WorldWideScience

Sample records for dense granular media

  1. Sound scattering in dense granular media

    Institute of Scientific and Technical Information of China (English)

    JIA XiaoPing; LAURENT J; KHIDAS Y; LANGLOIS V

    2009-01-01

    The sound propagation in a dense granular medium is basically characterized by the ratio of wave-length to the grain size. Two types of wave transport are distinguished: one corresponds to coherent waves in the long wavelength limit, the other to short-wavelength scattered waves by the inhomoge-neous contact force networks. These multiply scattered elastic waves are shown to exhibit a diffusive characteristics of transport over long distances of propagation. Determination of the transport mean free path l* and the inelastic absorption (Q~(-1)) allows the inference of the structural properties of the material such as the heterogeneity and internal dissipation. The relevance of our experiments for seismological applications is discussed. Moreover, we apply the correlation technique of the configu-ration-specific sound scattering to monitoring the dynamic behaviour of the granular medium (irre-versible rearrangements) under strong vibration, shearing and thermal cycling, respectively.

  2. Flow of Dense Granular Media; A Peculiar Liquid

    Science.gov (United States)

    Pouliquen, Olivier

    2007-11-01

    Rice flowing out of a silo, rocks tumbling down a slope, sand avalanching on a dune, are examples of simple granular flows. Their description still represents a challenge due to the lack of constitutive laws able to describe the rich phenomenology observed with granular materials. However, the numerous experiments and simulations carried out during the last ten years have given keys for a better understanding. This talk will review the general properties of granular flows, before focusing on the dense flow regime where granular media flow like a liquid. In this regime, simple constitutive laws can be proposed, in which the granular fluid is described as a peculiar visco-plastic liquid. This talk will show that this approach gives quantitative predictions in several configurations, providing a relevant framework for adressing granular hydrodynamic problems. The second part of this presentation will discuss the limits of this approach, the important open problems, and the consequences of this development for the more complex case of mixture of grains and fluid. This work has been done with Pierre Jop, Yoel Forterre and Mickael Paihla.

  3. Multiple-contact discrete-element model for simulating dense granular media

    Science.gov (United States)

    Brodu, Nicolas; Dijksman, Joshua A.; Behringer, Robert P.

    2015-03-01

    This article presents a new force model for performing quantitative simulations of dense granular materials. Interactions between multiple contacts (MC) on the same grain are explicitly taken into account. Our readily applicable MC-DEM method retains all the advantages of discrete-element method simulations and does not require the use of costly finite-element methods. The new model closely reproduces our recent experimental measurements, including contact force distributions in full 3D, at all compression levels of the packing up to the experimental maximum limit of 13%. Comparisons with classic simulations using the nondeformable spheres approach, as well as with alternative models for interactions between multiple contacts, are provided. The success of our model, compared to these alternatives, demonstrates that interactions between multiple contacts on each grain must be included for dense granular packings.

  4. Coupled discrete element modeling of fluid injection into dense granular media

    Science.gov (United States)

    Zhang, Fengshou; Damjanac, Branko; Huang, Haiying

    2013-06-01

    The coupled displacement process of fluid injection into a dense granular medium is investigated numerically using a discrete element method (DEM) code PFC2D® coupled with a pore network fluid flow scheme. How a dense granular medium behaves in response to fluid injection is a subject of fundamental and applied research interests to better understand subsurface processes such as fluid or gas migration and formation of intrusive features as well as engineering applications such as hydraulic fracturing and geological storage in unconsolidated formations. The numerical analysis is performed with DEM executing the mechanical calculation and the network model solving the Hagen-Poiseuille equation between the pore spaces enclosed by chains of particles and contacts. Hydromechanical coupling is realized by data exchanging at predetermined time steps. The numerical results show that increase in the injection rate and the invading fluid viscosity and decrease in the modulus and permeability of the medium result in fluid flow behaviors displaying a transition from infiltration-governed to infiltration-limited and the granular medium responses evolving from that of a rigid porous medium to localized failure leading to the development of preferential paths. The transition in the fluid flow and granular medium behaviors is governed by the ratio between the characteristic times associated with fluid injection and hydromechanical coupling. The peak pressures at large injection rates when fluid leakoff is limited compare well with those from the injection experiments in triaxial cells in the literature. The numerical analysis also reveals intriguing tip kinematics field for the growth of a fluid channel, which may shed light on the occurrence of the apical inverted-conical features in sandstone and magma intrusion in unconsolidated formations.

  5. Unified rheology of vibro-fluidized dry granular media: From slow dense flows to fast gas-like regimes

    Science.gov (United States)

    Gnoli, Andrea; Lasanta, Antonio; Sarracino, Alessandro; Puglisi, Andrea

    2016-01-01

    Granular media take on great importance in industry and geophysics, posing a severe challenge to materials science. Their response properties elude known soft rheological models, even when the yield-stress discontinuity is blurred by vibro-fluidization. Here we propose a broad rheological scenario where average stress sums up a frictional contribution, generalizing conventional μ(I)-rheology, and a kinetic collisional term dominating at fast fluidization. Our conjecture fairly describes a wide series of experiments in a vibrofluidized vane setup, whose phenomenology includes velocity weakening, shear thinning, a discontinuous thinning transition, and gaseous shear thickening. The employed setup gives access to dynamic fluctuations, which exhibit a broad range of timescales. In the slow dense regime the frequency of cage-opening increases with stress and enhances, with respect to μ(I)-rheology, the decrease of viscosity. Diffusivity is exponential in the shear stress in both thinning and thickening regimes, with a huge growth near the transition. PMID:27924928

  6. Constitutive relations for steady, dense granular flows

    Science.gov (United States)

    Vescovi, D.; Berzi, D.; di Prisco, C. G.

    2011-12-01

    In the recent past, the flow of dense granular materials has been the subject of many scientific works; this is due to the large number of natural phenomena involving solid particles flowing at high concentration (e.g., debris flows and landslides). In contrast with the flow of dilute granular media, where the energy is essentially dissipated in binary collisions, the flow of dense granular materials is characterized by multiple, long-lasting and frictional contacts among the particles. The work focuses on the mechanical response of dry granular materials under steady, simple shear conditions. In particular, the goal is to obtain a complete rheology able to describe the material behavior within the entire range of concentrations for which the flow can be considered dense. The total stress is assumed to be the linear sum of a frictional and a kinetic component. The frictional and the kinetic contribution are modeled in the context of the critical state theory [8, 10] and the kinetic theory of dense granular gases [1, 3, 7], respectively. In the critical state theory, the granular material approaches a certain attractor state, independent on the initial arrangement, characterized by the capability of developing unlimited shear strains without any change in the concentration. Given that a disordered granular packing exists only for a range of concentration between the random loose and close packing [11], a form for the concentration dependence of the frictional normal stress that makes the latter vanish at the random loose packing is defined. In the kinetic theory, the particles are assumed to interact through instantaneous, binary and uncorrelated collisions. A new state variable of the problem is introduced, the granular temperature, which accounts for the velocity fluctuations. The model has been extended to account for the decrease in the energy dissipation due to the existence of correlated motion among the particles [5, 6] and to deal with non

  7. 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

  8. Simulations of Granular Media

    Science.gov (United States)

    Herrmann, H. J.; Müller, M.

    For the last ten years there has been an enormous progress in the simulation of granular media like sand or powders. These simulations consist in simulating trajectories of each particle individually. Essentially one has to solve the Newton's equations including the effects of Coulomb friction and the physics occuring at a collision. But the details of the trajectories are not important for the collective behaviour. Therefore simplifications are introduced on the smallest scales. I will introduce various methods like molecular dynamics that are used to simulate large amounts of particles (over 109). Some of these medhods are based on the exploitation of parallelisation and metacomputing. Other approaches are more stochastic (DSMC Direct Simulation Monte Carlo) which simplify the calculation of collisions, positions and collision times. Very successful has been also the use of cellular automata which have been able to predict details such as the logarithmic tale of sand heaps. I will also discuss numerical techniques used for the surrounding fluid. This can be water in the case of sedimentation or air when one studies the formation of dunes in the desert. The calculation of velocity and pressure field of the fluid are done using multigrid techniques on parallel computers. We will compare the performance of the various techniques and show some benchmarks on the dependence on the size of the system, the density of particles and the number of processors used.

  9. Gravity-driven dense granular flows

    Energy Technology Data Exchange (ETDEWEB)

    ERTAS,DENIZ; GREST,GARY S.; HALSEY,THOMAS C.; DEVINE,DOV; SILBERT,LEONARDO E.

    2000-03-29

    The authors report and analyze the results of numerical studies of dense granular flows in two and three dimensions, using both linear damped springs and Hertzian force laws between particles. Chute flow generically produces a constant density profile that satisfies scaling relations suggestive of a Bagnold grain inertia regime. The type for force law has little impact on the behavior of the system. Failure is not initiated at the surface, consistent with the absence of surface flows and different principal stress directions at vs. below the surface.

  10. Stress transmission and incipient yield flow in dense granular materials

    Science.gov (United States)

    Blumenfeld, Raphael

    2010-05-01

    Jammed granular matter transmits stresses non-uniformly like no conventional solid, especially when it is on the verge of failure. Jamming is caused by self-organization of granular matter under external loads, often giving rise to networks of force chains that support the loads non-uniformly. An ongoing debate in the literature concerns the correct way to model the static stress field in such media: good old elasticity theory or newcomer isostaticity theory. The two differ significantly and, in particular in 2D, isostaticity theory leads naturally to force chain solutions. More recently, it has been proposed that real granular materials are made of mixtures of regions, some behaving elastically and some isostatically. The theory to describe these systems has been named stato-elasticity. In this paper, I first present the rationale for stato-elasticity theory. An important step towards the construction of this theory is a good understanding of stress transmission in the regions of pure isostatic states. A brief description is given of recently derived general solutions for 2D isostatic regions with nonuniform structures, which go well beyond the over-simplistic picture of force chains. I then show how the static stress equations are related directly to incipient yield flow and derive the equations that govern yield and creep rheology of dense granular matter at the initial stages of failure. These equations are general and describe strains in granular materials of both rigid and compliant particles.

  11. Inherent Segregation in Granular Media

    Directory of Open Access Journals (Sweden)

    Sánchez-Guzmán J.

    2011-10-01

    Full Text Available A study of the inherent segregation within granular media due to the relative size of the different particles is presented. A numerical model is used to simulate granular structures. For both simulation and granular structures evaluations, probability theory is widely used. Particles are idealized by disks (2D model and spheres (3D model. Strictly uniform grain size materials, bimodal (two particle sizes and continuous are simulated. Two variables representing segregation and allowing appreciating the grain-size parameters effects are considered. In uniform materials, the presence of spontaneous structuring is observed. In bimodal and continuous materials, inherent segregation mainly depends on the ratio between maximum and minimum diameters of particle. Some practical implications of inherent segregation in geotechnical problems and other disciplines are remarked.

  12. Bipedal locomotion in granular media

    Science.gov (United States)

    Kingsbury, Mark; Zhang, Tingnan; Goldman, Daniel

    Bipedal walking, locomotion characterized by alternating swing and double support phase, is well studied on ground where feet do not penetrate the substrate. On granular media like sand however, intrusion and extrusion phases also occur. In these phases, relative motion of the two feet requires that one or both feet slip through the material, degrading performance. To study walking in these phases, we designed and studied a planarized bipedal robot (1.6 kg, 42 cm) that walked in a fluidized bed of poppy seeds. We also simulated the robot in a multibody software environment (Chrono) using granular resistive force theory (RFT) to calculate foot forces. In experiment and simulation, the robot experienced slip during the intrusion phase, with the experiment presenting additional slip due to motor control error during the double support phase. This exaggerated slip gave insight (through analysis of ground reaction forces in simulation) into how slip occurs when relative motion exists between the two feet in the granular media, where the foot with higher relative drag forces (from its instantaneous orientation, rotation, relative direction of motion, and depth) remains stationary. With this relationship, we generated walking gaits for the robot to walk with minimal slip.

  13. Characteristics of undulatory locomotion in granular media

    Science.gov (United States)

    Peng, Zhiwei; Pak, On Shun; Elfring, Gwynn J.

    2016-03-01

    Undulatory locomotion is ubiquitous in nature and observed in different media, from the swimming of flagellated microorganisms in biological fluids, to the slithering of snakes on land, or the locomotion of sandfish lizards in sand. Despite the similarity in the undulating pattern, the swimming characteristics depend on the rheological properties of different media. Analysis of locomotion in granular materials is relatively less developed compared with fluids partially due to a lack of validated force models but recently a resistive force theory in granular media has been proposed and shown useful in studying the locomotion of a sand-swimming lizard. Here we employ the proposed model to investigate the swimming characteristics of a slender filament, of both finite and infinite length, undulating in a granular medium and compare the results with swimming in viscous fluids. In particular, we characterize the effects of drifting and pitching in terms of propulsion speed and efficiency for a finite sinusoidal swimmer. We also find that, similar to Lighthill's results using resistive force theory in viscous fluids, the sawtooth swimmer is the optimal waveform for propulsion speed at a given power consumption in granular media. The results complement our understanding of undulatory locomotion and provide insights into the effective design of locomotive systems in granular media.

  14. Characteristics of undulatory locomotion in granular media

    CERN Document Server

    Peng, Zhiwei; Elfring, Gwynn J

    2015-01-01

    Undulatory locomotion is ubiquitous in nature and observed in different media, from the swimming of flagellated microorganisms in biological fluids, to the slithering of snakes on land, or the locomotion of sandfish lizards in sand. Despite the similarity in the undulating pattern, the swimming characteristics depend on the rheological properties of different media. Analysis of locomotion in granular materials is relatively less developed compared with fluids partially due to a lack of validated force models but recently a resistive force theory in granular media has been proposed and shown useful in studying the locomotion of a sand-swimming lizard. Here we employ the proposed model to investigate the swimming characteristics of a slender filament, of both finite and infinite length, undulating in a granular medium and compare the results with swimming in viscous fluids. In particular, we characterize the effects of drifting and pitching in terms of propulsion speed and efficiency for a finite sinusoidal swi...

  15. Contact micromechanics in granular media with clay

    Energy Technology Data Exchange (ETDEWEB)

    Ita, Stacey Leigh [Univ. of California, Berkeley, CA (United States)

    1994-08-01

    Many granular materials, including sedimentary rocks and soils, contain clay particles in the pores, grain contacts, or matrix. The amount and location of the clays and fluids can influence the mechanical and hydraulic properties of the granular material. This research investigated the mechanical effects of clay at grain-to-grain contacts in the presence of different fluids. Laboratory seismic wave propagation tests were conducted at ultrasonic frequencies using spherical glass beads coated with Montmorillonite clay (SWy-1) onto which different fluids were adsorbed. For all bead samples, seismic velocity increased and attenuation decreased as the contact stiffnesses increased with increasing stress demonstrating that grain contacts control seismic transmission in poorly consolidated and unconsolidated granular material. Coating the beads with clay added stiffness and introduced viscosity to the mechanical contact properties that increased the velocity and attenuation of the propagating seismic wave. Clay-fluid interactions were studied by allowing the clay coating to absorb water, ethyl alcohol, and hexadecane. Increasing water amounts initially increased seismic attenuation due to clay swelling at the contacts. Attenuation decreased for higher water amounts where the clay exceeded the plastic limit and was forced from the contact areas into the surrounding open pore space during sample consolidation. This work investigates how clay located at grain contacts affects the micromechanical, particularly seismic, behavior of granular materials. The need for this work is shown by a review of the effects of clays on seismic wave propagation, laboratory measurements of attenuation in granular media, and proposed mechanisms for attenuation in granular media.

  16. Dynamic shear jamming in dense granular suspensions under extension

    Science.gov (United States)

    Majumdar, Sayantan; Peters, Ivo R.; Han, Endao; Jaeger, Heinrich M.

    2017-01-01

    Unlike dry granular materials, a dense granular suspension like cornstarch in water can strongly resist extensional flows. At low extension rates, such a suspension behaves like a viscous fluid, but rapid extension results in a response where stresses far exceed the predictions of lubrication hydrodynamics and capillarity. To understand this remarkable mechanical response, we experimentally measure the normal force imparted by a large bulk of the suspension on a plate moving vertically upward at a controlled velocity. We observe that, above a velocity threshold, the peak force increases by orders of magnitude. Using fast ultrasound imaging we map out the local velocity profiles inside the suspension, which reveal the formation of a growing jammed region under rapid extension. This region interacts with the rigid boundaries of the container through strong velocity gradients, suggesting a direct connection to the recently proposed shear-jamming mechanism.

  17. 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.

  18. Multiscale modelling of fluid-immersed granular media

    OpenAIRE

    Clément, Christian Paul André René

    2010-01-01

    In this thesis we present numerical simulation studies of fluid-immersed granular systems using models of varying scales and complexities. These techniques are used to examine the effects of an interstitial fluid on the dynamics of dense granular beds within a number of vibrated systems. After an introduction to the field of granular materials, we present the techniques used to model both the granular dynamics and the fluid flow. We introduce various multiscale techniques to couple the mo...

  19. 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

  20. Legged-locomotion on inclined granular media

    Science.gov (United States)

    Rieser, Jennifer; Qian, Feifei; Goldman, Daniel

    Animals traverse a wide variety of complex environments, including situations in which the ground beneath them can yield (e.g. dry granular media in desert dunes). Locomotion strategies that are effective on level granular media can fail when traversing a granular slope. Taking inspiration from successful legged-locomotors in sandy, uneven settings, we explore the ability of a small (15 cm long, 100 g), six-c-shaped legged robot to run uphill in a bed of 1-mm-diameter poppy seeds, using an alternating tripod gait. Our fully automated experiments reveal that locomotor performance can depend sensitively on both environmental parameters such as the inclination angle and volume fraction of the substrate, and robot morphology and control parameters like leg shape, step frequency, and the friction between the feet of the robot and the substrate. We assess performance by measuring the average speed of the robot, and we find that the robot tends to perform better at higher step frequency and lower inclination angles, and that average speed decreases more rapidly with increasing angle for higher step frequency.

  1. Force transmission in cohesive granular media

    Science.gov (United States)

    Radjai, Farhang; Topin, Vincent; Richefeu, Vincent; Voivret, Charles; Delenne, Jean-Yves; Azéma, Emilien; El Youssoufi, Said

    2010-05-01

    We use numerical simulations to investigate force and stress transmission in cohesive granular media covering a wide class of materials encountered in nature and industrial processing. The cohesion results either from capillary bridges between particles or from the presence of a solid binding matrix filling fully or partially the interstitial space. The liquid bonding is treated by implementing a capillary force law within a debonding distance between particles and simulated by the discrete element method. The solid binding matrix is treated by means of the Lattice Element Method (LEM) based on a lattice-type discretization of the particles and matrix. Our data indicate that the exponential fall-off of strong compressive forces is a generic feature of both cohesive and noncohesive granular media both for liquid and solid bonding. The tensile forces exhibit a similar decreasing exponential distribution, suggesting that this form basically reflects granular disorder. This is consistent with the finding that not only the contact forces but also the stress components in the bulk of the particles and matrix, accessible from LEM simulations in the case of solid bonding, show an exponential fall-off. We also find that the distribution of weak compressive forces is sensitive to packing anisotropy, particle shape and particle size distribution. In the case of wet packings, we analyze the self-equilibrated forces induced by liquid bonds and show that the positive and negative particle pressures form a bi-percolating structure.

  2. Shear Profiles and Velocity Distribution in Dense Shear Granular Flow

    Institute of Scientific and Technical Information of China (English)

    WANG Deng-Ming; ZHOU You-He

    2009-01-01

    We perform DEM simulations to investigate the influence of the packing fraction γ on the,shape of mean tan-gential velocity profile in a 2D annular dense shear granular flow. There is a critical packing fraction γc. For γ < γc, the mean tangential velocity profile shows a roughly exponential decay from the shearing boundary and is almost invariant to the imposed shear rate. However, for γ γc, the tangential velocity profile exhibits a rate-dependence feature and changes from linear to nonlinear gradually with the increasing shear rate. Fhrther-more, the distributions of normalized tangential velocities at different positions along radial direction exhibit the Gaussian or the composite Gaussian distributing features.

  3. Rainwater Channelization and Infiltration in Granular Media

    Science.gov (United States)

    Cejas, Cesare; Wei, Yuli; Barrois, Remi; Durian, Douglas; Dreyfus, Remi; Compass Team

    2013-03-01

    We investigate the formation of fingered flow in dry granular media under simulated rainfall using a quasi-2D experimental set-up composed of a random close packing of mono-disperse glass beads. We determine effects of grain diameter and surface wetting properties on the formation and infiltration of water channels. For hydrophilic granular media, rainwater initially infiltrates a shallow top layer of soil creating a uniform horizontal wetting front before instabilities occur and grow to form water channels. For hydrophobic media, rainwater ponds on the soil surface rather than infiltrates and water channels may still occur at a later time when the hydraulic pressure of the ponding water exceeds the capillary repellency of the soil. We probe the kinetics of the fingering instabilities that serve as precursors for the growth and drainage of water channels. We also examine the effects of several different methods on improving rainwater channelization such as varying the level of pre-saturation, modifying the soil surface flatness, and adding superabsorbent hydrogel particles.

  4. Structure and cluster formation in granular media

    Indian Academy of Sciences (India)

    S Luding

    2005-06-01

    The two most important phenomena at the basis of granular media are excluded volume and dissipation. The former is captured by the hard sphere model and is responsible for, e.g., crystallization, the latter leads to interesting structures like clusters in non-equilibrium dynamical, freely cooling states. The freely cooling system is examined concerning the energy decay and the cluster evolution in time. Corrections for crystallization and multi-particle contacts are provided, which become more and more important with increasing density.

  5. Assessment of the kinetic-frictional model for dense granular flow

    Institute of Scientific and Technical Information of China (English)

    Boon Ho Ng; Yulong Ding; Mojtaba Ghadiri

    2008-01-01

    This paper aims to quantitatively assess the application of kinetic-frictional model to simulate the motion of dry granular materials in dense condition, in particular, the annular shearing in Couette configuration. The weight of frictional stress was varied to study the contribution of the frictional stress in dense granular flows. The results show that the pure kinetic-theory-based computational fluid dynamics (CFD) model (without frictional stress) over-predicts the dominant solids motion of dense granular flow while adding frictional stress [Schaeffer, D. G. (1987). Instability in the evolution equations describing incompressible granular flow. Journal of Differential Equations, 66(1), 19-50] with the solids pressure of [Lun, C. KTK., Savage, S. B., Jeffrey, D. J., & Chepurniy, N. (1984). Kinetic theories for granular flow: Inelastic particles in Couette flow and slightly inelastic particles in a general flow field. Journal of Fluid Mechanics, 140, 223-256] in the CFD model improves the simulation to better conform available experimental results. The results also suggest that frictional stress transmission plays an important role in dense granular flow and should not be neglected in granular flow simulations. Compatible simulation results to the experimental data are seen by increasing the weight of frictional stress to a factor of 1.25-1.5. These improved simulation results suggest the current constitutive relations (kinetic-frictional model) need to be improved in order to better reflect the real dense granular flow.

  6. Head-on collisions of dense granular jets

    CERN Document Server

    Ellowitz, Jake

    2015-01-01

    When a dense stream of dry, non-cohesive grains hits a fixed target, a collimated sheet is ejected from the impact region, very similar to what happens for a stream of water. In this study, as a continuation of the investigation why such remarkably different incident fluids produce such similar ejecta, we use discrete particle simulations to collide two unequal-width granular jets head-on in two dimensions. In addition to the familiar coherent ejecta, we observe that the impact produces a far less familiar quasi-steady-state corresponding to a uniformly translating free surface and flow field. Upon repeating such impacts with multiple continuum fluid simulations, we show that this translational speed is controlled only by the total energy dissipation rate to the power $1.5$, and is independent of the details of the jet composition. Our findings, together with those from impacts against fixed targets, challenge the principle of scattering in which material composition is inferred from observing the ejecta prod...

  7. Resonance effects on the dynamics of dense granular beds: achieving optimal energy transfer in vibrated granular systems

    NARCIS (Netherlands)

    Windows-Yule, C.R.K.; Rosato, A.D.; Thornton, A.R.; Parker, D.J.

    2015-01-01

    Using a combination of experimental techniques and discrete particle method simulations, we investigate the resonant behaviour of a dense, vibrated granular system. We demonstrate that a bed of particles driven by a vibrating plate may exhibit marked differences in its internal energy dependent on t

  8. Pneumatic fractures in confined granular media

    Science.gov (United States)

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

    2017-06-01

    We perform experiments where air is injected at a constant overpressure Pin, 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 Pin below 10 kPa, to large thick channels formed by erosion and fingers merging for high Pin 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 ) ∝dβ , where β =0.68 is a typical value for all experiments, also over time. This indicates a singularity in the curvature d2d /d w2˜κ ˜d1 -2 β , but not of the slope d w /d d ˜dβ -1 , i.e., more rounded tips rather than pointy cusps, as they would be for the case β >1 . For increasing Pin, 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 v0 is found to scale with injection pressure as v0∝Pin3/2 , while at a critical time tc 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 developed patterns. For

  9. Dynamic aerofracture or hydrofracture of dense granular packing: pressure and viscosity control of the fracture patterns

    Science.gov (United States)

    Niebling, Michael J.; Toussaint, Renaud; Flekkøy, Eirik G.; Jørgen Måløy, Knut

    2013-04-01

    øy and K.J. Måløy, Dynamic aerofracture of dense granular packings, Phys. Rev. E 86, 061315 (2012). [4] Niebling, M., R. Toussaint, E.G. Flekkøy and K.J. Måløy, Estudios numéricos de Aerofractures en medios poros / Numerical Studies of Aerofractures in Porous Media, Revista Cubana de Fisica, 29, 1E, 1E66, 2012.

  10. Swirling flows in horizontally vibrated beds of dense granular materials

    Institute of Scientific and Technical Information of China (English)

    Ali Bakhshinejad; Piroz Zamankhan

    2012-01-01

    In a series of experiments,a granular material in a rectangular container with two hollow cylinders was studied as it underwent horizontal vibrations.At the peak values of acceleration,novel swirling granular flows were observed in the cylinders while the grains cascaded down the outer surface of the piles that formed outside the cylinders.Computer simulations were performed that supported our interpretation of the behaviour observed in the experiments.

  11. Particle deposition in granular media. Annual progress report

    Energy Technology Data Exchange (ETDEWEB)

    Tien, C.

    1980-01-01

    Studies performed under Contract DE-AC02-79-ER10386.A000 Particle Deposition in Granular Media during the period June 1, 1979 to date are described. These studies include the design and construction of apparatus for filtration experiments and a complete trajectory analysis for the calculation of the initial collection efficiency of granular media. The results of the trajectory analysis have been used to develop a generalized correlation of the collection efficiency.

  12. Self-burrowing seeds: drag reduction in granular media

    Science.gov (United States)

    Jung, Wonjong; Choi, Sung Mok; Kim, Wonjung; Kim, Ho-Young

    2014-11-01

    We present the results of a combined experimental and theoretical investigation of drag reduction of self-burrowing seeds in granular media. In response to environmental changes in humidity, the awn (a tail-like appendage of seed) of Pelargonium carnosum exhibits coiling-uncoiling deformation which induces the thrust and rotary motions of the head of the seed against the surface of the soil. Using various sizes of glass beads that mimic the granular soil, we measure the thrust forces required for the seed of Pelargonium carnosum to penetrate into granular media with and without rotation. Our quantitative measurements show that the rotation of the seed remarkably reduces the granular drag as compared to the drag against the non-spinning seed. This leads us to conclude that the hygroscopically active awns of Pelargonium carnosum enables its seed to dig into the relatively coarse granular soils.

  13. Wave propagation and energy dissipation in viscoelastic granular media

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    In terms of viscoelasticity, the relevant theory of wave in granular media is analyzed in this paper.Under the conditions of slight deformation of granules, wave equation, complex number expressions of propagation vector and attenuation vector, attenuation coefficient expressions of longitudinal wave and transverse wave,etc, are analyzed and deduced. The expressions of attenuation coefficients of viscoelastic longitudinal wave and transverse wave show that the attenuation of wave is related to frequency. The higher the frequency is, the more the attenuation is, which is tested by the laboratory experiment. In addition, the energy dissipation is related to the higher frequency wave that is absorbed by granular media. The friction amongst granular media also increase the energy dissipation. During the flowing situation the expression of transmission factor of energy shows that the granular density difference is the key factor which leads to the attenuation of vibrating energy.This has been proved by the experiment results.

  14. A Low-Dissipation Technique for Computing Dense Granular Compressible Flows with Shock Waves

    CERN Document Server

    Houim, Ryan W

    2013-01-01

    A low-dissipation numerical method was developed for solving kinetic theory-based granular multiphase models with volume fractions ranging from very dilute to very dense in highly compressible flows containing shock waves. The proposed numerical method takes advantage of particle incompressibility and allows computation of gas-phase and granular-phase hyperbolic fluxes to be decoupled while treating non-conservative terms consistent with their physical meaning. The technique converges under grid refinement even with very high volume fraction granular interfaces and is compatible with high-order numerical algorithms. The method can advect sharp granular interfaces that coincide with multi-species gaseous contacts without violating the pressure non-disturbing conditions. The method also reproduces features from multiphase shock tube problems, granular shocks, transmission angles of compaction waves, and shock wave and dust layer interactions. The proposed scheme is relatively straight-forward to implement and c...

  15. Euler-like modelling of dense granular flows: application to a rotating drum

    Science.gov (United States)

    Bonamy, D.; Chavanis, P.-H.; Cortet, P.-P.; Daviaud, F.; Dubrulle, B.; Renouf, M.

    2009-04-01

    General conservation equations are derived for 2D dense granular flows from the Euler equation within the Boussinesq approximation. In steady flows, the 2D fields of granular temperature, vorticity and stream function are shown to be encoded in two scalar functions only. We checked such prediction on steady surface flows in a rotating drum simulated through the Non-Smooth Contact Dynamics method even though granular flows are dissipative and therefore not necessarily compatible with Euler equation. Finally, we briefly discuss some possible ways to predict theoretically these two functions using statistical mechanics.

  16. Motility of small nematodes in wet granular media

    CERN Document Server

    Juarez, G; Sznitman, J; Arratia, P E

    2010-01-01

    The motility behavior of the \\textit{Caenorhabditis elegans} is investigated in wet granular medium as a function of area density ($\\phi$) and dispersity. Surprisingly, the locomotion speed increases in granular media compared to free swimming. The surrounding structure of the medium leads to enhanced undulatory propulsion due to its ability to sustain a finite shear stress and convert lateral force into forward motion. For $\\phi > 0.55$, the nematode is observed to change its gate from swimming to crawling in polydisperse media \\textit{only}. This highlights the subtle difference in local structure between media.

  17. Noise induces rare events in granular media.

    Science.gov (United States)

    Khain, Evgeniy; Sander, Leonard M

    2016-09-01

    The granular Leidenfrost effect [B. Meerson, et al., Phys. Rev. Lett. 91, 024301 (2003)PRLTAO0031-900710.1103/PhysRevLett.91.024301; P. Eshuis et al., Phys. Rev. Lett. 95, 258001 (2005)PRLTAO0031-900710.1103/PhysRevLett.95.258001] is the levitation of a mass of granular matter when a wall below the grains is vibrated, giving rise to a hot granular gas below the cluster. We find by simulation that for a range of parameters the system is bistable: the levitated cluster can occasionally break and give rise to two clusters and a hot granular gas above and below. We use techniques from the theory of rare events to compute the mean transition time for breaking to occur. This requires the introduction of a two-component reaction coordinate.

  18. A Terradynamics of Legged Locomotion on Granular Media

    CERN Document Server

    Li, Chen; Goldman, Daniel I; 10.1126/science.1229163

    2013-01-01

    The theories of aero- and hydrodynamics predict animal movement and device design in air and water through the computation of lift, drag, and thrust forces. Although models of terrestrial legged locomotion have focused on interactions with solid ground, many animals move on substrates that flow in response to intrusion. However, locomotor-ground interaction models on such flowable ground are often unavailable. We developed a force model for arbitrarily-shaped legs and bodies moving freely in granular media, and used this "terradynamics" to predict a small legged robot's locomotion on granular media using various leg shapes and stride frequencies. Our study reveals a complex but generic dependence of stresses in granular media on intruder depth, orientation, and movement direction and gives insight into the effects of leg morphology and kinematics on movement.

  19. Particle-size segregation in dense granular avalanches

    Science.gov (United States)

    Gray, John Mark Nicholas Timm; Gajjar, Parmesh; Kokelaar, Peter

    2015-01-01

    Particles of differing sizes are notoriously prone to segregate, which is a chronic problem in the manufacture of a wide variety of products that are used by billions of people worldwide every day. Segregation is the single most important factor in product non-uniformity, which can lead to significant handling problems as well as complete batches being discarded at huge financial loss. It is generally regarded that the most important mechanism for segregation is the combination of kinetic sieving and squeeze expulsion in shallow granular avalanches. These free-surface flows are more common than one might expect, often forming part of more complicated flows in drums, heaps and silos, where there is mass exchange with underlying regions of static or slowly moving grains. The combination of segregation and solid-fluid granular phase transitions creates incredibly complicated and beautiful patterns in the resulting deposits, but a full understanding of such effects lies beyond our capabilities at present. This paper reviews recent advances in our ability to model the basic segregation processes in a single avalanche (without mass exchange) and the subtle feedback effects that they can have on the bulk flow. This is particularly important for geophysical applications, where segregation can spontaneously self-channelize and lubricate the flow, significantly enhancing the run-out of debris-flows, pyroclastic flows, rock-falls and snow-slab avalanches.

  20. Particles size segregation and roll waves in dense granular flows

    Science.gov (United States)

    Viroulet, Sylvain; Baker, James; Kokelaar, Peter; Gray, Nico

    2015-11-01

    Geophysical granular flows, such as landslides, snow avalanches and pyroclastic flows commonly involve particles with different sizes which are prone to segregate during the flow. This particle-size segregation may lead to the formation of regions with different frictional properties which can have a feedback on the flow. This study aims to understand this effect in the context of bi-disperse roll waves in shallow granular free-surface flows. Experiments have been performed in a 3 meter long chute using several mixtures of spherical glass beads of diameter 75-150 and 400-600 microns flowing on a rough bed. These show that the waves propagate at constant speed that depends on the initial mixture composition. In addition, during their propagation, a higher concentration of large particles is localized at the front of the waves. A theoretical and numerical approach is presented using depth-averaged equations for the conservation of mass, momentum and depth-averaged small particle concentration. Results without frictional feedback are investigated and compared to those that include the enhanced frictional resistance to motion of the large grains.

  1. Rheology of binary granular mixtures in the dense flow regime

    Science.gov (United States)

    Tripathi, Anurag; Khakhar, D. V.

    2011-11-01

    We study the rheology of granular mixtures in a steady, fully developed, gravity-driven flow on an inclined plane, by means of discrete element method (DEM) simulations. Results are presented for a single component system and binary mixtures with particles of different size and density. Inclination angles, composition, size ratios and density ratios are varied to obtain different segregated configurations at equilibrium. Steady state profiles of the mean velocity, volume fractions, shear stress, shear rate, inertial number and apparent viscosity across the depth of the flowing layer are reported for the different cases. The viscosity varies with height and is found to depend on the local bulk density and composition, which, in turn, depend on the size ratio, the mass ratio and the degree of segregation. For a single component system, a viscoplastic rheological model [P. Jop et al., Nature 441, 727 (2006)] describes the data quite well. We propose a modification of the model for the case of mixtures. The mixture model predicts the viscosity for both well-mixed and segregated granular mixtures differing in size, density or both, using the same model parameters as obtained for the single component system. The predictions of a model for the volume fraction of the mixtures also agree well with simulation results.

  2. Dense granular flow rheology in turbulent bedload transport

    CERN Document Server

    Maurin, Raphael; Frey, Philippe

    2016-01-01

    The local granular rheology is investigated numerically in idealised turbulent bedload transport configurations. Using a coupled fluid-discrete element model, the stress tensor is computed as a function of the depth for a series of simulations varying the Shields number, the specific density and the particle diameter. The results are analyzed in the framework of the $\\mu(I)$ rheology and exhibit a collapse of both the shear to normal stress ratio and the solid volume fraction over a wide range of inertial numbers. The effect of the interstitial fluid on the granular rheology is shown to be negligible, supporting recent work suggesting the absence of a clear transition between the free-fall and the turbulent regime. In addition, the data collapse is observed up to unexpectedly high inertial numbers $I\\sim2$, challenging the existing conceptions and parametrization of the $\\mu(I)$ rheology. Focusing upon bedload transport modelling, the results are pragmatically analyzed in the $\\mu(I)$ framework in order to pr...

  3. Evolution of the effective moduli of an anisotropic, dense, granular material

    NARCIS (Netherlands)

    La Ragione, L.; Magnanimo, Vanessa

    2012-01-01

    We analyze the behavior of a dense granular aggregate made by identical, elastic spheres, uni-axially compressed at constant pressure. Our goal is to predict the evolution of the effective moduli along the loading path when small perturbations are applied to stressed states. The analytical model is

  4. Evolution of the effective moduli of an anisotropic, dense, granular material

    NARCIS (Netherlands)

    La Ragione, L.; Magnanimo, V.

    2012-01-01

    We analyze the behavior of a dense granular aggregate made by identical, elastic spheres, uni-axially compressed at constant pressure. Our goal is to predict the evolution of the effective moduli along the loading path when small perturbations are applied to stressed states. The analytical model is

  5. Velocity Fluctuations in Electrostatically Driven Granular Media

    OpenAIRE

    Aranson, I. S.; Olafsen, J. S.

    2001-01-01

    We study experimentally the particle velocity fluctuations in an electrostatically driven dilute granular gas. The experimentally obtained velocity distribution functions have strong deviations from Maxwellian form in a wide range of parameters. We have found that the tails of the distribution functions are consistent with a stretched exponential law with typical exponents of the order 3/2. Molecular dynamic simulations shows qualitative agreement with experimental data. Our results suggest t...

  6. Positron emission particle tracking and its application to granular media.

    Science.gov (United States)

    Parker, D J

    2017-05-01

    Positron emission particle tracking (PEPT) is a technique for tracking a single radioactively labelled particle. Accurate 3D tracking is possible even when the particle is moving at high speed inside a dense opaque system. In many cases, tracking a single particle within a granular system provides sufficient information to determine the time-averaged behaviour of the entire granular system. After a general introduction, this paper describes the detector systems (PET scanners and positron cameras) used to record PEPT data, the techniques used to label particles, and the algorithms used to process the data. This paper concentrates on the use of PEPT for studying granular systems: the focus is mainly on work at Birmingham, but reference is also made to work from other centres, and options for wider diversification are suggested.

  7. Rheology of dense granular chute flow: simulations to experiments

    Directory of Open Access Journals (Sweden)

    Bharathraj S

    2017-01-01

    Full Text Available Granular chute flow simulations reveal an interesting transition from a random disordered structure to an ordered one with hexagonally ordered sheets of spherical particles, when the base roughness is modulated. Two types of base roughness are considered. The first is a fixed base, where glued spherical particles form the base, and the base roughness is varied by changing the ratio of diameters of the base and flowing particles. In the second sinusoidal base, a smooth wall with sinusoidal height variation is used; the amplitude and wavelength of the base modulation determine the base roughness. The transition is studied as a function of these roughness parameters. For the fixed base, there is a critical base particle diameter below which ordered states are observed. For the sinusoidal base, the critical amplitude increases linearly with the wavelength at lower wavelengths, reaches a maximum depending on the height of the flowing layer, and then decreases as the wavelength is further increased. There is flow for angles of inclination from 15 ° ≤ θ ≤ 25 ° for the ordered state and 20 ° ≤ θ ≤ 25 ° for the disordered state. Flow confinement by sidewalls also influences the rheology of the system and we see that the ordering is induced by the sidewalls as well. Experiments on chute flow at low angles indicate the presence of two types of rheology depending on the system height. A transition is observed from an erodible base configuration, where a dead zone at the bottom supports a free surface reposing at the top, to a Bagnold rheology with considerable slip at the bottom.

  8. Collapse of granular media subjected to wetting

    Directory of Open Access Journals (Sweden)

    El Korchi Fatima Zahra

    2017-01-01

    Full Text Available This paper focuses on the collapse of granular materials subjected to wetting action. For soils, the collapse potential depends on several parameters such as liquid limit, matric suction, compactness, initial water content and the amount of fine particles. The effect of grain size, which plays a key role in the rearrangement of grains, remains little studied and poorly understood. To investigate the capillary origin of the collapse phenomenon, we present an experimental study on macroscopic and local scales. Our results show the effect of grain size and water content on collapse.

  9. Lizard locomotion in heterogeneous granular media

    Science.gov (United States)

    Schiebel, Perrin; Goldman, Daniel

    2014-03-01

    Locomotion strategies in heterogeneous granular environments (common substrates in deserts), are relatively unexplored. The zebra-tailed lizard (C. draconoides) is a useful model organism for such studies owing to its exceptional ability to navigate a variety of desert habitats at impressive speed (up to 50 body-lengths per second) using both quadrapedal and bidepal gaits. In laboratory experiments, we challenge the lizards to run across a field of boulders (2.54 cm diameter glass spheres or 3.8 cm 3D printed spheres) placed in a lattice pattern and embedded in a loosely packed granular medium of 0.3 mm diameter glass particles. Locomotion kinematics of the lizard are recorded using high speed cameras, with and without the scatterers. The data reveals that unlike the lizard's typical quadrupedal locomotion using a diagonal gait, when scatterers are present the lizard is most successful when using a bipedal gait, with a raised center of mass (CoM). We propose that the kinematics of bipedal running in conjunction with the lizard's long toes and compliant hind foot are the keys to this lizard's successful locomotion in the presence of such obstacles. NSF PoLS

  10. Ripples and Shear Bands in Plowed Granular Media

    CERN Document Server

    Gravish, Nick; Goldman, Daniel I

    2009-01-01

    Monodisperse packings of dry, air-fluidized granular media typically exist between volume fractions from $\\Phi$= 0.585 to 0.64. We demonstrate that the dynamics of granular drag are sensitive to volume fraction $\\Phi$ and their exists a transition in the drag force and material deformation from smooth to oscillatory at a critical volume fraction $\\Phi_{c}=0.605$. By dragging a submerged steel plate (3.81 cm width, 6.98 cm depth) through $300 \\mu m$ glass beads prepared at volume fractions between 0.585 to 0.635 we find that below $\\Phi_{c}$ the media deformation is smooth and non-localized while above $\\Phi_{c}$ media fails along distinct shear bands. At high $\\Phi$ the generation of these shear bands is periodic resulting in the ripples on the surface. Work funded by The Burroughs Wellcome Fund and the Army Research Lab MAST CTA

  11. Rheology of cohesive granular materials across multiple dense-flow regimes.

    Science.gov (United States)

    Gu, Yile; Chialvo, Sebastian; Sundaresan, Sankaran

    2014-09-01

    We investigate the dense-flow rheology of cohesive granular materials through discrete element simulations of homogeneous, simple shear flows of frictional, cohesive, spherical particles. Dense shear flows of noncohesive granular materials exhibit three regimes: quasistatic, inertial, and intermediate, which persist for cohesive materials as well. It is found that cohesion results in bifurcation of the inertial regime into two regimes: (a) a new rate-independent regime and (b) an inertial regime. Transition from rate-independent cohesive regime to inertial regime occurs when the kinetic energy supplied by shearing is sufficient to overcome the cohesive energy. Simulations reveal that inhomogeneous shear band forms in the vicinity of this transition, which is more pronounced at lower particle volume fractions. We propose a rheological model for cohesive systems that captures the simulation results across all four regimes.

  12. Shape of impact craters in granular media.

    Science.gov (United States)

    de Vet, Simon J; de Bruyn, John R

    2007-10-01

    We present the results of experiments studying the shape of craters formed by the normal impact of a solid spherical projectile into a deep noncohesive granular bed at low energies. The resultant impact crater surfaces are accurately digitized using laser profilometry, allowing for the detailed investigation of the crater shape. We find that these impact craters are very nearly hyperbolic in profile. Crater radii and depths are dependent on impact energy, as well as the projectile density and size. The precise crater shape is a function of the crater aspect ratio. While the dimensions of the crater are highly dependent on the impact energy, we show that the energy required to excavate the crater is only a tiny fraction (0.1%-0.5%) of the kinetic energy of the projectile.

  13. 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.

  14. Stability analysis of unbounded uniform dense granular shear flow based on a viscoplastic constitutive law

    Science.gov (United States)

    Chen, Wen-Yau; Lai, Jeng-You; Young, D. L.

    2010-11-01

    Asymptotic and transient stability analyses of unbounded uniform granular shear flow at high solids volume fractions were carried out in the paper, based on a model composed of the viscoplastic constitutive law [P. Jop, Y. Forterre, and O. Pouliquen, Nature (London) 441, 727 (2006)] and the dilatancy law [O. Pouliquen et al., J. Stat. Mech.: Theory Exp. (2006) P07020]. We refer to this model as the VPDL (meaning of the "viscoplastic and dilatancy laws") thereinafter. In this model, dense granular flows were treated as a viscoplastic fluid with a Drucker-Prager-like yielding criterion. We compared our results to those obtained using the frictional-kinetic model (FKM) [M. Alam and P. R. Nott, J. Fluid Mech. 343, 267 (1997)]. Our main result is that unbounded uniform dense granular shear flows are always asymptotically stable at large time based on the VPDL model, at least for two-dimensional perturbations. This is valid for disturbances of layering modes (i.e., the perturbations whose wavenumber vectors are aligned along the transverse coordinate) as well as for nonlayering modes (the streamwise component of the wavenumber vector is nonzero). By contrast, layering modes can be unstable based on the FKM constitutive laws. Interestingly, in the framework of the VPDL, the analysis shows that significant transient growth may occur owing to the non-normality of the linear system, although disturbances eventually decay at large time.

  15. General scaling relations for locomotion in granular media.

    Science.gov (United States)

    Slonaker, James; Motley, D Carrington; Zhang, Qiong; Townsend, Stephen; Senatore, Carmine; Iagnemma, Karl; Kamrin, Ken

    2017-05-01

    Inspired by dynamic similarity in fluid systems, we have derived a general dimensionless form for locomotion in granular materials, which is validated in experiments and discrete element method (DEM) simulations. The form instructs how to scale size, mass, and driving parameters in order to relate dynamic behaviors of different locomotors in the same granular media. The scaling can be derived by assuming intrusion forces arise from resistive force theory or equivalently by assuming the granular material behaves as a continuum obeying a frictional yield criterion. The scalings are experimentally confirmed using pairs of wheels of various shapes and sizes under many driving conditions in a common sand bed. We discuss why the two models provide such a robust set of scaling laws even though they neglect a number of the complexities of granular rheology. Motivated by potential extraplanetary applications, the dimensionless form also implies a way to predict wheel performance in one ambient gravity based on tests in a different ambient gravity. We confirm this using DEM simulations, which show that scaling relations are satisfied over an array of driving modes even when gravity differs between scaled tests.

  16. 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.

  17. Impact craters in granular media: grains against grains.

    Science.gov (United States)

    Pacheco-Vázquez, F; Ruiz-Suárez, J C

    2011-11-18

    Impact experiments in granular media are usually performed with solid projectiles that do not fragment at all. Contrastingly, we study here the morphology produced by the impact of spherical granular projectiles whose structure is utterly lost after collision. Simple and complex craters are observed, depending on the packing fraction of the balls. Their diameters D and depths z are analyzed as a function of the drop height h. We find the same power law D ∝ h(1/4) obtained with solid spheres, but a discontinuity at a certain threshold height, related to the cohesive energy of the projectiles, shows up. Counterintuitively, instead of a monotonic increase with the collisional energy, z becomes constant above this threshold.

  18. Minor Losses During Air Flow into Granular Porous Media

    DEFF Research Database (Denmark)

    Poulsen, Tjalfe Gorm; Minelgaite, Greta; Bentzen, Thomas Ruby

    2013-01-01

    Pressure gradients during uniform fluid flow in porous media are traditionally assumed to be linear. Thus, pressure loss across a sample of porous medium is assumed directly proportional to the thickness of the sample. In this study, measurements of pressure gradients inside coarse granular (2...... that the pressure loss in porous media consists of two components: (1) a linear pressure gradient and (2) an initial pressure loss near the inlet. This initial pressure loss is also known from hydraulics in tubes as a minor loss and is associated with abrupt changes in the flow field such as narrowings and bends....... The results further indicated that the minor loss depends on the particle size and particle size distribution in a manner similar to that of the linear pressure gradient. There is, thus, a close relation between these two components. In porous media, the minor loss is not instantaneous at the inlet point...

  19. Numerical Simulation on Dense Packing of Granular Materials by Container Oscillation

    Directory of Open Access Journals (Sweden)

    Jun Liu

    2013-01-01

    Full Text Available The packing of granular materials is a basic and important problem in geomechanics. An approach, which generates dense packing of spheres confined in cylindrical and cuboidal containers in three steps, is introduced in this work. A loose packing structure is first generated by means of a reference lattice method. Then a dense packing structure is obtained in a container by simulating dropping of particles under gravitational forces. Furthermore, a scheme that makes the bottom boundary fluctuate up and down was applied to obtain more denser packing. The discrete element method (DEM was employed to simulate the interactions between particle-particle and particle-boundary during the particles' motions. Finally, two cases were presented to indicate the validity of the method proposed in this work.

  20. Low-speed impact cratering in loose granular media

    Science.gov (United States)

    Durian, Douglas

    2005-03-01

    In this talk I shall describe the penetration of projectiles dropped into noncohesive granular media, and how the results vary with the properties of both the projectile and the medium. In contrast to wide assumption, the penetration depth and crater diameter represent two distinct length scales. The diameter scales as the 1/4 power of projectile energy, but curiously the depth is not a simple function of either the projectile energy or momentum at impact. Rather, it scales as the 1/2 power of density, the 2/3 power of projectile diameter, and the 1/3 power of total drop distance. This same result also holds for cylinders with a variety of tips, and so is not an accident of projectile shape. It is crucial to understand the penetration depth because it is directly related to the mechanics of impact, namely the average stopping force acting between projectile and medium. In addition to this discussion, I shall also present new data on the dynamics of impact. All experiments were constructed and carried out at UCLA by undergraduate physics majors: Jun Uehara, Katie Newhall, Chris Santore, and Mike Ambroso.[1] J.S. Uehara, M.A. Ambroso, R.P. Ojha, and D.J. Durian, ``Low-Speed Impact Craters in Loose Granular Media,'' Phys. Rev. Lett. 90, 194301 (2003).[2] K.A. Newhall and D.J. Durian, ``Projectile-shape dependence of impact craters in loose granular media,'' Phys. Rev. E 68, 06030R (2003).[3] M.A. Ambroso, C.R. Santore, A.R. Abate, and D.J. Durian, ``Penetration depth for shallow impact cratering,'' cond-mat/0411231 (2004).

  1. Discharge flow of a bidisperse granular media from a silo

    Science.gov (United States)

    Benyamine, M.; Djermane, M.; Dalloz-Dubrujeaud, B.; Aussillous, P.

    2014-09-01

    The discharge flow in a cylindrical and a rectangular silo using both monodisperse and bidisperse mixtures of spherical glass beads is studied experimentally. The flow rate is measured using a precision balance for a large range of particle diameters, size ratios, and outlet diameters. A simple physical model is proposed to describe the flow of bidisperse mixtures. It gives an expression for the flow rate and predicts that the bulk velocity follows a simple mixture law. This model implies that a mixture diameter cannot be simply defined. Moreover it is shown that bidisperse granular media allow for the transport of coarse particles below their jamming conditions.

  2. Vibrating Liquefaction Experiment and Mechanism Study in Saturated Granular Media

    Institute of Scientific and Technical Information of China (English)

    Li Jianhua; Xu Ming; Ju Haiyan; Zhao Jiangqian; Huang Hongyuan; Sun Yezhi

    2006-01-01

    By the vibrating liquefaction experiment of tailings and fine-ores of iron, it is observed and noted that the change of pore water pressure when the vibrating liquefaction takes place. Based on relevant suppositions, the equation of wave propagation in saturated granular media is obtained. This paper postulates the potential vector equation and the velocity expression of three kinds of body waves under normal conditions.Utilizing the wave theory and the experimental results, the influence of three body waves on pore water pressure and granules has been analyzed in detail. This revealed the rapid increment mechanism of pore water pressure and the wave mechanism of vibrating liquefaction.

  3. Nucleosynthesis in Hot and Dense Media

    CERN Document Server

    Masood, Samina S

    2014-01-01

    We study the finite temperature and density effects on beta decay rates to compute their contributions to nucleosynthesis. QED type corrections to beta decay from the hot and dense background are estimated in terms of the statistical corrections to the self-mass of an electron. For this purpose, we re-examine the hot and dense background contributions to the electron mass and compute its effect to the beta decay rate, helium yield, energy density of the universe as well as the change in neutrino temperature from the first order contribution to the self-mass of electrons during these processes. We explicitly show that the thermal contribution to the helium abundance at T = m of a cooling universe 0.045 % is higher than the corresponding contribution to helium abundance of a heating universe 0.031% due to the existence of hot fermions before the beginning of nucleosynthesis and their absence after the nucleosynthesis, in the early universe. Thermal contribution to helium abundance was a simple quadratic functio...

  4. No slip locomotion of hatchling sea turtles on granular media

    Science.gov (United States)

    Mazouchova, Nicole; Li, Chen; Gravish, Nick; Savu, Andrei; Goldman, Daniel

    2009-11-01

    Sea turtle locomotion occurs predominantly in aquatic environments. However after hatching from a nest on a beach, the juvenile turtles (hatchlings), must run across several hundred meters of granular media to reach the water. To discover how these organisms use aquatically adapted limbs for effective locomotion on sand, we use high speed infrared video to record hatchling Loggerhead sea turtles (Caretta caretta) kinematics in a field site on Jekyll Island, GA, USA. A portable fluidized bed trackway allows variation of the properties of the granular bed including volume fraction and angle up to the angle of repose. Despite being adapted for life in water, on all treatments the turtles use strategies similar to terrestrial organisms when moving on sand. Speeds up to 3 BL/sec are generated not by paddling in sand, but by limb movement that minimizes slip of the flippers, thus maintaining force below the yield stress of the medium. We predict turtle speed using a model which incorporates the yield stress of the granular medium as a function of surface angle.

