WorldWideScience

Sample records for model time granularity

  1. Study of Network Traffic Analysis Model Based on Time Granularity

    Institute of Scientific and Technical Information of China (English)

    Tan,Xi-aoling; Xu,Yong; Mei,Chenggang; Liu,Lan

    2005-01-01

    An analytic research on establishing different traffic models on the traffic nature of different time granularity can provide necessary academic foundation for network design and simulation as well as ensuring the quality of service and network management. This paper aims to make simulant predication by means of corresponding math tools on the modeling of real traftic of the different time granularity. The experimental results indicate that the predicated traffic is close to the real traffic distribution.

  2. Mathematical models of granular matter

    CERN Document Server

    Mariano, Paolo; Giovine, Pasquale

    2008-01-01

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

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

    DEFF Research Database (Denmark)

    Iftikhar, Nadeem; Pedersen, Torben Bach

    2010-01-01

    The majority of today’s systems increasingly require sophisticated data management as they need to store and to query large amounts of data for analysis and reporting purposes. In order to keep more “detailed” data available for longer periods, “old” data has to be reduced gradually to save space...... is 6 months old aggregate to 2 minutes level from 1 minute level and so on. The proposed solution introduces a time granularity based data structure, namely a relational time granularity table that enables long term storage of old data by maintaining it at different levels of granularity and effective...

  4. From Numeric Models to Granular System Modeling

    Directory of Open Access Journals (Sweden)

    Witold Pedrycz

    2015-03-01

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

  5. DISCRETE AND CONTINUUM MODELLING OF GRANULAR FLOW

    Institute of Scientific and Technical Information of China (English)

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

    2005-01-01

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

  6. Discrete Element Modeling of Complex Granular Flows

    Science.gov (United States)

    Movshovitz, N.; Asphaug, E. I.

    2010-12-01

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

  7. HYPERELASTIC MODELS FOR GRANULAR MATERIALS

    Energy Technology Data Exchange (ETDEWEB)

    Humrickhouse, Paul W; Corradini, Michael L

    2009-01-29

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

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

    Science.gov (United States)

    Gilberg, Dominik; Klar, Axel; Steiner, Konrad

    2017-06-01

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

  9. Preliminary 2D numerical modeling of common granular problems

    Science.gov (United States)

    Wyser, Emmanuel; Jaboyedoff, Michel

    2017-04-01

    Granular studies received an increasing interest during the last decade. Many scientific investigations were successfully addressed to acknowledge the ubiquitous behavior of granular matter. We investigate liquid impacts onto granular beds, i.e. the influence of the packing and compaction-dilation transition. However, a physically-based model is still lacking to address complex microscopic features of granular bed response during liquid impacts such as compaction-dilation transition or granular bed uplifts (Wyser et al. in review). We present our preliminary 2D numerical modeling based on the Discrete Element Method (DEM) using nonlinear contact force law (the Hertz-Mindlin model) for disk shape particles. The algorithm is written in C programming language. Our 2D model provides an analytical tool to address granular problems such as i) granular collapses and ii) static granular assembliy problems. This provides a validation framework of our numerical approach by comparing our numerical results with previous laboratory experiments or numerical works. Inspired by the work of Warnett et al. (2014) and Staron & Hinch (2005), we studied i) the axisymetric collapse of granular columns. We addressed the scaling between the initial aspect ratio and the final runout distance. Our numerical results are in good aggreement with the previous studies of Warnett et al. (2014) and Staron & Hinch (2005). ii) Reproducing static problems for regular and randomly stacked particles provides a valid comparison to results of Egholm (2007). Vertical and horizontal stresses within the assembly are quite identical to stresses obtained by Egholm (2007), thus demonstating the consistency of our 2D numerical model. Our 2D numerical model is able to reproduce common granular case studies such as granular collapses or static problems. However, a sufficient small timestep should be used to ensure a good numerical consistency, resulting in higher computational time. The latter becomes critical

  10. Micromechanical Behavior and Modelling of Granular Soil

    Science.gov (United States)

    1989-07-01

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

  11. Theoretical model of granular compaction

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-11-01

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

  12. Modeling Size Polydisperse Granular Flows

    Science.gov (United States)

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

    2014-11-01

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

  13. Two Classes of Models of Granular Computing

    Institute of Scientific and Technical Information of China (English)

    Daowu Pei

    2006-01-01

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

  14. Type-2 fuzzy granular models

    CERN Document Server

    Sanchez, Mauricio A; Castro, Juan R

    2017-01-01

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

  15. Linguistic granular model: design and realization

    Institute of Scientific and Technical Information of China (English)

    YUE Shihong; LI Ping; SONG Zhihuan

    2005-01-01

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

  16. Advanced Granular System Modeling Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Spaceports of the future will utilize new granular materials in unique applications including insulation for cryogenic tanks and Lunar regolith processing for usable...

  17. Discrete particle modelling of granular roll waves

    Science.gov (United States)

    Tsang, Jonathan; Dalziel, Stuart; Vriend, Nathalie

    2016-11-01

    A granular current flowing down an inclined chute or plane can undergo an instability that leads to the formation of surface waves, known as roll waves. Examples of roll waves are found in avalanches and debris flows in landslides, and in many industrial processes. Although related to the Kapitza instability of viscous fluid films, granular roll waves are not yet as well understood. Laboratory experiments typically measure the surface height and velocity of a current as functions of position and time, but they do not give insight into the processes below the surface: in particular, the possible formation of a boundary layer at the free surface as well as the base. To overcome this, we are running discrete particle model (DPM) simulations. Simulations are validated against our laboratory experiments, but they also allow us to examine a much larger range of parameters, such as material properties, chute geometry and particle size dispersity, than that which is possible in the lab. We shall present results from simulations in which we vary particle size and dispersity, and examine the implications on roll wave formation and propagation. Future work will include simulations in which the shape of the chute is varied, both cross-sectionally and in the downstream direction. EPSRC studentship (Tsang) and Royal Society Research Fellowship (Vriend).

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

    Science.gov (United States)

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

    2015-12-01

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

  19. Discrete element modelling of granular materials

    NARCIS (Netherlands)

    Van Baars, S.

    1996-01-01

    A new model is developed by the author, which does not use the equations of motion but the equations of equilibrium to describe granular materials. The numerical results show great similarities with reality and can generally be described by an advanced Mohr-Coulomb model. However, many contacts betw

  20. Continuum modeling of rate-dependent granular flows in SPH

    Science.gov (United States)

    Hurley, Ryan C.; Andrade, José E.

    2016-09-01

    We discuss a constitutive law for modeling rate-dependent granular flows that has been implemented in smoothed particle hydrodynamics (SPH). We model granular materials using a viscoplastic constitutive law that produces a Drucker-Prager-like yield condition in the limit of vanishing flow. A friction law for non-steady flows, incorporating rate-dependence and dilation, is derived and implemented within the constitutive law. We compare our SPH simulations with experimental data, demonstrating that they can capture both steady and non-steady dynamic flow behavior, notably including transient column collapse profiles. This technique may therefore be attractive for modeling the time-dependent evolution of natural and industrial flows.

  1. Continuum modeling of rate-dependent granular flows in SPH

    Science.gov (United States)

    Hurley, Ryan C.; Andrade, José E.

    2017-01-01

    We discuss a constitutive law for modeling rate-dependent granular flows that has been implemented in smoothed particle hydrodynamics (SPH). We model granular materials using a viscoplastic constitutive law that produces a Drucker-Prager-like yield condition in the limit of vanishing flow. A friction law for non-steady flows, incorporating rate-dependence and dilation, is derived and implemented within the constitutive law. We compare our SPH simulations with experimental data, demonstrating that they can capture both steady and non-steady dynamic flow behavior, notably including transient column collapse profiles. This technique may therefore be attractive for modeling the time-dependent evolution of natural and industrial flows.

  2. Dynamic Distribution Model with Prime Granularity for Parallel Computing

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    Dynamic distribution model is one of the best schemes for parallel volume rendering. However, in homogeneous cluster system, since the granularity is traditionally identical, all processors communicate almost simultaneously and computation load may lose balance. Due to problems above, a dynamic distribution model with prime granularity for parallel computing is presented.Granularities of each processor are relatively prime, and related theories are introduced. A high parallel performance can be achieved by minimizing network competition and using a load balancing strategy that ensures all processors finish almost simultaneously. Based on Master-Slave-Gleaner (MSG) scheme, the parallel Splatting Algorithm for volume rendering is used to test the model on IBM Cluster 1350 system. The experimental results show that the model can bring a considerable improvement in performance, including computation efficiency, total execution time, speed, and load balancing.

  3. Bipotential continuum models for granular mechanics

    Science.gov (United States)

    Goddard, Joe

    2014-03-01

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

  4. Computational Granular Dynamics Models and Algorithms

    CERN Document Server

    Pöschel, Thorsten

    2005-01-01

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

  5. Applying MDL to Learning Best Model Granularity

    CERN Document Server

    Gao, Q; Vitanyi, P; Gao, Qiong; Li, Ming; Vitanyi, Paul

    2000-01-01

    The Minimum Description Length (MDL) principle is solidly based on a provably ideal method of inference using Kolmogorov complexity. We test how the theory behaves in practice on a general problem in model selection: that of learning the best model granularity. The performance of a model depends critically on the granularity, for example the choice of precision of the parameters. Too high precision generally involves modeling of accidental noise and too low precision may lead to confusion of models that should be distinguished. This precision is often determined ad hoc. In MDL the best model is the one that most compresses a two-part code of the data set: this embodies ``Occam's Razor.'' In two quite different experimental settings the theoretical value determined using MDL coincides with the best value found experimentally. In the first experiment the task is to recognize isolated handwritten characters in one subject's handwriting, irrespective of size and orientation. Based on a new modification of elastic...

  6. A model for collisions in granular gases

    OpenAIRE

    Brilliantov, Nikolai V.; Spahn, Frank; Hertzsch, Jan-Martin; Poeschel, Thorsten

    2002-01-01

    We propose a model for collisions between particles of a granular material and calculate the restitution coefficients for the normal and tangential motion as functions of the impact velocity from considerations of dissipative viscoelastic collisions. Existing models of impact with dissipation as well as the classical Hertz impact theory are included in the present model as special cases. We find that the type of collision (smooth, reflecting or sticky) is determined by the impact velocity and...

  7. Multiscale modelling of fluid-immersed granular media

    OpenAIRE

    Clément, Christian Paul André René

    2010-01-01

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

  8. Rough – Granular Computing knowledge discovery models

    Directory of Open Access Journals (Sweden)

    Mohammed M. Eissa

    2016-11-01

    Full Text Available Medical domain has become one of the most important areas of research in order to richness huge amounts of medical information about the symptoms of diseases and how to distinguish between them to diagnose it correctly. Knowledge discovery models play vital role in refinement and mining of medical indicators to help medical experts to settle treatment decisions. This paper introduces four hybrid Rough – Granular Computing knowledge discovery models based on Rough Sets Theory, Artificial Neural Networks, Genetic Algorithm and Rough Mereology Theory. A comparative analysis of various knowledge discovery models that use different knowledge discovery techniques for data pre-processing, reduction, and data mining supports medical experts to extract the main medical indicators, to reduce the misdiagnosis rates and to improve decision-making for medical diagnosis and treatment. The proposed models utilized two medical datasets: Coronary Heart Disease dataset and Hepatitis C Virus dataset. The main purpose of this paper was to explore and evaluate the proposed models based on Granular Computing methodology for knowledge extraction according to different evaluation criteria for classification of medical datasets. Another purpose is to make enhancement in the frame of KDD processes for supervised learning using Granular Computing methodology.

  9. Mutiscale Modeling of Segregation in Granular Flows

    Energy Technology Data Exchange (ETDEWEB)

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

    2007-01-01

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

  10. Controlling mixing and segregation in time periodic granular flows

    Science.gov (United States)

    Bhattacharya, Tathagata

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

  11. Constitutive model development for flows of granular materials

    Science.gov (United States)

    Chialvo, Sebastian

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

  12. Granular Computing

    Institute of Scientific and Technical Information of China (English)

    2004-01-01

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

  13. Nonlocal modeling of granular flows down inclines.

    Science.gov (United States)

    Kamrin, Ken; Henann, David L

    2015-01-07

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

  14. Modelling of dc characteristics for granular semiconductors

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-11-01

    The dc characteristics of granular n-type semiconductors are calculated analytically with the drift-diffusion theory. Electronic trapping at the grain boundaries (GBs) is taken into account. The use of quadratic and linear GB potential profiles in the calculation is compared. The analytical model is verified with numerical simulation performed by SILVACO ATLAS. The agreement between the analytical and numerical results is excellent in a large voltage range. The results show that electronic trapping at the GBs has a remarkable effect on the highly nonlinear I-V characteristics of the material.

  15. Gaussian kinetic model for granular gases.

    Science.gov (United States)

    Dufty, James W; Baskaran, Aparna; Zogaib, Lorena

    2004-05-01

    A kinetic model for the Boltzmann equation is proposed and explored as a practical means to investigate the properties of a dilute granular gas. It is shown that all spatially homogeneous initial distributions approach a universal "homogeneous cooling solution" after a few collisions. The homogeneous cooling solution (HCS) is studied in some detail and the exact solution is compared with known results for the hard sphere Boltzmann equation. It is shown that all qualitative features of the HCS, including the nature of overpopulation at large velocities, are reproduced by the kinetic model. It is also shown that all the transport coefficients are in excellent agreement with those from the Boltzmann equation. Also, the model is specialized to one having a velocity independent collision frequency and the resulting HCS and transport coefficients are compared to known results for the Maxwell model. The potential of the model for the study of more complex spatially inhomogeneous states is discussed.

  16. Building designed granular towers one drop at a time

    Science.gov (United States)

    Chopin, Julien; Kudrolli, Arshad

    2012-02-01

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

  17. Multi-Granular Trend Detection for Time-Series Analysis.

    Science.gov (United States)

    Arthur Van, Goethem; Staals, Frank; Loffler, Maarten; Dykes, Jason; Speckmann, Bettina

    2017-01-01

    Time series (such as stock prices) and ensembles (such as model runs for weather forecasts) are two important types of one-dimensional time-varying data. Such data is readily available in large quantities but visual analysis of the raw data quickly becomes infeasible, even for moderately sized data sets. Trend detection is an effective way to simplify time-varying data and to summarize salient information for visual display and interactive analysis. We propose a geometric model for trend-detection in one-dimensional time-varying data, inspired by topological grouping structures for moving objects in two- or higher-dimensional space. Our model gives provable guarantees on the trends detected and uses three natural parameters: granularity, support-size, and duration. These parameters can be changed on-demand. Our system also supports a variety of selection brushes and a time-sweep to facilitate refined searches and interactive visualization of (sub-)trends. We explore different visual styles and interactions through which trends, their persistence, and evolution can be explored.

  18. A Granular Computing Model Based on Tolerance relation

    Institute of Scientific and Technical Information of China (English)

    WANG Guo-yin; HU Feng; HUANG Hai; WU Yu

    2005-01-01

    Granular computing is a new intelligent computing theory based on partition of problem concepts. It is an important problem in Rough Set theory to process incomplete information systems directly. In this paper, a granular computing model based on tolerance relation for processing incomplete information systems is developed. Furthermore, a criteria condition for attribution necessity is proposed in this model.

  19. Hard-sphere limit of soft-sphere model for granular materials: Stiffness dependence of steady granular flow

    OpenAIRE

    Mitarai, Namiko; Nakanishi, Hiizu

    2002-01-01

    Dynamical behavior of steady granular flow is investigated numerically in the inelastic hard sphere limit of the soft sphere model. We find distinctively different limiting behaviors for the two flow regimes, i.e., the collisional flow and the frictional flow. In the collisional flow, the hard sphere limit is straightforward; the number of collisions per particle per unit time converges to a finite value and the total contact time fraction with other particles goes to zero. For the frictional...

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

    Science.gov (United States)

    Jop, Pierre

    2008-03-01

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

  1. Modeling density segregation in granular flow

    Science.gov (United States)

    Xiao, Hongyi; Lueptow, Richard; Umbanhowar, Paul

    2015-11-01

    A recently developed continuum-based model accurately predicts segregation in flows of granular mixtures varying in particle size by considering the interplay of advection, diffusion and segregation. In this research, we extend the domain of the model to include density driven segregation. Discrete Element Method (DEM) simulations of density bidisperse flows of mono-sized particles in a quasi-2D bounded heap were performed to determine the dependence of the density driven segregation velocity on local shear rate, particle concentration, and a segregation length which scales with the particle size and the logarithm of the density ratio. With these inputs, the model yields theoretical predictions of density segregation patterns that quantitatively match the DEM simulations over a range of density ratios (1.11-3.33) and flow rates (19.2-113.6 cm3/s). Matching experiments with various combinations of glass, steel and ceramic particles were also performed which reproduced the segregation patterns obtained in both the simulations and the theory.

  2. An Emotional Agent Model Based on Granular Computing

    Directory of Open Access Journals (Sweden)

    Jun Hu

    2012-01-01

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

  3. Numeric Modeling of Granular Asteroid Growth

    Science.gov (United States)

    Beaumont, Benjamin; Lazzati, D.

    2014-01-01

    It is believed that planetesimals and asteroids are created by the constructive collisions of smaller objects, loosely bound under the effect of self-gravity and/or contact forces. However, the internal dynamics of these collisions and whether they trigger growth or fragmentation are poorly understood. Prior research in the topic has established regimes for the results of constructive collisions of particles under contact forces, but neglects gravity, a critical component once particles are no longer touching, and force chains, an uneven distribution of force inherent to granular materials. We run simulations binary collisions of clusters of particles modeled as hard spheres. Our simulations take into account self-gravity, dissipation of energy, friction, and use a potential function for overlapping particles to study force chains. We present here the collision outcome for clusters with variable masses, particle counts, velocities, and impact parameter. We compare our results to other models and simulations, and find that the collisions remain constructive at higher energies than classically predicted.

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

    Science.gov (United States)

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

    2011-12-01

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

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

    Science.gov (United States)

    Dunatunga, Sachith; Kamrin, Ken

    2017-03-01

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

  6. Modelling the field behaviour of a granular expansive barrier

    Science.gov (United States)

    Alonso, Eduardo; Hoffmann, Christian

    The large scale “Engineered Barrier” (EB) experiment, performed at the Mont Terri Underground Laboratory is described. A coupled hydromechanical model is then used to simulate the test performance. Constitutive parameters for the bentonite granular backfill are based on experimental work described in a companion paper. An elastoplastic model describes the granular fill, while the host rock is simulated by a damage model. Predictions of EDZ development around the tunnel are compared with some indirect measurements. Calculated evolutions of relative humidity and stresses within the buffer are compared with sensor records. Good agreement was found for the bentonite blocks supporting the canister. The granular expansive fill exhibit a more irregular behavior. Calculated displacements of the canister agree in absolute terms with actual measurements.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1996-12-31

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

  8. An experimental study of wave propagation and velocity distributions in a vertically driven time-dependent granular gas

    Science.gov (United States)

    Perez, John Anthony

    Averaged over appropriate space and time scales the dynamics of highly fluidized granular systems are often reminiscent of molecular fluid flows. As a result, theoretical efforts to describe these systems have borrowed heavily from continuum mechanics, particularly hydrodynamics. This has led to various proposed granular hydrodynamic theories which have been used to simulate granular materials in various states of confinement and excitation. These studies suggest that a continuum model for granular gasses can accurately reproduce the mean density, velocity and temperature profiles for an experimental granular gas. This thesis contributes to this body of work by presenting an experimental study of the hydrodynamic fields and velocity distributions within a vertically driven quasi-2D granular gas. We have taken pictures as fast as possible of a time-dependent granular gas using a high-speed CCD camera. We have extracted the positions and velocities of 57-564 particles per frame over 400 GB of raw images collected at 3700 fps. We used this data to compute the density, velocity and temperature fields as functions of time and space to a very high resolution. This approach led to the discovery of novel substructures within the hydrodynamic fields which would have been overlooked had we chosen to average over a drive cycle as earlier studies have done. In particular, the high spatial resolution available from our measurements reveals a serrated substructure in the shock waves which has not been reported before. This substructure is the result of collisional momentum transport . One of the current issues in formulating a granular continuum model is how to incorporate local and non-local dependencies between stress and strain correctly. In this thesis we demonstrate that the collisional transfer of momentum produces a non-local effect in the stress tensor which plays a major role in determining the mean flow. Current models have incorporated only the collisional or

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

    Science.gov (United States)

    Dartevelle, SéBastien

    2004-08-01

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

  10. A nonlinear feedback model for granular and surface charging

    Science.gov (United States)

    Shinbrot, Troy; Kozachkov, Leo; Siu, Theo

    2015-03-01

    Independent laboratories have experimentally demonstrated that identical materials brought into symmetric contact generate contact charges. Even the most basic features of this odd behavior remain to be explained. In this talk, we provide a simple, Ising-like, model that appears to account for many of the observed phenomena. We calculate the electric field acting on surface molecules in a lattice, and we show that if the molecules are polarizable, then infinitesimal random polarizations typically build exponentially rapidly in time. These polarizations self-assemble to produce surface patterns that come in two types, and we find that one of these types accounts for strong localized charging, while the other produces a weaker persistent surface charge pattern. We summarize predictions for both ideal surfaces and for defects in granular beds. This work was supported by NSF Grant DMR-1404792.

  11. Modeling gas formation and mineral precipitation in a granular iron column.

    Science.gov (United States)

    Jeen, Sung-Wook; Amos, Richard T; Blowes, David W

    2012-06-19

    In granular iron permeable reactive barriers (PRBs), hydrogen gas formation, entrapment and release of gas bubbles, and secondary mineral precipitation have been known to affect the permeability and reactivity. The multicomponent reactive transport model MIN3P was enhanced to couple gas formation and release, secondary mineral precipitation, and the effects of these processes on hydraulic properties and iron reactivity. The enhanced model was applied to a granular iron column, which was studied for the treatment of trichloroethene (TCE) in the presence of dissolved CaCO(3). The simulation reasonably reproduced trends in gas formation, secondary mineral precipitation, permeability changes, and reactivity changes observed over time. The simulation showed that the accumulation of secondary minerals reduced the reactivity of the granular iron over time, which in turn decreased the rate of mineral accumulation, and also resulted in a gradual decrease in gas formation over time. This study provides a quantitative assessment of the evolving nature of geochemistry and permeability, resulting from coupled processes of gas formation and mineral precipitation, which leads to a better understanding of the processes controlling the granular iron reactivity, and represents an improved method for incorporating these factors into the design of granular iron PRBs.

  12. Tapped granular column dynamics: simulations, experiments and modeling

    NARCIS (Netherlands)

    Rosato, A.D.; Zuo, L.; Blackmore, D.; Wu, H.; Horntrop, D.J.; Parker, D.J.; Windows-Yule, C.R.

    2015-01-01

    This paper communicates the results of a synergistic investigation that initiates our long term research goal of developing a continuum model capable of predicting a variety of granular flows. We consider an ostensibly simple system consisting of a column of inelastic spheres subjected to discrete t

  13. Editorial: Modelling and computational challenges in granular materials

    NARCIS (Netherlands)

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

    2015-01-01

    This is the editorial for the special issue on “Modelling and computational challenges in granular materials” in the journal on Computational Particle Mechanics (CPM). The issue aims to provide an opportunity for physicists, engineers, applied mathematicians and computational scientists to discuss

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

    Institute of Scientific and Technical Information of China (English)

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

    2012-01-01

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

  15. Formation, characterization and mathematical modeling of the aerobic granular sludge

    Energy Technology Data Exchange (ETDEWEB)

    Ni, Bing-Jie [Queensland Univ., Brisbane, QLD (Australia). Advanced Water Management Centre

    2013-07-01

    Reports on successful aerobic granulation of sludge in pilot-scale reactor for treatment of low-strength municipal wastewater and identifies the key factors responsible for this process. Develops comprehensive models for sludge granulation, microbial interactions and microbial products formation to provide insights into the dynamics of all the soluble and solid components in aerobic granular sludge system. Demonstrates accelerated start-up and optimization of the anaerobic ammonia oxidation process by seeding the reactor with aerobic granules. Aerobic granular sludge technology will play an important role as an innovative technology alternative to the present activated sludge process in industrial and municipal wastewater treatment in the near future. Intended to fill the gaps in the studies of aerobic granular sludge, this thesis comprehensively investigates the formation, characterization and mathematical modeling of aerobic granular sludge, through integrating the process engineering tools and advanced molecular microbiology. The research results of this thesis contributed significantly to the advance of understanding and optimization of the bacterial granulation processes, the next generation of technology for cost-effective biological wastewater treatment.

  16. Discrete particle modeling of granular temperature distribution in a bubbling fluidized bed

    Institute of Scientific and Technical Information of China (English)

    Yurong He; Tianyu Wang; Niels Deen; Martin van Sint Annaland; Hans Kuipers; Dongsheng Wen

    2012-01-01

    The discrete hard sphere particle model (DPM) is applied in this work to study numerically the distributions of particle and bubble granular temperatures in a bubbling fluidized bed.The dimensions of the bed and other parameters are set to correspond to those of Müller et al.(2008).Various drag models and operational parameters are investigated to find their influence on particle and bubble granular temperatures.Various inlet superficial gas velocities are used in this work to obtain their effect on flow characteristics.It is found that the superficial gas velocity has the most important effect on granular temperatures including bubble granular temperature,particle translational granular temperature and particle rotational granular temperature.The drag force model affects more seriously the large scale variables such as the bubble granular temperature.Restitution coefficient influences all granular temperatures to some degree.Simulation results are compared with experimental results by Müller et al.(2008) showing reasonable agreement.

  17. Solitary granular avalanches: stability, fingering and theoretical modeling

    Science.gov (United States)

    Malloggi, Florent; Andreotti, Bruno; Clément, Eric; Aronson, Igor; Tsimring, Lev

    2008-03-01

    Avalanching processes do not only occur in the air as we know of snow avalanches, mud flows and land-slides. Such events frequently happen below the see level as they take many forms from turbidity currents to thick sediment waves. In this study we report results on laboratory scale avalanche experiments taking place both in the air and under-water. In both cases a family of stable solitary erosion/deposition waves is observed [1]. At higher inclination angles, we show the existence of a long wavelength transverse instability followed by a coarsening and the onset of a fingering pattern. While the experiments strongly differ by the spatial and time scales, the agreement between the stability diagrams, the wavelengths selection and the avalanche morphology suggest a common erosion/deposition scenario. We also use these erosion/deposition waves to investigate the dynamics of granular flow and jamming in the frame work of the Partial Fluidization Theory (PFT) proposed by Aronson et al. to describe the dynamics of granular matter near jamming [2]. [1] F. Malloggi et al. Europhysics Letters, 2006, Erosion waves: Transverse instabilities and fingering 75, 825-831 [2] I. S. Aranson et al.. Transverse instability of avalanches in granular flows down an incline. Physical Review E, 2006, 73, 050302; I.S.Aronson et al., Non rheological properties of granular flows: exploring the near jamming limit, preprint (2007).

  18. Hard-sphere limit of soft-sphere model for granular materials: stiffness dependence of steady granular flow.

    Science.gov (United States)

    Mitarai, Namiko; Nakanishi, Hiizu

    2003-02-01

    Dynamical behavior of steady granular flow is investigated numerically in the inelastic hard-sphere limit of the soft-sphere model. We find distinctively different limiting behaviors for the two flow regimes, i.e., the collisional flow and the frictional flow. In the collisional flow, the hard-sphere limit is straightforward; the number of collisions per particle per unit time converges to a finite value and the total contact time fraction with other particles goes to zero. For the frictional flow, however, we demonstrate that the collision rate diverges as the power of the particle stiffness so that the time fraction of the multiple contacts remains finite even in the hard-sphere limit, although the contact time fraction for the binary collisions tends to zero.

  19. Time Granularity Transformation of Time Series Data for Failure Prediction of Overhead Line

    Science.gov (United States)

    Ma, Yan; Zhu, Wenbing; Yao, Jinxia; Gu, Chao; Bai, Demeng; Wang, Kun

    2017-01-01

    In this paper, we give an approach of transforming time series data with different time granularities into the same plane, which is the basis of further association analysis. We focus on the application of overhead line tripping. First all the relative state variables with line tripping are collected into our big data platform. We collect line account, line fault, lightning, power load and meteorological data. Second we respectively pre-process the five kinds of data to guarantee the integrality of data and simplicity of analysis. We use a representation way combining the aggregated representation and trend extraction methods, which considers both short term variation and long term trend of time sequence. Last we use extensive experiments to demonstrate that the proposed time granularity transformation approach not only lets multiple variables analysed on the same plane, but also has a high prediction accuracy and low running time no matter for SVM or logistic regression algorithm.

  20. Smoothed Particle Hydrodynamics modeling of granular column collapse

    CERN Document Server

    Szewc, Kamil

    2016-01-01

    The Smoothed Particle Hydrodynamics (SPH) is a particle-based, Lagrangian method for fluid-flow simulations. In this work, fundamental concepts of this method are first briefly recalled. Then, the ability to accurately model granular materials using an introduced visco-plastic constitutive rheological model is studied. For this purpose sets of numerical calculations (2D and 3D) of the fundamental problem of the collapse of initially vertical cylinders of granular materials are performed. The results of modeling of columns with different aspect ratios and different angles of internal friction are presented. The numerical outcomes are assessed not only with respect to the reference experimental data but also with respect to other numerical methods, namely the Distinct Element Method and the Finite Element Method. In order to improve the numerical efficiency of the method, the Graphics Processing Units implementation is presented and some related issues are discussed. It is believed that this study corresponds t...

  1. A Fractal Model for the Effective Thermal Conductivity of Granular Flow with Non-uniform Particles

    Institute of Scientific and Technical Information of China (English)

    ZHANG Duan-Ming; LEI Ya-Jie; YU Bo-Ming; ZHANG Mei-Jun; HUANG Ming-Tao; LI Zhi-Hua; GUAN Li

    2002-01-01

    The equipartition of energy applied in binary mixture of granular flow is extended to granular flow withnon-uniform particles. Based on the fractal characteristic of granular flow with non-uniform particles as well as energyequipartition, a fractal velocity distribution function and a fractal model of effective thermal conductivity are derived.Thermal conduction resulted from motions of particles in the granular flow, as well as the effect of fractal dimension oneffective thermal conductivity, is discussed.

  2. A depth integrated model for dry geophysical granular flows

    Science.gov (United States)

    Rossi, Giulia; Armanini, Aronne

    2017-04-01

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

  3. Implicit integration of plasticity models for granular materials

    DEFF Research Database (Denmark)

    Ahadi, A.; Krenk, Steen

    2003-01-01

    A stress integration algorithm for granular materials based on fully implicit integration with explicit updating is presented. In the implicit method the solution makes use of the gradient to the potential surface at the final stress state which is unknown. The final stress and hardening parameters...... are determined solving the non-linear equations iteratively so that the stress increment fulfills the consistency condition. The integration algorithm is applicable for models depending on all the three stress invariants and it is applied to a characteristic state model for granular material. Since tensile...... of the integration algorithm are illustrated by simulating both drained and undrained triaxial tests on sand. The algorithm is developed in a standard format which can be implemented in several general purpose finite element codes. It has been implemented as an ABAQUS subroutine, and a traditional geotechnical...

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

    Science.gov (United States)

    Chopin, Julien; Kudrolli, Arshad

    2011-11-11

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

  5. DEM modeling of flexible structures against granular material avalanches

    Science.gov (United States)

    Lambert, Stéphane; Albaba, Adel; Nicot, François; Chareyre, Bruno

    2016-04-01

    This article presents the numerical modeling of flexible structures intended to contain avalanches of granular and coarse material (e.g. rock slide, a debris slide). The numerical model is based on a discrete element method (YADE-Dem). The DEM modeling of both the flowing granular material and the flexible structure are detailed before presenting some results. The flowing material consists of a dry polydisperse granular material accounting for the non-sphericity of real materials. The flexible structure consists in a metallic net hanged on main cables, connected to the ground via anchors, on both sides of the channel, including dissipators. All these components were modeled as flexible beams or wires, with mechanical parameters defined from literature data. The simulation results are presented with the aim of investigating the variability of the structure response depending on different parameters related to the structure (inclination of the fence, with/without brakes, mesh size opening), but also to the channel (inclination). Results are then compared with existing recommendations in similar fields.

  6. Internal deformation within an unstable granular slope: insights from physical modeling

    Science.gov (United States)

    Liu, Z.; Koyi, H.; Nilfouroushan, F.; Swantesson, J.; Reshetyuk, Y.

    2012-04-01

    The collapses of granular materials frequently occur in nature in the form of, for example, rock avalanches, debris avalanches and debris flow. In previous studies of collapses of a granular material, most of the focus has been on the effect of initial geometry and mechanical properties of the granular materials, the run-out distance, and the topography of final deposit. In this study, results of analogue models and scanned natural failed slopes are used to outline the mode of failure of an unstable slope. Model results and field observations are used to argue that a granular mass moves downslope in a wavy pattern resulting in its intensive deformation. In the models, we mainly investigated the internal deformation of collapses of granular slopes in terms of their internal structures and the spatial and temporal distribution of the latter. Model results showed that a displaced mass of the granular slope has the following two features: (1) Initial collapse resulted in a series of normal faults, where hanging-wall blocks were slightly deformed, like the slump-shear structures in nature; (2) With further collapse, a set of secondary structures, such as deformed/folded fault surfaces, faulted folds, displaced inclined folds, and overturned folds formed near the slope surface. The occurrence of these structures reflects the failure process of the granular mass in space and time. In addition, our model results show that the nature of basal friction has a significant influence on the geometry and kinematics of these structures at the slope toe. Model results show also that the mass does not glide downslope along only one surface, but includes several gliding surfaces each of which take part of the sliding. These gliding surfaces become steeper deeper in the sliding mass. Some of these features observed in the models are also detected in the field. Scanned failed slope surfaces show a wavy pattern similar to that in the models, reflecting the presence of normal faults at

  7. A Granular Model of Rolling Grain Ripples

    CERN Document Server

    Andersen, K H

    1999-01-01

    A simple model is presented for the formation of rolling grain ripples on a flat sand bed by the oscillatory flow from a surface wave. The model is related to physical parameters of the problem, and is solved for the equilibrium spacing and height of the ripples. Good agreement between the model and measurements of rolling grain ripples is demonstrated. It is found that the length of the ripples scale with the square-root of the non-dimensional shear stress on a flat bed.

  8. Computer modelling of granular material microfracturing

    CSIR Research Space (South Africa)

    Malan, DF

    1995-08-15

    Full Text Available Microscopic observations indicate that intra- and transgranular fracturing are ubiquitous processes in the damage of rock fabrics. Extensive modelling of intergranular fracturing has been carried out previously using the distinct-element approach...

  9. Tapped granular column dynamics: simulations, experiments and modeling

    Science.gov (United States)

    Rosato, A. D.; Zuo, L.; Blackmore, D.; Wu, H.; Horntrop, D. J.; Parker, D. J.; Windows-Yule, C.

    2016-07-01

    This paper communicates the results of a synergistic investigation that initiates our long term research goal of developing a continuum model capable of predicting a variety of granular flows. We consider an ostensibly simple system consisting of a column of inelastic spheres subjected to discrete taps in the form of half sine wave pulses of amplitude a/ d and period τ . A three-pronged approach is used, consisting of discrete element simulations based on linear loading-unloading contacts, experimental validation, and preliminary comparisons with our continuum model in the form of an integro-partial differential equation.

  10. Modelling density segregation in flowing bidisperse granular materials

    Science.gov (United States)

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

    2016-07-01

    Preventing segregation in flowing granular mixtures is an ongoing challenge for industrial processes that involve the handling of bulk solids. A recent continuum-based modelling approach accurately predicts spatial concentration fields in a variety of flow geometries for mixtures varying in particle size. This approach captures the interplay between advection, diffusion and segregation using kinematic information obtained from experiments and/or discrete element method (DEM) simulations combined with an empirically determined relation for the segregation velocity. Here, we extend the model to include density-driven segregation, thereby validating the approach for the two important cases of practical interest. DEM simulations of density bidisperse flows of mono-sized particles in a quasi-two-dimensional-bounded heap were performed to determine the dependence of the density-driven segregation velocity on local shear rate and particle concentration. The model yields theoretical predictions of segregation patterns that quantitatively match the DEM simulations over a range of density ratios and flow rates. Matching experiments reproduce the segregation patterns and quantitative segregation profiles obtained in both the simulations and the model, thereby demonstrating that the modelling approach captures the essential physics of density-driven segregation in granular heap flow.

  11. Numerical modelling of granular flows: a reality check

    Science.gov (United States)

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

    2016-07-01

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

  12. Compaction of granular HMX: P-α porosity model in CTH hydrocode

    Science.gov (United States)

    Mahon, K. S.; Lee, T.-W.

    2015-12-01

    Compaction waves traveling through porous cyclotetramethylene-tetranitramine (HMX) are computationally modeled using the Eulerian hydrocode CTH and validated with gas gun experimental data. The method employed use of a newly generated set of P-α parameters for granular HMX in a Mie-Gruneisen equation of state. The P-α model adds a separate parameter to differentiate between the volume changes of a solid material due to compression from the volume change due to compaction, void collapse in a granular material. Computational results are compared via five validation schema for two different initial-porosity experiments. These schema include stress measurements, velocity rise times and arrival times, elastic sound speeds though the material and final compaction densities for a series of two different percent Theoretical Maximum Density (TMD) HMX sets of experimental data. There is a good agreement between the simulations and the experimental gas gun data with the largest source of error being an 11% overestimate of the peak stress which may be due to impedance mismatch on the experimental gauge interface. Determination of these P-α parameters are important as they enable modeling of porosity and are a vital first step in modeling of precursory hotspots, caused by hydrodynamic collapse of void regions or grain interactions, prior to deflagration to detonation transition of granular explosives.

  13. Compaction of granular HMX: P-α porosity model in CTH hydrocode

    Directory of Open Access Journals (Sweden)

    K. S. Mahon

    2015-12-01

    Full Text Available Compaction waves traveling through porous cyclotetramethylene-tetranitramine (HMX are computationally modeled using the Eulerian hydrocode CTH and validated with gas gun experimental data. The method employed use of a newly generated set of P-α parameters for granular HMX in a Mie-Gruneisen equation of state. The P-α model adds a separate parameter to differentiate between the volume changes of a solid material due to compression from the volume change due to compaction, void collapse in a granular material. Computational results are compared via five validation schema for two different initial-porosity experiments. These schema include stress measurements, velocity rise times and arrival times, elastic sound speeds though the material and final compaction densities for a series of two different percent Theoretical Maximum Density (TMD HMX sets of experimental data. There is a good agreement between the simulations and the experimental gas gun data with the largest source of error being an 11% overestimate of the peak stress which may be due to impedance mismatch on the experimental gauge interface. Determination of these P-α parameters are important as they enable modeling of porosity and are a vital first step in modeling of precursory hotspots, caused by hydrodynamic collapse of void regions or grain interactions, prior to deflagration to detonation transition of granular explosives.

  14. Three Perspectives of Granular Computing

    Institute of Scientific and Technical Information of China (English)

    Yiyu(Y.Y.) Yao

    2006-01-01

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

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

    CERN Document Server

    Aharonov, Einat; Sparks, David; Toussaint, Renaud

    2013-01-01

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

  16. Quantitative Simulation of Granular Collapse Experiments with Visco-Plastic Models

    Science.gov (United States)

    Mangeney, A.; Ionescu, I. R.; Bouchut, F.; Roche, O.

