Science.gov

Sample records for wet granular matter

  1. Equation of state of wet granular matter

    NASA Astrophysics Data System (ADS)

    Fingerle, A.; Herminghaus, S.

    2008-01-01

    An expression for the near-contact pair correlation function of D -dimensional weakly polydisperse hard spheres is presented, which arises from elementary free-volume arguments. Its derivative at contact agrees very well with our simulations for D=2 . For jammed states, the expression predicts that the number of exact contacts is equal to 2D, in agreement with established simulations. When the particles are wetted, they interact by the formation and rupture of liquid capillary bridges. Since formation and rupture events of capillary bonds are well separated in configuration space, the interaction is hysteretic with a characteristic energy loss Ecb . The pair correlation is strongly affected by this capillary interaction depending on the liquid-bond status of neighboring particles. A theory is derived for the nonequilibrium probability currents of the capillary interaction which determines the pair correlation function near contact. This finally yields an analytic expression for the equation of state, P=P(N/V,T) , of wet granular matter for D=2 , valid in the complete density range from gas to jamming. Driven wet granular matter exhibits a van der Waals-like unstable branch at granular temperatures Tgranular droplets reported for the free cooling of one-dimensional wet granular matter [A. Fingerle and S. Herminghaus, Phys. Rev. Lett. 97, 078001 (2006)], and extends the effect to higher dimensional systems. Since the limiting case of sticky bonds, Ecb≫T , is of relevance for aggregation in general, simulations have been performed which show very good

  2. Pattern formation in wet granular matter under vertical vibrations.

    PubMed

    Butzhammer, Lorenz; Völkel, Simeon; Rehberg, Ingo; Huang, Kai

    2015-07-01

    Experiments on a thin layer of cohesive wet granular matter under vertical vibrations reveal kink-separated domains that collide with the container at different phases. Due to the strong cohesion arising from the formation of liquid bridges between adjacent particles, the domains move collectively upon vibrations. Depending on the periodicity of this collective motion, the kink fronts may propagate, couple with each other, and form rotating spiral patterns in the case of period tripling or stay as standing wave patterns in the case of period doubling. Moreover, both patterns may coexist with granular "gas bubbles"-phase separation into a liquidlike and a gaslike state. Stability diagrams for the instabilities measured with various granular layer mass m and container height H are presented. The onsets for both types of patterns and their dependency on m and H can be quantitatively captured with a model considering the granular layer as a single particle colliding completely inelastically with the container. PMID:26274155

  3. Rheological behavior of partially-wet granular matter

    NASA Astrophysics Data System (ADS)

    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.

  4. Arrest stress of uniformly sheared wet granular matter

    NASA Astrophysics Data System (ADS)

    Ebrahimnazhad Rahbari, S. H.; Brinkmann, M.; Vollmer, J.

    2015-06-01

    We conduct extensive independent numerical experiments considering frictionless disks without internal degrees of freedom (rotation, etc.) in two dimensions. We report here that for a large range of the packing fractions below random-close packing, all components of the stress tensor of wet granular materials remain finite in the limit of zero shear rate. This is direct evidence for a fluid-to-solid arrest transition. The offset value of the shear stress characterizes plastic deformation of the arrested state which corresponds to dynamic yield stress of the system. Based on an analytical line of argument, we propose that the mean number of capillary bridges per particle, ν , follows a nontrivial dependence on the packing fraction, ϕ , and the capillary energy, ɛ . Most noticeably, we show that ν is a generic and universal quantity which does not depend on the driving protocol. Using this universal quantity, we calculate the arrest stress, σa, analytically based on a balance of the energy injection rate due to the external force driving the flow and the dissipation rate accounting for the rupture of capillary bridges. The resulting prediction of σa is a nonlinear function of the packing fraction, ϕ , and the capillary energy, ɛ . This formula provides an excellent, parameter-free prediction of the numerical data. Corrections to the theory for small and large packing fractions are connected to the emergence of shear bands and of contributions to the stress from repulsive particle interactions, respectively.

  5. Wet granular materials

    NASA Astrophysics Data System (ADS)

    Mitarai, Namiko; Nori, Franco

    2006-04-01

    Most studies on granular physics have focused on dry granular media, with no liquids between the grains. However, in geology and many real world applications (e.g. food processing, pharmaceuticals, ceramics, civil engineering, construction, and many industrial applications), liquid is present between the grains. This produces inter-grain cohesion and drastically modifies the mechanical properties of the granular media (e.g. the surface angle can be larger than 90 degrees). Here we present a review of the mechanical properties of wet granular media, with particular emphasis on the effect of cohesion. We also list several open problems that might motivate future studies in this exciting but mostly unexplored field.

  6. Granular flow: Dry and wet

    NASA Astrophysics Data System (ADS)

    Mitarai, N.; Nakanishi, H.

    2012-04-01

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

  7. Vibrheology of Granular Matter

    NASA Astrophysics Data System (ADS)

    Dijksman, Joshua; Wortel, Geert; van Hecke, Martin

    2009-03-01

    We show how weak agitations substantially modify the rheology of granular materials. We experimentally probe dry granular flows in a weakly vibrated split bottom shear cell -- the weak vibrations act as the agitation source. By tuning the applied stress and vibration strength, and monitoring the resulting strain, we uncover a rich phase diagram in which non-trivial transitions separate a jammed phase, a creep flow case, and a steady flow case.

  8. Wet granular materials submitted to thermal cycling

    NASA Astrophysics Data System (ADS)

    Lumay, Geoffroy; Ludewig, Francois; Fiscina, Jorge; Pakpour, Maryam; Vandewalle, Nicolas; Dorbolo, Stephane

    2015-03-01

    Many phenomenons observed in nature are related to the particular behavior of wet granular materials submitted to temperature cycling: ice-lens formation in soil leading to frost heaving, landslides, structures formation in permafrost, stone heave and possibly some geological formations observed on Mars. We present experimental results concerning the effect of thermal cycling on the packing fraction of equal spheres with the presence of water. First, the case corresponding to completely immersed granular piles is considered. Afterward, the effect of thermal cycling on unsaturated granular piles is discussed. The pile is submitted to temperature cycling ranging from T1 to T2. If the temperature is always higher than 4°C, the temperature increase (or decrease) induces a dilatation (or contraction) of the grains and of the water. We show that the packing fraction variation is mainly related to water dilatation and contraction. If the temperature decreases under 0°C during a cycle, the water situated between the grains experiences a strong dilatation during the freezing step and a contraction during the ice melting step. In this case, we show how the freeze-thaw transition affects the packing fraction of the pile.

  9. Hierarchical Structures in Granular Matter

    NASA Astrophysics Data System (ADS)

    González-Gutiérrez, J.; Carrillo-Estrada, J. L.; Ruiz-Suárez, J. C.

    2013-12-01

    Granular matter, under the proper conditions of vibration, exhibits a behavior that closely resembles that of gases, liquids or solids. In a vibrated mix of glass particles and magnetic steel particles, it is also possible to observe aggregation phenomena, as well as, processes of reconstruction of the generated clusters. In this work we discuss the effects of the so called granular temperature on the evolution of the agglomerates generated by the magnetic interactions. On the basis of a fractal analysis and the measured mass distribution, we analyze experimental results on the static structural aspects of the aggregates originated by two methods we call: granular diffusion limited aggregation (GDLA) and growth limited by concentration (GLC).

  10. Characterizing the rheology of fluidized granular matter.

    PubMed

    Desmond, Kenneth W; Villa, Umberto; Newey, Mike; Losert, Wolfgang

    2013-09-01

    In this study we characterize the rheology of fluidized granular matter subject to secondary forcing. Our approach consists of first fluidizing granular matter in a drum half filled with grains via simple rotation and then superimposing oscillatory shear perpendicular to the downhill flow direction. The response of the system is mostly linear, with a phase lag between the grain motion and the oscillatory forcing. The rheology of the system can be well characterized by the GDR MiDi model if the system is forced with slow oscillations. The model breaks down when the forcing time scale becomes comparable to the characteristic time for energy dissipation in the flow. PMID:24125256

  11. Motility of small nematodes in wet granular media

    NASA Astrophysics Data System (ADS)

    Juarez, G.; Lu, K.; Sznitman, J.; Arratia, P. E.

    2010-11-01

    The motility of the worm nematode Caenorhabditis elegans is investigated in shallow, wet granular media as a function of particle size dispersity and area density (phi). Surprisingly, we find that the nematode's propulsion speed is enhanced by the presence of particles in a fluid and is nearly independent of area density. The undulation speed, often used to differentiate locomotion gaits, is significantly affected by the bulk material properties of wet mono- and polydisperse granular media for phi>=0.55. This difference is characterized by a change in the nematode's waveform from swimming to crawling in dense polydisperse media only. This change highlights the organism's adaptability to subtle differences in local structure and response between monodisperse and polydisperse media.

  12. Smarticles: smart, active granular matter

    NASA Astrophysics Data System (ADS)

    Savoie, Will; Pazouki, Arman; Negrut, Dan; Goldman, Daniel

    We investigate a granular medium composed of smart, active particles, or ``smarticles''. Previously, we discovered that ensembles of ``u''-shaped particles exhibited geometrically-induced cohesion by mechanically entangling via particle interpenetration [Gravish et al., PRL, 2012]; the strength and/or extent of entanglement could be varied by changing particle level entanglement by changes in arm-to-base length of the u-particle. Since changing this parameter on demand is inconvenient, we develop a power-autonomous programmable robot composed of two motors and three links with an on-board microcontroller. This smarticle can be activated to change its configuration (specified by its two joint angles) through audio communication. To complement these experiments, since study large ensembles of smarticles is cost and labor prohibitive, we also develop a simulated smarticle in the Chrono multibody simulation environment. We systematically study ensemble cohesiveness and compaction as a function of shape changes of the smarticles. We find that suitable activation of smarticles allows ensembles to become cohesive to ``grip'' rigid objects and lose cohesion to release on command. Work supported by ARO.

  13. Penetration depth scaling for impact into wet granular packings.

    PubMed

    Brzinski, T A; Schug, J; Mao, K; Durian, D J

    2015-02-01

    We present experimental measurements of penetration depths for the impact of spheres into wetted granular media. We observe that the penetration depth in the liquid saturated case scales with projectile density, size, and drop height in a fashion consistent with the scaling observed in the dry case, but with smaller penetrations. Neither viscous drag nor density effects can explain the enhancement to the stopping force. The penetration depth exhibits a complicated dependence on liquid fraction, accompanied by a change in the drop-height dependence, that must be the consequence of accompanying changes in the conformation of the liquid phase in the interstices. PMID:25768493

  14. Dilute wet granular particles: Nonequilibrium dynamics and structure formation

    NASA Astrophysics Data System (ADS)

    Ulrich, Stephan; Aspelmeier, Timo; Zippelius, Annette; Roeller, Klaus; Fingerle, Axel; Herminghaus, Stephan

    2009-09-01

    We investigate a gas of wet granular particles covered by a thin liquid film. The dynamic evolution is governed by two-particle interactions, which are mainly due to interfacial forces in contrast to dry granular gases. When two wet grains collide, a capillary bridge is formed and stays intact up to a certain distance of withdrawal when the bridge ruptures, dissipating a fixed amount of energy. A freely cooling system is shown to undergo a nonequilibrium dynamic phase transition from a state with mainly single particles and fast cooling to a state with growing aggregates such that bridge rupture becomes a rare event and cooling is slow. In the early stage of cluster growth, aggregation is a self-similar process with a fractal dimension of the aggregates approximately equal to Df≈2 . At later times, a percolating cluster is observed which ultimately absorbs all the particles. The final cluster is compact on large length scales, but fractal with Df≈2 on small length scales.

  15. Locomotion and drag in wet and dry granular media

    NASA Astrophysics Data System (ADS)

    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.

  16. 1/f noise on the brink of wet granular melting

    NASA Astrophysics Data System (ADS)

    Huang, Kai

    2015-08-01

    The collective behavior of a two-dimensional wet granular cluster under horizontal swirling motions is investigated experimentally. Depending on the balance between the energy injection and dissipation, the cluster evolves into various nonequilibrium stationary states with strong internal structure fluctuations with time. Quantitative characterizations of the fluctuations with the bond orientational order parameter {q}6 reveal power spectra of the form {f}α with the exponent α closely related to the stationary states of the system. In particular, 1/f type of noise with α ≈ -1 emerges as melting starts from the free surface of the cluster, suggesting the possibility of using 1/f noise as an indicator for phase transitions in systems driven far from thermodynamic equilibrium.

  17. Motility of small nematodes in disordered wet granular media

    NASA Astrophysics Data System (ADS)

    Juarez, Gabriel; Lu, Kevin; Sznitman, Josue; Arratia, Paulo E.

    2010-11-01

    Organisms that evolve within complex fluidic environments often develop unique methods of locomotion that allow them to exploit the properties of the media. In this talk, we present an investigation on the motility of the worm nematode Caenorhabditis elegans in shallow, wet granular media as a function of particle size dispersity and area density (φ) using both particle- and nematode-tracking methods. Surprisingly, the nematode's propulsion speed is enhanced by the presence of particles in a fluid and is nearly independent of local area density. The undulation speed, often used to differentiate locomotion gaits, is significantly affected by particle size dispersity for area densities above φ> 0.55, and is characterized by a change in the nematode's waveform from swimming to crawling. This change occurs for dense polydisperse media only and highlights the organism's adaptability to subtle differences in local structure between monodisperse and polydisperse media.

  18. Pattern formation in vibrated beds of dry and wet granular materials

    NASA Astrophysics Data System (ADS)

    Chuan Lim, Eldin Wee

    2014-01-01

    The Discrete Element Method was coupled with a capillary liquid bridge force model for computational studies of pattern formation in vibrated granular beds containing dry or wet granular materials. Depending on the vibration conditions applied, hexagonal, stripes, or cellular pattern was observed in the dry vibrated granular bed. In each of these cases, the same hexagonal, stripes, or cellular pattern was also observed in the spatial distribution of the magnitudes of particle-particle collision forces prior to the formation of the corresponding actual pattern in physical distributions of the particles. This seemed to suggest that the pattern formation phenomenon of vibrated granular bed systems might be the result of a two-dimensional Newton's cradle effect. In the presence of a small amount of wetness, these patterns were no longer formed in the vibrated granular beds under the same corresponding set of vibration conditions. Despite the relatively much weaker capillary forces arising from the simulated liquid bridges between particles compared with particle-particle collision forces, the spatial distributions of these collision forces, physical distributions of particles, as well as time profiles of average collision forces were altered significantly in comparison with the corresponding distributions and profiles observed for the dry vibrated granular beds. This seemed to suggest the presence of a two-dimensional Stokes' cradle effect in these wet vibrated granular bed systems which disrupted the formation of patterns in the wet granular materials that would have been observed in their dry counterparts.

  19. Bottom pressure scaling of vibro-fluidized granular matter

    PubMed Central

    Katsuragi, Hiroaki

    2015-01-01

    Vibrated granular beds show various interesting phenomena such as convection, segregation, and so on. However, its fundamental physical properties (e.g., internal pressure structure) have not yet been understood well. Thus, in this study, the bottom wall pressure in a vertically vibrated granular column is experimentally measured and used to reveal the nature of granular fluidization. The scaling method allows us to elucidate the fluidization (softening) degree of a vibrated granular column. The peak value of the bottom pressure pm is scaled as Γ, where pJ, d, g, ω, H, and Γ are the Janssen pressure, grain diameter, gravitational acceleration, angular frequency, height of the column, and dimensionless vibrational acceleration, respectively. This scaling implies that the pressure of vibrated granular matter is quite different from the classical pressure forms: static and dynamic pressures. This scaling represents the importance of geometric factors for discussing the behavior of vibro-fluidized granular matter. The scaling is also useful to evaluate the dissipation degree in vibro-fluidized granular matter. PMID:26602973

  20. Penetration of spherical projectiles into wet granular media.

    PubMed

    Birch, S P D; Manga, M; Delbridge, B; Chamberlain, M

    2014-09-01

    We measure experimentally the penetration depth d of spherical particles into a water-saturated granular medium made of much smaller sand-sized grains. We vary the density, size R, and velocity U of the impacting spheres, and the size δ of the grains in the granular medium. We consider velocities between 7 and 107 m/s, a range not previously addressed, but relevant for impacts produced by volcanic eruptions. We find that d∝R(1/3)δ(1/3)U(2/3). The scaling with velocity is similar to that identified in previous, low-velocity collisions, but it also depends on the size of the grains in the granular medium. We develop a model, consistent with the observed scaling, in which the energy dissipation is dominated by the work required to rearrange grains along a network of force chains in the granular medium. PMID:25314438

  1. Impact phenomena in fluidized granular matter

    NASA Astrophysics Data System (ADS)

    Mayor, Patrick; Katsuragi, Hiroaki; Durian, Douglas

    2009-03-01

    Projectiles dropped into granular media form a crater and come to rest in a particular way that has been actively investigated in numerous studies. These impact phenomena illustrate how particulate materials respond to externally applied forces. Several recent experiments have focused on the penetration of projectiles impacting granular materials at relatively low speeds, and measured the dynamics of the impact process, yielding force laws accounting for the observations. We present results showing how granular impacts are affected when the load on the grains is modified using a vertical gas flow. Balls or cylinders are dropped into a dry, noncohesive granular medium and we measure the penetration depth when gas is flown upward (thus unloading the contacts) or downward (loading the contacts). We observe that the frictional drag decreases linearly with the flow rate, and vanishes completely once the system is fluidized. Different projectile geometries allow us to separate the effect of normal and tangential frictional forces. We also consider the case of objects that are lowered quasistatically into the granular medium and measure the net vertical force exerted by the granular system on the objects at each immersion depth. We then discuss how this resistance force compares with the forces observed in actual impacts experiments.

  2. Quantitatively mimicking wet colloidal suspensions with dry granular media.

    PubMed

    Messina, René; Aljawhari, Sarah; Bécu, Lydiane; Schockmel, Julien; Lumay, Geoffroy; Vandewalle, Nicolas

    2015-01-01

    Athermal two-dimensional granular systems are exposed to external mechanical noise leading to Brownian-like motion. Using tunable repulsive interparticle interaction, it is shown that the same microstructure as that observed in colloidal suspensions can be quantitatively recovered at a macroscopic scale. To that end, experiments on granular and colloidal systems made up of magnetized particles as well as computer simulations are performed and compared. Excellent agreement throughout the range of the magnetic coupling parameter is found for the pair distribution as well as the bond-orientational correlation functions. This finding opens new ways to efficiently and very conveniently explore phase transitions, crystallization, nucleation, etc in confined geometries. PMID:26030718

  3. Scaling of liquid-drop impact craters in wet granular media

    NASA Astrophysics Data System (ADS)

    Zhang, Qianyun; Gao, Ming; Zhao, Runchen; Cheng, Xiang

    2015-10-01

    Combining high-speed photography with laser profilometry, we study the dynamics and the morphology of liquid-drop impact cratering in wet granular media—a ubiquitous phenomenon relevant to many important geological, agricultural, and industrial processes. By systematically investigating important variables such as impact energy, the size of impinging drops, and the degree of liquid saturation in granular beds, we uncover a scaling law for the size of impact craters. We show that this scaling can be explained by considering the balance between the inertia of impinging drops and the strength of impacted surface. Such a theoretical understanding confirms that the unique energy partition originally proposed for liquid-drop impact cratering in dry granular media also applies for impact cratering in wet granular media. Moreover, we demonstrate that compressive stresses, instead of shear stresses, control the process of granular impact cratering. Our study enriches the picture of generic granular impact cratering and sheds light on the familiar phenomena of raindrop impacts in granular media.

  4. Scaling of liquid-drop impact craters in wet granular media.

    PubMed

    Zhang, Qianyun; Gao, Ming; Zhao, Runchen; Cheng, Xiang

    2015-10-01

    Combining high-speed photography with laser profilometry, we study the dynamics and the morphology of liquid-drop impact cratering in wet granular media-a ubiquitous phenomenon relevant to many important geological, agricultural, and industrial processes. By systematically investigating important variables such as impact energy, the size of impinging drops, and the degree of liquid saturation in granular beds, we uncover a scaling law for the size of impact craters. We show that this scaling can be explained by considering the balance between the inertia of impinging drops and the strength of impacted surface. Such a theoretical understanding confirms that the unique energy partition originally proposed for liquid-drop impact cratering in dry granular media also applies for impact cratering in wet granular media. Moreover, we demonstrate that compressive stresses, instead of shear stresses, control the process of granular impact cratering. Our study enriches the picture of generic granular impact cratering and sheds light on the familiar phenomena of raindrop impacts in granular media. PMID:26565233

  5. Flocking at a distance in granular matter

    NASA Astrophysics Data System (ADS)

    Soni, Harsh; Ramaswamy, Sriram

    2015-03-01

    A mixture of polar granular rods and spherical beads on a vibrated plate undergoes a phase transition to an orientationally ordered state above a critical bead concentration. We study this system using large scale numerical simulations with periodic boundary conditions. We find an intermediate state with banded structures between the disordered and the globally ordered state. We observe a single band whose width increases with rod concentration. We find that at high densities the rods and the beads phase separate. We also test the various theoretical predictions of the hydrodynamic theory in the ordered state. Our results, which are in good agreement with the theory, are following: We see a highly anisotropic dispersion relation are exhibited with two sound modes in all directions except along the flock. Further the rods are super diffusive in the transverse direction and exhibit large number fluctuations.

  6. Runaway Electrification of Friable Self-Replicating Granular Matter

    PubMed Central

    2013-01-01

    We establish that the nonlinear dynamics of collisions between particles favors the charging of an insulating, friable, self-replicating granular material that undergoes nucleation, growth, and fission processes; we demonstrate with a minimal dynamical model that secondary nucleation produces a positive feedback in an electrification mechanism that leads to runaway charging. We discuss ice as an example of such a self-replicating granular material: We confirm with laboratory experiments in which we grow ice from the vapor phase in situ within an environmental scanning electron microscope that charging causes fast-growing and easily breakable palmlike structures to form, which when broken off may form secondary nuclei. We propose that thunderstorms, both terrestrial and on other planets, and lightning in the solar nebula are instances of such runaway charging arising from this nonlinear dynamics in self-replicating granular matter. PMID:24041221

  7. Runaway electrification of friable self-replicating granular matter.

    PubMed

    Cartwright, Julyan H E; Escribano, Bruno; Grothe, Hinrich; Piro, Oreste; Sainz Díaz, C Ignacio; Tuval, Idan

    2013-10-15

    We establish that the nonlinear dynamics of collisions between particles favors the charging of an insulating, friable, self-replicating granular material that undergoes nucleation, growth, and fission processes; we demonstrate with a minimal dynamical model that secondary nucleation produces a positive feedback in an electrification mechanism that leads to runaway charging. We discuss ice as an example of such a self-replicating granular material: We confirm with laboratory experiments in which we grow ice from the vapor phase in situ within an environmental scanning electron microscope that charging causes fast-growing and easily breakable palmlike structures to form, which when broken off may form secondary nuclei. We propose that thunderstorms, both terrestrial and on other planets, and lightning in the solar nebula are instances of such runaway charging arising from this nonlinear dynamics in self-replicating granular matter. PMID:24041221

  8. Networks of Liquid Bridges and Clusters in Wet Granular Systems

    NASA Astrophysics Data System (ADS)

    Scheel, Mario; Herminghaus, Stephan; Seemann, Ralf

    2006-03-01

    The macroscopic mechanical properties of a dry granulate change dramatically when small amounts of liquid are added. This is due to capillary bridges forming between mutually adjacent grains in the pile, which exert an attractive force by virtue of the surface tension of the liquid. If much more liquid is added, the liquid clusters, and the stability of the pile is reduced. Although the tensile strength of wet granulates can be roughly estimated from the capillary forces, a quantitative theory of the mechanical properties of granulate requires a detailed understanding of the topology of the complex network of capillary bridges and clusters. We have determined the macroscopic properties in model granulates with a vertical fluidization experiment, as well as the microscopic geometry of the distribution of liquid within the pile via x-ray microtomography. The transition from capillary bridges to clusters or the percolation can be clearly observed in both the fluidization experiments and the tomographic imaging.

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

    PubMed

    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. PMID:26109565

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

    NASA Astrophysics Data System (ADS)

    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.

  11. Universality of slip avalanches in flowing granular matter.

    PubMed

    Denisov, D V; Lörincz, K A; Uhl, J T; Dahmen, K A; Schall, P

    2016-01-01

    The search for scale-bridging relations in the deformation of amorphous materials presents a current challenge with tremendous applications in material science, engineering and geology. While generic features in the flow and microscopic dynamics support the idea of a universal scaling theory of deformation, direct microscopic evidence remains poor. Here, we provide the first measurement of internal scaling relations in the deformation of granular matter. By combining macroscopic force fluctuation measurements with internal strain imaging, we demonstrate the existence of robust scaling relations from particle-scale to macroscopic flow. We identify consistent power-law relations truncated by systematic pressure-dependent cutoff, in agreement with recent mean-field theory of slip avalanches in elasto-plastic materials, revealing the existence of a mechanical critical point. These results experimentally establish scale-bridging relations in the flow of matter, paving the way to a new universal theory of deformation. PMID:26883071

  12. Universality of slip avalanches in flowing granular matter

    PubMed Central

    Denisov, D. V.; Lörincz, K. A.; Uhl, J. T.; Dahmen, K. A.; Schall, P.

    2016-01-01

    The search for scale-bridging relations in the deformation of amorphous materials presents a current challenge with tremendous applications in material science, engineering and geology. While generic features in the flow and microscopic dynamics support the idea of a universal scaling theory of deformation, direct microscopic evidence remains poor. Here, we provide the first measurement of internal scaling relations in the deformation of granular matter. By combining macroscopic force fluctuation measurements with internal strain imaging, we demonstrate the existence of robust scaling relations from particle-scale to macroscopic flow. We identify consistent power-law relations truncated by systematic pressure-dependent cutoff, in agreement with recent mean-field theory of slip avalanches in elasto-plastic materials, revealing the existence of a mechanical critical point. These results experimentally establish scale-bridging relations in the flow of matter, paving the way to a new universal theory of deformation. PMID:26883071

  13. Universality of slip avalanches in flowing granular matter

    NASA Astrophysics Data System (ADS)

    Denisov, D. V.; Lörincz, K. A.; Uhl, J. T.; Dahmen, K. A.; Schall, P.

    2016-02-01

    The search for scale-bridging relations in the deformation of amorphous materials presents a current challenge with tremendous applications in material science, engineering and geology. While generic features in the flow and microscopic dynamics support the idea of a universal scaling theory of deformation, direct microscopic evidence remains poor. Here, we provide the first measurement of internal scaling relations in the deformation of granular matter. By combining macroscopic force fluctuation measurements with internal strain imaging, we demonstrate the existence of robust scaling relations from particle-scale to macroscopic flow. We identify consistent power-law relations truncated by systematic pressure-dependent cutoff, in agreement with recent mean-field theory of slip avalanches in elasto-plastic materials, revealing the existence of a mechanical critical point. These results experimentally establish scale-bridging relations in the flow of matter, paving the way to a new universal theory of deformation.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  15. The Flow Of Granular Matter Under Reduced-Gravity Conditions

    NASA Astrophysics Data System (ADS)

    Hofmeister, P. G.; Blum, J.; Heißelmann, D.

