WorldWideScience

Sample records for granular flow encompasses

  1. Granular flow

    DEFF Research Database (Denmark)

    Mitarai, Namiko; Nakanishi, Hiizu

    2012-01-01

    Granular material is a collection of macroscopic particles that are visible with naked eyes. The non-equilibrium nature of the granular materials makes their rheology quite different from that of molecular systems. In this minireview, we present the unique features of granular materials focusing...... on the shear flow of dry granular materials and granule-liquid mixture....

  2. Granular flows in constrained geometries

    Science.gov (United States)

    Murthy, Tejas; Viswanathan, Koushik

    Confined geometries are widespread in granular processing applications. The deformation and flow fields in such a geometry, with non-trivial boundary conditions, determine the resultant mechanical properties of the material (local porosity, density, residual stresses etc.). We present experimental studies of deformation and plastic flow of a prototypical granular medium in different nontrivial geometries- flat-punch compression, Couette-shear flow and a rigid body sliding past a granular half-space. These geometries represent simplified scaled-down versions of common industrial configurations such as compaction and dredging. The corresponding granular flows show a rich variety of flow features, representing the entire gamut of material types, from elastic solids (beam buckling) to fluids (vortex-formation, boundary layers) and even plastically deforming metals (dead material zone, pile-up). The effect of changing particle-level properties (e.g., shape, size, density) on the observed flows is also explicitly demonstrated. Non-smooth contact dynamics particle simulations are shown to reproduce some of the observed flow features quantitatively. These results showcase some central challenges facing continuum-scale constitutive theories for dynamic granular flows.

  3. Granular flows: fundamentals and applications

    Science.gov (United States)

    Cleary, Paul W.

    DEM allows the prediction of complex industrial and geophysical particle flows. The importance of particle shape is demonstrated through a series of simple examples. Shape controls resistance to shear, the magnitude of collision stress, dilation and the angle of repose. We use a periodic flow of a bed of particles to demonstrate the different states of granular matter, the generation of dilute granular flow when granular temperature is high and the flow dependent nature of the granular thermodynamic boundary conditions. A series of industrial case studies examines how DEM can be used to understand and improve processes such as separation, mixing, grinding, excavation, hopper discharge, metering and conveyor interchange. Finally, an example of landslide motion over real topography is presented.

  4. A constitutive law for dense granular flows.

    Science.gov (United States)

    Jop, Pierre; Forterre, Yoël; Pouliquen, Olivier

    2006-06-08

    A continuum description of granular flows would be of considerable help in predicting natural geophysical hazards or in designing industrial processes. However, the constitutive equations for dry granular flows, which govern how the material moves under shear, are still a matter of debate. One difficulty is that grains can behave like a solid (in a sand pile), a liquid (when poured from a silo) or a gas (when strongly agitated). For the two extreme regimes, constitutive equations have been proposed based on kinetic theory for collisional rapid flows, and soil mechanics for slow plastic flows. However, the intermediate dense regime, where the granular material flows like a liquid, still lacks a unified view and has motivated many studies over the past decade. The main characteristics of granular liquids are: a yield criterion (a critical shear stress below which flow is not possible) and a complex dependence on shear rate when flowing. In this sense, granular matter shares similarities with classical visco-plastic fluids such as Bingham fluids. Here we propose a new constitutive relation for dense granular flows, inspired by this analogy and recent numerical and experimental work. We then test our three-dimensional (3D) model through experiments on granular flows on a pile between rough sidewalls, in which a complex 3D flow pattern develops. We show that, without any fitting parameter, the model gives quantitative predictions for the flow shape and velocity profiles. Our results support the idea that a simple visco-plastic approach can quantitatively capture granular flow properties, and could serve as a basic tool for modelling more complex flows in geophysical or industrial applications.

  5. A numerical study of granular dam-break flow

    Science.gov (United States)

    Pophet, N.; Rébillout, L.; Ozeren, Y.; Altinakar, M.

    2017-12-01

    Accurate prediction of granular flow behavior is essential to optimize mitigation measures for hazardous natural granular flows such as landslides, debris flows and tailings-dam break flows. So far, most successful models for these types of flows focus on either pure granular flows or flows of saturated grain-fluid mixtures by employing a constant friction model or more complex rheological models. These saturated models often produce non-physical result when they are applied to simulate flows of partially saturated mixtures. Therefore, more advanced models are needed. A numerical model was developed for granular flow employing a constant friction and μ(I) rheology (Jop et al., J. Fluid Mech. 2005) coupled with a groundwater flow model for seepage flow. The granular flow is simulated by solving a mixture model using Finite Volume Method (FVM). The Volume-of-Fluid (VOF) technique is used to capture the free surface motion. The constant friction and μ(I) rheological models are incorporated in the mixture model. The seepage flow is modeled by solving Richards equation. A framework is developed to couple these two solvers in OpenFOAM. The model was validated and tested by reproducing laboratory experiments of partially and fully channelized dam-break flows of dry and initially saturated granular material. To obtain appropriate parameters for rheological models, a series of simulations with different sets of rheological parameters is performed. The simulation results obtained from constant friction and μ(I) rheological models are compared with laboratory experiments for granular free surface interface, front position and velocity field during the flows. The numerical predictions indicate that the proposed model is promising in predicting dynamics of the flow and deposition process. The proposed model may provide more reliable insight than the previous assumed saturated mixture model, when saturated and partially saturated portions of granular mixture co-exist.

  6. Traffic and Granular Flow ’03

    CERN Document Server

    Luding, Stefan; Bovy, Piet; Schreckenberg, Michael; Wolf, Dietrich

    2005-01-01

    These proceedings are the fifth in the series Traffic and Granular Flow, and we hope they will be as useful a reference as their predecessors. Both the realistic modelling of granular media and traffic flow present important challenges at the borderline between physics and engineering, and enormous progress has been made since 1995, when this series started. Still the research on these topics is thriving, so that this book again contains many new results. Some highlights addressed at this conference were the influence of long range electric and magnetic forces and ambient fluids on granular media, new precise traffic measurements, and experiments on the complex decision making of drivers. No doubt the “hot topics” addressed in granular matter research have diverged from those in traffic since the days when the obvious analogies between traffic jams on highways and dissipative clustering in granular flow intrigued both c- munities alike. However, now just this diversity became a stimulating feature of the ...

  7. NMR Measurements of Granular Flow and Compaction

    Science.gov (United States)

    Fukushima, Eiichi

    1998-03-01

    Nuclear magnetic resonance (NMR) can be used to measure statistical distributions of granular flow velocity and fluctuations of velocity, as well as spatial distributions of particulate concentration, flow velocity, its fluctuations, and other parameters that may be derived from these. All measurements have been of protons in liquid-containing particles such as mustard seeds or pharmaceutical pills. Our favorite geometry has been the slowly rotating partially filled rotating drum with granular flow taking place along the free surface of the particles. All the above-mentioned parameters have been studied as well as a spatial distribution of particulate diffusion coefficients, energy dissipation due to collisions, as well as segregation of non-uniform mixtures of granular material. Finally, we describe some motions of granular material under periodic vibrations.

  8. Critical phenomenon of granular flow on a conveyor belt.

    Science.gov (United States)

    De-Song, Bao; Xun-Sheng, Zhang; Guang-Lei, Xu; Zheng-Quan, Pan; Xiao-Wei, Tang; Kun-Quan, Lu

    2003-06-01

    The relationship between the granular wafer movement on a two-dimensional conveyor belt and the size of the exit together with the velocity of the conveyor belt has been studied in the experiment. The result shows that there is a critical speed v(c) for the granular flow when the exit width d is fixed (where d=R/D, D being the diameter of a granular wafers). When vv(c), the flow rate Q is described as Q=Crho(v)(beta)(d-k)(3/2). These are the effects of the interaction among the granular wafers and the change of the states of the granular flow due to the changing of the speed or the exit width d.

  9. A hydrodynamic model for granular material flows including segregation effects

    Science.gov (United States)

    Gilberg, Dominik; Klar, Axel; Steiner, Konrad

    2017-06-01

    The simulation of granular flows including segregation effects in large industrial processes using particle methods is accurate, but very time-consuming. To overcome the long computation times a macroscopic model is a natural choice. Therefore, we couple a mixture theory based segregation model to a hydrodynamic model of Navier-Stokes-type, describing the flow behavior of the granular material. The granular flow model is a hybrid model derived from kinetic theory and a soil mechanical approach to cover the regime of fast dilute flow, as well as slow dense flow, where the density of the granular material is close to the maximum packing density. Originally, the segregation model has been formulated by Thornton and Gray for idealized avalanches. It is modified and adapted to be in the preferred form for the coupling. In the final coupled model the segregation process depends on the local state of the granular system. On the other hand, the granular system changes as differently mixed regions of the granular material differ i.e. in the packing density. For the modeling process the focus lies on dry granular material flows of two particle types differing only in size but can be easily extended to arbitrary granular mixtures of different particle size and density. To solve the coupled system a finite volume approach is used. To test the model the rotational mixing of small and large particles in a tumbler is simulated.

  10. The behaviour of free-flowing granular intruders

    Directory of Open Access Journals (Sweden)

    Wyburn Edward

    2017-01-01

    Full Text Available Particle shape affects both the quasi-static and dynamic behaviour of granular media. There has been significant research devoted to the flowability of systems of irregularly shaped particles, as well as the flow of grains around fixed intruders, however the behaviour of free flowing intruders within granular flows remains comparatively unexplored. Here, the effect of the shape of these intruder particles is studied, looking at the kinematic behaviour of the intruders and in particular their tendency of orientation. Experiments are carried out within the Stadium Shear Device, which is a novel apparatus able to continuously apply simple shear conditions to two-dimensional grain analogues. It is found that the intruder shows different behaviour to that of the bulk flow, and that this behaviour is strongly shape dependent. These insights could lead to the development of admixtures that alter the flowability of granular materials.

  11. How granular vortices can help understanding rheological and mixing properties of dense granular flows

    Directory of Open Access Journals (Sweden)

    Rognon Pierre

    2017-01-01

    Full Text Available Dense granular flows exhibit fascinating kinematic patterns characterised by strong fluctuations in grain velocities. In this paper, we analyse these fluctuations and discuss their possible role on macroscopic properties such as effective viscosity, non-locality and shear-induced diffusion. The analysis is based on 2D experimental granular flows performed with the stadium shear device and DEM simulations. We first show that, when subjected to shear, grains self-organised into clusters rotating like rigid bodies. The average size of these so-called granular vortices is found to increase and diverge for lower inertial numbers, when flows decelerate and stop. We then discuss how such a microstructural entity and its associated internal length scale, possibly much larger than a grain, may be used to explain two important properties of dense granular flows: (i the existence of shear-induced diffusion of grains characterised by a shear-rate independent diffusivity and (ii the development of boundary layers near walls, where the viscosity is seemingly lower than the viscosity far from walls.

  12. Granular flow down a flexible inclined plane

    Directory of Open Access Journals (Sweden)

    Sonar Prasad

    2017-01-01

    Full Text Available Discrete and continuous systems are commonly studied individually, but seldom together. Indeed, granular flows are typically studied through flows over a rigid base. Here, we investigate the behaviour of granular flows over an inclined, flexible base. The flexible base is modeled as a rigid platform mounted on springs and has one degree of freedom. The base vibrations are introduced by the flow. We simulate such flows through a discrete element method and compare with experiments. We find that a flexible base increased the upper limit of the inclination up to which a steady flow is possible by at least 3 degrees. This stabilized zone may have important implications in applications such as conveyor belts and chutes.

  13. Oblique shock waves in granular flows over bluff bodies

    Directory of Open Access Journals (Sweden)

    Gopan Nandu

    2017-01-01

    Full Text Available Granular flows around an object have been the focus of numerous analytical, experimental and simulation studies. The structure and nature of the oblique shock wave developed when a quasi-two dimensional flow of spherical granular particles streams past an immersed, fixed cylindrical obstacle forms the focus of this study. The binary granular mixture, consisting of particles of the same diameter but different material properties, is investigated by using a modified LIGGGHTS package as the simulation engine. Variations in the solid fraction and granular temperature within the resulting flow are studied. The Mach number is calculated and is used to distinguish between the subsonic and the supersonic regions of the bow shock.

  14. Centrifuge modelling of granular flows

    Science.gov (United States)

    Cabrera, Miguel Angel; Wu, Wei

    2015-04-01

    A common characteristic of mass flows like debris flows, rock avalanches and mudflows is that gravity is their main driving force. Gravity defines the intensity and duration of the main interactions between particles and their surrounding media (particle-particle, particle-fluid, fluid-fluid). At the same time, gravity delimits the occurrence of phase separation, inverse segregation, and mass consolidation, among other phenomena. Therefore, in the understanding of the flow physics it is important to account for the scaling of gravity in scaled models. In this research, a centrifuge model is developed to model free surface granular flows down an incline at controlled gravity conditions. Gravity is controlled by the action of an induced inertial acceleration field resulting from the rotation of the model in a geotechnical centrifuge. The characteristics of the induced inertial acceleration field during flow are discussed and validated via experimental data. Flow heights, velocity fields, basal pressure and impact forces are measured for a range of channel inclinations and gravity conditions. Preliminary results enlighten the flow characteristics at variable gravity conditions and open a discussion on the simulation of large scale processes at a laboratory scale. Further analysis on the flow physics brings valuable information for the validation of granular flows rheology.

  15. A particle-based method for granular flow simulation

    KAUST Repository

    Chang, Yuanzhang; Bao, Kai; Zhu, Jian; Wu, Enhua

    2012-01-01

    We present a new particle-based method for granular flow simulation. In the method, a new elastic stress term, which is derived from a modified form of the Hooke's law, is included in the momentum governing equation to handle the friction of granular materials. Viscosity force is also added to simulate the dynamic friction for the purpose of smoothing the velocity field and further maintaining the simulation stability. Benefiting from the Lagrangian nature of the SPH method, large flow deformation can be well handled easily and naturally. In addition, a signed distance field is also employed to enforce the solid boundary condition. The experimental results show that the proposed method is effective and efficient for handling the flow of granular materials, and different kinds of granular behaviors can be well simulated by adjusting just one parameter. © 2012 Science China Press and Springer-Verlag Berlin Heidelberg.

  16. A particle-based method for granular flow simulation

    KAUST Repository

    Chang, Yuanzhang

    2012-03-16

    We present a new particle-based method for granular flow simulation. In the method, a new elastic stress term, which is derived from a modified form of the Hooke\\'s law, is included in the momentum governing equation to handle the friction of granular materials. Viscosity force is also added to simulate the dynamic friction for the purpose of smoothing the velocity field and further maintaining the simulation stability. Benefiting from the Lagrangian nature of the SPH method, large flow deformation can be well handled easily and naturally. In addition, a signed distance field is also employed to enforce the solid boundary condition. The experimental results show that the proposed method is effective and efficient for handling the flow of granular materials, and different kinds of granular behaviors can be well simulated by adjusting just one parameter. © 2012 Science China Press and Springer-Verlag Berlin Heidelberg.

  17. 11th Traffic and Granular Flow Conference

    CERN Document Server

    Daamen, Winnie

    2016-01-01

    The Conference on Traffic and Granular Flow brings together international researchers from different fields ranging from physics to computer science and engineering to discuss the latest developments in traffic-related systems. Originally conceived to facilitate new ideas by considering the similarities of traffic and granular flow, TGF'15, organised by Delft University of Technology, now covers a broad range of topics related to driven particle and transport systems. Besides the classical topics of granular flow and highway traffic, its scope includes data transport (Internet traffic), pedestrian and evacuation dynamics, intercellular transport, swarm behaviour and the collective dynamics of other biological systems. Recent advances in modelling, computer simulation and phenomenology are presented, and prospects for applications, for example to traffic control, are discussed. The conference explores the interrelations between the above-mentioned fields and offers the opportunity to stimulate interdisciplinar...

  18. Traffic and Granular Flow ’07

    CERN Document Server

    Chevoir, François; Gondret, Philippe; Lassarre, Sylvain; Lebacque, Jean-Patrick; Schreckenberg, Michael

    2009-01-01

    This book covers several research fields, all of which deal with transport. Three main topics are treated: road traffic, granular matter, and biological transport. Different points of view, i.e. modelling, simulations, experiments, and phenomenological observations, are considered. Sub-topics include: highway or urban vehicular traffic (dynamics of traffic, macro/micro modelling, measurements, data analysis, security issues, psychological issues), pedestrian traffic, animal traffic (e.g. social insects), collective motion in biological systems (molecular motors...), granular flow (dense flows, intermittent flows, solid/liquid transition, jamming, force networks, fluid and solid friction), networks (biological networks, urban traffic, the internet, vulnerability of networks, optimal transport networks) and cellular automata applied to the various aforementioned fields.

  19. Assessing continuum postulates in simulations of granular flow

    Energy Technology Data Exchange (ETDEWEB)

    Rycroft, Chris; Kamrin, Ken; Bazant, Martin

    2008-08-26

    Continuum mechanics relies on the fundamental notion of a mesoscopic volume"element" in which properties averaged over discrete particles obey deterministic relationships. Recent work on granular materials suggests a continuum law may be inapplicable, revealing inhomogeneities at the particle level, such as force chains and slow cage breaking. Here, we analyze large-scale three-dimensional Discrete-Element Method (DEM) simulations of different granular flows and show that an approximate"granular element" defined at the scale of observed dynamical correlations (roughly three to five particle diameters) has a reasonable continuum interpretation. By viewing all the simulations as an ensemble of granular elements which deform and move with the flow, we can track material evolution at a local level. Our results confirm some of the hypotheses of classical plasticity theory while contradicting others and suggest a subtle physical picture of granular failure, combining liquid-like dependence on deformation rate and solid-like dependence on strain. Our computational methods and results can be used to guide the development of more realistic continuum models, based on observed local relationships betweenaverage variables.

  20. International Workshop on Traffic and Granular Flow

    CERN Document Server

    Herrmann, Hans; Schreckenberg, Michael; Wolf, Dietrich; Social, Traffic and Granular Dynamics

    2000-01-01

    "Are there common phenomena and laws in the dynamic behavior of granular materials, traffic, and socio-economic systems?" The answers given at the international workshop "Traffic and Granular Flow '99" are presented in this volume. From a physical standpoint, all these systems can be treated as (self)-driven many-particle systems with strong fluctuations, showing multistability, phase transitions, non-linear waves, etc. The great interest in these systems is due to several unexpected new discoveries and their practical relevance for solving some fundamental problems of today's societies. This includes intelligent measures for traffic flow optimization and methods from "econophysics" for stabilizing (stock) markets.

  1. Blurring the boundary between rapid granular flow and dense granular flow regimes: Evidence from DEM simulations

    Science.gov (United States)

    Tripathi, Anurag; Prasad, Mahesh; Kumar, Puneet

    2017-11-01

    The saturation of the effective friction coefficient for granular flows at high inertial numbers has been assumed widely by researchers, despite little simulation/experimental evidence. In contrast, a recent simulation study of plane shear flows by Mandal and Khakhar, suggests that the effective friction coefficient becomes maximum and then starts to decrease with increase in the inertial number for I > 0.5 . In order to investigate whether such a dip at higher inertial numbers is indeed a feature of granular rheology, we perform DEM simulations of chute flow of highly inelastic disks. We show that steady, fully developed flows are possible at inclinations much higher than those normally reported in literature. At such high inclinations, the flow is characterised by a significant slip at the base; the height of the layer increases by more than 300 % and kinetic energy of the layer increases by nearly 5 orders of magnitude. We observe, for the first time, steady chute flows at inertial number I 2 and show that the dip at higher inertial numbers can be observed in case of chute flow as well. The predictions of modified μ - I rheology, however, seem to remain valid in the bulk of the layer for packing fractions as low as 0.2. AT acknowledges the funding obtained from IIT Kanpur through the initiation Grant for this study.

  2. Physical modelling of granular flows at multiple-scales and stress levels

    Science.gov (United States)

    Take, Andy; Bowman, Elisabeth; Bryant, Sarah

    2015-04-01

    The rheology of dry granular flows is an area of significant focus within the granular physics, geoscience, and geotechnical engineering research communities. Studies performed to better understand granular flows in manufacturing, materials processing or bulk handling applications have typically focused on the behavior of steady, continuous flows. As a result, much of the research on relating the fundamental interaction of particles to the rheological or constitutive behaviour of granular flows has been performed under (usually) steady-state conditions and low stress levels. However, landslides, which are the primary focus of the geoscience and geotechnical engineering communities, are by nature unsteady flows defined by a finite source volume and at flow depths much larger than typically possible in laboratory experiments. The objective of this paper is to report initial findings of experimental studies currently being conducted using a new large-scale landslide flume (8 m long, 2 m wide slope inclined at 30° with a 35 m long horizontal base section) and at elevated particle self-weight in a 10 m diameter geotechnical centrifuge to investigate the granular flow behavior at multiple-scales and stress levels. The transparent sidewalls of the two flumes used in the experimental investigation permit the combination of observations of particle-scale interaction (using high-speed imaging through transparent vertical sidewalls at over 1000 frames per second) with observations of the distal reach of the landslide debris. These observations are used to investigate the applicability of rheological models developed for steady state flows (e.g. the dimensionless inertial number) in landslide applications and the robustness of depth-averaged approaches to modelling dry granular flow at multiple scales. These observations indicate that the dimensionless inertial number calculated for the flow may be of limited utility except perhaps to define a general state (e.g. liquid

  3. Experimental and analytical investigations of granular materials: Shear flow and convective heat transfer

    Science.gov (United States)

    Ahn, Hojin

    1989-12-01

    Granular materials flowing down an inclined chute were studied experimentally and analytically. Characteristics of convective heat transfer to granular flows were also investigated experimentally and numerically. Experiments on continuous, steady flows of granular materials in an inclined chute were conducted with the objectives of understanding the characteristics of chute flows and of acquiring information on the rheological behavior of granular material flow. Existing constitutive equations and governing equations were used to solve for fully developed chute flows of granular materials, and thus the boundary value problem was formulated with two parameters (the coefficient of restitution between particles, and the chute inclination) and three boundary values at the chute base wall (the values of solid fraction, granular temperature, and mean velocity at the wall). The boundary value problem was numerically solved by the shooting method. These analytical results were also compared with the present experimental values and with the computer simulations by other investigators in their literature. Experiments on heat transfer to granular flows over a flat heating plate were conducted with three sizes of glass beads, polystyrene beads, and mustard seeds. A modification on the existing model for the convective heat transfer was made using the effective Nusselt number and the effective Peclet number, which include the effects of solid fraction variations. The slightly modified model could describe the heat transfer characteristics of both fast and slow flows (supercritical and subcritical). A numerical analysis of the transfer to granular flows was also performed. The results were compared with the present experimental data, and reasonable agreement was found in the comparison.

  4. Measurements of granular flow dynamics with high speed digital images

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Jingeol [Univ. of Florida, Gainesville, FL (United States)

    1994-01-01

    The flow of granular materials is common to many industrial processes. This dissertation suggests and validates image processing algorithms applied to high speed digital images to measure the dynamics (velocity, temperature and volume fraction) of dry granular solids flowing down an inclined chute under the action of gravity. Glass and acrylic particles have been used as granular solids in the experiment. One technique utilizes block matching for spatially averaged velocity measurements of the glass particles. This technique is compared with the velocity measurement using an optic probe which is a conventional granular flow velocity measurement device. The other technique for measuring the velocities of individual acrylic particles is developed with correspondence using a Hopfield network. This technique first locates the positions of particles with pattern recognition techniques, followed by a clustering technique, which produces point patterns. Also, several techniques are compared for particle recognition: synthetic discriminant function (SDF), minimum average correlation energy (MACE) filter, modified minimum average correlation energy (MMACE) filter and variance normalized correlation. The author proposes an MMACE filter which improves generalization of the MACE filter by adjusting the amount of averaged spectrum of training images in the spectrum whitening stages of the MACE filter. Variance normalized correlation is applied to measure the velocity and temperature of flowing glass particles down the inclined chute. The measurements are taken for the steady and wavy flow and qualitatively compared with a theoretical model of granular flow.

  5. Bedrock erosion by sliding wear in channelized granular flow

    Science.gov (United States)

    Hung, C. Y.; Stark, C. P.; Capart, H.; Smith, B.; Maia, H. T.; Li, L.; Reitz, M. D.

    2014-12-01

    Boundary forces generated by debris flows can be powerful enough to erode bedrock and cause considerable damage to infrastructure during runout. Bedrock wear can be separated into impact and sliding wear processes. Here we focus on sliding wear. We have conducted experiments with a 40-cm-diameter grainflow-generating rotating drum designed to simulate dry channelized debris flows. To generate sliding erosion, we placed a 20-cm-diameter bedrock plate axially on the back wall of the drum. The rotating drum was half filled with 2.3-mm-diameter grains, which formed a thin grain-avalanching layer with peak flow speed and depth close to the drum axis. The whole experimental apparatus was placed on a 100g-ton geotechnical centrifuge and, in order to scale up the stress level, spun to a range of effective gravity levels. Rates and patterns of erosion of the bedrock plate were mapped after each experiment using 3d micro-photogrammetry. High-speed video and particle tracking were employed to measure granular flow dynamics. The resulting data for granular velocities and flow geometry were used to estimate impulse exchanges and forces on the bedrock plate. To address some of the complexities of granular flow under variable gravity levels, we developed a continuum model framed around a GDR MiDi rheology. This model allowed us to scale up boundary forcing while maintaining the same granular flow regime, and helped us to understand important aspects of the flow dynamics including e.g. fluxes of momentum and kinetic energy. In order to understand the detailed processes of boundary forcing, we performed numerical simulations with a new contact dynamics model. This model confirmed key aspects of our continuum model and provided information on second-order behavior such as fluctuations in the forces acting on the wall. By combining these measurements and theoretical analyses, we have developed and calibrated a constitutive model for sliding wear that is a threshold function of

  6. Granular flow through an aperture: influence of the packing fraction

    OpenAIRE

    Alejandra Aguirre , Maria; De Schant , Rosario; Géminard , Jean-Christophe

    2014-01-01

    For the last 50 years, the flow of a granular material through an aperture has been intensely studied in gravity-driven vertical systems (e.g. silos and hoppers). Nevertheless, in many industrial applications, grains are horizontally transported at constant velocity, lying on conveyor belts or floating on the surface of flowing liquids. Unlike fluid flows, that are controlled by the pressure, granular flow is not sensitive to the local pressure but rather to the local velocity of the grains a...

  7. Lift on side by side intruders of various geometries within a granular flow

    Science.gov (United States)

    Acevedo-Escalante, M. F.; Caballero-Robledo, G. A.

    2017-06-01

    Obstacles within fluids have been widely used in engineering and in physics to study hydrodynamic interactions. In granular matter, objects within a granular flow have helped to understand fundamental features of drag and lift forces. In our group, we have studied numerically the flow mediated interaction between two static disks within a vertical granular flow in a two-dimensional container where the flow velocity and the distance between obstacles were varied. Attractive and repulsive forces were found depending on flow velocity and separation between intruders. The simulations evidenced a relationship between the average flow velocity in a specific section ahead of the obstacles and the attractive-repulsive lift. On the other hand, it was showed that the lift force on an object dragged within a granular medium depends on the shape of the intruder. Here we present experimental results of the interaction between two side-by-side intruders of different shapes within a vertical granular flow. We built a quasi-two-dimensional container in which we placed the intruders and using load cells we measured lift and drag forces during the discharge process for different flow velocities.

  8. Experimental and numerical study of granular flow characteristics of absorber sphere pneumatic conveying process

    International Nuclear Information System (INIS)

    Zhang He; Li Tianjin; Qi Weiwei; Huang Zhiyong; Bo Hanliang

    2014-01-01

    Absorber sphere pneumatic conveying system is the main part of absorber sphere shutdown system and closely related to granular flow. Granular flow characteristics, such as mass flow rate, angle of repose, contact forces, etc., are crucial important for the optimization of absorber sphere pneumatic conveying process. Mass flow rate of granular flow through the sphere discharge valve and the bend tube are significant for the time of ball dropping and the time of conveying back rate, respectively. Experiments and DEM simulations have been conducted to investigate the granular flow characteristics. Experimental results showed that the relation between average mass flow rate through the sphere discharge valve and the valve stroke was composed of three zones i. e. the idle stroke zone, linearly zone and orifice restriction zone. The Beverloo's law was suitable for the granular flow through the multi-orifice during the orifice restriction zone. The variation of average mass flow rate with the valve stroke could be described by modified Beverloo's law based on the valve stroke. DEM simulation results showed that the drained angle of repose remained 23° at different valve strokes. Mass flow rate during steady granular flow through the sphere discharge valve at different valve strokes kept stable. The variation of mass flow rate through a bend tube was different from that through a circular orifice. (author)

  9. DEM simulation of granular flows in a centrifugal acceleration field

    Science.gov (United States)

    Cabrera, Miguel Angel; Peng, Chong; Wu, Wei

    2017-04-01

    The main purpose of mass-flow experimental models is abstracting distinctive features of natural granular flows, and allow its systematic study in the laboratory. In this process, particle size, space, time, and stress scales must be considered for the proper representation of specific phenomena [5]. One of the most challenging tasks in small scale models, is matching the range of stresses and strains among the particle and fluid media observed in a field event. Centrifuge modelling offers an alternative to upscale all gravity-driven processes, and it has been recently employed in the simulation of granular flows [1, 2, 3, 6, 7]. Centrifuge scaling principles are presented in Ref. [4], collecting a wide spectrum of static and dynamic models. However, for the case of kinematic processes, the non-uniformity of the centrifugal acceleration field plays a major role (i.e., Coriolis and inertial effects). In this work, we discuss a general formulation for the centrifugal acceleration field, implemented in a discrete element model framework (DEM), and validated with centrifuge experimental results. Conventional DEM simulations relate the volumetric forces as a function of the gravitational force Gp = mpg. However, in the local coordinate system of a rotating centrifuge model, the cylindrical centrifugal acceleration field needs to be included. In this rotating system, the centrifugal acceleration of a particle depends on the rotating speed of the centrifuge, as well as the position and speed of the particle in the rotating model. Therefore, we obtain the formulation of centrifugal acceleration field by coordinate transformation. The numerical model is validated with a series of centrifuge experiments of monodispersed glass beads, flowing down an inclined plane at different acceleration levels and slope angles. Further discussion leads to the numerical parameterization necessary for simulating equivalent granular flows under an augmented acceleration field. The premise of

  10. The Granular Blasius Problem: High inertial number granular flows

    Science.gov (United States)

    Tsang, Jonathan; Dalziel, Stuart; Vriend, Nathalie

    2017-11-01

    The classical Blasius problem considers the formation of a boundary layer through the change at x = 0 from a free-slip to a no-slip boundary beneath an otherwise steady uniform flow. Discrete particle model (DPM) simulations of granular gravity currents show that a similar phenomenon exists for a steady flow over a uniformly sloped surface that is smooth upstream (allowing slip) but rough downstream (imposing a no-slip condition). The boundary layer is a region of high shear rate and therefore high inertial number I; its dynamics are governed by the asymptotic behaviour of the granular rheology as I -> ∞ . The μ(I) rheology asserts that dμ / dI = O(1 /I2) as I -> ∞ , but current experimental evidence is insufficient to confirm this. We show that `generalised μ(I) rheologies', with different behaviours as I -> ∞ , all permit the formation of a boundary layer. We give approximate solutions for the velocity profile under each rheology. The change in boundary condition considered here mimics more complex topography in which shear stress increases in the streamwise direction (e.g. a curved slope). Such a system would be of interest in avalanche modelling. EPSRC studentship (Tsang) and Royal Society Dorothy Hodgkin Fellowship (Vriend).

  11. A review on numerical models for granular flow inside hoppers and its applications in PBR

    International Nuclear Information System (INIS)

    Tang Yushi; Guo Qiuju; Zhang Liguo

    2015-01-01

    Granular flow is the shearing motion of a collection of discrete solid particles which are commonly seen and widely utilized in various industrial applications. One of the essential applications of dense slow granular flow in engineering is the pebble flow in pebble-bed nuclear reactor (PBR). A number of numerical models have been established for researching the basic physical mechanisms and properties of granular flow. For the purpose of generating an appropriate model for high temperature reactor-pebblebed modules (HTR-PM) in the future, numerical models on granular flow in hoppers and some of their previous applications on PBRs are reviewed. In this paper, basic transport and contact mechanisms of granular flow are firstly introduced, then kinetic theory from gas molecules and plastic theory from metal mechanics approaches give descriptions of the macroscopic behavior of rapid flow and quasistatic flow regimes, respectively, subsequently kinematic continuum method and discrete element method (DEM) are presented to describe the bulk features of dense slow flow in hoppers. Since various kinematic models, DEM models and their modified versions for dense slow granular flow in hoppers have been experimentally verified and applied in prediction of pebble flow in PBRs, a promising model for HTR-PM is expected with further work to generate pebble flow profile in the future. (author)

  12. Simulation of 2D Granular Hopper Flow

    Science.gov (United States)

    Li, Zhusong; Shattuck, Mark

    2012-02-01

    Jamming and intermittent granular flow are big problems in industry, and the vertical hopper is a canonical example of these difficulties. We simulate gravity driven flow and jamming of 2D disks in a vertical hopper and compare with identical companion experiments presented in this session. We measure and compare the flow rate and probability for jamming as a function of particle properties and geometry. We evaluate the ability of standard Hertz-Mindlin contact mode to quantitatively predict the experimental flow.

  13. Granular-front formation in free-surface flow of concentrated suspensions

    Science.gov (United States)

    Leonardi, Alessandro; Cabrera, Miguel; Wittel, Falk K.; Kaitna, Roland; Mendoza, Miller; Wu, Wei; Herrmann, Hans J.

    2015-11-01

    A granular front emerges whenever the free-surface flow of a concentrated suspension spontaneously alters its internal structure, exhibiting a higher concentration of particles close to its front. This is a common and yet unexplained phenomenon, which is usually believed to be the result of fluid convection in combination with particle size segregation. However, suspensions composed of uniformly sized particles also develop a granular front. Within a large rotating drum, a stationary recirculating avalanche is generated. The flowing material is a mixture of a viscoplastic fluid obtained from a kaolin-water dispersion with spherical ceramic particles denser than the fluid. The goal is to mimic the composition of many common granular-fluid materials, such as fresh concrete or debris flow. In these materials, granular and fluid phases have the natural tendency to separate due to particle settling. However, through the shearing caused by the rotation of the drum, a reorganization of the phases is induced, leading to the formation of a granular front. By tuning the particle concentration and the drum velocity, it is possible to control this phenomenon. The setting is reproduced in a numerical environment, where the fluid is solved by a lattice-Boltzmann method, and the particles are explicitly represented using the discrete element method. The simulations confirm the findings of the experiments, and provide insight into the internal mechanisms. Comparing the time scale of particle settling with the one of particle recirculation, a nondimensional number is defined, and is found to be effective in predicting the formation of a granular front.

  14. Self-diffusion in dense granular shear flows.

    Science.gov (United States)

    Utter, Brian; Behringer, R P

    2004-03-01

    Diffusivity is a key quantity in describing velocity fluctuations in granular materials. These fluctuations are the basis of many thermodynamic and hydrodynamic models which aim to provide a statistical description of granular systems. We present experimental results on diffusivity in dense, granular shear flows in a two-dimensional Couette geometry. We find that self-diffusivities D are proportional to the local shear rate gamma; with diffusivities along the direction of the mean flow approximately twice as large as those in the perpendicular direction. The magnitude of the diffusivity is D approximately gamma;a(2), where a is the particle radius. However, the gradient in shear rate, coupling to the mean flow, and strong drag at the moving boundary lead to particle displacements that can appear subdiffusive or superdiffusive. In particular, diffusion appears to be superdiffusive along the mean flow direction due to Taylor dispersion effects and subdiffusive along the perpendicular direction due to the gradient in shear rate. The anisotropic force network leads to an additional anisotropy in the diffusivity that is a property of dense systems and has no obvious analog in rapid flows. Specifically, the diffusivity is suppressed along the direction of the strong force network. A simple random walk simulation reproduces the key features of the data, such as the apparent superdiffusive and subdiffusive behavior arising from the mean velocity field, confirming the underlying diffusive motion. The additional anisotropy is not observed in the simulation since the strong force network is not included. Examples of correlated motion, such as transient vortices, and Lévy flights are also observed. Although correlated motion creates velocity fields which are qualitatively different from collisional Brownian motion and can introduce nondiffusive effects, on average the system appears simply diffusive.

  15. Experimental observations of granular debris flows

    Science.gov (United States)

    Ghilardi, P.

    2003-04-01

    Various tests are run using two different laboratory flumes with rectangular cross section and transparent walls. The grains used in a single experiment have an almost constant grain sizes; mean diameter ranges from 5 mm to 20 mm. In each test various measurements are taken: hydrograms, velocity distribution near the transparent walls and on the free surface, average flow concentration. Concentration values are measured taking samples. Velocity distributions are obtained from movies recorded by high speed video cameras capable of 350 frames per second; flow rates and depth hydrograms are computed from the same velocity distributions. A gate is installed at the beginning of one of the flumes; this gate slides normally to the bed and opens very quickly, reproducing a dam-break. Several tests are run using this device, varying channel slope, sediment concentration, initial mixture thickness before the gate. Velocity distribution in the flume is almost constant from left to right, except for the flow sections near the front. The observed discharges and velocities are less than those given by a classic dam break formula, and depend on sediment concentration. The other flume is fed by a mixture with constant discharge and concentration, and is mainly used for measuring velocity distributions when the flow is uniform, with both rigid and granular bed, and to study erosion/deposition processes near debris flow dams or other mitigation devices. The equilibrium slope of the granular bed is very close to that given by the classical equilibrium formulas for debris flow. Different deposition processes are observed depending on mixture concentration and channel geometry.

  16. Numerical investigations on flow dynamics of prismatic granular materials using the discrete element method

    Science.gov (United States)

    Hancock, W.; Weatherley, D.; Wruck, B.; Chitombo, G. P.

    2012-04-01

    The flow dynamics of granular materials is of broad interest in both the geosciences (e.g. landslides, fault zone evolution, and brecchia pipe formation) and many engineering disciplines (e.g chemical engineering, food sciences, pharmaceuticals and materials science). At the interface between natural and human-induced granular media flow, current underground mass-mining methods are trending towards the induced failure and subsequent gravitational flow of large volumes of broken rock, a method known as cave mining. Cave mining relies upon the undercutting of a large ore body, inducement of fragmentation of the rock and subsequent extraction of ore from below, via hopper-like outlets. Design of such mines currently relies upon a simplified kinematic theory of granular flow in hoppers, known as the ellipsoid theory of mass movement. This theory assumes that the zone of moving material grows as an ellipsoid above the outlet of the silo. The boundary of the movement zone is a shear band and internal to the movement zone, the granular material is assumed to have a uniformly high bulk porosity compared with surrounding stagnant regions. There is however, increasing anecdotal evidence and field measurements suggesting this theory fails to capture the full complexity of granular material flow within cave mines. Given the practical challenges obstructing direct measurement of movement both in laboratory experiments and in-situ, the Discrete Element Method (DEM [1]) is a popular alternative to investigate granular media flow. Small-scale DEM studies (c.f. [3] and references therein) have confirmed that movement within DEM silo flow models matches that predicted by ellipsoid theory, at least for mono-disperse granular material freely outflowing at a constant rate. A major draw-back of these small-scale DEM studies is that the initial bulk porosity of the simulated granular material is significantly higher than that of broken, prismatic rock. In this investigation, more

  17. Unifying Suspension and Granular flows near Jamming

    Directory of Open Access Journals (Sweden)

    DeGiuli Eric

    2017-01-01

    Full Text Available Rheological properties of dense flows of hard particles are singular as one approaches the jamming threshold where flow ceases, both for granular flows dominated by inertia, and for over-damped suspensions. Concomitantly, the lengthscale characterizing velocity correlations appears to diverge at jamming. Here we review a theoretical framework that gives a scaling description of stationary flows of frictionless particles. Our analysis applies both to suspensions and inertial flows of hard particles. We report numerical results in support of the theory, and show the phase diagram that results when friction is added, delineating the regime of validity of the frictionless theory.

  18. Some exact velocity profiles for granular flow in converging hoppers

    Science.gov (United States)

    Cox, Grant M.; Hill, James M.

    2005-01-01

    Gravity flow of granular materials through hoppers occurs in many industrial processes. For an ideal cohesionless granular material, which satisfies the Coulomb-Mohr yield condition, the number of known analytical solutions is limited. However, for the special case of the angle of internal friction δ equal to ninety degrees, there exist exact parametric solutions for the governing coupled ordinary differential equations for both two-dimensional wedges and three-dimensional cones, both of which involve two arbitrary constants of integration. These solutions are the only known analytical solutions of this generality. Here, we utilize the double-shearing theory of granular materials to determine the velocity field corresponding to these exact parametric solutions for the two problems of gravity flow through converging wedge and conical hoppers. An independent numerical solution for other angles of internal friction is shown to coincide with the analytical solution.

  19. Critical state flow rules for CFD simulations of wet granular flows

    NARCIS (Netherlands)

    Schwarze, R.; Gladkyy, A.; Luding, Stefan; E. Onate M. Bischoff, E. Ramm; P. Wriggers,

    2013-01-01

    First rheological investigation results of weakly wet granular media are presented. The materials have been examined experimentally and numerically in well- defined shear configurations in steady state, in the intermediate flow regime. For the experiments, a Searl-type ring shear cell with rotating

  20. Effective Wall Friction in Wall-Bounded 3D Dense Granular Flows.

    Science.gov (United States)

    Artoni, Riccardo; Richard, Patrick

    2015-10-09

    We report numerical simulations on granular shear flows confined between two flat but frictional sidewalls. Novel regimes differing by their strain localization features are observed. They originate from the competition between dissipation at the sidewalls and dissipation in the bulk of the flow. The effective friction at sidewalls is characterized (effective friction coefficient and orientation of the friction force) for each regime, and its interdependence with slip and force fluctuations is pointed out. We propose a simple scaling law linking the slip velocity to the granular temperature in the main flow direction which leads naturally to another scaling law for the effective friction.

  1. Non-spherical granular flows down inclined chutes

    NARCIS (Netherlands)

    Hidalgo, R.C.; Rubio-Largo, S.M.; Alonso-Marroquin, F.; Weinhart, T.

    2017-01-01

    In this work, we numerically examine the steady-state granular flow of 3D non-spherical particles down an inclined plane. We use a hybrid CPU/GPU implementation of the discrete element method of nonspherical elongated particles. Thus, a systematic study of the system response is performed varying

  2. Spatial correlations in compressible granular flows

    OpenAIRE

    Van Noije, T. P. C.; Ernst, M. H.; Brito López, Ricardo

    1998-01-01

    The clustering instability in freely evolving granular fluids manifests itself in the density-density correlation function and structure factor. These functions are calculated from fluctuating hydrodynamics. As time increases, the structure factor of density fluctuations develops a maximum, which shifts to smaller wave numbers (growing correlation length). Furthermore, the inclusion of longitudinal velocity fluctuations changes long-range correlations in the flow field qualitatively and exten...

  3. Controlling mixing and segregation in time periodic granular flows

    Science.gov (United States)

    Bhattacharya, Tathagata

    Segregation is a major problem for many solids processing industries. Differences in particle size or density can lead to flow-induced segregation. In the present work, we employ the discrete element method (DEM)---one type of particle dynamics (PD) technique---to investigate the mixing and segregation of granular material in some prototypical solid handling devices, such as a rotating drum and chute. In DEM, one calculates the trajectories of individual particles based on Newton's laws of motion by employing suitable contact force models and a collision detection algorithm. Recently, it has been suggested that segregation in particle mixers can be thwarted if the particle flow is inverted at a rate above a critical forcing frequency. Further, it has been hypothesized that, for a rotating drum, the effectiveness of this technique can be linked to the probability distribution of the number of times a particle passes through the flowing layer per rotation of the drum. In the first portion of this work, various configurations of solid mixers are numerically and experimentally studied to investigate the conditions for improved mixing in light of these hypotheses. Besides rotating drums, many studies of granular flow have focused on gravity driven chute flows owing to its practical importance in granular transportation and to the fact that the relative simplicity of this type of flow allows for development and testing of new theories. In this part of the work, we observe the deposition behavior of both mono-sized and polydisperse dry granular materials in an inclined chute flow. The effects of different parameters such as chute angle, particle size, falling height and charge amount on the mass fraction distribution of granular materials after deposition are investigated. The simulation results obtained using DEM are compared with the experimental findings and a high degree of agreement is observed. Tuning of the underlying contact force parameters allows the achievement

  4. Experimental study and DEM simulation of granular flow through a new sphere discharge valve

    International Nuclear Information System (INIS)

    Zhang He; Li Tianjin; Huang Zhiyong; Gao Zhi; Qi Weiwei; Bo Hanliang

    2015-01-01

    Experiments and DEM simulation have been conducted to investigate the granular flow through a new type of sphere discharge valve. The new sphere discharge valve was based on the principle of angle of repose. The glass sphere was used in the granular discharge experiments. Experimental results showed that the relation between the averaging sphere discharge mass flow rate and the stroke of the sphere discharge valve were consisted of three zones, i.e. the idle stroke zone, linearly zone and orifice restriction zone. The Beverloo's law was suitable for the granular flow through multi-orifices in the orifice restriction zone. The variation of averaging sphere discharge mass flow rate with the stroke of the sphere discharge valve was described by Beverloo's law with the modification based on the stroke of the sphere discharge valve. DEM simulation results showed that the drained angle of repose during granular flow in the sphere storage vessel remained 23 degrees with different stroke of the sphere discharge valve. (authors)

  5. PFEM-based modeling of industrial granular flows

    Science.gov (United States)

    Cante, J.; Dávalos, C.; Hernández, J. A.; Oliver, J.; Jonsén, P.; Gustafsson, G.; Häggblad, H.-Å.

    2014-05-01

    The potential of numerical methods for the solution and optimization of industrial granular flows problems is widely accepted by the industries of this field, the challenge being to promote effectively their industrial practice. In this paper, we attempt to make an exploratory step in this regard by using a numerical model based on continuous mechanics and on the so-called Particle Finite Element Method (PFEM). This goal is achieved by focusing two specific industrial applications in mining industry and pellet manufacturing: silo discharge and calculation of power draw in tumbling mills. Both examples are representative of variations on the granular material mechanical response—varying from a stagnant configuration to a flow condition. The silo discharge is validated using the experimental data, collected on a full-scale flat bottomed cylindrical silo. The simulation is conducted with the aim of characterizing and understanding the correlation between flow patterns and pressures for concentric discharges. In the second example, the potential of PFEM as a numerical tool to track the positions of the particles inside the drum is analyzed. Pressures and wall pressures distribution are also studied. The power draw is also computed and validated against experiments in which the power is plotted in terms of the rotational speed of the drum.

  6. Friction dependence of shallow granular flows from discrete particle simulations

    NARCIS (Netherlands)

    Thornton, Anthony Richard; Weinhart, Thomas; Luding, Stefan; Bokhove, Onno

    2011-01-01

    A shallow-layer model for granular flows is completed with a closure relation for the macroscopic bed friction or basal roughness obtained from micro-scale discrete particle simulations of steady flows. We systematically vary the bed friction by changing the contact friction coefficient between

  7. Continuum modelling of segregating tridisperse granular chute flow

    Science.gov (United States)

    Deng, Zhekai; Umbanhowar, Paul B.; Ottino, Julio M.; Lueptow, Richard M.

    2018-03-01

    Segregation and mixing of size multidisperse granular materials remain challenging problems in many industrial applications. In this paper, we apply a continuum-based model that captures the effects of segregation, diffusion and advection for size tridisperse granular flow in quasi-two-dimensional chute flow. The model uses the kinematics of the flow and other physical parameters such as the diffusion coefficient and the percolation length scale, quantities that can be determined directly from experiment, simulation or theory and that are not arbitrarily adjustable. The predictions from the model are consistent with experimentally validated discrete element method (DEM) simulations over a wide range of flow conditions and particle sizes. The degree of segregation depends on the Péclet number, Pe, defined as the ratio of the segregation rate to the diffusion rate, the relative segregation strength κij between particle species i and j, and a characteristic length L, which is determined by the strength of segregation between smallest and largest particles. A parametric study of particle size, κij, Pe and L demonstrates how particle segregation patterns depend on the interplay of advection, segregation and diffusion. Finally, the segregation pattern is also affected by the velocity profile and the degree of basal slip at the chute surface. The model is applicable to different flow geometries, and should be easily adapted to segregation driven by other particle properties such as density and shape.

  8. Can Wet Rocky Granular Flows Become Debris Flows Due to Fine Sediment Production by Abrasion?

    Science.gov (United States)

    Arabnia, O.; Sklar, L. S.; Bianchi, G.; Mclaughlin, M. K.

    2015-12-01

    Debris flows are rapid mass movements in which elevated pore pressures are sustained by a viscous fluid matrix with high concentrations of fine sediments. Debris flows may form from coarse-grained wet granular flows as fine sediments are entrained from hillslope and channel material. Here we investigate whether abrasion of the rocks within a granular flow can produce sufficient fine sediments to create debris flows. To test this hypothesis experimentally, we used a set of 4 rotating drums ranging from 0.2 to 4.0 m diameter. Each drum has vanes along the boundary ensure shearing within the flow. Shear rate was varied by changing drum rotational velocity to maintain a constant Froude Number across drums. Initial runs used angular clasts of granodiorite with a tensile strength of 7.6 MPa, with well-sorted coarse particle size distributions linearly scaled with drum radius. The fluid was initially clear water, which rapidly acquired fine-grained wear products. After each 250 m tangential distance, we measured the particle size distributions, and then returned all water and sediment to the drums for subsequent runs. We calculate particle wear rates using statistics of size and mass distributions, and by fitting the Sternberg equation to the rate of mass loss from the size fraction > 2mm. Abundant fine sediments were produced in the experiments, but very little change in the median grain size was detected. This appears to be due to clast rounding, as evidenced by a decrease in the number of stable equilibrium resting points. We find that the growth in the fine sediment concentration in the fluid scales with unit drum power. This relationship can be used to estimate fine sediment production rates in the field. We explore this approach at Inyo Creek, a steep catchment in the Sierra Nevada, California. There, a significant debris flow occurred in July 2013, which originated as a coarse-grained wet granular flow. We use surveys to estimate flow depth and velocity where super

  9. Rheology of dense granular flows in two dimensions: Comparison of fully two-dimensional flows to unidirectional shear flow

    Science.gov (United States)

    Bhateja, Ashish; Khakhar, Devang V.

    2018-06-01

    We consider the rheology of steady two-dimensional granular flows, in different geometries, using discrete element method-based simulations of soft spheres. The flow classification parameter (ψ ), which defines the local flow type (ranging from pure rotation to simple shear to pure extension), varies spatially, to a significant extent, in the flows. We find that the material behaves as a generalized Newtonian fluid. The μ -I scaling proposed by Jop et al. [Nature (London) 441, 727 (2006), 10.1038/nature04801] is found to be valid in both two-dimensional and unidirectional flows, as observed in previous studies; however, the data for each flow geometry fall on a different curve. The results for the two-dimensional silo flow indicate that the viscosity does not depend directly on the flow type parameter, ψ . We find that the scaling based on "granular fluidity" [Zhang and Kamrin, Phys. Rev. Lett. 118, 058001 (2017), 10.1103/PhysRevLett.118.058001] gives good collapse of the data to a single curve for all the geometries. The data for the variation of the solid faction with inertial number show a reasonable collapse for the different geometries.

  10. Non-Steady Oscillatory Flow in Coarse Granular Materials

    DEFF Research Database (Denmark)

    Andersen, O. H.; Gent, M. R. A. van; Meer, J. W. van der

    1992-01-01

    Stationary and oscillatory flow through coarse granular materials have been investigated experimentally at Delft Hydraulics in their oscillating water tunnel with the objective of determining the coefficients of the extended Forchheimer equation. Cylinders, spheres and different types of rock have....... Further, for the non-stationary term, the virtual mass coefficient will be derived....

  11. NMRI Measurements of Flow of Granular Mixtures

    Science.gov (United States)

    Nakagawa, Masami; Waggoner, R. Allen; Fukushima, Eiichi

    1996-01-01

    We investigate complex 3D behavior of granular mixtures in shaking and shearing devices. NMRI can non-invasively measure concentration, velocity, and velocity fluctuations of flows of suitable particles. We investigate origins of wall-shear induced convection flow of single component particles by measuring the flow and fluctuating motion of particles near rough boundaries. We also investigate if a mixture of different size particles segregate into their own species under the influence of external shaking and shearing disturbances. These non-invasive measurements will reveal true nature of convecting flow properties and wall disturbance. For experiments in a reduced gravity environment, we will design a light weight NMR imager. The proof of principle development will prepare for the construction of a complete spaceborne system to perform experiments in space.

  12. Nonlocal rheological properties of granular flows near a jamming limit.

    Science.gov (United States)

    Aranson, Igor S; Tsimring, Lev S; Malloggi, Florent; Clément, Eric

    2008-09-01

    We study the rheology of sheared granular flows close to a jamming transition. We use the approach of partially fluidized theory (PFT) with a full set of equations extending the thin layer approximation derived previously for the description of the granular avalanches phenomenology. This theory provides a picture compatible with a local rheology at large shear rates [G. D. R. Midi, Eur. Phys. J. E 14, 341 (2004)] and it works in the vicinity of the jamming transition, where a description in terms of a simple local rheology comes short. We investigate two situations displaying important deviations from local rheology. The first one is based on a set of numerical simulations of sheared soft two-dimensional circular grains. The next case describes previous experimental results obtained on avalanches of sandy material flowing down an incline. Both cases display, close to jamming, significant deviations from the now standard Pouliquen's flow rule [O. Pouliquen, Phys. Fluids 11, 542 (1999); 11, 1956 (1999)]. This discrepancy is the hallmark of a strongly nonlocal rheology and in both cases, we relate the empirical results and the outcomes of PFT. The numerical simulations show a characteristic constitutive structure for the fluid part of the stress involving the confining pressure and the material stiffness that appear in the form of an additional dimensionless parameter. This constitutive relation is then used to describe the case of sandy flows. We show a quantitative agreement as far as the effective flow rules are concerned. A fundamental feature is identified in PFT as the existence of a jammed layer developing in the vicinity of the flow arrest that corroborates the experimental findings. Finally, we study the case of solitary erosive granular avalanches and relate the outcome with the PFT analysis.

  13. DEM study of granular flow around blocks attached to inclined walls

    Science.gov (United States)

    Samsu, Joel; Zhou, Zongyan; Pinson, David; Chew, Sheng

    2017-06-01

    Damage due to intense particle-wall contact in industrial applications can cause severe problems in industries such as mineral processing, mining and metallurgy. Studying the flow dynamics and forces on containing walls can provide valuable feedback for equipment design and optimising operations to prolong the equipment lifetime. Therefore, solids flow-wall interaction phenomena, i.e. induced wall stress and particle flow patterns should be well understood. In this work, discrete element method (DEM) is used to study steady state granular flow in a gravity-fed hopper like geometry with blocks attached to an inclined wall. The effects of different geometries, e.g. different wall angles and spacing between blocks are studied by means of a 3D DEM slot model with periodic boundary conditions. The findings of this work include (i) flow analysis in terms of flow patterns and particle velocities, (ii) force distributions within the model geometry, and (iii) wall stress vs. model height diagrams. The model enables easy transfer of the key findings to other industrial applications handling granular materials.

  14. DEM study of granular flow around blocks attached to inclined walls

    Directory of Open Access Journals (Sweden)

    Samsu Joel

    2017-01-01

    Full Text Available Damage due to intense particle-wall contact in industrial applications can cause severe problems in industries such as mineral processing, mining and metallurgy. Studying the flow dynamics and forces on containing walls can provide valuable feedback for equipment design and optimising operations to prolong the equipment lifetime. Therefore, solids flow-wall interaction phenomena, i.e. induced wall stress and particle flow patterns should be well understood. In this work, discrete element method (DEM is used to study steady state granular flow in a gravity-fed hopper like geometry with blocks attached to an inclined wall. The effects of different geometries, e.g. different wall angles and spacing between blocks are studied by means of a 3D DEM slot model with periodic boundary conditions. The findings of this work include (i flow analysis in terms of flow patterns and particle velocities, (ii force distributions within the model geometry, and (iii wall stress vs. model height diagrams. The model enables easy transfer of the key findings to other industrial applications handling granular materials.

  15. Granular shear flows of flexible rod-like particles

    Science.gov (United States)

    Guo, Y.; Curtis, J.; Wassgren, C.; Ketterhagen, W.; Hancock, B.

    2013-06-01

    Flexible particles are widely encountered in nature, e.g., stalks of plants, fiberglass particles, and ceramic nanofibers. Early studies indicated that the deformability of particles has a significant impact on the properties of granular materials and fiber suspensions. In this study, shear flows of flexible particles are simulated using the Discrete Element Method (DEM) to explore the effect of particle flexibility on the flow behavior and constitutive laws. A flexible particle is formed by connecting a number of constituent spheres in a straight line using elastic bonds. The forces/moments due to the normal, tangential, bending, and torsional deformation of a bond resist the relative movement between two bonded constituent spheres. The bond stiffness determines how difficult it is to make a particle deform, and the bond damping accounts for the energy dissipation in the particle vibration process. The simulation results show that elastically bonded particles have smaller coefficients of restitution compared to rigidly connected particles, due to the fact that kinetic energy is partially converted to potential energy in a contact between flexible particles. The coefficient of restitution decreases as the bond stiffness decreases and the bond damping coefficient increases. As a result, smaller stresses are obtained for granular flows of the flexible particles with smaller bond stiffness and larger bond damping coefficient.

  16. The respective roles of bulk friction and slip velocity during a granular mass flow

    Science.gov (United States)

    Staron, Lydie

    2016-04-01

    Catastrophic granular mass flows form an important natural hazard. Mitigation has motivated numerous studies on the properties of natural granular flows, and in particular, their ability to travel long distances away from the release point. The mobility of granular flows is commonly characterised through the definition of rheological properties and effective friction. Yet, it is widely accepted that the description in term of effective friction may include various lubrication effects, softening at the base of the flow and large slip velocities being a most likely one. In this case, flow bulk properties may obliterate the flow boundary conditions. In this contribution, we investigate how disentangling bulk properties from boundary conditions may improve our understanding of the flow. Using discrete simulations, we induce increasing slip velocities in different flow configurations. We show that increased mobility may be achieved without changing bulk properties. The results are interpreted in terms of a Robin-Navier slip condition and implemented in a continuum Navier-Stokes solver. We quantify the respective role of rheological bulk properties and boundary conditions in the general behaviour of a transient mass flow. We show that omitting the description of boundary conditions leads to misinterpretation of the flow properties. The outcome is discussed in terms of models reliability. References P.-Y. Lagrée et al, The granular column collapse as a continuum: validity of a two-dimensional Navier-Stokes model with the mu(I) rheology, J. Fluid Mech. 686, 378-408 (2011) L. Staron and E. Lajeunesse, Understanding how the volume affects the mobility of dry debris flows, Geophys. Res. Lett. 36, L12402 (2009) L. Staron, Mobility of long-runout rock flows: a discrete numerical investigation, Geophys. J. Int. 172, 455-463 (2008)

  17. Experimentally determined distribution of granular-flow characteristics in collisional bed load transport

    Directory of Open Access Journals (Sweden)

    Matoušek Václav

    2018-01-01

    Full Text Available A series of laboratory experiments on turbulent open-channel two-phase flow in a form of intense bed load transport is reported. Measurements in a laboratory tilting flume included camera based imaging techniques to identify the structure of the flow at the local level. Obtained experimental distributions of two-phase flow related parameters - granular velocity, concentration, and temperature - across a collisional transport layer are discussed. The results are analysed together with additional measured quantities (discharges of mixture and grains, flow depth, bed slope etc. Our major goal is to evaluate the distribution of granular stresses across the transport layer with a special attention paid to the interface between the transport layer and the bed. Furthermore, comparisons are discussed between the experimental results and predictions produced by suitable kinetic-theory based models.

  18. Flow Characteristics and Grain Size Distribution of Granular Gangue Mineral by Compaction Treatment

    Directory of Open Access Journals (Sweden)

    Ran Yuan

    2017-01-01

    Full Text Available A test system for water flow in granular gangue mineral was designed to study the flow characteristics by compaction treatment. With the increase of the compaction displacement, the porosity decreases and void in granular gangue becomes less. The main reason causing initial porosity decrease is that the void of larger size is filled with small particles. Permeability tends to decrease and non-Darcy flow factor increases under the compaction treatment. The change trend of flow characteristics shows twists and turns, which indicate that flow characteristics of granular gangue mineral are related to compaction level, grain size distribution, crushing, and fracture structure. During compaction, larger particles are crushed, which in turn causes the weight of smaller particles to increase, and water flow induces fine particles to migrate (weight loss; meanwhile, a sample with more weight of size (0–2.5 mm has a higher amount of weight loss. Water seepage will cause the decrease of some chemical components, where SiO2 decreased the highest in these components; the components decreased are more likely locked at fragments rather than the defect of the minerals. The variation of the chemical components has an opposite trend when compared with permeability.

  19. Granular flow through an aperture: Influence of the packing fraction

    Science.gov (United States)

    Aguirre, M. A.; De Schant, R.; Géminard, J.-C.

    2014-07-01

    For the last 50 years, the flow of a granular material through an aperture has been intensely studied in gravity-driven vertical systems (e.g., silos and hoppers). Nevertheless, in many industrial applications, grains are horizontally transported at constant velocity, lying on conveyor belts or floating on the surface of flowing liquids. Unlike fluid flows, that are controlled by the pressure, granular flow is not sensitive to the local pressure but rather to the local velocity of the grains at the outlet. We can also expect the flow rate to depend on the local density of the grains. Indeed, vertical systems are packed in dense configurations by gravity, but, in contrast, in horizontal systems the density can take a large range of values, potentially very small, which may significantly alter the flow rate. In the present article, we study, for different initial packing fractions, the discharge through an orifice of monodisperse grains driven at constant velocity by a horizontal conveyor belt. We report how, during the discharge, the packing fraction is modified by the presence of the outlet, and we analyze how changes in the packing fraction induce variations in the flow rate. We observe that variations of packing fraction do not affect the velocity of the grains at the outlet, and, therefore, we establish that flow-rate variations are directly related to changes in the packing fraction.

  20. Segregation-mobility feedback for bidisperse shallow granular flows: Towards understanding segregation in geophysical flows

    Science.gov (United States)

    Thornton, A.; Denissen, I.; Weinhart, T.; Van der Vaart, K.

    2017-12-01

    The flow behaviour of shallow granular chute flows for uniform particles is well-described by the hstop-rheology [1]. Geophysical flows, however, are often composed of highly non-uniform particles that differ in particle (size, shape, composition) or contact (friction, dissipation, cohesion) properties. The flow behaviour of such mixtures can be strongly influenced by particle segregation effects. Here, we study the influence of particle size-segregation on the flow behaviour of bidisperse flows using experiments and the discrete particle method. We use periodic DPM to derive hstop-rheology for the bi-dispersed granular shallow layer equations, and study their dependence on the segregation profile. In the periodic box simulations, size-segregation results in an upward coarsening of the size distribution with the largest grains collecting at the top of the flow. In geophysical flows, the fact the flow velocity is greatest at the top couples with the vertical segregation to preferentially transported large particles to the front. The large grains may be overrun, resegregated towards the surface and recirculated before being shouldered aside into lateral levees. Theoretically it has been suggested this process should lead to a breaking size-segregation (BSS) wave located between a large-particle-rich front and a small-particle-rich tail [2,3]. In the BSS wave large particles that have been overrun rise up again to the free-surface while small particles sink to the bed. We present evidence for the existences of the BSS wave. This is achieved through the study of three-dimensional bidisperse granular flows in a moving-bed channel. Our analysis demonstrates a relation between the concentration of small particles in the flow and the amount of basal slip, in which the structure of the BSS wave plays a key role. This leads to a feedback between the mean bulk flow velocity and the process of size-segregation. Ultimately, these findings shed new light on the recirculation of

  1. NMR studies of granular media and two-phase flow in porous media

    Science.gov (United States)

    Yang, Xiaoyu

    This dissertation describes two experimental studies of a vibrofluidized granular medium and a preliminary study of two-phase fluid flow in a porous medium using Nuclear Magnetic Resonance (NMR). The first study of granular medium is to test a scaling law of the rise in center of mass in a three-dimensional vibrofluidized granular system. Our granular system consisted of mustard seeds vibrated vertically at 40 Hz from 0g to 14g. We used Magnetic Resonance Imaging (MRI) to measure density profile in vibrated direction. We observed that the rise in center of mass scaled as nu 0alpha/Nlbeta with alpha = 1.0 +/- 0.2 and beta = 0.5 +/- 0.1, where nu 0 is the vibration velocity and Nl is the number of layers of grains in the container. A simple theory was proposed to explain the scaling exponents. In the second study we measured both density and velocity information in the same setup of the first study. Pulsed Field Gradient (PFG)-NMR combined with MRI was used to do this measurement. The granular system was fully fluidized at 14.85g 50 Hz with Nl ≤ 4. The velocity distributions at horizontal and vertical direction at different height were measured. The distributions were nearly-Gaussian far from sample bottom and non-Gaussian near sample bottom. Granular temperature profiles were calculated from the velocity distributions. The density and temperature profile were fit to a hydrodynamic theory. The theory agreed with experiments very well. A temperature inversion near top was also observed and explained by additional transport coefficient from granular hydrodynamics. The third study was the preliminary density measurement of invading phase profile in a two-phase flow in porous media. The purpose of this study was to test an invasion percolation with gradient (IPG) theory in two-phase flow of porous media. Two phases are dodecane and water doped with CuSO4. The porous medium was packed glass beads. The front tail width sigma and front width of invading phase were

  2. Sidewall-friction-driven ordering transition in granular channel flows: Implications for granular rheology.

    Science.gov (United States)

    Mandal, Sandip; Khakhar, D V

    2017-11-01

    We report a transition from a disordered state to an ordered state in the flow of nearly monodisperse granular matter flowing in an inclined channel with planar slide walls and a bumpy base, using discrete element method simulations. For low particle-sidewall friction coefficients, the flowing particles are disordered, however, for high sidewall friction, an ordered state is obtained, characterized by a layering of the particles and hexagonal packing of the particles in each layer. The extent of ordering, quantified by the local bond-orientational order parameter, varies in the cross section of the channel, with the highest ordering near the sidewalls. The flow transition significantly affects the local rheology-the effective friction coefficient is lower, and the packing fraction is higher, in the ordered state compared to the disordered state. A simple model, incorporating the extent of local ordering, is shown to describe the rheology of the system.

