Collapse of a granular column under rotation
TL;DR: Experimental results for the collapse of granular columns on a rotating table are presented in this article, where two flow regimes are exhibited dependent on the aspect ratio a = h 0/r0, where h 0 is the initial height and r 0 is initial column radius Scaling relations for the characteristic geometrical properties of the collapsed column under varying rotation rates are obtained as the rotation rate increases, material is lost from the main pile and travels to the edge of the rotating table.
About: This article is published in Powder Technology.The article was published on 2014-08-01. It has received 5 citations till now. The article focuses on the topics: Rotation & Radius.
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TL;DR: In this paper, a quasi-two-dimensional set-up with novel features including: a lifting gate activated by a parallelogram mechanism for material release, a reversible pneumatic circuit to impose fluidised and vacuum conditions to the initial granular column, a set of load cells to monitor the basal load distribution during flow propagation, a 3D laser line profile sensor to scan the free surface morphology of the samples at rest, and a high-speed video recording set to capture nearwall flow visualisations and relevant kinematic measures by particle image velocimetry.
7 citations
TL;DR: In this article, the authors performed a numerical investigation on the kinetic behaviors of dry granular flows generated by the collapse of granular columns with different fractal particle size distributions (FPSDs) using the discrete element method.
Abstract: This paper performs a numerical investigation on the kinetic behaviors of dry granular flows generated by the collapse of granular columns with different fractal particle size distributions (FPSDs) using the discrete element method. The FPSD has a remarkable impact on the regime and mobility of a granular flow. As the fractal dimension of a granular assembly increases, the translational velocities of the particles increase in the horizontal direction, whereas the rotational velocities decrease. The number of particles involved in the horizontal spreading increases due to the decreasing intensity of the contact shearing particle behavior. These increased translational velocities in the horizontal direction effectively facilitate particle spreading. A boundary layer is formed at the front bottom of the granular body in which the clockwise rotational velocities of particles are significantly increased, thereby benefiting particle spreading. The whole front of the granular flow obtains an immense spreading velocity. Moreover, the translational and rotational characteristics are dependent on the particle size. Smaller particles tend to translate and rotate faster than larger particles because of the greater particle contact forces of the former. As the fractal dimension increases, medium- and large-size particles obtain less kinetic energy than do small-size particles. Therefore, small-size particles play a crucial role in the mobility of granular flows in a granular assembly with a high fractal dimension.
3 citations
TL;DR: In this article, molecular sieve residues (MSRs) were sufficiently recycled and utilized due to their high specific surface area, porous structure, and outstanding adsorption property, and they were prepared by adding additives (starch, citric acid, and soluble glass) to MSRs and were then filled into a fixed bed for adsorbing and separating the oil.
Abstract: To deeply clean oily wastewater, molecular sieve residues (MSRs) were sufficiently recycled and utilized due to their high specific surface area, porous structure, and outstanding adsorption property. Molding MSRs (MMSRs) were prepared by adding additives (starch, citric acid, and soluble glass) to MSRs and were then filled into a fixed bed for adsorbing and separating the oil in wastewater. Sodium dodecylbenzenesulfonate was used to modify the MMSRs, and their adsorption property was also investigated. In addition, the MSRs were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, Brunauer–Emmett–Teller analysis, and Fourier transform infrared spectroscopy. The results indicated that MMSRs satisfied the filling requirement of fixed bed, and their dynamic adsorption capacity could reach 0.1854 mg g−1. Furthermore, the static adsorption capacity of MMSRs achieved 1.7346 mg g−1 in the optimum conditions, and the oil adsorption performance of modified MMSRs was further enhanced. Therefore, this work suggests that MSRs are promising alternatives in cleaning oily wastewater.
TL;DR: In this article , the authors investigated the effects of interparticle friction on the granular column collapses via the discrete element method (DEM) while eliminating the particle-size effects, and the motion patterns of the collapse were governed by the interparticles friction and initial aspect ratio through dimensional analysis.
TL;DR: In this paper , the authors have shown that the spatial distribution of particles with different densities significantly affects the flow and deposit characteristics of granular column collapse in binary mixtures of steel and aluminum particles.