    2009-06-01

    To gain a better understanding of the surfaces of planets and small bodies in the solar system, the flow behavior of granular material for various gravity levels is of utmost interest. We performed a set of reduced-gravity measurements to analyze the flow behavior of granular matter with a quasi-2D hourglass under coarse-vacuum conditions and with a tilting avalanche box. We used the Bremen drop tower and a small centrifuge to achieve residual-gravity levels between 0.01 g0 and 0.3 g0. Both experiments were carried out with basalt and glass grains as well as with two kinds of ordinary sand. For the hourglass experiments, the volume flow through the orifice, the repose and friction angles, and the flow behavior of the particles close to the surface were determined. In the avalanche-box experiment, we measured the duration of the avalanche, the maximum slope angle as well as the width of the avalanche as a function of the gravity level.

  16. Time-resolved dynamics of granular matter by random laser emission

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

    Because of the huge commercial importance of granular systems, the second-most used material in industry after water, intersecting the industry in multiple trades, like pharmacy and agriculture, fundamental research on grain-like materials has received an increasing amount of attention in the last decades. In photonics, the applications of granular materials have been only marginally investigated. We report the first phase-diagram of a granular as obtained by laser emission. The dynamics of vertically-oscillated granular in a liquid solution in a three-dimensional container is investigated by employing its random laser emission. The granular motion is function of the frequency and amplitude of the mechanical solicitation, we show how the laser emission allows to distinguish two phases in the granular and analyze its spectral distribution. This constitutes a fundamental step in the field of granulars and gives a clear evidence of the possible control on light-matter interaction achievable in grain-like system.

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

    NASA Astrophysics Data System (ADS)

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

    NASA Astrophysics Data System (ADS)

    Juanes, Ruben

    2015-11-01

    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.

  19. Avalanche to Continuous flow transition in wet and cohesive granular media

    NASA Astrophysics Data System (ADS)

    Orpe, Ashish; Basu, Saprativ; Doshi, Pankaj

    2013-11-01

    We have studied the flow of wet and cohesive granular media in a partially filled, horizontally rotating cylinder. Very small, amount of viscous liquid is added to dry granular particles and the mixture is rotated in the cylinder at various rotational speeds to determine the angle of repose in the avalanching regime, the continuous regime and at the transition rotational speed separating the two regimes. Every experimental run is carried out afresh at a pre-defined rotational speed using liquids with different free surface tension and added in different amounts. Increasing the liquid surface tension increases the angle of repose as well as shifts the transition rotational speed to increasingly higher values. Similar qualitative behaviour is also observed on increasing the amount liquid added. A linear dependence is observed when the transition angle of repose for all cases is plotted against the corresponding transition rotational speed. The entire flow regime is modeled using momentum and mass balance equations for the flowing layer of particles. The total stress in the flowing mass of particles is assumed to be a linear combination of frictional, collisional and capillary force contributions. The model equations are able to reproduce most of the observed flow behavior. Department of Science and Technology, India, (Grant No. SR/S3/CE/037/2009).

  20. Granular matter and the time-dependent viscous eikonal equation

    NASA Astrophysics Data System (ADS)

    Hadeler, K. P.; Schieborn, Dirk

    2012-03-01

    Deposition of granular matter under gravity can be described by the well-known two-layer model for a standing and a rolling layer. Matter from sources enters the rolling layer which flows along the gradient of the standing layer and finally enters the standing layer via interaction of the two layers. From this system of two coupled hyperbolic partial differential equations a time-dependent viscous eikonal equation is derived as a limiting case for weak sources, a thin rolling layer and fast convection of the rolling layer. This equation, supplied with boundary conditions, describes the deposition of dry sand from evenly distributed sources onto a flat table with a vertical rim of variable height. The stationary problem can also be seen as an application of the method of vanishing viscosity to the eikonal equation. For certain types of interaction between the two layers the resulting eikonal equation can be transformed into a linear equation. This transformation yields additional insight into the problem.

  1. Confocal Microscopy of Jammed Matter: From Elasticity to Granular Thermodynamics

    NASA Astrophysics Data System (ADS)

    Jorjadze, Ivane

    Packings of particles are ubiquitous in nature and are of interest not only to the scientific community but also to the food, pharmaceutical, and oil industries. In this thesis we use confocal microscopy to investigate packing geometry and stress transmission in 3D jammed particulate systems. By introducing weak depletion attraction we probe the accessible phase-space and demonstrate that a microscopic approach to jammed matter gives validity to statistical mechanics framework, which is intriguing because our particles are not thermally activated. We show that the fluctuations of the local packing parameters can be successfully captured by the recently proposed 'granocentric' model, which generates packing statistics according to simple stochastic processes. This model enables us to calculate packing entropy and granular temperature, the so-called 'compactivity', therefore, providing a basis for a statistical mechanics of granular matter. At a jamming transition point at which there are formed just enough number of contacts to guarantee the mechanical stability, theoretical arguments suggest a singularity which gives rise to the surprising scaling behavior of the elastic moduli and the microstructure, as observed in numerical simulations. Since the contact network in 3D is typically hidden from view, experimental test of the scaling law between the coordination number and the applied pressure is lacking in the literature. Our data show corrections to the linear scaling of the pressure with density which takes into account the creation of contacts. Numerical studies of vibrational spectra, in turn, reveal sudden features such as excess of low frequency modes, dependence of mode localization and structure on the pressure. Chapter four describes the first calculation of vibrational density of states from the experimental 3D data and is in qualitative agreement with the analogous computer simulations. We study the configurational role of the pressure and demonstrate

  2. Effective Reduction of Coulomb Repulsion in Charged Granular Matter

    NASA Astrophysics Data System (ADS)

    Scheffler, T.; Werth, J.; Wolf, D. E.

    2000-04-01

    This paper is an extension to a previous article by Scheffler and Wolfs.6 We study the rate of energy dissipation due to inelastic collisions in a charged granular gas. One observes that the electrostatic repulsion of two particles is effectively reduced by nearest neighbor interactions in a dense granular gas. We study the radial distribution function for dense systems, which leads to a better expression for the reduced energy barrier.

  3. Relevance of wet deposition of organic matter for alpine ecosystems

    NASA Astrophysics Data System (ADS)

    Mladenov, N.; Williams, M. W.; Schmidt, S. K.; Goss, N. R.; Reche, I.

    2011-12-01

    In barren, alpine environments, carbon inputs from atmospheric deposition may be very important for ecological processes. Recent findings suggest that atmospheric deposition influences the quality of dissolved organic matter (DOM) in alpine lakes on a global scale. Here, we evaluate the inputs of DOM in atmospheric wet deposition to alpine terrestrial ecosystems, in terms of both quantity and quality. We show that at the Niwot Ridge Long Term Ecological Research Station (Colorado, USA) wet deposition represents a seasonally variable (Figure 1) mass input of organic carbon, depositing on average 6 kg C/ha/yr or roughly 1500 kg C to the Green Lake 4 watershed at Niwot Ridge. Wet deposition is, therefore, a substantial input of dissolved organic carbon (DOC) to the catchment when compared to the annual DOC yield from Green Lake 4, estimated at just over 1800 kg C. In terms of DOM bioavailability for alpine microorganisms, our optical spectroscopic results showing high amounts of amino acid-like fluorescence and low aromaticity suggest that DOM in wet deposition may be particularly labile, especially in the summer months. The heterotrophic processing of this organic carbon input has important implications for the cycling of other nutrients, such as nitrogen, in alpine environments. We have also shown that the sources of DOM in wet deposition include bioaerosols, such as pollen, which represent much of the summer DOC loading. However, relationships with inorganic N and sulfate also suggest that organic pollutants in the atmosphere may have an equally important influence on DOM in wet deposition. Additionally, the quality of wet deposition DOM in the spring is similar to that of dust deposition observed near the Sahara and may be influenced by dust events, as shown from air mass trajectories originating in or near the Colorado Plateau. The seasonality of DOM quality appears to be related to these varying sources and is, therefore, a critical topic for future research.

  4. Unifying Impacts in Granular Matter from Quicksand to Cornstarch.

    PubMed

    Jerome, J John Soundar; Vandenberghe, Nicolas; Forterre, Yoël

    2016-08-26

    A sharp transition between liquefaction and transient solidification is observed during impact on a granular suspension depending on the initial packing fraction. We demonstrate, via high-speed pressure measurements and a two-phase modeling, that this transition is controlled by a coupling between the granular pile dilatancy and the interstitial fluid pressure generated by the impact. Our results provide a generic mechanism for explaining the wide variety of impact responses in particulate media, from dry quicksand in powders to impact hardening in shear-thickening suspensions like cornstarch. PMID:27610888

  5. Time-resolved dynamics of granular matter by random laser emission

    PubMed Central

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

    2013-01-01

    Because of the huge commercial importance of granular systems, the second-most used material in industry after water, intersecting the industry in multiple trades, like pharmacy and agriculture, fundamental research on grain-like materials has received an increasing amount of attention in the last decades. In photonics, the applications of granular materials have been only marginally investigated. We report the first phase-diagram of a granular as obtained by laser emission. The dynamics of vertically-oscillated granular in a liquid solution in a three-dimensional container is investigated by employing its random laser emission. The granular motion is function of the frequency and amplitude of the mechanical solicitation, we show how the laser emission allows to distinguish two phases in the granular and analyze its spectral distribution. This constitutes a fundamental step in the field of granulars and gives a clear evidence of the possible control on light-matter interaction achievable in grain-like system. PMID:23872642

  6. Eshelby inclusions in granular matter: Theory and simulations.

    PubMed

    McNamara, Sean; Crassous, Jérôme; Amon, Axelle

    2016-08-01

    We present a numerical implementation of an active inclusion in a granular material submitted to a biaxial test. We discuss the dependence of the response to this perturbation on two parameters: the intragranular friction coefficient on one hand, and the degree of the loading on the other hand. We compare the numerical results to theoretical predictions taking into account the change of volume of the inclusion as well as the anisotropy of the elastic matrix. PMID:27627380

  7. The minimization of mechanical work in vibrated granular matter.

    PubMed

    Clewett, James P D; Wade, Jack; Bowley, R M; Herminghaus, Stephan; Swift, Michael R; Mazza, Marco G

    2016-01-01

    Experiments and computer simulations are carried out to investigate phase separation in a granular gas under vibration. The densities of the dilute and the dense phase are found to follow a lever rule and obey an equation of state. Here we show that the Maxwell equal-areas construction predicts the coexisting pressure and binodal densities remarkably well, even though the system is far from thermal equilibrium. This construction can be linked to the minimization of mechanical work associated with density fluctuations without invoking any concept related to equilibrium-like free energies. PMID:27373719

  8. The minimization of mechanical work in vibrated granular matter

    NASA Astrophysics Data System (ADS)

    Clewett, James P. D.; Wade, Jack; Bowley, R. M.; Herminghaus, Stephan; Swift, Michael R.; Mazza, Marco G.

    2016-07-01

    Experiments and computer simulations are carried out to investigate phase separation in a granular gas under vibration. The densities of the dilute and the dense phase are found to follow a lever rule and obey an equation of state. Here we show that the Maxwell equal-areas construction predicts the coexisting pressure and binodal densities remarkably well, even though the system is far from thermal equilibrium. This construction can be linked to the minimization of mechanical work associated with density fluctuations without invoking any concept related to equilibrium-like free energies.

  9. The minimization of mechanical work in vibrated granular matter

    PubMed Central

    Clewett, James P. D.; Wade, Jack; Bowley, R. M.; Herminghaus, Stephan; Swift, Michael R.; Mazza, Marco G.

    2016-01-01

    Experiments and computer simulations are carried out to investigate phase separation in a granular gas under vibration. The densities of the dilute and the dense phase are found to follow a lever rule and obey an equation of state. Here we show that the Maxwell equal-areas construction predicts the coexisting pressure and binodal densities remarkably well, even though the system is far from thermal equilibrium. This construction can be linked to the minimization of mechanical work associated with density fluctuations without invoking any concept related to equilibrium-like free energies. PMID:27373719

  10. "Lock in accelerometry" to follow sink dynamics in shaken granular matter

    NASA Astrophysics Data System (ADS)

    Clement, Cecile; Sanchez-Colina, Gustavo; Alonso-Llanes, Laciel; Martinez-Roman, Etien; Batitsta-Leyva, Alfo-Jose; Toussaint, Renaud; Altshuler, Ernesto

    2015-04-01

    molecular dynamic algorithm to confirm or not this assumption. We modelized a granular bed with particles of the same size than the one used in the experiments. Because we have access to the velocity of every particles we can quantify the dynamic of each layers of the granular medium and find its "jammed" boundary. Reference [1] G Sánchez-Colina, L Alonso-Llanes, E Martínez, AJ Batista-Leyva, C Clement, C Fliedner, R Toussaint, and E Altshuler. Note :"lock-in accelerometry" to follow sink dynamics in shaken granular matter. Review of Scientific Instruments, 85(12) :126101, 2014.

  11. Intermittent Flow of Granular Matter in an Annular Geometry

    NASA Astrophysics Data System (ADS)

    Brzinski, Ted; Daniels, Karen E.

    Granular solids can be subjected to a finite stress below which the response is elastic. Above this yield stress, however, the material fails catastrophically, undergoing a rapid plastic deformation. In the case of a monotonically increasing stress the material exhibits a characteristic stick-slip response. We investigate the statistics of this intermittent failure in an annular shear geometry, driven with a linear-ramp torque in order to generate the stick-slip behavior. The apparatus is designed to allow visual access to particle trajectories and inter-particle forces (through the use of photoelastic materials). Additionally, twelve piezoelectric sensors at the outer wall measure acoustic emissions due to the plastic deformation of the material. We vary volume fraction, and use both fixed and deformable boundaries. We measure how the distribution of slip size and duration are related to the bulk properties of the packing, and compare to systems with similar governing statistics.

  12. Mechanisms for Acoustic Absorption in Dry and Weakly Wet Granular Media

    SciTech Connect

    Brunet, Th.; Jia, X.; Mills, P.

    2008-09-26

    The dissipation of an elastic wave in dry and wet glass bead packings is measured using multiple sound scattering. The interplay of a linear viscoelastic loss and a nonlinear frictional one is observed in dry media. The Mindlin model provides a qualitative description of the experiment, but fails to quantitatively account for the data due to grain roughness. In weakly wet media, we find that the dissipation is dominated by a linear viscous loss due to the liquid films trapped at the grain surface asperities. Adding more liquid enables us to form the capillary menisci but does not increase the energy loss.

  13. Liquid distribution and cohesion in wet granular assemblies beyond the capillary bridge regime

    NASA Astrophysics Data System (ADS)

    Scheel, M.; Seemann, R.; Brinkmann, M.; Di Michiel, M.; Sheppard, A.; Herminghaus, S.

    2008-12-01

    Dry sand turns into a stiff and moldable material as soon as it is mixed with some liquid. This is a direct consequence of the internal liquid-air interfaces spanning between the grains which causes capillary cohesion by virtue of the surface tension of the liquid. As a model for wet granulates we investigated random packings of submillimeter spherical beads mixed with water. Measurements of the tensile strength and the fluidization threshold demonstrate that the mechanical stiffness is rather insensitive to the liquid content over a wide range. Only for a high liquid content, when more than half of the available pore space is filled with liquid, does the capillary cohesion weaken. In order to understand the interplay between the mechanical properties and the liquid content, we investigated the liquid distribution in random packings of glass spheres by means of x-ray microtomography. The three-dimensional images reveal that the liquid forms a network of capillary bridges fused at local triangular bead configurations. The spontaneous organization of the liquid into these ramified structures, which exhibit a large liquid-air interface, is responsible for the constancy of the cohesive forces in a wide range of liquid contents beyond the onset of capillary bridge coalescence.

  14. Scale invariance and universality of force networks in static granular matter

    NASA Astrophysics Data System (ADS)

    Ostojic, Srdjan; Somfai, Ellák; Nienhuis, Bernard

    2006-02-01

    Force networks form the skeleton of static granular matter. They are the key factor that determines mechanical properties such as stability, elasticity and sound transmission, which are important for civil engineering and industrial processing. Previous studies have focused on investigations of the global structure of external forces (the boundary condition) and on the probability distribution of individual contact forces. So far, however, precise knowledge of the disordered spatial structure of the force network has remained elusive. Here we report that molecular dynamics simulations of realistic granular packings reveal scale invariance of clusters of particles interacting by means of relatively strong forces. Despite visual variation, force networks for various values of the confining pressure and other parameters have identical scaling exponents and scaling function, thereby determining a universality class. Unexpectedly, the flat ensemble of force configurations (a simple generalization of equilibrium statistical mechanics) belongs to this universality class, whereas some widely studied simplified models do not. This implies that the elasticity of the grains and their geometrical disorder do not affect the universal mechanical properties.

  15. Granular activated carbon for removal of organic matter and turbidity from secondary wastewater.

    PubMed

    Hatt, J W; Germain, E; Judd, S J

    2013-01-01

    A range of commercial granular activated carbon (GAC) media have been assessed as pretreatment technologies for a downstream microfiltration (MF) process. Media were assessed on the basis of reduction in both organic matter and turbidity, since these are known to cause fouling in MF membranes. Isotherm adsorption analysis through jar testing with supplementary column trials revealed a wide variation between the different adsorbent materials with regard to organics removal and adsorption kinetics. Comparison with previous work using powdered activated carbon (PAC) revealed that for organic removal above 60% the use of GAC media incurs a significantly lower carbon usage rate than PAC. All GACs tested achieved a minimum of 80% turbidity removal. This combination of turbidity and organic removal suggests that GAC would be expected to provide a significant reduction in fouling of a downstream MF process with improved product water quality. PMID:23306264

  16. Practical wet oxidation experiment to determine concentrations of particulate organic matter in seawater

    NASA Astrophysics Data System (ADS)

    Berger, V. Ya.; Mityaev, M. V.; Sukhotin, A. A.

    2016-03-01

    The report presents results of experiments testifying to the possibility of using wet oxidation to determine the concentrations of organic carbon in marine particulate matter. We describe a method for eliminating the measurement error caused by the influence of chlorides on the processes of dichromate oxidation of organic matter. We present an equation to calculate the concentration of organic carbon depending on that of sodium chloride.

  17. Laboratory Evaluation of Electrostatic Spray Wet Scrubber to Control Particulate Matter Emissions from Poultry Facilities

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Particulate matter (PM) is a major air pollutant emitted from animal production and has significant impacts on health and the environment. Abatement of PM emissions is imperative and effective PM control technologies are strongly needed. In this work, an electrostatic spray wet scrubber (ESWS) techn...

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    Fang, Chung

    2015-07-01

    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.

  20. Mechanisms for slow strengthening in granular materials

    PubMed

    Losert; Geminard; Nasuno; Gollub

    2000-04-01

    Several mechanisms cause a granular material to strengthen over time at low applied stress. The strength is determined from the maximum frictional force F(max) experienced by a shearing plate in contact with wet or dry granular material after the layer has been at rest for a waiting time tau. The layer strength increases roughly logarithmically with tau only if a shear stress is applied during the waiting time. The mechanisms of strengthening are investigated by sensitive displacement measurements, and by imaging of particle motion in the shear zone. Granular matter can strengthen due to a slow shift in the particle arrangement under shear stress. Humidity also leads to strengthening, but is found not to be its sole cause. In addition to these time dependent effects, the static friction coefficient can also be increased by compaction of the granular material under some circumstances, and by a cycling of the applied shear stress. PMID:11088198

  1. Note: "Lock-in accelerometry" to follow sink dynamics in shaken granular matter.

    PubMed

    Sánchez-Colina, G; Alonso-Llanes, L; Martínez, E; Batista-Leyva, A J; Clement, C; Fliedner, C; Toussaint, R; Altshuler, E

    2014-12-01

    Understanding the penetration dynamics of intruders in granular beds is relevant not only for fundamental physics, but also for geophysical processes and construction on sediments or granular soils in areas potentially affected by earthquakes. While the penetration of intruders in two dimensional (2D) laboratory granular beds can be followed using video recording, this is useless in three dimensional (3D) beds of non-transparent materials such as common sand. Here, we propose a method to quantify the sink dynamics of an intruder into laterally shaken granular beds based on the temporal correlations between the signals from a reference accelerometer fixed to the shaken granular bed, and a probe accelerometer deployed inside the intruder. Due to its analogy with the working principle of a lock-in amplifier, we call this technique lock-in accelerometry. PMID:25554337

  2. Fiat or Bona Fide Boundary—A Matter of Granular Perspective

    PubMed Central

    Vogt, Lars; Grobe, Peter; Quast, Björn; Bartolomaeus, Thomas

    2012-01-01

    Background Distinguishing bona fide (i.e. natural) and fiat (i.e. artificial) physical boundaries plays a key role for distinguishing natural from artificial material entities and is thus relevant to any scientific formal foundational top-level ontology, as for instance the Basic Formal Ontology (BFO). In BFO, the distinction is essential for demarcating two foundational categories of material entity: object and fiat object part. The commonly used basis for demarcating bona fide from fiat boundary refers to two criteria: (i) intrinsic qualities of the boundary bearers (i.e. spatial/physical discontinuity, qualitative heterogeneity) and (ii) mind-independent existence of the boundary. The resulting distinction of bona fide and fiat boundaries is considered to be categorial and exhaustive. Methodology/Principal Findings By referring to various examples from biology, we demonstrate that the hitherto used distinction of boundaries is not categorial: (i) spatial/physical discontinuity is a matter of scale and the differentiation of bona fide and fiat boundaries is thus granularity-dependent, and (ii) this differentiation is not absolute, but comes in degrees. By reducing the demarcation criteria to mind-independence and by also considering dispositions and historical relations of the bearers of boundaries, instead of only considering their spatio-structural properties, we demonstrate with various examples that spatio-structurally fiat boundaries can nevertheless be mind-independent and in this sense bona fide. Conclusions/Significance We argue that the ontological status of a given boundary is perspective-dependent and that the strictly spatio-structural demarcation criteria follow a static perspective that is ignorant of causality and the dynamics of reality. Based on a distinction of several ontologically independent perspectives, we suggest different types of boundaries and corresponding material entities, including boundaries based on function (locomotion

  3. Role and significance of extracellular polymeric substances from granular sludge for simultaneous removal of organic matter and ammonia nitrogen.

    PubMed

    Yan, Lilong; Liu, Yu; Wen, Yan; Ren, Yuan; Hao, Guoxin; Zhang, Ying

    2015-03-01

    This study analyzed the organics and content of metal ions in extracellular polymeric substances (EPSs), tightly (TB-EPSs) and loosely (LB-EPSs) bound EPSs of granular sludge with simultaneous removal of organic matters and ammonia nitrogen, studied the dynamic variation of metal ions in EPSs from granular sludge with different particle sizes and the change of zeta potential before and after cation exchange resin (CER) treatment. Results showed, with particle size increasing, the protein content gradually increased, the content of polysaccharide basically unchanged; the content of Ca, Mg, K, Na and Zn also increased, whereas others did not show a consistent regularity. The existence of metal ions reduced zeta potential of EPSs. The existence of metal ions helped to the adhesion among granules, in order to form a granule with bigger particle size. PMID:25575205

  4. Critical Phenomena in Driven Granular Matter: Jamming and Glassy Behavior - Final Report

    SciTech Connect

    Teitel, Stephen

    2013-02-20

    Granular materials, such as powders, seeds, grains, sand, rocks, etc., are ubiquitous both in nature and in industrial processes. At the scale of individual grains, granular systems are particularly simple: particles interact only when they touch. But when viewed in the aggregate, granular systems can display complex behavior. In particular, as the volume packing fraction of the grains increases, the system undergoes a jamming transition from a flowing liquid to a disordered but rigid solid. We study the critical behavior of such systems near the jamming transition using numerical simulations of a simple model of soft-core, bidisperse, frictionless disks in two dimensions. We seek to understand the structural and transport properties of such systems under a variety of physical perturbations such as steady state shear driven flow, and finite thermal fluctuations.

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

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

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

  6. Large nerve cells with long axons in the granular layer and white matter of the murine cerebellum.

    PubMed Central

    Müller, T

    1994-01-01

    The murine cerebellum was investigated by light microscopy using an improved modification of Ehrlich's methylene blue supravital staining technique. The dye exhibited a special affinity for the perikarya as well as the axons of Purkinje cells. In addition, large fusiform or stellate nerve cells which were characterised by long descending axons were seen to be distributed diffusely within the granular layer and the subcortical white matter. These findings indicate the existence of a 2nd type of projection neuron besides the Purkinje cells and are therefore in full accordance with older neuroanatomical observations based on silver impregnation. When correlated with recent studies on the occurrence of different calcium-binding proteins, the results show that the large perikarya demonstrated immunohistochemically within the granular layer seem to belong to the group of methylene blue positive neurons. Nevertheless, the definitive association of a single neuron with a nerve cell class is only possible if the axon is stained and clearly identifiable. Because of its selectivity for a special type of nerve cell, including its axon, the histological method used in this study may therefore also be suitable for investigating other parts of the brain and the spinal cord. Images Fig. 1 Fig. 2 PMID:7516932

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

    NASA Astrophysics Data System (ADS)

    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

  8. Flow of granular matter in a silo with multiple exit orifices: jamming to mixing.

    PubMed

    Kamath, Sandesh; Kunte, Amit; Doshi, Pankaj; Orpe, Ashish V

    2014-12-01

    We investigate the mixing characteristics of dry granular material while draining down a silo with multiple exit orifices. The mixing in the silo, which otherwise consists of noninteracting stagnant and flowing regions, is observed to improve significantly when the flow through specific orifices is stopped intermittently. This momentary stoppage of flow through the orifice is either controlled manually or is chosen by the system itself when the orifice width is small enough to cause spontaneous jamming and unjamming. We observe that the overall mixing behavior shows a systematic dependence on the frequency of closing and opening of specific orifices. In particular, the silo configuration employing random jamming and unjamming of any of the orifices shows early evidence of chaotic mixing. When operated in a multipass mode, the system exhibits a practical and efficient way of mixing particles. PMID:25615084

  9. Exact traveling wave solutions of the van der Waals normal form for fluidized granular matter

    NASA Astrophysics Data System (ADS)

    Abourabia, A. M.; Morad, A. M.

    2015-11-01

    Analytical solutions of the van der Waals normal form for fluidized granular media have been done to study the phase separation phenomenon by using two different exact methods. The Painlevé analysis is discussed to illustrate the integrability of the model equation. An auto-Bäcklund transformation is presented via the truncated expansion and symbolic computation. The results show that the exact solutions of the model introduce solitary waves of different types. The solutions of the hydrodynamic model and the van der Waals equation exhibit a behavior similar to the one observed in molecular dynamic simulations such that two pairs of shock and rarefaction waves appear and move away, giving rise to the bubbles. The dispersion properties and the relation between group and phase velocities of the model equation are studied using the plane wave assumption. The diagrams are drawn to illustrate the physical properties of the exact solutions, and indicate their stability and bifurcation.