  3. Sidewall-friction-driven ordering transition in granular channel flows: Implications for granular rheology

    Science.gov (United States)

    Mandal, Sandip; Khakhar, D. V.

    2017-11-01

    We report a transition from a disordered state to an ordered state in the flow of nearly monodisperse granular matter flowing in an inclined channel with planar slide walls and a bumpy base, using discrete element method simulations. For low particle-sidewall friction coefficients, the flowing particles are disordered, however, for high sidewall friction, an ordered state is obtained, characterized by a layering of the particles and hexagonal packing of the particles in each layer. The extent of ordering, quantified by the local bond-orientational order parameter, varies in the cross section of the channel, with the highest ordering near the sidewalls. The flow transition significantly affects the local rheology—the effective friction coefficient is lower, and the packing fraction is higher, in the ordered state compared to the disordered state. A simple model, incorporating the extent of local ordering, is shown to describe the rheology of the system.

  4. Creepy landscapes : river sediment entrainment develops granular flow rheology on creeping bed.

    Science.gov (United States)

    Prancevic, J.; Chatanantavet, P.; Ortiz, C. P.; Houssais, M.; Durian, D. J.; Jerolmack, D. J.

    2015-12-01

    To predict rates of river sediment transport, one must first address the zeroth-order question: when does sediment move? The concept and determination of the critical fluid shear stress remains hazy, as observing particle motion and determining sediment flux becomes increasingly hard in its vicinity. To tackle this problem, we designed a novel annular flume experiment - reproducing an infinite river channel - where the refractive index of particles and the fluid are matched. The fluid is dyed with a fluorescent powder and a green laser sheet illuminates the fluid only, allowing us to observe particle displacements in a vertical plane. Experiments are designed to highlight the basic granular interactions of sediment transport while suppressing the complicating effects of turbulence; accordingly, particles are uniform spheres and Reynolds numbers are of order 1. We have performed sediment transport measurements close to the onset of particle motion, at steady state, and over long enough time to record averaged rheological behavior of particles. We find that particles entrained by a fluid exhibit successively from top to bottom: a suspension regime, a dense granular flow regime, and - instead of a static bed - a creeping regime. Data from experiments at a range of fluid stresses can be collapsed onto one universal rheologic curve that indicates the effective friction is a monotonic function of a dimensionless number called the viscous number. These data are in remarkable agreement with the local rheology model proposed by Boyer et al., which means that dense granular flows, suspensions and bed-load transport are unified under a common frictional flow law. Importantly, we observe slow creeping of the granular bed even in the absence of bed load, at fluid stresses that are below the apparent critical value. This last observation challenges the classical definition of the onset of sediment transport, and points to a continuous transition from quasi-static deformation to

  5. Bulbous head formation in bidisperse shallow granular flows over inclined planes

    Science.gov (United States)

    Denissen, I.; Thornton, A.; Weinhart, T.; Luding, S.

    2017-12-01

    Predicting the behaviour of hazardous natural granular flows (e.g. debris-flows and pyroclastic flows) is vital for an accurate assessment of the risks posed by such events. In these situations, an inversely graded vertical particle-size distribution develops, with larger particles on top of smaller particles. As the surface velocity of such flows is larger than the mean velocity, the larger material is then transported to the flow front. This creates a downstream size-segregation structure, resulting in a flow front composed purely of large particles, that are generally more frictional in geophysical flows. Thus, this segregation process reduces the mobility of the flow front, resulting in the formation of, a so-called, bulbous head. One of the main challenges of simulating these hazardous natural granular flows is the enormous number of particles they contain, which makes discrete particle simulations too computationally expensive to be practically useful. Continuum methods are able to simulate the bulk flow- and segregation behaviour of such flows, but have to make averaging approximations that reduce the huge number of degrees of freedom to a few continuum fields. Small-scale periodic discrete particle simulations can be used to determine the material parameters needed for the continuum model. In this presentation, we use a depth-averaged model to predict the flow profile for particulate chute flows, based on flow height, depth-averaged velocity and particle-size distribution [1], and show that the bulbous head structure naturally emerges from this model. The long-time behaviour of this solution of the depth-averaged continuum model converges to a novel travelling wave solution [2]. Furthermore, we validate this framework against computationally expensive 3D particle simulations, where we see surprisingly good agreement between both approaches, considering the approximations made in the continuum model. We conclude by showing that the travelling distance and

  6. Scaling of wet granular flows in a rotating drum

    Directory of Open Access Journals (Sweden)

    Jarray Ahmed

    2017-01-01

    Full Text Available In this work, we investigate the effect of capillary forces and particle size on wet granular flows and we propose a scaling methodology that ensures the conservation of the bed flow. We validate the scaling law experimentally by using different size glass beads with tunable capillary forces. The latter is obtained using mixtures of ethanol-water as interstitial liquid and by increasing the hydrophobicity of glass beads with an ad-hoc silanization procedure. The scaling methodology in the flow regimes considered (slipping, slumping and rolling yields similar bed flow for different particle sizes including the angle of repose that normally increases when decreasing the particle size.

  7. Simulation of granular and gas-solid flows using discrete element method

    Science.gov (United States)

    Boyalakuntla, Dhanunjay S.

    2003-10-01

    In recent years there has been increased research activity in the experimental and numerical study of gas-solid flows. Flows of this type have numerous applications in the energy, pharmaceuticals, and chemicals process industries. Typical applications include pulverized coal combustion, flow and heat transfer in bubbling and circulating fluidized beds, hopper and chute flows, pneumatic transport of pharmaceutical powders and pellets, and many more. The present work addresses the study of gas-solid flows using computational fluid dynamics (CFD) techniques and discrete element simulation methods (DES) combined. Many previous studies of coupled gas-solid flows have been performed assuming the solid phase as a continuum with averaged properties and treating the gas-solid flow as constituting of interpenetrating continua. Instead, in the present work, the gas phase flow is simulated using continuum theory and the solid phase flow is simulated using DES. DES treats each solid particle individually, thus accounting for its dynamics due to particle-particle interactions, particle-wall interactions as well as fluid drag and buoyancy. The present work involves developing efficient DES methods for dense granular flow and coupling this simulation to continuum simulations of the gas phase flow. Simulations have been performed to observe pure granular behavior in vibrating beds. Benchmark cases have been simulated and the results obtained match the published literature. The dimensionless acceleration amplitude and the bed height are the parameters governing bed behavior. Various interesting behaviors such as heaping, round and cusp surface standing waves, as well as kinks, have been observed for different values of the acceleration amplitude for a given bed height. Furthermore, binary granular mixtures (granular mixtures with two particle sizes) in a vibrated bed have also been studied. Gas-solid flow simulations have been performed to study fluidized beds. Benchmark 2D

  8. Flow and Jamming of Granular Materials in a Two-dimensional Hopper

    Science.gov (United States)

    Tang, Junyao

    Flow in a hopper is both a fertile testing ground for understanding fundamental granular flow rheology and industrially highly relevant. Despite increasing research efforts in this area, a comprehensive physical theory is still lacking for both jamming and flow of granular materials in a hopper. In this work, I have designed a two dimensional (2D) hopper experiment using photoelastic particles (particles' shape: disk or ellipse), with the goal to build a bridge between macroscopic phenomenon of hopper flow and microscopic particle-scale dynamics. Through synchronized data of particle tracking and stress distributions in particles, I have shown differences between my data of the time-averaged velocity/stress profile of 2D hopper flow with previous theoretical predictions. I have also demonstrated the importance of a mechanical stable arch near the opening on controlling hopper flow rheology and suggested a heuristic phase diagram for the hopper flow/jamming transition. Another part of this thesis work is focused on studying the impact of particle shape of particles on hopper flow. By comparing particle-tracking and photoelastic data for ellipses and disks at the appropriate length scale, I have demonstrated an important role for the rotational freedom of elliptical particles in controlling flow rheology through particle tracking and stress analysis. This work has been supported by International Fine Particle Research Institute (IFPRI) .

  9. Averaging processes in granular flows driven by gravity

    Science.gov (United States)

    Rossi, Giulia; Armanini, Aronne

    2016-04-01

    One of the more promising theoretical frames to analyse the two-phase granular flows is offered by the similarity of their rheology with the kinetic theory of gases [1]. Granular flows can be considered a macroscopic equivalent of the molecular case: the collisions among molecules are compared to the collisions among grains at a macroscopic scale [2,3]. However there are important statistical differences in dealing with the two applications. In the two-phase fluid mechanics, there are two main types of average: the phasic average and the mass weighed average [4]. The kinetic theories assume that the size of atoms is so small, that the number of molecules in a control volume is infinite. With this assumption, the concentration (number of particles n) doesn't change during the averaging process and the two definitions of average coincide. This hypothesis is no more true in granular flows: contrary to gases, the dimension of a single particle becomes comparable to that of the control volume. For this reason, in a single realization the number of grain is constant and the two averages coincide; on the contrary, for more than one realization, n is no more constant and the two types of average lead to different results. Therefore, the ensamble average used in the standard kinetic theory (which usually is the phasic average) is suitable for the single realization, but not for several realization, as already pointed out in [5,6]. In the literature, three main length scales have been identified [7]: the smallest is the particles size, the intermediate consists in the local averaging (in order to describe some instability phenomena or secondary circulation) and the largest arises from phenomena such as large eddies in turbulence. Our aim is to solve the intermediate scale, by applying the mass weighted average, when dealing with more than one realizations. This statistical approach leads to additional diffusive terms in the continuity equation: starting from experimental

  10. Transient response in granular bounded heap flows

    Science.gov (United States)

    Xiao, Hongyi; Ottino, Julio M.; Lueptow, Richard M.; Umbanhowar, Paul B.

    2017-11-01

    Heap formation, a canonical granular flow, is common in industry and is also found in nature. Here, we study the transition between steady flow states in quasi-2D bounded heaps by suddenly changing the feed rate from one fixed value to another. During the transition, in both experiments and discrete element method simulations, an additional wedge of flowing particles propagates over the rising free surface. The downstream edge of the wedge - the wedge front - moves downstream with velocity inversely proportional to the square root of time. An additional longer duration transient process continues after the wedge front reaches the downstream wall. The transient flux profile during the entire transition is well modeled by a diffusion-like equation derived from local mass balance and a local linear relation between the flux and the surface slope. Scalings for the transient kinematics during the flow transitions are developed based on the flux profiles. Funded by NSF Grant CBET-1511450.

  11. 2D transient granular flows over obstacles: experimental and numerical work

    Science.gov (United States)

    Juez, Carmelo; Caviedes-Voullième, Daniel; Murillo, Javier; García-Navarro, Pilar

    2016-04-01

    Landslides are an ubiquitous natural hazard, and therefore human infrastructure and settlements are often at risk in mountainous regions. In order to better understand and predict landslides, systematic studies of the phenomena need to be undertaken. In particular, computational tools which allow for analysis of field problems require to be thoroughly tested, calibrated and validated under controlled conditions. And to do so, it is necessary for such controlled experiments to be fully characterized in the same terms as the numerical model requires. This work presents an experimental study of dry granular flow over a rough bed with topography which resembles a mountain valley. It has an upper region with a very high slope. The geometry of the bed describes a fourth order polynomial curve, with a low point with zero slope, and afterwards a short region with adverse slope. Obstacles are present in the lower regions which are used as model geometries of human structures. The experiments consisted of a sudden release a mass of sand on the upper region, and allowing it to flow downslope. Furthermore, it has been frequent in previous studies to measure final states of the granular mass at rest, but seldom has transient data being provided, and never for the entire field. In this work we present transient measurements of the moving granular surfaces, obtained with a consumer-grade RGB-D sensor. The sensor, developed for the videogame industry, allows to measure the moving surface of the sand, thus obtaining elevation fields. The experimental results are very consistent and repeatable. The measured surfaces clearly show the distinctive features of the granular flow around the obstacles and allow to qualitatively describe the different flow patterns. More importantly, the quantitative description of the granular surface allows for benchmarking and calibration of predictive numerical models, key in scaling the small-scale experimental knowledge into the field. In addition, as

  12. A granular refillable filter for glas-flows contaminated by radioactive impurities

    International Nuclear Information System (INIS)

    Bonn, J.W.

    1975-01-01

    Description is given of a granular charcoal refillable filter adapted to adsorb the radioactive impurities of a gaseous flow. That flow comprises a number of filtering layers, the consumed charcoal of which can be discharged by a pneumatic device without exposing the personnel to radioactivity. This can be applied to emergency devices in nuclear facilities [fr

  13. Dense granular Flows: a conceptual design of high-power neutron source

    Directory of Open Access Journals (Sweden)

    Yang Lei

    2017-01-01

    Full Text Available A high-power neutron source system is very useful for multifunctional applications, such as material facilities for advanced nuclear power, space radiation studies, radiography and tomography. Here the idea of inclined dense granular flow is utilized and developed in a new conceptual design of a compact high-power target to produce a high-energy and high-flux neutron irradiation (the flux is up to 1015 n/cm2/s or even 1016. Comparing to the traditional solid and liquid heavy metal targets, this design has advantages in material choice, fluid stability, heat removal, etc. In this paper the natures of the granular flows in an inclined chute are investigated and preliminary experimental and numerical results are reported. Then the feasibility of this design is discussed.

  14. Connecting grain-scale physics to macroscopic granular flow behavior using discrete contact-dynamics simulations, centrifuge experiments, and continuum modeling

    Science.gov (United States)

    Reitz, Meredith; Stark, Colin; Hung, Chi-Yao; Smith, Breannan; Grinspin, Eitan; Capart, Herve; Li, Liming; Crone, Timothy; Hsu, Leslie; Ling, Hoe

    2014-05-01

    A complete theoretical understanding of geophysical granular flow is essential to the reliable assessment of landslide and debris flow hazard and for the design of mitigation strategies, but several key challenges remain. Perhaps the most basic is a general treatment of the processes of internal energy dissipation, which dictate the runout velocity and the shape and scale of the affected area. Currently, dissipation is best described by macroscopic, empirical friction coefficients only indirectly related to the grain-scale physics. Another challenge is describing the forces exerted at the boundaries of the flow, which dictate the entrainment of further debris and the erosion of cohesive surfaces. While the granular effects on these boundary forces have been shown to be large compared to predictions from continuum approximations, the link between granular effects and erosion or entrainment rates has not been settled. Here we present preliminary results of a multi-disciplinary study aimed at improving our understanding of granular flow energy dissipation and boundary forces, through an effort to connect grain-scale physics to macroscopic behaviors. Insights into grain-scale force distributions and energy dissipation mechanisms are derived from discrete contact-dynamics simulations. Macroscopic erosion and flow behaviors are documented from a series of granular flow experiments, in which a rotating drum half-filled with grains is placed within a centrifuge payload, in order to drive effective gravity levels up to ~100g and approach the forces present in natural systems. A continuum equation is used to characterize the flowing layer depth and velocity resulting from the force balance between the down-slope pull of gravity and the friction at the walls. In this presentation we will focus on the effect of granular-specific physics such as force chain networks and grain-grain collisions, derived from the contact dynamics simulations. We will describe our efforts to

  15. Revisiting Johnson and Jackson boundary conditions for granular flows

    Energy Technology Data Exchange (ETDEWEB)

    Li, Tingwen; Benyahia, Sofiane

    2012-07-01

    In this article, we revisit Johnson and Jackson boundary conditions for granular flows. The oblique collision between a particle and a flat wall is analyzed by adopting the classic rigid-body theory and a more realistic semianalytical model. Based on the kinetic granular theory, the input parameter for the partial-slip boundary conditions, specularity coefficient, which is not measurable in experiments, is then interpreted as a function of the particle-wall restitution coefficient, the frictional coefficient, and the normalized slip velocity at the wall. An analytical expression for the specularity coefficient is suggested for a flat, frictional surface with a low frictional coefficient. The procedure for determining the specularity coefficient for a more general problem is outlined, and a working approximation is provided.

  16. Advances in studies of dense volcanic granular flows

    Energy Technology Data Exchange (ETDEWEB)

    Bursik, M [University of Buffalo, SUNY, Buffalo, NY 14260 (United States); Patra, A [University of Buffalo, SUNY, Buffalo, NY 14260 (United States); Pitman, E B [University of Buffalo, SUNY, Buffalo, NY 14260 (United States); Nichita, C [University of Buffalo, SUNY, Buffalo, NY 14260 (United States); Macias, J L [Universidad Nacional Autonoma de Mexico, Coyoacan, Mexico D F (Mexico); Saucedo, R [Universidad Nacional Autonoma de Mexico, Coyoacan, Mexico D F (Mexico); Girina, O [Institute of Volcanic Geology and Geochemistry, Russian Academy of Sciences, Petropavlovsk-Kamchatskii (Russian Federation)

    2005-02-01

    The collapse and decrepitation of a lava dome at the summit of a volcano generally results in the generation of dense granular flows, often referred to as block and ash flows. As the dome particles propagate from the source, they break apart by internal pressure as well as collision. The propagation of block and ash flows can be simulated to some accuracy with a depth averaged numerical model of the equations of continuity and momentum for a material with a frictional resistance. However, important features of such flows, such as the influence of remote stress through force chains, erosion of the volcano substrate, and shock formation and pressurization upon particle break up are poorly understood. In the near future, the influence of these factors will be incorporated into depth averaged models. Various numerical techniques based on particles will some day yield results that can be compared not only with bulk flow properties, but to the internal layering of block and ash flow deposits.

  17. A finite area scheme for shallow granular flows on three-dimensional surfaces

    Science.gov (United States)

    Rauter, Matthias

    2017-04-01

    Shallow granular flow models have become a popular tool for the estimation of natural hazards, such as landslides, debris flows and avalanches. The shallowness of the flow allows to reduce the three-dimensional governing equations to a quasi two-dimensional system. Three-dimensional flow fields are replaced by their depth-integrated two-dimensional counterparts, which yields a robust and fast method [1]. A solution for a simple shallow granular flow model, based on the so-called finite area method [3] is presented. The finite area method is an adaption of the finite volume method [4] to two-dimensional curved surfaces in three-dimensional space. This method handles the three dimensional basal topography in a simple way, making the model suitable for arbitrary (but mildly curved) topography, such as natural terrain. Furthermore, the implementation into the open source software OpenFOAM [4] is shown. OpenFOAM is a popular computational fluid dynamics application, designed so that the top-level code mimics the mathematical governing equations. This makes the code easy to read and extendable to more sophisticated models. Finally, some hints on how to get started with the code and how to extend the basic model will be given. I gratefully acknowledge the financial support by the OEAW project "beyond dense flow avalanches". Savage, S. B. & Hutter, K. 1989 The motion of a finite mass of granular material down a rough incline. Journal of Fluid Mechanics 199, 177-215. Ferziger, J. & Peric, M. 2002 Computational methods for fluid dynamics, 3rd edn. Springer. Tukovic, Z. & Jasak, H. 2012 A moving mesh finite volume interface tracking method for surface tension dominated interfacial fluid flow. Computers & fluids 55, 70-84. Weller, H. G., Tabor, G., Jasak, H. & Fureby, C. 1998 A tensorial approach to computational continuum mechanics using object-oriented techniques. Computers in physics 12(6), 620-631.

  18. Nonlinear stability, bifurcation and resonance in granular plane Couette flow

    Science.gov (United States)

    Shukla, Priyanka; Alam, Meheboob

    2010-11-01

    A weakly nonlinear stability theory is developed to understand the effect of nonlinearities on various linear instability modes as well as to unveil the underlying bifurcation scenario in a two-dimensional granular plane Couette flow. The relevant order parameter equation, the Landau-Stuart equation, for the most unstable two-dimensional disturbance has been derived using the amplitude expansion method of our previous work on the shear-banding instability.ootnotetextShukla and Alam, Phys. Rev. Lett. 103, 068001 (2009). Shukla and Alam, J. Fluid Mech. (2010, accepted). Two types of bifurcations, Hopf and pitchfork, that result from travelling and stationary linear instabilities, respectively, are analysed using the first Landau coefficient. It is shown that the subcritical instability can appear in the linearly stable regime. The present bifurcation theory shows that the flow is subcritically unstable to disturbances of long wave-lengths (kx˜0) in the dilute limit, and both the supercritical and subcritical states are possible at moderate densities for the dominant stationary and traveling instabilities for which kx=O(1). We show that the granular plane Couette flow is prone to a plethora of resonances.ootnotetextShukla and Alam, J. Fluid Mech. (submitted, 2010)

  19. Impurity in a granular gas under nonlinear Couette flow

    International Nuclear Information System (INIS)

    Vega Reyes, Francisco; Garzó, Vicente; Santos, Andrés

    2008-01-01

    We study in this work the transport properties of an impurity immersed in a granular gas under stationary nonlinear Couette flow. The starting point is a kinetic model for low-density granular mixtures recently proposed by the authors (Vega Reyes et al 2007 Phys. Rev. E 75 061306). Two routes have been considered. First, a hydrodynamic or normal solution is found by exploiting a formal mapping between the kinetic equations for the gas particles and for the impurity. We show that the transport properties of the impurity are characterized by the ratio between the temperatures of the impurity and gas particles and by five generalized transport coefficients: three related to the momentum flux (a nonlinear shear viscosity and two normal stress differences) and two related to the heat flux (a nonlinear thermal conductivity and a cross-coefficient measuring a component of the heat flux orthogonal to the thermal gradient). Second, by means of a Monte Carlo simulation method we numerically solve the kinetic equations and show that our hydrodynamic solution is valid in the bulk of the fluid when realistic boundary conditions are used. Furthermore, the hydrodynamic solution applies to arbitrarily (inside the continuum regime) large values of the shear rate, of the inelasticity, and of the rest of the parameters of the system. Preliminary simulation results of the true Boltzmann description show the reliability of the nonlinear hydrodynamic solution of the kinetic model. This shows again the validity of a hydrodynamic description for granular flows, even under extreme conditions, beyond the Navier–Stokes domain

  20. Flow and fracture in water-saturated, unconstrained granular beds

    Directory of Open Access Journals (Sweden)

    Germán eVaras

    2015-06-01

    Full Text Available The injection of gas in a liquid-saturated granular bed gives rise to a wide variety of invasion patterns. Many studies have focused on constrained porous media, in which the grains are fixed in the bed and only the interstitial fluid flows when the gas invades the system. With a free upper boundary, however, the grains can be entrained by the ascending gas or fluid motion, and the competition between the upward motion of grains and sedimentation leads to new patterns. We propose a brief review of the experimental investigation of the dynamics of air rising through a water-saturated, unconstrained granular bed, in both two and three dimensions. After describing the invasion pattern at short and long time, a tentative regime-diagram is proposed. We report original results showing a dependence of the fluidized zone shape, at long times, on the injection flow rate and grain size. A method based on image analysis makes it possible to detect not only the fluidized zone profile in the stationary regime, but also to follow the transient dynamics of its formation. Finally, we describe the degassing dynamics inside the fluidized zone, in the stationary regime. Depending on the experimental conditions, regular bubbling, continuous degassing, intermittent regime or even spontaneous flow-to-fracture transition are observed.

  1. Rheological Modeling of Macro Viscous Flows of Granular Suspension of Regular and Irregular Particles

    Directory of Open Access Journals (Sweden)

    Anna Maria Pellegrino

    2017-12-01

    Full Text Available This paper refers to complex granular-fluid mixtures involved into geophysical flows, such as debris and hyper-concentrated flows. For such phenomena, the interstitial fluids play a role when they are in the viscous regime. Referring to experiments on granular-fluid mixture carried out with pressure imposed annular shear cell, we study the rheological behaviour of dense mixture involving both spheres and irregular-shaped particles. For the case of viscous suspensions with irregular grains, a significant scatter of data from the trend observed for mixtures with spherical particles was evident. In effect, the shape of the particles likely plays a fundamental role in the flow dynamics, and the constitutive laws proposed by the frictional theory for the spheres are no longer valid. Starting from the frictional approach successfully applied to suspension of spheres, we demonstrate that also in case of irregular particles the mixture rheology may be fully characterized by the two relationships involving friction coefficient µ and volume concentration Ф as a function of the dimensionless viscous number Iv. To this goal, we provided a new consistent general model, referring to the volume fraction law and friction law, which accounts for the particle shape. In this way, the fitting parameters reduce just to the static friction angle µ1, and the two parameters, k and fs related to the grain shape. The resulting general model may apply to steady fully developed flows of saturated granular fluid mixture in the viscous regime, no matter of granular characteristics.

  2. An Investigation of Parallel Post-Laminar Flow through Coarse Granular Porous Media with the Wilkins Equation

    Directory of Open Access Journals (Sweden)

    Ashes Banerjee

    2018-02-01

    Full Text Available Behaviour of flow resistance with velocity is still undefined for post-laminar flow through coarse granular media. This can cause considerable errors during flow measurements in situations like rock fill dams, water filters, pumping wells, oil and gas exploration, and so on. Keeping the non-deviating nature of Wilkins coefficients with the hydraulic radius of media in mind, the present study further explores their behaviour to independently varying media size and porosity, subjected to parallel post-laminar flow through granular media. Furthermore, an attempt is made to simulate the post-laminar flow conditions with the help of a Computational Fluid Dynamic (CFD Model in ANSYS FLUENT, since conducting large-scale experiments are often costly and time-consuming. The model output and the experimental results are found to be in good agreement. Percentage deviations between the experimental and numerical results are found to be in the considerable range. Furthermore, the simulation results are statistically validated with the experimental results using the standard ‘Z-test’. The output from the model advocates the importance and applicability of CFD modelling in understanding post-laminar flow through granular media.

  3. Granular materials flow like complex fluids

    Science.gov (United States)

    Kou, Binquan; Cao, Yixin; Li, Jindong; Xia, Chengjie; Li, Zhifeng; Dong, Haipeng; Zhang, Ang; Zhang, Jie; Kob, Walter; Wang, Yujie

    2017-11-01

    Granular materials such as sand, powders and foams are ubiquitous in daily life and in industrial and geotechnical applications. These disordered systems form stable structures when unperturbed, but in the presence of external influences such as tapping or shear they `relax', becoming fluid in nature. It is often assumed that the relaxation dynamics of granular systems is similar to that of thermal glass-forming systems. However, so far it has not been possible to determine experimentally the dynamic properties of three-dimensional granular systems at the particle level. This lack of experimental data, combined with the fact that the motion of granular particles involves friction (whereas the motion of particles in thermal glass-forming systems does not), means that an accurate description of the relaxation dynamics of granular materials is lacking. Here we use X-ray tomography to determine the microscale relaxation dynamics of hard granular ellipsoids subject to an oscillatory shear. We find that the distribution of the displacements of the ellipsoids is well described by a Gumbel law (which is similar to a Gaussian distribution for small displacements but has a heavier tail for larger displacements), with a shape parameter that is independent of the amplitude of the shear strain and of the time. Despite this universality, the mean squared displacement of an individual ellipsoid follows a power law as a function of time, with an exponent that does depend on the strain amplitude and time. We argue that these results are related to microscale relaxation mechanisms that involve friction and memory effects (whereby the motion of an ellipsoid at a given point in time depends on its previous motion). Our observations demonstrate that, at the particle level, the dynamic behaviour of granular systems is qualitatively different from that of thermal glass-forming systems, and is instead more similar to that of complex fluids. We conclude that granular materials can relax

  4. Experimental Study of Dry Granular Flow and Impact Behavior Against a Rigid Retaining Wall

    Science.gov (United States)

    Jiang, Yuan-Jun; Towhata, Ikuo

    2013-07-01

    Shallow slope failure in mountainous regions is a common and emergent hazard in terms of its damage to important traffic routes and local communities. The impact of dry granular flows consisting of rock fragments and other particles resulting from shallow slope failures on retaining structures has yet to be systematically researched and is not covered by current design codes. As a preliminary study of the impact caused by dry granular flows, a series of dry granular impact experiments were carried out for one model of a retaining wall. It was indirectly verified that the total normal force exerted on a retaining wall consists of a drag force ( F d), a gravitational and frictional force ( F gf), and a passive earth force ( F p), and that the calculation of F d can be based on the empirical formula defined in NF EN Eurocode 1990 ( Eurocode structuraux. Base de calcul des structures, AFNOR La plaine Saint Denis, 2003). It was also indirectly verified that, for flow with Froude number from 6 to 11, the drag coefficient ( C d) can be estimated using the previously proposed empirical parameters.

  5. Granular flow in a rotating drum: Experiments and theory

    Science.gov (United States)

    Hung, C. Y.; Stark, C. P.; Capart, H.; Li, L.; Smith, B.; Grinspun, E.

    2015-12-01

    Erosion at the base of a debris flow fundamentally controls how large the flow will become and how far it will travel. Experimental observations of this important phenomenon are rather limited, and this lack has led theoretical treatments to making ad hoc assumptions about the basal process. In light of this, we carried out a combination of laboratory experiments and theoretical analysis of granular flow in a rotating drum, a canonical example of steady grain motion in which entrainment rates can be precisely controlled. Our main result is that basal sediment is entrained as the velocity profile adjusts to imbalance in the flow of kinetic energy.Our experimental apparatus consisted of a 40cm-diameter drum, 4cm-deep, half-filled with 2.3mm grains. Rotation rates varied from 1-70 rpm. We varied the effective scale by varying effective gravity from 1g to 70g on a geotechnical centrifuge. The field of grain motion was recorded using high-speed video and mapped using particle tracking velocimetry. In tandem we developed a depth-averaged theory using balance equations for mass, momentum and kinetic energy. We assumed a linearized GDR Midi granular rheology [da Cruz, 2005] and a Coulomb friction law along the sidewalls [Jop et al., 2005]. A scaling analysis of our equations yields a dimensionless "entrainment number" En, which neatly parametrizes the flow geometry in the drum for a wide range of variables, e.g., rotation rate and effective gravity. At low En, the flow profile is planar and kinetic energy is balanced locally in the flow layer. At high En, the flow profile is sigmoidal (yin-yang shaped) and the kinetic energy is dominated by longitudinal, streamwise transfer. We observe different scaling behavior under each of these flow regimes, e.g., between En and kinetic energy, surface slope and flow depth. Our theory correctly predicts their scaling exponents and the value of En at which the regime transition takes place. We are also able to make corrections for

  6. Fundamental changes of granular flows dynamics, deposition and erosion processes at high slope angles: insights from laboratory experiments.

    Science.gov (United States)

    Farin, Maxime; Mangeney, Anne; Roche, Olivier

    2014-05-01

    Geophysical granular flows commonly interact with their substrate in various ways depending on the mechanical properties of the underlying material. Granular substrates, resulting from deposition of earlier flows or various geological events, are often eroded by avalanches [see Hungr and Evans, 2004 for review]. The entrainment of underlying debris by the flow is suspected to affect flow dynamics because qualitative and quantitative field observations suggest that it can increase the flow velocity and deposit extent, depending on the geological setting and flow type [Sovilla et al., 2006; Iverson et al., 2011]. Direct measurement of material entrainment in nature, however, is very difficult. We conducted laboratory experiments on granular column collapse over an inclined channel with and without an erodible bed of granular material. The controlling parameters were the channel slope angle, the granular column volume and its aspect ratio (i.e. height over length), the inclination of the column with respect to the channel base, the channel width, and the thickness and compaction of the erodible bed. For slope angles below a critical value θc, between 10° and 16°, the runout distance rf is proportional to the initial column height h0 and is unaffected by the presence of an erodible bed. On steeper slopes, the flow dynamics change fundamentally since a last phase of slow propagation develops at the end of the flow front deceleration, and prolongates significantly the flow duration. This phase has similar characteristics that steady, uniform flows. The slow propagation phase lasts longer for increasing slope angle, column volume, column inclination with respect to the slope, and channel width, and for decreasing column aspect ratio. It is however independent of the maximum front velocity and, on an erodible bed, of the maximum depth of excavation within the bed. Both on rigid and erodible beds, the increase of the slow propagation phase duration has a crucial effect

  7. Reconfiguration of a flexible fiber immersed in a 2D dense granular flow close to the jamming transition

    Science.gov (United States)

    Kolb, Evelyne; Algarra, Nicolas; Vandembroucq, Damien; Lazarus, Arnaud

    2015-11-01

    We propose a new fluid/structure interaction in the unusual case of a dense granular medium flowing against an elastic fibre acting as a flexible intruder. We experimentally studied the deflection of a mylar flexible beam clamped at one side, the other free side facing a 2D granular flow in a horizontal cell moving at a constant velocity. We investigated the reconfiguration of the fibre as a function of the fibre's rigidity and of the granular packing fraction close but below the jamming in 2D. Imposing the fibre geometry like its length or thickness sets the critical buckling force the fibre is able to resist if it was not supported by lateral grains, while increasing the granular packing fraction might laterally consolidate the fibre and prevent it from buckling. But on the other side, the approach to jamming transition by increasing the granular packing fraction will be characterized by a dramatically increasing size of the cluster of connected grains forming a solid block acting against the fibre, which might promote the fibre's deflection. Thus, we investigated the granular flow fields, the fibre's deflexion as well as the forces experienced by the fibre and compared them with theoretical predictions from elastica for different loadings along the fibre. PMMH, CNRS UMR 7636, UPMC, ESPCI-ParisTech, 10 rue Vauquelin, 75231 Paris Cedex 05, France.

  8. Computational domain discretization in numerical analysis of flow within granular materials

    Science.gov (United States)

    Sosnowski, Marcin

    2018-06-01

    The discretization of computational domain is a crucial step in Computational Fluid Dynamics (CFD) because it influences not only the numerical stability of the analysed model but also the agreement of obtained results and real data. Modelling flow in packed beds of granular materials is a very challenging task in terms of discretization due to the existence of narrow spaces between spherical granules contacting tangentially in a single point. Standard approach to this issue results in a low quality mesh and unreliable results in consequence. Therefore the common method is to reduce the diameter of the modelled granules in order to eliminate the single-point contact between the individual granules. The drawback of such method is the adulteration of flow and contact heat resistance among others. Therefore an innovative method is proposed in the paper: single-point contact is extended to a cylinder-shaped volume contact. Such approach eliminates the low quality mesh elements and simultaneously introduces only slight distortion to the flow as well as contact heat transfer. The performed analysis of numerous test cases prove the great potential of the proposed method of meshing the packed beds of granular materials.

  9. Effective Wall Friction in Wall-Bounded 3D Dense Granular Flows

    OpenAIRE

    Artoni, Riccardo; Richard, Patrick

    2015-01-01

    to be published in Physical Review LettersThe numerical simulations were carried out at theCCIPL (Centre de Calcul Intensif des Pays de la Loire)under the project MTEEGD; We report numerical simulations on granular shear flows confined between two flat but frictional sidewalls. Novel regimes differing by their strain localization features are observed. They originate from the competition between dissipation at the sidewalls and dissipation in the bulk of the flow. The effective friction at si...

  10. Discharge flow of a granular media from a silo: effect of the packing fraction and of the hopper angle

    Science.gov (United States)

    Benyamine, Mebirika; Aussillous, Pascale; Dalloz-Dubrujeaud, Blanche

    2017-06-01

    Silos are widely used in the industry. While empirical predictions of the flow rate, based on scaling laws, have existed for more than a century (Hagen 1852, translated in [1] - Beverloo et al. [2]), recent advances have be made on the understanding of the control parameters of the flow. In particular, using continuous modeling together with a mu(I) granular rheology seem to be successful in predicting the flow rate for large numbers of beads at the aperture (Staron et al.[3], [4]). Moreover Janda et al.[5] have shown that the packing fraction at the outlet plays an important role when the number of beads at the apeture decreases. Based on these considerations, we have studied experimentally the discharge flow of a granular media from a rectangular silo. We have varied two main parameters: the angle of the hopper, and the bulk packing fraction of the granular material by using bidisperse mixtures. We propose a simple physical model to describe the effect of these parameters, considering a continuous granular media with a dilatancy law at the outlet. This model predicts well the dependance of the flow rate on the hopper angle as well as the dependance of the flow rate on the fine mass fraction of a bidisperse mixture.

  11. Relaxation-type nonlocal inertial-number rheology for dry granular flows

    Science.gov (United States)

    Lee, Keng-lin; Yang, Fu-ling

    2017-12-01

    We propose a constitutive model to describe the nonlocality, hysteresis, and several flow features of dry granular materials. Taking the well-known inertial number I as a measure of sheared-induced local fluidization, we derive a relaxation model for I according to the evolution of microstructure during avalanche and dissipation processes. The model yields a nonmonotonic flow law for a homogeneous flow, accounting for hysteretic solid-fluid transition and intermittency in quasistatic flows. For an inhomogeneous flow, the model predicts a generalized Bagnold shear stress revealing the interplay of two microscopic nonlocal mechanisms: collisions among correlated structures and the diffusion of fluidization within the structures. In describing a uniform flow down an incline, the model reproduces the hysteretic starting and stopping heights and the Pouliquen flow rule for mean velocity. Moreover, a dimensionless parameter reflecting the nonlocal effect on the flow is discovered, which controls the transition between Bagnold and creeping flow dynamics.

  12. A Stochastic Description of Transition Between Granular Flow States

    International Nuclear Information System (INIS)

    Huang Decai; Sun Gang; Lu Kunquan

    2007-01-01

    Two-dimensional granular flow in a channel with small exit is studied by molecular dynamics simulations. We firstly define a key area near the exit, which is considered to be the choke area of the system. Then we observe the time variation of the local packing fraction and flow rate in this area for several fixed inflow rate, and find that these quantities change abruptly when the transition from dilute flow state to dense flow state happens. A relationship between the local flow rate and the local packing fraction in the key area is also given. The relationship is a continuous function under the fixed particle number condition, and has the characteristic that the flow rate has a maximum at a moderate packing fraction and the packing fraction is terminated at a high value with negative slope. By use of the relationship, the properties of the flow states under the fixed inflow rate condition are discussed in detail, and the discontinuities and the complex time variation behavior observed in the preexisting works are naturally explained by a stochastic process.

  13. Capturing 2D transient surface data of granular flows against obstacles with an RGB-D sensor

    Science.gov (United States)

    Caviedes-Voullieme, Daniel; Juez, Carmelo; Murillo, Javier; Garcia-Navarro, Pilar

    2014-05-01

    Landslides are an ubiquitous natural hazard, and therefore human infrastructure and settlements are often at risk in mountainous regions. In order to better understand and predict landslides, systematic studies of the phenomena need to be undertaken. In particular, computational tools which allow for analysis of field problems require to be thoroughly tested, calibrated and validated under controlled conditions. And to do so, it is necessary for such controlled experiments to be fully characterized in the same terms as the numerical model requires. This work presents an experimental study of dry granular flow over a rough bed with topography which resembles a mountain valley. It has an upper region with a very high slope. The geometry of the bed describes a fourth order polynomial curve, with a low point with zero slope, and afterwards a short region with adverse slope. Obstacles are present in the lower regions which are used as model geometries of human structures. The experiments consisted of a sudden release a mass of sand on the upper region, and allowing it to flow downslope. Furthermore, it has been frequent in previous studies to measure final states of the granular mass at rest, but seldom has transient data being provided, and never for the entire field. In this work we present transient measurements of the moving granular surfaces, obtained with a consumer-grade RGB-D sensor. The sensor, developed for the videogame industry, allows to measure the moving surface of the sand, thus obtaining elevation fields. The experimental results are very consistent and repeatable. The measured surfaces clearly show the distinctive features of the granular flow around the obstacles and allow to qualitatively describe the different flow patterns. More importantly, the quantitative description of the granular surface allows for benchmarking and calibration of predictive numerical models, key in scaling the small-scale experimental knowledge into the field.

  14. Flow of Dense Granular Suspensions on an Inclined Plane

    Science.gov (United States)

    Bonnoit, C.; Lanuza, J.; Lindner, A.; Clément, E.

    2008-07-01

    We investigate the flow behavior of dense granular suspensions, by the use of an inclined plane. The suspensions are prepared at high packing fractions and consist of spherical non-Brownian particles density matched with the suspending fluid. On the inclined plane, we perform a systematic study of the surface velocity as a function of the layer thickness for various flow rates and tilt angles. We perform measurements on a classical rheometer (parallel-plate rheometer) that is shown to be in good agreement with existing models, up to a volume fraction of 50%. Comparing these results, we show that the flow on an inclined plane can, up to a volume fraction of 50%, indeed be described by a purely viscous model in agreement with the results from classical rheometry.

  15. Erosion by sliding wear in granular flows: Experiments with realistic contact forces

    Science.gov (United States)

    Stark, C. P.; Hung, C. Y.; Smith, B.; Li, L.; Grinspun, E.; Capart, H.

    2015-12-01

    Debris flow erosion is a powerful and sometimes dominant process in steep channels. Despite its importance, this phenomenon is relatively little studied in the lab. The large drum experiments of Hsu are a notable exception, in which almost-field-scale impact forces were generated at the head of a synthetic debris flow whose properties (grain size, proportion of fines, etc) were varied widely.A key challenge in these and similar experiments is to explore how erosion rate varies as a function of the scale of the flow (thereby varying inertial stresses, impact forces, etc). The geometrical limitations of most lab experiments, and their short run time, severely limit the scope of such explorations.We achieve this scale exploration in a set of drum erosion experiments by varying effective gravity across several orders of magnitude (1g, 10g, 100g) in a geotechnical centrifuge. By half-filling our 40cm-diameter drum with dry 2.3mm grains, placing a synthetic rock plate at the back and a glass plate at the front 3cm apart, and rotating the drum at 1-50rpm, we simulate wear in a channelized dry granular flow. In contrast to Hsu's experiments, we focus on sliding wear erosion at the flow boundary rather than impact/frictional wear at the flow head. By varying effective gravity from 1g-100g we can tune the pressure exerted by the grains at the boundary without having to change the scale of our apparatus. Using a recently developed depth-averaged, kinetic-energy closure theory for granular flow, we can simultaneously tune the drum rotation rate such that the flow dynamics remain invariant. We can thereby explore how changing the scale of a granular flow, and thus the contact forces of grains on the boundary, controls the rate of rock erosion. Using a small apparatus we can simulate the erosion generated by debris flows several meters deep involving grains up to 10cm in diameter.Our results suggest that sliding wear is the main erosion process, and are consistent with Archard

  16. Shear localization and effective wall friction in a wall bounded granular flow

    Science.gov (United States)

    Artoni, Riccardo; Richard, Patrick

    2017-06-01

    In this work, granular flow rheology is investigated by means of discrete numerical simulations of a torsional, cylindrical shear cell. Firstly, we focus on azimuthal velocity profiles and study the effect of (i) the confining pressure, (ii) the particle-wall friction coefficient, (iii) the rotating velocity of the bottom wall and (iv) the cell diameter. For small cell diameters, azimuthal velocity profiles are nearly auto-similar, i.e. they are almost linear with the radial coordinate. Different strain localization regimes are observed : shear can be localized at the bottom, at the top of the shear cell, or it can be even quite distributed. This behavior originates from the competition between dissipation at the sidewalls and dissipation in the bulk of the system. Then we study the effective friction at the cylindrical wall, and point out the strong link between wall friction, slip and fluctuations of forces and velocities. Even if the system is globally below the sliding threshold, force fluctuations trigger slip events, leading to a nonzero wall slip velocity and an effective wall friction coefficient different from the particle-wall one. A scaling law was found linking slip velocity, granular temperature in the main flow direction and effective friction. Our results suggest that fluctuations are an important ingredient for theories aiming to capture the interface rheology of granular materials.

  17. A theoretical and numerical study of the flow of granular materials down an inclined plane. [Quarterly progress report, January--March 1995

    Energy Technology Data Exchange (ETDEWEB)

    Rajagopal, K.R.

    1995-09-01

    The mechanics of the flowing granular materials such as coal, agricultural products, fertilizers, dry chemicals, metal ores, etc. have received a great deal of attention as it has relevance to several important technological problems. Despite wide interest and more than five decades of experimental and theoretical investigations, most aspects of the behavior of flowing granular materials are still not well understood. So Experiments have to be devised which quantify and describe the non-linear behavior of the granular materials, and theories developed which can explain the experimentally observed facts. Here we carry out a systematic numerical study of the flow of granular materials down an inclined plane using the models that stem from both the continuum theory approach and the kinetic theory approach. We also look at the existence of solutions, multiplicity and stability of solutions to the governing equations.

  18. Deformation-driven diffusion and plastic flow in amorphous granular pillars.

    Science.gov (United States)

    Li, Wenbin; Rieser, Jennifer M; Liu, Andrea J; Durian, Douglas J; Li, Ju

    2015-06-01

    We report a combined experimental and simulation study of deformation-induced diffusion in compacted quasi-two-dimensional amorphous granular pillars, in which thermal fluctuations play a negligible role. The pillars, consisting of bidisperse cylindrical acetal plastic particles standing upright on a substrate, are deformed uniaxially and quasistatically by a rigid bar moving at a constant speed. The plastic flow and particle rearrangements in the pillars are characterized by computing the best-fit affine transformation strain and nonaffine displacement associated with each particle between two stages of deformation. The nonaffine displacement exhibits exponential crossover from ballistic to diffusive behavior with respect to the cumulative deviatoric strain, indicating that in athermal granular packings, the cumulative deviatoric strain plays the role of time in thermal systems and drives effective particle diffusion. We further study the size-dependent deformation of the granular pillars by simulation, and find that different-sized pillars follow self-similar shape evolution during deformation. In addition, the yield stress of the pillars increases linearly with pillar size. Formation of transient shear lines in the pillars during deformation becomes more evident as pillar size increases. The width of these elementary shear bands is about twice the diameter of a particle, and does not vary with pillar size.

  19. Traffic and Granular Flow '11

    CERN Document Server

    Buslaev, Alexander; Bugaev, Alexander; Yashina, Marina; Schadschneider, Andreas; Schreckenberg, Michael; TGF11

    2013-01-01

    This book continues the biannual series of conference proceedings, which has become a classical reference resource in traffic and granular research alike. It addresses new developments at the interface between physics, engineering and computational science. Complex systems, where many simple agents, be they vehicles or particles, give rise to surprising and fascinating phenomena.   The contributions collected in these proceedings cover several research fields, all of which deal with transport. Topics include highway, pedestrian and internet traffic, granular matter, biological transport, transport networks, data acquisition, data analysis and technological applications. Different perspectives, i.e. modeling, simulations, experiments and phenomenological observations, are considered.

  20. Fundamental change of granular flows dynamics, deposition and erosion processes at sufficiently high slope angles: insights from laboratory experiments

    Science.gov (United States)

    Farin, M.; Mangeney, A.; Roche, O.

    2013-12-01

    Geophysical granular flows commonly interact with their substrate in various ways depending on the mechanical properties of the underlying material. Granular substrates, resulting from deposition of earlier flows or various geological events, are often eroded by avalanches [see Hungr and Evans, 2004 for review]. The entrainment of underlying debris by the flow is suspected to affect flow dynamics because qualitative and quantitative field observations suggest that it can increase the flow velocity and deposit extent, depending on the geological setting and flow type [Sovilla et al., 2006; Iverson et al., 2011]. Direct measurement of material entrainment in nature, however, is very difficult. We conducted laboratory experiments on granular column collapse over an inclined channel with and without an erodible bed of granular material. The controlling parameters were the channel slope angle, the granular column volume and its aspect ratio (i.e. height over length), the inclination of the column with respect to the channel base, the channel width, and the thickness and compaction of the erodible bed. For slope angles below a critical value θc, between 10° and 16°, the runout distance rf is proportional to the initial column height h0 and is unaffected by the presence of an erodible bed. On slopes greater than θc, the flow dynamics change fundamentally since a last phase of slow propagation develops at the end of the flow front deceleration, and prolongates significantly the flow duration. This phase has similar characteristics that steady, uniform flows. The slow propagation phase lasts longer for increasing column volume, column inclination with respect to the slope, and channel width, and for decreasing column aspect ratio. It is however independent of the maximum front velocity and, on an erodible bed, of the maximum depth of excavation within the bed. Both on rigid and erodible beds, the increase of the slow propagation phase duration has a crucial effect on

  1. Viscoinertial regime of immersed granular flows

    Science.gov (United States)

    Amarsid, L.; Delenne, J.-Y.; Mutabaruka, P.; Monerie, Y.; Perales, F.; Radjai, F.

    2017-07-01

    By means of extensive coupled molecular dynamics-lattice Boltzmann simulations, accounting for grain dynamics and subparticle resolution of the fluid phase, we analyze steady inertial granular flows sheared by a viscous fluid. We show that, for a broad range of system parameters (shear rate, confining stress, fluid viscosity, and relative fluid-grain density), the frictional strength and packing fraction can be described by a modified inertial number incorporating the fluid effect. In a dual viscous description, the effective viscosity diverges as the inverse square of the difference between the packing fraction and its jamming value, as observed in experiments. We also find that the fabric and force anisotropies extracted from the contact network are well described by the modified inertial number, thus providing clear evidence for the role of these key structural parameters in dense suspensions.

  2. Dynamic Deformation and Collapse of Granular Columns

    Science.gov (United States)

    Uenishi, K.; Tsuji, K.; Doi, S.

    2009-12-01

    Large dynamic deformation of granular materials may be found in nature not only in the failure of slopes and cliffs — due to earthquakes, rock avalanches, debris flows and landslides — but also in earthquake faulting itself. Granular surface flows often consist of solid grains and intergranular fluid, but the effect of the fluid may be usually negligible because the volumetric concentration of grains is in many cases high enough for interparticle forces to dominate momentum transport. Therefore, the investigation of dry granular flow of a mass might assist in further understanding of the above mentioned geophysical events. Here, utilizing a high-speed digital video camera system, we perform a simple yet fully-controlled series of laboratory experiments related to the collapse of granular columns. We record, at an interval of some microseconds, the dynamic transient granular mass flow initiated by abrupt release of a tube that contains dry granular materials. The acrylic tube is partially filled with glass beads and has a cross-section of either a fully- or semi-cylindrical shape. Upon sudden removal of the tube, the granular solid may fragment under the action of its own weight and the particles spread on a rigid horizontal plane. This study is essentially the extension of the previous ones by Lajeunesse et al. (Phys. Fluids 2004) and Uenishi and Tsuji (JPGU 2008), but the striped layers of particles in a semi-cylindrical tube, newly introduced in this contribution, allow us to observe the precise particle movement inside the granular column: The development of slip lines inside the column and the movement of particles against each other can be clearly identified. The major controlling parameters of the spreading dynamics are the initial aspect ratio of the granular (semi-)cylindrical column, the frictional properties of the horizontal plane (substrate) and the size of beads. We show the influence of each parameter on the average flow velocity and final radius

  3. Transient response in granular quasi-two-dimensional bounded heap flow.

    Science.gov (United States)

    Xiao, Hongyi; Ottino, Julio M; Lueptow, Richard M; Umbanhowar, Paul B

    2017-10-01

    We study the transition between steady flows of noncohesive granular materials in quasi-two-dimensional bounded heaps by suddenly changing the feed rate. In both experiments and simulations, the primary feature of the transition is a wedge of flowing particles that propagates downstream over the rising free surface with a wedge front velocity inversely proportional to the square root of time. An additional longer duration transient process continues after the wedge front reaches the downstream wall. The entire transition is well modeled as a moving boundary problem with a diffusionlike equation derived from local mass balance and a local relation between the flux and the surface slope.

  4. Flexible fiber in interaction with a dense granular flow close to the jamming transition

    Science.gov (United States)

    Algarra, Nicolas; Leang, Marguerite; Lazarus, Arnaud; Vandembroucq, Damien; Kolb, Evelyne

    2017-06-01

    We propose a new fluid/structure interaction in the unusual case of a dense granular medium flowing against an elastic fiber acting as a flexible intruder. We study experimentally the reconfiguration and the forces exerted on the flexible fiber produced by the flow at a constant and low velocity of a two-dimensional disordered packing of grains close but below the jamming transition.

  5. Granular flow considerations in the design of a cascade solid breeder reaction chamber

    International Nuclear Information System (INIS)

    Walton, O.R.

    1983-10-01

    Both horizontally and vertically oriented rotating chambers with granular material held on the inner surface by centrifugal action are examined. Modifications to the condition for controlled quasi-static flow on an incline plane, phi/sub w/ 0 +- 10 0 for ceramic particles and metal surfaces. For vertical orientations the maximum half-angle of the top cone is slightly less than the wall friction angle phi/sub w/ while the lower portion can have a half angle as large as (90 0 - phi/sub w). Percolation of fines through shearing granular solids is briefly discussed and recommended experimental and calculational studies to obtain a better understanding of this behavior are described

  6. Flexible fiber in interaction with a dense granular flow close to the jamming transition

    Directory of Open Access Journals (Sweden)

    Algarra Nicolas

    2017-01-01

    Full Text Available We propose a new fluid/structure interaction in the unusual case of a dense granular medium flowing against an elastic fiber acting as a flexible intruder. We study experimentally the reconfiguration and the forces exerted on the flexible fiber produced by the flow at a constant and low velocity of a two-dimensional disordered packing of grains close but below the jamming transition.

  7. Network flow model of force transmission in unbonded and bonded granular media.

    Science.gov (United States)

    Tordesillas, Antoinette; Tobin, Steven T; Cil, Mehmet; Alshibli, Khalid; Behringer, Robert P

    2015-06-01

    An established aspect of force transmission in quasistatic deformation of granular media is the existence of a dual network of strongly versus weakly loaded particles. Despite significant interest, the regulation of strong and weak forces through the contact network remains poorly understood. We examine this aspect of force transmission using data on microstructural fabric from: (I) three-dimensional discrete element models of grain agglomerates of bonded subspheres constructed from in situ synchrotron microtomography images of silica sand grains under unconfined compression and (II) two-dimensional assemblies of unbonded photoelastic circular disks submitted to biaxial compression under constant volume. We model force transmission as a network flow and solve the maximum flow-minimum cost (MFMC) problem, the solution to which yields a percolating subnetwork of contacts that transmits the "maximum flow" (i.e., the highest units of force) at "least cost" (i.e., the dissipated energy from such transmission). We find the MFMC describes a two-tier hierarchical architecture. At the local level, it encapsulates intraconnections between particles in individual force chains and in their conjoined 3-cycles, with the most common configuration having at least one force chain contact experiencing frustrated rotation. At the global level, the MFMC encapsulates interconnections between force chains. The MFMC can be used to predict most of the force chain particles without need for any information on contact forces, thereby suggesting the network flow framework may have potential broad utility in the modeling of force transmission in unbonded and bonded granular media.

  8. Rheology of confined granular flows: scale invariance, glass transition, and friction weakening.

    Science.gov (United States)

    Richard, P; Valance, A; Métayer, J-F; Sanchez, P; Crassous, J; Louge, M; Delannay, R

    2008-12-12

    We study fully developed, steady granular flows confined between parallel flat frictional sidewalls using numerical simulations and experiments. Above a critical rate, sidewall friction stabilizes the underlying heap at an inclination larger than the angle of repose. The shear rate is constant and independent of inclination over much of the flowing layer. In the direction normal to the free surface, the solid volume fraction increases on a scale equal to half the flowing layer depth. Beneath a critical depth at which internal friction is invariant, grains exhibit creeping and intermittent cage motion similar to that in glasses, causing gradual weakening of friction at the walls.

  9. An accurate tangential force-displacement model for granular-flow simulations: Contacting spheres with plastic deformation, force-driven formulation

    International Nuclear Information System (INIS)

    Vu-Quoc, L.; Lesburg, L.; Zhang, X.

    2004-01-01

    An elasto-plastic frictional tangential force-displacement (TFD) model for spheres in contact for accurate and efficient granular-flow simulations is presented in this paper; the present TFD is consistent with the elasto-plastic normal force-displacement (NFD) model presented in [ASME Journal of Applied Mechanics 67 (2) (2000) 363; Proceedings of the Royal Society of London, Series A 455 (1991) (1999) 4013]. The proposed elasto-plastic frictional TFD model is accurate, and is validated against non-linear finite-element analyses involving plastic flows under both loading and unloading conditions. The novelty of the present TFD model lies in (i) the additive decomposition of the elasto-plastic contact area radius into an elastic part and a plastic part, (ii) the correction of the particles' radii at the contact point, and (iii) the correction of the particles' elastic moduli. The correction of the contact-area radius represents an effect of plastic deformation in colliding particles; the correction of the radius of curvature represents a permanent indentation after impact; the correction of the elastic moduli represents a softening of the material due to plastic flow. The construction of both the present elasto-plastic frictional TFD model and its consistent companion, the elasto-plastic NFD model, parallels the formalism of the continuum theory of elasto-plasticity. Both NFD and TFD models form a coherent set of force-displacement (FD) models not available hitherto for granular-flow simulations, and are consistent with the Hertz, Cattaneo, Mindlin, Deresiewicz contact mechanics theory. Together, these FD models will allow for efficient simulations of granular flows (or granular gases) involving a large number of particles

  10. Confined granular flow in silos experimental and numerical investigations

    CERN Document Server

    Tejchman, Jacek

    2013-01-01

      During confined flow of bulk solids in silos some characteristic phenomena can be created, such as: —         sudden and significant increase of wall stresses, —         different flow patterns, —         formation and propagation of wall and interior shear zones, —         fluctuation of pressures and, —         strong autogenous dynamic effects. These phenomena have not been described or explained in detail yet. The main intention of the experimental and theoretical research presented in this book is to explain the above mentioned phenomena in granular bulk solids and to describe them with numerical FE models verified by experimental results.

  11. Coexistence and transition between shear zones in slow granular flows.

    Science.gov (United States)

    Moosavi, Robabeh; Shaebani, M Reza; Maleki, Maniya; Török, János; Wolf, Dietrich E; Losert, Wolfgang

    2013-10-04

    We report experiments on slow granular flows in a split-bottom Couette cell that show novel strain localization features. Nontrivial flow profiles have been observed which are shown to be the consequence of simultaneous formation of shear zones in the bulk and at the boundaries. The fluctuating band model based on a minimization principle can be fitted to the experiments over a large variation of morphology and filling height with one single fit parameter, the relative friction coefficient μ(rel) between wall and bulk. The possibility of multiple shear zone formation is controlled by μ(rel). Moreover, we observe that the symmetry of an initial state, with coexisting shear zones at both side walls, breaks spontaneously below a threshold value of the shear velocity. A dynamical transition between two asymmetric flow states happens over a characteristic time scale which depends on the shear strength.

  12. Incorporation of velocity-dependent restitution coefficient and particle surface friction into kinetic theory for modeling granular flow cooling.

    Science.gov (United States)

    Duan, Yifei; Feng, Zhi-Gang

    2017-12-01

    Kinetic theory (KT) has been successfully used to model rapid granular flows in which particle interactions are frictionless and near elastic. However, it fails when particle interactions become frictional and inelastic. For example, the KT is not able to accurately predict the free cooling process of a vibrated granular medium that consists of inelastic frictional particles under microgravity. The main reason that the classical KT fails to model these flows is due to its inability to account for the particle surface friction and its inelastic behavior, which are the two most important factors that need be considered in modeling collisional granular flows. In this study, we have modified the KT model that is able to incorporate these two factors. The inelasticity of a particle is considered by establishing a velocity-dependent expression for the restitution coefficient based on many experimental studies found in the literature, and the particle friction effect is included by using a tangential restitution coefficient that is related to the particle friction coefficient. Theoretical predictions of the free cooling process by the classical KT and the improved KT are compared with the experimental results from a study conducted on an airplane undergoing parabolic flights without the influence of gravity [Y. Grasselli, G. Bossis, and G. Goutallier, Europhys. Lett. 86, 60007 (2009)10.1209/0295-5075/86/60007]. Our results show that both the velocity-dependent restitution coefficient and the particle surface friction are important in predicting the free cooling process of granular flows; the modified KT model that integrates these two factors is able to improve the simulation results and leads to better agreement with the experimental results.

  13. Granular flows on erodible layers: type and evolution of flow and deposit structures

    Science.gov (United States)

    Crosta, G.; De Blasio, F.; De Caro, M.; Volpi, G.; Frattini, P.

    2012-04-01

    The interaction of a fast moving landslide mass with the basal layer over which movement takes place has been discussed in previous contributions. Nevertheless, the evolution of the structures within the moving mass and the erodible layer are still to be described in detail (Hungr and Evans, 2004; Crosta et al., 1992, 2006, 2009, 2011; Dufresne et al., 2010; Mangeney et al., 2010) and modeling results (Crosta et al., 2006, 2009, 2011; Mangeney et al., 2010). We present some of the results from a campaign of laboratory experiments aimed at studying the evolution of a granular flow at the impact with and during the successive spreading over a cohesionless erodible layer. We performed these test to study the processes and to collect data and evidences to compare them with the results of numerical simulations and to verify capabilities of numerical codes. The laboratory setup consists of an inclined slope and an horizontal sector where release and transport, and deposition take place, respectively. Materials used for the tests are: a uniform rounded siliceous sand (Hostun sand; 0.125-0.5 mm) commonly adopted in lab tests because free of scale effects, and a gravel made of angular elements (12 mm in ave. size). Both the materials have been tested in dry conditions. Different slope angles have been tested (40, 45, 50, 55, 50, 66°) as well as different thicknesses of the erodible layer (0, 0.5, 1, 2 cm) and volumes of the released material (1.5, 3, 5, 9.6 liters). Tests have been monitored by means of a high speed camera and the pre- and post-failure geometries have been surveyed by means of a laser scanner. Deposit description allowed also the computation of volumes and the characterization of the different structures developed and frozen into the deposit. Experiments allowed us to observe the extreme processes occurring during the movement and the mise en place of the deposits. In particular, we observe the formation of a clear wave-like feature developing during the

  14. Spreading of a granular droplet

    Science.gov (United States)

    Clement, Eric; Sanchez, Ivan; Raynaud, Franck; Lanuza, Jose; Andreotti, Bruno; Aranson, Igor

    2008-03-01

    The influence of controlled vibrations on the granular rheology is investigated in a specifically designed experiment in which a granular film spreads under the action of horizontal vibrations. A nonlinear diffusion equation is derived theoretically that describes the evolution of the deposit shape. A self-similar parabolic shape (the``granular droplet'') and a spreading dynamics are predicted that both agree quantitatively with the experimental results. The theoretical analysis is used to extract effective friction coefficients between the base and the granular layer under sustained and controlled vibrations. A shear thickening regime characteristic of dense granular flows is evidenced at low vibration energy, both for glass beads and natural sand. Conversely, shear thinning is observed at high agitation.

  15. Tracing Thermal Creep Through Granular Media

    Science.gov (United States)

    Steinpilz, Tobias; Teiser, Jens; Koester, Marc; Schywek, Mathias; Wurm, Gerhard

    2017-08-01

    A temperature gradient within a granular medium at low ambient pressure drives a gas flow through the medium by thermal creep. We measured the resulting air flow for a sample of glass beads with particle diameters between 290 μ m and 420 μ m for random close packing. Ambient pressure was varied between 1 Pa and 1000 Pa. The gas flow was quantified by means of tracer particles during parabolic flights. The flow varies systematically with pressure between 0.2 cm/s and 6 cm/s. The measured flow velocities are in quantitative agreement to model calculations that treat the granular medium as a collection of linear capillaries.

  16. Ill-posedness of Dynamic Equations of Compressible Granular Flow

    Science.gov (United States)

    Shearer, Michael; Gray, Nico

    2017-11-01

    We introduce models for 2-dimensional time-dependent compressible flow of granular materials and suspensions, based on the rheology of Pouliquen and Forterre. The models include density dependence through a constitutive equation in which the density or volume fraction of solid particles with material density ρ* is taken as a function of an inertial number I: ρ = ρ * Φ(I), in which Φ(I) is a decreasing function of I. This modelling has different implications from models relying on critical state soil mechanics, in which ρ is treated as a variable in the equations, contributing to a flow rule. The analysis of the system of equations builds on recent work of Barker et al in the incompressible case. The main result is the identification of a criterion for well-posedness of the equations. We additionally analyze a modification that applies to suspensions, for which the rheology takes a different form and the inertial number reflects the role of the fluid viscosity.

  17. The Rolling Transition in a Granular Flow along a Rotating Wall

    Directory of Open Access Journals (Sweden)

    Aurélie Le Quiniou

    2011-11-01

    Full Text Available The flow of a dry granular material composed of spherical particles along a rotating boundary has been studied by the discrete element method (DEM. This type of flow is used, among others, as a process to spread particles. The flow consists of several phases. A compression phase along the rotating wall is followed by an elongation of the flow along the same boundary. Eventually, the particles slide or roll independently along the boundary. We show that the main motion of the flow can be characterized by a complex deformation rate of traction/compression and shear. We define numerically an effective friction coefficient of the flow on the scale of the continuum and show a strong decrease of this effective friction beyond a certain critical friction coefficient μ*. We correlate this phenomenon with the apparition of a new transition from a sliding regime to a rolling without sliding regime that we called the rolling transition; this dynamic transition is controlled by the value of the friction coefficient between the particle and the wall. We show that the spherical shape for the particles may represent an optimum for the flow in terms of energetic.