  5. Role of arches in the generation of shear bands in a dense 3D granular system under shear

    Energy Technology Data Exchange (ETDEWEB)

    Sigaud, L [Instituto de Fisica, Universidade Federal do Rio de Janeiro, P.O. 68528, 21941-972 Rio de Janeiro, RJ (Brazil); Bordignon, A L; Lopes, H; Lewiner, T; Tavares, G [Departamento de Matematica, PontifIcia Universidade Catolica do Rio de Janeiro, C.P. 38071, 22452 970 Rio de Janeiro (Brazil); Morgado, W A M, E-mail: lucas@if.ufrj.b [Departamento de Fisica, PontifIcia Universidade Catolica do Rio de Janeiro and National Institute of Science and Technology for Complex Systems, C.P. 38071, 22452-970 Rio de Janeiro (Brazil)

    2010-09-01

    A model for propagation of arches on cubic lattices, to simulate the internal mobility of grains in a dense granular system under shear is proposed. In this model, the role of the arches in granular transportation presents a non-linear dependence on the local values of the stress components that can be modeled geometrically. In particular, we study a modified Couette flow and were able to reproduce qualitatively the experimental results found in the literature.

  6. A two-phase solid/fluid model for dense granular flows including dilatancy effects

    Science.gov (United States)

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

    2016-04-01

    Describing grain/fluid interaction in debris flows models is still an open and challenging issue with key impact on hazard assessment [{Iverson et al.}, 2010]. We present here a two-phase two-thin-layer model for fluidized debris flows that takes into account dilatancy effects. It describes the velocity of both the solid and the fluid phases, the compression/dilatation of the granular media and its interaction with the pore fluid pressure [{Bouchut et al.}, 2016]. 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.}, 2015]. In particular, {Pitman and Le} [2005] 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 model by closing the mixture equations by a weak compressibility relation following {Roux and Radjai} [1998]. This relation implies that the occurrence of dilation or contraction of the granular material in the model depends on whether the solid volume fraction is respectively higher or lower than a critical value. When dilation occurs, the fluid is sucked into the granular material, the pore pressure decreases and the friction force on the granular phase increases. On the contrary, in the case of contraction, the fluid is expelled from the mixture, the pore pressure increases and the friction force diminishes. To

  7. Wettability Control on Hydro-capillary Fracturing in Granular Media

    Science.gov (United States)

    Trojer, M.; de Anna, P.; Juanes, R.

    2015-12-01

    The flow of two or more immiscible phases within geologic porous media is important in natural and industrial processes like geologic CO2 sequestration, enhanced oil recovery, and hydraulic fracturing. The latter one, however, is a well-known reservoir stimulation technique, by which the permeability of the near-wellbore region is enhanced through the creation of tensile fractures within the rock, formed in the direction perpendicular to the least principal stress. While it is well known that fracturing of granular media strongly depends on the type of media and on the variability of its wetting properties, the effect of wettability on capillary-driven fracturing continues to challenge our microscopic and macroscopic descriptions. Here we study this problem experimentally, starting with the classic experiment of two-phase flow in a horizontal Hele-Shaw cell filled with a granular medium. We inject a low-viscosity fluid into a thin bed of glass beads initially saturated with a fluid 350 times more viscous. We investigate three control parameters: the injection rate of the less-viscous invading phase, the confining stress, and the contact angle, which we control by carefully chosen fluid pairs covering the entire range from drainage to imbibition. Our results demonstrate that wettability exerts a powerful influence on the invasion/fracturing morphology of unfavorable mobility displacements. High time resolution imaging techniques and particle image velocimetry (PIV) allow us to quantify matrix displacement and fracture opening dynamics. Our findings provide insights on fracture propagation, fracture length distribution and the fracture drainage area, parameters which are critically important to better understand long-term hydrocarbon production from shale.

  8. Erosion and deposition in depth-averaged models of dense, dry, inclined, granular flows

    Science.gov (United States)

    Jenkins, James T.; Berzi, Diego

    2016-11-01

    We derive expressions for the rates of erosion and deposition at the interface between a dense, dry, inclined granular flow and an erodible bed. In obtaining these, we assume that the interface between the flowing grains and the bed moves with the speed of a pressure wave in the flow, for deposition, or with the speed of a disturbance through the contacting particles in the bed, for erosion. We employ the expressions for the rates of erosion and deposition to show that after an abrupt change in the angle of inclination of the bed the characteristic time for the motion of the interface is much shorter than the characteristic time of the flow. This eliminates the need for introducing models of erosion and deposition rate in the mass balance; and the instantaneous value of the particle flux is the same function of the instantaneous value of the flow depth as in a steady, uniform flow.

  9. Impact of capillarity and wettability on fracturing in granular media

    Science.gov (United States)

    Juanes, R.; Trojer, M.; De Anna, P.

    2016-12-01

    The flow of two or more immiscible phases in porous media is important in natural and industrial processes like geologic CO2 sequestration, enhanced oil recovery, water infiltration in soil, and methane venting from submerged organic-rich sediments. Hydrocarbon recovery from low-permeability geologic formations relies on hydraulic fracturing—a well-known reservoir stimulation technique by which the permeability of the near-wellbore region is enhanced through the opening of fractures within the rock. Here we study this phenomenon experimentally in a horizontal Hele-Shaw cell filled with a granular medium. We inject a low-viscosity fluid into a thin bed of glass beads initially saturated with a more viscous fluid. We investigate the role of three control variables: (1) the injection rate, (2) the confining stress, and (3) the contact angle between the beads and the two fluids. We control the contact angle by carefully choosing the fluid pairs to achieve a wide range of wetting properties, from drainage to imbibition. We image the fluid-fluid displacement and the branching network of fractures via fluorescence tagging, and quantify the displacement of the granular pack by means of particle image velocimetry (PIV). We demonstrate the emergence of fracturing and, crucially, we show that the wetting properties exert a strong, non-monotonic impact on fracture morphology.

  10. Rheology of simple shear flows of dense granular assemblies in different regimes

    Science.gov (United States)

    Chialvo, Sebastian; Sun, Jin; Sundaresan, Sankaran

    2010-11-01

    Using the discrete element method, simulations of simple shear flow of dense assemblies of frictional particles have been carried out over a range of shear rates and volume fractions in order to characterize the transition from quasistatic or inertial flow to intermediate flow. In agreement with previous results for frictionless spheres [1], the pressure and shear stress in the intermediate regime are found to approach asymptotic power law relations with shear rate; curiously, these asymptotes appear to be common to all intermediate flows regardless of the value of the particle friction coefficient. The scaling relations for stress for the inertial and quasistatic regimes are consistent with a recent extension of kinetic theory to dense inertial flows [2] and a simple model for quasistatic flows [3], respectively. For the case of steady, simple shear flow, the different regimes can be bridged readily: a harmonic weighting function blends the inertial regime to the intermediate asymptote, while a simple additive rule combines the quasistatic and intermediate regimes. [4pt] [1] T. Hatano, et al., J. Phys. Soc. Japan 76, 023001 (2007). [0pt] [2] J. Jenkins, and D. Berzi, Granular Matter 12, 151 (2010). [0pt] [3] J. Sun, and S. Sundaresan, J. Fluid Mech. (under review).

  11. Shear strength and stress distribution in wet granular media

    Science.gov (United States)

    Richefeu, Vincent; Radjaï, Farhang; El Youssoufi, Moulay Saïd

    2009-06-01

    We investigate the shear strength and stress distribution properties of wet granular media in the pendular state where the liquid is mainly in the form of capillary bonds between particles. This work is based on a 3D discrete-element approach (molecular dynamics) with spherical particles enriched by a capillary force law. We show that the capillary force can be expressed as an explicit function of the gap and volume of the liquid bridge. The length scales involved in this expression are analyzed by comparing with direct integration of the Laplace-Young equation. In the simulations, we consider a maximum number density of liquid bonds in the bulk in agreement with equilibrium of each liquid bridge. This liquid bond number is a decisive parameter for the overall cohesion of wet granular materials. It is shown that the shear strength can be expressed as a function of liquid bond characteristics. The expression proposed initially by Rumpf is thus generalized to account for size polydispersity We show that this expression is in good agreement with our experimental data that will be briefly described. At low confining stress, the tensile action of capillary bonds induces a self-stressed particle network organized in a bi-percolating structure of positive and negative particle pressures. Various statistical descriptors of the microstructure and bond force network are used to characterize this partition. Two basic properties emerge: (i) The highest particle pressure is located in the bulk of each phase (positive and negative particle pressures); (ii) The lowest pressure level occurs at the interface between the two phases, involving also the largest connectivity of the particles via tensile and compressive bonds.

  12. 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.

  13. Transport of Fluorescently Labeled Hydroxyapatite Nanoparticles in Saturated Granular Media at Environmentally Relevant Concentrations of Surfactants

    Science.gov (United States)

    Little is known about the mobility of engineered nanoparticles (ENPs) in granular media at environmentally relevant concentration of surfactant, which represents a critical knowledge gap in employing ENPs for in-situ remediation of contaminated groundwater. In this study, transpo...

  14. Contact investigations of granular mechanical media in a tumbling sorting machine

    OpenAIRE

    2007-01-01

    Chapter 1 briefly introduced some contact problems in granular media with some computational procedures used in sequential and parallel computations. In Chapter 2, a general description of the molecular dynamic problems and clarification of the basics of the granular media are presented. Some of the frequently-used algorithms and models, e.g. Discrete Element Method (DEM) and penalty method of the spring-dashpot model are involved in this chapter.Some basic techniques for speeding up simu...

  15. A k-{\\varepsilon} turbulence closure model of an isothermal dry granular dense matter

    Science.gov (United States)

    Fang, Chung

    2016-07-01

    The turbulent flow characteristics of an isothermal dry granular dense matter with incompressible grains are investigated by the proposed first-order k-{\\varepsilon} turbulence closure model. Reynolds-filter process is applied to obtain the balance equations of the mean fields with two kinematic equations describing the time evolutions of the turbulent kinetic energy and dissipation. The first and second laws of thermodynamics are used to derive the equilibrium closure relations satisfying turbulence realizability conditions, with the dynamic responses postulated by a quasi-linear theory. The established closure model is applied to analyses of a gravity-driven stationary flow down an inclined moving plane. While the mean velocity decreases monotonically from its value on the moving plane toward the free surface, the mean porosity increases exponentially; the turbulent kinetic energy and dissipation evolve, respectively, from their minimum and maximum values on the plane toward their maximum and minimum values on the free surface. The evaluated mean velocity and porosity correspond to the experimental outcomes, while the turbulent dissipation distribution demonstrates a similarity to that of Newtonian fluids in turbulent shear flows. When compared to the zero-order model, the turbulent eddy evolution tends to enhance the transfer of the turbulent kinetic energy and plane shearing across the flow layer, resulting in more intensive turbulent fluctuation in the upper part of the flow. Solid boundary as energy source and sink of the turbulent kinetic energy becomes more apparent in the established first-order model.

  16. A DEM investigation on simple shear behavior of dense granular assemblies

    Institute of Scientific and Technical Information of China (English)

    史旦达; 薛剑峰; 赵振营; 史跻宇

    2015-01-01

    A micromechanical investigation on simple shear behavior of dense granular assemblies was carried out by discrete element method. Three series of numerical tests were performed to examine the effects of initial porosity, vertical stress and particle shape on simple shear behavior of the samples, respectively. It was found that during simple shear the directions of principal stress and principal strain increment rotate differently with shear strain level. The non-coaxiality between the two directions decreases with strain level and may greatly affect the shear behavior of the assemblies, especially their peak friction angles. The numerical modelling also reveals that the rotation of the principal direction of fabric anisotropy lags behind that of the major principal stress direction during simple shear, which is described as fabric hyteresis effect. The degrees of fabric and interparticle contact force anisotropies increase as particle angularity increases, whereas the orientations of these anisotropies have not been significantly influenced by particle shape. An extended stress–dilatancy relationship based on ROWE-DAVIS framework was proposed to consider the non-coaxiality effect under principal stress rotation. The model was validated by present numerical results as well as some published physical test and numerical modelled data.

  17. Toward generalized continuum models of granular soil and granular soil-tire interaction: A combined discrete element and thermomicromechanical continuum analysis of densely packed assemblies

    Science.gov (United States)

    2007-04-30

    of papers containing this body of work have described this as a highly innovative approach at the cutting edge of international geomechanics research...for publication in world-leading journals in granular media mechanics, multi-scale modelling, and experimental and theoretical geomechanics research...international geomechanics research”  “an innovative direction for modelling particulate systems”  “should be very useful, enriching the knowledge

  18. Some fundamental aspects of the continuumization problem in granular Media

    Science.gov (United States)

    Peters, John F.

    The central problem of devising mathematical models of granular materials is how to define a granular medium as a continuum. This paper outlines the elements of a theory that could be incorporated in discrete models such as the Discrete-Element Method, without recourse to a continuum description. It is shown that familiar concepts from continuum mechanics such as stress and strain can be defined for interacting discrete quantities. Established concepts for constitutive equations can likewise be applied to discrete quantities. The key problem is how to define the constitutive response in terms of truncated strain measures that are a practical necessity for analysis of large granular systems.

  19. Instationary compaction wave propagation in highly porous cohesive granular media

    Science.gov (United States)

    Gunkelmann, Nina; Ringl, Christian; Urbassek, Herbert M.

    2016-07-01

    We study the collision of a highly porous granular aggregate of adhesive \\upmu m-sized silica grains with a hard wall using a granular discrete element method. A compaction wave runs through the granular sample building up an inhomogeneous density profile. The compaction is independent of the length of the aggregate, within the regime of lengths studied here. Also short pulses, as they might be exerted by a piston pushing the granular material, excite a compaction wave that runs through the entire material. The speed of the compaction wave is larger than the impact velocity but considerably smaller than the sound speed. The wave speed is related to the compaction rate at the colliding surface and the average slope of the linear density profile.

  20. The propagation of blast pulses through dampened granular media

    Science.gov (United States)

    Badham, Henry; Chalmers, Max; Nguyen, Thuy-Tien Ngoc; Proud, William Graham

    2017-01-01

    The propagation of stress through granular and dampened granular material has been reported previously, the addition of significant amounts of liquid in granular beds causes the mechanism of transmission of blast from one of percolation through the bed pores to one of stress transmission through the granules of the bed. It has been shown, however, that limited amounts liquid can retard propagation within blast-loaded beds by approximately an order of magnitude. This paper presents data on percolation through dampened granular beds using a shock tube as the pressure driver. The effect of particle shape and size was investigated using angular grains of quartz sand as well as smooth glass microspheres. The effect of addition of small amounts of liquids is presented.

  1. The effect of limb kinematics on the speed of a legged robot on granular media

    CERN Document Server

    Li, Chen; Komsuoglu, Haldun; Goldman, Daniel I; 10.1007/s11340-010-9347-1

    2013-01-01

    Achieving effective locomotion on diverse terrestrial substrates can require subtle changes of limb kinematics. Biologically inspired legged robots (physical models of organisms) have shown impressive mobility on hard ground but suffer performance loss on unconsolidated granular materials like sand. Because comprehensive limb-ground interaction models are lacking, optimal gaits on complex yielding terrain have been determined empirically. To develop predictive models for legged devices and to provide hypotheses for biological locomotors, we systematically study the performance of SandBot, a small legged robot, on granular media as a function of gait parameters. High performance occurs only in a small region of parameter space. A previously introduced kinematic model of the robot combined with a new anisotropic granular penetration force law predicts the speed. Performance on granular media is maximized when gait parameters minimize body acceleration and limb interference, and utilize solidification features o...

  2. Generalized Phenomenological Cyclic Stress-Strain-Strength Characterization of Granular Media.

    Science.gov (United States)

    1984-09-02

    following special form of the general hypoelastic equation to model the behavior of granular media: dij = [a0 dem + a3 "pq d pq] 6ij + 1 dcij + C 2 dem...Phenomitno ogical I C.yclic Stress-Strain-Strength Characterization f Granular M~dia !RSO%.hL APT’.OR(S) M._McVay,_D._Seereeram,_P.__Linton andD... Granular Medi a, Vollow Cylinder. Cyclic Triaxial Test, Plasticity, Prediction Expanding Cavity LClic CTC rests ISTAAC? fCoom w mz_’-. ,f_.V,,A6’V "d

  3. Localization of Shear in Saturated Granular Media: Insights from a Multi-Scaled Granular-Fluid Model

    CERN Document Server

    Aharonov, Einat; Sparks, David; Toussaint, Renaud

    2013-01-01

    The coupled mechanics of fluid-filled granular media controls the behavior of many natural systems such as saturated soils, fault gouge, and landslides. The grain motion and the fluid pressure influence each other: It is well established that when the fluid pressure rises, the shear resistance of fluid-filled granular systems decreases, and as a result catastrophic events such as soil liquefaction, earthquakes, and accelerating landslides may be triggered. Alternatively, when the pore pressure drops, the shear resistance of these systems increases. Despite the great importance of the coupled mechanics of grains-fluid systems, the basic physics that controls this coupling is far from understood. We developed a new multi-scaled model based on the discrete element method, coupled with a continuum model of fluid pressure, to explore this dynamical system. The model was shown recently to capture essential feedbacks between porosity changes arising from rearrangement of grains, and local pressure variations due to ...

  4. Hydrodynamic modeling of dense gas-fluidised beds using the kinetic theory of granular flow: effect of coefficient of restitution on bed dynamics

    NARCIS (Netherlands)

    Goldschmidt, M.J.V.; Kuipers, J.A.M.; van Swaaij, Willibrordus Petrus Maria

    2000-01-01

    A two-dimensional multi-fluid Eulerian CFD model with closure laws according to the kinetic theory of granular flow has been applied to study the influence of the coefficient of restitution on the hydrodynamics of dense gas-fluidised beds. It is demonstrated that hydrodynamics of dense gas-fluidised

  5. Hydrodynamic modeling of dense gas-fluidised beds using the kinetic theory of granular flow: effect of coefficient of restitution on bed dynamics.

    NARCIS (Netherlands)

    Goldschmidt, M.J.V.; Kuipers, J.A.M.; van Swaaij, Willibrordus Petrus Maria

    2001-01-01

    A two-dimensional multi-fluid Eulerian CFD model with closure laws according to the kinetic theory of granular flow has been applied to study the influence of the coefficient of restitution on the hydrodynamics of dense gas-fluidised beds. It is demonstrated that hydrodynamics of dense gas-fluidised

  6. Hydrodynamic modeling of dense gas-fluidised beds using the kinetic theory of granular flow: effect of coefficient of restitution on bed dynamics

    NARCIS (Netherlands)

    Goldschmidt, M.J.V.; Kuipers, J.A.M.; Swaaij, van W.P.M.

    2000-01-01

    A two-dimensional multi-fluid Eulerian CFD model with closure laws according to the kinetic theory of granular flow has been applied to study the influence of the coefficient of restitution on the hydrodynamics of dense gas-fluidised beds. It is demonstrated that hydrodynamics of dense gas-fluidised

  7. Hydrodynamic modelling of dense gas-fluidised beds using the kinetic theory of granular flow: effect of coefficient of restitution on bed dynamics.

    NARCIS (Netherlands)

    Goldschmidt, M.J.V.; Kuipers, J.A.M.; Swaaij, van W.P.M.

    2001-01-01

    A two-dimensional multi-fluid Eulerian CFD model with closure laws according to the kinetic theory of granular flow has been applied to study the influence of the coefficient of restitution on the hydrodynamics of dense gas-fluidised beds. It is demonstrated that hydrodynamics of dense gas-fluidised

  8. Mechanisms of intruder motion in cyclically sheared granular media

    Science.gov (United States)

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

    2016-11-01

    We perform an experimental study showing how an intruder, a Teflon disk that experiences a moderate constant force, F, can advance through a granular material that is subject to quasi-static cyclic shear. The large Teflon disk is embedded in a layer of smaller bidisperse photoelastic disks. The granular medium and disk are contained in a horizontal cell, which is deformed from a square to a parallelogram and back again. The area of the cell remains constant throughout, and the protocol corresponds to cyclical simple shear. We find that the net intruder motion per cycle increases as a power law in Nc. The intruder motion relative to the granular background occurs primarily following strain reversals. We acknowledge support from NSF Grant No. DMR1206351, NASA Grant No. NNX15AD38G and the W.M. Keck Foundation.

  9. From the Cover: Sensitive dependence of the motion of a legged robot on granular media.

    Science.gov (United States)

    Li, Chen; Umbanhowar, Paul B; Komsuoglu, Haldun; Koditschek, Daniel E; Goldman, Daniel I

    2009-03-01

    Legged locomotion on flowing ground (e.g., granular media) is unlike locomotion on hard ground because feet experience both solid- and fluid-like forces during surface penetration. Recent bioinspired legged robots display speed relative to body size on hard ground comparable with high-performing organisms like cockroaches but suffer significant performance loss on flowing materials like sand. In laboratory experiments, we study the performance (speed) of a small (2.3 kg) 6-legged robot, SandBot, as it runs on a bed of granular media (1-mm poppy seeds). For an alternating tripod gait on the granular bed, standard gait control parameters achieve speeds at best 2 orders of magnitude smaller than the 2 body lengths/s (approximately 60 cm/s) for motion on hard ground. However, empirical adjustment of these control parameters away from the hard ground settings restores good performance, yielding top speeds of 30 cm/s. Robot speed depends sensitively on the packing fraction phi and the limb frequency omega, and a dramatic transition from rotary walking to slow swimming occurs when phi becomes small enough and/or omega large enough. We propose a kinematic model of the rotary walking mode based on generic features of penetration and slip of a curved limb in granular media. The model captures the dependence of robot speed on limb frequency and the transition between walking and swimming modes but highlights the need for a deeper understanding of the physics of granular media.

  10. Rapid penetration into granular media visualizing the fundamental physics of rapid earth penetration

    CERN Document Server

    Iskander, Magued

    2015-01-01

    Rapid Penetration into Granular Media: Visualizing the Fundamental Physics of Rapid Earth Penetration introduces readers to the variety of methods and techniques used to visualize, observe, and model the rapid penetration of natural and man-made projectiles into earth materials. It provides seasoned practitioners with a standard reference that showcases the topic's most recent developments in research and application. The text compiles the findings of new research developments on the subject, outlines the fundamental physics of rapid penetration into granular media, and assembles a com

  11. Probing density waves in fluidized granular media with diffusing-wave spectroscopy

    Science.gov (United States)

    Born, Philip; Reinhold, Steffen; Sperl, Matthias

    2016-09-01

    Density waves are characteristic for fluidized beds and affect measurements on liquidlike dynamics in fluidized granular media. Here the intensity autocorrelation function as obtainable with diffusing-wave spectroscopy is derived in the presence of density waves. The predictions by the derived form of the intensity autocorrelation function match experimental observations from a gas-fluidized bed. The model suggests separability of the contribution from density waves from the contribution by microscopic scatterer displacement to the decay of correlation and thus paves the way for characterizing microscopic particle motions using diffusing-wave spectroscopy as well as heterogeneities in fluidized granular media.

  12. Removal of nano and microparticles by granular filter media coated with nanoporous aluminium oxide

    Energy Technology Data Exchange (ETDEWEB)

    Lau, B.L.T.; Harrington, G.W.; Anderson, M.A.; Tejedor, I. [University of Wisconsin, Madison, WI (US). Dept. of Civil & Environmental Engineering

    2004-07-01

    Conventional filtration was designed to achieve high levels of particle and pathogen removal. Previous studies have examined the possibility of modifying filtration media to improve their ability to remove microorganisms and viruses. Although these studies have evaluated filter media coatings for this purpose, none have evaluated nanoscale particle suspensions as coating materials. The overall goal of this paper is to describe the preliminary test results of nanoporous aluminium oxide coated media that can be used to enhance filtration of nano and microparticles. Filtration tests were carried out using columns packed with uncoated and coated forms of granular anthracite or granular activated carbon. A positive correlation between isoelectric pH of filter media and particle removal was observed. The modified filter media with a higher isoelectric pH facilitated better removal of bacteriophage MS2 and 3 {mu}m latex microspheres, possibly due to increased favorable electrostatic interactions.

  13. Removal of nano and microparticles by granular filter media coated with nanoporous aluminium oxide.

    Science.gov (United States)

    Lau, B L T; Harrington, G W; Anderson, M A; Tejedor, I

    2004-01-01

    Conventional filtration was designed to achieve high levels of particle and pathogen removal. Previous studies have examined the possibility of modifying filtration media to improve their ability to remove microorganisms and viruses. Although these studies have evaluated filter media coatings for this purpose, none have evaluated nanoscale particle suspensions as coating materials. The overall goal of this paper is to describe the preliminary test results of nanoporous aluminium oxide coated media that can be used to enhance filtration of nano and microparticles. Filtration tests were carried out using columns packed with uncoated and coated forms of granular anthracite or granular activated carbon. A positive correlation between isoelectric pH of filter media and particle removal was observed. The modified filter media with a higher isoelectric pH facilitated better removal of bacteriophage MS2 and 3 microm latex microspheres, possibly due to increased favorable electrostatic interactions.

  14. Role of interparticle friction and particle-scale elasticity in the shear-strength mechanism of three-dimensional granular media

    Science.gov (United States)

    Antony, S. J.; Kruyt, N. P.

    2009-03-01

    The interlink between particle-scale properties and macroscopic behavior of three-dimensional granular media subjected to mechanical loading is studied intensively by scientists and engineers, but not yet well understood. Here we study the role of key particle-scale properties, such as interparticle friction and particle elastic modulus, in the functioning of dual contact force networks, viz., strong and weak contacts, in mobilizing shear strength in dense granular media subjected to quasistatic shearing. The study is based on three-dimensional discrete element method in which particle-scale constitutive relations are based on well-established nonlinear theories of contact mechanics. The underlying distinctive contributions of these force networks to the macroscopic stress tensor of sheared granular media are examined here in detail to find out how particle-scale friction and particle-scale elasticity (or particle-scale stiffness) affect the mechanism of mobilization of macroscopic shear strength and other related properties. We reveal that interparticle friction mobilizes shear strength through bimodal contribution, i.e., through both major and minor principal stresses. However, against expectation, the contribution of particle-scale elasticity is mostly unimodal, i.e., through the minor principal stress component, but hardly by the major principal stress. The packing fraction and the geometric stability of the assemblies (expressed by the mechanical coordination number) increase for decrease in interparticle friction and elasticity of particles. Although peak shear strength increases with interparticle friction, the deviator strain level at which granular systems attain peak shear strength is mostly independent of interparticle friction. Granular assemblies attain peak shear strength (and maximum fabric anisotropy of strong contacts) when a critical value of the mechanical coordination number is attained. Irrespective of the interparticle friction and elasticity

  15. Continuum modeling of projectile impact and penetration in dry granular media

    Science.gov (United States)

    Dunatunga, Sachith; Kamrin, Ken

    2017-03-01

    Modeling of impact into granular substrates is a topic of growing interest over the last decade. We present a fully continuum approach for this problem, which is shown to capture an array of experimentally observed behavior with regard to the intruder penetration dynamics as well as the flow and stress response of the granular media. The intruder is modeled as a stiff elastic body and the dry granular bulk is modeled using a 'trans-phase' constitutive relation. This relation has an elasto-viscoplastic response with pressure- and rate-sensitive yield behavior given by the μ (I) inertial rheology when the granular free volume is below a critical value. Above this critical value, the material is deemed to separate and is treated as a disconnected, stress-free medium. The Material Point Method is used to implement the impact problem numerically. Validations are conducted against a wide set of experimental data with a common granular material, which allows use of a single model calibration to test the agreement. In particular, continuum simulations of projectile impact with different shaped intruders and different impact energies show good agreement with experiments regarding of time-of-flight, penetration depth, and Poncelet drag force coefficients. Simultaneously, good agreement with experiments is found regarding the response of the granular media during impact, such as the pressure wave propagation process during the initial stage of impact, the flow fields that develop under the moving intruder, and the free-surface dynamics.

  16. Granular Media under Vibration in Zero Gravity: Transition from Rattling to Granular Gas

    CERN Document Server

    Evesque, P; Zhai, G; Hou, M

    2011-01-01

    We report on different experimental behaviours of granular dissipative matter excited by vibration as studied during the 43rd ESA campaign of Airbus A300-0g from CNES. The effect of g-jitter is quantified through the generation of a rattle effect. The French-European team's electromagnetic set-up is used, with 20Hz cam recording and high speed camera for a short duration (1s) during each parabola.

  17. Discharge flow of granular media from silos with a lateral orifice and injection of air

    Directory of Open Access Journals (Sweden)

    Aussillous Pascale

    2017-01-01

    Full Text Available Few studies concern the prediction of the mass flow rate of a granular media discharged from a silo with a lateral orifice. However, this situation can have pratical interest considering a tank of granular material with a leak on its side. We studied experimentally the discharge of a vertical silo filled by spherical glass beads. We consider rectangular silos with a rectangular orifice. The impact of size, aspect ratio and position of the orifice and the effect of an additional air flow were studied. The measured parameters are the mass flow rate and the pressure along the silo, whereas the controlled parameters are the size of particles, and the flow rate of air. We identified two regimes of discharge according to the aspect ratio (of width to height of the rectangular orifice. Increasing the air flow rate induces an increase of the granular media flow rate. Using a simple physical model to describe the grains and gas flow, we put in evidence the role played by the air pressure gradient at the outlet. Then we compared the experimental results with continuum Navier-Stokes simulations with the granular μ(I-rheology. We showed that the continuum μ(I-rheology describes well our discharge flow of granular media from silos, taking into account the effect of the position of the orifice as well as the coupling with the gas flow.

  18. Unifying suspension and granular rheology.

    Science.gov (United States)

    Boyer, François; Guazzelli, Élisabeth; Pouliquen, Olivier

    2011-10-28

    Using an original pressure-imposed shear cell, we study the rheology of dense suspensions. We show that they exhibit a viscoplastic behavior similarly to granular media successfully described by a frictional rheology and fully characterized by the evolution of the friction coefficient μ and the volume fraction ϕ with a dimensionless viscous number I(v). Dense suspension and granular media are thus unified under a common framework. These results are shown to be compatible with classical empirical models of suspension rheology and provide a clear determination of constitutive laws close to the jamming transition.

  19. Effect of boundary vibration on the frictional behavior of a dense sheared granular layer

    CERN Document Server

    Ferdowsi, B; Guyer, R A; Johnson, P A; Carmeliet, J

    2014-01-01

    We report results of 3D Discrete Element Method (DEM) simulations aiming at investigating the role of the boundary vibration in inducing frictional weakening in sheared granular layers. We study the role of different vibration amplitudes applied at various shear stress levels, for a granular layer in the stick-slip regime and in the steady-sliding regime. Results are reported in terms of friction drops and kinetic energy release associated with frictional weakening events. We find that larger vibration amplitude induces larger frictional weakening events. The results show evidence of a threshold below which no induced frictional weakening takes place. Friction drop size is found to be dependent on the shear stress at the time of vibration. A significant increase in the ratio between the number of slipping contacts to the number of sticking contacts in the granular layer is observed for large vibration amplitudes. These vibration-induced contact rearrangements enhance particle mobilization and induces a fricti...

  20. Electrification and Charge Distribution in Vertically Shaken Granular Media

    Science.gov (United States)

    Rojas, Ruben; Nordsiek, Freja; Lathrop, Daniel

    2016-11-01

    Granular charging of particle laden flows at large scales is a widespread phenomenon and has long been observed in nature: Volcanic ash clouds, desert sandstorms, dust devils, thunderstorms and snowstorms all undergo electrification at large scale. As a first approach to understand this phenomenon, we confined granular particles to a vertically oscillating cylindrical chamber with top and bottom conducting plates. Long term voltage transients between the plates and a high dependence on the total particle surface area suggested the preponderance of collective effects in the electrification processes. In order to further explore this hypothesis, we reduced the electrode area for the measurement with two 2-cm circular flat probes on the top plate. With this setup we detected differences in the charge distribution among the particles due to a more localized measurement of the voltage. This research was supported by the Julian Schwinger Foundation.

  1. Scaling Relations for Wheeled Locomotion in Granular Media

    Science.gov (United States)

    Slonaker, James; Kamrin, Ken

    Vehicular wheel design for use on granular material has not currently been perfected. Resistive Force Theory (RFT) is a reduced-order empirical model for granular drag, which shows promise to help simulate and understand locomotion processes to design more efficient wheels. Here we explore the fundamental scaling relations derived from RFT and their experimental validation. Similar to the non-dimensional scaling relations in fluid mechanics, the relative simplicity of RFT asserts that only one material parameter, the ''grain-structure coefficient'', is required, which reduces the complexity of the non-dimensional groups implied by the system. Therefore, wheels with differing input design parameters like size, mass, shape and even gravity, can be tested and their performance related to each other in predictable ways. We experimentally confirmed these relations by testing with 3D printed wheel geometries in a controlled sand bed.

  2. Density Waves in the Flows of Granular Media

    OpenAIRE

    1993-01-01

    We study density waves in the flows of granular particles through vertical tubes and hoppers using both analytic methods and molecular dynamics (MD) simulations. We construct equations of motion for quasi one-dimensional systems. The equations, combined with the Bagnold's law for friction, are used to describe the time evolutions of the density and the velocity fields for narrow tubes and hoppers. The solutions of the equations can have two types of density waves, kinetic and dynamic. For tub...

  3. Influence of granulometry in the Hurst exponent of air liquid interfaces formed during capillary rising in a granular media

    Directory of Open Access Journals (Sweden)

    Gontijo Guilherme L.

    2017-01-01

    Full Text Available We report results concerning the fractal dimension of a air/fluid interface formed during the capillary rising of a fluid into a dense granular media. The system consists in a modified Hele-Shaw cell filled with grains at different granulometries and confined in a narrow gap between the glass plates. The system is then placed onto a water reservoir, and the liquid penetrates the medium due to capillary forces. We measure the Hurst exponent of the liquid/air interface with help of image processing, and follow the temporal evolution of the profiles. We observe that the Hurst exponent can be related with the granulometry, but the range of values are odd to the predicted values from models or theory.

  4. Investigation of proper modeling of very dense granular flows in the recirculation system of CFBs

    Institute of Scientific and Technical Information of China (English)

    Aristeidis Nikolopoulos; Nikos Nikolopoulos; Nikos Varveris; Sotirios Karellas; Panagiotis Grammelis; Emmanuel Kakaras

    2012-01-01

    The aim of this paper is the development of new models and/or the improvement of existing numerical models,used for simulating granular flow in CFB (circulating fluidized bed) recirculation systems.Most recent models follow the TFM (two-fluid model) methodology,but they cannot effectively simulate the inter-particle friction forces in the recirculation system,because the respective stress tensor does not incorporate compressibility of flow due to change of effective particle density.As a consequence,the induced normal and shear stresses are not modeled appropriately during the flow of the granular phase in the CFB recirculation system.The failure of conventional models,such as that of von Mises/Coulomb,is mainly caused by false approximation of the yield criterion which is not applicable to the CFB recirculation system.The present work adopts an alternative yield function,used for the first time in TFM Eulerian modeling.The proposed model is based on the Pitman-Schaeffer-Gray-Stiles yield criterion.Both the temporal deformation of the solid granular phase and the repose angle that the granular phase forms are more accurately simulated by this model.The numerical results of the proposed model agree well with experimental data,implying that frictional forces are efficiently simulated by the new model.

  5. Frustration and disorder in granular media and tectonic blocks: implications for earthquake complexity

    Directory of Open Access Journals (Sweden)

    A. Sornette

    1994-01-01

    Full Text Available We present exploratory analogies and speculations on the mechanisms underlying the organization of faulting and earthquake in the earth crust. The mechanical properties of the brittle lithosphere at scales of the order or larger than a few kilometers are proposed to be analogous to those of non-cohesive granular media, since both systems present stress amplitudes controlled by gravity, and shear band (faulting localization is determined by a type of friction Mohr-Coulomb rupture criterion. here, we explore the implications of this correspondence with respect to the origin of tectonic and earthquake complexity, on the basis of the existing experimental data on granular media available in the mechanical literature. An important observation is that motions and deformations of non-cohesive granular media are characterized by important fluctuations both in time (sudden breaks, avalanches, which are analogous to earthquakes and space (strain localizations, yield surfaces forming sometimes complex patterns. This is in apparent contradiction with the conventional wisdom in mechanics, based on the standard tendency to homogenize, which has led to dismiss fluctuations as experimental noise. On the basis of a second analogy with spinglasses and neural networks, based on the existence of block and grain packing disorder and block rotation "frustration", we suggest that these fluctuations observed both at large scales and at the block scale constitute an intrinsic signature of the mechanics of granular media. The space-time complexity observed in faulting and earthquake phenomenology is thus proposed to result form the special properties of the mechanics of granular media, dominated by the "frustration" of the kinematic deformations of its constitutive blocks.

  6. A hierarchical model for cross-scale simulation of granular media

    Science.gov (United States)

    Guo, Ning; Zhao, Jidong

    2013-06-01

    This paper presents a multiscale modeling framework for granular media based on a hierarchical cross-scale approach. The overall material is treated as a continuum on the macroscale and the corresponding boundary value problem is solved by finite element method (FEM). At each Gauss point of the FEMmesh, a discrete element assembly is embedded from which the material behavior is obtained for the global FEM computation. It is demonstrated that this technique may capture the salient macroscopic behavior of granular media in a natural manner, and meanwhile helps to bypass the conventional phenomenological nature of continuum modeling approaches. Moreover, the framework provides us with rich information on the particle level which can be closely correlated to the macroscopic material response and hence helps to shed lights on the cross-scaling understanding of granular media. Specific linkages between the microscopic origins and mechanisms and the macroscopic responses can be conveniently developed. As a demonstrative example, the strain localization of granular sand in biaxial compression test is investigated by the multiscale approach to showcase the above features.

  7. Depth-Dependent Resistance of Granular Media to Vertical Penetration

    Science.gov (United States)

    Brzinski, T. A., III; Mayor, P.; Durian, D. J.

    2013-10-01

    We measure the quasistatic friction force acting on intruders moving downwards into a granular medium. By utilizing different intruder geometries, we demonstrate that the force acts locally normal to the intruder surface. By altering the hydrostatic loading of grain contacts by a sub-fluidizing airflow through the bed, we demonstrate that the relevant frictional contacts are loaded by gravity rather than by the motion of the intruder itself. Lastly, by measuring the final penetration depth versus airspeed and using an earlier result for inertial drag, we demonstrate that the same quasistatic friction force acts during impact. Altogether this force is set by a friction coefficient, hydrostatic pressure, projectile size and shape, and a dimensionless proportionality constant. The latter is the same in nearly all experiments, and is surprisingly greater than one.

  8. Shear flow of dense granular materials near smooth walls. I. Shear localization and constitutive laws in the boundary region.

    Science.gov (United States)

    Shojaaee, Zahra; Roux, Jean-Noël; Chevoir, François; Wolf, Dietrich E

    2012-07-01

    We report on a numerical study of the shear flow of a simple two-dimensional model of a granular material under controlled normal stress between two parallel smooth frictional walls moving with opposite velocities ± V. Discrete simulations, which are carried out with the contact dynamics method in dense assemblies of disks, reveal that, unlike rough walls made of strands of particles, smooth ones can lead to shear strain localization in the boundary layer. Specifically, we observe, for decreasing V, first a fluidlike regime (A), in which the whole granular layer is sheared, with a homogeneous strain rate except near the walls, then (B) a symmetric velocity profile with a solid block in the middle and strain localized near the walls, and finally (C) a state with broken symmetry in which the shear rate is confined to one boundary layer, while the bulk of the material moves together with the opposite wall. Both transitions are independent of system size and occur for specific values of V. Transient times are discussed. We show that the first transition, between regimes A and B, can be deduced from constitutive laws identified for the bulk material and the boundary layer, while the second one could be associated with an instability in the behavior of the boundary layer. The boundary zone constitutive law, however, is observed to depend on the state of the bulk material nearby.

  9. Inelastic gas: An experimental study of vibro-fluidized dilute granular media

    Science.gov (United States)

    Feitosa, Klebert Bezerra

    We conduct an experimental study of a two dimensional vibro-fluidized dilute granular medium. The system is composed of spherical beads confined to move in a vertical plane and excited by intense vertical vibrations. We perform full-field tracking of positions and orientations of the spheres by high speed photography. In steady-state, the motion of the grains resembles that of a molecular gas, thus the name granular gas. We study the distribution of linear velocities in the granular gas. The investigation shows that the distributions are non-gaussian, best fitted by the function P(v) ˜ exp(-beta| v|/sigma)1.5), and insensitive to number density, driving parameters and particle inelasticity. The distribution is a one parameter distribution, parameterized by the mean square velocity; which defines a granular temperature. T = ½ . We study binary mixtures of the granular media. We find that, in general, the granular temperature is not equal for the two types of spheres. However, the temperature ratio is constant in the bulk. The ratio depends strongly on the mass ratio of the spheres, but not on their inelasticity. The ratio is also insensitive to compositional parameters of the mixture such as number fraction and number density. We also investigate the statistics of the power flux into a subsystem of the granular gas. The power shows large fluctuations, including frequent large negative fluctuations. The relative probabilities of positive and negative fluctuations in the power flux are in close accord with the Fluctuation Theorem of Gallavotti and Cohen (Gallavotti & Cohen, 1995b). We also compare the effective temperature that emerges from this analysis to the kinetic granular temperature. Finally, we study the rotational dynamics of the granular gas. We find that the granular temperature is not equipartitioned between translational and rotational degrees of freedom. We also demonstrate that the ratio of rotational to translational energy is independent of the

  10. Water flow exchange characteristics in coarse granular filter media

    DEFF Research Database (Denmark)

    Andreasen, Rune Røjgaard; Pugliese, Lorenzo; Poulsen, Tjalfe

    2013-01-01

    in this study are performed at a concurrent airflow of 0.3 m s−1, water irrigation rates of 1–21 cm h−1 in materials with particle diameters ranging from 2 to 14 mm to represent media and operation conditions relevant for low flow biotrickling filter design. Specific surface area related elution velocity...... distribution was closely related to the filter water content, water irrigation rate, media specific surface area and particle size distribution. A predictive model linking the specific surface area related elution velocity distribution to irrigation rate, specific surface area and particle size distribution......Elution of inhibitory metabolites is a key parameter controlling the efficiency of air cleaning bio- and biotrickling filters. To the authors knowledge no studies have yet considered the relationship between specific surface area related elution velocity and physical media characteristics, which...

  11. Water flow exchange characteristics in coarse granular filter media

    DEFF Research Database (Denmark)

    Andreasen, Rune Røjgaard; Pugliese, Lorenzo; Poulsen, Tjalfe

    2013-01-01

    Elution of inhibitory metabolites is a key parameter controlling the efficiency of air cleaning bio- and biotrickling filters. To the authors knowledge no studies have yet considered the relationship between specific surface area related elution velocity and physical media characteristics, which...... in this study are performed at a concurrent airflow of 0.3 m s−1, water irrigation rates of 1–21 cm h−1 in materials with particle diameters ranging from 2 to 14 mm to represent media and operation conditions relevant for low flow biotrickling filter design. Specific surface area related elution velocity...... distribution was closely related to the filter water content, water irrigation rate, media specific surface area and particle size distribution. A predictive model linking the specific surface area related elution velocity distribution to irrigation rate, specific surface area and particle size distribution...

  12. Comparison of physical, numerical and resistive force models of undulatory locomotion within granular media

    Science.gov (United States)

    Goldman, Daniel I.; Maladen, Ryan D.; Ding, Yang; Umbanhowar, Paul

    2010-11-01

    We integrate biological experiments, empirical theory, numerical simulation, and a physical robot model to reveal principles of undulatory locomotion in granular media. High speed x-ray imaging of the sandfish, Scincus scincus, in 3 mm glass particles reveals that it swims within the medium without limb use by propagating a single period traveling sinusoidal wave down its body, resulting in a wave efficiency, η, the ratio of its average forward speed to wave speed, of 0.54,,.13. A resistive force theory (RFT) which balances granular thrust and drag forces along the body predicts η close to the observed value. We test this prediction against two other modeling approaches: a numerical model of the sandfish coupled to a Molecular Dynamics (MD) simulation of the granular medium, and an undulatory robot which swims within granular media. We use these models and analytic solutions of the RFT to vary the ratio of undulation amplitude to wavelength (A/λ) and demonstrate an optimal condition for sand-swimming that results from competition between η and λ. The RFT, in agreement with simulation and robot models, predicts that for a single period sinusoidal wave, maximal speed occurs for A/λ 0.2, the same kinematics used by the sandfish.

  13. Lubrication forces in dense granular flow with interstitial fluid: A simulation study with Discrete Element Method

    Science.gov (United States)

    Baran, Oleh; Ertas, Deniz; Halsey, Thomas; Zhou, Fuping

    2007-03-01

    Using three-dimensional molecular dynamics simulations, we study steady gravity-driven flows of frictional inelastic spheres of diameter d and density ρg down an incline, interacting through two-body lubrication forces in addition to granular contact forces. Scaling arguments suggest that, in 3D, these forces constitute the dominant perturbation of an interstitial fluid for small Reynolds number Re and low fluid densityρ. Two important parameters that characterize the strength of the lubrication forces are fluid viscosity and grain roughness. We observe that incline flows with lubrication forces exhibit a packing density that decreases with increasing distance from the surface. As the incline angle is increased, this results in a severely dilated basal layer that looks like ``hydroplaning'' similar to that observed in geological subaqueous debris flows. This is surprising since the model explicitly disallows any buildup of fluid pressure in the base of the flow, and suggests that hydroplaning might have other contributing factors besides this traditional explanation. The local packing density is still determined by the dimensionless strain rate I≡γ1ptd√ρg/p , where p is the average normal stress, obeying a ``dilatancy law'' similar to dry granular flows.

  14. Locomotion and drag in wet and dry granular media

    Science.gov (United States)

    Goldman, Daniel; Kuckuk, Robyn; Sharpe, Sarah

    2015-03-01

    Many animals move within substrates such as soil and dry sand; the resistive properties of such granular materials (GM) can depend on water content and compaction, but little is known about how such parameters affect locomotion or the relevant physics of drag and penetration. We developed a system to create homogeneous wet GM of varying moisture content and compaction in quantities sufficient to study the burial and subsurface locomotion of the Ocellated skink (C. ocellatus) a desert-generalist lizard. X-ray imaging revealed that in wet and dry GM the lizard slowly buried (~ 30 seconds) propagating a wave from head to tail, while moving in a start-stop motion. During forward movement, the head oscillated, and the forelimb on the convex side of the body propelled the animal. Although body kinematics (and ``slip'') were similar in both substrates, the burial depth was smaller in wet GM. Penetration and drag force experiments on smooth cylinders revealed that wet GM was ~ 3 × more resistive than dry GM, suggesting that during burial the lizard operated near its maximum force producing capability and was thus constrained by environmental properties. work supported by NSF PoLS.

  15. The effect of wettability on capillary fracturing in granular media

    Science.gov (United States)

    Trojer, M.; Szulczewski, M.; Juanes, R.

    2012-12-01

    During multiphase flow in a granular medium, capillary pressures can overcome cohesive forces between the grains and cause grain displacements that macroscopically resemble fracture patterns. These patterns were recently studied in experiments of air displacing water in a thin bed of glass beads, for which air is a strongly non-wetting fluid (Holtzman et al. 2012). The experiments showed that the transition from viscous fingering and capillary fingering to capillary fracturing could be predicted by a single dimensionless number called the fracturing number, which is the ratio of the capillary forces that promote grain displacements to the frictional forces that resist displacements. Here, we extend those experiments to study exclusively how the wettability of the invading fluid affects fracturing by visually observing the morphology of the pattern. As in the previous work, we inject a less viscous fluid into a thin bed of glass beads saturated with a more viscous fluid. However, we now vary the fluids to change the wettability of the invading fluid from perfectly non-wetting to wetting. We hypothesize that the emergence of fracturing can be predicted by a modified fracturing number that includes the contact angle to account for the effect of wettability on the capillary pressure. Since the contact angle is a function of the capillary number, we expect the emergence of fracturing will depend on the capillary number when the invading fluid is partially wetting.

  16. The impact of fluid flow on force chains in granular media

    Science.gov (United States)

    Mahabadi, Nariman; Jang, Jaewon

    2017-01-01

    Fluid flow through granular media is an important process found in nature and various engineering applications. The effect of fluid flow on the evolution of force chains in the granular media is explored using the photoelasticity theory. A transparent cell is designed to contain several photoelastic disks of different sizes and to allow fluid flow through the particle packing. Water is injected into the cell while the particle packing is under confining stress. Several images are taken for the conditions of different confining stresses and fluid injection rates. An algorithm of an image processing technique is developed to detect the orientation and magnitude of contact forces. The results show that forces in parallel and transverse to the flow direction increase with increasing water velocity, while parallel force shows a higher increasing rate.

  17. Experimental added modal damping induced by confined granular media on a single degree of freedom system

    Science.gov (United States)

    Sternberger, Antoine; Pelat, Adrien; Génevaux, Jean-Michel

    2017-06-01

    The use of granular media to induce vibration energy's dissipation in lighter huge industrial structures permits to decrease the mass of the structure and consequently to spare the construction's cost and to satisfy oil consumption. In fact, when the structure in which the granular media is in contact overtakes an acceleration threshold, relative movements of the grains appears which lead to a dissipation of energy. When the grains are confined inside a cavity, the dissipation's level depends on several parameters (the acceleration's amplitude, the frequency, the grain's characteristics, the cavity's dimensions, the cavity's filling ratio, the fluid between the particles, etc.). This study quantifies the influence of several parameters by exciting uniformly a given volume of grains. A modal damping coefficient of a single degree of freedom system (SDOF) can be thus calculated as a function of the preceding parameters.

  18. 3D Printer Instrumentation to Create Varied Geometries of Robotic Limbs and Heterogeneous Granular Media

    Science.gov (United States)

    2015-05-20

    11-May-2015 Approved for Public Release; Distribution Unlimited Final Report: 3D Printer Instrumentation to Create Varied Geometries of Robotic Limbs... 3D Printer Instrumentation to Create Varied Geometries of Robotic Limbs and Heterogeneous Granular Media Report Title There is a need for robotic...studies, we request Research Instrumentation (RI) to purchase two 3D printers , which we will use to fabricate a wide of variety of objects that will

  19. Generalized Phenomenological Cyclic Stress-Strain-Strength Characterization of Anisotropic Granular Media.

    Science.gov (United States)

    1985-06-27

    ANISOTROPIC GRANULAR MEDIA" 19. A review of existing elasto-plastic theory as related to soil mechanics showed only a few models of a phenomenological...characterizations, Prevost’s pressure sensitive model , was used in the prediction of the hollow cylinder tests. Although the model reasonably reproduced the...48 1. Cauchy Type Elasticity ...................... 49 2. Hyperelasticity or Green Type Elasticity .... 53 3. Hypoelasticity or Incremental Type

  20. Collapse dynamics and runout of dense granular materials in a fluid.

    Science.gov (United States)

    Topin, V; Monerie, Y; Perales, F; Radjaï, F

    2012-11-02

    We investigate the effect of an ambient fluid on the dynamics of collapse and spread of a granular column simulated by means of the contact dynamics method interfaced with computational fluid dynamics. The runout distance is found to increase as a power law with the aspect ratio of the column, and, surprisingly, for a given aspect ratio and packing fraction, it may be similar in the grain-inertial and fluid-inertial regimes but with considerably longer duration in the latter case. We show that the effect of fluid in viscous and fluid-inertial regimes is to both reduce the kinetic energy during collapse and enhance the flow by lubrication during spread. Hence, the runout distance in a fluid may be below or equal to that in the absence of fluid due to compensation between those effects.

  1. Evolvement of permeability of ore granular media during heap leaching based on image analysis

    Institute of Scientific and Technical Information of China (English)

    YANG Bao-hua; WU Ai-xiang; JIANG Huai-chun; CHEN Xue-song

    2008-01-01

    The column leaching experiment of ore granular media was carried out with the home-made multi-functional experimental apparatus and the pore structure of ore granular media was scanned by the X-ray computed tomography machine before and after leaching. The porosities of each section before and after leaching were calculated based on CT images processing, and the permeability of each zone before and after leaching were also calculated with Carman-Kozeny equation. The permeability evolvement law was disclosed. The results indicate that before leaching the permeability of the ore granular media in different height has not much difference and the value ranges from 5.70×10-4 mm2 to 1.11×10-3 mm2, where the lowest one locates in the bottom zone. After leaching the permeability distributes inhomogeneously along the height of the column and the value ranges from 3.44×10-4 mm2 to 2.25×10-2 mm2, where the lowest one is in the same place. Except for the bottom zone, the permeability of other zones increases after leaching, especially the top zone. Through comparison of the permeability at bottom zone before and after leaching, the whole permeability after leaching decreases by 39.65% that coincides with the measured experimental data.

  2. Elastic weakening of a dense granular pack by acoustic fluidization: slipping, compaction, and aging.

    Science.gov (United States)

    Jia, X; Brunet, Th; Laurent, J

    2011-08-01

    Sound velocity measurements in dense glass bead packs reveal significant softening effect at large amplitudes, due to the frictional nonlinearity at the grain contacts. Beyond a certain amplitude, the sound-matter interaction becomes irreversible, leaving the medium in a weakened and slightly compacted state. A slow recovery of the initial elastic modulus is observed after acoustic perturbation, revealing the plastic creep growth of microcontacts. The cross-correlation function of configuration-specific acoustic speckles highlights the relationship between the macroscopic elastic weakening and the local change of the contact networks, induced by strong sound vibration, in the absence of appreciable grain motion.

  3. Linear and nonlinear elastic properties of dense granular packings: a DEM exploration

    Directory of Open Access Journals (Sweden)

    Lemrich Laure

    2017-01-01

    Full Text Available Discrete Element Method modeling is used to study the frequency spectrum of particle motion in dense 3D packings of glass beads with Hertz-Mindlin contacts. Frequency sweeps show a dependency of the resonant frequencies on the drive amplitude and confining stress on the system, showing material changes in the system. The amplitude dependency of the second thickness mode 3λ/4 as identified by the internal strain field scales as f ∝ σ1/6 while the confining stress dependency scales as f ∝ σ 2/3, as predicted by Hertzian theory.

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

    Science.gov (United States)

    Dalbe, Marie-Julie; Juanes, Ruben

    2016-11-01

    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. 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.

  5. 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.

  6. Colloquium: Biophysical principles of undulatory self-propulsion in granular media

    Science.gov (United States)

    Goldman, Daniel I.