  10. Dissipation of Energy by Dry Granular Matter in a Rotating Cylinder

    PubMed Central

    Sack, Achim; Pöschel, Thorsten

    2016-01-01

    We study experimentally the dissipation of energy in a rotating cylinder which is partially filled by granular material. We consider the range of angular velocity corresponding to continous and stationary flow of the granulate. In this regime, the stationary state depends on the angular velocity and on the filling mass. For a wide interval of filling levels we find a universal behavior of the driving torque required to sustain the stationary state as a function of the angular velocity. The result may be of relevance to industrial applications, e.g. to understand the power consumption of ball mills or rotary kilns and also for damping applications where mechanical energy has to be dissipated in a controlled way. PMID:27255925

  11. Dissipation of Energy by Dry Granular Matter in a Rotating Cylinder.

    PubMed

    Sack, Achim; Pöschel, Thorsten

    2016-01-01

    We study experimentally the dissipation of energy in a rotating cylinder which is partially filled by granular material. We consider the range of angular velocity corresponding to continous and stationary flow of the granulate. In this regime, the stationary state depends on the angular velocity and on the filling mass. For a wide interval of filling levels we find a universal behavior of the driving torque required to sustain the stationary state as a function of the angular velocity. The result may be of relevance to industrial applications, e.g. to understand the power consumption of ball mills or rotary kilns and also for damping applications where mechanical energy has to be dissipated in a controlled way. PMID:27255925

  12. Dissipation of Energy by Dry Granular Matter in a Rotating Cylinder

    NASA Astrophysics Data System (ADS)

    Sack, Achim; Pöschel, Thorsten

    2016-06-01

    We study experimentally the dissipation of energy in a rotating cylinder which is partially filled by granular material. We consider the range of angular velocity corresponding to continous and stationary flow of the granulate. In this regime, the stationary state depends on the angular velocity and on the filling mass. For a wide interval of filling levels we find a universal behavior of the driving torque required to sustain the stationary state as a function of the angular velocity. The result may be of relevance to industrial applications, e.g. to understand the power consumption of ball mills or rotary kilns and also for damping applications where mechanical energy has to be dissipated in a controlled way.

  13. The effect of water temperature on the adsorption equilibrium of dissolved organic matter and atrazine on granular activated carbon

    SciTech Connect

    Bernd Schreiber; Viktor Schmalz; Thomas Brinkmann; Eckhard Worch

    2007-09-15

    The influence of water temperature on the adsorption of natural dissolved organic matter (DOM) on activated carbon has not been investigated intensively yet. In this study, batch experiments with granular activated carbon (GAC) F300, from bituminous coal, have been carried out at three temperatures (5, 20, 35{sup o} C) using a humic acid model water and different types of surface water (lake, river, canal). Furthermore, the adsorption of an anthropogenic contaminant, atrazine, was quantified in the absence and presence of DOM. The results indicate a significant influence of water temperature on the adsorption equilibrium of DOM and atrazine. Contrary to expectations, DOM and atrazine adsorption in surface water tends to be increased with increasing water temperature, whereas the extent of this effect is dependent on the type and concentration of DOM. Furthermore, the temperature effect on atrazine adsorption is controlled by competition of DOM and atrazine on adsorption sites. Some assumptions are proposed and discussed for explaining the temperature effects observed in the batch studies. 39 refs., 4 figs., 2 tabs.

  14. Permittivity of porous granular matter, in relation with Rosetta cometary mission

    NASA Astrophysics Data System (ADS)

    Brouet, Y.; Levasseur-Regourd, A. C.; Encrenaz, P.; Gulkis, S.

    2014-11-01

    We report measurements in laboratory conditions of the relative complex permittivity (hereafter permittivity) of porous material on a large range of frequencies from 50 MHz to 190 GHz. Such measurements, developed in preparation of the Rosetta mission to comet 67P/Churyumov-Gerasimenko, specifically for the MIRO radiometric experiment, were obtained with different instrumentations in three frequency bands: 50-500 MHz, 2.45 - 12 GHz and 190 GHz (center-band frequency of the millimeter receiver of MIRO, specially developed for our purpose). Considering the expected properties of cometary nuclei, they were carried out with porous granular materials of volcanic origin, with various sizes ranging from a few to 500 μm, i.e. Etna's ashes and NASA JSC Mars-1 martian soil simulant. The samples were split into several sub-samples with different size ranges and bulk densities. The real part and the imaginary part of the permittivity remain respectively in the 2.1 - 4.0 range and in the 0.05 - 0.31 range. Volume scattering becomes significant for the measurements at 190 GHz when the mean grain size of sub-samples is greater than about 200 μm and implies an increase of the real part and the imaginary part of the permittivity. Without this effect, for any sub-sample, the results are consistent over the frequency range. From 50 MHz to 190 GHz, evidence is provided for a slight decrease of the real part of the permittivity. Bulk densities of the sub-samples, being in the 800-1300 kg m-3 range, were determined during the measurements at 190 GHz. Taking into account the expected bulk density of the nucleus (100-370 kg m-3), as well as temperature for the surface and subsurface (in the 30-300 K range) and its composition (consisting both of silica-rich dust and ices, mostly of water), these first series of results allow an estimate of the real part and the imaginary part of the permittivity of the near-surface of the cometary nucleus: the real part is likely to be lower than 1

  15. Water drop dynamics on a granular layer

    NASA Astrophysics Data System (ADS)

    Llorens, Coraline; Biance, Anne-Laure; Ybert, Christophe; Pirat, Christophe; Liquids; Interfaces Team

    2015-11-01

    Liquid drop impacts, either on a solid surface or a liquid bath, have been studied for a while and are still subject of intense research. Less is known concerning impacts on granular layers that are shown to exhibit an intermediate situation between solid and liquid. In this study, we focus on water drop impacts on granular matter made of micrometer-sized spherical glass beads. In particular, we investigate the overall dynamics arising from the interplay between liquid and grains throughout the impact. Depending on the relevant parameters (impact velocity, drop and grain sizes, as well as their wetting properties), various behaviors are evidenced. In particular, the behavior of the beads at the liquid-gas interface (ball-bearing vs imbibition) is shown to greatly affect the spreading dynamics of the drop, as well as satellite droplets formation, beads ejection, and the final crater morphology.

  16. WET SOLIDS FLOW ENHANCEMENT

    SciTech Connect

    Hugo S. Caram; Natalie Foster

    1999-07-01

    The strain-stress behavior of a wet granular media was measured using a split Parfitt tensile tester. In all cases the stress increases linearly with distance until the maximum uniaxial tensile stress is reached. The stress then decreases exponentially with distance after this maximum is reached. The linear region indicates that wet solids behave elastically for stresses below the tensile stresses and can store significant elastic energy. The elastic deformation cannot be explained by analyzing the behavior of individual capillary bridges and requires accounting for the deformation of the solids particles. The elastic modulus of the wet granular material remains unexplained.

  17. WET SOLIDS FLOW ENHANCEMENT

    SciTech Connect

    Hugo S. Caram; Natalie Foster

    1998-03-30

    The strain-stress behavior of a wet granular media was measured using a split Parfitt tensile tester. In all cases the stress increases linearly with distance until the maximum uniaxial tensile stress is reached. The stress then decreases exponentially with distance after this maximum is reached. The linear region indicates that wet solids behave elastically for stresses below the tensile stresses and can store significant elastic energy. The elastic deformation cannot be explained by analyzing the behavior of individual capillary bridges and may require accounting for the deformation of the solids particles. The elastic modulus of the wet granular material remains unexplained.

  18. Removal of particulate matter in a tubular wet electrostatic precipitator using a water collection electrode.

    PubMed

    Kim, Jong-Ho; Yoo, Hee-Jung; Hwang, You-Seong; Kim, Hyeok-Gyu

    2012-01-01

    As one of the effective control devices of air pollutants, the wet electrostatic precipitator (ESP) is an effective technique to eliminate acid mist and fine particles that are re-entrained in a collection electrode. However, its collection efficiency can deteriorate, as its operation is subject to water-induced corrosion of the collection electrode. To overcome this drawback, we modified the wet ESP system with the installation of a PVC dust precipitator wherein water is supplied as a replacement of the collection electrode. With this modification, we were able to construct a compact wet ESP with a small specific collection area (SCA, 0.83 m(2)/(m(3)/min)) that can acquire a high collection efficiency of fine particles (99.7%). PMID:22577353

  19. COMBINED USE OF ION EXCHANGE RESINS AND GRANULAR ACTIVATED CARBON FOR THE CONTROL OF ORGANIC MATTER AND DISINFECTION BY PRODUCTS

    EPA Science Inventory

    The use of anion exchange resin as a pretreatment step to granular activated carbon is evaluated. erformance is evaluated by DOC, SAC, TOXFP, and THMFP parameters. hio River water and Palm Beach groundwater are used. he results show that resin pretreatment is significant in exten...

  20. The repeated drying-wetting and freezing-thawing cycles affect only the active pool of soil organic matter

    NASA Astrophysics Data System (ADS)

    Semenov, Vyacheslav; Zinyakova, Natalya; Tulina, Anastasiya

    2016-04-01

    The decrease in the content of soil organic carbon, particularly in active form, is one of the major problems of the 21st century, which is closely related to the disturbance of the biogeochemical carbon cycle and to the increase in the emission of carbon dioxide into the atmosphere. The main reasons for the SOM losses are the surplus of the SOM active pool losses due to mineralization, erosion, and infiltration over the input of fresh organic matter to the soil, as well as the changes in the soil conditions and processes due to natural and anthropogenic disturbing impacts. Experiments were carried out with mixed samples from the upper layers of soddy-podzolic soil, gray forest soil, and typical chernozems. Soil samples as controls were incubated after wetting for 150 days. The dynamics and cumulative production of C-CO2 under stable temperature (22°C) and moisture conditions were determined; the initial content of potentially mineralizable organic matter (C0) in the soil at the beginning of the incubation was then calculated to use these data as the control. Other soil samples were exposed in flasks to the following successive treatments: wetting →incubation → freezing → thawing → incubation →drying. Six repeated cycles of disturbing impacts were performed for 140 days of the experiment. After six cycles, the soil samples were incubated under stable temperature and moisture conditions for 150 days. The wetting of dried soils and the thawing of frozen soils are accompanied by the pulsed dynamics of the C-CO2 production with an abrupt increase in the rate of the C-CO2 emission within several days by 2.7-12.4 and 1.6-2.7 times, respectively, compared to the stable incubation conditions. The rate of the C-CO2 production pulses under each subsequent impact decreased compared to the preceding one similarly for all studied soils, which could be due to the depletion in potentially mineralizable soil organic matter (C0). The cumulative extra C-CO2 production by

  1. Enzymatic Hydrolysis and Ethanol Fermentation of High Dry Matter Wet-Exploded Wheat Straw at Low Enzyme Loading

    NASA Astrophysics Data System (ADS)

    Georgieva, Tania I.; Hou, Xiaoru; Hilstrøm, Troels; Ahring, Birgitte K.

    Wheat straw was pretreated by wet explosion using three different oxidizing agents (H2O2, O2, and air). The effect of the pretreatment was evaluated based on glucose and xylose liberated during enzymatic hydrolysis. The results showed that pretreatment with the use of O2 as oxidizing agent was the most efficient in enhancing overall convertibility of the raw material to sugars and minimizing generation of furfural as a by-product. For scale-up of the process, high dry matter (DM) concentrations of 15-20% will be necessary. However, high DM hydrolysis and fermentation are limited by high viscosity of the material, higher inhibition of the enzymes, and fermenting microorganism. The wet-explosion pretreatment method enabled relatively high yields from both enzymatic hydrolysis and simultaneous saccharification and fermentation (SSF) to be obtained when performed on unwashed slurry with 14% DM and a low enzyme loading of 10 FPU/g cellulose in an industrial acceptable time frame of 96 h. Cellulose and hemicellulose conversion from enzymatic hydrolysis were 70 and 68%, respectively, and an overall ethanol yield from SSF was 68%.

  2. Effects of surface-active organic matter on carbon dioxide nucleation in atmospheric wet aerosols: a molecular dynamics study.

    PubMed

    Daskalakis, Vangelis; Charalambous, Fevronia; Panagiotou, Fostira; Nearchou, Irene

    2014-11-21

    Organic matter (OM) uptake in cloud droplets produces water-soluble secondary organic aerosols (SOA) via aqueous chemistry. These play a significant role in aerosol properties. We report the effects of OM uptake in wet aerosols, in terms of the dissolved-to-gas carbon dioxide nucleation using molecular dynamics (MD) simulations. Carbon dioxide has been implicated in the natural rainwater as well as seawater acidity. Variability of the cloud and raindrop pH is assumed in space and time, as regional emissions, local human activities and geophysical characteristics differ. Rain scavenging of inorganic SOx, NOx and NH3 plays a major role in rain acidity in terms of acid-base activity, however carbon dioxide solubility also remains a key parameter. Based on the MD simulations we propose that the presence of surface-active OM promotes the dissolved-to-gas carbon dioxide nucleation in wet aerosols, even at low temperatures, strongly decreasing carbon dioxide solubility. A discussion is made on the role of OM in controlling the pH of a cloud or raindrop, as a consequence, without involving OM ionization equilibrium. The results are compared with experimental and computational studies in the literature. PMID:25272147

  3. Rain pH estimation based on the particulate matter pollutants and wet deposition study.

    PubMed

    Singh, Shweta; Elumalai, Suresh Pandian; Pal, Asim Kumar

    2016-09-01

    In forecasting of rain pH, the changes caused by particulate matter (PM) are generally neglected. In regions of high PM concentration like Dhanbad, the role of PM in deciding the rain pH becomes important. Present work takes into account theoretical prediction of rain pH by two methods. First method considers only acid causing gases (ACG) like CO2, SO2 and NOx in pH estimation, whereas, second method additionally accounts for effect of PM (ACG-PM). In order to predict the rain pH, site specific deposited dust that represents local PM was studied experimentally for its impact on pH of neutral water. After incorporation of PM correction factor, it was found that, rain pH values estimated were more representative of the observed ones. Fractional bias (FB) for the ACG-PM method reduced to values of the order of 10(-2) from those with order of 10(-1) for the ACG method. The study confirms neutralization of rain acidity by PM. On account of this, rain pH was found in the slightly acidic to near neutral range, despite of the high sulfate flux found in rain water. Although, the safer range of rain pH blurs the severity of acid rain from the picture, yet huge flux of acidic and other ions get transferred to water bodies, soil and ultimately to the ground water system. Simple use of rain pH for rain water quality fails to address the issues of its increased ionic composition due to the interfering pollutants and thus undermines severity of pollutants transferred from air to rain water and then to water bodies and soil. PMID:27139302

  4. Dissolved Organic Matter as a Mechanism for Carbon Stabilization at Depth in Wet Tropical Forest Volcanic Soils

    NASA Astrophysics Data System (ADS)

    Marin-Spiotta, E.; Kramer, M. G.; Chadwick, O. A.

    2007-12-01

    Dissolved organic matter (DOM) plays an important role in many biological and chemical processes in soils. Our understanding of the types of plant and microbially-derived organic matter that accumulate in soils and the mechanisms responsible for their transformation and stabilization is still limited. In particular, we know very little about how microbial activity and water movement contribute to the production of DOM and the formation of stable C in soils. In well-drained soils under wet climates, DOM is potentially a primary pathway for the transport of C from the surface litter layers and the zones of highest microbial activity to deeper horizons in the soil profile where the potential for long-term storage increases. The mechanisms for long-term stabilization of organic C in deep mineral horizons include an accumulation of chemically recalcitrant C, strong sorption of soluble and otherwise labile C to mineral and/or metals making them inaccessible to decomposers, and microenvironmental conditions (low pH, low O2) which result in incomplete decomposition and persistence of labile C. Although most work to date has focused on the role of dissolved organic C and N (DOC and DON) in the C and N cycles of temperate forests, DOM fluxes may be even more important in forests in the wet tropics, where high rainfall and high primary productivity could lead to greater DOM production. In order to address the role of DOC in the transport and stabilization of C in mineral horizons, we are studying DOC production, transformation, and loss pathways in volcanic soils dominated by highly reactive, non-crystalline minerals (allophane). We are quantifying flux and solute concentrations (C, N, cations, anions) in rainwater, throughfall, and in soil water. We have installed tension and zero tension lysimeters throughout sequentially deeper organic and mineral horizons in an intermediate aged soil (ca. 350k years) under wet (ca. 3000 mm mean annual rainfall) native tropical forest

  5. Stabilization of Stormwater Biofilters: Impacts of Wetting and Drying Phases and the Addition of Organic Matter to Filter Media

    NASA Astrophysics Data System (ADS)

    Subramaniam, D. N.; Egodawatta, P.; Mather, P.; Rajapakse, J. P.

    2015-09-01

    Ripening period refers to a phase of stabilization in sand filters in water treatment systems that follow a new installation or cleaning of the filter. Intermittent wetting and drying, a unique property of stormwater biofilters, would similarly be subjected to a phase of stabilization. Suspended solids are an important parameter that is often used to monitor the stabilization of sand filters in water treatment systems. Stormwater biofilters, however, contain organic material that is added to the filter layer to enhance nitrate removal, the dynamics of which is seldom analyzed in stabilization of stormwater biofilters. Therefore, in this study of stormwater biofiltration in addition to suspended solids (turbidity), organic matter (TOC, DOC, TN, and TKN) was also monitored as a parameter for stabilization of the stormwater biofilter. One Perspex bioretention column (94 mm internal diameter) was fabricated with filter layer that contained 8 % organic material and fed with tapwater with different antecedent dry days (0-40 day) at 100 mL/min. Samples were collected from the outflow at different time intervals between 2 and 150 min and were tested for total organic carbon, dissolved organic carbon, total nitrogen, total Kjeldhal nitrogen, and turbidity. The column was observed to experience two phases of stabilization, one at the beginning of each event that lasted for 30 min, while the other phase was observed across subsequent events that are related to the age of filter.

  6. Stabilization of Stormwater Biofilters: Impacts of Wetting and Drying Phases and the Addition of Organic Matter to Filter Media.

    PubMed

    Subramaniam, D N; Egodawatta, P; Mather, P; Rajapakse, J P

    2015-09-01

    Ripening period refers to a phase of stabilization in sand filters in water treatment systems that follow a new installation or cleaning of the filter. Intermittent wetting and drying, a unique property of stormwater biofilters, would similarly be subjected to a phase of stabilization. Suspended solids are an important parameter that is often used to monitor the stabilization of sand filters in water treatment systems. Stormwater biofilters, however, contain organic material that is added to the filter layer to enhance nitrate removal, the dynamics of which is seldom analyzed in stabilization of stormwater biofilters. Therefore, in this study of stormwater biofiltration in addition to suspended solids (turbidity), organic matter (TOC, DOC, TN, and TKN) was also monitored as a parameter for stabilization of the stormwater biofilter. One Perspex bioretention column (94 mm internal diameter) was fabricated with filter layer that contained 8 % organic material and fed with tapwater with different antecedent dry days (0-40 day) at 100 mL/min. Samples were collected from the outflow at different time intervals between 2 and 150 min and were tested for total organic carbon, dissolved organic carbon, total nitrogen, total Kjeldhal nitrogen, and turbidity. The column was observed to experience two phases of stabilization, one at the beginning of each event that lasted for 30 min, while the other phase was observed across subsequent events that are related to the age of filter. PMID:25971737

  7. Bioturbation and dissolved organic matter enhance contaminant fluxes from sediment treated with powdered and granular activated carbon.

    PubMed

    Kupryianchyk, D; Noori, A; Rakowska, M I; Grotenhuis, J T C; Koelmans, A A

    2013-05-21

    Sediment amendment with activated carbon (AC) is a promising technique for in situ sediment remediation. To date it is not clear whether this technique sufficiently reduces sediment-to-water fluxes of sediment-bound hydrophobic organic chemicals (HOCs) in the presence of bioturbators. Here, we report polychlorobiphenyl (PCB) pore water concentrations, fluxes, mass transfer coefficients, and survival data of two benthic species, for four treatments: no AC addition (control), powdered AC addition, granular AC addition and addition and subsequent removal of GAC (sediment stripping). AC addition decreased mass fluxes but increased apparent mass transfer coefficients because of dissolved organic carbon (DOC) facilitated transport across the benthic boundary layer (BBL). In turn, DOC concentrations depended on bioturbator activity which was high for the PAC tolerant species Asellus aquaticus and low for AC sensitive species Lumbriculus variegatus. A dual BBL resistance model combining AC effects on gradients, DOC facilitated transport and biodiffusion was evaluated against the data and showed how the type of resistance differs with treatment and chemical hydrophobicity. Data and simulations illustrate the complex interplay between AC and contaminant toxicity to benthic organisms and how differences in species tolerance affect mass fluxes from sediment to the water column. PMID:23590290

  8. Adsorption of organic contaminants by graphene nanosheets, carbon nanotubes and granular activated carbons under natural organic matter preloading conditions.

    PubMed

    Ersan, Gamze; Kaya, Yasemin; Apul, Onur G; Karanfil, Tanju

    2016-09-15

    The effect of NOM preloading on the adsorption of phenanthrene (PNT) and trichloroethylene (TCE) by pristine graphene nanosheets (GNS) and graphene oxide nanosheet (GO) was investigated and compared with those of a single-walled carbon nanotube (SWCNT), a multi-walled carbon nanotube (MWCNT), and two coal based granular activated carbons (GACs). PNT uptake was higher than TCE by all adsorbents on both mass and surface area bases. This was attributed to the hydrophobicity of PNT. The adsorption capacities of PNT and TCE depend on the accessibility of the organic molecules to the inner regions of the adsorbent which was influenced from the molecular size of OCs. The adsorption capacities of all adsorbents decreased as a result of NOM preloading due to site competition and/or pore/interstice blockage. However, among all adsorbents, GO was generally effected least from the NOM preloading for PNT, whereas there was not observed any trend of NOM competition with a specific adsorbent for TCE. In addition, SWCNT was generally affected most from the NOM preloading for TCE and there was not any trend for PNT. The overall results indicated that the fate and transport of organic contaminants by GNSs and CNTs type of nanoadsorbents and GACs in different natural systems will be affected by water quality parameters, characteristics of adsorbent, and properties of adsorbate. PMID:27107611

  9. WET SOLIDS FLOW ENHANCEMENT

    SciTech Connect

    Hugo S. Caram; Natalie Foster

    1997-03-31

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

  10. WET SOLIDS FLOW ENHANCEMENT

    SciTech Connect

    Hugo S. Caram; Natalie Foster

    1999-03-30

    The elastic modulus E of wet granular material was found to be of the order of 0.25 MPa, this value does not compare well with the value predicted for a cubic array of spheres under Hertzian contact were the predicted values were in the order of 250 MPa . The strain-stress behavior of a wet granular media was measured using a split Parfitt tensile tester. In all cases the stress increases linearly with distance until the maximum uniaxial tensile stress is reached. The stress then decreases exponentially with distance after this maximum is reached. The linear region indicates that wet solids behave elastically for stresses below the tensile stresses and can store significant elastic energy. The elastic deformation cannot be explained by analyzing the behavior of individual capillary bridges and requires accounting for the deformation of the solids particles. The elastic modulus of the wet granular material remains unexplained. New information was found to support the experimental finding and a first theory to explain the very small elastic modulus is presented. A new model based on the used of the finite element method is being developed.

  11. Effect of granular activated carbon concentration on the content of organic matter and salt, influencing E. coli activity and survival in fluidized bed disinfection reactor.

    PubMed

    Racyte, Justina; Langenhoff, Alette A M; Ribeiro, Ana F M M R; Paulitsch-Fuchs, Astrid H; Bruning, Harry; Rijnaarts, Huub H M

    2014-10-01

    Granular activated carbon (GAC) is used in water treatment systems, typically to remove pollutants such as natural organic matter, volatile organic compounds, chlorine, taste, and odor. GAC is also used as a key component of a new technology that combines a fluidized bed reactor with radio frequency electric fields for disinfection. So far, the effects of GAC on bacteria in these fluidized bed reactors are unclear. This paper describes a systematic study of the physico-chemical changes in five microbial media compositions caused by different concentrations (23-350 g/L) of GAC, and the effects of these physico-chemical changes on the metabolic activity and survival of a model microorganism (Escherichia coli YMc10) in a fluidized bed reactor. The chemical adsorption taking place in suspensions with specific GAC changed nutritional, osmotic, and pH conditions in the investigated microbial media (LB, diluted LB, PBS, diluted PBS, and tap water), leading to a decay of the metabolic activity and survival of E. coli. Especially media that are poor in organic and mineral compounds (e.g., PBS) with suspended GAC showed a concentration decay of 3.5 Log CFU/mL E. coli after 6 h. Organic compounds depletion and severe pH variation were enhanced in the presence of higher GAC concentrations. PMID:24729067

  12. Interfacial Instability during Granular Erosion

    NASA Astrophysics Data System (ADS)

    Lefebvre, Gautier; Merceron, Aymeric; Jop, Pierre

    2016-02-01

    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.

  13. Interfacial Instability during Granular Erosion.

    PubMed

    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. PMID:26919014

  14. Removal of dissolved organic matter by granular-activated carbon adsorption as a pretreatment to reverse osmosis of membrane bioreactor effluents.

    PubMed

    Gur-Reznik, Shirra; Katz, Ilan; Dosoretz, Carlos G

    2008-03-01

    The adsorption of dissolved organic matter (DOM) on granular-activated carbon (GAC) as a pretreatment to reverse osmosis (RO) desalination of membrane bioreactor (MBR) effluents was studied in lab- and pilot-scale columns. The pattern and efficiency of DOM adsorption and fate of the hydrophobic (HPO), transphilic (TPI) and hydrophilic (HPI) fractions were characterized, as well as their impact on organic fouling of the RO membranes. Relatively low DOM adsorption capacity and low intensity of adsorption were observed in batch studies. Continuous adsorption experiments performed within a range of hydraulic velocities of 0.9-12m/h depicted permissible values within the mass transfer zone up to 1.6m/h. The breakthrough curves within this range displayed a non-adsorbable fraction of 24+/-6% and a biodegradable fraction of 49+/-12%. Interestingly, the adsorbable fraction remained almost constant ( approximately 30%) in the entire hydraulic range studied. Comparative analysis by HPO interaction chromatography showed a steady removal (63-66%) of the HPO fraction. SUVA index and Fourier Transform Infrared (FTIR) spectra indicated that DOM changes during the adsorption phase were mainly due to elution of the more HPI components. GAC pretreatment in pilot-scale columns resulted in 80-90% DOM removal from MBR effluents, which in turn stabilized membrane permeability and increased permeate quality. FTIR analysis indicated that the residual DOM present in the RO permeate, regardless of the pretreatment, was mainly of HPI character (e.g., low-molecular-weight humics linked to polysaccharides and proteins). The DOM removed by GAC pretreatment is composed mainly of HPO and biodegradable components, which constitutes the fraction primarily causing organic fouling. PMID:17980400

  15. The effect of moisture content on the dynamic fragmentation of wet sand at high strain rates

    NASA Astrophysics Data System (ADS)

    Xue, Kun

    2014-03-01

    A comprehensive model is established to account for the instability onset of rapidly expanding granular shells subject to the explosion loadings generated by the detonation of the central explosives. The moisture content strongly influences the shock interactions in the wet particle beds and the ensuing evolvement of the granular compacts. A material model for granular materials which can account for the degree of saturation was incorporated into a non-linear dynamic simulation program to investigate the moisture of effect on the shock responses of wet granular materials. In conjunction with our instability model, the predicted instability diameters of the expanding dry/wet granular shells are in a good agreement with the experimental results. Particularly the postponed instability onset of the wet granular shell found both experimentally and analytically can largely be attributed to the significantly greater kinetic energy obtained by wet particles thanks to less energy of shock wave consumed in compacting the granular materials.