  18. Long runout landslides: a solution from granular mechanics

    Directory of Open Access Journals (Sweden)

    Stanislav eParez

    2015-10-01

    Full Text Available Large landslides exhibit surprisingly long runout distances compared to a rigid body sliding from the same slope, and the mechanism of this phenomena has been studied for decades. This paper shows that the observed long runouts can be explained quite simply via a granular pile flowing downhill, while collapsing and spreading, without the need for frictional weakening that has traditionally been suggested to cause long runouts. Kinematics of the granular flow is divided into center of mass motion and spreading due to flattening of the flowing mass. We solve the center of mass motion analytically based on a frictional law valid for granular flow, and find that center of mass runout is similar to that of a rigid body. Based on the shape of deposits observed in experiments with collapsing granular columns and numerical simulations of landslides, we derive a spreading length Rf~V^1/3. Spreading of a granular pile, leading to a deposit angle much lower than the angle of repose or the dynamic friction angle, is shown to be an important, often dominating, contribution to the total runout distance, accounting for the long runouts observed for natural landslides.

  19. A Two-Phase Solid/Fluid Model for Dense Granular Flows Including Dilatancy Effects

    Science.gov (United States)

    Mangeney, Anne; Bouchut, Francois; Fernandez-Nieto, Enrique; Narbona-Reina, Gladys

    2015-04-01

    We propose a thin layer depth-averaged two-phase model to describe solid-fluid mixtures such as debris flows. It describes the velocity of the two phases, the compression/dilatation of the granular media and its interaction with the pore fluid pressure, that itself modifies the friction within the granular phase (Iverson et al., 2010). The model is derived from a 3D two-phase model proposed by Jackson (2000) based on the 4 equations of mass and momentum conservation within the two phases. This system has 5 unknowns: the solid and fluid velocities, the solid and fluid pressures and the solid volume fraction. As a result, an additional equation inside the mixture is necessary to close the system. Surprisingly, this issue is inadequately accounted for in the models that have been developed on the basis of Jackson's work (Bouchut et al., 2014). In particular, Pitman and Le replaced this closure simply by imposing an extra boundary condition at the surface of the flow. When making a shallow expansion, this condition can be considered as a closure condition. However, the corresponding model cannot account for a dissipative energy balance. We propose here an approach to correctly deal with the thermodynamics of Jackson's equations. We close the mixture equations by a weak compressibility relation involving a critical density, or equivalently a critical pressure. Moreover, we relax one boundary condition, making it possible for the fluid to escape the granular media when compression of the granular mass occurs. Furthermore, we introduce second order terms in the equations making it possible to describe the evolution of the pore fluid pressure in response to the compression/dilatation of the granular mass without prescribing an extra ad-hoc equation for the pore pressure. We prove that the energy balance associated with this Jackson closure is dissipative, as well as its thin layer associated model. We present several numerical tests for the 1D case that are compared to the

  20. HYPERELASTIC MODELS FOR GRANULAR MATERIALS

    Energy Technology Data Exchange (ETDEWEB)

    Humrickhouse, Paul W; Corradini, Michael L

    2009-01-29

    A continuum framework for modeling of dust mobilization and transport, and the behavior of granular systems in general, has been reviewed, developed and evaluated for reactor design applications. The large quantities of micron-sized particles expected in the international fusion reactor design, ITER, will accumulate into piles and layers on surfaces, which are large relative to the individual particle size; thus, particle-particle, rather than particle-surface, interactions will determine the behavior of the material in bulk, and a continuum approach is necessary and justified in treating the phenomena of interest; e.g., particle resuspension and transport. The various constitutive relations that characterize these solid particle interactions in dense granular flows have been discussed previously, but prior to mobilization their behavior is not even fluid. Even in the absence of adhesive forces between particles, dust or sand piles can exist in static equilibrium under gravity and other forces, e.g., fluid shear. Their behavior is understood to be elastic, though not linear. The recent “granular elasticity” theory proposes a non-linear elastic model based on “Hertz contacts” between particles; the theory identifies the Coulomb yield condition as a requirement for thermodynamic stability, and has successfully reproduced experimental results for stress distributions in sand piles. The granular elasticity theory is developed and implemented in a stand- alone model and then implemented as part of a finite element model, ABAQUS, to determine the stress distributions in dust piles subjected to shear by a fluid flow. We identify yield with the onset of mobilization, and establish, for a given dust pile and flow geometry, the threshold pressure (force) conditions on the surface due to flow required to initiate it. While the granular elasticity theory applies strictly to cohesionless granular materials, attractive forces are clearly important in the interaction of

  1. Mathematical models of granular matter

    CERN Document Server

    Mariano, Paolo; Giovine, Pasquale

    2008-01-01

    Granular matter displays a variety of peculiarities that distinguish it from other appearances studied in condensed matter physics and renders its overall mathematical modelling somewhat arduous. Prominent directions in the modelling granular flows are analyzed from various points of view. Foundational issues, numerical schemes and experimental results are discussed. The volume furnishes a rather complete overview of the current research trends in the mechanics of granular matter. Various chapters introduce the reader to different points of view and related techniques. New models describing granular bodies as complex bodies are presented. Results on the analysis of the inelastic Boltzmann equations are collected in different chapters. Gallavotti-Cohen symmetry is also discussed.

  2. Flow above and within granular media composed of spherical and non-spherical particles - using a 3D numerical model

    Science.gov (United States)

    Bartzke, Gerhard; Kuhlmann, Jannis; Huhn, Katrin

    2016-04-01

    The entrainment of single grains and, hence, their erosion characteristics are dependent on fluid forcing, grain size and density, but also shape variations. To quantitatively describe and capture the hydrodynamic conditions around individual grains, researchers commonly use empirical approaches such as laboratory flume tanks. Nonetheless, it is difficult with such physical experiments to measure the flow velocities in the direct vicinity or within the pore spaces of sediments, at a sufficient resolution and in a non-invasive way. As a result, the hydrodynamic conditions in the water column, at the fluid-porous interface and within pore spaces of a granular medium of various grain shapes is not yet fully understood. For that reason, there is a strong need for numerical models, since these are capable of quantifying fluid speeds within a granular medium. A 3D-SPH (Smooth Particle Hydrodynamics) numerical wave tank model was set up to provide quantitative evidence on the flow velocities in the direct vicinity and in the interior of granular beds composed of two shapes as a complementary method to the difficult task of in situ measurement. On the basis of previous successful numerical wave tank models with SPH, the model geometry was chosen in dimensions of X=2.68 [m], Y=0.48 [m], and Z=0.8 [m]. Three suites of experiments were designed with a range of particle shape models: (1) ellipsoids with the long axis oriented in the across-stream direction, (2) ellipsoids with the long axis oriented in the along-stream direction, and (3) spheres. Particle diameters ranged from 0.04 [m] to 0.08 [m]. A wave was introduced by a vertical paddle that accelerated to 0.8 [m/s] perpendicular to the granular bed. Flow measurements showed that the flow velocity values into the beds were highest when the grains were oriented across the stream direction and lowest in case when the grains were oriented parallel to the stream, indicating that the model was capable to simulate simultaneously

  3. Dynamics of crater formations in immersed granular materials

    Science.gov (United States)

    Varas, G.; Vidal, V.; Géminard, J.

    2009-12-01

    Craters are part of the widespread phenomena observed in nature. Among the main applications to natural phenomena, aside from meteorite impact craters, are the formation and growth of volcanic edifices, by successive ejecta emplacement and/or erosion. The time evolution and dynamics play a crucial role here, as the competition between volcanic-jet mass-flux (degassing and ejecta) and crater-size evolution may control directly the eruptive regime. Crater morphology in dry granular material has been extensively studied, both experimentally and theoretically. Most of these studies investigate the final, steady crater shape resulting from the collision of solid bodies with the material surface and scaling laws are derived. In immersed granular material, craters generated by an underwater vortex ring, or underwater impact craters generated by landslide, have been reported. In a previous experimental study, Gostiaux et al. [Gran. Matt., 2002] have investigated the dynamics of air flowing through an immersed granular layer. They reported that, depending on the flow rate, the system exhibits two qualitatively different regimes: At small flow rate, the bubbling regime during which bubbles escape the granular layer independently one from another; At large flow rate, the open-channel regime which corresponds to the formation of a channel crossing the whole thickness of the granular bed through which air escapes almost continuously. At intermediate flow rate, a spontaneous alternation between these two regimes is observed. Here, we report the dynamics of crater formations at the free surface of an immersed granular bed, locally crossed by an ascending gas flow. We reproduce the experimental conditions of Gostiaux et al. (2002) in two dimensions: In a vertical Hele-Shaw cell, the crater consists of two sand piles which develop around the location of the gas emission. We observe that the typical size of the crater increases logarithmically with time, independently of the gas

  4. Segregating photoelastic particles in free-surface granular flows

    Science.gov (United States)

    Thomas, Amalia; Vriend, Nathalie; Environmental; Industrial Fluid Dynamics Team

    2017-11-01

    We present results from a novel experimental set-up creating 2D avalanches of photoelastic discs. Two distinct hoppers supply either monodisperse or bidisperse particles at adjustable flow-rates into a 2 meter long, narrow acrylic chute inclined at 20°. For 20-40 seconds the avalanche maintains a steady-state that accelerates and thins downstream. The chute basal roughness is variable, allowing for different flow profiles. Using a set of polarizers and a high-speed camera, we visualize and quantify the forces due to dynamic interactions between the discs using photoelastic theory. Velocity and density profiles are derived from particle tracking at different distances from the discharge point and are coarse-grained to obtain continuous fields. With the access to both force information and dynamical properties via particle-tracking, we can experimentally validate existing mu(I) and non-local rheologies. As an extension, we probe the effect of granular segregation in bimodal mixtures by using the two separate inflow hoppers. We derive the state of segregation along the avalanche channel and measure the segregation velocities of each species. This provides insight in, and a unique validation of, the fundamental physical processes that drive segregation in avalanching geometries.

  5. Concentration profiles in the wake of a sphere buried in a granular bed through which fluid flows

    International Nuclear Information System (INIS)

    Guedes de Carvalho, J.R.F.; Delgado, J.M.P.Q.; Alves, M.A.

    2005-01-01

    The concentration distribution in the wake of a soluble sphere immersed in a granular bed of inerts has been obtained numerically, for transport by both advection and diffusion/dispersion. Fluid flow in the granular bed around the sphere was assumed to follow Darcy's law and, at each point, dispersion of solute was considered in both the cross-stream and stream-wise directions. The elliptic PDE equation, resulting from a differential material balance on the solute, has been solved numerically over a wide range of values of the relevant parameters. (authors)

  6. Concentration profiles in the wake of a sphere buried in a granular bed through which fluid flows

    Energy Technology Data Exchange (ETDEWEB)

    Guedes de Carvalho, J.R.F.; Delgado, J.M.P.Q.; Alves, M.A. [Porto Univ., Dpet. de Engenharia Quimica, Faculdade de Engenharia (Portugal)

    2005-07-01

    The concentration distribution in the wake of a soluble sphere immersed in a granular bed of inerts has been obtained numerically, for transport by both advection and diffusion/dispersion. Fluid flow in the granular bed around the sphere was assumed to follow Darcy's law and, at each point, dispersion of solute was considered in both the cross-stream and stream-wise directions. The elliptic PDE equation, resulting from a differential material balance on the solute, has been solved numerically over a wide range of values of the relevant parameters. (authors)

  7. Self-Synchronization of Numerical Granular Flows: A Key to Musical Sands?

    Science.gov (United States)

    Staron, L.

    2011-12-01

    In some rare circumstances, sand flows at the surface of dunes are able to produce a loud sound known as "the song of dunes". The complex mechanisms at the source of these singing properties are far from fully understood. In this study, granular flows are simulated in two dimensions using the discrete Contact Dynamics algorithm. We show that the motion of grains at the surface of the flows exhibits a well-defined oscillation, the frequency of which is not described by the natural frequencies of the system, and does not depend on the rigid or erodible bottom condition. To explain this oscillation, we propose a simple synchronization model based on the existence of coherent structures, or clusters, at the surface of the flow, which yields successful prediction of the numerically observed frequencies. Our analysis gives consistent results when compared with field data from booming dunes, offers a possible explanation for the field observation of sound-generation velocity threshold, and provides new keys to the understanding of musical sands.

  8. Toward high-efficiency and detailed Monte Carlo simulation study of the granular flow spallation target

    Science.gov (United States)

    Cai, Han-Jie; Zhang, Zhi-Lei; Fu, Fen; Li, Jian-Yang; Zhang, Xun-Chao; Zhang, Ya-Ling; Yan, Xue-Song; Lin, Ping; Xv, Jian-Ya; Yang, Lei

    2018-02-01

    The dense granular flow spallation target is a new target concept chosen for the Accelerator-Driven Subcritical (ADS) project in China. For the R&D of this kind of target concept, a dedicated Monte Carlo (MC) program named GMT was developed to perform the simulation study of the beam-target interaction. Owing to the complexities of the target geometry, the computational cost of the MC simulation of particle tracks is highly expensive. Thus, improvement of computational efficiency will be essential for the detailed MC simulation studies of the dense granular target. Here we present the special design of the GMT program and its high efficiency performance. In addition, the speedup potential of the GPU-accelerated spallation models is discussed.

  9. Dispersed plug flow model for upflow anaerobic sludge bed reactors with focus on granular sludge dynamics

    NARCIS (Netherlands)

    Kalyuzhnyi, S.V.; Fedorovich, V.V.; Lens, P.N.L.

    2006-01-01

    A new approach to model upflow anaerobic sludge bed (UASB)-reactors, referred to as a one-dimensional dispersed plug flow model, was developed. This model focusses on the granular sludge dynamics along the reactor height, based on the balance between dispersion, sedimentation and convection using

  10. Collapse of tall granular columns in fluid

    Science.gov (United States)

    Kumar, Krishna; Soga, Kenichi; Delenne, Jean-Yves

    2017-06-01

    Avalanches, landslides, and debris flows are geophysical hazards, which involve rapid mass movement of granular solids, water, and air as a multi-phase system. In order to describe the mechanism of immersed granular flows, it is important to consider both the dynamics of the solid phase and the role of the ambient fluid. In the present study, the collapse of a granular column in fluid is studied using 2D LBM - DEM. The flow kinematics are compared with the dry and buoyant granular collapse to understand the influence of hydrodynamic forces and lubrication on the run-out. In the case of tall columns, the amount of material destabilised above the failure plane is larger than that of short columns. Therefore, the surface area of the mobilised mass that interacts with the surrounding fluid in tall columns is significantly higher than the short columns. This increase in the area of soil - fluid interaction results in an increase in the formation of turbulent vortices thereby altering the deposit morphology. It is observed that the vortices result in the formation of heaps that significantly affects the distribution of mass in the flow. In order to understand the behaviour of tall columns, the run-out behaviour of a dense granular column with an initial aspect ratio of 6 is studied. The collapse behaviour is analysed for different slope angles: 0°, 2.5°, 5° and 7.5°.

  11. Slow sedimentary processes on-a-chip: experiments on porous flow effects on granular bed creep

    Science.gov (United States)

    Houssais, M.; Maldarelli, C.; Shattuck, M.; Morris, J. F.

    2017-12-01

    Steep soils dynamics is hard to catch. they exhibit very slow granular creep most of the time, and sometimes, mostly under or after rain, turn into a landslide, a very fast avalanche flow.The conditions of transition from soil creep to avalanching remains a lot non-understood, and Safe Factor law (empirical criteria, function of rain intensity and duration). On another side, in marine fast deposition environments, compaction drives vertical porous flow, which makes bed shear resistance change, and form over time bed size patterns (pipes, dishes) or mechanical heterogeneities.Capturing how the slow creep dynamics depends on the porous flow would allow for much more accurate landscape evolution modeling.We present here preliminary results of an experimental investigation of one the major triggering condition for soils destabilization: rain infiltration, and more generally porous flow through a tilted granular bed. In a quasi-2D microfluidics channel, a flat sediment bed made of spherical particles is prepared, in fully submerged condition. It is thereafter tilted (at slope under critical slope of avalanching) and simultaneously put under vertical weak porous flow (well under the critical flow of liquefaction regarding positive pressure gradients). The two control parameters are varied, and local particles concentration and motion are measured. Interestingly, although staying in the sub-critical creeping regime, we observe an acceleration of the bed deformation downward, as the porous flow and the bed slope are increased, until the criteria for avalanching is reached. Those results appear to present similitudes with the case of tilted dry sediment bed under controlled vibrations. Consequently it opens the discussion about a potential universal model of landslides triggering due to frequent seismological and rainstorm events.

  12. Spatial correlations in compressible granular flows

    NARCIS (Netherlands)

    van Noije, T.P.C.; Ernst, M.H.; Brito, R.

    The clustering instability in freely evolving granular fluids manifests itself in the density-density correlation function and structure factor. These functions are calculated from fluctuating hydrodynamics. As time increases, the structure factor of density fluctuations develops a maximum, which

  13. Constitutive law of dense granular matter

    International Nuclear Information System (INIS)

    Hatano, Takahiro

    2010-01-01

    The frictional properties of dense granular matter under steady shear flow are investigated using numerical simulation. Shear flow tends to localize near the driving boundary unless the coefficient of restitution is close to zero and the driving velocity is small. The bulk friction coefficient is independent of shear rate in dense and slow flow, whereas it is an increasing function of shear rate in rapid flow. The coefficient of restitution affects the friction coefficient only in such rapid flow. Contrastingly, in dense and slow regime, the friction coefficient is independent of the coefficient of restitution and mainly determined by the elementary friction coefficient and the rotation of grains. It is found that the mismatch between the vorticity of flow and the angular frequency of grains plays a key role to the frictional properties of sheared granular matter.

  14. Gravity-driven, dry granular flows over a loose bed in stationary and homogeneous conditions

    Science.gov (United States)

    Meninno, Sabrina; Armanini, Aronne; Larcher, Michele

    2018-02-01

    Flows involving solid particulates have been widely studied in recent years, but their dynamics are still a complex issue to model because they strongly depend on the interaction with the boundary conditions. We report on laboratory investigations regarding homogeneous and steady flows of identical particles over a loose bed in a rectangular channel. Accurate measurements were carried out through imaging techniques to estimate profiles of the mean velocity, solid concentration, and granular temperature for a large set of flow rates and widths. Vertical and transversal structures observed in the flow change as interparticle interactions become more collisional, and they depend on the bottom over which the flow develops. The lateral confinement has a remarkable effect on the flow, especially for narrow channels compared with the grain size, and a hydraulic analogy is able to show how the walls influence the mechanisms of friction and energy dissipation.

  15. Gravity-driven granular flow in a silo: Characterizing local forces and rearrangements

    Directory of Open Access Journals (Sweden)

    Thackray Emma

    2017-01-01

    Full Text Available While the gravity-driven flow of a granular material in a silo geometry can be modeled by the Beverloo equation, the mesoscale-level particle rearrangements and interactions that drive this flow are not wellunderstood. We have constructed a quasi-two-dimensional system of bidisperse, millimeter-scale disks with photoelastic properties that make force networks within the material visible. The system is contained in an acrylic box with an adjustable bottom opening. We can approach the clogging transition by adjusting this opening. By placing the system between cross-polarizers, we can obtain high-speed video of this system during flow, and extract intensity signals that can be used to identify and quantify localized, otherwise indeterminate forces. We can simultaneously track individual particle motions, which can be used to identify shear transformation zones in the system. In this paper, we present our results thus far.

  16. Simulation of the effect of defence structures on granular flows using SPH

    Directory of Open Access Journals (Sweden)

    P. Lachamp

    2002-01-01

    Full Text Available This paper presents the SPH (Smoothed Particles Hydrodynamics numerical method adapted to complex rheology and free surface flow. It has been developed to simulate the local effect of a simple obstacle on a granular flow. We have introduced this specific rheology to the classical formalism of the method and thanks to experimental devices, we were able to validate the results. Two viscosity values have been simultaneously computed to simulate "plugs" and "dead zone" with the same code. First, some experiments have been done on a simple inclined slope to show the accuracy of the numerical results. We have fixed the mass flow rate to see the variations of the flow depth according to the channel slope. Then we put a weir to block the flow and we analysed the dependence between the obstacle height and the length of influence upstream from the obstacle. After having shown that numerical results were consistent, we have studied speed profiles and pressure impact on the structure. Also results with any topography will be presented. This will have a great interest to study real flow over natural topography while using the model for decision help.

  17. Erosion of a wet/dry granular interface

    Science.gov (United States)

    Jop, Pierre; Lefebvre, Gautier

    2013-04-01

    To model the dynamic of landslides, the evolution of the interface between the erodible ground and the flowing material is still studied experimentally or numerically (ie. Mangeney et al. 2010, Iverson 2012). In some cases, the basal material is more cohesive than the flowing one. Such situation arises for example due to cementation or humidity. What are the exchange rates between these phases? What is the coupling between the evolution of the interface and the flow? We studied the erosion phenomenon and performed laboratory experiments to focus on the interaction between a cohesive unsaturated granular material and a dry granular flow. Both materials were spherical grains, the cohesion being induced by adding a given mass of liquid to the grains. Two configurations were explored: a circular aggregate submitted to a dry flow in a rotating drum, and a granular flow eroding a wet granular pile. First, we focused on the influence of the cohesion, controlled by the liquid properties, such as the surface tension and the viscosity. Then the flow characteristics were modified by varying the grain size and density. These results allowed us to present a model for the erosion mechanisms, based on the flow and fluid properties. The main results are the need to take into account the whole probability distribution the stress applied on the wet grains and that both the surface tension and the viscosity are important since they play a different roles. The latter is mainly responsible of the time scale of the dynamic of a wet grain, while the former acts as a threshold on the force distribution. In the second configuration, we could also control the inclination of the slope. This system supported the previous model and moreover revealed an interface instability, leading the formation of steep steps, which is a reminiscence of the cyclic-steps observed during river-channel incision (Parker and Izumi 2000). We will present the dynamics of such granular steps. [1] Mangeney, A., O

  18. A theoretical and numerical study of the flow of granular materials down an inclined plane. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Rajagopal, K.R.

    1995-12-31

    The mechanics of the flowing granular materials such as coal, agricultural products, at deal of attention as it has fertilizers, dry chemicals, metal ores, etc. have received a great deal of attention as it has relevance to several important technological problems. Despite wide interest and more than five decades of experimental and theoretical investigations, most aspects of the behavior of flowing granular materials are still not well understood. So Experiments have to be devised which quantify and describe the non-linear behavior of the modular materials, and theories developed which can explain the experimentally observed facts. As many models have been suggested for describing the behavior of granular materials, from both continuum and kinetic theory viewpoints, we proposed to investigate the validity and usefulness of representative models from both the continuum and kinetic theory points of view, by determining the prediction of such a theory, in a representative flow, with respect to existence, non-existence, multiplicity and stability of solutions. The continuum model to be investigated is an outgrowth of a model due to Goodman and Cowin (1971, 1972) and the kinetic theory models being those due to Jenkins and Richman (1985) and Boyle and Massoudi (1989). In this report we present detailed results regarding the same. Interestingly, we find that the predictions of all the theories, in certain parameter space associated with these models, are qualitatively similar. This ofcourse depends on the values assumed for various material parameters in the models, which as yet are unknown, as reliable experiments have not been carried out as yet for their determination.

  19. 2D granular flows with the μ(I) rheology and side walls friction: A well-balanced multilayer discretization

    Science.gov (United States)

    Fernández-Nieto, E. D.; Garres-Díaz, J.; Mangeney, A.; Narbona-Reina, G.

    2018-03-01

    We present here numerical modelling of granular flows with the μ (I) rheology in confined channels. The contribution is twofold: (i) a model to approximate the Navier-Stokes equations with the μ (I) rheology through an asymptotic analysis; under the hypothesis of a one-dimensional flow, this model takes into account side walls friction; (ii) a multilayer discretization following Fernández-Nieto et al. (2016) [20]. In this new numerical scheme, we propose an appropriate treatment of the rheological terms through a hydrostatic reconstruction which allows this scheme to be well-balanced and therefore to deal with dry areas. Based on academic tests, we first evaluate the influence of the width of the channel on the normal profiles of the downslope velocity thanks to the multilayer approach that is intrinsically able to describe changes from Bagnold to S-shaped (and vice versa) velocity profiles. We also check the well-balanced property of the proposed numerical scheme. We show that approximating side walls friction using single-layer models may lead to strong errors. Secondly, we compare the numerical results with experimental data on granular collapses. We show that the proposed scheme allows us to qualitatively reproduce the deposit in the case of a rigid bed (i.e. dry area) and that the error made by replacing the dry area by a small layer of material may be large if this layer is not thin enough. The proposed model is also able to reproduce the time evolution of the free surface and of the flow/no-flow interface. In addition, it reproduces the effect of erosion for granular flows over initially static material lying on the bed. This is possible when using a variable friction coefficient μ (I) but not with a constant friction coefficient.

  20. Granular Materials and Risks In ISRU

    Science.gov (United States)

    Behringer, Robert P.; Wilkinson, R. Allen

    2004-01-01

    Working with soil, sand, powders, ores, cement and sintered bricks, excavating, grading construction sites, driving off-road, transporting granules in chutes and pipes, sifting gravel, separating solids from gases, and using hoppers are so routine that it seems straightforward to execute these operations on the Moon and Mars as we do on Earth. We discuss how little these processes are understood and point out the nature of trial-and-error practices that are used in today's massive over-design. Nevertheless, such designs have a high failure rate. Implementation and extensive incremental scaling up of industrial processes are routine because of the inadequate predictive tools for design. We present a number of pragmatic scenarios where granular materials play a role, the risks involved, what some of the basic issues are, and what understanding is needed to greatly reduce the risks. This talk will focus on a particular class of granular flow issues, those that pertain to dense materials, their physics, and the failure problems associated with them. In particular, key issues where basic predictability is lacking include stability of soils for the support of vehicles and facilities, ability to control the flow of dense materials (jamming and flooding/unjamming at the wrong time), the ability to predict stress profiles (hence create reliable designs) for containers such as bunkers or silos. In particular, stress fluctuations, which are not accounted for in standard granular design models, can be very large as granular materials flows, and one result is frequent catastrophic failure of granular devices.

  1. Three-dimensional granular model of semi-solid metallic alloys undergoing solidification: Fluid flow and localization of feeding

    International Nuclear Information System (INIS)

    Sistaninia, M.; Phillion, A.B.; Drezet, J.-M.; Rappaz, M.

    2012-01-01

    A three-dimensional (3-D) granular model which simulates fluid flow within solidifying alloys with a globular microstructure, such as that found in grain refined Al alloys, is presented. The model geometry within a representative volume element (RVE) consists of a set of prismatic triangular elements representing the intergranular liquid channels. The pressure field within the liquid channels is calculated using a finite elements (FEs) method assuming a Poiseuille flow within each channel and flow conservation at triple lines. The fluid flow is induced by solidification shrinkage and openings at grain boundaries due to deformation of the coherent solid. The granular model predictions are validated against bulk data calculated with averaging techniques. The results show that a fluid flow simulation of globular semi-solid materials is able to reproduce both a map of the 3-D intergranular pressure and the localization of feeding within the mushy zone. A new hot cracking sensitivity coefficient is then proposed. Based on a mass balance performed over a solidifying isothermal volume element, this coefficient accounts for tensile deformation of the semi-solid domain and for the induced intergranular liquid feeding. The fluid flow model is then used to calculate the pressure drop in the mushy zone during the direct chill casting of aluminum alloy billets. The predicted pressure demonstrates that deep in the mushy zone where the permeability is low the local pressure can be significantly lower than the pressure predicted by averaging techniques.

  2. An automata model of granular materials

    International Nuclear Information System (INIS)

    Gutt, G.M.; Haff, P.K.

    1990-01-01

    In this paper a new modeling technique (the Lattice Grain Model) is presented for the simulation of two-dimensional granular systems involving large numbers of grains. These granular systems may include both high shear rate regions as well as static plugs of grains and cannot easily be handled within the framework of existing continuum theories such as soil mechanics. The Lattice Grain Model (LGrM) is similar to the Lattice Gas Model (LBM). This allows large simulations to be programmed onto a hypercube concurrent processor in a straightforward manner. However, it differs from LBM in that it includes the inelastic collisions and volume-filling properties of macroscopic grains. Examples to be presented will include Couette flow, flow through an hourglass, and gravity-driven flows around obstacles

  3. Discrete Element Method simulations of standing jumps in granular flows down inclines

    Directory of Open Access Journals (Sweden)

    Méjean Ségolène

    2017-01-01

    Full Text Available This paper describes a numerical set-up which uses Discrete Element Method to produce standing jumps in flows of dry granular materials down a slope in two dimensions. The grain-scale force interactions are modeled by a visco-elastic normal force and an elastic tangential force with a Coulomb threshold. We will show how it is possible to reproduce all the shapes of the jumps observed in a previous laboratory study: diffuse versus steep jumps and compressible versus incompressible jumps. Moreover, we will discuss the additional measurements that can be done thanks to discrete element modelling.

  4. DEM GPU studies of industrial scale particle simulations for granular flow civil engineering applications

    Science.gov (United States)

    Pizette, Patrick; Govender, Nicolin; Wilke, Daniel N.; Abriak, Nor-Edine

    2017-06-01

    The use of the Discrete Element Method (DEM) for industrial civil engineering industrial applications is currently limited due to the computational demands when large numbers of particles are considered. The graphics processing unit (GPU) with its highly parallelized hardware architecture shows potential to enable solution of civil engineering problems using discrete granular approaches. We demonstrate in this study the pratical utility of a validated GPU-enabled DEM modeling environment to simulate industrial scale granular problems. As illustration, the flow discharge of storage silos using 8 and 17 million particles is considered. DEM simulations have been performed to investigate the influence of particle size (equivalent size for the 20/40-mesh gravel) and induced shear stress for two hopper shapes. The preliminary results indicate that the shape of the hopper significantly influences the discharge rates for the same material. Specifically, this work shows that GPU-enabled DEM modeling environments can model industrial scale problems on a single portable computer within a day for 30 seconds of process time.

  5. Effect of Bed Depth on Granular Flow and Homogenization in a Vertical Bladed Mixer via Discrete Element Method

    Czech Academy of Sciences Publication Activity Database

    Barczi, T.; Trávníčková, Tereza; Havlica, Jaromír; Kohout, M.

    2015-01-01

    Roč. 38, č. 7 (2015), s. 1195-1202 ISSN 0930-7516 R&D Projects: GA ČR(CZ) GAP105/12/0664 Institutional support: RVO:67985858 Keywords : granular mixing * DEM * flow patterns Subject RIV: CI - Industrial Chemistry, Chemical Engineering Impact factor: 2.385, year: 2015

  6. Rheology of granular flows immersed in a viscous fluid

    International Nuclear Information System (INIS)

    Amarsid, Lhassan

    2015-01-01

    We investigate the behavior of granular materials immersed in a viscous fluid by means of extensive simulations based on the Discrete Element Method for particle dynamics coupled with the Lattice Boltzmann method for the fluid. We show that, for a broad range of parameters such as shear rate, confining stress and viscosity, the internal friction coefficient and packing fraction are well described by a single 'visco-inertial' dimensionless parameter combining inertial and Stokes numbers. The frictional behavior under constant confining pressure is mapped into a viscous behavior under volume-controlled conditions, leading to the divergence of the effective normal and shear viscosities in inverse square of the distance to the critical packing fraction. The results are in excellent agreement with the experimental data of Boyer et al. (2011). The evolution of the force network in terms of connectivity and anisotropy as a function of the visco-inertial number, indicates that the increase of frictional strength is a direct consequence of structural anisotropy enhanced by both fluid viscosity and grain inertia. In view of application to a potential nuclear accident, we also study the fragmentation and flow of confined porous aggregates in a fluid under the action of local overpressures and pressure gradients as well as gravity-driven flow of immersed particles in an hourglass. (author)

  7. Storage and discharge of a granular fluid.

    Science.gov (United States)

    Pacheco-Martinez, Hector; van Gerner, Henk Jan; Ruiz-Suárez, J C

    2008-02-01

    Experiments and computational simulations are carried out to study the behavior of a granular column in a silo whose walls are able to vibrate horizontally. The column is brought to a steady fluidized state and it behaves similar to a hydrostatic system. We study the dynamics of the granular discharge through openings at the bottom of the silo in order to search for a Torricelli-like behavior. We show that the flow rate scales with the wall induced shear rate, and at high rates, the granular bed indeed discharges similar to a viscous fluid.

  8. Instability-induced ordering, universal unfolding and the role of gravity in granular Couette flow

    Science.gov (United States)

    Alam, Meheboob; Arakeri, V. H.; Nott, P. R.; Goddard, J. D.; Herrmann, H. J.

    2005-01-01

    Linear stability theory and bifurcation analysis are used to investigate the role of gravity in shear-band formation in granular Couette flow, considering a kinetic-theory rheological model. We show that the only possible state, at low shear rates, corresponds to a "plug" near the bottom wall, in which the particles are densely packed and the shear rate is close to zero, and a uniformly sheared dilute region above it. The origin of such plugged states is shown to be tied to the spontaneous symmetry-breaking instabilities of the gravity-free uniform shear flow, leading to the formation of ordered bands of alternating dilute and dense regions in the transverse direction, via an infinite hierarchy of pitchfork bifurcations. Gravity plays the role of an "imperfection", thus destroying the "perfect" bifurcation structure of uniform shear. The present bifurcation problem admits universal unfolding of pitchfork bifurcations which subsequently leads to the formation of a sequence of a countably infinite number of "isolas", with the solution structures being a modulated version of their gravity-free counterpart. While the solution with a plug near the bottom wall looks remarkably similar to the shear-banding phenomenon in dense slow granular Couette flows, a "floating" plug near the top wall is also a solution of these equations at high shear rates. A two-dimensional linear stability analysis suggests that these floating plugged states are unstable to long-wave travelling disturbances.The unique solution having a bottom plug can also be unstable to long waves, but remains stable at sufficiently low shear rates. The implications and realizability of the present results are discussed in the light of shear-cell experiments under "microgravity" conditions.

  9. Implementation and Re nement of a Comprehensive Model for Dense Granular Flows

    Energy Technology Data Exchange (ETDEWEB)

    Sundaresan, Sankaran [The Trustees Of Princeton University, Princeton, NJ (United States)

    2015-09-30

    Dense granular ows are ubiquitous in both natural and industrial processes. They manifest three di erent ow regimes, each exhibiting its own dependence on solids volume fraction, shear rate, and particle-level properties. This research project sought to develop continuum rheological models for dense granular ows that bridges multiple regimes of ow, implement them in open-source platforms for gas-particle ows and perform test simulations. The rst phase of the research covered in this project involved implementation of a steady- shear rheological model that bridges quasi-static, intermediate and inertial regimes of ow into MFIX (Multiphase Flow with Interphase eXchanges - a general purpose computer code developed at the National Energy Technology Laboratory). MFIX simulations of dense granular ows in hourglass-shaped hopper were then performed as test examples. The second phase focused on formulation of a modi ed kinetic theory for frictional particles that can be used over a wider range of particle volume fractions and also apply for dynamic, multi- dimensional ow conditions. To guide this work, simulations of simple shear ows of identical mono-disperse spheres were also performed using the discrete element method. The third phase of this project sought to develop and implement a more rigorous treatment of boundary e ects. Towards this end, simulations of simple shear ows of identical mono-disperse spheres con ned between parallel plates were performed and analyzed to formulate compact wall boundary conditions that can be used for dense frictional ows at at frictional boundaries. The fourth phase explored the role of modest levels of cohesive interactions between particles on the dense phase rheology. The nal phase of this project focused on implementation and testing of the modi ed kinetic theory in MFIX and running bin-discharge simulations as test examples.

  10. Vortex jamming in superconductors and granular rheology

    International Nuclear Information System (INIS)

    Yoshino, Hajime; Nogawa, Tomoaki; Kim, Bongsoo

    2009-01-01

    We demonstrate that a highly frustrated anisotropic Josephson junction array (JJA) on a square lattice exhibits a zero-temperature jamming transition, which shares much in common with those in granular systems. Anisotropy of the Josephson couplings along the horizontal and vertical directions plays roles similar to normal load or density in granular systems. We studied numerically static and dynamic response of the system against shear, i.e. injection of external electric current at zero temperature. Current-voltage curves at various strength of the anisotropy exhibit universal scaling features around the jamming point much as do the flow curves in granular rheology, shear-stress versus shear-rate. It turns out that at zero temperature the jamming transition occurs right at the isotropic coupling and anisotropic JJA behaves as exotic fragile vortex matter: it behaves as a superconductor (vortex glass) in one direction, whereas it is a normal conductor (vortex liquid) in the other direction even at zero temperature. Furthermore, we find a variant of the theoretical model for the anisotropic JJA quantitatively reproduces universal master flow-curves of the granular systems. Our results suggest an unexpected common paradigm stretching over seemingly unrelated fields-the rheology of soft materials and superconductivity.

  11. Analysis and Modeling of Structure Formation in Granular and Fluid-Solid Flows

    Science.gov (United States)

    Murphy, Eric

    Granular and multiphase flows are encountered in a number of industrial processes with particular emphasis in this manuscript given to the particular applications in cement pumping, pneumatic conveying, fluid catalytic cracking, CO2 capture, and fast pyrolysis of bio-materials. These processes are often modeled using averaged equations that may be simulated using computational fluid dynamics. Closure models are then required that describe the average forces that arise from both interparticle interactions, e.g. shear stress, and interphase interactions, such as mean drag. One of the biggest hurdles to this approach is the emergence of non-trivial spatio-temporal structures in the particulate phase, which can significantly modify the qualitative behavior of these forces and the resultant flow phenomenology. For example, the formation of large clusters in cohesive granular flows is responsible for a transition from solid-like to fluid-like rheology. Another example is found in gas-solid systems, where clustering at small scales is observed to significantly lower in the observed drag. Moreover, there remains the possibility that structure formation may occur at all scales, leading to a lack of scale separation required for traditional averaging approaches. In this context, several modeling problems are treated 1) first-principles based modeling of the rheology of cement slurries, 2) modeling the mean solid-solid drag experienced by polydisperse particles undergoing segregation, and 3) modeling clustering in homogeneous gas-solid flows. The first and third components are described in greater detail. In the study on the rheology of cements, several sub-problems are introduced, which systematically increase in the number and complexity of interparticle interactions. These interparticle interactions include inelasticity, friction, cohesion, and fluid interactions. In the first study, the interactions between cohesive inelastic particles was fully characterized for the

  12. The influence of the fractal particle size distribution on the mobility of dry granular materials

    Directory of Open Access Journals (Sweden)

    Vallejo Luis E.

    2017-01-01

    Full Text Available This study presents an experimental analysis on the influence of the particle size distribution (psd on the mobility of dry granular materials. The psd obeys a power law of the form: N(L>d=kd-Df, where N is the number of particles with diameter L greater than a given diameter d, k is a proportionality constant, and Df is the fractal dimension of the psd. No laboratory or numerical study has been conducted to date analysing how a fractal psd influences the mobility of granular flows as in the case of rock avalanches. In this study, the flow characteristics of poly-dispersed granular materials that have a fractal psd were investigated in the laboratory. Granular mixtures having different fractal psd values were placed in a hollow cylinder. The cylinder was lifted and the distance of flow of the mixture was measured with respect to the original position of the cylinder. It was determined that the distance of flow of the mixtures was directly related to their fractal psd values. That is, the larger the distance of flow of the mixture, the larger is the fractal psd of the granular mixture tested. Thus, the fractal psd in dry granular mixtures seems to have a large influence on the easiness by which dry granular mixtures move in the field.

  13. Similitude study of a moving bed granular filter

    Energy Technology Data Exchange (ETDEWEB)

    Robert C. Brown; Huawei Shi; Gerald Colver; Saw-Choon Soo [Iowa State University, IA (United States)

    2003-12-10

    The goal of this study was to evaluate the performance of a moving bed granular filter designed for hot gas clean up. This study used similitude theory to devise experiments that were conducted at near-ambient conditions while simulating the performance of filters operated at elevated temperatures and pressures (850{sup o}C and 1000 kPa). These experiments revealed that the proposed moving bed granular filter can operate at high collection efficiencies, typically exceeding 99%, and low pressure drops without the need for periodic regeneration through the use of a continuous flow of fresh granular filter media in the filter. In addition, important design constraints were discovered for the successful operation of the proposed moving bed granular filter.

  14. Evaluating Energy Flux in Vibrofluidized Granular Bed

    Directory of Open Access Journals (Sweden)

    N. A. Sheikh

    2013-01-01

    Full Text Available Granular flows require sustained input of energy for fluidization. A level of fluidization depends on the amount of heat flux provided to the flow. In general, the dissipation of the grains upon interaction balances the heat inputs and the resultant flow patterns can be described using hydrodynamic models. However, with the increase in packing fraction, the heat fluxes prediction of the cell increases. Here, a comparison is made for the proposed theoretical models against the MD simulations data. It is observed that the variation of packing fraction in the granular cell influences the heat flux at the base. For the elastic grain-base interaction, the predictions vary appreciably compared to MD simulations, suggesting the need to accurately model the velocity distribution of grains for averaging.

  15. Rheological Behavior of Dense Assemblies of Granular Materials

    International Nuclear Information System (INIS)

    Sundaresan, Sankaran; Tardos, Gabriel I.; Subramaniam, Shankar

    2011-01-01

    Assemblies of granular materials behave differently when they are owing rapidly, from when they are slowly deforming. The behavior of rapidly owing granular materials, where the particle-particle interactions occur largely through binary collisions, is commonly related to the properties of the constituent particles through the kinetic theory of granular materials. The same cannot be said for slowly moving or static assemblies of granular materials, where enduring contacts between particles are prevalent. For instance, a continuum description of the yield characteristics of dense assemblies of particles in the quasistatic ow regime cannot be written explicitly on the basis of particle properties, even for cohesionless particles. Continuum models for this regime have been proposed and applied, but these models typically assume that the assembly is at incipient yield and they are expressed in terms of the yield function, which we do not yet know how to express in terms of particle-level properties. The description of the continuum rheology in the intermediate regime is even less understood. Yet, many practically important flows in nature and in a wide range of technological applications occur in the dense flow regime and at the transition between dilute and dense regimes; the lack of validated continuum rheological models for particle assemblies in these regimes limits predictive modeling of such flows. This research project is aimed at developing such rheological models.

  16. Relating water and air flow characteristics in coarse granular materials

    DEFF Research Database (Denmark)

    Andreasen, Rune Røjgaard; Canga, Eriona; Poulsen, Tjalfe Gorm

    2013-01-01

    Water pressure drop as a function of velocity controls w 1 ater cleaning biofilter operation 2 cost. At present this relationship in biofilter materials must be determined experimentally as no 3 universal link between pressure drop, velocity and filter material properties have been established. 4...... Pressure drop - velocity in porous media is much simpler and faster to measure for air than for water. 5 For soils and similar materials, observations show a strong connection between pressure drop – 6 velocity relations for air and water, indicating that water pressure drop – velocity may be estimated 7...... from air flow data. The objective of this study was, therefore, to investigate if this approach is valid 8 also for coarse granular biofilter media which usually consists of much larger particles than soils. In 9 this paper the connection between the pressure drop – velocity relationships for air...

  17. Bubbling in vibrated granular films.

    Science.gov (United States)

    Zamankhan, Piroz

    2011-02-01

    With the help of experiments, computer simulations, and a theoretical investigation, a general model is developed of the flow dynamics of dense granular media immersed in air in an intermediate regime where both collisional and frictional interactions may affect the flow behavior. The model is tested using the example of a system in which bubbles and solid structures are produced in granular films shaken vertically. Both experiments and large-scale, three-dimensional simulations of this system are performed. The experimental results are compared with the results of the simulation to verify the validity of the model. The data indicate evidence of formation of bubbles when peak acceleration relative to gravity exceeds a critical value Γ(b). The air-grain interfaces of bubblelike structures are found to exhibit fractal structure with dimension D=1.7±0.05.

  18. Granular Silo collapse: an experimental study

    Science.gov (United States)

    Clement, Eric; Gutierriez, Gustavo; Boltenhagen, Philippe; Lanuza, Jose

    2008-03-01

    We present an experimental work that develop some basic insight into the pre-buckling behavior and the buckling transition toward plastic collapse of a granular silo. We study different patterns of deformation generated on thin paper cylindrical shells during granular discharge. We study the collapse threshold for different bed height, flow rates and grain sizes. We compare the patterns that appear during the discharge of spherical beads, with those obtained in the axially compressed cylindrical shells. When the height of the granular column is close to the collapse threshold, we describe a ladder like pattern that rises around the cylinder surface in a spiral path of diamond shaped localizations, and develops into a plastic collapsing fold that grows around the collapsing silo.

  19. Navier-Stokes hydrodynamics of thermal collapse in a freely cooling granular gas.

    Science.gov (United States)

    Kolvin, Itamar; Livne, Eli; Meerson, Baruch

    2010-08-01

    We show that, in dimension higher than one, heat diffusion and viscosity cannot arrest thermal collapse in a freely evolving dilute granular gas, even in the absence of gravity. Thermal collapse involves a finite-time blowup of the gas density. It was predicted earlier in ideal, Euler hydrodynamics of dilute granular gases in the absence of gravity, and in nonideal, Navier-Stokes granular hydrodynamics in the presence of gravity. We determine, analytically and numerically, the dynamic scaling laws that characterize the gas flow close to collapse. We also investigate bifurcations of a freely evolving dilute granular gas in circular and wedge-shaped containers. Our results imply that, in general, thermal collapse can only be arrested when the gas density becomes comparable with the close-packing density of grains. This provides a natural explanation to the formation of densely packed clusters of particles in a variety of initially dilute granular flows.

  20. Residence-Time Distributions in Laminar Flows and During the Passage of Granular Solids Through Rotary Kilns

    Energy Technology Data Exchange (ETDEWEB)

    Beek, W. J.; De Ridder, H. J. [Technische Hogeschool, Delft (Netherlands); Houtman, J. P.W.; Kuiper, D. [Reactor Instituut, Delft (Netherlands)

    1967-06-15

    Data on residence-time distributions are important in the design of apparatus for the chemical industry. Radioactive tracers can be useful in many cases, e.g. where a pulse technique is desired. Two examples are given in which a pulse of radioactive tracer is used. The first example deals with the residence-time distribution of a laminar, Newtonian flow in an annulus. This problem arises especially in the extrusion and injection moulding of polymers and in the coating of wires with plastics. In these cases the fractions of polymer with long residence times may have other properties than the polymer that flows fastest, because the polymerization reaction or the degradation reactions go on during the process. Two difficulties are to be considered: (a) the tracer pulse (a radioactive Au-sol suspended in the liquid used) cannot be distributed over the cross-section in proportion to the local flow velocity, and (b) the outflowing liquid must be sampled discontinuously. Both effects have been studied and corrections are indicated. When these corrections are applied to the measured distribution curve, the result is in fair agreement with the calculated residence-time distribution. The second example considers the residence-time distribution in a granular solid (sand) passing through a rotary kiln. The response was measured at the outlet to a pulse at the inlet of radioactive material (sand impregnated with a solution of radioactive AuCl{sub 3}). When calculating the residence-time distribution from the experimental data, difficulties were encountered because the duration of the pulse was of the same order of magnitude as the average residence time. Considering this, it was found that the axial dispersion of the flow of sand could be described by an effective dispersion coefficient. This dispersion coefficient proved to be very low (order of magnitude 10{sup -5} m{sup 2}/s); hence, in practical situations, the flow of granular material through a rotary kiln may often be

  1. Force and flow at the onset of drag in plowed granular media.

    Science.gov (United States)

    Gravish, Nick; Umbanhowar, Paul B; Goldman, Daniel I

    2014-04-01

    We study the transient drag force FD on a localized intruder in a granular medium composed of spherical glass particles. A flat plate is translated horizontally from rest through the granular medium to observe how FD varies as a function of the medium's initial volume fraction, ϕ. The force response of the granular material differs above and below the granular critical state, ϕc, the volume fraction which corresponds to the onset of grain dilatancy. For ϕϕc, FD rapidly rises to a maximum and then decreases over further displacement. The maximum force for ϕ>ϕc increases with increasing drag velocity. In quasi-two-dimensional drag experiments, we use granular particle image velocimetry (PIV) to measure time resolved strain fields associated with the horizontal motion of a plate started from rest. PIV experiments show that the maxima in FD for ϕ>ϕc are associated with maxima in the spatially averaged shear strain field. For ϕ>ϕc the shear strain occurs in a narrow region in front of the plate, a shear band. For ϕϕc, surface particles move only during the formation of the shear band, coincident with the maxima in FD, after which the particles remain immobile until the sheared region reaches the measurement region.

  2. Granular Gases: Probing the Boundaries of Hydrodynamics

    International Nuclear Information System (INIS)

    Goldhirsch, I.

    1999-01-01

    The dissipative nature of the particle interactions in granular systems renders granular gases mesoscopic and bearing some similarities to regular gases in the ''continuum transition regime'' where shear rates and/or thermal gradients are very large). The following properties of granular gases support the above claim: (i). Mean free times are of the same order as macroscopic time scales (inverse shear rates); (ii). Mean free paths can be macroscopic and comparable to the system's dimensions; (iii). Typical flows are supersonic; (iv). Shear rates are typically ''large''; (v). Stress fields are scale (resolution) dependent; (vi). Burnett and super-Burnett corrections to both the constitutive relations and the boundary conditions are of importance; (vii). Single particle distribution functions can be far from Gaussian. It is concluded that while hydrodynamic descriptions of granular gases are relevant, they are probing the boundaries of applicability of hydrodynamics and perhaps slightly beyond

  3. Anaerobic granular sludge and biofilm reactors

    DEFF Research Database (Denmark)

    Skiadas, Ioannis V.; Gavala, Hariklia N.; Schmidt, Jens Ejbye

    2003-01-01

    by the immobilization of the biomass, which forms static biofilms, particle-supported biofilms, or granules depending on the reactor's operational conditions. The advantages of the high-rate anaerobic digestion over the conventional aerobic wastewater treatment methods has created a clear trend for the change......-rate anaerobic treatment systems based on anaerobic granular sludge and biofilm are described in this chapter. Emphasis is given to a) the Up-flow Anaerobic Sludge Blanket (UASB) systems, b) the main characteristics of the anaerobic granular sludge, and c) the factors that control the granulation process...

  4. Anisotropy in cohesive, frictional granular media

    International Nuclear Information System (INIS)

    Luding, Stefan

    2005-01-01

    The modelling of cohesive, frictional granular materials with a discrete particle molecular dynamics is reviewed. From the structure of the quasi-static granular solid, the fabric, stress, and stiffness tensors are determined, including both normal and tangential forces. The influence of the material properties on the flow behaviour is also reported, including relations between the microscopic attractive force and the macroscopic cohesion as well as the dependence of the macroscopic friction on the microscopic contact friction coefficient. Related to the dynamics, the anisotropy of both structure and stress are exponentially approaching the maximum

  5. Structural evolution of a granular medium during simultaneous penetration

    Science.gov (United States)

    González-Gutiérrez, Jorge; Carreón, Yojana J. P.; Moctezuma, R. E.

    2018-01-01

    Typically, fluidized beds are granular systems composed of solid particles through which a fluid flows. They are relevant to a wide variety of disciplines such as physics, chemistry, engineering, among others. Generally, the fluidized beds are characterized by different flow regimes such as particulate, bubbling, slugging, turbulent, fast fluidization, and pneumatic conveying. Here, we report the experimental study of the structural evolution of a granular system due to simultaneous penetration of intruders in the presence of an upward airflow. We found that the granular medium evolves from the static state to the turbulent regime showing the coexistence of three regions in different flow regimes. Interestingly, the cooperative dynamic of intruders correlate with the formation of such regions. As a non-invasive method, we use lacunarity and fractal dimension to quantitatively describe the patterns arising within the system during the different stages of the penetration process. Finally, we found that our results would allow us to relate the evolution of the visual patterns appearing in the process with different physical properties of the system.

  6. Recent advances in understanding deformation and flow of granular matter

    Directory of Open Access Journals (Sweden)

    Mesarović Siniša Đ.

    2014-01-01

    Full Text Available By means of graph theory, we analyze the changes in topology of a granular assembly during deformation. The elementary mechanism of diffuse deformation consists of intermittent flips. We show that dilatancy is the direct result of: an increasing number of flips, and, elastic relaxation of particles upon flips. Both are dependent on particles' elastic potential energy prior to flip and after the flip. The latter is the result of non uniform distribution of interparticle forces in force chains. Next, we consider shear bands in granular materials. Formation of shear bands is accompanied by accompanied by massive rolling of particle. Since rolling is constrained by neighbors, a characteristic rolling correlation length appears. The transmission of rotations in a particular direction depends on the strength of the force chain branches in the direction of propagation and across. The maximum propagation distance is comparable to observed widths of shear bands. Finally, we turn to the question of vortex formation within shear bands and argue that vortex pattern minimizes the dissipation/resistance in granular fluid.

  7. Technological effect of vibroprocessing by flows of organic granular media

    Science.gov (United States)

    Lebedev, V. A.; Shishkina, A. P.; Davydova, I. V.; Morozova, A. V.

    2018-03-01

    The analysis of approaches to modeling of vibrational processing by granulated media is carried out. The vibroprocessing model which provides effective finishing of the surfaces of the parts due to the stone fruit organic media granules is developed. The model is based on the granule flow energy impact on the surface being treated. As the main characteristic of the organic media processing, a specific volumetric metal scrap is used, the physical meaning of which is the increase rate in the thickness of the material removed from the surface at a given velocity and pressure of the medium. It is shown that the metal scrap depends on the medium flow velocity, the height of the loading column of the granular medium, and the conditions for the formation of a medium stationary circulation motion. Based on the analysis of the results of experimental studies of the influence of amplitude-frequency characteristics on the removal of metal in the process of vibroprocessing with abrasive granules, the dependence of the specific volume metal removal is proposed for organic media processing, taking into account the threshold amplitude and frequency of oscillations of the working chamber, at which the effect of surface treatment is observed. The established set of relationships describing the effective conditions for vibroprocessing with stone organic media was obtained using experimental data, which allows us to assume that the model obtained is valid.

  8. Kinematics and statistics of dense, slow granular flow through vertical channels

    Science.gov (United States)

    Ananda, K. S.; Moka, Sudheshna; Nott, Prabhu R.

    We have investigated the flow of dry granular materials through vertical channels in the regime of dense slow flow using video imaging of the particles adjacent to a transparent wall. Using an image processing technique based on particle tracking velocimetry, the video movies were analysed to obtain the velocities of individual particles. Experiments were conducted in two- and three-dimensional channels. In the latter, glass beads and mustard seeds were used as model granular materials, and their translational velocities were measured. In the former, aluminium disks with a dark diametral stripe were used and their translational velocities and spin were measured. Experiments in the three-dimensional channels were conducted for a range of the channel width W, and for smooth and rough sidewalls. As in earlier studies, we find that shearing takes place predominantly in thin layers adjacent to the walls, while the rest of the material appears to move as a plug. However, there are large velocity fluctuations even in the plug, where the macroscopic deformation rate is negligibly small. The thickness of the shear layer, scaled by the particle diameter dp, increases weakly with W/dp. The experimental data for the velocity field are in good agreement with the Cosserat plasticity model proposed recently. We also measured the mean spin of the particles in the two-dimensional channel, and its deviation from half the vorticity. There is a clear, measurable deviation, which too is in qualitative agreement with the Cosserat plasticity model. The statistics of particle velocity and spin fluctuations in the two-dimensional channel were analysed by determining their probability distribution function, and their spatial and temporal correlation. They were all found to be broadly similar to previous observations for three-dimensional channels, but some differences are evident. The spatial correlation of the velocity fluctuations are much stronger in the two-dimensional channel, implying

  9. Granular filtration for airborne particles : correlation between experiments and models

    Energy Technology Data Exchange (ETDEWEB)

    Golshahi, L.; Tan, Z. [Calgary Univ., AB (Canada). Schulich School of Engineering, Mechanical and Manufacturing Dept.; Abedi, J. [Calgary Univ., AB (Canada). Schulich School of Engineering, Chemical and Petroleum Engineering Dept.

    2009-10-15

    A new design for a packed bed granular filter was presented. The cylindrical packed bed was designed to filter particles in the range of approximately 10 nm to 15 {mu}m in diameter in different kinetic conditions and configurations. The aim of the study was to develop a precise empirical model to predict the filtration efficiency of the packed beds. A collision-type atomizer was used to generate polydisperse sodium chloride aerosol particles. The effect of flow rates was studied using a thermal mass flow meter. A regression analysis technique was used to determine the correlation between single granule and total packed bed efficiency for the entire granular filter. The experimental data were then compared with results obtained from the theoretical analysis. The least square method was used to correlate experimental data and to develop generalized equations for single granule efficiency. The study showed that the granular filter media has a high filtration efficiency for both micron and submicron particles. It was concluded that the effect of media thickness was more significant at higher flow rates than at lower flow rates. 10 refs., 3 figs.

  10. Biodegradation of phenol in batch and continuous flow microbial fuel cells with rod and granular graphite electrodes.

    Science.gov (United States)

    Moreno, Lyman; Nemati, Mehdi; Predicala, Bernardo

    2018-01-01

    Phenol biodegradation was evaluated in batch and continuous flow microbial fuel cells (MFCs). In batch-operated MFCs, biodegradation of 100-1000 mg L -1 phenol was four to six times faster when graphite granules were used instead of rods (3.5-4.8 mg L -1  h -1 vs 0.5-0.9 mg L -1  h -1 ). Similarly maximum phenol biodegradation rates in continuous MFCs with granular and single-rod electrodes were 11.5 and 0.8 mg L -1  h -1 , respectively. This superior performance was also evident in terms of electrochemical outputs, whereby continuous flow MFCs with granular graphite electrodes achieved maximum current and power densities (3444.4 mA m -3 and 777.8 mW m -3 ) that were markedly higher than those with single-rod electrodes (37.3 mA m -3 and 0.8 mW m -3 ). Addition of neutral red enhanced the electrochemical outputs to 5714.3 mA m -3 and 1428.6 mW m -3 . Using the data generated in the continuous flow MFC, biokinetic parameters including μ m , K S , Y and K e were determined as 0.03 h -1 , 24.2 mg L -1 , 0.25 mg cell (mg phenol) -1 and 3.7 × 10 -4  h -1 , respectively. Access to detailed kinetic information generated in MFC environmental conditions is critical in the design, operation and control of large-scale treatment systems utilizing MFC technology.

  11. The Effect of Rotational Speed on Granular Flow in a Vertical Bladed Mixer

    Czech Academy of Sciences Publication Activity Database

    Havlica, Jaromír; Jirounková, K.; Trávníčková, Tereza; Kohout, M.

    2015-01-01

    Roč. 280, AUG (2015), s. 180-190 ISSN 0032-5910 R&D Projects: GA ČR(CZ) GAP105/12/0664 Institutional support: RVO:67985858 Keywords : DEM * granular mixing * granular dynamics Subject RIV: CI - Industrial Chemistry, Chemical Engineering Impact factor: 2.759, year: 2015

  12. Effect of particle stiffness on contact dynamics and rheology in a dense granular flow

    Science.gov (United States)

    Bharathraj, S.; Kumaran, V.

    2018-01-01

    Dense granular flows have been well described by the Bagnold rheology, even when the particles are in the multibody contact regime and the coordination number is greater than 1. This is surprising, because the Bagnold law should be applicable only in the instantaneous collision regime, where the time between collisions is much larger than the period of a collision. Here, the effect of particle stiffness on rheology is examined. It is found that there is a rheological threshold between a particle stiffness of 104-105 for the linear contact model and 105-106 for the Hertzian contact model above which Bagnold rheology (stress proportional to square of the strain rate) is valid and below which there is a power-law rheology, where all components of the stress and the granular temperature are proportional to a power of the strain rate that is less then 2. The system is in the multibody contact regime at the rheological threshold. However, the contact energy per particle is less than the kinetic energy per particle above the rheological threshold, and it becomes larger than the kinetic energy per particle below the rheological threshold. The distribution functions for the interparticle forces and contact energies are also analyzed. The distribution functions are invariant with height, but they do depend on the contact model. The contact energy distribution functions are well fitted by Gamma distributions. There is a transition in the shape of the distribution function as the particle stiffness is decreased from 107 to 106 for the linear model and 108 to 107 for the Hertzian model, when the contact number exceeds 1. Thus, the transition in the distribution function correlates to the contact regime threshold from the binary to multibody contact regime, and is clearly different from the rheological threshold. An order-disorder transition has recently been reported in dense granular flows. The Bagnold rheology applies for both the ordered and disordered states, even though

  13. Martian gullies: possible formation mechanism by dry granular material..

    Science.gov (United States)

    Cedillo-Flores, Y.; Durand-Manterola, H. J.

    section Some of the geomorphological features in Mars are the gullies Some theories developed tried explain its origin either by liquid water liquid carbon dioxide or flows of dry granular material We made a comparative analysis of the Martian gullies with the terrestrial ones We propose that the mechanism of formation of the gullies is as follows In winter CO 2 snow mixed with sand falls in the terrain In spring the CO 2 snow sublimate and gaseous CO 2 make fluid the sand which flows like liquid eroding the terrain and forming the gullies By experimental work with dry granular material we simulated the development of the Martian gullies injecting air in the granular material section We present the characteristics of some terrestrial gullies forms at cold environment sited at Nevado de Toluca Volcano near Toluca City M e xico We compare them with Martian gullies choose from four different areas to target goal recognize or to distinguish to identify possible processes evolved in its formation Also we measured the lengths of those Martian gullies and the range was from 24 m to 1775 meters Finally we present results of our experimental work at laboratory with dry granular material

  14. A trans-phase granular continuum relation and its use in simulation

    Science.gov (United States)

    Kamrin, Ken; Dunatunga, Sachith; Askari, Hesam

    The ability to model a large granular system as a continuum would offer tremendous benefits in computation time compared to discrete particle methods. However, two infamous problems arise in the pursuit of this vision: (i) the constitutive relation for granular materials is still unclear and hotly debated, and (ii) a model and corresponding numerical method must wear ``many hats'' as, in general circumstances, it must be able to capture and accurately represent the material as it crosses through its collisional, dense-flowing, and solid-like states. Here we present a minimal trans-phase model, merging an elastic response beneath a fictional yield criterion, a mu(I) rheology for liquid-like flow above the static yield criterion, and a disconnection rule to model separation of the grains into a low-temperature gas. We simulate our model with a meshless method (in high strain/mixing cases) and the finite-element method. It is able to match experimental data in many geometries, including collapsing columns, impact on granular beds, draining silos, and granular drag problems.

  15. Effects of Noise and Vibration on the Solid to Liquid Fluidization Transition in Small Dense Granular Systems Under Shear

    Science.gov (United States)

    Melhus, Martin Frederic

    2011-07-01

    Granular materials exhibit bulk properties that are distinct from conventional solids, liq- uids, and gases, due to the dissipative nature of the inter-granular forces. Understanding the fundamentals of granular materials draws upon and gives insight into many fields at the current frontiers of physics, such as plasticity of solids, fracture and friction, com- plex systems such as colloids, foams and suspensions, and a variety of biological systems. Particulate flows are widespread in geophysics, and are also essential to many industries. Despite the importance of these phenomena, we lack a theoretical model that explains most behaviors of granular materials. Since granular assemblies are highly dissipative, they are often far from mechanical equilibrium, making most classical analyses inappli- cable. A theory for dilute granular systems exists, but for dense granular systems (by far the majority of granular systems in the real world) no comparable theory is accepted. We approach this problem by examining the fluidization, or transition from solid to liquid, in dense granular systems. In this study, the separate effects of random noise and vibration on the static to flowing transition of a dense granular assembly under planar shear is studied numerically using soft contact particle dynamics simulations in two dimensions. We focus on small systems in a thin planar Couette cell, examining the bistable region while increasing shear, with varying amounts of random noise or vibration, and determine the statistics of the shear required for the onset of flow. We find that the applied power is the key parameter in determining the magnitude of the effects of the noise or vibration, with vibration frequency also having an influence. Similarities and differences between noise and vibration are determined, and the results compare favorably with a two phase model for dense granular flow.

  16. Granular contact dynamics using mathematical programming methods

    DEFF Research Database (Denmark)

    Krabbenhoft, K.; Lyamin, A. V.; Huang, J.

    2012-01-01

    granular contact dynamics formulation uses an implicit time discretization, thus allowing for large time steps. Moreover, in the limit of an infinite time step, the general dynamic formulation reduces to a static formulation that is useful in simulating common quasi-static problems such as triaxial tests...... is developed and it is concluded that the associated sliding rule, in the context of granular contact dynamics, may be viewed as an artifact of the time discretization and that the use of an associated flow rule at the particle scale level generally is physically acceptable. (C) 2012 Elsevier Ltd. All rights...

  17. A thermodynamically consistent model for granular-fluid mixtures considering pore pressure evolution and hypoplastic behavior

    Science.gov (United States)

    Hess, Julian; Wang, Yongqi

    2016-11-01

    A new mixture model for granular-fluid flows, which is thermodynamically consistent with the entropy principle, is presented. The extra pore pressure described by a pressure diffusion equation and the hypoplastic material behavior obeying a transport equation are taken into account. The model is applied to granular-fluid flows, using a closing assumption in conjunction with the dynamic fluid pressure to describe the pressure-like residual unknowns, hereby overcoming previous uncertainties in the modeling process. Besides the thermodynamically consistent modeling, numerical simulations are carried out and demonstrate physically reasonable results, including simple shear flow in order to investigate the vertical distribution of the physical quantities, and a mixture flow down an inclined plane by means of the depth-integrated model. Results presented give insight in the ability of the deduced model to capture the key characteristics of granular-fluid flows. We acknowledge the support of the Deutsche Forschungsgemeinschaft (DFG) for this work within the Project Number WA 2610/3-1.