    2014-07-01

    Biological locomotion, movement within environments through self-deformation, encompasses a range of time and length scales in an organism. These include the electrophysiology of the nervous system, the dynamics of muscle activation, the mechanics of the skeletal system, and the interaction mechanics of such structures within natural environments like water, air, sand, and mud. Unlike the many studies of cellular and molecular scale biophysical processes, movement of entire organisms (like flies, lizards, and snakes) is less explored. Further, while movement in fluids like air and water is also well studied, little is known in detail of the mechanics that organisms use to move on and within flowable terrestrial materials such as granular media, ensembles of small particles that collectively display solid, fluid, and gaslike behaviors. This Colloquium reviews recent progress to understand principles of biomechanics and granular physics responsible for locomotion of the sandfish, a small desert-dwelling lizard that "swims" within sand using undulation of its body. Kinematic and muscle activity measurements of sand swimming using high speed x-ray imaging and electromyography are discussed. This locomotion problem poses an interesting challenge: namely, that equations that govern the interaction of the lizard with its environment do not yet exist. Therefore, complementary modeling approaches are also described: resistive force theory for granular media, multiparticle simulation modeling, and robotic physical modeling. The models reproduce biomechanical and neuromechanical aspects of sand swimming and give insight into how effective locomotion arises from the coupling of the body movement and flow of the granular medium. The argument is given that biophysical study of movement provides exciting opportunities to investigate emergent aspects of living systems that might not depend sensitively on biological details.

  7. Shearing fluid-filled granular media: A coupled discrete element - continuous approach

    Science.gov (United States)

    Goren, L.; Aharonov, E.; Sparks, D.; Toussaint, R.; Marder, E.

    2012-04-01

    Fluid-filled granular layers are abundant in the Earth's shallow crust as saturated soils and poorly consolidated hillslope material, and as fluid-filled fault gouge layers. When such grains-fluid systems are subjected to excitation by the passage of seismic waves, tectonic loading, or gravitational loading they exhibit a highly non-trivial dynamical behavior that may lead to instabilities in the form of soil liquefaction, debris flow mobilization, and earthquakes. In order to study the basic coupled mechanics of fluid-filled granular media and the dynamical processes that are responsible for the emergence of instabilities we develop a model that couples granular dynamics (DEM) algorithm with a continuous Eulerian grid-based solver. The two components of the model represent the two phases (grains and fluid) in two different scales. Each grain is represented by a single element in the granular dynamics component, where grains interact by elastic collisions and frictional sliding. The compressible pore fluid is represented on a coarser Darcy scale grid that is super-imposed over the grains layer. The pore space geometry set by the evolving granular packing is used to define smooth porosity and permeability fields, and the individual grain velocities are interpolated to define a smooth field of a solid-fraction velocity. The porosity, permeability, and solid velocity fields are used in the continuous fluid grid-based solver to find pore fluid velocity and pressure. Pore fluid pressure gradients are interpolated back from the fluid grid to individual grains, where they enter the grains force balance equation as seepage forces. Boundary conditions are specified separately for the two phases. For the pore fluid we test two end-member drainage conditions: completely drained system (with infinite boundary permeability) and completely undrained system (with zero boundary permeability). For the grains, two-dimensional time dependent stress and velocity conditions are

  8. Propagation of Complex Laser Pulses in Optically Dense Media

    Science.gov (United States)

    Fetterman, M. R.; Davis, J. C.; Goswami, D.; Yang, W.; Warren, W. S.

    1999-05-01

    Ultrafast laser pulses with complex envelopes (amplitude and frequency modulated) are used to excite an optically dense column of rubidium vapor. Pulse reshaping, stimulated emission dynamics, and residual electronic excitation in the Rb vapor are all shown to depend strongly on the laser pulse shape. Pulses that produce adiabatic passage in the optically thin limit exhibit more complex behavior in optically thick samples, including an unexpected dependence on the sign of the frequency sweep. Numerical solutions of the Maxwell-Bloch equations are shown to account for our results.

  9. Effect of deformation on the thermal conductivity of granular porous media with rough grain surface

    Science.gov (United States)

    Askari, Roohollah; Hejazi, S. Hossein; Sahimi, Muhammad

    2017-08-01

    Heat transfer in granular porous media is an important phenomenon that is relevant to a wide variety of problems, including geothermal reservoirs and enhanced oil recovery by thermal methods. Resistance to flow of heat in the contact area between the grains strongly influences the effective thermal conductivity of such porous media. Extensive experiments have indicated that the roughness of the grains' surface follows self-affine fractal stochastic functions, and thus, the contact resistance cannot be accounted for by models based on smooth surfaces. Despite the significance of rough contact area, the resistance has been accounted for by a fitting parameter in the models of heat transfer. In this Letter we report on a study of conduction in a packing of particles that contains a fluid of a given conductivity, with each grain having a rough self-affine surface, and is under an external compressive pressure. The deformation of the contact area depends on the fractal dimension that characterizes the grains' rough surface, as well as their Young's modulus. Excellent qualitative agreement is obtained with experimental data. Deformation of granular porous media with grains that have rough self-affine fractal surface is simulated. Thermal contact resistance between grains with rough surfaces is incorporated into the numerical simulation of heat conduction under compressive pressure. By increasing compressive pressure, thermal conductivity is enhanced more in the grains with smoother surfaces and lower Young's modulus. Excellent qualitative agreement is obtained with the experimental data.

  10. Evolution of Force Networks in Dense Particulate Media

    CERN Document Server

    Kramar, Miroslav; Kondic, Lou; Mischaikow, Konstantin

    2014-01-01

    We introduce novel sets of measures with the goal of describing dynamical properties of force networks in dense particulate systems. The presented approach is based on persistent homology and allows for extracting precise, quantitative measures that describe the evolution of geometric features of the interparticle forces, without necessarily considering the details related to individual contacts between particles. The networks considered emerge from discrete element simulations of two dimensional particulate systems consisting of compressible frictional circular disks. We quantify the evolution of the networks for slowly compressed systems undergoing jamming transition. The main findings include uncovering significant but localized changes of force networks for unjammed systems, global (system-wide) changes as the systems evolve through jamming, to be followed by significantly less dramatic evolution for the jammed states. We consider both connected components, related in loose sense to force chains, and loop...

  11. Propagation of Electromagnetic Waves in Extremely Dense Media

    CERN Document Server

    Masood, Samina

    2016-01-01

    We study the propagation of electromagnetic (EM) waves in extremely dense exotic systems with very unique properties. These EM waves develop a longitudinal component due to its interaction with the medium. Renormalization scheme of QED is used to understand the propagation of EM waves in both longitudinal and transverse directions. The propagation of EM waves in a quantum statistically treatable medium affects the properties of the medium itself. The electric permittivity and the magnetic permeability of the medium are modified and influence the related behavior of the medium. All the electromagnetic properties of a medium become a function of temperature and chemical potential of the medium. We study in detail the modifications of electric permittivity and magnetic permeability and other related properties of a medium in the superdense stellar objects.

  12. Effects of acoustic waves on stick-slip in granular media and implications for earthquakes

    Science.gov (United States)

    Johnson, P.A.; Savage, H.; Knuth, M.; Gomberg, J.; Marone, Chris

    2008-01-01

    It remains unknown how the small strains induced by seismic waves can trigger earthquakes at large distances, in some cases thousands of kilometres from the triggering earthquake, with failure often occurring long after the waves have passed. Earthquake nucleation is usually observed to take place at depths of 10-20 km, and so static overburden should be large enough to inhibit triggering by seismic-wave stress perturbations. To understand the physics of dynamic triggering better, as well as the influence of dynamic stressing on earthquake recurrence, we have conducted laboratory studies of stick-slip in granular media with and without applied acoustic vibration. Glass beads were used to simulate granular fault zone material, sheared under constant normal stress, and subject to transient or continuous perturbation by acoustic waves. Here we show that small-magnitude failure events, corresponding to triggered aftershocks, occur when applied sound-wave amplitudes exceed several microstrain. These events are frequently delayed or occur as part of a cascade of small events. Vibrations also cause large slip events to be disrupted in time relative to those without wave perturbation. The effects are observed for many large-event cycles after vibrations cease, indicating a strain memory in the granular material. Dynamic stressing of tectonic faults may play a similar role in determining the complexity of earthquake recurrence. ??2007 Nature Publishing Group.

  13. An equation of state for granular media at the limit state of isotropic compression

    Science.gov (United States)

    Oquendo, W. F.; Muñoz, J. D.; Radjai, F.

    2016-04-01

    It is well believed that the volumetric entropy of Edwards captures part of the physics of granular media, but it is still unclear whether it can be applied to granular systems under mechanical stress. By working out a recent proposal by Aste, Di Matteo et al. to measure Edwards' compactivity from the volume distribution of Voronoï or Delaunay tessellations (Phys. Rev. E, 77 (2008) 021309), and assuming that the total volume divides into elementary cells of fixed minimal volume, we derive an equation of state relating the compactivity to the packing fraction, and we show by extensive molecular-dynamics simulations that this equation and its underlying assumption describe well the volumetric aspects of both the limit state of isotropic compression and the limit state of shear (also called critical state in soil mechanics) for three-dimensional ensembles of mono-disperse spheres, for a broad range of the sliding and rolling friction coefficients. In addition, by using the limit state of isotropic compression as testing ground, we find that the compactivity, the entropy per elementary cell and the number of elementary cells per grain computed by this method are the same within statistical precision, either by using Voronoï, Delaunay, or centroidal Voronoï tessellations, allowing thus for an objective definition. This means that not only Aste's cell method is robust and suitable to measure Edwards' compactivity of granular systems under mechanical stress but also the actual nature of the elementary cells might be unimportant.

  14. The evolution of orientational order in sheared, 2D granular media of convex and concave elongated particles

    Science.gov (United States)

    Marschall, Theodore; Teitel, Stephen

    We simulate granular media consisting of elongated grains in two dimensions with a uniform background shear. We study the orientational distribution and rotation over a wide range of packing fractions, and find that the distribution reaches a stable steady-state under most initial conditions. The nematic director increases with the packing fraction, but the nematic order parameter exhibits non-monotonic behavior, which occurs well below jamming. We observe the evolution of the orientational distribution starting from configurations with the director out of alignment from its steady state orientation, and the evolution of highly ordered initial states. In general, the tumbling motion caused by the background shear causes such systems to reorder into the steady-state, but some dense, highly-ordered configurations maintain their order and exhibit wagging behavior. This can occur both above and below the jamming transition. These results for smooth, convex, spherocylindrical particles are contrasted with those for concave cross-like particles. This work is supported by NSF Grant DMRPD-09-1765.

  15. Testing Occam's razor to characterize high-order connectivity in pore networks of granular media: Feature selection in machine learning

    Science.gov (United States)

    van der Linden, Joost; Tordesillas, Antoinette; Narsilio, Guillermo

    2017-06-01

    A perennial challenge for the characterization and modelling of phenomena involving granular media is that the internal connectivity of, and interactions between, the pores and the particles exhibit hallmarks of complexity: multi-scale and nonlinear interactions that lead to a plethora of patterns at the mesoscale, including fluid flow patterns that ultimately render a permeability of the granular media at the macroscale. A multitude of physical parameters exist to characterize geometry and structure, including pore/particle shape, volume and surface area, while a rich class of complex network parameters quantifies internal connectivity of the pore and particles in the material. A large collection of such variables is likely to exhibit a high degree of redundancy. Here we demonstrate how to use feature selection in machine learning theory to identify the most informative and non-redundant, yet parsimonious set of features that optimally characterizes the interstitial flow properties of porous, granular media, e.g., permeability, from high resolution data.

  16. Process Performance of Secondary Effluent Granular Media Filtration with and without Preozonation.

    Science.gov (United States)

    Merlo, Rion; De Las Casas, Carla; Henneman, Seppi; Witzgall, Robert; Yu, William; Ramberg, Steve; Parker, Denny; Ohlinger, Kurt

    2015-07-01

    A 10-month pilot study compared the performance of conventional granular media filtration (CGMF) with granular media filtration with preozonation (OGMF) to determine the effects of preozonation on filter performance. Filtration recoveries were lower for OGMF compared to CMGF when operated at a loading rate of 18.3 m/h. Operation at 18.3 m/h met turbidity requirements for California Department of Public Health Title 22 unrestricted reclaimed water requirements for both OGMF and CGMF. Preozonated secondary effluent at a transferred dose of 3 mg/L resulted in an increase in ultraviolet transmissivity (UVT) of approximately 6% and greater than 5-log inactivation of male-specific bacteriophage MS2. Wet weather flow events resulted in UVT decrease and a decline in MS2 inactivation to less than 3 log attributed to higher ozone demand in the secondary effluent. Preozonation increased N-nitrosodimethlyamine (NDMA) concentration approximately 10 times, but subsequent filtration reduced levels to secondary effluent values. A net increase in NDMA was observed at times.

  17. Fracturing in granular media: the role of capillarity, wetting, and disorder

    Science.gov (United States)

    Juanes, R.; Trojer, M.; de Anna, P.; Szulczewski, M. L.

    2015-12-01

    The advent of shale oil and shale gas into the energy landscape has relied on achieving vigorous stimulation of the rock by means of horizontal drilling and hydraulic fracturing. Traditionally, hydraulic fracturing is understood as a single-fluid-phase, pressure-driven process, in which the fluid (typically water with additives) is injected at a high-enough rate that the pressure builds up faster than it can dissipate by permeating into the rock, thereby fracturing it. However, the prevalent conditions for shale (ultra fine pore size, moderate overburden stress, and poor cementation) suggest that capillary forces could play an important role in the fracturing process. Here, we show the results of our recent experimental and theoretical studies on fracturing of granular media by means of injection of an immiscible fluid. We conduct carefully controlled injection experiments in a quasi-2D granular medium (a circular Hele-Shaw cell filled with glass beads), in an experimental set-up that allows us to systematically study the impact of capillarity (by varying injection rate, bead size, and fluid-fluid surface tension), wetting properties (by treating the beads and the cell plates by chemical vapor deposition of silane-based substances) and confinement (by varying the load on the cell). Our choice of defending and invading liquids and granular medium allows us to investigate a wide range of contact angles, from drainage to imbibition. We demonstrate that wettability exerts a powerful influence on the invasion/fracturing morphology of unfavorable mobility displacements. High time resolution imaging techniques and particle image velocimetry (PIV) allow us to quantify matrix displacement and fracture opening dynamics. Our results provide insights on fracture propagation, fracture length distribution and the fracture drainage area, parameters which are critically important to better understand long-term hydrocarbon production from shale.

  18. Liquid effect on the vibration of granular media in cylindrical cavities

    Science.gov (United States)

    Guzman, Enrique; Zenit, Roberto

    2010-11-01

    The study of the interactions of granular media with liquid phases is important both, from the academic applied points of view. A particularly interesting problem concerns the dispersion of the granular phase into the liquid phase. To this end, a series of experiments are being conducted in order to determine the conditions under which such dispersion takes place. The experimental apparatus consists of a short transparent cylinder (LvD) with its axis oriented in a horizontal position. The cavity is completely filled with liquid and a prescribed number of glass spheres forms a deposit layer at the bottom. The cylinder, which is initially at rest, is set into a vertical vibrating state of motion by means of an external actuator. While the amplitude of the excitation remains fixed, its frequency is swept (continously) from 5Hz to 15Hz. Synchronized high speed imaging is then used to identify the frequency at which the stratified-to-dispersed transition occurs. Preliminary results clearly indicate the essential role played by the properties of the liquid (i.e. density, viscosity and superficial tension) and of the spheres (i.e. size and number) during the process. The objective of the study is to determine the conditions required to produce appropriate dispersions for different combinations of liquids and spheres.

  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. Pseudo-hcp nonmagnetic intermediate layer for granular media with high perpendicular magnetic anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Hashimoto, Atsushi [Department of Electronic Engineering, Tohoku University, 6-6-05 Aoba, Aramaki, Aoba-ku, Sendai 980-8579 (Japan); Saito, Shin [Department of Electronic Engineering, Tohoku University, 6-6-05 Aoba, Aramaki, Aoba-ku, Sendai 980-8579 (Japan); Itagaki, Norikazu [Department of Electronic Engineering, Tohoku University, 6-6-05 Aoba, Aramaki, Aoba-ku, Sendai 980-8579 (Japan); Takahashi, Migaku [New Industry Creation Hatchery Center, Tohoku University, 6-6-10 Aoba, Aramaki, Aoba-ku, Sendai 980-8579 (Japan)

    2008-01-07

    Materials with the hexagonal close-packed structure (hcp) and the face-centred-cubic structure with stacking faults (pseudo-hcp) are examined for the nonmagnetic intermediate layer (NMIL) in order to suppress variant growth of magnetic grains for granular-type perpendicular recording media. Judging from the analysis of the epitaxial growth of Co-based magnetic grains, it has been found that a lattice misfit between NMIL and magnetic grain of less than 6% and a spreading coefficient of wettability of magnetic grain on NMIL of greater than 0.3 J m{sup -3} are required for the recording layer to have high perpendicular magnetic anisotropy energy. (fast track communication)

  1. Lattice Boltzmann Simulation of Permeability and Tortuosity for Flow through Dense Porous Media

    Directory of Open Access Journals (Sweden)

    Ping Wang

    2014-01-01

    Full Text Available Discrete element method (DEM is used to produce dense and fixed porous media with rigid mono spheres. Lattice Boltzmann method (LBM is adopted to simulate the fluid flow in interval of dense spheres. To simulating the same physical problem, the permeability is obtained with different lattice number. We verify that the permeability is irrelevant to the body force and the media length along flow direction. The relationships between permeability, tortuosity and porosity, and sphere radius are researched, and the results are compared with those reported by other authors. The obtained results indicate that LBM is suited to fluid flow simulation of porous media due to its inherent theoretical advantages. The radius of sphere should have ten lattices at least and the media length along flow direction should be more than twenty radii. The force has no effect on the coefficient of permeability with the limitation of slow fluid flow. For mono spheres porous media sample, the relationship of permeability and porosity agrees well with the K-C equation, and the tortuosity decreases linearly with increasing porosity.

  2. Influence of intergranular exchange coupling on the magnetization dynamics of CoCrPt:SiO{sub 2} granular media

    Energy Technology Data Exchange (ETDEWEB)

    Brandt, R.; Schmidt, H. [School of Engineering, University of California-Santa Cruz, 1156 High Street, Santa Cruz, California 95064 (United States); Tibus, S. [Department of Physics, University of Konstanz, D-78457 Konstanz (Germany); Institute of Physics, Chemnitz University of Technology, Reichenhainer Str. 70, 09126 Chemnitz (Germany); Springer, F. [Department of Physics, University of Konstanz, D-78457 Konstanz (Germany); Fassbender, J. [Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, D-01314 Dresden (Germany); Rohrmann, H. [OC Oerlikon Balzers AG, LI-9496 Balzers (Liechtenstein); Albrecht, M. [Institute of Physics, Chemnitz University of Technology, Reichenhainer Str. 70, 09126 Chemnitz (Germany)

    2012-08-01

    We investigate the effect of Co{sup +} irradiation on the magnetization dynamics of CoCrPt:SiO{sub 2} granular media. Increasing irradiation levels reduce the saturation magnetization and effective anisotropy, which decrease the intrinsic magnetization precession frequency. Furthermore, increasing intergranular exchange coupling results in a qualitative change in the behavior of the magnetic material from a collection of individual grains to a homogeneous thin film, as evidenced in both the switching behavior and dynamics. The frequency change cannot be explained by single crystal macrospin modeling, and can only be reproduced by the inclusion of the dipolar effects and anisotropy distribution inherent in a granular medium.

  3. Journey of an intruder through the fluidization and jamming transitions of a dense granular media.

    Science.gov (United States)

    Candelier, Raphaël; Dauchot, Olivier

    2010-01-01

    We study experimentally the motion of an intruder dragged into an amorphous monolayer of horizontally vibrated grains at high packing fractions. This motion exhibits two transitions. The first transition separates a continuous motion regime at comparatively low packing fractions and large dragging force from an intermittent motion one at high packing fraction and low dragging force. Associated to these different motions, we observe a transition from a linear rheology to a stiffer response. We thereby call "fluidization" this first transition. A second transition is observed within the intermittent regime when the intruder's motion is made of intermittent bursts separated by long waiting times. We observe a peak in the relative fluctuations of the intruder's displacements and a critical scaling of the burst amplitudes' distributions. This transition occurs at the jamming point phi(J) defined as the point where the static pressure (i.e., the pressure measured in the absence of vibration) vanishes. Investigating the motion of the surrounding grains, we show that below the fluidization transition, there is a permanent wake of free volume behind the intruder. This transition is marked by the evolution of the reorganization patterns around the intruder, which evolve from compact aggregates in the flowing regime to long-range branched shapes in the intermittent regime, suggesting an increasing role of the stress fluctuations. Remarkably, the distributions of the kinetic energy of these reorganization patterns also exhibit a critical scaling at the jamming transition.

  4. 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.

  5. 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.

  6. Light transport in dense composite media: role of near-field coupling

    Science.gov (United States)

    Rezvani Naraghi, Roxana; Sukhov, Sergey; Sáenz, Juan José; Dogariu, Aristide

    In scattering media, optical waves comprise both homogeneous and evanescent components. At very high concentrations of scatterers, particles are located in close proximity and interact through evanescent near fields. Thus, in this regime the energy is not only carried by propagating waves but it also evolves through evanescent coupling between individual scatterers. We have shown that in dense composite media additional transmission channels open because of these near-field interactions between close proximity scatters and, consequently, a new regime of transport emerges. This is clearly beyond simple descriptions of scatterers acting independently of their environment and framed in terms of far-field characteristics such as Mie cross-sections. We will show that, because in the dense media the energy can transfer through both diffusion and evanescent channels, the total transmittance is T =TCS +TNF = 1 1 L (lCS* +lNF*) L (lCS* +lNF*) . Correcting the total transmission in this manner is appealing because it is done in terms of physically meaningful and measurable quantities such a near-field (NF) scattering cross-section σNF.

  7. Elasticity-induced force reversal between active spinning particles in dense passive media.

    Science.gov (United States)

    Aragones, J L; Steimel, J P; Alexander-Katz, A

    2016-04-26

    The self-organization of active particles is governed by their dynamic effective interactions. Such interactions are controlled by the medium in which such active agents reside. Here we study the interactions between active agents in a dense non-active medium. Our system consists of actuated, spinning, active particles embedded in a dense monolayer of passive, or non-active, particles. We demonstrate that the presence of the passive monolayer alters markedly the properties of the system and results in a reversal of the forces between active spinning particles from repulsive to attractive. The origin of such reversal is due to the coupling between the active stresses and elasticity of the system. This discovery provides a mechanism for the interaction between active agents in complex and structured media, opening up opportunities to tune the interaction range and directionality via the mechanical properties of the medium.

  8. Pore structure of ore granular media by computerized tomography image processing

    Institute of Scientific and Technical Information of China (English)

    WU Ai-xiang; YANG Bao-hua; XI Yong; JIANG Huai-chun

    2007-01-01

    The pore structure images of ore particles located at different heights of leaching column were scanned with X-ray computerized tomography (CT) scanner, the porosity and pore size distribution were calculated and the geometrical shape and connectivity of pores were analyzed based on image process method, and the three dimensional reconstruction of pore structure images was realized. The results show that the porosity of ore particles bed in leaching column is 42.92%, 41.72%, 39.34% at top,middle and bottom zone, respectively. Obviously it has spatial variability and decreases appreciably along the height of the column.The overall average porosity obtained by image processing is 41.33% while the porosity gotten from general measurement method in laboratory is 42.77% showing the results of both methods are consistent well. The pore structure of ore granular media is characterized as a dynamical space network composed of interconnected pore bodies and pore throats. The ratio of throats with equivalent diameter less than 1.91 mm to the total pores is 29.31%, and that of the large pores with equivalent diameter more than 5.73 mm is 2.90%.

  9. Simple technique for texture function analysis in granular thin film media

    Energy Technology Data Exchange (ETDEWEB)

    El-Hilo, M., E-mail: mhilo@rocketmail.co [Physics Department, University of Bahrain, P.O. 32038, Sakhir (Bahrain); Al Saie, J. [Physics Department, University of Bahrain, P.O. 32038, Sakhir (Bahrain); Morales, M.P. [Instituto de Ciencia de Materiales de Madrid, CSIC. Sor Juana Ines de la Cruz 3, 28049 Cantoblanco, Madrid (Spain); Pita, M. [Chemistry and Biomolecular Sciences Department, Clarkson University, 8 Clarkson Avenue, Box 5810, Potsdam, NY 13699 (United States)

    2009-11-15

    In this work a simple technique to extract the texture function in granular thin film media is implemented. The technique is based on previous work in which the distribution function of particles easy axes f(alpha) is calculated from the measured parallel remanence curve (M{sub rp}(beta)). In this simple technique we consider that the measured M{sub rp}(beta) curve can be fitted to a series of cos(2beta), i.e. M{sub rp}(beta)=B{sub 0}+B{sub 2} cos(2beta)+B{sub 4} cos(4beta) where the angle beta is the angle by which the film is rotated. This approximation is found to be valid when the texture function has a standard deviation >20 deg. On this basis, the constants B{sub 0}, B{sub 2} and B{sub 4} can be determined by using only three data points for the parallel remanence, M{sub rp}(0), M{sub rp}(45 deg.) and M{sub rp}(90 deg.). The new technique is applied to a textured thin film consisting of cobalt ferrite particles 17 nm in diameter and to a commercial Sony video tape. Using this simple technique, the obtained texture functions are found to be similar to those obtained from the full M{sub rp}(beta) curves. This new technique will furnish a simple method with which the texture function in 2D systems can be obtained.

  10. Broken Symmetry in the Elastic Response to Temperature of Consolidated Granular Media

    Science.gov (United States)

    Ulrich, T. J.

    2006-05-01

    When subjected to externally applied forces consolidated granular media (CGM), take a Berea sandstone as example, are elastically soft, unusually nonlinear, and have hysteresis with end point memory. In response to a variety of transient external disturbances CGM exhibit slow dynamics, e.g. log(t) recovery of the strain following a step change in applied pressure. These elastic properties have led to a bricks (sand grains) and mortar (bond system) picture to describe the physics of the system. Because the grains are thermally anisotropic, temperature drives the bond system altogether differently than applied stress. Consequently temperature provides the means to probe new features in the elastic response of CGM. I describe an experiment/analysis in which the temperature, used to probe the elastic state of a CGM, reveals unusual behavior. The elastic state of CGM at fixed applied stress and temperature, is a function of the applied stress protocol and the temperature protocol. Working at constant stress I find that all aspects of the elastic response to temperature exhibit behavior which presents a broad range of time scales, i.e. slow dynamics, and the response to a transient temperature disturbance is asymmetric in the sign of ΔT(t).

  11. Controlled preparation of wet granular media reveals limits to lizard burial ability

    Science.gov (United States)

    Sharpe, Sarah S.; Kuckuk, Robyn; Goldman, Daniel I.

    2015-07-01

    Many animals move within ground composed of granular media (GM); the resistive properties of such substrates can depend on water content and compaction, but little is known about how such parameters affect locomotion or the physics of drag and penetration. Using apparatus to control compaction of GM, our recent studies of movement in dry GM have revealed locomotion strategies of specialized dry-sand-swimming reptiles. However, these animals represent a small fraction of the diversity and presumed burial strategies of fossorial reptilian fauna. Here we develop a system to create states of wet GM of varying moisture content and compaction in quantities sufficient to study the burial and subsurface locomotion of the Ocellated skink (C. ocellatus), a generalist lizard. X-ray imaging revealed that in wet and dry GM the lizard slowly buried (≈ 30 s) propagating a wave from head to tail, while moving in a start-stop motion. During forward movement, the head oscillated, and the forelimb on the convex side of the body propelled the animal. Although body kinematics and ‘slip’ were similar in both substrates, the burial depth was smaller in wet GM. Penetration and drag force experiments on smooth cylinders revealed that wet GM was ≈ 4× more resistive than dry GM. In total, our measurements indicate that while the rheology of the dry and wet GM differ substantially, the lizard's burial motor pattern is conserved across substrates, while its burial depth is largely constrained by environmental resistance.

  12. EXPERIMENTAL STUDIES OF STATIC BEHAVIOR OF GRANULAR MEDIA IN THE CAPACITIVE STRUCTURE

    Directory of Open Access Journals (Sweden)

    D. O. Bannikov

    2009-03-01

    Full Text Available In the paper the main results of experimental investigations made by the author on distribution of static pressure from granular material in a covered capacity structure are presented. The investigations were conducted on the small-sized steel constructions and provided for the variation both a row of constructive parameters of the experimental installation and the types of granular material.

  13. EXPERIMENTAL STUDIES OF STATIC BEHAVIOR OF GRANULAR MEDIA IN THE CAPACITIVE STRUCTURE

    OpenAIRE

    2009-01-01

    In the paper the main results of experimental investigations made by the author on distribution of static pressure from granular material in a covered capacity structure are presented. The investigations were conducted on the small-sized steel constructions and provided for the variation both a row of constructive parameters of the experimental installation and the types of granular material.

  14. Alternative granular media for the metal casting industry. Final report, September 30, 1994

    Energy Technology Data Exchange (ETDEWEB)

    Guichelaar, P.J.; Ramrattan, S.N.; Tieder, R.E. [Michigan Technological Univ., Houghton, MI (United States)

    1995-09-01

    Silica sand for foundry use is inexpensive to purchase, readily transported and widely available. As a result, it is universally used. However, three factors are becoming increasingly significant as more environmental regulations are promulgated. First, the disposal of waste foundry sand has become an excessively burdensome cost. Second, the phase changes which occur in the silica structure on heating and cooling cause thermal breakdown of the sand into smaller unusable fractions. Third, silica is a relatively weak mineral. Alternatives to silica sand which can withstand the rigors of repetitive reuse must be seriously evaluated as a way to control production costs of the domestic metal casting industry. Chromite sands, olivine sands and carbon sands have each been successfully used to solve operating problems and thus have developed their specific niches in the foundry materials inventory. However, there are several other materials that are candidates for replacing silica sand, such as fused alumina, sintered bauxite and sintered oil well proppants. These media, and others that are generically similar, are manufactured for specific purposes. Compositions and shapes could be readily tailored for used in a metal casting environment of total recycling and materials conservation. This study examines materials that are readily available as alternatives to silica sand from a functionality perspective and a cost perspective. Some of the alternative materials are natural and others are synthetic and thus referring to them as ``sands`` has the potential to cause confusion; the generic term ``granular medium`` is used in this study to mean any material that could functionally substitute for silica sand in the foundry process.

  15. Shear flow of dense granular materials near smooth walls. II. Block formation and suppression of slip by rolling friction.

    Science.gov (United States)

    Shojaaee, Zahra; Brendel, Lothar; Török, János; Wolf, Dietrich E

    2012-07-01

    The role of rotational degrees of freedom and of microscopic contact properties at smooth walls in two dimensional planar shear has been investigated by contact dynamics simulations of round hard frictional particles. Our default system setup consists of smooth frictional walls, giving rise to slip. We show that there exists a critical microscopic friction coefficient at the walls, above which they are able to shear the granular medium. We observe distinctive features at this critical point, which to our knowledge have not been reported before. Activating rolling friction at smooth walls reduces slip, leading to similar shear behavior as for rough walls (with particles glued on their surface). Our simulations with rough walls are in agreement with previous results, provided the roughness is strong enough. In the limit of small roughness amplitude, however, the distinctive features of shearing with smooth walls are confirmed.

  16. Simulation of cascades caused by UHE and EHE neutrinos in dense media

    CERN Document Server

    Zheleznykh, Igor; Dedenko, Grigorii; Mironovich, Anna

    2015-01-01

    A method of simulation of particle cascades induced by ultra-high (>10$^{15}$ eV) and extremely high (>10$^{18}$ eV) energy neutrinos in water or other dense medium has been elaborated. The lateral spread of high-energy particles in cascades due to Coulomb scattering is negligible. So it is possible to use an approximation of the one-dimensional development of the UHE (or EHE) cascade if energies of particles in it higher than 10-100 GeV. An original program of the one-dimensional development of UHE and EHE cascades in dense media taking into account fluctuations and the Landau-Pomeranchuk-Migdal effect has been elaborated. The GEANT4 package has been used when particle energies are below 1000 GeV, for example, or less to calculate correctly the longitudinal distribution of an energy deposition by charge particles in a cascade. In advance the library of longitudinal characteristics of cascades was calculated. When a particle with the energy E which is below the threshold energy (E<1000 GeV or E<10$^6$ G...

  17. Optical tomography of fluorophores in dense scattering media based on ultrasound-enhanced chemiluminescence

    Energy Technology Data Exchange (ETDEWEB)

    Kobayashi, Masaki, E-mail: masaki@tohtech.ac.jp; Kikuchi, Naoto; Sato, Akihiro [Department of Electronics and Intelligent Systems, Tohoku Institute of Technology, Sendai 982-8577 (Japan)

    2015-01-12

    This letter proposes and demonstrates ultrasound-combined optical imaging in dense scattering media. A peroxyoxalate chemiluminescence system that includes fluorophores to chemically excite the pigment is stimulated by ultrasound irradiation with power of less than 0.14 W/cm{sup 2}. Using focused ultrasound, the chemiluminescence is selectively spatially enhanced, which leads to imaging of the pigment when embedded in a light-scattering medium via scanning of the focal point. The ultrasonically enhanced intensity of the chemiluminescence depends on the base intensity of the chemiluminescence without the applied ultrasound irradiation, which thereby enables quantitative determination of the fluorophore concentration. The authors demonstrate the potential of this method to resolve chemiluminescent targets in a dense scattering medium that is comparable to biological tissue. An image was acquired of a chemiluminescent target that included indocyanine green as the fluorophore embedded at a depth of 20 mm in an Intralipid-10% 200 ml/l solution scattering medium (the reduced scattering coefficient was estimated to be approximately 1.3 mm{sup −1}), indicating the potential for expansion of this technique for use in biological applications.

  18. A parallel version of the non smooth contact dynamics algorithm applied to the simulation of granular media

    Science.gov (United States)

    Renouf, Mathieu; Dubois, Frederic; Alart, Pierre

    2004-07-01

    The NSCD method has shown its efficiency in the simulation of granular media. Since the number of particles and contact increases, the shape of the discrete elements becomes more complicated and the simulated problems becomes more complex, the numerical tools need to be improved in order to preserve reasonable elapsed CPU time. In this paper we present a parallelization approach of the NSCD algorithm and we investigate its influence on the numerical behaviour of the method. We illustrate the efficiency on an example made of hard disks: a free surface compaction.

  19. Investigation of 3D surface acoustic waves in granular media with 3-color digital holography

    Science.gov (United States)

    Leclercq, Mathieu; Picart, Pascal; Penelet, Guillaume; Tournat, Vincent

    2017-01-01

    This paper reports the implementation of digital color holography to investigate elastic waves propagating along a layer of a granular medium. The holographic set-up provides simultaneous recording and measurement of the 3D dynamic displacement at the surface. Full-field measurements of the acoustic amplitude and phase at different excitation frequencies are obtained. It is shown that the experimental data can be used to obtain the dispersion curve of the modes propagating in this granular medium layer. The experimental dispersion curve and that obtained from a finite element modeling of the problem are found to be in good agreement. In addition, full-field images of the interaction of an acoustic wave guided in the granular layer with a buried object are also shown.

  20. Cloning of Dense Granular (GRA 7 Gene of Toxoplasma gondii into pTZ57RT Vectors for Sub-Cloning in Prokaryotic and Eukaryotic Plasmids

    Directory of Open Access Journals (Sweden)

    Zahra Arab-Mazar

    2014-11-01

    Full Text Available Background: Serological assay based on dense granular (GRA proteins of Toxoplasma gondii (T. gondii is actually the most popular laboratory diagnostic tool to detection of toxoplasmosis. We aimed to construct a recombinant GRA7-pTZ57RT plasmid vectors that it is suitable for sub-cloning and GRA7 protein production.Materials and Methods: Souris mice were used for maintaining of T. gondii tachyzoites by serial intraperitoneal passage. The tachyzoites’ DNA was extracted, and the GRA7 gene was amplified by PCR. The purified DNA was inserted into pTZ57RT cloning vectors, and then transformed into TOP10 competent cells. Finally, cloning and transformation were confirmed by restriction enzymatic digestion and gene sequencing.Results: Agarose gel electrophoresis analysis on PCR products of genomic DNA, revealed 726 bp bands that were equal to the GRA7 gene. Both white (recombinant and blue (non-recombinant colonies appeared on ampicillin-LB agar. Results of enzymatic digestion and gene sequencing confirmed successful cloning and transformation procedures.Conclusion: The GRA7 gene of T. gondii was cloned into pTZ57RT plasmid, which is suggested to be further used as DNA vaccine or sub-cloned for production of recombinant GRA7 protein.

  1. Numerical inversion of the Laplace transform in some problems of granular media dynamics

    Science.gov (United States)

    Yavich, Nikolay B.

    2004-04-01

    Approximated value for the vertical displacement of a surface bounding a half space and a layer laying on rigid foundation filled with granular medium caused by a vertical symmetric load is received here. The results obtained for Kandaurov standard linear medium model are used. This model takes in account an internal friction. The Papoulis method of numerical inversion of the Laplace transform is applied.

  2. 筒仓内散体静态屈服的研究%Study of Static Yield of Granular Media in Silo

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    In this paper,the granular media in storage is supposed to be elastic-perfectly plastic behaviour material submitting to Mohr-Coulomb yield criterion,and friction effect between granular media and silo wall is supposed to be Coulomb friction contact problem.The factors influencing the yield state of static graunlar media in rigid silo are studied,a method is proposed which is using granular media critical internal friction angle to identify whether the static granular media is in yield state,and the problems are simulated numerically with finite element method.%认为仓贮散体为服从Mohr—Coulomb屈服准则的理想弹塑性材料,散体与仓壁之间的摩擦属于Coulomb摩擦接触问题。就刚性筒仓讨论研究了静态时影响散体进入屈服状态的有关因素,提出了一种由散体临界内摩擦角来判断静态散体是否进入屈服状态的方法,并用有限元法做了数值模拟。

  3. Quantifying the Micromechanical Effects of Variable Cement in Granular Porous Media

    Energy Technology Data Exchange (ETDEWEB)

    Goodwin, Laurel B.; Boutt David F.

    2010-02-18

    The mechanical and hydrologic behavior of clastic rocks and sediments is fundamentally controlled by variables such as grain size and shape, sorting, grain and cement mineralogy, porosity, and %cement - parameters that are not used directly in field-scale models of coupled flow and deformation. To improve our understanding of the relationship between these micromechanical properties and bulk behavior we focused on (1) relating detailed, quantitative characterization of the grain-pore systems to both hydrologic and mechanical properties of a suite of variably quartz-cemented quartz arenite samples and (2) the use of a combination of discrete element method (DEM) and poroelastic models parameterized by data from the natural samples to isolate and compare the influence of changes in the mechanical and hydrologic properties of granular porous media due to changes in degree of cementation. Quartz overgrowths, the most common form of authigenic cements in sandstones, are responsible for significant porosity and permeability reduction. The distribution of quartz overgrowths is controlled by available pore space and the crystallographic orientations of individual quartz grains. Study of the St. Peter Sandstone allowed evaluation of the relative effects of quartz cementation and compaction on final grain and pore morphology, showing that progressive quartz cementation modifies the grain framework in consistent, predictable ways. Detailed microstructural characterization and multiple regression analyses show that with progressive diagenesis, the number and length of grain contacts increases as the number of pores increases, the number of large, well-connected pores decreases, and pores become rounder. These changes cause a decrease in pore size variability that leads to a decrease in bulk permeability and both stiffening and strengthening of the grain framework. The consistent nature of these changes allows us to predict variations in hydrologic and mechanical properties

  4. Numerical simulation of the flow field in a dense-media cyclone

    Institute of Scientific and Technical Information of China (English)

    SHEN Li-juan; HU Yan-feng; CHEN Jian-zhong; ZHANG Peng; DAI Hua-zhen

    2009-01-01

    An analytical study of the flow and pressure fields inside a small-diameter dense-media cyclone is presented.The simulations were done with the help of the CFD software FLUENT.The following conclusions were reached: the tangential velocity tends to increase when moving from the center toward the exterior.The velocity then begins to decrease when the maximum velocity point is reached.The velocity field divides into two different sections; an inner swirling zone and an outer swirling zone.The axial velocity points down at the wall and gradually decreases toward the bottom.Continuing toward the bottom, the axial velocity passes through zero and then gradually increases in the opposite direction.In the cyclone's central zone, the pressure is negative and the suction of air allows an air column to be formed therein.At the center of the radial negative zone the pressure drops to its lowest value-phenomenon that has been verified by theoretical analysis.Some discrepancies between the observed data and the simulated data are noted when an analysis in made on a cyclone operating with either fresh water only or with water with added heavy particles.

  5. From continuum analytical description to discrete numerical modelling of localized fluidization in granular media

    Science.gov (United States)

    Puig i Montellà, Eduard; Toraldo, Marcella; Chareyre, Bruno; Sibille, Luc

    2017-06-01

    We present analytical and numerical results on localized fluidization within a granular layer subjected to a local injection of fluid. As the injection rate increases the three different regimes previously reported in the literature are recovered: homogeneous expansion of the bed, fluidized cavity in which fluidization starts developing above the injection area, and finally the chimney of fluidized grains when the fluidization zone reaches the free surface. The analytical approach is at the continuum scale, based on Darcy's law and Therzaghi's effective stress principle. It provides a good description of the phenomenon as long as the porosity of the granular assembly remains relatively homogeneous. The numerical approach is at the particle scale based on the coupled DEM-PFV method. It tackles the more heterogeneous situations which occur at larger injection rates. A direct link is evidenced between the occurrence of the different regimes of fluidization and the injection aperture. Finally, the merging of chimneys in case of two injection points is investigated.

  6. Two dimension porous media reconstruction using granular model under influence of gravity

    OpenAIRE

    Sundari, Pury; Fauzi, Umar; Irayani, Zaroh; Viridi, Sparisoma

    2011-01-01

    Modeling of pores generation in 2-D with granular grains using molecular dynamics method is reported in this work. Grains with certain diameter distribution are let falling due to gravity. Three configurations (larger diameter on top, smaller diameter on top, and mixed) and two kinds of mixture (same grains density and same grains mass) are used in the simulation. Mixture with heterogen density gives higher porosity than the homogen one for higher initial height, but change into opposite cond...

  7. Wave Propagation and Dynamic Load Transfer due to Explosive Loading in Heterogenous Granular Media with Microstructure

    Science.gov (United States)

    1992-09-30

    in Granular Assemblies with Microstructural Defects", J. of Engineering Mechanics, Vol. 118, No. 1, Jan . 1992, pp. 190-201. 8. Shukla A. and Sadd, M. H...equivalent micropolar continuum has been investigated by Banks and Sokolowski (1968), Bazant and Christensen (1972) and Sun and Yang (1975). The...pp. 17 -2 3 . Bazant , Z. P. and Chr ;tensen, M. (1972) "Analogy Between Micropolar Continuum and Grid Frameworks Under Initial Stress’, Int. J. Solids

  8. Role of interparticle friction and particle-scale elasticity in the shear-strength mechanism of three-dimensional granular media

    NARCIS (Netherlands)

    Antony, S.J.; Kruyt, N.P.

    2009-01-01

    The interlink between particle-scale properties and macroscopic behavior of three-dimensional granular media subjected to mechanical loading is studied intensively by scientists and engineers, but not yet well understood. Here we study the role of key particle-scale properties, such as interparticle

  9. Numerical simulation of two-dimensional granular shearing flows and the friction force of a moving slab on the granular media

    Institute of Scientific and Technical Information of China (English)

    Cai Qing-Dong; Chen Shi-Yi; Sheng Xiao-Wei

    2011-01-01

    This paper studies some interesting features of two-dimensional granular shearing flow by using molecular dynamic approach for a specific granular system. The obtained results show that the probability distribution function of velocities of particles is Gaussian at the central part, but diverts from Gaussian distribution nearby the wall. The macroscopic stress along the vertical direction has large fluctuation around a constant value, the non-zero average velocity occurs mainly near the moving wall, which forms a shearing zone. . In the shearing movement, the volume of the granular material behaves in a random manner. The equivalent friction coefficient between moving slab and granular material correlates with the moving speed at low velocity, and approaches constant as the velocity is large enough.

  10. Two dimension porous media reconstruction using granular model under influence of gravity

    Science.gov (United States)

    Sundari, Pury; Fauzi, Umar; Irayani, Zaroh; Viridi, Sparisoma

    2012-06-01

    Modeling of pores generation in 2-D with granular grains using molecular dynamics method is reported in this work. Grains with certain diameter distribution are let falling due to gravity. Three configurations (larger diameter in at upper layer, smaller diameter in at upper layer, and mixed) and two kinds of mixture (similar of grain density and mass) are used in the simulation. Mixture with heterogeneous density gives higher porosity than the homogeneous one for higher initial height, but change into opposite condition for lower initial height.

  11. Performance characteristics of pilot plant dense media hydrocyclone for beneficiation of coal and 3-D CFD simulation

    Energy Technology Data Exchange (ETDEWEB)

    Suresh, P.D.; Kumar, V.; Sripriya, R.; Chakraborty, S.; Meikap, B.C. [University of Kwazulu Natal, Durban (South Africa). School of Chemical Engineering

    2010-08-15

    Dense-medium separators have proven to be the most efficient processes for removing the undesirable material from run-of-mine coal. The application of high-pressure feed injection into dense-medium cyclones to provide an elevated centrifugal force has recently been found to allow efficient separation performances for the treatment of fine coal (i.e., < 1000 {mu} m). However, high-pressure injection requires specialized pumps and results in relatively high maintenance requirements. The current study involves experimental investigation of separation performance characteristics of the dense media hydrocyclone (DMC). A pilot plant DMC has been designed and fabricated for performance characterization. Experiments have been conducted on 300 mm dense medium cyclone treating coal in the size range of -6 to +2 mm using magnetite as the medium under operating conditions. The operating variable was the specific gravity of the medium, feed inlet pressure and feed inlet flow rate. The ash contents of the feed coal reporting to the overflow and underflow have been analyzed qualitatively. The result indicates that the use of magnetite as dense medium in DMC resulted in the yield of clean coal, which is 5% more when the air core is suppressed as compared to the same conditions when the air core remains. A 3-D geometry is created in Gambit to support the experimental findings by using CFD simulation. It is interesting to observe that experimental findings agree well with the simulation results.

  12. Modeling the impact of granular embedding media, and pulling versus pushing cells on growing cell clones

    Science.gov (United States)

    Drasdo, Dirk; Hoehme, Stefan

    2012-05-01

    In this paper, we explore how potential biomechanical influences on cell cycle entrance and cell migration affect the growth dynamics of cell populations. We consider cell populations growing in free, granular and tissue-like environments using a mathematical single-cell-based model. In a free environment we study the effect of pushing movements triggered by proliferation versus active pulling movements of cells stretching cell-cell contacts on the multi-cellular kinetics and the cell population morphotype. By growing cell clones embedded in agarose gel or cells of another type, one can mimic aspects of embedding tissues. We perform simulation studies of cell clones expanding in an environment of granular objects and of chemically inert cells. In certain parameter ranges, we find the formation of invasive fingers reminiscent of viscous fingering. Since the simulation studies are highly computation-time consuming, we mainly study one-cell-thick monolayers and show that for selected parameter settings the results also hold for multi-cellular spheroids. Finally, we compare our model to the experimentally observed growth dynamics of multi-cellular spheroids in agarose gel.

  13. Dissipation consistent fabric tensor definition from DEM to continuum for granular media

    Science.gov (United States)

    Li, X. S.; Dafalias, Y. F.

    2015-05-01

    In elastoplastic soil models aimed at capturing the impact of fabric anisotropy, a necessary ingredient is a measure of anisotropic fabric in the form of an evolving tensor. While it is possible to formulate such a fabric tensor based on indirect phenomenological observations at the continuum level, it is more effective and insightful to have the tensor defined first based on direct particle level microstructural observations and subsequently deduce a corresponding continuum definition. A practical means able to provide such observations, at least in the context of fabric evolution mechanisms, is the discrete element method (DEM). Some DEM defined fabric tensors such as the one based on the statistics of interparticle contact normals have already gained widespread acceptance as a quantitative measure of fabric anisotropy among researchers of granular material behavior. On the other hand, a fabric tensor in continuum elastoplastic modeling has been treated as a tensor-valued internal variable whose evolution must be properly linked to physical dissipation. Accordingly, the adaptation of a DEM fabric tensor definition to a continuum constitutive modeling theory must be thermodynamically consistent in regards to dissipation mechanisms. The present paper addresses this issue in detail, brings up possible pitfalls if such consistency is violated and proposes remedies and guidelines for such adaptation within a recently developed Anisotropic Critical State Theory (ACST) for granular materials.

  14. High-Performance Modeling and Simulation of Anchoring in Granular Media for NEO Applications

    Science.gov (United States)

    Quadrelli, Marco B.; Jain, Abhinandan; Negrut, Dan; Mazhar, Hammad

    2012-01-01

    NASA is interested in designing a spacecraft capable of visiting a near-Earth object (NEO), performing experiments, and then returning safely. Certain periods of this mission would require the spacecraft to remain stationary relative to the NEO, in an environment characterized by very low gravity levels; such situations require an anchoring mechanism that is compact, easy to deploy, and upon mission completion, easy to remove. The design philosophy used in this task relies on the simulation capability of a high-performance multibody dynamics physics engine. On Earth, it is difficult to create low-gravity conditions, and testing in low-gravity environments, whether artificial or in space, can be costly and very difficult to achieve. Through simulation, the effect of gravity can be controlled with great accuracy, making it ideally suited to analyze the problem at hand. Using Chrono::Engine, a simulation pack age capable of utilizing massively parallel Graphic Processing Unit (GPU) hardware, several validation experiments were performed. Modeling of the regolith interaction has been carried out, after which the anchor penetration tests were performed and analyzed. The regolith was modeled by a granular medium composed of very large numbers of convex three-dimensional rigid bodies, subject to microgravity levels and interacting with each other with contact, friction, and cohesional forces. The multibody dynamics simulation approach used for simulating anchors penetrating a soil uses a differential variational inequality (DVI) methodology to solve the contact problem posed as a linear complementarity method (LCP). Implemented within a GPU processing environment, collision detection is greatly accelerated compared to traditional CPU (central processing unit)- based collision detection. Hence, systems of millions of particles interacting with complex dynamic systems can be efficiently analyzed, and design recommendations can be made in a much shorter time. The figure

  15. A Study of the Behavior and Micromechanical Modelling of Granular Soil. Volume 3. A Numerical Investigation of the Behavior of Granular Media Using Nonlinear Discrete Element Simulation

    Science.gov (United States)

    1991-05-22

    Eisenberg 1987). Among other formulations, the existing models are based on the theories of elasticity, hypoelasticity , plasticity and viscoplasticity...AD-A238 158 AFOSR4R. 91 069.1 A STUDY OF THE BEHAVIOR AND MICROMECHANICAL MODELLING OF GRANULAR SOIL DTIC VOLUME mI ELECTIE A NUMERICAL INVESTIGATION...Final 1/6/ 9-5/15/91 4. nU AN SUS"Ll5. FUNDING NUMBERS A Study of the Behavior and Micromechanical Modelling of Grant AFOSR-89-0350 Granular Soil PR

  16. Fate and Transport of Graphene Oxide in Granular Porous Media: Experimental Results and Modeling

    Science.gov (United States)

    Gao, Bin

    2014-05-01

    Although graphene oxide (GO) has been used in many applications to improve human life quality, its environmental fate and behavior are still largely unknown. In this work, a range of laboratory experiments were conducted to explore the aggregation, deposition, and transport mechanisms of GO nano-sheets in porous media under various conditions. Stability experimental data showed that both cation valence and pH showed significant effect on the aggregation of GO sheets. The measured critical coagulation concentrations were in good agreement with the predictions of the extended Schulze-Hardy rule. Sand column experimental results indicated that deposition and transport of GO in porous media were strongly dependent on solution ionic strength. Particularly, GO showed high mobility under low ionic strength conditions in both saturated and unsaturated columns. Increasing ionic strength dramatically increased the retention of GO in porous media, mainly through secondary-minimum deposition. Recovery rates of GO in unsaturated sand columns were lower than that in saturated columns under the same ionic strength conditions, suggesting moisture content also played an important role in the retention of GO in porous media. Findings from the bubble column experiments showed that the GO did not attach to the air-water interface, which is consistent with the XDLVO predictions. Additional retention mechanisms, such as film straining, thus could be responsible to the reduced mobility of GO in unsaturated porous media. The breakthrough curves of GO in saturated and unsaturated columns could be accurately simulated by an advection-dispersion-reaction model.

  17. Propagation studies for the construction of atomic macro-coherence in dense media as a tool to investigate neutrino physics

    CERN Document Server

    Vaquero, J Martín; Conde, A Peralta

    2016-01-01

    In this manuscript we review the possibility of inducing large coherence in a macroscopic dense target by using adiabatic techniques. For this purpose we investigate the degradation of the laser pulse through propagation, which was also related to the size of the prepared medium. Our results show that, although adiabatic techniques offer the best alternative in terms of stability against experimental parameters, for very dense media it is necessary to engineer laser-matter interaction in order to minimize laser field degradation. This work has been triggered by the proposal of a new technique, namely Radiative Emission of Neutrino Pairs (RENP), capable of investigating neutrino physics through quantum optics concepts which require the preparation of a macrocoherent state.

  18. Slithering on sand: kinematics and controls for success on granular media

    Science.gov (United States)

    Schiebel, Perrin E.; Zhang, Tingnan; Dai, Jin; Gong, Chaohui; Yu, Miao; Astley, Henry C.; Travers, Matthew; Choset, Howie; Goldman, Daniel I.

    Previously, we studied the subsurfacelocomotion of undulatory sand-swimming snakes and lizards; using empirical drag response of GM to subsurface intrusion of simple objects allowed us to develop a granular resistive force theory (RFT) to model the locomotion and predict optimal movement patterns. However, our knowledge of the physics of GM at the surface is limited; this makes it impossible to determine how the desert-dwelling snake C. occipitalis moves effectively (0.45 +/-0.04 bodylengths/sec) on the surface of sand .We combine organism biomechanics studies, GM drag experiments, RFT calculations and tests of a physical model (a snake-like robot), to reveal how multiple factors acting together contribute to slithering on sandy surfaces. These include the kinematics--targeting an ideal waveform which maximizes speed while minimizing joint-level torque, the ability to modulate ground interactions by lifting body segments, and the properties of the GM. Based on the sensitive nature of the relationship between these factors, we hypothesize that having an element of force-based control, where the waveform is modulated in response to the forces acting between the body and the environment, is necessary for successful locomotion on yielding substrates.