  16. The effect of moisture content on the explosively driven fragmentation of wet sand

    NASA Astrophysics Data System (ADS)

    Xue, K.

    2014-05-01

    A comprehensive model is established to account for the instability onset of rapidly expanding granular shells subject to the explosion loadings generated by the detonation of the central explosives. The moisture content strongly influences the shock interactions in the wet particle beds and the ensuing evolvement of the granular compacts. A material model for granular materials which can account for the degree of saturation was incorporated into a nonlinear dynamic simulation program to investigate the moisture effect on the shock responses of wet granular materials. In conjunction with our instability model, the predicted instability diameters of the expanding dry/wet granular shells are in a good agreement with the experimental results. Particularly the postponed instability onset of the wet granular shell found both experimentally and analytically can largely be attributed to the significantly greater kinetic energy obtained by wet particles thanks to less energy of shock wave consumed in compacting the granular material.

  17. Dilatancy in Slow Granular Flows

    NASA Astrophysics Data System (ADS)

    Kabla, Alexandre J.; Senden, Tim J.

    2009-06-01

    When walking on wet sand, each footstep leaves behind a temporarily dry impression. This counterintuitive observation is the most common illustration of the Reynolds principle of dilatancy: that is, a granular packing tends to expand as it is deformed, therefore increasing the amount of porous space. Although widely called upon in areas such as soil mechanics and geotechnics, a deeper understanding of this principle is constrained by the lack of analytical tools to study this behavior. Using x-ray radiography, we track a broad variety of granular flow profiles and quantify their intrinsic dilatancy behavior. These measurements frame Reynolds dilatancy as a kinematic process. Closer inspection demonstrates, however, the practical importance of flow induced compaction which competes with dilatancy, leading more complex flow properties than expected.

  18. Dilatancy in slow granular flows.

    PubMed

    Kabla, Alexandre J; Senden, Tim J

    2009-06-01

    When walking on wet sand, each footstep leaves behind a temporarily dry impression. This counterintuitive observation is the most common illustration of the Reynolds principle of dilatancy: that is, a granular packing tends to expand as it is deformed, therefore increasing the amount of porous space. Although widely called upon in areas such as soil mechanics and geotechnics, a deeper understanding of this principle is constrained by the lack of analytical tools to study this behavior. Using x-ray radiography, we track a broad variety of granular flow profiles and quantify their intrinsic dilatancy behavior. These measurements frame Reynolds dilatancy as a kinematic process. Closer inspection demonstrates, however, the practical importance of flow induced compaction which competes with dilatancy, leading more complex flow properties than expected. PMID:19658906

  19. Crystalline silica dust and respirable particulate matter during indoor concrete grinding - wet grinding and ventilated grinding compared with uncontrolled conventional grinding.

    PubMed

    Akbar-Khanzadeh, Farhang; Milz, Sheryl; Ames, April; Susi, Pamela P; Bisesi, Michael; Khuder, Sadik A; Akbar-Khanzadeh, Mahboubeh

    2007-10-01

    The effectiveness of wet grinding (wet dust reduction method) and ventilated grinding (local exhaust ventilation method, LEV) in reducing the levels of respirable crystalline silica dust (quartz) and respirable suspended particulate matter (RSP) were compared with that of uncontrolled (no dust reduction method) conventional grinding. A field laboratory was set up to simulate concrete surface grinding using hand-held angle grinders in an enclosed workplace. A total of 34 personal samples (16 pairs side-by-side and 2 singles) and 5 background air samples were collected during 18 concrete grinding sessions ranging from 15-93 min. General ventilation had no statistically significant effect on operator's exposure to dust. Overall, the arithmetic mean concentrations of respirable crystalline silica dust and RSP in personal air samples during: (i) five sessions of uncontrolled conventional grinding were respectively 61.7 and 611 mg/m(3) (ii) seven sessions of wet grinding were 0.896 and 11.9 mg/m(3) and (iii) six sessions of LEV grinding were 0.155 and 1.99 mg/m(3). Uncontrolled conventional grinding generated relatively high levels of respirable silica dust and proportionally high levels of RSP. Wet grinding was effective in reducing the geometric mean concentrations of respirable silica dust 98.2% and RSP 97.6%. LEV grinding was even more effective and reduced the geometric mean concentrations of respirable silica dust 99.7% and RSP 99.6%. Nevertheless, the average level of respirable silica dust (i) during wet grinding was 0.959 mg/m(3) (38 times the American Conference of Governmental Industrial Hygienists [ACGIH] threshold limit value [TLV] of 0.025 mg/m(3)) and (ii) during LEV grinding was 0.155 mg/m(3) (6 times the ACGIH TLV). Further studies are needed to examine the effectiveness of a greater variety of models, types, and sizes of grinders on different types of cement in different positions and also to test the simulated field lab experimentation in the field

  20. Survey on granularity clustering.

    PubMed

    Ding, Shifei; Du, Mingjing; Zhu, Hong

    2015-12-01

    With the rapid development of uncertain artificial intelligent and the arrival of big data era, conventional clustering analysis and granular computing fail to satisfy the requirements of intelligent information processing in this new case. There is the essential relationship between granular computing and clustering analysis, so some researchers try to combine granular computing with clustering analysis. In the idea of granularity, the researchers expand the researches in clustering analysis and look for the best clustering results with the help of the basic theories and methods of granular computing. Granularity clustering method which is proposed and studied has attracted more and more attention. This paper firstly summarizes the background of granularity clustering and the intrinsic connection between granular computing and clustering analysis, and then mainly reviews the research status and various methods of granularity clustering. Finally, we analyze existing problem and propose further research. PMID:26557926

  1. Estimating Losses of Dry Matter from Wetted Alfalfa-Orchardgrass Mixtures Using Cell Wall Components as Internal Markers

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Methods previously used to measure recoveries of dry matter (DM) from forages following natural or simulated rainfall often have relied upon simple gravimetric techniques, which yielded inconclusive estimates of DM recovery. Our objective was to evaluate insoluble cell-wall constituents as internal ...

  2. Granular temperature field of monodisperse granular flows

    NASA Astrophysics Data System (ADS)

    Gollin, Devis; Bowman, Elisabeth; Shepley, Paul

    2015-04-01

    For dry granular flows as well as solid-fluid mixtures such as debris avalanches, the momentum transfer is carried by frictional and collisional stresses. The latter may be described by the granular temperature, which provides a measure of the energy contained within the fluctuating nature of the granular motion. Thus, granular temperature can be used as a valuable means to infer the ability of a granular system to flow. Granular materials are known for the difficulties they pose in obtaining accurate microscale laboratory measurements. This is why many theories, such as the kinetic theory of granular gases, are primarily compared to numerical simulations. However, thanks to recent advancements in optical techniques along with high-speed recording systems, experimentalists are now able to obtain robust measurements of granular temperature. At present, the role of granular temperature in granular flows still entails conjecture. As a consequence, it is extremely important to provide experimental data against which theories and simulations can be judged. This investigation focuses on dry granular flows of sand and spherical beads performed on a simple inclined chute geometry. Fluctuation velocity, granular temperature and velocity patterns are obtained by means of particle image velocimetry (PIV). Flow behaviour is probed for different spatial (interrogation sizes) and temporal (frame rates) resolutions. Through the variation of these parameters an attempt to demonstrate the consistency of the degree of unsteadiness within the flow is made. In many studies a uniform stationary flow state is usually sought or preferably assumed for the simplicity it provides in the calculations. If one tries to measure microscale fields such as granular temperature, this assumption may be inappropriate. Thus, a proper definition of the flow regime should be made in order to estimate the correct flow properties. In addition, PIV analysis is compared against particle tracking velocimetry

  3. WET SOLIDS FLOW ENHANCEMENT

    SciTech Connect

    Unknown

    2001-03-25

    The yield locus, tensile strength and fracture mechanisms of wet granular materials were studied. The yield locus of a wet material was shifted to the left of that of the dry specimen by a constant value equal to the compressive isostatic stress due to pendular bridges. for materials with straight yield loci, the shift was computed from the uniaxial tensile strength, either measured in a tensile strength tester or calculated from the correlation, and the angle of internal friction of the material. The predicted shift in the yield loci due to different moisture contents compare well with the measured shift in the yield loci of glass beads, crushed limestone, super D catalyst and Leslie coal. Measurement of the void fraction during the shear testing was critical to obtain the correct tensile strength theoretically or experimentally.

  4. Harnessing the instabilities of soft matter: Dynamically tuning of wetting, assembly and pattern transformation in polymer microstructures

    NASA Astrophysics Data System (ADS)

    Zhang, Ying

    2008-10-01

    In this dissertation, we have investigated the fabrication, mechanical instability and applications of two kinds of polymer micro/nano-structures: high-aspect-ratio (HAR) polymer pillar arrays, and periodic porous elastomer membranes. For HAR polymer pillar arrays, we demonstrated the fabrication of high-aspect-ratio (up to 18) polymer micropillars with different shapes and dimensions by replica molding. Capillary force lithography (CFL) is also demonstrated as a simple and flexible method to fabricate microstructures with controlled aspect ratios. Meanwhile, by introducing conventional photoresist SU-8, CFL is successfully coupled with photolithography and used to create hierarchical 2D or 3D structures, which greatly expand the capability of current capillary force lithography. The mechanical stability of HAR structures with varied materials and different aspect ratio, density and shape were also studied and the results show that the adhesive forces from environment are the major cause of structure collapsing. When HAR polymer pillars are subjected to different solvents treatment, both capillary force and solvent swelling need to be considered to completely understand the structure instability. On HAR micropillar array, thermoresponsive polymer brushes, poly ( N-isopropylacrylamide) (PNIPAAm), were selectively grafted at different locations for dynamically tuning surface wetting or pattern assembly. When the temperature changed from 40°C to 20°, depending on the location of polymer brushes, different wetting transitions, either from a composite solid/air state (Cassie state) to a composite solid/liquid state (Hemi-wicking state) or a transition between two Cassie states were observed. Meanwhile, the dynamically tuning of water contact angle enables us to control capillary drying force and thus harness pattern collapse to create superlattice micropatterns. For periodic porous elastomer membrane, a novel pattern transformation effect is discovered due to the

  5. Scaling of liquid-drop impact craters in granular media

    NASA Astrophysics Data System (ADS)

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

    Granular impact cratering by liquid drops is a ubiquitous phenomenon, directly relevant to many important natural and industrial processes such as soil erosion, drip irrigation, and dispersion of micro-organisms in soil. Here, by combining the high-speed photography with high precision laser profilometry, we investigate the liquid-drop impact dynamics on granular surfaces and monitor the morphology of resulting craters. Our experiments reveal novel scaling relations between the size of granular impact craters and important control parameters including the impact energy, the size of impinging drops and the degree of liquid saturation in a granular bed. Interestingly, we find that the scaling for liquid-drop impact cratering in dry granular media can be quantitatively described by the Schmidt-Holsapple scaling originally proposed for asteroid impact cratering. On the other hand, the scaling for impact craters in wet granular media can be understood by balancing the inertia of impinging drops and the strength of impacted surface. Our study sheds light on the mechanism governing liquid-drop impacts on dry/wet granular surfaces and reveals a remarkable analogy between familiar phenomena of raining and catastrophic asteroid strikes. Scaling of liquid-drop impact craters in granular media.

  6. Distribution and disinfection of bacterial loadings associated with particulate matter fractions transported in urban wet weather flows.

    PubMed

    Dickenson, Joshua A; Sansalone, John J

    2012-12-15

    Urban runoff is a resource for reuse water. However, runoff transports indicator and pathogenic organisms which are mobilized from sources of fecal contamination. These organisms are entrained with particulate matter (PM) that can serve as a mobile substrate for these organisms. Within a framework of additional treatment for reuse of treated runoff which requires the management of PM inventories in unit operations and drainage systems there is a need to characterize organism distributions on PM and the disinfection potential thereof. This study quantifies total coliform, Escherichia coli, fecal streptococcus, and enterococcus generated from 25 runoff events. With the ubiquity and hetero-dispersivity of PM in urban runoff this study examines organism distributions for suspended, settleable and sediment PM fractions differentiated based on PM size and transport functionality. Hypochlorite is applied in batch to elaborate inactivation of PM-associated organisms for each PM fraction. Results indicate that urban runoff bacterial loadings of indicator organisms exceed U.S. wastewater reuse, recreational contact, and Australian runoff reuse criteria as comparative metrics. All monitored events exceeded the Australian runoff reuse criteria for E. coli in non-potable residential and unrestricted access systems. In PM-differentiated events, bacteriological mobilization primarily occurred in the suspended PM fraction. However, sediment PM shielded PM-associated coliforms at all hypochlorite doses, whereas suspended and settleable PM fractions provide less shielding resulting in higher inactivation by hypochlorite. PMID:22244969

  7. Order-disorder transition in swirled granular disks

    NASA Astrophysics Data System (ADS)

    Krinninger, Philip; Fischer, Andreas; Fortini, Andrea

    2014-07-01

    We study the order-disorder transition of horizontally swirled dry and wet granular disks by means of computer simulations. Our systematic investigation of the local order formation as a function of amplitude and period of the external driving force shows that a large cluster of hexagonally ordered particles forms for both dry and wet granular particles at intermediate driving energies. Disordered states are found at small and large driving energies. Wet granular particles reach a higher degree of local hexagonal order with respect to the dry case. For both cases we report a qualitative phase diagram showing the amount of local order at different state points. Furthermore, we find that the transition from hexagonal order to a disordered state is characterized by the appearance of particles with square local order.

  8. PREFACE: Dynamics of wetting Dynamics of wetting

    NASA Astrophysics Data System (ADS)

    Grest, Gary S.; Oshanin, Gleb; Webb, Edmund B., III

    2009-11-01

    Capillary phenomena associated with fluids wetting other condensed matter phases have drawn great scientific interest for hundreds of years; consider the recent bicentennial celebration of Thomas Young's paper on equilibrium contact angles, describing the geometric shape assumed near a three phase contact line in terms of the relevant surface energies of the constituent phases [1]. Indeed, nearly a century has passed since the seminal papers of Lucas and Washburn, describing dynamics of capillary imbibition [2, 3]. While it is generally appreciated that dynamics of fluid wetting processes are determined by the degree to which a system is out of capillary equilibrium, myriad complications exist that challenge the fundamental understanding of dynamic capillary phenomena. The topic has gathered much interest from recent Nobel laureate Pierre-Gilles de Gennes, who provided a seminal review of relevant dissipation mechanisms for fluid droplets spreading on solid surfaces [4] Although much about the dynamics of wetting has been revealed, much remains to be learned and intrinsic technological and fundamental interest in the topic drives continuing high levels of research activity. This is enabled partly by improved experimental capabilities for resolving wetting processes at increasingly finer temporal, spatial, and chemical resolution. Additionally, dynamic wetting research advances via higher fidelity computational modeling capabilities, which drive more highly refined theory development. The significance of this topic both fundamentally and technologically has resulted in a number of reviews of research activity in wetting dynamics. One recent example addresses the evaluation of existing wetting dynamics theories from an experimentalist's perspective [5]. A Current Opinion issue was recently dedicated to high temperature capillarity, including dynamics of high temperature spreading [6]. New educational tools have recently emerged for providing instruction in wetting

  9. Wet solids flow enhancemant

    SciTech Connect

    Caram, H.S.; Foster, N.; Wildman, D.J.

    1996-12-31

    WE used glass beads of different sizes as.a model system to study the flow enhancing properties of Octadecyltrichlorosilane (OTS). 0TS provides Si(CH{sub 2}){sub 17}CH{sub 3} groups that bind with the surface hydrox groups to make it hydrophobic. Experimental data showed, indeed, that surface hydrophobicity promotes the flow of wet granular materials. Mixtures of different percentage of silanized/unsilanized particles were prepared for tensile strength measurements. The tensile strength decreased as more silanized particles were added to the samples. The relationship between dimensionless tensile strength and void fraction followed the correlation found by Pierrat (1994). Contact angles were larger for the silanized particles, as compared with unsilanized ones.

  10. [Wet work].

    PubMed

    Kieć-Swierczyńska, Marta; Chomiczewska, Dorota; Krecisz, Beata

    2010-01-01

    Wet work is one of the most important risk factors of occupational skin diseases. Exposure of hands to the wet environment for more than 2 hours daily, wearing moisture-proof protective gloves for a corresponding period of time or necessity to wash hands frequently lead to the disruption of epidermal stratum corneum, damage to skin barrier function and induction of irritant contact dermatitis. It may also promote penetration of allergens into the skin and increase the risk of sensitization to occupational allergens. Exposure to wet work plays a significant role in occupations, such as hairdressers and barbers, nurses and other health care workers, cleaning staff, food handlers and metalworkers. It is more common among women because many occupations involving wet work are female-dominated. The incidence of wet-work-induced occupational skin diseases can be reduced by taking appropriate preventive measures. These include identification of high-risk groups, education of workers, organization of work enabling to minimize the exposure to wet work, use of personal protective equipment and skin care after work. PMID:20437890

  11. On granular elasticity

    PubMed Central

    Sun, Qicheng; Jin, Feng; Wang, Guangqian; Song, Shixiong; Zhang, Guohua

    2015-01-01

    Mesoscopic structures form in dense granular materials due to the self-organisation of the constituent particles. These structures have internal structural degrees of freedom in addition to the translational degree of freedom. The resultant granular elasticity, which exhibits intrinsic variations and inevitable relaxation, is a key quantity that accounts for macroscopic solid- or fluid-like properties and the transitions between them. In this work, we propose a potential energy landscape (PEL) with local stable basins and low elastic energy barriers to analyse the nature of granular elasticity. A function for the elastic energy density is proposed for stable states and is further calibrated with ultrasonic measurements. Fluctuations in the elastic energy due to the evolution of internal structures are proposed to describe a so-called configuration temperature Tc as a counterpart of the classical kinetic granular temperature Tk that is attributed to the translational degrees of freedom. The two granular temperatures are chosen as the state variables, and a fundamental equation is established to develop non-equilibrium thermodynamics for granular materials. Due to the relatively low elastic energy barrier in the PEL, granular elasticity relaxes more under common mechanical loadings, and a simple model based on mean-field theory is developed to account for this behaviour. PMID:25951049

  12. Gravity and Granular Materials

    NASA Technical Reports Server (NTRS)

    Behringer, R. P.; Hovell, Daniel; Kondic, Lou; Tennakoon, Sarath; Veje, Christian

    1999-01-01

    We describe experiments that probe a number of different types of granular flow where either gravity is effectively eliminated or it is modulated in time. These experiments include the shaking of granular materials both vertically and horizontally, and the shearing of a 2D granular material. For the shaken system, we identify interesting dynamical phenomena and relate them to standard simple friction models. An interesting application of this set of experiments is to the mixing of dissimilar materials. For the sheared system we identify a new kind of dynamical phase transition.

  13. Dynamics of Granular Materials

    NASA Technical Reports Server (NTRS)

    Behringer, Robert P.

    1996-01-01

    Granular materials exhibit a rich variety of dynamical behavior, much of which is poorly understood. Fractal-like stress chains, convection, a variety of wave dynamics, including waves which resemble capillary waves, l/f noise, and fractional Brownian motion provide examples. Work beginning at Duke will focus on gravity driven convection, mixing and gravitational collapse. Although granular materials consist of collections of interacting particles, there are important differences between the dynamics of a collections of grains and the dynamics of a collections of molecules. In particular, the ergodic hypothesis is generally invalid for granular materials, so that ordinary statistical physics does not apply. In the absence of a steady energy input, granular materials undergo a rapid collapse which is strongly influenced by the presence of gravity. Fluctuations on laboratory scales in such quantities as the stress can be very large-as much as an order of magnitude greater than the mean.

  14. Rare events in granular media: a volcanic-like explosion

    NASA Astrophysics Data System (ADS)

    Khain, Evgeniy; Sander, Leonard

    2015-11-01

    Granular matter is ubiquitous in nature and exhibits a variety of nontrivial phenomena. Within the same system, different regions of granular media can be at a solid or a gas phase. Here we focus on a granular Leidenfrost effect: a solid-like cluster is levitating above the ``hot'' granular gas. This state was observed experimentally, when granular matter was vertically vibrated in a two-dimensional container. This solid-gas coexistence can be described by using granular hydrodynamics, taking into account the viscosity divergence in the solid cluster. The approach is similar to the one employed in investigating solid-fluid coexistence in dense shear granular flows. We performed extensive molecular dynamics simulations of a simple model of inelastic hard spheres driven by a ``thermal'' bottom wall. Simulations showed that for low wall temperatures, the levitating cluster is stable, while for high wall temperatures, it breaks down, and a hot gas bursts out resembling a volcanic explosion. We found a hysteresis: for a wide range of bottom wall temperatures, both the clustering state and the volcanic state are stable. However, even if the system is at the (stable) clustering state, a volcanic explosion is possible: it is a rare event driven by large fluctuations. We propose a special simulation technique that allows investigating such rare events.

  15. Force transmission in cohesive granular media

    NASA Astrophysics Data System (ADS)

    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.

  16. Self-Organization in Granular Slurries

    NASA Astrophysics Data System (ADS)

    Ottino, Julio M.; Jain, Nitin; Lueptow, Richard M.; Khakhar, Devang V.

    2000-11-01

    Mixtures of tumbled granular materials under flow exhibit various intriguing types of un-mixing or self-organization. Small differences in particles' density, size or shape may trigger the effect. Nearly all studies to date have addressed the case of dry granular media, where the interparticle fluid is typically air. Here we report the existence of self-organization in wet granular media or slurries, mixtures of particles of different sizes dispersed in a lower density liquid. Technological examples appear in cement, ceramics, fine chemicals, and in the food industry; examples in nature appear in evolution of landslides and transport in river sediments. In spite of significantly different physics at the particle level, both axial banding (alternating bands rich in small and large particles in a long rotating cylinder) and radial segregation (in quasi 2D containers) are observed in slurries. However, axial segregation is significantly faster and the spectrum of outcomes is richer. Moreover, experiments with suitable fluids, reveal, for the first time, the internal structure of axially segregated systems, something that up to now has been accessible only via magnetic resonance imaging (MRI) experimentation.

  17. Rainwater Channelization and Infiltration in Granular Media

    NASA Astrophysics Data System (ADS)

    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.

  18. Modeling Granular Materials

    NASA Astrophysics Data System (ADS)

    Brackbill, J. U.

    2000-11-01

    Granular materials are often cited as examples of systems with complex and unusual properties. Much of this complexity is captured by computational models in which the actual material properties of individual grains are idealized and simplified. Because material properties can be important under extreme conditions, we consider assemblies of grains with more realistic properties. Our model grains may deform, their resulting stresses are computed from elastic / plastic constitutive models, and their interactions with each other include Coulomb friction and bonding. Our model equations are solved using a particle-in-cell (PIC) method, which combines a Lagrangian representation of the materials with an adaptive grid [1]. Our contact model between grains is linear in the number of grains, and we model assemblies with statistically significant numbers of grains. With our model, we have studied the response of dense granular material to shear, with especial attention to the probability density function governing the volume distribution of stress for mono- and poly-disperse samples, circular and polygonal grains, and various values of microscopic friction coefficients, yield stresses, and packing fractions [2]. Remarkably, PDF's are similar in form for all cases simulated, and similar to those observed in experiments with granular materials under both compression and shear. Namely, the simulations yield an exponential probability of large stresses above the mean, and there is a finite chance that a few grains in a large assembly are subjected to extreme stresses at any given time, even at low strain rates. For energetic materials, such as explosives, this is a signficant finding. We have also studied the relationship between distributions of boundary tractions and volume distributions of stress. The ratio of normal and tangential components of traction on the boundary defines a bulk frictional response, which we find increases with the inter-granular friction coefficient

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

    NASA Astrophysics Data System (ADS)

    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.

  20. Flow of wet granular materials: A numerical study.

    PubMed

    Khamseh, Saeed; Roux, Jean-Noël; Chevoir, François

    2015-08-01

    We simulate dense assemblies of frictional spherical grains in steady shear flow under controlled normal stress P in the presence of a small amount of an interstitial liquid, which gives rise to capillary menisci, assumed isolated (pendular regime), and attractive forces, which are hysteretic: Menisci form at contact, but do not break until grains are separated by a finite rupture distance. The system behavior depends on two dimensionless control parameters, inertial number I and reduced pressure P*=aP/(πΓ), comparing confining forces ∼a2P to meniscus tensile strength F0=πΓa, for grains of diameter a joined by menisci with surface tension Γ. We pay special attention to the quasistatic limit of slow flow and observe systematic, enduring strain localization in some of the cohesion-dominated (P*∼0.1) systems. Homogeneous steady flows are characterized by the dependence of internal friction coefficient μ* and solid fraction Φ on I and P*. We also record normal stress differences, fairly small but not negligible and increasing for decreasing P*. The system rheology is moderately sensitive to saturation within the pendular regime, but would be different in the absence of capillary hysteresis. Capillary forces have a significant effect on the macroscopic behavior of the system, up to P* values of several units, especially for longer force ranges associated with larger menisci. The concept of effective pressure may be used to predict an order of magnitude for the strong increase of μ* as P* decreases but such a crude approach is unable to account for the complex structural changes induced by capillary cohesion, with a significant decrease of Φ and different agglomeration states and anisotropic fabric. Likewise, the Mohr-Coulomb criterion for pressure-dependent critical states is, at best, an approximation valid within a restricted range of pressures, with P*≥1. At small enough P*, large clusters of interacting grains form in slow flows, in which liquid bonds survive shear strains of several units. This affects the anisotropies associated with different interactions and the shape of function μ*(I), which departs more slowly from its quasistatic limit than in cohesionless systems (possibly explaining the shear banding tendency). PMID:26382388

  1. Flow of wet granular materials: A numerical study

    NASA Astrophysics Data System (ADS)

    Khamseh, Saeed; Roux, Jean-Noël; Chevoir, François

    2015-08-01

    We simulate dense assemblies of frictional spherical grains in steady shear flow under controlled normal stress P in the presence of a small amount of an interstitial liquid, which gives rise to capillary menisci, assumed isolated (pendular regime), and attractive forces, which are hysteretic: Menisci form at contact, but do not break until grains are separated by a finite rupture distance. The system behavior depends on two dimensionless control parameters, inertial number I and reduced pressure P*=a P /(π Γ ) , comparing confining forces ˜a2P to meniscus tensile strength F0=π Γ a , for grains of diameter a joined by menisci with surface tension Γ . We pay special attention to the quasistatic limit of slow flow and observe systematic, enduring strain localization in some of the cohesion-dominated (P*˜0.1 ) systems. Homogeneous steady flows are characterized by the dependence of internal friction coefficient μ* and solid fraction Φ on I and P*. We also record normal stress differences, fairly small but not negligible and increasing for decreasing P*. The system rheology is moderately sensitive to saturation within the pendular regime, but would be different in the absence of capillary hysteresis. Capillary forces have a significant effect on the macroscopic behavior of the system, up to P* values of several units, especially for longer force ranges associated with larger menisci. The concept of effective pressure may be used to predict an order of magnitude for the strong increase of μ* as P* decreases but such a crude approach is unable to account for the complex structural changes induced by capillary cohesion, with a significant decrease of Φ and different agglomeration states and anisotropic fabric. Likewise, the Mohr-Coulomb criterion for pressure-dependent critical states is, at best, an approximation valid within a restricted range of pressures, with P*≥1 . At small enough P*, large clusters of interacting grains form in slow flows, in which liquid bonds survive shear strains of several units. This affects the anisotropies associated with different interactions and the shape of function μ*(I ) , which departs more slowly from its quasistatic limit than in cohesionless systems (possibly explaining the shear banding tendency).

