Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session L10: Granular Flows: General 
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Chair: Anthony Rosato, NJIT Room: 110 
Monday, November 23, 2015 4:05PM  4:18PM 
L10.00001: Dynamics of a Tapped Granular Column Anthony Rosato, Denis Blackmore, Luo Zuo, Wu Hao, David Horntrop We consider the behavior of a column of spheres subjected to a timedependent vertical taps. Of interest are various dynamical properties, such as the motion of its mass center, its response to taps of different intensities and forms, and the effect of system size and material properties. The interplay between diverse time and length scales are the key contributors to the column's evolving dynamics. Soft sphere discrete element simulations were conducted over a very wide parameter space to obtain a portrait of column behavior as embodied by the collective dynamics of the mass center motion. Results compared favorably with a derived reducedorder paradigm of the mass center motion (surprisingly analogous to that for a single bouncing ball on an oscillating plate) with respect to dynamical regimes and their transitions. A continuum model obtained from a system of Newtonian equations, as a locally averaged limit in the transport mode along trajectories is described, and a numerical solution protocol for a onedimensional system is outlined. Typical trajectories and density evolution profiles are shown. We conclude with a discussion of our investigations to relate predictions of the continuum and reduced dynamical systems models with discrete simulations. [Preview Abstract] 
Monday, November 23, 2015 4:18PM  4:31PM 
L10.00002: Spreading granular material with a blade Emilie Dressaire, Vachitar Singh, Emma Grimaldi, Alban Sauret The spreading of a complex fluid with a blade is encountered in applications that range from the bulldozing of granular material in construction projects to the coating of substrates with fluids in industrial applications. This spreading process is also present in everyday life, when we use a knife to turn a lump of peanut butter into a thin layer over our morning toast. In this study, we rely on granular media in a model experiment to describe the threedimensional spreading of the material. Our experimental setup allows tracking the spreading of a sandpile on a translating flat surface as the blade remains fixed. We characterize the spreading dynamics and the shape of the spread fluid layer when varying the tilt of the blade, its spacing with the surface and its speed. Our findings suggest that it is possible to tune the spreading parameters to optimize the coating. [Preview Abstract] 
Monday, November 23, 2015 4:31PM  4:44PM 
L10.00003: Granular media in transformation: dynamics and structure Aymeric Merceron, Pierre Jop, Alban Sauret Sintering, glass melting and other industrially relevant processes turn batches of grains into continuous end products. Such processes involve complex and mostly misunderstood chemical and physical transformations of the granular packing. Affecting the contact network, physicochemical reactions entail mechanical rearrangements. But such reorganizations may also trigger new potential reactions. Granular reactive systems are strongly coupled and need investigations for achieving industrial optimizations. This study is focused on how transformations appearing on its components affect the response of the granular packing. Inert brass disks and grains undergoing wellknown transformations like volume decrease are mixed and then confined in a vertical 2D cell. While the system reacts, the granular packing is regularly photographed with a highresolution camera. Events largely distributed both spatially and temporally occur around reactive grains. Thanks to image processing, this reorganization process is then analyzed. Spatial and temporal amplitudes of events are quantified as well as their local and global impacts on the granular structure. [Preview Abstract] 
Monday, November 23, 2015 4:44PM  4:57PM 
L10.00004: DEM simulations of shear flow of spherical particles mixed with long granular rods Oleh Baran Using Discrete Element Method (DEM) I investigate the effect of adding rigid rodshape particles to the granular flow of spherical particles inside ring shear tester. The simulated geometry includes an annulus, bounded by two concentric cylindrical walls rested on a stationary bottom disk and covered with a top lid. Both the top lid and the bottom have protruding vanes oriented radially and uniformly spaced around the annulus, to prevent slipping of the bulk solid, see \underline {image at this link}. The top lid rotates with a controlled angular speed and applies a constant normal load to the tested material. I analyze the results for shear stress on the top lid as a function of time for the mixture of spheres and rods and compare these results with ones obtained for the same amount of spherical particles without rods. I also present the analysis of the orientation of granular rods in a shear flow and discuss the results in terms of new timescale related to the mobility of rods. [Preview Abstract] 
