Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session H30: Granular Flows: Collision, Impact and Deformation |
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Chair: Robert Behringer, Duke University Room: F151 |
Monday, November 21, 2016 10:40AM - 10:53AM |
H30.00001: Pulling an intruder from a granular material Yue Zhang, R.P. Behringer As a complement to 2D impact experiments, which involves a strongly fluctuating drag force involving collisional momentum transfer from intruder to grains, we consider a controlled 2D pull-out experiments, which is heuristically a reversed version of impact. During the pull-out experiment, a buried intruder is pulled out of a material, starting from rest. In the experiment, the intruder is subject to a gradually increasing upward vertical force, which we increase to the point where the intruder begins to accelerate upwards. To visualize this pulling process, we use 2D photoelastic disks from which circular intruders of different radii are pulled out. We will analyze the dynamics of the intruder and the structures of the force chains inside the granular system, which are captured by a high speed camera. [Preview Abstract] |
Monday, November 21, 2016 10:53AM - 11:06AM |
H30.00002: Dynamics of oblique impact in a 2D photoelastic granular medium Noah Cox, Xinyu Wu, Cacey Stevens Bester, Robert Behringer Penetration of a solid projectile into dry granular matter is studied via two-dimensional impact experiments with bidisperse photoelastic grains. The drag force acting on the projectile is determined by high-speed imaging of the projectile's dynamics combined with the local granular response of the photoelastic grains. This force was previously shown using vertical impact to be the sum of a static, depth-dependent drag and a velocity-dependent inertial drag. Here the impact occurs obliquely, invoking a significant horizontal drag force that has not been fully explored. Accordingly we study the drag force model for oblique impact. We consider the influence of the projectile's impact speed and initial impact angle on its resultant trajectory. The path of the projectile changes drastically with impact angle. We therefore connect the effect of the impact angle to the nature of the drag force exerted on the projectile by the granular medium. [Preview Abstract] |
Monday, November 21, 2016 11:06AM - 11:19AM |
H30.00003: Dynamics of drag force for projectile impact in granular media Lauren Behringer, Cacey Stevens Bester, Robert Behringer We study the way in which momentum is dissipated as a free-falling projectile impacts a dense granular target. An empirical force law has been widely accepted to describe this process, defining the stopping force as the sum of depth-dependent static force and velocity-dependent inertial drag. However, a complete understanding of the stopping force, incorporating grain-scale interactions during impact, remains unresolved. Using direct force measurements by way of a photoelastic imaging technique, we explore the complex fluctuating behavior of the forces acting on the projectile decelerating through a granular medium. Our results are used to study the static drag as the projectile comes to rest, as well as its connection to the effect of the container boundary of the granular target. We additionally vary the shape of the impeding object to infer intruder-grain interactions from force measurements. [Preview Abstract] |
Monday, November 21, 2016 11:19AM - 11:32AM |
H30.00004: Optimize Operating Conditions on Fine Particle Grinding Process with Vertically Stirred Media Mill Yang Yang, Neil Rowson, Andy Ingram Stirred media mill recently is commonly utilized among mining process due to its high stressing intensity and efficiency. However, the relationship between size reduction and flow pattern within the mixing pot is still not fully understand. Thus, this work investigates fine particle grinding process within vertically stirred media mills by altering stirrer geometry, tip speed and solids loading. Positron Emitting Particle Tracking (PEPT) technology is utilized to plot routine of particles velocity map. By tacking trajectory of a single particle movement within the mixing vessel, the overall flow pattern is possible to be plotted. Ground calcium carbonate, a main product of Imerys, is chosen as feeding material (feed size D80 30um) mixed with water to form high viscous suspension. To obtain fine size product (normally D80 approximately 2um), large amount of energy is drawn by grinding mill to break particles through impact, shear attrition or compression or a combination of them. The results indicate higher energy efficient is obtained with more dilute suspension. The optimized stirrer proves more energy-saving performance by altering the slurry circulate. [Preview Abstract] |
Monday, November 21, 2016 11:32AM - 11:45AM |
H30.00005: Biased Brownian motion in narrow channels with asymmetry and anisotropy Kiwing To, Zheng Peng We study Brownian motion of a single millimeter size bead confined in a quasi-two-dimensional horizontal channel with built-in anisotropy and asymmetry. Channel asymmetry is implemented by ratchet walls while anisotropy is introduced using a channel base that is grooved along the channel axis so that a bead can acquire a horizontal impulse perpendicular to the longitudinal direction when it collides with the base. When energy is injected to the channel by vertical vibration, the combination of asymmetric walls and anisotropic base induces an effective force which drives the bead into biased diffusive motion along the channel axis with diffusivity and drift velocity increase with vibration strength. The magnitude of this driving force, which can be measured in experiments of tilted channel, is found to be consistent to those obtained from dynamic mobility and position probability distribution measurements. These results are explained by a simple collision model that suggests the random kinetic energies transfer between different translational degrees of freedom may be turned into useful work in the presence of asymmetry and anisotropy. [Preview Abstract] |