  19. Predicting release and transport of pesticides from a granular formulation during unsaturated diffusion in porous media

    DEFF Research Database (Denmark)

    Paradelo Pérez, Marcos; Soto-Gómez, Diego; Pérez-Rodrígez, Paula

    2014-01-01

    The release and transport of active ingredients (AIs) from controlled-release formulations (CRFs) have potential to reduce groundwater pesticide pollution. These formulations have a major effect on the release rate and subsequent transport to groundwater. Therefore the influence of CRFs should...... be included in modeling non-point source pollution by pesticides. We propose a simplified approach that uses a phase transition equation coupled to the diffusion equation that describes the release rate of AIs from commercial CRFs in porous media; the parameters are as follows: a release coefficient......, the solubility of the AI, and diffusion transport with decay. The model gives acceptable predictions of the pesticides release from commercial CRFs in diffusion cells filled with quartz sand. This approach can be used to study the dynamics of the CRF-porous media interaction. It also could be implemented in fate...

  20. Thermal conductivity of granular porous media: A pore scale modeling approach

    Directory of Open Access Journals (Sweden)

    R. Askari

    2015-09-01

    Full Text Available Pore scale modeling method has been widely used in the petrophysical studies to estimate macroscopic properties (e.g. porosity, permeability, and electrical resistivity of porous media with respect to their micro structures. Although there is a sumptuous literature about the application of the method to study flow in porous media, there are fewer studies regarding its application to thermal conduction characterization, and the estimation of effective thermal conductivity, which is a salient parameter in many engineering surveys (e.g. geothermal resources and heavy oil recovery. By considering thermal contact resistance, we demonstrate the robustness of the method for predicting the effective thermal conductivity. According to our results obtained from Utah oil sand samples simulations, the simulation of thermal contact resistance is pivotal to grant reliable estimates of effective thermal conductivity. Our estimated effective thermal conductivities exhibit a better compatibility with the experimental data in companion with some famous experimental and analytical equations for the calculation of the effective thermal conductivity. In addition, we reconstruct a porous medium for an Alberta oil sand sample. By increasing roughness, we observe the effect of thermal contact resistance in the decrease of the effective thermal conductivity. However, the roughness effect becomes more noticeable when there is a higher thermal conductivity of solid to fluid ratio. Moreover, by considering the thermal resistance in porous media with different grains sizes, we find that the effective thermal conductivity augments with increased grain size. Our observation is in a reasonable accordance with experimental results. This demonstrates the usefulness of our modeling approach for further computational studies of heat transfer in porous media.

  1. Discrete volumetric digital image correlation for the investigation of granular type media at microscale: accuracy assessment

    Directory of Open Access Journals (Sweden)

    Bornert M.

    2010-06-01

    Full Text Available The recent development of efficient 3D imaging tools such as X-Rays computed microtomography combined with the extension to volumetric images of Digital Image Correlation (DIC techniques provide new insights on the analysis of materials and structures. Among many other possible fields of application, geomaterials are good candidates for such investigations, owing to their relative transparency to X-rays and the presence in many samples of a natural contrast suitable for deformation mapping. However, these materials often deform discontinuously at microscale, for instance in the form of the development of a networks of microcracks. Discontinuity is even the dominant rule in granular-type materials such as sand in which the contribution to overall deformation of the microcontinuous phenomena -elastic strains inside grains- are negligible. To investigate deformation at the scale of these discontinuous mechanisms, specific DIC algorithms are required, which override the assumption of continuity of the transformation at the scale of the correlation windows. The recent so-called Discrete-DIC procedure (Hall et al, 2010 is a possible answer. We recall here its general principles and focus on its potential accuracy, from both theoretical and practical points of view. We show that the position and the rotation of individual grains with an average diameter of 500µm can be determined from images recorded with a laboratory microCT scanner, with a 15µm voxel size, with an accuracy of the order of 1µm and 0,1 degree, respectively.

  2. 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.

  3. Hydraulic bridges in unsaturated coarse granular media: Influence of bridge size and conductivity on flow through clasts

    Science.gov (United States)

    Jayakody, Jeevan A.; Nicholl, Michael J.

    2016-10-01

    Unsaturated flow in coarse granular media must pass through hydraulic bridges (e.g., pendular water, porous connections) that form a physical connection between adjoining clasts. Previous studies suggest that volumetric flow through a porous clast (Q) will be linearly dependent on the cross-sectional area of the hydraulic bridges, and understate the importance of bridge conductivity. Numerical simulations were performed to explore steady-state flow through a spherical clast with identical bridges located at the top and bottom. The cross-sectional area of the bridges relative to that of the clast (Ar) was varied across six orders of magnitude. The ratio of hydraulic conductivity between bridges and clasts (Kb/Kc) was varied across 12 orders of magnitude to consider resistive, neutral, and conductive bridges. Results show that hydraulic bridges place a primary control on both Q and flux distribution within the clast. For neutral and conductive bridges (Kb/Kc ≥1), Ar is the dominant factor in determining Q, while Kb/Kc is the primary control for resistive bridges (Kb/Kc < 1). For all bridges, Q shows a non-linear dependency on both Ar and Kb/Kc. The intra-clast flow distribution shifts outwards as Ar increases. Conductive bridges promote this process and resistive bridges impede it.

  4. Machine learning framework for analysis of transport through complex networks in porous, granular media: A focus on permeability

    Science.gov (United States)

    van der Linden, Joost H.; Narsilio, Guillermo A.; Tordesillas, Antoinette

    2016-08-01

    We present a data-driven framework to study the relationship between fluid flow at the macroscale and the internal pore structure, across the micro- and mesoscales, in porous, granular media. Sphere packings with varying particle size distribution and confining pressure are generated using the discrete element method. For each sample, a finite element analysis of the fluid flow is performed to compute the permeability. We construct a pore network and a particle contact network to quantify the connectivity of the pores and particles across the mesoscopic spatial scales. Machine learning techniques for feature selection are employed to identify sets of microstructural properties and multiscale complex network features that optimally characterize permeability. We find a linear correlation (in log-log scale) between permeability and the average closeness centrality of the weighted pore network. With the pore network links weighted by the local conductance, the average closeness centrality represents a multiscale measure of efficiency of flow through the pore network in terms of the mean geodesic distance (or shortest path) between all pore bodies in the pore network. Specifically, this study objectively quantifies a hypothesized link between high permeability and efficient shortest paths that thread through relatively large pore bodies connected to each other by high conductance pore throats, embodying connectivity and pore structure.

  5. Experimental Study of the Composition and Structure of Granular Media in the Shear Bands Based on the HHC-Granular Model

    Directory of Open Access Journals (Sweden)

    Guang-jin Wang

    2014-01-01

    Full Text Available The researchers cannot control the composition and structure of coarse grained soil in the indoor experiment because the granular particles of different size have the characteristics of random distribution and no sorting. Therefore, on the basis of the laboratory tests with the coarse grained soil, the HHC-Granular model, which could simulate the no sorting and random distribution of different size particles in the coarse-grained soil, was developed by use of cellular automata method. Meanwhile, the triaxial numerical simulation experiments of coarse grained soil were finished with the different composition and structure soil, and the variation of shear strength was discussed. The results showed that the internal friction angle was likely to reduce with the increasing of gravel contents in the coarse-grained soil, but the mean internal friction angle significantly increased with the increment of gravel contents. It indicated that the gravel contents of shear bands were the major factor affecting the shear strength.

  6. Comparison of Modeling and Experimental Approaches for Improved Modeling of Filtration in Granular and Consolidated Media

    Science.gov (United States)

    Mirabolghasemi, M.; Prodanovic, M.; DiCarlo, D. A.

    2014-12-01

    Filtration is relevant to many disciplines from colloid transport in environmental engineering to formation damage in petroleum engineering. In this study we compare the results of the novel numerical modeling of filtration phenomenon on pore scale with the complementary experimental observations on laboratory scale and discuss how the results of comparison can be used to improve macroscale filtration models for different porous media. The water suspension contained glass beads of 200 micron diameter and flows through a packing of 1mm diameter glass beads, and thus the main filtration mechanism is straining and jamming of particles. The numerical model simulates the flow of suspension through a realistic 3D structure of an imaged, disordered sphere pack, which acts as the filter medium. Particle capture through size exclusion and jamming is modeled via a coupled Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) approach. The coupled CFD-DEM approach is capable of modeling the majority of particle-particle, particle-wall, and particle-fluid interactions. Note that most of traditional approaches require spherical particles both in suspension and the filtration medium. We adapted the interface between the pore space and the spherical grains to be represented as a triangulated surface and this allows extensions to any imaged media. The numerical and experimental results show that the filtration coefficient of the sphere pack is a function of the flow rate and concentration of the suspension, even for constant total particle flow rate. An increase in the suspension flow rate results in a decrease in the filtration coefficient, which suggests that the hydrodynamic drag force plays the key role in hindering the particle capture in random sphere packs. Further, similar simulations of suspension flow through a sandstone sample, which has a tighter pore space, show that filtration coefficient remains almost constant at different suspension flow rates. This

  7. Transient natural convection and heat transfer during the storage of granular media

    Energy Technology Data Exchange (ETDEWEB)

    Avila-Acevedo, J.G.; Tsotsas, E. [Institute of Process Engineering, Otto-von-Guericke-University, P.O. Box 4120, 39106 Magdeburg (Germany)

    2008-07-01

    Transient heat transfer in an originally isothermal cylinder filled with a porous medium after sudden change of wall temperature is studied experimentally and computationally. Lab-scale experiments with water as the interstitial fluid are used in order to imitate the conditions prevailing in large, air-filled industrial silos. The proposed model assumes isotropy of the porous medium, local thermal equilibrium between the phases, Darcy flow and applicability of the Boussinesq approximation. Its predictions are in satisfactory agreement with the experimental results. Simulations reveal the role of dimensionless parameters like the modified porous media Rayleigh number and the cylinder aspect ratio. A criterion for neglecting the influence of natural convection on heat transfer is established. (author)

  8. Photon storage in ¿-type optically dense atomic media. IV. Optimal control using gradient ascent

    DEFF Research Database (Denmark)

    Gorshkov, Alexey V.; Calarco, Tomasso; Lukin, Mikhail D.

    2008-01-01

    We use the numerical gradient ascent method from optimal control theory to extend efficient photon storage in -type media to previouslyinaccessible regimes and to provide simple intuitive explanations for our optimization techniques. In particular, by using gradient ascent to shape classical...... control pulses used to mediate photon storage, we open up the possibility of high efficiency photon storage in thenonadiabatic limit, in which analytical solutions to the equations of motion do not exist. This control shaping technique enables an order-of-magnitude increase in the bandwidth of the memory...

  9. Spectral and refractive effects in non-stationary radiative transfer: a theoretical study in dense media

    Energy Technology Data Exchange (ETDEWEB)

    Fumeron, S. [Departement des Sciences Appliquees, Groupe de Recherche en Ingenierie des Procedes et Systemes, Universite du Quebec a Chicoutimi, P4-3240, CURAL, Chicoutimi, 555 Boulevard de l' Universite, Chicoutimi, Quebec, G7H 2B1 (Canada); Charette, A. [Departement des Sciences Appliquees, Groupe de Recherche en Ingenierie des Procedes et Systemes, Universite du Quebec a Chicoutimi, P4-3240, CURAL, Chicoutimi, 555 Boulevard de l' Universite, Chicoutimi, Quebec, G7H 2B1 (Canada)]. E-mail: andre_charette@uqac.ca; Ben-Abdallah, P. [Laboratoire de Thermocinetique, UMR CNRS 6607, Ecole Polytechnique, Site de la Chantrerie, 44 306 Nantes cedex (France)

    2005-09-15

    A theoretical study of unsteady radiative heat transfer inside refractive heterogeneous participating media is presented. In the approximation of space-time geometrical optics, some new properties for propagating waves are exhibited. Physically, it is shown that the time dependency of refractive index can give rise to an effect of spectral bounce, whereas space dependency is responsible for the existence of confined trajectories for light. Then, the problem of energy transport is studied: from the shape of Clausius Invariant in unsteady processes, the transient radiative transfer equation is built and the existence of amplification effects for specific intensity is presented.

  10. Experimental investigation on steady granular flows interacting with an obstacle down an inclined channel: study of the dead zone upstream from the obstacle. Application to interaction between dense snow avalanches and defence structures

    Directory of Open Access Journals (Sweden)

    T. Faug

    2002-01-01

    Full Text Available An experimental investigation with dry granular flows passing over an obstacle down a rough inclined channel has been performed. The aim is to improve our understanding of the interaction between dense snow avalanches and defence structures. Specific attention was directed to the study of the zone of influence upstream from the obstacle, linked to the formation of a dead zone. The dead zone length L was systematically measured as a function of the obstacle height H and the channel inclination θ, for several discharges. In a whole range of channel inclinations, all the data are shown to collapse into a single curve when properly scaled. The scaling is based on the introduction of a theoretical deposit length (depending on H, θ and the internal friction angle of the material, φ and a Froude number of the flow depending on the obstacle height.

  11. Ultrasensitive detection in optically dense physiological media: applications to fast reliable biological assays

    Science.gov (United States)

    Matveeva, Evgenia G.; Gryczynski, Ignacy; Berndt, Klaus W.; Lakowicz, Joseph R.; Goldys, Ewa; Gryczynski, Zygmunt

    2006-02-01

    We present a novel approach for performing fluorescence immunoassay in serum and whole blood using fluorescently labeled anti-rabbit IgG. This approach, which is based on Surface Plasmon-Coupled Emission (SPCE), provides increased sensitivity and substantial background reduction due to exclusive selection of the signal from the fluorophores located near a bio-affinity surface. Effective coupling range for SPCE is only couple of hundred nanometers from the metallic surface. Excited fluorophores outside the coupling layer do not contribute to SPCE, and their free-space emission is not transmitted through the opaque metallic film into the glass substrate. An antigen (rabbit IgG) was adsorbed to a slide covered with a thin silver metal layer, and the SPCE signal from the fluorophore-labeled anti-rabbit antibody, binding to the immobilized antigen, was detected. The effect of the sample matrix (buffer, human serum, or human whole blood) on the end-point immunoassay SPCE signal is discussed. The kinetics of binding could be monitored directly in whole blood or serum. The results showed that human serum and human whole blood attenuate the SPCE end-point signal and the immunoassay kinetic signal only approximately 2- and 3-fold, respectively (compared to buffer), resulting in signals that are easily detectable even in whole blood. The high optical absorption of the hemoglobin can be tolerated because only fluorophores within a couple of hundred nanometers from the metallic film contribute to SPCE. Both glass and plastic slides can be used for SPCE-based assays. We believe that SPCE has the potential of becoming a powerful approach for performing immunoassays based on surface-bound analytes or antibodies for many biomarkers directly in dense samples such as whole blood, without any need for washing steps.

  12. Hydrodynamic modelling of dense gas-fluidised beds: comparison of the kinetic theory of granular flow with 3D hard-sphere discrete particle simulations

    NARCIS (Netherlands)

    Goldschmidt, M.J.V.; Beetstra, R.; Kuipers, J.A.M.

    2002-01-01

    A novel technique to sample particle velocity distributions and collision characteristics from dynamic discrete particle simulations of intrinsically unsteady, non-homogeneous systems, such as those encountered in dense gas-fluidised beds, is presented. The results are compared to the isotropic Maxw

  13. Instituto de Fisica, UFRGS, CP 15051, 91501-970, Porto Alegre RS, Brazil: Replica theory of granular media

    Science.gov (United States)

    Arenzon, Jeferson J.

    1999-03-01

    An infinite range spin-glass-like model for granular systems is introduced and studied through the replica mean-field formalism. Equilibrium, density-dependent properties under vibration and gravity are obtained that qualitatively resemble the results from real and numerical experiments.

  14. 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...

  15. The H2 + CO ↔ H2CO Reaction: Rate Constants and Relevance to Hot and Dense Astrophysical Media

    Science.gov (United States)

    Vichietti, R. M.; Spada, R. F. K.; da Silva, A. B. F.; Machado, F. B. C.; Haiduke, R. L. A.

    2016-07-01

    A theoretical thermochemical and kinetic investigation of the thermal H2 + CO ↔ H2CO reaction was performed for a temperature range from 200 to 4000 K. Geometries and vibrational frequencies of reactants, product, and transition state (TS) were obtained at CCSD/cc-pVxZ (x = T and Q) levels and scaling factors were employed to consider anharmonicity effects on vibrational frequencies, zero-point energies, and thermal corrections provided by these methodologies. Enthalpies Gibbs energies, and rate constants for this reaction were determined by including a complete basis set extrapolation correction for the electronic properties calculated at CCSD(T)/cc-pVyZ (y = Q and 5) levels. Our study indicates that enthalpy changes for this reaction are highly dependent on temperature. Moreover, forward and reverse (high-pressure limit) rate constants were obtained from variational TS theory with quantum tunneling corrections. Thus, modified Arrhenius’ equations were fitted by means of the best forward and reverse rate constant values, which provide very reliable estimates for these quantities within the temperature range between 700 and 4000 K. To our knowledge, this is the first kinetic study done for the forward H2 + CO \\to H2CO process in a wide temperature range. Finally, these results can be used to explain the formaldehyde abundance in hot and dense interstellar media, possibly providing data about the physical conditions associated with H2CO masers close to massive star-forming regions.

  16. Relationship between electrical conductivity anisotropy and fabric anisotropy in granular materials during drained triaxial compressive tests: a numerical approach

    Science.gov (United States)

    Niu, Qifei; Revil, André; Li, Zhaofeng; Wang, Yu-Hsing

    2017-07-01

    The anisotropy of granular media and its evolution during shearing are important aspects required in developing physics-based constitutive models in Earth sciences. The development of relationships between geoelectrical properties and the deformation of porous media has applications to the monitoring of faulting and landslides. However, such relationships are still poorly understood. In this study, we first investigate the definition of the electrical conductivity anisotropy tensor of granular materials in presence of surface conductivity of the grains. Fabric anisotropy is related to the components of the fabric tensor. We define an electrical anisotropy factor based on the Archie's exponent second-order symmetric tensor m of granular materials. We use numerical simulations to confirm a relationship between the evolution of electrical and fabric anisotropy factors during shearing. To realize the simulations, we build a virtual laboratory in which we can easily perform synthetic experiments. We first simulate drained compressive triaxial tests of loose and dense granular materials (porosity 0.45 and 0.38, respectively) using the discrete element method. Then, the electrical conductivity tensor of a set of deformed synthetic samples is computed using the finite-difference method. The numerical results show that shear strains are responsible for a measurable anisotropy in the bulk conductivity of granular media. The observed electrical anisotropy response, during shearing, is distinct for dense and loose synthetic samples. Electrical and fabric anisotropy factors exhibit however a unique linear correlation, regardless of the shear strain and the initial state (porosity) of the synthetic samples. The practical implication of this finding confirms the usefulness of the electrical conductivity method in studying the fabric tensor of granular media. This result opens the door in using time-lapse electrical resistivity to study non-intrusively the evolution of anisotropy

  17. Experimental investigation of the Rowe's dilatancy law on an atypical granular medium from a municipal solid waste incineration bottom ash

    Science.gov (United States)

    Becquart, Frédéric; Abriak, Nor Edine

    2013-06-01

    Municipal Solid Waste Incineration (MSWI) bottom ashes are irregular granular media because of their origin and are very heterogeneous with a large quantity of angular particles of different chemical species. MSWI bottom ash is a renewable granular resource alternative to the use of non-renewable standard granular materials. Beneficial use of these alternative granular materials mainly lies in road engineering. However, the studies about mechanical properties of such granular media still remain little developed, those being mainly based on empirical considerations. In this paper, a study of mechanical behaviour of a MSWI bottom ash under axisymmetric triaxial loadings conditions is presented. Samples are initially dense after Proctor compaction, are saturated and tested in drained conditions, under different effective confining pressures ranging from 100 to 600 kPa. The evolutions of volumetric strains show an initial contracting phase followed by a dilatancy phase, more pronounced when the confining pressure is low. The stresses ratios at the characteristic state and at the critical state appear in good agreement and with a null rate of volume variation. The angles of internal friction and dilatancy of the studied MSWI bottom ash are estimated and are similar to conventional granular materials used especially in road engineering. The dilatancy law of Rowe is well experimentally verified on this irregular recycled granular material.

  18. 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

  19. Modeling multi-layer effects in passive microwave remote sensing of dry snow using Dense Media Radiative Transfer Theory (DMRT) based on quasicrystalline approximation

    Science.gov (United States)

    Liang, D.; Xu, X.; Tsang, L.; Andreadis, K.M.; Josberger, E.G.

    2008-01-01

    The Dense Media Radiative Transfer theory (DMRT) of Quasicrystalline Approximation of Mie scattering by sticky particles is used to study the multiple scattering effects in layered snow in microwave remote sensing. Results are illustrated for various snow profile characteristics. Polarization differences and frequency dependences of multilayer snow model are significantly different from that of the single-layer snow model. Comparisons are also made with CLPX data using snow parameters as given by the VIC model. ?? 2007 IEEE.

  20. Rheology of dense suspensions of non colloidal particles

    Science.gov (United States)

    Guazzelli, Élisabeth

    2017-06-01

    Dense suspensions are materials with broad applications both in industrial processes (e.g. waste disposal, concrete, drilling muds, metalworking chip transport, and food processing) and in natural phenomena (e.g. flows of slurries, debris, and lava). Despite its long research history and its practical relevance, the mechanics of dense suspensions remain poorly understood. The major difficulty is that the grains interact both by hydrodynamic interactions through the liquid and by mechanical contact. These systems thus belong to an intermediate regime between pure suspensions and granular flows. We show that we can unify suspension and granular rheology under a common framework by transferring the frictional approach of dry granular media to wet suspensions of spherical particles. We also discuss non-Newtonian behavior such as normal-stress differences and shear-induced migration. Beyond the classical problem of dense suspension of hard spheres which is far from being completely resolved, there are also entirely novel avenues of study concerning more complex mixtures of particles and fluids such as those involving other types of particles (e.g. fibers) or non-Newtonian fluids that we will also address.

  1. Rheology of dense suspensions of non colloidal particles

    Directory of Open Access Journals (Sweden)

    Guazzelli Élisabeth

    2017-01-01

    Full Text Available Dense suspensions are materials with broad applications both in industrial processes (e.g. waste disposal, concrete, drilling muds, metalworking chip transport, and food processing and in natural phenomena (e.g. flows of slurries, debris, and lava. Despite its long research history and its practical relevance, the mechanics of dense suspensions remain poorly understood. The major difficulty is that the grains interact both by hydrodynamic interactions through the liquid and by mechanical contact. These systems thus belong to an intermediate regime between pure suspensions and granular flows. We show that we can unify suspension and granular rheology under a common framework by transferring the frictional approach of dry granular media to wet suspensions of spherical particles. We also discuss non-Newtonian behavior such as normal-stress differences and shear-induced migration. Beyond the classical problem of dense suspension of hard spheres which is far from being completely resolved, there are also entirely novel avenues of study concerning more complex mixtures of particles and fluids such as those involving other types of particles (e.g. fibers or non-Newtonian fluids that we will also address.

  2. Granular Computing

    Institute of Scientific and Technical Information of China (English)

    2004-01-01

    The basic ideas and principles of granular computing (GrC) have been studied explicitly or implicitly in many fields in isolation. With the recent renewed and fast growing interest, it is time to extract the commonality from a diversity of fields and to study systematically and formally the domain independent principles of granular computing in a unified model. A framework of granular computing can be established by applying its own principles. We examine such a framework from two perspectives,granular computing as structured thinking and structured problem solving. From the philosophical perspective or the conceptual level,granular computing focuses on structured thinking based on multiple levels of granularity. The implementation of such a philosophy in the application level deals with structured problem solving.

  3. Gas-solute dispersivity ratio in granular porous media as related to particle size distribution and particle shape

    DEFF Research Database (Denmark)

    Pugliese, Lorenzo; Poulsen, Tjalfe; Straface, Salvatore

    2013-01-01

    data. This paper evaluates the possibility for estimating solute dispersion based on gas dispersion measurements. Breakthrough measurements were carried out at different fluid velocities (covering the same range in Reynolds number), using O2 and NaCl as gas and solute tracers, respectively. Three...... different, granular porous materials were used: (1) crushed granite (very angular particles), (2) gravel (particles of intermediate roundness) and (3) Leca® (almost spherical particles). For each material, 21 different particle size fractions were used. Gas and solute dispersion coefficients were determined...

  4. Characters of Wave Propagation in Granular Media%振动场中散体介质波的传播规律

    Institute of Scientific and Technical Information of China (English)

    孙业志; 吴爱祥; 黎剑华; 赵国彦

    2001-01-01

    Real granular media manifest such characters as nonuniformity, ani sotropy and lamellar distribution and have gas, liquid and solid phases. Therefo re propogation of waves in them is very complex. When their strain number, ε <1×10-4, they are elastic media. According to this, the authors ana lyse and give the wave motion equation of elastic waves in isotropic media and t he expression of wave propogation velocity and wave energy, as well as the wave motion equation of elastic waves in horizontally isotropic media and the express ion of energy penetration coefficient of elastic waves. The tests show that ener gy attenuation has relation to the density of layered media. Rayleigh wave is a type of superimposition wave forming by vibration of P and S waves. According to the characteristic, the authors analyse the propagation characters of Rayleigh wave in isotropic media and horizontally isotropic media in semi-infinite body . In addition, Love wave is a kind of interference wave which is caused by total reflection of SH waves. The study shows that its characters depend on the thick ness of granular media and the velocity of shear waves, etc.%非理想散体介质显现出非匀质性、各向异性和层状分布等特点,且有气、液、固三相,其波 的传播比较复杂。当应变值ε<1×10-4时,散体介质为弹性介质,据此分析并给 出 了各向同性散体介质中弹性波的波动方程、传播速度和波动能量的表达式,以及横观各向同 性介质中弹性波的波动方程和能量透过系数表达式,并通过试验验证了能量衰减与分层介质 密度有关。此外,根据瑞利波由P波和S波振动叠加而成的特点,分析了无限半空间各向同性 介质和横观各向同性介质中瑞利波的传播特性;又由于勒夫波由SH波经多次全反射加强干涉 产生,研究表明其运动特性与散体厚度和剪切波速度等因素有关。

  5. Transport and abatement of fluorescent silica nanoparticle (SiO2 NP) in granular filtration: effect of porous media and ionic strength

    Science.gov (United States)

    Zeng, Chao; Shadman, Farhang; Sierra-Alvarez, Reyes

    2017-03-01

    The extensive production and application of engineered silica nanoparticles (SiO2 NPs) will inevitably lead to their release into the environment. Granular media filtration, a widely used process in water and wastewater treatment plants, has the potential for NP abatement. In this work, laboratory-scale column experiments were performed to study the transport and retention of SiO2 NPs on three widely used porous materials, i.e., sand, anthracite, and granular activated carbon (GAC). Synthetic fluorescent core-shell SiO2 NPs (83 nm) were used to facilitate NP detection. Sand showed very low capacity for SiO2 filtration as this material had a surface with limited surface area and a high concentration of negative charge. Also, we found that the stability and transport of SiO2 NP were strongly dependent on the ionic strength of the solution. Increasing ionic strength led to NP agglomeration and facilitated SiO2 NP retention, while low ionic strength resulted in release of captured NPs from the sand bed. Compared to sand, anthracite and GAC showed higher affinity for SiO2 NP capture. The superior capacity of GAC was primarily due to its porous structure and high surface area. A process model was developed to simulate NP capture in the packed bed columns and determine fundamental filtration parameters. This model provided an excellent fit to the experimental data. Taken together, the results obtained indicate that GAC is an interesting material for SiO2 NP filtration.

  6. Sulfur toxicity and media capacity for H{sub 2}S removal in biofilters packed with a natural or a commercial granular medium

    Energy Technology Data Exchange (ETDEWEB)

    Kim Jones; Alvaro Martinez; Mohammad Rizwan; Jim Boswell [Texas A& M University-Kingsville, Kingsville, TX (United States). Department of Environmental Engineering

    2005-04-01

    Two types of biofilter media, a natural medium (wood chips) and a commercially engineered medium, were evaluated for sulfur inhibition and capacity for removal of hydrogen sulfide (H{sub 2}S). Sulfate was added artificially (40, 65, and 100 mg of S/g of medium) to test its effect on removal efficiency and the media. A humidified gas stream of 50 ppm by volume H{sub 2}S was passed through the media-packed columns, and effluent readings for H{sub 2}S at the outlet were measured continuously. The overall H{sub 2}S baseline removal efficiencies of the column packed with natural medium remained 95% over a 2-day period even with the accumulated sulfur species. Added sulfate at a concentration high enough to saturate the biofilter moisture phase did not appear to affect the H{sub 2}S removal process efficiency. The results of additional experiments with a commercial granular medium also demonstrated that the accumulation of amounts of sulfate sufficient enough to saturate the moisture phase of the medium did not have a significant effect on H{sub 2}S removal. When the pH of the biofilter medium was lowered to 4, H{sub 2}S removal efficiency did drop to 36%. This work suggests that sulfate mass transfer through the moisture phase to the biofilm phase does not appear to inhibit H{sub 2}S removal rates in biofilters. Thus, performance degradation for odor-removing biofilters or H{sub 2}S breakthrough in field applications is probably caused by other consequences of high H{sub 2}S loading, such as sulfur precipitation. 12 refs., 4 figs., 2 tabs.

  7. Instability in Shocked Granular Gases

    CERN Document Server

    Sirmas, Nick; Radulescu, Matei

    2013-01-01

    Shocks in granular media, such as vertically oscillated beds, have been shown to develop instabilities. Similar jet formation has been observed in explosively dispersed granular media. Our previous work addressed this instability by performing discrete-particle simulations of inelastic media undergoing shock compression. By allowing finite dissipation within the shock wave, instability manifests itself as distinctive high density non-uniformities and convective rolls within the shock structure. In the present study we have extended this work to investigate this instability at the continuum level. We modeled the Euler equations for granular gases with a modified cooling rate to include an impact velocity threshold necessary for inelastic collisions. Our results showed a fair agreement between the continuum and discrete-particle models. Discrepancies, such as higher frequency instabilities in our continuum results may be attributed to the absence of higher order effects.

  8. Instability in shocked granular gases

    Science.gov (United States)

    Sirmas, Nick; Falle, Sam; Radulescu, Matei

    2014-05-01

    Shocks in granular media, such as vertically oscillated beds, have been shown to develop instabilities. Similar jet formation has been observed in explosively dispersed granular media. Our previous work addressed this instability by performing discrete-particle simulations of inelastic media undergoing shock compression. By allowing finite dissipation within the shock wave, instability manifests itself as distinctive high density non-uniformities and convective rolls within the shock structure. In the present study we have extended this work to investigate this instability at the continuum level. We modeled the Euler equations for granular gases with a modified cooling rate to include an impact velocity threshold necessary for inelastic collisions. Our results showed a fair agreement between the continuum and discrete-particle models. Discrepancies, such as higher frequency instabilities in our continuum results may be attributed to the absence of higher order effects.

  9. Grain scale simulation of multiphase flow through porous media; Simulacao em escala granular do escoamento multifasico em meio poroso

    Energy Technology Data Exchange (ETDEWEB)

    Domingos, Ricardo Golghetto; Cheng, Liang-Yee [Universidade de Sao Paulo (USP), SP (Brazil). Escola Politecnica

    2012-07-01

    Since the grain scale modeling of multi-phase flow in porous media is of great interest for the oil industry, the aim of the present research is to show an implementation of Moving Particle Semi-Implicit (MPS) method for the grain scale simulation of multi-phase flow in porous media. Geometry data obtained by a high-resolution CT scan of a sandstone sample has been used as input for the simulations. The results of the simulations performed considering different resolutions are given, the head loss and permeability obtained numerically, as well as the influence of the wettability of the fluids inside the sample of the reservoir's sandstone. (author)

  10. Micromechanical Behavior and Modelling of Granular Soil

    Science.gov (United States)

    1989-07-01

    elasticity, hypoelasticity , plasticity and viscoplasticity. Despite the large number of models , there is no consensus yet within the research community on...Classification) (U) Micromechanical Behavior and Modelling of Granular MOWo I... 12. PERSONAL AUTHOR(S) Emmanuel Petrakis and Ricardo Dobry 13a. TYPE OF...Institute (RPI) on the behavior and modelling of granular media is summarized. The final objective is to develol a constitutive law for granular soil

  11. Dynamical compressibility of dense granular shear flows

    OpenAIRE

    Trulsson, Martin; Bouzid, Mehdi; Claudin, Philippe; Andreotti, Bruno

    2012-01-01

    It has been conjectured by Bagnold [1] that an assembly of hard non-deformable spheres could behave as a compressible medium when slowly sheared, as the average density of such a system effectively depends on the confining pressure. Here we use discrete element simulations to show the existence of transverse and sagittal waves associated to this dynamical compressibility. For this purpose, we study the resonance of these waves in a linear Couette cell and compare the results with those predic...

  12. Micromechanical Effects of Cement on Deformation of Porous Granular Media: Example from the San Gregorio Fault, California and Laboratory Studies

    Science.gov (United States)

    Cook, J.; Goodwin, L.; Boutt, D.; Bucheitt, T.; Cook, B.

    2006-12-01

    The San Gregorio fault, part of the San Andreas fault system, provides a structural record of transitions in deformation mechanisms with progressive lithification. The San Gregorio is an active, predominantly dextral strike-slip fault with cumulative offset of 90 - 150 km. Within the study area the fault cuts syntectonic mudstones, siltstones, and sandstones of the Purisma Formation. Detailed mapping documents a post- lithification damage zone that overprinted pre-lithification mixed zones that bracket a well-developed, exceptionally wide (greater than 15 m) fault core. Deformation within the mixed zone was distributed and characterized by increasing disorganization and boudinage of relatively competent sedimentary layers. Multiple sandstone dikes crosscut these structures, demonstrating that they formed prior to lithification. Deformation is inferred to have occurred largely through particulate flow. The brittle damage zone, which consists of discrete fractures, minor faults, and veins that crosscut both boudins and sandstone dikes, is less extensive than the mixed zone. The transition in macroscale deformation behavior that these structures record is inferred to reflect a transition in grain-scale mechanics with progressive consolidation, tectonic compaction, and cementation. To quantitatively assess the importance of intergranular cements we are conducting experimental investigations of the micromechanical behavior of cemented granular systems, using both synthetic and natural samples. Synthetic samples have been created with both calcite and amorphous silica cement. Natural samples are sandstones with variations in primary grain and cement composition, cement abundance and distribution, and porosity, including selected samples from the San Gregorio fault. Synthetic grain assemblages will be tested in tension, compression, and shear. Nanoindentation and mm-scale deformation experiments will be used to probe the mechanical properties, including modulus, hardness

  13. Predicted Disappearance of Saturation Hysteresis in Coarse Granular Media Based on Capillary and Gravity Scaling, and Experimental Tests

    Science.gov (United States)

    Tokunaga, T. K.; Olson, K. R.; Wan, J.

    2002-12-01

    Since the classic work of W. B. Haines (1930), hysteresis in the relation between matric (capillary) potential versus water content has been recognized as a basic aspect of interactions between water and variably saturated porous media. This lack of unique correspondence between potential and saturation has well-recognized consequences for equilibrium, flow, and transport. Although hysteresis in moisture characteristic relations has several causes, the existence of different pore-sizes within porous media (the "ink bottle" effect) is primary. This capillarity-dependent phenomenon has a grain-size limit imposed by the influence of gravity, and more generally by the relations between surface and body forces, and length scales. Above this limit, capillary hysteresis vanishes. The grain-size associated with vanishing of capillary hysteresis was predicted in two ways; first with a simple pore-size model, and second by Miller-Miller scaling. Both methods predict that hysteresis vanishes when characteristic grain-sizes exceed about 8 mm, when the water-air surface tension is 72 mN/m, and when the body force is due to ordinary gravity. More generally, capillary hysteresis is predicted to disappear when the Haines Number (dependent on grain-size, surface tension, the body force, density difference between immiscible fluids) exceeds 8. The predicted critical grain-size was experimentally supported through measurements of drainage and wetting curves of sands and gravels, with grain-sizes ranging from 0.2 up to 11 mm. We also consider effects of interfacial tension variation (surfactants), variation of the body force (centrifugal field), and capillarity associated with grain-surface roughness.

  14. Potential of a spectroscopic measurement method using adding-doubling to retrieve the bulk optical properties of dense microalgal media.

    Science.gov (United States)

    Bellini, Sarah; Bendoula, Ryad; Latrille, Eric; Roger, Jean-Michel

    2014-01-01

    In the context of algal mass cultivation, current techniques used for the characterization of algal cells require time-consuming sample preparation and a large amount of costly, standard instrumentation. As the physical and chemical properties of the algal cells strongly affect their optical properties, the optical characterization is seen as a promising method to provide an early diagnosis in the context of mass cultivation monitoring. This article explores the potential of a spectroscopic measurement method coupled with the inversion of the radiative transfer theory for the retrieval of the bulk optical properties of dense algal samples. Total transmittance and total reflectance measurements were performed over the 380-1020 nm range on dense algal samples with a double integrating sphere setup. The bulk absorption and scattering coefficients were thus extracted over the 380-1020 nm range by inverting the radiative transfer theory using inverse-adding-doubling computations. The experimental results are presented and discussed; the configuration of the optical setup remains a critical point. The absorption coefficients obtained for the four samples of this study appear not to be more informative about pigment composition than would be classical methods in analytical spectroscopy; however, there is a real added value in measuring the reduced scattering coefficient, as it appears to be strongly correlated to the size distribution of the algal cells.

  15. Transport of ARS-labeled hydroxyapatite nanoparticles in saturated granular media is influenced by surface charge variability even in the presence of humic acid

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Dengjun [Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, No. 71 East Beijing Road, Nanjing 210008 (China); Graduate School of the Chinese Academy of Sciences, Beijing 100049 (China); Bradford, Scott A. [U.S. Salinity Laboratory, Agricultural Research Service, United States Department of Agriculture, 450 W. Big Springs Road, Riverside, CA 92507 (United States); Harvey, Ronald W. [U.S. Geological Survey, 3215 Marine Street, Boulder, CO 80303 (United States); Hao, Xiuzhen [Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, No. 71 East Beijing Road, Nanjing 210008 (China); Zhou, Dongmei, E-mail: dmzhou@issas.ac.cn [Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, No. 71 East Beijing Road, Nanjing 210008 (China)

    2012-08-30

    Highlights: Black-Right-Pointing-Pointer The transport and retention kinetics of ARS-labeled hydroxyapatite nanoparticles (ARS-nHAP) were investigated over a range of ionic strengths in the presence of humic acid. Black-Right-Pointing-Pointer A two-site kinetic attachment model predicted both the breakthrough curves and retention profiles of ARS-nHAP quite well. Black-Right-Pointing-Pointer The retention profiles of ARS-nHAP exhibited hyperexponential shapes for all the test conditions. Black-Right-Pointing-Pointer Surface charge heterogeneities on the collector surfaces and especially within the ARS-nHAP population contributed to hyperexponential retention profiles. - Abstract: Hydroxyapatite nanoparticle (nHAP) is increasingly being used to remediate soils and water polluted by metals and radionuclides. The transport and retention of Alizarin red S (ARS)-labeled nHAP were investigated in water-saturated granular media. Experiments were carried out over a range of ionic strength (I{sub c}, 0-50 mM NaCl) conditions in the presence of 10 mg L{sup -1} humic acid. The transport of ARS-nHAP was found to decrease with increasing suspension I{sub c} in part, because of enhanced aggregation and chemical heterogeneity. The retention profiles (RPs) of ARS-nHAP exhibited hyperexponential shapes (a decreasing rate of retention with increasing transport distance) for all test conditions, suggesting that some of the attachment was occurring under unfavorable conditions. Surface charge heterogeneities on the collector surfaces and especially within the ARS-nHAP population were contributing causes for the hyperexponential RPs. Consideration of the effect(s) of I{sub c} in the presence of HA is needed to improve the efficacy of nHAP for scavenging metals and actinides in real soils and groundwater environments.

  16. Interfacial Instability during Granular Erosion.

    Science.gov (United States)

    Lefebvre, Gautier; Merceron, Aymeric; Jop, Pierre

    2016-02-12

    The complex interplay between the topography and the erosion and deposition phenomena is a key feature to model granular flows such as landslides. Here, we investigated the instability that develops during the erosion of a wet granular pile by a dry dense granular flow. The morphology and the propagation of the generated steps are analyzed in relation to the specific erosion mechanism. The selected flowing angle of the confined flow on a dry heap appears to play an important role both in the final state of the experiment, and for the shape of the structures. We show that the development of the instability is governed by the inertia of the flow through the Froude number. We model this instability and predict growth rates that are in agreement with the experiment results.

  17. Effect of Porous Media and Fluid Properties on Dense Non-Aqueous Phase Liquid Migration and Dilution Mass Flux

    Science.gov (United States)

    2005-08-01

    system wettability that is directly related to contact angle. Fink (1970) experimentally measured breakthrough pressure for water repellent soils to...this study was to conduct water entry pressure, air and oil entry pressure tests for silica sand with various fractions of organic ( silane ) coated media... Water Repellency Based upon Contact Angle-Surface Tension Relationships, Soil Science Society of America Proceedings, 34:841-844, 1970. Wilson, J.L

  18. 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 ...

  19. The effects of layers in dry snow on its passive microwave emissions using dense media radiative transfer theory based on the quasicrystalline approximation (QCA/DMRT)

    Science.gov (United States)

    Liang, D.; Xu, X.; Tsang, L.; Andreadis, K.M.; Josberger, E.G.

    2008-01-01

    A model for the microwave emissions of multilayer dry snowpacks, based on dense media radiative transfer (DMRT) theory with the quasicrystalline approximation (QCA), provides more accurate results when compared to emissions determined by a homogeneous snowpack and other scattering models. The DMRT model accounts for adhesive aggregate effects, which leads to dense media Mie scattering by using a sticky particle model. With the multilayer model, we examined both the frequency and polarization dependence of brightness temperatures (Tb's) from representative snowpacks and compared them to results from a single-layer model and found that the multilayer model predicts higher polarization differences, twice as much, and weaker frequency dependence. We also studied the temporal evolution of Tb from multilayer snowpacks. The difference between Tb's at 18.7 and 36.5 GHz can be S K lower than the single-layer model prediction in this paper. By using the snowpack observations from the Cold Land Processes Field Experiment as input for both multi- and single-layer models, it shows that the multilayer Tb's are in better agreement with the data than the single-layer model. With one set of physical parameters, the multilayer QCA/DMRT model matched all four channels of Tb observations simultaneously, whereas the single-layer model could only reproduce vertically polarized Tb's. Also, the polarization difference and frequency dependence were accurately matched by the multilayer model using the same set of physical parameters. Hence, algorithms for the retrieval of snowpack depth or water equivalent should be based on multilayer scattering models to achieve greater accuracy. ?? 2008 IEEE.

  20. Perfect fluid flow from granular jet impact

    CERN Document Server

    Ellowitz, Jake; Zhang, Wendy W

    2012-01-01

    Experiments on the impact of a densely-packed jet of non-cohesive grains onto a fixed target show that the impact produces an ejecta sheet comprised of particles in collimated motion. The ejecta sheet leaves the target at a well-defined angle whose value agrees quantitatively with the sheet angle produced by water jet impact. Motivated by these experiments, we examine the idealized problem of dense granular jet impact onto a frictionless target in two dimensions. Numerical results for the velocity and pressure fields within the granular jet agree quantitatively with predictions from an exact solution for 2D perfect-fluid impact. This correspondence demonstrates that the continuum limit controlling the coherent collective motion in dense granular impact is Euler flow.

  1. Software for fitting and simulating fate and transport of dense colloids and biocolloids in one-dimensional porous media: Re-introducing ColloidFit.

    Science.gov (United States)

    Katzourakis, Vasileios; Chrysikopoulos, Constantinos

    2016-04-01

    The present work re-introduces ColloidFit, which is an autonomous, modular, multipurpose fitting software for dense colloid and biocolloid transport phenomena in porous media. The initial version of ColloidFit, introduced by Sim and Chrysikopoulos (1995), was substantially improved and combined with a relatively intuitive and easy to use graphical user interface. The re-introduced ColloidFit can simulate the migration of suspended colloid or biocolloid particles in one-dimensional, water saturated, homogeneous porous media with uniform flow, accounting for non-equilibrium attachment onto the solid matrix, as well as gravitational effects. Furthermore, the improved ColloidFit software employs a variety of non-equilibrium, linear and nonlinear models for the simulation of colloid attachment onto a solid matrix under batch experimental conditions. The re-introduced ColloidFit uses the state of the art fitting software "Pest" to estimate unknown model parameter values, together with their 95% confidence intervals. Pest is a model-independent parameter estimation software capable of adjusting model parameters, so that discrepancies between model-generated data and the corresponding experimental measurements are reduced to a user preselected minimum. The fitting process is graphed and displayed in real time. The user is allowed to overview every step of the fitting progress, and if needed to change the initial parameter values. The re-introduced ColloidFit software is expected to make the fitting process of colloid and biocolloid transport data, just a simple task.

  2. Batch and continuous production of stable dense suspensions of drug nanoparticles in a wet stirred media mill

    Science.gov (United States)

    Afolabi, Afola we mi

    One way to improve the bioavailability of poorly water-soluble drugs is to reduce particle size of drug crystals down to nanoscale via wet stirred media milling. An increase in total surface area per mass loading of the drug and specific surface area as well as reduced external mass transfer resistance allow a faster dissolution of the poorly-water soluble drug from nanocrystals. To prevent aggregation of nanoparticles, polymers and surfactants are dissolved in water acting as stabilizers via adsorption onto the drug crystals. In the last two decades, ample experimental data were generated in the area of wet stirred media milling for the production of drug nanoparticle suspensions. However, a fundamental scientific/engineering understanding of various aspects of this process is still lacking. These challenges include elucidation of the governing mechanism(s) during nanoparticle formation and physical stabilization of the nanosuspension with the use of polymers and surfactants (formulation parameters), understanding the impact of process parameters in the context of first-principle-based models, and production of truly nanosized drug particles (10-100 nm) with acceptable physical stability and minimal contamination with the media. Recirculation mode of milling operation, where the drug suspension in a holding tank continuously circulates through the stirred media mill, has been commonly used in lab, pilot, and commercial scales. Although the recirculation is continuous, the recirculation operation mode is overall a batch operation, requiring significant number of batches for a large-volume pharmaceutical product. Hence, development and investigation of a truly continuous process should offer significant advantages. To explain the impact of some of the processing parameters, stress intensity and stress number concepts were widely used in literature, which do not account for the effect of suspension viscosity explicitly. The impact of the processing parameters has not

  3. Phase transition and bistable phenomenon of granular flows down a chute with successive turnings

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Guo-Cheng; Liu, Qi-Yi [School of Engineering Science, University of Science and Technology of China, Hefei 230026 (China); Hu, Mao-Bin, E-mail: humaobin@ustc.edu.cn [School of Engineering Science, University of Science and Technology of China, Hefei 230026 (China); Kavli Institute for Theoretical Physics China at the Chinese Academy of Sciences, Beijing 100190 (China); Jiang, Rui; Wu, Qing-Song [School of Engineering Science, University of Science and Technology of China, Hefei 230026 (China)

    2014-03-01

    This paper studies the granular flow down a chute with two successive turnings, which play the role of bottlenecks for the granular flow system and determine the granular flow state in main section between them. With the increase of main section width D, phase transition from dilute to dense granular flow is observed: When the main section width D is small (large), the granular flow at upper (lower) bottleneck is dense and the granular flow is dilute (dense) in the main section. More interestingly, a bistable region is exhibited, in which either dilute flow or dense flow may occur and continue for the entire run. In this region, the packing in the reservoir will affect initial flow rate and then affect the flow pattern. This study can be viewed as a paradigm for the jamming and unjamming transitions under shear due to gravity.

  4. Simulation of the microwave emission of multi-layered snowpacks using the dense media radiative transfer theory: the DMRT-ML model

    Directory of Open Access Journals (Sweden)

    G. Picard

    2012-11-01

    Full Text Available DMRT-ML is a physically-based numerical model designed to compute the thermal microwave emission of a given snowpack. Its main application is the simulation of brightness temperatures at frequencies in the range 1–200 GHz similar to those acquired routinely by space-based microwave radiometers. The model is based on the Dense Media Radiative Transfer (DMRT theory for the computation of the snow scattering and extinction coefficients and on the Discrete Ordinate Method (DISORT to numerically solve the radiative transfer equation. The snowpack is modeled as a stack of multiple horizontal snow layers and an optional underlying interface representing the soil or the bottom ice. The model handles both dry and wet snow conditions. Such a general design allows the user to account for a wide range of snow conditions. Hitherto, the model has been used to simulate the thermal emission of the deep firn on ice sheets, shallow snowpacks overlying soil in Arctic and Alpine regions, and overlying ice on the large ice-sheet margins and glaciers. DMRT-ML has thus been validated in three very different conditions: Antarctica, Barnes Ice Cap (Canada and Canadian tundra. It has been recently used in conjunction with inverse methods to retrieve snow grain size from remote sensing data. The model is written in Fortran90 and available to the snow remote sensing community as an open-source software.

  5. Simulation of the microwave emission of multi-layered snowpacks using the Dense Media Radiative transfer theory: the DMRT-ML model

    Directory of Open Access Journals (Sweden)

    G. Picard

    2013-07-01

    Full Text Available DMRT-ML is a physically based numerical model designed to compute the thermal microwave emission of a given snowpack. Its main application is the simulation of brightness temperatures at frequencies in the range 1–200 GHz similar to those acquired routinely by space-based microwave radiometers. The model is based on the Dense Media Radiative Transfer (DMRT theory for the computation of the snow scattering and extinction coefficients and on the Discrete Ordinate Method (DISORT to numerically solve the radiative transfer equation. The snowpack is modeled as a stack of multiple horizontal snow layers and an optional underlying interface representing the soil or the bottom ice. The model handles both dry and wet snow conditions. Such a general design allows the model to account for a wide range of snow conditions. Hitherto, the model has been used to simulate the thermal emission of the deep firn on ice sheets, shallow snowpacks overlying soil in Arctic and Alpine regions, and overlying ice on the large ice-sheet margins and glaciers. DMRT-ML has thus been validated in three very different conditions: Antarctica, Barnes Ice Cap (Canada and Canadian tundra. It has been recently used in conjunction with inverse methods to retrieve snow grain size from remote sensing data. The model is written in Fortran90 and available to the snow remote sensing community as an open-source software. A convenient user interface is provided in Python.

  6. Simulation of the Microwave Emission of Multi-layered Snowpacks Using the Dense Media Radiative Transfer Theory: the DMRT-ML Model

    Science.gov (United States)

    Picard, G.; Brucker, Ludovic; Roy, A.; Dupont, F.; Fily, M.; Royer, A.; Harlow, C.

    2013-01-01

    DMRT-ML is a physically based numerical model designed to compute the thermal microwave emission of a given snowpack. Its main application is the simulation of brightness temperatures at frequencies in the range 1-200 GHz similar to those acquired routinely by spacebased microwave radiometers. The model is based on the Dense Media Radiative Transfer (DMRT) theory for the computation of the snow scattering and extinction coefficients and on the Discrete Ordinate Method (DISORT) to numerically solve the radiative transfer equation. The snowpack is modeled as a stack of multiple horizontal snow layers and an optional underlying interface representing the soil or the bottom ice. The model handles both dry and wet snow conditions. Such a general design allows the model to account for a wide range of snow conditions. Hitherto, the model has been used to simulate the thermal emission of the deep firn on ice sheets, shallow snowpacks overlying soil in Arctic and Alpine regions, and overlying ice on the large icesheet margins and glaciers. DMRT-ML has thus been validated in three very different conditions: Antarctica, Barnes Ice Cap (Canada) and Canadian tundra. It has been recently used in conjunction with inverse methods to retrieve snow grain size from remote sensing data. The model is written in Fortran90 and available to the snow remote sensing community as an open-source software. A convenient user interface is provided in Python.

  7. Vibrational dynamics of 3D granular media composed with polyhedral grains -- Din\\'amica vibracional de un medio granular 3D compuesto de part\\'iculas poli\\'edricas

    CERN Document Server

    Azema, Émilien; Peyroux, R; Dubois, Frédéric; Saussine, G

    2008-01-01

    By means of tree-dimensional contact dynamics simulations, we analyze the vibrational dynamics of a confined granular layer in response to harmonic forcing. The sample is composed of polyedric grains with a shape derived from digitalized ballast. The system involves a jammed state separating passive (loading) and active (unloading) states. We show that an approximate expression of the packing resistance force as a function of the displacement of the free retaining wall from the jamming position provides a good description of the dynamics. We study in detail the scaling of displacements and velocities with loading parameters. In particular, we find that, for a wide range of frequencies, the data collapse by scaling the displacements with the inverse square of frequency, the inverse of the force amplitude and the square of gravity. We show that the mean compaction rate increases linearly with frequency up to a characteristic frequency of 10 Hz and then it declines in inverse proportion to frequency.

  8. Dense Breasts

    Science.gov (United States)

    ... also appear white on mammography, they can be hidden by or within dense breast tissue. Other imaging ... understanding of the possible charges you will incur. Web page review process: This Web page is reviewed ...

  9. Metastable Pions in Dense Media

    CERN Document Server

    Loewe, Marcelo; Villavicencio, Cristian

    2016-01-01

    We study the leptonic decay of charged pions in a compact star environment. Considering leptons as a degenerated Fermi system, pions are tightly constrained to decay into these particles because their Fermi levels are occupied. Thus, pion decay is only possible through thermal fluctuations. Under these circumstances, pion life-time is larger and hence can be considered to reach a metastable state. We explore restrictions under which such a metastability is possible. We also study conditions for pion-lepton chemical equilibrium and obtain the neutrino emissivity from metastable pions. Scenarios which favor this metastable state are protoneutron stars.