(Author Not Attending)

L10.00005: Novel Discrete Element Method for 3D nonspherical granular particles. Luuk Seelen, Johan Padding, Hans Kuipers Granular materials are common in many industries and nature. The different properties from solid behavior to fluid like behavior are well known but less well understood. The main aim of our work is to develop a discrete element method (DEM) to simulate nonspherical granular particles. The nonspherical shape of particles is important, as it controls the behavior of the granular materials in many situations, such as static systems of packed particles. In such systems the packing fraction is determined by the particle shape. We developed a novel 3D discrete element method that simulates the particleparticle interactions for a wide variety of shapes. The model can simulate quadratic shapes such as spheres, ellipsoids, cylinders. More importantly, any convex polyhedron can be used as a granular particle shape. These polyhedrons are very well suited to represent nonrounded sand particles. The main difficulty of any nonspherical DEM is the determination of particleparticle overlap. Our model uses two iterative geometric algorithms to determine the overlap. The algorithms are robust and can also determine multiple contact points which can occur for these shapes. With this method we are able to study different applications such as the discharging of a hopper or silo. Another application the creation of a random close packing, to determine the solid volume fraction as a function of the particle shape. [Preview Abstract] 
Monday, November 23, 2015 5:10PM  5:23PM 
L10.00006: Stability and Structure of StarShape Granules Yuchen Zhao, Jonathan Bares, Matthew Zheng, Karola Dierichs, Achim Menges, Robert Behringer Columns are made of convex noncohesive grains like sand collapse after being released from initial positions. On the other hand, various architectures built by concave grains can maintain stability. We explore why these structures are stable, and how stable they can be. We performed experiments by randomly pouring identical starshape particles into hollow cylinders left on glass and a rough base, and observed stable granular columns after lifting the cylinders. Particles have six $9\,mm$ arms, which extend symmetrically in the xyz directions. Both the probability of creating a stable column and mechanical stability aspects have been investigated. We define $r$ as the weight fraction of particles that fall out of the column after removing confinement. $r$ gradually increases as the column height increases, or the column diameter decreases. We also explored different experiment conditions such as vibration of columns with confinement, or large basal friction. We also consider different stability measures such as the maximum inclination angle or maximum weight a column can support. In order to understand structure leading to stability, 3D CT scan reconstructions of columns have been done and coordination number and packing density will be discussed. [Preview Abstract] 
Monday, November 23, 2015 5:23PM  5:36PM 
L10.00007: Simulating flow and segregation of cylindrical particles Yongzhi Zhao, Paul B. Umbanhowar, Richard M. Lueptow Efficient and accurate simulation of cylindrical particles using discrete element method (DEM) is a challenge. Typical approaches to simulating cylindrical particle systems are based on the glued spheres method, which has low accuracy, or real shape models, which have high computational cost. In this work we utilize superellipsoids, which belong to superquadrics, to model cylindrical particles in DEM simulations. Simulations of a single cylinder impacting a flat wall indicate that superellipsoids provide the same accuracy as real shape models and much better accuracy than the glued sphere method. Simulations of superellipsoid cylindrical particles in rotating tumblers result in nearly the same angle of repose as experiments and real shape simulations, demonstrating the accuracy of superellipsoid DEM simulations for multiparticle systems. The segregation of bidisperse cylindrical particles differing in length in a bounded heap was simulated by superellipsoid DEM, and the results are similar to the experiment. In spite of these advantages of using superellipsoid cylindrical particles, simulations of filling a box with particles indicate that the simulation times for superellipsoid cylinders is about an order of magnitude longer than that for the same number of spherical particles. [Preview Abstract] 
Monday, November 23, 2015 5:36PM  5:49PM 