    2014-12-01

    One of the key issues in landslide modeling is to define the appropriate rheological behavior of these natural granular flows. In particular the description of the static and of the flowing states of granular media is still an open issue. This plays a crucial role in erosion/deposition processes. A first step to address this issue is to derive models able to reproduce laboratory experiments of granular flows. We propose here a mechanical and numerical model of dry granular flows that quantitatively well reproduces granular column collapse over inclined planes, with rheological parameters directly derived from the laboratory experiments. We reformulate the so-called μ(I) rheology proposed by Jop et al. (2006) where I is the so-called inertial number in the framework of Drucker-Prager plasticity with yield stress and a viscosity η(||D||, p) depending on both the pressure p and the norm of the strain rate tensor ||D||. The resulting dynamic viscosity varies from very small values near the free surface and near the front to 1.5 Pa.s within the quasi-static zone. We show that taking into account a constant mean viscosity during the flow (η = 1 Pa.s here) provides results very similar to those obtained with the variable viscosity deduced from the μ(I) rheology, while significantly reducing the computational cost. This has important implication for application to real landslides and rock avalanches. The numerical results show that the flow is essentially located in a surface layer behind the front, while the whole granular material is flowing near the front where basal sliding occurs. The static/flowing interface changes as a function of space and time, in good agreement with experimental observations. Heterogeneities are observed within the flow with low and high pressure zones, localized small upward velocity zones and vortices near the transition between the flowing and static grains. These instabilities create 'sucking zones' and have some characteristics similar

  17. A discrete element model for simulating saturated granular soil

    Institute of Scientific and Technical Information of China (English)

    Mahan Lamei; Ali Asghar Mirghasemi

    2011-01-01

    A numerical model is developed to simulate saturated granular soil,based on the discrete element method.Soil particles are represented by Lagrangian discrete elements,and pore fluid,by appropriate discrete elements which represent alternately Lagrangian mass of water and Eulerian volume of space.Macroscale behavior of the model is verified by simulating undrained biaxial compression tests.Micro-scale behavior is compared to previous literature through pore pressure pattern visualization during shear tests,it is demonstrated that dynamic pore pressure patterns are generated by superposed stress waves.These pore-pressure patterns travel much faster than average drainage rate of the pore fluid and may initiate soil fabric change,ultimately leading to liquefaction in loose sands.Thus,this work demonstrates a tool to roughly link dynamic stress wave patterns to initiation of liquefaction phenomena.

  18. Modelling of Granular Materials Using the Discrete Element Method

    DEFF Research Database (Denmark)

    Ullidtz, Per

    1997-01-01

    With the Discrete Element Method it is possible to model materials that consists of individual particles where a particle may role or slide on other particles. This is interesting because most of the deformation in granular materials is due to rolling or sliding rather that compression...... of the grains. This is true even of the resilient (or reversible) deformations. It is also interesting because the Discrete Element Method models resilient and plastic deformations as well as failure in a single process.The paper describes two types of calculations. One on a small sample of angular elements...... subjected to a pulsating (repeated) biaxial loading and another of a larger sample of circular element subjected to a plate load. Both cases are two dimensional, i.e. plane strain.The repeated biaxial loading showed a large increase in plastic strain for the first load pulse at a given load level...

  19. Timing information and pileup rejection for the High Granularity Calorimeter

    CERN Document Server

    MONET, Geoffrey

    2015-01-01

    The Large Hadron Collider (LHC) at CERN is the world’s largest and most energetic hadron collider. The first run of the LHC (March 2010 - December 2012) has led to several measurements and discoveries, amongst which the Higgs boson candidate. In order to further increase its discovery potential beyond 2020 a leap in luminosity, by a factor of 10, is needed. It is what we call High Luminosity LHC (HL-LHC). Increase the total number of collision would provide more accurate measurements of new particles and enable observation of rare processes that occur below the current sensitivity level. The increase in luminosity will be achieved at the cost of an increase in pileup, i.e. the number of simultaneous collisions. Not only the LHC machine will be upgraded but also the detectors, namely CMS . To cope with this high pileup environment and reconstruct physics objects such as electrons, photons, jets and taus, High Granularity Calorimeter is being proposed as a substitute of the current endcap calorimeters of CMS...

  20. Properties of granular analogue model materials: A community wide survey

    Science.gov (United States)

    Klinkmüller, M.; Schreurs, G.; Rosenau, M.; Kemnitz, H.

    2016-08-01

    We report the material properties of 26 granular analogue materials used in 14 analogue modelling laboratories. We determined physical characteristics such as bulk density, grain size distribution, and grain shape, and performed ring shear tests to determine friction angles and cohesion, and uniaxial compression tests to evaluate the compaction behaviour. Mean grain size of the materials varied between c. 100 and 400 μm. Analysis of grain shape factors shows that the four different classes of granular materials (14 quartz sands, 5 dyed quartz sands, 4 heavy mineral sands and 3 size fractions of glass beads) can be broadly divided into two groups consisting of 12 angular and 14 rounded materials. Grain shape has an influence on friction angles, with most angular materials having higher internal friction angles (between c. 35° and 40°) than rounded materials, whereas well-rounded glass beads have the lowest internal friction angles (between c. 25° and 30°). We interpret this as an effect of intergranular sliding versus rolling. Most angular materials have also higher basal friction angles (tested for a specific foil) than more rounded materials, suggesting that angular grains scratch and wear the foil. Most materials have an internal cohesion in the order of 20-100 Pa except for well-rounded glass beads, which show a trend towards a quasi-cohesionless (C < 20 Pa) Coulomb-type material. The uniaxial confined compression tests reveal that rounded grains generally show less compaction than angular grains. We interpret this to be related to the initial packing density after sifting, which is higher for rounded grains than for angular grains. Ring-shear test data show that angular grains undergo a longer strain-hardening phase than more rounded materials. This might explain why analogue models consisting of angular grains accommodate deformation in a more distributed manner prior to strain localisation than models consisting of rounded grains.

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

    Institute of Scientific and Technical Information of China (English)

    Boon Ho Ng; Yulong Ding; Mojtaba Ghadiri

    2008-01-01

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

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

    Science.gov (United States)

    Zhang, Fengshou; Damjanac, Branko; Huang, Haiying

    2013-06-01

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

  3. MODELING THE ELECTROLYTIC DECHLORINATION OF TRICHLOROETHYLENE IN A GRANULAR GRAPHITE-PACKED REACTOR

    Science.gov (United States)

    A comprehensive reactor model was developed for the electrolytic dechlorination of trichloroethylene (TCE) at a granular-graphite cathode. The reactor model describes the dynamic processes of TCE dechlorination and adsorption, and the formation and dechlorination of all the major...

  4. Experimental study on remodeling strength of granular materials under different loads and lengths of time

    Institute of Scientific and Technical Information of China (English)

    韩流; 周伟; 才庆祥; 舒继森; 靖洪文; 李鑫

    2015-01-01

    Remodeled clay and sand rock specimens were prepared by designing lateral confinement and water drainage experiments based on the stress exerted on granular materials in a waste dump. An in situ test was conducted in an internal waste dump; the physical and mechanical parameters of the remodeled rock mass dumped at different time and depths were measured. Based on statistics, regression analysis was performed with regard to the shearing stress parameters acquired from the two tests. Other factors, such as remodeling pressure (burial depth), remodeling time (amount of time since waste was dumped), and the corresponding functional relationship, were determined. Analysis indicates that the cohesion of the remodeled clay and its remodeling pressure are correlated by a quadratic function but are not correlated with remodeling time length. In situ experimental results indicate that the shear strength of reshaped granular materials in the internal dump is positively correlated with burial depth but poorly correlated with time length. CohesionC and burial depthH follow a quadratic function, specifically for a short time since waste has been dumped. As revealed by both in situ and laboratory experiments, the remodeling strength of granular materials varies in a certain pattern. The consistency of such materials verifies the reliability of the remodeling experimental program.

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

    Energy Technology Data Exchange (ETDEWEB)

    Rycroft, Chris; Orpe, Ashish; Kudrolli, Arshad

    2009-01-15

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

  6. Granularity as a Cognitive Factor in the Effectiveness of Business Process Model Reuse

    Science.gov (United States)

    Holschke, Oliver; Rake, Jannis; Levina, Olga

    Reusing design models is an attractive approach in business process modeling as modeling efficiency and quality of design outcomes may be significantly improved. However, reusing conceptual models is not a cost-free effort, but has to be carefully designed. While factors such as psychological anchoring and task-adequacy in reuse-based modeling tasks have been investigated, information granularity as a cognitive concept has not been at the center of empirical research yet. We hypothesize that business process granularity as a factor in design tasks under reuse has a significant impact on the effectiveness of resulting business process models. We test our hypothesis in a comparative study employing high and low granularities. The reusable processes provided were taken from widely accessible reference models for the telecommunication industry (enhanced Telecom Operations Map). First experimental results show that Recall in tasks involving coarser granularity is lower than in cases of finer granularity. These findings suggest that decision makers in business process management should be considerate with regard to the implementation of reuse mechanisms of different granularities. We realize that due to our small sample size results are not statistically significant, but this preliminary run shows that it is ready for running on a larger scale.

  7. Micromechanics and statistics of slipping events in a granular seismic fault model

    Energy Technology Data Exchange (ETDEWEB)

    Arcangelis, L de [Department of Information Engineering and CNISM, Second University of Naples, Aversa (Italy); Ciamarra, M Pica [CNR-SPIN, Dipartimento di Scienze Fisiche, Universita di Napoli Federico II (Italy); Lippiello, E; Godano, C, E-mail: dearcangelis@na.infn.it [Department of Environmental Sciences and CNISM, Second University of Naples, Caserta (Italy)

    2011-09-15

    The stick-slip is investigated in a seismic fault model made of a confined granular system under shear stress via three dimensional Molecular Dynamics simulations. We study the statistics of slipping events and, in particular, the dependence of the distribution on model parameters. The distribution consistently exhibits two regimes: an initial power law and a bump at large slips. The initial power law decay is in agreement with the the Gutenberg-Richter law characterizing real seismic occurrence. The exponent of the initial regime is quite independent of model parameters and its value is in agreement with experimental results. Conversely, the position of the bump is solely controlled by the ratio of the drive elastic constant and the system size. Large slips also become less probable in absence of fault gouge and tend to disappear for stiff drives. A two-time force-force correlation function, and a susceptibility related to the system response to pressure changes, characterize the micromechanics of slipping events. The correlation function unveils the micromechanical changes occurring both during microslips and slips. The mechanical susceptibility encodes the magnitude of the incoming microslip. Numerical results for the cellular-automaton version of the spring block model confirm the parameter dependence observed for size distribution in the granular model.

  8. Microscopic Description of the Granular Fluidity Field in Nonlocal Flow Modeling

    Science.gov (United States)

    Zhang, Qiong; Kamrin, Ken

    2017-02-01

    A recent granular rheology based on an implicit "granular fluidity" field has been shown to quantitatively predict many nonlocal phenomena. However, the physical nature of the field has not been identified. Here, the granular fluidity is found to be a kinematic variable given by the velocity fluctuation and packing fraction. This is verified with many discrete element simulations, which show that the operational fluidity definition, solutions of the fluidity model, and the proposed microscopic formula all agree. Kinetic theoretical and Eyring-like explanations shed insight into the obtained form.

  9. Microscopic Description of the Granular Fluidity Field in Nonlocal Flow Modeling.

    Science.gov (United States)

    Zhang, Qiong; Kamrin, Ken

    2017-02-03

    A recent granular rheology based on an implicit "granular fluidity" field has been shown to quantitatively predict many nonlocal phenomena. However, the physical nature of the field has not been identified. Here, the granular fluidity is found to be a kinematic variable given by the velocity fluctuation and packing fraction. This is verified with many discrete element simulations, which show that the operational fluidity definition, solutions of the fluidity model, and the proposed microscopic formula all agree. Kinetic theoretical and Eyring-like explanations shed insight into the obtained form.

  10. Pion Transverse Momentum Spectrum, Elliptic Flow, and Interferometry in the Granular Source Model for RHIC and LHC Heavy Ion Collisions

    Directory of Open Access Journals (Sweden)

    Jing Yang

    2015-01-01

    Full Text Available We systematically investigate the pion transverse momentum spectrum, elliptic flow, and Hanbury-Brown-Twiss (HBT interferometry in the granular source model for the heavy ion collisions of Au-Au at sNN=200 GeV and Pb-Pb at sNN=2.76 TeV with different centralities. The granular source model can well reproduce the experimental results of the heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC and the Large Hadron Collider (LHC. We examine the parameters involved in the granular source model. The experimental data of the momentum spectrum, elliptic flow, and HBT radii for the two collision energies and different centralities impose very strict constraints on the model parameters. They exhibit certain regularities for collision centrality and energy. The space-time structure and expansion velocities of the granular sources for the heavy ion collisions at the RHIC and LHC energies with different centralities are investigated.

  11. Modeling liquefaction of water saturated granular material under undrained cyclic shearing

    Institute of Scientific and Technical Information of China (English)

    Juhua Zhang

    2005-01-01

    The tendency of particles in a water-saturated granular mass to re-arrange into a denser state during cyclic shearing under pressure results in an increase in pore water pressure. The increase in the pore water pressure causes a reduction in the inner particle contact forces, and in turn easier re-arrangement of the particles. Eventually, the material loses its shear strength, partially or almost completely. In this paper, a general three-dimensional continuum mechanics model is presented for the deformation of granular materials.A physically based model is also presented for characterization of liquefaction of the water saturated granular material under undrained cyclic shearing. The model incorporates the fabric of the granular mass, which develops as the frictional granular mass is deformed in shear. It includes the coupling between shearing and excess pore water pressure. The model parameters are estimated, based on the results of cyclic shearing experiments on large hollow cylindrical samples of silica sand. Basically, the calculation results utilizing this model can embody liquefaction phenomena of the water saturated granular material under undrained cyclic shearing.

  12. A hybrid model for the computationally-efficient simulation of the cerebellar granular layer

    Directory of Open Access Journals (Sweden)

    Anna eCattani

    2016-04-01

    Full Text Available The aim of the present paper is to efficiently describe the membrane potential dynamics of neural populations formed by species having a high density difference in specific brain areas. We propose a hybrid model whose main ingredients are a conductance-based model (ODE system and its continuous counterpart (PDE system obtained through a limit process in which the number of neurons confined in a bounded region of the brain tissue is sent to infinity. Specifically, in the discrete model, each cell is described by a set of time-dependent variables, whereas in the continuum model, cells are grouped into populations that are described by a set of continuous variables.Communications between populations, which translate into interactions among the discrete and the continuous models, are the essence of the hybrid model we present here. The cerebellum and cerebellum-like structures show in their granular layer a large difference in the relative density of neuronal species making them a natural testing ground for our hybrid model. By reconstructing the ensemble activity of the cerebellar granular layer network and by comparing our results to a more realistic computational network, we demonstrate that our description of the network activity, even though it is not biophysically detailed, is still capable of reproducing salient features of neural network dynamics. Our modeling approach yields a significant computational cost reduction by increasing the simulation speed at least $270$ times. The hybrid model reproduces interesting dynamics such as local microcircuit synchronization, traveling waves, center-surround and time-windowing.

  13. Modelling of a viscoplastic granular column collapse and comparison with experiments

    Science.gov (United States)

    Martin, Nathan; Ionescu, Ioan; Mangeney, Anne; Bouchut, François; Roche, Olivier; Farin, Maxime

    2015-04-01

    Landslides and, more generally, large scale granular flows, represent a wide variety of geophysical flows also including mud or debris flow and snow avalanches. In a continuum mechanics context, the accurate simulation of these flows strongly depends on the modelling of their rheology and their boundary conditions, namely the sliding law and processes of erosion. In particular the description of the static and of the flowing states of granular media is still an open issue. We focus here on the quantitative reproduction of laboratory experiments using a mechanical and numerical model of dry granular flows with the so-called μ(I) rheology associated to a Drucker-Prager plasticity criterion and a shear rate and pressure dependent viscosity η(||D||,p). A Coulomb type friction law is considered at the base of the flow. The modelling is achieved in a finite-element context using the software FreeFem++. The simulations are bidimensionnal and well reproduce quantitatively both the dynamical and final shapes of the deposit. The effects of the sidewalls of the experimental channel, neglected in 2D simulations, are investigated by introducing an extra term in the equations varying with the inverse of the width of the channel, providing an enhanced agreement with the experiments. The numerical results show that the flow is essentially located in a surface layer behind the front, while the whole granular material is flowing near the front where basal sliding occurs. The static/flowing interface changes as a function of space and time, in good agreement with experimental observations. The resulting dynamic viscosity varies from very small values near the free surface and near the front to 1.5Pa.s within the quasi-static zone. The results show a rather small yet computationnaly expensive difference between a constant viscosity model and a μ(I) rheology in the case of a rigid bed. This has important implication for application to real geophysical flows. The role of an erodible

  14. Two-dimension tissue growth model based on circular granular cells for cells with small overlap

    CERN Document Server

    Viridi, Sparisoma; Aprianti, Devi; Haris, Luman; Haryanto, Freddy

    2014-01-01

    Tissue growth can be modeled in two dimension by only using circular granular cells, which can grow and produce child. Linear spring-dashpot model is used to bind the cells with a cut-off interaction range of 1.1 times sum of radii of interacted cells. Simulation steps must be divided into explicit and implicit ones due to cell growing stage and cell position rearrangement. This division is aimed to avoid simulation problem. Only in the explicit steps time changes is performed. Large cells overlap is chosen as termination condition of tissue growth. Only some cells configuration can growth to infinite time without encountering the large cells overlap. These configurations, and the other also, are presented in this work.

  15. A High-Granularity Timing Detector (HGTD) in ATLAS: Performance at the HL-LHC

    CERN Document Server

    Makovec, Nikola; The ATLAS collaboration

    2017-01-01

    The expected increase of the particle flux at the high luminosity phase of the LHC (HL-LHC) with instantaneous luminosities up to L ≃ 7.5 × 1034 cm−2 s−1 will have a severe impact on the ATLAS deetctor performance. The pile-up is expected to increase on average to 200 interactions per bunch crossing resulting in a vertex density that can be larger than 1.5 per mm. The reconstruction and performance for electrons, photons, jets and transverse missing energy will be severely degraded in the end-cap and forward region, where the liquid Argon based electromagnetic calorimeter has coarser granularity compared to the central region. The High Granularity Timing Detector (HGTD) is proposed in front of the liquid Argon end-cap calorimeters for pile-up mitigation. Using the high granularity and the excellent timing capabilities of the detector with 30 ps per MIP, electron and jet reconstruction (b tagging) are presented as well as the impact on the pileup jet suppression and missing ET. The expected improvement ...

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

    Science.gov (United States)

    Drasdo, Dirk; Hoehme, Stefan

    2012-05-01

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

  17. Mechanical behaviour of granular materials used in analogue modelling: insights from grain characterisation, ring-shear tests and analogue experiments

    Science.gov (United States)

    Panien, Marion; Schreurs, Guido; Pfiffner, Adrian

    2006-09-01

    The mechanical behaviour of several dry granular materials is investigated through ring-shear tests, grain characterisation, and simple analogue experiments analysed by X-ray computed tomography. An improved knowledge of granular materials is essential to determine their suitability as analogues for upper crustal rocks in experimental models and to compare analogue and numerical experiments. The ring-shear tests show that the granular materials have an elastic/frictional plastic behaviour with strain-hardening preceding failure at peak strength, followed by strain softening until a dynamic-stable value is reached. This is similar to the behaviour exhibited by experimentally deformed rocks. The physical characteristics of the grains determine the amount of diffuse deformation before failure, the percentage of strain softening and act on the thickness of the shear zones before broadening. Initial shear zone width in extensional and contractional experiments is between 11 and 16 times the mean grain size. The angle of internal friction defining one of the mechanical properties of granular materials and thus fault dip is not only related to physical characteristics of the grains and to the handling technique used (e.g. sieving or pouring), but also to the overburden and to the experimental setup used.

  18. Stimulus-dependent state transition between synchronized oscillation and randomly repetitive burst in a model cerebellar granular layer.

    Directory of Open Access Journals (Sweden)

    Takeru Honda

    2011-07-01

    Full Text Available Information processing of the cerebellar granular layer composed of granule and Golgi cells is regarded as an important first step toward the cerebellar computation. Our previous theoretical studies have shown that granule cells can exhibit random alternation between burst and silent modes, which provides a basis of population representation of the passage-of-time (POT from the onset of external input stimuli. On the other hand, another computational study has reported that granule cells can exhibit synchronized oscillation of activity, as consistent with observed oscillation in local field potential recorded from the granular layer while animals keep still. Here we have a question of whether an identical network model can explain these distinct dynamics. In the present study, we carried out computer simulations based on a spiking network model of the granular layer varying two parameters: the strength of a current injected to granule cells and the concentration of Mg²⁺ which controls the conductance of NMDA channels assumed on the Golgi cell dendrites. The simulations showed that cells in the granular layer can switch activity states between synchronized oscillation and random burst-silent alternation depending on the two parameters. For higher Mg²⁺ concentration and a weaker injected current, granule and Golgi cells elicited spikes synchronously (synchronized oscillation state. In contrast, for lower Mg²⁺ concentration and a stronger injected current, those cells showed the random burst-silent alternation (POT-representing state. It is suggested that NMDA channels on the Golgi cell dendrites play an important role for determining how the granular layer works in response to external input.

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

    Science.gov (United States)

    Jenkins, James T.; Berzi, Diego

    2016-11-01

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

  20. New advance on non-hydrostatic shallow granular flow model in a global Cartesian coordinate system

    CERN Document Server

    Yuan, L; Zhai, J; Wu, S F; Patra, A K; Pitman, E B

    2016-01-01

    Mathematical modeling of granular avalanche flows over a general topography needs appropriate forms of shallow granular flow models. Current shallow granular flow models suited to arbitrary topography can be grossly divided into two types, those formulated in bed-fitted curvilinear coordinates (e.g., Ref.~\\cite{{Puda2003}}), and those formulated in global Cartesian coordinates (e.g., Refs.~\\cite{{Bouchut2004},{Denlinger2004},{Castro2014}}). In the recent years, several improvements have been made in global Cartesian formulations for shallow granular flows. In this paper, we first perform a review of the Cartesian model of Denlinger and Iverson \\cite{Denlinger2004} and the Cartesian Boussinesq-type granular flow theory of Castr-Ogaz \\emph{et al.} \\cite{Castro2014}. Both formulations account for the effect of nonzero vertical acceleration on depth-averaged momentum fluxes and stress states. We then further calculate the vertical normal stress of Castr-Ogaz \\emph{et al.}~\\cite{Castro2014} and the basal normal st...

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

    NARCIS (Netherlands)

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

    2006-01-01

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

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

    Science.gov (United States)

    1991-05-22

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

  3. Physically-based modelling of granular flows with Open Source GIS

    Directory of Open Access Journals (Sweden)

    M. Mergili

    2012-01-01

    Full Text Available Computer models, in combination with Geographic Information Sciences (GIS, play an important role in up-to-date studies of travel distance, impact area, velocity or energy of granular flows (e.g. snow or rock avalanches, flows of debris or mud. Simple empirical-statistical relationships or mass point models are frequently applied in GIS-based modelling environments. However, they are only appropriate for rough overviews at the regional scale. In detail, granular flows are highly complex processes and physically-based, distributed models are required for detailed studies of travel distance, velocity, and energy of such phenomena. One of the most advanced theories for understanding and modelling granular flows is the Savage-Hutter type model, a system of differential equations based on the conservation of mass and momentum. The equations have been solved for a number of idealized topographies, but only few attempts to find a solution for arbitrary topography or to integrate the model with GIS are known up to now. The work presented is understood as an initiative to integrate a fully physically-based model for the motion of granular flows, based on the extended Savage-Hutter theory, with GRASS, an Open Source GIS software package. The potentials of the model are highlighted, employing the Val Pola Rock Avalanche (Northern Italy, 1987 as the test event, and the limitations as well as the most urging needs for further research are discussed.

  4. Physically-based modelling of granular flows with Open Source GIS

    Science.gov (United States)

    Mergili, M.; Schratz, K.; Ostermann, A.; Fellin, W.

    2012-01-01

    Computer models, in combination with Geographic Information Sciences (GIS), play an important role in up-to-date studies of travel distance, impact area, velocity or energy of granular flows (e.g. snow or rock avalanches, flows of debris or mud). Simple empirical-statistical relationships or mass point models are frequently applied in GIS-based modelling environments. However, they are only appropriate for rough overviews at the regional scale. In detail, granular flows are highly complex processes and physically-based, distributed models are required for detailed studies of travel distance, velocity, and energy of such phenomena. One of the most advanced theories for understanding and modelling granular flows is the Savage-Hutter type model, a system of differential equations based on the conservation of mass and momentum. The equations have been solved for a number of idealized topographies, but only few attempts to find a solution for arbitrary topography or to integrate the model with GIS are known up to now. The work presented is understood as an initiative to integrate a fully physically-based model for the motion of granular flows, based on the extended Savage-Hutter theory, with GRASS, an Open Source GIS software package. The potentials of the model are highlighted, employing the Val Pola Rock Avalanche (Northern Italy, 1987) as the test event, and the limitations as well as the most urging needs for further research are discussed.

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

    CERN Document Server

    Folli, Viola; 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.

  6. A visco-elasto-plastic model for granular materials under simple shear conditions

    NARCIS (Netherlands)

    Redaelli, I.; di Prisco, C.; Vescovi, Dalila

    2016-01-01

    The numerical simulation of rapid landslides is quite complex mainly because constitutive models capable of simulating the mechanical behaviour of granular materials in the pre-collapse and post-collapse regimes are still missing. The goal of this paper is to introduce a constitutive model capable

  7. A visco-elasto-plastic model for granular materials under simple shear conditions

    NARCIS (Netherlands)

    Redaelli, I.; Prisco, di C.; Vescovi, D.

    2016-01-01

    The numerical simulation of rapid landslides is quite complex mainly because constitutive models capable of simulating the mechanical behaviour of granular materials in the pre-collapse and post-collapse regimes are still missing. The goal of this paper is to introduce a constitutive model capable o

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

    Science.gov (United States)

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

    2012-01-01

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

  9. Lattice Discrete Particle Model (LDPM) for pressure-dependent inelasticity in granular rocks

    CERN Document Server

    Ashari, Shiva Esna; Cusatis, Gianluca

    2016-01-01

    This paper deals with the formulation, calibration, and validation of a Lattice Discrete Particle Model (LDPM) for the simulation of the pressure-dependent inelastic response of granular rocks. LDPM is formulated in the framework of discrete mechanics and it simulates the heterogeneous deformation of cemented granular systems by means of discrete compatibility/equilibrium equations defined at the grain scale. A numerical strategy is proposed to generate a realistic microstructure based on the actual grain size distribution of a sandstone and the capabilities of the method are illustrated with reference to the particular case of Bleurswiller sandstone, i.e. a granular rock that has been extensively studied at the laboratory scale. LDPM micromechanical parameters are calibrated based on evidences from triaxial experiments, such as hydrostatic compression, brittle failure at low confinement and plastic behavior at high confinement. Results show that LDPM allows exploring the effect of fine-scale heterogeneity on...

  10. Multi-granularity immunization strategy based on SIRS model in scale-free network

    Science.gov (United States)

    Nian, Fuzhong; Wang, Ke

    2015-04-01

    In this paper, a new immunization strategy was established to prevent the epidemic spreading based on the principle of "Multi-granularity" and "Pre-warning Mechanism", which send different pre-warning signal with the risk rank of the susceptible node to be infected. The pre-warning means there is a higher risk that the susceptible node is more likely to be infected. The multi-granularity means the susceptible node is linked with multi-infected nodes. In our model, the effect of the different situation of the multi-granularity immunizations is compared and different spreading rates are adopted to describe the epidemic behavior of nodes. In addition the threshold value of epidemic outbreak is investigated, which makes the result more convincing. The theoretical analysis and the simulations indicate that the proposed immunization strategy is effective and it is also economic and feasible.

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

    Science.gov (United States)

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

    2010-11-01

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

  12. Characterization, Modeling and Application of Aerobic Granular Sludge for Wastewater Treatment

    Science.gov (United States)

    Liu, Xian-Wei; Yu, Han-Qing; Ni, Bing-Jie; Sheng, Guo-Ping

    Recently extensive studies have been carried out to cultivate aerobic granular sludge worldwide, including in China. Aerobic granules, compared with conventional activated sludge flocs, are well known for their regular, dense, and strong microbial structure, good settling ability, high biomass retention, and great ability to withstand shock loadings. Studies have shown that the aerobic granules could be applied for the treatment of low- or high-strength wastewaters, simultaneous removal of organic carbon, nitrogen and phosphorus, and decomposition of toxic wastewaters. Thus, this new form of activate sludge, like anaerobic granular sludge, could be employed for the treatment of municipal and industrial wastewaters in near future. This chapter attempts to provide an up-to-date review on the definition, cultivation, characterization, modeling and application of aerobic granular sludge for biological wastewater treatment. This review outlines some important discoveries with regard to the factors affecting the formation of aerobic granular sludge, their physicochemical characteristics, as well as their microbial structure and diversity. It also summarizes the modeling of aerobic granule formation. Finally, this chapter highlights the applications of aerobic granulation technology in the biological wastewater treatment. It is concluded that the knowledge regarding aerobic granular sludge is far from complete. Although previous studies in this field have undoubtedly improved our understanding on aerobic granular sludge, it is clear that much remains to be learned about the process and that many unanswered questions still remain. One of the challenges appears to be the integration of the existing and growing scientific knowledge base with the observations and applications in practice, which this paper hopes to partially achieve.

  13. Constitutive Modelling for Granular Material under Finite Strains with Particle Slidings and Fabric Changes

    Science.gov (United States)

    1992-02-04

    Eartquake Engineering, Chang, C.S., Chang, Y. and Kabir, M.G. (1991b), "Micromechanics Modelling for the Stress-Strain-Strength Behavior of Granular Materials...Principal Stress on the Strength of Sand," Proceedings of the Seventh International Conference on Soil Mechanics and Foundation Engineering, Mexico

  14. Pile-up Rejection in the High Granularity Time Detector for the High Luminosity LHC

    CERN Document Server

    McNulty, Paul

    2016-01-01

    The High Granularity Timing Detector, a proposed upgrade to the Liquid Argon Calorimeter during the transition to the High Luminosity LHC, will provide increased resolution in the time domain and offer an avenue for efficiently mitigating the expected increase in pile-up jets. This study analyzes how effectively current algorithms are using a signal jet peak calculation to disentangle desired information from other events. Two samples, one with only hard-scattering events and another that also included pile-up events, were used. A transverse momentum range of 30GeV to 70GeV and pseudo-rapidity range of 2.4 to 4.8 divided the sample to see how the HGTD performed when calculating the signal peak for each jet and how many cells had detections in and out of that peak for each sample.

  15. Modelling of a recirculating granular medium filter's processes.

    Science.gov (United States)

    Boutin, C; Parouty, R; Ménoret, C; Liénard, A; Brissaud, F

    2002-01-01

    The effluents of French small farm factories will soon be submitted to regulation. Only a few treatment techniques are available to deal with these kind of effluent (high concentration and small daily volumes). To allow the treatment, in the particular economic context of small food processing industries, Cemagref is trying to adapt a treatment based on attached growth cultures on fine media, a system known to be easy to operate and relatively inexpensive. A model, based on four sub-models (hydrodynamic characteristics, oxygen transport, solute transport in the mobile and immobile phases and bacterial evolution) describes this process. Based on wastewater concentration, hydraulic load, applied organic loads, feeding/rest cycles and recycling phases number, this model predicts: eliminated organic loads and the discharge concentration as a function of time, oxygen and biomass contents as a function of time and depth. The determination of the model's parameters is based on a comparison between simulations and performances achieved on experimental columns. This model would be helpful in sizing full-scale filters treating different types of agro-food wastewater. The aim of this article is to present the model's structure, to give all parameter values and to compare the simulations with the results obtained on pilot and full scale plants.

  16. Euler-Euler granular flow model of liquid fuels combustion in a fluidized reactor

    Directory of Open Access Journals (Sweden)

    Nemoda Stevan

    2015-01-01

    Full Text Available The paper deals with the numerical simulation of liquid fuel combustion in a fluidized reactor using a two-fluid Eulerian-Eulerian fluidized bed modeling incorporating the kinetic theory of granular flow (KTGF to gas and solid phase flow prediction. The comprehensive model of the complex processes in fluidized combustion chamber incorporates, besides gas and particular phase velocity fields’ prediction, also the energy equations for gas and solid phase and the transport equations of chemical species conservation with the source terms due to the conversion of chemical components. Numerical experiments show that the coefficients in the model of inter-phase interaction drag force have a significant effect, and they have to be adjusted for each regime of fluidization. A series of numerical experiments was performed with combustion of the liquid fuels in fluidized bed (FB, with and without significant water content. The given estimations are related to the unsteady state, and the modeled time period corresponds to flow passing time throw reactor column. The numerical experiments were conducted to examine the impact of the water content in a liquid fuel on global FB combustion kinetics.

  17. Adsorption of selected pharmaceuticals and an endocrine disrupting compound by granular activated carbon. 2. Model prediction

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Z.; Peldszus, S.; Huck, P.M. [University of Waterloo, Waterloo, ON (Canada). NSERC Chair in Water Treatment

    2009-03-01

    The adsorption of two representative pharmaceutically active compounds (PhACs) naproxen and carbamazepine and one endocrine disrupting compound (EDC) nonylphenol was studied in pilot-scale granular activated carbon (GAC) adsorbers using post-sedimentation (PS) water from a full-scale drinking water treatment plant. The GAC adsorbents were coal-based Calgon Filtrasorb 400 and coconut shell-based PICA CTIF TE. Acidic naproxen broke through fastest while nonylphenol was removed best, which was consistent with the degree to which fouling affected compound removals. Model predictions and experimental data were generally in good agreement for all three compounds, which demonstrated the effectiveness and robustness of the pore and surface diffusion model (PSDM) used in combination with the time-variable parameter approach for predicting removals at environmentally relevant concentrations (i.e., ng/L range). Sensitivity analyses suggested that accurate determination of film diffusion coefficients was critical for predicting breakthrough for naproxen and carbamazepine, in particular when high removals are targeted. Model simulations demonstrated that GAC carbon usage rates (CURs) for naproxen were substantially influenced by the empty bed contact time (EBCT) at the investigated conditions. Model-based comparisons between GAC CURs and minimum CURs for powdered activated carbon (PAC) applications suggested that PAC would be most appropriate for achieving 90% removal of naproxen, whereas GAC would be more suitable for nonylphenol. 25 refs., 4 figs., 1 tab.

  18. Multiscale modeling of rapid granular flow with a hybrid discrete-continuum method

    CERN Document Server

    Chen, Xizhong; Li, Jinghai

    2015-01-01

    Both discrete and continuum models have been widely used to study rapid granular flow, discrete model is accurate but computationally expensive, whereas continuum model is computationally efficient but its accuracy is doubtful in many situations. Here we propose a hybrid discrete-continuum method to profit from the merits but discard the drawbacks of both discrete and continuum models. Continuum model is used in the regions where it is valid and discrete model is used in the regions where continuum description fails, they are coupled via dynamical exchange of parameters in the overlap regions. Simulation of granular channel flow demonstrates that the proposed hybrid discrete-continuum method is nearly as accurate as discrete model, with much less computational cost.

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

    Science.gov (United States)

    Guo, Ning; Zhao, Jidong

    2013-06-01

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

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

    Science.gov (United States)

    Fang, Chung

    2016-07-01

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

  1. Micro-macro transition and simplified contact models for wet granular materials

    Science.gov (United States)

    Roy, Sudeshna; Singh, Abhinendra; Luding, Stefan; Weinhart, Thomas

    2016-11-01

    Wet granular materials in a quasistatic steady-state shear flow have been studied with discrete particle simulations. Macroscopic quantities, consistent with the conservation laws of continuum theory, are obtained by time averaging and spatial coarse graining. Initial studies involve understanding the effect of liquid content and liquid properties like the surface tension on the macroscopic quantities. Two parameters of the liquid bridge contact model have been identified as the constitutive parameters that influence the macroscopic rheology (i) the rupture distance of the liquid bridge model, which is proportional to the liquid content, and (ii) the maximum adhesive force, as controlled by the surface tension of the liquid. Subsequently, a correlation is developed between these microparameters and the steady-state cohesion in the limit of zero confining pressure. Furthermore, as second result, the macroscopic torque measured at the walls, which is an experimentally accessible parameter, is predicted from our simulation results with the same dependence on the microparameters. Finally, the steady- state cohesion of a realistic non-linear liquid bridge contact model scales well with the steady-state cohesion for a simpler linearized irreversible contact model with the same maximum adhesive force and equal energy dissipated per contact.

  2. Modeling size segregation of granular materials: the roles of segregation, advection and diffusion

    CERN Document Server

    Fan, Yi; Umbanhowar, Paul B; Ottino, Julio M; Lueptow, Richard M

    2014-01-01

    Predicting segregation of granular materials composed of different-sized particles is a challenging problem. In this paper, we develop and implement a theoretical model that captures the interplay between advection, segregation, and diffusion in size bidisperse granular materials. The fluxes associated with these three driving factors depend on the underlying kinematics, whose characteristics play key roles in determining particle segregation configurations. Unlike previous models for segregation, our model uses parameters based on kinematic measures from discrete element method simulations instead of arbitrarily adjustable fitting parameters, and it achieves excellent quantitative agreement with both experimental and simulation results when applied to quasi-two-dimensional bounded heaps. The model yields two dimensionless control parameters, both of which are only functions of physically control parameters (feed rate, particle sizes, and system size) and kinematic parameters (diffusion coefficient, flowing l...

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

    Science.gov (United States)

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

    2015-03-01

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

  4. Quantitative test of the time dependent Gintzburg-Landau equation for sheared granular flow in two dimensions

    NARCIS (Netherlands)

    Saitoh, K.; Hayakawa, Hisao

    2013-01-01

    We examine the validity of the time-dependent Ginzburg-Landau equation of granular fluids for a plane shear flow under the Lees-Edwardsboundary condition derivedfrom a weakly nonlinear analysis through the comparison with the result of discrete element method.We verify quantitative agreements in the

  5. Modeling the Collisional-Plastic Stress Transition for Bin Discharge of Granular Material

    Science.gov (United States)

    Pannala, Sreekanth; Daw, C. Stuart; Finney, Charles E. A.; Benyahia, Sofiane; Syamlal, Madhava; O'Brien, Thomas J.

    2009-06-01

    We propose a heuristic model for the transition between collisional and frictional/plastic stresses in the flow of granular material. Our approach is based on a physically motivated, nonlinear `blending' function that produces a weighted average of the limiting stresses, depending on the local void fraction in the flow field. Previously published stress models are utilized to describe the behavior in the collisional (Lun et al., 1984) and quasi-static limits (Schaeffer, 1987 and Syamlal et al.., 1993). Sigmoidal and hyperbolic tangent functions are used to mimic the observed smooth yet rapid transition between the collisional and plastic stress zones. We implement our stress transition model in an open-source multiphase flow solver, MFIX (Multiphase Flow with Interphase eXchanges, www.mfix.org) and demonstrate its application to a standard bin discharge problem. The model's effectiveness is illustrated by comparing computational predictions to the experimentally derived Beverloo correlation. With the correct choice of function parameters, the model predicts bin discharge rates within the error margins of the Beverloo correlation and is more accurate than one of the alternative granular stress models proposed in the literature. Although a second granular stress model in the literature is also reasonably consistent with the Beverloo correlation, we propose that our alternative blending function is likely to be more adaptable to situations with more complex solids properties (e.g., `sticky' solids).