  10. Long-range interactions in dilute granular systems

    NARCIS (Netherlands)

    Müller, Micha-Klaus

    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 diss

  11. Helical Locomotion in a Granular Medium

    Science.gov (United States)

    Darbois Texier, Baptiste; Ibarra, Alejandro; Melo, Francisco

    2017-08-01

    The physical mechanisms that bring about the propulsion of a rotating helix in a granular medium are considered. A propulsive motion along the axis of the rotating helix is induced by both symmetry breaking due to the helical shape, and the anisotropic frictional forces undergone by all segments of the helix in the medium. Helix dynamics is studied as a function of helix rotation speed and its geometrical parameters. The effect of the granular pressure and the applied external load were also investigated. A theoretical model is developed based on the anisotropic frictional force experienced by a slender body moving in a granular material, to account for the translation speed of the helix. A good agreement with experimental data is obtained, which allows for predicting the helix design to propel optimally within granular media. These results pave the way for the development of an efficient sand robot operating according to this mode of locomotion.

  12. Stress Response of Granular Systems

    Science.gov (United States)

    Ramola, Kabir; Chakraborty, Bulbul

    2017-10-01

    We develop a framework for stress response in two dimensional granular media, with and without friction, that respects vector force balance at the microscopic level. We introduce local gauge degrees of freedom that determine the response of contact forces between constituent grains on a given, disordered, contact network, to external perturbations. By mapping this response to the spectral properties of the graph Laplacian corresponding to the underlying contact network, we show that this naturally leads to spatial localization of forces. We present numerical evidence for localization using exact diagonalization studies of network Laplacians of soft disk packings. Finally, we discuss the role of other constraints, such as torque balance, in determining the stability of a granular packing to external perturbations.

  13. Stress Response of Granular Systems

    Science.gov (United States)

    Ramola, Kabir; Chakraborty, Bulbul

    2017-08-01

    We develop a framework for stress response in two dimensional granular media, with and without friction, that respects vector force balance at the microscopic level. We introduce local gauge degrees of freedom that determine the response of contact forces between constituent grains on a given, disordered, contact network, to external perturbations. By mapping this response to the spectral properties of the graph Laplacian corresponding to the underlying contact network, we show that this naturally leads to spatial localization of forces. We present numerical evidence for localization using exact diagonalization studies of network Laplacians of soft disk packings. Finally, we discuss the role of other constraints, such as torque balance, in determining the stability of a granular packing to external perturbations.

  14. Cobalt toxicity in anaerobic granular sludge: influence of chemical speciation

    NARCIS (Netherlands)

    Bartacek, J.; Fermoso, F.G.; Baldo-Urrutia, A.M.; Hullebusch, van E.D.; Lens, P.N.L.

    2008-01-01

    The influence of cobalt speciation on the toxicity of cobalt to methylotrophic methanogenesis in anaerobic granular sludge was investigated. The cobalt speciation was studied with three different media that contained varying concentrations of complexing ligands [carbonates, phosphates and ethylenedi

  15. Technical note: Measurement and expression of granular filter ...

    African Journals Online (AJOL)

    Technical note: Measurement and expression of granular filter cleanliness. ... To aid the systematic analysis of filter media and the troubleshooting of problem filters, this paper firstly proposes a standard procedure for ... Article Metrics.

  16. Cobalt toxicity in anaerobic granular sludge: influence of chemical speciation

    NARCIS (Netherlands)

    Bartacek, J.; Fermoso, F.G.; Baldo-Urrutia, A.M.; Hullebusch, van E.D.; Lens, P.N.L.

    2008-01-01

    The influence of cobalt speciation on the toxicity of cobalt to methylotrophic methanogenesis in anaerobic granular sludge was investigated. The cobalt speciation was studied with three different media that contained varying concentrations of complexing ligands [carbonates, phosphates and

  17. Cobalt toxicity in anaerobic granular sludge: influence of chemical speciation

    NARCIS (Netherlands)

    Bartacek, J.; Fermoso, F.G.; Baldo-Urrutia, A.M.; Hullebusch, van E.D.; Lens, P.N.L.

    2008-01-01

    The influence of cobalt speciation on the toxicity of cobalt to methylotrophic methanogenesis in anaerobic granular sludge was investigated. The cobalt speciation was studied with three different media that contained varying concentrations of complexing ligands [carbonates, phosphates and ethylenedi

  18. 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

  19. Granular contact dynamics using mathematical programming methods

    DEFF Research Database (Denmark)

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

    2012-01-01

    A class of variational formulations for discrete element analysis of granular media is presented. These formulations lead naturally to convex mathematical programs that can be solved using standard and readily available tools. In contrast to traditional discrete element analysis, the present...

  20. 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.

  1. C. elegans in Complex Media

    CERN Document Server

    Shen, X N; Arratia, P E

    2011-01-01

    We experimentally studied the locomotion of the nematode C. elegans in both fluidic and granular media. In this fluid dynamics video, we show the motility gaits of the nematode in these two environments. The motility of the nematode C. elegans is investigated using particle tracking methods. Experimental results show that different transport patterns emerge from the fluidic and granular media during the nematode locomotion.

  2. Pulling rigid bodies through granular material

    Science.gov (United States)

    Kubik, Ryan; Dressaire, Emilie

    2016-11-01

    The need for anchoring systems in granular materials such as sand is present in the marine transportation industry, e.g. to layout moorings, keep vessels and docks fixed in bodies of water, build oil rigs, etc. The holding power of an anchor is associated with the force exerted by the granular media. Empirical evidence indicates that the holding power depends on the size and shape of the anchoring structure. In this model study, we use a two-dimensional geometry in which a rigid body is pulled through a granular media at constant velocity to determine the drag and lift forces exerted by a granular medium on a moving object. The method allows measuring the drag force and recording the trajectory of the rigid object through the sand. We systematically vary the size and geometry of the rigid body, the properties of the granular medium and the extraction speed. For different initial positions of a cylindrical object pulled horizontally through the medium, we record large variations in magnitude of the drag and a significant lift force that pulls the object out of the sand.

  3. Hydrodynamic modeling of granular flows in a modified Couette cell.

    Science.gov (United States)

    Jop, Pierre

    2008-03-01

    We present simulations of granular flows in a modified Couette cell, using a continuum model recently proposed for dense granular flows. Based on a friction coefficient, which depends on an inertial number, the model captures the positions of the wide shear bands. We show that a smooth transition in velocity-profile shape occurs when the height of the granular material is increased, leading to a differential rotation of the central part close to the surface. The numerical predictions are in qualitative agreement with previous experimental results. The model provides predictions for the increase of the shear band width when the rotation rate is increased.

  4. Microstructure evolution during impact on granular matter.

    Science.gov (United States)

    Kondic, L; Fang, X; Losert, W; O'Hern, C S; Behringer, R P

    2012-01-01

    We study the impact of an intruder on a dense granular material. The process of impact and interaction between the intruder and the granular particles is modeled using discrete element simulations in two spatial dimensions. In the first part of the paper we discuss how the intruder's dynamics depends on (1) the intruder's properties, including its size, shape and composition, (2) the properties of the grains, including friction, polydispersity, structural order, and elasticity, and (3) the properties of the system, including its size and gravitational field. It is found that polydispersity and related structural order, and frictional properties of the granular particles, play a crucial role in determining impact dynamics. In the second part of the paper we consider the response of the granular system itself. We discuss the force networks that develop, including their topological evolution. The influence of friction and structural order on force propagation, including the transition from hyperbolic-like to elastic-like behavior is discussed, as well as the affine and nonaffine components of the grain dynamics. Several broad observations include the following: tangential forces between granular particles are found to play a crucial role in determining impact dynamics; both force networks and particle dynamics are correlated with the dynamics of the intruder itself. © 2012 American Physical Society

  5. Development of granular pial cells and granular perithelial cells in the spinal cords of mouse and rabbit.

    OpenAIRE

    1987-01-01

    Free cells containing large dense granules first appear in the leptomeninges of spinal cord at E14 in the mouse and at E16 in the rabbit. These ages represent a similar stage of development of the spinal cord and meninges. Despite the early appearance of granular pial cells, granular perithelial cells are not found around blood vessels in the spinal cord until 5 days postnatum in the mouse and E28 in the rabbit. The first appearance of granular perithelial cells coincides with the development...

  6. Onset of sediment transport is a continuous transition driven by fluid shear and granular creep.

    Science.gov (United States)

    Houssais, Morgane; Ortiz, Carlos P; Durian, Douglas J; Jerolmack, Douglas J

    2015-03-09

    Fluid-sheared granular transport sculpts landscapes and undermines infrastructure, yet predicting the onset of sediment transport remains notoriously unreliable. For almost a century, this onset has been treated as a discontinuous transition at which hydrodynamic forces overcome gravity-loaded grain-grain friction. Using a custom laminar-shear flume to image slow granular dynamics deep into the bed, here we find that the onset is instead a continuous transition from creeping to granular flow. This transition occurs inside the dense granular bed at a critical viscous number, similar to granular flows and colloidal suspensions and inconsistent with hydrodynamic frameworks. We propose a new phase diagram for sediment transport, where 'bed load' is a dense granular flow bounded by creep below and suspension above. Creep is characteristic of disordered solids and reminiscent of soil diffusion on hillslopes. Results provide new predictions for the onset and dynamics of sediment transport that challenge existing models.

  7. On Granular Knowledge Structures

    CERN Document Server

    Zeng, Yi

    2008-01-01

    Knowledge plays a central role in human and artificial intelligence. One of the key characteristics of knowledge is its structured organization. Knowledge can be and should be presented in multiple levels and multiple views to meet people's needs in different levels of granularities and from different perspectives. In this paper, we stand on the view point of granular computing and provide our understanding on multi-level and multi-view of knowledge through granular knowledge structures (GKS). Representation of granular knowledge structures, operations for building granular knowledge structures and how to use them are investigated. As an illustration, we provide some examples through results from an analysis of proceeding papers. Results show that granular knowledge structures could help users get better understanding of the knowledge source from set theoretical, logical and visual point of views. One may consider using them to meet specific needs or solve certain kinds of problems.

  8. Grain- and Pore-level Analysis of Drainage in Fractionally-wet Granular Media using Synchrotron X-ray Computed Microtomography

    Science.gov (United States)

    Willson, C. S.; Bradley, S.; Thompson, K. E.

    2011-12-01

    Numerous lab- and field-scale experimental studies have shown the strong impact of wettability on multiphase flow constitutive relations and how increased water repellency can lead to preferential flow paths and a heterogeneous water distribution. In conjunction, theoretical and pore-scale modeling work has been performed seeking to improve our understanding of the impact of grain-level wettability properties. Advances in high-resolution X-ray computed tomography (XCT) techniques now make it possible to nondestructively image opaque materials providing previously hard-to-observe qualitative and quantitative data and information. Furthermore, the characteristics of synchrotron X-rays make it possible to monochromatize the incident energy allowing for both k-edge absorption differencing and segmentation of fluids and materials that have even slightly different chemical composition. Concurrent with these advances has been the development of methods to extract granular packing and pore network structure data from XCT images. In this talk, we will present results from a series of experiments designed to obtain grain-, pore- and fluid-scale details during the drainage of water in fractionally-wet glass bead systems. Here, two sets of glass beads were used each having slightly different chemical compositions and thus, different X-ray absorption properties. One set was treated so that the bead surface was water neutral while the other set remained hydrophilic. Three sets of drainage experiments were conducted on three fractionally-wet systems: 100, 90, and 75% hydrophilic by weight. First, traditional lab-scale drainage experiments were performed to obtain a baseline set of characteristic drainage curves for the three systms. Next, a set of tomography-scale (i.e., 5.5 mm inner diameter column) drainage experiments were conducted in the lab to ensure that the drainage curves in the smaller columns were consistent with the lab-scale curves. Finally, tomography-scale drainage

  9. Granular Solid-liquid Transition: Experiment and Simulation

    Science.gov (United States)

    Fei, M.; Xu, X.; Sun, Q.

    2015-12-01

    Granular media are amorphous materials, which differs from traditional solid or liquid. In different circumstance, granular behavior varies from solid-like to liquid-like, and the transitions between these regimes are always related to many complex natural progresses such as the failure of soil foundation and the occurrence of landslide and debris flow. The mechanic of elastic instability during the transition from solid-like to liquid-like regime, and the quantitative description of irreversible deformation during flow are the key problems to interpret these transition phenomena. In this work, we developed a continuum model with elastic stable condition and irreversible flow rule of granular material based on a thermal dynamical model, the Two-Granular-Temperature model (TGT). Since infinitesimal elastic deformation in solid-like regime and significant plastic large deformation in liquid-like regime can coexist in the granular solid-liquid transition process, the material point method (MPM) was used to build an effective numerical model. Collapse of rectangular granular pile contains both the transition from granular solid to granular liquid and the inverse process, thus in this work we carried out collapse experiment with clay particles, and simulated the experiment with our continuum model and an open-source DEM model YADE to study the transition processes. Results between experiment and simulations were compared and good agreements on collapse shape and velocity profiles were achieved, and the new model proposed in this work seems to work well on the description of granular solid-liquid transition.

  10. Shock Waves in Dense Hard Disk Fluids

    OpenAIRE

    Sirmas, Nick; Tudorache, Marion; Barahona, Javier; Radulescu, Matei I.

    2011-01-01

    Media composed of colliding hard disks (2D) or hard spheres (3D) serve as good approximations for the collective hydrodynamic description of gases, liquids and granular media. In the present study, the compressible hydrodynamics and shock dynamics are studied for a two-dimensional hard-disk medium at both the continuum and discrete particle level descriptions. For the continuum description, closed form analytical expressions for the inviscid hydrodynamic description, shock Hugoniot, isentropi...

  11. Vibration-induced liquefaction of granular suspensions.

    Science.gov (United States)

    Hanotin, C; Kiesgen de Richter, S; Marchal, P; Michot, L J; Baravian, C

    2012-05-11

    We investigate the mechanical behavior of granular suspensions subjected to coupled vibrations and shear. At high shear stress, whatever the mechanical vibration energy and bead size, the system behaves like a homogeneous suspension of hard spheres. At low shear stress, in addition to a dependence on bead size, vibration energy drastically influences the viscosity of the material that can decrease by more than 2 orders of magnitude. All experiments can be rationalized by introducing a hydrodynamical Peclet number defined as the ratio between the lubrication stress induced by vibrations and granular pressure. The behavior of vibrated wet and dry granular materials can then be unified by assimilating the hookean stress in dry media to the lubrication stress in suspensions.

  12. Pore-scale Modelling of Capillarity in Swelling Granular Materials

    Science.gov (United States)

    Hassanizadeh, S. M.; Sweijen, T.; Nikooee, E.; Chareyre, B.

    2015-12-01

    Capillarity in granular porous media is a common and important phenomenon in earth materials and industrial products, and therefore has been studied extensively. To model capillarity in granular porous media, one needs to go beyond current models which simulate either two-phase flow in porous media or mechanical behaviour in granular media. Current pore-scale models for two-phase flow such as pore-network models are tailored for rigid pore-skeletons, even though in many applications, namely hydro-mechanical coupling in soils, printing, and hygienic products, the porous structure does change during two-phase flow. On the other hand, models such as Discrete Element Method (DEM), which simulate the deformable porous media, have mostly been employed for dry or saturated granular media. Here, the effects of porosity change and swelling on the retention properties was studied, for swelling granular materials. A pore-unit model that was capable to construct the capillary pressure - saturation curve was coupled to DEM. Such that the capillary pressure - saturation curve could be constructed for varying porosities and amounts of absorbed water. The study material was super absorbent polymer particles, which are capable to absorb water 10's to 200 times their initial weight. We have simulated quasi-static primary imbibition for different porosities and amounts of absorbed water. The results reveal a 3 dimensional surface between capillary pressure, saturation, and porosity, which can be normalized by means of the entry pressure and the effective water saturation to a unique curve.

  13. Cystic Granular Cell Ameloblastoma

    OpenAIRE

    Thillaikarasi, Rathnavel; Balaji, Jayaram; Gupta, Bhawna; Ilayarja, Vadivel; Vani, Nandimandalam Venkata; Vidula, Balachander; Saravanan, Balasubramaniam; Ponniah, Irulandy

    2010-01-01

    Ameloblastoma is a locally aggressive benign epithelial odontogenic tumor, while unicystic ameloblastoma is a relatively less aggressive variant. Although rare in unicystic or cystic ameloblastoma, granular cell change in ameloblastoma is a recognized phenomenon. The purpose of the present article is to report a case of cystic granular cell ameloblastoma in 34-year old female.

  14. Discrete Element Modeling of Complex Granular Flows

    Science.gov (United States)

    Movshovitz, N.; Asphaug, E. I.

    2010-12-01

    Granular materials occur almost everywhere in nature, and are actively studied in many fields of research, from food industry to planetary science. One approach to the study of granular media, the continuum approach, attempts to find a constitutive law that determines the material's flow, or strain, under applied stress. The main difficulty with this approach is that granular systems exhibit different behavior under different conditions, behaving at times as an elastic solid (e.g. pile of sand), at times as a viscous fluid (e.g. when poured), or even as a gas (e.g. when shaken). Even if all these physics are accounted for, numerical implementation is made difficult by the wide and often discontinuous ranges in continuum density and sound speed. A different approach is Discrete Element Modeling (DEM). Here the goal is to directly model every grain in the system as a rigid body subject to various body and surface forces. The advantage of this method is that it treats all of the above regimes in the same way, and can easily deal with a system moving back and forth between regimes. But as a granular system typically contains a multitude of individual grains, the direct integration of the system can be very computationally expensive. For this reason most DEM codes are limited to spherical grains of uniform size. However, spherical grains often cannot replicate the behavior of real world granular systems. A simple pile of spherical grains, for example, relies on static friction alone to keep its shape, while in reality a pile of irregular grains can maintain a much steeper angle by interlocking force chains. In the present study we employ a commercial DEM, nVidia's PhysX Engine, originally designed for the game and animation industry, to simulate complex granular flows with irregular, non-spherical grains. This engine runs as a multi threaded process and can be GPU accelerated. We demonstrate the code's ability to physically model granular materials in the three regimes

  15. Generation of homogeneous granular packings: Contact dynamics method with coupling to an external pressure bath

    CERN Document Server

    Shaebani, M Reza; Kertesz, Janos

    2008-01-01

    The contact dynamics method (CD) is an efficient simulation technique of dense granular media where unilateral and frictional contact problems for a large number of rigid bodies have to be solved. In this paper we present a modified version of the contact dynamics to generate homogeneous random packings of rigid grains. CD is coupled to an external pressure bath, which allows the variation of the size of a periodically repeated cell. We follow the concept of the Andersen dynamics and show how it can be applied within the framework of the contact dynamics method. The main challenge here is to handle the interparticle interactions properly, which are based on constraint forces in CD. We implement the proposed algorithm, perform test simulations and investigate the properties of the final packings.

  16. Bipotential continuum models for granular mechanics

    Science.gov (United States)

    Goddard, Joe

    2014-03-01

    Most currently popular continuum models for granular media are special cases of a generalized Maxwell fluid model, which describes the evolution of stress and internal variables such as granular particle fraction and fabric,in terms of imposed strain rate. It is shown how such models can be obtained from two scalar potentials, a standard elastic free energy and a ``dissipation potential'' given rigorously by the mathematical theory of Edelen. This allows for a relatively easy derivation of properly invariant continuum models for granular media and fluid-particle suspensions within a thermodynamically consistent framework. The resulting continuum models encompass all the prominent regimes of granular flow, ranging from the quasi-static to rapidly sheared, and are readily extended to include higher-gradient or Cosserat effects. Models involving stress diffusion, such as that proposed recently by Kamrin and Koval (PRL 108 178301), provide an alternative approach that is mentioned in passing. This paper provides a brief overview of a forthcoming review articles by the speaker (The Princeton Companion to Applied Mathematics, and Appl. Mech. Rev.,in the press, 2013).

  17. 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.

  18. 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.

  19. 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.

  20. Congenital granular cell epulis.

    Science.gov (United States)

    Conrad, Rachel; Perez, Mia C N

    2014-01-01

    Congenital granular cell epulis is a rarely reported lesion of unknown histogenesis with a strong predilection for the maxillary alveolar ridge of newborn girls. Microscopically, it demonstrates nests of polygonal cells with granular cytoplasm, a prominent capillary network, and attenuated overlying squamous epithelium. The lesion lacks immunoreactivity for S-100, laminin, chromogranin, and most other markers except neuron-specific enolase and vimentin. Through careful observation of its unique clinical, histopathologic, and immunohistochemical features, this lesion can be distinguished from the more common adult granular cell tumor as well as other differential diagnoses.

  1. Numerical modeling of geophysical granular flows: 1. A comprehensive approach to granular rheologies and geophysical multiphase flows

    Science.gov (United States)

    Dartevelle, SéBastien

    2004-08-01

    Geophysical granular materials display a wide variety of behaviors and features. Typically, granular flows (1) are multiphase flows, (2) are very dissipative over many different scales, (3) display a wide range of grain concentrations, and (4), as a final result of these previous features, display complex nonlinear, nonuniform, and unsteady rheologies. Therefore the objectives of this manuscript are twofold: (1) setting up a hydrodynamic model which acknowledges the multiphase nature of granular flows and (2) defining a comprehensive rheological model which accounts for all the different forms of viscous dissipations within granular flows at any concentration. Hence three important regimes within granular flows must be acknowledged: kinetic (pure free flights of grain), kinetic-collisional, and frictional. The momentum and energy transfer will be different according to the granular regimes, i.e., strain rate dependent in the kinetic and kinetic-collisional cases and strain rate independent in the frictional case. A "universal" granular rheological model requires a comprehensive unified stress tensor able to adequately describe viscous stress within the flow for any of these regimes, and without imposing a priori what regime will dominate over the others. The kinetic-collisional viscous regime is defined from a modified Boltzmann's kinetic theory of dense gas. The frictional viscous regime is defined from the plastic potential and the critical state theories which account for compressibility of granular matter (e.g., dilatancy, consolidation, and critical state). In the companion paper [, 2004] we will introduce a multiphase computer code, (G)MFIX, which accounts for all the granular regimes and rheology and present typical simulations of diluted (e.g., plinian clouds) and concentrated geophysical granular flows (i.e., pyroclastic flows and surges).

  2. 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.

  3. Partially saturated granular column collapse

    Science.gov (United States)

    Turnbull, Barbara; Johnson, Chris

    2017-04-01

    Debris flows are gravity-driven sub-aerial mass movements containing water, sediments, soil and rocks. These elements lead to characteristics common to dry granular media (e.g. levee formation) and viscous gravity currents (viscous fingering and surge instabilities). The importance of pore fluid in these flows is widely recognised, but there is significant debate over the mechanisms of build up and dissipation of pore fluid pressure within debris flows, and the resultant effect this has on dilation and mobility of the grains. Here we specifically consider the effects of the liquid surface in the flow. We start with a simple experiment constituting a classical axisymmetric granular column collapse, but with fluid filling the column up to a depth comparable to the depth of grains. Thus, as the column collapses, capillary forces may be generated between the grains that prevent dilation. We explore a parameter space to uncover the effects of fluid viscosity, particle size, column size, aspect ratio, grain shape, saturation level, initial packing fraction and significantly, the effects of fine sediments in suspension which can alter the capillary interaction between wetted macroscopic grains. This work presents an initial scaling analysis and attempts to relate the findings to current debris flow modelling approaches.

  4. 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.

  5. 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.

  6. Building designed granular towers one drop at a time.

    Science.gov (United States)

    Chopin, Julien; Kudrolli, Arshad

    2011-11-11

    A dense granular suspension dripping on an imbibing surface is observed to give rise to slender mechanically stable structures that we call granular towers. Successive drops of grain-liquid mixtures are shown to solidify rapidly upon contact with a liquid absorbing substrate. A balance of excess liquid flux and drainage rate is found to capture the typical growth and height of the towers. The tower width is captured by the Weber number, which gives the relative importance of inertia and capillary forces. Various symmetric, smooth, corrugated, zigzag, and chiral structures are observed by varying the impact velocity and the flux rate from droplet to jetting regime.

  7. Some New Lidar Equations for Laser Pulses Scattered Back from Optically Thick Media Such as Clouds, Dense Aerosol Plumes, Sea Ice, Snow, and Turbid Coastal Waters

    Science.gov (United States)

    Davis, Anthony B.

    2013-01-01

    I survey the theoretical foundations of the slowly-but-surely emerging field of multiple scattering lidar, which has already found applications in atmospheric and cryospheric optics that I also discuss. In multiple scattering lidar, returned pulses are stretched far beyond recognition, and there is no longer a one-to-one connection between range and return-trip timing. Moreover, one can exploit the radial profile of the diffuse radiance field excited by the laser source that, by its very nature, is highly concentrated in space and collimated in direction. One needs, however, a new class of lidar equations to explore this new phenomenology. A very useful set is derived from radiative diffusion theory, which is found at the opposite asymptotic limit of radiative transfer theory than the conventional (single-scattering) limit used to derive the standard lidar equation. In particular, one can use it to show that, even if the simple time-of-flight-to-range connection is irretrievably lost, multiply-scattered lidar light can be used to restore a unique profiling capability with coarser resolution but much deeper penetration into a wide variety of optical thick media in nature. Several new applications are proposed, including a laser bathymetry technique that should work for highly turbid coastal waters.

  8. Numerical simulations of granular dynamics II. Particle dynamics in a shaken granular material

    CERN Document Server

    Murdoch, Naomi; Richardson, Derek C; Nordstrom, Kerstin; Berardi, Christian R; Green, Simon F; Losert, Wolfgang

    2013-01-01

    Surfaces of planets and small bodies of our Solar System are often covered by a layer of granular material that can range from a fine regolith to a gravel-like structure of varying depths. Therefore, the dynamics of granular materials are involved in many events occurring during planetary and small-body evolution thus contributing to their geological properties. We demonstrate that the new adaptation of the parallel N-body hard-sphere code pkdgrav has the capability to model accurately the key features of the collective motion of bidisperse granular materials in a dense regime as a result of shaking. As a stringent test of the numerical code we investigate the complex collective ordering and motion of granular material by direct comparison with laboratory experiments. We demonstrate that, as experimentally observed, the scale of the collective motion increases with increasing small-particle additive concentration. We then extend our investigations to assess how self-gravity and external gravity affect collect...

  9. Shaken Granular Lasers

    CERN Document Server

    Folli, Viola; Leuzzi, Luca; Conti, Claudio

    2012-01-01

    Granular materials have been studied for decades, also driven by industrial and technological applications. These very simple systems, composed by agglomerations of mesoscopic particles, are characterized, in specific regimes, by a large number of metastable states and an extreme sensitivity (e.g., in sound transmission) on the arrangement of grains; they are not substantially affected by thermal phenomena, but can be controlled by mechanical solicitations. Laser emission from shaken granular matter is so far unexplored; here we provide experimental evidence that it can be affected and controlled by the status of motion of the granular, we also find that competitive random lasers can be observed. We hence demonstrate the potentialities of gravity affected moving disordered materials for optical applications, and open the road to a variety of novel interdisciplinary investigations, involving modern statistical mechanics and disordered photonics.

  10. Shaken granular lasers.

    Science.gov (United States)

    Folli, Viola; Puglisi, Andrea; Leuzzi, Luca; Conti, Claudio

    2012-06-15

    Granular materials have been studied for decades, driven by industrial and technological applications. These very simple systems, composed of agglomerations of mesoscopic particles, are characterized, in specific regimes, by a large number of metastable states and an extreme sensitivity (e.g., in sound transmission) to the arrangement of grains; they are not substantially affected by thermal phenomena, but can be controlled by mechanical solicitations. Laser emission from shaken granular matter is so far unexplored. Here we provide experimental evidence that laser emission can be affected and controlled by the status of the motion of the granular material; we also find that competitive random lasers can be observed. We hence demonstrate the potentialities of gravity-affected moving disordered materials for optical applications, and open the road to a variety of novel interdisciplinary investigations, involving modern statistical mechanics and disordered photonics.

  11. 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.

  12. Granular vortices: Identification, characterization and conditions for the localization of deformation

    Science.gov (United States)

    Tordesillas, Antoinette; Pucilowski, Sebastian; Lin, Qun; Peters, John F.; Behringer, Robert P.

    2016-05-01

    We relate the micromechanics of vortex evolution to that of force chain buckling and, on this basis, formulate the conditions for strain localization in a continuum model of dense granular media. Using the traditional bifurcation analysis of shear bands, we show that kinematic vortex fields are in fact solutions to the boundary value problem satisfying null boundary conditions. To establish an empirical basis for our study, we first develop a method to identify the location of the core and boundary of each vortex from a given displacement field in two dimensions. We then employ this method to characterize the residual deformation field (i.e., the deviation of particle motions from the continuum deformation) in a physical experiment and a discrete element simulation of dense granular samples submitted to biaxial compression. Vortices in the failure regime are essentially confined to the shear band. Primary vortices, the clear majority, rotate in the same direction as the shear band; secondary vortices, the so-called wakes, rotate in the opposite direction. Primary vortices align in spatial succession along the central axis of the band; wakes form next to the band boundaries, in between and beside two adjacent primary vortices. Force chain buckling, the governing mechanism for shear bands, is responsible for vortex formation in the failure regime. Vortex dynamics are consistent with stick-slip dynamics. From quiescent conditions of jamming or stick, vortical motions arise from force chain buckling and associated relative particle rotations and sliding; these in turn precipitate intermittent periods of unjamming or slip, evident in the attendant drops in stress ratio and bursts in both kinetic energy and local nonaffine deformation. A kinematic vortex field inside shear bands is proposed that is consistent with the equations of continuum mechanics and the underlying instability of force chain buckling: such a field is periodic with a repeating unit cell comprising a

  13. Failure of granular assemblies

    OpenAIRE

    Welker, Philipp

    2011-01-01

    This work investigates granular assemblies subjected to increasing external forces in the quasi-static limit. In this limit, the system’s evolution depends on static properties of the system, but is independent of the particles’ inertia. At the failure, which occurs at a certain value of the external forces, the particles’ motions increase quickly. In this thesis, the properties of granular systems during the weakening process and at the failure are investigated with the Discrete Element Meth...

  14. Rough-Granular Computing

    Institute of Scientific and Technical Information of China (English)

    Andrzej Skowron

    2006-01-01

    Solving complex problems by multi-agent systems in distributed environments requires new approximate reasoning methods based on new computing paradigms. One such recently emerging computing paradigm is Granular Computing(GC). We discuss the Rough-Granular Computing(RGC) approach to modeling of computations in complex adaptive systems and multiagent systems as well as for approximate reasoning about the behavior of such systems. The RGC methods have been successfully applied for solving complex problems in areas such as identification of objects or behavioral patterns by autonomous systems, web mining, and sensor fusion.

  15. 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.

  16. Mutiscale Modeling of Segregation in Granular Flows

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Jin [Iowa State Univ., Ames, IA (United States)

    2007-01-01

    Modeling and simulation of segregation phenomena in granular flows are investigated. Computational models at different scales ranging from particle level (microscale) to continuum level (macroscale) are employed in order to determine the important microscale physics relevant to macroscale modeling. The capability of a multi-fluid model to capture segregation caused by density difference is demonstrated by simulating grain-chaff biomass flows in a laboratory-scale air column and in a combine harvester. The multi-fluid model treats gas and solid phases as interpenetrating continua in an Eulerian frame. This model is further improved by incorporating particle rotation using kinetic theory for rapid granular flow of slightly frictional spheres. A simplified model is implemented without changing the current kinetic theory framework by introducing an effective coefficient of restitution to account for additional energy dissipation due to frictional collisions. The accuracy of predicting segregation rate in a gas-fluidized bed is improved by the implementation. This result indicates that particle rotation is important microscopic physics to be incorporated into the hydrodynamic model. Segregation of a large particle in a dense granular bed of small particles under vertical. vibration is studied using molecular dynamics simulations. Wall friction is identified as a necessary condition for the segregation. Large-scale force networks bearing larger-than-average forces are found with the presence of wall friction. The role of force networks in assisting rising of the large particle is analyzed. Single-point force distribution and two-point spatial force correlation are computed. The results show the heterogeneity of forces and a short-range correlation. The short correlation length implies that even dense granular flows may admit local constitutive relations. A modified minimum spanning tree (MST) algorithm is developed to asymptotically recover the force statistics in the

  17. Effect of sorption kinetics on nickel toxicity in methanogenic granular sludge

    NARCIS (Netherlands)

    Bartacek, J.; Fermoso, F.G.; Catena, A.B.; Lens, P.N.L.

    2010-01-01

    This study investigates the effect of nickel speciation and its equilibrium kinetics on the nickel toxicity to methylotrophic methanogenic activity. Toxicity tests were done with anaerobic granular sludge in three different media containing variable concentrations of complexing ligands. A correlatio

  18. Entropy Maximization in the Force Network Ensemble for Granular Solids

    NARCIS (Netherlands)

    Tighe, B.P.; Van Eerd, A.R.T.; Vlugt, T.J.H.

    2008-01-01

    A long-standing issue in the area of granular media is the tail of the force distribution, in particular, whether this is exponential, Gaussian, or even some other form. Here we resolve the issue for the case of the force network ensemble in two dimensions. We demonstrate that conservation of the to

  19. Local rheology of suspensions and dry granular materials

    NARCIS (Netherlands)

    de Cagny, H.; Fall, A.; Denn, M.M.; Bonn, D.

    2015-01-01

    The flow of dry and wet granular media is investigated in a Couette geometry using magnetic resonance imaging in order to test the applicability of the "fluidity model" for nonlocality in these materials. Local volume fraction measurements show that the systems become heterogeneous during flow. We f

  20. Numerical simulations of granular dynamics II: Particle dynamics in a shaken granular material

    Science.gov (United States)

    Murdoch, Naomi; Michel, Patrick; Richardson, Derek C.; Nordstrom, Kerstin; Berardi, Christian R.; Green, Simon F.; Losert, Wolfgang

    2012-05-01

    Surfaces of planets and small bodies of our Solar System are often covered by a layer of granular material that can range from a fine regolith to a gravel-like structure of varying depths. Therefore, the dynamics of granular materials are involved in many events occurring during planetary and small-body evolution thus contributing to their geological properties. We demonstrate that the new adaptation of the parallel N-body hard-sphere code pkdgrav has the capability to model accurately the key features of the collective motion of bidisperse granular materials in a dense regime as a result of shaking. As a stringent test of the numerical code we investigate the complex collective ordering and motion of granular material by direct comparison with laboratory experiments. We demonstrate that, as experimentally observed, the scale of the collective motion increases with increasing small-particle additive concentration. We then extend our investigations to assess how self-gravity and external gravity affect collective motion. In our reduced-gravity simulations both the gravitational conditions and the frequency of the vibrations roughly match the conditions on asteroids subjected to seismic shaking, though real regolith is likely to be much more heterogeneous and less ordered than in our idealised simulations. We also show that collective motion can occur in a granular material under a wide range of inter-particle gravity conditions and in the absence of an external gravitational field. These investigations demonstrate the great interest of being able to simulate conditions that are to relevant planetary science yet unreachable by Earth-based laboratory experiments.

  1. Dense topological spaces and dense continuity

    Science.gov (United States)

    Aldwoah, Khaled A.

    2013-09-01

    There are several attempts to generalize (or "widen") the concept of topological space. This paper uses equivalence relations to generalize the concept of topological space via the concept of equivalence relations. By the generalization, we can introduce from particular topology on a nonempty set X many new topologies, we call anyone of these new topologies a dense topology. In addition, we formulate some simple properties of dense topologies and study suitable generalizations of the concepts of limit points, closeness and continuity, as well as Jackson, Nörlund and Hahn dense topologies.

  2. Radiative properties of dense nanofluids.

    Science.gov (United States)

    Wei, Wei; Fedorov, Andrei G; Luo, Zhongyang; Ni, Mingjiang

    2012-09-01

    The radiative properties of dense nanofluids are investigated. For nanofluids, scattering and absorbing of electromagnetic waves by nanoparticles, as well as light absorption by the matrix/fluid in which the nanoparticles are suspended, should be considered. We compare five models for predicting apparent radiative properties of nanoparticulate media and evaluate their applicability. Using spectral absorption and scattering coefficients predicted by different models, we compute the apparent transmittance of a nanofluid layer, including multiple reflecting interfaces bounding the layer, and compare the model predictions with experimental results from the literature. Finally, we propose a new method to calculate the spectral radiative properties of dense nanofluids that shows quantitatively good agreement with the experimental results.

  3. Packing induced bistable phenomenon in granular flow:analysis from complex network perspective

    Institute of Scientific and Technical Information of China (English)

    胡茂彬; 刘启一; 孙王平; 姜锐; 吴清松

    2014-01-01

    The effects of packing configurations on the phase transition of straight granular chute flow with two bottlenecks are studied. The granular flow shows a dilute-to-dense flow transition when the channel width is varied, accompanied with a peculiar bistable phenomenon. The bistable phenomenon is induced by the initial packing config-uration of particles. When the packing is dense, the initial flux is small and will induce a dense flow. When the packing is loose, the initial flux is large and will induce a di-lute flow. The fabric network of granular packing is analyzed from a complex network perspective. The degree distribution shows quantitatively different characteristics for the configurations. A two-dimensional (2D) packing clustering coefficient is defined to better quantify the fabric network.

  4. Influence of stress-path on pore size distribution in granular materials

    Directory of Open Access Journals (Sweden)

    Das Arghya

    2017-01-01

    Full Text Available Pore size distribution is an important feature of granular materials in the context of filtration and erosion in soil hydraulic structures. Present study focuses on the evolution characteristics of pore size distribution for numerically simulated granular assemblies while subjected to various compression boundary constrain, namely, conventional drained triaxial compression, one-dimensional or oedometric compression and isotropic compression. We consider the effects initial packing of the granular assembly, loose or dense state. A simplified algorithm based on Delaunay tessellation is used for the estimation of pore size distribution for the deforming granular assemblies at various stress states. The analyses show that, the evolution of pore size is predominantly governed by the current porosity of the granular assembly while the stress path or loading process has minimal influence. Further it has also been observed that pore volume distribution reaches towards a critical distribution at the critical porosity during shear enhanced loading process irrespective of the deformation mechanism either compaction or dilation.

  5. Influence of stress-path on pore size distribution in granular materials

    Science.gov (United States)

    Das, Arghya; Kumar, Abhinav

    2017-06-01

    Pore size distribution is an important feature of granular materials in the context of filtration and erosion in soil hydraulic structures. Present study focuses on the evolution characteristics of pore size distribution for numerically simulated granular assemblies while subjected to various compression boundary constrain, namely, conventional drained triaxial compression, one-dimensional or oedometric compression and isotropic compression. We consider the effects initial packing of the granular assembly, loose or dense state. A simplified algorithm based on Delaunay tessellation is used for the estimation of pore size distribution for the deforming granular assemblies at various stress states. The analyses show that, the evolution of pore size is predominantly governed by the current porosity of the granular assembly while the stress path or loading process has minimal influence. Further it has also been observed that pore volume distribution reaches towards a critical distribution at the critical porosity during shear enhanced loading process irrespective of the deformation mechanism either compaction or dilation.

  6. 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.

  7. Geophysical granular and particle-laden flows: review of the field.

    Science.gov (United States)

    Hutter, Kolumban

    2005-07-15

    An introduction is given to the title theme, in general, and the specific topics treated in detail in the articles of this theme issue of the Philosophical Transactions. They fit into the following broader subjects: (i) dense, dry and wet granular flows as avalanche and debris flow events, (ii) air-borne particle-laden turbulent flows in air over a granular base as exemplified in gravity currents, aeolian transport of sand, dust and snow and (iii) transport of a granular mass on a two-dimensional surface in ripple formations of estuaries and rivers and the motion of sea ice.

  8. Constitutive model development for flows of granular materials

    Science.gov (United States)

    Chialvo, Sebastian

    Granular flows are ubiquitous in both natural and industrial processes. When com- posed of dry, noncohesive particles, they manifest three different flow regimes---commonly referred to as the quasistatic, inertial, and intermediate regimes---each of which exhibits its own dependences on solids volume fraction, shear rate, and particle-level properties. The differences in these regimes can be attributed to microscale phenomena, with quasistatic flows being dominated by enduring, frictional contacts between grains, inertial flows by grain collisions, and intermediate flows by a combination of the two. Existing constitutive models for the solids-phase stress tend to focus on one or two regimes at a time, with a limited degree of success; the same is true of models for wall-boundary conditions for granular flows. Moreover, these models tend not to be based on detailed particle-level flow data, either from experiment or simulation. Clearly, a comprehensive modeling framework is lacking. The work in this thesis aims to address these issues by proposing continuum models constructed on the basis of discrete element method (DEM) simulations of granular shear flows. Specifically, we propose (a) a constitutive stress model that bridges the three dense flow regimes, (b) an modified kinetic-theory model that covers both the dense and dilute ends of the inertial regime, and (c) a boundary-condition model for dense, wall-bounded flows. These models facilitate the modeling of a wide range of flow systems of practical interest and provide ideas for further model development and refinement.

  9. Building designed granular towers one drop at a time

    Science.gov (United States)

    Chopin, Julien; Kudrolli, Arshad

    2012-02-01

    The impact of a drop on a surface leads to beautiful dynamical shapes that result from a subtle interplay between inertial effects, fluid properties and substrate characteristics. In this talk, we will present an experiment where the successive impacts of drops lead to surprisingly slender mechanically stable structures that we called granular towers. They are created by dripping a dense granular suspension on a liquid absorbing surface such as a blotter paper or a dry granular bed. These towers formed by rapid solidification of the drop upon impact are analogous to many natural structures found in nature including frozen lava flows, icicles and stalagmites. We find that the height can be determined by balancing the excess liquid flux and the drainage through the granular tower. The velocity impact, the free fall time and the density of the suspension are found to control the tower width and its detailed morphology. We show that these facts can be manipulated to obtain various symmetric, smooth, corrugated, zigzag, and chiral structures. Further, the shape of the tower can be used as a quick diagnostic tool to characterize the rheology of a granular suspension. [J. Chopin and A. Kudrolli, Phys. Rev. Lett. 107, 208304 (2011)

  10. Going Public on Social Media

    Directory of Open Access Journals (Sweden)

    Greg Elmer

    2015-04-01

    Full Text Available This brief essay questions the disconnect between the financial goals of social media properties and the concerns of privacy advocates and other new media critics. It is argued that critics of social media often fail to recognize the financial imperative of social media companies, one that requires users to divulge and publicize ever more granular aspects of their daily lives, thoughts, and feelings.

  11. The rise of granular computing

    Institute of Scientific and Technical Information of China (English)

    YAO Yi-yu

    2008-01-01

    This paper has two purposes. One is to present a critical examination of the rise of granular computing and the other is to suggest a triarchic theory of granular computing. By examining the reasons, justifications, and motivations for the rise of granular computing, we may be able to fully appreciate its scope, goal and potential values. The results enable us to formulate a triarchic theory in the light of research results from many disciplines. The three components of the theory are labeled as the philosophy, the methodology, and the computation. The integration of the three offers a unified view of gran-ular computing as a way of structured thinking, a method of structured problem solving, and a paradigm of structured infor-mation processing, focusing on hierarchical granular structures. The triarchic theory is an important effort in synthesizing the various theories and models of granular computing.

  12. Three Perspectives of Granular Computing

    Institute of Scientific and Technical Information of China (English)

    Yiyu(Y.Y.) Yao

    2006-01-01

    As an emerging field of study, granular computing has received much attention. Many models, frameorks, methods and techniques have been proposed and studied. It is perhaps the time to seek for a general and unified view so that fundamental issues can be examined and clarified. This paper examines granular computing from three perspectives. By viewing granular computing as a way of structured thinking,we focus on its philosophical foundations in modeling human perception of the reality. By viewing granular computing as a method of structured problem solving, we examine its theoretical and methodological foundations in solving a wide range of real-world problems. By viewing granular computing as a paradigm of information processing,we turn our attention to its more concrete techniques. The three perspectives together offer a holistic view of granular computing.

  13. Nucleosynthesis in Hot and Dense Media

    CERN Document Server

    Masood, Samina S

    2013-01-01

    We study the finite temperature and density effects on beta decay rates to compute their contributions to nucleosynthesis. QED type corrections to beta decay from the background are studied in the standard model with massless neutrinos. So we re-examine the electron mass contributions and compute the beta decay rate, helium yield, energy density of the universe as well as the change in neutrino temperature, directly from the first order contribution to the selfmass of electrons during these processes. We express nucleosynthesis parameters as a function of temperature and density in different astronomical systems of interest. In this paper, we notice that the helium abundance at T=m of a cooling universe (0.045%) is higher than the helium abundance of a heating universe (0.031%) indicates that the universe started to produce helium at T>m and stopped after some point at T

  14. 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.

  15. 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.

  16. Dense with Sense

    Science.gov (United States)

    Aletras, Anthony H.; Ingkanisorn, W. Patricia; Mancini, Christine; Arai, Andrew E.

    2005-09-01

    Displacement encoding with stimulated echoes (DENSE) with a low encoding strength phase-cycled meta-DENSE readout and a two fold SENSE acceleration ( R = 2) is described. This combination reduces total breath-hold times for increased patient comfort during cardiac regional myocardial contractility studies. Images from phantoms, normal volunteers, and a patient are provided to demonstrate the SENSE-DENSE combination of methods. The overall breath-hold time is halved while preserving strain map quality.

  17. 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.

  18. 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.

  19. Sensitivity analysis of Immersed Boundary Method simulations of fluid flow in dense polydisperse random grain packings

    Directory of Open Access Journals (Sweden)

    Knight Chris

    2017-01-01

    Full Text Available Polydisperse granular materials are ubiquitous in nature and industry. Despite this, knowledge of the momentum coupling between the fluid and solid phases in dense saturated grain packings comes almost exclusively from empirical correlations [2–4, 8] with monosized media. The Immersed Boundary Method (IBM is a Computational Fluid Dynamics (CFD modelling technique capable of resolving pore scale fluid flow and fluid-particle interaction forces in polydisperse media at the grain scale. Validation of the IBM in the low Reynolds number, high concentration limit was performed by comparing simulations of flow through ordered arrays of spheres with the boundary integral results of Zick and Homsy [10]. Random grain packings were studied with linearly graded particle size distributions with a range of coefficient of uniformity values (Cu = 1.01, 1.50, and 2.00 at a range of concentrations (ϕ ∈ [0.396; 0.681] in order to investigate the influence of polydispersity on drag and permeability. The sensitivity of the IBM results to the choice of radius retraction parameter [1] was investigated and a comparison was made between the predicted forces and the widely used Ergun correlation [3].

  20. Drop floating on a granular raft

    Science.gov (United States)

    Jambon-Puillet, Etienne; Josserand, Christophe; Protiere, Suzie

    2015-11-01

    When a droplet comes in contact with a bath of the same liquid, it coalesces to minimize the surface energy. This phenomenon reduces emulsion stability and is usually fought with surfactant molecules. Another way to slow down coalescence is to use colloidal solid particles. In this case the particles spontaneously migrate to the interface to form ``Pickering'' emulsions and act as a barrier between droplets. Here we use dense, large particles (~ 500 μm) which form a monolayer at an oil/water interface that we call a granular raft. When a droplet is placed on top of such a raft, for a given set of particle properties (contact angle/size), the raft prevents coalescence indefinitely. However, in contrast to what happens when a droplet is placed on a hydrophobic surface and never wets the surface, here the droplet is strongly anchored to the raft and deforms it. We will use this specific configuration to probe the mechanical response of the granular raft: by controlling the droplet volume we can impose tensile or compressive stresses. Finally we will show that the drop, spherical at first, slowly takes a more complex shape as it's volume increases. This shape is not reversible as the drop volume is decreased. The drop can become oblate or prolate with wrinkling of the raft.

  1. Granular mechanics of normally consolidated fine soils

    Science.gov (United States)

    Yanqui, Calixtro

    2017-06-01

    In this paper, duality is demonstrated to be one of the inherent properties of granular packings, by mapping the stress-strain curve into the diagram that relates the pore ratio and the localization of the contact point. In this way, it is demonstrated that critical state is not related to the maximum void ratio, but to a unique value related to two different angles of packing, one limiting the domain of the dense state, and other limiting the domain of the loose state. As a consequence, packings can be dilative or contractive, as mutually exclusive states, except by the critical state point, where equations for both granular packings are equally valid. Further analysis shows that stresses, in a dilative packing, are transmitted by chains of contact forces, and, in a contractive packing, by shear forces. So that, stresses, for the first case, depend on the initial void ratio, and, for the second case, are independent. As it is known, normally consolidated and lightly overconsolidated fine soils are in loose state, and, hence, their strength is constant, because it does not depend on their initial void ratio; except at the critical state, for which, the consolidated-drained angle of friction is related to the plasticity index or the liquid limit. In this fashion, experimental results reported by several authors around the world are confronted with the theory, showing a good agreement.

  2. Granular flows : fluidization and anisotropy

    NARCIS (Netherlands)

    Wortel, Gerrit Herman

    2014-01-01

    This work discusses the flow of granular materials (e.g. sand). Even though a single particle is a simple object, the collective behavior of billions of particles can be very complex. In a surprisingly large amount of cases, it is not exactly known how a granular material behaves, and this while the

  3. Atoms in dense plasmas

    Energy Technology Data Exchange (ETDEWEB)

    More, R.M.

    1986-01-01

    Recent experiments with high-power pulsed lasers have strongly encouraged the development of improved theoretical understanding of highly charged ions in a dense plasma environment. This work examines the theory of dense plasmas with emphasis on general rules which govern matter at extreme high temperature and density. 106 refs., 23 figs.

  4. Quantum dense key distribution

    CERN Document Server

    Degiovanni, I P; Castelletto, S; Rastello, M L; Bovino, F A; Colla, A M; Castagnoli, G C

    2004-01-01

    This paper proposes a new protocol for quantum dense key distribution. This protocol embeds the benefits of a quantum dense coding and a quantum key distribution and is able to generate shared secret keys four times more efficiently than BB84 one. We hereinafter prove the security of this scheme against individual eavesdropping attacks, and we present preliminary experimental results, showing its feasibility.

  5. Bulldozing of granular material

    CERN Document Server

    Sauret, A; Caulfield, C P; McElwaine, J N

    2014-01-01

    We investigate the bulldozing motion of a granular sandpile driven forwards by a vertical plate. The problem is set up in the laboratory by emplacing the pile on a table rotating underneath a stationary plate; the continual circulation of the bulldozed material allows the dynamics to be explored over relatively long times, and the variation of the velocity with radius permits one to explore the dependence on bulldozing speed within a single experiment. We measure the time-dependent surface shape of the dune for a range of rotation rates, initial volumes and radial positions, for four granular materials, ranging from glass spheres to irregularly shaped sand. The evolution of the dune can be separated into two phases: a rapid initial adjustment to a state of quasi-steady avalanching perpendicular to the blade, followed by a much slower phase of lateral spreading and radial migration. The quasi-steady avalanching sets up a well-defined perpendicular profile with a nearly constant slope. This profile can be scale...

  6. Jamming in granular materials

    Science.gov (United States)

    Behringer, Robert P.

    2015-01-01

    Granular materials are one of a class of materials which undergo a transition from mechanically unstable to mechanically stable states as key system parameters change. Pioneering work by Liu and Nagel and O'Hern et al. focused on models consisting of frictionless grains. In this case, density, commonly expressed in terms of the packing fraction, ϕ, is of particular importance. For instance, O'Hern et al. found that there is a minimum ϕ =ϕJ, such that below this value there are no jammed states, and that above this value, all stress-isotropic states are jammed. Recently, simulations and experiments have explored the case of grains with friction. This case is more subtle, and ϕ does not play such a simple role. Recently, several experiments have shown that there exists a range of relatively low ϕ's such that at the same ϕ it is possible to have jammed, unjammed, and fragile states in the sense of Cates et al. This review discusses some of this recent work, and contrasts the cases of jamming for frictionless and frictional granular systems.

  7. Acoustic emissions in granular structures under gravitational destabilization

    Science.gov (United States)

    Thirot, J.-L.; Le Gonidec, Y.; Kergosien, B.

    2012-05-01

    In this work, we perform experiments in an acoustic tank to record acoustic emissions (AEs) occurring when a granular medium is submitted to a gravitational destabilization. The granular medium is composed of monodisperse glass beads filling a box which can be inclined from α=0° up to the avalanche threshold angle α0=28°. To respect quasi-static conditions, the angle increases by steps less than 3°/mn. An omnidirectional hydrophone records the continuous acoustic field in the bead structure until the avalanche occurs. We compare the results for different experimental configurations, in particular for dry and water saturated granular media, but also for different bead diameters (d=8, 3 and 0.3 mm) in order to span the viscosity range of the granular structure. We show that the AE signatures strongly depend on the viscosity parameter, which can be related to the Stokes number and the fluid/solid density ratio. The transition from a viscous to an inertial dynamic of the granular structure is discussed, based on these experimental results.

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

    DEFF Research Database (Denmark)

    Iftikhar, Nadeem; Pedersen, Torben Bach

    2010-01-01

    The majority of today’s systems increasingly require sophisticated data management as they need to store and to query large amounts of data for analysis and reporting purposes. In order to keep more “detailed” data available for longer periods, “old” data has to be reduced gradually to save space...... 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...

  9. 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.

  10. Liquefaction of a Horizontally Vibrated Granular Bed Friction, Dilation and Segregation

    CERN Document Server

    Tennakoon, S G K; Tennakoon, Sarath G.

    1997-01-01

    We present experimental observations of the onset of flow (liquefaction) for horizontally vibrated granular materials. As the acceleration increases above certain value, the top layer of granular material liquefies, while the remainder of the layer moves with the shaker in solid body motion. With increasing acceleration, more of the layer becomes fluidized. The initial bifurcation is backward, and the amount of hysteresis depends mainly on frictional properties of the granular media. A small amount of fluidization by gas flow lifts the hysteresis. Modest differences in the frictional properties of otherwise identical particles leads to rapid segregation.