L10.00008: Cohesion of wet grains at high liquid content Pascal Raux, Lyderic Bocquet, AnneLaure Biance Adding liquid to a granular medium highly increases its cohesion, due to the creation of capillary bridges between grains. From the paste obtained by mixing a large amount of water to spherical glass beads ($\sim 100~\mathrm{\mu m}$), we cast a compact beam. We study its rupture under its own weight, then deduce the cohesive strength, which increases with water content. This behavior diverges from what is expected from individual capillary bridges, suggesting a role of the liquid repartition in the granular medium. [Preview Abstract] 

L10.00009: ABSTRACT WITHDRAWN 
Monday, November 23, 2015 6:02PM  6:15PM 
L10.00010: Flowing layer kinematics for constant dimension flowing layers with variable erosion velocities Adam Spitulnik, Nicholas Pohlman Simulations of granular flow assume a consistent flowing layer profile observed in circular tumblers that were half full. While the constant shear rate model predicts mixing kinematics adequately, the model has not been empirically tested in systems where the erosion from the solid body has velocity components along the dynamic angle of repose. This research reports on experiments where the relationship between tumbler fill fraction and the kinematics of the erosion boundary transition into the flowing layer is analyzed. Tumblers greater than 50\% full have inertial velocity along the angle of repose; fill conditions less than 50\% enter with velocity opposite the free surface angle. Results show that varying the fill level while maintaining constant flowing layer length does not change the advection pattern within the flowing layer. The conclusion is that the 50\% model is independent of fill level due to the kinetic energy of the flowing layer exceeding the potential energy at the erosion boundary. [Preview Abstract] 
Monday, November 23, 2015 6:15PM  6:28PM 
L10.00011: Models for grains and gas ejection dynamics from a silo Yixian Zhou, Pascale Aussillous, Pierre Ruyer In the hypothetical conditions of a reactivity initiated accident in a nuclear power plant, some of the fuel rods could break. If fuel fragmentation occurs, hot fuel particles and pressurized gas could interact with the surrounding fluid. The violence of this interaction depends on the discharge rate toward the fluid. In the present work, we study the discharge dynamics and identify the parameters governing this flow. In this paper, we focus on the experimental study of the discharge of a silo composed of spherical glass beads, with an orifice either lateral or at the bottom, with or without air flow. The measured parameters are the mass flow rate and the pressure along the silo, whereas the controlled parameters are the size of particles, the size of orifices, and the flow rate of air. For the case without air flow we found that the flow rate of particles ejected from the bottom orifice is 3 times greater than from the lateral orifice. For the case of a lateral orifice, when the form of the orifice is rectangular with width $W$ and height $D$, we identify two regimes which depend on the ratio of width to height $W/D$. For the case with air flow, we found that the flow rate increases with the air flow. A simple physical model is proposed to describe the grains and gas ejection. [Preview Abstract] 
Monday, November 23, 2015 6:28PM  6:41PM 
L10.00012: Sound of silo's: An experimental investigation into sound emissions from granular flows in a vertical tube Elze Porte, Marc Masen, Nathalie Vriend, Andre de Boer When large storage silo’s containing granular material are discharged, a loud sound emits from the silo. The noise causes disturbances for people working on site and for nearby residential areas. Insufficient knowledge exists to solve the problem efficiently and adequately. An experimental study using a scaled silo setup shows that the particle flow dynamics and system characteristics are both actors in determining the occurrence of the sound and its frequency. The extensive use of frequency analysis provides new insights into the complexity of the related parameters. The particle flow and tube characteristics are manipulated by changing the outflow rate, bulk material, wall material, wall pressure and tube dimensions. Frequency analysis of the recorded sound shows that the frequency depends on both the externally forced parameter changes and internal changes during flow. The latter indicates that during the flow, characteristic properties such as the packing fraction and sound speed change. As a result, the frequency changes as well. However, the external parameters that are manipulated as an initial condition are equally important in describing the frequency response. [Preview Abstract] 
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