  18. Granular flow in static mixers by coupled DEM/CFD approach

    Directory of Open Access Journals (Sweden)

    Pezo Lato

    2016-01-01

    Full Text Available The mixing process greatly influence the mixing efficiency, as well as the quality and the price of the intermediate and/or the final product. Static mixer is used for premixing action before the main mixing process, for significant reduction of mixing time and energy consumption. This type of premixing action is not investigated in detail in the open literature. In this article, the novel numerical approach called Discrete Element Method is used for modelling of granular flow in multiple static mixer applications (1 - 3 Komax or Ross mixing elements were utilized, while the Computational Fluid Dynamic method was chosen for fluid flow modelling, using the Eulerian multiphase model. The main aim of this article is to predict the behaviour of granules being gravitationally transported in different mixer configuration and to choose the best configuration of the mixer taking into account the total particle path, the number of mixing elements and the quality of the obtained mixture. The results of the numerical simulations in the static mixers were compared to experimental results, the mixing quality is examined by RSD (relative standard deviation criterion, and the effects on the mixer type and the number of mixing elements on mixing process were studied. The effects of the mixer type and the number of mixing elements on mixing process were studied using analysis of variance (ANOVA. Mathematical modelling is used for optimization of number of Ross and Komax segments in mixer in order to gain desirable mixing results. [Projekat Ministarstva nauke Republike Srbije, br. TR31055

  19. In situ bioremediation: A network model of diffusion and flow in granular porous media

    Energy Technology Data Exchange (ETDEWEB)

    Griffiths, S.K.; Nilson, R.H.; Bradshaw, R.W.

    1997-04-01

    In situ bioremediation is a potentially expedient, permanent and cost- effective means of waste site decontamination. However, permeability reductions due to the transport and deposition of native fines or due to excessive microorganism populations may severely inhibit the injection of supplemental oxygen in the contamination zone. To help understand this phenomenon, we have developed a micro-mechanical network model of flow, diffusion and particle transport in granular porous materials. The model differs from most similar models in that the network is defined by particle positions in a numerically-generated particle array. The model is thus widely applicable to computing effective transport properties for both ordered and realistic random porous media. A laboratory-scale apparatus to measure permeability reductions has also been designed, built and tested.

  20. A soft-rigid contact model of MPM for granular flow impact on retaining structures

    Science.gov (United States)

    Li, Xinpo; Xie, Yanfang; Gutierrez, Marte

    2018-02-01

    Protective measures against hazards associated with rapid debris avalanches include a variety of retaining structures such as rock/boulder fences, gabions, earthfill barriers and retaining walls. However, the development of analytical and numerical methods for the rational assessment of impact force generated by granular flows is still a challenge. In this work, a soft-rigid contact model is built under the coding framework of MPM which is a hybrid method with Eulerian-Lagrangian description. The soft bodies are discretized into particles (material points), and the rigid bodies are presented by rigid node-based surfaces. Coulomb friction model is used to implement the modeled contact mechanics, and a velocity-dependent friction coefficient is coupled into the model. Simulations of a physical experiment show that the peak and residual value of impact forces are well captured by the MPM model. An idealized scenario of debris avalanche flow down a hillslope and impacting on a retaining wall are analyzed using the MPM model. The calculated forces can provide a quantitative estimate from which mound design could proceed for practical implementation in the field.

  1. Cahn-Hiliard theory for unstable granular fluids

    NARCIS (Netherlands)

    van Noije, T.P.C.; Ernst, M.H.

    A Cahn-Hilliard-type theory for hydrodynamic fluctuations is proposed that gives a quantitative description of the slowly evolving spatial correlations and structures in density and flow fields in the early stages of evolution of freely cooling granular fluids. Two mechanisms for pattern selection

  2. Clogging arches in grains, colloids, and pedestrians flowing through constrictions

    Science.gov (United States)

    Zuriguel, Iker

    When a group of particles pass through a narrow orifice, the flow might become intermittent due to the development of clogs that obstruct the constriction. This effect has been observed in many different fields such as mining transport, microbial growing, crowd dynamics, colloids, granular and active matter. In this work we introduce a general framework in which research in some of such scenarios can be encompassed. In particular, we analyze the statistical properties of the bottleneck flow in different experiments and simulations: granular media within vibrated silos, colloids, a flock of sheep and pedestrian evacuations. We reveal a common phenomenology that allows us to rigorously define a transition to a clogged state. Using this definition we explore the main variables involved, which are then grouped into three generic parameters. In addition, we will present results of the geometrical characteristics that the clogging arches have which are related with their stability against perturbations. We experimentally analyse the temporal evolution of the arches evidencing important differences among the structures that are easily destroyed and those that seem to resist forever (longer than the temporal window employed in our measurements). Ministerio de Economía y Competitividad (Spanish Government). Project No. FIS2014-57325.

  3. Unjamming a granular hopper by vibration

    Science.gov (United States)

    Janda, A.; Maza, D.; Garcimartín, A.; Kolb, E.; Lanuza, J.; Clément, E.

    2009-07-01

    We present an experimental study of the outflow of a hopper continuously vibrated by a piezoelectric device. Outpouring of grains can be achieved for apertures much below the usual jamming limit observed for non-vibrated hoppers. Granular flow persists down to the physical limit of one grain diameter, a limit reached for a finite vibration amplitude. For the smaller orifices, we observe an intermittent regime characterized by alternated periods of flow and blockage. Vibrations do not significantly modify the flow rates both in the continuous and the intermittent regime. The analysis of the statistical features of the flowing regime shows that the flow time significantly increases with the vibration amplitude. However, at low vibration amplitude and small orifice sizes, the jamming time distribution displays an anomalous statistics.

  4. Disentangling the role of athermal walls on the Knudsen paradox in molecular and granular gases

    Science.gov (United States)

    Gupta, Ronak; Alam, Meheboob

    2018-01-01

    The nature of particle-wall interactions is shown to have a profound impact on the well-known "Knudsen paradox" [or the "Knudsen minimum" effect, which refers to the decrease of the mass-flow rate of a gas with increasing Knudsen number Kn, reaching a minimum at Kn˜O (1 ) and increasing logarithmically with Kn as Kn→∞ ] in the acceleration-driven Poiseuille flow of rarefied gases. The nonmonotonic variation of the flow rate with Kn occurs even in a granular or dissipative gas in contact with thermal walls. The latter result is in contradiction with recent work [Alam et al., J. Fluid Mech. 782, 99 (2015), 10.1017/jfm.2015.523] that revealed the absence of the Knudsen minimum in granular Poiseuille flow for which the flow rate was found to decrease at large values of Kn. The above conundrum is resolved by distinguishing between "thermal" and "athermal" walls, and it is shown that, for both molecular and granular gases, the momentum transfer to athermal walls is much different than that to thermal walls which is directly responsible for the anomalous flow-rate variation with Kn in the rarefied regime. In the continuum limit of Kn→0 , the athermal walls are shown to be closely related to "no-flux" ("adiabatic") walls for which the Knudsen minimum does not exist either. A possible characterization of athermal walls in terms of (1) an effective specularity coefficient for the slip velocity and (2) a flux-type boundary condition for granular temperature is suggested based on simulation results.

  5. Startup and oxygen concentration effects in a continuous granular mixed flow autotrophic nitrogen removal reactor.

    Science.gov (United States)

    Varas, Rodrigo; Guzmán-Fierro, Víctor; Giustinianovich, Elisa; Behar, Jack; Fernández, Katherina; Roeckel, Marlene

    2015-08-01

    The startup and performance of the completely autotrophic nitrogen removal over nitrite (CANON) process was tested in a continuously fed granular bubble column reactor (BCR) with two different aeration strategies: controlling the oxygen volumetric flow and oxygen concentration. During the startup with the control of oxygen volumetric flow, the air volume was adjusted to 60mL/h and the CANON reactor had volumetric N loadings ranging from 7.35 to 100.90mgN/Ld with 36-71% total nitrogen removal and high instability. In the second stage, the reactor was operated at oxygen concentrations of 0.6, 0.4 and 0.2mg/L. The best condition was 0.2 mgO2/L with a total nitrogen removal of 75.36% with a CANON reactor activity of 0.1149gN/gVVSd and high stability. The feasibility and effectiveness of CANON processes with oxygen control was demonstrated, showing an alternative design tool for efficiently removing nitrogen species. Copyright © 2015 Elsevier Ltd. All rights reserved.

  6. Granular chaos and mixing: Whirled in a grain of sand

    Energy Technology Data Exchange (ETDEWEB)

    Shinbrot, Troy, E-mail: shinbrot@rutgers.edu [Department of Biomedical Engineering, Rutgers University, Piscataway, New Jersey 08854 (United States)

    2015-09-15

    In this paper, we overview examples of chaos in granular flows. We begin by reviewing several remarkable behaviors that have intrigued researchers over the past few decades, and we then focus on three areas in which chaos plays an intrinsic role in granular behavior. First, we discuss pattern formation in vibrated beds, which we show is a direct result of chaotic scattering combined with dynamical dissipation. Next, we consider stick-slip motion, which involves chaotic scattering on the micro-scale, and which results in complex and as yet unexplained peculiarities on the macro-scale. Finally, we examine granular mixing, which we show combines micro-scale chaotic scattering and macro-scale stick-slip motion into behaviors that are well described by dynamical systems tools, such as iterative mappings.

  7. Granular chaos and mixing: Whirled in a grain of sand.

    Science.gov (United States)

    Shinbrot, Troy

    2015-09-01

    In this paper, we overview examples of chaos in granular flows. We begin by reviewing several remarkable behaviors that have intrigued researchers over the past few decades, and we then focus on three areas in which chaos plays an intrinsic role in granular behavior. First, we discuss pattern formation in vibrated beds, which we show is a direct result of chaotic scattering combined with dynamical dissipation. Next, we consider stick-slip motion, which involves chaotic scattering on the micro-scale, and which results in complex and as yet unexplained peculiarities on the macro-scale. Finally, we examine granular mixing, which we show combines micro-scale chaotic scattering and macro-scale stick-slip motion into behaviors that are well described by dynamical systems tools, such as iterative mappings.

  8. Resolved granular debris-flow simulations with a coupled SPH-DCDEM model

    Science.gov (United States)

    Birjukovs Canelas, Ricardo; Domínguez, José M.; Crespo, Alejandro J. C.; Gómez-Gesteira, Moncho; Ferreira, Rui M. L.

    2016-04-01

    Debris flows represent some of the most relevant phenomena in geomorphological events. Due to the potential destructiveness of such flows, they are the target of a vast amount of research (Takahashi, 2007 and references therein). A complete description of the internal processes of a debris-flow is however still an elusive achievement, explained by the difficulty of accurately measuring important quantities in these flows and developing a comprehensive, generalized theoretical framework capable of describing them. This work addresses the need for a numerical model applicable to granular-fluid mixtures featuring high spatial and temporal resolution, thus capable of resolving the motion of individual particles, including all interparticle contacts. This corresponds to a brute-force approach: by applying simple interaction laws at local scales the macro-scale properties of the flow should be recovered by upscaling. This methodology effectively bypasses the complexity of modelling the intermediate scales by resolving them directly. The only caveat is the need of high performance computing, a demanding but engaging research challenge. The DualSPHysics meshless numerical implementation, based on Smoothed Particle Hydrodynamics (SPH), is expanded with a Distributed Contact Discrete Element Method (DCDEM) in order to explicitly solve the fluid and the solid phase. The model numerically solves the Navier-Stokes and continuity equations for the liquid phase and Newton's motion equations for solid bodies. The interactions between solids are modelled with classical DEM approaches (Kruggel-Emden et al, 2007). Among other validation tests, an experimental set-up for stony debris flows in a slit check dam is reproduced numerically, where solid material is introduced trough a hopper assuring a constant solid discharge for the considered time interval. With each sediment particle undergoing tens of possible contacts, several thousand time-evolving contacts are efficiently treated

  9. Using a Time Granularity Table for Gradual Granular Data Aggregation

    DEFF Research Database (Denmark)

    Iftikhar, Nadeem; Pedersen, Torben Bach

    2010-01-01

    solution for data reduction based on gradual granular data aggregation. With the gradual granular data aggregation mechanism, older data can be made coarse-grained while keeping the newest data fine-grained. For instance, when data is 3 months old aggregate to 1 minute level from 1 second level, when data...... and improve query performance, especially on resource-constrained systems with limited storage and query processing capabilities. A number of data reduction solutions have been developed, however an effective solution particularly based on gradual data reduction is missing. This paper presents an effective...... is 6 months old aggregate to 2 minutes level from 1 minute level and so on. The proposed solution introduces a time granularity based data structure, namely a relational time granularity table that enables long term storage of old data by maintaining it at different levels of granularity and effective...

  10. Association of inclusion body myositis with T cell large granular lymphocytic leukaemia

    DEFF Research Database (Denmark)

    Greenberg, Steven A; Pinkus, Jack L; Amato, Anthony A

    2016-01-01

    SEE HOHLFELD AND SCHULZE-KOOPS DOI101093/BRAIN/AWW053 FOR A SCIENTIFIC COMMENTARY ON THIS ARTICLE: Inclusion body myositis and T cell large granular lymphocytic leukaemia are rare diseases involving pathogenic cytotoxic CD8+ T cells. After encountering four patients with both disorders, we...... prospectively screened 38 patients with inclusion body myositis for the presence of expanded large granular lymphocyte populations by standard clinical laboratory methods (flow cytometry, examination of blood smears, and T cell receptor gene rearrangements), and performed muscle immunohistochemistry for CD8, CD......57, and TIA1. Most (22/38; 58%) patients with inclusion body myositis had aberrant populations of large granular lymphocytes in their blood meeting standard diagnostic criteria for T cell large granular lymphocytic leukaemia. These T cell populations were clonal in 20/20 patients and stably present...

  11. Deformation of a 3D granular media caused by fluid invasion

    Science.gov (United States)

    Dalbe, M. J.; Juanes, R.

    2016-12-01

    Multiphase flow in porous media plays a fundamental role in many natural and engineered subsurface processes. The interplay between fluid flow, medium deformation and fracture is essential in geoscience problems as disparate as fracking for unconventional hydrocarbon production, conduit formation and methane venting from lake and ocean sediments, and desiccation cracks in soil. Several experimental and computational studies have shown that the competition between capillary and friction forces can lead to different regimes of deformation, from frictional fingering to hydro-capillary fracturing (Sandnes et al., Nat. Comm. 2011, Holtzman et al., PRL 2012). Most of these investigations have focused, however, on 2D or quasi-2D systems. Here, we develop an experimental set-up that allows us to observe two-phase flow in a fully 3D granular bed and measure the fluid pressure while controlling the level of confining stress. We use an index matching technique to directly visualize the injection of a liquid in a granular media saturated with another, immiscible liquid. We extract the deformation the whole granular bulk as well as at the particle level. Our results show the existence of different regimes of invasion patterns depending on key dimensionless groups that control the system.

  12. Aerofractures in Confined Granular Media

    Science.gov (United States)

    Eriksen, Fredrik K.; Turkaya, Semih; Toussaint, Renaud; Måløy, Knut J.; Flekkøy, Eirik G.

    2015-04-01

    We will present the optical analysis of experimental aerofractures in confined granular media. The study of this generic process may have applications in industries involving hydraulic fracturing of tight rocks, safe construction of dams, tunnels and mines, and in earth science where phenomena such as mud volcanoes and sand injectites are results of subsurface sediment displacements driven by fluid overpressure. It is also interesting to increase the understanding the flow instability itself, and how the fluid flow impacts the solid surrounding fractures and in the rest of the sample. Such processes where previously studied numerically [Niebling 2012a, Niebling 2012b] or in circular geometries. We will here explore experimentally linear geometries. We study the fracturing patterns that form when air flows into a dense, non-cohesive porous medium confined in a Hele-Shaw cell - i.e. into a packing of dry 80 micron beads placed between two glass plates separated by ~1mm. The cell is rectangular and fitted with a semi-permeable boundary to the atmosphere - blocking beads but not air - on one short edge, while the other three edges are impermeable. The porous medium is packed inside the cell between the semi-permeable boundary and an empty volume at the sealed side where the air pressure can be set and kept at a constant overpressure (1-2bar). Thus, for the air trapped inside the cell to release the overpressure it has to move through the solid. At high enough overpressures the air flow deforms the solid and increase permeability in some regions along the air-solid interface, which results in unstable flow and aerofracturing. Aerofractures are thought to be an analogue to hydrofractures, and an advantage of performing aerofracturing experiments in a Hele-Shaw cell is that the fracturing process can easily be observed in the lab. Our experiments are recorded with a high speed camera with a framerate of 1000 frames per second. In the analysis, by using various image

  13. Interface stability of granular filter structures under currents

    NARCIS (Netherlands)

    Verheij, H.J.; Hoffmans, G.; Dorst, K.; Van de Sande, S.

    2012-01-01

    Granular filters are used for protection of structures against scour and erosion. For a proper functioning it is necessary that the interfaces between the filter structure, the subsoil and the water flowing above the filter structure are stable. Stability means that there is no transport of subsoil

  14. Voltage fluctuations in granular superconductors in the perpendicular configuration

    International Nuclear Information System (INIS)

    Gerashchenko, O V

    2003-01-01

    The spectral density of voltage fluctuations in granular YBa 2 Cu 3 O 7-δ superconductors in the perpendicular configuration has been studied in the flux flow mode. It has been found that, in this case, the 1/f-voltage noise observed depends weakly on temperature and is associated with motion of a magnetic flux in the superconductor. A comparison of the data obtained with the results of previous measurements in parallel configuration has shown that voltage noise is produced by a single common source, which is presumably associated with self-organization of the critical state in granular superconductors

  15. Granular deformation mechanisms in semi-solid alloys

    International Nuclear Information System (INIS)

    Gourlay, C.M.; Dahle, A.K.; Nagira, T.; Nakatsuka, N.; Nogita, K.; Uesugi, K.; Yasuda, H.

    2011-01-01

    Deformation mechanisms in equiaxed, partially solid Al-15 wt.% Cu are studied in situ by coupling shear-cell experiments with synchrotron X-ray radiography. Direct evidence is presented for granular deformation mechanisms in both globular and equiaxed-dendritic samples at solid fractions shortly after crystal impingement. It is demonstrated that dilatancy, arching and jamming occur at the crystal scale, and that these can cause stick-slip flow due to periodic dilation and compaction at low displacement rate. Granular deformation is found to be similar in globular and equiaxed-dendritic samples if length is scaled by the crystal size and packing is considered to occur among crystal envelopes. Rheological differences between the morphologies are discussed in terms of the competition between crystal rearrangement and crystal deformation.

  16. A two-phase debris-flow model that includes coupled evolution of volume fractions, granular dilatancy, and pore-fluid pressure

    Science.gov (United States)

    George, David L.; Iverson, Richard M.

    2011-01-01

    Pore-fluid pressure plays a crucial role in debris flows because it counteracts normal stresses at grain contacts and thereby reduces intergranular friction. Pore-pressure feedback accompanying debris deformation is particularly important during the onset of debrisflow motion, when it can dramatically influence the balance of forces governing downslope acceleration. We consider further effects of this feedback by formulating a new, depth-averaged mathematical model that simulates coupled evolution of granular dilatancy, solid and fluid volume fractions, pore-fluid pressure, and flow depth and velocity during all stages of debris-flow motion. To illustrate implications of the model, we use a finite-volume method to compute one-dimensional motion of a debris flow descending a rigid, uniformly inclined slope, and we compare model predictions with data obtained in large-scale experiments at the USGS debris-flow flume. Predictions for the first 1 s of motion show that increasing pore pressures (due to debris contraction) cause liquefaction that enhances flow acceleration. As acceleration continues, however, debris dilation causes dissipation of pore pressures, and this dissipation helps stabilize debris-flow motion. Our numerical predictions of this process match experimental data reasonably well, but predictions might be improved by accounting for the effects of grain-size segregation.

  17. Traffic and Granular Flow’05

    CERN Document Server

    Pöschel, Thorsten; Kühne, Reinhart; Schreckenberg, Michael; Wolf, Dietrich

    2007-01-01

    The conference series Tra?c and Granular Flow has been established in 1995 and has since then been held biannually. At that time, the investigation of granular materials and tra?c was still somewhat exotic and was just starting to become popular among physicists. Originally the idea behind this conference series was to facilitate the c- vergence of the two ?elds, inspired by the similarities of certain phenomena and the use of similar theoretical methods. However, in recent years it has become clear that probably the di?erences between the two systems are much more interesting than the similarities. Nevertheless, the importance of various interrelations among these ?elds is still growing. The workshop continues to o?er an opportunity to stimulate this interdisciplinary research. Over the years the spectrum of topics has become much broader and has included also problems related to topics ranging from social dynamics to - ology. The conference manages to bring together people with rather di?erent background, r...

  18. Kinetics and mass transfer phenomena in anaerobic granular sludge

    NARCIS (Netherlands)

    Gonzalez-Gil, G.; Seghezzo, L.; Lettinga, G.; Kleerebezem, R.

    2001-01-01

    The kinetic properties of acetate-degrading methanogenic granular sludge of different mean diameters were assessed at different up-flow velocities (Vup). Using this approach, the influence of internal and external mass transfer could be estimated. First, the apparent Monod constant (KS) for each

  19. Granular patterns

    CERN Document Server

    Aranson, Igor S

    2009-01-01

    This title presents a review of experiments and novel theoretical concepts needed to understand the mechanisms of pattern formation in granular materials. An effort is made to connect concepts and ideas developed in granular physics with new emergent fields, especially in biology, such as cytoskeleton dynamics.

  20. Measurements of Grain Motion in a Dense, Three-Dimensional Granular Fluid

    Science.gov (United States)

    Yang, Xiaoyu; Huan, Chao; Candela, D.; Mair, R. W.; Walsworth, R. L.

    2002-03-01

    We have used NMR to measure the short-time, three-dimensional displacement of grains in a system of mustard seeds vibrated vertically at 15g. The measurements are in the ballistic regime, giving direct access to the granular temperature profile. The data are compared to a recent hydrodynamic theory developed for high density granular flows. We find that the hydrodynamic theory works well for the dense, lower portion of the sample but breaks down near the free surface, where the mean free path becomes long.

  1. Unsteady non-Newtonian hydrodynamics in granular gases.

    Science.gov (United States)

    Astillero, Antonio; Santos, Andrés

    2012-02-01

    The temporal evolution of a dilute granular gas, both in a compressible flow (uniform longitudinal flow) and in an incompressible flow (uniform shear flow), is investigated by means of the direct simulation Monte Carlo method to solve the Boltzmann equation. Emphasis is laid on the identification of a first "kinetic" stage (where the physical properties are strongly dependent on the initial state) subsequently followed by an unsteady "hydrodynamic" stage (where the momentum fluxes are well-defined non-Newtonian functions of the rate of strain). The simulation data are seen to support this two-stage scenario. Furthermore, the rheological functions obtained from simulation are well described by an approximate analytical solution of a model kinetic equation. © 2012 American Physical Society

  2. Stretched exponentials and power laws in granular avalanching

    Science.gov (United States)

    Head, D. A.; Rodgers, G. J.

    1999-02-01

    We introduce a model for granular surface flow which exhibits both stretched exponential and power law avalanching over its parameter range. Two modes of transport are incorporated, a rolling layer consisting of individual particles and the overdamped, sliding motion of particle clusters. The crossover in behaviour observed in experiments on piles of rice is attributed to a change in the dominant mode of transport. We predict that power law avalanching will be observed whenever surface flow is dominated by clustered motion.

  3. Granular computing: perspectives and challenges.

    Science.gov (United States)

    Yao, JingTao; Vasilakos, Athanasios V; Pedrycz, Witold

    2013-12-01

    Granular computing, as a new and rapidly growing paradigm of information processing, has attracted many researchers and practitioners. Granular computing is an umbrella term to cover any theories, methodologies, techniques, and tools that make use of information granules in complex problem solving. The aim of this paper is to review foundations and schools of research and to elaborate on current developments in granular computing research. We first review some basic notions of granular computing. Classification and descriptions of various schools of research in granular computing are given. We also present and identify some research directions in granular computing.

  4. On the rheology of dilative granular media: Bridging solid- and fluid-like behavior

    Science.gov (United States)

    Andrade, José E.; Chen, Qiushi; Le, Phong H.; Avila, Carlos F.; Matthew Evans, T.

    2012-06-01

    A new rate-dependent plasticity model for dilative granular media is presented, aiming to bridge the seemingly disparate solid- and fluid-like behavioral regimes. Up to date, solid-like behavior is typically tackled with rate-independent plasticity models emanating from Mohr-Coulomb and Critical State plasticity theory. On the other hand, the fluid-like behavior of granular media is typically treated using constitutive theories amenable to viscous flow, e.g., Bingham fluid. In our proposed model, the material strength is composed of a dilation part and a rate-dependent residual strength. The dilatancy strength plays a key role during solid-like behavior but vanishes in the fluid-like regime. The residual strength, which in a classical plasticity model is considered constant and rate-independent, is postulated to evolve with strain rate. The main appeal of the model is its simplicity and its ability to reconcile the classic plasticity and rheology camps. The applicability and capability of the model are demonstrated by numerical simulation of granular flow problems, as well as a classical shear banding problem, where the performance of the continuum model is compared to discrete particle simulations and physical experiment. These results shed much-needed light onto the mechanics and physics of granular media at various shear rates.

  5. Physical test of a particle simulation model in a sheared granular system

    Energy Technology Data Exchange (ETDEWEB)

    Rycroft, Chris; Orpe, Ashish; Kudrolli, Arshad

    2009-01-15

    We report a detailed comparison of a slow gravity driven sheared granular flow with a computational model performed with the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS). To our knowledge, this is the first thorough test of the LAMMPS model with a laboratory granular flow. In the experiments, grains flow inside a silo with a rectangular cross-section, and are sheared by a rough boundary on one side and smooth boundaries on the other sides. Individual grain position and motion are measured using a particle index matching imaging technique where a fluorescent dye is added to the interstitial liquid which has the same refractive index as the glass beads. The boundary imposes a packing order, and the grains are observed to flow in layers which get progressively more disordered with distance from the walls. The computations use a Cundall--Strack contact model between the grains, using contact parameters that have been used in many other previous studies, and ignore the hydrodynamic effects of the interstitial liquid. Computations are performed to understand the effect of particle coefficient of friction, elasticity, contact model, and polydispersity on mean flow properties. After appropriate scaling, we find that the mean velocity of the grains and the number density as a function of flow cross-section observed in the experiments and the simulations are in excellent agreement. The mean flow profile is observed to be unchanged over a broad range of coefficient of friction, except near the smooth wall. We show that the flow profile is not sensitive to atleast 10\\percent polydispersity in particle size. Because the grain elasticity used is smaller in the computations as compared with glass grains, wave-like features can be noted over short time scales in the mean velocity and the velocity auto-correlations measured in the simulations. These wave features occur over an intermediate timescale larger than the particle interaction but smaller than the

  6. IN-SITU REGENERATION OF GRANULAR ACTIVATED CARBON (GAC) USING FENTON'S REAGENTS

    Science.gov (United States)

    Fenton-dependent regeneration of granular activated carbon (GAC) initially saturated with one of several chlorinated aliphatic contaminants was studied in batch and continuous-flow reactors. Homogeneous and heterogeneous experiments were designed to investigate the effects of va...

  7. Hopper Flow: Experiments and Simulation

    Science.gov (United States)

    Li, Zhusong; Shattuck, Mark

    2013-03-01

    Jamming and intermittent granular flow are important problems in industry, and the vertical hopper is a canonical example. Clogging of granular hoppers account for significant losses across many industries. We use realistic DEM simulations of gravity driven flow in a hopper to examine flow and jamming of 2D disks and compare with identical companion experiments. We use experimental data to validate simulation parameters and the form of the inter particle force law. We measure and compare flow rate, emptying times, jamming statistics, and flow fields as a function of opening angle and opening size in both experiment and simulations. Suppored by: NSF-CBET-0968013

  8. Continuum viscoplastic simulation of a granular column collapse on large slopes : μ(I) rheology and lateral wall effects

    Science.gov (United States)

    Martin, Nathan; Mangeney, Anne; Ionescu, Ioan; Bouchut, Francois

    2016-04-01

    The description of the mechanical behaviour of granular flows and in particular of the static/flowing transition is still an open and challenging issue with strong implication for hazard assessment [{Delannay et al.}, 2016]. In particular, {detailed quantitative} comparison between numerical models and observations is necessary to go further in this direction. We simulate here dry granular flows resulting from the collapse of granular columns on an inclined channel (from horizontal to 22^o) and compare precisely the results with laboratory experiments performed by {Mangeney et al.} [2010] and {Farin et al.} [2014]. Incompressibility is assumed despite the dilatancy observed in the experiments (up to 10%). The 2-D model is based on the so-called μ(I) rheology that induces a Drucker-Prager yield stress and a variable viscosity. A nonlinear Coulomb friction term, representing the friction on the lateral walls of the channel is added to the model. We demonstrate that this term is crucial to accurately reproduce granular collapses on slopes higher than 10o whereas it remains of little effect on horizontal slope [{Martin et al.}, 2016]. We show that the use of a variable or a constant viscosity does not change significantly the results provided that these viscosities are of the same order [{Ionescu et al.}, 2015]. However, only a fine tuning of the constant viscosity (η = 1 Pa.s) makes it possible to predict the slow propagation phase observed experimentally on large slopes. This was not possible when using, without tuning, the variable viscosity calculated from the μ(I) rheology with the parameters estimated from experiments. Finally, we discuss the well-posedness of the model with variable and constant viscosity based in particular on the development of shear bands observed in the numerical simulations. References Delannay, R., Valance, A., Mangeney, A., Roche, O., and Richard, P., 2016. Granular and particle-laden flows: from laboratory experiments to field

  9. A new solver for granular avalanche simulation: Indoor experiment verification and field scale case study

    Science.gov (United States)

    Wang, XiaoLiang; Li, JiaChun

    2017-12-01

    A new solver based on the high-resolution scheme with novel treatments of source terms and interface capture for the Savage-Hutter model is developed to simulate granular avalanche flows. The capability to simulate flow spread and deposit processes is verified through indoor experiments of a two-dimensional granular avalanche. Parameter studies show that reduction in bed friction enhances runout efficiency, and that lower earth pressure restraints enlarge the deposit spread. The April 9, 2000, Yigong avalanche in Tibet, China, is simulated as a case study by this new solver. The predicted results, including evolution process, deposit spread, and hazard impacts, generally agree with site observations. It is concluded that the new solver for the Savage-Hutter equation provides a comprehensive software platform for granular avalanche simulation at both experimental and field scales. In particular, the solver can be a valuable tool for providing necessary information for hazard forecasts, disaster mitigation, and countermeasure decisions in mountainous areas.

  10. Granular fingering as a mechanism for ridge formation in debris avalanche deposits: Laboratory experiments and implications for Tutupaca volcano, Peru

    Science.gov (United States)

    Valderrama, P.; Roche, O.; Samaniego, P.; van Wyk des Vries, B.; Araujo, G.

    2018-01-01

    The origin of subparallel, regularly-spaced longitudinal ridges often observed at the surface of volcanic and other rock avalanche deposits remains unclear. We addressed this issue through analogue laboratory experiments on flows of bi-disperse granular mixtures, because this type of flow is known to exhibit granular fingering that causes elongated structures resembling the ridges observed in nature. We considered four different mixtures of fine (300-400 μm) glass beads and coarse (600-710 μm to 900-1000 μm) angular crushed fruit stones, with particle size ratios of 1.9-2.7 and mass fractions of the coarse component of 5-50 wt%. The coarse particles segregated at the flow surface and accumulated at the front where flow instabilities with a well-defined wavelength grew. These formed granular fingers made of coarse-rich static margins delimiting fines-rich central channels. Coalescence of adjacent finger margins created regular spaced longitudinal ridges, which became topographic highs as finger channels drained at final emplacement stages. Three distinct deposit morphologies were observed: 1) Joined fingers with ridges were formed at low (≤ 1.9) size ratio and moderate (10-20 wt%) coarse fraction whereas 2) separate fingers or 3) poorly developed fingers, forming series of frontal lobes, were created at larger size ratios and/or higher coarse contents. Similar ridges and lobes are observed at the debris avalanche deposits of Tutupaca volcano, Peru, suggesting that the processes operating in the experiments can also occur in nature. This implies that volcanic (and non-volcanic) debris avalanches can behave as granular flows, which has important implications for interpretation of deposits and for modeling. Such behaviour may be acquired as the collapsing material disaggregates and forms a granular mixture composed by a right grain size distribution in which particle segregation can occur. Limited fragmentation and block sliding, or grain size distributions

  11. Granular gas dynamics

    CERN Document Server

    Brilliantov, Nikolai

    2003-01-01

    While there is not yet any general theory for granular materials, significant progress has been achieved for dilute systems, also called granular gases. The contributions in this book address both the kinetic approach one using the Boltzmann equation for dissipative gases as well as the less established hydrodynamic description. The last part of the book is devoted to driven granular gases and their analogy with molecular fluids. Care has been taken so as to present the material in a pedagogical and self-contained way and this volume will thus be particularly useful to nonspecialists and newcomers to the field.

  12. Enhanced desalination performance of membrane capacitive deionization cells by packing the flow chamber with granular activated carbon.

    Science.gov (United States)

    Bian, Yanhong; Yang, Xufei; Liang, Peng; Jiang, Yong; Zhang, Changyong; Huang, Xia

    2015-11-15

    A new design of membrane capacitive deionization (MCDI) cell was constructed by packing the cell's flow chamber with granular activated carbon (GAC). The GAC packed-MCDI (GAC-MCDI) delivered higher (1.2-2.5 times) desalination rates than the regular MCDI at all test NaCl concentrations (∼ 100-1000 mg/L). The greatest performance enhancement by packed GAC was observed when treating saline water with an initial NaCl concentration of 100 mg/L. Several different GAC materials were tested and they all exhibited similar enhancement effects. Comparatively, packing the MCDI's flow chamber with glass beads (GB; non-conductive) and graphite granules (GG; conductive but with lower specific surface area than GAC) resulted in inferior desalination performance. Electrochemical impedance spectroscopy (EIS) analysis showed that the GAC-MCDI had considerably smaller internal resistance than the regular MCDI (∼ 19.2 ± 1.2 Ω versus ∼ 1222 ± 15 Ω at 100 mg/L NaCl). The packed GAC also decreased the ionic resistance across the flow chamber (∼ 1.49 ± 0.05 Ω versus ∼ 1130 ± 12 Ω at 100 mg/L NaCl). The electric double layer (EDL) formed on the GAC surface was considered to store salt ions during electrosorption, and facilitate the ion transport in the flow chamber because of the higher ion conductivity in the EDLs than in the bulk solution, thereby enhancing the MCDI's desalination rate. Copyright © 2015 Elsevier Ltd. All rights reserved.

  13. Computational investigation of the flow field contribution to improve electricity generation in granular activated carbon-assisted microbial fuel cells

    Science.gov (United States)

    Zhao, Lei; Li, Jian; Battaglia, Francine; He, Zhen

    2016-11-01

    Microbial fuel cells (MFCs) offer an alternative approach to treat wastewater with less energy input and direct electricity generation. To optimize MFC anodic performance, adding granular activated carbon (GAC) has been proved to be an effective way, most likely due to the enlarged electrode surface for biomass attachment and improved mixing of the flow field. The impact of a flow field on the current enhancement within a porous anode medium (e.g., GAC) has not been well understood before, and thus is investigated in this study by using mathematical modeling of the multi-order Butler-Volmer equation with computational fluid dynamics (CFD) techniques. By comparing three different CFD cases (without GAC, with GAC as a nonreactive porous medium, and with GAC as a reactive porous medium), it is demonstrated that adding GAC contributes to a uniform flow field and a total current enhancement of 17%, a factor that cannot be neglected in MFC design. However, in an actual MFC operation, this percentage could be even higher because of the microbial competition and energy loss issues within a porous medium. The results of the present study are expected to help with formulating strategies to optimize MFC with a better flow pattern design.

  14. Textural evidence for jamming and dewatering of a sub-surface, fluid-saturated granular flow

    Science.gov (United States)

    Sherry, T. J.; Rowe, C. D.; Kirkpatrick, J. D.; Brodsky, E. E.

    2011-12-01

    Sand injectites are spectacular examples of large-scale granular flows involving migration of hundreds of cubic meters of sand slurry over hundreds of meters to kilometers in the sub-surface. By studying the macro- and microstructural textures of a kilometer-scale sand injectite, we interpret the fluid flow regimes during emplacement and define the timing of formation of specific textures in the injected material. Fluidized sand sourced from the Santa Margarita Fm., was injected upward into the Santa Cruz Mudstone, Santa Cruz County, California. The sand injectite exposed at Yellow Bank Beach records emplacement of both hydrocarbon and aqueous sand slurries. Elongate, angular mudstone clasts were ripped from the wall rock during sand migration, providing evidence for high velocity, turbid flow. However, clast long axis orientations are consistently sub-horizontal suggesting the slurry transitioned to a laminar flow as the flow velocity decreased in the sill-like intrusion. Millimeter to centimeter scale laminations are ubiquitous throughout the sand body and are locally parallel to the mudstone clast long axes. The laminations are distinct in exposure because alternating layers are preferentially cemented with limonite sourced from later groundwater infiltration. Quantitative microstructural analyses show that the laminations are defined by subtle oscillations in grain alignment between limonite and non-limonite stained layers. Grain packing, size and shape distributions do not vary. The presence of limonite in alternating layers results from differential infiltration of groundwater, indicating permeability changes between the layers despite minimal grain scale differences. Convolute dewatering structures deform the laminations. Dolomite-cemented sand, a signature of hydrocarbon saturation, forms irregular bodies that cross-cut the laminations and dewatering structures. Laminations are not formed in the dolomite-cemented sand. The relative viscosity difference

  15. Granular avalanches on the Moon: Mass-wasting conditions, processes, and features

    Science.gov (United States)

    Kokelaar, B. P.; Bahia, R. S.; Joy, K. H.; Viroulet, S.; Gray, J. M. N. T.

    2017-09-01

    Seven lunar crater sites of granular avalanches are studied utilizing high-resolution images (0.42-1.3 m/pixel) from the Lunar Reconnaissance Orbiter Camera; one, in Kepler crater, is examined in detail. All the sites are slopes of debris extensively aggraded by frictional freezing at their dynamic angle of repose, four in craters formed in basaltic mare and three in the anorthositic highlands. Diverse styles of mass wasting occur, and three types of dry-debris flow deposit are recognized: (1) multiple channel-and-lobe type, with coarse-grained levees and lobate terminations that impound finer debris, (2) single-surge polylobate type, with subparallel arrays of lobes and fingers with segregated coarse-grained margins, and (3) multiple-ribbon type, with tracks reflecting reworked substrate, minor levees, and no coarse terminations. The latter type results from propagation of granular erosion-deposition waves down slopes dominantly of fine regolith, and it is the first recognized natural example. Dimensions, architectures, and granular segregation styles of the two coarse-grained deposit types are like those formed in natural and experimental avalanches on Earth, although the timescale of motion differs due to the reduced gravity. Influences of reduced gravity and fine-grained regolith on dynamics of granular flow and deposition appear slight, but we distinguish, for the first time, extensive remobilization of coarse talus by inundation with finer debris. The (few) sites show no clear difference attributable to the contrasting mare basalt and highland megaregolith host rocks and their fragmentation. This lunar study offers a benchmarking of deposit types that can be attributed to formation without influence of liquid or gas.

  16. Type-2 fuzzy granular models

    CERN Document Server

    Sanchez, Mauricio A; Castro, Juan R

    2017-01-01

    In this book, a series of granular algorithms are proposed. A nature inspired granular algorithm based on Newtonian gravitational forces is proposed. A series of methods for the formation of higher-type information granules represented by Interval Type-2 Fuzzy Sets are also shown, via multiple approaches, such as Coefficient of Variation, principle of justifiable granularity, uncertainty-based information concept, and numerical evidence based. And a fuzzy granular application comparison is given as to demonstrate the differences in how uncertainty affects the performance of fuzzy information granules.

  17. Grain-scale numerical modeling of granular mechanics and fluid dynamics and application in a glacial context

    DEFF Research Database (Denmark)

    Damsgaard, Anders; Egholm, David Lundbek; Beem, Lucas H.

    The macroscopic behavior of granular materials is the result of the self-organizing complexity of the constituent grains. Granular materials are known for their ability to change phase, where each phase is characterized by distinct mechanical properties. This rich generic phenomenology has made...... it difficult to constrain generalized and adequate mathematical models for their mechanical behavior. Glaciers and ice streams often move by deformation of underlying melt-water saturated sediments. Glacier flow models including subglacial sediment deformation use simplified a priori assumptions for sediment......, the method imposes intense computational requirements on the computational time step. The majority of steps in the granular dynamics algorithm are massively parallel, which makes the DEM an obvious candidate for exploiting the capabilities of modern GPUs. The granular computations are coupled to a fluid...

  18. Granular-relational data mining how to mine relational data in the paradigm of granular computing ?

    CERN Document Server

    Hońko, Piotr

    2017-01-01

    This book provides two general granular computing approaches to mining relational data, the first of which uses abstract descriptions of relational objects to build their granular representation, while the second extends existing granular data mining solutions to a relational case. Both approaches make it possible to perform and improve popular data mining tasks such as classification, clustering, and association discovery. How can different relational data mining tasks best be unified? How can the construction process of relational patterns be simplified? How can richer knowledge from relational data be discovered? All these questions can be answered in the same way: by mining relational data in the paradigm of granular computing! This book will allow readers with previous experience in the field of relational data mining to discover the many benefits of its granular perspective. In turn, those readers familiar with the paradigm of granular computing will find valuable insights on its application to mining r...

  19. Segregation of a binary granular mixture in a vibrating sawtooth base container

    NARCIS (Netherlands)

    Mobarakabadi, Shahin; Adrang, Neda; Habibi, Mehdi; Oskoee, Ehsan Nedaaee

    2017-01-01

    Abstract.: A granular mixture of identical particles of different densities can be segregated when the system is shaken. We present an efficient method of continuously segregating a flow of randomly mixed identical spherical particles of different densities by shaking them in a

  20. Large granular lymphocytosis in a patient infected with HTLV-II.

    Science.gov (United States)

    Martin, M P; Biggar, R J; Hamlin-Green, G; Staal, S; Mann, D

    1993-08-01

    HTLV-II has been associated with a variety of lymphoproliferative disorders, including atypical hairy cell leukemia, chronic T cell leukemia, T prolymphocytic leukemia, and large granular lymphocytic leukemia. However, a direct or indirect role for HTLV-II in these disorders is not yet firmly established. We studied a patient diagnosed as having leukemia of the large granular lymphocyte (LGL) type who was HTLV-II seropositive, to determine if the expanded cell population was infected. Two populations of CD3-CD16+ LGL were identified; one was CD8+, the other CD8-. Populations of cells with these surface markers as well as normal CD3+CD4+ and CD3+CD8+ cells were separated by flow cytometric methods, DNA extracted, and gene regions of HTLV-II pol and tax amplified, using the polymerase chain reaction, and probed after Southern blotting. HTLV-II was detected in the CD3+CD8+ population, and not in the CD3-CD16+ large granular lymphocyte population. This finding indicates that the role of HTLV-II, if any, in LGL proliferation is indirect.

  1. Liquid-Gas-Like Phase Transition in Sand Flow Under Microgravity

    Science.gov (United States)

    Huang, Yu; Zhu, Chongqiang; Xiang, Xiang; Mao, Wuwei

    2015-06-01

    In previous studies of granular flow, it has been found that gravity plays a compacting role, causing convection and stratification by density. However, there is a lack of research and analysis of the characteristics of different particles' motion under normal gravity contrary to microgravity. In this paper, we conduct model experiments on sand flow using a model test system based on a drop tower under microgravity, within which the characteristics and development processes of granular flow under microgravity are captured by high-speed cameras. The configurations of granular flow are simulated using a modified MPS (moving particle simulation), which is a mesh-free, pure Lagrangian method. Moreover, liquid-gas-like phase transitions in the sand flow under microgravity, including the transitions to "escaped", "jumping", and "scattered" particles are highlighted, and their effects on the weakening of shear resistance, enhancement of fluidization, and changes in particle-wall and particle-particle contact mode are analyzed. This study could help explain the surface geology evolution of small solar bodies and elucidate the nature of granular interaction.

  2. Computer simulation of hopper flow

    International Nuclear Information System (INIS)

    Potapov, A.V.; Campbell, C.S.

    1996-01-01

    This paper describes two-dimensional computer simulations of granular flow in plane hoppers. The simulations can reproduce an experimentally observed asymmetric unsteadiness for monodispersed particle sizes, but also could eliminate it by adding a small amount of polydispersity. This appears to be a result of the strong packings that may be formed by monodispersed particles and is thus a noncontinuum effect. The internal stress state was also sampled, which among other things, allows an evaluation of common assumptions made in granular material models. These showed that the internal friction coefficient is far from a constant, which is in contradiction to common models based on plasticity theory which assume that the material is always at the point of imminent yield. Furthermore, it is demonstrated that rapid granular flow theory, another common modeling technique, is inapplicable to this problem even near the exit where the flow is moving its fastest. copyright 1996 American Institute of Physics

  3. Microfluidics of soft granular gels

    Science.gov (United States)

    Nixon, Ryan; Bhattacharjee, Tapomoy; Sawyer, W. Gregory; Angelini, Thomas E.

    Microfluidic methods for encapsulating cells and particles typically involve drop making with two immiscible fluids. The main materials constraint in this approach is surface tension, creating inherent instability between the two fluids. We can eliminate this instability by using miscible inner and outer phases. This is achieved by using granular micro gels which are chemically miscible but physically do not mix. These microgels are yield stress materials, so they flow as solid plugs far from shear gradients, and fluidize where gradients are generated - near an injection nozzle for example. We have found that tuning the yield stress of the material by varying polymer concentration, device performance can be controlled. The solid like behavior of the gel allows us to produces infinitely stable jets that maintain their integrity and configuration over long distances and times. These properties can be combined and manipulated to produce discrete particulate bunches of an inner phase, flowing inside of an outer phase, well enough even to print a Morse code message suspended within flow chambers about a millimeter in diameter moving at millimeters a second.

  4. The physics of debris flows

    Science.gov (United States)

    Iverson, Richard M.

    1997-08-01

    Recent advances in theory and experimentation motivate a thorough reassessment of the physics of debris flows. Analyses of flows of dry, granular solids and solid-fluid mixtures provide a foundation for a comprehensive debris flow theory, and experiments provide data that reveal the strengths and limitations of theoretical models. Both debris flow materials and dry granular materials can sustain shear stresses while remaining static; both can deform in a slow, tranquil mode characterized by enduring, frictional grain contacts; and both can flow in a more rapid, agitated mode characterized by brief, inelastic grain collisions. In debris flows, however, pore fluid that is highly viscous and nearly incompressible, composed of water with suspended silt and clay, can strongly mediate intergranular friction and collisions. Grain friction, grain collisions, and viscous fluid flow may transfer significant momentum simultaneously. Both the vibrational kinetic energy of solid grains (measured by a quantity termed the granular temperature) and the pressure of the intervening pore fluid facilitate motion of grains past one another, thereby enhancing debris flow mobility. Granular temperature arises from conversion of flow translational energy to grain vibrational energy, a process that depends on shear rates, grain properties, boundary conditions, and the ambient fluid viscosity and pressure. Pore fluid pressures that exceed static equilibrium pressures result from local or global debris contraction. Like larger, natural debris flows, experimental debris flows of ˜10 m³ of poorly sorted, water-saturated sediment invariably move as an unsteady surge or series of surges. Measurements at the base of experimental flows show that coarse-grained surge fronts have little or no pore fluid pressure. In contrast, finer-grained, thoroughly saturated debris behind surge fronts is nearly liquefied by high pore pressure, which persists owing to the great compressibility and moderate

  5. The physics of debris flows

    Science.gov (United States)

    Iverson, R.M.

    1997-01-01

    Recent advances in theory and experimentation motivate a thorough reassessment of the physics of debris flows. Analyses of flows of dry, granular solids and solid-fluid mixtures provide a foundation for a comprehensive debris flow theory, and experiments provide data that reveal the strengths and limitations of theoretical models. Both debris flow materials and dry granular materials can sustain shear stresses while remaining static; both can deform in a slow, tranquil mode characterized by enduring, frictional grain contacts; and both can flow in a more rapid, agitated mode characterized by brief, inelastic grain collisions. In debris flows, however, pore fluid that is highly viscous and nearly incompressible, composed of water with suspended silt and clay, can strongly mediate intergranular friction and collisions. Grain friction, grain collisions, and viscous fluid flow may transfer significant momentum simultaneously. Both the vibrational kinetic energy of solid grains (measured by a quantity termed the granular temperature) and the pressure of the intervening pore fluid facilitate motion of grains past one another, thereby enhancing debris flow mobility. Granular temperature arises from conversion of flow translational energy to grain vibrational energy, a process that depends on shear rates, grain properties, boundary conditions, and the ambient fluid viscosity and pressure. Pore fluid pressures that exceed static equilibrium pressures result from local or global debris contraction. Like larger, natural debris flows, experimental debris flows of ???10 m3 of poorly sorted, water-saturated sediment invariably move as an unsteady surge or series of surges. Measurements at the base of experimental flows show that coarse-grained surge fronts have little or no pore fluid pressure. In contrast, finer-grained, thoroughly saturated debris behind surge fronts is nearly liquefied by high pore pressure, which persists owing to the great compressibility and moderate

  6. EFFECTS OF REACTOR CONDITIONS ON ELECTROCHEMICAL DECHLORINATION OF TRICHLOROETHYLENE USING GRANULAR-GRAPHITE ELECTRODE.

    Science.gov (United States)

    Trichloroethylene (TCE) was electrochemically dechlorinated in aqueous environments using granular graphite cathode in a mixed reactor. Effects of pH, current, electrolyte type, and flow rate on TCE dechlorination rate were evaluated. TCE dechlorination rate constant and gas pr...

  7. Study of performances, stability and microbial characterization of a Sequencing Batch Biofilter Granular Reactor working at low recirculation flow.

    Science.gov (United States)

    De Sanctis, Marco; Beccari, Mario; Di Iaconi, Claudio; Majone, Mauro; Rossetti, Simona; Tandoi, Valter

    2013-02-01

    The Sequencing Batch Biofilter Granular Reactor (SBBGR) is a promising wastewater treatment technology characterized by high biomass concentration in the system, good depuration performance and low sludge production. Its main drawback is the high energy consumption required for wastewater recirculation through the reactor bed to ensure both shear stress and oxygen supply. Therefore, the effect of low recirculation flow on the long-term (38 months) performance of a laboratory scale SBBGR was studied. Both the microbial components of the granules, and their main metabolic activities were evaluated (heterotrophic oxidation, nitrification, denitrification, fermentation, sulphate reduction and methanogenesis). The results indicate that despite reduced recirculation, the SBBGR system maintained many of its advantageous characteristics. Copyright © 2012 Elsevier Ltd. All rights reserved.

  8. Why granular media are thermal after all

    Science.gov (United States)

    Liu, Mario; Jiang, Yimin

    2017-06-01

    Two approaches exist to account for granular behavior. The thermal one considers the total entropy, which includes microscopic degrees of freedom such as phonons; the athermal one (as with the Edward entropy) takes grains as elementary. Granular solid hydrodynamics (GSH) belongs to the first, DEM, granular kinetic theory and athermal statistical mechanics (ASM) to the second. A careful discussion of their conceptual differences is given here. Three noteworthy insights or results are: (1) While DEM and granular kinetic theory are well justified to take grains as elementary, any athermal entropic consideration is bound to run into trouble. (2) Many general principles are taken as invalid in granular media. Yet within the thermal approach, energy conservation and fluctuation-dissipation theorem remain valid, granular temperatures equilibrate, and phase space is well explored in a grain at rest. Hence these are abnormalities of the athermal approximation, not of granular media as such. (3) GSH is a wide-ranged continuum mechanical description of granular dynamics.

  9. Educational NASA Computational and Scientific Studies (enCOMPASS)

    Science.gov (United States)

    Memarsadeghi, Nargess

    2013-01-01

    Educational NASA Computational and Scientific Studies (enCOMPASS) is an educational project of NASA Goddard Space Flight Center aimed at bridging the gap between computational objectives and needs of NASA's scientific research, missions, and projects, and academia's latest advances in applied mathematics and computer science. enCOMPASS achieves this goal via bidirectional collaboration and communication between NASA and academia. Using developed NASA Computational Case Studies in university computer science/engineering and applied mathematics classes is a way of addressing NASA's goals of contributing to the Science, Technology, Education, and Math (STEM) National Objective. The enCOMPASS Web site at http://encompass.gsfc.nasa.gov provides additional information. There are currently nine enCOMPASS case studies developed in areas of earth sciences, planetary sciences, and astrophysics. Some of these case studies have been published in AIP and IEEE's Computing in Science and Engineering magazines. A few university professors have used enCOMPASS case studies in their computational classes and contributed their findings to NASA scientists. In these case studies, after introducing the science area, the specific problem, and related NASA missions, students are first asked to solve a known problem using NASA data and past approaches used and often published in a scientific/research paper. Then, after learning about the NASA application and related computational tools and approaches for solving the proposed problem, students are given a harder problem as a challenge for them to research and develop solutions for. This project provides a model for NASA scientists and engineers on one side, and university students, faculty, and researchers in computer science and applied mathematics on the other side, to learn from each other's areas of work, computational needs and solutions, and the latest advances in research and development. This innovation takes NASA science and

  10. Role of gravity or confining pressure and contact stiffness in granular rheology

    NARCIS (Netherlands)

    Singh, A.; Saitoh, K.; Magnanimo, Vanessa; Luding, Stefan

    2015-01-01

    The steady-state shear rheology of granular materials is investigated in slow quasistatic and inertial flows. The effect of gravity (thus the local pressure) and the often-neglected contact stiffness are the focus of this study. A series of particle simulations are performed on a weakly frictional

  11. Direct numerical simulation of granular flows with fluid; Simulation numerique directe d'ecoulements granulaires en presence de fluide

    Energy Technology Data Exchange (ETDEWEB)

    Komiwes, V.

    1999-09-01

    Numerical models applied to simulation of granular flow with fluid are developed. The physical model selected to describe particles flow is a discrete approach. Particle trajectories are calculated by the Newton law and collision is describe by a soft-sphere approach. The fluid flow is modelled by Navier-Stokes equations. The modelling of the momentum transfer depends on the resolution scale: for a scale of the order of the particle diameter, it is modelled by a drag-law and for a scale smaller than the particle diameter, it is directly calculated by stress tensor computation around particles. The direct model is used to find representative elementary volume and prove the local character of the Ergun's law. This application shows the numerical (mesh size), physical (Reynolds number) and computational (CPU time and memory consumptions) limitations. The drag law model and the direct model are validated with analytical and empirical solutions and compared. For the two models, the CPU time and the memory consumptions are discussed. The drag law model is applied to the simulation of gas-solid dense fluidized-beds. In the case of uniform gas distribution, the fluidized-bed simulation heights are compared to experimental data for particle of group A and B of the Geldart classification. (author)

  12. Breakthrough of toluene vapours in granular activated carbon filled packed bed reactor

    International Nuclear Information System (INIS)

    Mohan, N.; Kannan, G.K.; Upendra, S.; Subha, R.; Kumar, N.S.

    2009-01-01

    The objective of this research was to determine the toluene removal efficiency and breakthrough time using commercially available coconut shell-based granular activated carbon in packed bed reactor. To study the effect of toluene removal and break point time of the granular activated carbon (GAC), the parameters studied were bed lengths (2, 3, and 4 cm), concentrations (5, 10, and 15 mg l -1 ) and flow rates (20, 40, and 60 ml/min). The maximum percentage removal of 90% was achieved and the maximum carbon capacity for 5 mg l -1 of toluene, 60 ml/min flow rate and 3 cm bed length shows 607.14 mg/g. The results of dynamic adsorption in a packed bed were consistent with those of equilibrium adsorption by gravimetric method. The breakthrough time and quantity shows that GAC with appropriate surface area can be utilized for air cleaning filters. The result shows that the physisorption plays main role in toluene removal.

  13. Correlations and the Ring-Kinetic Equation in Dense Sheared Granular Flows

    Science.gov (United States)

    Kumaran, V.

    A formal way of deriving fluctuation-correlation relations in densesheared granular media, starting with the Enskog approximation for the collision integral in the Chapman-Enskog theory, is discussed. The correlation correction to the viscosity is obtained using the ring-kinetic equation, in terms of the correlations in the hydrodynamic modes of the linearised Enskog equation. It is shown that the Green-Kubo formula for the shear viscosity emerges from the two-body correlation function obtained from the ring-kinetic equation.

  14. Impact Compaction of a Granular Material

    Science.gov (United States)

    Fenton, Gregg; Asay, Blaine; Todd, Steve; Grady, Dennis

    2017-06-01

    The dynamic behavior of granular materials has importance to a variety of engineering applications. Although, the mechanical behavior of granular materials have been studied extensively for several decades, the dynamic behavior of these materials remains poorly understood. High-quality experimental data are needed to improve our general understanding of granular material compaction physics. This paper describes how an instrumented plunger impact system can be used to measure the compaction process for granular materials at high and controlled strain rates and subsequently used for computational modelling. The experimental technique relies on a gas-gun driven plunger system to generate a compaction wave through a volume of granular material. This volume of material has been redundantly instrumented along the bed length to track the progression of the compaction wave, and the piston displacement is measured with Photon Doppler Velocimetry (PDV). Using the gathered experimental data along with the initial material tap density, a granular material equation of state can be determined.

  15. Granular boycott effect: How to mix granulates

    Science.gov (United States)

    Duran, J.; Mazozi, T.

    1999-11-01

    Granular material can display the basic features of the Boycott effect in sedimentation. A simple experiment shows that granular material falls faster in an inclined tube than in a vertical tube, in analogy with the Boycott effect. As long as the inclination of the tube is above the avalanche threshold, descent of granular material in the tube causes internal convection which in turn results in an efficient mixture of the granular components. By contrast, as in analogous experiments in two dimensions, a vertical fall of granular material occurs via successive block fragmentation, resulting in poor mixing.

  16. Modeling of Hydrodynamics of a Highly Concentrated Granular Medium on the Basis of a Power-Law

    Directory of Open Access Journals (Sweden)

    Shvab Alexander

    2016-01-01

    Full Text Available The paper deals with the movement of the granular medium at a high concentration on the basis of the “power” of the liquid. Based on the original partial slip boundary conditions on the walls of protection obtained with experimental and numerical data to flow in the channel at a flow obstacle.

  17. Tap density equations of granular powders based on the rate process theory and the free volume concept.

    Science.gov (United States)

    Hao, Tian

    2015-02-28

    The tap density of a granular powder is often linked to the flowability via the Carr index that measures how tight a powder can be packed, under an assumption that more easily packed powders usually flow poorly. Understanding how particles are packed is important for revealing why a powder flows better than others. There are two types of empirical equations that were proposed to fit the experimental data of packing fractions vs. numbers of taps in the literature: the inverse logarithmic and the stretched exponential. Using the rate process theory and the free volume concept under the assumption that particles will obey similar thermodynamic laws during the tapping process if the "granular temperature" is defined in a different way, we obtain the tap density equations, and they are reducible to the two empirical equations currently widely used in literature. Our equations could potentially fit experimental data better with an additional adjustable parameter. The tapping amplitude and frequency, the weight of the granular materials, and the environmental temperature are grouped into this parameter that weighs the pace of the packing process. The current results, in conjunction with our previous findings, may imply that both "dry" (granular) and "wet" (colloidal and polymeric) particle systems are governed by the same physical mechanisms in term of the role of the free volume and how particles behave (a rate controlled process).

  18. Settling properties of aerobic granular sludge (AGS) and aerobic granular sludge molasses (AGSM)

    Science.gov (United States)

    Mat Saad, Azlina; Aini Dahalan, Farrah; Ibrahim, Naimah; Yasina Yusuf, Sara; Aqlima Ahmad, Siti; Khalil, Khalilah Abdul

    2018-03-01

    Aerobic granulation technology is applied to treat domestic and industrial wastewater. The Aerobic granular sludge (AGS) cultivated has strong properties that appears to be denser and compact in physiological structure compared to the conventional activated sludge. It offers rapid settling for solid:liquid separation in wastewater treatment. Aerobic granules were developed using sequencing batch reactor (SBR) with intermittent aerobic - anaerobic mode with 8 cycles in 24 hr. This study examined the settling velocity performance of cultivated aerobic granular sludge (AGS) and aerobic granular sludge molasses (AGSM). The elemental composition in both AGS and AGSM were determined using X-ray fluorescence (XRF). The results showed that AGSM has higher settling velocity 30.5 m/h compared to AGS.

  19. Uniform shock waves in disordered granular matter

    NARCIS (Netherlands)

    Gómez, L.R.; Turner, A.M.; Vitelli, V.

    2012-01-01

    The confining pressure P is perhaps the most important parameter controlling the properties of granular matter. Strongly compressed granular media are, in many respects, simple solids in which elastic perturbations travel as ordinary phonons. However, the speed of sound in granular aggregates

  20. Granular packing as model glass formers

    International Nuclear Information System (INIS)

    Wang Yujie

    2017-01-01

    Static granular packings are model hard-sphere glass formers. The nature of glass transition has remained a hotly debated issue. We review recent experimental progresses in using granular materials to study glass transitions. We focus on the growth of glass order with five-fold symmetry in granular packings and relate the findings to both geometric frustration and random first-order phase transition theories. (paper)

  1. Kinetics and mass-transfer phenomena in anaerobic granular sludge.

    Science.gov (United States)

    Gonzalez-Gil, G; Seghezzo, L; Lettinga, G; Kleerebezem, R

    2001-04-20

    The kinetic properties of acetate-degrading methanogenic granular sludge of different mean diameters were assessed at different up-flow velocities (V(up)). Using this approach, the influence of internal and external mass transfer could be estimated. First, the apparent Monod constant (K(S)) for each data set was calculated by means of a curve-fitting procedure. The experimental results revealed that variations in the V(up) did not affect the apparent K(S)-value, indicating that external mass-transport resistance normally can be neglected. With regard to the granule size, a clear increase in K(S) was found at increasing granule diameters. The experimental data were further used to validate a dynamic mathematical biofilm model. The biofilm model was able to describe reaction-diffusion kinetics in anaerobic granules, using a single value for the effective diffusion coefficient in the granules. This suggests that biogas formation did not influence the diffusion-rates in the granular biomass. Copyright 2001 John Wiley & Sons, Inc.

  2. Software compensation in particle flow reconstruction

    Energy Technology Data Exchange (ETDEWEB)

    Tran, Huong Lan; Krueger, Katja; Sefkow, Felix [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Green, Steven; Marshall, John; Thomson, Mark [Cavendish Laboratory, Cambridge (United Kingdom); Simon, Frank [Max-Planck-Institut fuer Physik, Muenchen (Germany)

    2017-10-15

    The particle flow approach to calorimetry benefits from highly granular calorimeters and sophisticated software algorithms in order to reconstruct and identify individual particles in complex event topologies. The high spatial granularity, together with analogue energy information, can be further exploited in software compensation. In this approach, the local energy density is used to discriminate electromagnetic and purely hadronic sub-showers within hadron showers in the detector to improve the energy resolution for single particles by correcting for the intrinsic non-compensation of the calorimeter system. This improvement in the single particle energy resolution also results in a better overall jet energy resolution by improving the energy measurement of identified neutral hadrons and improvements in the pattern recognition stage by a more accurate matching of calorimeter energies to tracker measurements. This paper describes the software compensation technique and its implementation in particle flow reconstruction with the Pandora Particle Flow Algorithm (PandoraPFA). The impact of software compensation on the choice of optimal transverse granularity for the analogue hadronic calorimeter option of the International Large Detector (ILD) concept is also discussed.

  3. Software compensation in particle flow reconstruction

    Energy Technology Data Exchange (ETDEWEB)

    Tran, Huong Lan; Krueger, Katja; Sefkow, Felix [Deutsches Elektronen-Synchrotron DESY, Hamburg (Germany); Green, Steven; Marshall, John; Thomson, Mark [Cavendish Laboratory, Cambridge (United Kingdom); Simon, Frank [Max-Planck-Institut fuer Physik, Muenchen (Germany)

    2017-10-15

    The particle flow approach to calorimetry benefits from highly granular calorimeters and sophisticated software algorithms in order to reconstruct and identify individual particles in complex event topologies. The high spatial granularity, together with analogue energy information, can be further exploited in software compensation. In this approach, the local energy density is used to discriminate electromagnetic and purely hadronic sub-showers within hadron showers in the detector to improve the energy resolution for single particles by correcting for the intrinsic non-compensation of the calorimeter system. This improvement in the single particle energy resolution also results in a better overall jet energy resolution by improving the energy measurement of identified neutral hadrons and improvements in the pattern recognition stage by a more accurate matching of calorimeter energies to tracker measurements. This paper describes the software compensation technique and its implementation in particle flow reconstruction with the Pandora Particle Flow Algorithm (PandoraPFA). The impact of software compensation on the choice of optimal transverse granularity for the analogue hadronic calorimeter option of the International Large Detector (ILD) concept is also discussed. (orig.)

  4. Software compensation in particle flow reconstruction

    International Nuclear Information System (INIS)

    Tran, Huong Lan; Krueger, Katja; Sefkow, Felix; Green, Steven; Marshall, John; Thomson, Mark; Simon, Frank

    2017-10-01

    The particle flow approach to calorimetry benefits from highly granular calorimeters and sophisticated software algorithms in order to reconstruct and identify individual particles in complex event topologies. The high spatial granularity, together with analogue energy information, can be further exploited in software compensation. In this approach, the local energy density is used to discriminate electromagnetic and purely hadronic sub-showers within hadron showers in the detector to improve the energy resolution for single particles by correcting for the intrinsic non-compensation of the calorimeter system. This improvement in the single particle energy resolution also results in a better overall jet energy resolution by improving the energy measurement of identified neutral hadrons and improvements in the pattern recognition stage by a more accurate matching of calorimeter energies to tracker measurements. This paper describes the software compensation technique and its implementation in particle flow reconstruction with the Pandora Particle Flow Algorithm (PandoraPFA). The impact of software compensation on the choice of optimal transverse granularity for the analogue hadronic calorimeter option of the International Large Detector (ILD) concept is also discussed.