  11. Granular impact cratering by liquid drops: Understanding raindrop imprints through an analogy to asteroid strikes.

    Science.gov (United States)

    Zhao, Runchen; Zhang, Qianyun; Tjugito, Hendro; Cheng, Xiang

    2015-01-13

    When a granular material is impacted by a sphere, its surface deforms like a liquid yet it preserves a circular crater like a solid. Although the mechanism of granular impact cratering by solid spheres is well explored, our knowledge on granular impact cratering by liquid drops is still very limited. Here, by combining high-speed photography with high-precision laser profilometry, we investigate liquid-drop impact dynamics on granular surface and monitor the morphology of resulting impact craters. Surprisingly, we find that despite the enormous energy and length difference, granular impact cratering by liquid drops follows the same energy scaling and reproduces the same crater morphology as that of asteroid impact craters. Inspired by this similarity, we integrate the physical insight from planetary sciences, the liquid marble model from fluid mechanics, and the concept of jamming transition from granular physics into a simple theoretical framework that quantitatively describes all of the main features of liquid-drop imprints in granular media. Our study sheds light on the mechanisms governing raindrop impacts on granular surfaces and reveals a remarkable analogy between familiar phenomena of raining and catastrophic asteroid strikes.

  12. Shock Waves in Dense Hard Disk Fluids

    CERN Document Server

    Sirmas, Nick; Barahona, Javier; Radulescu, Matei I

    2011-01-01

    Media composed of colliding hard disks (2D) or hard spheres (3D) serve as good approximations for the collective hydrodynamic description of gases, liquids and granular media. In the present study, the compressible hydrodynamics and shock dynamics are studied for a two-dimensional hard-disk medium at both the continuum and discrete particle level descriptions. For the continuum description, closed form analytical expressions for the inviscid hydrodynamic description, shock Hugoniot, isentropic exponent and shock jump conditions were obtained using the Helfand equation of state. The closed-form analytical solutions permitted us to gain physical insight on the role of the material's density on its compressibility, i.e. how the medium compresses under mechanical loadings and sustains wave motion. Furthermore, the predictions were found in excellent agreement with calculations using the Event Driven Molecular Dynamic method involving 30,000 particles over the entire range of compressibility spanning the dilute id...

  13. Advanced Granular System Modeling Project

    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...

  14. Localizing energy in granular materials

    CERN Document Server

    Przedborski, Michelle A; Sen, Surajit

    2016-01-01

    A device for absorbing and storing short duration impulses in an initially uncompressed one-dimensional granular chain is presented. Simply stated, short regions of sufficiently soft grains are embedded in a hard granular chain. These grains exhibit long-lived standing waves of predictable frequencies regardless of the timing of the arrival of solitary waves from the larger matrix. We explore the origins, symmetry, and energy content of the soft region and its intrinsic modes.

  15. The dynamics of thin vibrated granular layers

    Energy Technology Data Exchange (ETDEWEB)

    Melby, P [Department of Physics, Georgetown University, Washington, DC 20057 (United States); Vega Reyes, F [Department of Physics, Georgetown University, Washington, DC 20057 (United States); Prevost, A [Laboratoire de Physique Statistique de l' Ecole Normale Superieure, CNRS-UMR 8550, 24 rue Lhomond, 75231 Paris cedex 05 (France); Robertson, R [Department of Physics, Georgetown University, Washington, DC 20057 (United States); Kumar, P [Department of Physics, Georgetown University, Washington, DC 20057 (United States); Egolf, D A [Department of Physics, Georgetown University, Washington, DC 20057 (United States); Urbach, J S [Department of Physics, Georgetown University, Washington, DC 20057 (United States)

    2005-06-22

    We describe a series of experiments and computer simulations on vibrated granular media in a geometry chosen to eliminate gravitationally induced settling. The system consists of a collection of identical spherical particles on a horizontal plate vibrating vertically, with or without a confining lid. Previously reported results are reviewed, including the observation of homogeneous, disordered liquid-like states, an instability to a 'collapse' of motionless spheres on a perfect hexagonal lattice, and a fluctuating, hexagonally ordered state. In the presence of a confining lid we see a variety of solid phases at high densities and relatively high vibration amplitudes, several of which are reported for the first time in this article. The phase behaviour of the system is closely related to that observed in confined hard-sphere colloidal suspensions in equilibrium, but with modifications due to the effects of the forcing and dissipation. We also review measurements of velocity distributions, which range from Maxwellian to strongly non-Maxwellian depending on the experimental parameter values. We describe measurements of spatial velocity correlations that show a clear dependence on the mechanism of energy injection. We also report new measurements of the velocity autocorrelation function in the granular layer and show that increased inelasticity leads to enhanced particle self-diffusion.

  16. Nonlocal modeling of granular flows down inclines.

    Science.gov (United States)

    Kamrin, Ken; Henann, David L

    2015-01-07

    Flows of granular media down a rough inclined plane demonstrate a number of nonlocal phenomena. We apply the recently proposed nonlocal granular fluidity model to this geometry and find that the model captures many of these effects. Utilizing the model's dynamical form, we obtain a formula for the critical stopping height of a layer of grains on an inclined surface. Using an existing parameter calibration for glass beads, the theoretical result compares quantitatively to existing experimental data for glass beads. This provides a stringent test of the model, whose previous validations focused on driven steady-flow problems. For layers thicker than the stopping height, the theoretical flow profiles display a thickness-dependent shape whose features are in agreement with previous discrete particle simulations. We also address the issue of the Froude number of the flows, which has been shown experimentally to collapse as a function of the ratio of layer thickness to stopping height. While the collapse is not obvious, two explanations emerge leading to a revisiting of the history of inertial rheology, which the nonlocal model references for its homogeneous flow response.

  17. Validation of a two-fluid model used for the simulation of dense fluidized beds; Validation d`un modele a deux fluides applique a la simulation des lits fluidises denses

    Energy Technology Data Exchange (ETDEWEB)

    Boelle, A.

    1997-02-17

    A two-fluid model applied to the simulation of gas-solid dense fluidized beds is validated on micro scale and on macro scale. Phase coupling is carried out in the momentum and energy transport equation of both phases. The modeling is built on the kinetic theory of granular media in which the gas action has been taken into account in order to get correct expressions of transport coefficients. A description of hydrodynamic interactions between particles in high Stokes number flow is also incorporated in the model. The micro scale validation uses Lagrangian numerical simulations viewed as numerical experiments. The first validation case refers to a gas particle simple shear flow. It allows to validate the competition between two dissipation mechanisms: drag and particle collisions. The second validation case is concerted with sedimenting particles in high Stokes number flow. It allows to validate our approach of hydrodynamic interactions. This last case had led us to develop an original Lagrangian simulation with a two-way coupling between the fluid and the particles. The macro scale validation uses the results of Eulerian simulations of dense fluidized bed. Bed height, particles circulation and spontaneous created bubbles characteristics are studied and compared to experimental measurement, both looking at physical and numerical parameters. (author) 159 refs.

  18. Axisymmetric Granular Collapse: A Transient 3D Flow Test of Viscoplasticity

    Science.gov (United States)

    Lacaze, Laurent; Kerswell, Rich R.

    2009-03-01

    A viscoplastic continuum theory has recently been proposed to model dense, cohesionless granular flows [P. Jop , Nature (London)NATUAS0028-0836 441, 727 (2006)10.1038/nature04801]. We confront this theory for the first time with a transient, three-dimensional flow situation—the simple collapse of a cylinder of granular matter onto a horizontal plane—by extracting stress and strain rate tensors directly from soft particle simulations. These simulations faithfully reproduce the different flow regimes and capture the observed scaling laws for the final deposit. Remarkably, the theoretical hypothesis that there is a simple stress-strain rate tensorial relationship does seem to hold across the whole flow even close to the rough boundary provided the flow is dense enough. These encouraging results suggest viscoplastic theory is more generally applicable to transient, multidirectional, dense flows and open the way for quantitative predictions in real applications.

  19. Granular Superconductors and Gravity

    Science.gov (United States)

    Noever, David; Koczor, Ron

    1999-01-01

    As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (approx. 10(exp -6) g cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with a relatively high percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 104 was reported above a stationary (non-rotating) superconductor. In experiments using a sensitive gravimeter, bulk YBCO superconductors were stably levitated in a DC magnetic field and exposed without levitation to low-field strength AC magnetic fields. Changes in observed gravity signals were measured to be less than 2 parts in 108 of the normal gravitational acceleration. Given the high sensitivity of the test, future work will examine variants on the basic magnetic behavior of granular superconductors, with particular focus on quantifying their proposed importance to gravity.

  20. Modelling dense relational data

    DEFF Research Database (Denmark)

    Herlau, Tue; Mørup, Morten; Schmidt, Mikkel Nørgaard;

    2012-01-01

    Relational modelling classically consider sparse and discrete data. Measures of influence computed pairwise between temporal sources naturally give rise to dense continuous-valued matrices, for instance p-values from Granger causality. Due to asymmetry or lack of positive definiteness they are no......Relational modelling classically consider sparse and discrete data. Measures of influence computed pairwise between temporal sources naturally give rise to dense continuous-valued matrices, for instance p-values from Granger causality. Due to asymmetry or lack of positive definiteness...... they are not naturally suited for kernel K-means. We propose a generative Bayesian model for dense matrices which generalize kernel K-means to consider off-diagonal interactions in matrices of interactions, and demonstrate its ability to detect structure on both artificial data and two real data sets....

  1. Effects of cohesion on the flow patterns of granular materials in spouted beds

    Science.gov (United States)

    Zhu, Runru; Li, Shuiqing; Yao, Qiang

    2013-02-01

    Two-dimensional spouted bed, capable to provide both dilute granular gas and dense granular solid flow patterns in one system, was selected as a prototypical system for studying granular materials. Effects of liquid cohesion on such kind of complex granular patterns were studied using particle image velocimetry. It is seen that the addition of liquid oils by a small fraction of 10-3-10-2 causes a remarkable narrowing (about 15%) of the spout area. In the dense annulus, as the liquid fraction increases, the downward particle velocity gradually decreases and approaches a minimum where, at a microscopic grain scale, the liquid bridge reaches spherical regimes with a maximum capillarity. Viscous lubrication effect is observed at a much higher fraction but is really weak with respect to the capillary effect. In the dilute spout, in contrast to the dry grains, the wet grains have a lightly smaller acceleration in the initial 1/3 of the spout, but have a dramatically higher acceleration in the rest of the spout. We attribute the former to the additional work needed to overcome interparticle cohesion during particle entrainment at the spout-annulus interface. Then, using mass and momentum balances, the latter is explained by the relative higher drag force resulting from both higher gas velocities and higher voidages due to spout narrowing in the wet system. The experimental findings will provide useful data for the validation of discrete element simulation of cohesive granular-fluid flows.

  2. Wave propagation of spectral energy content in a granular chain

    Science.gov (United States)

    Shrivastava, Rohit Kumar; Luding, Stefan

    2017-06-01

    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. 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.

  4. Silo Collapse under Granular Discharge

    Science.gov (United States)

    Gutiérrez, G.; Colonnello, C.; Boltenhagen, P.; Darias, J. R.; Peralta-Fabi, R.; Brau, F.; Clément, E.

    2015-01-01

    We investigate, at a laboratory scale, the collapse of cylindrical shells of radius R and thickness t induced by a granular discharge. We measure the critical filling height for which the structure fails upon discharge. We observe that the silos sustain filling heights significantly above an estimation obtained by coupling standard shell-buckling and granular stress distribution theories. Two effects contribute to stabilize the structure: (i) below the critical filling height, a dynamical stabilization due to granular wall friction prevents the localized shell-buckling modes to grow irreversibly; (ii) above the critical filling height, collapse occurs before the downward sliding motion of the whole granular column sets in, such that only a partial friction mobilization is at play. However, we notice also that the critical filling height is reduced as the grain size d increases. The importance of grain size contribution is controlled by the ratio d /√{R t }. We rationalize these antagonist effects with a novel fluid-structure theory both accounting for the actual status of granular friction at the wall and the inherent shell imperfections mediated by the grains. This theory yields new scaling predictions which are compared with the experimental results.

  5. Continuum modelling of the collapse of a granular mass and its subsequent flow

    Science.gov (United States)

    Lagrée, P.; Staron, L.; Popinet, S.

    2011-12-01

    The continuum modelling of transient granular flows is of primary importance in the context of prediction and risk mitigation in relation with rock avalanches and dry debris flows. In this perspective, the granular column collapse experiment provides an interesting benchmark, due to both its relevance to natural granular flows and its challenging complexity (Lube 2004 et al, Lajeunesse et al 2006). In this contribution, we present 2D continuum simulations of granular column collapse using the Navier-Stokes solver Gerris (Popinet 2003), solving the full Navier-Stokes equations. The rheology implemented to model the granular media is the so-called μ (I) rheology, relating the frictional properties and the viscosity of the material to the pressure and shear rate (Jop et al 2006). In addition, discrete simulations using the Contact Dynamics method are performed for systematic comparison between the granular flow dynamics and its continuum counterpart (Staron & Hinch 2005). We find a good agreement, recovering the shape of the flow in the course of time, the internal flow structure, as well as experimental scaling laws for the run-out. A systematic underestimation of the latter is nevertheless observed, and discussed in terms of physical and numerical modeling. This work opens important new prospect for the simulation of more complex situations relevant to geophysical granular flows.

  6. Granular cell ameloblastoma of mandible.

    Science.gov (United States)

    Jansari, Trupti R; Samanta, Satarupa T; Trivedi, Priti P; Shah, Manoj J

    2014-01-01

    Ameloblastoma is a neoplasm of odontogenic epithelium, especially of enamel organ-type tissue that has not undergone differentiation to the point of hard tissue formation. Granular cell ameloblastoma is a rare condition, accounting for 3-5% of all ameloblastoma cases. A 30-year-old female patient presented with the chief complaint of swelling at the right lower jaw region since 1 year. Orthopantomogram and computed tomography scan was suggestive of primary bone tumor. Histopathologically, diagnosis of granular cell ameloblastoma of right mandible was made.

  7. 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.

  8. River-bed armoring as a granular segregation phenomenon

    CERN Document Server

    Ferdowsi, Behrooz; Houssais, Morgane; Jerolmack, Douglas J

    2016-01-01

    Gravel-river beds typically have an "armored" layer of coarse grains on the surface, which acts to protect finer particles underneath from erosion. River bed-load transport is a kind of dense granular flow, and such flows are known to vertically segregate grains. The contribution of granular physics to river-bed armoring, however, has not been investigated. Here we examine these connections in a laboratory river with bimodal sediment size, by tracking the motion of particles from the surface to deep inside the bed, and find that armor develops by two distinct mechanisms. Bed-load transport in the near-surface layer drives rapid segregation, with a vertical advection rate proportional to the granular shear rate. Creeping grains beneath the bed-load layer give rise to slow but persistent segregation, which is diffusion dominated and insensitive to shear rate. We verify these findings with a continuum phenomenological model and discrete element method simulations. Our results suggest that river beds armor by gra...

  9. Rheological behavior of partially-wet granular matter

    Science.gov (United States)

    Ghelichi, Ramin; Kamrin, Ken; Kamrin Group Team

    The topic of wet granular material modeling is an open area of study. In this talk we present a comprehensive continuum model for wet granular matter, which is informed by a novel Discrete Element Method (DEM), which tracks the fluid content coating each grain as well as a variable fluid-bridge volume. We have devloped a DEM simulation method with a history-dependent potential based on the Hertz-Mindlin contact in compression and evolving capillary forces in tension. The capillary bridge in the simulations forms based on the volume of the fluid on each particle. First, we determine the cohesive force between grains, which is a function of grain separation, bridge volume, grain geometry, and fluid properties. The volume of the bridges also evolves in time, which affects the cut-off distance in bridges and the force-separation function. The other important factor which has been considered in the model is the particle roughness, which has a significant effect on the capillary force function. The effect of fluid viscosity is also considered. The second step in this work is to utilize the DEM results to identify a constitutive model that can explain the plastic behavior (flow rule) of a dense granular assembly under varying degrees of wetness.

  10. Phase Diagram of Vertically Shaken Granular Matter

    CERN Document Server

    Eshuis, P; Lohse, D; Van der Meer, D; Van der Weele, K; Bos, Robert; Eshuis, Peter; Lohse, Detlef; Meer, Devaraj van der; Weele, Ko van der

    2006-01-01

    A shallow, vertically shaken granular bed in a quasi 2-D container is studied experimentally yielding a wider variety of phenomena than in any previous study: (1) bouncing bed, (2) undulations, (3) granular Leidenfrost effect, (4) convection rolls, and (5) granular gas. These phenomena and the transitions between them are characterized by dimensionless control parameters and combined in a full experimental phase diagram.

  11. Penetration in bimodal, polydisperse granular material

    Science.gov (United States)

    Kouraytem, N.; Thoroddsen, S. T.; Marston, J. O.

    2016-11-01

    We investigate the impact penetration of spheres into granular media which are compositions of two discrete size ranges, thus creating a polydisperse bimodal material. We examine the penetration depth as a function of the composition (volume fractions of the respective sizes) and impact speed. Penetration depths were found to vary between δ =0.5 D0 and δ =7 D0 , which, for mono-modal media only, could be correlated in terms of the total drop height, H =h +δ , as in previous studies, by incorporating correction factors for the packing fraction. Bimodal data can only be collapsed by deriving a critical packing fraction for each mass fraction. The data for the mixed grains exhibit a surprising lubricating effect, which was most significant when the finest grains [ds˜O (30 ) μ m ] were added to the larger particles [dl˜O (200 -500 ) μ m ] , with a size ratio, ɛ =dl/ds , larger than 3 and mass fractions over 25%, despite the increased packing fraction. We postulate that the small grains get between the large grains and reduce their intergrain friction, only when their mass fraction is sufficiently large to prevent them from simply rattling in the voids between the large particles. This is supported by our experimental observations of the largest lubrication effect produced by adding small glass beads to a bed of large sand particles with rough surfaces.

  12. Penetration in bimodal, polydisperse granular material

    KAUST Repository

    Kouraytem, N.

    2016-11-07

    We investigate the impact penetration of spheres into granular media which are compositions of two discrete size ranges, thus creating a polydisperse bimodal material. We examine the penetration depth as a function of the composition (volume fractions of the respective sizes) and impact speed. Penetration depths were found to vary between delta = 0.5D(0) and delta = 7D(0), which, for mono-modal media only, could be correlated in terms of the total drop height, H = h + delta, as in previous studies, by incorporating correction factors for the packing fraction. Bimodal data can only be collapsed by deriving a critical packing fraction for each mass fraction. The data for the mixed grains exhibit a surprising lubricating effect, which was most significant when the finest grains [d(s) similar to O(30) mu m] were added to the larger particles [d(l) similar to O(200 - 500) mu m], with a size ratio, epsilon = d(l)/d(s), larger than 3 and mass fractions over 25%, despite the increased packing fraction. We postulate that the small grains get between the large grains and reduce their intergrain friction, only when their mass fraction is sufficiently large to prevent them from simply rattling in the voids between the large particles. This is supported by our experimental observations of the largest lubrication effect produced by adding small glass beads to a bed of large sand particles with rough surfaces.

  13. Gas flow within Martian soil: experiments on granular Knudsen compressors

    Science.gov (United States)

    Koester, Marc; Kelling, Thorben; Teiser, Jens; Wurm, Gerhard

    2017-09-01

    Thermal creep efficiently transports gas through Martian soil. To quantify the Martian soil pump we carried out laboratory analog experiments with illuminated granular media at low ambient pressure. We used samples of 1 μm to 5 μm SiO2 (quartz), basalt with a broad size distribution between 63 μm and 125 μm, and JSC-Mars 1A with a size fraction from 125 μm to 250 μm. The mean ambient pressure was varied between 50 Pa and 9000 Pa. Illumination was varied between 100 W/m2 and 6700 W/m2. The experiments confirm strong directed gas flows within granular and dusty soil and local sub-soil pressure variations. We find that Martian soil pumps can be described with existing models of thermal creep for capillaries, using the average grain size and light flux related temperatures.

  14. Quantifying Interparticle Forces and Heterogeneity in 3D Granular Materials.

    Science.gov (United States)

    Hurley, R C; Hall, S A; Andrade, J E; Wright, J

    2016-08-26

    Interparticle forces in granular materials are intimately linked to mechanical properties and are known to self-organize into heterogeneous structures, or force chains, under external load. Despite progress in understanding the statistics and spatial distribution of interparticle forces in recent decades, a systematic method for measuring forces in opaque, three-dimensional (3D), frictional, stiff granular media has yet to emerge. In this Letter, we present results from an experiment that combines 3D x-ray diffraction, x-ray tomography, and a numerical force inference technique to quantify interparticle forces and their heterogeneity in an assembly of quartz grains undergoing a one-dimensional compression cycle. Forces exhibit an exponential decay above the mean and partition into strong and weak networks. We find a surprising inverse relationship between macroscopic load and the heterogeneity of interparticle forces, despite the clear emergence of two force chains that span the system.

  15. Dense Plasma Focus Modeling

    Energy Technology Data Exchange (ETDEWEB)

    Li, Hui [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Li, Shengtai [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Jungman, Gerard [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Hayes-Sterbenz, Anna Catherine [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-08-31

    The mechanisms for pinch formation in Dense Plasma Focus (DPF) devices, with the generation of high-energy ions beams and subsequent neutron production over a relatively short distance, are not fully understood. Here we report on high-fidelity 2D and 3D numerical magnetohydrodynamic (MHD) simulations using the LA-COMPASS code to study the pinch formation dynamics and its associated instabilities and neutron production.

  16. Erosion and basal forces in granular flow experiments

    Science.gov (United States)

    Sanvitale, Nicoletta; Bowman, Elisabeth

    2016-04-01

    Extreme mass wasting avalanche events such as rock, snow and ice avalanches, debris flows, and pyroclastic flows are among the most hazardous geological phenomena. These events driven by gravity, can travel for long distance and high speed, increasing their volumes as they can entertain material along their path. The erosion of material and its entrainment can greatly affect the overall dynamics of transportation, either enhancing or impeding the avalanche mobility depending on flow dynamics and characteristics of the substrate. However, the mechanisms and processes acting at the base as they travel over deformable or erodible substrates are still poor understood. Experiments, simulations and field measurements indicate that large fluctuations can occur in basal forces and stresses, which may be the result of non-uniform load transfer within the mass, and rolling, bouncing and sliding of the particles along the bed. In dense granular materials, force distributions can propagate through filamentary chain structures that carry a large fraction of the forces within the system. Photoelastic experiments on two-dimensional, monodisperse, gravity-driven flows have shown that force chains can transmit high localized forces to the boundary of dense granular flows. Here we describe the preliminary setup and results of 2D experiments on polydisperse granular flows of photoelastic disks down a small flume designed to acquire the forces exerted at the boundaries of the flow and to analyze their effects on an erodible bed. The intended outcome of this research is to provide better information on the complex mechanism of erosion and its effects on avalanche behaviour.

  17. Multiple shear band development and related instabilities in granular materials

    Science.gov (United States)

    Gajo, A.; Bigoni, D.; Wood, D. Muir

    2004-12-01

    A new, small-strain constitutive model, incorporating elastoplastic coupling to describe developing elastic anisotropy, and density as a state variable to capture compaction and dilation, is proposed to simulate the behaviour of granular materials, in particular sand. This developing elastic anisotropy is related to grain reorientation and is shown to be crucial to obtain localisation during strain hardening, as experiments exhibit. Post-localisation analysis is also performed under simplificative assumptions, which evinces a number of features, including softening induced by localisation, size effects and snap-back, all phenomena found in qualitative and quantitative agreement with experiments. No prior model of granular material deformation correctly captures all these behaviours. The post-localisation analysis has revealed a new form of material instability in granular materials, consisting of a saturation mechanism, in which shear bands just formed unload, permitting new bands to form. This phenomenon shares similarities with the mechanics of phase transformation in metal strips and results in a stress oscillation during increasing deformation. The investigation of this mechanism of localised deformation reveals that loose and dense sands behave in qualitatively different ways. In particular, saturation is not persistent in dense sand; rather, after several shear bands form and saturate, this process is terminated by the formation of a differently inclined shear band occurring in the material transformed by previous strain localisation. In this case, the resulting 'global' stress-strain curve exhibits a few stress oscillations followed by a strong softening. On the other hand, band saturation is found to be a persistent phenomenon in loose sand, yielding a continuing stress oscillation. This provides a consistent description of specific experimental results.

  18. From Numeric Models to Granular System Modeling

    Directory of Open Access Journals (Sweden)

    Witold Pedrycz

    2015-03-01

    To make this study self-contained, we briefly recall the key concepts of granular computing and demonstrate how this conceptual framework and its algorithmic fundamentals give rise to granular models. We discuss several representative formal setups used in describing and processing information granules including fuzzy sets, rough sets, and interval calculus. Key architectures of models dwell upon relationships among information granules. We demonstrate how information granularity and its optimization can be regarded as an important design asset to be exploited in system modeling and giving rise to granular models. With this regard, an important category of rule-based models along with their granular enrichments is studied in detail.

  19. A depth integrated model for dry geophysical granular flows

    Science.gov (United States)

    Rossi, Giulia; Armanini, Aronne

    2017-04-01

    Granular flows are rapid to very rapid flows, made up of dry sediment (rock and snow avalanches) or mixture of water and sediment (debris flows). They are among the most dangerous and destructive natural phenomena and the definition of run-out scenarios for risk assessment has received wide interest in the last decades. Nowadays there are many urbanized mountain areas affected by these phenomena, which cause several properties damages and loss of lives. The numerical simulation is a fundamental step to analyze these phenomena and define the runout scenarios. For this reason, a depth-integrated model is developed to analyze the case of dry granular flows, representative of snow avalanches or rock avalanches. The model consists of a two-phase mathematical description of the flow motion: it is similar to the solid transport equations but substantially different since there is no water in this case. A set of partial differential equations is obtained and written in the form of a hyperbolic system. The numerical solution is computed through a path-conservative SPH (Smoothed Particles Hydrodynamics) scheme, in the two dimensional case. Appropriate closure relations are necessary, with respect to the concentration C and the shear stress at the bed τ0. In first approximation, it is possible to derive a formulation for the two closure relations from appropriate rheological models (Bagnold theory and dense gas analogy). The model parameters are determined by means of laboratory tests on dry granular material and the effectiveness of the closure relation verified through a comparison with the experimental results. In particular, the experimental investigation aims to reproduce two case of study for dry granular material: the dam-break test problem and the stationary motion with changes in planimetry. The experiments are carried out in the Hydraulic Laboratory of the University of Trento, by means of channels with variable slope and variable shape. The mathematical model will

  20. Trace organics variation across the wastewater treatment system of a Class-B refinery and estimate of removal of refractory organics by add-on mixed-media filtration and granular activated carbon at pilot scale

    Energy Technology Data Exchange (ETDEWEB)

    Raphaelian, L. A.; Harrison, W.

    1978-06-01

    Wastewater at SOHIO's Toledo refinery was sampled every four hours for four successive days in December 1976. Effluents from the full-scale system (dissolved-air-flotation (DAF) unit and final clarifier for the activated-sludge unit) and an add-on pilot-scale unit (mixed-media filter and activated-carbon columns) were sampled for analysis of common wastewater parameters and trace organic compounds. Grab samples taken every four hours were composited daily. Organics were isolated into acid, base, and neutral fractions. Four-day composites of these daily extracts were analyzed by capillary-column gas chromatography/mass spectrometry. Some 304 compounds were identified in the neutral fraction of the DAF effluent and removal of these organics by the activated-sludge and add-on treatment units was estimated. Numerous data for the approximate concentration of organic compounds are presented. Common wastewater parameters are also presented for comparison to specific organics concentration data. The activated-sludge unit removed aromatic compounds better than it did nonaromatics whereas the activated-carbon unit was better at removal of nonaromatic compounds. Average percentage removal of those organics present in the DAF effluent was greater than 99 percent (activated sludge), approximately 0 percent (mixed-media filter), and less than 1 percent (activated carbon). Of the approximately 1 percent of trace organics remaining in the final-clarifier effluent, 81 percent (by weight) were removed by the activated carbon. Because of variations in extraction efficiencies, amount of sample injected, losses on the GC column and transfer lines, and other sources of error, these are only approximate removal estimates.

  1. Impact of Wettability on Fracturing of Nano-Granular Materials

    Science.gov (United States)

    Trojer, M.; Juanes, R.

    2014-12-01

    Hydraulic fracturing, or fracking, is a well-known reservoir stimulation technique, by which the permeability of the near-wellbore region is enhanced through the creation of tensile fractures within the rock, formed in the direction perpendicular to the least principal stress. While it is well known that fracturing of granular media strongly depends on the type of media, the pore fluids, and the fracking fluids, the interplay between multiphase flow, wettability and fracture mechanics of shale-like (nano-granular) materials remains poorly understood. Here, we study experimentally the dynamics of multiphase-flow fracking in nano-porous media and its dependence on the wetting properties of the system. The experiments consist in saturating a thin bed of glass beads with a viscous fluid, injecting a less viscous fluid, and imaging the invasion morphology. We investigate three control parameters: the injection rate of the less-viscous invading phase, the confining stress, and the contact angle, which we control by altering the surface chemistry of the beads and the Hele-Shaw cell. We quantify the dynamic fracture pattern by means of particle image velocimetry (PIV), and elucidate the role of wettability on the emerging flow physics at the length scale of the viscous-frictional instability.

  2. Using MR Elastography to Image Force Chains in a Quasi-Static Granular Assembly

    Science.gov (United States)

    Sanfratello, L.; Altobelli, S. A.; Behringer, R. P.; Fukushima, E.

    2008-03-01

    Questions about the internal structure of dense granular assemblies remain unanswered for lack of 3D experimental data. It is known from 2D observations and from the boundaries of 3D systems that non-uniform stresses are present on container boundaries as well as at the bottom of granular piles. These forces are seen in 2D to be distributed by force chains, where most of the stress is transmitted through a small number of chains with much of the assembly transmitting little or none of the force. However, force chains have yet to be fully visualized in 3D. We propose a variation of magnetic resonance elastography (MRE) to image 3D force chains within a densely packed granular assembly. MRE is an MRI technique whereby small periodic displacements within an elastic material can be measured. Multiple bipolar motion encoding gradients incorporated into a typical pulse sequence, and applied at the frequency of mechanical oscillations, are used to detect the displacements. We have verified our MRE technique using a gel (Perma-Gel). We now extend this method to image force chains within a 3D granular assembly of particles under stress, on top of which is superimposed a small-amplitude vibration. It is our hypothesis that significant coherent displacements will be found only along force chains while most particles will move randomly. Experimental results will be presented.

  3. Simulating granular materials by energy minimization

    Science.gov (United States)

    Krijgsman, D.; Luding, S.

    2016-11-01

    Discrete element methods are extremely helpful in understanding the complex behaviors of granular media, as they give valuable insight into all internal variables of the system. In this paper, a novel discrete element method for performing simulations of granular media is presented, based on the minimization of the potential energy in the system. Contrary to most discrete element methods (i.e., soft-particle method, event-driven method, and non-smooth contact dynamics), the system does not evolve by (approximately) integrating Newtons equations of motion in time, but rather by searching for mechanical equilibrium solutions for the positions of all particles in the system, which is mathematically equivalent to locally minimizing the potential energy. The new method allows for the rapid creation of jammed initial conditions (to be used for further studies) and for the simulation of quasi-static deformation problems. The major advantage of the new method is that it allows for truly static deformations. The system does not evolve with time, but rather with the externally applied strain or load, so that there is no kinetic energy in the system, in contrast to other quasi-static methods. The performance of the algorithm for both types of applications of the method is tested. Therefore we look at the required number of iterations, for the system to converge to a stable solution. For each single iteration, the required computational effort scales linearly with the number of particles. During the process of creating initial conditions, the required number of iterations for two-dimensional systems scales with the square root of the number of particles in the system. The required number of iterations increases for systems closer to the jamming packing fraction. For a quasi-static pure shear deformation simulation, the results of the new method are validated by regular soft-particle dynamics simulations. The energy minimization algorithm is able to capture the evolution of the

  4. Warm dense crystallography

    Science.gov (United States)

    Valenza, Ryan A.; Seidler, Gerald T.

    2016-03-01

    The intense femtosecond-scale pulses from x-ray free electron lasers (XFELs) are able to create and interrogate interesting states of matter characterized by long-lived nonequilibrium semicore or core electron occupancies or by the heating of dense phases via the relaxation cascade initiated by the photoelectric effect. We address here the latter case of "warm dense matter" (WDM) and investigate the observable consequences of x-ray heating of the electronic degrees of freedom in crystalline systems. We report temperature-dependent density functional theory calculations for the x-ray diffraction from crystalline LiF, graphite, diamond, and Be. We find testable, strong signatures of condensed-phase effects that emphasize the importance of wide-angle scattering to study nonequilibrium states. These results also suggest that the reorganization of the valence electron density at eV-scale temperatures presents a confounding factor to achieving atomic resolution in macromolecular serial femtosecond crystallography (SFX) studies at XFELs, as performed under the "diffract before destroy" paradigm.

  5. Dense Suspension Splash

    Science.gov (United States)

    Zhang, Wendy; Dodge, Kevin M.; Peters, Ivo R.; Ellowitz, Jake; Klein Schaarsberg, Martin H.; Jaeger, Heinrich M.

    2014-03-01

    Upon impact onto a solid surface at several meters-per-second, a dense suspension plug splashes by ejecting liquid-coated particles. We study the mechanism for splash formation using experiments and a numerical model. In the model, the dense suspension is idealized as a collection of cohesionless, rigid grains with finite surface roughness. The grains also experience lubrication drag as they approach, collide inelastically and rebound away from each other. Simulations using this model reproduce the measured momentum distribution of ejected particles. They also provide direct evidence supporting the conclusion from earlier experiments that inelastic collisions, rather than viscous drag, dominate when the suspension contains macroscopic particles immersed in a low-viscosity solvent such as water. Finally, the simulations reveal two distinct routes for splash formation: a particle can be ejected by a single high momentum-change collision. More surprisingly, a succession of small momentum-change collisions can accumulate to eject a particle outwards. Supported by NSF through its MRSEC program (DMR-0820054) and fluid dynamics program (CBET-1336489).

  6. Dense Axion Stars

    CERN Document Server

    Braaten, Eric; Zhang, Hong

    2015-01-01

    If the dark matter consists of axions, gravity can cause them to coalesce into axion stars, which are stable gravitationally bound Bose-Einstein condensates of axions. In the previously known axion stars, gravity and the attractive force between pairs of axions are balanced by the kinetic pressure.If the axion mass energy is $mc^2= 10^{-4}$ eV, these dilute axion stars have a maximum mass of about $10^{-14} M_\\odot$. We point out that there are also dense axion stars in which gravity is balanced by the mean-field pressure of the axion condensate. We study axion stars using the leading term in a systematically improvable approximation to the effective potential of the nonrelativistic effective field theory for axions. Using the Thomas-Fermi approximation in which the kinetic pressure is neglected, we find a sequence of new branches of axion stars in which gravity is balanced by the mean-field interaction energy of the axion condensate. If $mc^2 = 10^{-4}$ eV, the first branch of these dense axion stars has mas...

  7. Dense Axion Stars

    Science.gov (United States)

    Braaten, Eric; Mohapatra, Abhishek; Zhang, Hong

    2016-09-01

    If the dark matter particles are axions, gravity can cause them to coalesce into axion stars, which are stable gravitationally bound systems of axions. In the previously known solutions for axion stars, gravity and the attractive force between pairs of axions are balanced by the kinetic pressure. The mass of these dilute axion stars cannot exceed a critical mass, which is about 10-14M⊙ if the axion mass is 10-4 eV . We study axion stars using a simple approximation to the effective potential of the nonrelativistic effective field theory for axions. We find a new branch of dense axion stars in which gravity is balanced by the mean-field pressure of the axion Bose-Einstein condensate. The mass on this branch ranges from about 10-20M⊙ to about M⊙ . If a dilute axion star with the critical mass accretes additional axions and collapses, it could produce a bosenova, leaving a dense axion star as the remnant.

  8. Dense Axion Stars

    Science.gov (United States)

    Mohapatra, Abhishek; Braaten, Eric; Zhang, Hong

    2016-03-01

    If the dark matter consists of axions, gravity can cause them to coalesce into axion stars, which are stable gravitationally bound Bose-Einstein condensates of axions. In the previously known axion stars, gravity and the attractive force between pairs of axions are balanced by the kinetic pressure. If the axion mass energy is mc2 =10-4 eV, these dilute axion stars have a maximum mass of about 10-14M⊙ . We point out that there are also dense axion stars in which gravity is balanced by the mean-field pressure of the axion condensate. We study axion stars using the leading term in a systematically improvable approximation to the effective potential of the nonrelativistic effective field theory for axions. Using the Thomas-Fermi approximation in which the kinetic pressure is neglected, we find a sequence of new branches of axion stars in which gravity is balanced by the mean-field interaction energy of the axion condensate. If mc2 =10-4 4 eV, the first branch of these dense axion stars has mass ranging from about 10-11M⊙ toabout M⊙.

  9. DENSE MEDIUM CYCLONE OPTIMIZATON

    Energy Technology Data Exchange (ETDEWEB)

    Gerald H. Luttrell; Chris J. Barbee; Peter J. Bethell; Chris J. Wood

    2005-06-30

    Dense medium cyclones (DMCs) are known to be efficient, high-tonnage devices suitable for upgrading particles in the 50 to 0.5 mm size range. This versatile separator, which uses centrifugal forces to enhance the separation of fine particles that cannot be upgraded in static dense medium separators, can be found in most modern coal plants and in a variety of mineral plants treating iron ore, dolomite, diamonds, potash and lead-zinc ores. Due to the high tonnage, a small increase in DMC efficiency can have a large impact on plant profitability. Unfortunately, the knowledge base required to properly design and operate DMCs has been seriously eroded during the past several decades. In an attempt to correct this problem, a set of engineering tools have been developed to allow producers to improve the efficiency of their DMC circuits. These tools include (1) low-cost density tracers that can be used by plant operators to rapidly assess DMC performance, (2) mathematical process models that can be used to predict the influence of changes in operating and design variables on DMC performance, and (3) an expert advisor system that provides plant operators with a user-friendly interface for evaluating, optimizing and trouble-shooting DMC circuits. The field data required to develop these tools was collected by conducting detailed sampling and evaluation programs at several industrial plant sites. These data were used to demonstrate the technical, economic and environmental benefits that can be realized through the application of these engineering tools.

  10. Symmetry breaking and coarsening of clusters in a prototypical driven granular gas.

    Science.gov (United States)

    Livne, Eli; Meerson, Baruch; Sasorov, Pavel V

    2002-11-01

    Granular hydrodynamics predicts symmetry-breaking instability in a two-dimensional ensemble of nearly elastically colliding smooth hard disks driven, at zero gravity, by a rapidly vibrating sidewall. Supercritical and subcritical symmetry-breaking bifurcations of the stripe state are identified, and the supercritical bifurcation curve is computed. The cluster dynamics proceed as a coarsening process mediated by the gas phase. Well above the bifurcation point the final steady state, selected by coarsening, represents a single strongly localized densely packed "droplet."

  11. 10,000 - A reason to study granular heat convection

    Energy Technology Data Exchange (ETDEWEB)

    Einav, I.; Rognon, P.; Gan, Y.; Miller, T.; Griffani, D. [Particles and Grains Laboratory, School of Civil Engineering, University of Sydney, Sydney, NSW 2006 (Australia)

    2013-06-18

    In sheared granular media, particle motion is characterized by vortex-like structures; here this is demonstrated experimentally for disks system undergoing indefinite deformation during simple shear, as often imposed by the rock masses hosting earthquake fault gouges. In traditional fluids it has been known for years that vortices represent a major factor of heat transfer enhancement via convective internal mixing, but in analyses of heat transfer through earthquake faults and base planes of landslides this has been continuously neglected. Can research proceed by neglecting heat convection by internal mixing? Our answer is astonishingly far from being yes.

  12. Multiscale Phenomena in the Solid-Liquid Transition State of a Granular Material: Analysis and Modelling of Dense Granular Materials

    Science.gov (United States)

    2011-09-26

    Geomechanics , (02 2011): 264. doi: 10.1002/nag.910 2011/08/24 01:39:39 10 David M. Walker, Antoinette Tordesillas, Colin Thornton, Robert P. Behringer, Jie...Computational Geomechanics . 2011/04/26 10:00:00, . : , 2011/08/30 08:52:12 17 TOTAL: 3 (d) Manuscripts Number of Peer-Reviewed Conference Proceeding...Bifurcations and Degradations in Geomechanics . (In press) The techniques in [1]-[2] are extended to a broader range of experimental and simulation

  13. The effect of inter-particle contact time in granular flows -- A network theory

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, D.Z.; Rauenzahn, R.M.

    1996-12-31

    In a kinetic theory, it is usually assumed that the time duration of particle collision is vanishingly small and only binary collisions are considered. The validity of these assumptions depends on the ratio of collision time to mean free flight time. If this ratio is small, the kinetic theory description is appropriate. In a dense system, however, this ratio is usually large, and the dynamics of the multi-particle interactions have to be considered. For instance, during a collision, the contacting pair usually has a relative tangential velocity that causes a change in the direction of rebound. This implies a dependence of the granular stress on the vorticity of the mean flows field. Due to the inherent energy dissipation in a particle collision, and the consistent rearrangement of particles, there are relaxation times associated with them. In a binary collision, this energy dissipation is represented by coefficient of restitution. In a dense granular system, multi-particle interactions occur frequently. The energy dissipation and system relaxation have to be studied by the consideration of the dynamics in the duration of particle interaction and cannot be represented by a single coefficient of restitution. In this case, the relaxation times must be introduced explicitly. By modification of the network theory for rubber material, a constitutive model for dense granular material is developed based on the dynamics of multi-particle interaction. The finite particle interaction time and system relaxation times are considered.

  14. Hyperons in dense matter

    Energy Technology Data Exchange (ETDEWEB)

    Dapo, Haris

    2009-01-28

    The hyperon-nucleon YN low momentum effective interaction (V{sub low} {sub k}) allows for an extensive study of the behavior of hyperons in dense matter, together with an investigation of effects of the presence of hyperons on dense matter. The first step towards this goal is the construction of the matrix elements for the hyperon-nucleon low momentum potential. In order to assess the different properties of hyperons within these potentials we calculate the hyperon single-particle potentials in the Hartree-Fock approximation for all of the interactions. Their dependence on both momentum and density, is studied. The single-particle potentials are then used to determine the chemical potential of hyperons in neutron stars. For nucleonic properties, the nucleon-nucleon V{sub low} {sub k} can be used with the caveat that the calculation of the ground-state energy of symmetric nuclear matter does not correctly reproduce the properties of matter at saturation. With the nucleon-nucleon V{sub low} {sub k} one is unable to reach the densities needed for the calculation of neutron star masses. To circumvent this problem we use two approaches: in the first one, we parametrize the entire nucleonic sector. In the second one, we replace only the three-body force. The former will enable us to study neutron star masses, and the latter for studying the medium's response to the external probe. In this thesis we take the external probe to be the neutrino. By combining this parametrization with the YN V{sub low} {sub k} potential, we calculate the equation of state of equilibrated matter. Performing the calculation in the Hartree-Fock approximation at zero temperature, the concentrations of all particles are calculated. From these we can ascertain at which densities hyperons appear for a wide range of parameters. Finally, we calculate the masses of neutron stars with these concentrations. For the calculation of the medium's response to an external probe, we replace the three

  15. Influence of vibration on granular flowability and its mechanism of aided flow

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Regarding flowing granular media as weak transverse isotropic media, the phase velocity expressions of wave P, wave SH and wave SV were deduced, the propagation characteristics of waves in flowing granular media were analyzed. The experiments show that vibration has great influence on granular fluidity. The wavefront of wave P is elliptic or closely elliptic, the wavefront of wave SH is elliptic, and the wavefront of wave SV is not elliptic. Wave propagation in the granular flowing field attenuates layer after layer. The theory and experiment both substantiate that the density difference is the key factor which leads to the attenuation of vibrating energy. In terms of characteristics of wave propagation one can deduce that vibrating waves have less influence on flowability of granules when the amplitude and frequency are small. However, when the amplitude and frequency increase gradually, the eccentricity of ellipsoid, the viscosity resistance and inner friction among granules, and shear intensity of granules decrease, and the loosening coefficient of granules increases, which shows the granules have better flowability.

  16. Wave propagation in random granular chains.

    Science.gov (United States)

    Manjunath, Mohith; Awasthi, Amnaya P; Geubelle, Philippe H

    2012-03-01

    The influence of randomness on wave propagation in one-dimensional chains of spherical granular media is investigated. The interaction between the elastic spheres is modeled using the classical Hertzian contact law. Randomness is introduced in the discrete model using random distributions of particle mass, Young's modulus, or radius. Of particular interest in this study is the quantification of the attenuation in the amplitude of the impulse associated with various levels of randomness: two distinct regimes of decay are observed, characterized by an exponential or a power law, respectively. The responses are normalized to represent a vast array of material parameters and impact conditions. The virial theorem is applied to investigate the transfer from potential to kinetic energy components in the system for different levels of randomness. The level of attenuation in the two decay regimes is compared for the three different sources of randomness and it is found that randomness in radius leads to the maximum rate of decay in the exponential regime of wave propagation.

  17. 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...

  18. Numerical modelling of granular flows: a reality check

    Science.gov (United States)

    Windows-Yule, C. R. K.; Tunuguntla, D. R.; Parker, D. J.

    2016-07-01

    Discrete particle simulations provide a powerful tool for the advancement of our understanding of granular media, and the development and refinement of the multitudinous techniques used to handle and process these ubiquitous materials. However, in order to ensure that this tool can be successfully utilised in a meaningful and reliable manner, it is of paramount importance that we fully understand the degree to which numerical models can be trusted to accurately and quantitatively recreate and predict the behaviours of the real-world systems they are designed to emulate. Due to the complexity and diverse variety of physical states and dynamical behaviours exhibited by granular media, a simulation algorithm capable of closely reproducing the behaviours of a given system may be entirely unsuitable for other systems with different physical properties, or even similar systems exposed to differing control parameters. In this paper, we focus on two widely used forms of granular flow, for which discrete particle simulations are shown to provide a full, quantitative replication of the behaviours of real industrial and experimental systems. We identify also situations for which quantitative agreement may fail are identified, but important general, qualitative trends are still recreated, as well as cases for which computational models are entirely unsuitable. By assembling this information into a single document, we hope not only to provide researchers with a useful point of reference when designing and executing future studies, but also to equip those involved in the design of simulation algorithms with a clear picture of the current strengths and shortcomings of contemporary models, and hence an improved knowledge of the most valuable areas on which to focus their work.

  19. Particle Dispersion Behaviors of Dense Gas-Particle Flows in Bubble Fluidized Bed

    OpenAIRE

    Xue Liu; Guohui Li; Sihao Lv

    2013-01-01

    An Euler-Euler two-fluid model incorporating a developed momentum transfer empirical coefficient is developed to study the particle dispersion behaviors of dense gas-particle flows in gas-fluidization reactor. In this model, the four-way couplings among gas-particles, particle-gas, and particle-particle collisions are fully considered based on kinetic theory of granular flows and an improved smooth continuous drag coefficient is utilized. Gas turbulent flow is solved by large eddy simulation....

  20. Conductive dense hydrogen

    Science.gov (United States)

    Eremets, M.; Troyan, I.

    2012-12-01

    Hydrogen at ambient pressures and low temperatures forms a molecular crystal which is expected to display metallic properties under megabar pressures. This metal is predicted to be superconducting with a very high critical temperature Tc of 200-400 K. The superconductor may potentially be recovered metastably at ambient pressures, and it may acquire a new quantum state as a metallic superfluid and a superconducting superfluid. Recent experiments performed at low temperatures T 220 GPa, new Raman modes arose, providing evidence for the transformation to a new opaque and electrically conductive phase IV. Above 260 GPa, in the next phase V, hydrogen reflected light well. Its resistance was nearly temperature-independent over a wide temperature range, down to 30 K, indicating that the hydrogen was metallic. Releasing the pressure induced the metallic phase to transform directly into molecular hydrogen with significant hysteresis at 200 GPa and 295 K. These data were published in our paper: M. I. Eremets and I. A. Troyan "Conductive dense hydrogen." Nature Materials 10: 927-931. We will present also new results on hydrogen: phase diagram with phases IV and V determined in P,T domain up to 300 GPa and 350 K. We will also discuss possible structures of phase IV based on our Raman and infrared measurements up to 300 GPa.

  1. Dense Hypervelocity Plasma Jets

    Science.gov (United States)

    Case, Andrew; Witherspoon, F. Douglas; Messer, Sarah; Bomgardner, Richard; Phillips, Michael; van Doren, David; Elton, Raymond; Uzun-Kaymak, Ilker

    2007-11-01

    We are developing high velocity dense plasma jets for fusion and HEDP applications. Traditional coaxial plasma accelerators suffer from the blow-by instability which limits the mass accelerated to high velocity. In the current design blow-by is delayed by a combination of electrode shaping and use of a tailored plasma armature created by injection of a high density plasma at a few eV generated by arrays of capillary discharges or sparkgaps. Experimental data will be presented for a complete 32 injector gun system built for driving rotation in the Maryland MCX experiment, including data on penetration of the plasma jet through a magnetic field. We present spectroscopic measurements of plasma velocity, temperature, and density, as well as total momentum measured using a ballistic pendulum. Measurements are in agreement with each other and with time of flight data from photodiodes and a multichannel PMT. Plasma density is above 10^15 cm-3, velocities range up to about 100 km/s. Preliminary results from a quadrature heterodyne HeNe interferometer are consistent with these results.

  2. Evolution of shock instability in granular gases with viscoelastic collisions

    Science.gov (United States)

    Sirmas, Nick; Radulescu, Matei

    2014-12-01

    Shocks in granular media have been shown to develop instabilities. We address the role that early stages of shock development have on this type of instability. We look at the evolution of shock waves driven by a piston in a dilute system of smooth inelastic disks, using both discrete particle and continuum modelling. To mimic a realistic granular gas, viscoelastic collisions are approximated with an impact velocity threshold u* needed for inelastic collisions to occur. We show that behaviour of the shock evolution is dependent on the ratio of piston velocity to impact velocity threshold up/u*, and the coefficient of restitution ɛ. For up/u* = 2.0, we recover shock evolution behaving similar to that observed in purely inelastic media. This is characterized by a short period where the shock front pulls towards the piston before attaining a developed structure. No pullback is seen for up/u* = 1.0. Results show the onset of instability for these stronger shocks during this evolving stage. These results suggest that the early stages of shock evolution play an important role in the shock instability.

  3. Perspicuity and Granularity in Refinement

    CERN Document Server

    Boiten, Eerke

    2011-01-01

    This paper reconsiders refinements which introduce actions on the concrete level which were not present at the abstract level. It draws a distinction between concrete actions which are "perspicuous" at the abstract level, and changes of granularity of actions between different levels of abstraction. The main contribution of this paper is in exploring the relation between these different methods of "action refinement", and the basic refinement relation that is used. In particular, it shows how the "refining skip" method is incompatible with failures-based refinement relations, and consequently some decisions in designing Event-B refinement are entangled.

  4. Quantum percolation in granular metals.

    Science.gov (United States)

    Feigel'man, M V; Ioselevich, A S; Skvortsov, M A

    2004-09-24

    Theory of quantum corrections to conductivity of granular metal films is developed for the realistic case of large randomly distributed tunnel conductances. Quantum fluctuations of intergrain voltages (at energies E much below the bare charging energy scale E(C)) suppress the mean conductance g (E) much more strongly than its standard deviation sigma(E). At sufficiently low energies E(*) any distribution becomes broad, with sigma(E(*)) approximately g (E(*)), leading to strong local fluctuations of the tunneling density of states. The percolative nature of the metal-insulator transition is established by a combination of analytic and numerical analysis of the matrix renormalization group equations.

  5. Theoretical model of granular compaction

    Energy Technology Data Exchange (ETDEWEB)

    Ben-Naim, E. [Los Alamos National Lab., NM (United States); Knight, J.B. [Princeton Univ., NJ (United States). Dept. of Physics; Nowak, E.R. [Univ. of Illinois, Urbana, IL (United States). Dept. of Physics]|[Univ. of Chicago, IL (United States). James Franck Inst.; Jaeger, H.M.; Nagel, S.R. [Univ. of Chicago, IL (United States). James Franck Inst.

    1997-11-01

    Experimental studies show that the density of a vibrated granular material evolves from a low density initial state into a higher density final steady state. The relaxation towards the final density follows an inverse logarithmic law. As the system approaches its final state, a growing number of beads have to be rearranged to enable a local density increase. A free volume argument shows that this number grows as N = {rho}/(1 {minus} {rho}). The time scale associated with such events increases exponentially e{sup {minus}N}, and as a result a logarithmically slow approach to the final state is found {rho} {infinity} {minus}{rho}(t) {approx_equal} 1/lnt.

  6. 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.

  7. Heavy mesons in dense matter

    NARCIS (Netherlands)

    Tolos, Laura; Gamermann, Daniel; Garcia-Recio, Carmen; Molina, Raquel; Nieves, Juan; Oset, Eulogio; Ramos, Angels; LlanesEstrada, FJ; Pelaez,

    2011-01-01

    Charmed mesons in dense matter are studied within a unitary coupled-channel approach which takes into account Pauli-blocking effects and meson self-energies in a self-consistent manner. We obtain the open-charm meson spectral functions in this dense medium, and discuss their implications on hidden c

  8. Fast spectral solution of the generalized Enskog equation for dense gases

    Science.gov (United States)

    Wu, Lei; Zhang, Yonghao; Reese, Jason M.

    2015-12-01

    We propose a fast spectral method for solving the generalized Enskog equation for dense gases. For elastic collisions, the method solves the Enskog collision operator with a computational cost of O (M d - 1Nd log ⁡ N), where d is the dimension of the velocity space, and M d - 1 and Nd are the number of solid angle and velocity space discretizations, respectively. For inelastic collisions, the cost is N times higher. The accuracy of this fast spectral method is assessed by comparing our numerical results with analytical solutions of the spatially-homogeneous relaxation of heated granular gases. We also compare our results for force-driven Poiseuille flow and Fourier flow with those from molecular dynamics and Monte Carlo simulations. Although it is phenomenological, the generalized Enskog equation is capable of capturing the flow dynamics of dense granular gases, and the fast spectral method is accurate and efficient. As example applications, Fourier and Couette flows of a dense granular gas are investigated. In addition to the temperature profile, both the density and the high-energy tails in the velocity distribution functions are found to be strongly influenced by the restitution coefficient.

  9. Equilibrium and column adsorption studies of 2,4-dinitroanisole (DNAN) on surface modified granular activated carbons.