  2. In Granular Charging, Does Size Really Matter?

    NASA Astrophysics Data System (ADS)

    Siu, Theodore; Mattson, Gregory; Shinbrot, Troy

    2014-03-01

    Spontaneous charging in systems of particles, causing particle separation and electrical discharges, is commonly observed in pharmaceutical powder beds, sandstorms and natural dust plumes. Previous studies have attributed size difference or external factors such as wind or an outside electric field as the primary driving force behind such large scale charging. In this talk we discuss experimental results showing that systems of uniformly sized particles with no external field still exhibit net polarization and charging buildup. We also present computational results modeled from a variation of Dyson's Ising model, which validates this behavior and predicts new types of phenomena.

  3. Spreading of triboelectrically charged granular matter

    PubMed Central

    Kumar, Deepak; Sane, A.; Gohil, Smita.; Bandaru, P. R.; Bhattacharya, S.; Ghosh, Shankar

    2014-01-01

    We report on the spreading of triboelectrically charged glass particles on an oppositely charged surface of a plastic cylindrical container in the presence of a constant mechanical agitation. The particles spread via sticking, as a monolayer on the cylinder's surface. Continued agitation initiates a sequence of instabilities of this monolayer, which first forms periodic wavy-stripe-shaped transverse density modulation in the monolayer and then ejects narrow and long particle-jets from the tips of these stripes. These jets finally coalesce laterally to form a homogeneous spreading front that is layered along the spreading direction. These remarkable growth patterns are related to a time evolving frictional drag between the moving charged glass particles and the countercharges on the plastic container. The results provide insight into the multiscale time-dependent tribolelectric processes and motivates further investigation into the microscopic causes of these macroscopic dynamical instabilities and spatial structures. PMID:24919483

  4. Granular convection in microgravity.

    PubMed

    Murdoch, N; Rozitis, B; Nordstrom, K; Green, S F; Michel, P; de Lophem, T-L; Losert, W

    2013-01-01

    We investigate the role of gravity on convection in a dense granular shear flow. Using a microgravity-modified Taylor-Couette shear cell under the conditions of parabolic flight microgravity, we demonstrate experimentally that secondary, convective-like flows in a sheared granular material are close to zero in microgravity and enhanced under high-gravity conditions, though the primary flow fields are unaffected by gravity. We suggest that gravity tunes the frictional particle-particle and particle-wall interactions, which have been proposed to drive the secondary flow. In addition, the degree of plastic deformation increases with increasing gravitational forces, supporting the notion that friction is the ultimate cause. PMID:23383851

  5. A Chiral Granular Gas

    NASA Astrophysics Data System (ADS)

    Tsai, J.-C.; Ye, Fangfu; Rodriguez, Juan; Gollub, J. P.; Lubensky, T. C.

    2005-05-01

    Inspired by rattleback toys, we created small chiral wires that rotate in a preferred direction on a vertically oscillating platform and quantified their motion with experiment and simulation. We demonstrate experimentally that angular momentum of rotation about particle centers of mass is converted to collective angular momentum of center-of-mass motion in a granular gas of these wires, and we introduce a continuum model that explains our observations.

  6. A chiral granular gas.

    PubMed

    Tsai, J-C; Ye, Fangfu; Rodriguez, Juan; Gollub, J P; Lubensky, T C

    2005-06-01

    Inspired by rattleback toys, we created small chiral wires that rotate in a preferred direction on a vertically oscillating platform and quantified their motion with experiment and simulation. We demonstrate experimentally that angular momentum of rotation about particle centers of mass is converted to collective angular momentum of center-of-mass motion in a granular gas of these wires, and we introduce a continuum model that explains our observations. PMID:16090323

  7. Wet Adhesion and Adhesive Locomotion of Snails on Anti-Adhesive Non-Wetting Surfaces

    PubMed Central

    Shirtcliffe, Neil J.; McHale, Glen; Newton, Michael I.

    2012-01-01

    Creating surfaces capable of resisting liquid-mediated adhesion is extremely difficult due to the strong capillary forces that exist between surfaces. Land snails use this to adhere to and traverse across almost any type of solid surface of any orientation (horizontal, vertical or inverted), texture (smooth, rough or granular) or wetting property (hydrophilic or hydrophobic) via a layer of mucus. However, the wetting properties that enable snails to generate strong temporary attachment and the effectiveness of this adhesive locomotion on modern super-slippy superhydrophobic surfaces are unclear. Here we report that snail adhesion overcomes a wide range of these microscale and nanoscale topographically structured non-stick surfaces. For the one surface which we found to be snail resistant, we show that the effect is correlated with the wetting response of the surface to a weak surfactant. Our results elucidate some critical wetting factors for the design of anti-adhesive and bio-adhesion resistant surfaces. PMID:22693563

  8. Spatiotemporally resolved granular acoustics

    NASA Astrophysics Data System (ADS)

    Owens, Eli; Daniels, Karen

    2011-03-01

    Acoustic techniques provide a non-invasive method of characterizing granular material properties; however, there are many challenges in formulating accurate models of sound propagation due to the inherently heterogeneous nature of granular materials. In order to quantify acoustic responses in space and time, we perform experiments in a photoelastic granular material in which the internal stress pattern (in the form of force chains) is visible. We utilize two complementary methods, high-speed imaging and piezoelectric transduction, to provide particle-scale measurements of the amplitude of the acoustic wave. We observe that the average wave amplitude is largest within particles experiencing the largest forces. The force-dependence of this amplitude is in qualitative agreement with a simple Hertzian-like model for contact area. In addition, we investigate the power spectrum of the propagating signal using the piezoelectric sensors. For a Gaussian wave packet input, we observe a broad spectrum of transmitted frequencies below the driving frequency, and we quantify the characteristic frequencies and corresponding length scales of our material as the system pressure is varied.

  9. PREFACE: Wetting: introductory note

    NASA Astrophysics Data System (ADS)

    Herminghaus, S.

    2005-03-01

    The discovery of wetting as a topic of physical science dates back two hundred years, to one of the many achievements of the eminent British scholar Thomas Young. He suggested a simple equation relating the contact angle between a liquid surface and a solid substrate to the interfacial tensions involved [1], γlg cos θ = γsg - γsl (1) In modern terms, γ denotes the excess free energy per unit area of the interface indicated by its indices, with l, g and s corresponding to the liquid, gas and solid, respectively [2]. After that, wetting seems to have been largely ignored by physicists for a long time. The discovery by Gabriel Lippmann that θ may be tuned over a wide range by electrochemical means [3], and some important papers about modifications of equation~(1) due to substrate inhomogeneities [4,5] are among the rare exceptions. This changed completely during the seventies, when condensed matter physics had become enthusiastic about critical phenomena, and was vividly inspired by the development of the renormalization group by Kenneth Wilson [6]. This had solved the long standing problem of how to treat fluctuations, and to understand the universal values of bulk critical exponents. By inspection of the critical exponents of the quantities involved in equation~(1), John W Cahn discovered what he called critical point wetting: for any liquid, there should be a well-defined transition to complete wetting (i.e., θ = 0) as the critical point of the liquid is approached along the coexistence curve [7]. His paper inspired an enormous amount of further work, and may be legitimately viewed as the entrance of wetting into the realm of modern physics. Most of the publications directly following Cahn's work were theoretical papers which elaborated on wetting in relation to critical phenomena. A vast amount of interesting, and in part quite unexpected, ramifications were discovered, such as the breakdown of universality in thin film systems [8]. Simultaneously, a number

  10. Unified force law for granular impact cratering

    NASA Astrophysics Data System (ADS)

    Katsuragi, Hiroaki; Durian, Douglas J.

    2007-06-01

    Experiments on the low-speed impact of solid objects into granular media have been used both to mimic geophysical events and to probe the unusual nature of the granular state of matter. Observations have been interpreted in terms of conflicting stopping forces: product of powers of projectile depth and speed; linear in speed; constant, proportional to the initial impact speed; and proportional to depth. This is reminiscent of high-speed ballistics impact in the nineteenth and twentieth centuries, when a plethora of empirical rules were proposed. To make progress, we developed a means to measure projectile dynamics with 100nm and 20μs precision. For a 1-inch-diameter steel sphere dropped from a wide range of heights into non-cohesive glass beads, we reproduce previous observations either as reasonable approximations or as limiting behaviours. Furthermore, we demonstrate that the interaction between the projectile and the medium can be decomposed into the sum of velocity-dependent inertial drag plus depth-dependent friction. Thus, we achieve a unified description of low-speed impact phenomena and show that the complex response of granular materials to impact, although fundamentally different from that of liquids and solids, can be simply understood.

  11. Constitutive relations for steady, dense granular flows

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    -instantaneous collisions [4]. We have shown that the present theory is capable of reproducing, qualitatively and quantitatively, the numerical simulations on disks [2] and the experiments on incline flows of glass spere [9]. [1] C. S. Campbell, Annual Review of Fluid Mechanics 22, 57 (1990) [2] F. da Cruz, S. Emam, M. Prochnow, J. Roux, and F. Chevoir, Physical Review E 72, 021309 (2005) [3] I. Goldhirsch, Annual Review of Fluid Mechanics 35, 267 (2003). [4] H. Hwang and K. Hutter, Continuum Mechanics and Thermodynamics 7, 357 (1995) [5] J. T. Jenkins, Granular Matter 10, 47 (2007) [6] J. T. Jenkins, Physics of Fluids 18, 103307 (2006) [7] J. T. Jenkins and M. W. Richman, Archive for Rational Mechanics and Analysis 87, 355 (1985) [8] D. Muir Wood, Geotechnical modelling (Spon Press, New York, 2004) [9] O. Pouliquen, Physics of Fluids 11, 542 (1999) [10] A. N. Schofield and C. P. Wroth, Critical state soil mechanics (McGraw-Hill, London, U.K., 1968) [11] C. Song, P. Wang, and H. A. Makse, Nature 453, 629 (2008)

  12. Effect of cohesion on granular-fluid flows in spouted beds: PIV measurement and DEM simulations

    NASA Astrophysics Data System (ADS)

    Zhu, Runru; LI, Shuiqing; Yao, Qiang

    2013-06-01

    In contrast to wet granular flows, the effect of cohesion on complex granular-fluid flows is intriguing but much challenging. The liquid bridges, forming between binary particles with the addition of a small amount of liquids, might significantly change the granular-fluid system due to both cohesion and lubrication effects. In this paper, a spouted bed, among various fluidization technologies, is particularly selected as a prototypical system for studying granular-fluid flows, since it can provide a quasi-steady flow pattern of granular particles, i.e., a core of upward granular-fluid flow called the "spout" and a surrounding region of downward quasi-static granular flow called the "annulus". Firstly, using self-developed particle image velocimetery (PIV) technique, the effects of cohesion on the spout-annulus interface (namely the spout width) and on the particle velocity profiles in distinct zones are examined. Further, the discrete element method (DEM), by incorporating liquid bridge adhesion into soft-sphere model, is established and used to predict the microdynamic behavior of particles in spouted beds. Finally, based on both experiments and DEM validation, the effects on the granular patterns in these two zones are comparatively discussed.

  13. Granular mechanics and rifting

    NASA Astrophysics Data System (ADS)

    Reber, Jacqueline E.; Hayman, Nicholas W.; Lavier, Luc L.

    2013-04-01

    Numerical models have proved useful in the interpretation of seismic-scale images of rifted margins. In an effort to both test and further illuminate predictions of numerical models, workers have made some strides using map-scale field relations, microstructures, and strain analyses. Yet, fundamental predictions of modeling and tectonic restorations are not able to capture critical observations. For example, many models and interpretations call on continuous faults with restorable kinematic histories. In contrast, s-reflectors and other interpreted shear fabrics in the middle crust tend to be discontinuous and non-planar across a margin. Additionally, most rift-evolution models and interpretations call on end-member ductile flow laws over a range of mechanical and thermal conditions. In contrast, field observations have found that a range of "brittle" fault rocks (e.g., cataclasites and breccias) form in the deeper crust. Similarly, upper crustal materials in deep basins and fault zones can deform through both distributed and localized deformation. Altogether, there appears to be reason to bring a new perspective to aspects of the structural evolution of rifted margins. A granular mechanics approach to crustal deformation studies has several important strengths. Granular materials efficiently localize shear and exhibit a range of stick-slip behaviors, including quasi-viscous rheological responses. These behaviors emerge in discrete element models, analog-materials experiments, and natural and engineered systems regardless of the specific micromechanical flow law. Yet, strictly speaking, granular deformation occurs via failure of frictional contacts between elastic grains. Here, we explore how to relate granular-mechanics models to mesoscale (outcrop) structural evolution, in turn providing insight into basin- and margin- scale evolution. At this stage we are focusing on analog-materials experiments and micro-to-mesoscale observations linking theoretical predictions

  14. Subsurface Explosions in Granular Media

    NASA Astrophysics Data System (ADS)

    Lai, Shuyue; Houim, Ryan; Oran, Elaine

    2015-11-01

    Numerical simulations of coupled gas-granular flows are used to study properties of shock formation and propagation in media, such as sand or regolith on the moon, asteroids, or comets. The simulations were performed with a multidimensional fully compressible model, GRAF, which solves two sets of coupled Navier-Stokes equations, one for the gas and one for the granular medium. The specific case discussed here is for a subsurface explosion in a granular medium initiated by an equivalent of 200g of TNT in depths ranging from 0.1m to 3m. The background conditions of 100K, 10 Pa and loose initial particle volume fraction of 25% are consistent with an event on a comet. The initial blast creates a cavity as a granular shock expands outwards. Since the gas-phase shock propagates faster than the granular shock in loose, granular material, some gas and particles are ejected before the granular shock arrives. When the granular shock reaches the surface, a cap-like structure forms. This cap breaks and may fall back on the surface and in this process, relatively dense particle clusters form. At lower temperatures, the explosion timescales are increased and entrained particles are more densely packed.

  15. Drop floating on a granular raft

    NASA Astrophysics Data System (ADS)

    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.

  16. An Application of the Study of Granular Shocks to Aerospace Problems

    NASA Astrophysics Data System (ADS)

    Padgett, David Alan

    Granular systems are collections of macroscopic particles which interact with each other through contact. Common examples of granular systems are piles of sand, actual grain in silos or other storage facilities, and industrial powders. Researchers display a heavy interest in granular materials because they are ubiquitous in the world, but their states and interactions with other matter are difficult to describe mathematically. One of the many counterintuitive facts about granular systems is that, under certain circumstances, granular systems can behave like fluids and exhibit shock wave behavior. This dissertation details the development of an event-driven simulation to study the behavior of granular systems as well as some observations made by examining different granular systems as they impact wedges and discs. This dissertation also discusses a novel method of exploiting the shock behavior of granular systems in order to investigate problems in aerospace engineering. Typical computational fluid dynamics solvers can be inefficient when dealing with flows which include shock waves. Prior knowledge of the location of shock waves in a flow can help engineers create CFD grids that allow fluid dynamics solvers to converge faster than they otherwise would and still preserve the accuracy of the solution. By investigating an ideal fluid system with an analogous granular system, the locations of the shock waves are observed and efficient grids for solving the Navier- Stokes equations are developed. Through case studies, this dissertation will show that such efficient grids lead to fluid flow solutions which converge in much less time than comparable fine grids.

  17. Heterogeneities in granular dynamics.

    PubMed

    Mehta, A; Barker, G C; Luck, J M

    2008-06-17

    The absence of Brownian motion in granular media is a source of much complexity, including the prevalence of heterogeneity, whether static or dynamic, within a given system. Such strong heterogeneities can exist as a function of depth in a box of grains; this is the system we study here. First, we present results from three-dimensional, cooperative and stochastic Monte Carlo shaking simulations of spheres on heterogeneous density fluctuations. Next, we juxtapose these with results obtained from a theoretical model of a column of grains under gravity; frustration via competing local fields is included in our model, whereas the effect of gravity is to slow down the dynamics of successively deeper layers. The combined conclusions suggest that the dynamics of a real granular column can be divided into different phases-ballistic, logarithmic, activated, and glassy-as a function of depth. The nature of the ground states and their retrieval (under zero-temperature dynamics) is analyzed; the glassy phase shows clear evidence of its intrinsic ("crystalline") states, which lie below a band of approximately degenerate ground states. In the other three phases, by contrast, the system jams into a state chosen randomly from this upper band of metastable states. PMID:18541918

  18. PREFACE: Wetting: introductory note

    NASA Astrophysics Data System (ADS)

    Herminghaus, S.

    2005-03-01

    The discovery of wetting as a topic of physical science dates back two hundred years, to one of the many achievements of the eminent British scholar Thomas Young. He suggested a simple equation relating the contact angle between a liquid surface and a solid substrate to the interfacial tensions involved [1], γlg cos θ = γsg - γsl (1) In modern terms, γ denotes the excess free energy per unit area of the interface indicated by its indices, with l, g and s corresponding to the liquid, gas and solid, respectively [2]. After that, wetting seems to have been largely ignored by physicists for a long time. The discovery by Gabriel Lippmann that θ may be tuned over a wide range by electrochemical means [3], and some important papers about modifications of equation~(1) due to substrate inhomogeneities [4,5] are among the rare exceptions. This changed completely during the seventies, when condensed matter physics had become enthusiastic about critical phenomena, and was vividly inspired by the development of the renormalization group by Kenneth Wilson [6]. This had solved the long standing problem of how to treat fluctuations, and to understand the universal values of bulk critical exponents. By inspection of the critical exponents of the quantities involved in equation~(1), John W Cahn discovered what he called critical point wetting: for any liquid, there should be a well-defined transition to complete wetting (i.e., θ = 0) as the critical point of the liquid is approached along the coexistence curve [7]. His paper inspired an enormous amount of further work, and may be legitimately viewed as the entrance of wetting into the realm of modern physics. Most of the publications directly following Cahn's work were theoretical papers which elaborated on wetting in relation to critical phenomena. A vast amount of interesting, and in part quite unexpected, ramifications were discovered, such as the breakdown of universality in thin film systems [8]. Simultaneously, a number

  19. Swirling granular solidlike clusters

    NASA Astrophysics Data System (ADS)

    Scherer, Michael A.; Kötter, Karsten; Markus, Mario; Goles, Eric; Rehberg, Ingo

    2000-04-01

    Experiments and three-dimensional numerical simulations are presented to elucidate the dynamics of granular material in a cylindrical dish driven by a horizontal, periodic motion. The following phenomena are obtained both in the experiments and in the simulations: First, for large particle numbers N the particles describe hypocycloidal trajectories. In this state the particles are embedded in a solidlike cluster (``pancake'') which counter-rotates with respect to the external driving (reptation). Self-organization within the cluster occurs such that the probability distribution of the particles consists of concentric rings. Second, the system undergoes phase transitions. These can be identified by changes of the quantity dEkin/dN (Ekin is the mean kinetic energy) between zero (rotation), positive (reptation), and negative values (appearance of the totality of concentric rings).

  20. Granular Materials Research at NASA-Glenn

    NASA Technical Reports Server (NTRS)

    Agui, Juan H.; Daidzic, Nihad; Green, Robert D.; Nakagawa, Masami; Nayagam, Vedha; Rame, Enrique; Wilkinson, Allen

    2002-01-01

    This paper presents viewgraphs of granular materials research at NASA-Glenn. The topics include: 1) Impulse dispersion of a tapered granular chain; 2) High Speed Digital Images of Tapered Chain Dynamics; 3) Impulse Dispersion; 4) Three Dimensional Granular Bed Experimental Setup; 5) Magnetic Resonance Imaging of Fluid Flow in Porous Media; and 6) Net Charge on Granular Materials (NCharG).

  1. Congenital granular-cell myoblastoma.

    PubMed

    Cussen, L J; MacMahon, R A

    1975-04-01

    The clinical and pathologic features of congenital granular-cell myoblastoma in five infant girls are reported. One lesion, treated expectantly, progressively decreased in size and after 3 yr and 9 mo could not be detected, while two lesions which were imcompletely excised did not recur. It is suggested that congenital granular-cell myoblastoma is caused by an intrauterine stimulus, and that this stimulus may possible be production of estrogen by the fetus. Congential granular-cell myoblastoma should be treated expectantly or by limited excision, and has an excellent prognosis. PMID:164527

  2. Granular temperature profiles in three-dimensional vibrofluidized granular beds

    SciTech Connect

    Wildman, R. D.; Huntley, J. M.; Parker, D. J.

    2001-06-01

    The motion of grains in a three-dimensional vibrofluidized granular bed has been measured using the technique of positron emission particle tracking, to provide three-dimensional packing fraction and granular temperature distributions. The mean square fluctuation velocity about the mean was calculated through analysis of the short time mean squared displacement behavior, allowing measurement of the granular temperature at packing fractions of up to {eta}{similar_to}0.15. The scaling relationship between the granular temperature, the number of layers of grains, and the base velocity was determined. Deviations between the observed scaling exponents and those predicted by recent theories are attributed to the influence of dissipative grain-sidewall collisions.

  3. Intermittency in dilute granular flows

    NASA Astrophysics Data System (ADS)

    Guo, Wenxuan; Zhang, Qiang; Wylie, Jonathan J.

    2016-07-01

    In this letter, we show that dilute granular systems can exhibit a type of intermittency that has no analogue in gas dynamics. We consider a simple system in which a very dilute set of granular particles falls under gravity through a nozzle. This setting is analogous to the classical problem of high-speed nozzle flow in the study of compressible gases. It is well known that very dilute granular systems exhibit behavior qualitatively similar to gases, and that gas flowing through a nozzle does not exhibit intermittency. Nevertheless, we show that the intermittency in dilute granular nozzle flows can occur and corresponds to complicated transitions between supersonic and subsonic regimes. We also provide detailed explanations of the mechanism underlying this phenomenon.

  4. Directed clustering in driven compartmentalized granular gas systems in zero gravity

    NASA Astrophysics Data System (ADS)

    Li, Y.; Hou, M.; Evesque, P.

    2011-12-01

    Clustering of shaken fluidized granular matter in connected compartments has been observed and studied in the laboratory. This clustering behavior in granular gas systems is related to the dissipative nature of granular system, and therefore shall not depend on gravity. This clustering phenomenon in compartmental configuration may provide a means for particle depletion and transportation in microgravity environment. In this work we propose different configurations for possible directed clustering in zero gravity. The related experiment has been planned for the Chinese satellite SJ-10.

  5. Optimized Simulation of Granular Materials

    NASA Astrophysics Data System (ADS)

    Holladay, Seth

    Visual effects for film and animation often require simulated granular materials, such as sand, wheat, or dirt, to meet a director's needs. Simulating granular materials can be time consuming, in both computation and labor, as these particulate materials have complex behavior and an enormous amount of small-scale detail. Furthermore, a single cubic meter of granular material, where each grain is a cubic millimeter, would contain a billion granules, and simulating all such interacting granules would take an impractical amount of time for productions. This calls for a simplified model for granular materials that retains high surface detail and granular behavior yet requires significantly less computational time. Our proposed method simulates a minimal number of individual granules while retaining particulate detail on the surface by supporting surface particles with simplified interior granular models. We introduce a multi-state model where, depending on the material state of the interior granules, we replace interior granules with a simplified simulation model for the state they are in and automate the transitions between those states. The majority of simulation time can thus be focused on visible portions of the material, reducing the time spent on non-visible portions, while maintaining the appearance and behavior of the mass as a whole.

  6. Enuresis (Bed-Wetting)

    MedlinePlus

    ... their development. Bed-wetting is more common among boys than girls. What causes bed-wetting? A number of things ... valves in boys or in the ureter in girls or boys Abnormalities in the spinal cord A small bladder ...

  7. Granular Superconductors and Gravity

    NASA Technical Reports Server (NTRS)

    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.

  8. [Large granular lymphocyte leukemia].

    PubMed

    Lazaro, Estibaliz; Caubet, Olivier; Menard, Fanny; Pellegrin, Jean-Luc; Viallard, Jean-François

    2007-11-01

    Large granular lymphocyte (LGL) leukemia is a clonal proliferation of cytotoxic cells, either CD3(+) (T-cell) or CD3(-) (natural killer, or NK). Both subtypes can manifest as indolent or aggressive disorders. T-LGL leukemia is associated with cytopenias and autoimmune diseases and most often has an indolent course and good prognosis. Rheumatoid arthritis and Felty syndrome are frequent. NK-LGL leukemias can be more aggressive. LGL expansion is currently hypothesized to be a virus (Ebstein Barr or human T-cell leukemia viruses) antigen-driven T-cell response that involves disruption of apoptosis. The diagnosis of T-LGL is suggested by flow cytometry and confirmed by T-cell receptor gene rearrangement studies. Clonality is difficult to determine in NK-LGL but use of monoclonal antibodies specific for killer cell immunoglobulin-like receptor (KIR) has improved this process. Treatment is required when T-LGL leukemia is associated with recurrent infections secondary to chronic neutropenia. Long-lasting remission can be obtained with immunosuppressive treatments such as methotrexate, cyclophosphamide, and cyclosporine A. NK-LGL leukemias may be more aggressive and refractory to conventional therapy. PMID:17596907

  9. Subharmonic instability of a self-organized granular jet

    PubMed Central

    Kollmer, J. E.; Pöschel, T.

    2016-01-01

    Downhill flows of granular matter colliding in the lowest point of a valley, may induce a self-organized jet. By means of a quasi two-dimensional experiment where fine grained sand flows in a vertically sinusoidally agitated cylinder, we show that the emergent jet, that is, a sheet of ejecta, does not follow the frequency of agitation but reveals subharmonic response. The order of the subharmonics is a complex function of the parameters of driving. PMID:27001207

  10. Subharmonic instability of a self-organized granular jet

    NASA Astrophysics Data System (ADS)

    Kollmer, J. E.; Pöschel, T.

    2016-03-01

    Downhill flows of granular matter colliding in the lowest point of a valley, may induce a self-organized jet. By means of a quasi two-dimensional experiment where fine grained sand flows in a vertically sinusoidally agitated cylinder, we show that the emergent jet, that is, a sheet of ejecta, does not follow the frequency of agitation but reveals subharmonic response. The order of the subharmonics is a complex function of the parameters of driving.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

    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. PMID:23496504

  13. Active microrheology of driven granular particles.

    PubMed

    Wang, Ting; Grob, Matthias; Zippelius, Annette; Sperl, Matthias

    2014-04-01

    When pulling a particle in a driven granular fluid with constant force Fex, the probe particle approaches a steady-state average velocity v. This velocity and the corresponding friction coefficient of the probe ζ=Fex/v are obtained within a schematic model of mode-coupling theory and compared to results from event-driven simulations. For small and moderate drag forces, the model describes the simulation results successfully for both the linear as well as the nonlinear region: The linear response regime (constant friction) for small drag forces is followed by shear thinning (decreasing friction) for moderate forces. For large forces, the model demonstrates a subsequent increasing friction in qualitative agreement with the data. The square-root increase of the friction with force found in [Fiege et al., Granul. Matter 14, 247 (2012)] is explained by a simple kinetic theory. PMID:24827243

  14. Granular structure determined by terahertz scattering

    NASA Astrophysics Data System (ADS)

    Born, Philip; Rothbart, Nick; Sperl, Matthias; Hübers, Heinz-Wilhelm

    2014-05-01

    Light scattering from particles reveals static and dynamical information about the particles and their correlations. Such methods are particularly powerful when the wavelength of the light is chosen similar to the sizes and distances of the particles. To apply scattering to investigate granular matter in particular —or other objects of similar submillimeter size— light of suitable wavelength in the terahertz regime needs to be chosen. By using a quantum cascade laser in a benchtop setup we determine the angle-dependent scattering of spherical particles as well as coffee powder and sugar grains. The scattering from single particles can be interpreted by form factors derived within the Mie theory. In addition, collective correlations can be extracted as static structure factors and compared to recent computer simulations.