  6. Modeling the Collisional-Plastic Stress Transition for Bin Discharge of Granular Material

    Energy Technology Data Exchange (ETDEWEB)

    Pannala, Sreekanth [ORNL; Daw, C Stuart [ORNL; FINNEY, Charles E A [ORNL; Benyahia, S. [National Energy Technology Laboratory (NETL); Syamlal, M. [National Energy Technology Laboratory (NETL); O' Brien, T. J. [National Energy Technology Laboratory (NETL)

    2009-01-01

    We propose a heuristic model for the transition between collisional and frictional/plastic stresses in the flow of granular material. Our approach is based on a physically motivated, nonlinear blending function that produces a weighted average of the limiting stresses, depending on the local void fraction in the flow field. Previously published stress models are utilized to describe the behavior in the collisional (Lun et al., 1984) and quasi-static limits (Schaeffer, 1987 and Syamlal et al., 1993). Sigmoidal and hyperbolic tangent functions are used to mimic the observed smooth yet rapid transition between the collisional and plastic stress zones. We implement our stress transition model in an opensource multiphase flow solver, MFIX (Multiphase Flow with Interphase eXchanges, www.mfix.org) and demonstrate its application to a standard bin discharge problem. The model s effectiveness is illustrated by comparing computational predictions to the experimentally derived Beverloo correlation. With the correct choice of function parameters, the model predicts bin discharge rates within the error margins of the Beverloo correlation and is more accurate than one of the alternative granular stress models proposed in the literature. Although a second granular stress model in the literature is also reasonably consistent with the Beverloo correlation, we propose that our alternative blending function is likely to be more adaptable to situations with more complex solids properties (e.g., sticky solids).

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

    Science.gov (United States)

    2007-04-30

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

  8. A two-dimensional model for the dynamics of granular avalanches

    OpenAIRE

    2005-01-01

    Zoning of avalanche risk areas is one important task of land-use planning in alpine areas. The lack of records, due to the low frequency of these events, makes it dicult to implement a statistical analysis. Simulations made with physical and mathematical models can improve the knowledge of the dynamics of these events. In this thesis three didifferent mathematical and numerical models, based on the rheological theory of Savage and Hutter for granular flows, are introduced. A one dimensi...

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

    Science.gov (United States)

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

    2016-04-01

    Describing grain/fluid interaction in debris flows models is still an open and challenging issue with key impact on hazard assessment [{Iverson et al.}, 2010]. We present here a two-phase two-thin-layer model for fluidized debris flows that takes into account dilatancy effects. It describes the velocity of both the solid and the fluid phases, the compression/dilatation of the granular media and its interaction with the pore fluid pressure [{Bouchut et al.}, 2016]. The model is derived from a 3D two-phase model proposed by {Jackson} [2000] based on the 4 equations of mass and momentum conservation within the two phases. This system has 5 unknowns: the solid and fluid velocities, the solid and fluid pressures and the solid volume fraction. As a result, an additional equation inside the mixture is necessary to close the system. Surprisingly, this issue is inadequately accounted for in the models that have been developed on the basis of Jackson's work [{Bouchut et al.}, 2015]. In particular, {Pitman and Le} [2005] replaced this closure simply by imposing an extra boundary condition at the surface of the flow. When making a shallow expansion, this condition can be considered as a closure condition. However, the corresponding model cannot account for a dissipative energy balance. We propose here an approach to correctly deal with the thermodynamics of Jackson's model by closing the mixture equations by a weak compressibility relation following {Roux and Radjai} [1998]. This relation implies that the occurrence of dilation or contraction of the granular material in the model depends on whether the solid volume fraction is respectively higher or lower than a critical value. When dilation occurs, the fluid is sucked into the granular material, the pore pressure decreases and the friction force on the granular phase increases. On the contrary, in the case of contraction, the fluid is expelled from the mixture, the pore pressure increases and the friction force diminishes. To

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

    Science.gov (United States)

    Hess, Julian; Wang, Yongqi

    2016-11-01

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

  11. A High Granularity Timing Detector for the Phase-2 Upgrade of the ATLAS Calorimeter

    CERN Document Server

    Grinstein, Sebastian; The ATLAS collaboration

    2017-01-01

    The expected increase of the particle flux at the high luminosity phase of the LHC with instantaneous luminosities up to L ≃ 7.5 × 10^{34} cm^{−2} s^{−1} will have a severe impact on pile-up. The pile-up is expected to increase on average to 200 interactions per bunch crossing. The reconstruction and trigger performance for especially jets and transverse missing energy will be severely degraded in the end-cap and forward region. A High Granularity Timing Detector (HGTD) is proposed in front of the liquid Argon end-cap calorimeters for pile-up mitigation at Level-0 (L0) trigger level and in the offline reconstruction. This device cover the pseudo-rapidity range of 2.4 to about 4.2. Four layers of Silicon sensors, possibly interleaved with Tungsten, are foreseen to provide precision timing information for charged and neutral particles with a time resolution of the order of 30 pico-seconds per readout cell in order to assign the energy deposits in the calorimeter to different proton-proton collision verti...

  12. Fiber bundle models for stress release and energy bursts during granular shearing

    Science.gov (United States)

    Michlmayr, Gernot; Or, Dani; Cohen, Denis

    2012-12-01

    Fiber bundle models (FBMs) offer a versatile framework for representing transitions from progressive to abrupt failure in disordered material. We report a FBM-based description of mechanical interactions and associated energy bursts during shear deformation of granular materials. For strain-controlled shearing, where elements fail in a sequential order, we present analytical expressions for strain energy release and failure statistics. Results suggest that frequency-magnitude characteristics of fiber failure vary considerably throughout progressive shearing. Predicted failure distributions were in good agreement with experimentally observed shear stress fluctuations and associated bursts of acoustic emissions. Experiments also confirm a delayed release of acoustic emission energy relative to shear stress buildup, as anticipated by the model. Combined with data-rich acoustic emission measurements, the modified FBM offers highly resolved contact-scale insights into granular media dynamics of shearing processes.

  13. High-Fidelity Gas and Granular Flow Physics Models for Rocket Exhaust Interaction with Lunar Soil Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Current modeling of Lunar and Martian soil erosion and debris transport caused by rocket plume impingement lacks essential physics from the peculiar granular...

  14. Energy decay in a granular gas collapse

    Science.gov (United States)

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

    2017-01-01

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

  15. Robust PLS Prediction Model for Saikosaponin A in Bupleurum chinense DC. Coupled with Granularity-Hybrid Calibration Set

    Directory of Open Access Journals (Sweden)

    Zhisheng Wu

    2015-01-01

    Full Text Available This study demonstrated particle size effect on the measurement of saikosaponin A in Bupleurum chinense DC. by near infrared reflectance (NIR spectroscopy. Four types of granularity were prepared including powder samples passed through 40-mesh, 65-mesh, 80-mesh, and 100-mesh sieve. Effects of granularity on NIR spectra were investigated, which showed to be wavelength dependent. NIR intensity was proportional to particle size in the first combination-overtone and combination region. Local partial least squares model was constructed separately for every kind of samples, and data-preprocessing techniques were performed to optimize calibration model. The 65-mesh model exhibited the best prediction ability with root mean of square error of prediction (RMSEP = 0.492 mg·g−1, correlation coefficient RP=0.9221, and relative predictive determinant (RPD = 2.58. Furthermore, a granularity-hybrid calibration model was developed by incorporating granularity variation. Granularity-hybrid model showed better performance than local model. The model performance with 65-mesh samples was still the most accurate with RMSEP = 0.481 mg·g−1, RP=0.9279, and RPD = 2.64. All the results presented the guidance for construction of a robust model coupled with granularity-hybrid calibration set.

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

    OpenAIRE

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

    2011-01-01

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

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

    DEFF Research Database (Denmark)

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

    rheology, which limit our ability to predict ice sheet dynamics in a changing climate. In this talk I will present the soft-body Discrete Element Method which is a Lagrangian method I use in order to simulate the unique and diverse nature of granular dynamics in the subglacial environment. However......, the method imposes intense computational requirements on the computational time step. The majority of steps in the granular dynamics algorithm are massively parallel, which makes the DEM an obvious candidate for exploiting the capabilities of modern GPUs. The granular computations are coupled to a fluid...

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

    Directory of Open Access Journals (Sweden)

    Guang-jin Wang

    2014-01-01

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

  19. Continuum modelling of shock waves through granular gases and the role of statistical fluctuations

    Science.gov (United States)

    Sirmas, Nick; Radulescu, Matei I.

    2016-11-01

    Previous experiments have revealed that shock waves driven through dissipative gases may become unstable, for example, in granular gases. The mechanisms controlling these instabilities are not well understood. Two-dimensional event-driven Molecular Dynamics (MD) simulations were previously completed to investigate the stability of piston driven shock waves through dilute granular gases. By considering viscoelastic collisions, allowing for finite dissipation within the shock wave, instabilities were found in the form of distinctive high density non-uniformities and convective rolls within the shock structure. This work is now extended to the continuum level. Euler and Navier-Stokes equations for granular gases are modelled with a modified cooling rate to include an impact threshold necessary for inelastic collisions. The shock structure predicted by the continuum formulation is found in good agreement with the structure obtained by MD. Introducing strong perturbations to the incoming density field, in accordance with the spacial fluctuations in the upstream state seen in MD, yields similar instabilities as those previously observed. While the inviscid model predicts a highly turbulent structure from these perturbations, the inclusion of viscosity and heat conductivity yields comparable wavelengths of pattern formations to those seen in MD.

  20. Computer Modeling of Electrostatic Aggregation of Granular Materials in Planetary and Astrophysical Settings

    Science.gov (United States)

    Marshall, J.; Sauke, T.

    1999-01-01

    Electrostatic forces strongly influence the behavior of granular materials in both dispersed (cloud) systems and semi-packed systems. These forces can cause aggregation or dispersion of particles and are important in a variety of astrophysical and planetary settings. There are also many industrial and commercial settings where granular matter and electrostatics become partners for both good and bad. This partnership is important for human exploration on Mars where dust adheres to suits, machines, and habitats. Long-range Coulombic (electrostatic) forces, as opposed to contact-induced dipoles and van der Waals attractions, are generally regarded as resulting from net charge. We have proposed that in addition to net charge interactions, randomly distributed charge carriers on grains will result in a dipole moment regardless of any net charge. If grains are unconfined, or fluidized, they will rotate so that the dipole always induces attraction between grains. Aggregates are readily formed, and Coulombic polarity resulting from the dipole produces end-to-end stacking of grains to form filamentary aggregates. This has been demonstrated in USML experiments on Space Shuttle where microgravity facilitated the unmasking of static forces. It has also been demonstrated in a computer model using grains with charge carriers of both sign. Model results very closely resembled micro-g results with actual sand grains. Further computer modeling of the aggregation process has been conducted to improve our understanding of the aggregation process, and to provide a predictive tool for microgravity experiments slated for Space Station. These experiments will attempt to prove the dipole concept as outlined above. We have considerably enhanced the original computer model: refinements to the algorithm have improved the fidelity of grain behavior during grain contact, special attention has been paid to simulation time steps to enable establishment of a meaningful, quantitative time axis

  1. Radiation hardness and precision timing study of silicon detectors for the CMS High Granularity Calorimeter (HGC)

    Science.gov (United States)

    Currás, Esteban; Fernández, Marcos; Gallrapp, Christian; Gray, Lindsey; Mannelli, Marcello; Meridiani, Paolo; Moll, Michael; Nourbakhsh, Shervin; Scharf, Christian; Silva, Pedro; Steinbrueck, Georg; Fatis, Tommaso Tabarelli de; Vila, Iván

    2017-02-01

    The high luminosity upgraded LHC or Phase-II is expected to increase the instantaneous luminosity by a factor of 10 beyond the LHC's design value, expecting to deliver 250 fb-1 per year for a further 10 years of operation. Under these conditions the performance degradation due to integrated radiation dose will need to be addressed. The CMS collaboration is planning to upgrade the forward calorimeters. The replacement is called the High Granularity Calorimeter (HGC) and it will be realized as a sampling calorimeter with layers of silicon detectors interleaved. The sensors will be realized as pad detectors with sizes of less that ∼1.0 cm2 and an active thickness between 100 and 300 μm depending on the position, respectively, the expected radiation levels. For an integrated luminosity of 3000 fb-1, the electromagnetic calorimetry will sustain integrated doses of 1.5 MGy (150 Mrads) and neutron fluences up to 1016 neq/cm2. A radiation tolerance study after neutron irradiation of 300, 200, and 100 μm n-on-p and p-on-n silicon pads irradiated to fluences up to 1.6×1016 neq/cm2 is presented. The properties of these diodes studied before and after irradiation were leakage current, capacitance, charge collection efficiency, annealing effects and timing capability. The results of these measurements validate these sensors as candidates for the HGC system.

  2. Elasto-plastic constitutive modeling for granular materials

    Institute of Scientific and Technical Information of China (English)

    彭芳乐; 李建中

    2004-01-01

    Based on the modified plastic strain energy approach, an elasto-plastic constitutive modeling for sand was proposed. The hardening function between the modified plastic strain energy and a stress parameter was presented, which was independent of stress history and stress paths. The proposed model was related to an isotropically work-hardening and softening, non-associated and elasto-plastic material description. It is shown that the constitutive modeling, the inherent and stress system-induced cross-anisotropic elasticity is also considered. The constitutive model is capable of simulating the effects on the deformation characteristics of stress history and stress path, pressure level and anisotropic strength.

  3. Modelling hydraulic transport and anaerobic uptake by PAOs and GAOs during wastewater feeding in EBPR granular sludge reactors.

    Science.gov (United States)

    Weissbrodt, David G; Holliger, Christof; Morgenroth, Eberhard

    2017-03-21

    New-generation bioprocesses using granular sludge aim for a high-rate removal of nutrients from wastewater with low footprint. Achieving enhanced biological phosphorus removal (EBPR) relies on the design of sludge beds and wastewater feeding conditions to optimally load the biomass and to select for polyphosphate- (PAOs) over glycogen-accumulating organisms (GAOs) and other heterotrophs. A hydraulic-metabolic mathematical model was developed to elucidate the impact of hydraulic transport patterns and environmental conditions on the PAO/GAO competition during up-flow feeding through an EBPR granular sludge bed. Tracer experiments highlighted plug-flow regimes with dispersion under both rapid (9 m h(-1) , Rebed  = 1.6, Pez  = 7.2, Pet  = 4.6) and slow (0.9 m h(-1) , Rebed  = 0.2, Pez  = 21.3, Pet  = 3.4) feeding. Non-turbulent regimes (Rebed Feeding time, pH, and temperature significantly impacted bacterial competition for carbon uptake under anaerobic slow feeding. Feeding duration should be designed to avoid full depletion of intracellular storage polymers within static granules. PAOs bear twice longer feeding than GAOs by using both polyphosphate and glycogen hydrolysis to sustain anaerobic C-uptake. Alkaline conditions (pH 7.25-8.0) by, e.g., dosing lime in the feed select for PAOs independently of temperature (10 - 30°C). A twice higher bed is required for full anaerobic conversions at 10 rather than 20 °C. Biosystem responses for anaerobic C-uptake can be anticipated using the model toward designing robust anaerobic selectors to manage the microbial resource in EBPR granular sludge. This article is protected by copyright. All rights reserved.

  4. A Study of the Behavior and Micromechanical Modelling of Granular Soil. Volume 1. A Constitutive Relation for Granular Materials Based on the Contact Law Between Two Spheres

    Science.gov (United States)

    1991-05-22

    hypoelasticity , plasticity, and viscoplasticity. Despite the large number of models there has been no consensus within the research community on the best...AD-A238 091 FosR-- C)1 0 19 IIIIII1IIII111 11111111l A STUDY OF THE BEHAVIOR AND MICROMECHANICAL MODELLING OF GRANULAR SOIL VOLUME I A CONSTITUTIVE...COVERED IMay 22, 1991 Final 1/6/ 89-5/15/91 4 TITLE AND SUBTITILI S. FUNDING NUMIEgRS A Study of the Behavior and Micromechanical Modelling of Grant

  5. An Elastic Plastic Contact Model with Strain Hardening for the LAMMPS Granular Package

    Energy Technology Data Exchange (ETDEWEB)

    Kuhr, Bryan [Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States); Brake, Matthew Robert [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Component Science and Mechanics; Lechman, Jeremy B. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Nanoscale and Reactive Processes

    2015-03-01

    The following details the implementation of an analytical elastic plastic contact model with strain hardening for normal im pacts into the LAMMPS granular package. The model assumes that, upon impact, the co llision has a period of elastic loading followed by a period of mixed elastic plas tic loading, with contributions to each mechanism estimated by a hyperbolic seca nt weight function. This function is implemented in the LAMMPS source code as the pair style gran/ep/history. Preliminary tests, simulating the pouring of pure nickel spheres, showed the elastic/plastic model took 1.66x as long as similar runs using gran/hertz/history.

  6. Granular mixtures modeled as elastic hard spheres subject to a drag force.

    Science.gov (United States)

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

    2007-06-01

    Granular gaseous mixtures under rapid flow conditions are usually modeled as a multicomponent system of smooth inelastic hard disks (two dimensions) or spheres (three dimensions) with constant coefficients of normal restitution alpha{ij}. In the low density regime an adequate framework is provided by the set of coupled inelastic Boltzmann equations. Due to the intricacy of the inelastic Boltzmann collision operator, in this paper we propose a simpler model of elastic hard disks or spheres subject to the action of an effective drag force, which mimics the effect of dissipation present in the original granular gas. For each collision term ij, the model has two parameters: a dimensionless factor beta{ij} modifying the collision rate of the elastic hard spheres, and the drag coefficient zeta{ij}. Both parameters are determined by requiring that the model reproduces the collisional transfers of momentum and energy of the true inelastic Boltzmann operator, yielding beta{ij}=(1+alpha{ij})2 and zeta{ij} proportional, variant1-alpha{ij}/{2}, where the proportionality constant is a function of the partial densities, velocities, and temperatures of species i and j. The Navier-Stokes transport coefficients for a binary mixture are obtained from the model by application of the Chapman-Enskog method. The three coefficients associated with the mass flux are the same as those obtained from the inelastic Boltzmann equation, while the remaining four transport coefficients show a general good agreement, especially in the case of the thermal conductivity. The discrepancies between both descriptions are seen to be similar to those found for monocomponent gases. Finally, the approximate decomposition of the inelastic Boltzmann collision operator is exploited to construct a model kinetic equation for granular mixtures as a direct extension of a known kinetic model for elastic collisions.

  7. Modeling granular material flows: The angle of repose, fluidization and the cliff collapse problem

    Science.gov (United States)

    Holsapple, Keith A.

    2013-07-01

    I discuss theories of granular material flows, with application to granular flows on the earth and planets. There are two goals. First, there is a lingering belief of some that the standard continuum plasticity Mohr-Coulomb and/or Drucker-Prager models are not adequate for many large-scale granular flow problems. The stated reason for those beliefs is the fact that the final slopes of the run-outs in collapse, landslide problems, and large-scale cratering are well below the angle of repose of the material. That observation, combined with the supposition that in those models flow cannot occur with slopes less than the angle of repose, has led to a number of researchers suggesting a need for lubrication or fluidization mechanisms and modeling. That issue is investigated in detail and shown to be false. A complete analysis of slope failures according to the Mohr-Coulomb model is presented, with special attention to the relations between the angle of repose and slope failures. It is shown that slope failure can occur for slope angles both larger than and smaller than the angle of repose. Second, to study the details of landslide run-outs, finite-difference continuum code simulations of the prototypical cliff collapse problem, using the classical plasticity models, are presented, analyzed and compared to experiments. Although devoid of any additional fluidization models, those simulations match experiments in the literature extremely well. The dynamics of this problem introduces additional important features relating to the run-out and final slope angles. The vertical free surface begins to fall at the initial 90° and flow continues to a final slope less than 10°. The detail in the calculation is examined to show why flow persists at slope angles that appear to be less than the angle of repose. The motions include regions of solid-like, fluid-like, and gas-like flows without invoking any additional models.

  8. Modeling intragranular diffusion in low-connectivity granular media

    Science.gov (United States)

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

    2012-03-01

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

  9. Vector-based model of elastic bonds for simulation of granular solids.

    Science.gov (United States)

    Kuzkin, Vitaly A; Asonov, Igor E

    2012-11-01

    A model (further referred to as the V model) for the simulation of granular solids, such as rocks, ceramics, concrete, nanocomposites, and agglomerates, composed of bonded particles (rigid bodies), is proposed. It is assumed that the bonds, usually representing some additional gluelike material connecting particles, cause both forces and torques acting on the particles. Vectors rigidly connected with the particles are used to describe the deformation of a single bond. The expression for potential energy of the bond and corresponding expressions for forces and torques are derived. Formulas connecting parameters of the model with longitudinal, shear, bending, and torsional stiffnesses of the bond are obtained. It is shown that the model makes it possible to describe any values of the bond stiffnesses exactly; that is, the model is applicable for the bonds with arbitrary length/thickness ratio. Two different calibration procedures depending on bond length/thickness ratio are proposed. It is shown that parameters of the model can be chosen so that under small deformations the bond is equivalent to either a Bernoulli-Euler beam or a Timoshenko beam or short cylinder connecting particles. Simple analytical expressions, relating parameters of the V model with geometrical and mechanical characteristics of the bond, are derived. Two simple examples of computer simulation of thin granular structures using the V model are given.

  10. Hydrodynamic Burnett equations for inelastic Maxwell models of granular gases

    Science.gov (United States)

    Khalil, Nagi; Garzó, Vicente; Santos, Andrés

    2014-05-01

    The hydrodynamic Burnett equations and the associated transport coefficients are exactly evaluated for generalized inelastic Maxwell models. In those models, the one-particle distribution function obeys the inelastic Boltzmann equation, with a velocity-independent collision rate proportional to the γ power of the temperature. The pressure tensor and the heat flux are obtained to second order in the spatial gradients of the hydrodynamic fields with explicit expressions for all the Burnett transport coefficients as functions of γ, the coefficient of normal restitution, and the dimensionality of the system. Some transport coefficients that are related in a simple way in the elastic limit become decoupled in the inelastic case. As a byproduct, existing results in the literature for three-dimensional elastic systems are recovered, and a generalization to any dimension of the system is given. The structure of the present results is used to estimate the Burnett coefficients for inelastic hard spheres.

  11. A new model for analysing thermal stress in granular composite

    Institute of Scientific and Technical Information of China (English)

    郑茂盛; 金志浩; 浩宏奇

    1995-01-01

    A double embedding model of inletting reinforcement grain and hollow matrix ball into the effective media of the particulate-reinforced composite is advanced. And with this model the distributions of thermal stress in different phases of the composite during cooling are studied. Various expressions for predicting elastic and elastoplastic thermal stresses are derived. It is found that the reinforcement suffers compressive hydrostatic stress and the hydrostatic stress in matrix zone is a tensile one when temperature decreases; when temperature further decreases, yield area in matrix forms; when the volume fraction of reinforcement is enlarged, compressive stress on grain and tensile hydrostatic stress in matrix zone decrease; the initial temperature difference of the interface of reinforcement and matrix yielding rises, while that for the matrix yielding overall decreases.

  12. Drying and Heating Modelling of Granular Flow: Application to the Mix-Asphalt Processes

    Directory of Open Access Journals (Sweden)

    L Le Guen

    2011-01-01

    Full Text Available Concrete asphalt is a hydrocarbon material that includes a mix of mineral components along with a bituminous binder. Prior to mixing, its production protocol requires drying and heating the aggregates. Generally performed in a rotary drum, these drying and heating steps within mix asphalt processes have never been studied from a physical perspective. We are thus proposing in the present paper to analyze the drying and heating mechanisms when granular materials and hot gases are involved in a co-current flow. This process step accounts for a large proportion of the overall energy consumed during hot-mix asphalt manufacturing. In the present context, the high energy cost associated with this step has encouraged developing new strategies specifically for the drying process. Applying new asphalt techniques so that an amount of moisture can be preserved in the asphalt concrete appears fundamental to such new strategies. This low-energy asphalt, also referred to as the "warm technique", depends heavily on a relevant prediction of the actual moisture content inside asphalt concrete during the mixing step. The purpose of this paper is to present a physical model dedicated to the evolution in temperature and moisture of granular solids throughout the drying and heating steps carried out inside a rotary drum. An initial experimental campaign to visualize inside a drum at the pilot scale (i.e. 1/3 scale has been carried out in order to describe the granular flow and establish the necessary physical assumptions for the drying and heating model. Energy and mass balance equations are solved by implementing an adequate heat and mass transfer coupling, yielding a 1D model from several parameters that in turn drives the physical modeling steps. Moreover, model results will be analyzed and compared to several measurements performed in an actual asphalt mix plant at the industrial scale (i.e. full scale.

  13. Granular flow

    DEFF Research Database (Denmark)

    Mitarai, Namiko; Nakanishi, Hiizu

    2012-01-01

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

  14. Modeling of state parameter and hardening function for granular materials

    Institute of Scientific and Technical Information of China (English)

    彭芳乐; 李建中

    2004-01-01

    A modified plastic strain energy as hardening state parameter for dense sand was proposed, based on the results from a series of drained plane strain tests on saturated dense Japanese Toyoura sand with precise stress and strain measurements along many stress paths. In addition, a unique hardening function between the plastic strain energy and the instantaneous stress path was also presented, which was independent of stress history. The proposed state parameter and hardening function was directly verified by the simple numerical integration method. It is shown that the proposed hardening function is independent of stress history and stress path and is appropriate to be used as the hardening rule in constitutive modeling for dense sand, and it is also capable of simulating the effects on the deformation characteristics of stress history and stress path for dense sand.

  15. A micromechanical model for effective conductivity in granular electrode structures

    Science.gov (United States)

    Ott, Julia; Völker, Benjamin; Gan, Yixiang; McMeeking, Robert M.; Kamlah, Marc

    2013-10-01

    Optimization of composition and microstructure is important to enhance performance of solid oxide fuel cells (SOFC) and lithium-ion batteries (LIB). For this, the porous electrode structures of both SOFC and LIB are modeled as a binary mixture of electronic and ionic conducting particles to estimate effective transport properties. Particle packings of 10 000 spherical, binary sized and randomly positioned particles are created numerically and densified considering the different manufacturing processes in SOFC and LIB: the sintering of SOFC electrodes is approximated geometrically, whereas the calendering process and volume change due to intercalation in LIB are modeled physically by a discrete element approach. A combination of a tracking algorithm and a resistor network approach is developed to predict the connectivity and effective conductivity for the various densified structures. For SOFC, a systematic study of the influence of morphology on connectivity and conductivity is performed on a large number of assemblies with different compositions and particle size ratios between 1 and 10. In comparison to percolation theory, an enlarged percolation area is found, especially for large size ratios. It is shown that in contrast to former studies the percolation threshold correlates to varying coordination numbers. The effective conductivity shows not only an increase with volume fraction as expected but also with size ratio. For LIB, a general increase of conductivity during the intercalation process was observed in correlation with increasing contact forces. The positive influence of calendering on the percolation threshold and the effective conductivity of carbon black is shown. The anisotropy caused by the calendering process does not influence the carbon black phase.

  16. Nonvibrating granular model for a glass-forming liquid: Equilibration and aging

    Science.gov (United States)

    Tapia-Ignacio, C.; Garcia-Serrano, J.; Donado, F.

    2016-12-01

    We studied experimentally a model of a glass-forming liquid on the basis of a nonvibrating magnetic granular system under an unsteady magnetic field. A sudden quenching was produced that drove the system from a liquid state to a different final state with lower temperature; the latter could be a liquid state or a solid state. We determined the mean-squared displacement in temporal windows to obtain the dynamic evolution of the system, and we determined the radial distribution function to obtain its structural characteristics. The results were analyzed using the intermediate scattering function and the effective potential between two particles. We observed that when quenching drives the system to a final state in the liquid phase far from the glass-transition temperature, equilibration occurs very quickly. When the final state has a temperature far below the glass-transition temperature, the system reaches its equilibrium state very quickly. In contrast, when the final state has an intermediate temperature but is below that corresponding to the glass transition, the system falls into a state that evolves slowly, presenting aging. The system evolves by an aging process toward more ordered states. However, after a waiting time, the dynamic behavior changes. It was observed that some particles get close enough to overpass the repulsive interactions and form small stable aggregates. In the effective potential curves, it was observed that the emergence of a second effective well due to the attraction quickly evolves and results in a deeper well than the initial effective well due to the repulsion. With the increase in time, more particles fall in the attractive well forming inhomogeneities, which produce a frustration in the aging process.

  17. Acoustic response of cemented granular sedimentary rocks: molecular dynamics modeling.

    Science.gov (United States)

    García, Xavier; Medina, Ernesto

    2007-06-01

    The effect of cementation processes on the acoustical properties of sands is studied via molecular dynamics simulation methods. We propose numerical methods where the initial uncemented sand is built by simulating the settling process of sediments. Uncemented samples of different porosity are considered by emulating natural mechanical compaction of sediments due to overburden. Cementation is considered through a particle-based model that captures the underlying physics behind the process. In our simulations, we consider samples with different degrees of compaction and cementing materials with distinct elastic properties. The microstructure of cemented sands is taken into account while adding cement at specific locations within the pores, such as grain-to-grain contacts. Results show that the acoustical properties of cemented sands are strongly dependent on the amount of cement, its stiffness relative to the hosting medium, and its location within the pores. Simulation results are in good correspondence with available experimental data and compare favorably with some theoretical predictions for the sound velocity within a range of cement saturation, porosity, and confining pressure.

  18. Analysis of the Tangjiaxi landslide-generated waves in the Zhexi Reservoir, China, by a granular flow coupling model

    Science.gov (United States)

    Huang, Bolin; Yin, Yueping; Wang, Shichang; Tan, Jianmin; Liu, Guangning

    2017-05-01

    A rocky granular flow is commonly formed after the failure of rocky bank slopes. An impulse wave disaster may also be initiated if the rocky granular flow rushes into a river with a high velocity. Currently, the granular mass-water body coupling study is an important trend in the field of landslide-induced impulse waves. In this paper, a full coupling numerical model for landslide-induced impulse waves is developed based on a non-coherent granular flow equation, i.e., the Mih equation. In this model, the Mih equation for continuous non-coherent granular flow controls movements of sliding mass, the two-phase flow equation regulates the interaction between sliding mass and water, and the renormalization group (RNG) turbulence model governs the movement of the water body. The proposed model is validated and applied for the 2014 Tangjiaxi landslide of the Zhexi Reservoir located in Hunan Province, China, to analyze the characteristics of both landslide motion and its following impulse waves. On 16 July 2014, a rocky debris flow was formed after the failure of the Tangjiaxi landslide, damming the Tangjiaxi stream and causing an impulse wave disaster with three dead and nine missing bodies. Based on the full coupling numerical analysis, the granular flow impacts the water with a maximum velocity of about 22.5 m s-1. Moreover, the propagation velocity of the generated waves reaches up to 12 m s-1. The maximum calculated run-up of 21.8 m is close enough to the real value of 22.7 m. The predicted landslide final deposit and wave run-up heights are in a good agreement with the field survey data. These facts verify the ability of the proposed model for simulating the real impulse wave generated by rocky granular flow events.

  19. Continuum modeling of segregation for tridisperse granular materials in developing chute flow

    Science.gov (United States)

    Deng, Zhekai; Umbanhowar, Paul; Lueptow, Richard

    2015-11-01

    Predicting segregation and mixing of size polydisperse granular material is a challenging problem and is relevant to many industrial applications. We develop and implement a continuum-based theoretical model that captures the effects of segregation, diffusion and advection on size tridisperse granular flow in developing quasi-two-dimensional chute flow. Unlike segregation models that rely on arbitrary fitting parameters, our model uses parameters based on kinematics measured using discrete element method (DEM) simulations. The model depends on both the Péclet number, Pe, which we defined as the ratio of the segregation rate to the diffusion rate, and the relative segregation strength between particle species. At large Pe, segregation dominates and chute flow consists of distinct stratified regions of small(bottom), medium(center) and large (top) particles, whereas at small Pe, diffusion dominates, which results in a well mixed flow. As relative segregation strength between any two particle species is increased, the segregation between them becomes quicker. However, as relative segregation strength between them is decreased, they remain mixed with each other. Preliminary results from DEM simulations support our theoretical model.

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

    Science.gov (United States)

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

    2016-04-01

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

  1. Testing Hadronic Interaction Models using a Highly Granular Silicon-Tungsten Calorimeter

    CERN Document Server

    Bilki, B.; Schlereth, J.; Xia, L.; Deng, Z.; Li, Y.; Wang, Y.; Yue, Q.; Yang, Z.; Eigen, G.; Mikami, Y.; Price, T.; Watson, N.K.; Thomson, M.A.; Ward, D.R.; Benchekroun, D.; Hoummada, A.; Khoulaki, Y.; Carloganu, C.; Chang, S.; Khan, A.; Kim, D.H.; Kong, D.J.; Oh, Y.D.; Blazey, G.C.; Dyshkant, A.; Francis, K.; Lima, J.G.R.; Salcido, P.; Zutshi, V.; Boisvert, V.; Green, B.; Misiejuk, A.; Salvatore, F.; Kawagoe, K.; Miyazaki, Y.; Sudo, Y.; Suehara, T.; Tomita, T.; Ueno, H.; Yoshioka, T.; Apostolakis, J.; Folger, G.; Ivantchenko, V.; Ribon, A.; Uzhinskiy, V.; Cauwenbergh, S.; Tytgat, M.; Zaganidis, N.; Hostachy, J.Y.; Morin, L.; Gadow, K.; Göttlicher, P.; Günter, C.; Krüger, K.; Lutz, B.; Reinecke, M.; Sefkow, F.; Feege, N.; Garutti, E.; Laurien, S.; Lu, S.; Marchesini, I.; Matysek, M.; Ramilli, M.; Kaplan, A.; Norbeck, E.; Northacker, D.; Onel, Y.; Kim, E.J.; van Doren, B.; Wilson, G.W.; Wing, M.; Bobchenko, B.; Chadeeva, M.; Chistov, R.; Danilov, M.; Drutskoy, A.; Epifantsev, A.; Markin, O.; Mizuk, R.; Novikov, E.; Popov, V.; Rusinov, V.; Tarkovsky, E.; Besson, D.; Popova, E.; Gabriel, M.; Kiesling, C.; Simon, F.; Soldner, C.; Szalay, M.; Tesar, M.; Weuste, L.; Amjad, M.S.; Bonis, J.; Callier, S.; Conforti di Lorenzo, S.; Cornebise, P.; Doublet, Ph.; Dulucq, F.; Faucci-Giannelli, M.; Fleury, J.; Frisson, T.; Kégl, B.; van der Kolk, N.; Li, H.; Martin-Chassard, G.; Richard, F.; de la Taille, Ch.; Pöschl, R.; Raux, L.; Rouëne, J.; Seguin-Moreau, N.; Anduze, M.; Balagura, V.; Becheva, E.; Boudry, V.; Brient, J.-C.; Cornat, R.; Frotin, M.; Gastaldi, F.; Magniette, F.; Matthieu, A.; Mora de Freitas, P.; Videau, H.; Augustin, J.-E.; David, J.; Ghislain, P.; Lacour, D.; Lavergne, L.; Zacek, J.; Cvach, J.; Gallus, P.; Havranek, M.; Janata, M.; Kvasnicka, J.; Lednicky, D.; Marcisovsky, M.; Polak, I.; Popule, J.; Tomasek, L.; Tomasek, M.; Ruzicka, P.; Sicho, P.; Smolik, J.; Vrba, V.; Zalesak, J.; Jeans, D.; Götze, M.

    2015-01-01

    A detailed study of hadronic interactions is presented using data recorded with the highly granular CALICE silicon-tungsten electromagnetic calorimeter. Approximately 600,000 selected negatively changed pion events at energies between 2 and 10 GeV have been studied. The predictions of several physics models available within the GEANT4 simulation tool kit are compared to this data. Although a reasonable overall description of the data is observed, there are significant quantitative discrepancies in the longitudinal and transverse distributions of reconstructed energy.

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

    Science.gov (United States)

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

    2012-06-01

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

  3. Pion transverse-momentum spectrum, elliptic flow, and Hanbury-Brown-Twiss interferometry in a viscous granular source model

    CERN Document Server

    Yang, Jing; Ren, Yan-Yu

    2016-01-01

    We examine the evolution of quark-gluon plasma (QGP) droplets with viscous hydrodynamics and analyze pion transverse-momentum spectrum, elliptic flow, and Hanbury-Brown-Twiss (HBT) interferometry in a granular source model consisting of the viscous QGP droplets. The shear viscosity of the QGP droplet speeds up the droplet evolution and the effect of the bulk viscosity on the evolution is negligible. Although there are viscous effects on the droplet evolution, the pion momentum spectrum and elliptic flow change little for the granular sources with and without viscosity. On the other hand, the influence of viscosity on HBT radius $R_{\\rm out}$ is significant. It makes $R_{\\rm out}$ decrease in the granular source model. We determine the model parameters of granular sources by the experimental data of pion transverse-momentum spectrum, elliptic flow, and HBT radii together, and investigate the effects of viscosity on the model parameters. The results indicate that the granular source model may reproduce the expe...

  4. Importance of surface diffusivities in pesticide adsorption kinetics onto granular versus powdered activated carbon: experimental determination and modeling.

    Science.gov (United States)

    Baup, S; Wolbert, D; Laplanche, A

    2002-10-01

    Three pesticides (atrazine, bromoxynil and diuron) and two granular activated carbons are involved in equilibrium and kinetic adsorption experiments. Equilibrium is represented by Freundlich isotherm law and kinetic is described by the Homogeneous Surface Diffusion Model, based on external mass transfer and intraparticle surface diffusion. Equilibrium and long-term experiments are conducted to compare Powdered Activated Carbon and Granular Activated Carbon. These first investigations show that crushing GAC into PAC improves the accessibility of the adsorption sites without increasing the number of these sites. In a second part, kinetics experiments are carried out using a Differential Column Batch Reactor. Thanks to this experimental device, the external mass transfer coefficient k(f) is calculated from empirical correlation and the effect of external mass transfer on adsorption is likely to be minimized. In order to obtain the intraparticle surface diffusion coefficient D. for these pesticides, comparisons between experimental kinetic data and simulations are conducted and the best agreement leads to the Ds coefficient. This procedure appears to be an efficient way to acquire surface diffusion coefficients for the adsorption of pesticides onto GAC. Finally it points out the role of surface diffusivity in the adsorption rate. As a matter of fact, even if the amount of the target-compound that could be potentially adsorbed is really important, its surface diffusion coefficient may be small, so that its adsorption may not have enough contact time to be totally achieved.

  5. The contact density to characterize the mechanics of cohesive granular materials: application to snow microstructure modeling.

    Science.gov (United States)

    Gaume, Johan; Löwe, Henning

    2016-04-01

    Microstructural properties are essential to characterize the mechanics of loose and cohesive granular materials such as snow. In particular, mechanical properties and physical processes of porous media are often related to the volume fraction ν. Low-density microstructures typically allow for considerable structural diversity at a given volume fraction, leading to uncertainties in modeling approaches using ν-based parametrizations only. We have conducted discrete element simulations of cohesive granular materials with initial configurations which are drawn from Baxter's sticky hard sphere (SHS) model. This method allows to control independently the initial volume fraction ν and the average coordination number Z. We show that variations in elasticity and strength of the samples can be fully explained by the initial contact density C = νZ over a wide range of volume fractions and coordination numbers. Hence, accounting for the contact density C allows to resolve the discrepancies in particle based modeling between samples with similar volume fractions but different microstructures. As an application, we applied our method to the microstructure of real snow samples which have been imaged by micro-computed tomography and reconstructed using the SHS model. Our new approach opens a promising route to evaluate snow physical and mechanical properties from field measurements, for instance using the Snow Micro Penetrometer (SMP), by linking the penetration resistance to the contact density.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-09-30

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

  7. Continuum modelling of piston driven shock waves through granular gases and ensuing pattern formations

    Science.gov (United States)

    Sirmas, Nick; Radulescu, Matei

    2015-11-01

    Two-dimensional event-driven Molecular Dynamics (MD) simulations were previously completed to investigate the stability of piston driven shock waves through dilute granular gases. By considering viscoelastic collisions, allowing for finite dissipation within the shock wave, instabilities were found in the form of distinctive high density non-uniformities and convective rolls within the shock structure. This work is now extended to the continuum level. Euler and Navier-Stokes equations for granular gases are modelled with a modified cooling rate to include an impact threshold necessary for inelastic collisions. The shock structure predicted by the continuum formulation is found in good agreement with the structure obtained by MD. Non-linear stability analyses of the travelling wave solution are performed, showing a neutrally stable structure and responding only to fluctuations in the upstream state. Introducing strong perturbations to the incoming density field, in accordance with the spacial fluctuations in upstream state seen in MD, yields similar instabilities as those previously observed. While the inviscid model predicts a highly turbulent structure from these perturbations, the inclusion of viscosity yields comparable wavelengths of pattern formations to those seen in MD.