    Science.gov (United States)

    Boddu, V M; Abburi, K; Fredricksen, A J; Maloney, S W; Damavarapu, R

    2009-02-01

    2,4-Dinitroanisole (DNAN) is used as a component extensively in the development of insensitive munitions. This may result in release of DNAN into the environment. Here, the results are reported of a study on the removal characteristics of DNAN through adsorption on granular activated carbon (GAC), chitosan coated granular activated carbon (CGAC), acid treated granular activated carbon (AGAC) and alkali treated granular activated carbon (BGAC) under equilibrium and column flow conditions. The effect of pH, contact time, concentration of DNAN, and presence of electrolytes on the uptake of DNAN by the adsorbents was investigated. The equilibrium data were fitted to different types of adsorption isotherms. The data were further analysed on the basis of Lagergren first-order, pseudo second-order and intraparticle diffusion kinetic models. Breakthrough curves were obtained based on column flow results. All the adsorbents were capable of removing about 99% of DNAN from aqueous media, except CGAC which adsorbed about 87% of DNAN.

  10. Two Classes of Models of Granular Computing

    Institute of Scientific and Technical Information of China (English)

    Daowu Pei

    2006-01-01

    This paper reviews a class of important models of granular computing which are induced by equivalence relations, or by general binary relations, or by neighborhood systems, and propose a class of models of granular computing which are induced by coverings of the given universe.

  11. Granular cell tumors of the tracheobronchial tree.

    NARCIS (Netherlands)

    Maten, van der J; Blaauwgeers, JL; Sutedja, G.; Kwa, HB; Postmus, P.E.; Wagenaar, SS

    2003-01-01

    OBJECTIVE: To describe the population-based incidence and clinical characteristics of granular cell tumors of the tracheobronchial tree. METHODS: All newly registered tracheobronchial granular cell tumors in the Dutch Network and National Database for Pathology for 10 consecutive years (1990-1999) w

  12. Some open problems in granular matter mechanics

    Institute of Scientific and Technical Information of China (English)

    Qicheng Sun; Guangqian Wang; Kaiheng Hu

    2009-01-01

    Granular matter is a large assemblage of solid particles,which is fundamentally different from any other type of matters,such as solid and liquid.Most models presented for granular matter are phenomenological and are only suitable for solving engineering problems.Many fundamental mechanical problems remain open.By analyzing characteristics of internal state structure,we propose that granularmatter is intrinsically multiscale,i.e.microscale of particle size,mesoscale of force chain,and macroscale of the bulk of granular matter.The correlations among difference scales would be crucial.The mesoscale force chain network is determined by both particle properties and macroscopic boundary conditions.The evolution of the force the chain network contributes to macroscopic mechanical properties of granular matter.In addition,we discuss the drawbacks in simplifying contact forces in the current models,and the difficulties in analyzing the interaction of interstitial fluid in wet granular matter.As an appropriate application of granular matter,debris flow can be studied with granular matter mechanics;meanwhile,debris flow brings more challenges which certainly motivate future studies on granular matter.(C) 2008 National Natural Science Foundation of China and Chinese Academy of Sciences.Published by Elsevier Limited and Science in China Press.All rights reserved.

  13. 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 applica

  14. A micromechanical study of dilatancy of granular materials

    Science.gov (United States)

    Kruyt, N. P.; Rothenburg, L.

    2016-10-01

    In micromechanics of granular materials, relationships are investigated between micro-scale characteristics of particles and contacts and macro-scale, continuum characteristics. Dilatancy is an important property of granular materials, defined as volume changes (dilative or compressive) induced by shear deformation. To obtain detailed information at the micro-scale, two-dimensional Discrete Element Method simulations of isobaric tests with disk-shaped particles have been performed. The required information includes the fabric tensor which characterizes statistical properties of the contact network. The dependence of the dilatancy rate on the shear strength and the fabric tensor has been investigated, based on the results of the simulations employing a dense and a loose initial system. The dilatancy rate depends in a complex, non-unique way on the shear strength, while the dependence on the fabric tensor is more amenable to analytical description. Two micromechanical mechanisms of dilatancy have been identified: (i) dilatancy due to deformation of loops that are determined by the interparticle contact network and (ii) dilatancy due to topological changes in the interparticle contact network that correspond to the creation or disruption of contacts. For the first mechanism the anisotropy in the contact network is the primary parameter, while for the second mechanism the average number of contacts per particle is the primary parameter. A fabric-based micromechanical relation for the dilatancy rate has been formulated that describes these identified mechanisms. Parameters present in this relation are determined by fitting this relation to the results of the Discrete Element Method simulations, using combined data for the dense and the loose initial system. Employing these fitted coefficients, good agreement is obtained between the results of the simulations and the predictions of the micromechanical dilatancy relation.

  15. 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

  16. 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...

  17. Modeling Size Polydisperse Granular Flows

    Science.gov (United States)

    Lueptow, Richard M.; Schlick, Conor P.; Isner, Austin B.; Umbanhowar, Paul B.; Ottino, Julio M.

    2014-11-01

    Modeling size segregation of granular materials has important applications in many industrial processes and geophysical phenomena. We have developed a continuum model for granular multi- and polydisperse size segregation based on flow kinematics, which we obtain from discrete element method (DEM) simulations. The segregation depends on dimensionless control parameters that are functions of flow rate, particle sizes, collisional diffusion coefficient, shear rate, and flowing layer depth. To test the theoretical approach, we model segregation in tri-disperse quasi-2D heap flow and log-normally distributed polydisperse quasi-2D chute flow. In both cases, the segregated particle size distributions match results from full-scale DEM simulations and experiments. While the theory was applied to size segregation in steady quasi-2D flows here, the approach can be readily generalized to include additional drivers of segregation such as density and shape as well as other geometries where the flow field can be characterized including rotating tumbler flow and three-dimensional bounded heap flow. Funded by The Dow Chemical Company and NSF Grant CMMI-1000469.

  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. BOOK REVIEW: Kinetic Theory of Granular Gases

    Science.gov (United States)

    Trizac, Emmanuel

    2005-11-01

    restitution coefficients, that are again velocity dependent. This seems to be the price of a consistent approach, which does not lend itself to much insight. In addition, the behaviour of driven systems is not addressed, whereas in the realm of granular media, force-free systems are the exception rather than the rule. The differences between constant ɛ and visco-elastic models is presumably less pronounced in the driven case. Study of driven systems also reveals that the rheology of granular gases is intrinsically non-Newtonian, which is a key feature. Finally, the powerful direct simulation Monte Carlo technique is not described, whereas it is an important tool, particularly relevant for the physics of the Boltzmann equation, and straightforward to implement in its simplest version. N Brilliantov and T Pöschel concentrate on the (equally relevant) molecular dynamics method instead. In conclusion, the book fills a gap in the field. The companion webpage from where molecular dynamics and symbolic algebra programs can be downloaded is also useful.

  20. Numerical Simulations of Granular Processes

    Science.gov (United States)

    Richardson, Derek C.; Michel, Patrick; Schwartz, Stephen R.; Ballouz, Ronald-Louis; Yu, Yang; Matsumura, Soko

    2014-11-01

    Spacecraft images and indirect observations including thermal inertia measurements indicate most small bodies have surface regolith. Evidence of granular flow is also apparent in the images. This material motion occurs in very low gravity, therefore in a completely different gravitational environment than on the Earth. Understanding and modeling these motions can aid in the interpretation of imaged surface features that may exhibit signatures of constituent material properties. Also, upcoming sample-return missions to small bodies, and possible future manned missions, will involve interaction with the surface regolith, so it is important to develop tools to predict the surface response. We have added new capabilities to the parallelized N-body gravity tree code pkdgrav [1,2] that permit the simulation of granular dynamics, including multi-contact physics and friction forces, using the soft-sphere discrete-element method [3]. The numerical approach has been validated through comparison with laboratory experiments (e.g., [3,4]). Ongoing and recently completed projects include: impacts into granular materials using different projectile shapes [5]; possible tidal resurfacing of asteroid Apophis during its 2029 encounter [6]; the Brazil-nut effect in low gravity [7]; and avalanche modeling.Acknowledgements: DCR acknowledges NASA (grants NNX08AM39G, NNX10AQ01G, NNX12AG29G) and NSF (AST1009579). PM acknowledges the French agency CNES. SRS works on the NEOShield Project funded under the European Commission’s FP7 program agreement No. 282703. SM acknowledges support from the Center for Theory and Computation at U Maryland and the Dundee Fellowship at U Dundee. Most simulations were performed using the YORP cluster in the Dept. of Astronomy at U Maryland and on the Deepthought High-Performance Computing Cluster at U Maryland.References: [1] Richardson, D.C. et al. 2000, Icarus 143, 45; [2] Stadel, J. 2001, Ph.D. Thesis, U Washington; [3] Schwartz, S.R. et al. 2012, Gran

  1. Beneath Our Feet: Strategies for Locomotion in Granular Media

    Science.gov (United States)

    Hosoi, A. E.; Goldman, Daniel I.

    2015-01-01

    “If you find yourself in a hole, stop digging.” Although Denis Healey's famous adage ( Metcalfe 2007 ) may offer sound advice for politicians, it is less relevant to worms, clams, and other higher organisms that rely on their digging ability for survival. In this article, we review recent work on the development of simple models that elucidate the fundamental principles underlying digging and burrowing strategies employed by biological systems. Four digging regimes are identified based on dimensionless digger size and the dimensionless inertial number. We select biological organisms to represent three of the four regimes: razor clams, sandfish, and nematodes. Models for all three diggers are derived and discussed, and analogies are drawn to low-Reynolds number swimmers.

  2. Fluidization of granular media wetted by liquid 4He.

    Science.gov (United States)

    Huang, K; Sohaili, M; Schröter, M; Herminghaus, S

    2009-01-01

    We explore experimentally the fluidization of vertically agitated polymethylmethacrylate spheres wetted by liquid 4He . By controlling the temperature around the lambda point, we change the properties of the wetting liquid from a normal fluid (helium I) to a superfluid (helium II). For wetting by helium I, the critical acceleration for fluidization (Gamma_{c}) shows a steep increase close to the saturation of the vapor pressure in the sample cell. For helium II wetting, Gamma_{c} starts to increase at about 75% saturation, indicating that capillary bridges are enhanced by the superflow of the unsaturated helium film. Above saturation, Gamma_{c} enters a plateau regime where the capillary force between particles is independent of the bridge volume. The plateau value is found to vary with temperature and shows a peak at 2.1K , which we attribute to the influence of the specific heat of liquid helium.

  3. Dynamics of the Contact Stress in Granular Media

    Science.gov (United States)

    Glam, B.; Britan, A.; Ben-Dor, G.; Igra, O.; Goldenberg, A.

    2004-07-01

    Experiments were conducted in a vertical shock tube with an optically transparent single straight chain of 20-mm diameter discs made of epoxy. The dynamic time dependent fringe patterns of the stress in the contact points between the discs were registered using a Q-switched YAG laser, a transmission polariscope and CCD cameras. The main details of the experiment, the data acquisition and the computer aid processing are briefly discussed first. Thereafter the stress wave propagation and its reflection at the chain boundaries are analyzed based on the results of photo elastic experiments and their comparison with those obtained using strain gauges.

  4. Optimizing packing fraction in granular media composed of overlapping spheres.

    Science.gov (United States)

    Roth, Leah K; Jaeger, Heinrich M

    2016-01-28

    What particle shape will generate the highest packing fraction when randomly poured into a container? In order to explore and navigate the enormous search space efficiently, we pair molecular dynamics simulations with artificial evolution. Arbitrary particle shape is represented by a set of overlapping spheres of varying diameter, enabling us to approximate smooth surfaces with a resolution proportional to the number of spheres included. We discover a family of planar triangular particles, whose packing fraction of ϕ ∼ 0.73 is among the highest experimental results for disordered packings of frictionless particles. We investigate how ϕ depends on the arrangement of spheres comprising an individual particle and on the smoothness of the surface. We validate the simulations with experiments using 3D-printed copies of the simplest member of the family, a planar particle consisting of three overlapping spheres with identical radius. Direct experimental comparison with 3D-printed aspherical ellipsoids demonstrates that the triangular particles pack exceedingly well not only in the limit of large system size but also when confined to small containers.

  5. Sudden Chain Energy Transfer Events in Vibrated Granular Media

    Science.gov (United States)

    Rivas, Nicolás; Ponce, Suomi; Soto, Rodrigo; Cordero, Patricio; Mujica, Nicolás; Risso, Dino; Gallet, Basille

    2012-02-01

    In a mixture of two species of grains of equal size but different mass, placed in a vertically vibrated shallow box, there is spontaneous segregation. Once the system is at least partly segregated and clusters of the heavy particles have formed, there are sudden peaks of the horizontal kinetic energy of the heavy particles, that is otherwise small. Together with the energy peaks the clusters rapidly expand and the segregation is partially lost. The process repeats once segregation has taken place again, either randomly or with some regularity in time depending on the experimental or numerical parameters. An explanation for these events is provided based on the existence of a fixed point for an isolated particle bouncing with only vertical motion. The horizontal energy peaks occur when the energy stored in the vertical motion is partly transferred into horizontal energy through a chain reaction of collisions between heavy particles.

  6. Dynamical heterogeneities in glasses colloids and granular media

    CERN Document Server

    2011-01-01

    Most everyday solid materials, from plastics to cosmetic gels, exist in a non-crystalline, amorphous form: they are glasses. Yet we are still seeking an explanation as to what glasses really are and to why they form. Here, leading experts present broad perspectives on one of the deepest mysteries of condensed matter physics.

  7. Modeling intragranular diffusion in low-connectivity granular media

    Science.gov (United States)

    Ewing, Robert P.; Liu, Chongxuan; Hu, Qinhong

    2012-03-01

    Characterizing the diffusive exchange of solutes between bulk water in an aquifer and water in the intragranular pores of the solid phase is still challenging despite decades of study. Many disparities between observation and theory could be attributed to low connectivity of the intragranular pores. The presence of low connectivity indicates that a useful conceptual framework is percolation theory. The present study was initiated to develop a percolation-based finite difference (FD) model, and to test it rigorously against both random walk (RW) simulations of diffusion starting from nonequilibrium, and data on Borden sand published by Ball and Roberts (1991a,b) and subsequently reanalyzed by Haggerty and Gorelick (1995) using a multirate mass transfer (MRMT) approach. The percolation-theoretical model is simple and readily incorporated into existing FD models. The FD model closely matches the RW results using only a single fitting parameter, across a wide range of pore connectivities. Simulation of the Borden sand experiment without pore connectivity effects reproduced the MRMT analysis, but including low pore connectivity effects improved the fit. Overall, the theory and simulation results show that low intragranular pore connectivity can produce diffusive behavior that appears as if the solute had undergone slow sorption, despite the absence of any sorption process, thereby explaining some hitherto confusing aspects of intragranular diffusion.

  8. The granular silo as a continuum plastic flow: the hour-glass vs the clepsydra

    CERN Document Server

    Staron, Lydie; Popinet, Stéphane; 10.1063/1.4757390

    2012-01-01

    The granular silo is one of the many interesting illustrations of the thixotropic property of granular matter: a rapid flow develops at the outlet, propagating upwards through a dense shear flow while material at the bottom corners of the container remains static. For large enough outlets, the discharge flow is continuous; however, by contrast with the clepsydra for which the flow velocity depends on the height of fluid left in the container, the discharge rate of granular silos is constant. Implementing a plastic rheology in a 2D Navier-Stokes solver (following the mu(I)-rheology or a constant friction), we simulate the continuum counterpart of the granular silo. Doing so, we obtain a constant flow rate during the discharge and recover the Beverloo scaling independently of the initial filling height of the silo. We show that lowering the value of the coefficient of friction leads to a transition toward a different behavior, similar to that of a viscous fluid, and where the filling height becomes active in th...

  9. Understanding the effects of inter-particle contact friction on the elastic moduli of granular materials

    Science.gov (United States)

    Taghizadeh, K.; Kumar, N.; Magnanimo, V.; Luding, S.

    2015-09-01

    Understanding the mechanical stiffness of closely packed, dense granular systems is of interest in many fields, such as soil mechanics, material science and physics. The main difficulty arises due to discreteness and disorder in granular materials at the microscopic scale which requires a multi-scale approach. The Discrete Element Method (DEM) is a powerful tool to inspect the influence of the microscopic contact properties of its individual constituents on the bulk behavior of granular assemblies. In this study, the isotropic deformation mode of polydisperse packings of frictionless and frictional spheres are modeled by using DEM, to investigate the effective stiffness of the granular assembly. At various volume fractions, for every sample, we determine the stress and fabric incremental response that result from the application of strain-probes. As we are interested first in the reversible, elastic response, the amplitude of the applied perturbations has to be small enough to avoid opening and closing of too many contacts, which would lead to irreversible rearrangements in the sample. Counterintuitively, with increasing inter-particle contact friction, the bulk modulus decreases systematically with the coefficient of friction for samples with the same volume fraction. We explain this by the difference in microstructure (isotropic fabric) the samples get when compressed to the same density.

  10. 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.

  11. The granular silo as a continuum plastic flow: The hour-glass vs the clepsydra

    Science.gov (United States)

    Staron, L.; Lagrée, P.-Y.; Popinet, S.

    2012-10-01

    The granular silo is one of the many interesting illustrations of the thixotropic property of granular matter: a rapid flow develops at the outlet, propagating upwards through a dense shear flow while material at the bottom corners of the container remains static. For large enough outlets, the discharge flow is continuous; however, by contrast with the clepsydra for which the flow velocity depends on the height of fluid left in the container, the discharge rate of granular silos is constant. Implementing a plastic rheology in a 2D Navier-Stokes solver (following the μ(I)-rheology or a constant friction), we simulate the continuum counterpart of the granular silo. Doing so, we obtain a constant flow rate during the discharge and recover the Beverloo scaling independently of the initial filling height of the silo. We show that lowering the value of the coefficient of friction leads to a transition toward a different behavior, similar to that of a viscous fluid, and where the filling height becomes active in the discharge process. The pressure field shows that large enough values of the coefficient of friction (≃0.3) allow for a low-pressure cavity to form above the outlet, and can thus explain the Beverloo scaling. In conclusion, the difference between the discharge of a hourglass and a clepsydra seems to reside in the existence or not of a plastic yield stress.

  12. 76 FR 4936 - Granular Polytetrafluoroethylene Resin From Italy

    Science.gov (United States)

    2011-01-27

    ... COMMISSION Granular Polytetrafluoroethylene Resin From Italy AGENCY: United States International Trade... antidumping duty order on granular polytetrafluoroethylene resin (``granular PTFE resin'') from Italy. DATES... on granular PTFE resin from Italy and Japan (75 FR 67082-67083 and 67105-67108, November 1,...

  13. 21 CFR 133.145 - Granular cheese for manufacturing.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 2 2010-04-01 2010-04-01 false Granular cheese for manufacturing. 133.145 Section... Standardized Cheese and Related Products § 133.145 Granular cheese for manufacturing. Granular cheese for manufacturing conforms to the definition and standard of identity prescribed for granular cheese by § 133.144...

  14. Densely crosslinked polycarbosiloxanes .1. Synthesis

    NARCIS (Netherlands)

    Flipsen, T.A C; Derks, R.; van der Vegt, H.A.; Pennings, A.J; Hadziioannou, G

    1997-01-01

    Novel densely crosslinked polycarbosiloxanes were obtained by using functional branched prepolymers. Two types of soluble prepolymers were prepared from di- and trifunctional alkoxysilane monomers via cohydrolysis/condensation and for both final crosslinking occurred via hydrosilylation. The prepoly

  15. Shear failure of granular materials

    Science.gov (United States)

    Degiuli, Eric; Balmforth, Neil; McElwaine, Jim; Schoof, Christian; Hewitt, Ian

    2012-02-01

    Connecting the macroscopic behavior of granular materials with the microstructure remains a great challenge. Recent work connects these scales with a discrete calculus [1]. In this work we generalize this formalism from monodisperse packings of disks to 2D assemblies of arbitrarily shaped grains. In particular, we derive Airy's expression for a symmetric, divergence-free stress tensor. Using these tools, we derive, from first-principles and in a mean-field approximation, the entropy of frictional force configurations in the Force Network Ensemble. As a macroscopic consequence of the Coulomb friction condition at contacts, we predict shear failure at a critical shear stress, in accordance with the Mohr-Coulomb failure condition well known in engineering. Results are compared with numerical simulations, and the dependence on the microscopic geometric configuration is discussed. [4pt] [1] E. DeGiuli & J. McElwaine, PRE 2011. doi: 10.1103/PhysRevE.84.041310

  16. Wet granular walkers and climbers

    Energy Technology Data Exchange (ETDEWEB)

    Khan, Z S; Steinberger, A; Seemann, R; Herminghaus, S, E-mail: audrey.steinberger@ens-lyon.fr [Max Planck Institute for Dynamics and Self-Organization, Bunsenstrasse 10, D-37073 Goettingen (Germany)

    2011-05-15

    Mechanisms of locomotion in microscopic systems are of great interest not only for technological applications but also for the sake of understanding, and potentially harnessing, processes far from thermal equilibrium. Downscaling is a particular challenge and has led to a number of interesting concepts, including thermal ratchet systems and asymmetric swimmers. Here we present a granular ratchet system employing a particularly robust mechanism that can be implemented in various settings. The system consists of wetted spheres of different sizes that adhere to each other, and are subject to a symmetric oscillating, zero average external force field. An inherent asymmetry in the mutual force network leads to force rectification and hence to locomotion. We present a simple model that accounts for the observed behaviour, underscores its robustness and suggests a potential scalability of the concept.

  17. Kinetic approach to granular gases.

    Science.gov (United States)

    Puglisi, A; Loreto, V; Marini Bettolo Marconi, U; Vulpiani, A

    1999-05-01

    We address the problem of the so-called "granular gases," i.e., gases of massive particles in rapid movement undergoing inelastic collisions. We introduce a class of models of driven granular gases for which the stationary state is the result of the balance between the dissipation and the random forces which inject energies. These models exhibit a genuine thermodynamic limit, i.e., at fixed density the mean values of kinetic energy and dissipated energy per particle are independent of the number N of particles, for large values of N. One has two regimes: when the typical relaxation time tau of the driving Brownian process is small compared with the mean collision time tau(c) the spatial density is nearly homogeneous and the velocity probability distribution is Gaussian. In the opposite limit tau>tau(c) one has strong spatial clustering, with a fractal distribution of particles, and the velocity probability distribution strongly deviates from the Gaussian one. Simulations performed in one and two dimensions under the Stosszahlansatz Boltzmann approximation confirm the scenario. Furthermore, we analyze the instabilities bringing to the spatial and the velocity clusterization. Firstly, in the framework of a mean-field model, we explain how the existence of the inelasticity can lead to a spatial clusterization; on the other hand, we discuss, in the framework of a Langevin dynamics treating the collisions in a mean-field way, how a non-Gaussian distribution of velocity can arise. The comparison between the numerical and the analytical results exhibits an excellent agreement.

  18. Linguistic granular model: design and realization

    Institute of Scientific and Technical Information of China (English)

    YUE Shihong; LI Ping; SONG Zhihuan

    2005-01-01

    A new linguistic granular model is proposed and the effect of its parameters on the output is analyzed. The design of the model consists of two stages: using conditional fuzzy clustering for information granular, and integrating all information granules to final output. The integrating tool is fuzzy integral based on fuzzy measure, and the generalization of fuzzy integral increases flexibility of the linguistic granular model greatly. A heuristic algorithm to determine the parameters in the fuzzy integral is used to realize the linguistic model. Two experiments verify the feasibility of the proposed model.

  19. Energy decay in a granular gas collapse

    Science.gov (United States)

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

    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.

  20. 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...

  1. Wireless Fractal Ultra-Dense Cellular Networks.

    Science.gov (United States)

    Hao, Yixue; Chen, Min; Hu, Long; Song, Jeungeun; Volk, Mojca; Humar, Iztok

    2017-04-12

    With the ever-growing number of mobile devices, there is an explosive expansion in mobile data services. This represents a challenge for the traditional cellular network architecture to cope with the massive wireless traffic generated by mobile media applications. To meet this challenge, research is currently focused on the introduction of a small cell base station (BS) due to its low transmit power consumption and flexibility of deployment. However, due to a complex deployment environment and low transmit power of small cell BSs, the coverage boundary of small cell BSs will not have a traditional regular shape. Therefore, in this paper, we discuss the coverage boundary of an ultra-dense small cell network and give its main features: aeolotropy of path loss fading and fractal coverage boundary. Simple performance analysis is given, including coverage probability and transmission rate, etc., based on stochastic geometry theory and fractal theory. Finally, we present an application scene and discuss challenges in the ultra-dense small cell network.

  2. Solids flow rate measurement in dense slurries

    Energy Technology Data Exchange (ETDEWEB)

    Porges, K.G.; Doss, E.D.

    1993-09-01

    Accurate and rapid flow rate measurement of solids in dense slurries remains an unsolved technical problem, with important industrial applications in chemical processing plants and long-distance solids conveyance. In a hostile two-phase medium, such a measurement calls for two independent parameter determinations, both by non-intrusive means. Typically, dense slurries tend to flow in laminar, non-Newtonian mode, eliminating most conventional means that usually rely on calibration (which becomes more difficult and costly for high pressure and temperature media). These issues are reviewed, and specific solutions are recommended in this report. Detailed calculations that lead to improved measuring device designs are presented for both bulk density and average velocity measurements. Cross-correlation, chosen here for the latter task, has long been too inaccurate for practical applications. The cause and the cure of this deficiency are discussed using theory-supported modeling. Fluid Mechanics are used to develop the velocity profiles of laminar non-Newtonian flow in a rectangular duct. This geometry uniquely allows the design of highly accurate `capacitive` devices and also lends itself to gamma transmission densitometry on an absolute basis. An absolute readout, though of less accuracy, is also available from a capacitive densitometer and a pair of capacitive sensors yields signals suitable for cross-correlation velocity measurement.

  3. Infrared Opacities in Dense Atmospheres of Cool White Dwarf Stars

    CERN Document Server

    Kowalski, Piotr M; Dufour, Patrick

    2016-01-01

    Dense, He-rich atmospheres of cool white dwarfs represent a challenge to the modeling. This is because these atmospheres are constituted of a dense fluid in which strong multi-atomic interactions determine their physics and chemistry. Therefore, the ideal-gas-based description of absorption is no longer adequate, which makes the opacities of these atmospheres difficult to model. This is illustrated with severe problems in fitting the spectra of cool, He-rich stars. Good description of the infrared (IR) opacity is essential for proper assignment of the atmospheric parameters of these stars. Using methods of computational quantum chemistry we simulate the IR absorption of dense He/H media. We found a significant IR absorption from He atoms (He-He-He CIA opacity) and a strong pressure distortion of the H$_2$-He collision-induced absorption (CIA). We discuss the implication of these results for interpretation of the spectra of cool stars.

  4. Infrared Opacities in Dense Atmospheres of Cool White Dwarf Stars

    Science.gov (United States)

    Kowalski, P. M.; Blouin, S.; Dufour, P.

    2017-03-01

    Dense, He-rich atmospheres of cool white dwarfs represent a challenge to the modeling. This is because these atmospheres are constituted of a dense fluid in which strong multi-atomic interactions determine their physics and chemistry. Therefore, the ideal-gas-based description of absorption is no longer adequate, which makes the opacities of these atmospheres difficult to model. This is illustrated with severe problems in fitting the spectra of cool, He-rich stars. Good description of the infrared (IR) opacity is essential for proper assignment of the atmospheric parameters of these stars. Using methods of computational quantum chemistry we simulate the IR absorption of dense He/H media. We found a significant IR absorption from He atoms (He-He-He CIA opacity) and a strong pressure distortion of the H2-He collision-induced absorption (CIA). We discuss the implication of these results for the interpretation of the spectra of cool stars.

  5. The distribution of saturated clusters in wetted granular materials

    Science.gov (United States)

    Li, Shuoqi; Hanaor, Dorian; Gan, Yixiang

    2017-06-01

    The hydro-mechanical behaviour of partially saturated granular materials is greatly influenced by the spatial and temporal distribution of liquid within the media. The aim of this paper is to characterise the distribution of saturated clusters in granular materials using an optical imaging method under different water drainage conditions. A saturated cluster is formed when a liquid phase fully occupies the pore space between solid grains in a localized region. The samples considered here were prepared by vibrating mono-sized glass beads to form closely packed assemblies in a rectangular container. A range of drainage conditions were applied to the specimen by tilting the container and employing different flow rates, and the liquid pressure was recorded at different positions in the experimental cell. The formation of saturated clusters during the liquid withdrawal processes is governed by three competing mechanisms arising from viscous, capillary, and gravitational forces. When the flow rate is sufficiently large and the gravity component is sufficiently small, the viscous force tends to destabilize the liquid front leading to the formation of narrow fingers of saturated material. As the water channels along these liquid fingers break, saturated clusters are formed inside the specimen. Subsequently, a spatial and temporal distribution of saturated clusters can be observed. We investigated the resulting saturated cluster distribution as a function of flow rate and gravity to achieve a fundamental understanding of the formation and evolution of such clusters in partially saturated granular materials. This study serves as a bridge between pore-scale behavior and the overall hydro-mechanical characteristics in partially saturated soils.

  6. Conjugate gradient type algorithms for frictional multi-contact problems: applications to granular materials

    OpenAIRE

    Renouf, Mathieu; Alart, Pierre

    2005-01-01

    International audience; This paper presents gradient type algorithms to solve frictional multi contact problems written as quasi optimization problems. A single loop scheme formally close to the classical conjugate gradient method is proposed with some adap tations of the iterate corrections and gradient projections. Since the convergence is difficult to prove, various tests in the field of granular media are performed with comparison with the non linear Gauss Seidel scheme.

  7. Numerical Algorithms for Two-Dimensional Dry Granular Flow with Deformable Elastic Grain

    Energy Technology Data Exchange (ETDEWEB)

    Boateng, H A; Elander, V; Jin, C; Li, Y; Vasquez, P; Fast, P

    2005-08-11

    The authors consider the dynamics of interacting elastic disks in the plane. This is an experimentally realizable two-dimensional model of dry granular flow where the stresses can be visualized using the photoelastic effect. As the elastic disks move in a vacuum, they interact through collisions with each other and with the surrounding geometry. Because of the finite propagation speed of deformations inside each grain it can be difficult to capture computationally even simple experiments involving just a few interacting grains. The goal of this project is to improve our ability to simulate dense granular flow in complex geometry. They begin this process by reviewing some past work, how they can improve upon previous work. the focus of this project is on capturing the elastic dynamics of each grain in an approximate, computationally tractable, model that can be coupled to a molecular dynamics scheme.

  8. Investigation of Heat Exchange Efficiency in the Heat Exchanger Waste Heat Recovery with Granular Nozzle

    Directory of Open Access Journals (Sweden)

    Boshkova I.L.

    2016-12-01

    Full Text Available The article analyzes the characteristics of the heat transfer process between the dispersed and gaseous medium for the moving and fixed layer of particulate material. The methods of calculus of thermal and hydraulic regimes of heat exchangers with a dense layer of particles were elaborated. The results of experimental studies of the process of heating of different kinds of granular material, intended for use as a nozzle in the recuperative heat exchanger. The influence of the height of heating chamber, the particle diameter on the output temperature of the granular material has been determined. The dependence of the temperature of the gas and solid components of the height of the nozzle has been presented.

  9. 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

  10. Sliding through a superlight granular medium.

    Science.gov (United States)

    Pacheco-Vázquez, F; Ruiz-Suárez, J C

    2009-12-01

    We explore the penetration dynamics of an intruder in a granular medium composed of expanded polystyrene spherical particles. Three features distinguish our experiment from others studied so far in granular physics: (a) the impact is horizontal, decoupling the effects of gravity and the drag force; (b) the density of the intruder rho(i) is up to 350 times larger than the density of the granular medium rho(m); and (c) the way the intruder moves through the material, sliding at the bottom of the column with small friction. Under these conditions we find that the final penetration D scales with (rho(i)/rho(m)) and the drag force Fd and D saturate with the height of the granular bed.

  11. Multiscale Phenomena in the Solid-Liquid Transition State of a Granular Material: Analysis, Modeling and Experimentation

    Science.gov (United States)

    2010-11-21

    Methods in Geomechanics 33 pp 1737-1768. Tordesillas, A, Shi, J and Muhlhaus, H (2009) “Non-coaxiality and force chain evolution” International...Buckling force chains in dense granular assemblies: physical and numerical experiments” Geomechanics and Geoengineering 4(1) pp 3-16. Tordesillas, A...J, Tshaikiwsky, T (2010) “Stress-dilatancy and force chain evolution”, International Journal of Numerical and Analytical Methods in Geomechanics DOI

  12. [Granular cell tumor of the larynx].

    Science.gov (United States)

    Modrzyński, M; Wróbel, B; Zawisza, E; Drozd, K

    1999-09-01

    Granular cell tumor is an unusual growth of probably neuroectodermal histogenesis, first reported by Abrikossoff in 1926 with the name of myoblastenmyoma. Authors described a case of a 54 year man with laryngeal seat of granular-cell myoblastoma. In this case Abrikossoff tumor was located in the right vocal chord. The tumor was treated successfully surgically by microlaryngoscopy. The etiology, clinical features and diagnostic difficulties are discussed.

  13. 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.

  14. 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.

  15. DISCRETE AND CONTINUUM MODELLING OF GRANULAR FLOW

    Institute of Scientific and Technical Information of China (English)

    H. P. Zhu; Y. H. WU; A. B. Yu

    2005-01-01

    This paper analyses three popular methods simulating granular flow at different time and length scales:discrete element method (DEM), averaging method and viscous, elastic-plastic continuum model. The theoretical models of these methods and their applications to hopper flows are discussed. It is shown that DEM is an effective method to study the fundamentals of granular flow at a particle or microscopic scale. By use of the continuum approach, granular flow can also be described at a continuum or macroscopic scale. Macroscopic quantities such as velocity and stress can be obtained by use of such computational method as FEM. However, this approach depends on the constitutive relationship of materials and ignores the effect of microscopic structure of granular flow. The combined approach of DEM and averaging method can overcome this problem. The approach takes into account the discrete nature of granular materials and does not require any global assumption and thus allows a better understanding of the fundamental mechanisms of granular flow. However, it is difficult to adapt this approach to process modelling because of the limited number of particles which can be handled with the present computational capacity, and the difficulty in handling non-spherical particles.Further work is needed to develop an appropriate approach to overcome these problems.

  16. An elastoplastic framework for granular materials becoming cohesive through mechanical densification. Part II - the formulation of elastoplastic coupling at large strain

    CERN Document Server

    Piccolroaz, Andrea; Gajo, Alessandro

    2010-01-01

    The two key phenomena occurring in the process of ceramic powder compaction are the progressive gain in cohesion and the increase of elastic stiffness, both related to the development of plastic deformation. The latter effect is an example of `elastoplastic coupling', in which the plastic flow affects the elastic properties of the material, and has been so far considered only within the framework of small strain assumption (mainly to describe elastic degradation in rock-like materials), so that it remains completely unexplored for large strain. Therefore, a new finite strain generalization of elastoplastic coupling theory is given to describe the mechanical behaviour of materials evolving from a granular to a dense state. The correct account of elastoplastic coupling and of the specific characteristics of materials evolving from a loose to a dense state (for instance, nonlinear --or linear-- dependence of the elastic part of the deformation on the forming pressure in the granular --or dense-- state) makes the...

  17. Granular filters for water treatment: heterogeneity and diagnostic tools

    DEFF Research Database (Denmark)

    Lopato, Laure Rose

    the last barrier against disinfection resistant protozoan pathogens and this has led to increased regulation of the filtration process. To be able to produce high-quality filtrate in a constant and reliable manner while meeting stricter drinking water guideline values, it is important to be able...... to be able to observe the physical state of the filter. The aim of this PhD study is to contribute to the understanding and optimization of the granular media filtration process. The focus of the work is to develop methodologies and diagnostic tools to analyze the physical state of rapid filters and improve....... Similarly, despite the importance of nitrification in groundwater treatment, the removal of ammonium and the determination of the kinetics of nitrification have been insufficiently researched in full-scale filters. A tool is developed to describe nitrification quantitatively on full-scale filters under real...

  18. Fluctuations of Internal Energy Flow in a Vibrated Granular Gas

    Science.gov (United States)

    Puglisi, Andrea; Visco, Paolo; Barrat, Alain; Trizac, Emmanuel; van Wijland, Frédéric

    2005-09-01

    The nonequilibrium fluctuations of power flux in a fluidized granular media have been recently measured in an experiment [Phys. Rev. Lett. 92, 164301 (2004)PRLTAO0031-900710.1103/PhysRevLett.92.164301], which was announced to be a verification of the fluctuation relation (FR) by Gallavotti and Cohen. An effective temperature was also identified and proposed to be a useful probe for such nonequilibrium systems. We explain these results in terms of a two-temperature Poisson process. Within this model, supported by independent molecular dynamics simulations, power flux fluctuations do not satisfy the FR and the nature of the effective temperature is clarified. In the pursuit of a hypothetical global quantity fulfilling the FR, this points to the need of considering candidates other than the power flux.

  19. Self-assembled granular towers

    Science.gov (United States)

    Pacheco-Vazquez, Felipe; Moreau, Florian; Vandewalle, Nicolas; Dorbolo, Stephan; GroupResearch; Applications in Statistical Physics Team

    2013-03-01

    When some water is added to sand, cohesion among the grains is induced. In fact, only 1% of liquid volume respect to the total pore space of the sand is necessary to built impressive sandcastles. Inspired on this experience, the mechanical properties of wet piles and sand columns have been widely studied during the last years. However, most of these studies only consider wet materials with less than 35% of liquid volume. Here we report the spontaneous formation of granular towers produced when dry sand is poured on a highly wet sand bed: The impacting grains stick on the wet grains due to instantaneous liquid bridges created during the impact. The grains become wet by the capillary ascension of water and the process continues, giving rise to stable narrow sand towers. Actually, the towers can reach the maximum theoretical limit of stability predicted by previous models, only expected for low liquid volumes. The authors would like to thank FNRS and Conacyt Mexico for financial support. FPV is a beneficiary of a movility grant from BELSPO/Marie Curie and the University of Liege.

  20. Driven fragmentation of granular gases.

    Science.gov (United States)

    Cruz Hidalgo, Raúl; Pagonabarraga, Ignacio

    2008-06-01

    The dynamics of homogeneously heated granular gases which fragment due to particle collisions is analyzed. We introduce a kinetic model which accounts for correlations induced at the grain collisions and analyze both the kinetics and relevant distribution functions these systems develop. The work combines analytical and numerical studies based on direct simulation Monte Carlo calculations. A broad family of fragmentation probabilities is considered, and its implications for the system kinetics are discussed. We show that generically these driven materials evolve asymptotically into a dynamical scaling regime. If the fragmentation probability tends to a constant, the grain number diverges at a finite time, leading to a shattering singularity. If the fragmentation probability vanishes, then the number of grains grows monotonously as a power law. We consider different homogeneous thermostats and show that the kinetics of these systems depends weakly on both the grain inelasticity and driving. We observe that fragmentation plays a relevant role in the shape of the velocity distribution of the particles. When the fragmentation is driven by local stochastic events, the long velocity tail is essentially exponential independently of the heating frequency and the breaking rule. However, for a Lowe-Andersen thermostat, numerical evidence strongly supports the conjecture that the scaled velocity distribution follows a generalized exponential behavior f(c) approximately exp(-cn) , with n approximately 1.2 , regarding less the fragmentation mechanisms.

  1. NMR measurement of the magnetic field correlation function in porous media.

    Science.gov (United States)

    Cho, H; Song, Yi-Qiao

    2008-01-18

    The structure factor provides a fundamental characterization of porous and granular materials as it is the key for solid crystals via measurements of x-ray and neutron scattering. Here, we demonstrate that the structure factor of the granular and porous media can be approximated by the pair correlation function of the inhomogeneous internal magnetic field, which arises from the susceptibility difference between the pore filling liquid and the solid matrix. In-depth understanding of the internal field is likely to contribute to further development of techniques to study porous and granular media.

  2. Mechanics of granular environments; Mecanique des milieux granulaires

    Energy Technology Data Exchange (ETDEWEB)

    Lanier, J. [Universite Joseph-Fourier, Grenoble I, 38 (France)

    2001-07-01

    This book aims at presenting different aspects of the behaviour of granular materials as encountered in natural environments (mainly soils), in industries involving the handling of granular products (cereals..) or powders (chemistry, metal industry..). It brings together the contributions of various specialists of physics and mechanics: mechanics of collisions between solids; gravity flows; grain flows; solid transport as example of two-phase granular flow; wave propagation inside a model of granular environment; propagation of waves in soils; enrockments and stability of rocky slopes; soils behaviour; coupled heat and mass transfers in granular environments; thermo-mechanical properties of granular environments. (J.S.)

  3. Constructing dense genetic linkage maps

    NARCIS (Netherlands)

    Jansen, J.; Jong, de A.G.; Ooijen, van J.W.

    2001-01-01

    This paper describes a novel combination of techniques for the construction of dense genetic linkage maps. The construction of such maps is hampered by the occurrence of even small proportions of typing errors. Simulated annealing is used to obtain the best map according to the optimality criterion:

  4. Method for dense packing discovery.

    Science.gov (United States)

    Kallus, Yoav; Elser, Veit; Gravel, Simon

    2010-11-01

    The problem of packing a system of particles as densely as possible is foundational in the field of discrete geometry and is a powerful model in the material and biological sciences. As packing problems retreat from the reach of solution by analytic constructions, the importance of an efficient numerical method for conducting de novo (from-scratch) searches for dense packings becomes crucial. In this paper, we use the divide and concur framework to develop a general search method for the solution of periodic constraint problems, and we apply it to the discovery of dense periodic packings. An important feature of the method is the integration of the unit-cell parameters with the other packing variables in the definition of the configuration space. The method we present led to previously reported improvements in the densest-known tetrahedron packing. Here, we use the method to reproduce the densest-known lattice sphere packings and the best-known lattice kissing arrangements in up to 14 and 11 dimensions, respectively, providing numerical evidence for their optimality. For nonspherical particles, we report a dense packing of regular four-dimensional simplices with density ϕ=128/219≈0.5845 and with a similar structure to the densest-known tetrahedron packing.

  5. Unconditional Continuous Variable Dense Coding

    CERN Document Server

    Ralph, T C

    2002-01-01

    We investigate the conditions under which unconditional dense coding can be achieved using continuous variable entanglement. We consider the effect of entanglement impurity and detector efficiency and discuss experimental verification. We conclude that the requirements for a strong demonstration are not as stringent as previously thought and are within the reach of present technology.

  6. Fluctuation-dissipation relations for motions of center of mass in driven granular fluids under gravity.

    Science.gov (United States)

    Wakou, Jun'ichi; Isobe, Masaharu

    2012-06-01

    We investigated the validity of fluctuation-dissipation relations in the nonequilibrium stationary state of fluidized granular media under gravity by two independent approaches, based on theory and numerical simulations. A phenomenological Langevin-type theory describing the fluctuation of center of mass height, which was originally constructed for a one-dimensional granular gas on a vibrating bottom plate, was generalized to any dimensionality, even for the case in which the vibrating bottom plate is replaced by a thermal wall. The theory predicts a fluctuation-dissipation relation known to be satisfied at equilibrium, with a modification that replaces the equilibrium temperature by an effective temperature defined by the center of mass kinetic energy. To test the validity of the fluctuation-dissipation relation, we performed extensive and accurate event-driven molecular dynamics simulations for the model system with a thermal wall at the bottom. The power spectrum and response function of the center of mass height were measured and closely compared with theoretical predictions. It is shown that the fluctuation-dissipation relation for the granular system is satisfied, especially in the high-frequency (short time) region, for a wide range of system parameters. Finally, we describe the relationship between systematic deviations in the low-frequency (long time) region and the time scales of the driven granular system.

  7. Convection and segregation in fluidised granular systems exposed to two-dimensional vibration

    Science.gov (United States)

    Windows-Yule, C. R. K.

    2016-03-01

    Convection and segregation in granular systems not only provide a rich phenomenology of scientifically interesting behaviours but are also crucial to numerous ‘real-world’ processes ranging from important and widely used industrial procedures to potentially cataclysmic geophysical phenomena. Simple, small-scale experimental or simulated test systems are often employed by researchers in order to gain an understanding of the fundamental physics underlying the behaviours of granular media. Such systems have been the subject of extensive research over several decades, with numerous system geometries and manners of producing excitation explored. Energy is commonly provided to granular assemblies through the application of vibration—the simplicity of the dynamical systems produced and the high degree of control afforded over their behaviour make vibrated granular beds a valuable canonical system by which to explore a diverse range of phenomena. Although a wide variety of vibrated systems have been explored in the existing literature, the vast majority are exposed to vibration along only a single spatial direction. In this paper, we study highly fluidised systems subjected to strong, multi-directional driving, providing a first insight into the dynamics and behaviours of these systems which may potentially hold valuable new information relevant to important industrial and natural processes. With a particular focus on the processes of convection and segregation, we analyse the various states and phase transitions exhibited by our system, detailing a number of previously unobserved dynamical phenomena and system states.

  8. Granular computing with multiple granular layers for brain big data processing.

    Science.gov (United States)

    Wang, Guoyin; Xu, Ji

    2014-12-01

    Big data is the term for a collection of datasets so huge and complex that it becomes difficult to be processed using on-hand theoretical models and technique tools. Brain big data is one of the most typical, important big data collected using powerful equipments of functional magnetic resonance imaging, multichannel electroencephalography, magnetoencephalography, Positron emission tomography, near infrared spectroscopic imaging, as well as other various devices. Granular computing with multiple granular layers, referred to as multi-granular computing (MGrC) for short hereafter, is an emerging computing paradigm of information processing, which simulates the multi-granular intelligent thinking model of human brain. It concerns the processing of complex information entities called information granules, which arise in the process of data abstraction and derivation of information and even knowledge from data. This paper analyzes three basic mechanisms of MGrC, namely granularity optimization, granularity conversion, and multi-granularity joint computation, and discusses the potential of introducing MGrC into intelligent processing of brain big data.

  9. Warm Dense Matter: An Overview

    Energy Technology Data Exchange (ETDEWEB)

    Kalantar, D H; Lee, R W; Molitoris, J D

    2004-04-21

    This document provides a summary of the ''LLNL Workshop on Extreme States of Materials: Warm Dense Matter to NIF'' which was held on 20, 21, and 22 February 2002 at the Wente Conference Center in Livermore, CA. The warm dense matter regime, the transitional phase space region between cold material and hot plasma, is presently poorly understood. The drive to understand the nature of matter in this regime is sparking scientific activity worldwide. In addition to pure scientific interest, finite temperature dense matter occurs in the regimes of interest to the SSMP (Stockpile Stewardship Materials Program). So that obtaining a better understanding of WDM is important to performing effective experiments at, e.g., NIF, a primary mission of LLNL. At this workshop we examined current experimental and theoretical work performed at, and in conjunction with, LLNL to focus future activities and define our role in this rapidly emerging research area. On the experimental front LLNL plays a leading role in three of the five relevant areas and has the opportunity to become a major player in the other two. Discussion at the workshop indicated that the path forward for the experimental efforts at LLNL were two fold: First, we are doing reasonable baseline work at SPLs, HE, and High Energy Lasers with more effort encouraged. Second, we need to plan effectively for the next evolution in large scale facilities, both laser (NIF) and Light/Beam sources (LCLS/TESLA and GSI) Theoretically, LLNL has major research advantages in areas as diverse as the thermochemical approach to warm dense matter equations of state to first principles molecular dynamics simulations. However, it was clear that there is much work to be done theoretically to understand warm dense matter. Further, there is a need for a close collaboration between the generation of verifiable experimental data that can provide benchmarks of both the experimental techniques and the theoretical capabilities

  10. Computational Granular Dynamics Models and Algorithms

    CERN Document Server

    Pöschel, Thorsten

    2005-01-01

    Computer simulations not only belong to the most important methods for the theoretical investigation of granular materials, but also provide the tools that have enabled much of the expanding research by physicists and engineers. The present book is intended to serve as an introduction to the application of numerical methods to systems of granular particles. Accordingly, emphasis is placed on a general understanding of the subject rather than on the presentation of the latest advances in numerical algorithms. Although a basic knowledge of C++ is needed for the understanding of the numerical methods and algorithms in the book, it avoids usage of elegant but complicated algorithms to remain accessible for those who prefer to use a different programming language. While the book focuses more on models than on the physics of granular material, many applications to real systems are presented.

  11. 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.

  12. Compaction dynamics of wet granular packings

    Science.gov (United States)

    Vandewalle, Nicolas; Ludewig, Francois; Fiscina, Jorge E.; Lumay, Geoffroy

    2013-03-01

    The extremely slow compaction dynamics of wet granular assemblies has been studied experimentally. The cohesion, due to capillary bridges between neighboring grains, has been tuned using different liquids having specific surface tension values. The characteristic relaxation time for compaction τ grows strongly with cohesion. A kinetic model, based on a free volume kinetic equations and the presence of a capillary energy barrier (due to liquid bridges), is able to reproduce quantitatively the experimental curves. This model allows one to describe the cohesion in wet granular packing. The influence of relative humidity (RH) on the extremely slow compaction dynamics of a granular assembly has also been investigated in the range 20 % - 80 % . Triboelectric and capillary condensation effects have been introduced in the kinetic model. Results confirm the existence of an optimal condition at RH ~ 45 % for minimizing cohesive interactions between glass beads.

  13. Ultrasound features of orbital granular cell tumor.

    Science.gov (United States)

    Ayres, Bernadete; Miller, Neil R; Eberhart, Charles G; Dibernardo, Cathy W

    2009-01-01

    The authors report the echographic characteristics of a rare orbital granular cell tumor and correlate these findings with histopathology. A 56-year-old woman presented with proptosis. Complete ophthalmic and ultrasound examinations were performed. Ultrasound revealed an oval, well-outlined orbital mass in the intraconal space with low-medium reflectivity and regular internal structure. An orbitotomy with complete excision of the tumor was performed. Histopathologic evaluation showed sheets and nests of cells with abundant eosinophilic and granular cytoplasm in a uniform distribution throughout the lesion. The echographic characteristics correlated well with the morphologic surgical findings and the histologic architecture. This is the first report describing the echographic characteristics of orbital granular cell tumor.

  14. 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...

  15. Tsunami generated by a granular collapse down a rough inclined plane

    CERN Document Server

    Viroulet, Sylvain; Kimmoun, Olivier

    2014-01-01

    In this Letter, we experimentally investigate the collapse of initially dry granular media into water and the subsequent impulse waves. We systematically characterize the influence of the slope angle and the granular material on the initial amplitude of the generated leading wave and the evolution of its amplitude during the propagation. The experiments show that whereas the evolution of the leading wave during the propagation is well predicted by a solution of the linearized Korteweg-de Vries equation, the generation of the wave is more complicated to describe. Our results suggest that the internal properties of the granular media and the interplay with the surrounding fluid are important parameters for the generation of waves at low velocity impacts. Moreover, the amplitude of the leading wave reaches a maximum value at large slope angle. The runout distance of the collapse is also shown to be smaller in the presence of water than under totally dry conditions. This study provides a first insight into tsunam...

  16. Utilization of granular solidification during terrestrial locomotion of hatchling sea turtles.

    Science.gov (United States)

    Mazouchova, Nicole; Gravish, Nick; Savu, Andrei; Goldman, Daniel I

    2010-06-23

    Biological terrestrial locomotion occurs on substrate materials with a range of rheological behaviour, which can affect limb-ground interaction, locomotor mode and performance. Surfaces like sand, a granular medium, can display solid or fluid-like behaviour in response to stress. Based on our previous experiments and models of a robot moving on granular media, we hypothesize that solidification properties of granular media allow organisms to achieve performance on sand comparable to that on hard ground. We test this hypothesis by performing a field study examining locomotor performance (average speed) of an animal that can both swim aquatically and move on land, the hatchling Loggerhead sea turtle (Caretta caretta). Hatchlings were challenged to traverse a trackway with two surface treatments: hard ground (sandpaper) and loosely packed sand. On hard ground, the claw use enables no-slip locomotion. Comparable performance on sand was achieved by creation of a solid region behind the flipper that prevents slipping. Yielding forces measured in laboratory drag experiments were sufficient to support the inertial forces at each step, consistent with our solidification hypothesis.

  17. Direct observation of dynamic shear jamming in dense suspensions

    Science.gov (United States)

    Peters, Ivo R.; Majumdar, Sayantan; Jaeger, Heinrich M.

    2016-04-01

    Liquid-like at rest, dense suspensions of hard particles can undergo striking transformations in behaviour when agitated or sheared. These phenomena include solidification during rapid impact, as well as strong shear thickening characterized by discontinuous, orders-of-magnitude increases in suspension viscosity. Much of this highly non-Newtonian behaviour has recently been interpreted within the framework of a jamming transition. However, although jamming indeed induces solid-like rigidity, even a strongly shear-thickened state still flows and thus cannot be fully jammed. Furthermore, although suspensions are incompressible, the onset of rigidity in the standard jamming scenario requires an increase in particle density. Finally, whereas shear thickening occurs in the steady state, impact-induced solidification is transient. As a result, it has remained unclear how these dense suspension phenomena are related and how they are connected to jamming. Here we resolve this by systematically exploring both the steady-state and transient regimes with the same experimental system. We demonstrate that a fully jammed, solid-like state can be reached without compression and instead purely with shear, as recently proposed for dry granular systems. This state is created by transient shear-jamming fronts, which we track directly. We also show that shear stress, rather than shear rate, is the key control parameter. From these findings we map out a state diagram with particle density and shear stress as variables. We identify discontinuous shear thickening with a marginally jammed regime just below the onset of full, solid-like jamming. This state diagram provides a unifying framework, compatible with prior experimental and simulation results on dense suspensions, that connects steady-state and transient behaviour in terms of a dynamic shear-jamming process.