References
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TL;DR: In this article, a model to predict the flow of an initially stationary mass of cohesionless granular material down rough curved beds is described, where the constitutive behaviour of the material making up the pile is described by a Mohr-Coulomb criterion while the bed boundary condition is treated by a similar Coulomb-type basal friction law assumption.
Abstract: This paper describes a model to predict the flow of an initially stationary mass of cohesion-less granular material down rough curved beds. This work is of interest in connection with the motion of rock and ice avalanches and dense flow snow avalanches. The constitutive behaviour of the material making up the pile is assumed to be described by a Mohr-Coulomb criterion while the bed boundary condition is treated by a similar Coulomb-type basal friction law assumption. By depth averaging the incompressible conservation of mass and linear momentum equations that are written in terms of a curvilinear coordinate system aligned with the curved bed, we obtain evolution equations for the depthh and the depth averaged velocityū. Three characteristic length scales are defined for use in the non-dimensionalization and scaling of the governing equations. These are a characteristic avalanche lengthL, a characteristic heightH, and a characteristic bed radius of curvatureR. Three independent parameters emerge in the non-dimensionalized equations of motion. One, which is the aspect ratio e-H/L, is taken to be small. By choosing different orderings for the other two, the tangent of the bed friction angle δ and the characteristic non-dimensional curvature λ=L/R, we can obtain different sets of equations of motion which appropriately display the desired importance of bed friction and bed curvature effects. The equations, correct to order e for moderate curvature, are discretized in the form of a Lagrangian-type finite difference representation which proved to be successful in the earlier studies of Savage and Hutter [24] for granular flow down rough plane surfaces. Laboratory experiments were performed with plastic particles flowing down a chute having a bed made up of a straight, inclined portion, a curved part and a horizontal portion. Numerical solutions are presented for conditions corresponding to the laboratory experiments. It is found that the predicted temporal-evolutions of the rear and front of the pile of granular material as well as the shape of the pile agree quite well with the laboratory experiments.
482 citations
TL;DR: In this paper, the authors have looked at models based upon inelastic collisions among particles, and with the aid of computer simulations of these models they have tried to build a ''statistical dynamics'' of the collisions, which can dissipate energy and drive the system toward frozen or glassy configurations.
Abstract: Granulated materials, like sand and sugar and salt, are composed of many pieces that can move independently. The study of collisions and flow in these materials requires new theoretical ideas beyond those in the standard statistical mechanics or hydrodynamics or traditional solid mechanics. Granular materials differ from standard molecular materials in that frictional forces among grains can dissipate energy and drive the system toward frozen or glassy configurations. In experimental studies of these materials, one sees complex flow patterns similar to those of ordinary liquids, but also freezing, plasticity, and hysteresis. To explain these results, theorists have looked at models based upon inelastic collisions among particles. With the aid of computer simulations of these models they have tried to build a ``statistical dynamics'' of inelastic collisions. One effect seen, called inelastic collapse, is a freezing of some of the degrees of freedom induced by an infinity of inelastic collisions. More often some degrees of freedom are partially frozen, so that there can be a rather cold clump of material in correlated motion. Conversely, thin layers of material may be mobile, while all the material around them is frozen. In these and other ways, granular motion looks different from movement in other kinds of materials. Simulations in simple geometries may also be used to ask questions like When does the usual Boltzmann-Gibbs-Maxwell statistical mechanics arise?, What are the nature of the probability distributions for forces between the grains?, and Might the system possibly be described by uniform partial differential equations? One might even say that the study of granular materials gives one a chance to reinvent statistical mechanics in a new context.
419 citations
TL;DR: In this paper, experimental observations of the collapse of initially vertical columns of small grains are presented, mainly with dry grains of salt or sand, with some additional experiments using couscous, sugar or rice.