  8. Effect of system and particle properties on closure relations for granular segregation models

    Science.gov (United States)

    Singh, Abhinendra; Tunuguntla, D. R.; Thornton, A. R.; Multi Scale mechanics Team

    2015-03-01

    In recent years, much effort has been made on developing valid constitutive laws for continuum models to describe kinetic sieving driven segregation in granular flows over inclined channels. Surprisingly, the existing closure relations for such continuum models have not considered factors such as particle contact stiffness, coefficient of restitution etc. Using Discrete Element method simulations, we investigate the effects of these factors on particle segregation and thereby formulate a constitutive law which takes particle properties into account. Additionally, apart from studying the effects of particle properties on segregating flows, we investigate the effects of gravity on our granular system. We consider a varied range of gravity and find that rate of segregation, for bidisperse mixtures varying in size alone, is proportional to the square root of gravity which is often assumed but was never validated. To be more precise concerning the effects of varying gravity on the steady states of bidisperse flows, varying in size alone, we investigate how the Peclet number (ratio of the segregation rate to diffusion) is affected.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-04-01

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

  10. Modeling the Mechanics of Dynamic Triggering of Earthquakes in Granular Fault Gouge

    Science.gov (United States)

    Payne, R. M.; Sparks, D. W.

    2015-12-01

    On faults where the static stress state is near but below the failure criterion, dynamic stress perturbations from passing seismic waves may initiate earthquakes. To study how these transient stresses can cause failure, we perform Discrete Element Method numerical simulations of shear failure in a layer of non-cohesive granular material. The granular material mimics crushed gouge in the fault core - the weakest part of the fault and the region most likely to initiate slip. The applied shear stress is slowly increased until failure (a slip event) to determine the frictional strength of the granular layer under non-perturbed conditions. Pre-failure states of the gouge layer are saved during the loading process and used as initial conditions in triggering experiments: one boundary of the gouge is subjected to a transient pulse in boundary stresses, to simulate a passing seismic waves. Various amplitudes and frequencies of the stress pulse are tested on layers at different static stress levels from 0.95 to 0.99 of the failure strength. In order to trigger an immediate failure, the pulse must increase the normal stress ratio to reach the previously measured frictional strength of the layer. However, we find that this is not a sufficient condition for immediate failure. The stress state must be above the frictional strength threshold long enough to allow for significant grain shifting (~ 0.1 grain diameters). This introduces a frequency dependence in addition to the amplitude dependence of the pulse. For low pre-stress levels, high frequency pulses do not remain above the threshold long enough and are incapable of causing immediate triggering. This frequency cutoff is directly proportional to the stress level, meaning lower frequencies can cause immediate triggering at a wider range of initial stress levels. Systems that are not immediately triggered may still experience "delayed triggering" - slip induced by the pulse after a time delay. This implies that transient

  11. A distribution model for the aerial application of granular agricultural particles

    Science.gov (United States)

    Fernandes, S. T.; Ormsbee, A. I.

    1978-01-01

    A model is developed to predict the shape of the distribution of granular agricultural particles applied by aircraft. The particle is assumed to have a random size and shape and the model includes the effect of air resistance, distributor geometry and aircraft wake. General requirements for the maintenance of similarity of the distribution for scale model tests are derived and are addressed to the problem of a nongeneral drag law. It is shown that if the mean and variance of the particle diameter and density are scaled according to the scaling laws governing the system, the shape of the distribution will be preserved. Distributions are calculated numerically and show the effect of a random initial lateral position, particle size and drag coefficient. A listing of the computer code is included.

  12. A High-Granularity Timing Detector for the Phase-II upgrade of the ATLAS Calorimeter system

    CERN Document Server

    Masetti, Lucia; The ATLAS collaboration

    2017-01-01

    The expected increase of the particle flux at the high luminosity phase of the LHC (HL-LHC) with instantaneous luminosities up to L=7.5 x 10^34 cm^-2 s^-1 will have a severe impact on pile-up. The pile-up is expected to increase on average to 200 interactions per bunch crossing. The reconstruction and trigger performance for electrons, photons as well as jets and transverse missing energy will be severely degraded in the end-cap and forward region, where the liquid Argon based electromagnetic calorimeter has coarser granularity compared to the central region. A High Granular Timing Detector (HGTD) is proposed in front of the liquid Argon end-cap calorimeters for pile-up mitigation at Level-0 (L0) trigger level and in offline reconstruction. This device should cover the pseudo-rapidity range of 2.4 to about 4.2. Four layers of Silicon sensors, possibly interleaved with Tungsten, are foreseen to provide precision timing information for charged and neutral particles with a time resolution of the order of 50 pico...

  13. High-Granularity Timing Detector for the Phase-II up-grade of the ATLAS Calorimeter system

    CERN Document Server

    Gkougkousis, Evangelos Leonidas; The ATLAS collaboration

    2017-01-01

    The expected increase of the particle flux at the high luminosity phase of the LHC (HL-LHC) with instantaneous luminosities up to L ≃ 7.5×1034 cm−2s−1 will have a severe impact on pile-up. The pile-up is expected to increase on average to 200 interactions per bunch crossing. The reconstruction and trigger performance for electrons, photons as well as jets and transverse missing energy will be severely degraded in the end-cap and forward region, where the liquid Argon based electromagnetic calorimeter has coarser granularity compared to the central region. A High Granular Timing Detector (HGTD) is proposed in front of the liquid Argon end-cap calorimeters for pile-up mitigation at Level-0 (L0) trigger level and in offline reconstruction. This device should cover the pseudo-rapidity range of 2.4 to about 4.2. Four layers of Silicon sensors, possibly interleaved with Tungsten, are foreseen to provide precision timing information for charged and neutral particles with a time resolution of the order of 50 p...

  14. A High-Granularity Timing Detector for the Phase-II upgrade of the ATLAS Calorimeter system

    CERN Document Server

    Lenzi, Bruno; The ATLAS collaboration

    2017-01-01

    The expected increase of the particle flux at the high luminosity phase of the LHC (HL-LHC) with instantaneous luminosities up to L = 7.5 x 10^34 cm−2s−1 will have a severe impact on pile-up. The pile-up is expected to increase on average to 200 interactions per bunch crossing. The reconstruction and trigger performance for electrons, photons as well as jets and transverse missing energy will be severely degraded in the end-cap and forward region, where the liquid Argon based electromagnetic calorimeter has coarser granularity compared to the central region. A High Granularity Timing Detector (HGTD) is proposed in front of the liquid Argon end-cap calorimeters for pile-up mitigation at Level-0 (L0) trigger level and in the offline reconstruction. This device should cover the pseudo-rapidity range of 2.4 to about 4.2. Four layers of Silicon sensors, possibly interleaved with Tungsten, are foreseen to provide precision timing information for charged and neutral particles with a time resolution of the order ...

  15. Transient Combustion in Granular Propellant Beds. Part I. Theoretical Modeling and Numerical Solution of Transient Combustion Processes in Mobile Granular Propellant Beds

    Science.gov (United States)

    1977-08-01

    To advice the statt-of-che- art in the combustion of granular prope..lents by forwilating a complete theoretical model describ".•j the Important...d~~+W s (-.1 1-3. Where the vector products of W , W/2 , W/ , W/ and W/ vith I arte •iVn as Wl#’. m II -VVW ,÷I&. -Wig I,÷W,4A+. j IS÷ I-P(/. W/r...5wItu-gto, r! 05402 Sacro Ci 9581 1 General ziactric comany Flisht ?ropulaicm Diwisiou 1 ADO Incorporated ATM I: ch Llb AIM Mr. 2. Dougbarty Clac~ati an

  16. Numerical Modeling of Particle-Fluid Mixtures in a Subglacial Setting: Granular Deformation and Hydrological Flow Response

    Science.gov (United States)

    Damsgaard, A.; Egholm, D. L.; Piotrowski, J. A.; Tulaczyk, S. M.; Larsen, N. K.

    2014-12-01

    The coupled mechanical response of ice, water and sediment may control the flow of warm-based glaciers residing on deformable sediment. This is most clearly expressed by the fast flowing ice streams in Greenland and Antarctica, where low levels of basal friction are thought to support the high flow rates. These ice streams are of particular interest since they are large constituents of the polar ice sheet mass balance. The study of these ice streams and their future impact on the ice sheets necessitates a deeper understanding of their basal dynamics, including the rheology of water-saturated sediment. We present the methodology and first results of a coupled numerical model for computational experiments on granular-fluid mixtures under dynamic conditions similar to those in subglacial settings. The granular phase is simulated on a per-particle basis by the soft body discrete element method. The fluid phase is handled as a continuum by solving the incompressible Navier-Stokes equations. The particle and fluid phases are coupled by mass conservation and momentum exchanges. The hydraulic diffusivity and permeability is compared to previous laboratory studies on tills. We demonstrate how the onset and halt of granular deformation is an efficient mechanism to create fluid pressure fluctuations due to local porosity changes. These pressure anomalies are driving transient hydraulic flows, and they influence directly the rheology of granular-fluid mixtures. Our results highlight the nonlinear nature of water saturated granular deformation, and demonstrate how the mechanical behaviour of granular materials may include both brittle and viscous components depending on the rates of deformation and the hydrological properties.

  17. The Time Structure of Hadronic Showers in Highly Granular Calorimeters with Tungsten and Steel Absorbers

    CERN Document Server

    Adloff, C.; Chefdeville, M.; Drancourt, C.; Gaglione, R.; Geffroy, N.; Karyotakis, Y.; Koletsou, I.; Prast, J.; Vouters, G.; Repond, J.; Schlereth, J.; Xia, L.; Baldolemar, E.; Li, J.; Park, S.T.; Sosebee, M.; White, A.P.; Yu, J.; Eigen, G.; Thomson, M.A.; Ward, D.R.; Benchekroun, D.; Hoummada, A.; Khoulaki, Y.; Apostolakis, J.; Arfaoui, A.; Benoit, M.; Dannheim, D.; Elsener, K.; Folger, G.; Grefe, C.; Ivantchenko, V.; Killenberg, M.; Klempt, W.; van der Kraaij, E.; Linssen, L.; Lucaci-Timoce, A.-I.; Münnich, A.; Poss, S.; Ribon, A.; Roloff, P.; Sailer, A.; Schlatter, D.; Sicking, E.; Strube, J.; Uzhinskiy, V.; Carloganu, C.; Gay, P.; Manen, S.; Royer, L.; Cornett, U.; David, D.; Ebrahimi, A.; Falley, G.; Feege, N.; Gadow, K.; Göttlicher, P.; Günter, C.; Hartbrich, O.; Hermberg, B.; Karstensen, S.; Krivan, F.; Krüger, K.; Lu, S.; Lutz, B.; Morozov, S.; Morgunov, V.; Neubüser, C.; Reinecke, M.; Sefkow, F.; Smirnov, P.; Terwort, M.; Fagot, A.; Tytgat, M.; Zaganidis, N.; Hostachy, J.-Y.; Morin, L.; Garutti, E.; Laurien, S.; Marchesini, I.; Matysek, M.; Ramilli, M.; Briggl, K.; Eckert, P.; Harion, T.; Schultz-Coulon, H.-Ch.; Shen, W.; Stamen, R.; Chang, S.; Khan, A.; Kim, D.H.; Kong, D.J.; Oh, Y.D.; Bilki, B.; Norbeck, E.; Northacker, D.; Onel, Y.; Wilson, G.W.; Kawagoe, K.; Miyazaki, Y.; Sudo, Y.; Ueno, H.; Yoshioka, T.; Dauncey, P.D.; Cortina Gil, E.; Mannai, S.; Baulieu, G.; Calabria, P.; Caponetto, L.; Combaret, C.; Della Negra, R.; Ete, R.; Grenier, G.; Han, R.; Ianigro, J-C.; Kieffer, R.; Laktineh, I.; Lumb, N.; Mathez, H.; Mirabito, L.; Petrukhin, A.; Steen, A.; Tromeur, W.; Vander Donckt, M.; Zoccarato, Y.; Berenguer Antequera, J.; Calvo Alamillo, E.; Fouz, M.-C.; Puerta-Pelayo, J.; Corriveau, F.; Bobchenko, B.; Chadeeva, M.; Danilov, M.; Epifantsev, A.; Markin, O.; Mizuk, R.; Novikov, E.; Rusinov, V.; Tarkovsky, E.; Kozlov, V.; Soloviev, Y.; Besson, D.; Buzhan, P.; Ilyin, A.; Kantserov, V.; Kaplin, V.; Popova, E.; Tikhomirov, V.; Gabriel, M.; Kiesling, C.; Seidel, K.; Simon, F.; Soldner, C.; Szalay, M.; Tesar, M.; Weuste, L.; Amjad, M.S.; Bonis, J.; Conforti di Lorenzo, S.; Cornebise, P.; Fleury, J.; Frisson, T.; van der Kolk, N.; Richard, F.; Pöschl, R.; Rouene, J.; Anduze, M.; Balagura, V.; Becheva, E.; Boudry, V.; Brient, J-C.; Cornat, R.; Frotin, M.; Gastaldi, F.; Guliyev, E.; Haddad, Y.; Magniette, F.; Ruan, M.; Tran, T.H.; Videau, H.; Callier, S.; Dulucq, F.; Martin-Chassard, G.; de la Taille, Ch.; Raux, L.; Seguin-Moreau, N.; Zacek, J.; Cvach, J.; Gallus, P.; Havranek, M.; Janata, M.; Kvasnicka, J.; Lednicky, D.; Marcisovsky, M.; Polak, I.; Popule, J.; Tomasek, L.; Tomasek, M.; Ruzicka, P.; Sicho, P.; Smolik, J.; Vrba, V.; Zalesak, J.; Belhorma, B.; Ghazlane, H.; Kotera, K.; Ono, H.; Takeshita, T.; Uozumi, S.; Chai, J.S.; Song, H.S.; Lee, S.H.; Götze, M.; Sauer, J.; Weber, S.; Zeitnitz, C.

    2014-01-01

    The intrinsic time structure of hadronic showers influences the timing capability and the required integration time of hadronic calorimeters in particle physics experiments, and depends on the active medium and on the absorber of the calorimeter. With the CALICE T3B experiment, a setup of 15 small plastic scintillator tiles read out with Silicon Photomultipliers, the time structure of showers is measured on a statistical basis with high spatial and temporal resolution in sampling calorimeters with tungsten and steel absorbers. The results are compared to GEANT4 (version 9.4 patch 03) simulations with different hadronic physics models. These comparisons demonstrate the importance of using high precision treatment of low-energy neutrons for tungsten absorbers, while an overall good agreement between data and simulations for all considered models is observed for steel.

  18. The time structure of hadronic showers in highly granular calorimeters with tungsten and steel absorbers

    Science.gov (United States)

    Adloff, C.; Blaising, J.-J.; Chefdeville, M.; Drancourt, C.; Gaglione, R.; Geffroy, N.; Karyotakis, Y.; Koletsou, I.; Prast, J.; Vouters, G.; Repond, J.; Schlereth, J.; Xia, L.; Baldolemar, E.; Li, J.; Park, S. T.; Sosebee, M.; White, A. P.; Yu, J.; Eigen, G.; Thomson, M. A.; Ward, D. R.; Benchekroun, D.; Hoummada, A.; Khoulaki, Y.; Apostolakis, J.; Arfaoui, S.; Benoit, M.; Dannheim, D.; Elsener, K.; Folger, G.; Grefe, C.; Ivantchenko, V.; Killenberg, M.; Klempt, W.; van der Kraaij, E.; Linssen, L.; Lucaci-Timoce, A.-I.; Münnich, A.; Poss, S.; Ribon, A.; Roloff, P.; Sailer, A.; Schlatter, D.; Sicking, E.; Strube, J.; Uzhinskiy, V.; Cârloganu, C.; Gay, P.; Manen, S.; Royer, L.; Cornett, U.; David, D.; Ebrahimi, A.; Falley, G.; Feege, N.; Gadow, K.; Göttlicher, P.; Günter, C.; Hartbrich, O.; Hermberg, B.; Karstensen, S.; Krivan, F.; Krüger, K.; Lu, S.; Lutz, B.; Morozov, S.; Morgunov, V.; Neubüser, C.; Reinecke, M.; Sefkow, F.; Smirnov, P.; Terwort, M.; Fagot, A.; Tytgat, M.; Zaganidis, N.; Hostachy, J.-Y.; Morin, L.; Garutti, E.; Laurien, S.; Marchesini, I.; Matysek, M.; Ramilli, M.; Briggl, K.; Eckert, P.; Harion, T.; Schultz-Coulon, H.-Ch; Shen, W.; Stamen, R.; Chang, S.; Khan, A.; Kim, D. H.; Kong, D. J.; Oh, Y. D.; Bilki, B.; Norbeck, E.; Northacker, D.; Onel, Y.; Wilson, G. W.; Kawagoe, K.; Miyazaki, Y.; Sudo, Y.; Ueno, H.; Yoshioka, T.; Dauncey, P. D.; Cortina Gil, E.; Mannai, S.; Baulieu, G.; Calabria, P.; Caponetto, L.; Combaret, C.; Della Negra, R.; Eté, R.; Grenier, G.; Han, R.; Ianigro, J.-C.; Kieffer, R.; Laktineh, I.; Lumb, N.; Mathez, H.; Mirabito, L.; Petrukhin, A.; Steen, A.; Tromeur, W.; Vander Donckt, M.; Zoccarato, Y.; Berenguer Antequera, J.; Calvo Alamillo, E.; Fouz, M.-C.; Puerta-Pelayo, J.; Corriveau, F.; Bobchenko, B.; Chadeeva, M.; Danilov, M.; Epifantsev, A.; Markin, O.; Mizuk, R.; Novikov, E.; Rusinov, V.; Tarkovsky, E.; Kozlov, V.; Soloviev, Y.; Besson, D.; Buzhan, P.; Ilyin, A.; Kantserov, V.; Kaplin, V.; Popova, E.; Tikhomirov, V.; Gabriel, M.; Kiesling, C.; Seidel, K.; Simon, F.; Soldner, C.; Szalay, M.; Tesar, M.; Weuste, L.; Amjad, M. S.; Bonis, J.; Conforti di Lorenzo, S.; Cornebise, P.; Fleury, J.; Frisson, T.; van der Kolk, N.; Richard, F.; Pöschl, R.; Rouëné, J.; Anduze, M.; Balagura, V.; Becheva, E.; Boudry, V.; Brient, J.-C.; Cornat, R.; Frotin, M.; Gastaldi, F.; Guliyev, E.; Haddad, Y.; Magniette, F.; Ruan, M.; Tran, T. H.; Videau, H.; Callier, S.; Dulucq, F.; Martin-Chassard, G.; de la Taille, Ch; Raux, L.; Seguin-Moreau, N.; Zacek, J.; Cvach, J.; Gallus, P.; Havranek, M.; Janata, M.; Kvasnicka, J.; Lednicky, D.; Marcisovsky, M.; Polak, I.; Popule, J.; Tomasek, L.; Tomasek, M.; Ruzicka, P.; Sicho, P.; Smolik, J.; Vrba, V.; Zalesak, J.; Belhorma, B.; Ghazlane, H.; Kotera, K.; Ono, H.; Takeshita, T.; Uozumi, S.; Chai, J. S.; Song, H. S.; Lee, S. H.; Götze, M.; Sauer, J.; Weber, S.; Zeitnitz, C.

    2014-07-01

    The intrinsic time structure of hadronic showers influences the timing capability and the required integration time of hadronic calorimeters in particle physics experiments, and depends on the active medium and on the absorber of the calorimeter. With the CALICE T3B experiment, a setup of 15 small plastic scintillator tiles read out with Silicon Photomultipliers, the time structure of showers is measured on a statistical basis with high spatial and temporal resolution in sampling calorimeters with tungsten and steel absorbers. The results are compared to GEANT4 (version 9.4 patch 03) simulations with different hadronic physics models. These comparisons demonstrate the importance of using high precision treatment of low-energy neutrons for tungsten absorbers, while an overall good agreement between data and simulations for all considered models is observed for steel.

  19. Proposal for initial collection efficiency models for direct granular upflow filtration

    Directory of Open Access Journals (Sweden)

    Alexandre Botari

    2015-05-01

    Full Text Available Mathematical models of the filtration process are based on the mass balance in the filter bed. Models of the filtration phenomenon describe the mass balance in bed filtration in terms of particle removal mechanisms, and allow for the determination of global particle removal efficiencies. This phenomenon is defined in terms of the geometry and the characteristic elements of granule collectors, particles and fluid, and the composition of the balance of forces that act in the particle collector system. This type of resolution is well known as the trajectory analysis theory. Particle trajectory analysis by mathematical correlation of the dimensionless numbers that represent fluid and particle characteristics is considered the main approach for mathematically modeling the initial collection efficiency of particle removal in water filtration. The existing initial collection efficiency models are designed for downflow filtration. This study analyzes initial collection efficiency models, and proposes an adaptation of these models to direct upflow filtration in a granular bed of coarse sand and gravel, taking into account the contribution of the gravitational factor of the settling removal efficiency in the proposal of initial collection efficiency models.

  20. A multilayer shallow model for dry granular flows with the $\\mu(I)$ rheology: Application to granular collapse on erodible beds

    CERN Document Server

    Fernández-Nieto, Enrique D; Mangeney, Anne; Narbona-Reina, Gladys

    2015-01-01

    In this work we present a multilayer shallow model to approximate the Navier-Stokes equations with hydrostatic pressure and the $\\mu(I)$-rheology. The main advantages of this approximation are (i) the low cost associated with the numerical treatment of the free surface of the modelled flows, (ii) exact conservation of mass and (iii) the ability to compute 3D profiles of the velocities in the directions along and normal to the slope. The derivation of the model follows [14] and introduces a dimensional analysis based on the shallow flow hypothesis. The proposed first order multilayer model fully satisfies a dissipative energy equation. A comparison with an analytical solution with a non-constant normal profile of the downslope velocity demonstrates the accuracy of the numerical model. Finally, by comparing the numerical results with experimental data, we show that the proposed multilayer model with the $\\mu(I)$-rheology reproduces qualitatively the effect of the erodible bed on granular flow dynamics and depos...

  1. Creep stability of the proposed AIDA mission target 65803 Didymos: I. Discrete cohesionless granular physics model

    Science.gov (United States)

    Zhang, Yun; Richardson, Derek C.; Barnouin, Olivier S.; Maurel, Clara; Michel, Patrick; Schwartz, Stephen R.; Ballouz, Ronald-Louis; Benner, Lance A. M.; Naidu, Shantanu P.; Li, Junfeng

    2017-09-01

    As the target of the proposed Asteroid Impact & Deflection Assessment (AIDA) mission, the near-Earth binary asteroid 65803 Didymos represents a special class of binary asteroids, those whose primaries are at risk of rotational disruption. To gain a better understanding of these binary systems and to support the AIDA mission, this paper investigates the creep stability of the Didymos primary by representing it as a cohesionless self-gravitating granular aggregate subject to rotational acceleration. To achieve this goal, a soft-sphere discrete element model (SSDEM) capable of simulating granular systems in quasi-static states is implemented and a quasi-static spin-up procedure is carried out. We devise three critical spin limits for the simulated aggregates to indicate their critical states triggered by reshaping and surface shedding, internal structural deformation, and shear failure, respectively. The failure condition and mode, and shear strength of an aggregate can all be inferred from the three critical spin limits. The effects of arrangement and size distribution of constituent particles, bulk density, spin-up path, and interparticle friction are numerically explored. The results show that the shear strength of a spinning self-gravitating aggregate depends strongly on both its internal configuration and material parameters, while its failure mode and mechanism are mainly affected by its internal configuration. Additionally, this study provides some constraints on the possible physical properties of the Didymos primary based on observational data and proposes a plausible formation mechanism for this binary system. With a bulk density consistent with observational uncertainty and close to the maximum density allowed for the asteroid, the Didymos primary in certain configurations can remain geo-statically stable without requiring cohesion.

  2. Fracture of granular materials composed of arbitrary grain shapes: A new cohesive interaction model

    Science.gov (United States)

    Neveu, A.; Artoni, R.; Richard, P.; Descantes, Y.

    2016-10-01

    Discrete Element Methods (DEM) are a useful tool to model the fracture of cohesive granular materials. For this kind of application, simple particle shapes (discs in 2D, spheres in 3D) are usually employed. However, dealing with more general particle shapes allows to account for the natural heterogeneity of grains inside real materials. We present a discrete model allowing to mimic cohesion between contacting or non-contacting particles whatever their shape in 2D and 3D. The cohesive interactions are made of cohesion points placed on interacting particles, with the aim of representing a cohesive phase lying between the grains. Contact situations are solved according to unilateral contact and Coulomb friction laws. In order to test the developed model, 2D unixial compression simulations are performed. Numerical results show the ability of the model to mimic the macroscopic behavior of an aggregate grain subject to axial compression, as well as fracture initiation and propagation. A study of the influence of model and sample parameters provides important information on the ability of the model to reproduce various behaviors.

  3. Modelling Methane Production and Sulfate Reduction in Anaerobic Granular Sludge Reactor with Ethanol as Electron Donor

    Science.gov (United States)

    Sun, Jing; Dai, Xiaohu; Wang, Qilin; Pan, Yuting; Ni, Bing-Jie

    2016-10-01

    In this work, a mathematical model based on growth kinetics of microorganisms and substrates transportation through biofilms was developed to describe methane production and sulfate reduction with ethanol being a key electron donor. The model was calibrated and validated using experimental data from two case studies conducted in granule-based Upflow Anaerobic Sludge Blanket reactors. The results suggest that the developed model could satisfactorily describe methane and sulfide productions as well as ethanol and sulfate removals in both systems. The modeling results reveal a stratified distribution of methanogenic archaea, sulfate-reducing bacteria and fermentative bacteria in the anaerobic granular sludge and the relative abundances of these microorganisms vary with substrate concentrations. It also indicates sulfate-reducing bacteria can successfully outcompete fermentative bacteria for ethanol utilization when COD/SO42‑ ratio reaches 0.5. Model simulation suggests that an optimal granule diameter for the maximum methane production efficiency can be achieved while the sulfate reduction efficiency is not significantly affected by variation in granule size. It also indicates that the methane production and sulfate reduction can be affected by ethanol and sulfate loading rates, and the microbial community development stage in the reactor, which provided comprehensive insights into the system for its practical operation.

  4. Compaction dynamics of wet granular packings

    Science.gov (United States)

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

    2013-03-01

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

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

    Science.gov (United States)

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

    2009-04-01

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

  6. Numerical simulation of failure behavior of granular debris flows based on flume model tests.

    Science.gov (United States)

    Zhou, Jian; Li, Ye-xun; Jia, Min-cai; Li, Cui-na

    2013-01-01

    In this study, the failure behaviors of debris flows were studied by flume model tests with artificial rainfall and numerical simulations (PFC(3D)). Model tests revealed that grain sizes distribution had profound effects on failure mode, and the failure in slope of medium sand started with cracks at crest and took the form of retrogressive toe sliding failure. With the increase of fine particles in soil, the failure mode of the slopes changed to fluidized flow. The discrete element method PFC(3D) can overcome the hypothesis of the traditional continuous medium mechanic and consider the simple characteristics of particle. Thus, a numerical simulations model considering liquid-solid coupled method has been developed to simulate the debris flow. Comparing the experimental results, the numerical simulation result indicated that the failure mode of the failure of medium sand slope was retrogressive toe sliding, and the failure of fine sand slope was fluidized sliding. The simulation result is consistent with the model test and theoretical analysis, and grain sizes distribution caused different failure behavior of granular debris flows. This research should be a guide to explore the theory of debris flow and to improve the prevention and reduction of debris flow.

  7. Numerical Simulation of Failure Behavior of Granular Debris Flows Based on Flume Model Tests

    Directory of Open Access Journals (Sweden)

    Jian Zhou

    2013-01-01

    Full Text Available In this study, the failure behaviors of debris flows were studied by flume model tests with artificial rainfall and numerical simulations (PFC3D. Model tests revealed that grain sizes distribution had profound effects on failure mode, and the failure in slope of medium sand started with cracks at crest and took the form of retrogressive toe sliding failure. With the increase of fine particles in soil, the failure mode of the slopes changed to fluidized flow. The discrete element method PFC3D can overcome the hypothesis of the traditional continuous medium mechanic and consider the simple characteristics of particle. Thus, a numerical simulations model considering liquid-solid coupled method has been developed to simulate the debris flow. Comparing the experimental results, the numerical simulation result indicated that the failure mode of the failure of medium sand slope was retrogressive toe sliding, and the failure of fine sand slope was fluidized sliding. The simulation result is consistent with the model test and theoretical analysis, and grain sizes distribution caused different failure behavior of granular debris flows. This research should be a guide to explore the theory of debris flow and to improve the prevention and reduction of debris flow.

  8. A theoretical model for calculation of the detective quantum efficiency in granular scintillators

    Energy Technology Data Exchange (ETDEWEB)

    Cavouras, D. E-mail: cavouras@hol.gr; Kandarakis, I.; Tsoukos, S.; Kateris, A.; Nomicos, C.D.; Panayiotakis, G.S

    2001-11-01

    A theoretical model has been developed for calculating the detective quantum efficiency (DQE) of scintillators, by taking into account the internal structure of granular scintillators often used in medical imaging detectors. Scintillators were considered to consist of N elementary thin layers containing spherical scintillating grains of equal size. Grains were assumed to be regularly distributed within each thin layer, the thickness of the latter being equal to the grain diameter. Values of the X-ray absorption and X-ray attenuation coefficients, of the intrinsic X-ray to light conversion efficiency and of the optical scattering and absorption coefficients were used as input data to the model. Optical scattering and optical absorption coefficients were determined by fitting the model to experimental luminescence data. The model was employed to calculate the detective quantum efficiency of La{sub 2}O{sub 2}S:Tb, Y{sub 2}O{sub 2}S:Tb, Y{sub 2}O{sub 2}S:Eu, ZnSCdS:Ag, ZnSCdS:Au,Cu scintillators. Results of the calculations were found close to values published in previous studies.

  9. Nonergodic dynamics of force-free granular gases

    OpenAIRE

    Bodrova, Anna; Chechkin, Aleksei V.; Cherstvy, Andrey G.; Metzler, Ralf

    2015-01-01

    We study analytically and by event-driven molecular dynamics simulations the nonergodic and aging properties of force-free cooling granular gases with both constant and velocity-dependent (viscoelastic) restitution coefficient $\\varepsilon$ for particle pair collisions. We compare the granular gas dynamics with an effective single particle stochastic model based on an underdamped Langevin equation with time dependent diffusivity. We find that both models share the same behavior of the ensembl...

  10. Radiation hardness and precision timing study of Silicon detectors for the CMS High Granularity Calorimeter (HGC)

    CERN Document Server

    Curras, E; Gallrapp, C; Gray, L; Mannelli, M; Meridiani, P; Moll, M; Nourbakhsh, S; Scharf, C; Silva, P; Steinbrueck, G; Tabarelli de Fatis, T; Vila, I

    2016-01-01

    The high luminosity upgraded LHC or Phase-II is expected to increase the instantaneous luminosity by a factor of 10 beyond the LHC's design value, expecting to deliver 250 fb^−1 per year for a further 10 years of operation. Under these conditions the performance degradation due to integrated radiation dose will need to be addressed. The CMS collaboration is planning to upgrade the forward calorimeters. The replacement is called the High Granularity Calorimeter (HGC) and it will be realized as a sampling calorimeter with layers of silicon detectors interleaved. The sensors will be realized as pad detectors with sizes of less that ∼1.0 cm^2 and an active thickness between 100 and 300 μm depending on the position, respectively, the expected radiation levels. For an integrated luminosity of 3000 fb^−1, the electromagnetic calorimetry will sustain integrated doses of 1.5 MGy (150 Mrads) and neutron fluences up to 10^16 neq/cm^2. A radiation tolerance study after neutron irradiation of 300, 200, and 100 μ...

  11. Radiation hardness and precision timing study of Silicon Detectors for the CMS High Granularity Calorimeter (HGCAL)

    CERN Document Server

    Curras Rivera, Esteban

    2016-01-01

    The high luminosity LHC (HL-LHC or Phase-II) is expected to increase the instantaneous luminosity of the LHC by a factor of about five, delivering about 250 fba-1 per year between 2025 and 2035. Under these conditions the performance degradation of detectors due to integrated radiation dose/fluence will need to be addressed. The CMS collaboration is planning to upgrade many components, including the forward calorimeters. The replacement for the existing endcap preshower, electromagnetic and hadronic calorimeters is called the High Granularity Calorimeter (HGCAL) and it will be realized as a sampling calorimeter, including 30 layers of silicon detectors totalling 600m^2. The sensors will be realized as pad detectors with cell sizes of between 0.5-1.0 cm^2 and an active thickness between 100 um and 300 um depending on their location in the endcaps the thinner sensors will be used in the highest radiation environment. For an integrated luminosity of 3000 fba-1, the electromagnetic calorimetry will sustain integ...

  12. Stress distribution retrieval in granular materials: A multi-scale model and digital image correlation measurements

    Science.gov (United States)

    Bruno, Luigi; Decuzzi, Paolo; Gentile, Francesco

    2016-01-01

    The promise of nanotechnology lies in the possibility of engineering matter on the nanoscale and creating technological interfaces that, because of their small scales, may directly interact with biological objects, creating new strategies for the treatment of pathologies that are otherwise beyond the reach of conventional medicine. Nanotechnology is inherently a multiscale, multiphenomena challenge. Fundamental understanding and highly accurate predictive methods are critical to successful manufacturing of nanostructured materials, bio/mechanical devices and systems. In biomedical engineering, and in the mechanical analysis of biological tissues, classical continuum approaches are routinely utilized, even if these disregard the discrete nature of tissues, that are an interpenetrating network of a matrix (the extra cellular matrix, ECM) and a generally large but finite number of cells with a size falling in the micrometer range. Here, we introduce a nano-mechanical theory that accounts for the-non continuum nature of bio systems and other discrete systems. This discrete field theory, doublet mechanics (DM), is a technique to model the mechanical behavior of materials over multiple scales, ranging from some millimeters down to few nanometers. In the paper, we use this theory to predict the response of a granular material to an external applied load. Such a representation is extremely attractive in modeling biological tissues which may be considered as a spatial set of a large number of particulate (cells) dispersed in an extracellular matrix. Possibly more important of this, using digital image correlation (DIC) optical methods, we provide an experimental verification of the model.

  13. Continuous Time Model Estimation

    OpenAIRE

    Carl Chiarella; Shenhuai Gao

    2004-01-01

    This paper introduces an easy to follow method for continuous time model estimation. It serves as an introduction on how to convert a state space model from continuous time to discrete time, how to decompose a hybrid stochastic model into a trend model plus a noise model, how to estimate the trend model by simulation, and how to calculate standard errors from estimation of the noise model. It also discusses the numerical difficulties involved in discrete time models that bring about the unit ...

  14. Development of a fluidized bed agglomeration modeling methodology to include particle-level heterogeneities in ash chemistry and granular physics

    Science.gov (United States)

    Khadilkar, Aditi B.

    The utility of fluidized bed reactors for combustion and gasification can be enhanced if operational issues such as agglomeration are mitigated. The monetary and efficiency losses could be avoided through a mechanistic understanding of the agglomeration process and prediction of operational conditions that promote agglomeration. Pilot-scale experimentation prior to operation for each specific condition can be cumbersome and expensive. So the development of a mathematical model would aid predictions. With this motivation, the study comprised of the following model development stages- 1) development of an agglomeration modeling methodology based on binary particle collisions, 2) study of heterogeneities in ash chemical composition and gaseous atmosphere, 3) computation of a distribution of particle collision frequencies based on granular physics for a poly-disperse particle size distribution, 4) combining the ash chemistry and granular physics inputs to obtain agglomerate growth probabilities and 5) validation of the modeling methodology. The modeling methodology comprised of testing every binary particle collision in the system for sticking, based on the extent of dissipation of the particles' kinetic energy through viscous dissipation by slag-liquid (molten ash) covering the particles. In the modeling methodology developed in this study, thermodynamic equilibrium calculations are used to estimate the amount of slag-liquid in the system, and the changes in particle collision frequencies are accounted for by continuously tracking the number density of the various particle sizes. In this study, the heterogeneities in chemical composition of fuel ash were studied by separating the bulk fuel into particle classes that are rich in specific minerals. FactSage simulations were performed on two bituminous coals and an anthracite to understand the effect of particle-level heterogeneities on agglomeration. The mineral matter behavior of these constituent classes was studied

  15. The rise of granular computing

    Institute of Scientific and Technical Information of China (English)

    YAO Yi-yu

    2008-01-01

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

  16. Lightweight Expression of Granular Objects (LEGO) Content Modeling Using the SNOMED CT Observables Model to Represent Nursing Assessment Data.

    Science.gov (United States)

    Johnson, Christie

    2016-01-01

    This poster presentation presents a content modeling strategy using the SNOMED CT Observable Model to represent large amounts of detailed clinical data in a consistent and computable manner that can support multiple use cases. Lightweight Expression of Granular Objects (LEGOs) represent question/answer pairs on clinical data collection forms, where a question is modeled by a (usually) post-coordinated SNOMED CT expression. LEGOs transform electronic patient data into a normalized consumable, which means that the expressions can be treated as extensions of the SNOMED CT hierarchies for the purpose of performing subsumption queries and other analytics. Utilizing the LEGO approach for modeling clinical data obtained from a nursing admission assessment provides a foundation for data exchange across disparate information systems and software applications. Clinical data exchange of computable LEGO patient information enables the development of more refined data analytics, data storage and clinical decision support.

  17. A rough-granular computing in discovery of process models from data and domain knowledge

    Institute of Scientific and Technical Information of China (English)

    NGUYEN Hung Son; SKOWRON Andrzej

    2008-01-01

    The rapid expansion of the Internet has resulted not only in the ever growing amount of data therein stored, but also in the burgeoning complexity of the concepts and phenomena pertaining to those data. This issue has been vividly com- pared by the renowned statistician, prof. Friedman of Stanford University, to the advances in human mobility from the pe- riod of walking afoot to the era of jet travel. These essential changes in data have brought new challenges to the develop- ment of new data mining methods, especially that the treatment of these data increasingly involves complex processes that e- lude classic modeling paradigms. "Hot" datasets like biomedical, financial or net user behavior data are just a few examples. Mining such temporal or stream data is on the agenda of many research centers and companies worldwide. In the data min- ing community, there is a rapidly growing interest in developing methods for process mining, e. g. , for discovery of struc- tures of temporal processes from data. Works on process mining have recently been undertaken by many renowned centers worldwide. This research is also related to functional data analysis , cognitive networks , and dynamical system modeling, e. g. , in biology. In the lecture, we outline an approach to discovery of processes from data and domain knowledge which is based on the rough-granular computing.

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

    Science.gov (United States)

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

    2009-09-01

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

  19. Physical modelling of rainfall-induced flow failures in loose granular soils

    Science.gov (United States)

    Take, W. A.; Beddoe, R. A.

    2015-09-01

    The tragic consequences of the March 2014 Oso landslide in Washington, USA were particularly high due to the mobility of the landslide debris. Confusingly, a landslide occurred at that exact same location a number of years earlier, but simply slumped into the river at the toe of the slope. Why did these two events differ so drastically in their mobility? Considerable questions remain regarding the conditions required to generate flow failures in loose soils. Geotechnical centrifuge testing, in combination with high-speed cameras and advanced image analysis has now provided the landslides research community with a powerful new tool to experimentally investigate the complex mechanics leading to high mobility landslides. This paper highlights recent advances in our understanding of the process of static liquefaction in loose granular soil slopes achieved through observations of highly-instrumented physical models. In particular, the paper summarises experimental results aimed to identify the point of initiation of the chain-reaction required to trigger liquefaction flow failures, to assess the effect of slope inclination on the likelihood of a flowslide being triggered, and to quantify the effect of antecedent groundwater levels on the distal reach of landslide debris with the objective of beginning to explain why neighbouring slopes can exhibit such a wide variation in landslide travel distance upon rainfall-triggering.