  5. Segregation of a binary granular mixture in a vibrating sawtooth base container.

    Science.gov (United States)

    Mobarakabadi, Shahin; Adrang, Neda; Habibi, Mehdi; Oskoee, Ehsan Nedaaee

    2017-09-01

    A granular mixture of identical particles of different densities can be segregated when the system is shaken. We present an efficient method of continuously segregating a flow of randomly mixed identical spherical particles of different densities by shaking them in a quasi-two-dimensional container with a sawtooth-shaped base. Using numerical simulation we study the effect of direction of shaking (horizontal/vertical), geometry of the sawtooth, and the friction coefficient between the grains and the container walls on the segregation quality. Finally by performing experiments on the same system we compare our simulation results with the experimental results. The good agreement between our simulation and experiment indicates the validity of our simulation approach and will provide a practical way for granular segregation in industrial applications.

  6. A 3D coupled hydro-mechanical granular model for the prediction of hot tearing formation

    International Nuclear Information System (INIS)

    Sistaninia, M; Drezet, J-M; Rappaz, M; Phillion, A B

    2012-01-01

    A new 3D coupled hydro-mechanical granular model that simulates hot tearing formation in metallic alloys is presented. The hydro-mechanical model consists of four separate 3D modules. (I) The Solidification Module (SM) is used for generating the initial solid-liquid geometry. Based on a Voronoi tessellation of randomly distributed nucleation centers, this module computes solidification within each polyhedron using a finite element based solute diffusion calculation for each element within the tessellation. (II) The Fluid Flow Module (FFM) calculates the solidification shrinkage and deformation-induced pressure drop within the intergranular liquid. (III) The Semi-solid Deformation Module (SDM) is used to simulate deformation of the granular structure via a combined finite element / discrete element method. In this module, deformation of the solid grains is modeled using an elasto-viscoplastic constitutive law. (IV) The Failure Module (FM) is used to simulate crack initiation and propagation with the fracture criterion estimated from the overpressure required to overcome the capillary forces at the liquid-gas interface. The FFM, SDM, and FM are coupled processes since solid deformation, intergranular flow, and crack initiation are deeply linked together. The granular model predictions have been validated against bulk data measured experimentally and calculated with averaging techniques.

  7. The dependence of granular plasticity on particle shape

    Science.gov (United States)

    Murphy, Kieran; Jaeger, Heinrich

    Granular materials plastically deform through reworking an intricate network of particle-particle contacts. Some particle rearrangements have only a fleeting effect before being forgotten while others set in motion global restructuring. How particle shape affects local interactions and how those, in turn, influence the nature of the aggregate's plasticity is far from clear, especially in three dimensions. Here we investigate the remarkably wide range of behaviors in the yielding regime, from quiescent flow to violent jerks, depending on particle shape. We study this complex dependence via uniaxial compression experiments on aggregates of 3D-printed particles, and complement stress-strain data with simultaneous x-ray videos and volumetric strain measurements. We find power law distributions of the slip magnitudes, and discuss their universality. Our data show that the multitude of small slips serves to gradually dilate the packing whereas the fewer large ones accompany significant compaction events. Our findings provide new insights into general features of granular materials during plastic deformation and highlight how small changes in particle shape can give rise to drastic differences in yielding behavior.

  8. Mechanics of a granular skin

    Science.gov (United States)

    Karmakar, Somnath; Sane, Anit; Bhattacharya, S.; Ghosh, Shankar

    2017-04-01

    Magic sand, a hydrophobic toy granular material, is widely used in popular science instructions because of its nonintuitive mechanical properties. A detailed study of the failure of an underwater column of magic sand shows that these properties can be traced to a single phenomenon: the system self-generates a cohesive skin that encapsulates the material inside. The skin, consisting of pinned air-water-grain interfaces, shows multiscale mechanical properties: they range from contact-line dynamics in the intragrain roughness scale, to plastic flow at the grain scale, all the way to sample-scale mechanical responses. With decreasing rigidity of the skin, the failure mode transforms from brittle to ductile (both of which are collective in nature) to a complete disintegration at the single-grain scale.

  9. Controlling wave propagation through nonlinear engineered granular systems

    Science.gov (United States)

    Leonard, Andrea

    We study the fundamental dynamic behavior of a special class of ordered granular systems in order to design new, structured materials with unique physical properties. The dynamic properties of granular systems are dictated by the nonlinear, Hertzian, potential in compression and zero tensile strength resulting from the discrete material structure. Engineering the underlying particle arrangement of granular systems allows for unique dynamic properties, not observed in natural, disordered granular media. While extensive studies on 1D granular crystals have suggested their usefulness for a variety of engineering applications, considerably less attention has been given to higher-dimensional systems. The extension of these studies in higher dimensions could enable the discovery of richer physical phenomena not possible in 1D, such as spatial redirection and anisotropic energy trapping. We present experiments, numerical simulation (based on a discrete particle model), and in some cases theoretical predictions for several engineered granular systems, studying the effects of particle arrangement on the highly nonlinear transient wave propagation to develop means for controlling the wave propagation pathways. The first component of this thesis studies the stress wave propagation resulting from a localized impulsive loading for three different 2D particle lattice structures: square, centered square, and hexagonal granular crystals. By varying the lattice structure, we observe a wide range of properties for the propagating stress waves: quasi-1D solitary wave propagation, fully 2D wave propagation with tunable wave front shapes, and 2D pulsed wave propagation. Additionally the effects of weak disorder, inevitably present in real granular systems, are investigated. The second half of this thesis studies the solitary wave propagation through 2D and 3D ordered networks of granular chains, reducing the effective density compared to granular crystals by selectively placing wave

  10. Fine-granularity electromagnetic calorimeter using plastic scintillator strip-array

    International Nuclear Information System (INIS)

    Nagano, A.; Yamauchi, S.; Matsunaga, H.; Kim, S.; Matsumoto, T.; Sekiguchi, K.; Uchida, N.; Yamada, Y.; Yamamoto, S.; Evtoukhovitch, P.; Fujii, Y.; Garutti, E.; Iba, S.; Itoh, S.; Kajino, F.; Kalinnikov, V.; Kallies, W.; Kanzaki, J.; Kawagoe, K.; Kishimoto, S.; Miyata, H.; Mzavia, D.; Nakajima, N.; Nakamura, R.; Ono, H.; Samoilov, V.; Sanchez, A.L.C.; Takeshita, T.; Tamura, Y.; Tsamalaidze, Z.

    2006-01-01

    For the future linear collider calorimetry, fine-granularity is indispensable for energy measurements based on particle flow algorithm, which could achieve better energy resolution for jets than the conventional method. To explore the possibility for such a calorimeter using scintillator, an electromagnetic calorimeter test module, made of scintillator-strips and lead plates, was constructed and tested with test beams. Performance of the test module is presented in this article, in terms of the shower profile studies as well as energy and spatial measurements

  11. Thermal conductivity of granular materials

    Energy Technology Data Exchange (ETDEWEB)

    Buyevich, Yu A

    1974-01-01

    Stationary heat transfer in a granular material consisting of a continuous medium containing spherical granules of other substances is considered under the assumption that the spatial distribution of granules is random. The effective thermal conductivity characterizing macroscopic heat transfer in such a material is expressed as a certain function of the conductivities and volume fractions of the medium and dispersed substances. For reasons of mathematical analogy, all the results obtained for the thermal conductivity are valid while computing the effective diffusivity of some admixture in granular materials as well as for evaluation of the effective electric conductivity or the mean dielectric and magnetic permeabilities of granular conductors and dielectrics. (23 refs.)

  12. Cavitation and multiphase flow forum - 1985

    International Nuclear Information System (INIS)

    Hoyt, J.W.; Furuya, O.

    1985-01-01

    This book presents the papers given at a conference on fluid flow. Topics considered at the conference included cavitation inception, bubble growth, cavitation noise, holography, axial flow pumps, vortices, cavitation erosion, two-phase flow in nozzles, coal slurry valves, hopper flows of granular materials, helium bubble transport in a closed vertical duct, and a numerical model for flow in a venturi scrubber

  13. Statistical and visual probing of evolving granular assemblies

    International Nuclear Information System (INIS)

    Smith, Laurence M.

    2002-01-01

    The majority of processes in the chemical and allied industries involve the storage and conveyancing of granular material, the physics of which is still not particularly well understood. Whilst some non-invasive techniques have been developed, much experimental work unfortunately interferes with the fields being investigated. For this reason and in conjunction with increasing computing power, there has been an increase in simulation based studies. Granular dynamics simulations, being based upon inter-particle interaction laws, give the potential to investigate assemblies at the 'micro-level' and have been successful in modelling process conditions in a number of granular flow situations. To date, most analyses of these simulations are essentially static in nature involving 'time snapshots'. However, in a granular dynamics simulation there is a wealth of data available on a time referenced basis which has the potential to allow a quantitative analysis of the dynamics of assembly evolution. This dissertation describes the development and application of a toolkit for post-simulation analysis. However, the utilities within the toolkit would be equally applicable to large experimental data sets should such data sets exist. The application of the toolset focuses largely on the dynamics of heap evolution in both 2D and 3D with some supportive 3D work on hopper discharge. A major part of the work involves the application of time series techniques (including the wavelet transform) in the context of variable coupling during avalanching. Segregation by self-diffusion receives particular attention and a new mechanism is proposed by which segregation by particle size takes place in the boundary layer of a low impact feed heap displaying a clear velocity gradient during discrete avalanching. Periodic lateral surging is shown to enforce mixing for a high impact feed, a phenomenon which appears to switch off below a certain feed impact. Segregation by self-diffusion is also shown

  14. Clogging in constricted suspension flows

    Science.gov (United States)

    Marin, Alvaro; Lhuissier, Henri; Rossi, Massimiliano; Kähler, Christian J.

    2018-02-01

    The flow of a charged-stabilized suspension through a single constricted channel is studied experimentally by tracking the particles individually. Surprisingly, the behavior is found to be qualitatively similar to that of inertial dry granular systems: For small values of the neck-to-particle size ratio (D /d reported for granular systems and agree for moderate particle volume fraction (ϕ ≈20 % ) with a simple stochastic model for the number of particles at the neck. For larger neck sizes (D /d >3 ), even at the largest ϕ (≈60 %) achievable in the experiments, an uninterrupted particle flow is observed, which resembles that of an hourglass. This particularly small value of D /d (≃3 ) at the transition to a practically uninterrupted flow is attributed to the low effective friction between the particles, achieved by the particle's functionalization and lubrication.

  15. Particle-size segregation and diffusive remixing in shallow granular avalanches

    Science.gov (United States)

    Gray, J. M. N. T.; Chugunov, V. A.

    2006-12-01

    Segregation and mixing of dissimilar grains is a problem in many industrial and pharmaceutical processes, as well as in hazardous geophysical flows, where the size-distribution can have a major impact on the local rheology and the overall run-out. In this paper, a simple binary mixture theory is used to formulate a model for particle-size segregation and diffusive remixing of large and small particles in shallow gravity-driven free-surface flows. This builds on a recent theory for the process of kinetic sieving, which is the dominant mechanism for segregation in granular avalanches provided the density-ratio and the size-ratio of the particles are not too large. The resulting nonlinear parabolic segregation remixing equation reduces to a quasi-linear hyperbolic equation in the no-remixing limit. It assumes that the bulk velocity is incompressible and that the bulk pressure is lithostatic, making it compatible with most theories used to compute the motion of shallow granular free-surface flows. In steady-state, the segregation remixing equation reduces to a logistic type equation and the ‘S’-shaped solutions are in very good agreement with existing particle dynamics simulations for both size and density segregation. Laterally uniform time-dependent solutions are constructed by mapping the segregation remixing equation to Burgers equation and using the Cole Hopf transformation to linearize the problem. It is then shown how solutions for arbitrary initial conditions can be constructed using standard methods. Three examples are investigated in which the initial concentration is (i) homogeneous, (ii) reverse graded with the coarse grains above the fines, and, (iii) normally graded with the fines above the coarse grains. Time-dependent two-dimensional solutions are also constructed for plug-flow in a semi-infinite chute.

  16. Start-up performance and granular sludge features of an improved external circulating anaerobic reactor for algae-laden water treatment.

    Science.gov (United States)

    Yu, Yaqin; Lu, Xiwu

    2017-09-01

    The microbial characteristics of granular sludge during the rapid start of an enhanced external circulating anaerobic reactor were studied to improve algae-laden water treatment efficiency. Results showed that algae laden water was effectively removed after about 35 d, and the removal rates of chemical oxygen demand (COD) and algal toxin were around 85% and 92%, respectively. Simultaneously, the gas generation rate was around 380 mL/gCOD. The microbial community structure in the granular sludge of the reactor was complicated, and dominated by coccus and filamentous bacteria. Methanosphaera , Methanolinea , Thermogymnomonas , Methanoregula , Methanomethylovorans , and Methanosaeta were the major microorganisms in the granular sludge. The activities of protease and coenzyme F 420 were high in the granular sludge. The intermittent stirring device and the reverse-flow system were further found to overcome the disadvantage of the floating and crusting of cyanobacteria inside the reactor. Meanwhile, the effect of mass transfer inside the reactor can be accelerated to help give the reactor a rapid start.

  17. Nonlinear theory of nonstationary low Mach number channel flows of freely cooling nearly elastic granular gases.

    Science.gov (United States)

    Meerson, Baruch; Fouxon, Itzhak; Vilenkin, Arkady

    2008-02-01

    We employ hydrodynamic equations to investigate nonstationary channel flows of freely cooling dilute gases of hard and smooth spheres with nearly elastic particle collisions. This work focuses on the regime where the sound travel time through the channel is much shorter than the characteristic cooling time of the gas. As a result, the gas pressure rapidly becomes almost homogeneous, while the typical Mach number of the flow drops well below unity. Eliminating the acoustic modes and employing Lagrangian coordinates, we reduce the hydrodynamic equations to a single nonlinear and nonlocal equation of a reaction-diffusion type. This equation describes a broad class of channel flows and, in particular, can follow the development of the clustering instability from a weakly perturbed homogeneous cooling state to strongly nonlinear states. If the heat diffusion is neglected, the reduced equation becomes exactly soluble, and the solution develops a finite-time density blowup. The blowup has the same local features at singularity as those exhibited by the recently found family of exact solutions of the full set of ideal hydrodynamic equations [I. Fouxon, Phys. Rev. E 75, 050301(R) (2007); I. Fouxon,Phys. Fluids 19, 093303 (2007)]. The heat diffusion, however, always becomes important near the attempted singularity. It arrests the density blowup and brings about previously unknown inhomogeneous cooling states (ICSs) of the gas, where the pressure continues to decay with time, while the density profile becomes time-independent. The ICSs represent exact solutions of the full set of granular hydrodynamic equations. Both the density profile of an ICS and the characteristic relaxation time toward it are determined by a single dimensionless parameter L that describes the relative role of the inelastic energy loss and heat diffusion. At L>1 the intermediate cooling dynamics proceeds as a competition between "holes": low-density regions of the gas. This competition resembles Ostwald

  18. Size-induced axial band structure and directional flow of a ternary-size granular material in a 3-D horizontal rotating drum

    Science.gov (United States)

    Yang, Shiliang; Sun, Yuhao; Ma, Honghe; Chew, Jia Wei

    2018-05-01

    Differences in the material property of the granular material induce segregation which inevitably influences both natural and industrial processes. To understand the dynamical segregation behavior, the band structure, and also the spatial redistribution of particles induced by the size differences of the particles, a ternary-size granular mixture in a three-dimensional rotating drum operating in the rolling flow regime is numerically simulated using the discrete element method. The results demonstrate that (i) the axial bands of the medium particles are spatially sandwiched in between those of the large and small ones; (ii) the total mass in the active and passive regions is a global parameter independent of segregation; (iii) nearly one-third of all the particles are in the active region, with the small particles having the highest mass fraction; (iv) the axial bands initially appear near the end wall, then become wider and purer in the particular species with time as more axial bands form toward the axial center; and (v) the medium particle type exhibits segregation later and has the narrowest axial bandwidth and least purity in the bands. Compared to the binary-size system, the presence of the medium particle type slightly increases the total mass in the active region, leads to larger mass fractions of the small and large particle types in the active region, and enhances the axial segregation in the system. The results obtained in the current work provide valuable insights regarding size segregation, and band structure and formation in the rotating drum with polydisperse particles.

  19. Hierarchical self-assembly of PDMA-b-PS chains into granular nanoparticles: genesis and fate.

    Science.gov (United States)

    Bianchi, Alberto; Mauri, Michele; Bonetti, Simone; Koynov, Kaloian; Kappl, Michael; Lieberwirth, Ingo; Butt, Hans-Jürgen; Simonutti, Roberto

    2014-12-01

    The hierarchical self-assembly of an amphiphilic block copolymer, poly(N,N-dimethylacrylamide)-block-polystyrene with a very short hydrophilic block (PDMA10 -b-PS62 ), in large granular nanoparticles is reported. While these nanoparticles are stable in water, their disaggregation can be induced either mechanically (i.e., by applying a force via the tip of the cantilever of an atomic force microscope (AFM)) or by partial hydrolysis of the acrylamide groups. AFM force spectroscopy images show the rupture of the particle as a combination of collapse and flow, while scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of partly hydrolyzed nanoparticles provide a clear picture of the granular structure. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. [Research on Cultivation and Stability of Nitritation Granular Sludge in Integrated ABR-CSTR Reactor].

    Science.gov (United States)

    Wu, Kai-cheng; Wu, Peng; Shen, Yao-liang; Li, Yue-han; Wang, Han-fang; Xu, Yue-zhong

    2015-11-01

    Abstract: The last two compartments of the Anaerobic Baffled Readtor ( ABR) were altered into aeration tank and sedimentation tank respectively to get an integrated anaerobic-aerobic reactor, using anaerobic granular sludge in anaerobic zone and aerobic granular sludge in aerobic zone as seed sludge. The research explored the condition to cultivate nitritation granular sludge, under the condition of continuous flow. The C/N rate was decreased from 1 to 0.4 and the ammonia nitrogen volumetric loading rate was increased from 0.89 kg x ( m3 x d)(-1) to 2.23 kg x (m3 x d)(-1) while the setting time of 1 h was controlled in the aerobic zone. After the system was operated for 45 days, the mature nitritation granular sludge in aerobic zone showed a compact structure and yellow color while the nitrite accumulation rate was about 80% in the effluent. The associated inhibition of free ammonia (FA) and free nitrous acid (FNA) dominated the nitritation. Part of granules lost stability during the initial period of operation and flocs appeared in the aerobic zone. However, the flocs were transformed into newly generated small particles in the following reactor operation, demonstrating that organic carbon was benefit to granulation and the enrichment of slow-growing nitrifying played an important role in the stability of granules.

  1. Terminal velocity of liquids and granular materials dispersed by a high explosive

    Science.gov (United States)

    Loiseau, J.; Pontalier, Q.; Milne, A. M.; Goroshin, S.; Frost, D. L.

    2018-04-01

    The explosive dispersal of a layer of solid particles or a layer of liquid surrounding a spherical high-explosive charge generates a turbulent, multiphase flow. Shock compression of the material layer during the initial acceleration may partially consolidate the material, leading to the formation of jet-like structures when the layer fragments and sheds particles upon release. Similarly, release of a shock-compressed liquid shell causes the nucleation of cavitation sites, leading to the radial breakup of the shell and the formation of jets upon expansion. In the current study, a wide variety of granular materials and liquids were explosively dispersed. The maximum terminal jet tip or shell velocity was measured using high-speed videography. Charges were constructed using thin-walled glass bulbs of various diameters and contained a central C-4 charge surrounded by the material to be dispersed. This permitted variation of the ratio of material mass to charge mass (M/C) from 4 to 300. Results indicated that material velocity broadly correlates with predictions of the Gurney model. For liquids, the terminal velocity was accurately predicted by the Gurney model. For granular materials, Gurney over-predicted the terminal velocity by 25-60%, depending on the M/C ratio, with larger M/C values exhibiting larger deficits. These deficits are explained by energy dissipation during the collapse of voids in the granular material bed. Velocity deficits were insensitive to the degree of jetting and granular material properties. Empirical corrections to the Gurney model are presented with improved agreement with the dry powder experimental velocities.

  2. Terminal velocity of liquids and granular materials dispersed by a high explosive

    Science.gov (United States)

    Loiseau, J.; Pontalier, Q.; Milne, A. M.; Goroshin, S.; Frost, D. L.

    2018-05-01

    The explosive dispersal of a layer of solid particles or a layer of liquid surrounding a spherical high-explosive charge generates a turbulent, multiphase flow. Shock compression of the material layer during the initial acceleration may partially consolidate the material, leading to the formation of jet-like structures when the layer fragments and sheds particles upon release. Similarly, release of a shock-compressed liquid shell causes the nucleation of cavitation sites, leading to the radial breakup of the shell and the formation of jets upon expansion. In the current study, a wide variety of granular materials and liquids were explosively dispersed. The maximum terminal jet tip or shell velocity was measured using high-speed videography. Charges were constructed using thin-walled glass bulbs of various diameters and contained a central C-4 charge surrounded by the material to be dispersed. This permitted variation of the ratio of material mass to charge mass ( M/ C) from 4 to 300. Results indicated that material velocity broadly correlates with predictions of the Gurney model. For liquids, the terminal velocity was accurately predicted by the Gurney model. For granular materials, Gurney over-predicted the terminal velocity by 25-60%, depending on the M/ C ratio, with larger M/ C values exhibiting larger deficits. These deficits are explained by energy dissipation during the collapse of voids in the granular material bed. Velocity deficits were insensitive to the degree of jetting and granular material properties. Empirical corrections to the Gurney model are presented with improved agreement with the dry powder experimental velocities.

  3. Impact of granular drops

    KAUST Repository

    Marston, J. O.

    2013-07-15

    We investigate the spreading and splashing of granular drops during impact with a solid target. The granular drops are formed from roughly spherical balls of sand mixed with water, which is used as a binder to hold the ball together during free-fall. We measure the instantaneous spread diameter for different impact speeds and find that the normalized spread diameter d/D grows as (tV/D)1/2. The speeds of the grains ejected during the “splash” are measured and they rarely exceed twice that of the impact speed.

  4. Impact of granular drops

    KAUST Repository

    Marston, J. O.; Mansoor, Mohammad M.; Thoroddsen, Sigurdur T

    2013-01-01

    We investigate the spreading and splashing of granular drops during impact with a solid target. The granular drops are formed from roughly spherical balls of sand mixed with water, which is used as a binder to hold the ball together during free-fall. We measure the instantaneous spread diameter for different impact speeds and find that the normalized spread diameter d/D grows as (tV/D)1/2. The speeds of the grains ejected during the “splash” are measured and they rarely exceed twice that of the impact speed.

  5. Viscosity evolution of anaerobic granular sludge

    NARCIS (Netherlands)

    Pevere, A.; Guibaud, G.; Hullebusch, van E.D.; Lens, P.N.L.; Baudu, M.

    2006-01-01

    The evolution of the apparent viscosity at steady shear rate of sieved anaerobic granular sludge (20¿315 ¿m diameter) sampled from different full-scale anaerobic reactors was recorded using rotation tests. The ¿limit viscosity¿ of sieved anaerobic granular sludge was determined from the apparent

  6. Release of Extracellular Polymeric Substance and Disintegration of Anaerobic Granular Sludge under Reduced Sulfur Compounds-Rich Conditions

    Directory of Open Access Journals (Sweden)

    Takuro Kobayashi

    2015-07-01

    Full Text Available The effect of reduced form of sulfur compounds on granular sludge was investigated. Significant release of extracellular polymeric substance (EPS from the granular sludge occurred in the presence of sulfide and methanethiol according to various concentrations. Granular sludge also showed a rapid increase in turbidity and decrease in diameter in accordance with sulfide concentration during the long-term shaking, suggesting that the strength of the granules was reduced with high-concentration sulfide. A continuous experiment of up-flow anaerobic sludge blanket reactors with different concentrations of sulfide (10, 200, 500 mg-S/L influence demonstrated that the reactor fed with higher concentration of sulfide allowed more washout of small particle-suspended solid (SS content and soluble carbohydrate and protein, which were considered as EPS released from biofilm. Finally, the presence of sulfide negatively affected methane production, chemical oxygen demand removal and sludge retention in operational performance.

  7. Erosion onset of a cohesionless granular medium by an immersed impinging round jet

    Science.gov (United States)

    Brunier-Coulin, Florian; Cuéllar, Pablo; Philippe, Pierre

    2017-03-01

    Among different devices developed quite recently to quantify the resistance to erosion of natural soil within the broader context of dyke safety, the most commonly used is probably the jet erosion test in which a scouring crater is induced by impingement of an immersed water jet. A comprehensive experimental investigation on the jet erosion in the specific situation of a cohesionless granular material is presented here. The tests were performed by combining special optical techniques allowing for an accurate measurement of the scouring onset and evolution inside an artificially translucent granular sample. The impinging jet hydrodynamics are also analyzed, empirically validating the use of a self-similar theoretical framework for the laminar round jet. The critical conditions at the onset of erosion appear to be best described by a dimensionless Shields number based on the inertial drag force created by the fluid flow on the eroded particles rather than on the pressure gradients around them. To conclude, a tentative empirical model for the maximal flow velocity initiating erosion at the bottom of the scoured crater is put forward and discussed in the light of some preliminary results.

  8. A continuum theory for two-phase flows of particulate solids: application to Poiseuille flows

    Science.gov (United States)

    Monsorno, Davide; Varsakelis, Christos; Papalexandris, Miltiadis V.

    2015-11-01

    In the first part of this talk, we present a novel two-phase continuum model for incompressible fluid-saturated granular flows. The model accounts for both compaction and shear-induced dilatancy and accommodates correlations for the granular rheology in a thermodynamically consistent way. In the second part of this talk, we exercise this two-phase model in the numerical simulation of a fully-developed Poiseuille flow of a dense suspension. The numerical predictions are shown to compare favorably against experimental measurements and confirm that the model can capture the important characteristics of the flow field, such as segregation and formation of plug zones. Finally, results from parametric studies with respect to the initial concentration, the magnitude of the external forcing and the width of the channel are presented and the role of these physical parameters is quantified. Financial Support has been provided by SEDITRANS, an Initial Training Network of the European Commission's 7th Framework Programme

  9. Preliminary study on aerobic granular biomass formation with aerobic continuous flow reactor

    Science.gov (United States)

    Yulianto, Andik; Soewondo, Prayatni; Handajani, Marissa; Ariesyady, Herto Dwi

    2017-03-01

    A paradigm shift in waste processing is done to obtain additional benefits from treated wastewater. By using the appropriate processing, wastewater can be turned into a resource. The use of aerobic granular biomass (AGB) can be used for such purposes, particularly for the processing of nutrients in wastewater. During this time, the use of AGB for processing nutrients more reactors based on a Sequencing Batch Reactor (SBR). Studies on the use of SBR Reactor for AGB demonstrate satisfactory performance in both formation and use. SBR reactor with AGB also has been applied on a full scale. However, the use use of SBR reactor still posses some problems, such as the need for additional buffer tank and the change of operation mode from conventional activated sludge to SBR. This gives room for further reactor research with the use of a different type, one of which is a continuous reactor. The purpose of this study is to compare AGB formation using continuous reactor and SBR with same operation parameter. Operation parameter are Organic Loading Rate (OLR) set to 2,5 Kg COD/m3.day with acetate as substrate, aeration rate 3 L/min, and microorganism from Hospital WWTP as microbial source. SBR use two column reactor with volumes 2 m3, and continuous reactor uses continuous airlift reactor, with two compartments and working volume of 5 L. Results from preliminary research shows that although the optimum results are not yet obtained, AGB can be formed on the continuous reactor. When compared with AGB generated by SBR, then the characteristics of granular diameter showed similarities, while the sedimentation rate and Sludge Volume Index (SVI) characteristics showed lower yields.

  10. Fast spot-based multiscale simulations of granular drainage

    Energy Technology Data Exchange (ETDEWEB)

    Rycroft, Chris H.; Wong, Yee Lok; Bazant, Martin Z.

    2009-05-22

    We develop a multiscale simulation method for dense granular drainage, based on the recently proposed spot model, where the particle packing flows by local collective displacements in response to diffusing"spots'" of interstitial free volume. By comparing with discrete-element method (DEM) simulations of 55,000 spheres in a rectangular silo, we show that the spot simulation is able to approximately capture many features of drainage, such as packing statistics, particle mixing, and flow profiles. The spot simulation runs two to three orders of magnitude faster than DEM, making it an appropriate method for real-time control or optimization. We demonstrateextensions for modeling particle heaping and avalanching at the free surface, and for simulating the boundary layers of slower flow near walls. We show that the spot simulations are robust and flexible, by demonstrating that they can be used in both event-driven and fixed timestep approaches, and showing that the elastic relaxation step used in the model can be applied much less frequently and still create good results.

  11. Survivable integrated grooming in multi-granularity optical networks

    Science.gov (United States)

    Wu, Jingjing; Guo, Lei; Wei, Xuetao; Liu, Yejun

    2012-05-01

    Survivability is an important issue to ensure the service continuity in optical network. At the same time, with the granularity of traffic demands ranging from sub-wavelength-level to wavelength-level, traffic demands need to be aggregated and carried over the network in order to utilize resources effectively. Therefore, multi-granularity grooming is proposed to save the cost and reduce the number of switching ports in Optical-Cross Connects (OXCs). However, current works mostly addressed the survivable wavelength or waveband grooming. Therefore, in this paper, we propose three heuristic algorithms called Multi-granularity Dedicated Protection Grooming (MDPG), Multi-granularity Shared Protection Grooming (MSPG) and Multi-granularity Mixed Protection Grooming (MMPG), respectively. All of them are performed based on the Survivable Multi-granularity Integrated Auxiliary Graph (SMIAG) that includes one Wavelength Integrated Auxiliary Graph (WIAG) for wavelength protection and one waveBand Integrated Auxiliary Graph (BIAG) for waveband protection. Numerical results show that MMPG has the lowest average port-cost, the best resource utilization ratio and the lowest blocking probability among these three algorithms. Compared with MDPG, MSPG has lower average port-cost, better resource utilization ratio and lower blocking probability.

  12. Superconductivity in inhomogeneous granular metals

    International Nuclear Information System (INIS)

    McLean, W.L.

    1980-01-01

    A model of elongated metal ellipsoids imbedded in a granular metal is treated by an effective medium approach to explain the observed temperature dependence of the normal-state conductivity of superconducting granular aluminum. Josephson tunneling is thus still required to account for the superconductivity. The model predicts the same kind of contrasting behavior on opposite sides of the metal-insulator transition as is found in the recent scaling treatment of Anderson localization

  13. Pneumatic fractures in confined granular media.

    Science.gov (United States)

    Eriksen, Fredrik K; Toussaint, Renaud; Turquet, Antoine L; Måløy, Knut J; Flekkøy, Eirik G

    2017-06-01

    We perform experiments where air is injected at a constant overpressure P_{in}, ranging from 5 to 250 kPa, into a dry granular medium confined within a horizontal linear Hele-Shaw cell. The setup allows us to explore compacted configurations by preventing decompaction at the outer boundary, i.e., the cell outlet has a semipermeable filter such that beads are stopped while air can pass. We study the emerging patterns and dynamic growth of channels in the granular media due to fluid flow, by analyzing images captured with a high speed camera (1000 images/s). We identify four qualitatively different flow regimes, depending on the imposed overpressure, ranging from no channel formation for P_{in} below 10 kPa, to large thick channels formed by erosion and fingers merging for high P_{in} around 200 kPa. The flow regimes where channels form are characterized by typical finger thickness, final depth into the medium, and growth dynamics. The shape of the finger tips during growth is studied by looking at the finger width w as function of distance d from the tip. The tip profile is found to follow w(d)∝d^{β}, where β=0.68 is a typical value for all experiments, also over time. This indicates a singularity in the curvature d^{2}d/dw^{2}∼κ∼d^{1-2β}, but not of the slope dw/dd∼d^{β-1}, i.e., more rounded tips rather than pointy cusps, as they would be for the case β>1. For increasing P_{in}, the channels generally grow faster and deeper into the medium. We show that the channel length along the flow direction has a linear growth with time initially, followed by a power-law decay of growth velocity with time as the channel approaches its final length. A closer look reveals that the initial growth velocity v_{0} is found to scale with injection pressure as v_{0}∝P_{in}^{3/2}, while at a critical time t_{c} there is a cross-over to the behavior v(t)∝t^{-α}, where α is close to 2.5 for all experiments. Finally, we explore the fractal dimension of the fully

  14. Nonlinear coherent structures in granular crystals

    Science.gov (United States)

    Chong, C.; Porter, Mason A.; Kevrekidis, P. G.; Daraio, C.

    2017-10-01

    The study of granular crystals, which are nonlinear metamaterials that consist of closely packed arrays of particles that interact elastically, is a vibrant area of research that combines ideas from disciplines such as materials science, nonlinear dynamics, and condensed-matter physics. Granular crystals exploit geometrical nonlinearities in their constitutive microstructure to produce properties (such as tunability and energy localization) that are not conventional to engineering materials and linear devices. In this topical review, we focus on recent experimental, computational, and theoretical results on nonlinear coherent structures in granular crystals. Such structures—which include traveling solitary waves, dispersive shock waves, and discrete breathers—have fascinating dynamics, including a diversity of both transient features and robust, long-lived patterns that emerge from broad classes of initial data. In our review, we primarily discuss phenomena in one-dimensional crystals, as most research to date has focused on such scenarios, but we also present some extensions to two-dimensional settings. Throughout the review, we highlight open problems and discuss a variety of potential engineering applications that arise from the rich dynamic response of granular crystals.

  15. On inconsistency in frictional granular systems

    Science.gov (United States)

    Alart, Pierre; Renouf, Mathieu

    2018-04-01

    Numerical simulation of granular systems is often based on a discrete element method. The nonsmooth contact dynamics approach can be used to solve a broad range of granular problems, especially involving rigid bodies. However, difficulties could be encountered and hamper successful completion of some simulations. The slow convergence of the nonsmooth solver may sometimes be attributed to an ill-conditioned system, but the convergence may also fail. The prime aim of the present study was to identify situations that hamper the consistency of the mathematical problem to solve. Some simple granular systems were investigated in detail while reviewing and applying the related theoretical results. A practical alternative is briefly analyzed and tested.

  16. Statistical mechanics of dense granular media

    International Nuclear Information System (INIS)

    Coniglio, A; Fierro, A; Nicodemi, M; Ciamarra, M Pica; Tarzia, M

    2005-01-01

    We discuss some recent results on the statistical mechanics approach to dense granular media. In particular, by analytical mean field investigation we derive the phase diagram of monodisperse and bidisperse granular assemblies. We show that 'jamming' corresponds to a phase transition from a 'fluid' to a 'glassy' phase, observed when crystallization is avoided. The nature of such a 'glassy' phase turns out to be the same as found in mean field models for glass formers. This gives quantitative evidence for the idea of a unified description of the 'jamming' transition in granular media and thermal systems, such as glasses. We also discuss mixing/segregation transitions in binary mixtures and their connections to phase separation and 'geometric' effects

  17. Characterization of Unbound Granular Materials for Pavements

    NARCIS (Netherlands)

    Araya, A.A.

    2011-01-01

    This research is focused on the characterization of the mechanical behavior of unbound granular road base materials (UGMs). An extensive laboratory investigation is described, in which various methods for determination of the mechanical properties of granular materials are examined for their

  18. Low-velocity impact cratering experiments in granular slopes

    Science.gov (United States)

    Hayashi, Kosuke; Sumita, Ikuro

    2017-07-01

    Low-velocity impact cratering experiments are conducted in sloped granular targets to study the effect of the slope angle θ on the crater shape and its scales. We use two types of granular matter, sand and glass beads, former of which has a larger friction coefficient μs = tanθr , where θr is the angle of repose. Experiments show that as θ increases, the crater becomes shallower and elongated in the direction of the slope. Furthermore the crater floor steepens in the upslope side and a thick rim forms in the downslope side, thus forming an asymmetric profile. High-speed images show that these features are results of ejecta being dispersed farther towards the downslope side and the subsequent avalanche which buries much of the crater floor. Such asymmetric ejecta dispersal can be explained by combining the Z-model and a ballistic model. Using the topographic maps of the craters, we classify crater shape regimes I-III, which transition with increasing θ : a full-rim crater (I), a broken-rim crater (II), and a depression (III). The critical θ for the regime transitions are larger for sand compared to glass beads, but collapse to close values when we use a normalized slope θ^ = tanθ / tanθr . Similarly we derive θ^-dependences of the scaled crater depth, length, width and their ratios which collapse the results for different targets and impact energies. We compare the crater profiles formed in our experiments with deep craters on asteroid Vesta and find that some of the scaled profiles nearly overlap and many have similar depth / length ratios. This suggests that these Vestan craters may also have formed in the gravity regime and that the formation process can be approximated by a granular flow with a similar effective friction coefficient.

  19. Rheology of sediment transported by a laminar flow

    Science.gov (United States)

    Houssais, M.; Ortiz, C. P.; Durian, D. J.; Jerolmack, D. J.

    2016-12-01

    Understanding the dynamics of fluid-driven sediment transport remains challenging, as it occurs at the interface between a granular material and a fluid flow. Boyer, Guazzelli, and Pouliquen [Phys. Rev. Lett. 107, 188301 (2011)], 10.1103/PhysRevLett.107.188301 proposed a local rheology unifying dense dry-granular and viscous-suspension flows, but it has been validated only for neutrally buoyant particles in a confined and homogeneous system. Here we generalize the Boyer, Guazzelli, and Pouliquen model to account for the weight of a particle by addition of a pressure P0 and test the ability of this model to describe sediment transport in an idealized laboratory river. We subject a bed of settling plastic particles to a laminar-shear flow from above, and use refractive-index-matching to track particles' motion and determine local rheology—from the fluid-granular interface to deep in the granular bed. Data from all experiments collapse onto a single curve of friction μ as a function of the viscous number Iv over the range 3 ×10-5 ≤Iv≤2 , validating the local rheology model. For Ivcreeping regime where we observe a continuous decay of the friction coefficient μ ≤μs as Iv decreases. The rheology of this creep regime cannot be described by the local model, and more work is needed to determine whether a nonlocal rheology model can be modified to account for our findings.

  20. Tsunamis generated by long and thin granular landslides in a large flume

    Science.gov (United States)

    Miller, Garrett S.; Andy Take, W.; Mulligan, Ryan P.; McDougall, Scott

    2017-01-01

    In this experimental study, granular material is released down slope to investigate landslide-generated waves. Starting with a known volume and initial position of the landslide source, detailed data are obtained on the velocity and thickness of the granular flow, the shape and location of the submarine landslide deposit, the amplitude and shape of the near-field wave, the far-field wave evolution, and the wave runup elevation on a smooth impermeable slope. The experiments are performed on a 6.7 m long 30° slope on which gravity accelerates the landslides into a 2.1 m wide and 33.0 m long wave flume that terminates with a 27° runup ramp. For a fixed landslide volume of 0.34 m3, tests are conducted in a range of still water depths from 0.05 to 0.50 m. Observations from high-speed cameras and measurements from wave probes indicate that the granular landslide moves as a long and thin train of material, and that only a portion of the landslide (termed the "effective mass") is engaged in activating the leading wave. The wave behavior is highly dependent on the water depth relative to the size of the landslide. In deeper water, the near-field wave behaves as a stable solitary-like wave, while in shallower water, the wave behaves as a breaking dissipative bore. Overall, the physical model observations are in good agreement with the results of existing empirical equations when the effective mass is used to predict the maximum near-field wave amplitude, the far-field amplitude, and the runup of tsunamis generated by granular landslides.

  1. Uniform shock waves in disordered granular matter.

    Science.gov (United States)

    Gómez, Leopoldo R; Turner, Ari M; Vitelli, Vincenzo

    2012-10-01

    The confining pressure P is perhaps the most important parameter controlling the properties of granular matter. Strongly compressed granular media are, in many respects, simple solids in which elastic perturbations travel as ordinary phonons. However, the speed of sound in granular aggregates continuously decreases as the confining pressure decreases, completely vanishing at the jamming-unjamming transition. This anomalous behavior suggests that the transport of energy at low pressures should not be dominated by phonons. In this work we use simulations and theory to show how the response of granular systems becomes increasingly nonlinear as pressure decreases. In the low-pressure regime the elastic energy is found to be mainly transported through nonlinear waves and shocks. We numerically characterize the propagation speed, shape, and stability of these shocks and model the dependence of the shock speed on pressure and impact intensity by a simple analytical approach.

  2. Shock waves in weakly compressed granular media.

    Science.gov (United States)

    van den Wildenberg, Siet; van Loo, Rogier; van Hecke, Martin

    2013-11-22

    We experimentally probe nonlinear wave propagation in weakly compressed granular media and observe a crossover from quasilinear sound waves at low impact to shock waves at high impact. We show that this crossover impact grows with the confining pressure P0, whereas the shock wave speed is independent of P0-two hallmarks of granular shocks predicted recently. The shocks exhibit surprising power law attenuation, which we model with a logarithmic law implying that shock dissipation is weak and qualitatively different from other granular dissipation mechanisms. We show that elastic and potential energy balance in the leading part of the shocks.

  3. Role of hydraulic retention time and granular medium in microbial removal in tertiary treatment reed beds.

    Science.gov (United States)

    García, Joan; Vivar, Joan; Aromir, Maria; Mujeriego, Rafael

    2003-06-01

    The main objective of this paper is to evaluate the role of hydraulic retention time (HRT) and granular medium in faecal coliform (FC) and somatic coliphage (SC) removal in tertiary reed beds. Experiments were carried out in a pilot plant with four parallel reed beds (horizontal subsurface flow constructed wetlands), each one containing a different type of granular medium. This pilot plant is located in a wastewater treatment plant in Montcada i Reixac, near Barcelona, in northeastern Spain. The microbial inactivation ratios obtained in the different beds are compared as a function of three selected HRTs. Secondary effluent from the wastewater treatment plant was used as the influent of the pilot system. The microbial inactivation ratio ranged between 0.1 and 2.7 log-units for FC and from 0.5 to 1.7 log-units for SC in beds with coarser granular material (5-25mm), while it ranged between 0.7 and 3.4 log-units for FC and from 0.9 to 2.6 log-units for SC in the bed with finer material (2-13mm). HRT and granular medium are both key factors in microbial removal in the tertiary reed beds. The microbial inactivation ratio rises as the HRT increases until it reaches a saturation value (in general at an HRT of 3 days). The value of the microbial inactivation ratio at the saturation level depends on the granular medium contained in the bed. The specific surface area necessary to reach 2-3 log-units of FC and SC is approximately 3m(2)/person-equivalent.

  4. Concepts and design of the CMS high granularity calorimeter Level-1 trigger

    CERN Document Server

    Sauvan, Jean-Baptiste

    2016-01-01

    The CMS experiment has chosen a novel high granularity calorimeter for the forward region as part of its planned upgrade for the high luminosity LHC. The calorimeter will have a fine segmentation in both the transverse and longitudinal directions and will be the first such calorimeter specifically optimised for particle flow reconstruction to operate at a colliding beam experiment. The high granularity results in around six million readout channels in total and so presents a significant challenge in terms of data manipulation and processing for the trigger; the trigger data volumes will be an order of magnitude above those currently handled at CMS. In addition, the high luminosity will result in an average of 140 to 200 interactions per bunch crossing, giving a huge background rate in the forward region that needs to be efficiently reduced by the trigger algorithms. Efficient data reduction and reconstruction algorithms making use of the fine segmentation of the detector have been simulated and evaluated. The...

  5. Defining and testing a granular continuum element

    Energy Technology Data Exchange (ETDEWEB)

    Rycroft, Chris H.; Kamrin, Ken; Bazant, Martin Z.

    2007-12-03

    Continuum mechanics relies on the fundamental notion of amesoscopic volume "element" in which properties averaged over discreteparticles obey deterministic relationships. Recent work on granularmaterials suggests a continuum law may be inapplicable, revealinginhomogeneities at the particle level, such as force chains and slow cagebreaking. Here, we analyze large-scale Discrete-Element Method (DEM)simulations of different granular flows and show that a "granularelement" can indeed be defined at the scale of dynamical correlations,roughly three to five particle diameters. Its rheology is rather subtle,combining liquid-like dependence on deformation rate and solid-likedependence on strain. Our results confirm some aspects of classicalplasticity theory (e.g., coaxiality of stress and deformation rate),while contradicting others (i.e., incipient yield), and can guide thedevelopment of more realistic continuum models.

  6. An Emotional Agent Model Based on Granular Computing

    Directory of Open Access Journals (Sweden)

    Jun Hu

    2012-01-01

    Full Text Available Affective computing has a very important significance for fulfilling intelligent information processing and harmonious communication between human being and computers. A new model for emotional agent is proposed in this paper to make agent have the ability of handling emotions, based on the granular computing theory and the traditional BDI agent model. Firstly, a new emotion knowledge base based on granular computing for emotion expression is presented in the model. Secondly, a new emotional reasoning algorithm based on granular computing is proposed. Thirdly, a new emotional agent model based on granular computing is presented. Finally, based on the model, an emotional agent for patient assistant in hospital is realized, experiment results show that it is efficient to handle simple emotions.

  7. A theoretical framework for an access programme encompassing ...

    African Journals Online (AJOL)

    A theoretical framework for an access programme encompassing further education training: remedy for educational wastage? ... learners who have dropped out of school without completing their secondary-school education, there are the special needs of adult learners in the workplace that must be taken into consideration.

  8. Long-range interactions in dilute granular systems

    NARCIS (Netherlands)

    Müller, M.K

    2008-01-01

    In this thesis, on purpose, we focussed on the most challenging, longest ranging potentials. We analyzed granular media of low densities obeying 1/r long-range interaction potentials between the granules. Such systems are termed granular gases and differ in their behavior from ordinary gases by

  9. Friction law and hysteresis in granular materials

    Science.gov (United States)

    DeGiuli, E.; Wyart, M.

    2017-08-01

    The macroscopic friction of particulate materials often weakens as the flow rate is increased, leading to potentially disastrous intermittent phenomena including earthquakes and landslides. We theoretically and numerically study this phenomenon in simple granular materials. We show that velocity weakening, corresponding to a nonmonotonic behavior in the friction law, μ(I), is present even if the dynamic and static microscopic friction coefficients are identical, but disappears for softer particles. We argue that this instability is induced by endogenous acoustic noise, which tends to make contacts slide, leading to faster flow and increased noise. We show that soft spots, or excitable regions in the materials, correspond to rolling contacts that are about to slide, whose density is described by a nontrivial exponent θs. We build a microscopic theory for the nonmonotonicity of μ(I), which also predicts the scaling behavior of acoustic noise, the fraction of sliding contacts χ, and the sliding velocity, in terms of θs. Surprisingly, these quantities have no limit when particles become infinitely hard, as confirmed numerically. Our analysis rationalizes previously unexplained observations and makes experimentally testable predictions.

  10. Consideration of reinforcement mechanism in the short fiber mixing granular materials by granular element simulations

    Science.gov (United States)

    Mori, Kentaro; Kaneko, Kenji; Hashizume, Yutaka

    2017-06-01

    The short fiber mixing method is well known as one of the method to improve the strength of gran- ular soils in geotechnical engineering. Mechanical properties of the short fiber mixing granular materials are influenced by many factors, such as the mixture ratio of the short fiber, the material of short fiber, the length, and the orientation. In particular, the mixture ratio of the short fibers is very important in mixture design. In the past study, we understood that the strength is reduced by too much short fiber mixing by a series of tri-axial compression experiments. Namely, there is "optimum mixture ratio" in the short fiber mixing granular soils. In this study, to consider the mechanism of occurrence of the optimum mixture ratio, we carried out the numerical experiments by granular element method. As the results, we can understand that the strength decrease when too much grain-fiber contact points exist, because a friction coefficient is smaller than the grain-grain contact points.

  11. Storage and discharge of a granular fluid

    NARCIS (Netherlands)

    Pacheco-Martinez, Hector; van Gerner, H.J.; Ruiz-Suarez, J.C.

    2008-01-01

    Experiments and computational simulations are carried out to study the behavior of a granular column in a silo whose walls are able to vibrate horizontally. The column is brought to a steady fluidized state and it behaves similar to a hydrostatic system. We study the dynamics of the granular

  12. The role of fluid viscosity in an immersed granular collapse

    Science.gov (United States)

    Yang, Geng Chao; Kwok, Chung Yee; Sobral, Yuri Dumaresq

    2017-06-01

    Instabilities of immersed slopes and cliffs can lead to catastrophic events that involve a sudden release of huge soil mass. The scaled deposit height and runout distance are found to follow simple power laws when a granular column collapses on a horizontal plane. However, if the granular column is submerged in a fluid, the mobility of the granular collapse due to high inertia effects will be reduced by fluid-particle interactions. In this study, the effects of fluid viscosity on granular collapse is investigated qualitatively by adopting a numerical approach based on the coupled lattice Boltzmann method (LBM) and discrete element method (DEM). It is found that the granular collapse can be dramatically slowed down due to the presence of viscous fluids. For the considered granular configuration, when the fluid viscosity increases. the runout distance decreases and the final deposition shows a larger deposit angle.

  13. The role of fluid viscosity in an immersed granular collapse

    Directory of Open Access Journals (Sweden)

    Yang Geng Chao

    2017-01-01

    Full Text Available Instabilities of immersed slopes and cliffs can lead to catastrophic events that involve a sudden release of huge soil mass. The scaled deposit height and runout distance are found to follow simple power laws when a granular column collapses on a horizontal plane. However, if the granular column is submerged in a fluid, the mobility of the granular collapse due to high inertia effects will be reduced by fluid-particle interactions. In this study, the effects of fluid viscosity on granular collapse is investigated qualitatively by adopting a numerical approach based on the coupled lattice Boltzmann method (LBM and discrete element method (DEM. It is found that the granular collapse can be dramatically slowed down due to the presence of viscous fluids. For the considered granular configuration, when the fluid viscosity increases. the runout distance decreases and the final deposition shows a larger deposit angle.

  14. VELOCITY FIELD COMPUTATION IN VIBRATED GRANULAR MEDIA USING AN OPTICAL FLOW BASED MULTISCALE IMAGE ANALYSIS METHOD

    Directory of Open Access Journals (Sweden)

    Johan Debayle

    2011-05-01

    Full Text Available An image analysis method has been developed in order to compute the velocity field of a granular medium (sand grains, mean diameter 600 μm submitted to different kinds of mechanical stresses. The differential method based on optical flow conservation consists in describing a dense motion field with vectors associated to each pixel. A multiscale, coarse-to-fine, analytical approach through tailor sized windows yields the best compromise between accuracy and robustness of the results, while enabling an acceptable computation time. The corresponding algorithmis presented and its validation discussed through different tests. The results of the validation tests of the proposed approach show that the method is satisfactory when attributing specific values to parameters in association with the size of the image analysis window. An application in the case of vibrated sand has been studied. An instrumented laboratory device provides sinusoidal vibrations and enables external optical observations of sand motion in 3D transparent boxes. At 50 Hz, by increasing the relative acceleration G, the onset and development of two convective rolls can be observed. An ultra fast camera records the grain avalanches, and several pairs of images are analysed by the proposed method. The vertical velocity profiles are deduced and allow to precisely quantify the dimensions of the fluidized region as a function of G.

  15. Fractal dimension analysis in a highly granular calorimeter

    CERN Document Server

    Ruan, M; Brient, J.C; Jeans, D; Videau, H

    2015-01-01

    The concept of “particle flow” has been developed to optimise the jet energy resolution by distinguishing the different jet components. A highly granular calorimeter designed for the particle flow algorithm provides an unprecedented level of detail for the reconstruction of calorimeter showers and enables new approaches to shower analysis. In this paper the measurement and use of the fractal dimension of showers is described. The fractal dimension is a characteristic number that measures the global compactness of the shower. It is highly dependent on the primary particle type and energy. Its application in identifying particles and estimating their energy is described in the context of a calorimeter designed for the International Linear Collider.

  16. Energy decay in a granular gas collapse

    International Nuclear Information System (INIS)

    Almazán, Lidia; Serero, Dan; Pöschel, Thorsten; Salueña, Clara

    2017-01-01

    An inelastic hard ball bouncing repeatedly off the ground comes to rest in finite time by performing an infinite number of collisions. Similarly, a granular gas under the influence of external gravity, condenses at the bottom of the confinement due to inelastic collisions. By means of hydrodynamical simulations, we find that the condensation process of a granular gas reveals a similar dynamics as the bouncing ball. Our result is in agreement with both experiments and particle simulations, but disagrees with earlier simplified hydrodynamical description. Analyzing the result in detail, we find that the adequate modeling of pressure plays a key role in continuum modeling of granular matter. (paper)

  17. Periurethral granular cell tumor: a case report

    International Nuclear Information System (INIS)

    Kim, Jeong Kon; Choi, Hyo Gyeong; Cho, Kyoung Sik

    1998-01-01

    Granular cell tumors are uncommon soft tissue tumors which arise as solitary or multiple masses. Lesions commonly arise in the head, neck, and chest wall, but can occur in any part of the body. To our knowledge, periurethral granular cell tumor has not been previously reported. We report one such case

  18. Granular motor in the non-Brownian limit

    NARCIS (Netherlands)

    Oyarte Galvez, Loreto Alejandra; van der Meer, Roger M.

    2016-01-01

    In this work we experimentally study a granular rotor which is similar to the famous Smoluchowski–Feynman device and which consists of a rotor with four vanes immersed in a granular gas. Each side of the vanes can be composed of two different materials, creating a rotational asymmetry and turning

  19. Pore-Scale Investigation on Stress-Dependent Characteristics of Granular Packs and Their Impact on Multiphase Fluid Distribution

    Science.gov (United States)

    Torrealba, V.; Karpyn, Z.; Yoon, H.; Hart, D. B.; Klise, K. A.

    2013-12-01

    The pore-scale dynamics that govern multiphase flow under variable stress conditions are not well understood. This lack of fundamental understanding limits our ability to quantitatively predict multiphase flow and fluid distributions in natural geologic systems. In this research, we focus on pore-scale, single and multiphase flow properties that impact displacement mechanisms and residual trapping of non-wetting phase under varying stress conditions. X-ray micro-tomography is used to image pore structures and distribution of wetting and non-wetting fluids in water-wet synthetic granular packs, under dynamic load. Micro-tomography images are also used to determine structural features such as medial axis, surface area, and pore body and throat distribution; while the corresponding transport properties are determined from Lattice-Boltzmann simulations performed on lattice replicas of the imaged specimens. Results are used to investigate how inter-granular deformation mechanisms affect fluid displacement and residual trapping at the pore-scale. This will improve our understanding of the dynamic interaction of mechanical deformation and fluid flow during enhanced oil recovery and geologic CO2 sequestration. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  20. Encompassing Sexual Medicine within Psychiatry: Pros and Cons

    Science.gov (United States)

    Segraves, Robert Taylor

    2010-01-01

    Objective: This article examines the positive and negative aspects of psychiatry encompassing sexual medicine within its purview. Methods: MEDLINE searches for the period between 1980 to the present were performed with the terms "psychiatry," "sexual medicine," and "sexual dysfunction." In addition, sexual medicine texts were reviewed for chapters…

  1. Fracture surfaces of granular pastes.

    Science.gov (United States)

    Mohamed Abdelhaye, Y O; Chaouche, M; Van Damme, H

    2013-11-01

    Granular pastes are dense dispersions of non-colloidal grains in a simple or a complex fluid. Typical examples are the coating, gluing or sealing mortars used in building applications. We study the cohesive rupture of thick mortar layers in a simple pulling test where the paste is initially confined between two flat surfaces. After hardening, the morphology of the fracture surfaces was investigated, using either the box counting method to analyze fracture profiles perpendicular to the mean fracture plane, or the slit-island method to analyze the islands obtained by cutting the fracture surfaces at different heights, parallel to the mean fracture plane. The fracture surfaces were shown to exhibit scaling properties over several decades. However, contrary to what has been observed in the brittle or ductile fracture of solid materials, the islands were shown to be mass fractals. This was related to the extensive plastic flow involved in the fracture process.

  2. Pneumatic fractures in Confined Granular Media

    Science.gov (United States)

    Eriksen, Fredrik K.; Toussaint, Renaud; Jørgen Måløy, Knut; Grude Flekkøy, Eirik; Turkaya, Semih

    2016-04-01

    We will present our ongoing study of the patterns formed when air flows into a dry, non-cohesive porous medium confined in a horizontal Hele-Shaw cell. This is an optically transparent system consisting of two glass plates separated by 0.5 to 1 mm, containing a packing of dry 80 micron beads in between. The cell is rectangular and has an air-permeable boundary (blocking beads) at one short edge, while the other three edges are completely sealed. The granular medium is loosely packed against the semi-permeable boundary and fills about 80 % of the cell volume. This leaves an empty region at the sealed side, where an inlet allows us to set and maintain the air at a constant overpressure (0.1 - 2 bar). For the air trapped inside the cell to relax its overpressure it has to move through the deformable granular medium. Depending on the applied overpressure and initial density of the medium, we observe a range of different behaviors such as seepage through the pore-network with or without an initial compaction of the solid, formation of low density bubbles with rearrangement of particles, granular fingering/fracturing, and erosion inside formed channels/fractures. The experiments are recorded with a high-speed camera at a framerate of 1000 images/s and a resolution of 1024x1024 pixels. We use various image processing techniques to characterize the evolution of the air invasion patterns and the deformations in the surrounding material. The experiments are similar to deformation processes in porous media which are driven by pore fluid overpressure, such as mud volcanoes and hydraulic or pneumatic (gas-induced) fracturing, and the motivation is to increase the understanding of such processes by optical observations. In addition, this setup is an experimental version of the numerical models analyzed by Niebling et al. [1,2], and is useful for comparison with their results. In a directly related project [3], acoustic emissions from the cell plate are recorded during

  3. Real-time monitoring of arsenic filtration by granular ferric hydroxide

    International Nuclear Information System (INIS)

    Fleming, D.E.B.; Eddy, I.S.; Gherase, M.R.; Gibbons, M.K.; Gagnon, G.A.

    2008-01-01

    Full text: Contamination of drinking water by arsenic is a serious public health issue in many parts of the world. One recent approach to this problem has been to filter out arsenic by use of granular ferric hydroxide (GFH), an adsorbent developed specifically for the selective removal of arsenic from water. Previous studies have documented the efficiency and high treatment capacity of this approach. We present a novel X-ray fluorescence method to monitor the accumulation of arsenic within a specially designed GFH column, as both a function of time (or water volume) and location along the column. Using a miniature X-ray tube and silicon PiN diode detector, X-ray fluorescence is used to detect characteristic X-rays of arsenic excited from within the GFH. Trials were performed using a water flow rate of approximately 1.5 litres per hour, with an added arsenic concentration of approximately 1000 μg per litre. In this paper, trial results are presented and potential applications described. Characteristic arsenic Kα X-ray peak area as a function of time, as measured at various locations along a granular ferric hydroxide (GFH) water filtration column

  4. Surface instabilities in shock loaded granular media

    Science.gov (United States)

    Kandan, K.; Khaderi, S. N.; Wadley, H. N. G.; Deshpande, V. S.

    2017-12-01

    The initiation and growth of instabilities in granular materials loaded by air shock waves are investigated via shock-tube experiments and numerical calculations. Three types of granular media, dry sand, water-saturated sand and a granular solid comprising PTFE spheres were experimentally investigated by air shock loading slugs of these materials in a transparent shock tube. Under all shock pressures considered here, the free-standing dry sand slugs remained stable while the shock loaded surface of the water-saturated sand slug became unstable resulting in mixing of the shocked air and the granular material. By contrast, the PTFE slugs were stable at low pressures but displayed instabilities similar to the water-saturated sand slugs at higher shock pressures. The distal surfaces of the slugs remained stable under all conditions considered here. Eulerian fluid/solid interaction calculations, with the granular material modelled as a Drucker-Prager solid, reproduced the onset of the instabilities as seen in the experiments to a high level of accuracy. These calculations showed that the shock pressures to initiate instabilities increased with increasing material friction and decreasing yield strain. Moreover, the high Atwood number for this problem implied that fluid/solid interaction effects were small, and the initiation of the instability is adequately captured by directly applying a pressure on the slug surface. Lagrangian calculations with the directly applied pressures demonstrated that the instability was caused by spatial pressure gradients created by initial surface perturbations. Surface instabilities are also shown to exist in shock loaded rear-supported granular slugs: these experiments and calculations are used to infer the velocity that free-standing slugs need to acquire to initiate instabilities on their front surfaces. The results presented here, while in an idealised one-dimensional setting, provide physical understanding of the conditions required to

  5. Distrofia corneal granular

    Directory of Open Access Journals (Sweden)

    Alexeide de la C Castillo Pérez

    Full Text Available Las distrofias corneales constituyen un conjunto de enfermedades que presentan, en su mayoría, una baja incidencia y se caracterizan por acúmulo de material hialino o amiloide que disminuyen la transparencia corneal. La distrofia granular es una enfermedad autosómica dominante que presenta opacidades grises en el estroma superficial central de la córnea y se hacen visibles en la primera y segunda décadas de la vida, lo que provoca disminución de la visión más significativa cerca de los 40 años de edad. Presentamos dos casos clínicos de distrofia granular en pacientes hermanos de diferentes sexos, quienes acudieron a la consulta y refirieron visión nublada. El estudio de la historia familiar nos ayuda en el correcto diagnóstico y la biomicroscopia constituye el elemento más importante.

  6. Multi-scale kinetic description of granular clusters: invariance, balance, and temperature

    Science.gov (United States)

    Capriz, Gianfranco; Mariano, Paolo Maria

    2017-12-01

    We discuss a multi-scale continuum representation of bodies made of several mass particles flowing independently each other. From an invariance procedure and a nonstandard balance of inertial actions, we derive the balance equations introduced in earlier work directly in pointwise form, essentially on the basis of physical plausibility. In this way, we analyze their foundations. Then, we propose a Boltzmann-type equation for the distribution of kinetic energies within control volumes in space and indicate how such a distribution allows us to propose a definition of (granular) temperature along processes far from equilibrium.

  7. Small-signal analysis of granular semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Varpula, Aapo; Sinkkonen, Juha; Novikov, Sergey, E-mail: aapo.varpula@tkk.f [Department of Micro and Nanosciences, Aalto University, PO Box 13500, FI-00076 Aalto, Espoo (Finland)

    2010-11-01

    The small-signal ac response of granular n-type semiconductors is calculated analytically using the drift-diffusion theory when electronic trapping at grain boundaries is present. An electrical equivalent circuit (EEC) model of a granular n-type semiconductor is presented. The analytical model is verified with numerical simulation performed by SILVACO ATLAS. The agreement between the analytical and numerical results is very good in a broad frequency range at low dc bias voltages.

  8. Small-signal analysis of granular semiconductors

    International Nuclear Information System (INIS)

    Varpula, Aapo; Sinkkonen, Juha; Novikov, Sergey

    2010-01-01

    The small-signal ac response of granular n-type semiconductors is calculated analytically using the drift-diffusion theory when electronic trapping at grain boundaries is present. An electrical equivalent circuit (EEC) model of a granular n-type semiconductor is presented. The analytical model is verified with numerical simulation performed by SILVACO ATLAS. The agreement between the analytical and numerical results is very good in a broad frequency range at low dc bias voltages.

  9. Applicability and trends of anaerobic granular sludge treatment processes

    International Nuclear Information System (INIS)

    Lim, Seung Joo; Kim, Tak-Hyun

    2014-01-01

    Anaerobic granular sludge treatment processes have been continuously developed, although the anaerobic sludge granulation process was not clearly understood. In this review, an upflow anaerobic sludge blanket (UASB), an expanded granule sludge blanket (EGSB), and a static granular bed reactor (SGBR) were introduced as components of a representative anaerobic granular sludge treatment processes. The characteristics and application trends of each reactor were presented. The UASB reactor was developed in the late 1970s and its use has been rapidly widespread due to the excellent performance. With the active granules, this reactor is able to treat various high-strength wastewaters as well as municipal wastewater. Most soluble industrial wastewaters can be efficiently applied using a UASB. The EGSB reactor was developed owing to give more chance to contact between wastewater and the granules. Dispersed sludge is separated from mature granules using the rapid upward velocity in this reactor. The EGSB reactor shows the excellent performance in treating low-strength and/or high-strength wastewater, especially under low temperatures. The SGBR, developed at Iowa State University, is one of anaerobic granular sludge treatment processes. Although the configuration of the SGBR is very simple, the performance of this system is similar to that of the UASB or EGSB reactor. The anaerobic sludge granulation processes showed excellent performance for various wastewaters at a broad range of organic loading rate in lab-, pilot-scale tests. This leads to erect thousands of full-scale granular processes, which has been widely operated around the world. -- Highlights: • Anaerobic sludge granulation is a key parameter for maintaining granular processes. • Anaerobic granular digestion processes are applicable for various wastewaters. • The UASB is an economic high-rate anaerobic granular process. • The EGSB can treat high-strength wastewater using expanding granules. • The SGBR is

  10. Stable aerobic granules in continuous-flow bioreactor with self-forming dynamic membrane.

    Science.gov (United States)

    Liu, Hongbo; Li, Yajie; Yang, Changzhu; Pu, Wenhong; He, Liu; Bo, Fu

    2012-10-01

    A novel continuous-flow bioreactor with aerobic granular sludge and self-forming dynamic membrane (CGSFDMBR) was developed for efficient wastewater treatment. Under continuous-flow operation, aerobic granular sludge was successfully cultivated and characterized with small particle size of about 0.1-1.0mm, low settling velocity of about 15-25 m/h, loose structure and high water content of about 96-98%. To maintain the stability of aerobic granular sludge, strategies based on the differences of settling velocity and particle-size between granular and flocculent sludge were implemented. Moreover, in CGSFDMBR, membrane fouling was greatly relieved. Dynamic membrane was just cleaned once in more than 45 days' operation. CGSFDMBR presented good performance in treating septic tank wastewater, obtaining average COD, NH(4)(+)-N, TN and TP removal rates of 83.3%, 73.3%, 67.3% and 60%, respectively, which was more efficient than conventional bioreactors since that carbon, nitrogen and phosphorus were simultaneously removed in a single aerobic reactor. Copyright © 2012 Elsevier Ltd. All rights reserved.