  18. Inhomogeneous quasistationary state of dense fluids of inelastic hard spheres.

    Science.gov (United States)

    Fouxon, Itzhak

    2014-05-01

    We study closed dense collections of freely cooling hard spheres that collide inelastically with constant coefficient of normal restitution. We find inhomogeneous states (ISs) where the density profile is spatially nonuniform but constant in time. The states are exact solutions of nonlinear partial differential equations that describe the coupled distributions of density and temperature valid when inelastic losses of energy per collision are small. The derivation is performed without modeling the equations' coefficients that are unknown in the dense limit (such as the equation of state) using only their scaling form specific for hard spheres. Thus the IS is the exact state of this dense many-body system. It captures a fundamental property of inelastic collections of particles: the possibility of preserving nonuniform temperature via the interplay of inelastic cooling and heat conduction that generalizes previous results. We perform numerical simulations to demonstrate that arbitrary initial state evolves to the IS in the limit of long times where the container has the geometry of the channel. The evolution is like a gas-liquid transition. The liquid condenses in a vanishing part of the total volume but takes most of the mass of the system. However, the gaseous phase, which mass grows only logarithmically with the system size, is relevant because its fast particles carry most of the energy of the system. Remarkably, the system self-organizes to dissipate no energy: The inelastic decay of energy is a power law [1+t/t(c)](-2), where t(c) diverges in the thermodynamic limit. This is reinforced by observing that for supercritical systems the IS coincide in most of the space with the steady states of granular systems heated at one of the walls. We discuss the relation of our results to the recently proposed finite-time singularity in other container's geometries.

  19. Performance of Anammox granular sludge bed reactor started up with nitrifying granular sludge

    Institute of Scientific and Technical Information of China (English)

    ZHENG Ping; LIN Feng-mei; HU Bao-lan; CHEN Jian-song

    2004-01-01

    The anaerobic ammonia oxidation(Anammox) granular sludge bed reactor was started up successfully withnitrifying granular sludge. During the operation, the nitrifying granular sludge was gradually converted into Anammoxgranular sludge with good settling property and high conversion activity. The Anammox reactor worked well with theshortest HRT of 2.43 h. Under the condition that HRT was 6.39 h and influent concentration of ammonia and nitritewas 10 mmol/L, the removal of ammonia and nitrite was 97.17% and 100.00%, respectively. Corresponding

  20. Structural Transitions in Dense Networks

    CERN Document Server

    Lambiotte, R; Bhat, U; Redner, S

    2016-01-01

    We introduce an evolving network model in which a new node attaches to a randomly selected target node and also to each of its neighbors with probability $p$. The resulting network is sparse for $p<\\frac{1}{2}$ and dense (average degree increasing with number of nodes $N$) for $p\\geq \\frac{1}{2}$. In the dense regime, individual networks realizations built by this copying mechanism are disparate and not self-averaging. Further, there is an infinite sequence of structural anomalies at $p=\\frac{2}{3}$, $\\frac{3}{4}$, $\\frac{4}{5}$, etc., where the dependences on $N$ of the number of triangles (3-cliques), 4-cliques, undergo phase transitions. When linking to second neighbors of the target can occur, the probability that the resulting graph is complete---where all nodes are connected---is non-zero as $N\\to\\infty$.

  1. Holographic Renormalization in Dense Medium

    Directory of Open Access Journals (Sweden)

    Chanyong Park

    2014-01-01

    describes a dense medium at finite temperature, is investigated in this paper. In a dense medium, two different thermodynamic descriptions are possible due to an additional conserved charge. These two different thermodynamic ensembles are classified by the asymptotic boundary condition of the bulk gauge field. It is also shown that in the holographic renormalization regularity of all bulk fields can reproduce consistent thermodynamic quantities and that the Bekenstein-Hawking entropy is nothing but the renormalized thermal entropy of the dual field theory. Furthermore, we find that the Reissner-Nordström AdS black brane is dual to a theory with conformal matter as expected, whereas a charged black brane with a nontrivial dilaton profile is mapped to a theory with nonconformal matter although its leading asymptotic geometry still remains as AdS space.

  2. Dilatons for Dense Hadronic Matter

    CERN Document Server

    Lee, Hyun Kyu

    2009-01-01

    The idea that the explicit breaking of scale invariance by the trace anomaly of QCD can be rephrased as a spontaneous breaking has been recently exploited to capture the low-energy strong interaction dynamics of dense (and also hot) matter in terms of two dilaton fields, the "soft" (chi_s) and the "hard" (chi_h) fields, in the frame work of the hidden local gauge symmetry. In the Freund-Nambu model, the spontaneous symmetry breaking of scale symmetry is induced by an explicitly breaking term, while the spontaneous symmetry breaking is possible in the flat potential model which is scale symmetric. We discuss the interplay of the soft and hard dilatons using the spontaneously broken scale symmetry schemes and uncover a novel structure of dense matter hitherto unexplored.

  3. Impulse absorption by horizontal magnetic granular chain

    Directory of Open Access Journals (Sweden)

    Dingxin Leng

    2016-02-01

    Full Text Available The granular medium is known as a protecting material for shock mitigation. We study the impulse absorption of an alignment of magnetic spheres placed horizontally under a non-uniform magnetic field. The phenomenon of the wave dispersion is presented. This system can absorb 85% ∼ 95% (88% ∼ 98% of the incident peak force (energy under the applied magnetic field strength in 0.1 T ∼ 1.0 T. The shock attenuation capacities are enhanced by the increment of field strength. With an intelligent control system, it is conceivable that the magnetic granular chain may offer possibilities in developing adaptive shock protectors.

  4. 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.

  5. A kinetic approach to granular gases

    OpenAIRE

    Puglisi, A.; Loreto, V.; Marconi, U. Marini Bettolo; Vulpiani, A.

    1998-01-01

    We address the problem of the so-called ``granular gases'', i.e. gases of massive particles in rapid movement undergoing inelastic collisions. We introduce a class of models of driven granular gases for which the stationary state is the result of the balance between the dissipation and the random forces which inject energies. These models exhibit a genuine thermodynamic limit, i.e. at fixed density the mean values of kinetic energy and dissipated energy per particle are independent of the num...

  6. Challenges in Predicting Planetary Granular Mechanics

    Science.gov (United States)

    Metzger, Philip T.

    2005-01-01

    Through the course of human history, our needs in agriculture, habitat construction, and resource extraction have driven us to gain more experience working with the granular materials of planet Earth than with any other type of substance in nature, with the possible exception being water. Furthermore, throughout the past two centuries we have seen a dramatic and ever growing interest among scientists and engineers to understand and predict both its static and rheological properties. Ironically, however, despite this wealth of experience we still do not have a fundamental understanding of the complex physical phenomena that emerge even as just ordinary sand is shaken, squeezed or poured. As humanity is now reaching outward through the solar system, not only robotic ally but also with our immediate human presence, the need to understand and predict granular mechanics has taken on a new dimension. We must learn to farm, build and mine the regoliths of other planets where the environmental conditions are different than on Earth, and we are rapidly discovering that the effects of these environmental conditions are not trivial. Some of the relevant environmental features include the regolith formation processes throughout a planet's geologic and hydrologic history, the unknown mixtures of volatiles residing within the soil, the relative strength of gravitation, d the atm9spheric pressure and its seasonal variations. The need to work with soils outside our terrestrial experience base provides us with both a challenge and an opportunity. The challenge is to learn how to extrapolate our experience into these new planetary conditions, enabling the engineering decisions that are needed right now as we take the next few steps in solar system exploration. The opportunity is to use these new planetary environments as laboratories that will help us to see granular mechanics in new ways, to challenge our assumptions, and to help us finally unravel the elusive physics that lie

  7. Granular Impact Dynamics: Acoustics and Fluctuations

    CERN Document Server

    Clark, Abram H

    2012-01-01

    In the corresponding fluid dynamics video, created for the APS DFD 2012 Gallery of Fluid Motion, we show high-speed videos of 2D granular impact experiments, where an intruder strikes a collection of bidisperse photoelastic disks from above. We discuss the force beneath the intruder, which is strongly fluctuating in space and time. These fluctuations correspond to acoustic pulses which propagate into the medium. Analysis shows that this process, in our experiments, is dominated by collisions with grain clusters. The energy from these collisions is carried into the granular medium along networks of grains, where is it dissipated.

  8. 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...

  9. The cerebellar Golgi cell and spatiotemporal organization of granular layer activity

    Directory of Open Access Journals (Sweden)

    Egidio eD‘Angelo

    2013-05-01

    Full Text Available The cerebellar granular layer has been suggested to perform a complex spatiotemporal reconfiguration of incoming mossy fiber signals. Central to this role is the inhibitory action exerted by Golgi cells over granule cells: Golgi cells inhibit granule cells through double feedforward and feedback inhibitory loops and generate a broad lateral inhibition that extends beyond the afferent synaptic field. This characteristic connectivity has recently been investigated in great detail and been correlated with specific functional properties of the neuron. These include theta-frequency pacemaking, network entrainment into coherent oscillations and phase resetting. Important advances have also been made in terms of determining the membrane and synaptic properties of the neuron, and clarifying the mechanisms of activation by input bursts. Moreover, voltage sensitive dye imaging and multi-electrode array recordings, combined with mathematical simulations based on realistic computational models, have improved our understanding of the impact of Golgi cell activity on granular layer circuit computations. These investigations have highlighted the critical role of Golgi cells in: generating dense clusters of granule cell activity organized in center-surround structures, implementing combinatorial operations on multiple mossy fiber inputs, regulating transmission gain and cut-off frequency, controlling spike timing and burst transmission, and determining the sign, intensity and extension of long-term synaptic plasticity at the mossy fiber-granule cell relay. This review considers recent advances in the field, highlighting the functional implications of Golgi cells for granular layer network computation and indicating new challenges for cerebellar research.

  10. Onset of Stationary Flows of a Cohesive Granular Material in a Channel

    Science.gov (United States)

    de Ryck, A.; Louisnard, O.

    The handling of bulk materials and powders in process engineering remains an important issue. To obtain reliable gravitational flows, starting and remaining stationary, the hoppers and transport channels must be designed at a scale appropriate for the friction and cohesive properties of the granular material. To describe such dense flows (the interaction with the surrounding ambient fluid is negligible compared to the weight of the particles and interparticles forces), they can be modelled by continuum mechanics, associated with a constitutive equation taking into account the friction behaviour (Mohr-Coulomb or Druger-Prager plasticity criterion). We use here the rheology proposed by Jop et al. (Nature 441: 727-730, 2006) which combines this with an associated flow rule (co-linearity of the stress and strain tensors) (Jenike, Powder Technol. 50: 229-236, 1987) and a viscous dependency of the coefficient of friction on the strain (Da Cruz et al., Phys. Rev. E 72: 021309, 2005).Using the method of characteristics to describe the flow structure (de Ryck, Granular Matter 10: 361-367, 2008), we deduce the minimal slope to obtain a stationary flow of cohesive granular materials on a finite width channel, whose lateral walls are rough or smooth. We also obtain the depth of the flow (maximal at the centre of the channel). In the case of weak cohesive materials, these results are formulated with simple analytical expressions.

  11. 76 FR 39896 - Granular Polytetrafluoroethylene Resin From Italy

    Science.gov (United States)

    2011-07-07

    ... COMMISSION Granular Polytetrafluoroethylene Resin From Italy Determination On the basis of the record \\1... antidumping duty order on granular polytetrafluoroethylene resin from Italy would be likely to lead to... Granular Polytetrafluoroethylene Resin from Italy: Investigation No. 731-TA-385 (Third Review). By order...

  12. Mechanical and Structural Behavior of Granular Material Packed Beds for Space Life Support System Applications

    Science.gov (United States)

    Malla, Ramesh B.; Anandakumar, Ganesh

    2005-01-01

    Long-term human mission to space, such as living in International Space Station (ISS), Lunar, and Martian bases, and travel to Mars, must m ake use of Advanced Life Support Systems (ALSS) to generate and recycle critical life supporting elements like oxygen and water. Oxygen Gen eration Assembly (OGA) and Water Processor Assembly (WPA), critical c omponents of ALSS, make use of series of granular material packed beds for generation and recycling of oxygen and water. Several granular m aterials can be used for generation, recycling, processing and recovery of oxygen and water. For example, they may include soft bed media, e.g. ion exchange resins for oxygen generation assembly and hard bed media such as, activated alumina, magchem (Magnesium oxide) and activa ted carbon to remove organic species like ethanol, methanol, and urea from wastewater in Water recovery/processing assembly. These beds are generally packed using a plate-spring mechanism to provide sufficien t compaction to the bed media throughout the course of operation. This paper presents results from an experimental study of a full-scale, 3 8.1 cm (15 inches) long and 3.7 cm (1.44 inches) diameter. activated alumina bed enclosed in a cylinder determining its force-displacement behavior, friction mobilizing force, and axial normal stress distribu tion under various axially applied loads and at different levels of packing. It is observed that force-displacement behavior is non-linear for low compaction level and becomes linear with increase in compaction of the bed media. Axial normal stress distribution along the length of the bed media decreased non-linearly with increase in depth from the loading end of the granular media. This paper also presents experimental results on the amount of particulates generated corresponding to various compaction levels. Particulates generated from each of the tests were measured using standard US sieves. It was found that the p articulates and the overall displacement of

  13. Assessment of bacterial and structural dynamics in aerobic granular biofilms

    Directory of Open Access Journals (Sweden)

    David G. Weissbrodt

    2013-07-01

    Full Text Available Aerobic granular sludge is based on self-granulated flocs forming mobile biofilms with a gel-like consistence. Bacterial and structural dynamics from flocs to granules were followed in anaerobic-aerobic sequencing batch reactors fed with synthetic wastewater, namely a bubble column (BC-SBR operated under wash-out conditions for fast granulation, and two stirred-tank enrichments of Accumulibacter (PAO-SBR and Competibacter (GAO-SBR operated at steady-state. In the BC-SBR, granules formed within two weeks by swelling of Zoogloea colonies around flocs, developing subsequently smooth zoogloeal biofilms. However, Zoogloea predominance (37-79% led to deteriorated nutrient removal during the first months of reactor operation. Upon maturation, improved nitrification (80-100%, nitrogen removal (43-83%, and high but unstable dephosphatation (75-100% were obtained. Proliferation of dense clusters of nitrifiers, Accumulibacter, and Competibacter from granule cores outwards resulted in heterogeneous bioaggregates, inside which only low abundance Zoogloea (<5% were detected in biofilm interstices. The presence of different extracellular glycoconjugates detected by fluorescence lectin-binding analysis showed the complex nature of the intracellular matrix of these granules. In the PAO-SBR, granulation occurred within two months with abundant and active Accumulibacter populations (56±10% that were selected under full anaerobic uptake of volatile fatty acids and that aggregated as dense clusters within heterogeneous granules. Flocs self-granulated in the GAO-SBR after 480 days during a period of over-aeration caused by biofilm growth on the oxygen sensor. Granules were dominated by heterogeneous clusters of Competibacter (37±11%. Zoogloea were never abundant in biomass of both PAO- and GAO-SBRs. This study showed that Zoogloea, Accumulibacter, and Competibacter affiliates can form granules, and that the granulation mechanisms rely on the dominant population

  14. Assessment of bacterial and structural dynamics in aerobic granular biofilms

    Science.gov (United States)

    Weissbrodt, David G.; Neu, Thomas R.; Kuhlicke, Ute; Rappaz, Yoan; Holliger, Christof

    2013-01-01

    Aerobic granular sludge (AGS) is based on self-granulated flocs forming mobile biofilms with a gel-like consistence. Bacterial and structural dynamics from flocs to granules were followed in anaerobic-aerobic sequencing batch reactors (SBR) fed with synthetic wastewater, namely a bubble column (BC-SBR) operated under wash-out conditions for fast granulation, and two stirred-tank enrichments of Accumulibacter (PAO-SBR) and Competibacter (GAO-SBR) operated at steady-state. In the BC-SBR, granules formed within 2 weeks by swelling of Zoogloea colonies around flocs, developing subsequently smooth zoogloeal biofilms. However, Zoogloea predominance (37–79%) led to deteriorated nutrient removal during the first months of reactor operation. Upon maturation, improved nitrification (80–100%), nitrogen removal (43–83%), and high but unstable dephosphatation (75–100%) were obtained. Proliferation of dense clusters of nitrifiers, Accumulibacter, and Competibacter from granule cores outwards resulted in heterogeneous bioaggregates, inside which only low abundance Zoogloea (<5%) were detected in biofilm interstices. The presence of different extracellular glycoconjugates detected by fluorescence lectin-binding analysis showed the complex nature of the intracellular matrix of these granules. In the PAO-SBR, granulation occurred within two months with abundant and active Accumulibacter populations (56 ± 10%) that were selected under full anaerobic uptake of volatile fatty acids and that aggregated as dense clusters within heterogeneous granules. Flocs self-granulated in the GAO-SBR after 480 days during a period of over-aeration caused by biofilm growth on the oxygen sensor. Granules were dominated by heterogeneous clusters of Competibacter (37 ± 11%). Zoogloea were never abundant in biomass of both PAO- and GAO-SBRs. This study showed that Zoogloea, Accumulibacter, and Competibacter affiliates can form granules, and that the granulation mechanisms rely on the dominant

  15. 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

  16. Fiber bundle models for stress release and energy bursts during granular shearing

    Science.gov (United States)

    Michlmayr, Gernot; Or, Dani; Cohen, Denis

    2012-12-01

    Fiber bundle models (FBMs) offer a versatile framework for representing transitions from progressive to abrupt failure in disordered material. We report a FBM-based description of mechanical interactions and associated energy bursts during shear deformation of granular materials. For strain-controlled shearing, where elements fail in a sequential order, we present analytical expressions for strain energy release and failure statistics. Results suggest that frequency-magnitude characteristics of fiber failure vary considerably throughout progressive shearing. Predicted failure distributions were in good agreement with experimentally observed shear stress fluctuations and associated bursts of acoustic emissions. Experiments also confirm a delayed release of acoustic emission energy relative to shear stress buildup, as anticipated by the model. Combined with data-rich acoustic emission measurements, the modified FBM offers highly resolved contact-scale insights into granular media dynamics of shearing processes.

  17. Percolation study for the capillary ascent of a liquid through a granular soil

    CERN Document Server

    Cárdenas-Barrantes, M A; Araujo, N A M

    2016-01-01

    Capillary rise plays a crucial role in the construction of road embankments in flood zones, where hydrophobic compounds are added to the soil to suppress the rising of water and avoid possible damage of the pavement. Water rises through liquid bridges, menisci and trimers, whose width and connectivity depends on the maximal half-length {\\lambda} of the capillary bridges among grains. Low {\\lambda} generate a disconnect structure, with small clusters everywhere. On the contrary, for high {\\lambda}, create a percolating cluster of trimers and enclosed volumes that form a natural path for capillary rise. Hereby, we study the percolation transition of this geometric structure as a function of {\\lambda} on a granular media of monodisperse spheres in a random close packing. We determine both the percolating threshold {\\lambda}_{c} = (0.049 \\pm 0.004)R (with R the radius of the granular spheres), and the critical exponent of the correlation length {\

  18. Influence of loading pulse duration on dynamic load transfer in a simulated granular medium

    Science.gov (United States)

    Shukla, A.; Sadd, M. H.; Xu, Y.; Tai, Q. M.

    1993-11-01

    AN EXPERIMENTAL and numerical investigation was conducted to study the dynamic response of granular media when subjected to impact loadings with different periods or wavelengths. The granular medium was simulated by a one-dimensional assembly of circular disks arranged in a straight single chain. In the experimental study, the dynamic loading was produced using projectile impact from a gas gun onto one end of the granular assembly, and the measured wave signal was collected using strain gages. The numerical simulations were conducted using the distinct element method. It was found from the experiments and numerical simulations that input waves with a short period (τ ≈ 90 μs) will propagate in this granular medium with little waveform change under steady amplitude attenuation ; whereas longer waves (τ $̆200 μs) will propagate with significant waveform dispersion. For these longer wavelength signals, the smooth waveform will undergo separation into a series of short oscillatory signals, and this rearrangement of energy allows a portion of the transmitted signal to increase in amplitude during the initial phases of propagation. Thus the granular medium acts as a nonlinear wave guide, and local microstructure and contact nonlinearity will allow input signals of sufficiently long wavelength to excite resonant sub-units of the medium to produce this observed ringing separation. Following a modeling scheme originally proposed by NESTERENKO[J. Appl. Mech. Tech. Phys. 5,733 (1983)], a nonlinear wave equation model was developed which is related to soliton dynamics and leads to travelling wave solutions of specific wavelength found in our experimental and numerical studies.

  19. Synthesis and cytotoxicity evaluation of granular magnesium substituted -tricalcium phosphate

    Directory of Open Access Journals (Sweden)

    Debora dos Santos TAVARES

    2013-03-01

    Full Text Available Objective The aim of this study was to produce dense granules of tricalcium phosphate (β-TCP and magnesium (Mg substituted β-TCP, also known as β-TCMP (Mg/Ca=0.15 mol, in order to evaluate the impact of Mg incorporation on the physicochemical parameters and in vitro biocompatibility of this novel material. Material and Methods The materials were characterized using X-ray diffraction (XRD, infrared spectroscopy (FTIR, electron microscopy and inductively coupled plasma (ICP. Biocompatibility was assayed according to ISO 10993-12:2007 and 7405:2008, by two different tests of cell survival and integrity (XTT and CVDE. Results The XRD profile presented the main peaks of β-TCP (JCPDS 090169 and β-TCMP (JCPDS 130404. The characteristic absorption bands of TCP were also identified by FTIR. The ICP results of β-TCMP granules extract showed a precipitation of calcium and release of Mg into the culture medium. Regarding the cytotoxicity assays, β-TCMP dense granules did not significantly affect the mitochondrial activity and relative cell density in relation to β-TCP dense granules, despite the release of Mg from granules into the cell culture medium. Conclusion β-TCMP granules were successfully produced and were able to release Mg into media without cytotoxicity, indicating the suitability of this promising material for further biological studies on its adequacy for bone therapy.

  20. 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.

  1. A Stochastic Description of Transition Between Granular Flow States

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Two-dimensional granular flow in a channel with small exit is studied by molecular dynamics simulations. We Erstly 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 How state to dense Bow 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 How 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.

  2. Active dry granular flows: Rheology and rigidity transitions

    Science.gov (United States)

    Peshkov, Anton; Claudin, Philippe; Clément, Eric; Andreotti, Bruno

    2016-10-01

    The constitutive relations of a dense granular flow composed of self-propelling frictional hard particles are investigated by means of DEM numerical simulations. We show that the rheology, which relates the dynamical friction μ and the volume fraction ϕ to the inertial number I, depends on a dimensionless number A , which compares the active force to the confining pressure. Two liquid/solid transitions —in the Maxwell rigidity sense— are observed. As soon as the activity is turned on, the packing becomes an “active solid” with a mean number of particle contacts larger than the isostatic value. The quasi-static values of μ and ϕ decrease with A . At a finite value of the activity At , corresponding to the isostatic condition, a second “active rigidity transition” is observed beyond which the quasi-static values of the friction vanishes and the rheology becomes Newtonian. For A>At , we provide evidence for a highly intermittent dynamics of this “active fluid”.

  3. Discrete element modelling of granular materials

    NARCIS (Netherlands)

    Van Baars, S.

    1996-01-01

    A new model is developed by the author, which does not use the equations of motion but the equations of equilibrium to describe granular materials. The numerical results show great similarities with reality and can generally be described by an advanced Mohr-Coulomb model. However, many contacts betw

  4. Micromechanical study of plasticity of granular materials

    NARCIS (Netherlands)

    Kruyt, N.P.

    2010-01-01

    Plastic deformation of granular materials is investigated from the micromechanical viewpoint, in which the assembly of particles and interparticle contacts is considered as a mechanical structure. This is done in three ways. Firstly, by investigating the degree of redundancy of the system by compari

  5. Localized fluidization in a granular medium.

    Science.gov (United States)

    Philippe, P; Badiane, M

    2013-04-01

    We present here experimental results on the progressive development of a fluidized zone in a bed of grains, immersed in a liquid, under the effect of a localized upward flow injected through a small orifice at the bottom of the bed. Visualization inside the model granular medium consisting of glass beads is made possible by the combined use of two optical techniques: refractive index matching between the liquid and the beads and planar laser-induced fluorescence. Gradually increasing the injection rate, three regimes are successively observed: static bed, fluidized cavity that does not open to the upper surface of the granular bed, and finally fluidization over the entire height of the granular bed inside a fluidized chimney. The phase diagram is plotted and partially interpreted using a model previously developed by Zoueshtiagh and Merlen [F. Zoueshtiagh and A. Merlen, Phys. Rev. E 75, 053613 (2007)]. A typical sequence, where the flow rate is first increased and then decreased back to zero, reveals a strong hysteretic behavior since the stability of the fluidized cavity is considerably strengthened during the defluidization phase. This effect can be explained by the formation of force arches within the granular packing when the chimney closes up at the top of the bed. A study of the expansion rate of the fluidized cavity was also conducted as well as the analysis of the interaction between two injection orifices with respect to their spacing.

  6. Experimental velocity distributions in a granular submonolayer

    Science.gov (United States)

    Cadillo-Martínez, Alejandra T.; Sánchez, Rodrigo

    2017-01-01

    Experimental speed distributions are obtained for driven granular submonolayers of binary mixtures of single spheres and dimers of spheres. The results are well-described by a distribution originally developed for a single-species one-dimensional system. This suggests that such a distribution may be extended to other mixtures such as systems exhibiting aggregation and dissociation.

  7. Scales and kinetics of granular flows.

    Science.gov (United States)

    Goldhirsch, I.

    1999-09-01

    When a granular material experiences strong forcing, as may be the case, e.g., for coal or gravel flowing down a chute or snow (or rocks) avalanching down a mountain slope, the individual grains interact by nearly instantaneous collisions, much like in the classical model of a gas. The dissipative nature of the particle collisions renders this analogy incomplete and is the source of a number of phenomena which are peculiar to "granular gases," such as clustering and collapse. In addition, the inelasticity of the collisions is the reason that granular gases, unlike atomic ones, lack temporal and spatial scale separation, a fact manifested by macroscopic mean free paths, scale dependent stresses, "macroscopic measurability" of "microscopic fluctuations" and observability of the effects of the Burnett and super-Burnett "corrections." The latter features may also exist in atomic fluids but they are observable there only under extreme conditions. Clustering, collapse and a kinetic theory for rapid flows of dilute granular systems, including a derivation of boundary conditions, are described alongside the mesoscopic properties of these systems with emphasis on the effects, theoretical conclusions and restrictions imposed by the lack of scale separation. (c) 1999 American Institute of Physics.

  8. Anomalous intruder response in diverse granular systems

    NARCIS (Netherlands)

    Oyarte Galvez, Loreto Alejandra

    2017-01-01

    The definition of granular matter is extremely broad; any collection of conglomeration of particles larger than 100 micrometers can be considered as part of this group, and virtually the entire universe is composed of them. Examples are found in many fields, e.g. in nature (dunes, avalanches,

  9. On the granular stress-geometry equation

    Science.gov (United States)

    DeGiuli, Eric; Schoof, Christian

    2014-01-01

    Using discrete calculus, we derive the missing stress-geometry equation for rigid granular materials in two dimensions, in the mean-field approximation. We show that i) the equation imposes that the voids cannot carry stress, ii) stress transmission is generically elliptic and has a quantitative relation to anisotropic elasticity, and iii) the packing fabric plays an essential role.

  10. Granular materials interacting with thin flexible rods

    Science.gov (United States)

    Neto, Alfredo Gay; Campello, Eduardo M. B.

    2017-04-01

    In this work, we develop a computational model for the simulation of problems wherein granular materials interact with thin flexible rods. We treat granular materials as a collection of spherical particles following a discrete element method (DEM) approach, while flexible rods are described by a large deformation finite element (FEM) rod formulation. Grain-to-grain, grain-to-rod, and rod-to-rod contacts are fully permitted and resolved. A simple and efficient strategy is proposed for coupling the motion of the two types (discrete and continuum) of materials within an iterative time-stepping solution scheme. Implementation details are shown and discussed. Validity and applicability of the model are assessed by means of a few numerical examples. We believe that robust, efficiently coupled DEM-FEM schemes can be a useful tool to the simulation of problems wherein granular materials interact with thin flexible rods, such as (but not limited to) bombardment of grains on beam structures, flow of granular materials over surfaces covered by threads of hair in many biological processes, flow of grains through filters and strainers in various industrial segregation processes, and many others.

  11. Granular avalanches down inclined and vibrated planes

    Science.gov (United States)

    Gaudel, Naïma; Kiesgen de Richter, Sébastien; Louvet, Nicolas; Jenny, Mathieu; Skali-Lami, Salaheddine

    2016-09-01

    In this article, we study granular avalanches when external mechanical vibrations are applied. We identify conditions of flow arrest and compare with the ones classically observed for nonvibrating granular flows down inclines [Phys. Fluids 11, 542 (1999), 10.1063/1.869928]. We propose an empirical law to describe the thickness of the deposits with the inclination angle and the vibration intensity. The link between the surface velocity and the depth of the flow highlights a competition between gravity and vibrations induced flows. We identify two distinct regimes: (a) gravity-driven flows at large angles where vibrations do not modify dynamical properties but the deposits (scaling laws in this regime are in agreement with the literature for nonvibrating granular flows) and (b) vibrations-driven flows at small angles where no flow is possible without applied vibrations (in this last regime, the flow behavior can be properly described by a vibration induced activated process). We show, in this study, that granular flows down inclined planes can be finely tuned by external mechanical vibrations.

  12. Random packing of colloids and granular matter

    NARCIS (Netherlands)

    Wouterse, A.

    2008-01-01

    This thesis deals with the random packing of colloids and granular matter. A random packing is a stable disordered collection of touching particles, without long-range positional and orientational order. Experimental random packings of particles with the same shape but made of different materials sh

  13. Mechanical properties of wet granular materials

    Energy Technology Data Exchange (ETDEWEB)

    Fournier, Z; Geromichalos, D; Herminghaus, S; Kohonen, M M; Mugele, F; Scheel, M; Schulz, M; Schulz, B; Schier, Ch; Seemann, R; Skudelny, A

    2005-03-09

    We elaborate on the impact of liquids upon the mechanical properties of granular materials. We find that most of the experimental and simulation results may be accounted for by a simple model assuming frictionless, spherical grains, with a hysteretic attractive interaction between neighbouring grains due to capillary forces.

  14. Granular materials interacting with thin flexible rods

    Science.gov (United States)

    Neto, Alfredo Gay; Campello, Eduardo M. B.

    2016-01-01

    In this work, we develop a computational model for the simulation of problems wherein granular materials interact with thin flexible rods. We treat granular materials as a collection of spherical particles following a discrete element method (DEM) approach, while flexible rods are described by a large deformation finite element (FEM) rod formulation. Grain-to-grain, grain-to-rod, and rod-to-rod contacts are fully permitted and resolved. A simple and efficient strategy is proposed for coupling the motion of the two types (discrete and continuum) of materials within an iterative time-stepping solution scheme. Implementation details are shown and discussed. Validity and applicability of the model are assessed by means of a few numerical examples. We believe that robust, efficiently coupled DEM-FEM schemes can be a useful tool to the simulation of problems wherein granular materials interact with thin flexible rods, such as (but not limited to) bombardment of grains on beam structures, flow of granular materials over surfaces covered by threads of hair in many biological processes, flow of grains through filters and strainers in various industrial segregation processes, and many others.

  15. Granular cell tumour of the urinary bladder

    Directory of Open Access Journals (Sweden)

    Christoph von Klot

    2012-04-01

    Full Text Available With only 16 cases reported in the literature, the mostly benign granular cell tumour of the urinary bladder is exceptionally rare. We present the case of a 68-year old patient with one of these lesions demonstrating our histological findings including several immunohistochemical stainings used to differentiate between other more common entities.

  16. Order and instabilities in dense bacterial colonies

    Science.gov (United States)

    Tsimring, Lev

    2012-02-01

    The structure of cell colonies is governed by the interplay of many physical and biological factors, ranging from properties of surrounding media to cell-cell communication and gene expression in individual cells. The biomechanical interactions arising from the growth and division of individual cells in confined environments are ubiquitous, yet little work has focused on this fundamental aspect of colony formation. By combining experimental observations of growing monolayers of non-motile strain of bacteria Escherichia coli in a shallow microfluidic chemostat with discrete-element simulations and continuous theory, we demonstrate that expansion of a dense colony leads to rapid orientational alignment of rod-like cells. However, in larger colonies, anisotropic compression may lead to buckling instability which breaks perfect nematic order. Furthermore, we found that in shallow cavities feedback between cell growth and mobility in a confined environment leads to a novel cell streaming instability. Joint work with W. Mather, D. Volfson, O. Mondrag'on-Palomino, T. Danino, S. Cookson, and J. Hasty (UCSD) and D. Boyer, S. Orozco-Fuentes (UNAM, Mexico).

  17. Constructing Dense Graphs with Unique Hamiltonian Cycles

    Science.gov (United States)

    Lynch, Mark A. M.

    2012-01-01

    It is not difficult to construct dense graphs containing Hamiltonian cycles, but it is difficult to generate dense graphs that are guaranteed to contain a unique Hamiltonian cycle. This article presents an algorithm for generating arbitrarily large simple graphs containing "unique" Hamiltonian cycles. These graphs can be turned into dense graphs…

  18. Granular analyzing of weapon SoS demand description

    Institute of Scientific and Technical Information of China (English)

    Zhao Qingsong; Yang Kewei; Chen Yingwu; Li Mengjun

    2009-01-01

    The systematism of weapon combat is the typical characteristic of a modern battlefield. The process of combat is complex and the demand description of weapon system of systems (SOS) is difficult. Granular analyzing is an important method for solving the complex problem in the world. Granular thinking is introduced into the demand description of weapon SoS. Granular computing and granular combination based on a relation of compatibility is proposed. Based on the level of degree and degree of detail, the granular resolution of weapon SoS is defined and an example is illustrated at the end.

  19. Granular flow over inclined channels with constrictions

    Science.gov (United States)

    Tunuguntla, Deepak; Weinhart, Thomas; Thornton, Anthony; Bokhove, Onno

    2013-04-01

    Study of granular flows down inclined channels is essential in understanding the dynamics of natural grain flows like landslides and snow avalanches. As a stepping stone, dry granular flow over an inclined channel with a localised constriction is investigated using both continuum methods and particle simulations. Initially, depth-averaged equations of motion (Savage & Hutter 1989) containing an unknown friction law are considered. The shallow-layer model for granular flows is closed with a friction law obtained from particle simulations of steady flows (Weinhart et al. 2012) undertaken in the open source package Mercury DPM (Mercury 2010). The closed two-dimensional (2D) shallow-layer model is then width-averaged to obtain a novel one-dimensional (1D) model which is an extension of the one for water flows through contraction (Akers & Bokhove 2008). Different flow states are predicted by this novel one-dimensional theory. Flow regimes with distinct flow states are determined as a function of upstream channel Froude number, F, and channel width ratio, Bc. The latter being the ratio of the channel exit width and upstream channel width. Existence of multiple steady states is predicted in a certain regime of F - Bc parameter plane which is in agreement with experiments previously undertaken by (Akers & Bokhove 2008) and for granular flows (Vreman et al. 2007). Furthermore, the 1D model is verified by solving the 2D shallow granular equations using an open source discontinuous Galerkin finite element package hpGEM (Pesch et al. 2007). For supercritical flows i.e. F > 1 the 1D asymptotics holds although the two-dimensional oblique granular jumps largely vary across the converging channel. This computationally efficient closed 1D model is validated by comparing it to the computationally more expensiveaa three-dimensional particle simulations. Finally, we aim to present a quasi-steady particle simulation of inclined flow through two rectangular blocks separated by a gap

  20. Monodisperse granular flows in viscous dispersions in a centrifugal acceleration field

    Science.gov (United States)

    Cabrera, Miguel Angel; Wu, Wei

    2016-04-01

    Granular flows are encountered in geophysical flows and innumerable industrial applications with particulate materials. When mixed with a fluid, a complex network of interactions between the particle- and fluid-phase develops, resulting in a compound material with a yet unclear physical behaviour. In the study of granular suspensions mixed with a viscous dispersion, the scaling of the stress-strain characteristics of the fluid phase needs to account for the level of inertia developed in experiments. However, the required model dimensions and amount of material becomes a main limitation for their study. In recent years, centrifuge modelling has been presented as an alternative for the study of particle-fluid flows in a reduced scaled model in an augmented acceleration field. By formulating simple scaling principles proportional to the equivalent acceleration Ng in the model, the resultant flows share many similarities with field events. In this work we study the scaling principles of the fluid phase and its effects on the flow of granular suspensions. We focus on the dense flow of a monodisperse granular suspension mixed with a viscous fluid phase, flowing down an inclined plane and being driven by a centrifugal acceleration field. The scaled model allows the continuous monitoring of the flow heights, velocity fields, basal pressure and mass flow rates at different Ng levels. The experiments successfully identify the effects of scaling the plastic viscosity of the fluid phase, its relation with the deposition of particles over the inclined plane, and allows formulating a discussion on the suitability of simulating particle-fluid flows in a centrifugal acceleration field.

  1. Modeling of dilute and dense dispersed fluid-particle flow

    Energy Technology Data Exchange (ETDEWEB)

    Laux, Harald

    1998-08-01

    A general two-fluid model is derived and applied in CFD computations to various test cases of important industrial multiphase flows. It is general in the sense of its applicability to dilute and dense dispersed fluid-particle flows. The model is limited to isothermal flow without mass transfer and only one particle phase is described. The instantaneous fluid phase equations, including the phase interaction terms, are derived from a volume averaging technique, and the instantaneous particle phase equations are derived from the kinetic theory of granular material. Whereas the averaging procedure, the treatment of the interaction terms, and the kinetic theory approach have been reported in literature prior to this work the combination of the approaches is new. The resulting equations are derived without ambiguity in the interpretation of the particle phase pressure (equation-of-state of particle phase). The basic modeling for the particle phase is improved in two steps. Because in the basic modeling only stresses due to kinetic and collisional interactions are included, a simple model for an effective viscosity is developed in order to allow also frictional stresses within the particle phase. Moreover, turbulent stresses and turbulent dispersion of particles play often an important role for the transport processes. Therefore in a second step, a two-equation turbulence model for both fluid and particle phase turbulence is derived by applying the phasic average to the instantaneous equations. The resulting k-{epsilon}-k{sup d}-{epsilon}{sup d} model is new. Mathematical closure is attempted such that the resulting set of equations is valid for both dilute arid dense flows. During the development of the closure relations a clear distinction is made between granular or ''viscous'' microscale fluctuations and turbulent macro scale fluctuations (true particle turbulence) within the particle phase. The set of governing equations is discretized by using a

  2. Probing Cold Dense Nuclear Matter

    Energy Technology Data Exchange (ETDEWEB)

    Subedi, Ramesh; Shneor, R.; Monaghan, Peter; Anderson, Bryon; Aniol, Konrad; Annand, John; Arrington, John; Benaoum, Hachemi; Benmokhtar, Fatiha; Bertozzi, William; Boeglin, Werner; Chen, Jian-Ping; Choi, Seonho; Cisbani, Evaristo; Craver, Brandon; Frullani, Salvatore; Garibaldi, Franco; Gilad, Shalev; Gilman, Ronald; Glamazdin, Oleksandr; Hansen, Jens-Ole; Higinbotham, Douglas; Holmstrom, Timothy; Ibrahim, Hassan; Igarashi, Ryuichi; De Jager, Cornelis; Jans, Eddy; Jiang, Xiaodong; Kaufman, Lisa; Kelleher, Aidan; Kolarkar, Ameya; Kumbartzki, Gerfried; LeRose, John; Lindgren, Richard; Liyanage, Nilanga; Margaziotis, Demetrius; Markowitz, Pete; Marrone, Stefano; Mazouz, Malek; Meekins, David; Michaels, Robert; Moffit, Bryan; Perdrisat, Charles; Piasetzky, Eliazer; Potokar, Milan; Punjabi, Vina; Qiang, Yi; Reinhold, Joerg; Ron, Guy; Rosner, Guenther; Saha, Arunava; Sawatzky, Bradley; Shahinyan, Albert; Sirca, Simon; Slifer, Karl; Solvignon, Patricia; Sulkosky, Vince; Sulkosky, Vincent; Sulkosky, Vince; Sulkosky, Vincent; Urciuoli, Guido; Voutier, Eric; Watson, John; Weinstein, Lawrence; Wojtsekhowski, Bogdan; Wood, Stephen; Zheng, Xiaochao; Zhu, Lingyan

    2008-06-01

    The protons and neutrons in a nucleus can form strongly correlated nucleon pairs. Scattering experiments, in which a proton is knocked out of the nucleus with high-momentum transfer and high missing momentum, show that in carbon-12 the neutron-proton pairs are nearly 20 times as prevalent as proton-proton pairs and, by inference, neutron-neutron pairs. This difference between the types of pairs is due to the nature of the strong force and has implications for understanding cold dense nuclear systems such as neutron stars.

  3. Probing Cold Dense Nuclear Matter

    CERN Document Server

    Subedi, R; Monaghan, P; Anderson, B D; Aniol, K; Annand, J; Arrington, J; Benaoum, H; Benmokhtar, F; Bertozzi, W; Boeglin, W; Chen, J -P; Choi, Seonho; Cisbani, E; Craver, B; Frullani, S; Garibaldi, F; Gilad, S; Gilman, R; Glamazdin, O; Hansen, J -O; Higinbotham, D W; Holmstrom, T; Ibrahim, H; Igarashi, R; De Jager, C W; Jans, E; Jiang, X; Kaufman, L; Kelleher, A; Kolarkar, A; Kumbartzki, G; LeRose, J J; Lindgren, R; Liyanage, N; Margaziotis, D J; Markowitz, P; Marrone, S; Mazouz, M; Meekins, D; Michaels, R; Moffit, B; Perdrisat, C F; Piasetzky, E; Potokar, M; Punjabi, V; Qiang, Y; Reinhold, J; Ron, G; Rosner, G; Saha, A; Sawatzky, B; Shahinyan, A; Širca, S; Slifer, K; Solvignon, P; Sulkosky, V; Urciuoli, G; Voutier, E; Watson, J W; Weinstein, L B; Wojtsekhowski, B; Wood, S; Zheng, X -C; Zhu, L; 10.1126/science.1156675

    2009-01-01

    The protons and neutrons in a nucleus can form strongly correlated nucleon pairs. Scattering experiments, where a proton is knocked-out of the nucleus with high momentum transfer and high missing momentum, show that in 12C the neutron-proton pairs are nearly twenty times as prevalent as proton-proton pairs and, by inference, neutron-neutron pairs. This difference between the types of pairs is due to the nature of the strong force and has implications for understanding cold dense nuclear systems such as neutron stars.

  4. Dilatons in Dense Baryonic Matter

    CERN Document Server

    Lee, Hyun Kyu

    2013-01-01

    We discuss the role of dilaton, which is supposed to be representing a special feature of scale symmetry of QCD, trace anomaly, in dense baryonic matter. The idea that the scale symmetry breaking of QCD is responsible for the spontaneous breaking of chiral symmetry is presented along the similar spirit of Freund-Nambu model. The incorporation of dilaton field in the hidden local symmetric parity doublet model is briefly sketched with the possible role of dilaton at high density baryonic matter, the emergence of linear sigma model in dilaton limit.

  5. Parton energy loss in hot and dense QCD medium

    Institute of Scientific and Technical Information of China (English)

    LIU Jie; MAO Yaxian; XIANG Wenchang; ZHOU Daicui

    2006-01-01

    Induced gluon radiation and energy loss of heavy quark in hot and dense QCD media are discussed. Using the light-cone path integral approach, an analytical formula of the energy loss of heavy quark is derived. The results show that the quark energy loss obviously depends on the mass of quark, i. e. a remarkable suppression occurs in the case of heavy quark comparing to a light one. The radiative energy loss of energetic quark is proportional to L2, where L is the length of the medium. The dependence of energy loss on L2 turns to L with decreasing quark energy.

  6. Interaction of multiarmed spirals in bistable media.

    Science.gov (United States)

    He, Ya-feng; Ai, Bao-quan; Liu, Fu-cheng

    2013-05-01

    We study the interaction of both dense and sparse multiarmed spirals in bistable media modeled by equations of the FitzHugh-Nagumo type. A dense one-armed spiral is characterized by its fixed tip. For dense multiarmed spirals, when the initial distance between tips is less than a critical value, the arms collide, connect, and disconnect continuously as the spirals rotate. The continuous reconstruction between the front and the back drives the tips to corotate along a rough circle and to meander zigzaggedly. The rotation frequency of tip, the frequency of zigzagged displacement, the frequency of spiral, the oscillation frequency of media, and the number of arms satisfy certain relations as long as the control parameters of the model are fixed. When the initial distance between tips is larger than the critical value, the behaviors of individual arms within either dense or sparse multiarmed spirals are identical to that of corresponding one-armed spirals.

  7. Characteristics of a UASB reactor granular sludge at low ascending rate; Caracterizacion de lodo granular de un reactor de UASB operando a bajas velocidades ascensionales

    Energy Technology Data Exchange (ETDEWEB)

    Obraya Abreu, M. C.; Valdes Jimenez, E.; Cuellar Marrero, A.

    2003-07-01

    Some structural, physical and chemical characteristics of a granular sludge, from a pilot plant for the treatment of alcohol distillery wastewater at suboptimal reactor performance, was investigated. From scanning electron microscopic observations it was possible to infer that these granules have a definite layered structure formed by two layers of different kind of microorganisms, a dense outer of diverse morphology, surrounding a loosely inner center which contain predominantly Methanosaeta sp. Because of the low ascending a rate and low biogas production, the sludge be remain almost static,the reactions rates and biomass-substates contact were deficient, producing cellular lysis in the core of the granules. The limitations of mass transfer can significantly affect the biological activity of the granules and this could be the reason of the low specific methanogenic activity encountered. (Author) 24 refs.

  8. Bit Patterned Magnetic Recording: Theory, Media Fabrication, and Recording Performance

    OpenAIRE

    Albrecht, Thomas R.; Arora, Hitesh; Ayanoor-Vitikkate, Vipin; Beaujour, Jean-Marc; Bedau, Daniel; Berman, David; Bogdanov, Alexei L.; Chapuis, Yves-Andre; Cushen, Julia; Dobisz, Elizabeth E.; Doerk, Gregory; Gao, He; Grobis, Michael; Gurney, Bruce; Hanson, Weldon

    2015-01-01

    Bit Patterned Media (BPM) for magnetic recording provide a route to densities $>1 Tb/in^2$ and circumvents many of the challenges associated with conventional granular media technology. Instead of recording a bit on an ensemble of random grains, BPM uses an array of lithographically defined isolated magnetic islands, each of which stores one bit. Fabrication of BPM is viewed as the greatest challenge for its commercialization. In this article we describe a BPM fabrication method which combine...

  9. Scaling of granular convective velocity and timescale of asteroidal resurfacing

    Science.gov (United States)

    Yamada, Tomoya; Ando, Kousuke; Morota, Tomokatsu; Katsuragi, Hiroaki

    Granular convection is one of the well-known phenomena observed in a vertically vibrated granular bed. Recently, the possbile relation between granular convection and asteroidal surface processes has been discussed. The granular convection on the surface of small asteroids might be induced by seismic vibration resulting from meteorite impacts. To quantitatively evaluate the timescale of asteroidal resurfacing by granular convection, the granular convective velocity under various conditions must be revealed. As a first step to approach this problem, we experimentally study the velocity scaling of granular convection using a vertically vibrated glass-beads layer. By systematic experiments, a scaling form of granular convective velocity has been obtained. The obtained scaling form implies that the granular convective velocity can be written by a power-law product of two characteristic velocity components: vibrational and gravitational velocities. In addition, the system size dependence is also scaled. According to the scaling form, the granular convective velocity is almost proportional to gravitatinal acceleration. Using this scaling form, we have estimated the resurfacing timescale on small asteroid surface.

  10. Media education.

    Science.gov (United States)

    Strasburger, Victor C

    2010-11-01

    The American Academy of Pediatrics recognizes that exposure to mass media (eg, television, movies, video and computer games, the Internet, music lyrics and videos, newspapers, magazines, books, advertising) presents health risks for children and adolescents but can provide benefits as well. Media education has the potential to reduce the harmful effects of media and accentuate the positive effects. By understanding and supporting media education, pediatricians can play an important role in reducing harmful effects of media on children and adolescents.

  11. Applying MDL to Learning Best Model Granularity

    CERN Document Server

    Gao, Q; Vitanyi, P; Gao, Qiong; Li, Ming; Vitanyi, Paul

    2000-01-01

    The Minimum Description Length (MDL) principle is solidly based on a provably ideal method of inference using Kolmogorov complexity. We test how the theory behaves in practice on a general problem in model selection: that of learning the best model granularity. The performance of a model depends critically on the granularity, for example the choice of precision of the parameters. Too high precision generally involves modeling of accidental noise and too low precision may lead to confusion of models that should be distinguished. This precision is often determined ad hoc. In MDL the best model is the one that most compresses a two-part code of the data set: this embodies ``Occam's Razor.'' In two quite different experimental settings the theoretical value determined using MDL coincides with the best value found experimentally. In the first experiment the task is to recognize isolated handwritten characters in one subject's handwriting, irrespective of size and orientation. Based on a new modification of elastic...

  12. Velocity distributions in dilute granular systems.

    Science.gov (United States)

    van Zon, J S; MacKintosh, F C

    2005-11-01

    We investigate the idea that velocity distributions in granular gases are determined mainly by eta, 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 as functions of eta, concentration phi, and particle number N with various heating mechanisms. For a wide range of parameters, we find Gaussian velocity distributions for uniform heating and non-Gaussian velocity distributions for boundary heating. Comparison between these results and velocity distributions obtained by other heating mechanisms and for a simple model of a granular gas without spatial degrees of freedom, shows that uniform and boundary heating can be understood as different limits of q, with q>1 and q < or approximately 1 respectively. We review the literature for evidence of the role of q in the recent experiments.

  13. 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.

  14. 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.

  15. Erosion dynamics of a wet granular medium.

    Science.gov (United States)

    Lefebvre, Gautier; Jop, Pierre

    2013-09-01

    Liquid may give strong cohesion properties to a granular medium, and confer a solidlike behavior. We study the erosion of a fixed circular aggregate of wet granular matter subjected to a flow of dry grains inside a half-filled rotating drum. During the rotation, the dry grains flow around the fixed obstacle. We show that its diameter decreases linearly with time for low liquid content, as wet grains are pulled out of the aggregate. This erosion phenomenon is governed by the properties of the liquids. The erosion rate decreases exponentially with the surface tension while it depends on the viscosity to the power -1. We propose a model based on the force fluctuations arising inside the flow, explaining both dependencies: The capillary force acts as a threshold and the viscosity controls the erosion time scale. We also provide experiments using different flowing grains, confirming our model.

  16. Compaction of granular material inside confined geometries

    Science.gov (United States)

    Marks, Benjy; Sandnes, Bjornar; Dumazer, Guillaume; Eriksen, Jon Alm; Måløy, Knut Jørgen

    2015-06-01

    In both nature and the laboratory, loosely packed granular materials are often compacted inside confined geometries. Here, we explore such behaviour in a quasi-two dimensional geometry, where parallel rigid walls provide the confinement. We use the discrete element method to investigate the stress distribution developed within the granular packing as a result of compaction due to the displacement of a rigid piston. We observe that the stress within the packing increases exponentially with the length of accumulated grains, and show an extension to current analytic models which fits the measured stress. The micromechanical behaviour is studied for a range of system parameters, and the limitations of existing analytic models are described. In particular, we show the smallest sized systems which can be treated using existing models. Additionally, the effects of increasing piston rate, and variations of the initial packing fraction, are described.

  17. Viscoelastic behavior of dense microemulsions

    Science.gov (United States)

    Cametti, C.; Codastefano, P.; D'arrigo, G.; Tartaglia, P.; Rouch, J.; Chen, S. H.

    1990-09-01

    We have performed extensive measurements of shear viscosity, ultrasonic absorption, and sound velocity in a ternary system consisting of water-decane-sodium di(2-ethylhexyl)sulfo- succinate(AOT), in the one-phase region where it forms a water-in-oil microemulsion. We observe a rapid increase of the static shear viscosity in the dense microemulsion region. Correspondingly the sound absorption shows unambiguous evidence of a viscoelastic behavior. The absorption data for various volume fractions and temperatures can be reduced to a universal curve by scaling both the absorption and the frequency by the measured static shear viscosity. The sound absorption can be interpreted as coming from the high-frequency tail of the viscoelastic relaxation, describable by a Cole-Cole relaxation formula with unusually small elastic moduli.

  18. Neutrino Oscillations in Dense Matter

    Science.gov (United States)

    Lobanov, A. E.

    2017-03-01

    A modification of the electroweak theory, where the fermions with the same electroweak quantum numbers are combined in multiplets and are treated as different quantum states of a single particle, is proposed. In this model, mixing and oscillations of particles arise as a direct consequence of the general principles of quantum field theory. The developed approach enables one to calculate the probabilities of the processes taking place in the detector at long distances from the particle source. Calculations of higher-order processes, including computation of the contributions due to radiative corrections, can be performed in the framework of the perturbation theory using the regular diagram technique. As a result, the analog to the Dirac-Schwinger equation of quantum electrodynamics describing neutrino oscillations and its spin rotation in dense matter can be obtained.

  19. DPIS for warm dense matter

    Energy Technology Data Exchange (ETDEWEB)

    Kondo, K.; Kanesue, T.; Horioka, K.; Okamura, M.

    2010-05-23

    Warm Dense Matter (WDM) offers an challenging problem because WDM, which is beyond ideal plasma, is in a low temperature and high density state with partially degenerate electrons and coupled ions. WDM is a common state of matter in astrophysical objects such as cores of giant planets and white dwarfs. The WDM studies require large energy deposition into a small target volume in a shorter time than the hydrodynamical time and need uniformity across the full thickness of the target. Since moderate energy ion beams ({approx} 0.3 MeV/u) can be useful tool for WDM physics, we propose WDM generation using Direct Plasma Injection Scheme (DPIS). In the DPIS, laser ion source is connected to the Radio Frequency Quadrupole (RFQ) linear accelerator directly without the beam transport line. DPIS with a realistic final focus and a linear accelerator can produce WDM.

  20. A model for collisions in granular gases

    OpenAIRE

    Brilliantov, Nikolai V.; Spahn, Frank; Hertzsch, Jan-Martin; Poeschel, Thorsten

    2002-01-01

    We propose a model for collisions between particles of a granular material and calculate the restitution coefficients for the normal and tangential motion as functions of the impact velocity from considerations of dissipative viscoelastic collisions. Existing models of impact with dissipation as well as the classical Hertz impact theory are included in the present model as special cases. We find that the type of collision (smooth, reflecting or sticky) is determined by the impact velocity and...