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

    Science.gov (United States)

    Bartzke, Gerhard; Kuhlmann, Jannis; Huhn, Katrin

    2016-04-01

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

  1. Distribution Network Fault Diagnosis Method Based on Granular Computing-BP

    Directory of Open Access Journals (Sweden)

    CHEN Zhong-xiao

    2013-01-01

    Full Text Available To deal with the complexity and uncertainty of distribution network fault information, a method of fault diagnosis based on granular computing and BP is proposed. This method uses attribute reduction advantages of granular computing theory and self-learning and knowledge acquisition ability of BP neural network. It put granular computing theory as the front-end processor of the BP neural network, namely simplify primitive information making use of granular computing reduction, and according to the concepts of relative granularity and significance of attributes based on binary granular computing are proposed to select input of BP, thereby reducing solving scale, and then construct neural network based on the minimum attribute sets, using BP neural network to model and parameter identify, reduce the BP study training time, improve the accuracy of the fault diagnosis. The distribution network example verifies the rationality and effectiveness of the proposed method.

  2. Investigation of Fast Timing Capabilities of Silicon Sensors for the CMS High Granularity Calorimeter at HL-LHC

    CERN Document Server

    Apresyan, Artur

    2016-01-01

    The High Granularity Calorimeter (HGCAL) is the technology choice of the CMS collaboration for the endcap calorimetry upgrade planned to cope with the harsh radiation and unprecedented in-time event pileup projected at the High Luminosity-LHC era. In this context, profiting from fast-timing information (~tens of picoseconds) embedded in the calorimeter would represent a unique capability for resolving information from individual collisions at the HL-LHC. This will enhance the reconstruction and physics capabilities of the CMS detector in terms of pileup mitigation and particle identification. The HGCAL is realized as a sampling calorimeter, including 40 layers of silicon pad detectors with pad areas of 0.5 â?? 1.0 cm^2 and three active thicknesses 320, 200 and 120 μm. Prototype p-in-n and n-in-p 5x5mm^2 silicon pads, with thicknesses of 285, 211 and 133μm, were tested with high-energy electrons at the CERN SPS. We present the motivation for this study including the concept and use of fast-timing in th...

  3. DEM/CFD modelling of the deposition of dilute granular systems in a vertical container

    Institute of Scientific and Technical Information of China (English)

    YU Shen; GUO Yu; WU ChuanYu

    2009-01-01

    Deposition of granular materials into a container is a general industrial packing process. In this study, the deposition behaviour of dilute granular mixtures consisting of two types of particles that were of the same particle size but different particle densities in the presence of air was numerically analyzed using a coupled discrete element method (DEM) and computational fluid dynamics (CFD). Bilayer gra-nular mixtures with light particles at bottom and heavy particles at top were first simulated. It was found that the presence of air significantly affected the flow behaviour of the bilayer mixtures. For the system with a relatively low initial void fraction, the air entrapped inside the container escaped through the dilated zones induced due to the friction between the powder bed and wall surfaces. The escaping air streams entrained light particles that were originally located at the bottom of the granular system. Consequently, these light particles were migrated to the top of the granular bed at the end of deposition process. More light particles were migrated when the deposition distance was increased. For the sys-tem with a high initial void fraction, some light particles penetrated into the top layer of heavy particles and created a mixing zone. Deposition of random mixtures with different initial void fractions was also investigated and the influence of initial void fraction on the segregation behaviour was explored as well. It was found that the increase of void fraction promoted segregation during the deposition in air. It was demonstrated that, for granular mixtures consisting of particles of different air sensitivities, the pres-ence of air had a significant impact on the mixing and segregation behaviour during the deposition.

  4. Rough-Granular Computing

    Institute of Scientific and Technical Information of China (English)

    Andrzej Skowron

    2006-01-01

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

  5. Modeling and simulations of the removal of formaldehyde using silver nano-particles attached to granular activated carbon.

    Science.gov (United States)

    Shin, SeungKyu; Song, JiHyeon

    2011-10-30

    A combined reaction, consisting of granular activated carbon (GAC) adsorption and catalytic oxidation, has been proposed to improve the removal efficiencies of formaldehyde, one of the major indoor air pollutants. In this study, silver nano-particles attached onto the surface of GAC (Ag-GAC) using the sputtering method were evaluated for the simultaneous catalytic oxidation and adsorption of formaldehyde. The evolution of CO(2) from the silver nano-particles indicated that formaldehyde was catalytically oxidized to its final product, with the oxidation kinetics expressed as pseudo-first order. In addition, a packed column test showed that the mass of formaldehyde removed by the Ag-GAC was 2.4 times higher than that by the virgin GAC at a gas retention time of 0.5s. However, a BET analysis showed that the available surface area and micro-pore volume of the Ag-GAC were substantially decreased due to the deposition of the silver nano-particles. To simulate the performance of the Ag-GAC, the homogeneous surface diffusion model (HSDM), developed for the prediction of the GAC column adsorption, was modified to incorporate the catalytic oxidation taking place on the Ag-GAC surface. The modified HSDM demonstrated that numerical simulations were consistent with the experimental data collected from the Ag-GAC column tests. The model predictions implied that the silver nano-particles deposited on the GAC reduced the adsorptive capacity due to decreasing the available surface for the diffusion of formaldehyde into the GAC, but the overall mass of formaldehyde removed by the Ag-GAC was increased due to catalytic oxidation as a function of the ratio of the surface coverage by the nano-particles.

  6. Multi-scale coupling strategy for fully two-dimensional and depth-averaged models for granular flows

    Science.gov (United States)

    Pudasaini, Shiva P.; Domnik, Birte; Miller, Stephen A.

    2013-04-01

    We developed a full two-dimensional Coulomb-viscoplastic model and applied it for inclined channel flows of granular materials from initiation to their deposition. The model includes the basic features and observed phenomena in dense granular flows like the exhibition of a yield strength and a non-zero slip velocity. A pressure-dependent yield strength is proposed to account for the frictional nature of granular materials. The yield strength can be related to the internal friction angle of the material and plays an important role, for example, in deposition processes. The interaction of the flow with the solid boundary is modelled by a pressure and rate-dependent Coulomb-viscoplastic sliding law. We developed an innovative multi-scale strategy to couple the full two-dimensional, non depth-averaged model (N-DAM) with a one-dimensional, depth-averaged model (DAM). The coupled model reduces computational complexity dramatically by using DAM only in regions with smooth changes of flow variables. The numerics uses N-DAM in regions where depth-averaging becomes inaccurate, for instance, in the initiation and deposition regions, and (particularly) when the flow hits an obstacle or a defense structure. In these regions, momentum transfer must be, and is, considered in all directions. We observe very high coupling performance, and show that the numerical results deviate only slightly from results of the much more cumbersome full two-dimensional model. This shows that the coupled model, which retains all the basic physics of the flow, is an attractive alternative to an expensive, full two-dimensional simulations. We compare simulation results with different experimental data for shock waves appearing in rapid granular flows down inclined channels and impacting a wall. The model predicts the evolution of the strong shock wave and the impact force on a rigid wall for different inclination angles and sliding surfaces. It is demonstrated that the internal friction angle plays an

  7. Vibrationally-Fluidized Granular Flows: Impact and Bulk Velocity Measurements Compared with Discrete Element and Continuum Models

    Science.gov (United States)

    Hashemnia, Kamyar

    A new laser displacement probe was developed to measure the impact velocities of particles within vibrationally-fluidized beds. The sensor output was also used to measure bulk flow velocity along the probe window and to provide a measure of the media packing. The displacement signals from the laser sensors were analyzed to obtain the probability distribution functions of the impact velocity of the particles. The impact velocity was affected by the orientation of the laser probe relative to the bulk flow velocity, and the density and elastic properties of the granular media. The impact velocities of the particles were largely independent of their bulk flow speed and packing density. Both the local impact and bulk flow velocities within a tub vibratory finisher were predicted using discrete element modelling (DEM) and compared to the measured values for spherical steel media. It was observed that the impact and bulk flow velocities were relatively insensitive to uncertainties in the contact coefficients of friction and restitution. It was concluded that the predicted impact and bulk flow velocities were dependent on the number of layers in the model. Consequently, the final DE model mimicked the key aspects of the experimental setup, including the submerged laser sensor. The DE method predictions of both impact velocity and bulk flow velocity were in reasonable agreement with the experimental measurements, with maximum differences of 20% and 30%, respectively. Discrete element modeling of granular flows is effective, but requires large numerical models. In an effort to reduce computational effort, this work presents a finite element (FE) continuum model of a vibrationally-fluidized granular flow. The constitutive equations governing the continuum model were calibrated using the discrete element method (DEM). The bulk flow behavior of the equivalent continuum media was then studied using both Lagrangian and Eulerian FE formulations. The bulk flow velocities predicted

  8. Modeling Complex Time Limits

    Directory of Open Access Journals (Sweden)

    Oleg Svatos

    2013-01-01

    Full Text Available In this paper we analyze complexity of time limits we can find especially in regulated processes of public administration. First we review the most popular process modeling languages. There is defined an example scenario based on the current Czech legislature which is then captured in discussed process modeling languages. Analysis shows that the contemporary process modeling languages support capturing of the time limit only partially. This causes troubles to analysts and unnecessary complexity of the models. Upon unsatisfying results of the contemporary process modeling languages we analyze the complexity of the time limits in greater detail and outline lifecycles of a time limit using the multiple dynamic generalizations pattern. As an alternative to the popular process modeling languages there is presented PSD process modeling language, which supports the defined lifecycles of a time limit natively and therefore allows keeping the models simple and easy to understand.

  9. Grain-scale deformation in granular materials: time-lapse XCT-imaging of a deforming reservoir sandstone

    Science.gov (United States)

    Hangx, Suzanne; Cordonnier, Benoît; Pijnenburg, Ronald; Renard, François; Spiers, Christopher

    2017-04-01

    Relating macroscopic deformation of granular media to grain-scale processes, such as grain fracturing, has been a focus of many studies. Understanding these processes is key for predicting surface subsidence and induced seismicity caused by hydrocarbon depletion, the hydraulic fracturing response of geothermal reservoirs, and post-seismic crustal deformation. With the development of state-of-the-art techniques, such as time-lapse X-ray tomography imaging during triaxial deformation, new avenues to investigate the operating mechanisms have opened up. As a first step to understanding grain-scale deformation processes, we performed a deformation experiment on highly porous sandstone, obtained from a depleting gas reservoir, using a novel small-scale triaxial deformation apparatus coupled to high-resolution 4D X-ray tomography, available at the European Synchrotron Radiation Facility (ESRF, Grenoble) and Université Grenoble Alpes. This state-of-the-art apparatus allows for 3D time-lapse imaging of samples, while deforming at pressure, temperature and fluid flow conditions relevant for geological reservoirs. We performed our experiment at relevant in-situ reservoir conditions (T = 100˚ C, 10 MPa pore pressure, 40 MPa effective confining pressure). Axial stress was increased step-wise until failure occurred, while continuously imaging deformation. This enables us to monitor progressive grain failure, and strain localisation, during deformation in real-time. Though the vast amount of data obtained from even a single test poses challenges for data analysis, this presentation will address the first results obtained from this experiment.

  10. Constitutive models for granular materials including quasi-static frictional behaviour: Toward a thermodynamic theory of plasticity

    Science.gov (United States)

    Svendsen, B.; Hutter, K.; Laloui, L.

    This work deals with the thermodynamic formulation of constitutive models for materials whose quasi-static behaviour is governed by internal friction, e.g., dry granular materials. The process of internal friction is represented here phenomenologically with the help of a second-order, symmetric-tensor-valued internal variable. A general class of models for the evolution of this variable is considered, including as special cases a hypoelastic-like form for this relation as well as the hypoplastic form of Kolymbas (1991). The thermodynamic formulation is carried out in the context of the Müller-Liu entropy principle. Among other things, it is shown that for the hypoelastic-type models, a true equilibrium inelastic Cauchy stress exists. On the other hand, such a stress does not exist for the hypoplastic model due to its rate-independence and incremental non-linearity. With the help of a slight generalization of the notion of thermodynamic equilibrium, i.e., to thermodynamic ``quasi-equilibrium,'' however, such a Cauchy stress can be formulated for the hypoplastic model. As it turns out, this quasi-equilibrium for the Cauchy stress represents a thermodynamic generalization of the so-called quasi-static stress postulated for example by Goddard (1986) in the context of his viscoplastic model for a frictional-dissipative, and in particular for granular, materials.

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

    Science.gov (United States)

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

    2017-06-01

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

  12. Discrete element modeling of inherently anisotropic granular assemblies with polygonal particles

    Institute of Scientific and Technical Information of China (English)

    Ehsan Seyedi Hosseininia

    2012-01-01

    In the present article,we study the effect of inherent anisotropy,i.e.,initial bedding angle of particles and associated voids on macroscopic mechanical behavior of granular materials,by numerical simulation of several biaxial compression tests using the discrete element method (DEM).Particle shape is considered to be irregular convex-polygonal.The effect of inherent anisotropy is investigated by following the evolution of mobilized shear strength and volume change during loading.As experimental tests have already shown,numerical simulations also indicate that initial anisotropic condition has a great influence on the strength and deformational behavior of granular assemblies.Comparison of simulations with tests using oval particles,shows that angularity influences both the mobilized shear strength and the volume change regime,which originates from the interlocking resistance between particles.

  13. Toward Generalized Continuum Models of Granular Soil and Soil-Tire Interaction

    Science.gov (United States)

    2007-11-02

    Geomechanics , BIT Numerik Mathematik, International Journal of Solids and Structures. In addition, we have four more papers currently in review: one in...Methods in Geomechanics . 6. Technology Transfer Our group is collaborating with Dr. John Peters of the Geotechnical Laboratory at ERDC on a number of...Numerical and Analytical Methods in Geomechanics , in press [5] Walsh, S and Tordesillas, A (2004) “The stress response of a semi-infinite granular material

  14. A modified kinematic model for the discharge of a granular-like material from long vertical cylinders

    Science.gov (United States)

    Weir, Graham J.; Dolby, Carl E.

    1999-07-01

    The rapid and uncontrolled discharge of a large-sized granular-like material from a vertical cylinder is modelled assuming a modified kinematic relationship exists between granular pressure, speed and density. Discharge is driven by the initial Janssen pressure, and a Beverloo-type equation is derived for the initial discharge. A shock occurs at the bottom of the cylinder, and another upwards travelling shock separates static and moving material. The initial discharge is non-constant, with the constant density and discharge case violating the `entropy' condition. Two sets of characteristics are found : one travelling upwards, associated with the motion of voids; and the other travelling downwards, associated with work performed by the particle pressure. Contrary to hopper models, a low density of solids is predicted about the cylinder exit. The modified kinematic model allows density waves to travel either up or down through the cylinder, but the frequency and speed of the waves is not fixed uniquely by the model. The waves exhibit a saw-tooth behaviour, with a continuously increasing magnitude in flux at the orifice, interspersed with discontinuous decreases.

  15. Granular materials interacting with thin flexible rods

    Science.gov (United States)

    Neto, Alfredo Gay; Campello, Eduardo M. B.

    2017-04-01

    In this work, we develop a computational model for the simulation of problems wherein granular materials interact with thin flexible rods. We treat granular materials as a collection of spherical particles following a discrete element method (DEM) approach, while flexible rods are described by a large deformation finite element (FEM) rod formulation. Grain-to-grain, grain-to-rod, and rod-to-rod contacts are fully permitted and resolved. A simple and efficient strategy is proposed for coupling the motion of the two types (discrete and continuum) of materials within an iterative time-stepping solution scheme. Implementation details are shown and discussed. Validity and applicability of the model are assessed by means of a few numerical examples. We believe that robust, efficiently coupled DEM-FEM schemes can be a useful tool to the simulation of problems wherein granular materials interact with thin flexible rods, such as (but not limited to) bombardment of grains on beam structures, flow of granular materials over surfaces covered by threads of hair in many biological processes, flow of grains through filters and strainers in various industrial segregation processes, and many others.

  16. Granular materials interacting with thin flexible rods

    Science.gov (United States)

    Neto, Alfredo Gay; Campello, Eduardo M. B.

    2016-01-01

    In this work, we develop a computational model for the simulation of problems wherein granular materials interact with thin flexible rods. We treat granular materials as a collection of spherical particles following a discrete element method (DEM) approach, while flexible rods are described by a large deformation finite element (FEM) rod formulation. Grain-to-grain, grain-to-rod, and rod-to-rod contacts are fully permitted and resolved. A simple and efficient strategy is proposed for coupling the motion of the two types (discrete and continuum) of materials within an iterative time-stepping solution scheme. Implementation details are shown and discussed. Validity and applicability of the model are assessed by means of a few numerical examples. We believe that robust, efficiently coupled DEM-FEM schemes can be a useful tool to the simulation of problems wherein granular materials interact with thin flexible rods, such as (but not limited to) bombardment of grains on beam structures, flow of granular materials over surfaces covered by threads of hair in many biological processes, flow of grains through filters and strainers in various industrial segregation processes, and many others.

  17. On the similarity in shape between debris-flow channels and high-gradient flood channels: Initial insight from continuum models for granular and water flow

    Science.gov (United States)

    Kean, J. W.; McCoy, S. W.; Tucker, G. E.

    2011-12-01

    The cross-sectional shape of high-gradient bedrock channels carved by debris flows is often very similar to that of channels formed by fluvial erosion. Both tend to have narrow U-shapes with width-to-depth ratios much less than 10. Gullies and channels cut into colluvium by both water erosion and debris-flow erosion have similarly narrow geometries. Given that the physics governing debris flow and turbulent water flow are very different, why are channels eroded by these two processes so similar in shape? To begin to investigate this question, we conducted a series of numerical simulations using continuum models for the end-member cases of granular flow and water flow. Each model is used to evolve the steady-state channel shape formed by uniform flow of the respective material. The granular model is based on the constitutive equation for dense granular flow proposed by Jop et al. (Nature, 2006). They demonstrated that without any fitting parameters, a numerical model using this constitutive equation could reproduce the velocity and depth profiles observed in granular-flow laboratory experiments. The model for water flow uses a ray-isovel turbulence closure to calculate the boundary shear stress across the wetted perimeter of the channel. This fully predictive model has also been shown to be in good agreement with laboratory data. We start the calculations for the granular and water-flow cases by determining the velocity and boundary shear-stress fields in an initial V-shape cross section. We then erode both channels using a simple wear law scaled linearly by the bed-normal boundary shear stress. The calculation is repeated until the channel reaches an equilibrium shape. Initial comparisons of the granular and water-flow channels show that they have very similar width-to-depth ratios of about four, and only moderate differences in bottom geometries and boundary shear-stress distributions. The structure of the velocity field differs more substantially between the two

  18. Modeling of light dynamic cone penetration test - Panda 3 ® in granular material by using 3D Discrete element method

    Science.gov (United States)

    Tran, Quoc Anh; Chevalier, Bastien; Benz, Miguel; Breul, Pierre; Gourvès, Roland

    2017-06-01

    The recent technological developments made on the light dynamic penetration test Panda 3 ® provide a dynamic load-penetration curve σp - sp for each impact. This curve is influenced by the mechanical and physical properties of the investigated granular media. In order to analyze and exploit the load-penetration curve, a numerical model of penetration test using 3D Discrete Element Method is proposed for reproducing tests in dynamic conditions in granular media. All parameters of impact used in this model have at first been calibrated by respecting mechanical and geometrical properties of the hammer and the rod. There is a good agreement between experimental results and the ones obtained from simulations in 2D or 3D. After creating a sample, we will simulate the Panda 3 ®. It is possible to measure directly the dynamic load-penetration curve occurring at the tip for each impact. Using the force and acceleration measured in the top part of the rod, it is possible to separate the incident and reflected waves and then calculate the tip's load-penetration curve. The load-penetration curve obtained is qualitatively similar with that obtained by experimental tests. In addition, the frequency analysis of the measured signals present also a good compliance with that measured in reality when the tip resistance is qualitatively similar.

  19. Erosion dynamics of a wet granular medium.

    Science.gov (United States)

    Lefebvre, Gautier; Jop, Pierre

    2013-09-01

    Liquid may give strong cohesion properties to a granular medium, and confer a solidlike behavior. We study the erosion of a fixed circular aggregate of wet granular matter subjected to a flow of dry grains inside a half-filled rotating drum. During the rotation, the dry grains flow around the fixed obstacle. We show that its diameter decreases linearly with time for low liquid content, as wet grains are pulled out of the aggregate. This erosion phenomenon is governed by the properties of the liquids. The erosion rate decreases exponentially with the surface tension while it depends on the viscosity to the power -1. We propose a model based on the force fluctuations arising inside the flow, explaining both dependencies: The capillary force acts as a threshold and the viscosity controls the erosion time scale. We also provide experiments using different flowing grains, confirming our model.

  20. Dynamic Properties of Two-Dimensional Polydisperse Granular Gases

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    We propose a two-dimensional model of polydisperse granular mixtures with a power-law size distribution in the presence of stochastic driving. A fractal dimension D is introduced as a measurement of the inhomogeneity of the size distribution of particles. We define the global and partial granular temperatures of the multi-component mixture. By direct simulation Monte Carlo, we investigate how the inhomogeneity of the size distribution influences the dynamic properties of the mixture, focusing on the granular temperature, dissipated energy, velocity distribution, spatial clusterization, and collision time. We get the following results: a single granular temperature does not characterize a multi-component mixture and each species attains its own "granular temperature"; The velocity deviation from Gaussian distribution becomes more and more pronounced and the partial density of the assembly is more inhomogeneous with the increasing value of the fractal dimension D; The global granular temperature decreases and average dissipated energy per particle increases as the value of D augments.

  1. Localizing energy in granular materials

    CERN Document Server

    Przedborski, Michelle A; Sen, Surajit

    2016-01-01

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

  2. Periodic Time Series Models

    NARCIS (Netherlands)

    Ph.H.B.F. Franses (Philip Hans); R. Paap (Richard)

    2004-01-01

    textabstractThis book considers periodic time series models for seasonal data, characterized by parameters that differ across the seasons, and focuses on their usefulness for out-of-sample forecasting. Providing an up-to-date survey of the recent developments in periodic time series, the book

  3. Model Selection of Cooling Equipment for Granular Fertilizers%颗粒肥料冷却设备的选型

    Institute of Scientific and Technical Information of China (English)

    李秋萍; 程建伟; 邵国兴

    2011-01-01

    在颗粒肥料生产中,产品的冷却是直接影响产品包装及成品质量的重要过程之一.介绍了转鼓冷却器、流化床冷却器、波面冷却器等几种适合于颗粒肥料冷却的设备,并对它们的工作原理和性能特点作了简单介绍和评述,供用户在设备选型时参考.%In the production of granular fertilizers, product cooling is one of the important processes that affect directly the product packaging and quality. Several cooling facilities are described suitable for granular fertilizers, such as the rotary drum cooler, fluid-bed cooler, wave surface cooler, etc.A brief account and review are given of their working principles and performance characteristics, as a reference for users in their model selection of equipment.

  4. 一种基于多时间粒度的实时客流查询优化算法%An Optimization Algorithm of Real-time Customer-counting Query Based on Multiple Time Granularities

    Institute of Scientific and Technical Information of China (English)

    苏礼楷

    2011-01-01

    The real-time flow of customer data changed with time is classified as the time series. According to the receiving frequency , the relational model is applied for the storage of the customer data. In order to weaken the influence of the query efficiency of the real-time customer-counting by the receiving frequency, the views of the customer data with multiple time granularities are established and the query efficiency is improved.%随时间实时变化的客流数据属于时间序列数据,本文根据客流数据的接收频率,应用关系模型实现客流数据的存储建模;为了减弱数据采集频率对实时客流查询效率的影响,建立多时间粒度的客流视图,可提高实时客流查询的计算效率.

  5. Thermoelectric properties of nano-granular indium-tin-oxide within modified electron filtering model with chemisorption-type potential barriers

    Science.gov (United States)

    Brinzari, V.; Nika, D. L.; Damaskin, I.; Cho, B. K.; Korotcenkov, G.

    2016-07-01

    In this work, an approach to the numerical study of the thermoelectric parameters of nanoscale indium tin oxide (ITO, Sn content<10 at%) based on an electron filtering model (EFM) was developed. Potential barriers at grain boundaries were assumed to be responsible for a filtering effect. In the case of the dominant inelastic scattering of electrons, the maximal distance between potential barriers was limited in this modified model. The algorithm for such characteristic length calculation was proposed, and its value was evaluated for ITO. In addition, the contributions of different scattering mechanisms (SMs) in electron transport were examined. It was confirmed that in bulk ITO, the scattering on polar optical phonons (POPs) and ionized impurities dominates, limiting electron transport. In the framework of the filtering model, the basic thermoelectric parameters (i.e., electrical conductivity, mobility, Seebeck coefficient, and power factor (PF)) were calculated for ITO in the temperature range of 100-500 °C as a function of potential barrier height. The results demonstrated a sufficient rise of the Seebeck coefficient with an increase in barrier height and specific behavior of PF. It was found that PF is very sensitive to barrier height, and at its optimal value for granular ITO, it may exceed the PF for bulk ITO by 3-5 times. The PF maximum was achieved by band bending, slightly exceeding Fermi energy. The nature of surface potential barriers in nano-granular ITO with specific grains is due to the oxygen chemisorption effect, and this can be observed despite of the degeneracy of the conduction band (CB). This hypothesis and the corresponding calculations are in good agreement with recent experimental studies [Brinzari et al. Thin Solid Films 552 (2014) 225].

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

    Science.gov (United States)

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

    2014-12-01

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

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

    Science.gov (United States)

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

    2014-05-01

    characterize both the convergence of these grain-scale parameters toward the empirical coefficients of the macroscopic descriptions, and the deviations from continuum model predictions caused by nonlocal granular effects for quantities such as erosion rate. We will also summarize the context and implications of our work for both granular physics theory and granular flow hazard risk assessment.

  8. Langevin Simulation of Non-Uniform Granular Gases

    Institute of Scientific and Technical Information of China (English)

    张端明; 雷雅洁; 潘贵军; 郁伯铭

    2003-01-01

    We present and study a fractal model of a non-uniform granular system for the first time, based on which we numerically solve the dynamics actions in the system successfully in one-dimensional case. The multi-mixture is composed of N different particles, whose granularity distribution has the fractal characteristic. The particles are subject to inelastic mutual collisions and obey to Langevin equation between collisions. Far from the equilibrium,i.e. the given typical relaxation time T of the driving Brownian process is much larger than the mean collision time Tc, the results of simulation indicate that the degree of inhomogeneity in the granularity distribution signed by the fractal dimension D of size distribution has great influence on the dynamics actions of the system. The velocity distribution deviates obviously from the Gaussian distribution and the particles cluster more pronouncedly with the larger value of D in the system. The velocity distribution and spatial clusterization change with D are presented.

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

    Science.gov (United States)

    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.

  10. Modeling Granular Materials as Compressible Non-Linear Fluids: Heat Transfer Boundary Value Problems

    Energy Technology Data Exchange (ETDEWEB)

    Massoudi, M.C.; Tran, P.X.

    2006-01-01

    We discuss three boundary value problems in the flow and heat transfer analysis in flowing granular materials: (i) the flow down an inclined plane with radiation effects at the free surface; (ii) the natural convection flow between two heated vertical walls; (iii) the shearing motion between two horizontal flat plates with heat conduction. It is assumed that the material behaves like a continuum, similar to a compressible nonlinear fluid where the effects of density gradients are incorporated in the stress tensor. For a fully developed flow the equations are simplified to a system of three nonlinear ordinary differential equations. The equations are made dimensionless and a parametric study is performed where the effects of various dimensionless numbers representing the effects of heat conduction, viscous dissipation, radiation, and so forth are presented.

  11. Validation of GEANT4 Monte Carlo models with a highly granular scintillator-steel hadron calorimeter

    Science.gov (United States)

    Adloff, C.; Blaha, J.; Blaising, J.-J.; Drancourt, C.; Espargilière, A.; Gaglione, R.; Geffroy, N.; Karyotakis, Y.; Prast, J.; Vouters, G.; Francis, K.; Repond, J.; Schlereth, J.; Smith, J.; Xia, L.; Baldolemar, E.; Li, J.; Park, S. T.; Sosebee, M.; White, A. P.; Yu, J.; Buanes, T.; Eigen, G.; Mikami, Y.; Watson, N. K.; Mavromanolakis, G.; Thomson, M. A.; Ward, D. R.; Yan, W.; Benchekroun, D.; Hoummada, A.; Khoulaki, Y.; Apostolakis, J.; Dotti, A.; Folger, G.; Ivantchenko, V.; Uzhinskiy, V.; Benyamna, M.; Cârloganu, C.; Fehr, F.; Gay, P.; Manen, S.; Royer, L.; Blazey, G. C.; Dyshkant, A.; Lima, J. G. R.; Zutshi, V.; Hostachy, J.-Y.; Morin, L.; Cornett, U.; David, D.; Falley, G.; Gadow, K.; Göttlicher, P.; Günter, C.; Hermberg, B.; Karstensen, S.; Krivan, F.; Lucaci-Timoce, A.-I.; Lu, S.; Lutz, B.; Morozov, S.; Morgunov, V.; Reinecke, M.; Sefkow, F.; Smirnov, P.; Terwort, M.; Vargas-Trevino, A.; Feege, N.; Garutti, E.; Marchesini, I.; Ramilli, M.; Eckert, P.; Harion, T.; Kaplan, A.; Schultz-Coulon, H.-Ch; Shen, W.; Stamen, R.; Bilki, B.; Norbeck, E.; Onel, Y.; Wilson, G. W.; Kawagoe, K.; Dauncey, P. D.; Magnan, A.-M.; Bartsch, V.; Wing, M.; Salvatore, F.; Calvo Alamillo, E.; Fouz, M.-C.; Puerta-Pelayo, J.; Bobchenko, B.; Chadeeva, M.; Danilov, M.; Epifantsev, A.; Markin, O.; Mizuk, R.; Novikov, E.; Popov, V.; Rusinov, V.; Tarkovsky, E.; Kirikova, N.; Kozlov, V.; Smirnov, P.; Soloviev, Y.; Buzhan, P.; Ilyin, A.; Kantserov, V.; Kaplin, V.; Karakash, A.; Popova, E.; Tikhomirov, V.; Kiesling, C.; Seidel, K.; Simon, F.; Soldner, C.; Szalay, M.; Tesar, M.; Weuste, L.; Amjad, M. S.; Bonis, J.; Callier, S.; Conforti di Lorenzo, S.; Cornebise, P.; Doublet, Ph; Dulucq, F.; Fleury, J.; Frisson, T.; van der Kolk, N.; Li, H.; Martin-Chassard, G.; Richard, F.; de la Taille, Ch; Pöschl, R.; Raux, L.; Rouëné, J.; Seguin-Moreau, N.; Anduze, M.; Boudry, V.; Brient, J.-C.; Jeans, D.; Mora de Freitas, P.; Musat, G.; Reinhard, M.; Ruan, M.; Videau, H.; Bulanek, B.; Zacek, J.; Cvach, J.; Gallus, P.; Havranek, M.; Janata, M.; Kvasnicka, J.; Lednicky, D.; Marcisovsky, M.; Polak, I.; Popule, J.; Tomasek, L.; Tomasek, M.; Ruzicka, P.; Sicho, P.; Smolik, J.; Vrba, V.; Zalesak, J.; Belhorma, B.; Ghazlane, H.; Takeshita, T.; Uozumi, S.; Götze, M.; Hartbrich, O.; Sauer, J.; Weber, S.; Zeitnitz, C.

    2013-07-01

    Calorimeters with a high granularity are a fundamental requirement of the Particle Flow paradigm. This paper focuses on the prototype of a hadron calorimeter with analog readout, consisting of thirty-eight scintillator layers alternating with steel absorber planes. The scintillator plates are finely segmented into tiles individually read out via Silicon Photomultipliers. The presented results are based on data collected with pion beams in the energy range from 8 GeV to 100 GeV. The fine segmentation of the sensitive layers and the high sampling frequency allow for an excellent reconstruction of the spatial development of hadronic showers. A comparison between data and Monte Carlo simulations is presented, concerning both the longitudinal and lateral development of hadronic showers and the global response of the calorimeter. The performance of several GEANT4 physics lists with respect to these observables is evaluated.

  12. Validation of GEANT4 Monte Carlo Models with a Highly Granular Scintillator-Steel Hadron Calorimeter

    CERN Document Server

    Adloff, C; Blaising, J J; Drancourt, C; Espargiliere, A; Gaglione, R; Geffroy, N; Karyotakis, Y; Prast, J; Vouters, G; Francis, K; Repond, J; Schlereth, J; Smith, J; Xia, L; Baldolemar, E; Li, J; Park, S T; Sosebee, M; White, A P; Yu, J; Buanes, T; Eigen, G; Mikami, Y; Watson, N K; Mavromanolakis, G; Thomson, M A; Ward, D R; Yan, W; Benchekroun, D; Hoummada, A; Khoulaki, Y; Apostolakis, J; Dotti, A; Folger, G; Ivantchenko, V; Uzhinskiy, V; Benyamna, M; Cârloganu, C; Fehr, F; Gay, P; Manen, S; Royer, L; Blazey, G C; Dyshkant, A; Lima, J G R; Zutshi, V; Hostachy, J Y; Morin, L; Cornett, U; David, D; Falley, G; Gadow, K; Gottlicher, P; Gunter, C; Hermberg, B; Karstensen, S; Krivan, F; Lucaci-Timoce, A I; Lu, S; Lutz, B; Morozov, S; Morgunov, V; Reinecke, M; Sefkow, F; Smirnov, P; Terwort, M; Vargas-Trevino, A; Feege, N; Garutti, E; Marchesini, I; Ramilli, M; Eckert, P; Harion, T; Kaplan, A; Schultz-Coulon, H Ch; Shen, W; Stamen, R; Bilki, B; Norbeck, E; Onel, Y; Wilson, G W; Kawagoe, K; Dauncey, P D; Magnan, A M; Bartsch, V; Wing, M; Salvatore, F; Alamillo, E Calvo; Fouz, M C; Puerta-Pelayo, J; Bobchenko, B; Chadeeva, M; Danilov, M; Epifantsev, A; Markin, O; Mizuk, R; Novikov, E; Popov, V; Rusinov, V; Tarkovsky, E; Kirikova, N; Kozlov, V; Smirnov, P; Soloviev, Y; Buzhan, P; Ilyin, A; Kantserov, V; Kaplin, V; Karakash, A; Popova, E; Tikhomirov, V; Kiesling, C; Seidel, K; Simon, F; Soldner, C; Szalay, M; Tesar, M; Weuste, L; Amjad, M S; Bonis, J; Callier, S; Conforti di Lorenzo, S; Cornebise, P; Doublet, Ph; Dulucq, F; Fleury, J; Frisson, T; van der Kolk, N; Li, H; Martin-Chassard, G; Richard, F; de la Taille, Ch; Poschl, R; Raux, L; Rouene, J; Seguin-Moreau, N; Anduze, M; Boudry, V; Brient, J-C; Jeans, D; Mora de Freitas, P; Musat, G; Reinhard, M; Ruan, M; Videau, H; Bulanek, B; Zacek, J; Cvach, J; Gallus, P; Havranek, M; Janata, M; Kvasnicka, J; Lednicky, D; Marcisovsky, M; Polak, I; Popule, J; Tomasek, L; Tomasek, M; Ruzicka, P; Sicho, P; Smolik, J; Vrba, V; Zalesak, J; Belhorma, B; Ghazlane, H; Takeshita, T; Uozumi, S; Gotze, M; Hartbrich, O; Sauer, J; Weber, S; Zeitnitz, C

    2013-01-01

    Calorimeters with a high granularity are a fundamental requirement of the Particle Flow paradigm. This paper focuses on the prototype of a hadron calorimeter with analog readout, consisting of thirty-eight scintillator layers alternating with steel absorber planes. The scintillator plates are finely segmented into tiles individually read out via Silicon Photomultipliers. The presented results are based on data collected with pion beams in the energy range from 8GeV to 100GeV. The fine segmentation of the sensitive layers and the high sampling frequency allow for an excellent reconstruction of the spatial development of hadronic showers. A comparison between data and Monte Carlo simulations is presented, concerning both the longitudinal and lateral development of hadronic showers and the global response of the calorimeter. The performance of several GEANT4 physics lists with respect to these observables is evaluated.

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

    NARCIS (Netherlands)

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

    2000-01-01

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

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

    NARCIS (Netherlands)

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

    2001-01-01

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

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

    NARCIS (Netherlands)

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

    2000-01-01

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

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

    NARCIS (Netherlands)

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

    2001-01-01

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

  17. Breakthrough behavior of granular ferric hydroxide (GFH) fixed-bed adsorption filters: modeling and experimental approaches.

    Science.gov (United States)

    Sperlich, Alexander; Werner, Arne; Genz, Arne; Amy, Gary; Worch, Eckhard; Jekel, Martin

    2005-03-01

    Breakthrough curves (BTC) for the adsorption of arsenate and salicylic acid onto granulated ferric hydroxide (GFH) in fixed-bed adsorbers were experimentally determined and modeled using the homogeneous surface diffusion model (HSDM). The input parameters for the HSDM, the Freundlich isotherm constants and mass transfer coefficients for film and surface diffusion, were experimentally determined. The BTC for salicylic acid revealed a shape typical for trace organic compound adsorption onto activated carbon, and model results agreed well with the experimental curves. Unlike salicylic acid, arsenate BTCs showed a non-ideal shape with a leveling off at c/c0 approximately 0.6. Model results based on the experimentally derived parameters over-predicted the point of arsenic breakthrough for all simulated curves, lab-scale or full-scale, and were unable to catch the shape of the curve. The use of a much lower surface diffusion coefficient D(S) for modeling led to an improved fit of the later stages of the BTC shape, pointing on a time-dependent D(S). The mechanism for this time dependence is still unknown. Surface precipitation was discussed as one possible removal mechanism for arsenate besides pure adsorption interfering the determination of Freundlich constants and D(S). Rapid small-scale column tests (RSSCT) proved to be a powerful experimental alternative to the modeling procedure for arsenic.

  18. A High Granular Timing Detector for the Phase-II upgrade of the ATLAS Calorimeter system: detector concept description and first beam test results

    CERN Document Server

    Lacour, Didier; The ATLAS collaboration

    2017-01-01

    The expected increase of the particle flux at the high luminosity phase of the LHC (HL-LHC) with instantaneous luminosities up to L ≃ 7.5 × 1034 cm−2 s-1 will have a severe impact on the ATLAS detector performance. The pile-up is expected to increase on average to 200 interactions per bunch crossing. The reconstruction and trigger performance for electrons, photons as well as jets and transverse missing energy will be severely degraded in the end-cap and forward region, where the liquid Argon based electromagnetic calorimeter has coarser granularity compared to the central region. A High Granularity Timing Detector (HGTD) is proposed in front of the liquid Argon end-cap calorimeters for pile-up mitigation at Level-0 (L0) trigger level and in the offline reconstruction. This device should cover the pseudo-rapidity range of 2.4 to about 4.2. Four layers of Silicon sensors are foreseen to provide a precision timing information for minimum ionizing particle with a time resolution better than 50 pico-seconds ...

  19. Effect of Cohesion Uncertainty of Granular Materials on the Kinematics of Scaled Models of Fold-and-Thrust Belts

    Science.gov (United States)

    Nilfouroushan, F.; Pysklywec, R.; Cruden, S.