  11. 76 FR 8774 - Granular Polytetrafluoroethylene Resin From Japan

    Science.gov (United States)

    2011-02-15

    ... INTERNATIONAL TRADE COMMISSION [Investigation No. 731-TA-386 (Third Review)] Granular Polytetrafluoroethylene Resin From Japan AGENCY: United States International Trade Commission. ACTION: Termination of five... revocation of the antidumping duty order on granular polytetrafluoroethylene resin from Japan would be likely...

  12. Leucemia de grandes linfócitos granulares Large granular lymphocyte leukemia

    Directory of Open Access Journals (Sweden)

    Bruno Terra

    2010-01-01

    Full Text Available O presente estudo tem como objetivo o estabelecimento de fundamentação teórica atualizada baseada em revisão bibliográfica sobre a leucemia de grandes linfócitos granulares (LGLG, doença onco-hematológica, que, devido à sua relativa raridade, é pouco conhecida e subdiagnosticada. A LGLG é caracterizada pela proliferação clonal de linfócitos T ou NK na medula óssea e/ou no sangue periférico. Dentre as manifestações clínico-laboratoriais, podem ocorrer citopenias (anemia e/ou neutropenia e/ou plaquetopenia, linfocitose (não costuma ser acentuada, linfadenomegalia, hepatoesplenomegalia, alterações imunológicas e sintomas constitucionais (emagrecimento, febre e sudorese. O curso clínico da LGLG é bastante variável, sendo que no subtipo T costuma ser indolente ou oligossintomática, enquanto no subtipo NK a evolução costuma ser desfavorável. O diagnóstico é firmado através de imunofenotipagem por citometria de fluxo e estudo de clonalidade por métodos de biologia molecular. Seu tratamento é bastante diversificado e é definido de acordo com a apresentação clínica da doença.This is a literature review about large granular lymphocyte leukemia (LGLL, a rare and misdiagnosed oncohematological disease, characterized by a clonal expansion of T-cells (T-LGLL or NK-cells (NK-LGLL in the bone marrow and/or peripheral blood. The clinical features of LGLL include cytopenias (anemia, neutropenia and thrombocytopenia, lymphocytosis (usually discrete, lymphadenopathy, hepatomegaly, splenomegaly, immune abnormalities and constitutional symptoms (fever, night sweats and weight loss. The diagnosis is based on the confirmation of the clonality of T-cells or NK-cells (polymerase chain reaction and Southern blot are the two methods most commonly used and typical findings of the immunophenotypic analysis of peripheral blood lymphocytes (flow cytometry analyses for specific surface antigens. In contrast to the chronic and indolent

  13. Planning for the Collection and Analysis of Samples of Martian Granular Materials Potentially to be Returned by Mars Sample Return

    Science.gov (United States)

    Carrier, B. L.; Beaty, D. W.

    2017-12-01

    NASA's Mars 2020 rover is scheduled to land on Mars in 2021 and will be equipped with a sampling system capable of collecting rock cores, as well as a specialized drill bit for collecting unconsolidated granular material. A key mission objective is to collect a set of samples that have enough scientific merit to justify returning to Earth. In the case of granular materials, we would like to catalyze community discussion on what we would do with these samples if they arrived in our laboratories, as input to decision-making related to sampling the regolith. Numerous scientific objectives have been identified which could be achieved or significantly advanced via the analysis of martian rocks, "regolith," and gas samples. The term "regolith" has more than one definition, including one that is general and one that is much more specific. For the purpose of this analysis we use the term "granular materials" to encompass the most general meaning and restrict "regolith" to a subset of that. Our working taxonomy includes the following: 1) globally sourced airfall dust (dust); 2) saltation-sized particles (sand); 3) locally sourced decomposed rock (regolith); 4) crater ejecta (ejecta); and, 5) other. Analysis of martian granular materials could serve to advance our understanding areas including habitability and astrobiology, surface-atmosphere interactions, chemistry, mineralogy, geology and environmental processes. Results of these analyses would also provide input into planning for future human exploration of Mars, elucidating possible health and mechanical hazards caused by the martian surface material, as well as providing valuable information regarding available resources for ISRU and civil engineering purposes. Results would also be relevant to matters of planetary protection and ground-truthing orbital observations. We will present a preliminary analysis of the following, in order to generate community discussion and feedback on all issues relating to: What are the

  14. "EGM" (Electrostatics of Granular Matter): A Space Station Experiment to Examine Natural Particulate Systems

    Science.gov (United States)

    Marshall, J.; Sauke, T.; Buehler, M.; Farrell, W.; Green, R.; Birchenough, A.

    1999-09-01

    A granular-materials experiment is being developed for a 2002 launch for Space Station deployment. The experiment is funded by NASA HQ and managed through NASA Lewis Research Center. The experiment will examine electrostatic aggregation of coarse granular materials with the goals of (a) obtaining proof for an electrostatic dipole model of grain interactions, and (b) obtaining knowledge about the way aggregation affects the behavior of natural particulate masses: (1) in unconfined dispersions (clouds such as nebulae, aeolian dust palls, volcanic plumes), (2) in semi-confined, self-loaded masses as in fluidized flows (pyroclastic surges, avalanches) and compacted regolith, or (3) in semi-confined non-loaded masses as in dust layers adhering to solar cells or space suits on Mars. The experiment addresses both planetary/astrophysical issues as well as practical concerns for human exploration of Mars or other solar system bodies. Additional information is contained in the original.

  15. Neurohypophysis granular cell tumours. Upon neurohypophysis rare tumours

    International Nuclear Information System (INIS)

    Barrande, G.; Kujas, M.; Gancel, A.; Turpin, G.; Bruckert, E.; Kuhn, J.M.; Luton, J.P.

    1995-01-01

    Granular cell tumours of neurohypophysis are rare. These tumours are more often encountered as incidental autopsy findings seen in up to 17 % of unselected adult autopsy cases. There are few reports of para-sellar granular cell tumours large enough to cause symptoms. We present three cases of neurohypophysis granular cell tumour and a review of the literature. In one patient, the asymptomatic granular cell tumour was incidentally discovered at surgical removal of a corticotrophic micro-adenoma. The remaining 2 patients had a symptomatic tumour which caused neurological symptoms such as visual disturbance and headaches and endocrine disorders such as hypopituitarism or hyper-prolactinaemia. In these 2 cases, computerized tomography showed a well-circumscribed, contrast-enhanced, intra-sellar and supra-sellar mass. Magnetic resonance imaging demonstrated an isointense gadolinium-enhanced mass in T1-weighted-images. Trans-sphenoidal partial resection was performed and histology was interpreted as a granular cell tumour. The immunohistochemical study was positive for glial fibrillary acidic protein (GEAP) and neuron specific enolase (NSE) in 1 of the 2 tumours and positive for S100 protein and vimentin in both tumours but negative for CD68. The histogenesis of neurohypophysis granular cell tumours is still controversial but ultrastructural and immunohistochemical studies support the theory that may arise from pituicytes, the glial cells of neurohypophysis. Management of these benign, slow growing, tumours is based mainly on neurosurgical resection. Data from the literature do not support a beneficial effect of post operative radiation therapy on postoperative recurrences. (authors). 23 refs., 4 figs., 1 tab

  16. Granular Cell Tumor

    African Journals Online (AJOL)

    1). Her packed cell volume was 40%, she was system, gastro-intestinal tract, brain, heart, and negative to human immunodeficiency virus. 2 female reproductive . ... histocytes and neurons at various times. They granules. The granules are probably of lysosmal were consequently termed granular cell origin and contain ...

  17. Scaling up debris-flow experiments on a centrifuge

    Science.gov (United States)

    Hung, C.; Capart, H.; Crone, T. J.; Grinspum, E.; Hsu, L.; Kaufman, D.; Li, L.; Ling, H.; Reitz, M. D.; Smith, B.; Stark, C. P.

    2013-12-01

    Boundary forces generated by debris flows can be powerful enough to erode bedrock and cause considerable damage to infrastructure during runout. Formulation of an erosion-rate law for debris flows is therefore a high priority, and it makes sense to build such a law around laboratory experiments. However, running experiments big enough to generate realistic boundary forces is a logistical challenge to say the least [1]. One alternative is to run table-top simulations with unnaturally weak but fast-eroding pseudo-bedrock, another is to extrapolate from micro-erosion of natural substrates driven by unnaturally weak impacts; hybrid-scale experiments have also been conducted [2]. Here we take a different approach in which we scale up granular impact forces by running our experiments under enhanced gravity in a geotechnical centrifuge [3]. Using a 40cm-diameter rotating drum [2] spun at up to 100g, we generate debris flows with an effective depth of over several meters. By varying effective gravity from 1g to 100g we explore the scaling of granular flow forces and the consequent bed and wall erosion rates. The velocity and density structure of these granular flows is monitored using laser sheets, high-speed video, and particle tracking [4], and the progressive erosion of the boundary surfaces is measured by laser scanning. The force structures and their fluctuations within the granular mass and at the boundaries are explored with contact dynamics numerical simulations that mimic the lab experimental conditions [5]. In this presentation we summarize these results and discuss how they can contribute to the formulation of debris-flow erosion law. [1] Major, J. J. (1997), Journal of Geology 105: 345-366, doi:10.1086/515930 [2] Hsu, L. (2010), Ph.D. thesis, University of California, Berkeley [3] Brucks, A., et al (2007), Physical Review E 75, 032301, doi:10.1103/PhysRevE.75.032301 [4] Spinewine, B., et al (2011), Experiments in Fluids 50: 1507-1525, doi: 10.1007/s00348

  18. Development of granular powder manufacturing technology by spray pyrolysis

    International Nuclear Information System (INIS)

    Katoh, Yoshiyuki; Kawase, Keiichi; Takahashi, Yoshiharu; Todokoro, Akio

    1996-01-01

    For shortening of mixed-oxide (MOX) fuel manufacturing process and improvement in treatment of MOX-powder, we have been developing the granular powder production technology. Since the granular powders have excellent fluidity owing to the spherical shape, there is the possibility of modifying scattering and adcering of the powder in the process equipment. In this paper, spray pyrolysis process in adopted as the process of manufacturing the granular powders and the basic feasibility study has been carried out. The experimental results show that the manufactured granular powders have excellent fluidity and the diameter of the powders is controllable. Furthermore, high density pellets are formed by sintering the powders. Thus, it is clarified that this process is promising for the actual MOX fuel fabrication. (author)

  19. Enhanced selection of micro-aerobic pentachlorophenol degrading granular sludge

    Energy Technology Data Exchange (ETDEWEB)

    Lv, Yuancai, E-mail: donkey1204@hotmail.com [State Key Laboratory of Pulp and Paper Engineering, College of Light Industry and Food Science, South China University of Technology, Guangzhou 510640 (China); Chen, Yuancai, E-mail: chenyc@scut.edu.cn [State Key Laboratory of Pulp and Paper Engineering, College of Light Industry and Food Science, South China University of Technology, Guangzhou 510640 (China); Ministry of Education Key Laboratory of Pollution Control and Ecological Remediation for Industrial Agglomeration Area, College of Environment and Energy, South China University of Technology, Guangzhou 510006 (China); Song, Wenzhe, E-mail: songwenzhe007@126.com [Ministry of Education Key Laboratory of Pollution Control and Ecological Remediation for Industrial Agglomeration Area, College of Environment and Energy, South China University of Technology, Guangzhou 510006 (China); Hu, Yongyou, E-mail: ppyyhu@scut.edu.cn [State Key Laboratory of Pulp and Paper Engineering, College of Light Industry and Food Science, South China University of Technology, Guangzhou 510640 (China); Ministry of Education Key Laboratory of Pollution Control and Ecological Remediation for Industrial Agglomeration Area, College of Environment and Energy, South China University of Technology, Guangzhou 510006 (China)

    2014-09-15

    Graphical abstract: In this work, an aerobic column reactor was placed before the USB to maintain micro-oxygen condition in the reactor and the micro-aerobic pentachlorophenol (PCP) degrading granular sludge under oxygen-limited conditions (0.1–0.2 mg L{sup −1}) was successfully obtained. PCP degradation by the micro-aerobic system was studied and the variance of microbial community was also discussed by using PCR-DGGE analysis. - Highlights: • Micro-aerobic granular sludge was cultivated in column-type combined reactors. • PCP biodegradation, VFA accumulation and biogas production were studied. • The function of Methanogenic archaeon in the system was investigated. • Fluctuation and diversity of microbial community were discussed by DGGE analysis. • The dominated microorganisms were identified by 16S rDNA sequences. - Abstract: Column-type combined reactors were designed to cultivate micro-aerobic pentachlorophenol (PCP) degrading granular sludge under oxygen-limited conditions (0.1–0.2 mg L{sup −1}) over 39-day experimental period. Micro-aerobic granular had both anaerobic activity (SMA: 2.34 mMCH{sub 4}/h g VSS) and aerobic activity (SOUR: 2.21 mMO{sub 2}/h g VSS). Metabolite analysis results revealed that PCP was sequentially dechlorinated to TCP, DCP, and eventually to MCP. Methanogens were not directly involved in the dechlorination of PCP, but might played a vital role in stabilizing the overall structure of the granule sludge. For Eubacteria, the Shannon Index (2.09 in inoculated granular sludge) increased both in micro-aerobic granular sludge (2.61) and PCP-degradation granular sludge (2.55). However, for Archaea, it decreased from 2.53 to 1.85 and 1.84, respectively. Although the Shannon Index demonstrated slight difference between micro-aerobic granular sludge and PCP-degradation granular sludge, the Principal Component Analysis (PCA) indicated obvious variance of the microbial composition, revealing significant effect of micro

  20. Enhanced selection of micro-aerobic pentachlorophenol degrading granular sludge

    International Nuclear Information System (INIS)

    Lv, Yuancai; Chen, Yuancai; Song, Wenzhe; Hu, Yongyou

    2014-01-01

    Graphical abstract: In this work, an aerobic column reactor was placed before the USB to maintain micro-oxygen condition in the reactor and the micro-aerobic pentachlorophenol (PCP) degrading granular sludge under oxygen-limited conditions (0.1–0.2 mg L −1 ) was successfully obtained. PCP degradation by the micro-aerobic system was studied and the variance of microbial community was also discussed by using PCR-DGGE analysis. - Highlights: • Micro-aerobic granular sludge was cultivated in column-type combined reactors. • PCP biodegradation, VFA accumulation and biogas production were studied. • The function of Methanogenic archaeon in the system was investigated. • Fluctuation and diversity of microbial community were discussed by DGGE analysis. • The dominated microorganisms were identified by 16S rDNA sequences. - Abstract: Column-type combined reactors were designed to cultivate micro-aerobic pentachlorophenol (PCP) degrading granular sludge under oxygen-limited conditions (0.1–0.2 mg L −1 ) over 39-day experimental period. Micro-aerobic granular had both anaerobic activity (SMA: 2.34 mMCH 4 /h g VSS) and aerobic activity (SOUR: 2.21 mMO 2 /h g VSS). Metabolite analysis results revealed that PCP was sequentially dechlorinated to TCP, DCP, and eventually to MCP. Methanogens were not directly involved in the dechlorination of PCP, but might played a vital role in stabilizing the overall structure of the granule sludge. For Eubacteria, the Shannon Index (2.09 in inoculated granular sludge) increased both in micro-aerobic granular sludge (2.61) and PCP-degradation granular sludge (2.55). However, for Archaea, it decreased from 2.53 to 1.85 and 1.84, respectively. Although the Shannon Index demonstrated slight difference between micro-aerobic granular sludge and PCP-degradation granular sludge, the Principal Component Analysis (PCA) indicated obvious variance of the microbial composition, revealing significant effect of micro-aerobic condition and

  1. A study of energy dissipation and critical speed of granular flow in a rotating cylinder

    Science.gov (United States)

    Dragomir, Sergiu C.; Sinnott, Mathew D.; Semercigil, S. Eren; Turan, Özden F.

    2014-12-01

    Tuned vibration absorbers may improve the safety of flexible structures which are prone to excessive oscillation magnitudes under dynamic loads. A novel absorber design proposes sloshing of granular material in a rotating cylinder where the granular material is the energy dissipating agent. As the conventional dissipative elements require maintenance due to the nature of their function, the new design may represent a virtually maintenance free alternative. The angular speed of the cylinder containing particles has a critical centrifuging speed, after which particles remain permanently in contact with the walls and there can be no further dissipation. Until the critical speed, however, dissipation increases proportionally with the angular speed. It is then vital to know the value of the critical speed as the limit of dissipation. The focus of the present study is on determination of the critical centrifuge speed. This critical speed is also of practical importance in bulk-material handling rotary mills, such as dryers and crushers. Experiments and numerical simulations, using Discrete Element Method, are used to determine the critical centrifuging speed. In addition, predictions are given and guidelines are offered for the choice of material properties to maximize the energy dissipation. As a result of a parametric study, the coefficient of friction is found to have the greatest significance on the centrifuging speed.

  2. Software compensation in Particle Flow reconstruction

    CERN Document Server

    Lan Tran, Huong; Sefkow, Felix; Green, Steven; Marshall, John; Thomson, Mark; Simon, Frank

    2017-01-01

    The Particle Flow approach to calorimetry requires highly granular calorimeters and sophisticated software algorithms in order to reconstruct and identify individual particles in complex event topologies. The high spatial granularity, together with analog energy information, can be further exploited in software compensation. In this approach, the local energy density is used to discriminate electromagnetic and purely hadronic sub-showers within hadron showers in the detector to improve the energy resolution for single particles by correcting for the intrinsic non-compensation of the calorimeter system. This improvement in the single particle energy resolution also results in a better overall jet energy resolution by improving the energy measurement of identified neutral hadrons and improvements in the pattern recognition stage by a more accurate matching of calorimeter energies to tracker measurements. This paper describes the software compensation technique and its implementation in Particle Flow reconstruct...

  3. On the submerging of a spherical intruder into granular beds

    Directory of Open Access Journals (Sweden)

    Wu Chuan-Yu

    2017-01-01

    Full Text Available Granular materials are complex systems and their mechanical behaviours are determined by the material properties of individual particles, the interaction between particles and the surrounding media, which are still incompletely understood. Using an advanced discrete element method (DEM, we simulate the submerging process of a spherical projectile (an intruder into granular materials of various properties with a zero penetration velocity (i.e. the intruder is touching the top surface of the granular bed and released from stationary and examine its settling behaviour. By systematically changing the density and size of the intruder and the particle density (i.e. the density of the particles in the granular bed, we find that the intruder can sink deep into the granular bed even with a zero penetration velocity. Furthermore, we confirm that under certain conditions the granular bed can behave like a Newtonian liquid and the submerging intruder can reach a constant velocity, i.e. the terminal velocity, identical to the settling of a sphere in a liquid, as observed experimentally. A mathematical model is also developed to predict the maximum penetration depth of the intruder. The model predictions are compared with experimental data reported in the literature,good agreement was obtained, demonstrating the model can accurately predict the submerging behaviour of the intruder in the granular media.

  4. Jamming by compressing a system of granular crosses

    Science.gov (United States)

    Zheng, Hu; Wang, Dong; Barés, Jonathan; Behringer, Robert

    2017-06-01

    A disordered stress-free granular packing can be jammed, transformed into a mechanically rigid structure, by increasing the density of particles or by applying shear deformation. The jamming behavior of systems made of 2D circular discs has been investigated in detail, but very little is known about jamming for non-spherical particles, and particularly, non-convex particles. Here, we perform an experimental study on jamming by compression of a system of quasi-2D granular crosses made of photo-elastic crosses. We measure the pressure evolution during cyclic compression and decompression. The Jamming packing fraction of these quasi-2D granular crosses is ϕJ ≃ 0.475, which is much smaller than the value ϕJ ≃ 0.84 for-2D granular disks. The packing fraction shifts systematically to higher values under compressive cycling, corresponding to systematic shifts in the stress-strain response curves. Associated with these shifts are rotations of the crosses, with minimal changes in their centers of mass.

  5. Friction law and hysteresis in granular materials.

    Science.gov (United States)

    DeGiuli, E; Wyart, M

    2017-08-29

    The macroscopic friction of particulate materials often weakens as the flow rate is increased, leading to potentially disastrous intermittent phenomena including earthquakes and landslides. We theoretically and numerically study this phenomenon in simple granular materials. We show that velocity weakening, corresponding to a nonmonotonic behavior in the friction law, [Formula: see text], is present even if the dynamic and static microscopic friction coefficients are identical, but disappears for softer particles. We argue that this instability is induced by endogenous acoustic noise, which tends to make contacts slide, leading to faster flow and increased noise. We show that soft spots, or excitable regions in the materials, correspond to rolling contacts that are about to slide, whose density is described by a nontrivial exponent [Formula: see text] We build a microscopic theory for the nonmonotonicity of [Formula: see text], which also predicts the scaling behavior of acoustic noise, the fraction of sliding contacts [Formula: see text], and the sliding velocity, in terms of [Formula: see text] Surprisingly, these quantities have no limit when particles become infinitely hard, as confirmed numerically. Our analysis rationalizes previously unexplained observations and makes experimentally testable predictions.

  6. Modelling transient 3D multi-phase criticality in fluidised granular materials - the FETCH code

    International Nuclear Information System (INIS)

    Pain, C.C.; Gomes, J.L.M.A.; Eaton, M.D.; Ziver, A.K.; Umpleby, A.P.; Oliveira, C.R.E. de; Goddard, A.J.H.

    2003-01-01

    The development and application of a generic model for modelling criticality in fluidised granular materials is described within the Finite Element Transient Criticality (FETCH) code - which models criticality transients in spatial and temporal detail from fundamental principles, as far as is currently possible. The neutronics model in FETCH solves the neutron transport in full phase space with a spherical harmonics angle of travel representation, multi-group in neutron energy, Crank Nicholson based in time stepping, and finite elements in space. The fluids representation coupled with the neutronics model is a two-fluid-granular-temperature model, also finite element fased. A separate fluid is used to represent the liquid/vapour gas and the solid fuel particle phases, respectively. Particle-particle, particle-wall interactions are modelled using a kinetic theory approach on an analogy between the motion of gas molecules subject to binary collisions and granular flows. This model has been extensively validated by comparison with fluidised bed experimental results. Gas-fluidised beds involve particles that are often extremely agitated (measured by granular temperature) and can thus be viewed as a particularly demanding application of the two-fluid model. Liquid fluidised systems are of criticality interest, but these can become demanding with the production of gases (e.g. radiolytic and water vapour) and large fluid/particle velocities in energetic transients. We present results from a test transient model in which fissile material ( 239 Pu) is presented as spherical granules subsiding in water, located in a tank initially at constant temperature and at two alternative over-pressures in order to verify the theoretical model implemented in FETCH. (author)

  7. WET SOLIDS FLOW ENHANCEMENT; SEMIANNUAL

    International Nuclear Information System (INIS)

    Hugo S. Caram; Natalie Foster

    1997-01-01

    The objective was to visualize the flow of granular materials in flat bottomed silo. This was done by for dry materials introducing mustard seeds and poppy seeds as tracer particles and imaging them using Nuclear Magnetic Resonance. The region sampled was a cylinder 25 mm in diameter and 40 mm in length. Eight slices containing 128*128 to 256*256 pixels were generated for each image. The size of the silo was limited by the size of the high resolution NMR imager available. Cross-sections of 150mm flat bottomed silos, with the tracer layers immobilized by a gel, showed similar qualitative patterns for both dry and wet granular solids

  8. Investigation of granular impact using positron emission particle tracking

    KAUST Repository

    Marston, Jeremy O.

    2015-04-01

    We present results from an experimental study of granular impact using a combination of high-speed video and positron emission particle tracking (PEPT). The PEPT technique exploits the annihilation of photons from positron decay to determine the position of tracer particles either inside a small granular bed or attached to the object which impacts the bed. We use dense spheres as impactors and the granular beds are comprised of glass beads which are fluidised to achieve a range of different initial packing states. For the first time, we have simultaneously investigated both the trajectory of the sphere, the motion of particles in a 3-D granular bed and particles which jump into the resultant jet, which arises from the collapse of the cavity formed by the impacting sphere.

  9. Simulation study on insoluble granular corrosion products deposited in PWR core

    International Nuclear Information System (INIS)

    Yang Xu; Zhou Tao; Ru Xiaolong; Lin Daping; Fang Xiaolu

    2014-01-01

    In the operation of reactor, such as fuel rods, reactor vessel internals etc. will be affected by corrosion erosion of high pressure coolant. It will produce many insoluble corrosion products. The FLUENT software is adopted to simulate insoluble granular corrosion products deposit distribution in the reactor core. The fluid phase uses the standard model to predict the flow field in the channel and forecast turbulence variation in the near-wall region. The insoluble granular corrosion products use DPM (Discrete Phase Model) to track the trajectory of the particles. The discrete phase model in FLUENT follows the Euler-Lagrange approach. The fluid phase is treated as a continuum by solving the Navier-Stokes equations, while the dispersed phase is solved by tracking a large number of particles through the calculated flow field. Through the study found, Corrosion products particles form high concentration area near the symmetry, and the entrance section of the corrosion products particles concentration is higher than export section. Corrosion products particles deposition attached on large area for the entrance of the cladding, this will change the core neutron flux distribution and the thermal conductivity of cladding material, and cause core axial offset anomaly (AOA). Corrosion products particles dot deposit in the outlet of cladding, which can lead to pitting phenomenon in a sheath. Pitting area will cause deterioration of heat transfer, destroy the cladding integrity. In view of the law of corrosion products deposition and corrosion characteristics of components in the reactor core. this paper proposes regular targeted local cleanup and other mitigation measures. (authors)

  10. Paraqueratose granular: relato de seis casos em crianças Granular parakeratosis: a report of six cases in children

    Directory of Open Access Journals (Sweden)

    Susana Giraldi

    2006-02-01

    Full Text Available A paraqueratose granular é alteração da queratinização, primeiramente descrita em adultos, caracterizada por pápulas e placas hiperqueratósicas nas áreas intertriginosas. Os autores descrevem seis casos de paraqueratose granular em crianças. Um paciente apresentava lesões nas regiões glúteas, dois em ambas as axilas e região cervical (apresentações inéditas na literatura. Três pacientes apresentavam lesões em pregas inguinais. Realizam também revisão da literatura e discutem a possível etiologia dessa rara dermatose.Granular parakeratosis is an alteration of keratinization that was first described in adults. It is characterized by hiperkeratotic plaques and papules in intertriginous areas. The authors describe six cases of granular parakeratosis in children. One patient had lesions on the buttocks; two children presented papules in both axillae and cervical region (presentations never described before in the literature. The remaining three patients presented with lesions in the inguinal folds. Review of the literature and discussion on the pathogenesis of this rare dermatosis are presented.

  11. Granular mixing and segregation in a horizontal rotating drum: A simulation study on the impact of rotational speed and fill level

    NARCIS (Netherlands)

    Arntz, M.M.H.D.; Otter, W.K. den; Briels, W.J.; Bussmann, P.J.T.; Beeltink, H.H.; Boom, R.M.

    2008-01-01

    The rich phase behavior of granular beds of bidisperse hard spherical particles in a rotating horizontal drum is studied by Discrete Element Method (DEM) simulations. Several flow regimes and various forms of radial segregation, as well as mixing, are observed by systematically varying the

  12. Leaching and accumulation of trace elements in sulfate reducing granular sludge under concomitant thermophilic and low pH conditions

    NARCIS (Netherlands)

    Gonzalez-Gil, G.; Lopes, S.I.C.; Saikaly, P.E.; Lens, P.N.L.

    2012-01-01

    The leaching and/or accumulation of trace elements in sulfate reducing granular sludge systems was investigated. Two thermophilic up-flow anaerobic sludge bed (UASB) reactors operated at pH 5 were fed with sucrose (4 g COD l(reactor)(-1) d(-1)) and sulfate at different COD/SO42- ratios. During the

  13. Effect of horizontal vibration on pile of cylinder avalanches as a pseudo-two dimensional granular system

    International Nuclear Information System (INIS)

    Mardiansyah, Y; Yulia; Khotimah, S N; Viridi, S; Suprijadi

    2016-01-01

    Dynamics of pseudo-two dimensional granular material consisted of two layers cylinder piles positioned on top of a horizontally vibrated plate is reported in this work. It is aimed to observe structural change of the cylinder pile vibrated in certain frequency and amplitude. Dimensionless acceleration Γ= 4π 2 f 2 A/g (with g is gravitational acceleration), which is generally used in granular materials to observe transition between states, e.g. stable, rotating without slipping, rolling and slipping in Γ-f plane, does not work well for this system. For this system additional states for the piles can also be observed, e.g. stable and flowing states. Observations parameters are frequency f (measured in Hz) and amplitude A (measured in cm). These parameters are used to construct the A-f plane instead of Γ-f one. (paper)

  14. Dynamics of electrostatically driven granular media: Effects of humidity

    International Nuclear Information System (INIS)

    Howell, D. W.; Aronson, Igor S.; Crabtree, G. W.

    2001-01-01

    We performed experimental studies of the effect of humidity on the dynamics of electrostatically driven granular materials. Both conducting and dielectric particles undergo a phase transition from an immobile state (granular solid) to a fluidized state (granular gas) with increasing applied field. Spontaneous precipitation of solid clusters from the gas phase occurs as the external driving is decreased. The clustering dynamics in conducting particles is primarily controlled by screening of the electric field but is aided by cohesion due to humidity. It is shown that humidity effects dominate the clustering process with dielectric particles

  15. USE OF GRANULAR GRAPHITE FOR ELECTROLYTIC DECHLORINATION OF TRICHLOROETHYLENE

    Science.gov (United States)

    Granular graphite is a potential electrode material for the electrochemical remediation of refractory chlorinated organic compounds such as trichloroethylene (TCE). However, the use of granular graphite can complicate the experimental results. On one hand, up to 99% of TCE was re...

  16. Stable solutions of a scalar conservation law for particle-size segregation in dense granular avalanches

    OpenAIRE

    Shearer, M.; Gray, J. M N T; Thornton, A. R.

    2008-01-01

    Dense, dry granular avalanches are very efficient at sorting the larger particles towards the free surface of the flow, and finer grains towards the base, through the combined processes of kinetic sieving and squeeze expulsion. This generates an inversely graded particle-size distribution, which is fundamental to a variety of pattern formation mechanisms, as well as subtle size-mobility feedback effects, leading to the formation of coarse-grained lateral levees that create channels in geophys...

  17. Granular cell tumor: An uncommon benign neoplasm

    Directory of Open Access Journals (Sweden)

    Tirthankar Gayen

    2015-01-01

    Full Text Available Granular cell tumor is a distinctly rare neoplasm of neural sheath origin. It mainly presents as a solitary asymptomatic swelling in the oral cavity, skin, and rarely internal organs in the middle age. Histopathology is characteristic, showing polyhedral cells containing numerous fine eosinophilic granules with indistinct cell margins. We present a case of granular cell tumor on the back of a 48-year-old woman which was painful, mimicking an adnexal tumor.

  18. Density-Driven segregation in Binary and Ternary Granular Systems

    NARCIS (Netherlands)

    Windows-Yule, Kit; Parker, David

    2015-01-01

    We present a first experimental study of density-induced segregation within a three-dimensional, vibrofluidised, ternary granular system. Using Positron Emission Particle Tracking (PEPT), we study the steady-state particle distributions achieved by binary and ternary granular beds under a variety of

  19. Massive granular cell ameloblastoma with dural extension and atypical morphology

    Directory of Open Access Journals (Sweden)

    Vandana Raghunath

    2014-01-01

    Full Text Available Ameloblastomas are rare histologically benign, locally aggressive tumors arising from the oral ectoderm that occasionally reach a gigantic size. Giant ameloblastomas are a rarity these days with the advent of panoramic radiography in routine dental practice. Furthermore, the granular cell variant is an uncommon histological subtype of ameloblastoma where the central stellate reticulum like cells in tumor follicles is replaced by granular cells. Although granular cell ameloblastoma (GCA is considered to be a destructive tumor with a high recurrence rate, the significance of granular cells in predicting its biologic behavior is debatable. However, we present a rare case of giant GCA of remarkable histomorphology showing extensive craniofacial involvement and dural extension that rendered a good prognosis following treatment.

  20. Tunneling magnetoresistance in granular cermet films with particle size distribution

    International Nuclear Information System (INIS)

    Vovk, A.Ya.; Golub, V.O.; Malkinski, L.; Kravets, A.F.; Pogorily, A.M.; Shypil', O.V.

    2004-01-01

    The correlation between tunneling magnetoresistance (TMR) and field sensitivity (dMR/dH) for granular films (Co 50 Fe 50 ) x -(Al 2 O 3 ) 1-x was studied. The position of TMR maximum is shifted towards the lower x in the higher applied magnetic fields. Such a behavior was observed for metal granular nanocomposites but is first reported for granular cermets. However the highest dMR/dH was found for the compositions just below the percolation threshold

  1. Geomorphic dam-break flows. Part I: conceptual model

    OpenAIRE

    Leal, JGAB; Ferreira, RML; Cardoso, AH

    2010-01-01

    Proceedings of the Institution of Civil Engineers - Water Management 163 Issue WM6 This paper presents a one-dimensional conceptual model for simulating geomorphic dam-break flows. The model is based on conservation laws drawn from continuum mixture theory that are integrated over the flow depth,assuming that the f10w is composed of two transport layers. Closure equations were derived from the review and reanalysis of previous studies on granular flow,debris f10w and sheet flow. The sedime...

  2. Influence of granular strontium chloride as additives on some ...

    Indian Academy of Sciences (India)

    Influence of granular strontium chloride as additives on some electrical and mechanical properties for pure polyvinyl alcohol. A B Elaydy M Hafez ... Keywords. Polyvinyl-alcohol (PVA); granular strontium chloride, SrCl2; a.c. electrical conductivity; dielectric constant; dielectric loss; Young's modulus; creep relaxation curve.

  3. Real-time magnetic resonance imaging of highly dynamic granular phenomena

    Science.gov (United States)

    Penn, Alexander; Pruessmann, Klaas P.; Müller, Christoph

    Probing non-intrusively the interior of three-dimensional granular systems is a challenging task for which a number of imaging techniques have been applied including positron emission particle tracking, X-ray tomography and magnetic resonance imaging (MRI). A particular advantage of MRI is its versatility allowing quantitative velocimetry through phase contrast encoding and tagging, arbitrary slice orientations and the flexibility to trade spatial for temporal resolution and vice versa during image reconstruction. However, previous attempts to image granular systems using MRI were often limited to (pseudo-) steady state systems due to the poor temporal resolution of conventional imaging methodology. Here we present an experimental approach that overcomes previous limitations in temporal resolution by implementing a variety of methodological advances, viz. parallel data acquisition through tailored multiple receiver coils, fast gradient readouts for time-efficient data sampling and engineered granular materials that contain signal sources of high proton density. Achieving a spatial and temporal resolution of, respectively, 2 mm x 2 mm and 50 ms, we were able to image highly dynamic phenomena in granular media such as bubble coalescence and granular compaction waves.

  4. Wet granular matter a truly complex fluid

    CERN Document Server

    Herminghaus, Stephan

    2013-01-01

    This is a monograph written for the young and advanced researcher who is entering the field of wet granular matter and keen to understand the basic physical principles governing this state of soft matter. It treats wet granulates as an instance of a ternary system, consisting of the grains, a primary, and a secondary fluid. After addressing wetting phenomena in general and outlining the basic facts on dry granular systems, a chapter on basic mechanisms and their effects is dedicated to every region of the ternary phase diagram. Effects of grain shape and roughness are considered as well. Rather than addressing engineering aspects such as existing books on this topic do, the book aims to provide a generalized framework suitable for those who want to understand these systems on a more fundamental basis. Readership: For the young and advanced researcher entering the field of wet granular matter.

  5. Acceleration of coupled granular flow and fluid flow simulations in pebble bed energy systems

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yanheng, E-mail: liy19@rpi.edu [Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY (United States); Ji, Wei, E-mail: jiw2@rpi.edu [Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY (United States)

    2013-05-15

    Highlights: ► Fast simulation of coupled pebble flow and coolant flow in PBR systems is studied. ► Dimension reduction based on axisymmetric geometry shows significant speedup. ► Relaxation of coupling frequency is investigated and an optimal range is determined. ► A total of 80% efficiency increase is achieved by the two fast strategies. ► Fast strategies can be applied to simulating other general fluidized bed systems. -- Abstract: Fast and accurate approaches to simulating the coupled particle flow and fluid flow are of importance to the analysis of large particle-fluid systems. This is especially needed when one tries to simulate pebble flow and coolant flow in Pebble Bed Reactor (PBR) energy systems on a routine basis. As one of the Generation IV designs, the PBR design is a promising nuclear energy system with high fuel performance and inherent safety. A typical PBR core can be modeled as a particle-fluid system with strong interactions among pebbles, coolants and reactor walls. In previous works, the coupled Discrete Element Method (DEM)-Computational Fluid Dynamics (CFD) approach has been investigated and applied to modeling PBR systems. However, the DEM-CFD approach is computationally expensive due to large amounts of pebbles in PBR systems. This greatly restricts the PBR analysis for the real time prediction and inclusion of more physics. In this work, based on the symmetry of the PBR geometry and the slow motion characteristics of the pebble flow, two acceleration strategies are proposed. First, a simplified 3D-DEM/2D-CFD approach is proposed to speed up the DEM-CFD simulation without loss of accuracy. Pebble flow is simulated by a full 3D DEM, while the coolant flow field is calculated with a 2D CFD simulation by averaging variables along the annular direction in the cylindrical and annular geometries. Second, based on the slow motion of pebble flow, the impact of the coupling frequency on the computation accuracy and efficiency is

  6. Acceleration of coupled granular flow and fluid flow simulations in pebble bed energy systems

    International Nuclear Information System (INIS)

    Li, Yanheng; Ji, Wei

    2013-01-01

    Highlights: ► Fast simulation of coupled pebble flow and coolant flow in PBR systems is studied. ► Dimension reduction based on axisymmetric geometry shows significant speedup. ► Relaxation of coupling frequency is investigated and an optimal range is determined. ► A total of 80% efficiency increase is achieved by the two fast strategies. ► Fast strategies can be applied to simulating other general fluidized bed systems. -- Abstract: Fast and accurate approaches to simulating the coupled particle flow and fluid flow are of importance to the analysis of large particle-fluid systems. This is especially needed when one tries to simulate pebble flow and coolant flow in Pebble Bed Reactor (PBR) energy systems on a routine basis. As one of the Generation IV designs, the PBR design is a promising nuclear energy system with high fuel performance and inherent safety. A typical PBR core can be modeled as a particle-fluid system with strong interactions among pebbles, coolants and reactor walls. In previous works, the coupled Discrete Element Method (DEM)-Computational Fluid Dynamics (CFD) approach has been investigated and applied to modeling PBR systems. However, the DEM-CFD approach is computationally expensive due to large amounts of pebbles in PBR systems. This greatly restricts the PBR analysis for the real time prediction and inclusion of more physics. In this work, based on the symmetry of the PBR geometry and the slow motion characteristics of the pebble flow, two acceleration strategies are proposed. First, a simplified 3D-DEM/2D-CFD approach is proposed to speed up the DEM-CFD simulation without loss of accuracy. Pebble flow is simulated by a full 3D DEM, while the coolant flow field is calculated with a 2D CFD simulation by averaging variables along the annular direction in the cylindrical and annular geometries. Second, based on the slow motion of pebble flow, the impact of the coupling frequency on the computation accuracy and efficiency is

  7. Origin of the resistivity minima in granular superconductors

    International Nuclear Information System (INIS)

    Simanek, E.

    1982-01-01

    The recently observed minima in the temperature dependence of the electrical resistivity of a granular superconductor are explained with use of a percolation model of a disordered granular array, which takes into account the electrostatic charging energy. The thermally activated tunneling of Cooper pairs is shown to play an important role in the interpretation of the experimental data on tin films

  8. Hierarchical modular granular neural networks with fuzzy aggregation

    CERN Document Server

    Sanchez, Daniela

    2016-01-01

    In this book, a new method for hybrid intelligent systems is proposed. The proposed method is based on a granular computing approach applied in two levels. The techniques used and combined in the proposed method are modular neural networks (MNNs) with a Granular Computing (GrC) approach, thus resulting in a new concept of MNNs; modular granular neural networks (MGNNs). In addition fuzzy logic (FL) and hierarchical genetic algorithms (HGAs) are techniques used in this research work to improve results. These techniques are chosen because in other works have demonstrated to be a good option, and in the case of MNNs and HGAs, these techniques allow to improve the results obtained than with their conventional versions; respectively artificial neural networks and genetic algorithms.

  9. Surface effects in the acetylation of granular potato starch

    NARCIS (Netherlands)

    Steeneken, P.A.M.; Woortman, A.J.J.

    2008-01-01

    The occurrence of surface effects in the acetylation of granular potato starch with acetic anhydride to degrees of substitution 0.04-0.2 was studied by two different approaches. The first approach involved the fractionation of granular starch acetates into five different size classes and analysis of

  10. Torsional shear flow of granular materials: shear localization and minimum energy principle

    Science.gov (United States)

    Artoni, Riccardo; Richard, Patrick

    2018-01-01

    The rheological properties of granular matter submitted to torsional shear are investigated numerically by means of discrete element method. The shear cell is made of a cylinder filled by grains which are sheared by a bumpy bottom and submitted to a vertical pressure which is applied at the top. Regimes differing by their strain localization features are observed. They originate from the competition between dissipation at the sidewalls and dissipation in the bulk of the system. The effects of the (i) the applied pressure, (ii) sidewall friction, and (iii) angular velocity are investigated. A model, based on the purely local μ (I)-rheology and a minimum energy principle is able to capture the effect of the two former quantities but unable to account the effect of the latter. Although, an ad hoc modification of the model allows to reproduce all the numerical results, our results point out the need for an alternative rheology.

  11. Tuning strain of granular matter by basal assisted Couette shear

    Directory of Open Access Journals (Sweden)

    Zhao Yiqiu

    2017-01-01

    Full Text Available We present a novel Couette shear apparatus capable of generating programmable azimuthal strain inside 2D granular matter under Couette shear. The apparatus consists of 21 independently movable concentric rings and two boundary wheels with frictional racks. This makes it possible to quasistatically shear the granular matter not only from the boundaries but also from the bottom. We show that, by specifying the collective motion of wheels and rings, the apparatus successfully generates the desired strain profile inside the sample granular system, which is composed of about 2000 photoelastic disks. The motion and stress of each particle is captured by an imaging system utilizing reflective photoelasticimetry. This apparatus provides a novel method to investigate shear jamming properties of granular matter with different interior strain profiles and unlimited strain amplitudes.

  12. Acoustic monitoring of a ball sinking in vibrated granular sediments

    Science.gov (United States)

    van den Wildenberg, Siet; Léopoldès, Julien; Tourin, Arnaud; Jia, Xiaoping

    2017-06-01

    We develop an ultrasound probing to investigate the dynamics of a high density ball sinking in 3D opaque dense granular suspensions under horizontal weak vibrations. We show that the motion of the ball in these horizontally vibrated glass bead packings saturated by water is consistent with the frictional rheology. The extracted stress-strain relation evidences an evolution of flow behaviour from frictional creep to inertial regimes. Our main finding is that weak external vibration primarily affects the yield stress and controls the depth of sinking via vibration-induced sliding at the grain contact. Also, we observe that the extracted rheological parameters depend on the size of the probing ball, suggesting thus a non-local rheology.

  13. Synthesis of Biodiesel in Batch and Packed-Bed Reactors Using Powdered and Granular Sugar Catalyst

    Science.gov (United States)

    Janaun, J.; Lim, P. M.; Balan, W. S.; Yaser, A. Z.; Chong, K. P.

    2017-06-01

    Increasing world production of palm oil warrants effective utilization of its waste. In particular, conversion of waste cooking oil into biodiesel has obtained global interest because of renewable energy need and reduction of CO2 emission. In this study, oleic acid used as a model compound for waste cooking oil conversion using esterification reaction catalysed by sugar catalyst (SC) in powdered (P-SC) and granular (G-SC) forms. The catalysts were synthesized via incomplete carbonization of D-glucose followed by functionalization with concentrated sulphuric acid. Catalysts characterizations were done for their physical and chemical properties using modern tools. Batch and packed-bed reactor systems were used to evaluate the reactivity of the catalysts. The results showed that G-SC had slightly higher total acidity and more porous than P-SC. The experimental conditions for batch reaction were temperature of 60°C, molar ratio of 1:20 (Oleic Acid:Methanol) and 2 wt. catalyst with respect to oleic acid. The results showed the maximum oleic acid conversion using G-SC and P-SC were 52 and 48, respectively. Whereas, the continuous reaction with varying feed flow rate as a function of retention time was studied by using 3 g of P-SC in 60 °C and 1:20 molar ratio in a packed-bed reactor. The results showed that a longer retention time which was 6.48 min and feed flow rate 1.38 ml/min, achieved higher average conversion of 9.9 and decreased with further increasing flow rate. G-SC showed a better average conversion of 10.8 at lowest feed flow rate of 1.38 ml/min in continuous reaction experiments. In a broader perspective, large scale continuous biodiesel production is feasible using granular over powdered catalyst mainly due to it lower pressure drop.

  14. Emotional Granularity Effects on Event-Related Brain Potentials during Affective Picture Processing.

    Science.gov (United States)

    Lee, Ja Y; Lindquist, Kristen A; Nam, Chang S

    2017-01-01

    There is debate about whether emotional granularity , the tendency to label emotions in a nuanced and specific manner, is merely a product of labeling abilities, or a systematic difference in the experience of emotion during emotionally evocative events. According to the Conceptual Act Theory of Emotion (CAT) (Barrett, 2006), emotional granularity is due to the latter and is a product of on-going temporal differences in how individuals categorize and thus make meaning of their affective states. To address this question, the present study investigated the effects of individual differences in emotional granularity on electroencephalography-based brain activity during the experience of emotion in response to affective images. Event-related potentials (ERP) and event-related desynchronization and synchronization (ERD/ERS) analysis techniques were used. We found that ERP responses during the very early (60-90 ms), middle (270-300 ms), and later (540-570 ms) moments of stimulus presentation were associated with individuals' level of granularity. We also observed that highly granular individuals, compared to lowly granular individuals, exhibited relatively stable desynchronization of alpha power (8-12 Hz) and synchronization of gamma power (30-50 Hz) during the 3 s of stimulus presentation. Overall, our results suggest that emotional granularity is related to differences in neural processing throughout emotional experiences and that high granularity could be associated with access to executive control resources and a more habitual processing of affective stimuli, or a kind of "emotional complexity." Implications for models of emotion are also discussed.

  15. Small solar system bodies as granular systems

    Science.gov (United States)

    Hestroffer, Daniel; Campo Bagatín, Adriano; Losert, Wolfgang; Opsomer, Eric; Sánchez, Paul; Scheeres, Daniel J.; Staron, Lydie; Taberlet, Nicolas; Yano, Hajime; Eggl, Siegfried; Lecomte, Charles-Edouard; Murdoch, Naomi; Radjai, Fahrang; Richardson, Derek C.; Salazar, Marcos; Schwartz, Stephen R.; Tanga, Paolo

    2017-06-01

    Asteroids and other Small Solar System Bodies (SSSBs) are currently of great scientific and even industrial interest. Asteroids exist as the permanent record of the formation of the Solar System and therefore hold many clues to its understanding as a whole, as well as insights into the formation of planetary bodies. Additionally, SSSBs are being investigated in the context of impact risks for the Earth, space situational awareness and their possible industrial exploitation (asteroid mining). In all these aspects, the knowledge of the geophysical characteristics of SSSB surface and internal structure are of great importance. Given their size, constitution, and the evidence that many SSSBs are not simple monoliths, these bodies should be studied and modelled as self-gravitating granular systems in general, or as granular systems in micro-gravity environments in particular contexts. As such, the study of the geophysical characteristics of SSSBs is a multi-disciplinary effort that lies at the crossroads between Granular Mechanics, Celestial Mechanics, Soil Mechanics, Aerospace Engineering and Computer Sciences.

  16. Advances in the simulation and automated measurement of well-sorted granular material: 1. Simulation

    Science.gov (United States)

    Daniel Buscombe,; Rubin, David M.

    2012-01-01

    1. In this, the first of a pair of papers which address the simulation and automated measurement of well-sorted natural granular material, a method is presented for simulation of two-phase (solid, void) assemblages of discrete non-cohesive particles. The purpose is to have a flexible, yet computationally and theoretically simple, suite of tools with well constrained and well known statistical properties, in order to simulate realistic granular material as a discrete element model with realistic size and shape distributions, for a variety of purposes. The stochastic modeling framework is based on three-dimensional tessellations with variable degrees of order in particle-packing arrangement. Examples of sediments with a variety of particle size distributions and spatial variability in grain size are presented. The relationship between particle shape and porosity conforms to published data. The immediate application is testing new algorithms for automated measurements of particle properties (mean and standard deviation of particle sizes, and apparent porosity) from images of natural sediment, as detailed in the second of this pair of papers. The model could also prove useful for simulating specific depositional structures found in natural sediments, the result of physical alterations to packing and grain fabric, using discrete particle flow models. While the principal focus here is on naturally occurring sediment and sedimentary rock, the methods presented might also be useful for simulations of similar granular or cellular material encountered in engineering, industrial and life sciences.

  17. Thermal diffusion segregation of an impurity in a driven granular fluid

    Energy Technology Data Exchange (ETDEWEB)

    Reyes, Francisco Vega; Garzó, Vicente [Departamento de Física, Universidad de Extremadura, E-06071 Badajoz, Spain and Instituto de Computación Científica Avanzada (ICCAEx), Universidad de Extremadura, E-06071 Badajoz (Spain)

    2014-12-09

    We study segregation of an impurity in a driven granular fluid under two types of steady states. In the first state, the granular gas is driven by a stochastic volume force field with a Fourier-type profile while in the second state, the granular gas is sheared in such a way that inelastic cooling is balanced by viscous heating. We compare theoretical results derived from a solution of the (inelastic) Boltzmann equation at Navier-Stokes (NS) order with those obtained from the Direct Monte Carlo simulation (DSMC) method and molecular dynamics (MD) simulations. Good agreement is found between theory and simulation, which provides strong evidence of the reliability of NS granular hydrodynamics for these steady states (including the dynamics of the impurity), even at high inelasticity. In addition, preliminary results for thermal diffusion in granular fluids at moderate densities are also presented. As for dilute gases, excellent agreement is also found in this more general case.

  18. Characterization of sulfate-reducing granular sludge in the SANI(®) process.

    Science.gov (United States)

    Hao, Tianwei; Wei, Li; Lu, Hui; Chui, Hokwong; Mackey, Hamish R; van Loosdrecht, Mark C M; Chen, Guanghao

    2013-12-01

    Hong Kong practices seawater toilet flushing covering 80% of the population. A sulfur cycle-based biological nitrogen removal process, the Sulfate reduction, Autotrophic denitrification and Nitrification Integrated (SANI(®)) process, had been developed to close the loop between the hybrid water supply and saline sewage treatment. To enhance this novel process, granulation of a Sulfate-Reducing Up-flow Sludge Bed (SRUSB) reactor has recently been conducted for organic removal and provision of electron donors (sulfide) for subsequent autotrophic denitrification, with a view to minimizing footprint and maximizing operation resilience. This further study was focused on the biological and physicochemical characteristics of the granular sulfate-reducing sludge. A lab-scale SRUSB reactor seeded with anaerobic digester sludge was operated with synthetic saline sewage for 368 days. At 1 h nominal hydraulic retention time (HRT) and 6.4 kg COD/m(3)-d organic loading rate, the SRUSB reactor achieved 90% COD and 75% sulfate removal efficiencies. Granular sludge was observed within 30 days, and became stable after 4 months of operation with diameters of 400-500 μm, SVI5 of 30 ml/g, and extracellular polymeric substances of 23 mg carbohydrate/g VSS. Fluorescence in situ hybridization (FISH) analysis revealed that the granules were enriched with abundant sulfate-reducing bacteria (SRB) as compared with the seeding sludge. Pyrosequencing analysis of the 16S rRNA gene in the sulfate-reducing granules on day 90 indicated that the microbial community consisted of a diverse SRB genera, namely Desulfobulbus (18.1%), Desulfobacter (13.6%), Desulfomicrobium (5.6%), Desulfosarcina (0.73%) and Desulfovibrio (0.6%), accounting for 38.6% of total operational taxonomic units at genera level, with no methanogens detected. The microbial population and physicochemical properties of the granules well explained the excellent performance of the granular SRUSB reactor. Copyright © 2013 Elsevier

  19. Electrical transport properties in Fe-Cr nanocluster-assembled granular films

    Science.gov (United States)

    Wang, Xiong-Zhi; Wang, Lai-Sen; Zhang, Qin-Fu; Liu, Xiang; Xie, Jia; Su, A.-Mei; Zheng, Hong-Fei; Peng, Dong-Liang

    2017-09-01

    The Fe100-xCrx nanocluster-assembled granular films with Cr atomic fraction (x) ranging from 0 to 100 were fabricated by using a plasma-gas-condensation cluster deposition system. The TEM characterization revealed that the uniform Fe clusters were coated with a Cr layer to form a Fe-Cr core-shell structure. Then, the as-prepared Fe100-xCrx nanoclusters were randomly assembled into a granular film in vacuum environments with increasing the deposition time. Because of the competition between interfacial resistance and shunting effect of Cr layer, the room temperature resistivity of the Fe100-xCrx nanocluster-assembled granular films first increased and then decreased with increasing the Cr atomic fraction (x), and revealed a maximum of 2 × 104 μΩ cm at x = 26 at.%. The temperature-dependent longitudinal resistivity (ρxx), magnetoresistance (MR) effect and anomalous Hall effect (AHE) of these Fe100-xCrx nanocluster-assembled granular films were also studied systematically. As the x increased from 0 to 100, the ρxx of all samples firstly decreased and then increased with increasing the measuring temperature. The dependence of ρxx on temperature could be well addressed by a mechanism incorporated for the fluctuation-induced-tunneling (FIT) conduction process and temperature-dependent scattering effect. It was found that the anomalous Hall effect (AHE) had no legible scaling relation in Fe100-xCrx nanocluster-assembled granular films. However, after deducting the contribution of tunneling effect, the scaling relation was unambiguous. Additionally, the Fe100-xCrx nanocluster-assembled granular films revealed a small negative magnetoresistance (MR), which decreased with the increase of x. The detailed physical mechanism of the electrical transport properties in these Fe100-xCrx nanocluster-assembled granular films was also studied.

  20. Dermatofibroma-like granular cell tumour: a potential diagnostic pitfall

    Directory of Open Access Journals (Sweden)

    Jiri Soukup

    2016-11-01

    Full Text Available Dermatofibroma-like granular cell tumour (GCT is a rare entity, with only two cases having been described so far. We report another case in a 62-year-old woman, discuss histopathological features, and review other tumours in which granular changes have been observed. Our tumour was composed predominantly of oval-to-spindle granular cells with prominent nucleoli, arranged in short fascicles and storiform pattern, infiltrating around collagen bundles. Immunohistochemical analysis with antibodies against CD31, CD56, CD68, CD117, S-100 protein, inhibin, calretinin, EMA, p53 and MIB-1 was performed, showing expression of CD56, CD68, S-100 protein, inhibin and calretinin. The diagnosis of atypical dermatofibroma-like GCT was made.

  1. Characteristics and performance of aerobic algae-bacteria granular consortia in a photo-sequencing batch reactor.

    Science.gov (United States)

    Liu, Lin; Zeng, Zhichao; Bee, Mingyang; Gibson, Valerie; Wei, Lili; Huang, Xu; Liu, Chaoxiang

    2018-05-05

    The characteristics and performance of algae-bacteria granular consortia which cultivated with aerobic granules and targeted algae (Chlorella and Scenedesmus), and the essential difference between granular consortia and aerobic granules were investigated in this experiment. The result indicated that algae-bacteria granular consortia could be successfully developed, and the algae present in the granular consortia were mainly Chlorella and Scenedesmus. Although the change of chlorophyll composition revealed the occurrence of light limitation for algal growth, the granular consortia could maintain stable granular structure, and even showed better settling property than aerobic granules. Total nitrogen and phosphate in the algal-bacterial granular system showed better removal efficiencies (50.2% and 35.7%) than those in the aerobic granular system (32.8% and 25.6%) within one cycle (6 h). The biodiesel yield of aerobic granules could be significantly improved by algal coupled process, yet methyl linolenate and methyl palmitoleate were the dominant composition of biodiesel obtained from granular consortia and aerobic granules, respectively. Meanwhile, the difference of dominant bacterial communities in the both granules was found at the order level and family level, and alpha diversity indexes revealed the granular consortia had a higher microbial diversity. Copyright © 2018. Published by Elsevier B.V.

  2. User-centric Query Refinement and Processing Using Granularity Based Strategies

    NARCIS (Netherlands)

    Zeng, Y.; Zhong, N.; Wang, Y.; Qin, Y.; Huang, Z.; Zhou, H; Yao, Y; van Harmelen, F.A.H.

    2011-01-01

    Under the context of large-scale scientific literatures, this paper provides a user-centric approach for refining and processing incomplete or vague query based on cognitive- and granularity-based strategies. From the viewpoints of user interests retention and granular information processing, we

  3. A new data-processing approach to study particle motion using ultrafast X-ray tomography scanner: case study of gravitational mass flow

    Science.gov (United States)

    Waktola, Selam; Bieberle, Andre; Barthel, Frank; Bieberle, Martina; Hampel, Uwe; Grudzień, Krzysztof; Babout, Laurent

    2018-04-01

    In most industrial products, granular materials are often required to flow under gravity in various kinds of silo shapes and usually through an outlet in the bottom. There are several interrelated parameters which affect the flow, such as internal friction, bulk and packing density, hopper geometry, and material type. Due to the low-spatial resolution of electrical capacitance tomography or scanning speed limitation of standard X-ray CT systems, it is extremely challenging to measure the flow velocity and possible centrifugal effects of granular materials flow effectively. However, ROFEX (ROssendorf Fast Electron beam X-ray tomography) opens new avenues of granular flow investigation due to its very high temporal resolution. This paper aims to track particle movements and evaluate the local grain velocity during silo discharging process in the case of mass flow. The study has considered the use of the Seramis material, which can also serve as a type of tracer particles after impregnation, due to its porous nature. The presented novel image processing and analysis approach allows satisfyingly measuring individual particle velocities but also tracking their lateral movement and three-dimensional rotations.

  4. Large mid-esophageal granular cell tumor: benign versus malignant

    Directory of Open Access Journals (Sweden)

    Prarthana Roselil Christopher

    2015-06-01

    Full Text Available Granular cell tumors are rare soft tissue neoplasms, among which only 2% are malignant, arising from nervous tissue. Here we present a case of a large esophageal granular cell tumor with benign histopathological features which metastasized to the liver, but showing on positron emission tomography-computerized tomography standardized uptake value suggestive of a benign lesion.

  5. Adsorption Study of Cobalt on Treated Granular Activated Carbon

    OpenAIRE

    Y. V. Hete; S. B. Gholase; R. U. Khope

    2012-01-01

    This study is carried out for the removal of cobalt from aqueous solution using granular activated carbon in combination with p-nitro benzoic acid at temperature 25±1 °C. The adsorption isotherm of cobalt on granular activated carbon has been determined and the data fitted reasonably well to the Langmuir and Freundlich isotherm for activated carbon.

  6. Swelling pressure and water absorption property of compacted granular bentonite during water absorption

    International Nuclear Information System (INIS)

    Oyamada, T.; Komine, H.; Murakami, S.; Sekiguchi, T.; Sekine, I.

    2012-01-01

    Document available in extended abstract form only. Bentonite is currently planned to be used as buffer materials in engineered barrier of radioactive waste disposal. Granular bentonites are expected as the materials used in constructions as buffer materials by in-situ compaction methods. After applying these buffer materials, it is expected that the condition of the buffer area changes in long-term by the seepage of groundwater into buffer area. Therefore, it is important to understand water movement and swelling behavior of the buffer materials for evaluating the performance of engineered barrier. In this study, we investigated water absorption property and swelling pressure of compacted granular bentonite. Specifically, the process of swelling pressure and amount of water absorption of granular bentonite-GX (Kunigel-GX, produced at the Tsukinuno mine in Japan) were observed by laboratory tests. To discuss the influence of maximum grain size of bentonite particle on swelling pressure and water absorption property, two types of samples were used. One is granular sample which is Bentonite-GX controlled under 2 mm the maximum grain size, the other is milled sample which is Bentonite-GX with the maximum grain size under 0.18 mm by milling with the agate mortar. In addition, the mechanism on the swelling pressure of compacted granular bentonite was considered and discussed. In the cases of granular sample, swelling pressure increases rapidly, then gradually continues to increase up to maximum value. In the cases of milled sample, swelling pressure also increases rapidly at first. However, then its value decreases before progressing of gradual increase continues. Especially, this trend was clearly observed at a relatively low dry density. At the peaks of these curves, the swelling pressure of granular samples is lower than that of milled samples. In addition, the increasing of swelling pressure by the time the peak observed during the process of swelling pressure from

  7. Physical test of a particle simulation model in a sheared granular system.

    Science.gov (United States)

    Rycroft, Chris H; Orpe, Ashish V; Kudrolli, Arshad

    2009-09-01

    We report a detailed comparison of a slow gravity-driven sheared granular flow with a discrete-element simulation performed in the same geometry. In the experiments, grains flow inside a silo with a rectangular cross section and are sheared by a rough boundary on one side and smooth boundaries on the other sides. Individual grain position and motion are measured using a particle index-matching imaging technique where a fluorescent dye is added to the interstitial liquid which has the same refractive index as the glass beads. The simulations use a Cundall-Strack contact model between the grains using contact parameters that have been used in many other previous studies and ignore the hydrodynamic effects of the interstitial liquid. Computations are performed to understand the effect of particle coefficient of friction, elasticity, contact model, and polydispersity on mean flow properties. We then perform a detailed comparison of the particle fluctuation properties as measured by the displacement probability distribution function and the mean square displacement. All in all, our study suggests a high level of quantitative agreement between the simulations and experiments.

  8. Editorial: Modelling and computational challenges in granular materials

    OpenAIRE

    Weinhart, Thomas; Thornton, Anthony Richard; Einav, Itai

    2015-01-01

    This is the editorial for the special issue on “Modelling and computational challenges in granular materials” in the journal on Computational Particle Mechanics (CPM). The issue aims to provide an opportunity for physicists, engineers, applied mathematicians and computational scientists to discuss the current progress and latest advancements in the field of advanced numerical methods and modelling of granular materials. The focus will be on computational methods, improved algorithms and the m...

  9. Can one ``Hear'' the aggregation state of a granular system?

    Science.gov (United States)

    Kruelle, Christof A.; Sánchez, Almudena García

    2013-06-01

    If an ensemble of macroscopic particles is mechanically agitated the constant energy input is dissipated into the system by multiple inelastic collisions. As a result, the granular material can exhibit, depending on the magnitude of agitation, several physical states - like a gaseous phase for high energy input or a condensed state for low agitation. Here we introduce a new method for quantifying the acoustical response of the granular system. Our experimental system consists of a monodisperse packing of glass beads with a free upper surface, which is confined inside a cylindrical container. An electro-mechanical shaker exerts a sinusoidal vertical vibration at normalized accelerations well above the fluidization threshold for a monolayer of particles. By increasing the number of beads the granular gas suddenly collapses if a critical threshold is exceeded. The transition can be detected easily with a microphone connected to the soundcard of a PC. From the recorded audio track a FFT is calculated in real-time. Depending on either the number of particles at a fixed acceleration or the amount of energy input for a given number of particles, the resulting rattling noise exhibits a power spectrum with either the dominating (shaker) frequency plus higher harmonics for a granular crystal or a high-frequency broad-band noise for a granular gas, respectively. Our new method demonstrates that it is possible to quantify analytically the subjective audio impressions of a careful listener and thus to distinguish easily between different aggregation states of an excited granular system.

  10. Nonlinear instability and convection in a vertically vibrated granular bed

    NARCIS (Netherlands)

    Shukla, P.; Ansari, I.H.; van der Meer, Roger M.; Lohse, Detlef; Alam, M.

    2014-01-01

    The nonlinear instability of the density-inverted granular Leidenfrost state and the resulting convective motion in strongly shaken granular matter are analysed via a weakly nonlinear analysis of the hydrodynamic equations. The base state is assumed to be quasi-steady and the effect of harmonic

  11. Enhanced electrochemical oxidation of synthetic dyeing wastewater using SnO2-Sb-doped TiO2-coated granular activated carbon electrodes with high hydroxyl radical yields

    International Nuclear Information System (INIS)

    Li, Xinyang; Wu, Yue; Zhu, Wei; Xue, Fangqing; Qian, Yi; Wang, Chengwen

    2016-01-01

    Highlights: • We study granular activated carbon (GAC) electrodes coated with catalysts. • GAC coated with ATOT demonstrates an impressive ·OH yield. • This electrode can be used in continuous-flow three-dimensional electrode reactors. • We use Rhodamine B as a model organic compound for removal. • The GAC/ATOT performs better than all other electrodes examined. - Abstract: In this study, granular activated carbon (GAC) coated with SnO 2 -Sb doped TiO 2 (GAC/ATOT) with a high hydroxyl radical (·OH) yield is prepared via the sol-gel method. This material is utilized as a granular electrode in a continuous-flow three-dimensional electrode reactor (CTDER) for the enhanced treatment of synthetic dyeing wastewater containing Rhodamine B (RhB). We then characterize the physical properties, electrochemical properties, and electrochemical oxidation performance of the granular electrode. The results show that using the GAC/ATOT electrode in a CTDER significantly enhances the chemical oxygen demand (COD) removal, decreases the energy consumption, and improves the current efficiency of the wastewater. This is primarily attributed to the higher catalytic activity of GAC/ATOT for ·OH production compared to that of other candidates, such as TiO 2 coated GAC (GAC/T), Sb doped SnO 2 coated GAC (GAC/ATO), and pure GAC. The mechanism of the enhanced electrochemical oxidation afforded by using GAC/ATOT indicates that the high ·OH yield in the reactor packed with GAC/ATOT electrodes contributes to the enhanced electrochemical oxidation performance with respect to organic compounds.