  15. Dynamic granularity of imaging systems

    NASA Astrophysics Data System (ADS)

    Geissel, Matthias; Smith, Ian C.; Shores, Jonathon E.; Porter, John L.

    2015-11-01

    Imaging systems that include a specific source, imaging concept, geometry, and detector have unique properties such as signal-to-noise ratio, dynamic range, spatial resolution, distortions, and contrast. Some of these properties are inherently connected, particularly dynamic range and spatial resolution. It must be emphasized that spatial resolution is not a single number but must be seen in the context of dynamic range and consequently is better described by a function or distribution. We introduce the "dynamic granularity" G dyn as a standardized, objective relation between a detector's spatial resolution (granularity) and dynamic range for complex imaging systems in a given environment rather than the widely found characterization of detectors such as cameras or films by themselves. This relation can partly be explained through consideration of the signal's photon statistics, background noise, and detector sensitivity, but a comprehensive description including some unpredictable data such as dust, damages, or an unknown spectral distribution will ultimately have to be based on measurements. Measured dynamic granularities can be objectively used to assess the limits of an imaging system's performance including all contributing noise sources and to qualify the influence of alternative components within an imaging system. This article explains the construction criteria to formulate a dynamic granularity and compares measured dynamic granularities for different detectors used in the X-ray backlighting scheme employed at Sandia's Z-Backlighter facility.

  16. Silo collapse under granular discharge.

    PubMed

    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/√[Rt]. 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. PMID:25615503

  17. Granular fountains: Convection cascade in a compartmentalized granular gas

    NASA Astrophysics Data System (ADS)

    van der Meer, Devaraj; van der Weele, Ko; Reimann, Peter

    2006-06-01

    This paper extends the two-compartment granular fountain [D. van der Meer, P. Reimann, K. van der Weele, and D. Lohse, Phys. Rev. Lett. 92, 184301 (2004)] to an arbitrary number of compartments: The tendency of a granular gas to form clusters is exploited to generate spontaneous convective currents, with particles going down in the well-filled compartments and going up in the diluted ones. We focus upon the bifurcation diagram of the general K -compartment system, which is constructed using a dynamical flux model and which proves to agree quantitatively with results from molecular dynamics simulations.

  18. Different Effects of Roughness (Granularity) and Hydrophobicity

    NASA Astrophysics Data System (ADS)

    Shirtcliffe, Neil; McHale, Glen; Hamlett, Christopher; Newton, Michael

    2010-05-01

    With thanks to Stefan Doerr and Jorge Mataix-Solera for their invitation Superhydrophobicity is an interesting effect that appears to be simple on the outset; increased surface area from roughness increases interfacial area and therefore energy loss or gain. More extreme roughness prevents total wetting, resulting in gas pockets present at the surface and a drastic change in the properties of the system. Increases in complexity of the system, by adding porosity (granularity), allowing the structures to move, varying the shape of the roughness or the composition of the liquid used often has unexpected effects. Here we will consider a few of these related to complex topography. Overhanging features are commonly used in test samples as they perform better in some tests than simple roughness. It has been shown to be a prerequisite for superoleophobic surfaces as it allows liquids to be suspended for contact angles considerably below 90°. It also allows trapping of gas in lower layers even if the first layer is flooded. This is important in soils as a fixed bed of granules behaves just like a surface with overhanging roughness. Using simple geometry it is possible to predict at what contact angle penetration will occur. Plants have some structured superhydrophobic surfaces and we have shown that some use them in conjunction with other structured surfaces to control water flows. This allows some plants to survive in difficult environments and shows us how subtly different structures interact completely differently with water. Long fibres can either cause water droplets to roll over a plant surface or halt it in its tracks. Implications of this in soils include predicting when particles will adhere more strongly to water drops and why organic fibrous material may play a greater role in the behaviour of water in soils than may be expected from the amount present. The garden snail uses a biosurfactant that is very effective at wetting surfaces and can crawl over most

  19. Rhizoctonia seed, seedling, and wet root rot

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Wet root rot caused by Rhizoctonia solani Kühn can cause seed and seedling rot of both lentil and chickpea as well as many other agricultural crops worldwide. The pathogen is favored in cool, sandy soil with high organic matter under no-till or reduced-till soil management practices. Survival spor...

  20. Wetting in electrolyte solutions.

    PubMed

    Ibagon, Ingrid; Bier, Markus; Dietrich, S

    2013-06-01

    Wetting of a charged substrate by an electrolyte solution is investigated by means of classical density functional theory applied to a lattice model. Within the present model the pure, i.e., salt-free solvent, for which all interactions are of the nearest-neighbor type only, exhibits a second-order wetting transition for all strengths of the substrate-particle and the particle-particle interactions for which the wetting transition temperature is nonzero. The influences of the substrate charge density and of the ionic strength on the wetting transition temperature and on the order of the wetting transition are studied. If the substrate is neutral, the addition of salt to the solvent changes neither the order nor the transition temperature of the wetting transition of the system. If the surface charge is nonzero, upon adding salt this continuous wetting transition changes to first-order within the wide range of substrate surface charge densities and ionic strengths studied here. As the substrate surface charge density is increased, at fixed ionic strength, the wetting transition temperature decreases and the prewetting line associated with the first-order wetting transition becomes longer. This decrease of the wetting transition temperature upon increasing the surface charge density becomes more pronounced by decreasing the ionic strength. PMID:23758391

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

    NASA Astrophysics Data System (ADS)

    Shukla, Priyanka; Ansari, I. H.; van der Meer, D.; Lohse, Detlef; Alam, Meheboob

    2015-11-01

    The nonlinear instability of the density-inverted granular Leidenfrost state and the resulting convective motion in strongly shaken granular matter are analysed via a weakly nonlinear analysis. Under a quasi-steady ansatz, the base state temperature decreases with increasing height away from from the vibrating plate, but the density profile consists of three distinct regions: (i) a collisional dilute layer at the bottom, (ii) a levitated dense layer at some intermediate height and (iii) a ballistic dilute layer at the top of the granular bed. For the nonlinear stability analysis, the nonlinearities up-to cubic order in perturbation amplitude are retained, leading to the Landau equation. The genesis of granular convection is shown to be tied to a supercritical pitchfork bifurcation from the Leidenfrost state. Near the bifurcation point the equilibrium amplitude is found to follow a square-root scaling law, Ae √{ ▵} , with the distance ▵ from bifurcation point. The strength of convection is maximal at some intermediate value of the shaking strength, with weaker convection both at weaker and stronger shaking. Our theory predicts a novel floating-convection state at very strong shaking.

  2. Granular Rayleigh-Taylor instability

    SciTech Connect

    Vinningland, Jan Ludvig; Johnsen, Oistein; Flekkoey, Eirik G.; Maaloey, Knut Joergen; Toussaint, Renaud

    2009-06-18

    A granular instability driven by gravity is studied experimentally and numerically. The instability arises as grains fall in a closed Hele-Shaw cell where a layer of dense granular material is positioned above a layer of air. The initially flat front defined by the grains subsequently develops into a pattern of falling granular fingers separated by rising bubbles of air. A transient coarsening of the front is observed right from the start by a finger merging process. The coarsening is later stabilized by new fingers growing from the center of the rising bubbles. The structures are quantified by means of Fourier analysis and quantitative agreement between experiment and computation is shown. This analysis also reveals scale invariance of the flow structures under overall change of spatial scale.

  3. Shear Instabilities in Granular Flows

    NASA Astrophysics Data System (ADS)

    Shinbrot, Troy

    2003-03-01

    Unstable waves have long been studied in fluid shear layers. These waves affect transport in the atmosphere and oceans as well as slipstream stability behind ships, planes, and heat transfer devices. Corresponding instabilities in granular flows have not previously been documented, despite the importance of these flows in geophysical and industrial systems. We report here that breaking waves can form at the interface between two streams of identical grains downstream of a splitter plate. These waves appear abruptly in flow down an inclined plane as either shear rate or angle of incline is changed, and we analyze a granular flow model that qualitatively agrees with our experimental data. The waves appear from the model to be a manifestation of a competition between shear and extensional strains in the flowing granular bed, and we propose a dimensionless group to govern the transition between steady and wavy flows.

  4. Shear instabilities in granular flows

    NASA Astrophysics Data System (ADS)

    Goldfarb, David J.; Glasser, Benjamin J.; Shinbrot, Troy

    2002-01-01

    Unstable waves have been long studied in fluid shear layers. These waves affect transport in the atmosphere and oceans, in addition to slipstream stability behind ships, aeroplanes and heat-transfer devices. Corresponding instabilities in granular flows have not been previously documented, despite the importance of these flows in geophysical and industrial systems. Here we report that breaking waves can form at the interface between two streams of identical grains flowing on an inclined plane downstream of a splitter plate. Changes in either the shear rate or the angle of incline cause such waves to appear abruptly. We analyse a granular flow model that agrees qualitatively with our experimental data; the model suggests that the waves result from competition between shear and extensional strains in the flowing granular bed. We propose a dimensionless shear number that governs the transition between steady and wavy flows.

  5. Shear instabilities in granular flows.

    PubMed

    Goldfarb, David J; Glasser, Benjamin J; Shinbrot, Troy

    2002-01-17

    Unstable waves have been long studied in fluid shear layers. These waves affect transport in the atmosphere and oceans, in addition to slipstream stability behind ships, aeroplanes and heat-transfer devices. Corresponding instabilities in granular flows have not been previously documented, despite the importance of these flows in geophysical and industrial systems. Here we report that breaking waves can form at the interface between two streams of identical grains flowing on an inclined plane downstream of a splitter plate. Changes in either the shear rate or the angle of incline cause such waves to appear abruptly. We analyse a granular flow model that agrees qualitatively with our experimental data; the model suggests that the waves result from competition between shear and extensional strains in the flowing granular bed. We propose a dimensionless shear number that governs the transition between steady and wavy flows. PMID:11797003

  6. Initiation of immersed granular avalanches

    NASA Astrophysics Data System (ADS)

    Mutabaruka, Patrick; Delenne, Jean-Yves; Soga, Kenichi; Radjai, Farhang

    2014-05-01

    By means of coupled molecular dynamics-computational fluid dynamics simulations, we analyze the initiation of avalanches in a granular bed of spherical particles immersed in a viscous fluid and inclined above its angle of repose. In quantitative agreement with experiments, we find that the bed is unstable for a packing fraction below 0.59 but is stabilized above this packing fraction by negative excess pore pressure induced by the effect of dilatancy. From detailed numerical data, we explore the time evolution of shear strain, packing fraction, excess pore pressures, and granular microstructure in this creeplike pressure redistribution regime, and we show that they scale excellently with a characteristic time extracted from a model based on the balance of granular stresses in the presence of a negative excess pressure and its interplay with dilatancy. The cumulative shear strain at failure is found to be ≃0.2, in close agreement with the experiments, irrespective of the initial packing fraction and inclination angle. Remarkably, the avalanche is triggered when dilatancy vanishes instantly as a result of fluctuations while the average dilatancy is still positive (expanding bed) with a packing fraction that declines with the initial packing fraction. Another nontrivial feature of this creeplike regime is that, in contrast to dry granular materials, the internal friction angle of the bed at failure is independent of dilatancy but depends on the inclination angle, leading therefore to a nonlinear dependence of the excess pore pressure on the inclination angle. We show that this behavior may be described in terms of the contact network anisotropy, which increases with a nearly constant connectivity and levels off at a value (critical state) that increases with the inclination angle. These features suggest that the behavior of immersed granular materials is controlled not only directly by hydrodynamic forces acting on the particles but also by the influence of the

  7. Initiation of immersed granular avalanches.

    PubMed

    Mutabaruka, Patrick; Delenne, Jean-Yves; Soga, Kenichi; Radjai, Farhang

    2014-05-01

    By means of coupled molecular dynamics-computational fluid dynamics simulations, we analyze the initiation of avalanches in a granular bed of spherical particles immersed in a viscous fluid and inclined above its angle of repose. In quantitative agreement with experiments, we find that the bed is unstable for a packing fraction below 0.59 but is stabilized above this packing fraction by negative excess pore pressure induced by the effect of dilatancy. From detailed numerical data, we explore the time evolution of shear strain, packing fraction, excess pore pressures, and granular microstructure in this creeplike pressure redistribution regime, and we show that they scale excellently with a characteristic time extracted from a model based on the balance of granular stresses in the presence of a negative excess pressure and its interplay with dilatancy. The cumulative shear strain at failure is found to be ≃ 0.2, in close agreement with the experiments, irrespective of the initial packing fraction and inclination angle. Remarkably, the avalanche is triggered when dilatancy vanishes instantly as a result of fluctuations while the average dilatancy is still positive (expanding bed) with a packing fraction that declines with the initial packing fraction. Another nontrivial feature of this creeplike regime is that, in contrast to dry granular materials, the internal friction angle of the bed at failure is independent of dilatancy but depends on the inclination angle, leading therefore to a nonlinear dependence of the excess pore pressure on the inclination angle. We show that this behavior may be described in terms of the contact network anisotropy, which increases with a nearly constant connectivity and levels off at a value (critical state) that increases with the inclination angle. These features suggest that the behavior of immersed granular materials is controlled not only directly by hydrodynamic forces acting on the particles but also by the influence of the

  8. DUNE - a granular flow code

    SciTech Connect

    Slone, D M; Cottom, T L; Bateson, W B

    2004-11-23

    DUNE was designed to accurately model the spectrum of granular. Granular flow encompasses the motions of discrete particles. The particles are macroscopic in that there is no Brownian motion. The flow can be thought of as a dispersed phase (the particles) interacting with a fluid phase (air or water). Validation of the physical models proceeds in tandem with simple experimental confirmation. The current development team is working toward the goal of building a flexible architecture where existing technologies can easily be integrated to further the capability of the simulation. We describe the DUNE architecture in some detail using physics models appropriate for an imploding liner experiment.

  9. Density waves in granular flow

    NASA Astrophysics Data System (ADS)

    Herrmann, H. J.; Flekkøy, E.; Nagel, K.; Peng, G.; Ristow, G.

    Ample experimental evidence has shown the existence of spontaneous density waves in granular material flowing through pipes or hoppers. Using Molecular Dynamics Simulations we show that several types of waves exist and find that these density fluctuations follow a 1/f spectrum. We compare this behaviour to deterministic one-dimensional traffic models. If positions and velocities are continuous variables the model shows self-organized criticality driven by the slowest car. We also present Lattice Gas and Boltzmann Lattice Models which reproduce the experimentally observed effects. Density waves are spontaneously generated when the viscosity has a nonlinear dependence on density which characterizes granular flow.

  10. Origins of Wetting.

    PubMed

    Extrand, Charles W

    2016-08-01

    This feature article provides an overview of wetting phenomena. Much of the analysis done on wetting in the last 100 years assumes that the phenomena are determined by molecular interactions within the interfacial area between the liquid and solid. However, there is now ample evidence that wetting is controlled by interactions in the vicinity of the contact line where the liquid and solid meet. Recent experiments and modeling that demonstrate this are reviewed. PMID:27459085

  11. Adsorption of Methyl Tertiary Butyl Ether on Granular Zeolites: Batch and Column Studies

    PubMed Central

    Abu-Lail, Laila; Bergendahl, John A.; Thompson, Robert W.

    2010-01-01

    Methyl tertiary butyl ether (MTBE) has been shown to be readily removed from water with powdered zeolites, but the passage of water through fixed beds of very small powdered zeolites produces high friction losses not encountered in flow through larger sized granular materials. In this study, equilibrium and kinetic adsorption of MTBE onto granular zeolites, a coconut shell granular activated carbon (CS-1240), and a commercial carbon adsorbent (CCA) sample was evaluated. In addition, the effect of natural organic matter (NOM) on MTBE adsorption was evaluated. Batch adsorption experiments determined that ZSM-5 was the most effective granular zeolite for MTBE adsorption. Further equilibrium and kinetic experiments verified that granular ZSM-5 is superior to CS-1240 and CCA in removing MTBE from water. No competitive-adsorption effects between NOM and MTBE were observed for adsorption to granular ZSM-5 or CS-1240, however there was competition between NOM and MTBE for adsorption onto the CCA granules. Fixed-bed adsorption experiments for longer run times were performed using granular ZSM-5. The bed depth service time model (BDST) was used to analyze the breakthrough data. PMID:20153106

  12. Wet solids flow enhancement

    SciTech Connect

    Caram, H.S.; Agrawal, D.K.; Foster, N.

    1997-07-01

    The objective was to visualize the flow of granular materials in the silo using Nuclear Magnetic Resonance. This was done by introducing traces. Mustard seeds and poppy seeds were used as trace particles. The region sampled was a cylinder 25 mm in diameter and 40 mm in length. Eight slices containing 128 by 128 to 256 by 256 pixels were generated for each image.

  13. Wetting and spreading

    NASA Astrophysics Data System (ADS)

    Bonn, Daniel; Eggers, Jens; Indekeu, Joseph; Meunier, Jacques; Rolley, Etienne

    2009-04-01

    Wetting phenomena are ubiquitous in nature and technology. A solid substrate exposed to the environment is almost invariably covered by a layer of fluid material. In this review, the surface forces that lead to wetting are considered, and the equilibrium surface coverage of a substrate in contact with a drop of liquid. Depending on the nature of the surface forces involved, different scenarios for wetting phase transitions are possible; recent progress allows us to relate the critical exponents directly to the nature of the surface forces which lead to the different wetting scenarios. Thermal fluctuation effects, which can be greatly enhanced for wetting of geometrically or chemically structured substrates, and are much stronger in colloidal suspensions, modify the adsorption singularities. Macroscopic descriptions and microscopic theories have been developed to understand and predict wetting behavior relevant to microfluidics and nanofluidics applications. Then the dynamics of wetting is examined. A drop, placed on a substrate which it wets, spreads out to form a film. Conversely, a nonwetted substrate previously covered by a film dewets upon an appropriate change of system parameters. The hydrodynamics of both wetting and dewetting is influenced by the presence of the three-phase contact line separating “wet” regions from those that are either dry or covered by a microscopic film only. Recent theoretical, experimental, and numerical progress in the description of moving contact line dynamics are reviewed, and its relation to the thermodynamics of wetting is explored. In addition, recent progress on rough surfaces is surveyed. The anchoring of contact lines and contact angle hysteresis are explored resulting from surface inhomogeneities. Further, new ways to mold wetting characteristics according to technological constraints are discussed, for example, the use of patterned surfaces, surfactants, or complex fluids.

  14. Dynamic granularity of imaging systems

    SciTech Connect

    Geissel, Matthias; Smith, Ian C.; Shores, Jonathon E.; Porter, John L.

    2015-11-04

    Imaging systems that include a specific source, imaging concept, geometry, and detector have unique properties such as signal-to-noise ratio, dynamic range, spatial resolution, distortions, and contrast. Some of these properties are inherently connected, particularly dynamic range and spatial resolution. It must be emphasized that spatial resolution is not a single number but must be seen in the context of dynamic range and consequently is better described by a function or distribution. We introduce the “dynamic granularity” Gdyn as a standardized, objective relation between a detector’s spatial resolution (granularity) and dynamic range for complex imaging systems in a given environment rather than the widely found characterization of detectors such as cameras or films by themselves. We found that this relation can partly be explained through consideration of the signal’s photon statistics, background noise, and detector sensitivity, but a comprehensive description including some unpredictable data such as dust, damages, or an unknown spectral distribution will ultimately have to be based on measurements. Measured dynamic granularities can be objectively used to assess the limits of an imaging system’s performance including all contributing noise sources and to qualify the influence of alternative components within an imaging system. Our article explains the construction criteria to formulate a dynamic granularity and compares measured dynamic granularities for different detectors used in the X-ray backlighting scheme employed at Sandia’s Z-Backlighter facility.

  15. Dynamic granularity of imaging systems

    DOE PAGESBeta

    Geissel, Matthias; Smith, Ian C.; Shores, Jonathon E.; Porter, John L.

    2015-11-04

    Imaging systems that include a specific source, imaging concept, geometry, and detector have unique properties such as signal-to-noise ratio, dynamic range, spatial resolution, distortions, and contrast. Some of these properties are inherently connected, particularly dynamic range and spatial resolution. It must be emphasized that spatial resolution is not a single number but must be seen in the context of dynamic range and consequently is better described by a function or distribution. We introduce the “dynamic granularity” Gdyn as a standardized, objective relation between a detector’s spatial resolution (granularity) and dynamic range for complex imaging systems in a given environment rathermore » than the widely found characterization of detectors such as cameras or films by themselves. We found that this relation can partly be explained through consideration of the signal’s photon statistics, background noise, and detector sensitivity, but a comprehensive description including some unpredictable data such as dust, damages, or an unknown spectral distribution will ultimately have to be based on measurements. Measured dynamic granularities can be objectively used to assess the limits of an imaging system’s performance including all contributing noise sources and to qualify the influence of alternative components within an imaging system. Our article explains the construction criteria to formulate a dynamic granularity and compares measured dynamic granularities for different detectors used in the X-ray backlighting scheme employed at Sandia’s Z-Backlighter facility.« less

  16. Mechanics of Granular Materials (MGM)

    NASA Technical Reports Server (NTRS)

    Alshibli, Khalid A.; Costes, Nicholas C.; Porter, Ronald F.

    1996-01-01

    The constitutive behavior of uncemented granular materials such as strength, stiffness, and localization of deformations are to a large extend derived from interparticle friction transmitted between solid particles and particle groups. Interparticle forces are highly dependent on gravitational body forces. At very low effective confining pressures, the true nature of the Mohr envelope, which defines the Mohr-Coulomb failure criterion for soils, as well as the relative contribution of each of non-frictional components to soil's shear strength cannot be evaluated in terrestrial laboratories. Because of the impossibility of eliminating gravitational body forces on earth, the weight of soil grains develops interparticle compressive stresses which mask true soil constitutive behavior even in the smallest samples of models. Therefore the microgravity environment induced by near-earth orbits of spacecraft provides unique experimental opportunities for testing theories related to the mechanical behavior of terrestrial granular materials. Such materials may include cohesionless soils, industrial powders, crushed coal, etc. This paper will describe the microgravity experiment, 'Mechanics of Granular Materials (MGM)', scheduled to be flown on Space Shuttle-MIR missions. The paper will describe the experiment's hardware, instrumentation, specimen preparation procedures, testing procedures in flight, as well as a brief summary of the post-mission analysis. It is expected that the experimental results will significantly improve the understanding of the behavior of granular materials under very low effective stress levels.

  17. Mechanics of granular materials (MGM)

    NASA Astrophysics Data System (ADS)

    Alshibli, Khalid A.; Costes, Nicholas C.; Porter, Ronald F.

    1996-07-01

    The constitutive behavior of uncemented granular materials such as strength, stiffness, and localization of deformations are to a large extent derived from interparticle friction transmitted between solid particles and particle groups. Interparticle forces are highly dependent on gravitational body forces. At very low effective confining pressures, the true nature of the Mohr envelope, which defines the Mohr-Coulomb failure criterion for soils, as well as the relative contribution of each of non-frictional components to soil's shear strength cannot be evaluated in terrestrial laboratories. Because of the impossibility of eliminating gravitational body forces on earth, the weight of soil grains develops interparticle compressive stresses which mask true soil constitutive behavior even in the smallest samples of models. Therefore the microgravity environment induced by near-earth orbits of spacecraft provides unique experimental opportunities for testing theories related to the mechanical behavior of terrestrial granular materials. Such materials may include cohesionless soils, industrial powders, crushed coal, etc. This paper will describe the microgravity experiment, 'Mechanics of Granular Materials (MGM)', scheduled to be flown on Space Shuttle-MIR missions. The paper will describe the experiment's hardware, instrumentation, specimen preparation procedures, testing procedures in flight, as well as a brief summary of the post-mission analysis. It is expected that the experimental results will significantly improve the understanding of the behavior of granular materials under very low effective stress levels.

  18. Particle deposition in granular media: Progress report

    SciTech Connect

    Tien, Chi

    1987-01-01

    This paper discusses topics on particle deposition in granular media. The six topics discussed are: experimental determination of initial collection efficiency in granular beds - an assessment of the effect of instrument sensitivity and the extent of particle bounce-off; deposition of polydispersed aerosols in granular media; in situ observation of aerosol deposition in a two-dimensional model filter; solid velocity in cross-flow granular moving bed; aerosol deposition in granular moving bed; and aerosol deposition in a magnetically stabilized fluidized bed. (LSP)

  19. Armoring a droplet: Soft jamming of a dense granular interface

    NASA Astrophysics Data System (ADS)

    Lagubeau, Guillaume; Rescaglio, Antonella; Melo, Francisco

    2014-09-01

    Droplets and bubbles protected by armors of particles have found vast applications in encapsulation, stabilization of emulsions and foams, or flotation processes. The liquid phase stores capillary energy, while concurrently the solid contacts of the granular network induce friction and energy dissipation, leading to hybrid interfaces of combined properties. By means of nonintrusive tensiometric methods and structural measurements, we distinguish three surface phases of increasing rigidity during the evaporation of armored droplets. The emergence of surface rigidity is reminiscent of jamming of granular matter, but it occurs differently since it is marked by a step by step hardening under surface compression. These results show that the concept of the effective surface tension remains useful only below the first jamming transition. Beyond this point, the surface stresses become anisotropic.

  20. Very, Very Fast Wetting

    NASA Technical Reports Server (NTRS)

    Jacqmin, David; Lee, Chi-Ming (Technical Monitor); Salzman, Jack (Technical Monitor)

    2001-01-01

    Just after formation, optical fibers are wetted stably with acrylate at capillary numbers routinely exceeding 1000. It is hypothesized that this is possible because of dissolution of air into the liquid coating. A lubrication/boundary integral analysis that includes gas diffusion and solubility is developed. It is applied using conservatively estimated solubility and diffusivity coefficients and solutions are found that are consistent with industry practice and with the hypothesis. The results also agree with the claim of Deneka, Kar & Mensah (1988) that the use of high solubility gases to bathe a wetting line allows significantly greater wetting speeds. The solutions indicate a maximum speed of wetting which increases with gas solubility and with reduction in wetting-channel diameter.

  1. Kinetics of Reactive Wetting

    SciTech Connect

    YOST, FREDERICK G.