    2009-05-01

    Cohesionless or very low cohesion granular materials are widely used in analogue/physical models to simulate brittle rocks in the upper crust. Selection of materials with appropriate cohesion values in such models is important for the simulation of the dynamics of brittle rock deformation in nature. Uncertainties in the magnitude of cohesion (due to measurement errors, extrapolations at low normal stresses, or model setup) in laboratory experiments can possibly result in misinterpretation of the styles and mechanisms of deformation in natural fold-and thrust belts. We ran a series of 2-D numerical models to investigate systematically the effect of cohesion uncertainties on the evolution of models of fold-and-thrust belts. The analyses employ SOPALE, a geodynamic code based on the arbitrary Lagrangian-Eulerian (ALE) finite element method. Similar to analogue models, the material properties of sand and transparent silicone (PDMS) are used to simulate brittle and viscous behaviors of upper crustal rocks. The suite of scaled brittle and brittle-viscous numerical experiments have the same initial geometry but the cohesion value of the brittle layers is increased systematically from 0 to 100 Pa. The stress and strain distribution in different sets of models with different cohesion values are compared and analyzed. The kinematics and geometry of thrust wedges including the location and number of foreland- and hinterland- verging thrust faults, pop-up structures, tapers and topography are also explored and their sensitivity to cohesion value is discussed.

  20. Mechanics of granular environments; Mecanique des milieux granulaires

    Energy Technology Data Exchange (ETDEWEB)

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

    2001-07-01

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

  1. Multi-scale modeling of inter-granular fracture in UO2

    Energy Technology Data Exchange (ETDEWEB)

    Chakraborty, Pritam [Idaho National Lab. (INL), Idaho Falls, ID (United States); Zhang, Yongfeng [Idaho National Lab. (INL), Idaho Falls, ID (United States); Tonks, Michael R. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Biner, S. Bulent [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2015-03-01

    A hierarchical multi-scale approach is pursued in this work to investigate the influence of porosity, pore and grain size on the intergranular brittle fracture in UO2. In this approach, molecular dynamics simulations are performed to obtain the fracture properties for different grain boundary types. A phase-field model is then utilized to perform intergranular fracture simulations of representative microstructures with different porosities, pore and grain sizes. In these simulations the grain boundary fracture properties obtained from molecular dynamics simulations are used. The responses from the phase-field fracture simulations are then fitted with a stress-based brittle fracture model usable at the engineering scale. This approach encapsulates three different length and time scales, and allows the development of microstructurally informed engineering scale model from properties evaluated at the atomistic scale.

  2. Strength of anisotropy in a granular material: Linear versus nonlinear contact model.

    Science.gov (United States)

    La Ragione, Luigi; Gammariello, Marica; Recchia, Giuseppina

    2016-12-01

    In this paper, we deal with anisotropy in an idealized granular material made of a collection of frictional, elastic, contacting particles. We present a theoretical analysis for an aggregate of particles isotropically compressed and then sheared, in which two possible contacts laws between particles are considered: a linear contact law, where the contact stiffness is constant; and a nonlinear contact law, where the contact stiffness depends on the overlapping between particles. In the former case the anisotropy observed in the aggregate is associated with particle arrangement. In fact, although the aggregate is initially characterized by an isotropic network of contacts, during the loading, an anisotropic texture develops, which is measured by a fabric tensor. With a nonlinear contact law it is possible to develop anisotropy because contacting stiffnesses are different, depending on the orientation of the contact vectors with respect to the axis of the applied deformation. We find that before the peak load is reached, an aggregate made of particles with a linear contact law develops a much smaller anisotropy compared with that of an aggregate with a nonlinear law.

  3. Strength of anisotropy in a granular material: Linear versus nonlinear contact model

    Science.gov (United States)

    La Ragione, Luigi; Gammariello, Marica; Recchia, Giuseppina

    2016-12-01

    In this paper, we deal with anisotropy in an idealized granular material made of a collection of frictional, elastic, contacting particles. We present a theoretical analysis for an aggregate of particles isotropically compressed and then sheared, in which two possible contacts laws between particles are considered: a linear contact law, where the contact stiffness is constant; and a nonlinear contact law, where the contact stiffness depends on the overlapping between particles. In the former case the anisotropy observed in the aggregate is associated with particle arrangement. In fact, although the aggregate is initially characterized by an isotropic network of contacts, during the loading, an anisotropic texture develops, which is measured by a fabric tensor. With a nonlinear contact law it is possible to develop anisotropy because contacting stiffnesses are different, depending on the orientation of the contact vectors with respect to the axis of the applied deformation. We find that before the peak load is reached, an aggregate made of particles with a linear contact law develops a much smaller anisotropy compared with that of an aggregate with a nonlinear law.

  4. Predictive simulation of granular flows applied to compressible multiphase flow modeling

    Science.gov (United States)

    Goetsch, Ryan J.; Regele, Jonathan D.

    2014-11-01

    Multiphase flows have been an active area of research for decades due to their complex nature and occurrence in many engineering applications. However, little information exists about the dense compressible flow regime. Recent experimental work [Wagner et al., Exp. Fluids 52, 1507 (2012)] using a multiphase shock tube has studied gas-solid flows with high solid volume fractions (α = 0 . 2) by measuring shock wave-particle cloud interactions. It is still unclear what occurs at the particle scale inside and behind the particle cloud during this interaction. The objective of this work is to perform direct numerical simulations to understand this phenomena. With this goal in mind, a discrete element method (DEM) solver was developed to predict the properties of a particle cloud formed by gravity driven granular flow through a slit opening. For validation purposes, the results are compared with experimental channel flow data. It is found that the mean velocity profile and mass flow rates correlate well with the experiment, however the fluctuation velocities are significantly under-predicted for both smooth and rough wall cases.

  5. Inherent Segregation in Granular Media

    Directory of Open Access Journals (Sweden)

    Sánchez-Guzmán J.

    2011-10-01

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

  6. Two-pion interferometry for the granular sources in ultrarelativistic heavy ion collisions

    CERN Document Server

    Zhang, Wei-ning; Ren, Yan-Yu

    2011-01-01

    We investigate the two-pion interferometry in ultrarelativistic heavy ion collisions in the granular source model of quark-gluon plasma droplets. The pion transverse momentum spectra and HBT radii of the granular sources agree well with the experimental data of the $\\sqrt{s_{NN}}=200$ GeV Au-Au and $\\sqrt{s_{NN}}=2.76$ TeV Pb-Pb most central collisions. In the granular source model the larger initial system breakup time may lead to the larger HBT radii $R_{\\rm out}$, $R_{\\rm side}$, and $R_{\\rm long}$. However, the large droplet transverse expansion and limited average relative emitting time of particles in the granular source lead to small ratios of the transverse HBT radii $R_{\\rm out}/R_{\\rm side}$.

  7. A Granularity-Aware Parallel Aggregation Method for Data Streams

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    This paper focuses on the parallel aggregation processing of data streams based on the shared-nothing architecture. A novel granularity-aware parallel aggregating model is proposed. It employs parallel sampling and linear regression to describe the characteristics of the data quantity in the query window in order to determine the partition granularity of tuples, and utilizes equal depth histogram to implement partitioning. This method can avoid data skew and reduce communication cost. The experiment results on both synthetic data and actual data prove that the proposed method is efficient, practical and suitable for time-varying data streams processing.

  8. Terahertz scattering by granular composite materials: An effective medium theory

    Science.gov (United States)

    Kaushik, Mayank; Ng, Brian W.-H.; Fischer, Bernd M.; Abbott, Derek

    2012-01-01

    Terahertz (THz) spectroscopy and imaging have emerged as important tools for identification and classification of various substances, which exhibit absorption characteristics at distinct frequencies in the THz range. The spectral fingerprints can potentially be distorted or obscured by electromagnetic scattering caused by the granular nature of some substances. In this paper, we present THz time domain transmission measurements of granular polyethylene powders in order to investigate an effective medium theory that yields a parameterized model, which can be used to estimate the empirical measurements to good accuracy.

  9. Kinetics of Nitrogen Diffusion in Granular Manganese

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jin-zhu; XU Chu-shao; ZHAO Yue-ping

    2008-01-01

    The kinetics and the influence of time on granular manganese nitriding were studied by means of a vacuum resistance furnace, X-ray diffraction technique, and LECO TC-436 oxygen/nitrogen determinator. The longer the nitriding time, the more the nitrogen pickup. Except for a trace of oxide MnO that developed, the metal manganese could thoroughly be nitrided to form Mn4N and a little ζ-phase (the stoichiometric components as Mn2N) with the nitriding time lasting. A kinetic model is developed to reveal the nitriding situation and agrees well with the experimental results.

  10. Kinetic approach to granular gases.

    Science.gov (United States)

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

    1999-05-01

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

  11. Time and position resolution of high granularity, high counting rate MRPC for the inner zone of the CBM-TOF wall

    CERN Document Server

    Petriş, M; Caragheorgheopol, G.; Deppner, I.; Frühauf, J.; Herrmann, N.; Kiš, M.; Loizeau, P-A.; Petrovici, M.; Rǎdulescu, L.; Simion, V.; Simon, C.

    2016-01-01

    Multi-gap RPC prototypes with readout on a multi-strip electrode were developed for the small polar angle region of the CBM-TOF subdetector, the most demanding zone in terms of granularity and counting rate. The prototypes are based on low resistivity ($\\sim$10$^{10}$ $\\Omega$cm) glass electrodes for performing in high counting rate environment. The strip width/pitch size was chosen such to fulfill the impedance matching with the front-end electronics and the granularity requirements of the innermost zone of the CBM-TOF wall. The in-beam tests using secondary particles produced in heavy ion collisions on a Pb target at SIS18 - GSI Darmstadt and SPS - CERN were focused on the performance of the prototype in conditions similar to the ones expected at SIS100/FAIR. An efficiency larger than 98\\% and a system time resolution in the order of 70~-~80~ps were obtained in high counting rate and high multiplicity environment.

  12. Time and position resolution of high granularity, high counting rate MRPC for the inner zone of the CBM-TOF wall

    Science.gov (United States)

    Petriş, M.; Bartoş, D.; Caragheorgheopol, G.; Deppner, I.; Frühauf, J.; Herrmann, N.; Kiš, M.; Loizeau, P.-A.; Petrovici, M.; Rădulescu, L.; Simion, V.; Simon, C.

    2016-09-01

    Multi-gap RPC prototypes with a multi-strip-electrode readout were developed for the small polar angle region of the CBM-TOF subdetector, the most demanding zone in terms of granularity and counting rate. The prototypes are based on using low resistivity (~ 1010 Ω·cm) glass electrodes for performing in high counting rate environment. The strip width/pitch size was chosen such to fulfill the impedance matching with the front-end electronics and the granularity requirements of the innermost zone of the CBM-TOF wall. The in-beam tests using secondary particles produced in heavy ion collisions on a Pb target at SIS18—GSI Darmstadt and SPS—CERN were focused on the performance of the prototypes in conditions similar to the ones expected at SIS100/FAIR. An efficiency larger than 98% and a system time resolution in the order of 70-80 ps were obtained in high counting rate and high multiplicity environment.

  13. Gap timing and the spectral timing model.

    Science.gov (United States)

    Hopson, J W

    1999-04-01

    A hypothesized mechanism underlying gap timing was implemented in the Spectral Timing Model [Grossberg, S., Schmajuk, N., 1989. Neural dynamics of adaptive timing and temporal discrimination during associative learning. Neural Netw. 2, 79-102] , a neural network timing model. The activation of the network nodes was made to decay in the absence of the timed signal, causing the model to shift its peak response time in a fashion similar to that shown in animal subjects. The model was then able to accurately simulate a parametric study of gap timing [Cabeza de Vaca, S., Brown, B., Hemmes, N., 1994. Internal clock and memory processes in aminal timing. J. Exp. Psychol.: Anim. Behav. Process. 20 (2), 184-198]. The addition of a memory decay process appears to produce the correct pattern of results in both Scalar Expectancy Theory models and in the Spectral Timing Model, and the fact that the same process should be effective in two such disparate models argues strongly that process reflects a true aspect of animal cognition.

  14. Instability in Shocked Granular Gases

    CERN Document Server

    Sirmas, Nick; Radulescu, Matei

    2013-01-01

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

  15. Instability in shocked granular gases

    Science.gov (United States)

    Sirmas, Nick; Falle, Sam; Radulescu, Matei

    2014-05-01

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

  16. Interfacial Instability during Granular Erosion.

    Science.gov (United States)

    Lefebvre, Gautier; Merceron, Aymeric; Jop, Pierre

    2016-02-12

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

  17. Subsidence Modeling of the Over-exploited Granular Aquifer System in Aguascalientes, Mexico

    Science.gov (United States)

    Solano Rojas, D. E.; Wdowinski, S.; Minderhoud, P. P. S.; Pacheco, J.; Cabral, E.

    2016-12-01

    The valley of Aguascalientes in central Mexico experiences subsidence rates of up to 100 [mm/yr] due to overexploitation of its aquifer system, as revealed from satellite-based geodetic observations. The spatial pattern of the subsidence over the valley is inhomogeneous and affected by shallow faulting. The understanding of the subsoil mechanics is still limited. A better understanding of the subsidence process in Aguascalientes is needed to provide insights for future subsidence in the valley. We present here a displacement-constrained finite-element subsidence model using Deltares iMOD (interactive MODeling), based on the USGS MODFLOW software. The construction of our model relies on 3 main inputs: (1) groundwater level time series obtained from extraction wells' hydrographs, (2) subsurface lithostratigraphy interpreted from well drilling logs, and (3) hydrogeological parameters obtained from field pumping tests. The groundwater level measurements were converted to pore pressure in our model's layers, and used in Terzaghi's equation for calculating effective stress. We then used the effective stresse along with the displacement obtained from geodetic observations to constrain and optimize five geo-mechanical parameters: compression ratio, reloading ratio, secondary compression index, over consolidation ratio, and consolidation coefficient. Finally, we use the NEN-Bjerrum linear stress model formulation for settlements to determine elastic and visco-plastic strain, accounting for the aquifer system units' aging effect. Preliminary results show higher compaction response in clay-saturated intervals (i.e. aquitards) of the aquifer system, as reflected in the spatial pattern of the surface deformation. The forecasted subsidence for our proposed scenarios show a much more pronounced deformation when we consider higher groundwater extraction regimes.

  18. Modeling, Experimentation, and Control of Autotrophic Nitrogen Removal in Granular Sludge Systems

    DEFF Research Database (Denmark)

    Vangsgaard, Anna Katrine

    and control perspective, due to the smaller number of actuators available. In this work, an integrated modeling and experimental approach was used to improve the understanding of the process, and subsequently use this understanding to design novel control strategies, providing alternatives to the current ones......Complete autotrophic nitrogen removal (CANR) is a novel process that can increase the treatment capacity for wastewaters containing high concentrations of nitrogen and low organic carbon to nitrogen ratios, through an increase of the volumetric removal rate by approximately five times. This process...... is convenient for treating anaerobic digester liquor, landfill leachate, or special industrial wastewaters, because costs related to the need for aeration and carbon addition are lowered by 60% and 100%, respectively, compared to conventional nitrification denitrification treatment. Energy and capital costs can...

  19. A granular-biomass high temperature pyrolysis model based on the Darcy flow

    Science.gov (United States)

    Guan, Jian; Qi, Guoli; Dong, Peng

    2015-03-01

    We established a model for the chemical reaction kinetics of biomass pyrolysis via the high-temperature thermal cracking of liquid products. We divided the condensable volatiles into two groups, based on the characteristics of the liquid prdoducts., tar and biomass oil. The effects of temperature, residence time, particle size, velocity, pressure, and other parameters on biomass pyrolysis and high-temperature tar cracking were investigated numerically, and the results were compared with experimental data. The simulation results showed a large endothermic pyrolysis reaction effect on temperature and the reaction process. The pyrolysis reaction zone had a constant temperature period in several layers near the center of large biomass particles. A purely physical heating process was observed before and after this period, according to the temperature index curve.

  20. Some open problems in granular matter mechanics

    Institute of Scientific and Technical Information of China (English)

    Qicheng Sun; Guangqian Wang; Kaiheng Hu

    2009-01-01

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

  1. Traffic and Granular Flow '11

    CERN Document Server

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

    2013-01-01

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

  2. Unifying suspension and granular rheology.

    Science.gov (United States)

    Boyer, François; Guazzelli, Élisabeth; Pouliquen, Olivier

    2011-10-28

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

  3. Bulldozing of granular material

    CERN Document Server

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

    2014-01-01

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

  4. Bonding Strength Effects in Hydro-Mechanical Coupling Transport in Granular Porous Media by Pore-Scale Modeling

    Directory of Open Access Journals (Sweden)

    Zhiqiang Chen

    2016-03-01

    Full Text Available The hydro-mechanical coupling transport process of sand production is numerically investigated with special attention paid to the bonding effect between sand grains. By coupling the lattice Boltzmann method (LBM and the discrete element method (DEM, we are able to capture particles movements and fluid flows simultaneously. In order to account for the bonding effects on sand production, a contact bond model is introduced into the LBM-DEM framework. Our simulations first examine the experimental observation of “initial sand production is evoked by localized failure” and then show that the bonding or cement plays an important role in sand production. Lower bonding strength will lead to more sand production than higher bonding strength. It is also found that the influence of flow rate on sand production depends on the bonding strength in cemented granular media, and for low bonding strength sample, the higher the flow rate is, the more severe the erosion found in localized failure zone becomes.

  5. Traffic and Granular Flow ’03

    CERN Document Server

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

    2005-01-01

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

  6. Differences in granular materials for analogue modelling: Insights from repeated compression tests analyzed with X-ray Computed Tomography and image analysis software

    Science.gov (United States)

    Klinkmueller, M.; Schreurs, G.

    2009-12-01

    Six different granular materials for analogue modelling have been investigated using a sandbox with a compressional set-up and X-ray computed tomography (XRCT). The evolving structures were evaluated with image analysis software. The sandbox has one movable sidewall that is driven by a computer-controlled servomotor at 20 cm/h. A 12 cm wide and 20 cm long sheet of hard cardboard was placed on the base of the sandbox and attached to the moving sidewall creating a velocity discontinuity. The whole sandbox was covered on the inside with Alkor foil to reduce sidewall friction. Computed Tomography was used to scan the whole volume in 3 mm increments of shortening until 15 mm maximum deformation was reached. The second approach was a scanning procedure to a maximum deformation of 80 mm in 2 mm increments of shortening for the first 10 mm and in 5 mm increments for the last 70 mm. The short deformation scans were repeated three times to investigate reproducibility. The long deformation scans were performed twice. The physical properties of the materials (table 1) have been described in a previous material benchmark. Four natural quartz sands and two artificial granular materials, corundum brown sand and glass beads, have been used. The two artificial materials were used for this experimental series as examples for very angular and very rounded sands in contrast to the sub-rounded to angular natural quartz sands. The short deformation experiments show partly large differences in thrust angles of both front and back-thrust, in timing of thrust initiation, and in the degree of undulation of thrusts. The coarse-grained sands show smooth and low undulating thrusts that are only affected by the sidewall friction whereas the thrusts in fine-grained sands undulate significantly and partly divide and merge in an anastomosing fashion. The coarse-grained sand thrusts are clearer visualized by XRCT, which indicates a wider shear zone where the material dilates. Furthermore, the

  7. Modelling urban travel times

    NARCIS (Netherlands)

    Zheng, F.

    2011-01-01

    Urban travel times are intrinsically uncertain due to a lot of stochastic characteristics of traffic, especially at signalized intersections. A single travel time does not have much meaning and is not informative to drivers or traffic managers. The range of travel times is large such that certain tr

  8. Modelling urban travel times

    NARCIS (Netherlands)

    Zheng, F.

    2011-01-01

    Urban travel times are intrinsically uncertain due to a lot of stochastic characteristics of traffic, especially at signalized intersections. A single travel time does not have much meaning and is not informative to drivers or traffic managers. The range of travel times is large such that certain

  9. Modelling urban travel times

    NARCIS (Netherlands)

    Zheng, F.

    2011-01-01

    Urban travel times are intrinsically uncertain due to a lot of stochastic characteristics of traffic, especially at signalized intersections. A single travel time does not have much meaning and is not informative to drivers or traffic managers. The range of travel times is large such that certain tr

  10. Jamming in granular materials

    Science.gov (United States)

    Behringer, Robert P.

    2015-01-01

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

  11. Decreased expression of proteins involved in energy metabolism in the hippocampal granular layer of rats submitted to the pilocarpine epilepsy model.

    Science.gov (United States)

    Araujo, Bruno; Torres, Laila; Stein, Mariana; Cabral, Francisco Romero; Herai, Roberto; Okamoto, Oswaldo; Cavalheiro, Esper

    2014-02-21

    Long-term structural and functional changes in the hippocampus have been identified as the primary physiopathological basis for temporal lobe epilepsy. These changes include reactive gliosis and granule cell axonal sprouting within the dentate gyrus. The intimate mechanisms of these changes are beginning to be revealed. Here, we show the possibility of using laser capture microdissection (LCM) to isolate the dentate granular cell layer of Wistar rats submitted to the pilocarpine model of epilepsy. Using two-dimensional gel electrophoresis (2-D PAGE) and mass spectrometry for laser-captured cells, we identified molecular events that could be altered as part of the epileptic pathogenic process. According to our results, eight proteins related to energy metabolism were differentially expressed between both the control and pilocarpine-treated animals. These results provide, for the first time, new molecular insights into the altered protein profile of the epileptogenic dentate gyrus and can contribute to a better understanding of the phenomena involved in the genesis and maintenance of the epileptic state.

  12. Introduction to Time Series Modeling

    CERN Document Server

    Kitagawa, Genshiro

    2010-01-01

    In time series modeling, the behavior of a certain phenomenon is expressed in relation to the past values of itself and other covariates. Since many important phenomena in statistical analysis are actually time series and the identification of conditional distribution of the phenomenon is an essential part of the statistical modeling, it is very important and useful to learn fundamental methods of time series modeling. Illustrating how to build models for time series using basic methods, "Introduction to Time Series Modeling" covers numerous time series models and the various tools f

  13. Structure and cluster formation in granular media

    Indian Academy of Sciences (India)

    S Luding

    2005-06-01

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

  14. Some Considerations about the Bouchaud-Cates-Ravi-Edwards model for granular flow

    OpenAIRE

    Alamino, Roberto C.; Prado, Carmen P. C.

    2001-01-01

    In this paper we discuss some features of the BCRE model. We show that this model can be understood as a mapping from a two-dimensional to a one-dimensional problem, if some conditions are satisfied. We propose some modifications that (a) guarantee mass conservation in the model (what is not assured in its original form) and (b) correct undesired behaviors that appear when there are irregularities in the surface of the static phase. We also show that a similar model can be deduced both from t...

  15. On Granular Knowledge Structures

    CERN Document Server

    Zeng, Yi

    2008-01-01

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

  16. Development of Soft-Sphere Contact Models for Thermal Heat Conduction in Granular Flows

    Energy Technology Data Exchange (ETDEWEB)

    Morris, A. B.; Pannala, S.; Ma, Zhiwen; Hrenya, C. M.

    2016-12-01

    Conductive heat transfer to flowing particles occurs when two particles (or a particle and wall) come into contact. The direct conduction between the two bodies depends on the collision dynamics, namely the size of the contact area and the duration of contact. For soft-sphere discrete-particle simulations, it is computationally expensive to resolve the true collision time because doing so would require a restrictively small numerical time step. To improve the computational speed, it is common to increase the 'softness' of the material to artificially increase the collision time, but doing so affects the heat transfer. In this work, two physically-based correction terms are derived to compensate for the increased contact area and time stemming from artificial particle softening. By including both correction terms, the impact that artificial softening has on the conductive heat transfer is removed, thus enabling simulations at greatly reduced computational times without sacrificing physical accuracy.

  17. Calibration and validation of a model describing complete autotrophic nitrogen removal in a granular SBR system

    DEFF Research Database (Denmark)

    Vangsgaard, Anna Katrine; Mutlu, Ayten Gizem; Gernaey, Krist

    2013-01-01

    -up. RESULTS: A model was calibrated using a step-wise procedure customized for the specific needs of the system. The important steps in the procedure were initialization, steady-state and dynamic calibration, and validation. A fast and effective initialization approach was developed to approximate pseudo...... screening of the parameter space proposed by Sin et al. (2008) - to find the best fit of the model to dynamic data. Finally, the calibrated model was validated with an independent data set. CONCLUSION: The presented calibration procedure is the first customized procedure for this type of system...... and is expected to contribute to achieve a fast and effective model calibration, an important enabling tool for various biochemical engineering design, control and operation problems....

  18. 基于粒计算的入侵检测系统研究%Research of Intrusion Detection System Model Based on Granular Computing

    Institute of Scientific and Technical Information of China (English)

    邓飞; 潘华

    2011-01-01

    The intrusion detection system as a key technology and important means to protect network security has become a hotspot. Granular computing as a kind of new idea and method in the artificial intelligence has important practical significance in intrusion detection. To discuss the direction of unresolving issues and trends of development, the methods of using equivalence relatian to describe the granular and using granular to describe the concept are proposed. Besides. the experiment verifies that this model can separate the normal system call from the abnormal one effectively. The conclusion is that the methodology of granular computing can be used to solve the problem of intrusion detection.%入侵检测系统作为保护网络系统安全的关键技术和重要手段,已经成为当前网络安全研究方面的热点.粒计算作为人工智能领域中的一种新理论和新方法,将其应用在入侵检测中具有重要的现实意义.为了讨论该方向上尚未解决的问题和发展趋势,采用了用等价关系来描述粒,用粒来描述概念的方法,并用实验证明了该模型能非常有效地将正常和异常的系统调用序列区分开,得到用粒计算的方法论可以解决入侵检测问题的结论.

  19. FINE-GRAINED DISTRIBUTED MULTIMEDIA SYNCHRONIZA- TION MODEL--ENHANCED FUZZY-TIMING PETRI NET

    Institute of Scientific and Technical Information of China (English)

    韩莹洁; 孙永强; 吴哲辉

    2001-01-01

    A fine-grained distributed multimedia synchronization model--Enhanced Fuzzy timing Petri Net was proposed which is good at modeling indeterminacy and fuzzy. To satisfy the need of maximum tolerable jitter, the sufficient conditions are given in intra-object synchronization. Method to find a proper granularity in inter-object synchronization is also given to satisfy skew. Exceptions are detected and corrected as early as possible using restricted blocking method.

  20. A new elliptic-parabolic yield surface model revised by an adaptive criterion for granular soils

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    An adaptive criterion for shear yielding as well as shear failure of soils is proposed in this paper to address the fact that most criteria,including the Mohr-Coulomb criterion,the Lade criterion and the Matsuoka-Nakai criterion,cannot agree well with the experimental results when the value of the intermediate principal stress parameter is too big.The new criterion can adjust an adaptive parameter based on the experimental results in order to make the theoretical calculations fit the test results more accurately.The original elliptic-parabolic yield surface model can capture both soil contraction and dilation behaviors.However,it normally over-predicts the soil strength due to its application of the Extended Mises criterion.A new elliptic-parabolic yield surface mode is presented in this paper,which introduces the adaptive criterion in three-dimensional principal stress space.The new model can well model the stress-strain behavior of soils under general stress conditions.Compared to the original model which can only simulate soil behavior under triaxial compression conditions,the new model can simulate soil behaviors under both triaxial compression conditions and general stress conditions.

  1. Hydrodynamics for a model of a confined quasi-two-dimensional granular gas.

    Science.gov (United States)

    Brey, J Javier; Buzón, V; Maynar, P; García de Soria, M I

    2015-05-01

    The hydrodynamic equations for a model of a confined quasi-two-dimensional gas of smooth inelastic hard spheres are derived from the Boltzmann equation for the model, using a generalization of the Chapman-Enskog method. The heat and momentum fluxes are calculated to Navier-Stokes order, and the associated transport coefficients are explicitly determined as functions of the coefficient of normal restitution and the velocity parameter involved in the definition of the model. Also an Euler transport term contributing to the energy transport equation is considered. This term arises from the gradient expansion of the rate of change of the temperature due to the inelasticity of collisions, and it vanishes for elastic systems. The hydrodynamic equations are particularized for the relevant case of a system in the homogeneous steady state. The relationship with previous works is analyzed.

  2. Small-signal analysis of granular semiconductors

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-11-01

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

  3. A Study of the Behavior and Micromechanical Modelling of Granular Soil. Volume 2. An Experimental Investigation of the Behavior of Granular Media Under Load

    Science.gov (United States)

    1991-05-22

    on the failure of sand. Whitman and Luscher (1962) studied the strength characteristics of hollow cylinders of sand, and Broms and Jamal (1965) and...Distortional Yield Model," J. Appl. Mechanics, ASME, Vol. 57, pp. 537-547. Whitman, R.V. and Luscher , U. (1962), "Basic Experiment into Soil-Structure

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

    Directory of Open Access Journals (Sweden)

    Shvab Alexander

    2016-01-01

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

  5. Modeling wave-induced pore pressure and effective stress in a granular seabed

    Science.gov (United States)

    Scholtès, Luc; Chareyre, Bruno; Michallet, Hervé; Catalano, Emanuele; Marzougui, Donia

    2015-01-01

    The response of a sandy seabed under wave loading is investigated on the basis of numerical modeling using a multi-scale approach. To that aim, the discrete element method is coupled to a finite volume method specially enhanced to describe compressible fluid flow. Both solid and fluid phase mechanics are upscaled from considerations established at the pore level. Model's predictions are validated against poroelasticity theory and discussed in comparison with experiments where a sediment analog is subjected to wave action in a flume. Special emphasis is put on the mechanisms leading the seabed to liquefy under wave-induced pressure variation on its surface. Liquefaction is observed in both dilative and compactive regimes. It is shown that the instability can be triggered for a well-identified range of hydraulic conditions. Particularly, the results confirm that the gas content, together with the permeability of the medium are key parameters affecting the transmission of pressure inside the soil.

  6. A Modification and Analysis of Lagrangian Trajectory Modeling and Granular Dynamics of Lunar Dust Particles

    Science.gov (United States)

    Long, Jason M.; Lane, John E.; Metzger, Philip T.

    2008-01-01

    A previously developed mathematical model is amended to more accurately incorporate the effects of lift and drag on single dust particles in order to predict their behavior in the wake of high velocity gas flow. The model utilizes output from a CFD or DSMC simulation of exhaust from a rocket nozzle hot gas jet. An extension of the Saffman equation for lift based on the research of McLaughlin (1991) and Mei (1992) is used, while an equation for the Magnus force modeled after the work of Oesterle (1994) and Tsuji et al (1985) is applied. A relationship for drag utilizing a particle shape factor (phi = 0.8) is taken from the work of Haider and Levenspiel (1989) for application to non-spherical particle dynamics. The drag equation is further adjusted to account for rarefaction and compressibility effects in rarefied and high Mach number flows according to the work of Davies (1945) and Loth (2007) respectively. Simulations using a more accurate model with the correction factor (Epsilon = 0.8 in a 20% particle concentration gas flow) given by Richardson and Zaki (1954) and Rowe (1961) show that particles have lower ejection angles than those that were previously calculated. This is more prevalent in smaller particles, which are shown through velocity and trajectory comparison to be more influenced by the flow of the surrounding gas. It is shown that particles are more affected by minor changes to drag forces than larger adjustments to lift forces, demanding a closer analysis of the shape and behavior of lunar dust particles and the composition of the surrounding gas flow.

  7. Linking discrete particle simulation to continuum process modelling for granular matter: Theory and application

    Institute of Scientific and Technical Information of China (English)

    H.P. Zhu; Z.Y. Zhou; Q.F. Hou; A.B. YU

    2011-01-01

    Two approaches are widely used to describe particle systems:the continuum approach at macroscopic scale and the discrete approach at particle scale,Each has its own advantages and disadvantages in the modelling of particle systems.It is of paramount significance to develop a theory to overcome the disadvantages of the two approaches.Averaging method to link the discrete to continuum approach is a potential technique to develop such a theory.This paper introduces an averaging method,including the theory and its application to the particle flow in a hopper and the particle-fluid flow in an ironmaking blast furnace.

  8. Compaction and shear settlement of granular materials

    Science.gov (United States)

    Morland, L. W.

    1993-03-01

    S HEARING of granular materials causes rearrangement of the granular structure which induces irreversible volume decrease and shear strain, in addition to reversible strain. A model is presented which describes the reversible strain by a hypoelastic law, and the irreversible compaction and shear by evolutionary laws. The latter are differential relations defining the progress of irreversible strain as an appropriate time-independent monotonic loading parameter increases, which incorporate dependence on the current state, and which require a direction for the irreversible shear strain increment. Such a model allows a variety of choices and combinations for the loading parameter, shear increment direction and arguments reflecting the current state. A wide selection of possible choices is incorporated in a systematic analysis of the initial shearing response of an unstressed material. It is shown that a physically sensible response restricts the choice to essentially two forms of dependence, and further restricts the initial shapes of the constitutive functions. The simpler model form reduces to three coupled non-linear differential equations for shearing, from which some general conclusions can be drawn, and numerical illustrations for shear stress and shear strain cycling are presented for simple valid model functions.

  9. Development of a predictive model to determine micropollutant removal using granular activated carbon

    Directory of Open Access Journals (Sweden)

    D. J. de Ridder

    2009-12-01

    Full Text Available The occurrence of organic micropollutants in drinking water and its sources has opened up a field of study related to monitoring concentration levels in water sources, evaluating their toxicity and estimating their removal in drinking water treatment processes. Because a large number of organic micropollutants is currently present (although in relatively low concentrations in drinking water sources, a method should be developed to select which micropollutants has to be evaluated with priority. In this paper, a screening model is presented that can predict solute removal by activated carbon, in ultrapure water and in natural water. Solute removal prediction is based on a combination of solute hydrophobicity (expressed as log D, the pH corrected log Kow, solute charge and the carbon dose. Solute molecular weight was also considered as model input parameter, but this solute property appeared to relate insufficiently to solute removal.

    Removal of negatively charged solutes by preloaded activated carbon was reduced while the removal of positively charged solutes was increased, compared with freshly regenerated activated carbon. Differences in charged solute removal by freshly regenerated activated carbon were small, indicating that charge interactions are an important mechanism in adsorption onto preloaded carbon. The predicted solute removal was within 20 removal-% deviation of experimentally measured values for most solutes.

  10. Development of a predictive model to determine micropollutant removal using granular activated carbon

    Directory of Open Access Journals (Sweden)

    D. J. de Ridder

    2009-10-01

    Full Text Available The occurrence of organic micropollutants in drinking water and its sources has opened up a field of study related to monitoring concentration levels in water sources, evaluating their toxicity and estimating their removal in drinking water treatment processes. Because a large number of organic micropollutants is currently present (although in relatively low concentrations in drinking water sources, a method should be developed to select which micropollutants has to be evaluated with priority. In this paper, a screening model is presented that can predict solute removal by activated carbon, in ultrapure water and in natural water. Solute removal prediction is based on a combination of solute hydrophobicity (expressed as log D, the pH corrected log Kow, solute charge and the carbon dose. Solute molecular weight was also considered as model input parameter, but this solute property appeared to relate insufficiently to solute removal.

    Removal of negatively charged solutes by preloaded activated carbon was reduced while the removal of positively charged solutes was increased, compared with freshly regenerated activated carbon. Differences in charged solute removal by freshly regenerated activated carbon were small, indicating that charge interactions are an important mechanism in adsorption onto preloaded carbon. The predicted solute removal was within 20 removal-% deviation of experimentally measured values.

  11. Cystic Granular Cell Ameloblastoma

    OpenAIRE

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

    2010-01-01

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

  12. Pore Fluid Effects on Shear Modulus in a Model of Heterogeneous Rocks, Reservoirs, and Granular Media

    Energy Technology Data Exchange (ETDEWEB)

    Berryman, J G

    2005-03-23

    To provide quantitative measures of the importance of fluid effects on shear waves in heterogeneous reservoirs, a model material called a ''random polycrystal of porous laminates'' is introduced. This model poroelastic material has constituent grains that are layered (or laminated), and each layer is an isotropic, microhomogeneous porous medium. All grains are composed of exactly the same porous constituents, and have the same relative volume fractions. The order of lamination is not important because the up-scaling method used to determine the transversely isotropic (hexagonal) properties of the grains is Backus averaging, which--for quasi-static or long-wavelength behavior--depends only on the volume fractions and layer properties. Grains are then jumbled together totally at random, filling all space, and producing an overall isotropic poroelastic medium. The poroelastic behavior of this medium is then analyzed using the Peselnick-Meister-Watt bounds (of Hashin-Shtrikman type). We study the dependence of the shear modulus on pore fluid properties and determine the range of behavior to be expected. In particular we compare and contrast these results to those anticipated from Gassmann's fluid substitution formulas, and to the predictions of Mavko and Jizba for very low porosity rocks with flat cracks. This approach also permits the study of arbitrary numbers of constituents, but for simplicity the numerical examples are restricted here to just two constituents. This restriction also permits the use of some special exact results available for computing the overall effective stress coefficient in any two-component porous medium. The bounds making use of polycrystalline microstructure are very tight. Results for the shear modulus demonstrate that the ratio of compliance differences R (i.e., shear compliance changes over bulk compliance changes when going from drained to undrained behavior, or vice versa) is usually nonzero and can take a wide

  13. Two-Pion Interferometry for the Granular Sources in Ultrarelativistic Heavy Ion Collisions at the RHIC and the LHC

    Institute of Scientific and Technical Information of China (English)

    张卫宁; 尹洪杰; 任延宇

    2011-01-01

    We investigate the two-pion interferometry in ultrarelativistic heavy ion collisions in the granular source model of quark-gluon plasma droplets.The pion transverse momentum spectra and HBT radii of the granular sources agree well with the experimental data of the most central Au-Au collisions at √8NN =200 GeV at the RHIC and Pb-Pb collisions at √8NN =2.76 TeV at the LHC.In the granular source model the larger initial system breakup time for the LHC collisions as compared to the RHIC collisions may lead to the larger HBT radii Rout,Rside and Rlong.However,the large droplet transverse expansion and limited average relative emitting time of particles in the granular source lead to slightly smaller ratios of the transverse Hanbury-Brown-Twiss radii Rout/Rside.%We investigate the two-pion interferometry in uitrarelativistic heavy ion collisions in the granular source model of quark-gluon plasma droplets. The pion transverse momentum spectra and HBT radii of the granular sources agree well with the experimental data of the most central Au-Au collisions at √sNN = 200 GeV at the RHIC and Pb-Pb collisions at √sNN - 2.76 TeV at the LHC. In the granular source model the larger initial system breakup time for the LHC collisions as compared to the RHIC collisions may lead to the larger HBT radii Rout, Rside and Rlong- However, the large droplet transverse expansion and limited average relative emitting time of particles in the granular source lead to slightly smaller ratios of the transverse Hanbury-Brown-Twiss radii Rout/Raide-

  14. Semantic Multi-granular Lock model for Object Oriented Distributed Systems

    Directory of Open Access Journals (Sweden)

    V.Geetha

    2013-04-01

    Full Text Available In object oriented distributed systems (OODS, the objects are viewed as resources. Concurrency control techniques are usually applied on the database tier. This has the limitations of lack of support of legacy files and requirement of separate concurrency control mechanisms for each database model. Hence concurrency control on the objects at server tier is explored. To implement concurrency control on the objects participating in a system, the impact of method types, properties and class relationships namely inheritance, association and aggregation are to be analyzed. In this paper, the types and properties of classes and attributes are analysed. The semantics of the class relationships are analysed to ascertain their lock modes, granule sizes for defining concurrency control in OODS. It is also intended to propose compatibility matrix among all these object relationships.