Monday, November 21, 2016 11:45AM - 11:58AM |
H30.00006: Mechanisms of intruder motion in cyclically sheared granular media Hu Zheng, Jonathan Barés, Dong Wang, Robert Behringer We perform an experimental study showing how an intruder, a Teflon disk that experiences a moderate constant force, F, can advance through a granular material that is subject to quasi-static cyclic shear. The large Teflon disk is embedded in a layer of smaller bidisperse photoelastic disks. The granular medium and disk are contained in a horizontal cell, which is deformed from a square to a parallelogram and back again. The area of the cell remains constant throughout, and the protocol corresponds to cyclical simple shear. We find that the net intruder motion per cycle increases as a power law in Nc. The intruder motion relative to the granular background occurs primarily following strain reversals. [Preview Abstract] |
Monday, November 21, 2016 11:58AM - 12:11PM |
H30.00007: Coefficient of restitution and surface deformation for inelastic particle collisions in a liquid Angel Ruiz-Angulo, Melany Hunt Granular flow simulations rely on models of the coefficient of restitution (ratio of rebound speed to impact speed). For collisions in a liquid, the rebound speed depends primarily on the impact Stokes number. In this study, we measure the coefficient of restitution for conditions in which two parameters are important: the Stokes number, St, and the ratio of impact velocity to yield velocity, U$^{\mathrm{\ast }}=$U$_{\mathrm{i}}$/U$_{\mathrm{y}}$, where the yield velocity, U$_{\mathrm{y}}$, is the maximum speed for an elastic collision. We also measure the surface deformation (crater depth and radius) for a range of St, U*, and material properties. The results demonstrate that the surface deformation depends primarily on a corrected U*, which incorporates the velocity decrease due to lubrication forces acting on the particle prior to collision. The particle rebound depends on the elastic strain energy stored during impact and on lubrication losses; these effects are incorporated in a model for the coefficient of restitution. [Preview Abstract] |
Monday, November 21, 2016 12:11PM - 12:24PM |
H30.00008: Effect of bi-modality on sphere penetration into granular media Nadia Kouraytem, Sigurdur Thoroddsen, Jeremy Marston We investigate the penetration of spheres impacting onto granular media, which are compositions of two discrete size ranges, thus creating a bi-modal material. We systematically vary the volume fraction of the two materials and measured the penetration depth over a wide range of impact speeds (0 to 5 m/s), as well as different sphere densities. We see maximum lubricating effects when we add 55{\%} of the small 31-micrometer glass beads to 178-micrometer glass beads. Here the expected penetration depth increases by 60{\%} when compared to a simple model, which is based on interpolating between the values obtained with the two pure monodisperse grains. Less effect is observed when 178-micrometer beads are mixed with a large 425-micrometer beads. We also study the lubrication effect of fine beads on larger rough Ottawa sand, seeing significant effects. [Preview Abstract] |
Monday, November 21, 2016 12:24PM - 12:37PM |
H30.00009: Study of an athermal quasi static plastic deformation in a 2D granular material jie zhang, jie zheng In crystalline materials, the plasticity has been well understood in terms of dynamics of dislocation, i.e. flow defects in the crystals where the flow defects can be directly visualized under a microscope. In a contrast, the plasticity in amorphous materials, i.e. glass, is still poorly understood due to the disordered nature of the materials. In this talk, I will discuss the recent results we have obtained in our ongoing research of the plasticity of a 2D glass in the athermal quasi static limit where the 2D glass is made of bi-disperse granular disks with very low friction. Starting from a densely packed homogeneous and isotropic initial state, we apply pure shear deformation to the system. For a sufficiently small strain, the response of the system is linear and elastic like; when the strain is large enough, the plasticity of the system gradually develops and eventually the shear bands are fully developed. In this study, we are particularly interested in how to relate the local plastic deformation to the macroscopic response of the system and also in the development of the shear bands. [Preview Abstract] |
Monday, November 21, 2016 12:37PM - 12:50PM |
H30.00010: What causes the emergence of force chains in granular materials? Krishnaraj KP, Prabhu R Nott A dense collection of grains may be viewed as a network of contacts which transmit forces. Force transmission in this network is influenced by constraints of geometry and packing, making it significantly different from information, transportation, or power networks. Experiments on two-dimensional disks report the presence of anisotropic quasi-linear structures called force chains, which are assumed to be the cause of their uncommon macroscopic behaviour. Studies have tried to quantify the properties of these structures, but the problem largely remains unresolved. We show using a simple discrete model, that force chain-like features are generic to any Euclidean packing of particles. The packing structure is sufficient to predict the essential features of the force network, regardless of the external forcing or boundary conditions. Using a novel method to study the structure of packing, we quantify the long range correlations in the system. The method reveals important, phase transition-like, properties in particle packings, the critical parameters and exponents of which characterize the geometry of the particle arrangements. [Preview Abstract] |
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