  12. COMPORTAMIENTO RESILIENTE DE MATERIALES GRANULARES EN PAVIMENTOS FLEXIBLES: ESTADO DEL CONOCIMIENTO RESILIENT BEHAVIOR OF GRANULAR MATERIALS IN FLEXIBLE PAVEMENTS: STATE OF THE ART

    Directory of Open Access Journals (Sweden)

    Hugo Alexander Rondón Quintana

    2007-07-01

    Full Text Available Los vehículos que circulan sobre una estructura de pavimento inducen ciclos de carga y descarga que generan dentro de las capas granulares deformaciones recuperables (resilientes y permanentes (plásticas. La ingeniería de pavimentos ha venido desarrollando estudios desde la década de los 60 con el fin de intentar comprender el comportamiento elastoplástico que experimentan materiales granulares cuando conforman capas de base y subbase en estructuras flexibles. La mayor parte de las investigaciones que se han realizado en esta área se han concentrado en estudiar su comportamiento resiliente. El estado del conocimiento de estudios desarrollados para medir la respuesta resiliente y la deformación permanente en materiales granulares es presentado en dos artículos por separado. En este primer artículo se presenta la forma como ha sido estudiado el comportamiento resiliente de materiales granulares y se discuten los factores que influyen en dicho comportamiento. Al final del artículo se presenta la evolución de las ecuaciones matemáticas desarrolladas a partir de resultados de estudios teóricos y experimentales. Un estado del conocimiento sobre el fenómeno de deformación permanente es presentado en un segundo artículo.When vehicles move on a pavement structure, they induce load cycles that generate resilient and permanent strains inside granular layers. Since the 60's, pavement engineering has developed studies in order to understand the elasto-plastic behavior that granular materials experiment on base and sub-base layers of flexible pavements. Most of the researches that have been made in this area have concentrated in studying their resilient behavior. A state of the art about the behavior of granular materials in flexible pavements is presented in two separate papers. This first paper tries on resilient stress-strain characteristics of such materials. The mathematical equations found in the literature to predict the resilient

  13. Submammary Granular Parakeratosis Treated With Mastopexy.

    Science.gov (United States)

    Nelson, Garrett; Lien, Mary H; Messina, Jane L; Ranjit, Sonali; Fenske, Neil Alan

    2017-08-01

    Granular parakeratosis, originally named axillary granular parakeratosis, is an uncommon disease with an unclear etiology. It is thought to result from defective processing of profillagrin to fillagrin, causing retention of keratohyaline granules in the epidermis. A myriad of causative factors has been proposed, including friction, moisture, heat, and contact irritants such as deodorants. We present a case in the inframammary area that resolved with mastopexy, further supporting the role of friction, moisture, and heat. Furthermore, we present electron microscopic evidence demonstrating non-degraded keratohyaline granules upon epidermal maturation. This entity, we believe, is reactive and represents a protective response of the body to moisture and heat. J Drugs Dermatol. 2017;16(8):810-812..

  14. Tumor of granular cells of esophagus

    International Nuclear Information System (INIS)

    Gonzalez Fabian, Licet; Diaz Anaya, Amnia; Perez de la Torre, Georgina

    2010-01-01

    Granular cells tumors are rare and asymptomatic lesions and by general, it is an incidental finding en high or low endoscopy. They were described for the first time by Abrikossoff in 1926. The more frequent locations are the buccal mucosa, dermis and subcutaneous cellular tissue, most of these tumors has a benign origin. This is the case of a woman aged 44 with a pyrosis history from a year ago; by high endoscopy it is noted a 8 mm lesion distal to esophagus and confirmed by histological study of granular cells tumor. Elective treatment of this lesion is the endoscopic polypectomy. Despite that the malign potential is low; we suggested a close clinical and endoscopic follow-up.

  15. STUDY OF HYDRODYNAMICS IN FIXED BED OF COMPOSITE GRANULAR MATERIALS

    Directory of Open Access Journals (Sweden)

    Stelian Petrescu

    2010-12-01

    Full Text Available This study aims at the experimental determination of pressure drop and friction factor at gas flow through fixed beds of granular silica gel, alumina and activated carbon, and establishment of an equation containing a modified friction factor Fm to calculate pressure drop. In order to calculate the modified friction factor, an equation was suggested.The experimental values for pressure drop and friction factor were determined using spherical grains of silica gel, cylindrical grains of alumina and silica gel, alumina and activated carbon impregnated with calcium chloride. By means of the suggested equation, the values of pressure drop in fixed bed were calculated and compared with the experimental values. A good agreement between the predicted and experimental data is noticed.

  16. Failure evolution in granular material retained by rigid wall in active mode

    Science.gov (United States)

    Pietrzak, Magdalena; Leśniewska, Danuta

    2012-10-01

    This paper presents a detailed study of a selected small scale model test, performed on a sample of surrogate granular material, retained by a rigid wall (typical geotechnical problem of earth thrust on a retaining wall). The experimental data presented in this paper show that the deformation of granular sample behind retaining wall can undergo some cyclic changes. The nature of these cycles is not clear - it is probably related to some micromechanical features of granular materials, which are recently extensively studied in many research centers in the world. Employing very precise DIC (PIV) method can help to relate micro and macro-scale behavior of granular materials.

  17. Granular Leidenfrost effect: Experiment and theory of floating particle clusters

    NARCIS (Netherlands)

    Eshuis, Peter; Eshuis, P.G.; van der Meer, Roger M.; van der Weele, J.P.; Lohse, Detlef

    2005-01-01

    Granular material is vertically vibrated in a 2D container: above a critical shaking strength, and for a sufficient number of beads, a crystalline cluster is elevated and supported by a dilute gaseous layer of fast beads underneath. We call this phenomenon the granular Leidenfrost effect. The

  18. Elliptic Flow, Initial Eccentricity and Elliptic Flow Fluctuations in Heavy Ion Collisions at RHIC

    Science.gov (United States)

    Nouicer, Rachid; Alver, B.; Back, B. B.; Baker, M. D.; Ballintijn, M.; Barton, D. S.; Betts, R. R.; Bickley, A. A.; Bindel, R.; Busza, W.; Carroll, A.; Chai, Z.; Decowski, M. P.; García, E.; Gburek, T.; George, N.; Gulbrandsen, K.; Halliwell, C.; Hamblen, J.; Hauer, M.; Henderson, C.; Hofman, D. J.; Hollis, R. S.; Holzman, B.; Iordanova, A.; Kane, J. L.; Khan, N.; Kulinich, P.; Kuo, C. M.; Li, W.; Lin, W. T.; Loizides, C.; Manly, S.; Mignerey, A. C.; Nouicer, R.; Olszewski, A.; Pak, R.; Reed, C.; Roland, C.; Roland, G.; Sagerer, J.; Seals, H.; Sedykh, I.; Smith, C. E.; Stankiewicz, M. A.; Steinberg, P.; Stephans, G. S. F.; Sukhanov, A.; Tonjes, M. B.; Trzupek, A.; Vale, C.; van Nieuwenhuizen, G. J.; Vaurynovich, S. S.; Verdier, R.; Veres, G. I.; Walters, P.; Wenger, E.; Wolfs, F. L. H.; Wosiek, B.; Woźniak, K.; Wysłouch, B.

    2008-12-01

    We present measurements of elliptic flow and event-by-event fluctuations established by the PHOBOS experiment. Elliptic flow scaled by participant eccentricity is found to be similar for both systems when collisions with the same number of participants or the same particle area density are compared. The agreement of elliptic flow between Au+Au and Cu+Cu collisions provides evidence that the matter is created in the initial stage of relativistic heavy ion collisions with transverse granularity similar to that of the participant nucleons. The event-by-event fluctuation results reveal that the initial collision geometry is translated into the final state azimuthal particle distribution, leading to an event-by-event proportionality between the observed elliptic flow and initial eccentricity.

  19. Adsorption Study of Cobalt on Treated Granular Activated Carbon

    Directory of Open Access Journals (Sweden)

    Y. V. Hete

    2012-01-01

    Full Text Available This study is carried out for the removal of cobalt from aqueous solution using granular activated carbon in combination with p-nitro benzoic acid at temperature 25±1 °C. The adsorption isotherm of cobalt on granular activated carbon has been determined and the data fitted reasonably well to the Langmuir and Freundlich isotherm for activated carbon.

  20. Granular computing in decision approximation an application of rough mereology

    CERN Document Server

    Polkowski, Lech

    2015-01-01

    This book presents a study in knowledge discovery in data with knowledge understood as a set of relations among objects and their properties. Relations in this case are implicative decision rules and the paradigm in which they are induced is that of computing with granules defined by rough inclusions, the latter introduced and studied  within rough mereology, the fuzzified version of mereology. In this book basic classes of rough inclusions are defined and based on them methods for inducing granular structures from data are highlighted. The resulting granular structures are subjected to classifying algorithms, notably k—nearest  neighbors and bayesian classifiers. Experimental results are given in detail both in tabular and visualized form for fourteen data sets from UCI data repository. A striking feature of granular classifiers obtained by this approach is that preserving the accuracy of them on original data, they reduce  substantially the size of the granulated data set as well as the set of granular...

  1. Disinfection of bacteria attached to granular activated carbon.

    Science.gov (United States)

    LeChevallier, M W; Hassenauer, T S; Camper, A K; McFeters, G A

    1984-01-01

    Heterotrophic plate count bacteria, coliform organisms, and pathogenic microorganisms attached to granular activated carbon particles were examined for their susceptibility to chlorine disinfection. When these bacteria were grown on carbon particles and then disinfected with 2.0 mg of chlorine per liter (1.4 to 1.6 mg of free chlorine residual per liter after 1 h) for 1 h, no significant decrease in viable counts was observed. Washed cells attached to the surface of granular activated carbon particles showed similar resistance to chlorine, but a progressive increase in sublethal injury was found. Observations made by scanning electron microscope indicated that granular activated carbon was colonized by bacteria which grow in cracks and crevices and are coated by an extracellular slime layer. These data suggest a possible mechanism by which treatment and disinfection barriers can be penetrated and pathogenic bacteria may enter drinking water supplies. Images PMID:6508306

  2. Granular cells Tumor in the gastrointestinal tract

    International Nuclear Information System (INIS)

    Castano LL, Rodrigo; Gaitan B, Maria H; Juliao E, Fabian

    2005-01-01

    Granular cells tumors are ubiquitous lesions in the gastrointestinal tract, are rare and asymptomatic and they are generally an incidental discovery at gastroduodenoscopy or colonoscopy. In the gastrointestinal tract they are more frequently located in the esophagus, right colon and rectum, stomach, appendix, small intestine or biliopancreatic tract. This article describes three patients with four tumors of granular cells in rectum, esophagus (2 lesions) and appendix. It becomes special emphasis in their neural origin, their benign behavior that justifies the endoscopic resections or limited surgical excisions and the necessity of a pursuit for the possibility, although little, of malignant transformation

  3. Advanced Granular System Modeling, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — Spaceports of the future will utilize new granular materials in unique applications including insulation for cryogenic tanks and Lunar regolith processing for usable...

  4. Multiscale modeling of transport of grains through granular assemblies

    Directory of Open Access Journals (Sweden)

    Tejada Ignacio G

    2017-01-01

    Full Text Available We investigate the transport of moderately large passive particles through granular assemblies caused by seeping flows. This process can only be described by highly nonlinear continuum models, since the local permeability, the advection and dispersion mechanisms are strongly determined by the concentration of transported particles. Particles may sometimes get temporally trapped and thus proper kinetic mass transfer models are required. The mass transfer depends on the complexity of the porous medium, the kind of interaction forces and the concentration of transported particles. We study these two issues by means of numerical and laboratory experiments. In the laboratory we use an oedo-permeameter to force sand grains to move through a gravel bed under conditions of constant hydraulic pressure drop. To understand the process, numerical experiments were performed to approach particle transport at the grain scale with a fully coupled method. The DEM-PFV combines the discrete element method with a pore scale finite volume formulation to solve the interstitial fluid flow and particle transport problems. These experiments help us to set up a continuum transport model that can be used in a boundary value problem.

  5. Boundary effects in a quasi-two-dimensional driven granular fluid.

    Science.gov (United States)

    Smith, N D; Smith, M I

    2017-12-01

    The effect of a confining boundary on the spatial variations in granular temperature of a driven quasi-two-dimensional layer of particles is investigated experimentally. The radial drop in the relative granular temperature ΔT/T exhibits a maximum at intermediate particle numbers which coincides with a crossover from kinetic to collisional transport of energy. It is also found that at low particle numbers, the distributions of radial velocities are increasingly asymmetric as one approaches the boundary. The radial and tangential granular temperatures split, and in the tails of the radial velocity distribution there is a higher population of fast moving particles traveling away rather than towards the boundary.

  6. Impact induced splash and spill in a quasi-confided granular medium

    Science.gov (United States)

    Ogale, S. B.

    2005-03-01

    Dissipation of the energy of impact in a granular medium and its effects has been a subject of considerable scientific for quite some time. In this work we have explored and analyzed the splash and spill effects caused by the impact of a ball dropped from a height into a granular medium in a open container. Three different granular media, namely rice, mustard seeds, and cream of wheat were used. The amount of spilled-over granular matter was measured as a function of the ball-drop height. Digital pictures of the splash process were also recorded. The quantity of spilled granular matter varies linearly with the impact energy. However additional step like structures are also noted. Specifically, a distinct and large jump is seen in the spilled quantity at a specific impact energy in the case of mustard seeds, which also exhibit obvious charging effects and repulsion. Although the parameters such as mass per grain and packing density for the case of mustard seeds are intermediate between those for rice and cream of wheat, the spill quantity for comparable impact energy is considerably higher. These data will be presented and discussed.

  7. On creating macroscopically identical granular systems with different numbers of particles

    Science.gov (United States)

    van der Meer, Devaraj; Rivas, Nicolas

    2015-11-01

    One of the fundamental differences between granular and molecular hydrodynamics is the enormous difference in the total number of constituents. The small number of particles implies that the role of fluctuations in granular dynamics is of paramount importance. To obtain more insight in these fluctuations, we investigate to what extent it is possible to create identical granular hydrodynamic states with different number of particles. A definition is given of macroscopically equivalent systems, and the dependency of the conservation equations on the particle size is studied. We show that, in certain cases, and by appropriately scaling the microscopic variables, we are able to compare systems with significantly different number of particles that present the same macroscopic phenomenology. We apply these scalings in simulations of a vertically vibrated system, namely the density inverted granular Leidenfrost state and its transition to a buoyancy-driven convective state.

  8. Effect of Wetting and Contamination of Granular Beds During Sphere Impact

    KAUST Repository

    Kouraytem, Nadia

    2013-03-01

    This thesis presents results from an experimental study of the impact of dense solid spheres onto granular beds. The overall aim is to further our understanding of the dynamical response of granular materials to impact. In order to do this, we will study both the initial penetration stages and peak acceleration exerted on the sphere by using high-speed imaging. Another critical part is to measure the penetration depth of the sphere and calculate the corresponding depth-averaged stopping force. Both of these main focal points will be assessed for not only dry, but wet and “contaminated” grains, whereby the granular bed will be comprised of two distinct size ranges of base grains. In doing so, we aim to broadly determine whether contaminated grains or wet grains are more effective at increasing the tensile strength of granular materials.

  9. Slow creep in soft granular packings.

    Science.gov (United States)

    Srivastava, Ishan; Fisher, Timothy S

    2017-05-14

    Transient creep mechanisms in soft granular packings are studied numerically using a constant pressure and constant stress simulation method. Rapid compression followed by slow dilation is predicted on the basis of a logarithmic creep phenomenon. Characteristic scales of creep strain and time exhibit a power-law dependence on jamming pressure, and they diverge at the jamming point. Microscopic analysis indicates the existence of a correlation between rheology and nonaffine fluctuations. Localized regions of large strain appear during creep and grow in magnitude and size at short times. At long times, the spatial structure of highly correlated local deformation becomes time-invariant. Finally, a microscale connection between local rheology and local fluctuations is demonstrated in the form of a linear scaling between granular fluidity and nonaffine velocity.

  10. Effect of Wetting and Contamination of Granular Beds During Sphere Impact

    KAUST Repository

    Kouraytem, Nadia

    2013-01-01

    This thesis presents results from an experimental study of the impact of dense solid spheres onto granular beds. The overall aim is to further our understanding of the dynamical response of granular materials to impact. In order to do this, we

  11. Syn-eruptive, soft-sediment deformation of deposits from dilute pyroclastic density current: triggers from granular shear, dynamic pore pressure, ballistic impacts and shock waves

    Science.gov (United States)

    Douillet, G. A.; Taisne, B.; Tsang-Hin-Sun, E.; Muller, S. K.; Kueppers, U.; Dingwell, D. B.

    2015-05-01

    Soft-sediment deformation structures can provide valuable information about the conditions of parent flows, the sediment state and the surrounding environment. Here, examples of soft-sediment deformation in deposits of dilute pyroclastic density currents are documented and possible syn-eruptive triggers suggested. Outcrops from six different volcanoes have been compiled in order to provide a broad perspective on the variety of structures: Soufriere Hills (Montserrat), Tungurahua (Ecuador), Ubehebe craters (USA), Laacher See (Germany), and Tower Hill and Purrumbete lakes (both Australia). The variety of features can be classified in four groups: (1) tubular features such as pipes; (2) isolated, laterally oriented deformation such as overturned or oversteepened laminations and vortex-shaped laminae; (3) folds-and-faults structures involving thick (>30 cm) units; (4) dominantly vertical inter-penetration of two layers such as potatoids, dishes, or diapiric flame-like structures. The occurrence of degassing pipes together with basal intrusions suggest fluidization during flow stages, and can facilitate the development of other soft-sediment deformation structures. Variations from injection dikes to suction-driven, local uplifts at the base of outcrops indicate the role of dynamic pore pressure. Isolated, centimeter-scale, overturned beds with vortex forms have been interpreted to be the signature of shear instabilities occurring at the boundary of two granular media. They may represent the frozen record of granular, pseudo Kelvin-Helmholtz instabilities. Their recognition can be a diagnostic for flows with a granular basal boundary layer. Vertical inter-penetration and those folds-and-faults features related to slumps are driven by their excess weight and occur after deposition but penecontemporaneous to the eruption. The passage of shock waves emanating from the vent may also produce trains of isolated, fine-grained overturned beds that disturb the surface bedding

  12. Alternating anoxic feast/aerobic famine condition for improving granular sludge formation in sequencing batch airlift reactor at reduced aeration rate.

    Science.gov (United States)

    Wan, Junfeng; Bessière, Yolaine; Spérandio, Mathieu

    2009-12-01

    In this study the influence of a pre-anoxic feast period on granular sludge formation in a sequencing batch airlift reactor is evaluated. Whereas a purely aerobic SBR was operated as a reference (reactor R2), another reactor (R1) was run with a reduced aeration rate and an alternating anoxic-aerobic cycle reinforced by nitrate feeding. The presence of pre-anoxic phase clearly improved the densification of aggregates and allowed granular sludge formation at reduced air flow rate (superficial air velocity (SAV)=0.63cms(-1)). A low sludge volume index (SVI(30)=45mLg(-1)) and a high MLSS concentration (9-10gL(-1)) were obtained in the anoxic/aerobic system compared to more conventional results for the aerobic reactor. A granular sludge was observed in the anoxic/aerobic system whilst only flocs were observed in the aerobic reference even when operated at a high aeration rate (SAV=2.83cms(-1)). Nitrification was maintained efficiently in the anoxic/aerobic system even when organic loading rate (OLR) was increased up to 2.8kgCODm(-3)d(-1). In the contrary nitrification was unstable in the aerobic system and dropped at high OLR due to competition between autotrophic and heterotrophic growth. The presence of a pre-anoxic period positively affected granulation process via different mechanisms: enhancing heterotrophic growth/storage deeper in the internal anoxic layer of granule, reducing the competition between autotrophic and heterotrophic growth. These processes help to develop dense granular sludge at a moderate aeration rate. This tends to confirm that oxygen transfer is the most limiting factor for granulation at reduced aeration. Hence the use of an alternative electron acceptor (nitrate or nitrite) should be encouraged during feast period for reducing energy demand of the granular sludge process.

  13. Characterization of granular collapse onto hard substrates by acoustic emissions

    Science.gov (United States)

    Farin, Maxime; Mangeney, Anne; Toussaint, Renaud; De Rosny, Julien

    2013-04-01

    Brittle deformation in granular porous media can generate gravitational instabilities such as debris flows and rock avalanches. These phenomena constitute a major natural hazard for the population in mountainous, volcanic and coastal areas but their direct observation on the field is very dangerous. Recent studies showed that gravitational instabilities can be detected and characterized (volume, duration,...) thanks to the seismic signal they generate. In an avalanche, individual block bouncing and rolling on the ground are expected to generated signals of higher frequencies than the main flow spreading. The identification of the time/frequency signature of individual blocks in the recorded signal remains however difficult. Laboratory experiments were conducted to investigate the acoustic signature of diverse simple sources corresponding to grains falling over thin plates of plexiglas and rock blocks. The elastic energy emitted by a single bouncing steel bead into the support was first quantitatively estimated and compared to the potential energy of fall and to the potential energy change during the shock. Next, we consider the collapse of granular columns made of steel spherical beads onto hard substrates. Initially, these columns were held by a magnetic field allowing to suppress suddenly the cohesion between the beads, and thus to minimize friction effects that would arise from side walls. We varied systematically the column volume, the column aspect ratio (height over length) and the grain size. This is shown to affect the signal envelope and frequency content. In the experiments, two types of acoustic sensors were used to record the signals in a wide frequency range: accelerometers (1 Hz to 56 kHz) and piezoelectric sensors (100 kHz to 1 MHz). The experiments were also monitored optically using fast cameras. We developed a technique to use quantitatively both types of sensors to evaluate the elastic energy emitted by the sources. Eventually, we looked at what

  14. Density profiles of granular gases studied by molecular dynamics and Brownian bridges

    Science.gov (United States)

    Peñuñuri, F.; Montoya, J. A.; Carvente, O.

    2018-02-01

    Despite the inherent frictional forces and dissipative collisions, confined granular matter can be regarded as a system in a stationary state if we inject energy continuously. Under these conditions, both the density and the granular temperature are, in general, non-monotonic variables along the height of the container. In consequence, an analytical description of a granular system is hard to conceive. Here, by using molecular dynamics simulations, we measure the packing fraction profiles for a vertically vibrating three-dimensional granular system in several gaseous-like stationary states. We show that by using the Brownian bridge concept, the determined packing fraction profiles can be reproduced accurately and give a complete description of the distribution of the particles inside the simulation box.

  15. Propulsion via flexible flapping in granular media

    Science.gov (United States)

    Peng, Zhiwei; Ding, Yang; Pietrzyk, Kyle; Elfring, Gwynn; Pak, On Shun

    2017-11-01

    Biological locomotion in nature is often achieved by the interaction between a flexible body and its surrounding medium. The interaction of a flexible body with granular media is less understood compared with viscous fluids partially due to its complex rheological properties. In this work, we explore the effect of flexibility on granular propulsion by considering a simple mechanical model in which a rigid rod is connected to a torsional spring that is under a displacement actuation using a granular resistive force theory. Through a combined numerical and asymptotic investigation, we characterize the propulsive dynamics of such a flexible flapper in relation to the actuation amplitude and spring stiffness, and we compare these dynamics with those observed in a viscous fluid. In addition, we demonstrate that the maximum possible propulsive force can be obtained in the steady propulsion limit with a finite spring stiffness and large actuation amplitude. These results may apply to the development of synthetic locomotive systems that exploit flexibility to move through complex terrestrial media. Funding for Z.P. and Y.D. was partially provided by NSFC 394 Grant No. 11672029 and NSAF-NSFC Grant No. U1530401.

  16. Rough – Granular Computing knowledge discovery models

    Directory of Open Access Journals (Sweden)

    Mohammed M. Eissa

    2016-11-01

    Full Text Available Medical domain has become one of the most important areas of research in order to richness huge amounts of medical information about the symptoms of diseases and how to distinguish between them to diagnose it correctly. Knowledge discovery models play vital role in refinement and mining of medical indicators to help medical experts to settle treatment decisions. This paper introduces four hybrid Rough – Granular Computing knowledge discovery models based on Rough Sets Theory, Artificial Neural Networks, Genetic Algorithm and Rough Mereology Theory. A comparative analysis of various knowledge discovery models that use different knowledge discovery techniques for data pre-processing, reduction, and data mining supports medical experts to extract the main medical indicators, to reduce the misdiagnosis rates and to improve decision-making for medical diagnosis and treatment. The proposed models utilized two medical datasets: Coronary Heart Disease dataset and Hepatitis C Virus dataset. The main purpose of this paper was to explore and evaluate the proposed models based on Granular Computing methodology for knowledge extraction according to different evaluation criteria for classification of medical datasets. Another purpose is to make enhancement in the frame of KDD processes for supervised learning using Granular Computing methodology.

  17. Flowability of granular materials with industrial applications - An experimental approach

    Science.gov (United States)

    Torres-Serra, Joel; Romero, Enrique; Rodríguez-Ferran, Antonio; Caba, Joan; Arderiu, Xavier; Padullés, Josep-Manel; González, Juanjo

    2017-06-01

    Designing bulk material handling equipment requires a thorough understanding of the mechanical behaviour of powders and grains. Experimental characterization of granular materials is introduced focusing on flowability. A new prototype is presented which performs granular column collapse tests. The device consists of a channel whose design accounts for test inspection using visualization techniques and load measurements. A reservoir is attached where packing state of the granular material can be adjusted before run-off to simulate actual handling conditions by fluidisation and deaeration of the pile. Bulk materials on the market, with a wide range of particle sizes, can be tested with the prototype and the results used for classification in terms of flowability to improve industrial equipment selection processes.

  18. Characterization, Modeling and Application of Aerobic Granular Sludge for Wastewater Treatment

    Science.gov (United States)

    Liu, Xian-Wei; Yu, Han-Qing; Ni, Bing-Jie; Sheng, Guo-Ping

    Recently extensive studies have been carried out to cultivate aerobic granular sludge worldwide, including in China. Aerobic granules, compared with conventional activated sludge flocs, are well known for their regular, dense, and strong microbial structure, good settling ability, high biomass retention, and great ability to withstand shock loadings. Studies have shown that the aerobic granules could be applied for the treatment of low- or high-strength wastewaters, simultaneous removal of organic carbon, nitrogen and phosphorus, and decomposition of toxic wastewaters. Thus, this new form of activate sludge, like anaerobic granular sludge, could be employed for the treatment of municipal and industrial wastewaters in near future. This chapter attempts to provide an up-to-date review on the definition, cultivation, characterization, modeling and application of aerobic granular sludge for biological wastewater treatment. This review outlines some important discoveries with regard to the factors affecting the formation of aerobic granular sludge, their physicochemical characteristics, as well as their microbial structure and diversity. It also summarizes the modeling of aerobic granule formation. Finally, this chapter highlights the applications of aerobic granulation technology in the biological wastewater treatment. It is concluded that the knowledge regarding aerobic granular sludge is far from complete. Although previous studies in this field have undoubtedly improved our understanding on aerobic granular sludge, it is clear that much remains to be learned about the process and that many unanswered questions still remain. One of the challenges appears to be the integration of the existing and growing scientific knowledge base with the observations and applications in practice, which this paper hopes to partially achieve.

  19. Superconductivity effects near metal-insulator transition in granular idnium films

    International Nuclear Information System (INIS)

    Belevtsev, B.I.; Komnik, Yu.F.; Fomin, A.V.

    1986-01-01

    The influence of granules superconductivity on the electric properties of granular indium films is investigated under the conditions of partial or full granular localization of electrons. At temperatures below 5 K a minimum of electric resistance and negative magnetoresistance are revealed which are attributed to the competition of hopping conductivity and Josephson intergranular tunneling of electrons

  20. Acoustic waves in granular materials

    NARCIS (Netherlands)

    Mouraille, O.J.P.; Luding, Stefan

    2008-01-01

    Dynamic simulations with discrete elements are used to obtain more insight into the wave propagation in dense granular media. A small perturbation is created on one side of a dense, static packing and examined during its propagation until it arrives at the opposite side. The influence of

  1. Seismic wave propagation in granular media

    Science.gov (United States)

    Tancredi, Gonzalo; López, Francisco; Gallot, Thomas; Ginares, Alejandro; Ortega, Henry; Sanchís, Johnny; Agriela, Adrián; Weatherley, Dion

    2016-10-01

    Asteroids and small bodies of the Solar System are thought to be agglomerates of irregular boulders, therefore cataloged as granular media. It is a consensus that many asteroids might be considered as rubble or gravel piles.Impacts on their surface could produce seismic waves which propagate in the interior of these bodies, thus causing modifications in the internal distribution of rocks and ejections of particles and dust, resulting in a cometary-type comma.We present experimental and numerical results on the study of propagation of impact-induced seismic waves in granular media, with special focus on behavior changes by increasing compression.For the experiment, we use an acrylic box filled with granular materials such as sand, gravel and glass spheres. Pressure inside the box is controlled by a movable side wall and measured with sensors. Impacts are created on the upper face of the box through a hole, ranging from free-falling spheres to gunshots. We put high-speed cameras outside the box to record the impact as well as piezoelectic sensors and accelerometers placed at several depths in the granular material to detect the seismic wave.Numerical simulations are performed with ESyS-Particle, a software that implements the Discrete Element Method. The experimental setting is reproduced in the numerical simulations using both individual spherical particles and agglomerates of spherical particles shaped as irregular boulders, according to rock models obtained with a 3D scanner. The numerical experiments also reproduces the force loading on one of the wall to vary the pressure inside the box.We are interested in the velocity, attenuation and energy transmission of the waves. These quantities are measured in the experiments and in the simulations. We study the dependance of these three parameters with characteristics like: impact speed, properties of the target material and the pressure in the media.These results are relevant to understand the outcomes of impacts in

  2. Magnetoresistances in Ni80Fe20-ITO granular film

    International Nuclear Information System (INIS)

    Gao Chunhong; Chen Ke; Yang Yanxia; Xiong Yuanqiang; Chen Peng

    2012-01-01

    Highlights: ► Magnetoresistance (MR) in Ni 80 Fe 20 -ITO granular film are investigated. ► MR is positive at high temperature, and is negative at low temperature. ► MR results from the competition among three mechanisms. - Abstract: The magnetic properties, electrical properties and magnetoresistance are investigated in Ni 80 Fe 20 -ITO granular film with various volume fractions V NF of Ni 80 Fe 20 . The room temperature magnetization hysteresis of sample with V NF = 25% shows superparamagnetic behavior. Current-voltage curve of sample with V NF = 25% at 175 K shows typical tunneling-type behavior. The magnetoresistances of samples with low V NF are positive at high temperature, and are negative at low temperature. The temperature-dependent magnetoresistances result from the competition among ordinary magnetoresistances, the granular-typed tunneling magnetoresistance and the spin-mixing induced magnetoresistances.

  3. The CMS High Granularity Calorimeter for HL-LHC

    CERN Document Server

    Mastrolorenzo, Luca

    2017-01-01

    The High Luminosity LHC (HL-LHC) will integrate 10 times more luminosity than the LHC, posing significant challenges for radiation tolerance and event pileup on detectors, especially for forward calorimetry, and hallmarks the issue for future colliders. As part of its HL-LHC upgrade program, the CMS collaboration is designing a High Granularity Calorimeter to replace the existing endcap calorimeters. It features unprecedented transverse and longitudinal segmentation for both electromagnetic (ECAL) and hadronic (HCAL) compartments. This will facilitate particle-flow calorimetry, where the fine structure of showers can be measured and used to enhance pileup rejection and particle identification, whilst still achieving good energy resolution. The ECAL and a large fraction of HCAL will be based on hexagonal silicon sensors of 0.5 - 1 cm$^2$ cell size, with the remainder of the HCAL based on highly-segmented scintillators with SiPM readout. The intrinsic high-precision timing capabilities of the silicon sensors wi...

  4. Granular nanocrystalline zirconia electrolyte layers deposited on porous SOFC cathode substrates

    International Nuclear Information System (INIS)

    Seydel, Johannes; Becker, Michael; Ivers-Tiffee, Ellen; Hahn, Horst

    2009-01-01

    Thin granular yttria-stabilized zirconia (YSZ) electrolyte layers were prepared by chemical vapor synthesis and deposition (CVD/CVS) on a porous substoichiometric lanthanum-strontium-manganite (ULSM) solid oxide fuel cell cathode substrate. The substrate porosity was optimized with a screen printed fine porous buffer layer. Structural analysis by scanning electron microscopy showed a homogeneous, granular nanocrystalline layer with a microstructure that was controlled via reactor settings. The CVD/CVS gas-phase process enabled the deposition of crack-free granular YSZ films on porous ULSM substrates. The electrolyte layers characterized with impedance spectroscopy exhibited enhanced grain boundary conductivity.

  5. Multi-granularity synthesis segmentation for high spatial resolution Remote sensing images

    International Nuclear Information System (INIS)

    Yi, Lina; Liu, Pengfei; Qiao, Xiaojun; Zhang, Xiaoning; Gao, Yuan; Feng, Boyan

    2014-01-01

    Traditional segmentation method can only partition an image in a single granularity space, with segmentation accuracy limited to the single granularity space. This paper proposes a multi-granularity synthesis segmentation method for high spatial resolution remote sensing images based on a quotient space model. Firstly, we divide the whole image area into multiple granules (regions), each region is consisted of ground objects that have similar optimal segmentation scale, and then select and synthesize the sub-optimal segmentations of each region to get the final segmentation result. To validate this method, the land cover category map is used to guide the scale synthesis of multi-scale image segmentations for Quickbird image land use classification. Firstly, the image is coarsely divided into multiple regions, each region belongs to a certain land cover category. Then multi-scale segmentation results are generated by the Mumford-Shah function based region merging method. For each land cover category, the optimal segmentation scale is selected by the supervised segmentation accuracy assessment method. Finally, the optimal scales of segmentation results are synthesized under the guide of land cover category. Experiments show that the multi-granularity synthesis segmentation can produce more accurate segmentation than that of a single granularity space and benefit the classification

  6. Mathematics and Mechanics of Granular Materials

    CERN Document Server

    Hill, James M

    2005-01-01

    Granular or particulate materials arise in almost every aspect of our lives, including many familiar materials such as tea, coffee, sugar, sand, cement and powders. At some stage almost every industrial process involves a particulate material, and it is usually the cause of the disruption to the smooth running of the process. In the natural environment, understanding the behaviour of particulate materials is vital in many geophysical processes such as earthquakes, landslides and avalanches. This book is a collection of current research from some of the major contributors in the topic of modelling the behaviour of granular materials. Papers from every area of current activity are included, such as theoretical, numerical, engineering and computational approaches. This book illustrates the numerous diverse approaches to one of the outstanding problems of modern continuum mechanics.

  7. Self-assembly and speed distributions of active granular particles

    Science.gov (United States)

    Sánchez, R.; Díaz-Leyva, P.

    2018-06-01

    The relationship between the dynamics of self-propelled systems and the self-assembly of structured clusters are studied via the experimental speed distributions of submonolayers of self-propelled granular particles. A distribution developed for non-self-propelled granular particles describes the speed distributions remarkably well, despite some of the assumptions behind its original derivation not being applicable. This is explained in terms of clustering and dissipation being the key phenomena governing this regime.

  8. Performance of the fixed-bed of granular activated carbon for the removal of pesticides from water supply.

    Science.gov (United States)

    Alves, Alcione Aparecida de Almeida; Ruiz, Giselle Louise de Oliveira; Nonato, Thyara Campos Martins; Müller, Laura Cecilia; Sens, Maurício Luiz

    2018-02-26

    The application of a fixed bed adsorption column of granular activated carbon (FBAC-GAC), in the removal of carbaryl, methomyl and carbofuran at a concentration of 25 μg L -1 for each carbamate, from the public water supply was investigated. For the determination of the presence of pesticides in the water supply, the analytical technique of high-performance liquid chromatography with post-column derivatization was used. Under conditions of constant diffusivity, the FBAC-GAC was saturated after 196 h of operation on a pilot scale. The exhaust rate of the granular activated carbon (GAC) in the FBAC-GAC until the point of saturation was 0.02 kg GAC m -3 of treated water. By comparing a rapid small-scale column test and FBAC-GAC, it was confirmed that the predominant intraparticle diffusivity in the adsorption column was constant diffusivity. Based on the results obtained on a pilot scale, it was possible to estimate the values to be applied in the FBAC-GAC (full scale) to remove the pesticides, which are particle size with an average diameter of 1.5 mm GAC; relationship between the internal diameter of the column and the average diameter of GAC ≥50 in order to avoid preferential flow near the adsorption column wall; surface application rate 240 m 3  m -2  d -1 and an empty bed contact time of 3 min. BV: bed volume; CD: constant diffusivity; EBCT: empty bed contact time; FBAC-GAC: fixed bed adsorption column of granular activated carbon; GAC: granular activated carbon; MPV: maximum permitted values; NOM: natural organic matter; PD: proportional diffusivity; pH PCZ : pH of the zero charge point; SAR: surface application rate; RSSCT: rapid small-scale column test; WTCS: water treated conventional system.

  9. A mesoscale granular model for the mechanical behavior of alloys during solidification

    Energy Technology Data Exchange (ETDEWEB)

    Vernede, Stephane [Computational Materials Laboratory, Ecole Polytechnique Federale de Lausanne, Station 12, Lausanne CH-1015 (Switzerland); Alcan Centre de Recherches de Voreppe, ZI Centr' Alp, 725 rue Aristide Berges, BP 27, Voreppe FR-38341 (France)], E-mail: stephane.vernede@alcan.com; Dantzig, Jonathan A. [Computational Materials Laboratory, Ecole Polytechnique Federale de Lausanne, Station 12, Lausanne CH-1015 (Switzerland); Department of Mechanical Science and Engineering, University of Illinois, 1206 West Green Street Urbana, IL 61801 (United States); Rappaz, Michel [Computational Materials Laboratory, Ecole Polytechnique Federale de Lausanne, Station 12, Lausanne CH-1015 (Switzerland)

    2009-03-15

    We present a two-dimensional granular model for the mechanical behavior of an ensemble of globular grains during solidification. The grain structure is produced by a Voronoi tessellation based on an array of predefined nuclei. We consider the fluid flow caused by grain movement and solidification shrinkage in the network of channels that is formed by the faces of the grains in the tessellation. We develop the governing equations for the flow rate and pressure drop across each channel when the grains are allowed to move, and we then assemble the equations into a global expression that conserves mass and force in the system. We show that the formulation is consistent with dissipative formulations of non-equilibrium thermodynamics. Several example problems are presented to illustrate the effect of tensile strains and the availability of liquid to feed the deforming microstructure. For solid fractions below g{sub s}=0.97, we find that the fluid is able to feed the deformation at low strain, even if external feeding is not permitted. For solid fractions above g{sub s}=0.97, clusters of grains with 'dry' boundaries form and fluid flow becomes highly localized.

  10. Grain scale observations of stick-slip dynamics in fluid saturated granular fault gouge

    Science.gov (United States)

    Johnson, P. A.; Dorostkar, O.; Guyer, R. A.; Marone, C.; Carmeliet, J.

    2017-12-01

    We are studying granular mechanics during slip. In the present work, we conduct coupled computational fluid dynamics (CFD) and discrete element method (DEM) simulations to study grain scale characteristics of slip instabilities in fluid saturated granular fault gouge. The granular sample is confined with constant normal load (10 MPa), and sheared with constant velocity (0.6 mm/s). This loading configuration is chosen to promote stick-slip dynamics, based on a phase-space study. Fluid is introduced in the beginning of stick phase and characteristics of slip events i.e. macroscopic friction coefficient, kinetic energy and layer thickness are monitored. At the grain scale, we monitor particle coordination number, fluid-particle interaction forces as well as particle and fluid kinetic energy. Our observations show that presence of fluids in a drained granular fault gouge stabilizes the layer in the stick phase and increases the recurrence time. In saturated model, we observe that average particle coordination number reaches higher values compared to dry granular gouge. Upon slip, we observe that a larger portion of the granular sample is mobilized in saturated gouge compared to dry system. We also observe that regions with high particle kinetic energy are correlated with zones of high fluid motion. Our observations highlight that spatiotemporal profile of fluid dynamic pressure affects the characteristics of slip instabilities, increasing macroscopic friction coefficient drop, kinetic energy release and granular layer compaction. We show that numerical simulations help characterize the micromechanics of fault mechanics.

  11. Discussion of “The relation between dilatancy, effective stress and dispersive pressure in granular avalanches” by P. Bartelt and O. Buser (DOI: 10.1007/s11440-016-0463-7)

    Science.gov (United States)

    Iverson, Richard M.; George, David L.

    2016-01-01

    A paper recently published by Bartelt and Buser (hereafter identified as “the authors”) aims to clarify relationships between granular dilatancy and dispersive pressure and to question the effective stress principle and its application to shallow granular avalanches (Bartelt and Buser in Act Geotech 11:549–557, 2). The paper also criticizes our own recent work, which utilizes the concepts of evolving dilatancy and effective stress to model the initiation and dynamics of water-saturated landslides and debris flows. Here we first explain why we largely agree with the authors’ views of dilatancy and dispersive pressure as they apply to depth-integrated granular avalanche models, and why we disagree with their views of effective stress and pore-fluid pressure. We conclude by explaining why the authors’ characterization of our recently developed D-Claw model is inaccurate.

  12. Experimental Tests of Particle Flow Calorimetry

    CERN Document Server

    Sefkow, Felix; Kawagoe, Kiyotomo; Pöschl, Roman; Repond, José

    2016-01-01

    Precision physics at future colliders requires highly granular calorimeters to support the Particle Flow Approach for event reconstruction. This article presents a review of about 10 - 15 years of R\\&D, mainly conducted within the CALICE collaboration, for this novel type of detector. The performance of large scale prototypes in beam tests validate the technical concept of particle flow calorimeters. The comparison of test beam data with simulation, of e.g.\\ hadronic showers, supports full detector studies and gives deeper insight into the structure of hadronic cascades than was possible previously.

  13. Experimental tests of particle flow calorimetry

    International Nuclear Information System (INIS)

    Sefkow, Felix; White, Andy; Kawagoe, Kiyotomo; Poeschl, Roman; Repond, Jose

    2015-07-01

    Precision physics at future colliders requires highly granular calorimeters to support the Particle Flow Approach for event reconstruction. This article presents a review of about 10-15 years of R and D, mainly conducted within the CALICE collaboration, for this novel type of detector. The performance of large scale prototypes in beam tests validate the technical concept of particle flow calorimeters. The comparison of test beam data with simulation, of e.g. hadronic showers, supports full detector studies and gives deeper insight into the structure of hadronic cascades than was possible previously.

  14. Latest developments on the highly granular Silicon-Tungsten Electromagnetic Calorimeter technological prototype for the International Large Detector

    CERN Document Server

    Irles, Adrián

    2017-01-01

    High precision physics at future colliders requires unprecedented highly granular calorimeters for the application of the Particle Flow (PF) algorithm. The physical proof of concept was given in the previous campaign of beam tests of physic prototypes within the CALICE collaboration. We present here the latest beam and laboratory test results and R&D developments for the Silicon-Tungsten Electromagnetic Calorimeter technological prototype with fully embedded very front-end (VFE) electronics for the International Large Detector at the International Linear Collider project.

  15. An update on blast furnace granular coal injection

    Energy Technology Data Exchange (ETDEWEB)

    Hill, D.G. [Bethlehem Steel Corp., Burns Harbor, IN (United States); Strayer, T.J.; Bouman, R.W. [Bethlehem Steel Corp., PA (United States)

    1997-12-31

    A blast furnace coal injection system has been constructed and is being used on the furnace at the Burns Harbor Division of Bethlehem Steel. The injection system was designed to deliver both granular (coarse) and pulverized (fine) coal. Construction was completed on schedule in early 1995. Coal injection rates on the two Burns Harbor furnaces were increased throughout 1995 and was over 200 lbs/ton on C furnace in September. The injection rate on C furnace reached 270 lbs/ton by mid-1996. A comparison of high volatile and low volatile coals as injectants shows that low volatile coal replaces more coke and results in a better blast furnace operation. The replacement ratio with low volatile coal is 0.96 lbs coke per pound of coal. A major conclusion of the work to date is that granular coal injection performs very well in large blast furnaces. Future testing will include a processed sub-bituminous coal, a high ash coal and a direct comparison of granular versus pulverized coal injection.

  16. Biodegradation of methyl tertiary butyl ether (MTBE) using a granular activated carbon trickling filter

    Energy Technology Data Exchange (ETDEWEB)

    Converse, B.M.; Schroeder, E.D.; Chang, D.P.Y.

    1999-07-01

    A pilot scale trickling filter was constructed using granular activated carbon (GAC) as the packing medium and inoculated with a microbial culture known to degrade MTBE. The packing dimensions were 0.076 m in diameter and 0.22 m deep. The unit operated with recycling flow for two months before a biofilm was observed on the GAC. After two additional months the biofilm had visibly spread throughout the packing. A few pieces of GAC were placed in a sealed bottle with MTBE-contaminated water and nutrients. Headspace analysis performed over 14 days confirmed that MTBE degradation was occurring. The trickling filter was converted to continuous flow and operated for one month at a nominal flow rate of 0.1 L/min and a hydraulic loading rate of 32 m{sup 3}/m{sup 2}-d. Samples were collected for analysis at the spray nozzle and at the bottom of the trickling filter. Fractional removal varied with influent MTBE concentration, temperature and liquid flow rate. Percent MTBE removal was as high as 85%. A mechanical failure resulted in the trickling filter bed drying and percent removal dropping to less than 1 percent. However, the system recovered within five days.

  17. Breakage mechanics for granular materials in surface-reactive environments

    Science.gov (United States)

    Zhang, Yida; Buscarnera, Giuseppe

    2018-03-01

    It is known that the crushing behaviour of granular materials is sensitive to the state of the fluids occupying the pore space. Here, a thermomechanical theory is developed to link such macroscopic observations with the physico-chemical processes operating at the microcracks of individual grains. The theory relies on the hypothesis that subcritical fracture propagation at intra-particle scale is the controlling mechanism for the rate-dependent, water-sensitive compression of granular specimens. First, the fracture of uniaxially compressed particles in surface-reactive environments is studied in light of irreversible thermodynamics. Such analysis recovers the Gibbs adsorption isotherm as a central component linking the reduction of the fracture toughness of a solid to the increase of vapour concentration. The same methodology is then extended to assemblies immersed in wet air, for which solid-fluid interfaces have been treated as a separate phase. It is shown that this choice brings the solid surface energy into the dissipation equations of the granular matrix, thus providing a pathway to (i) integrate the Gibbs isotherm with the continuum description of particle assemblies and (ii) reproduce the reduction of their yield strength in presence of high relative humidity. The rate-effects involved in the propagation of cracks and the evolution of breakage have been recovered by considering non-homogenous dissipation potentials associated with the creation of surface area at both scales. It is shown that the proposed model captures satisfactorily the compression response of different types of granular materials subjected to varying relative humidity. This result was achieved simply by using parameters based on the actual adsorption characteristics of the constituting minerals. The theory therefore provides a physically sound and thermodynamically consistent framework to study the behaviour of granular solids in surface-reactive environments.

  18. Granularity as a Cognitive Factor in the Effectiveness of Business Process Model Reuse

    Science.gov (United States)

    Holschke, Oliver; Rake, Jannis; Levina, Olga

    Reusing design models is an attractive approach in business process modeling as modeling efficiency and quality of design outcomes may be significantly improved. However, reusing conceptual models is not a cost-free effort, but has to be carefully designed. While factors such as psychological anchoring and task-adequacy in reuse-based modeling tasks have been investigated, information granularity as a cognitive concept has not been at the center of empirical research yet. We hypothesize that business process granularity as a factor in design tasks under reuse has a significant impact on the effectiveness of resulting business process models. We test our hypothesis in a comparative study employing high and low granularities. The reusable processes provided were taken from widely accessible reference models for the telecommunication industry (enhanced Telecom Operations Map). First experimental results show that Recall in tasks involving coarser granularity is lower than in cases of finer granularity. These findings suggest that decision makers in business process management should be considerate with regard to the implementation of reuse mechanisms of different granularities. We realize that due to our small sample size results are not statistically significant, but this preliminary run shows that it is ready for running on a larger scale.

  19. PALLADIUM-FACILITATED ELECTROLYTIC DECHLORINATION OF 2-CHLOROBIPHENYL USING A GRANULAR-GRAPHITE ELECTRODE.

    Science.gov (United States)

    Palladium-assisted electrocatalytic dechlorination of 2-chlorobiphenyl (2-Cl BP) in aqueous solutions was conducted in a membrane-separated electrochemical reactor with granular-graphite packed electrodes. The dechlorination took place at a granular-graphite cathode while Pd was ...

  20. Granular cell tumor in an endangered Puerto Rican Amazon parrot (Amazon vittata)

    Science.gov (United States)

    Quist, C.F.; Latimer, K.S.; Goldade, S.L.; Rivera, A.; Dein, F.J.

    1999-01-01

    A 3 cm diameter mass from the metacarpus of a Puerto Rican Amazon parrot was diagnosed as a granular cell tumour based on light microscopy. The cytoplasmic granules were periodic-acid Schiff positive and diastase resistant. Ultrastructural characteristics of the cells included convoluted nuclei and the presence of numerous cytoplasmic tertiary lysosomes. This is only the second granular cell tumour reported in a bird. We speculate that most granular cell tumours are derived from cells that are engaged in some type of cellular degradative process, creating a similar morphologic appearance, but lacking a uniform histogenesis.

  1. Quantifying non-ergodic dynamics of force-free granular gases.

    Science.gov (United States)

    Bodrova, Anna; Chechkin, Aleksei V; Cherstvy, Andrey G; Metzler, Ralf

    2015-09-14

    Brownian motion is ergodic in the Boltzmann-Khinchin sense that long time averages of physical observables such as the mean squared displacement provide the same information as the corresponding ensemble average, even at out-of-equilibrium conditions. This property is the fundamental prerequisite for single particle tracking and its analysis in simple liquids. We study analytically and by event-driven molecular dynamics simulations the dynamics of force-free cooling granular gases and reveal a violation of ergodicity in this Boltzmann-Khinchin sense as well as distinct ageing of the system. Such granular gases comprise materials such as dilute gases of stones, sand, various types of powders, or large molecules, and their mixtures are ubiquitous in Nature and technology, in particular in Space. We treat-depending on the physical-chemical properties of the inter-particle interaction upon their pair collisions-both a constant and a velocity-dependent (viscoelastic) restitution coefficient ε. Moreover we compare the granular gas dynamics with an effective single particle stochastic model based on an underdamped Langevin equation with time dependent diffusivity. We find that both models share the same behaviour of the ensemble mean squared displacement (MSD) and the velocity correlations in the limit of weak dissipation. Qualitatively, the reported non-ergodic behaviour is generic for granular gases with any realistic dependence of ε on the impact velocity of particles.

  2. In situ grain fracture mechanics during uniaxial compaction of granular solids

    Science.gov (United States)

    Hurley, R. C.; Lind, J.; Pagan, D. C.; Akin, M. C.; Herbold, E. B.

    2018-03-01

    Grain fracture and crushing are known to influence the macroscopic mechanical behavior of granular materials and be influenced by factors such as grain composition, morphology, and microstructure. In this paper, we investigate grain fracture and crushing by combining synchrotron x-ray computed tomography and three-dimensional x-ray diffraction to study two granular samples undergoing uniaxial compaction. Our measurements provide details of grain kinematics, contacts, average intra-granular stresses, inter-particle forces, and intra-grain crystal and fracture plane orientations. Our analyses elucidate the complex nature of fracture and crushing, showing that: (1) the average stress states of grains prior to fracture vary widely in their relation to global and local trends; (2) fractured grains experience inter-particle forces and stored energies that are statistically higher than intact grains prior to fracture; (3) fracture plane orientations are primarily controlled by average intra-granular stress and contact fabric rather than the orientation of the crystal lattice; (4) the creation of new surfaces during fracture accounts for a very small portion of the energy dissipated during compaction; (5) mixing brittle and ductile grain materials alters the grain-scale fracture response. The results highlight an application of combined x-ray measurements for non-destructive in situ analysis of granular solids and provide details about grain fracture that have important implications for theory and modeling.

  3. Effective elasticity coefficients of native rocks and consolidated granular matter

    International Nuclear Information System (INIS)

    Schulz, Beatrix M.; Schulz, Michael

    2008-01-01

    The elastic coefficients of binary heterogeneous materials, such as several native rock materials or consolidated granular matter will be determined in terms of a perturbation expansion. Furthermore, in order to check the validity of the obtained results, these are compared with numerical investigations using Boole's model of randomly distributed spheres. Finally, we apply the results on several classes of native rocks and consolidated granular materials

  4. Microbiological aspects of granular methanogenic sludge

    NARCIS (Netherlands)

    Dolfing, J.

    1987-01-01

    The settling characteristics of anaerobic sludge are enhanced by the formation of microbial conglomerates. Various types of conglomerates having different structures, were distinguished in the present study, viz. granules, pellets and flocs (chapter 1). Granular methanogenic sludge, often

  5. Microservices: Granularity vs. Performance

    OpenAIRE

    Shadija, Dharmendra; Rezai, Mo; Hill, Richard

    2017-01-01

    Microservice Architectures (MA) have the potential to increase the agility of software development. In an era where businesses require software applications to evolve to support emerging software requirements, particularly for Internet of Things (IoT) applications, we examine the issue of microservice granularity and explore its effect upon application latency. Two approaches to microservice deployment are simulated; the first with microservices in a single container, and the second with micr...

  6. Anomalous infrared absorption in granular superconductors

    International Nuclear Information System (INIS)

    Carr, G.L.; Garland, J.C.; Tanner, D.B.

    1983-01-01

    Granular superconductors are shown to have a far-infrared absorption that is larger when the samples are superconducting than when they are normal. By constrast, theoretical models for these materials predict that when the samples become superconducting, the absorption should decrease

  7. Hadron showers in a highly granular calorimeter

    International Nuclear Information System (INIS)

    Lutz, Benjamin

    2010-11-01

    A future electron-positron collider like the planned International Linear Collider (ILC) needs excellent detectors to exploit the full physics potential. Different detector concepts have been evaluated for the ILC and two concepts on the particle-flow approach were validated. To make particle-flow work, a new type of imaging calorimeters is necessary in combination with a high performance tracking system, to be able to track the single particles through the full detector system. These calorimeters require an unprecedented level of both longitudinal and lateral granularity. Several calorimeter technologies promise to reach the required readout segmentation and are currently studied. This thesis addresses one of these: The analogue hadron calorimeter technology. It combines work on the technological aspects of a highly granular calorimeter with the study of hadron shower physics. The analogue hadron calorimeter technology joins a classical scintillator-steel sandwich design with a modern photo-sensor technology, the silicon photomultiplier (SiPM). The SiPM is a millimetre sized, magnetic field insensitive, and low cost photo-sensor, that opens new possibilities in calorimeter design. This thesis outlines the working principle and characteristics of these devices. The requirements for an application specific integrated circuit (ASIC) to read the SiPM are discussed; the performance of a prototype chip for SiPM readout, the SPIROC, is quantified. Also the SiPM specific reconstruction of a multi-thousand channel prototype calorimeter, the CALICE AHCAL, is explained; the systematic uncertainty of the calibration method is derived. The AHCAL does not only offer a test of the calorimeter technology, it also allows to record hadron showers with an unprecedented level of details. Test-beam measurements have been performed with the AHCAL and provide a unique sample for the development of novel analysis techniques and the validation of hadron shower simulations. A method to

  8. Hadron showers in a highly granular calorimeter

    Energy Technology Data Exchange (ETDEWEB)

    Lutz, Benjamin

    2010-11-15

    A future electron-positron collider like the planned International Linear Collider (ILC) needs excellent detectors to exploit the full physics potential. Different detector concepts have been evaluated for the ILC and two concepts on the particle-flow approach were validated. To make particle-flow work, a new type of imaging calorimeters is necessary in combination with a high performance tracking system, to be able to track the single particles through the full detector system. These calorimeters require an unprecedented level of both longitudinal and lateral granularity. Several calorimeter technologies promise to reach the required readout segmentation and are currently studied. This thesis addresses one of these: The analogue hadron calorimeter technology. It combines work on the technological aspects of a highly granular calorimeter with the study of hadron shower physics. The analogue hadron calorimeter technology joins a classical scintillator-steel sandwich design with a modern photo-sensor technology, the silicon photomultiplier (SiPM). The SiPM is a millimetre sized, magnetic field insensitive, and low cost photo-sensor, that opens new possibilities in calorimeter design. This thesis outlines the working principle and characteristics of these devices. The requirements for an application specific integrated circuit (ASIC) to read the SiPM are discussed; the performance of a prototype chip for SiPM readout, the SPIROC, is quantified. Also the SiPM specific reconstruction of a multi-thousand channel prototype calorimeter, the CALICE AHCAL, is explained; the systematic uncertainty of the calibration method is derived. The AHCAL does not only offer a test of the calorimeter technology, it also allows to record hadron showers with an unprecedented level of details. Test-beam measurements have been performed with the AHCAL and provide a unique sample for the development of novel analysis techniques and the validation of hadron shower simulations. A method to

  9. NMR experiments on a three-dimensional vibrofluidized granular medium

    Science.gov (United States)

    Huan, Chao; Yang, Xiaoyu; Candela, D.; Mair, R. W.; Walsworth, R. L.

    2004-04-01

    A three-dimensional granular system fluidized by vertical container vibrations was studied using pulsed field gradient NMR coupled with one-dimensional magnetic resonance imaging. The system consisted of mustard seeds vibrated vertically at 50 Hz, and the number of layers Nl⩽4 was sufficiently low to achieve a nearly time-independent granular fluid. Using NMR, the vertical profiles of density and granular temperature were directly measured, along with the distributions of vertical and horizontal grain velocities. The velocity distributions showed modest deviations from Maxwell-Boltzmann statistics, except for the vertical velocity distribution near the sample bottom, which was highly skewed and non-Gaussian. Data taken for three values of Nl and two dimensionless accelerations Γ=15,18 were fitted to a hydrodynamic theory, which successfully models the density and temperature profiles away from the vibrating container bottom. A temperature inversion near the free upper surface is observed, in agreement with predictions based on the hydrodynamic parameter μ which is nonzero only in inelastic systems.

  10. Sealing of boreholes using natural, compatible materials: Granular salt

    International Nuclear Information System (INIS)

    Finley, R.E.; Zeuch, D.H.; Stormont, J.C.; Daemen, J.J.K.

    1994-01-01

    Granular salt can be used to construct high performance permanent seals in boreholes which penetrate rock salt formations. These seals are described as seal systems comprised of the host rock, the seal material, and the seal rock interface. The performance of these seal systems is defined by the complex interactions between these seal system components through time. The interactions are largely driven by the creep of the host formation applying boundary stress on the seal forcing host rock permeability with time. The immediate permeability of these seals is dependent on the emplaced density. Laboratory test results suggest that careful emplacement techniques could results in immediate seal system permeability on the order of 10 -16 m 2 to 10 -18 m 2 (10 -4 darcy to 10 -6 ). The visco-plastic behavior of the host rock coupled with the granular salts ability to ''heal'' or consolidate make granular salt an ideal sealing material for boreholes whose permanent sealing is required

  11. Effects of Particles Collision on Separating Gas–Particle Two-Phase Turbulent Flows

    KAUST Repository

    Sihao, L. V.; Yang, Weihua; Li, Xiangli; Li, Guohui

    2013-01-01

    A second-order moment two-phase turbulence model incorporating a particle temperature model based on the kinetic theory of granular flow is applied to investigate the effects of particles collision on separating gas–particle two-phase turbulent

  12. Extension of PIV for measuring granular temperature field in dense fluidized beds.

    NARCIS (Netherlands)

    Dijkhuizen, W.; Bokkers, G.A.; Deen, N.G.; van Sint Annaland, M.; Kuipers, J.A.M.

    2007-01-01

    In this work a particle image velocimetry (PIV) technique has been extended to enable the simultaneous measurement of the instantaneous velocity and granular temperature fields. The PIV algorithm has been specifically optimized for dense granular systems and has been thoroughly tested with

  13. Granular corneal dystrophy

    OpenAIRE

    Castillo Pérez, Alexeide de la C; Vilches Lescaille, Daysi; Noriega, Justo Luis; Martínez Balido, Daneel; León Balbón, Bárbaro Ramón; León Bernal, Danysleidi

    2015-01-01

    Las distrofias corneales constituyen un conjunto de enfermedades que presentan, en su mayoría, una baja incidencia y se caracterizan por acúmulo de material hialino o amiloide que disminuyen la transparencia corneal. La distrofia granular es una enfermedad autosómica dominante que presenta opacidades grises en el estroma superficial central de la córnea y se hacen visibles en la primera y segunda décadas de la vida, lo que provoca disminución de la visión más significativa cerca de los 40 año...

  14. Production and reception of meaningful sound in Foville's 'encompassing convolution'.

    Science.gov (United States)

    Schiller, F

    1999-04-01

    In the history of neurology. Achille Louis Foville (1799-1879) is a name deserving to be remembered. In the course of time, his circonvolution d'enceinte of 1844 (surrounding the Sylvian fissure) became the 'convolution encompassing' every aspect of aphasiology, including amusia, ie., the localization in a coherent semicircle of semicircle of cerebral cortext serving the production and perception of language, song and instrumental music in health and disease.

  15. Bonding Strength Effects in Hydro-Mechanical Coupling Transport in Granular Porous Media by Pore-Scale Modeling

    Directory of Open Access Journals (Sweden)

    Zhiqiang Chen

    2016-03-01

    Full Text Available The hydro-mechanical coupling transport process of sand production is numerically investigated with special attention paid to the bonding effect between sand grains. By coupling the lattice Boltzmann method (LBM and the discrete element method (DEM, we are able to capture particles movements and fluid flows simultaneously. In order to account for the bonding effects on sand production, a contact bond model is introduced into the LBM-DEM framework. Our simulations first examine the experimental observation of “initial sand production is evoked by localized failure” and then show that the bonding or cement plays an important role in sand production. Lower bonding strength will lead to more sand production than higher bonding strength. It is also found that the influence of flow rate on sand production depends on the bonding strength in cemented granular media, and for low bonding strength sample, the higher the flow rate is, the more severe the erosion found in localized failure zone becomes.

  16. Leaching and accumulation of trace elements in sulfate reducing granular sludge under concomitant thermophilic and low pH conditions

    KAUST Repository

    Gonzalez-Gil, Graciela; Lopes, Sí lvia I C; Saikaly, Pascal; Lens, Piet Nl L

    2012-01-01

    The leaching and/or accumulation of trace elements in sulfate reducing granular sludge systems was investigated. Two thermophilic up-flow anaerobic sludge bed (UASB) reactors operated at pH 5 were fed with sucrose (4gCODl reactor -1d -1) and sulfate at different COD/SO 4 2- ratios. During the start-up of such acidogenic systems, an initial leaching of trace elements from the inoculum sludge occurred regardless of trace elements supplementation in the reactor influent. The granular sludge maintained the physical structure despite high Fe leaching. After start-up and nonetheless the acidic conditions, Co, Ni, Cu, Zn, Mo and Se were retained or accumulated by the sludge when added. Particularly, Ni and Co accumulated in the carbonates and exchangeable fractions ensuring potential bioavailability. Otherwise, the initial stock in the inoculum sludge sufficed to operate the process for nearly 1year without supplementation of trace elements and no significant sludge wash-out occurred. © 2012 Elsevier Ltd.

  17. Leaching and accumulation of trace elements in sulfate reducing granular sludge under concomitant thermophilic and low pH conditions

    KAUST Repository

    Gonzalez-Gil, Graciela

    2012-12-01

    The leaching and/or accumulation of trace elements in sulfate reducing granular sludge systems was investigated. Two thermophilic up-flow anaerobic sludge bed (UASB) reactors operated at pH 5 were fed with sucrose (4gCODl reactor -1d -1) and sulfate at different COD/SO 4 2- ratios. During the start-up of such acidogenic systems, an initial leaching of trace elements from the inoculum sludge occurred regardless of trace elements supplementation in the reactor influent. The granular sludge maintained the physical structure despite high Fe leaching. After start-up and nonetheless the acidic conditions, Co, Ni, Cu, Zn, Mo and Se were retained or accumulated by the sludge when added. Particularly, Ni and Co accumulated in the carbonates and exchangeable fractions ensuring potential bioavailability. Otherwise, the initial stock in the inoculum sludge sufficed to operate the process for nearly 1year without supplementation of trace elements and no significant sludge wash-out occurred. © 2012 Elsevier Ltd.

  18. Micromechanical definition of an entropy for quasi-static deformation of granular materials

    NARCIS (Netherlands)

    Rothenburg, L.; Kruyt, Nicolaas P.