    1999-09-09

    The importance of interfacial processes in materials joining has a long history. A significant amount of work has suggested that processes collateral to wetting can affect the extent of wetting and moderate or retard wetting rate. Even very small additions of a constituent, known to react with the substrate, cause pronounced improvement in wetting and are exploited in braze alloys, especially those used for joining to ceramics. The wide diversity of processes, such as diffusion, chemical reaction, and fluxing, and their possible combinations suggest that various rate laws should be expected for wetting kinetics depending on the controlling processes. These rate laws are expected to differ crucially from the standard fluid controlled wetting models found in the literature. Voitovitch et al. and Mortensen et al. have shown data that suggests diffusion control for some systems and reaction control for others. They also presented a model of wetting kinetics controlled by the diffusion of a constituent contained by the wetting fluid. In the following a model will be constructed for the wetting kinetics of a small droplet of metal containing a constituent that diffuses to the wetting line and chemically reacts with a flat, smooth substrate. The model is similar to that of Voitovitch et al. and Mortensen et al. but incorporates chemical reaction kinetics such that the result contains both diffusion and reaction kinetics. The model is constructed in the circular cylinder coordinate system, satisfies the diffusion equation under conditions of slow flow, and considers diffusion and reaction at the wetting line to be processes in series. This is done by solving the diffusion equation with proper initial and boundary conditions, computing the diffusive flux at the wetting line and equating this to both the convective flux and reaction flux. This procedure is similar to equating the current flowing in components of a series circuit. The wetting rate will be computed versus time

  2. HYPERELASTIC MODELS FOR GRANULAR MATERIALS

    SciTech Connect

    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

  3. Stop and restart of granular clock in a vibrated compartmentalized bidisperse granular system

    NASA Astrophysics Data System (ADS)

    Liu, Qi-Yi; Hu, Mao-Bin; Jiang, Rui; Wu, Yong-Hong

    2013-01-01

    This paper studies a bidisperse granular mixture consisting of two species of stainless steel spheres in a vertically vibrated compartmentalized container. The experiments show that with proper vibration acceleration, the granular clock stops when horizontal segregation of the large spheres residing in the far end from the barrier wall occurs. When the segregation is broken, the granular clock restarts. We present the phase diagrams of vibration acceleration versus container width and small particle number, which exhibits three different regions, namely, clustering state, stop-restart of the granular clock, and the granular clock. A generalized flux model is proposed to reproduce the phenomenon of stop and restart of the granular clock.

  4. Kinetics of reactive wetting

    SciTech Connect

    Yost, F.G.

    2000-04-14

    The importance of interfacial processes in materials joining has a long history. A significant amount of work has suggested that processes collateral to wetting can affect the extent of wetting and moderate or retard wetting rate. Even very small additions of a constituent, known to react with the substrate, cause pronounced improvement in wetting and are exploited in braze alloys, especially those used for joining to ceramics. In the following a model will be constructed for the wetting kinetics of a small droplet of metal containing a constituent that diffuses to the wetting line and chemically reacts with a flat, smooth substrate. The model is similar to that of Voitovitch et al. and Mortensen et al. but incorporates chemical reaction kinetics such that the result contains both diffusion and reaction kinetics. The model is constructed in the circular cylinder coordinate system, satisfies the diffusion equation under conditions of slow flow, and considers diffusion and reaction at the wetting line to be processes in series. This is done by solving the diffusion equation with proper initial and boundary conditions, computing the diffusive flux at the wetting line, and equating this to both the convective flux and reaction flux. This procedure is similar to equating the current flowing in components of a series circuit. The wetting rate will be computed versus time for a variety of diffusion and reaction conditions. A transition is observed from nonlinear (diffusive) to linear (reactive) behavior as the control parameters (such as the diffusion coefficient) are modified. This is in agreement with experimental observations. The adequacy of the slow flow condition, used in this type of analysis, is discussed and an amended procedure is suggested.

  5. Shear deformation in granular materials

    SciTech Connect

    Bardenhagen, S.G.; Brackbill, J.U.; Sulsky, D.L.

    1998-12-31

    An investigation into the properties of granular materials is undertaken via numerical simulation. These simulations highlight that frictional contact, a defining characteristic of dry granular materials, and interfacial debonding, an expected deformation mode in plastic bonded explosives, must be properly modeled. Frictional contact and debonding algorithms have been implemented into FLIP, a particle in cell code, and are described. Frictionless and frictional contact are simulated, with attention paid to energy and momentum conservation. Debonding is simulated, with attention paid to the interfacial debonding speed. A first step toward calculations of shear deformation in plastic bonded explosives is made. Simulations are performed on the scale of the grains where experimental data is difficult to obtain. Two characteristics of deformation are found, namely the intermittent binding of grains when rotation and translation are insufficient to accommodate deformation, and the role of the binder as a lubricant in force chains.

  6. Compaction Behavior of Granular Materials

    NASA Astrophysics Data System (ADS)

    Endicott, Mark R.; Kenkre, V. M.; Glass, S. Jill; Hurd, Alan J.

    1996-03-01

    We report the results of our recent study of compaction of granular materials. A theoretical model is developed for the description of the compaction of granular materials exemplified by granulated ceramic powders. Its predictions are compared to observations of uniaxial compaction tests of ceramic granules of PMN-PT, spray dried alumina and rutile. The theoretical model employs a volume-based statistical mechanics treatment and an activation analogy. Results of a computer simulation of random packing of discs in two dimensions are also reported. The effect of type of particle size distribution and other parameters of that distribution on the calculated quantities are discussed. We examine the implications of the results of the simulation for the theoretical model.

  7. Electrification of Shaken Granular Media

    NASA Astrophysics Data System (ADS)

    Kara, Onur; Nordsiek, Freja; Lathrop, Daniel

    2015-11-01

    Granular charging of particle laden flows are widespread and has long been observed. Volcanic ash clouds, desert sandstorms, dust devils, thunderstorms and snowstorms all undergo electrification at large scale. However the mechanism by which such processes occur, is not yet well understood. We confine granular particles to an oscillating cylindrical chamber which is enclosed and sealed by two conducting plates. The primary measurement obtained is the voltage between the two plates. We find that collective effects occurring in the bulk of the material play a significant role in the electrification process. We extend the previous results by the addition of photodectection capabilities to the experimental chamber. We present simultaneous measurements of voltage and light emission.

  8. Mott transition in granular aluminum

    NASA Astrophysics Data System (ADS)

    Bachar, N.; Lerer, S.; Levy, A.; Hacohen-Gourgy, S.; Almog, B.; Saadaoui, H.; Salman, Z.; Morenzoni, E.; Deutscher, G.

    2015-01-01

    A Mott transition in granular Al films is observed by probing the increase of the spin-flip scattering rate of conduction electrons as the nanosize metallic grains are being progressively decoupled. The presence of free spins in granular Al films is directly demonstrated by μ SR measurements. Analysis of the magnetoresistance in terms of an effective Fermi energy shows that it becomes of the order of the grains electrostatic charging energy at a room temperature resistivity ρ300 K≈50000 μ Ω cm , at which a metal to insulator transition is known to exist. As this transition is approached the magnetoresistance exhibits a heavy-fermion-like behavior, consistent with an increased electron effective mass.

  9. Dynamic compaction of granular materials

    PubMed Central

    Favrie, N.; Gavrilyuk, S.

    2013-01-01

    An Eulerian hyperbolic multiphase flow model for dynamic and irreversible compaction of granular materials is constructed. The reversible model is first constructed on the basis of the classical Hertz theory. The irreversible model is then derived in accordance with the following two basic principles. First, the entropy inequality is satisfied by the model. Second, the corresponding ‘intergranular stress’ coming from elastic energy owing to contact between grains decreases in time (the granular media behave as Maxwell-type materials). The irreversible model admits an equilibrium state corresponding to von Mises-type yield limit. The yield limit depends on the volume fraction of the solid. The sound velocity at the yield surface is smaller than that in the reversible model. The last one is smaller than the sound velocity in the irreversible model. Such an embedded model structure assures a thermodynamically correct formulation of the model of granular materials. The model is validated on quasi-static experiments on loading–unloading cycles. The experimentally observed hysteresis phenomena were numerically confirmed with a good accuracy by the proposed model. PMID:24353466

  10. Bipedal locomotion in granular media

    NASA Astrophysics Data System (ADS)

    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.

  11. Haptic perception of wetness.

    PubMed

    Bergmann Tiest, Wouter M; Kosters, N Dolfine; Kappers, Astrid M L; Daanen, Hein A M

    2012-10-01

    In daily life, people interact with textiles of different degrees of wetness, but little is known about the mechanics of wetness perception. This paper describes an experiment with six conditions regarding haptic discrimination of the wetness of fabrics. Three materials were used: cotton wool, sponge-structured viscose and thin viscose. Two ways of touching were investigated: static touching, in which only thermal cues were available, and dynamic touching, in which additional mechanical cues were available. For dynamic touching, average Weber fractions for discrimination were around 0.3, whereas for static touching, they ranged from 0.34 to 0.63. The results show that people can make use of the additional mechanical cues to significantly improve their discrimination performance. There was no significant difference between Weber fractions for the three materials, showing that wetness can be judged as a separate perceptual quantity, independent of the material. PMID:22964056

  12. In-Situ Regeneration of Saturated Granular Activated Carbon by an Iron Oxide Nanocatalyst

    EPA Science Inventory

    Granular activated carbon (GAC) can remove trace organic pollutants and natural organic matter (NOM) from industrial and municipal waters. This paper evaluates an iron nanocatalyst approach, based on Fenton-like oxidation reactions, to regenerate spent GAC within a packed bed con...

  13. Anisotropy of weakly vibrated granular flows

    NASA Astrophysics Data System (ADS)

    Wortel, Geert H.; van Hecke, Martin

    2015-10-01

    We experimentally probe the anisotropy of weakly vibrated flowing granular media. Depending on the driving parameters—flow rate and vibration strength—this anisotropy varies significantly. We show how the anisotropy collapses when plotted as a function of the driving stresses, uncovering a direct link between stresses and anisotropy. Moreover, our data suggest that for small anisotropies, the shear stresses vanish. Anisotropy of the fabric of granular media thus plays a crucial role in determining the rheology of granular flows.

  14. Anisotropy of weakly vibrated granular flows.

    PubMed

    Wortel, Geert H; van Hecke, Martin

    2015-10-01

    We experimentally probe the anisotropy of weakly vibrated flowing granular media. Depending on the driving parameters-flow rate and vibration strength-this anisotropy varies significantly. We show how the anisotropy collapses when plotted as a function of the driving stresses, uncovering a direct link between stresses and anisotropy. Moreover, our data suggest that for small anisotropies, the shear stresses vanish. Anisotropy of the fabric of granular media thus plays a crucial role in determining the rheology of granular flows. PMID:26565148

  15. Impact induced splash and spill in a quasi-confided granular medium

    NASA Astrophysics Data System (ADS)

    Ogale, S. B.

    2005-03-01

    Dissipation of the energy of impact in a granular medium and its effects has been a subject of considerable scientific for quite some time. In this work we have explored and analyzed the splash and spill effects caused by the impact of a ball dropped from a height into a granular medium in a open container. Three different granular media, namely rice, mustard seeds, and cream of wheat were used. The amount of spilled-over granular matter was measured as a function of the ball-drop height. Digital pictures of the splash process were also recorded. The quantity of spilled granular matter varies linearly with the impact energy. However additional step like structures are also noted. Specifically, a distinct and large jump is seen in the spilled quantity at a specific impact energy in the case of mustard seeds, which also exhibit obvious charging effects and repulsion. Although the parameters such as mass per grain and packing density for the case of mustard seeds are intermediate between those for rice and cream of wheat, the spill quantity for comparable impact energy is considerably higher. These data will be presented and discussed.

  16. Robophysical study of jumping dynamics on granular media

    NASA Astrophysics Data System (ADS)

    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. Experimental velocity fields and forces for a cylinder penetrating into a granular medium.

    PubMed

    Seguin, A; Bertho, Y; Martinez, F; Crassous, J; Gondret, P

    2013-01-01

    We present here a detailed granular flow characterization together with force measurements for the quasi-bidimensional situation of a horizontal cylinder penetrating vertically at a constant velocity in dry granular matter between two parallel glass walls. In the velocity range studied here, the drag force on the cylinder does not depend on the velocity V(0) and is mainly proportional to the cylinder diameter d. While the force on the cylinder increases with its penetration depth, the granular velocity profile around the cylinder is found to be stationary with fluctuations around a mean value leading to the granular temperature profile. Both mean velocity profile and temperature profile exhibit strong localization near the cylinder. The mean flow perturbation induced by the cylinder decreases exponentially away from the cylinder on a characteristic length λ that is mainly governed by the cylinder diameter for a large enough cylinder/grain size ratio d/d(g): λ~d/4+2d(g). The granular temperature exhibits a constant plateau value T(0) in a thin layer close to the cylinder of extension δ(T(0))~λ/2 and decays exponentially far away with a characteristic length λ(T) of a few grain diameters (λ(T)~3d(g)). The granular temperature plateau T(0) that scales as V(0)(2)d(g)/d is created by the flow itself from the balance between the "granular heat" production by the shear rate V(0)/λ over δ(T(0)) close to the cylinder and the granular dissipation far away. PMID:23410320

  18. Membrane-based wet electrostatic precipitation

    SciTech Connect

    David J. Bayless; Liming Shi; Gregory Kremer; Ben J. Stuart; James Reynolds; John Caine

    2005-06-01

    Emissions of fine particulate matter, PM2.5, in both primary and secondary form, are difficult to capture in typical dry electrostatic precipitators (ESPs). Wet (or waterbased) ESPs are well suited for collection of acid aerosols and fine particulates because of greater corona power and virtually no re-entrainment. However, field disruptions because of spraying (misting) of water, formation of dry spots (channeling), and collector surface corrosion limit the applicability of current wet ESPs in the control of secondary PM2.5. Researchers at Ohio University have patented novel membrane collection surfaces to address these problems. Water-based cleaning in membrane collectors made of corrosion-resistant fibers is facilitated by capillary action between the fibers, maintaining an even distribution of water. This paper presents collection efficiency results of lab-scale and pilot-scale testing at First Energy's Bruce Mansfield Plant for the membrane-based wet ESP. The data indicate that a membrane wet ESP was more effective at collecting fine particulates, acid aerosols, and oxidized mercury than the metal-plate wet ESP, even with {approximately}15% less collecting area. 15 refs., 7 figs., 6 tabs.

  19. Experimental quantification of a granular crater induced by a liquid-to-granular impact using a 3D scanner

    NASA Astrophysics Data System (ADS)

    Wyser, Emmanuel; Abellan, Antonio; Carrea, Dario; Rudaz, Benjamin; Jaboyedoff, Michel

    2015-04-01

    Granular impacts have been extensively studied but much remains to be investigated regarding the complex topic of liquid-to-granular impact. Its applications to Geosciences are of interest regarding recent advances in the investigation of the raindrop erosion or the sediment flux. In our study, we focus on the quantification of both the excavated and deposited volumes resulting from a water-droplet impact onto a fine granular. The quantification of the existing relationships between the impact energy, the packing fraction and the excavated volume is also of interest. Indeed, the relationship between the packing fraction and the excavated volume has still to be investigated for constant impact energy (fixed height of fall and droplet size). Moreover, the volume distribution of the granular matter around the impact target has still to be achieved regarding the previous studies. Much of the previous work was focused on the ejected particles distribution but less is known about the volume distribution of the ejected mass. In this study, we have developed a specific methodology in order to investigate these two topics, as follows: a) First of all, we carried out experimental investigations in laboratory on a setup inspired by the previous works of Long et al. (2014) and Furbish et al. (2007). Granular samples were prepared using a compaction device in order to produce various packing fractions. Pre- and post-impact surface geometries were recorded using a high precision 3D scanner (KONICA MINOLTA VIVID 9i). This provided an accurate point cloud of the impact crater and ejecta deposits. b) Afterwards, we processed each point cloud pairs using different softwares (PolyWorks & MATLAB). We used an accurate change detection method by computing orthogonal distance from points (post-geometry) to reference meshed surface (pre-geometry) to extract the points belonging to deposits (positive distance) or crater (negative distance). Then, we used the computational geometry toolbox

  20. Electroretinographic wet electrode.

    PubMed

    Carpi, Federico; Benini, Gabriella; Tomei, Franca; Figliuzzi, Rosa Maria; De Napoli, Alberto

    2009-10-01

    This paper presents the first systematic characterisation of a new electroretinographic (ERG) electrode, recently described. The new 'wet' electrode uses a conducting liquid as a distributed electrical interface between the eye and a solid electronic conductor; the latter detects the ERG potential without any direct contact with the ocular surface. This technique avoids the contact-induced discomfort of both corneal and conjunctival standard electrodes. The wet electrode was tested on 10 volunteers, in comparison with a conjunctival electrode (HK loop), as the most comfortable standard. It was also compared with a cutaneous (cup) electrode, which is even more comfortable, although not standard. Results showed the efficacy of the wet electrode for detecting morphologically accurate ERG responses, with amplitudes respectively analogous and higher of those measured by the conjunctival and cutaneous electrodes. Properties of wet electrodes include: no solid interface with the eye, no need for anaesthesia, intrinsic safety, mechanical and electrical stability against ocular movements, tolerance to misplacements and immunity to lacrimation. As a drawback, the liquid can still be a source of discomfort for some patients and it requires care against possible leakage. All these features suggest a possible use of wet electrodes as an additional tool for ERG procedures, although limited to tests of short duration. PMID:19501539

  1. Dynamics of Sheared Granular Materials

    NASA Technical Reports Server (NTRS)

    Kondic, Lou; Utter, Brian; Behringer, Robert P.

    2002-01-01

    This work focuses on the properties of sheared granular materials near the jamming transition. The project currently involves two aspects. The first of these is an experiment that is a prototype for a planned ISS (International Space Station) flight. The second is discrete element simulations (DES) that can give insight into the behavior one might expect in a reduced-g environment. The experimental arrangement consists of an annular channel that contains the granular material. One surface, say the upper surface, rotates so as to shear the material contained in the annulus. The lower surface controls the mean density/mean stress on the sample through an actuator or other control system. A novel feature under development is the ability to 'thermalize' the layer, i.e. create a larger amount of random motion in the material, by using the actuating system to provide vibrations as well control the mean volume of the annulus. The stress states of the system are determined by transducers on the non-rotating wall. These measure both shear and normal components of the stress on different size scales. Here, the idea is to characterize the system as the density varies through values spanning dense almost solid to relatively mobile granular states. This transition regime encompasses the regime usually thought of as the glass transition, and/or the jamming transition. Motivation for this experiment springs from ideas of a granular glass transition, a related jamming transition, and from recent experiments. In particular, we note recent experiments carried out by our group to characterize this type of transition and also to demonstrate/ characterize fluctuations in slowly sheared systems. These experiments give key insights into what one might expect in near-zero g. In particular, they show that the compressibility of granular systems diverges at a transition or critical point. It is this divergence, coupled to gravity, that makes it extremely difficult if not impossible to

  2. Dynamics of Sheared Granular Materials

    NASA Astrophysics Data System (ADS)

    Kondic, Lou; Utter, Brian; Behringer, Robert P.

    2002-11-01

    This work focuses on the properties of sheared granular materials near the jamming transition. The project currently involves two aspects. The first of these is an experiment that is a prototype for a planned ISS (International Space Station) flight. The second is discrete element simulations (DES) that can give insight into the behavior one might expect in a reduced-g environment. The experimental arrangement consists of an annular channel that contains the granular material. One surface, say the upper surface, rotates so as to shear the material contained in the annulus. The lower surface controls the mean density/mean stress on the sample through an actuator or other control system. A novel feature under development is the ability to 'thermalize' the layer, i.e. create a larger amount of random motion in the material, by using the actuating system to provide vibrations as well control the mean volume of the annulus. The stress states of the system are determined by transducers on the non-rotating wall. These measure both shear and normal components of the stress on different size scales. Here, the idea is to characterize the system as the density varies through values spanning dense almost solid to relatively mobile granular states. This transition regime encompasses the regime usually thought of as the glass transition, and/or the jamming transition. Motivation for this experiment springs from ideas of a granular glass transition, a related jamming transition, and from recent experiments. In particular, we note recent experiments carried out by our group to characterize this type of transition and also to demonstrate/ characterize fluctuations in slowly sheared systems. These experiments give key insights into what one might expect in near-zero g. In particular, they show that the compressibility of granular systems diverges at a transition or critical point. It is this divergence, coupled to gravity, that makes it extremely difficult if not impossible to

  3. Inter/intra granular exchange and thermal activation in nanoscale granular magnetic materials

    NASA Astrophysics Data System (ADS)

    Morrison, C.; Saharan, L.; Hrkac, G.; Schrefl, T.; Ikeda, Y.; Takano, K.; Miles, J. J.; Thomson, T.

    2011-09-01

    We explain the effect of inter/intra granular exchange coupling and thermal activation on the switching behavior of nano-scale granular magnetic materials. For an ideal, non-interacting granular system, the minimum switching field occurs at 45° from the easy axis of the grains. We show through simulation and measurements, using a CoCrPt oxide-segregated granular film as a model system, that there is a clear shift in the angle of applied field at which the minimum switching field occurs. This arises solely due to incoherent reversal induced by inter-granular exchange coupling or incoherency within larger grains, rather than thermal activation.

  4. Thermoelectric performance of granular semiconductors.

    SciTech Connect

    Glatz, A.; Beloborodov, I. S.; Materials Science Division; California State Univ.

    2009-01-01

    We study the effects of doping and confinement on the thermoelectric properties of nanocrystalline semiconductors. We calculate the thermopower and figure of merit for temperatures less than the charging energy. For weakly coupled semiconducting grains it is shown that the figure of merit is optimized for grain sizes of order 5 nm for typical materials, and that its value can be larger than one. Using the similarities between granular semiconductors and electron or Coulomb glasses allows for a quantitative description of inhomogeneous semiconducting thermoelectrics.

  5. Where the Granular Flows Bend

    NASA Astrophysics Data System (ADS)

    Khomenko, E.; Martínez Pillet, V.; Solanki, S. K.; del Toro Iniesta, J. C.; Gandorfer, A.; Bonet, J. A.; Domingo, V.; Schmidt, W.; Barthol, P.; Knölker, M.

    2010-11-01

    Based on IMaX/SUNRISE data, we report on a previously undetected phenomenon in solar granulation. We show that in a very narrow region separating granules and intergranular lanes, the spectral line width of the Fe I 5250.2 Å line becomes extremely small. We offer an explanation of this observation with the help of magneto-convection simulations. These regions with extremely small line widths correspond to the places where the granular flows bend from upflow in granules to downflow in intergranular lanes. We show that the resolution and image stability achieved by IMaX/SUNRISE are important requisites to detect this interesting phenomenon.

  6. Theoretical model of granular compaction

    SciTech Connect

    Ben-Naim, E.; Knight, J.B.; Nowak, E.R. |; Jaeger, H.M.; Nagel, S.R.

    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.

  7. Hydrodynamic modes for granular gases.

    PubMed

    Dufty, James W; Brey, J Javier

    2003-09-01

    The eigenfunctions and eigenvalues of the linearized Boltzmann equation for inelastic hard spheres (d=3) or disks (d=2) corresponding to d+2 hydrodynamic modes are calculated in the long wavelength limit for a granular gas. The transport coefficients are identified and found to agree with those from the Chapman-Enskog solution. The dominance of hydrodynamic modes at long times and long wavelengths is studied via an exactly solvable kinetic model. A collisional continuum is bounded away from the hydrodynamic spectrum, assuring a hydrodynamic description at long times. The bound is closely related to the power law decay of the velocity distribution in the reference homogeneous cooling state. PMID:14524742

  8. Aging in humid granular media.

    PubMed

    Restagno, Frédéric; Ursini, Cécile; Gayvallet, Hervé; Charlaix, Elisabeth

    2002-08-01

    Aging behavior is an important effect in the friction properties of solid surfaces. In this paper we investigate the temporal evolution of the static properties of a granular medium by studying the aging over time of the maximum stability angle of submillimetric glass beads. We report the effect of several parameters on these aging properties, such as the wear on the beads, the stress during the resting period, and the humidity content of the atmosphere. Aging effects in an ethanol atmosphere are also studied. These experimental results are discussed at the end of the paper. PMID:12241167

  9. Wet storage integrity update

    SciTech Connect

    Bailey, W.J.; Johnson, A.B. Jr.

    1983-09-01

    This report includes information from various studies performed under the Wet Storage Task of the Spent Fuel Integrity Project of the Commercial Spent Fuel Management (CSFM) Program at Pacific Northwest Laboratory. An overview of recent developments in the technology of wet storage of spent water reactor fuel is presented. Licensee Event Reports pertaining to spent fuel pools and the associated performance of spent fuel and storage components during wet storage are discussed. The current status of fuel that was examined under the CSFM Program is described. Assessments of the effect of boric acid in spent fuel pool water on the corrosion and stress corrosion cracking of stainless steel and the stress corrosion cracking of stainless steel piping containing stagnant water at spent fuel pools are discussed. A list of pertinent publications is included. 84 references, 21 figures, 11 tables.

  10. Partitioning of fresh crude oil between floating, dispersed and sediment phases: Effect of exposure order to dispersant and granular materials.

    PubMed

    Boglaienko, Daria; Tansel, Berrin

    2016-06-15

    When three or more high and low energy substrates are mixed, wetting order can significantly affect the behavior of the mixture. We analyzed the phase distribution of fresh floating Louisiana crude oil into dispersed, settled and floating phases depending on the exposure sequence to Corexit 9500A (dispersant) and granular materials. In the experiments artificial sea water at salinity 34‰ was used. Limestone (2.00-0.300 mm) and quartz sand (0.300-0.075 mm) were used as the natural granular materials. Dispersant Corexit 9500A increased the amount of dispersed oil up to 33.76 ± 7.04%. Addition of granular materials after the dispersant increased dispersion of oil to 47.96 ± 1.96%. When solid particles were applied on the floating oil before the dispersant, oil was captured as oil-particle aggregates and removed from the floating layer. However, dispersant addition led to partial release of the captured oil, removing it from the aggregated form to the dispersed and floating phases. There was no visible oil aggregation with the granular materials when quartz or limestone was at the bottom of the flask before the addition of oil and dispersant. The results show that granular materials can be effective when applied from the surface for aggregating or dispersing oil. However, the granular materials in the sediments are not effective neither for aggregating nor dispersing floating oil. PMID:27019358

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

    NASA Astrophysics Data System (ADS)

    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.

  12. Collective workload organization in confined excavation of granular media

    NASA Astrophysics Data System (ADS)

    Monaenkova, Daria; Linevich, Vadim; Goodisman, Michael A.; Goldman, Daniel I.

    2015-03-01

    Many social insects collectively construct large nests in complex substrates; such structures are often composed of narrow tunnels. The benefits of collective construction, including reduced construction costs per worker come with challenges of navigation in crowded, confined spaces. Here we study the workforce organization of groups of S. invicta fire ants creating tunnels in wet granular media. We monitor the activity levels of marked (painted) workers-defined as a number of tunnel visits over 12 hours- during initiation of tunnels. The activity levels are described by a Lorenz curve with a Gini coefficient of ~ 0 . 7 indicating that a majority of the excavation is performed by a minority of workers. We hypothesize that this workload distribution is beneficial for excavation in crowded conditions, and use a 2D cellular automata (CA) model to reproduce behaviors of the excavating ants. CA simulations reveal that tunnel construction rates decrease in groups of equally active animals compared to groups with the natural workload distribution. We use predictions of the CA model to organize collective excavation of granular material by teams of digging robots, and use the robots to test hypotheses of crowded excavation in the physical world. We acknowledge support of National Science Foundation, Physics of Living Systems division.