  15. Discrete element modelling approach to assessment of granular properties in concrete

    Institute of Scientific and Technical Information of China (English)

    Piet STROEVEN; Huan HE; Martijn STROEVEN

    2011-01-01

    This paper presents the technological relevance of a concurrent algorithm-based discrete element modelling (DEM)system, HADES. This new system is the successor of SPACE that is limited to spherical grains only. It can realistically simulate the packing of arbitrary-shaped particles up to the fully compacted state. Generation of families of such particles, i.e., generally representing aggregate of fluvial origin and crushed rock, respectively, and the forming way of particulate structure are described.Similarly shaped particles are proposed for simulation of cement paste because of conformity with experimental results obtained by the X-ray tomography method. Technologically relevant territories inside and outside concrete technology are presently explored in this efficient, reliable, and economic way. Some results obtained by this DEM approach are presented.

  16. Complex networks and SOA: Mathematical modelling of granularity based web service compositions

    Indian Academy of Sciences (India)

    S Chatla; S Kadam; D Kolluru; S Sinha; A Viswandhuni; A Vaidya

    2011-08-01

    Service Oriented Architecture (SOA) can be defined as a way of defining and implementing enterprise applications that deals with the intercommunication of loosely coupled, coarse grained (business level), reusable artifacts (services). In this paper, we attempt to mathematically model the preliminary steps in the larger problem of providing an optimal architecture. The problem is treated as a complex network, particularly a process-task-network. We employ statistical and graph-theoretic methods namely, Jaccard’s distance analysis, Multiple Correspondence method and the Minimum Spanning Tree method, to find appropriate clusters. These methods are used to cluster tasks across business processes to propose services. Additional properties and features of these clusters are discussed. We propose a leverage factor which demonstrates the importance of a task within the service and its impact on service composition.

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

    Directory of Open Access Journals (Sweden)

    R. Askari

    2015-09-01

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

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

    Science.gov (United States)

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

    2015-04-01

    Understanding the penetration dynamics of intruders in granular beds is relevant not only for fundamental Physics, but also for geophysical processes and construction on granular soils in earthquake areas. Indeed a phenomenon named soil liquefaction can cause buildings to sink or tilt in areas separated of 1000 km from the epicentre in the worst cases. The damages on the constructions, the pipes and the roads may be huge. There is a conventional understanding of liquefaction from which scientists made theoretical and empirical laws for geotechnical use and building construction, but the dynamical penetration of buildings into the soil is still not well understood. While the penetration of intruders in 2D laboratory granular beds can be followed using video recording, it is useless in 3D beds of non-transparent materials such as common sand. Wireless accelerometry constitutes a natural alternative that has been used in very few occasions, however, it has never been used to quantify the penetration into horizontally shaken granular beds. Here we propose a method to quantify the sink dynamics of an intruder into laterally shaken, fluidized granular bed. We developped an embarked accelerometer small enough to fit into a modelized building. This sensor allows us to follow the intruder in realistic conditions namely buried in a 3D box of sand. Our method is based on the temporal correlations between the signals from a reference accelerometer fixed to the shaken granular bed, and the accelerometer deployed inside the intruder. We demonstrate that our method is able to determine the time interval of sinking of an intruder into shaken granular beds for both quasi-2D and 3D systems [1]. Due to its analogy with the working principle of a lock in amplifier, we call this technique Lock in accelerometry (LIA). In the experiments the intruder stops at a depth that we assume to be the beginning of the "jammed" granular phase. We are now developing numerical simulations based on a

  19. Destabilization of confined granular packings due to fluid flow

    Science.gov (United States)

    Monloubou, Martin; Sandnes, Bjørnar

    2016-04-01

    Fluid flow through granular materials can cause fluidization when fluid drag exceeds the frictional stress within the packing. Fluid driven failure of granular packings is observed in both natural and engineered settings, e.g. soil liquefaction and flowback of proppants during hydraulic fracturing operations. We study experimentally the destabilization and flow of an unconsolidated granular packing subjected to a point source fluid withdrawal using a model system consisting of a vertical Hele-Shaw cell containing a water-grain mixture. The fluid is withdrawn from the cell at a constant rate, and the emerging flow patterns are imaged in time-lapse mode. Using Particle Image Velocimetry (PIV), we show that the granular flow gets localized in a narrow channel down the center of the cell, and adopts a Gaussian velocity profile similar to those observed in dry grain flows in silos. We investigate the effects of the experimental parameters (flow rate, grain size, grain shape, fluid viscosity) on the packing destabilization, and identify the physical mechanisms responsible for the observed complex flow behaviour.

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

    Science.gov (United States)

    Shrivastava, Rohit Kumar; Luding, Stefan

    2017-06-01

    A mechanical wave is propagation of vibration with transfer of energy and momentum. Understanding the spectral energy characteristics of a propagating wave through disordered granular media can assist in understanding the overall properties of wave propagation through inhomogeneous materials like soil. The study of these properties is aimed at modeling wave propagation for oil, mineral or gas exploration (seismic prospecting) or non-destructive testing of the internal structure of solids. The focus is on the total energy content of a pulse propagating through an idealized one-dimensional discrete particle system like a mass disordered granular chain, which allows understanding the energy attenuation due to disorder since it isolates the longitudinal P-wave from shear or rotational modes. It is observed from the signal that stronger disorder leads to faster attenuation of the signal. An ordered granular chain exhibits ballistic propagation of energy whereas, a disordered granular chain exhibits more diffusive like propagation, which eventually becomes localized at long time periods. For obtaining mean-field macroscopic/continuum properties, ensemble averaging has been used, however, such an ensemble averaged spectral energy response does not resolve multiple scattering, leading to loss of information, indicating the need for a different framework for micro-macro averaging.

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

    Directory of Open Access Journals (Sweden)

    Shrivastava Rohit Kumar

    2017-01-01

    Full Text Available A mechanical wave is propagation of vibration with transfer of energy and momentum. Understanding the spectral energy characteristics of a propagating wave through disordered granular media can assist in understanding the overall properties of wave propagation through inhomogeneous materials like soil. The study of these properties is aimed at modeling wave propagation for oil, mineral or gas exploration (seismic prospecting or non-destructive testing of the internal structure of solids. The focus is on the total energy content of a pulse propagating through an idealized one-dimensional discrete particle system like a mass disordered granular chain, which allows understanding the energy attenuation due to disorder since it isolates the longitudinal P-wave from shear or rotational modes. It is observed from the signal that stronger disorder leads to faster attenuation of the signal. An ordered granular chain exhibits ballistic propagation of energy whereas, a disordered granular chain exhibits more diffusive like propagation, which eventually becomes localized at long time periods. For obtaining mean-field macroscopic/continuum properties, ensemble averaging has been used, however, such an ensemble averaged spectral energy response does not resolve multiple scattering, leading to loss of information, indicating the need for a different framework for micro-macro averaging.

  2. Prediction of shear bands in sand based on granular flow model and two-phase equilibrium

    Institute of Scientific and Technical Information of China (English)

    张义同; 齐德瑄; 杜如虚; 任述光

    2008-01-01

    In contrast to the traditional interpretation of shear bands in sand as a bifurcation problem in continuum mechanics,shear bands in sand are considered as high-strain phase(plastic phase) of sand and the materials outside the bands are still in low-strain phase(elastic phase),namely,the two phases of sand can coexist under certain condition.As a one-dimensional example,the results show that,for materials with strain-softening behavior,the two-phase solution is a stable branch of solutions,but the method to find two-phase solutions is very different from the one for bifurcation analysis.The theory of multi-phase equilibrium and the slow plastic flow model are applied to predict the formation and patterns of shear bands in sand specimens,discontinuity of deformation gradient and stress across interfaces between shear bands and other regions is considered,the continuity of displacements and traction across interfaces is imposed,and the Maxwell relation is satisfied.The governing equations are deduced.The critical stress for the formation of a shear band,both the stresses and strains inside the band and outside the band,and the inclination angle of the band can all be predicted.The predicted results are consistent with experimental measurements.

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

    Science.gov (United States)

    Gao, Bin

    2014-05-01

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

  4. Experimental investigation of impinging jet erosion on model cohesive granular materials

    Science.gov (United States)

    Brunier-Coulin, Florian; Sarrat, Jean-Loup; Cuéllar, Pablo; Philippe, Pierre

    2017-06-01

    Erosion of soils affects both natural landscapes and engineering constructions as embankment dams or levees. Improving the safety of such earthen structures requires in particular finding out more about the elementary mechanisms involved in soil erosion. Towards this end, an experimental work was undertaken in three steps. First, several model materials were developed, made of grains (mostly glass beads) with solid bridges at particle contacts whose mechanical yield strength can be continuously varied. Furthermore, for most of them, we succeeded in obtaining a translucent system for the purpose of direct visualization. Second, these materials were tested against surface erosion by an impinging jet to determine a critical shear stress and a kinetic coefficient [2, 3]. Note that an adapted device based on optical techniques (combination of Refractive Index Matching and Planar Laser Induced Fluorescence [3]) was used specifically for the transparent media. Third, some specifically developed mechanical tests, and particularly traction tests, were implemented to estimate the mechanical strength of the solid bridges both at micro-scale (single contact) and at macro-scale (sample) and to investigate a supposed relationship with soil resistance to erosion.

  5. A model of continuous granular medium. Waves in the reduced Cosserat continuum

    Directory of Open Access Journals (Sweden)

    V.V. Lalin

    2012-08-01

    Full Text Available In the description of vibrational properties of deformable bodies, it is usually assumed that the size of the oscillating particles is negligible in comparison with the average distance between them, so to describe the kinematics of such media only the displacement vector is used. In the majority of work is considered that when the independent rotational degrees of freedom are taken into account it become necessary to introduce the couple stress. Such models of continuous media are well known, for example, moment theory of elasticity or Cosserat media.A distinctive feature of the reduced Cosserat medium is that the stress tensor is asymmetric, and in static problems, this tensor becomes symmetric. Thus, in statics the reduced Cosserat media is indistinguishable from the the classical continuum in which the rotational degrees of freedom are not independent, as they are expressed in terms of displacement and the stress tensor is symmetric.In this paper we investigate the wave motion of a three-dimensional, isotropic, elastic reduced Cosserat medium, the characteristic velocities of wave propagation are finding, we also construct and analyze the dispersion curve for the dynamic equations.

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

    Science.gov (United States)

    2010-11-21

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

  7. Granular Solid-liquid Transition: Experiment and Simulation

    Science.gov (United States)

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

    2015-12-01

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

  8. A Classical Approach in Simple Nuclear Fusion Reaction 1H2 + 1H3 using Two-Dimension Granular Molecular Dynamics Model

    CERN Document Server

    Viridi, Sparisoma; Waris, Abdul; Perkasa, Yudha Satya

    2011-01-01

    Molecular dynamics in 2-D accompanied by granular model provides an opportunity to investigate binding between nuclei particles and its properties that arises during collision in a fusion reaction. A fully classical approach is used to observe the influence of initial angle of nucleus orientation to the product yielded by the reaction. As an example, a simplest fusion reaction between 1H2 and 1H3 is observed. Several products of the fusion reaction have been obtained, even the unreported ones, including temporary 2He4 nucleus.

  9. Noise induces rare events in granular media.

    Science.gov (United States)

    Khain, Evgeniy; Sander, Leonard M

    2016-09-01

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

  10. Sliding through a superlight granular medium.

    Science.gov (United States)

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

    2009-12-01

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

  11. Helical Locomotion in a Granular Medium

    Science.gov (United States)

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

    2017-08-01

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

  12. Granular gas dynamics

    CERN Document Server

    Brilliantov, Nikolai

    2003-01-01

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

  13. Congenital granular cell epulis.

    Science.gov (United States)

    Conrad, Rachel; Perez, Mia C N

    2014-01-01

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

  14. Blow up Analysis for Anomalous Granular Gases

    CERN Document Server

    Rey, Thomas

    2011-01-01

    We investigate in this article the long-time behaviour of the solutions to the energy-dependent, spatially-homogeneous, inelastic Boltzmann equation for hard spheres. This model describes a diluted gas composed of hard spheres under statistical description, that dissipates energy during collisions. We assume that the gas is "anomalous", in the sense that the energy dissipation increases when the temperature decreases. This allows the gas to cool down in finite time. We study the existence, uniqueness and attractiveness of blow up profiles for this model and the cooling law associated, generalizing the classical Haff's Law for granular gases. To this end, we give some new estimates about the third order moment of the inelastic Boltzmann equation with drift term and we introduce new strongly "non-linear" self-similar variables

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

    Science.gov (United States)

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

    2017-04-01

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

  16. 基于粒计算的SDG模型简化方法%The Simplified Method of SDG Model Based on Granular Computing

    Institute of Scientific and Technical Information of China (English)

    王培鑫; 田娟; 谢刚

    2012-01-01

    本文针对传统简化SDG模型方法存在简化不精、人工经验要求多的问题,提出了一种基于粒计算的SDG模型简化方法。该方法利用二进制粒矩阵约简节点组成的条件属性中的节点,在不影响完备性的前提下,达到简化模型的目的。最后以除氧器系统为例验证此方法的可行性。%In this paper, the author propose a simplified method of SDG model based on granular computing to solve problems which are the simplification is not refinded and a lots specialistic experience is required. Without affecting the completeness of SDG model, this method make use of bit granular matrix(BGrM) to simplify condition’s attributes for simplifying model. Finally, the deaerator system is as an example to verify the feasibility of this method.

  17. Driven fragmentation of granular gases.

    Science.gov (United States)

    Cruz Hidalgo, Raúl; Pagonabarraga, Ignacio

    2008-06-01

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

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

    Science.gov (United States)

    Wang, Guoyin; Xu, Ji

    2014-12-01

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

  19. Modeling of light dynamic cone penetration test – Panda 3 ® in granular material by using 3D Discrete element method

    Directory of Open Access Journals (Sweden)

    Tran Quoc Anh

    2017-01-01

    Full Text Available The recent technological developments made on the light dynamic penetration test Panda 3 ® provide a dynamic load–penetration curve σp – sp for each impact. This curve is influenced by the mechanical and physical properties of the investigated granular media. In order to analyze and exploit the load-penetration curve, a numerical model of penetration test using 3D Discrete Element Method is proposed for reproducing tests in dynamic conditions in granular media. All parameters of impact used in this model have at first been calibrated by respecting mechanical and geometrical properties of the hammer and the rod. There is a good agreement between experimental results and the ones obtained from simulations in 2D or 3D. After creating a sample, we will simulate the Panda 3 ®. It is possible to measure directly the dynamic load–penetration curve occurring at the tip for each impact. Using the force and acceleration measured in the top part of the rod, it is possible to separate the incident and reflected waves and then calculate the tip’s load-penetration curve. The load–penetration curve obtained is qualitatively similar with that obtained by experimental tests. In addition, the frequency analysis of the measured signals present also a good compliance with that measured in reality when the tip resistance is qualitatively similar.

  20. Models for dependent time series

    CERN Document Server

    Tunnicliffe Wilson, Granville; Haywood, John

    2015-01-01

    Models for Dependent Time Series addresses the issues that arise and the methodology that can be applied when the dependence between time series is described and modeled. Whether you work in the economic, physical, or life sciences, the book shows you how to draw meaningful, applicable, and statistically valid conclusions from multivariate (or vector) time series data.The first four chapters discuss the two main pillars of the subject that have been developed over the last 60 years: vector autoregressive modeling and multivariate spectral analysis. These chapters provide the foundational mater

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

    Science.gov (United States)

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

    2009-02-01

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

  2. Transitions in Shaken Granular Materials: Friction, Noise, and Bifurcations

    Science.gov (United States)

    Behringer, Robert P.

    2000-03-01

    I will describe a set of experiments and models that address the transition from solid to fluid granular states and vice versa. The experiments were carried out with a shaker that provided independent oscillations in the vertical and horizontal directions. A container of material with rectangular horizontal cross section was placed on this shaker, and the accelerations, Γh and Γv in the horizontal and vertical directions, were varied. With Γv = 0 and with increasing Γ_h, there was a transition from granular solid to fluid at Γ_hu and with decreasing Γ_h, there was a reverse transition from fluid to solid at Γ_hlweight. This hysteresis is not contained in Coulomb-like models of granular friction. However, we can introduce hysteresis in a model by assuming that the friction coefficient evolves with a characteristic time τ as the phase changes. Experimental measurements of τ show that it is a powerlaw function of ɛ, ɛ = A/τ, where ɛ measures the distance past the transition point, and where A is the same for both transitions. I will also consider other tests of friction and comparisions to models for which there is combined vertical and horizontal shaking.

  3. Rheological behavior of partially-wet granular matter

    Science.gov (United States)

    Ghelichi, Ramin; Kamrin, Ken; Kamrin Group Team

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

  4. Granular motions near the threshold of entrainment

    Science.gov (United States)

    Valyrakis, Manousos; Alexakis, athanasios-Theodosios

    2016-04-01

    Our society is continuously impacted by significant weather events many times resulting in catastrophes that interrupt our normal way of life. In the context of climate change and increasing urbanisation these "extreme" hydrologic events are intensified both in magnitude and frequency, inducing costs of the order of billions of pounds. The vast majority of such costs and impacts (even more to developed societies) are due to water related catastrophes such as the geomorphic action of flowing water (including scouring of critical infrastructure, bed and bank destabilisation) and flooding. New tools and radically novel concepts are in need, to enable our society becoming more resilient. This presentation, emphasises the utility of inertial sensors in gaining new insights on the interaction of flow hydrodynamics with the granular surface at the particle scale and for near threshold flow conditions. In particular, new designs of the "smart-sphere" device are discussed with focus on the purpose specific sets of flume experiments, designed to identify the exact response of the particle resting at the bed surface for various below, near and above threshold flow conditions. New sets of measurements are presented for particle entrainment from a Lagrangian viewpoint. Further to finding direct application in addressing real world challenges in the water sector, it is shown that such novel sensor systems can also help the research community (both experimentalists and computational modellers) gain a better insight on the underlying processes governing granular dynamics.

  5. Predictive modelling of running and dwell times in railway traffic

    NARCIS (Netherlands)

    Kecman, P.; Goverde, R.M.P.

    2015-01-01

    Accurate estimation of running and dwell times is important for all levels of planning and control of railway traffic. The availability of historical track occupation data with a high degree of granularity inspired a data-driven approach for estimating these process times. In this paper we present

  6. Gas-driven subharmonic waves in a vibrated two-phase granular material.

    Science.gov (United States)

    Matas, J-P; Uehara, J; Behringer, R P

    2008-04-01

    Vibrated powders exhibit striking phenomena: subharmonic waves, oscillons, convection, heaping, and even bubbling. We demonstrate novel rectangular profile subharmonic waves for vibrated granular material, that occur uniquely in the two-phase case of grains, and a fluid, such as air. These waves differ substantially from those for the gas-free case, exhibit different dispersion relations, and occur for specific shaking parameters and air pressure, understandable with gas-particle flow models. These waves occur when the gas diffusively penetrates the granular layer in a time comparable to the shaker period. As the pressure is lowered towards P =0, the granular-gas system exhibits a Knudsen regime. This instability provides an opportunity to quantitatively test models of two-phase flow.

  7. Multi-granularity Color Image Segmentation Based on Cloud Model%基于云模型的多粒度彩色图像分割

    Institute of Scientific and Technical Information of China (English)

    马鸿耀; 王国胤; 张清华; 徐宁

    2012-01-01

    Image information contains a lot of uncertainty which may cause the unsatisfactory image segmentation effect. In order to solve this problem, this paper proposes a algorithm of color image segmentation based on granular computing and cloud model. It granulates color images in HSV color space, and cloud-granule concept is generated in multi-granularity and multi-level, finally the color image is segmented. Experimental results show that the proposed algorithm has better performance compares with PCNN and K-means algorithm.%图像信息中存在的不确定性问题会影响图像的分割效果.为此,提出一种基于粒计算和云模型的彩色图像分割算法.研究多粒度认知模型,在HSV颜色空间中利用云模型构建彩色图像的信息粒,进行多粒度、多层次的云粒合成,实现彩色图像分割.实验结果表明,与PCNN算法和K均值算法相比,该算法的分割效果较好.

  8. Multiple impacts in dissipative granular chains

    CERN Document Server

    Nguyen, Ngoc Son

    2014-01-01

    The extension of collision models for single impacts between two bodies, to the case of multiple impacts (which take place when several collisions occur at the same time in a multibody system) is a challenge in Solid Mechanics, due to the complexity of such phenomena, even in the frictionless case. This monograph aims at presenting the main multiple collision rules proposed in the literature. Such collisions typically occur in granular materials, the simplest of which are made of chains of aligned balls. These chains are used throughout the book to analyze various multiple impact rules which extend the classical Newton (kinematic restitution), Poisson (kinetic restitution) and Darboux-Keller (energetic or kinetic restitution) approaches for impact modelling. The shock dynamics in various types of chains of aligned balls (monodisperse, tapered, decorated, stepped chains) is carefully studied and shown to depend on several parameters: restitution coefficients, contact stiffness ratios, elasticity coefficients (...

  9. Granular computing: perspectives and challenges.

    Science.gov (United States)

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

    2013-12-01

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

  10. Simulations of Granular Media

    Science.gov (United States)

    Herrmann, H. J.; Müller, M.

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

  11. Combining Discrete Element Modeling, Finite Element Analysis, and Experimental Calibrations for Modeling of Granular Material Systems Project

    Data.gov (United States)

    National Aeronautics and Space Administration — The current state-of-the-art in DEM modeling has two major limitations which must be overcome to ensure that the technique can be useful to NASA engineers and the...

  12. A simple probabilistic model of initiation of motion of poorly-sorted granular mixtures subjected to a turbulent flow

    Science.gov (United States)

    Ferreira, Rui M. L.; Ferrer-Boix, Carles; Hassan, Marwan

    2015-04-01

    Initiation of sediment motion is a classic problem of sediment and fluid mechanics that has been studied at wide range of scales. By analysis at channel scale one means the investigation of a reach of a stream, sufficiently large to encompass a large number of sediment grains but sufficiently small not to experience important variations in key hydrodynamic variables. At this scale, and for poorly-sorted hydraulically rough granular beds, existing studies show a wide variation of the value of the critical Shields parameter. Such uncertainty constitutes a problem for engineering studies. To go beyond Shields paradigm for the study of incipient motion at channel scale this problem can be can be cast in probabilistic terms. An empirical probability of entrainment, which will naturally account for size-selective transport, can be calculated at the scale of the bed reach, using a) the probability density functions (PDFs) of the flow velocities {{f}u}(u|{{x}n}) over the bed reach, where u is the flow velocity and xn is the location, b) the PDF of the variability of competent velocities for the entrainment of individual particles, {{f}{{up}}}({{u}p}), where up is the competent velocity, and c) the concept of joint probability of entrainment and grain size. One must first divide the mixture in into several classes M and assign a correspondent frequency p_M. For each class, a conditional PDF of the competent velocity {{f}{{up}}}({{u}p}|M) is obtained, from the PDFs of the parameters that intervene in the model for the entrainment of a single particle: [ {{u}p}/√{g(s-1){{di}}}={{Φ }u}( { {{C}k} },{{{φ}k}},ψ,{{u}p/{di}}{{{ν}(w)}} )) ] where { Ck } is a set of shape parameters that characterize the non-sphericity of the grain, { φk} is a set of angles that describe the orientation of particle axes and its positioning relatively to its neighbours, ψ is the skin friction angle of the particles, {{{u}p}{{d}i}}/{{{ν}(w)}} is a particle Reynolds number, di is the sieving

  13. Shaken Granular Lasers

    CERN Document Server

    Folli, Viola; Leuzzi, Luca; Conti, Claudio

    2012-01-01

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

  14. Shaken granular lasers.

    Science.gov (United States)

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

    2012-06-15

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

  15. Robophysical study of jumping dynamics on granular media

    Science.gov (United States)

    Aguilar, Jeffrey; Goldman, Daniel I.

    2016-03-01

    Characterizing forces on deformable objects intruding into sand and soil requires understanding the solid- and fluid-like responses of such substrates and their effect on the state of the object. The most detailed studies of intrusion in dry granular media have revealed that interactions of fixed-shape objects during free impact (for example, cannonballs) and forced slow penetration can be described by hydrostatic- and hydrodynamic-like forces. Here we investigate a new class of granular interactions: rapid intrusions by objects that change shape (self-deform) through passive and active means. Systematic studies of a simple spring-mass robot jumping on dry granular media reveal that jumping performance is explained by an interplay of nonlinear frictional and hydrodynamic drag as well as induced added mass (unaccounted by traditional intrusion models) characterized by a rapidly solidified region of grains accelerated by the foot. A model incorporating these dynamics reveals that added mass degrades the performance of certain self-deformations owing to a shift in optimal timing during push-off. Our systematic robophysical experiment reveals both new soft-matter physics and principles for robotic self-deformation and control, which together provide principles of movement in deformable terrestrial environments.

  16. Characteristics of undulatory locomotion in granular media

    Science.gov (United States)

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

    2016-03-01

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

  17. Thermomechanics of the granular bed T-joint water heater

    Science.gov (United States)

    Teplitskii, Yu. S.; Belonovich, D. G.

    2012-11-01

    On the basis of the heat transfer model taking into account the radiative transport the temperature distribution and the resistance of the water heater with a granular packing having two independent air inlets have been investigated. The generalized dependence for calculating the resistance of the granular bed has been obtained.

  18. A kinetic approach to granular gases

    OpenAIRE

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

    1998-01-01

    We address the problem of the so-called ``granular gases'', i.e. gases of massive particles in rapid movement undergoing inelastic collisions. We introduce a class of models of driven granular gases for which the stationary state is the result of the balance between the dissipation and the random forces which inject energies. These models exhibit a genuine thermodynamic limit, i.e. at fixed density the mean values of kinetic energy and dissipated energy per particle are independent of the num...

  19. Localization and instability in sheared granular materials: Role of friction and vibration

    CERN Document Server

    Kothari, Konik R

    2016-01-01

    Shear banding and stick-slip instabilities have been long observed in sheared granular materials. Yet, their microscopic underpinnings, interdependencies and variability under different loading conditions have not been fully explored. Here, we use a non-equilibrium thermodynamics model, the Shear Transformation Zone theory, to investigate the dynamics of strain localization and its connection to stability of sliding in sheared, dry, granular materials. We consider frictional and frictionless grains as well as presence and absence of acoustic vibrations. Our results suggest that at low and intermediate strain rates, persistent shear bands develop only in the absence of vibrations. Vibrations tend to fluidize the granular network and de-localize slip at these rates. Stick-slip is only observed for frictional grains and it is confined to the shear band. At high strain rates, stick-slip disappears and the different systems exhibit similar stress-slip response. Changing the vibration intensity, duration or time of...

  20. Failure of granular assemblies

    OpenAIRE

    Welker, Philipp

    2011-01-01

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

  1. Impact of granular drops

    KAUST Repository

    Marston, J. O.

    2013-07-15

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

  2. Characteristics of undulatory locomotion in granular media

    CERN Document Server

    Peng, Zhiwei; Elfring, Gwynn J

    2015-01-01

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

  3. Performance of on-site pilot static granular bed reactor (SGBR) for treating dairy processing wastewater and chemical oxygen demand balance modeling under different operational conditions.

    Science.gov (United States)

    Oh, Jin Hwan; Park, Jaeyoung; Ellis, Timothy G

    2015-02-01

    The performance and operational stability of a pilot-scale static granular bed reactor (SGBR) for the treatment of dairy processing wastewater were investigated under a wide range of organic and hydraulic loading rates and temperature conditions. The SGBR achieved average chemical oxygen demand (COD), biological oxygen demand (BOD), and total suspended solids (TSS)-removal efficiencies higher than 90% even at high loading rates up to 7.3 kg COD/m(3)/day, with an hydraulic retention time (HRT) of 9 h, and at low temperatures of 11 °C. The average methane yield of 0.26 L CH4/g COD(removed) was possibly affected by a high fraction of particulate COD and operation at low temperatures. The COD mass balance indicated that soluble COD was responsible for most of the methane production. The reactor showed the capacity of the methanogens to maintain their activity and withstand organic and hydraulic shock loads.

  4. Research on Granular Computing Model for Non-taxonomic Relations Learning%非分类关系学习的粒计算模型研究

    Institute of Scientific and Technical Information of China (English)

    邱桃荣; 黄海泉; 段文影; 周石林; 李向军

    2012-01-01

    以领域信息系统为研究对象,探讨学习非分类关系的粒计算模型.通过信息函数的扩展,给出了领域信息系统的形式化描述;研究了领域信息系统的粒化方法和领域概念粒度空间生成;对不同领域概念粒度空间,通过分析粒间上下文,提出了基于不同领域概念粒度空间的概念粒间交叉关系学习模型.示例与测试表明所提出的模型有助于实现领域本体的非分类关系的获取.%A granular computing model for non-taxonomic relation learning from a domain information system was proposed. Firstly,an information function was extended and a domain information system was described formally ; Secondly, one method of hierarchy granulating with respect to the domain information system was proposed. The method could generate information granules of different abstract degrees; According to different domain concept granular spaces and the context analysis between concept granules,an approach to acquiring cross relationship between concept granules was proposed. The proposed model could provide one feasible method and technology of ontology non-taxonomic relations learning.

  5. Pulling rigid bodies through granular material

    Science.gov (United States)

    Kubik, Ryan; Dressaire, Emilie

    2016-11-01

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

  6. Microstructure evolution during impact on granular matter.

    Science.gov (United States)

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

    2012-01-01

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

  7. Nitrate adsorption from aqueous solution using granular chitosan-Fe{sup 3+} complex

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Qili [School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing, 100083 (China); Key Laboratory of Groundwater Cycle and Environment Evolution,China University of Geosciences (Beijing), Ministry of Education, Beijing, 100083 (China); Chen, Nan, E-mail: chennan@cugb.edu.cn [School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing, 100083 (China); Key Laboratory of Groundwater Cycle and Environment Evolution, China University of Geosciences (Beijing), Ministry of Education, Beijing, 100083 (China); Feng, Chuanping [School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing, 100083 (China); Key Laboratory of Groundwater Cycle and Environment Evolution, China University of Geosciences (Beijing), Ministry of Education, Beijing, 100083 (China); Hu, WeiWu [The Journal Center, China University of Geosciences (Beijing), Beijing, 100083 (China)

    2015-08-30

    Highlights: • Granular chitosan-Fe{sup 3+} complex had high performance for nitrate adsorption. • Granular chitosan-Fe{sup 3+} complex had shorter equilibrium time (1.5 h). • Nitrate adsorption was ascribed to ion exchange and electrostatic attraction. • Granular chitosan-Fe{sup 3+} complex could be regenerated using NaCl solution. - Abstract: In the present study, In order to efficiently remove nitrate, granular chitosan-Fe{sup 3+} complex with high chemical stability and good environmental adaptation was synthesized through precipitation method and characterized using SEM, XRD, BET and FTIR. The nitrate adsorption performance was evaluated by batch experiments. The results indicated that granular chitosan-Fe{sup 3+} complex was an amorphous and mesoporous material. The BET specific surface area and average pore size were 8.98 m{sup 2} g{sup −1} and 56.94 Å, respectively. The point of zero charge was obtained at pH 5. The maximum adsorption capacity reached 8.35 mg NO{sub 3}{sup −}-N g{sup −1} based on Langmuir–Freundlich model. Moreover, no significant change in the nitrate removal efficiency was observed in the pH range of 3.0–10.0. The adverse influence of sulphate on nitrate removal was the most significant, followed by bicarbonate and fluoride, whereas chloride had slightly adverse effect. Adsorption process followed the pseudo-second-order kinetic model, and the experimental equilibrium data were fitted well with the Langmuir–Freundlich and D–R isotherm models. Thermodynamic parameters revealed that nitrate adsorption was a spontaneous and exothermic process. Granular chitosan-Fe{sup 3+} complex could be effectively regenerated by NaCl solution.

  8. 11th Traffic and Granular Flow Conference

    CERN Document Server

    Daamen, Winnie

    2016-01-01

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

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

    Science.gov (United States)

    Kamrin, Ken; Dunatunga, Sachith; Askari, Hesam

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

  10. Granular Impact Dynamics: Acoustics and Fluctuations

    CERN Document Server

    Clark, Abram H

    2012-01-01

    In the corresponding fluid dynamics video, created for the APS DFD 2012 Gallery of Fluid Motion, we show high-speed videos of 2D granular impact experiments, where an intruder strikes a collection of bidisperse photoelastic disks from above. We discuss the force beneath the intruder, which is strongly fluctuating in space and time. These fluctuations correspond to acoustic pulses which propagate into the medium. Analysis shows that this process, in our experiments, is dominated by collisions with grain clusters. The energy from these collisions is carried into the granular medium along networks of grains, where is it dissipated.

  11. Timing analysis by model checking

    Science.gov (United States)

    Naydich, Dimitri; Guaspari, David

    2000-01-01

    The safety of modern avionics relies on high integrity software that can be verified to meet hard real-time requirements. The limits of verification technology therefore determine acceptable engineering practice. To simplify verification problems, safety-critical systems are commonly implemented under the severe constraints of a cyclic executive, which make design an expensive trial-and-error process highly intolerant of change. Important advances in analysis techniques, such as rate monotonic analysis (RMA), have provided a theoretical and practical basis for easing these onerous restrictions. But RMA and its kindred have two limitations: they apply only to verifying the requirement of schedulability (that tasks meet their deadlines) and they cannot be applied to many common programming paradigms. We address both these limitations by applying model checking, a technique with successful industrial applications in hardware design. Model checking algorithms analyze finite state machines, either by explicit state enumeration or by symbolic manipulation. Since quantitative timing properties involve a potentially unbounded state variable (a clock), our first problem is to construct a finite approximation that is conservative for the properties being analyzed-if the approximation satisfies the properties of interest, so does the infinite model. To reduce the potential for state space explosion we must further optimize this finite model. Experiments with some simple optimizations have yielded a hundred-fold efficiency improvement over published techniques.

  12. Conceptual model of leachate migration in a granular aquifer derived from the integration of multi-source characterization data (St-Lambert, Canada)

    Science.gov (United States)

    Tremblay, Laurie; Lefebvre, René; Paradis, Daniel; Gloaguen, Erwan

    2014-05-01

    Numerical models encompassing source zones and receptors, based on representative conceptual models and accounting for aquifer heterogeneity, are needed to understand contaminant migration and fate; however, aquifer characterization seldom provides the necessary data. This study aimed to develop a workflow for field characterization and data integration, which could: (1) be adapted to the definition of subwatershed-scale aquifer heterogeneity (over 10 km2) and (2) adequately support mass transport model development. The study involved the field investigation of a shallow granular aquifer in a 12-km2 subwatershed in Saint-Lambert-de-Lauzon, Canada, in which a decommissioned landfill is emitting a leachate plume managed by natural attenuation. Using proven field methods, the characterization sequence was designed to optimize each method in terms of location, scale of acquisition, density and quality. The emphasis was on the acquisition of detailed indirect geophysical data that were integrated with direct hydraulic and geochemical data. This report focuses on the first qualitative and geostatistical data integration steps of the workflow leading to the development of a hydrogeological conceptual model. This is a prerequisite for further integration steps: prediction of hydrofacies and hydraulic conductivity ( K), geostatistical simulations of K, studies of geochemical processes and numerical modeling.

  13. Mechanical properties of wet granular materials

    Energy Technology Data Exchange (ETDEWEB)

    Fournier, Z; Geromichalos, D; Herminghaus, S; Kohonen, M M; Mugele, F; Scheel, M; Schulz, M; Schulz, B; Schier, Ch; Seemann, R; Skudelny, A

    2005-03-09

    We elaborate on the impact of liquids upon the mechanical properties of granular materials. We find that most of the experimental and simulation results may be accounted for by a simple model assuming frictionless, spherical grains, with a hysteretic attractive interaction between neighbouring grains due to capillary forces.

  14. Modelling of Attentional Dwell Time

    DEFF Research Database (Denmark)

    Petersen, Anders; Kyllingsbæk, Søren; Bundesen, Claus

    2009-01-01

    into the temporal domain. In the neural interpretation of TVA (NTVA; Bundesen, Habekost and Kyllingsbæk, 2005), processing resources are implemented as allocation of cortical cells to objects in the visual field. A feedback mechanism is then used to keep encoded objects in VSTM alive. The proposed model...... of attentional dwell time extends these mechanisms by proposing that the processing resources (cells) already engaged in a feedback loop (i.e. allocated to an object) are locked in VSTM and therefore cannot be allocated to other objects in the visual field before the encoded object has been released...

  15. Quantifying non-ergodic dynamics of force-free granular gases.

    Science.gov (United States)

    Bodrova, Anna; Chechkin, Aleksei V; Cherstvy, Andrey G; Metzler, Ralf

    2015-09-14

    Brownian motion is ergodic in the Boltzmann-Khinchin sense that long time averages of physical observables such as the mean squared displacement provide the same information as the corresponding ensemble average, even at out-of-equilibrium conditions. This property is the fundamental prerequisite for single particle tracking and its analysis in simple liquids. We study analytically and by event-driven molecular dynamics simulations the dynamics of force-free cooling granular gases and reveal a violation of ergodicity in this Boltzmann-Khinchin sense as well as distinct ageing of the system. Such granular gases comprise materials such as dilute gases of stones, sand, various types of powders, or large molecules, and their mixtures are ubiquitous in Nature and technology, in particular in Space. We treat-depending on the physical-chemical properties of the inter-particle interaction upon their pair collisions-both a constant and a velocity-dependent (viscoelastic) restitution coefficient ε. Moreover we compare the granular gas dynamics with an effective single particle stochastic model based on an underdamped Langevin equation with time dependent diffusivity. We find that both models share the same behaviour of the ensemble mean squared displacement (MSD) and the velocity correlations in the limit of weak dissipation. Qualitatively, the reported non-ergodic behaviour is generic for granular gases with any realistic dependence of ε on the impact velocity of particles.

  16. Traffic and Granular Flow’05

    CERN Document Server

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

    2007-01-01

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

  17. Partially saturated granular column collapse

    Science.gov (United States)

    Turnbull, Barbara; Johnson, Chris

    2017-04-01

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

  18. The Microstructural Response of Granular Soil Under Uniaxial Strain

    Science.gov (United States)

    1993-10-01

    contacts or granular motions will provide insight into more accurate modeling of the material response. The microstructural theory can be directly...use of a flow rule, the ramifications of using an associated or nonassociated flow rule for modeling the response of granular materials will also be...plasticity-based models has been developed over the past 30 yr. Common variations include perfect (ideal) plasticity, hypoelasticity , and viscoplasticity

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

    Science.gov (United States)

    Wakou, Jun'ichi; Isobe, Masaharu

    2012-06-01

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

  20. Analysis of vertical projectile penetration in granular soils

    Science.gov (United States)

    Boguslavskii, Yu; Drabkin, S.; Salman, A.

    1996-03-01

    A model of vertical dynamic penetration of projectiles in granular soils was developed based on known experiments and the theory of dimensions. The depth of penetration is derived as a function of initial velocity and material properties. Velocity and acceleration are obtained as functions of time and depth of penetration. Under certain conditions two acceleration peaks are observed, an initial one due to dynamic and a second one due to static characteristics of penetration. Static properties of soils are derived using dynamic measurements. Numerical examples are provided. Theoretical and experimental results coincide reasonably well.

  1. Granular flow over inclined channels with linear contraction

    CERN Document Server

    Tunuguntla, D R; Thornton, A R; Bokhove, O

    2015-01-01

    We consider dry granular flow down an inclined chute with a localised contraction theoretically and numerically. The flow regimes are predicted through a novel extended one-dimensional hydraulic theory. A discrete particle method validated empirical constitutive law is used to close this one-dimensional asymptotic model. The one-dimensional model is verified by solving the two-dimensional shallow granular equations through discontinuous Galerkin finite element method (DGFEM). For supercritical flows, the one-dimensional asymptotic theory surprisingly holds although the two-dimensional oblique granular jumps largely vary across the converging channel.

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

    Science.gov (United States)

    Peters, John F.

