Sands, Powders, and Grains

Duran, J.

doi:10.1007/978-1-4612-0499-2

Cited by 519 publications

(229 citation statements)

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“…If one probes in more detail the granular structure within the silo and especially when considering the dynamics of the granular material, Janssen's approach no longer yields satisfactory answers [10]. That said, it is quite remarkable that Janssen already postulates that it is arching within the granular assembly what prevented him from measuring the bottom pressure at various points.…”

Section: Impact Of Janssen's Papermentioning

confidence: 99%

Experiments on corn pressure in silo cells – translation and comment of Janssen's paper from 1895

2005

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The German engineer H.A. Janssen gave one of the first accounts of the often peculiar behavior of granular material in a paper published in German in 1895. From simple experiments with corn he inferred the saturation of pressure with height in a granular system. Subsequently, Janssen derived the equivalent of the barometric formula for granular material from the main assumption that the walls carry part of the weight. The following is a translation of this article. The wording is chosen as close as possible to the original. While drawings are copied from the original, figures displaying data are redone for better readability. The translation is complemented by some bibliographical notes and an assessment of earlier work, wherein Hagen predicted the saturation of pressure with depth in 1852, and HuberBurnand demonstrated that saturation qualitatively as early as in 1829. We conclude with a brief discussion of more recent developments resting on Janssen's work.

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Section: Impact Of Janssen's Papermentioning

confidence: 99%

Experiments on corn pressure in silo cells – translation and comment of Janssen's paper from 1895

2005

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“…In addition, this specific experimental configuration makes it possible to get information on the system dynamics from a single image of the disks that rest on the conveyor belt after the discharge. The flow of granular media through an orifice presents some interesting features that have been intensely studied in the last 50 years [1][2][3][4][5][6][7][8][9][10][11]. What mainly differentiates the discharge of a container filled with granular matter from one filled with a viscous liquid is that the mass flowrate does not depend on the height h of material above the outlet.…”

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Pressure Independence of Granular Flow through an Aperture

et al. 2010

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We experimentally demonstrate that the flow rate of granular material through an aperture is controlled by the exit velocity imposed to the particles and not by the pressure at the base, contrary to what is often assumed in previous works. This result is achieved by studying the discharge process of a dense packing of monosized disks through an orifice. The flow is driven by a conveyor belt. This two-dimensional horizontal setup allows to uncouple pressure and velocity and, therefore, to independently control the velocity at which the disks escape the horizontal silo and the pressure in the vicinity of the aperture. The flow rate is found to be directly proportional to the belt velocity, independent of the amount of disks in the container and, thus, independent of the pressure in the outlet region. In addition, this specific experimental configuration makes it possible to get information on the system dynamics from a single image of the disks that rest on the conveyor belt after the discharge.

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“…Mg, 83.50.Ax Shear bands in dense granular materials are localized regions of large velocity gradients; they are the antithesis of the broad uniform flows seen in slowly-sheared Newtonian fluids [1,2,3,4,5,6]. Until recently it was generally assumed that all granular shear bands were narrow.…”

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Three-Dimensional Shear in Granular Flow

et al. 2006

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The evolution of granular shear flow is investigated as a function of height in a split-bottom Couette cell. Using particle tracking, magnetic-resonance imaging, and large-scale simulations we find a transition in the nature of the shear as a characteristic height H * is exceeded. Below H * there is a central stationary core; above H * we observe the onset of additional axial shear associated with torsional failure. Radial and axial shear profiles are qualitatively different: the radial extent is wide and increases with height while the axial width remains narrow and fixed.PACS numbers: 45.70. Mg, 83.50.Ax Shear bands in dense granular materials are localized regions of large velocity gradients; they are the antithesis of the broad uniform flows seen in slowly-sheared Newtonian fluids [1,2,3,4,5,6]. Until recently it was generally assumed that all granular shear bands were narrow. However, in 2003 Fenistein et al. [7] discovered that in modified Couette cells granular shear bands can be made arbitrarily broad. In this geometry, the bottom of a cylindrical container is split at radius r = R s and shear is produced by rotating both the outer ring and the cylindrical boundary of the container while keeping the central disk (r < R s ) stationary. For very shallow packs, the shear band measured at the top surface is narrow and located at r = R s so that the inner region directly above the central disk is stationary while the remaining part rotates as a solid. As the filling height of the material, H, increases, the shear band increases in radial width and moves toward the cylinder axis. For sufficiently large H, the shear band overlaps the axis at r = 0 and one might expect qualitatively new behavior. Indeed, Unger et al. [8] predicted that the shape of the boundary between moving and stationary material would undergo a first-order transition as H is increased past a threshold value H * : the shearing region which for H < H * is open at the top and intersects the free surface abruptly collapses to a closed cupola completely buried inside the bulk.Previous experiments focused primarily on the surface flows in shallow containers and left unexplored many questions about the shape and evolution of the shear profiles for large H. Here, we combine magnetic resonance imaging (MRI) and high-speed video observations with large-scale simulations to explore shear flow both for shallow and tall packs. In addition to monitoring the evolution of the flow profiles in the radial direction, we also examine shear in the vertical direction. Instead of a first order collapse of the shear zone as proposed by Unger et al.[8], we find that above H * ≃ 0.6R s , the inner core of immobile material disappears gradually as shear along the central axis of the cylinder sets in. Our setup is similar to that of Fenistein et al. [7] except that we rotate the inner disk instead of the outer ring and cylinder (Fig.1b inset). In the absence of inertial effects, this makes no difference to the results. For surface observations with high-speed video ...

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Sands, Powders, and Grains

Cited by 519 publications

References 0 publications

Experiments on corn pressure in silo cells – translation and comment of Janssen's paper from 1895

Experiments on corn pressure in silo cells – translation and comment of Janssen's paper from 1895

Pressure Independence of Granular Flow through an Aperture

Three-Dimensional Shear in Granular Flow

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