    2009-01-01

    A micromechanical theory is formulated for quasi-static deformation of granular materials, which is based on information theory. A reasoning is presented that leads to the definition of an information entropy that is appropriate for quasi-static deformation of granular materials. This definition is

  19. Discrete Element study of granular material - Bumpy wall interface behavior

    Science.gov (United States)

    El Cheikh, Khadija; Rémond, Sébastien; Pizette, Patrick; Vanhove, Yannick; Djelal, Chafika

    2016-09-01

    This paper presents a DEM study of a confined granular material sheared between two parallel bumpy walls. The granular material consists of packed dry spherical particles. The bumpiness is modeled by spheres of a given diameter glued on horizontal planes. Different bumpy surfaces are modeled by varying diameter or concentration of glued spheres. The material is sheared by moving the two bumpy walls at fixed velocity. During shear, the confining pressure applied on each bumpy wall is controlled. The effect of wall bumpiness on the effective friction coefficient and on the granular material behavior at the bumpy walls is reported for various shearing conditions. For given bumpiness and confining pressure that we have studied, it is found that the shear velocity does not affect the shear stress. However, the effective friction coefficient and the behavior of the granular material depend on the bumpiness. When the diameter of the glued spheres is larger than about the average grains diameter of the medium, the latter is uniformly sheared and the effective friction coefficient remains constant. For smaller diameters of the glued spheres, the effective friction coefficient increases with the diameter of glued spheres. The influence of glued spheres concentration is significant only for small glued spheres diameters, typically half of average particle diameter of the granular material. In this case, increasing the concentration of glued spheres leads to a decrease in effective friction coefficient and to shear localization at the interface. For different diameters and concentrations of glued spheres, we show that the effect of bumpiness on the effective friction coefficient can be characterized by the depth of interlocking.

  20. Fragility and hysteretic creep in frictional granular jamming.

    Science.gov (United States)

    Bandi, M M; Rivera, M K; Krzakala, F; Ecke, R E

    2013-04-01

    The granular jamming transition is experimentally investigated in a two-dimensional system of frictional, bidispersed disks subject to quasistatic, uniaxial compression without vibrational disturbances (zero granular temperature). Three primary results are presented in this experimental study. First, using disks with different static friction coefficients (μ), we experimentally verify numerical results that predict jamming onset at progressively lower packing fractions with increasing friction. Second, we show that the first compression cycle measurably differs from subsequent cycles. The first cycle is fragile-a metastable configuration with simultaneous jammed and unjammed clusters-over a small packing fraction interval (φ(1)disk displacements over the same packing fraction interval. This fragile behavior is explained through a percolation mechanism of stressed contacts where cluster growth exhibits spatial correlation with disk displacements and contributes to recent results emphasizing fragility in frictional jamming. Control experiments show that the fragile state results from the experimental incompatibility between the requirements for zero friction and zero granular temperature. Measurements with several disk materials of varying elastic moduli E and friction coefficients μ show that friction directly controls the start of the fragile state but indirectly controls the exponential pressure rise. Finally, under repetitive loading (compression) and unloading (decompression), we find the system exhibits pressure hysteresis, and the critical packing fraction φ(c) increases slowly with repetition number. This friction-induced hysteretic creep is interpreted as the granular pack's evolution from a metastable to an eventual structurally stable configuration. It is shown to depend on the quasistatic step size Δφ, which provides the only perturbative mechanism in the experimental protocol, and the friction coefficient μ, which acts to stabilize the pack.

  1. Magnetic heat pump flow director

    Science.gov (United States)

    Howard, Frank S. (Inventor)

    1995-01-01

    A fluid flow director is disclosed. The director comprises a handle body and combed-teeth extending from one side of the body. The body can be formed of a clear plastic such as acrylic. The director can be used with heat exchangers such as a magnetic heat pump and can minimize the undesired mixing of fluid flows. The types of heat exchangers can encompass both heat pumps and refrigerators. The director can adjust the fluid flow of liquid or gas along desired flow directions. A method of applying the flow director within a magnetic heat pump application is also disclosed where the comb-teeth portions of the director are inserted into the fluid flow paths of the heat pump.

  2. Wave propagation of spectral energy content in a granular chain

    Directory of Open Access Journals (Sweden)

    Shrivastava Rohit Kumar

    2017-01-01

    Full Text Available A mechanical wave is propagation of vibration with transfer of energy and momentum. Understanding the spectral energy characteristics of a propagating wave through disordered granular media can assist in understanding the overall properties of wave propagation through inhomogeneous materials like soil. The study of these properties is aimed at modeling wave propagation for oil, mineral or gas exploration (seismic prospecting or non-destructive testing of the internal structure of solids. The focus is on the total energy content of a pulse propagating through an idealized one-dimensional discrete particle system like a mass disordered granular chain, which allows understanding the energy attenuation due to disorder since it isolates the longitudinal P-wave from shear or rotational modes. It is observed from the signal that stronger disorder leads to faster attenuation of the signal. An ordered granular chain exhibits ballistic propagation of energy whereas, a disordered granular chain exhibits more diffusive like propagation, which eventually becomes localized at long time periods. For obtaining mean-field macroscopic/continuum properties, ensemble averaging has been used, however, such an ensemble averaged spectral energy response does not resolve multiple scattering, leading to loss of information, indicating the need for a different framework for micro-macro averaging.

  3. Numerical insight into the micromechanics of jet erosion of a cohesive granular material

    Directory of Open Access Journals (Sweden)

    Cuéllar Pablo

    2017-01-01

    Full Text Available Here we investigate the physical mechanisms behind the surface erosion of a cohesive granular soil induced by an impinging jet by means of numerical simulations coupling fluid and grains at the microscale. The 2D numerical model combines the Discrete Element and Lattice Boltzmann methods (DEM-LBM and accounts for the granular cohesion with a contact model featuring a paraboloidal yield surface. Here we review first the hydrodynamical conditions imposed by the fluid jet on a solid granular packing, turning then the attention to the impact of cohesion on the erosion kinetics. Finally, the use of an additional subcritical debonding damage model based on the work of Silvani and co-workers provides a novel insight into the internal solicitation of the cohesive granular sample by the impinging jet.

  4. Numerical insight into the micromechanics of jet erosion of a cohesive granular material

    Science.gov (United States)

    Cuéllar, Pablo; Benseghier, Zeyd; Luu, Li-Hua; Bonelli, Stéphane; Delenne, Jean-Yves; Radjaï, Farhang; Philippe, Pierre

    2017-06-01

    Here we investigate the physical mechanisms behind the surface erosion of a cohesive granular soil induced by an impinging jet by means of numerical simulations coupling fluid and grains at the microscale. The 2D numerical model combines the Discrete Element and Lattice Boltzmann methods (DEM-LBM) and accounts for the granular cohesion with a contact model featuring a paraboloidal yield surface. Here we review first the hydrodynamical conditions imposed by the fluid jet on a solid granular packing, turning then the attention to the impact of cohesion on the erosion kinetics. Finally, the use of an additional subcritical debonding damage model based on the work of Silvani and co-workers provides a novel insight into the internal solicitation of the cohesive granular sample by the impinging jet.

  5. Robophysical study of jumping dynamics on granular media

    Science.gov (United States)

    Aguilar, Jeffrey; Goldman, Daniel I.

    2016-03-01

    Characterizing forces on deformable objects intruding into sand and soil requires understanding the solid- and fluid-like responses of such substrates and their effect on the state of the object. The most detailed studies of intrusion in dry granular media have revealed that interactions of fixed-shape objects during free impact (for example, cannonballs) and forced slow penetration can be described by hydrostatic- and hydrodynamic-like forces. Here we investigate a new class of granular interactions: rapid intrusions by objects that change shape (self-deform) through passive and active means. Systematic studies of a simple spring-mass robot jumping on dry granular media reveal that jumping performance is explained by an interplay of nonlinear frictional and hydrodynamic drag as well as induced added mass (unaccounted by traditional intrusion models) characterized by a rapidly solidified region of grains accelerated by the foot. A model incorporating these dynamics reveals that added mass degrades the performance of certain self-deformations owing to a shift in optimal timing during push-off. Our systematic robophysical experiment reveals both new soft-matter physics and principles for robotic self-deformation and control, which together provide principles of movement in deformable terrestrial environments.

  6. Jamming and chaotic dynamics in different granular systems

    Science.gov (United States)

    Maghsoodi, Homayoon; Luijten, Erik

    Although common in nature and industry, the jamming transition has long eluded a concrete, mechanistic explanation. Recently, Banigan et al. (Nat. Phys. 9, 288-292, 2013) proposed a method for characterizing this transition in a granular system in terms of the system's chaotic properties, as quantified by the largest Lyapunov exponent. They demonstrated that in a two-dimensional shear cell the jamming transition coincides with the bulk density at which the system's largest Lyapunov exponent changes sign, indicating a transition between chaotic and non-chaotic regimes. To examine the applicability of this observation to realistic granular systems, we study a model that includes frictional forces within an expanded phase space. Furthermore, we test the generality of the relation between chaos and jamming by investigating the relationship between jamming and the chaotic properties of several other granular systems, notably sheared systems (Howell, D., Behringer R. P., Veje C., Phys. Rev. Lett. 82, 5241-5244, 1999) and systems with a free boundary. Finally, we quantify correlations between the largest Lyapunov vector and collective rearrangements of the system to demonstrate the predictive capabilities enabled by adopting this perspective of jamming.

  7. Some effects of gas-induced fluidization in dry granular media

    Energy Technology Data Exchange (ETDEWEB)

    Nermoen, Anders

    2010-06-15

    The main body of this thesis consists of three papers in which aspects of fluid induced deformation in granular materials are studied. Insight from experiments, dimensional analysis, numerical modeling and analytic predictions are combined to interpret observations various aspects of piercement structures in the geological record. A fourth paper is included showing how analogue modeling has been used to understand a geological processes. Paper 1 presents experimental work on the segregation pattern forming in partially fluidized, bi-modal sized granular mixtures. The experiments are performed on a vertically oriented Hele-Shaw cell (HS-cell), the narrow box between two parallel glass plates, filled with glass beads. Gas flow is imparted through the bottom of the bed causing fluidization when the system is driven at velocities exceeding a critical limit. The co-existence of fluidized and static zones is termed partial fluidization and occurs when the imposed gas flux is insufficient to fluidize the whole system. Within the fluidized zones, the particles re-organize and the large particles sediment down while the small particles remains fluidized. The re-organization is caused by differences in the ratio of the weight to the viscous drag. A pipe-like pattern develops due to a feedback mechanism in which the flow is focused through domains dominated by large particles. The focusing of the flow localizes the fluidization, which in turn enables the sedimentation of the large grains. Paper 2 presents an experimental and analytical study of the critical conditions for fluidization of a dry granular material. Based on the experiments, we find that the critical velocity of fluidization scales almost linear with the ratio of the filling height to the inlet width. An analytic model for the pressure field is obtained by solving the Laplace equation for the velocity boundary conditions given by the geometry of the experimental setup. By integrating the vertical component of the

  8. Kovacs-Like Memory Effect in Driven Granular Gases

    Science.gov (United States)

    Prados, A.; Trizac, E.

    2014-05-01

    While memory effects have been reported for dense enough disordered systems such as glasses, we show here by a combination of analytical and simulation techniques that they are also intrinsic to the dynamics of dilute granular gases. By means of a certain driving protocol, we prepare the gas in a state where the granular temperature T coincides with its long time limit. However, T does not subsequently remain constant but exhibits a nonmonotonic evolution before reaching its nonequilibrium steady value. The corresponding so-called Kovacs hump displays a normal behavior for weak dissipation (as observed in molecular systems) but is reversed under strong dissipation, where it, thus, becomes anomalous.

  9. A new method for measurement of granular velocities

    International Nuclear Information System (INIS)

    Nyborg Andersen, B.

    1984-01-01

    A new, supplementary method to measure granular velocities is presented. The method utilizes the Doppler shift caused by the line of sight component of the solar rotation to cause a wavelength shift through spectral lines as function of heliocentric angle. By measuring the center-to-limb variation of the granular intensity fluctations at different wavelength positions in the lines, the velocities are found. To do this, assumptions regarding the geometrical structure of the velocity and intensity fields have to be made. Preliminary application of the method results in a steep velocity gradient suggesting zero velocity at a hight of 200 km above tau 500 = 1. Possible causes are discussed

  10. Multi-scale mechanics of granular solids from grain-resolved X-ray measurements

    Science.gov (United States)

    Hurley, R. C.; Hall, S. A.; Wright, J. P.

    2017-11-01

    This work discusses an experimental technique for studying the mechanics of three-dimensional (3D) granular solids. The approach combines 3D X-ray diffraction and X-ray computed tomography to measure grain-resolved strains, kinematics and contact fabric in the bulk of a granular solid, from which continuum strains, grain stresses, interparticle forces and coarse-grained elasto-plastic moduli can be determined. We demonstrate the experimental approach and analysis of selected results on a sample of 1099 stiff, frictional grains undergoing multiple uniaxial compression cycles. We investigate the inter-particle force network, elasto-plastic moduli and associated length scales, reversibility of mechanical responses during cyclic loading, the statistics of microscopic responses and microstructure-property relationships. This work serves to highlight both the fundamental insight into granular mechanics that is furnished by combined X-ray measurements and describes future directions in the field of granular materials that can be pursued with such approaches.

  11. Removal of oxytetracycline and determining its biosorption properties on aerobic granular sludge.

    Science.gov (United States)

    Mihciokur, Hamdi; Oguz, Merve

    2016-09-01

    This study investigates biosorption of Oxytetracycline, a broad-spectrum antibiotic, using aerobic granular sludge as an adsorbent in aqueous solutions. A sequencing batch reactor fed by a synthetic wastewater was operated to create aerobic granular sludge. Primarily, the pore structure and surface area of granular sludge, the chemical structure and the molecular sizes of the pharmaceutical, operating conditions, such as pH, stirring rate, initial concentration of Oxytetracycline, during adsorption process was verified. Subsequently, thermodynamic and kinetic aspects of the adsorption were examined and adsorption isotherm studies were carried out. It was shown that the aerobic granular sludge was a good alternative for biosorption of this pharmaceutical. The pharmaceutical was adsorbed better at pH values of 6-8. The adsorption efficiency increased with rising ionic strength. Also, it was seen that the adsorption process was an exothermic process in terms of thermodynamics. The adsorption can be well explained by Langmuir isotherm model. Copyright © 2016 Elsevier B.V. All rights reserved.

  12. Simultaneous Cr(VI) bio-reduction and methane production by anaerobic granular sludge.

    Science.gov (United States)

    Hu, Qian; Sun, Jiaji; Sun, Dezhi; Tian, Lan; Ji, Yanan; Qiu, Bin

    2018-08-01

    Wastewater containing toxic hexavalent chromium (Cr(VI)) were treated with well-organized anaerobic granular sludge in this study. Results showed that the anaerobic granular sludge rapidly removed Cr(VI), and 2000 µg·L -1 Cr(VI) was completely eliminated within 6 min, which was much faster than the reported duration of removal by reported artificial materials. Sucrose added as a carbon source acted as an initial electron donor to reduce Cr(VI) to Cr(III). This process was considered as the main mechanism of Cr(VI) removal. Methane production by anaerobic granular sludge was improved by the addition of Cr(VI) at a concentration lower than 500 µg·L -1 . Anaerobic granular sludge had a well-organized structure, which presented good resistance against toxic Cr(VI). Trichoccus accelerated the degradation of organic substances to generate acetates with a low Cr(VI) concentration, thereby enhancing methane production by acetotrophic methanogens. Copyright © 2018 Elsevier Ltd. All rights reserved.

  13. Tunable evolutions of shock absorption and energy partitioning in magnetic granular chains

    Science.gov (United States)

    Leng, Dingxin; Liu, Guijie; Sun, Lingyu

    2018-01-01

    In this paper, we investigate the tunable characteristics of shock waves propagating in one-dimensional magnetic granular chains at various chain lengths and magnetic flux densities. According to the Hertz contact theory and Maxwell principle, a discrete element model with coupling elastic and field-induced interaction potentials of adjacent magnetic grains is proposed. We also present hard-sphere approximation analysis to describe the energy partitioning features of magnetic granular chains. The results demonstrate that, for a fixed magnetic field strength, when the chain length is greater than two times of the wave width of the solitary wave, the chain length has little effect on the output energy of the system; for a fixed chain length, the shock absorption and energy partitioning features of magnetic granular chains are remarkably influenced by varying magnetic flux densities. This study implies that the magnetic granular chain is potential to construct adaptive shock absorption components for impulse mitigation.

  14. Three-Dimensional Flows

    CERN Document Server

    Araujo, Vitor; Viana, Marcelo

    2010-01-01

    In this book, the authors present the elements of a general theory for flows on three-dimensional compact boundaryless manifolds, encompassing flows with equilibria accumulated by regular orbits. The book aims to provide a global perspective of this theory and make it easier for the reader to digest the growing literature on this subject. This is not the first book on the subject of dynamical systems, but there are distinct aspects which together make this book unique. Firstly, this book treats mostly continuous time dynamical systems, instead of its discrete counterpart, exhaustively treated

  15. Iodine Gas Trapping using Granular Porous Bismuth

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Jae Hwan; Shin, Jin Myeong; Park, Jang Jin; Park, Geun Il [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Yim, Mansung [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of)

    2014-05-15

    {sup 129}I is a radionuclide with a very long half-life of 1.57 Χ 10{sup 7} years and has negative health effects to the human body. Therefore, the emission of {sup 129}I into the air is closely regulated by the Environmental Protection Agency (EPA). Many methods for trapping gaseous {sup 129}I have been developed thus far, including wet scrubbing and adsorption using silver loaded zeolites. Although wet scrubbing can effectively remove iodine, it suffers from corrosion of the vessel due to high concentration of the scrubbing solution. Silver loaded zeolites also show effectiveness in capturing {sup 129}I gas, yet weak thermal stability of physisorbed iodine remains a challenge. We studied a novel and facile method to trap iodine gas using bismuth. Granular bismuth having many pores was synthesized using bismuth nitrate and polyvinyl alcohol as a bismuth precursor and pore forming agent, respectively. Reaction of iodine and our samples resulted in an iodine capturing capacity of more than 2 times that of the commercial grade silver exchanged zeolite (AgX). Granular porous bismuths synthesized using bismuth nitrate and PVA show a promising performance in capturing iodine gas. The use of bismuth in trapping {sup 129}I gas can reduce the process cost as bismuth is cheap. Further study is going on to improve the mechanical property of granular porous bismuths for their easy handling.

  16. Iodine Gas Trapping using Granular Porous Bismuth

    International Nuclear Information System (INIS)

    Yang, Jae Hwan; Shin, Jin Myeong; Park, Jang Jin; Park, Geun Il; Yim, Mansung

    2014-01-01

    129 I is a radionuclide with a very long half-life of 1.57 Χ 10 7 years and has negative health effects to the human body. Therefore, the emission of 129 I into the air is closely regulated by the Environmental Protection Agency (EPA). Many methods for trapping gaseous 129 I have been developed thus far, including wet scrubbing and adsorption using silver loaded zeolites. Although wet scrubbing can effectively remove iodine, it suffers from corrosion of the vessel due to high concentration of the scrubbing solution. Silver loaded zeolites also show effectiveness in capturing 129 I gas, yet weak thermal stability of physisorbed iodine remains a challenge. We studied a novel and facile method to trap iodine gas using bismuth. Granular bismuth having many pores was synthesized using bismuth nitrate and polyvinyl alcohol as a bismuth precursor and pore forming agent, respectively. Reaction of iodine and our samples resulted in an iodine capturing capacity of more than 2 times that of the commercial grade silver exchanged zeolite (AgX). Granular porous bismuths synthesized using bismuth nitrate and PVA show a promising performance in capturing iodine gas. The use of bismuth in trapping 129 I gas can reduce the process cost as bismuth is cheap. Further study is going on to improve the mechanical property of granular porous bismuths for their easy handling

  17. A new methodology to simulate subglacial deformation of water saturated granular material

    DEFF Research Database (Denmark)

    Damsgaard, Anders; Egholm, David Lundbek; Piotrowski, Jan A.

    2015-01-01

    The dynamics of glaciers are to a large degree governed by processes operating at the ice-bed interface, and one of the primary mechanisms of glacier flow over soft unconsolidated sediments is subglacial deformation. However, it has proven difficult to constrain the mechanical response of subglac......The dynamics of glaciers are to a large degree governed by processes operating at the ice-bed interface, and one of the primary mechanisms of glacier flow over soft unconsolidated sediments is subglacial deformation. However, it has proven difficult to constrain the mechanical response...... or weakening components, depending on the rate of deformation, the material state, clay mineral content, and the hydrological properties of the material. The influence of the fluid phase is negligible when relatively permeable sediment is deformed. However, by reducing the local permeability, fast deformation...... can cause variations in the pore-fluid pressure. The pressure variations weaken or strengthen the granular phase, and in turn influence the distribution of shear strain with depth. In permeable sediments the strain distribution is governed by the grain-size distribution and effective normal stress...

  18. Some comments on combusting flows and instrumentation for two-phase flows

    International Nuclear Information System (INIS)

    Whitelaw, J.H.

    1985-01-01

    Measurements of the velocity characteristics of combusting flows have been reported over the past 15 years and have Encompassed an extensive range of flows configurations. Difficulties in applying instrumentation and interpreting results are, however, still experienced and this presentation describes two experiments which are useful examples of successful applications. The first is concerned with a gas-turbine combustion chamber which involves limited optical access with high heat release but does not require measurement accuracy such as that of, for example, external aerodynamic flows. The second combines laser velocimetry with digitally compensated thermocouples to provide detailed information of a premixed, bluff-body stabilized flame and involves conditionally sampled results so as to determine the separate flow characteristics of products and reactants

  19. Numerical and experimental approaches to study soil transport and clogging in granular filters

    Science.gov (United States)

    Kanarska, Y.; Smith, J. J.; Ezzedine, S. M.; Lomov, I.; Glascoe, L. G.

    2012-12-01

    Failure of a dam by erosion ranks among the most serious accidents in civil engineering. The best way to prevent internal erosion is using adequate granular filters in the transition areas where important hydraulic gradients can appear. In case of cracking and erosion, if the filter is capable of retaining the eroded particles, the crack will seal and the dam safety will be ensured. Numerical modeling has proved to be a cost-effective tool for improving our understanding of physical processes. Traditionally, the consideration of flow and particle transport in porous media has focused on treating the media as continuum. Practical models typically address flow and transport based on the Darcy's law as a function of a pressure gradient and a medium-dependent permeability parameter. Additional macroscopic constitutes describe porosity, and permeability changes during the migration of a suspension through porous media. However, most of them rely on empirical correlations, which often need to be recalibrated for each application. Grain-scale modeling can be used to gain insight into scale dependence of continuum macroscale parameters. A finite element numerical solution of the Navier-Stokes equations for fluid flow together with Lagrange multiplier technique for solid particles was applied to the simulation of soil filtration in the filter layers of gravity dam. The numerical approach was validated through comparison of numerical simulations with the experimental results of base soil particle clogging in the filter layers performed at ERDC. The numerical simulation correctly predicted flow and pressure decay due to particle clogging. The base soil particle distribution was almost identical to those measured in the laboratory experiment. It is believed that the agreement between simulations and experimental data demonstrates the applicability of the proposed approach for prediction of the soil transport and clogging in embankment dams. To get more precise understanding of

  20. Stability of parallel flows

    CERN Document Server

    Betchov, R

    2012-01-01

    Stability of Parallel Flows provides information pertinent to hydrodynamical stability. This book explores the stability problems that occur in various fields, including electronics, mechanics, oceanography, administration, economics, as well as naval and aeronautical engineering. Organized into two parts encompassing 10 chapters, this book starts with an overview of the general equations of a two-dimensional incompressible flow. This text then explores the stability of a laminar boundary layer and presents the equation of the inviscid approximation. Other chapters present the general equation

  1. Contact force structure and force chains in 3D sheared granular systems

    Science.gov (United States)

    Mair, Karen; Jettestuen, Espen; Abe, Steffen

    2010-05-01

    Faults often exhibit accumulations of granular debris, ground up to create a layer of rock flour or fault gouge separating the rigid fault walls. Numerical simulations and laboratory experiments of sheared granular materials, suggest that applied loads are preferentially transmitted across such systems by transient force networks that carry enhanced forces. The characterisation of such features is important since their nature and persistence almost certainly influence the macroscopic mechanical stability of these systems and potentially that of natural faults. 3D numerical simulations of granular shear are a valuable investigation tool since they allow us to track individual particle motions, contact forces and their evolution during applied shear, that are difficult to view directly in laboratory experiments or natural fault zones. In characterising contact force distributions, it is important to use global structure measures that allow meaningful comparisons of granular systems having e.g. different grain size distributions, as may be expected at different stages of a fault's evolution. We therefore use a series of simple measures to characterise the structure, such as distributions and correlations of contact forces that can be mapped onto a force network percolation problem as recently proposed by Ostojic and coworkers for 2D granular systems. This allows the use of measures from percolation theory to both define and characterise the force networks. We demonstrate the application of this method to 3D simulations of a sheared granular material. Importantly, we then compare our measure of the contact force structure with macroscopic frictional behaviour measured at the boundaries of our model to determine the influence of the force networks on macroscopic mechanical stability.

  2. Nitrate adsorption from aqueous solution using granular chitosan-Fe{sup 3+} complex

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Qili [School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing, 100083 (China); Key Laboratory of Groundwater Cycle and Environment Evolution,China University of Geosciences (Beijing), Ministry of Education, Beijing, 100083 (China); Chen, Nan, E-mail: chennan@cugb.edu.cn [School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing, 100083 (China); Key Laboratory of Groundwater Cycle and Environment Evolution, China University of Geosciences (Beijing), Ministry of Education, Beijing, 100083 (China); Feng, Chuanping [School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing, 100083 (China); Key Laboratory of Groundwater Cycle and Environment Evolution, China University of Geosciences (Beijing), Ministry of Education, Beijing, 100083 (China); Hu, WeiWu [The Journal Center, China University of Geosciences (Beijing), Beijing, 100083 (China)

    2015-08-30

    Highlights: • Granular chitosan-Fe{sup 3+} complex had high performance for nitrate adsorption. • Granular chitosan-Fe{sup 3+} complex had shorter equilibrium time (1.5 h). • Nitrate adsorption was ascribed to ion exchange and electrostatic attraction. • Granular chitosan-Fe{sup 3+} complex could be regenerated using NaCl solution. - Abstract: In the present study, In order to efficiently remove nitrate, granular chitosan-Fe{sup 3+} complex with high chemical stability and good environmental adaptation was synthesized through precipitation method and characterized using SEM, XRD, BET and FTIR. The nitrate adsorption performance was evaluated by batch experiments. The results indicated that granular chitosan-Fe{sup 3+} complex was an amorphous and mesoporous material. The BET specific surface area and average pore size were 8.98 m{sup 2} g{sup −1} and 56.94 Å, respectively. The point of zero charge was obtained at pH 5. The maximum adsorption capacity reached 8.35 mg NO{sub 3}{sup −}-N g{sup −1} based on Langmuir–Freundlich model. Moreover, no significant change in the nitrate removal efficiency was observed in the pH range of 3.0–10.0. The adverse influence of sulphate on nitrate removal was the most significant, followed by bicarbonate and fluoride, whereas chloride had slightly adverse effect. Adsorption process followed the pseudo-second-order kinetic model, and the experimental equilibrium data were fitted well with the Langmuir–Freundlich and D–R isotherm models. Thermodynamic parameters revealed that nitrate adsorption was a spontaneous and exothermic process. Granular chitosan-Fe{sup 3+} complex could be effectively regenerated by NaCl solution.

  3. Evolution of fluid-like granular ejecta generated by sphere impact

    KAUST Repository

    Marston, Jeremy

    2012-05-01

    We present results from an experimental study of the speed and shape of the ejecta formed when a solid sphere impacts onto a granular bed. We use high-speed imaging at frame rates up to 100 000 f.p.s. to provide direct measurement of individual grain velocities and ejecta angles as well as the overall evolution of the granular ejecta. For larger grain sizes, the emergence velocities of the grains during the early stage flow, i.e. before the main ejecta curtain forms, increase with the kinetic energy of the impacting sphere but are inversely proportional to the time from impact. We also observe that the fastest grains, which can obtain velocities up to five times that of the impacting sphere (V g/V 0 = 5), generally emerge at the earliest times and with the lowest ejection angles. As the grain size is decreased, a more fluid-like behaviour is observed whereby the ejected material first emerges as a thin sheet of grains between the sphere and the bed surface, which is also seen when a sphere impacts a liquid pool. In this case, the sheet velocity is approximately double that of the impacting sphere (V s/V 0 = 2) and independent of the bulk packing fraction. For the finest grains we provide evidence of the existence of a vortex ring inside the ejecta curtain where grains following the air flow are entrained through the curtain. In contrast to predictions from previous studies, we find that the temporal evolution of the ejecta neck radius is not initially quadratic but rather approaches a square-root dependence on time, for the finest grains with the highest impact kinetic energy. The evolution therefore approaches that seen for the crown evolution in liquid drop impacts. By using both spherical glass beads and coarse sands, we show that the size and shape distribution are critical in determining the post-impact dynamics whereby the sands exhibit a qualitatively different response to impact, with grains ejected at lower speeds and at later times than for the glass

  4. Studies of elasticity, sound propagation and attenuation of acoustic modes in granular media: final report

    Energy Technology Data Exchange (ETDEWEB)

    Makse, Hernan A. [City College of New York, NY (United States). Levich Inst., Dept. of Physcis; Johnson, David L. [Schlumberger-Doll Research, Cambridge, MA (United States)

    2014-09-03

    This is the final report describing the results of DOE Grant # DE-FG02-03ER15458 with original termination date of April 31, 2013, which has been extended to April 31, 2014. The goal of this project is to develop a theoretical and experimental understanding of sound propagation, elasticity and dissipation in granular materials. The topic is relevant for the efficient production of hydrocarbon and for identifying and characterizing the underground formation for storage of either CO2 or nuclear waste material. Furthermore, understanding the basic properties of acoustic propagation in granular media is of importance not only to the energy industry, but also to the pharmaceutical, chemical and agricultural industries. We employ a set of experimental, theoretical and computational tools to develop a study of acoustics and dissipation in granular media. These include the concept effective mass of granular media, normal modes analysis, statistical mechanics frameworks and numerical simulations based on Discrete Element Methods. Effective mass measurements allow us to study the mechanisms of the elastic response and attenuation of acoustic modes in granular media. We perform experiments and simulations under varying conditions, including humidity and vacuum, and different interparticle force-laws to develop a fundamental understanding of the mechanisms of damping and acoustic propagation in granular media. A theoretical statistical approach studies the necessary phase space of configurations in pressure, volume fraction to classify granular materials.

  5. Memory effect in uniformly heated granular gases

    Science.gov (United States)

    Trizac, E.; Prados, A.

    2014-07-01

    We evidence a Kovacs-like memory effect in a uniformly driven granular gas. A system of inelastic hard particles, in the low density limit, can reach a nonequilibrium steady state when properly forced. By following a certain protocol for the drive time dependence, we prepare the gas in a state where the granular temperature coincides with its long time value. The temperature subsequently does not remain constant but exhibits a nonmonotonic evolution with either a maximum or a minimum, depending on the dissipation and on the protocol. We present a theoretical analysis of this memory effect at Boltzmann-Fokker-Planck equation level and show that when dissipation exceeds a threshold, the response can be called anomalous. We find excellent agreement between the analytical predictions and direct Monte Carlo simulations.

  6. ENGINEERING BULLETIN: GRANULAR ACTIVATED CARBON TREATMENT

    Science.gov (United States)

    Granular activated carbon (GAC) treatment is a physicochemical process that removes a wide variety of contaminants by adsorbing them from liquid and gas streams [1, p. 6-3]. This treatment is most commonly used to separate organic contaminants from water or air; however, it can b...

  7. Velocity distributions in dilute granular systems

    NARCIS (Netherlands)

    van Zon, J.S.; Mac Kintosh, F.C.

    2005-01-01

    We investigate the idea that velocity distributions in granular gases are determined mainly by η, the coefficient of restitution and q, which measures the relative importance of heating (or energy input) to collisions. To this end, we study by numerical simulation the properties of inelastic gases

  8. Granular cell tumor of the esophagus. Report of three cases.

    Science.gov (United States)

    Cohle, S D; McKechnie, J C; Truong, L; Jurco, S

    1981-06-01

    Granular cell tumors, (formerly called myoblastomas) involving the esophagus were encountered in three patients. In all three the tumors were asymptomatic and in two they were multiple. The first published endoscopic photographs of such a tumor are presented. The successful total removal of this neoplasm using the endoscope is described. The pathologic, radiologic and therapeutic aspects of previously reported cases of granular cell tumor of the esophagus are reviewed and compared with the three reported herein.

  9. Experimental study of energy exchanges between two coupled granular gases

    OpenAIRE

    Chastaing , J.-Y; Géminard , J.-C; Naert , A

    2016-01-01

    International audience; We report on the energy exchanges between two granular gases of different densities coupled electrome-chanically by immersed blades attached to dc motors. Zeroing the energy flux between the two subsystems, we demonstrate that an immersed blade is a convenient way to assess the properties of the granular gases, provided that the dissipation in the motor is properly taken into account. In addition, when the two gases have different densities, the fluctuations of the ene...

  10. Experimental investigation of granular dynamics close to the jamming transition

    Science.gov (United States)

    Caballero, G.; Kolb, E.; Lindner, A.; Lanuza, J.; Clément, E.

    2005-06-01

    We present different experiments on dense granular assemblies with the aim of clarifying the notion of 'jamming transition' for these assemblies of non-Brownian particles. The experimental set-ups differ in the way in which external perturbations are applied in order to unjam the systems. The first experiment monitors the response to a locally applied deformation of a model packing at rest. The two other experiments study local and collective dynamics in a granular assembly weakly excited by vibration.

  11. Fine-granularity inference and estimations to network traffic for SDN.

    Directory of Open Access Journals (Sweden)

    Dingde Jiang

    Full Text Available An end-to-end network traffic matrix is significantly helpful for network management and for Software Defined Networks (SDN. However, the end-to-end network traffic matrix's inferences and estimations are a challenging problem. Moreover, attaining the traffic matrix in high-speed networks for SDN is a prohibitive challenge. This paper investigates how to estimate and recover the end-to-end network traffic matrix in fine time granularity from the sampled traffic traces, which is a hard inverse problem. Different from previous methods, the fractal interpolation is used to reconstruct the finer-granularity network traffic. Then, the cubic spline interpolation method is used to obtain the smooth reconstruction values. To attain an accurate the end-to-end network traffic in fine time granularity, we perform a weighted-geometric-average process for two interpolation results that are obtained. The simulation results show that our approaches are feasible and effective.

  12. Fine-granularity inference and estimations to network traffic for SDN.

    Science.gov (United States)

    Jiang, Dingde; Huo, Liuwei; Li, Ya

    2018-01-01

    An end-to-end network traffic matrix is significantly helpful for network management and for Software Defined Networks (SDN). However, the end-to-end network traffic matrix's inferences and estimations are a challenging problem. Moreover, attaining the traffic matrix in high-speed networks for SDN is a prohibitive challenge. This paper investigates how to estimate and recover the end-to-end network traffic matrix in fine time granularity from the sampled traffic traces, which is a hard inverse problem. Different from previous methods, the fractal interpolation is used to reconstruct the finer-granularity network traffic. Then, the cubic spline interpolation method is used to obtain the smooth reconstruction values. To attain an accurate the end-to-end network traffic in fine time granularity, we perform a weighted-geometric-average process for two interpolation results that are obtained. The simulation results show that our approaches are feasible and effective.

  13. Interactions of Particles with Momenta of 1–10 GeV in a Highly Granular Hadronic Calorimeter with Tungsten Absorbers

    CERN Document Server

    Lam, Ching Bon; van Eijk, Bob

    Linear electron-positron colliders are proposed to complement and extend the physics programme of the Large Hadron Collider at CERN. In order to satisfy the physics goal requirements at linear colliders, detector concepts based on the Particle Flow approach are developed. Central to this approach are a high resolution tracker and a highly granular calorimeter which provide excellent jet energy resolution and background separation. The Compact Linear Collider (CLIC) is an electron-positron collider under study, aiming at centre-of-mass energies up to 3TeV. For the barrel hadronic calorimeter of experiments at CLIC, a detector with tungsten absorber plates is considered, as it is able to contain shower jets while keeping the diameter of the surrounding solenoid magnet limited. A highly granular analogue hadron calorimeter with tungsten absorbers was built by the CALICE collaboration. This thesis presents the analysis of the low-momentum data (1 GeV $\\leq$ p $\\leq$ 10 GeV) recorded in 2010 at the CERN Proton Syn...

  14. Experimental Flow Characterization of a Flow Diverting Device

    Science.gov (United States)

    Sparrow, Eph; Chow, Ricky; Campbell, Gary; Divani, Afshin; Sheng, Jian

    2012-11-01

    Flow diverters, such as the Pipeline Embolization Device, are a new class of endovascular devices for the treatment of intracranial aneurysms. While clinical studies have demonstrated safety and efficacy, their impact on intra-aneurysmal flow is not confirmed experimentally. As such, optimization of the flow diversion behavior is not currently possible. A quasi-3D PIV technique was developed and applied in various glass models at Re = 275 and 550 to determine the changes to flow characteristics due to the deployment of a flow diverter across the aneurysm neck. Outcomes such as mean velocity, wall shear stress, and others metrics will be presented. Glass models with varying radii of curvature and aneurysm locations will be examined. Experiments were performed in a fully index-matched flow facility using ~10 μm diameter polystyrene particles doped with Rhodium 6G dye. The particles were illuminated with a 532nm laser sheet and observed with a CCD camera and a 592nm +/-43 nm bandpass filter. A quasi 3D flow field was reconstructed from multiple orthogonal planes (spaced 0.4mm apart) encompassing the entire glass model. Wall stresses were evaluated from the near-wall flow viscous stresses.

  15. Analysis of Cylindrical Granular Material Silos under Seismic Excitation

    Directory of Open Access Journals (Sweden)

    Christoph Butenweg

    2017-07-01

    Full Text Available Silos generally work as storage structures between supply and demand for various goods, and their structural safety has long been of interest to the civil engineering profession. This is especially true for dynamically loaded silos, e.g., in case of seismic excitation. Particularly thin-walled cylindrical silos are highly vulnerable to seismic induced pressures, which can cause critical buckling phenomena of the silo shell. The analysis of silos can be carried out in two different ways. In the first, the seismic loading is modeled through statically equivalent loads acting on the shell. Alternatively, a time history analysis might be carried out, in which nonlinear phenomena due to the filling as well as the interaction between the shell and the granular material are taken into account. The paper presents a comparison of these approaches. The model used for the nonlinear time history analysis considers the granular material by means of the intergranular strain approach for hypoplasticity theory. The interaction effects between the granular material and the shell is represented by contact elements. Additionally, soil–structure interaction effects are taken into account.

  16. The CMS High Granularity Calorimeter for the High Luminosity LHC

    CERN Document Server

    Sauvan, Jean-baptiste

    2017-01-01

    The High Luminosity LHC (HL-LHC) will integrate 10 times more luminosity than the LHC, posing significant challenges for radiation tolerance and event pileup on detectors, especially for forward calorimetry, and hallmarks the issue for future colliders. As part of its HL-LHC upgrade program, the CMS collaboration is designing a High Granularity Calorimeter to replace the existing endcap calorimeters. It features unprecedented transverse and longitudinal segmentation for both electromagnetic (ECAL) and hadronic (HCAL) compartments. This will facilitate particle-flow calorimetry, where the fine structure of showers can be measured and used to enhance pileup rejection and particle identification, whilst still achieving good energy resolution. The ECAL and a large fraction of HCAL will be based on hexagonal silicon sensors of 0.5 - 1 cm$^2$ cell size, with the remainder of the HCAL based on highly-segmented scintillators with silicon photomultiplier (SiPM) readout. The intrinsic high-precision timing capabilities...

  17. Dynamical Heterogeneity in Granular Fluids and Structural Glasses

    Science.gov (United States)

    Avila, Karina E.

    Our current understanding of the dynamics of supercooled liquids and other similar slowly evolving (glassy) systems is rather limited. One aspect that is particularly poorly understood is the origin and behavior of the strong non trivial fluctuations that appear in the relaxation process toward equilibrium. Glassy systems and granular systems both present regions of particles moving cooperatively and at different rates from other regions. This phenomenon is known as spatially heterogeneous dynamics. A detailed explanation of this phenomenon may lead to a better understanding of the slow relaxation process, and perhaps it could even help to explain the presence of the glass transition. This dissertation concentrates on studying dynamical heterogeneity by analyzing simulation data for models of granular materials and structural glasses. For dissipative granular fluids, the growing behavior of dynamical heterogeneities is studied for different densities and different degrees of inelasticity in the particle collisions. The correlated regions are found to grow rapidly as the system approaches dynamical arrest. Their geometry is conserved even when probing at different cutoff length in the correlation function or when the energy dissipation in the system is increased. For structural glasses, I test a theoretical framework that models dynamical heterogeneity as originated in the presence of Goldstone modes, which emerge from a broken continuous time reparametrization symmetry. This analysis is based on quantifying the size and the spatial correlations of fluctuations in the time variable and of other kinds of fluctuations. The results obtained here agree with the predictions of the hypothesis. In particular, the fluctuations associated to the time reparametrization invariance become stronger for low temperatures, long timescales, and large coarse graining lengths. Overall, this research points to dynamical heterogeneity to be described for granular systems similarly than

  18. Whole-genome sequencing of a malignant granular cell tumor with metabolic response to pazopanib

    Science.gov (United States)

    Wei, Lei; Liu, Song; Conroy, Jeffrey; Wang, Jianmin; Papanicolau-Sengos, Antonios; Glenn, Sean T.; Murakami, Mitsuko; Liu, Lu; Hu, Qiang; Conroy, Jacob; Miles, Kiersten Marie; Nowak, David E.; Liu, Biao; Qin, Maochun; Bshara, Wiam; Omilian, Angela R.; Head, Karen; Bianchi, Michael; Burgher, Blake; Darlak, Christopher; Kane, John; Merzianu, Mihai; Cheney, Richard; Fabiano, Andrew; Salerno, Kilian; Talati, Chetasi; Khushalani, Nikhil I.; Trump, Donald L.; Johnson, Candace S.; Morrison, Carl D.

    2015-01-01

    Granular cell tumors are an uncommon soft tissue neoplasm. Malignant granular cell tumors comprise T transitions, particularly when immediately preceded by a 5′ G. A loss-of-function mutation was detected in a newly recognized tumor suppressor candidate, BRD7. No mutations were found in known targets of pazopanib. However, we identified a receptor tyrosine kinase pathway mutation in GFRA2 that warrants further evaluation. To the best of our knowledge, this is only the second reported case of a malignant granular cell tumor exhibiting a response to pazopanib, and the first whole-genome sequencing of this uncommon tumor type. The findings provide insight into the genetic basis of malignant granular cell tumors and identify potential targets for further investigation. PMID:27148567

  19. Kinematics of flow and sediment particles at entrainment and deposition

    Science.gov (United States)

    Antico, Federica; Sanches, Pedro; Aleixo, Rui; Ferreira, Rui M. L.

    2015-04-01

    A cohesionless granular bed subjected to a turbulent open-channel flow is analysed. The key objective is to clarify the kinematics of entrainment and deposition of individual sediment particles. In particular, we quantify a) the turbulent flow field in the vicinity of particles at the instants of their entrainment and of their deposition; b) the initial particle velocity and the particle velocity immediately before returning to rest. The experimental work was performed at the Hydraulics Laboratory of IST-UL in a 12.5 m long, 0.405 m wide glass-walled flume recirculating water and sediment through independent circuits. The granular bed was a 4.0 m long and 2.5 cm deep reach filled with 5 mm diameter glass beads packed (with some vibration) to a void fraction of 0.356, typical of random packing. Upstream the mobile bed reach the bed was composed of glued particles to ensure the development of a boundary layer with the same roughness. Laboratory tests were run under conditions of weak beadload transport with Shields parameters in the range 0.007 to 0.03. Froude numbers ranged from 0.63 to 0.95 while boundary Reynolds numbers were in the range 130 to 300. It was observed that the bed featured patches of regular arrangements: face centered cubic (fcc) or hexagonal close packing (hcp) blocks alternate with and body centered cubic (bcc) blocks. The resulting bed surface exhibits cleavage lines between blocks and there are spatial variations of bed elevation. The option for artificial sediment allowed for a simplified description of particle positioning at the instant of entrainment. In particular support and pivoting angles are found analytically. Skin friction angles were determind experimentally. The only relevant variables are exposure (defined as the ratio of the actual frontal projection of the exposed area to the area of a circle with 5 mm diameter) and protrusion (defined as the vertical distance between the apex of the particle and the mean local bed elevation

  20. Shear dilatancy and acoustic emission in dry and saturated granular materials

    Science.gov (United States)

    Brodsky, E. E.; Siman-Tov, S.

    2017-12-01

    Shearing of granular materials plays a strong role in naturally sheared systems as landslides and faults. Many works on granular flows have concentrated on dry materials, but relatively little work has been done on water saturated sands. Here we experimentally investigate dry versus saturated quartz-rich sand to understand the effect of the fluid medium on the rheology and acoustic waves emission of the sheared sand. The sand was sheared in a rotary shear rheometer under applied constant normal stress boundary at low (100 µm/s) to high (1 m/s) velocities. Mechanical, acoustic data and deformation were continuously recorded and imaged. For dry and water saturated experiments the granular volume remains constant for low shear velocities ( 10-3 m/s) and increases during shearing at higher velocities ( 1 m/s). Continuous imaging of the sheared sand show that the steady state shear band thickness is thicker during the high velocity steps. No significant change observed in the shear band thickness between dry and water saturated experiments. In contrast, the amount of dilation during water saturated experiments is about half the value measured for dry material. The measured decrease cannot be explained by shear band thickness change as such is not exist. However, the reduced dilation is supported by our acoustic measurements. In general, the event rate and acoustic event amplitudes increase with shear velocity. While isolated events are clearly detected during low velocities at higher the events overlap, resulting in a noisy signal. Although detection is better for saturated experiments, during the high velocity steps the acoustic energy measured from the signal is lower compared to that recorded for dry experiments. We suggest that the presence of fluid suppresses grain motion and particles impacts leading to mild increase in the internal pressure and therefore for the reduced dilation. In addition, the viscosity of fluids may influence the internal pressure via

  1. Mathematical modelling of the transport of a poorly sorted granular mixture as a debris-flow. The case of Madeira Island torrential floods in 2010

    Science.gov (United States)

    Ferreira, Rui M. L.; Oliveira, Rodrigo P.; Conde, Daniel

    2016-04-01

    On the 20th February 2010, heavy rainfall was registered at Madeira Island, North Atlantic. Stony debris flows, mudflows and mudslides ensued causing severe property loss, 1.5 m thick sediment deposits at downtown Funchal including 16th century monuments, and a death toll of 47 lives. Debris-flow fronts propagated downstream while carrying very high concentrations of solid material. These two-phase solid-fluid flows were responsible for most of the infrastructural damage across the island, due to their significantly increased mass and momentum. The objective of the present modelling work is to validate a 2DH model for torrential flows featuring the transport and interaction of several size fractions of a poorly-sorted granular mixture typical of stony debris flow in Madeira. The module for the transport of poorly-sorted material was included in STAV-2D (CERIS-IST), a shallow-water and morphology solver based on a finite-volume method using a flux-splitting technique featuring a reviewed Roe-Riemann solver, with appropriate source-term formulations to ensure full conservativeness. STAV-2D also includes formulations of flow resistance and bedload transport adequate for debris-flows with natural mobile beds (Ferreira et al., 2009) and has been validated with both theoretical solutions and laboratory data (Soares-Frazão et al., 2012; Canelas et al., 2013). The modelling of the existing natural and built environment is fully explicit. All buildings, streets and channels are accurately represented within the mesh geometry. Such detail is relevant for the reliability of the validation using field data, since the major sedimentary deposits within the urban meshwork of Funchal were identified and characterized in terms of volume and grain size distribution during the aftermath of the 20th February of 2010 event. Indeed, the measure of the quality of the numerical results is the agreement between simulated and estimated volume of deposited sediment and between estimated and

  2. The critical current of granular superconductor

    International Nuclear Information System (INIS)

    Ignat'ev, V.K.

    1998-01-01

    A mechanism of hyper vortex pinning in granular superconductors is proposed to describe the field dependence of the critical current density and pinning potential. The results are in a good agreement with the experiment. The model represents the peak effect and the percolation mechanism of conductivity in ceramic superconductors

  3. Tumor de células granulares bifocal em mucosa jugal

    Directory of Open Access Journals (Sweden)

    Victor Yuri Nicolau Ferreira

    Full Text Available O tumor de células granulares é uma lesão incomum que apresenta predileção pela cavidade oral, por apresentar baixa taxa de recidiva, o tratamento de escolha é a excisão cirúrgica simples. O objetivo caracterizar um caso de tumor de células granulares bifocal em mucosa jugal e explanar características clínicas e histopatológicas acerca da lesão. Relata-se o caso de uma paciente de 60 anos apresentando dois pequenos nódulos de superfície lisa em mucosa jugal, consistência fibroelástica e coloração levemente amarelada. Foi realizada a excisão cirúrgica das duas lesões a partir de uma biópsia excisional, onde microscopicamente foi observada uma neoplasia de células granulares arranjadas em ilhas, chegando ao diagnóstico de Tumor de células granulares. O diagnóstico final da lesão foi obtido a partir do exame histopatológico, visto que, a aparência clínica da lesão é inespecífica, sendo de extrema importância a realização da biópsia excisional. A paciente continua em acompanhamento há 6 meses e não demonstra recidiva da lesão.

  4. Universal scaling of permeability through the granular-to-continuum transition

    Science.gov (United States)

    Wadsworth, F. B.; Scheu, B.; Heap, M. J.; Kendrick, J. E.; Vasseur, J.; Lavallée, Y.; Dingwell, D. B.

    2015-12-01

    Magmas fragment forming a transiently granular material, which can weld back to a fluid-continuum. This process results in dramatic changes in the gas-volume fraction of the material, which impacts the gas permeability. We collate published data for the gas-volume fraction and permeability of volcanic and synthetic materials which have undergone this process to different amounts and note that in all cases there exists a discontinuity in the relationship between these two properties. By discriminating data for which good microstructural information are provided, we use simple scaling arguments to collapse the data in both the still-granular, high gas-volume fraction regime and the fluid-continuum low gas-volume fraction regime such that a universal description can be achieved. We use this to argue for the microstructural meaning of the well-described discontinuity between gas-permeability and gas-volume fraction and to infer the controls on the position of this transition between dominantly granular and dominantly fluid-continuum material descriptions. As a specific application, we consider the transiently granular magma transported through and deposited in fractures in more-coherent magmas, thought to be a primary degassing pathway in high viscosity systems. We propose that our scaling coupled with constitutive laws for densification can provide insights into the longevity of such degassing channels, informing sub-surface pressure modelling at such volcanoes.

  5. Determination of the attrition resistance of granular charcoals

    International Nuclear Information System (INIS)

    Dietz, V.R.

    1979-01-01

    A laboratory procedure has been developed to evaluate the attrition of granular adsorbent charcoals on passing an air flow through the bed. Two factors observed in plant operations were selected as relevant: (1) the characteristic structural vibrations in plant scale equipment (motors, fans, etc.) that are transmitted to charcoal particles and cause the particles to move and rub each other, and (2) the rapid air flow that results in the movement of the attrited dust. In the test a container for charcoal [50 mm diameter and 50 mm high] was vibrated at a frequency of 60 Hz and at a constant energy input manually controlled using a vibration meter in the acceleration mode. Simultaneously, air was applied and exited through glass fiber filter paper. The quantity of dust trapped on the exit filter was then determined, either optically or gravimetrically. The dust formed per minute (attrition coefficient) was found to approach a constant value. The plateau-values from sequential determinations varied with the source of the charcoal; a 5-fold difference was found among a large variety of commercial products. The first testing of a sample released the excess dust accumulated in previous handling of the charcoal. The plateau values were then attained in the succeeding tests and these were characteristic of the material. The results were compared with those obtained for the same charcoals using older test methods such as the Ball and Pan Hardness Test described in RDTM16-1T

  6. Resistance capability of microaerobic granular sludge for ...

    African Journals Online (AJOL)

    enoh

    2012-02-08

    Feb 8, 2012 ... The resistance capability to pH shock of microaerobic granular sludge for pentachlorophenol (PCP) ... process with chlorine gas in pulp and paper, leather and spinning ... nitrifying bacteria in the aerobic zone, and then trans-.

  7. SedFoam-2.0: a 3-D two-phase flow numerical model for sediment transport

    Directory of Open Access Journals (Sweden)

    J. Chauchat

    2017-11-01

    Full Text Available In this paper, a three-dimensional two-phase flow solver, SedFoam-2.0, is presented for sediment transport applications. The solver is extended from twoPhaseEulerFoam available in the 2.1.0 release of the open-source CFD (computational fluid dynamics toolbox OpenFOAM. In this approach the sediment phase is modeled as a continuum, and constitutive laws have to be prescribed for the sediment stresses. In the proposed solver, two different intergranular stress models are implemented: the kinetic theory of granular flows and the dense granular flow rheology μ(I. For the fluid stress, laminar or turbulent flow regimes can be simulated and three different turbulence models are available for sediment transport: a simple mixing length model (one-dimensional configuration only, a k − ε, and a k − ω model. The numerical implementation is demonstrated on four test cases: sedimentation of suspended particles, laminar bed load, sheet flow, and scour at an apron. These test cases illustrate the capabilities of SedFoam-2.0 to deal with complex turbulent sediment transport problems with different combinations of intergranular stress and turbulence models.

  8. SedFoam-2.0: a 3-D two-phase flow numerical model for sediment transport

    Science.gov (United States)

    Chauchat, Julien; Cheng, Zhen; Nagel, Tim; Bonamy, Cyrille; Hsu, Tian-Jian

    2017-11-01

    In this paper, a three-dimensional two-phase flow solver, SedFoam-2.0, is presented for sediment transport applications. The solver is extended from twoPhaseEulerFoam available in the 2.1.0 release of the open-source CFD (computational fluid dynamics) toolbox OpenFOAM. In this approach the sediment phase is modeled as a continuum, and constitutive laws have to be prescribed for the sediment stresses. In the proposed solver, two different intergranular stress models are implemented: the kinetic theory of granular flows and the dense granular flow rheology μ(I). For the fluid stress, laminar or turbulent flow regimes can be simulated and three different turbulence models are available for sediment transport: a simple mixing length model (one-dimensional configuration only), a k - ɛ, and a k - ω model. The numerical implementation is demonstrated on four test cases: sedimentation of suspended particles, laminar bed load, sheet flow, and scour at an apron. These test cases illustrate the capabilities of SedFoam-2.0 to deal with complex turbulent sediment transport problems with different combinations of intergranular stress and turbulence models.

  9. Removal of organochlorine pesticides from water using virgin and regenerated granular activated carbon

    Directory of Open Access Journals (Sweden)

    MIRJANA B. NINKOVIĆ

    2010-04-01

    Full Text Available Public water systems use granular activated carbon in order to eliminate pesticides. After saturation, the used activated carbon is regenerated and reused in order to reduce the costs of water production and minimize waste. In this study, the adsorption of 10 different chlorinated pesticides from water using columns packed with commercial virgin and regenerated granular activated carbon was simulated in order to compare their adsorption capacities for different chlorinated pesticides. The breakthrough curves showed that chlorinated pesticides from the group of hexachlorocyclohexane (HCH were poorly adsorbed, followed by cyclodiens as averagely adsorbed and the derivatives of halogenated aromatic hydrocarbons (DDT as strongly adsorbed. However, the adsorption capacity of regenerated granular activated carbon was considerably lower for tested pesticides compared to the virgin granular carbon. In addition, rinsing of the pesticides after the saturation point is a far more efficient process on regenerated carbon.

  10. Segregation of granular binary mixtures by a ratchet mechanism.

    Science.gov (United States)

    Farkas, Zénó; Szalai, Ferenc; Wolf, Dietrich E; Vicsek, Tamás

    2002-02-01

    We report on a segregation scheme for granular binary mixtures, where the segregation is performed by a ratchet mechanism realized by a vertically shaken asymmetric sawtooth-shaped base in a quasi-two-dimensional box. We have studied this system by computer simulations and found that most binary mixtures can be segregated using an appropriately chosen ratchet, even when the particles in the two components have the same size and differ only in their normal restitution coefficient or friction coefficient. These results suggest that the components of otherwise nonsegregating granular mixtures may be separated using our method.

  11. Permeability of granular beds emplaced in vertical drill holes

    International Nuclear Information System (INIS)

    Griffiths, S.K.; Morrison, F.A. Jr.

    1979-01-01

    To determine the permeabilities of granular materials emplaced in vertical drill holes used for underground nuclear tests, an experiment at the USDOE Nevada Test Site (NTS) was conducted. As the hole is being filled, falling material increases pressure above and within the granular beds beneath. When the filling operation starts or stops, a transient pressure response occurs within the beds; measurements of this response in beds of various compositions were made. The permeabilities after emplacement were found by matching analytical predictions of the response to these data. This information is useful in assuring the containment of nuclear tests conducted in such drill holes

  12. Effect of powder sample granularity on fluorescent intensity and on thermal parameters in x-ray diffraction Rietveld analysis

    International Nuclear Information System (INIS)

    Sparks, C.J.; Specht, E.D.; Ice, G.E.; Kumar, R.; Zschack, P.; Shiraishi, T.; Hisatsune, K.

    1991-01-01

    The effect of sample granularity on diffracted x-ray intensity was evaluated by measuring the 2θ dependence of x-ray fluorescence from various samples. Measurements were made in the symmetric geometry on samples ranging from single crystals to highly absorbing coarse powders. A characteristic shape for the absorption correction was observed. A demonstration of the sensitivity of Rietveld refined site occupation parameters is made on CuAu and Cu 50 Au 44 Ni 6 alloys refined with and without granularity corrections. These alloys provide a good example of the effect of granularity due to their large linear x-ray absorption coefficients. Sample granularity and refined thermal parameters obtained from the Rietveld analysis were found to be correlated. Without a granularity correction, the refined thermal parameters are too low and can actually become negative in an attempt to compensate for granularity. A general shape for granularity correction can be included in refinement procedures. If no granularity correction is included, data should be restricted to above 30 degrees 2θ, and thermal parameters should be ignored unless extreme precautions are taken to produce >5 μm particles and high packing densities

  13. Paediatric laryngeal granular cell tumour

    Directory of Open Access Journals (Sweden)

    Dauda Ayuba

    2009-01-01

    Full Text Available Granular cell tumour (GCT affecting the larynx is not common, especially in children. Most cases are apt to be confused with respiratory papilloma and may even be mistaken for a malignant neoplasia. We present a case of laryngeal GCT in a 12-year-old child to emphasize that the tumour should be regarded in the differential of growths affecting the larynx in children.

  14. Sorption of cobalt and nickel on anaerobic granular sludges: isotherms and sequential extraction

    NARCIS (Netherlands)

    Hullebusch, van E.D.; Peerbolte, A.; Zandvoort, M.H.; Lens, P.N.L.

    2005-01-01

    The objective of this study was to investigate the sorption capacity and the fractionation of sorbed nickel and cobalt onto anaerobic granular sludges. Two different anaerobic granular sludges (non-fed, pH = 7) were loaded with nickel and cobalt in. adsorption experiments (monometal and competitive

  15. Density-wave fronts on the brink of wet granular condensation

    Science.gov (United States)

    Huang, Kai; Zippelius, Andreas; Sand lab @ University of Bayreuth Team

    2017-11-01

    From sand dunes to Faraday heaping, driven granular matter, i.e., large agglomeration of macroscopic particles, is rich pattern forming system. When a granular material is partially wet (e.g., wet sand on the beach), a different pattern forming scenario arises due to the cohesive particle-particle interactions. Here, we focus on the formation of density-wave fronts in an oscillated wet granular layer undergoing a gas-liquid-like transition. The threshold of the instability is governed by the amplitude of the vertical vibrations. Fronts, which are curved into a spiral shape, propagate coherently along the circular rim of the container with leading edges. They are stable beyond a critical distance from the container center. Based on the measurement of the critical distance and the rotation frequency, we propose a model for the pattern formation by considering the competition between the time scale for the collapse of cohesive particles and that of the energy injection resisting this process. Deutsche Forschungsgemeinschaft (Grant No. HU1939 4-1).

  16. Granularity controlled irradiation response of cuprate superconductors

    International Nuclear Information System (INIS)

    Mishra, N.C.; Behera, D.; Mohanty, T.; Mohanta, D.; Kanjilal, D.; Mehta, G.K.; Pinto, R.

    1999-01-01

    Confining to an energy range where ions can neither create defects through elastic energy loss nor they can create defects through latent track formation, we study the effect of 140 MeV Si-ion irradiation in YBa 2 Cu 3 O 7-x (YBCO). We show that the evolution of superconducting and normal state properties in such situation is largely governed by the initial defects structure, particularly the grain boundary characteristics of the YBCO system. Both intra- and inter-granular defect structure in films of two batches were made widely different by having Ag as composite and substituent in one and by aging the other prior to irradiation. Evolution of the resistivity vs temperature characteristics in these films with ion fluence reveals the importance of Ag in bringing about both inter- and intra-granular modifications and making the films insensitive to ion irradiation

  17. "Coulombic Viscosity" In Granular Materials: Planetary and Astrophysical Implications

    Science.gov (United States)

    Marshall, J. R.

    1999-01-01

    . It is predicted that this will lead to an increase with time of both the aerodynamic and bed-dilatancy thresholds (3). Because of Paschen discharge effects in the martian atmosphere, the electrostatic charging in a saltation cloud may be partially abated, but this will lead to greater grain mobility, more charging, and thus to a charge-discharge steady state mediated by mechanical interactions. II. Dry colluvial systems: Sand avalanches on dunes, dry debris flows, talus flows, avalanches, and pyroclastic surges are examples of gravity-driven, dense granular flows where rock/grain fragmentation and grain-to-grain interactions cause triboelectrification (sometimes augmented by other electrical charging processes), and where the grain densities of the systems are such that strong dipole-dipole interactions between grains might be expected to be present. Because it is expected that the Coulombic forces between grains will cause a sluggishness or enhanced granular-flow viscosity, the motion of a grain mass will be retarded or damped so that this will assist, ultimately, in terminating the flow. The greatest Coulombic viscosity will be created in the most highly charged systems, which will also be the most energetic. Thus, grain flows have some tendency to be self-limiting by internal energy partitioning; gravitational potential is converted to Coulombic potential, which manifests itself as a drag force between the grains. III. Volcanic eruption plumes and impact ejecta curtains: The violence of these systems leads to powerful electrical charging of particulates. Lightning storms emanating from volcanic plumes are a testimony to the levels of charging. As pyroclastic grains interact forcefully and frequently within eruption plumes, it is reasonable to predict that the internal turbulent motions of the plume will be significantly damped by the Coulombic viscosity exerted by grain charges. Additional information is contained in the original.

  18. "Coulombic Viscosity" In Granular Materials: Planetary and Astrophysical Implications

    Science.gov (United States)

    Marshall, J. R.

    1999-09-01

    . It is predicted that this will lead to an increase with time of both the aerodynamic and bed-dilatancy thresholds (3). Because of Paschen discharge effects in the martian atmosphere, the electrostatic charging in a saltation cloud may be partially abated, but this will lead to greater grain mobility, more charging, and thus to a charge-discharge steady state mediated by mechanical interactions. II. Dry colluvial systems: Sand avalanches on dunes, dry debris flows, talus flows, avalanches, and pyroclastic surges are examples of gravity-driven, dense granular flows where rock/grain fragmentation and grain-to-grain interactions cause triboelectrification (sometimes augmented by other electrical charging processes), and where the grain densities of the systems are such that strong dipole-dipole interactions between grains might be expected to be present. Because it is expected that the Coulombic forces between grains will cause a sluggishness or enhanced granular-flow viscosity, the motion of a grain mass will be retarded or damped so that this will assist, ultimately, in terminating the flow. The greatest Coulombic viscosity will be created in the most highly charged systems, which will also be the most energetic. Thus, grain flows have some tendency to be self-limiting by internal energy partitioning; gravitational potential is converted to Coulombic potential, which manifests itself as a drag force between the grains. III. Volcanic eruption plumes and impact ejecta curtains: The violence of these systems leads to powerful electrical charging of particulates. Lightning storms emanating from volcanic plumes are a testimony to the levels of charging. As pyroclastic grains interact forcefully and frequently within eruption plumes, it is reasonable to predict that the internal turbulent motions of the plume will be significantly damped by the Coulombic viscosity exerted by grain charges. Additional information is contained in the original.

  19. Transport and fluctuations in granular fluids from Boltzmann equation to hydrodynamics, diffusion and motor effects

    CERN Document Server

    Puglisi, Andrea

    2015-01-01

    This brief offers a concise presentation of granular fluids from the  point of view of non-equilibrium statistical physics. The emphasis is on fluctuations, which can be large in granular fluids due to the small system size (the number of grains is many orders of magnitude smaller than in molecular fluids). Firstly, readers will be introduced to the most intriguing experiments on fluidized granular fluids. Then granular fluid theory, which goes through increasing levels of coarse-graining and emerging collective phenomena, is described. Problems and questions are initially posed at the level of kinetic theory, which describes particle densities in full or reduced phase-space. Some answers become clear through hydrodynamics, which describes the evolution of slowly evolving fields. Granular fluctuating hydrodynamics, which builds a bridge to the most recent results in non-equilibrium statistical mechanics, is also introduced. Further and more interesting answers come when the dynamics of a massive intruder are...

  20. On the One-Dimensional Steady and Unsteady Porous Flow Equation

    DEFF Research Database (Denmark)

    Andersen, O. H.; Burcharth, H. F.

    1995-01-01

    Porous flow in coarse granular media is discussed theoretically with special concern given to the variation of the flow resistance with the porosity. For steady state flow, the Navier-Stokes equation is applied as a basis for the derivations. A turbulent flow equation is suggested. Alternative...... derivations based on dimensional analysis and a pipe analogy, respectively, are discussed. For non-steady state flow, the derivations are based on a cylinder/sphere analogy leading to a virtual mass coefficient. For the fully turbulent flow regime, existing experimental data values of the quadratic flow...... resistance coefficients are presented. Moreover, a simple formula for estimation of the turbulent flow coefficient is given. Virtual mass coefficients based on existing data are presented, however, no definite conclusions can be given due to the scarce data available....