  13. Compaction Waves in Granular HMX

    SciTech Connect

    E. Kober; R. Menikoff

    1999-01-01

    Piston driven compaction waves in granular HMX are simulated with a two-dimensional continuum mechanics code in which individual grains are resolved. The constitutive properties of the grains are modeled with a hydrostatic pressure and a simple elastic-plastic model for the shear stress. Parameters are chosen to correspond to inert HMX. For a tightly packed random grain distribution (with initial porosity of 19%) we varied the piston velocity to obtain weak partly compacted waves and stronger fully compacted waves. The average stress and wave speed are compatible with the porous Hugoniot locus for uni- axial strain. However, the heterogeneities give rise to stress concentrations, which lead to localized plastic flow. For weak waves, plastic deformation is the dominant dissipative mechanism and leads to dispersed waves that spread out in time. In addition to dispersion, the granular heterogeneities give rise to subgrain spatial variation in the thermodynamic variables. The peaks in the temperature fluctuations, known as hot spots, are in the range such that they are the critical factor for initiation sensitivity.

  14. Centrifuge modelling of granular flows

    NASA Astrophysics Data System (ADS)

    Cabrera, Miguel Angel; Wu, Wei

    2015-04-01

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

  15. Modeling Size Polydisperse Granular Flows

    NASA Astrophysics Data System (ADS)

    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.

  16. Extensional Rheology of Granular Staples

    NASA Astrophysics Data System (ADS)

    Franklin, Scott

    2013-03-01

    Collections of U-shaped granular materials (e.g. staples) show a surprising resistance to being pulled apart. We conduct extensional stress-strain experiments on staple piles with vary arm/spine (barb) ratio. The elongation is not smooth, with the pile growing in bursts, reminiscent of intruder motion through ordinary and rod-like granular materials. The force-distance curve shows a power-law scaling, consistent with previous intruder experiments. Surprisingly, there is significant plastic creep of the pile as particles rearrange slightly in response to the increasing force. There is a broad distribution of yield forces that does not seem to evolve as the pile lengthens, suggesting that each yield event is independent of the pile's history. The distribution of yield forces can be interpreted in the context of a Weibullian weakest-link theory that predicts the maximum pile strength to decrease sharply with increasing pile length. From this interpretation arise length and force scales that may be used to characterize the sample. This research supported in part by the NSF (CBET-#1133722) and ACS-PRF (#51438-UR10).

  17. Shear viscosity of a model for confined granular media

    NASA Astrophysics Data System (ADS)

    Soto, Rodrigo; Risso, Dino; Brito, Ricardo

    2014-12-01

    The shear viscosity in the dilute regime of a model for confined granular matter is studied by simulations and kinetic theory. The model consists on projecting into two dimensions the motion of vibrofluidized granular matter in shallow boxes by modifying the collision rule: besides the restitution coefficient that accounts for the energy dissipation, there is a separation velocity that is added in each collision in the normal direction. The two mechanisms balance on average, producing stationary homogeneous states. Molecular dynamics simulations show that in the steady state the distribution function departs from a Maxwellian, with cumulants that remain small in the whole range of inelasticities. The shear viscosity normalized with stationary temperature presents a clear dependence with the inelasticity, taking smaller values compared to the elastic case. A Boltzmann-like equation is built and analyzed using linear response theory. It is found that the predictions show an excellent agreement with the simulations when the correct stationary distribution is used but a Maxwellian approximation fails in predicting the inelasticity dependence of the viscosity. These results confirm that transport coefficients depend strongly on the mechanisms that drive them to stationary states.

  18. Shear viscosity of a model for confined granular media.

    PubMed

    Soto, Rodrigo; Risso, Dino; Brito, Ricardo

    2014-12-01

    The shear viscosity in the dilute regime of a model for confined granular matter is studied by simulations and kinetic theory. The model consists on projecting into two dimensions the motion of vibrofluidized granular matter in shallow boxes by modifying the collision rule: besides the restitution coefficient that accounts for the energy dissipation, there is a separation velocity that is added in each collision in the normal direction. The two mechanisms balance on average, producing stationary homogeneous states. Molecular dynamics simulations show that in the steady state the distribution function departs from a Maxwellian, with cumulants that remain small in the whole range of inelasticities. The shear viscosity normalized with stationary temperature presents a clear dependence with the inelasticity, taking smaller values compared to the elastic case. A Boltzmann-like equation is built and analyzed using linear response theory. It is found that the predictions show an excellent agreement with the simulations when the correct stationary distribution is used but a Maxwellian approximation fails in predicting the inelasticity dependence of the viscosity. These results confirm that transport coefficients depend strongly on the mechanisms that drive them to stationary states. PMID:25615082

  19. BOOK REVIEW: Kinetic Theory of Granular Gases

    NASA Astrophysics Data System (ADS)

    Trizac, Emmanuel

    2005-11-01

    Granular gases are composed of macroscopic bodies kept in motion by an external energy source such as a violent shaking. The behaviour of such systems is quantitatively different from that of ordinary molecular gases: due to the size of the constituents, external fields have a stronger effect on the dynamics and, more importantly, the kinetic energy of the gas is no longer a conserved quantity. The key role of the inelasticity of collisions has been correctly appreciated for about fifteen years, and the ensuing consequences in terms of phase behaviour or transport properties studied in an increasing and now vast body of literature. The purpose of this book is to help the newcomer to the field in acquiring the essential theoretical tools together with some numerical techniques. As emphasized by the authors—who were among the pioneers in the domain— the content could be covered in a one semester course for advanced undergraduates, or it could be incorporated in a more general course dealing with the statistical mechanics of dissipative systems. The book is self-contained, clear, and avoids mathematical complications. In order to elucidate the main physical ideas, heuristic points of views are sometimes preferred to a more rigorous route that would lead to a longer discussion. The 28 chapters are short; they offer exercises and worked examples, solved at the end of the book. Each part is supplemented with a relevant foreword and a useful summary including take-home messages. The editorial work is of good quality, with very few typographical errors. In spite of the title, kinetic theory stricto sensu is not the crux of the matter covered. The authors discuss the consequences of the molecular chaos assumption both at the individual particle level and in terms of collective behaviour. The first part of the book addresses the mechanics of grain collisions. It is emphasized that considering the coefficient of restitution ɛ —a central quantity governing the

  20. Linking acoustic emission signatures with grain-scale mechanical interactions during granular shearing

    NASA Astrophysics Data System (ADS)

    Michlmayr, G.; Cohen, D.; Or, D.

    2012-04-01

    Acoustic Emissions (AE) are high frequency (kHz range) elastic body waves, generated in deforming granular material during particle collisions, frictional slip, or other types of abrupt grain-scale mechanical interactions. The direct link with particle micro-mechanics makes AE a useful tool for gaining insights into mechanical aspects of progressive shear failure in granular material and slow granular flows. The formation of shear plane in granular matter involves numerous internal restructuring and failure events with distinct dynamics resembling features of critical phase transition. Following establishment of a shear plane, subsequent deformation involves episodic slip events interrupted by arrested flow (stick-slip behavior). We developed a model for interpreting measured AE signatures in terms of micro-failures during progressive granular shear a considering AE generation mechanisms and propagation of acoustic signals within granular material. Results from shear frame experiments include information on strains, stresses and acoustic emissions during deformation controlled tests on glass beads and sand. The number of failure associated AE event rates peaks with maximum shear resistance of the granular material. Intermittent slip events during stick-slip deformation are found to be closely related to low frequency AE events (~1kHz). Statistics of AE events and their temporal development are reproduced using a simple fiber-bundle model. A conceptual AE generation and propagation model accounts for conversion of mechanical events into elastic waves. In addition to gaining insights concerning grain-scale mechanical interactions, the AE method offers a useful tool for monitoring hazardous geologic mass movements, such as landslides, rock avalanches or debris flows.

  1. Numerical Simulations of Granular Processes

    NASA Astrophysics Data System (ADS)

    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

  2. Quantitative DEM of granular packings

    NASA Astrophysics Data System (ADS)

    Brodu, Nicolas; Dijksman, Joshua; Behringer, Robert

    2014-03-01

    We introduce a new model for simulating granular assemblies. This model explicitely accounts for the cross-influence of multiple contacts on grains. It maintains the surface deformations of the grains induced by the contacts, improving on the classical non-deformable interpenetrable spheres model, for a reasonable computational cost. We show that both multiple contacts and surface deformations are necessary for reproducing quantitatively the 3D force measurements we recently demonstrated. We also show that friction has a dramatic effect on the forces and number of contacts, so it cannot be ignored even for very small values. This work was funded by NASA grant NNX10AU01G, NSF grant DMR12-06351 and ARO grant W911NF-1-11-0110.

  3. Aerofractures in Confined Granular Media

    NASA Astrophysics Data System (ADS)

    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

  4. Granular metamaterials for vibration mitigation

    NASA Astrophysics Data System (ADS)

    Gantzounis, G.; Serra-Garcia, M.; Homma, K.; Mendoza, J. M.; Daraio, C.

    2013-09-01

    Acoustic metamaterials that allow low-frequency band gaps are interesting for many practical engineering applications, where vibration control and sound insulation are necessary. In most prior studies, the mechanical response of these structures has been described using linear continuum approximations. In this work, we experimentally and theoretically address the formation of low-frequency band gaps in locally resonant granular crystals, where the dynamics of the system is governed by discrete equations. We investigate the quasi-linear behavior of such structures. The analysis shows that a stopband can be introduced at about one octave lower frequency than in materials without local resonances. Broadband and multi-frequency stopband characteristics can also be achieved by strategically tailoring the non-uniform local resonance parameters.

  5. 21 CFR 133.145 - Granular cheese for manufacturing.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 2 2012-04-01 2012-04-01 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 §...

  6. 21 CFR 133.145 - Granular cheese for manufacturing.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 2 2013-04-01 2013-04-01 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 §...

  7. 21 CFR 133.145 - Granular cheese for manufacturing.

    Code of Federal Regulations, 2010 CFR

    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 §...

  8. 21 CFR 133.145 - Granular cheese for manufacturing.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 2 2014-04-01 2014-04-01 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 §...

  9. 21 CFR 133.145 - Granular cheese for manufacturing.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 2 2011-04-01 2011-04-01 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 §...

  10. Force distributions in granular materials

    NASA Astrophysics Data System (ADS)

    Jaeger, Heinrich M.

    2002-03-01

    A fundamental problem in the study of disordered materials concerns the propagation of forces. Static granular media, such as sand particles inside a rigid container, have emerged as an important model system as they embody the zero temperature limit of disordered materials comprised of hardsphere repulsive particles. In this talk, I will review recent results on the distribution forces along the boundaries of granular material subjected to an applied load. While the spatial distribution of mean forces sensitively reflects the (macroscopic) packing structure of the material, the ensemble-averaged probability distribution of force fluctuations around the mean value, P(f), exhibits universal behavior. The shape of P(f) is found to be independent not only of the macroscopic packing arrangement but also of the inter-particle friction and, over a wide range, of the applied external stress. This shape is characterized by an exponential decay in the probability density for fluctuations above the mean force and only a small reduction, by no more than a factor two, for fluctuations below the mean [1]. Surprisingly, the exponential, non-Gaussian behavior appears to hold up even in the case of highly compressible grains, and it also has been observed in simulations of supercooled liquids [2]. I will discuss the implications of these findings on our current understanding of stress transmission in disordered media in general, and on glassy behavior in particular. [1] D. L. Blair, N. W. Mueggenburg, A. H. Marshall, H. M. Jaeger, and S. R. Nagel, Phys. Rev. E 63, 041304 (2001). [2] S. O’Hern, S. A. Langer, A. J. Liu, and S. R. Nagel, Phys. Rev. Lett. 86, 111 (2001). * Work performed in collaboration with D. L. Blair, J. M. Erikson, A. H. Marshall, N. W. Mueggenburg, and S. R. Nagel.

  11. Recent bright gully deposits on Mars: Wet or dry flow?

    USGS Publications Warehouse

    Pelletier, J.D.; Kolb, K.J.; McEwen, A.S.; Kirk, R.L.

    2008-01-01

    Bright gully sediments attributed to liquid water flow have been deposited on Mars within the past several years. To test the liquid water flow hypothesis, we constructed a high-resolution (1 m/pixel) photogrammetric digital elevation model of a crater in the Centauri Montes region, where a bright gully deposit formed between 2001 and 2005. We conducted one-dimensional (1-D) and 2-D numerical flow modeling to test whether the deposit morphology is most consistent with liquid water or dry granular How. Liquid water flow models that incorporate freezing can match the runout distance of the flow for certain freezing rates but fail to reconstruct the distributary lobe morphology of the distal end of the deposit. Dry granular flow models can match both the observed runout distance and the distal morphology. Wet debris flows with high sediment concentrations are also consistent with the observed morphology because their rheologies are often similar to that of dry granular flows. As such, the presence of liquid water in this flow event cannot be ruled out, but the available evidence is consistent with dry landsliding. ?? 2008 The Geological Society of America.

  12. Continuum description of avalanches in granular media.

    SciTech Connect

    Aranson, I. S.; Tsimring, L. S.

    2000-12-05

    A continuum theory of partially fluidized granular flows is proposed. The theory is based on a combination of the mass and momentum conservation equations with the order parameter equation which describes the transition between flowing and static components of the granular system. We apply this model to the dynamics of avalanches in chutes. The theory provides a quantitative description of recent observations of granular flows on rough inclined planes (Daerr and Douady 1999): layer bistability, and the transition from triangular avalanches propagating downhill at small inclination angles to balloon-shaped avalanches also propagating uphill for larger angles.

  13. Impact compaction of a granular material

    SciTech Connect

    Fenton, Gregg; Asay, Blaine; Dalton, Devon

    2015-05-19

    The dynamic behavior of granular materials has importance to a variety of engineering applications. Structural seismic coupling, planetary science, and earth penetration mechanics, are just a few of the application areas. Although the mechanical behavior of granular materials of various types have been studied extensively for several decades, the dynamic behavior of such materials remains poorly understood. High-quality experimental data are needed to improve our general understanding of granular material compaction physics. This study will describe how an instrumented plunger impact system can be used to measure pressure-density relationships for model materials at high and controlled strain rates and subsequently used for computational modeling.

  14. Wet chemistry instrument prototype

    NASA Technical Reports Server (NTRS)

    1974-01-01

    A wet chemistry instrument prototype for detecting amino acids in planetary soil samples was developed. The importance of amino acids and their condensation products to the development of life forms is explained. The characteristics of the instrument and the tests which were conducted to determine the materials compatibility are described. Diagrams are provided to show the construction of the instrument. Data obtained from the performance tests are reported.

  15. Capillary Movement in Granular Beds in Microgravity

    NASA Technical Reports Server (NTRS)

    Yendler, Boris S.; Bula, Ray J.; Kliss, Mark (Technical Monitor)

    1996-01-01

    Understanding the dynamics of capillary flow through unsaturated porous media is very important for the development of an effective water and nutrient delivery system for growing plants in microgravity and chemical engineering applications. Experiments were conducted on the Space Shuttle during the STS-63 mission using three experimental cuvettes called "Capillary Testbed-M." These experiments studied the effect of bead diameter on capillary flow by comparing the capillary flow in three different granular beds. It was observed that the speed of water propagation in the granular bed consisting of 1.5 mm diameter particles was less than that in the bed consisting of 1.0 mm. diameter particles. Such results contradict the existing theory of capillary water propagation in granular beds. It was found also that in microgravity water propagates independently in adjacent layers of a layered granular bed .

  16. NMR Measurements of Granular Flow and Compaction

    NASA Astrophysics Data System (ADS)

    Fukushima, Eiichi

    1998-03-01

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

  17. Acoustical properties of double porosity granular materials.

    PubMed

    Venegas, Rodolfo; Umnova, Olga

    2011-11-01

    Granular materials have been conventionally used for acoustic treatment due to their sound absorptive and sound insulating properties. An emerging field is the study of the acoustical properties of multiscale porous materials. An example of these is a granular material in which the particles are porous. In this paper, analytical and hybrid analytical-numerical models describing the acoustical properties of these materials are introduced. Image processing techniques have been employed to estimate characteristic dimensions of the materials. The model predictions are compared with measurements on expanded perlite and activated carbon showing satisfactory agreement. It is concluded that a double porosity granular material exhibits greater low-frequency sound absorption at reduced weight compared to a solid-grain granular material with similar mesoscopic characteristics. PMID:22087905

  18. Granular crystals: Nonlinear dynamics meets materials engineering

    SciTech Connect

    Porter, Mason A.; Kevrekidis, Panayotis G.; Daraio, Chiara

    2015-11-01

    In this article, the freedom to choose the size, stiffness, and spatial distribution of macroscopic particles in a lattice makes granular crystals easily tailored building blocks for shock-absorbing materials, sound-focusing devices, acoustic switches, and other exotica.

  19. Tunable magneto-granular phononic crystals

    NASA Astrophysics Data System (ADS)

    Allein, F.; Tournat, V.; Gusev, V. E.; Theocharis, G.

    2016-04-01

    This paper reports on the study of the dynamics of 1D magneto-granular phononic crystals composed of a chain of spherical steel beads inside a properly designed magnetic field. This field is induced by an array of permanent magnets, located in a holder at a given distance from the chain. The theoretical and experimental results of the band gap structure are displayed, including all six degrees of freedom for the beads, i.e., three translations and three rotations. Experimental evidence of transverse-rotational modes of propagation is presented; moreover, by changing the strength of the magnetic field, the dynamic response of the granular chain is tuned. The combination of non-contact tunability with the potentially strong nonlinear behavior of granular systems ensures the suitability of magneto-granular phononic crystals as nonlinear, tunable mechanical metamaterials for use in controlling elastic wave propagation.

  20. Rheology of weakly vibrated granular materials

    NASA Astrophysics Data System (ADS)

    Dijksman, J. A.; Wortel, G.; van Hecke, M.

    2009-06-01

    We show how weak vibrations substantially modify the rheology of granular materials. We experimentally probe dry granular flows in a weakly vibrated split bottom shear cell—the weak vibrations modulate gravity and act as an agitation source. By tuning the applied stress and vibration strength, and monitoring the resulting strain as a function of time, we uncover a rich phase diagram in which non-trivial transitions separate a jammed phase, a creep flow case, and a steady flow case.

  1. Rheology of weakly vibrated granular media

    NASA Astrophysics Data System (ADS)

    Wortel, Geert H.; Dijksman, Joshua A.; van Hecke, Martin

    2014-01-01

    We probe the rheology of weakly vibrated granular flows as function of flow rate, vibration strength, and pressure by performing experiments in a vertically vibrated split-bottom shear cell. For slow flows, we establish the existence of a vibration-dominated granular flow regime, where the driving stresses smoothly vanish as the driving rate is diminished. We distinguish three qualitatively different vibration-dominated rheologies, most strikingly a regime where the shear stresses no longer are proportional to the pressure.

  2. Shear dispersion in dense granular flows

    DOE PAGESBeta

    Christov, Ivan C.; Stone, Howard A.

    2014-04-18

    We formulate and solve a model problem of dispersion of dense granular materials in rapid shear flow down an incline. The effective dispersivity of the depth-averaged concentration of the dispersing powder is shown to vary as the Péclet number squared, as in classical Taylor–Aris dispersion of molecular solutes. An extension to generic shear profiles is presented, and possible applications to industrial and geological granular flows are noted.

  3. Aerobic granular processes: Current research trends.

    PubMed

    Zhang, Quanguo; Hu, Jianjun; Lee, Duu-Jong

    2016-06-01

    Aerobic granules are large biological aggregates with compact interiors that can be used in efficient wastewater treatment. This mini-review presents new researches on the development of aerobic granular processes, extended treatments for complicated pollutants, granulation mechanisms and enhancements of granule stability in long-term operation or storage, and the reuse of waste biomass as renewable resources. A discussion on the challenges of, and prospects for, the commercialization of aerobic granular process is provided. PMID:26873285

  4. Granular Cell Tumor: An Uncommon Benign Neoplasm

    PubMed Central

    Gayen, Tirthankar; Das, Anupam; Shome, Kaushik; Bandyopadhyay, Debabrata; Das, Dipti; Saha, Abanti

    2015-01-01

    Granular cell tumor is a distinctly rare neoplasm of neural sheath origin. It mainly presents as a solitary asymptomatic swelling in the oral cavity, skin, and rarely internal organs in the middle age. Histopathology is characteristic, showing polyhedral cells containing numerous fine eosinophilic granules with indistinct cell margins. We present a case of granular cell tumor on the back of a 48-year-old woman which was painful, mimicking an adnexal tumor. PMID:26120181

  5. Clogging and Jamming Transitions in Granular Matter Flowing Through Obstacles

    NASA Astrophysics Data System (ADS)

    Reichhardt, Cynthia Olson; Reichhardt, Charles

    2015-03-01

    We consider a two-dimensional system of bidisperse disks driven through a landscape of fixed obstacles. In the limit of a single obstacle, the disks cease moving when the disk density is increased to the jamming density. The threshold density value decreases as the number of obstacles increases, but we also observe a change in the nature of the frozen state. At low obstacle density we find a homogeneous jammed state, but for higher obstacle density we instead find a heterogeneous clogged state containing void areas and possessing a memory of the driving direction. The transition to the clogged state is strongly stochastic and we observe large fluctuations in clogging time both for clogging in the original driving direction and for transverse clogging when the drive is suddenly rotated by 90 degrees. We find evidence for a diverging clogging transition time at a critical disk density well below the jamming density in a clean system.

  6. Surface wave acoustics of granular packing under gravity

    SciTech Connect

    Clement, Eric; Andreotti, Bruno; Bonneau, Lenaic

    2009-06-18

    Due to the non-linearity of Hertzian contacts, the speed of sound in granular matter increases with pressure. For a packing under gravity and in the presence of a free surface, bulk acoustic waves cannot propagate due to the inherent refraction toward the surface (the mirage effect). Thus, only modes corresponding to surface waves (Raleigh-Hertz modes) are able to propagate the acoustic signal. First, based on a non-linear elasticity model, we describe the main features associated to these surface waves. We show that under gravity, a granular packing is from the acoustic propagation point of view an index gradient waveguide that selects modes of two distinct families i.e. the sagittal and transverse waves localized in the vicinity of the free surface. A striking feature of these surface waves is the multi-modal propagation: for both transverse and sagittal waves, we show the existence of a infinite but discrete series of propagating modes. In each case, we determine the mode shape and and the corresponding dispersion relation. In the case of a finite size system, a geometric waveguide is superimposed to the index gradient wave guide. In this later case, the dispersion relations are modified by the appearance of a cut-off frequency that scales with depth. The second part is devoted to an experimental study of surface waves propagating in a granular packing confined in a long channel. This set-up allows to tune a monomodal emission by taking advantage of the geometric waveguide features combined with properly designed emitters. For both sagittal and transverses waves, we were able to isolate a single mode (the fundamental one) and to plot the dispersion relation. This measurements agree well with the Hertzian scaling law as predicted by meanfield models. Furthermore, it allows us to determine quantitatively relations on the elastic moduli. However, we observe that our data yield a shear modulus abnormally weak when compared to several meanfield predictions.

  7. Surface wave acoustics of granular packing under gravity

    NASA Astrophysics Data System (ADS)

    Clement, Eric; Bonneau, Lenaic; Andreotti, Bruno

    2009-06-01

    Due to the non-linearity of Hertzian contacts, the speed of sound in granular matter increases with pressure. For a packing under gravity and in the presence of a free surface, bulk acoustic waves cannot propagate due to the inherent refraction toward the surface (the mirage effect). Thus, only modes corresponding to surface waves (Raleigh-Hertz modes) are able to propagate the acoustic signal. First, based on a non-linear elasticity model, we describe the main features associated to these surface waves. We show that under gravity, a granular packing is from the acoustic propagation point of view an index gradient waveguide that selects modes of two distinct families i.e. the sagittal and transverse waves localized in the vicinity of the free surface. A striking feature of these surface waves is the multi-modal propagation: for both transverse and sagittal waves, we show the existence of a infinite but discrete series of propagating modes. In each case, we determine the mode shape and and the corresponding dispersion relation. In the case of a finite size system, a geometric waveguide is superimposed to the index gradient wave guide. In this later case, the dispersion relations are modified by the appearance of a cut-off frequency that scales with depth. The second part is devoted to an experimental study of surface waves propagating in a granular packing confined in a long channel. This set-up allows to tune a monomodal emission by taking advantage of the geometric waveguide features combined with properly designed emitters. For both sagittal and transverses waves, we were able to isolate a single mode (the fundamental one) and to plot the dispersion relation. This measurements agree well with the Hertzian scaling law as predicted by meanfield models. Furthermore, it allows us to determine quantitatively relations on the elastic moduli. However, we observe that our data yield a shear modulus abnormally weak when compared to several meanfield predictions.

  8. Prediction of permeability of monodisperse granular materials with a micromechanics approach

    NASA Astrophysics Data System (ADS)

    Yang, Rongwei; Lemarchand, Eric; Fen-Chong, Teddy; Li, Kefei

    2016-04-01

    Prediction of the permeability of porous media is of vital importance to such fields as petroleum engineering, agricultural engineering and civil engineering. The liquid water within unsaturated granular materials is distinguished as the intergranular layer, the wetting layer and the water film. By means of the micromechanics approach, a physical conceptual model is developed to predict the permeability (intrinsic and relative permeabilities) of the monodisperse granular materials. The proposed model has been validated by comparing the available experimental data and the empirical models, and has been used to re-interpret the Kozeny-Carman's relation in particular. The results obtained with this model show that the intergranular water will dominate the flow transport when the saturation degree is higher than the residual saturation degree; when the saturation degree is below the residual saturation degree, the wetting layer will govern the flow transport and the relative permeability will decrease by 3 to 8 orders of magnitude depending on the connectivity of the wetting layer.

  9. Contact micromechanics in granular media with clay

    SciTech Connect

    Ita, S.L.

    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.

  10. Steady flow dynamics during granular impact

    NASA Astrophysics Data System (ADS)

    Clark, Abram H.; Kondic, Lou; Behringer, Robert P.

    2016-05-01

    We study experimentally and computationally the dynamics of granular flow during impacts where intruders strike a collection of disks from above. In the regime where granular force dynamics are much more rapid than the intruder motion, we find that the particle flow near the intruder is proportional to the instantaneous intruder speed; it is essentially constant when normalized by that speed. The granular flow is nearly divergence free and remains in balance with the intruder, despite the latter's rapid deceleration. Simulations indicate that this observation is insensitive to grain properties, which can be explained by the separation of time scales between intergrain force dynamics and intruder dynamics. Assuming there is a comparable separation of time scales, we expect that our results are applicable to a broad class of dynamic or transient granular flows. Our results suggest that descriptions of static-in-time granular flows might be extended or modified to describe these dynamic flows. Additionally, we find that accurate grain-grain interactions are not necessary to correctly capture the granular flow in this regime.