on granular heap stability

Cited by 76 publications

References 19 publications

Maximum angle of stability of a wet granular pile

Maximum angle of stability of a wet granular pile

Model of sheared granular material and application to surface-driven granular flows under gravity

Slow axial drift in three-dimensional granular tumbler flow

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