Abstract: Experimental observations of the collapse of initially vertical columns of small grains are presented. The experiments were performed mainly with dry grains of salt or sand, with some additional experiments using couscous, sugar or rice. Some of the experimental flows were analysed using high-speed video. There are three different flow regimes, dependent on the value of the aspect ratio a = hi/ri ,w herehi and ri are the initial height and radius of the granular column respectively. The differing forms of flow behaviour are described for each regime. In all cases a central, conically sided region of angle approximately 59 ◦ , corresponding to an aspect ratio of 1.7, remains undisturbed throughout the motion. The main experimental results for the final extent of the deposit and the time for emplacement are systematically collapsed in a quantitative way independent of any friction coefficients. Along with the kinematic data for the rate of spread of the front of the collapsing column, this is interpreted as indicating that frictional effects between individual grains in the bulk of the moving flow only play a role in the last instant of the flow, as it comes to an abrupt halt. For a< 1.7, the measured final runout radius, r∞, is related to the initial radius by r∞ = ri(1 + 1.24a); while for 1.7
315 citations
"Collapse of a granular column under..." refers result in this paper
...The collapse in the non-rotating case is well reported by previous authors [7,8]....
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TL;DR: In this article, a Navier-Stokes solver is used to simulate the column collapse of granular columns over a wide range of aspect ratios in the case of a steady infinite two-dimensional granular layer avalanching on an inclined plane.
Abstract: There is a large amount of experimental and numerical work dealing with dry granular flows (such as sand, glass beads, etc.) that supports the so-called -rheology. The reliability of the -rheology in the case of complex transient flows is not fully ascertained, however. From this perspective, the granular column collapse experiment provides an interesting benchmark. In this paper we implement the -rheology in a Navier–Stokes solver (Gerris) and compare the resulting solutions with both analytical solutions and two-dimensional contact dynamics discrete simulations. In a first series of simulations, we check the numerical model in the case of a steady infinite two-dimensional granular layer avalanching on an inclined plane. A second layer of Newtonian fluid is then added over the granular layer in order to recover a close approximation of a free-surface condition. Comparisons with analytical and semi-analytical solutions provide conclusive validation of the numerical implementation of the -rheology. In a second part, we simulate the unsteady two-dimensional collapse of granular columns over a wide range of aspect ratios. Systematic comparisons with discrete two-dimensional contact dynamics simulations show good agreement between the two methods for the inner deformations and the time evolution of the shape during most of the flow, while a systematic underestimation of the final run-out is observed. The experimental scalings of spreading of the column as a function of the aspect ratio available from the literature are also recovered. A discussion follows on the performances of other rheologies, and on the sensitivity of the simulations to the parameters of the -rheology.
311 citations
"Collapse of a granular column under..." refers methods in this paper
...[24] provides excellent agreement for low to intermediate aspect ratios, but extension of the model to the rotating case requires experimental data prior for verification such as that provided by this study....
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TL;DR: In this paper, the transient surface flow occurring when a cylindrical pile of dry granular material is suddenly allowed to spread on a horizontal plane is investigated experimentally as a function of the released mass M, the initial aspect ratio a of the granular cylinder pile, the properties of the underlying substrate (smooth or rough, rigid or erodible) and the bead size.
Abstract: The transient surface flow occurring when a cylindrical pile of dry granular material is suddenly allowed to spread on a horizontal plane is investigated experimentally as a function of the released mass M, the initial aspect ratio a of the granular cylinder pile, the properties of the underlying substrate (smooth or rough, rigid or erodible) and the bead size. Two different flow regimes leading to three different deposit morphologies are observed as a function of the initial aspect ratio a, whatever the substrate properties and the bead size. For a≲3, the granular mass spreads through an avalanche on its flanks producing either truncated cone or conical deposits. For a≳3, the upper part of the column descends conserving its shape while the foot of the pile propagates radially outward. The obtained deposit looks like a “Mexican hat” and the slope angle at the foot of the deposit is observed to saturate at a value of the order of 5°. For a given ground and bead size, the flow dynamics and the deposit morph...
310 citations
"Collapse of a granular column under..." refers background or result in this paper
...The collapse in the non-rotating case is well reported by previous authors [7,8]....
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...[8], where the avalanching occurs over an internal cone of radius r0 and base angle θμ....
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