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

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

    Directory of Open Access Journals (Sweden)

    Wu Chuan-Yu

    2017-01-01

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

  4. Localized fluidization in a granular medium.

    Science.gov (United States)

    Philippe, P; Badiane, M

    2013-04-01

    We present here experimental results on the progressive development of a fluidized zone in a bed of grains, immersed in a liquid, under the effect of a localized upward flow injected through a small orifice at the bottom of the bed. Visualization inside the model granular medium consisting of glass beads is made possible by the combined use of two optical techniques: refractive index matching between the liquid and the beads and planar laser-induced fluorescence. Gradually increasing the injection rate, three regimes are successively observed: static bed, fluidized cavity that does not open to the upper surface of the granular bed, and finally fluidization over the entire height of the granular bed inside a fluidized chimney. The phase diagram is plotted and partially interpreted using a model previously developed by Zoueshtiagh and Merlen [F. Zoueshtiagh and A. Merlen, Phys. Rev. E 75, 053613 (2007)]. A typical sequence, where the flow rate is first increased and then decreased back to zero, reveals a strong hysteretic behavior since the stability of the fluidized cavity is considerably strengthened during the defluidization phase. This effect can be explained by the formation of force arches within the granular packing when the chimney closes up at the top of the bed. A study of the expansion rate of the fluidized cavity was also conducted as well as the analysis of the interaction between two injection orifices with respect to their spacing.

  5. A rheometer for measuring the material moduli for granular solids. Quarterly progress report, March 1, 1993--May 31, 1993

    Energy Technology Data Exchange (ETDEWEB)

    Rajagopal, K.R.

    1996-02-01

    This report describes the design of an orthogonal rheometer for the measuring of properties of granular materials such as coal. A section is presented on constitutive modeling of granular materials based on continuum theory.

  6. A rheometer for measuring the material moduli for granular solids. Quarterly progress report, December 1, 1992--February 28, 1993

    Energy Technology Data Exchange (ETDEWEB)

    Rajajopal, K.R.

    1996-02-01

    The design of an orthogonal rheometer for measuring the properties of granular solids is described. A section is presented on the constitutive modeling of granular materials based on continuum theory.

  7. Granular flow over inclined channels with constrictions

    Science.gov (United States)

    Tunuguntla, Deepak; Weinhart, Thomas; Thornton, Anthony; Bokhove, Onno

    2013-04-01

    Study of granular flows down inclined channels is essential in understanding the dynamics of natural grain flows like landslides and snow avalanches. As a stepping stone, dry granular flow over an inclined channel with a localised constriction is investigated using both continuum methods and particle simulations. Initially, depth-averaged equations of motion (Savage & Hutter 1989) containing an unknown friction law are considered. The shallow-layer model for granular flows is closed with a friction law obtained from particle simulations of steady flows (Weinhart et al. 2012) undertaken in the open source package Mercury DPM (Mercury 2010). The closed two-dimensional (2D) shallow-layer model is then width-averaged to obtain a novel one-dimensional (1D) model which is an extension of the one for water flows through contraction (Akers & Bokhove 2008). Different flow states are predicted by this novel one-dimensional theory. Flow regimes with distinct flow states are determined as a function of upstream channel Froude number, F, and channel width ratio, Bc. The latter being the ratio of the channel exit width and upstream channel width. Existence of multiple steady states is predicted in a certain regime of F - Bc parameter plane which is in agreement with experiments previously undertaken by (Akers & Bokhove 2008) and for granular flows (Vreman et al. 2007). Furthermore, the 1D model is verified by solving the 2D shallow granular equations using an open source discontinuous Galerkin finite element package hpGEM (Pesch et al. 2007). For supercritical flows i.e. F > 1 the 1D asymptotics holds although the two-dimensional oblique granular jumps largely vary across the converging channel. This computationally efficient closed 1D model is validated by comparing it to the computationally more expensiveaa three-dimensional particle simulations. Finally, we aim to present a quasi-steady particle simulation of inclined flow through two rectangular blocks separated by a gap

  8. Fate and transport of furrow-applied granular tefluthrin and seed-coated clothianidin insecticides: Comparison of field-scale observations and model estimates.

    Science.gov (United States)

    Huff Hartz, Kara E; Edwards, Tracye M; Lydy, Michael J

    2017-05-30

    The transport of agricultural insecticides to water bodies may create risk of exposure to non-target organisms. Similarly, widespread use of furrow-applied and seed-coated insecticides may increase risk of exposure, yet accessible exposure models are not easily adapted for furrow application, and only a few examples of model validation of furrow-applied insecticides exist using actual field data. The goal of the current project was to apply an exposure model, the Pesticide in Water Calculator (PWC), to estimate the concentrations of two in-furrow insecticides applied to maize: the granular pyrethroid, tefluthrin, and the seed-coated neonicotinoid, clothianidin. The concentrations of tefluthrin and clothianidin in surface runoff water, sampled from a field in central Illinois (USA), were compared to the PWC modeled pesticide concentrations in surface runoff. The tefluthrin concentrations were used to optimize the application method in the PWC, and the addition of particulate matter and guttation droplets improved the models prediction of clothianidin concentrations. Next, the tefluthrin and clothianidin concentrations were calculated for a standard farm pond using both the optimized application method and the application methods provided in PWC. Estimated concentrations in a standard farm pond varied by a factor of 100 for tefluthrin and 50 for clothianidin depending on the application method used. The addition of guttation droplets and particulate matter to the model increased the annual clothianidin concentration in a standard farm pond by a factor of 1.5, which suggested that these transport routes should also be considered when assessing neonicotinoid exposure.

  9. Collision Statistics of Driven Polydisperse Granular Gases

    Institute of Scientific and Technical Information of China (English)

    CHEN Zhi-Yuan; ZHANG Duan-Ming; LI Zhong-Ming; YANG Feng-Xia; GUO Xin-Ping

    2008-01-01

    We present a dynamicai model of two-dimensional polydisperse granular gases with fractal size distribution, in which the disks are subject to inelastic mutual collisions and driven by standard white noise. The inhomogeneity of the disk size distribution can be measured by a fractal dimension df. By Monte Carlo simulations, we have mainly investigated the effect of the inhomogeneity on the statistical properties of the system in the same inelasticity case. Some novel results are found that the average energy of the system decays exponentiaUy with a tendency to achieve a stable asymptotic value, and the system finally reaches a nonequilibrium steady state after a long evolution time. Furthermore, the inhomogeneity has great influence on the steady-state statisticai properties. With the increase of the fractal dimension df, the distributions of path lengths and free times between collisions deviate more obviously from expected theoretical forms for elastic spheres and have an overpopulation of short distances and time bins. The collision rate increases with df, but it is independent of time. Meanwhile, the velocity distribution deviates more strongly from the Gaussian one, but does not demonstrate any apparent universal behavior.

  10. ENERGY AND MASS TRANSPORT PROCESSES IN THE GRANULAR BED OF AN INDIRECTLY HEATED ROTARY KILN

    Institute of Scientific and Technical Information of China (English)

    Wolfgang Klose; Arndt-Peter Schinkel

    2004-01-01

    The transport mechanisms of momentum, mass, species, and energy are investigated in detail for the rotary kiln process. The residence time prediction of the granular bed is well improved by considering different flow patterns in the drum. Introducing a mixed flow pattem of the basic slipping and slumping behaviour has the most important effect on the improvement of the residence time prediction. The granular bed is assumed to behave as a Bingham fluid in the active layer of the bed. The transport mechanisms of momentum, species, and energy are modelled on the basis of this assumption and using the kinetic gas theory. Additionally, a mathematical transformation is presented to save computational time. The model results of the temperature field are in very good agreement with experimental data.

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

    Science.gov (United States)

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

    2017-07-01

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

  12. Scales and kinetics of granular flows.

    Science.gov (United States)

    Goldhirsch, I.

    1999-09-01

    When a granular material experiences strong forcing, as may be the case, e.g., for coal or gravel flowing down a chute or snow (or rocks) avalanching down a mountain slope, the individual grains interact by nearly instantaneous collisions, much like in the classical model of a gas. The dissipative nature of the particle collisions renders this analogy incomplete and is the source of a number of phenomena which are peculiar to "granular gases," such as clustering and collapse. In addition, the inelasticity of the collisions is the reason that granular gases, unlike atomic ones, lack temporal and spatial scale separation, a fact manifested by macroscopic mean free paths, scale dependent stresses, "macroscopic measurability" of "microscopic fluctuations" and observability of the effects of the Burnett and super-Burnett "corrections." The latter features may also exist in atomic fluids but they are observable there only under extreme conditions. Clustering, collapse and a kinetic theory for rapid flows of dilute granular systems, including a derivation of boundary conditions, are described alongside the mesoscopic properties of these systems with emphasis on the effects, theoretical conclusions and restrictions imposed by the lack of scale separation. (c) 1999 American Institute of Physics.

  13. Numerical Simulations of Granular Processes

    Science.gov (United States)

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

    2014-11-01

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

  14. Compaction shock dissipation in low density granular explosive

    Science.gov (United States)

    Rao, Pratap T.; Gonthier, Keith A.; Chakravarthy, Sunada

    2016-06-01

    The microstructure of granular explosives can affect dissipative heating within compaction shocks that can trigger combustion and initiate detonation. Because initiation occurs over distances that are much larger than the mean particle size, homogenized (macroscale) theories are often used to describe local thermodynamic states within and behind shocks that are regarded as the average manifestation of thermodynamic fields at the particle scale. In this paper, mesoscale modeling and simulation are used to examine how the initial packing density of granular HMX (C4H8N8O8) C4H8N8O8 having a narrow particle size distribution influences dissipation within resolved, planar compaction shocks. The model tracks the evolution of thermomechanical fields within large ensembles of particles due to pore collapse. Effective shock profiles, obtained by averaging mesoscale fields over space and time, are compared with those given by an independent macroscale compaction theory that predicts the variation in effective thermomechanical fields within shocks due to an imbalance between the solid pressure and a configurational stress. Reducing packing density is shown to reduce the dissipation rate within shocks but increase the integrated dissipated work over shock rise times, which is indicative of enhanced sensitivity. In all cases, dissipated work is related to shock pressure by a density-dependent power law, and shock rise time is related to pressure by a power law having an exponent of negative one.

  15. Compaction shock dissipation in low density granular explosive

    Energy Technology Data Exchange (ETDEWEB)

    Rao, Pratap T.; Gonthier, Keith A., E-mail: gonthier@me.lsu.edu; Chakravarthy, Sunada [Mechanical and Industrial Engineering Department, Louisiana State University, Baton Rouge, Louisiana 70803 (United States)

    2016-06-14

    The microstructure of granular explosives can affect dissipative heating within compaction shocks that can trigger combustion and initiate detonation. Because initiation occurs over distances that are much larger than the mean particle size, homogenized (macroscale) theories are often used to describe local thermodynamic states within and behind shocks that are regarded as the average manifestation of thermodynamic fields at the particle scale. In this paper, mesoscale modeling and simulation are used to examine how the initial packing density of granular HMX (C{sub 4}H{sub 8}N{sub 8}O{sub 8}) C{sub 4}H{sub 8}N{sub 8}O{sub 8} having a narrow particle size distribution influences dissipation within resolved, planar compaction shocks. The model tracks the evolution of thermomechanical fields within large ensembles of particles due to pore collapse. Effective shock profiles, obtained by averaging mesoscale fields over space and time, are compared with those given by an independent macroscale compaction theory that predicts the variation in effective thermomechanical fields within shocks due to an imbalance between the solid pressure and a configurational stress. Reducing packing density is shown to reduce the dissipation rate within shocks but increase the integrated dissipated work over shock rise times, which is indicative of enhanced sensitivity. In all cases, dissipated work is related to shock pressure by a density-dependent power law, and shock rise time is related to pressure by a power law having an exponent of negative one.

  16. Onset of silo collapse under gravity-driven granular discharges

    Science.gov (United States)

    Colonnello, Claudia; Gutiérrez, Gustavo; Reyes, Leonardo; Brau, Fabian; Clément, Eric

    2015-03-01

    Thin walled silos exhibit a critical filling height, Lc, above which the lateral wall buckles as a consequence of the frictional forces exerted by the grains during the granular discharge, producing a catastrophic failure of the structure. We use laboratory scale silos made of paper to study this process experimentally. Based on the observation of the deformation pattern that develops on the silo wall during the discharge, we have proposed a criterion for determining the time of onset of collapse, allowing us to study the conditions under which the collapse is triggered. In particular, we study the behavior of the grains in contact with the wall during the time interval before failure occurs and find that, according to this criterion, the collapse is triggered before a maximal mobilization of the grain-to-wall effective friction force is reached. This can be related to a theoretical model which treats the silo as a thin cylindrical shell subjected to an axial stress with the profile predicted by Janssen's model for the stresses in a silo filled with a granular material. This model predicts correctly the experimental scaling of Lc with various parameters of the system.

  17. Surface Instability of a Vertically Oscillating Granular Layer

    Institute of Scientific and Technical Information of China (English)

    SUI Lei; MIAO Guo-Qing; WEI Rong-Jue

    2001-01-01

    In the study of the surface instability of a vertically oscillating granular layer, we obtained experimentally thephase diagram for the surface states of the layer in the driving frequency-acceleration plane, and measured thedispersion relation for the surface waves in a granular layer in comparison to that in viscous fluids. Our experiments show that the onset dimensionless acceleration increases with the driving frequency, and the wavelengthof the surface waves increases with the depth of granular layer. These experimental results are in agreement withour theoretical model qualitatively.

  18. Microscopic study on stress-strain relation of granular materials

    Institute of Scientific and Technical Information of China (English)

    LIU SiHong; YAO YangPing; SUN QiCheng; LI TieJun; LIU MinZhi

    2009-01-01

    A biaxial shearing test on granular materials is numerically simulated by distinct element method (DEM). The evolution of the microstructures of granular materials during isotropic compression and shearing is investigated, on which a yield function is derived. The new yield function has a similar form as the one used in the modified Cam-clay model and explains the yield characteristics of granular materials under the isotropic compression and shear process through the change of the contact distribution N(θ) defining the contacts at particle contact angle θ.

  19. Theoretical Modeling Based on Granular Computing in Logistics Nodes Location%基于粒计算的物流节点选址理论建模

    Institute of Scientific and Technical Information of China (English)

    张丽岩; 马健

    2012-01-01

    The paper firstly cireumscribes a new concept of the logistics node from the three-dimensional aspect. Accord-ing to the characteristics of the logistics node and the nature of human decision-making, it puts forward a theoretical framework of pyramid, which starts from objective data and is based on " bounded rationality", "limited memory", " group decision" and " granular computing". Simultaneously, it pre- sents the application framework of logistics location from the process of the decision-making thought and the point of view of data mining, which can provide the reference pattern and standardized application flow for the pyramid model under the actual scenario of logistics location.%首先对物流节点进行了三维界定,从物流节点选址问题的特点及人的决策思维模式,以客观数据为出发点,以"有限理性"、"有限记忆"、"群体决策"和"粒计算"为理论基础,提出了金字塔理论架构,并应用于物流节点选址问题,进而提出了数据挖掘模型。该模型与选址的决策思维过程相适应,具有很好的理论指导意义。

  20. The Thermal Conductivity Theory of Non-uniform Granular Flow and the Mechanism Analysis

    Institute of Scientific and Technical Information of China (English)

    ZHANGDuan-Ming; LEIYa-Jie; YUBo-Ming; PANGui-Jun

    2003-01-01

    According to the fractal characteristics appearing in non-uniform granular system, we found the fractal model to study the effective thermal conductivity in the mixed system. Considering the quasi-equilibrium, we bring forward the fractal velocity probability distribution function. The equipartition of energy is employed to the non-uniform granular system, and the granular temperature is derived. We investigate the thermal conductivity in granular flow due to the movement of the particles, namely the heat transfer induced by the streaming mode only. The thermal conductivity in the mixed system changes with the fractal parameters such as the solid fraction v, structural character parameter η, and fractal dimension D of size distribution. These parameters depict the characteristics of the thermal conductivity in the actual complex granular system. Comparing our conclusion with the correlative experimental data and the theoretical conclusion of binary mixture of granular materials, the results can qualitatively confirm the generality of our prediction on the granular system.

  1. Wet granular walkers and climbers

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-05-15

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

  2. Structure and stability of methanogenic granular sludge.

    OpenAIRE

    Grotenhuis, J.T.C.

    1992-01-01

    Immobilization of anaerobic bacteria was essential for the development of high rate anaerobic systems for the treatment of waste waters. The most widely applied anaerobic reactor type in which solids retention time is uncoupled from the hydraulic retention time is the Upflow Anaerobic Sludge Blanket (UASB) reactor. In this reactor type methanogenic granular sludge is formed by self-immobilization of methanogenic consortia. The aim of the work presented in this thesis was to study microbiologi...

  3. Two-Pion Interferometry for the Granular Source in Heavy Ion Collisions at LHC Energies

    Institute of Scientific and Technical Information of China (English)

    尹洪杰; 安飞; 张卫宁

    2012-01-01

    The space-time characters of the pion-emitting sources produced in the heavy ion collisions at the Large Hadron Collider (LHC) energies are investigated in a granular source model of quark-gluon plasma droplets. The results of two-pion interferometry indicate that the longi- tudinal interferometry radius is sensitive to the initial breakup time of the system. For a larger breakup time the values of the longitudinal interferometry radius for the LHC source are larger than that of the source produced in the collisions at the Relativistic Heavy Ion Collider's (RHIC) top energy. However, the values of the longitudinal radius are smaller if the source fragments at a smaller breakup time with a higher initial temperature of the droplets. The values of the transverse interferometry radius in the "side" direction for the LHC sources are larger than those for the RHIC source. The imaging analyses for the characteristic quantities of the granular sources are consistent with the interferometry radii.

  4. Granular flows : fluidization and anisotropy

    NARCIS (Netherlands)

    Wortel, Gerrit Herman

    2014-01-01

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

  5. Evaluating Energy Flux in Vibrofluidized Granular Bed

    Directory of Open Access Journals (Sweden)

    N. A. Sheikh

    2013-01-01

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

  6. Compaction of granular material inside confined geometries

    Science.gov (United States)

    Marks, Benjy; Sandnes, Bjornar; Dumazer, Guillaume; Eriksen, Jon Alm; Måløy, Knut Jørgen

    2015-06-01

    In both nature and the laboratory, loosely packed granular materials are often compacted inside confined geometries. Here, we explore such behaviour in a quasi-two dimensional geometry, where parallel rigid walls provide the confinement. We use the discrete element method to investigate the stress distribution developed within the granular packing as a result of compaction due to the displacement of a rigid piston. We observe that the stress within the packing increases exponentially with the length of accumulated grains, and show an extension to current analytic models which fits the measured stress. The micromechanical behaviour is studied for a range of system parameters, and the limitations of existing analytic models are described. In particular, we show the smallest sized systems which can be treated using existing models. Additionally, the effects of increasing piston rate, and variations of the initial packing fraction, are described.

  7. Experimental and Simulation Analysis for the Impact of a Two-Link Chain with Granular Matter

    Directory of Open Access Journals (Sweden)

    Eliza A. Banu

    2015-01-01

    Full Text Available The resistance force of the granular matter is modeled as a linear superposition of a static (quadratic depth-dependent resistance force and a dynamic (quadratic velocity-dependent frictional force. The impact is defined from the moment the end point of the system comes in contact with the granular matter surface until the vertical linear velocity of the end point is zero. The variables of interest are the final depth at the end of the penetration phase and the stopping time. The results for a two-link kinematic chain with two points of contact were compared to the results obtained by applying the resistance force formulation developed to corresponding CAD simulation models. The results revealed that the final displacement increases with initial velocity, while the stopping time decreases. The sensitivity to the initial velocity was studied and an improvement to the resistance force formulated as a result. A series of expressions are proposed for the resistance force coefficients.

  8. Nonequilibrium Statistical Mechanics and Hydrodynamics for a Granular Fluid

    OpenAIRE

    Dufty, James W.

    2007-01-01

    Granular fluids consist of collections of activated mesoscopic or macroscopic particles (e.g., powders or grains) whose flows often appear similar to those of normal fluids. To explore the qualitative and quantitative description of these flows an idealized model for such fluids, a system of smooth inelastic hard spheres, is considered. The single feature distinguishing granular and normal fluids being explored in this way is the inelasticity of collisions. The dominant differences observed i...

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

    Science.gov (United States)

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

    2010-11-01

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

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

    DEFF Research Database (Denmark)

    Iftikhar, Nadeem

    2014-01-01

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

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

    DEFF Research Database (Denmark)

    Iftikhar, Nadeem; Pedersen, Torben Bach

    2014-01-01

    The majority of today’s systems increasingly require sophisticated data management as they need to store and to query large amounts of data for analysis and reporting purposes. In order to keep more “detailed” data available for longer periods, “old” data has to be reduced gradually to save space...... query processing due to a reduction in data volume. In addition, the paper describes the implementation strategy derived from a farming case study using standard database technologies....

  12. Constitutive relations for steady, dense granular flows

    Science.gov (United States)

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

    2011-12-01

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

  13. Parallel contributing area calculation with granularity control on massive grid terrain datasets

    Science.gov (United States)

    Jiang, Ling; Tang, Guoan; Liu, Xuejun; Song, Xiaodong; Yang, Jianyi; Liu, Kai

    2013-10-01

    The calculation of contributing areas from digital elevation models (DEMs) is one of the important tasks in digital terrain analysis (DTA). The computational process usually involves two steps in a real application: (1) calculating flow directions via a flow model, and (2) computing the contributing area for each grid cell in the DEM. The traditional algorithm for calculating contributing areas is coded as a sequential program executed on a single processor. With the increase of scope and resolution of DEMs, the serial algorithm has become increasingly difficult to perform and is often very time-consuming, especially for DEMs of large areas and fine scales. In recent years, parallel computing is able to meet this challenge with the development of computer technology. However, the parallel implementation with granularity control, an efficient strategy to reap the best parallel performance and to break the limitation of computing resources in processing massive grid terrain datasets, has not been found in DTA research field. This paper develops a message-passing-interface (MPI) parallel approach with granularity control to calculate contributing areas. According to the proposed parallelization strategy, the parallel D8 algorithm with granularity control is designed as well as the parallel AreaD8 algorithm. Based on the domain decomposition of DEM data, it is possible for each process to process multiple partitions decomposed under a grain size. According to an iterative procedure of reading source data, executing the operator and writing resulting data, the partitions achieve the calculation results one by one in each process. The experimental results on a multi-node cluster show that the proposed parallel algorithms with granularity control are the powerful tools to process the big dataset and the parallel D8 algorithm is insensitive to granularity, while the parallel AreaD8 algorithm has an optimal grain size to reap the best parallel performance.

  14. Traffic and Granular Flow ’07

    CERN Document Server

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

    2009-01-01

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

  15. Aerofractures in Confined Granular Media

    Science.gov (United States)

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

    2015-04-01

    processing techniques, we segment out and study the aerofractures over time looking at growth dynamics, fractal dimension and characteristics such as average finger thickness as function of depth into the solid. Also, by performing image correlation on two subsequent frames we estimate displacement fields and investigate the surrounding stress and strain fields in the solid around the fractures. Several experiments are performed with various overpressures and packing densities, and we compare the results. In a directly related project, acoustic emissions are recorded on a cell plate during experiments, and one of our goals is to correlate acoustic events and observations. We will also compare the dependence of the patterns on the saturation of the initial deformable porous material, by comparing experiments performed by air injection in air saturated granular media, to some in liquid saturated granular media. References: MJ Niebling, R Toussaint, EG Flekkøy, KJ Måløy, 2012, Dynamic aerofracture of dense granular packings, 2012, Physical Review E 86 (6), 061315 M Niebling, R Toussaint, EG Flekkøy, KJ Måløy, 2012, Numerical studies of aerofractures in porous media, Revista Cubana de Fisica 29 (1E), pp. 1E66-1E70

  16. Mathematical Models of Waiting Time.

    Science.gov (United States)

    Gordon, Sheldon P.; Gordon, Florence S.

    1990-01-01

    Considered are several mathematical models that can be used to study different waiting situations. Problems involving waiting at a red light, bank, restaurant, and supermarket are discussed. A computer program which may be used with these problems is provided. (CW)

  17. Ruin Probability in Linear Time Series Model

    Institute of Scientific and Technical Information of China (English)

    ZHANG Lihong

    2005-01-01

    This paper analyzes a continuous time risk model with a linear model used to model the claim process. The time is discretized stochastically using the times when claims occur, using Doob's stopping time theorem and martingale inequalities to obtain expressions for the ruin probability as well as both exponential and non-exponential upper bounds for the ruin probability for an infinite time horizon. Numerical results are included to illustrate the accuracy of the non-exponential bound.

  18. BOOK REVIEW: Kinetic Theory of Granular Gases

    Science.gov (United States)

    Trizac, Emmanuel

    2005-11-01

    inelasticity of inter-grain encounters—as velocity independent is inconsistent with the mechanical point of view. An asymptotic expression for the impact velocity dependence of ɛ is therefore derived for visco-elastic spheres. The important inelastic Boltzmann equation is introduced in part II and the associated velocity distribution characterized for a force-free medium (so-called free cooling regime). Transport processes can then be analyzed in part III at the single particle level, and part IV from a more macroscopic viewpoint. The corresponding Chapman Enskog-like hydrodynamic approach is worked out in detail, in a clear fashion. Finally, the tendency of granular gases to develop instabilities is illustrated in part V where the hydrodynamic picture plays a pivotal role. This book clearly sets the stage. For the sake of simplicity, the authors have discarded some subtle points, such as the open questions underlying the hydrodynamic description (why include the temperature among the hydrodynamic modes, and what about the separation of space and time scales between kinetic and hydrodynamic excitations?). Such omissions are understandable. To a certain extent however, the scope of the book is centered on previous work by the authors, and I have a few regrets. Special emphasis is put on the (variable ɛ) visco-elastic model, which enhances the technical difficulty of the presentation. On the other hand, the important physical effects including scaling laws, hydrodynamic behaviour and structure formation, can be understood in two steps, from the results derived within the much simpler constant ɛ model, allowing subsequently \\varepsilon to depend on the granular temperature. The authors justify their choice with the inconsistency of the constant ɛ route. The improvements brought by the visco-elastic model remain to be assessed, since the rotational degrees of freedom, discarded in the book, play an important role and require due consideration of both tangential and normal

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

    Science.gov (United States)

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

    2012-04-01

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

  20. Investigation of granular impact using positron emission particle tracking

    KAUST Repository

    Marston, Jeremy O.

    2015-04-01

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

  1. Self-Structuring of Granular material under Capillary Bulldozing

    Science.gov (United States)

    Dumazer, Guillaume; Sandnes, Bjørnar; Ayaz, Monem; Måløy, Knut Jørgen; Flekkøy, Eirik

    2017-06-01

    An experimental observation of the structuring of a granular suspension under the progress of a gas/liquid meniscus in a narrow tube is reported here. The granular material is moved and compactifies as a growing accumulation front. The frictional interaction with the confining walls increases until the pore capillary entry pressure is reached. The gas then penetrates the clogged granular packing and a further accumulation front is formed at the far side of the plug. This cyclic process continues until the gas/liquid interface reaches the tube's outlet, leaving a trail of plugs in the tube. Such 1D pattern formation belongs to a larger family of patterning dynamics observed in 2D Hele-Shaw geometry. The cylindrical geometry considered here provides an ideal case for a theoretical modelling for forced granular matter oscillating between a long frictional phase and a sudden viscous fluidization.

  2. Dynamic models in space and time

    NARCIS (Netherlands)

    Elhorst, J.P.

    2001-01-01

    This paper presents a first-order autoregressive distributed lag model in both space and time. It is shown that this model encompasses a wide series of simpler models frequently used in the analysis of space-time data as well as models that better fit the data and have never been used before. A fram

  3. Development of a Screening Model for Design and Costing of an Innovative Tailored Granular Activated Carbon Technology to Treat Perchlorate-Contaminated Water

    Science.gov (United States)

    2007-03-01

    1 Background ...Granular Activated Carbon Technology to Treat Perchlorate-Contaminated Water I. Introduction 1.1 Background Perchlorate is commonly used... Hypothyroidism is a condition where the thyroid makes insufficient amounts of these hormones with varying health effects, including impaired

  4. Time lags in biological models

    CERN Document Server

    MacDonald, Norman

    1978-01-01

    In many biological models it is necessary to allow the rates of change of the variables to depend on the past history, rather than only the current values, of the variables. The models may require discrete lags, with the use of delay-differential equations, or distributed lags, with the use of integro-differential equations. In these lecture notes I discuss the reasons for including lags, especially distributed lags, in biological models. These reasons may be inherent in the system studied, or may be the result of simplifying assumptions made in the model used. I examine some of the techniques available for studying the solution of the equations. A large proportion of the material presented relates to a special method that can be applied to a particular class of distributed lags. This method uses an extended set of ordinary differential equations. I examine the local stability of equilibrium points, and the existence and frequency of periodic solutions. I discuss the qualitative effects of lags, and how these...

  5. Finite element analysis of magnetization reversal in granular thin films

    CERN Document Server

    Spargo, A W

    2002-01-01

    This thesis develops a Galerkin finite element model of magnetisation dynamics in granular thin films. The governing equations of motion are the Gilbert equations with an effective magnetic field taking contributions from exchange interactions, magnetocrystalline anisotropy, applied magnetic field as well as the magnetostatic field given by Maxwells equations. The magnetostatic field is formulated as a scalar potential described by Poissons equation which is solved using a second order finite element method. The Gilbert equations are discretized in time using an implicit midpoint method which naturally conserves the magnitude of the magnetisation vector. An infinite thin film is approximated using periodic boundary conditions with material microstructure represented using the Voronoi tessellation. The effects of thermal fluctuations are modelled by the stochastic Langevin-Gilbert equations, again solved by a Galerkin finite element method. The implicit midpoint time-stepping scheme ensures that solutions conv...

  6. Velocity distributions in dilute granular systems.

    Science.gov (United States)

    van Zon, J S; MacKintosh, F C

    2005-11-01

    We investigate the idea that velocity distributions in granular gases are determined mainly by eta, the coefficient of restitution and q, which measures the relative importance of heating (or energy input) to collisions. To this end, we study by numerical simulation the properties of inelastic gases as functions of eta, concentration phi, and particle number N with various heating mechanisms. For a wide range of parameters, we find Gaussian velocity distributions for uniform heating and non-Gaussian velocity distributions for boundary heating. Comparison between these results and velocity distributions obtained by other heating mechanisms and for a simple model of a granular gas without spatial degrees of freedom, shows that uniform and boundary heating can be understood as different limits of q, with q>1 and q < or approximately 1 respectively. We review the literature for evidence of the role of q in the recent experiments.

  7. Mathematics and Mechanics of Granular Materials

    CERN Document Server

    Hill, James M

    2005-01-01

    Granular or particulate materials arise in almost every aspect of our lives, including many familiar materials such as tea, coffee, sugar, sand, cement and powders. At some stage almost every industrial process involves a particulate material, and it is usually the cause of the disruption to the smooth running of the process. In the natural environment, understanding the behaviour of particulate materials is vital in many geophysical processes such as earthquakes, landslides and avalanches. This book is a collection of current research from some of the major contributors in the topic of modelling the behaviour of granular materials. Papers from every area of current activity are included, such as theoretical, numerical, engineering and computational approaches. This book illustrates the numerous diverse approaches to one of the outstanding problems of modern continuum mechanics.

  8. Fluctuations of Power Injection in Randomly Driven Granular Gases

    Science.gov (United States)

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

    2006-11-01

    We investigate the large deviation function π∞( w) for the fluctuations of the power W( t) = wt, integrated over a time t, injected by a homogeneous random driving into a granular gas, in the infinite time limit. Our analytical study starts from a generalized Liouville equation and exploits a Molecular Chaos-like assumption. We obtain an equation for the generating function of the cumulants μ(λ) which appears as a generalization of the inelastic Boltzmann equation and has a clear physical interpretation. Reasonable assumptions are used to obtain μ(λ) in a closed analytical form. A Legendre transform is sufficient to get the large deviation function π∞( w). Our main result, apart from an estimate of all the cumulants of W( t) at large times t, is that π∞ has no negative branch. This immediately results in the inapplicability of the Gallavotti-Cohen Fluctuation Relation (GCFR), that in previous studies had been suggested to be valid for injected power in driven granular gases. We also present numerical results, in order to discuss the finite time behavior of the fluctuations of W ( t) . We discover that their probability density function converges extremely slowly to its asymptotic scaling form: the third cumulant saturates after a characteristic time τ larger than ˜50 mean free times and the higher order cumulants evolve even slower. The asymptotic value is in good agreement with our theory. Remarkably, a numerical check of the GCFR is feasible only at small times (at most τ/10), since negative events disappear at larger times. At such small times this check leads to the misleading conclusion that GCFR is satisfied for π∞( w). We offer an explanation for this remarkable apparent verification. In the inelastic Maxwell model, where a better statistics can be achieved, we are able to numerically observe the "failure" of GCFR.

  9. Topology, Structure and Functionality: Analysis, Modelling and Experimentation of Dense Granular Deformation in 2D and 3D

    Science.gov (United States)

    2015-01-05

    perspective, we can think of φJ as corresponding to random close packing ( rcp ) and the lowest density, φS ( ≈ 0.78 in 2D) for which shear jamming...In addition, coordinated video data is obtained for the region of the material that is under the slider. This is, in essence, a classic slip...the classical value. The energy and time scales are nevertheless set by (Mg)2 /kp, and ω-1, respectively. The photoelastic video data yield

  10. A General Model for People Movements Based on Multi Granularity and Its Application%多粒度的人群移动模拟通用模型及其应用

    Institute of Scientific and Technical Information of China (English)

    张仁军; Daniel Z Sui; 惠红

    2011-01-01

    人群的移动模拟应用广泛,但为不同时空尺度模拟需求开发不同的模拟系统十分困难和繁琐.该文设计了一种人群的空间移动模型(GMPM),GMPM具有多粒度特性,可应用于不同的领域,满足不同空间尺度、时间尺度的人群移动模拟需求;同时,GMPM又是一种通用开发模型原型,基于GMPM可以构造针对不同应用领域的人群空间移动模拟模型.最后,介绍了不同时空尺度人群移动模拟应用案例.%In this paper, the general model for people movements (GMPM) which can simulate different granularity movements for different purposes was discussed. GMPM is a platform, based on which the specialists can develop different application system for terminal users,just by inputting different rules and spatial region definitions. The spatial region can be defined in multiscales, and rules can be defined for different purpose or from different viewpoints, so GMPM is a multipurpose and multi-granularity model. GMPM consists of four modules: interface, rules and spatial region definition, database, and computation module.The spatial region is represented by a task-oriented model. The rules modeled include 3 types: the basic movement rules, the rules of basic rules changes,and the rules of attributes changes. An event-based database is used to record the movement and attributes changes. The computation module is based on the operations of database. Two case studies are presented, and studies show that the general model is compatible with different application and can simulate people movement over multi-granularity.

  11. Connectionist and diffusion models of reaction time.

    Science.gov (United States)

    Ratcliff, R; Van Zandt, T; McKoon, G

    1999-04-01

    Two connectionist frameworks, GRAIN (J. L. McClelland, 1993) and brain-state-in-a-box (J. A. Anderson, 1991), and R. Ratcliff's (1978) diffusion model were evaluated using data from a signal detection task. Dependent variables included response probabilities, reaction times for correct and error responses, and shapes of reaction-time distributions. The diffusion model accounted for all aspects of the data, including error reaction times that had previously been a problem for all response-time models. The connectionist models accounted for many aspects of the data adequately, but each failed to a greater or lesser degree in important ways except for one model that was similar to the diffusion model. The findings advance the development of the diffusion model and show that the long tradition of reaction-time research and theory is a fertile domain for development and testing of connectionist assumptions about how decisions are generated over time.

  12. Footprints in Sand: The Response of a Granular Material to Local Perturbations

    Energy Technology Data Exchange (ETDEWEB)

    Geng, Junfei; Howell, D.; Longhi, E.; Behringer, R. P.; Reydellet, G.; Vanel, L.; Clement, E.; Luding, S.

    2001-07-16

    We experimentally determine ensemble-averaged responses of granular packings to point forces, and we compare these results to recent models for force propagation in a granular material. We use 2D granular arrays consisting of photoelastic particles: either disks or pentagons, thus spanning the range from ordered to disordered packings. A key finding is that spatial ordering of the particles is a key factor in the force response. Ordered packings have a propagative component that does not occur in disordered packings.

  13. Time-Weighted Balanced Stochastic Model Reduction

    DEFF Research Database (Denmark)

    Tahavori, Maryamsadat; Shaker, Hamid Reza

    2011-01-01

    A new relative error model reduction technique for linear time invariant (LTI) systems is proposed in this paper. Both continuous and discrete time systems can be reduced within this framework. The proposed model reduction method is mainly based upon time-weighted balanced truncation and a recent...

  14. Model checking timed automata : techniques and applications

    NARCIS (Netherlands)

    Hendriks, Martijn.

    2006-01-01

    Model checking is a technique to automatically analyse systems that have been modeled in a formal language. The timed automaton framework is such a formal language. It is suitable to model many realistic problems in which time plays a central role. Examples are distributed algorithms, protocols, emb

  15. Lag space estimation in time series modelling

    DEFF Research Database (Denmark)

    Goutte, Cyril

    1997-01-01

    The purpose of this article is to investigate some techniques for finding the relevant lag-space, i.e. input information, for time series modelling. This is an important aspect of time series modelling, as it conditions the design of the model through the regressor vector a.k.a. the input layer...

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

    CERN Document Server

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

    2013-01-01

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

  17. Modelling expertise at different levels of granularity using semantic similarity measures in the context of collaborative knowledge-curation platforms.

    Science.gov (United States)

    Ziaimatin, Hasti; Groza, Tudor; Tudorache, Tania; Hunter, Jane

    2016-12-01

    Collaboration platforms provide a dynamic environment where the content is subject to ongoing evolution through expert contributions. The knowledge embedded in such platforms is not static as it evolves through incremental refinements - or micro-contributions. Such refinements provide vast resources of tacit knowledge and experience. In our previous work, we proposed and evaluated a Semantic and Time-dependent Expertise Profiling (STEP) approach for capturing expertise from micro-contributions. In this paper we extend our investigation to structured micro-contributions that emerge from an ontology engineering environment, such as the one built for developing the International Classification of Diseases (ICD) revision 11. We take advantage of the semantically related nature of these structured micro-contributions to showcase two major aspects: (i) a novel semantic similarity metric, in addition to an approach for creating bottom-up baseline expertise profiles using expertise centroids; and (ii) the application of STEP in this new environment combined with the use of the same semantic similarity measure to both compare STEP against baseline profiles, as well as to investigate the coverage of these baseline profiles by STEP.

  18. Physical modelling of tsunamis generated by three-dimensional deformable granular landslides on planar and conical island slopes.

    Science.gov (United States)

    McFall, Brian C; Fritz, Hermann M

    2016-04-01

    Tsunamis generated by landslides and volcanic island collapses account for some of the most catastrophic events recorded, yet critically important field data related to the landslide motion and tsunami evolution remain lacking. Landslide-generated tsunami source and propagation scenarios are physically modelled in a three-dimensional tsunami wave basin. A unique pneumatic landslide tsunami generator was deployed to simulate landslides with varying geometry and kinematics. The landslides were generated on a planar hill slope and divergent convex conical hill slope to study lateral hill slope effects on the wave characteristics. The leading wave crest amplitude generated on a planar hill slope is larger on average than the leading wave crest generated on a convex conical hill slope, whereas the leading wave trough and second wave crest amplitudes are smaller. Between 1% and 24% of the landslide kinetic energy is transferred into the wave train. Cobble landslides transfer on average 43% more kinetic energy into the wave train than corresponding gravel landslides. Predictive equations for the offshore propagating wave amplitudes, periods, celerities and lengths generated by landslides on planar and divergent convex conical hill slopes are derived, which allow an initial rapid tsunami hazard assessment.

  19. Mathematical modelling of the transport of a poorly sorted granular mixture as a debris-flow. The case of Madeira Island torrential floods in 2010

    Science.gov (United States)

    Ferreira, Rui M. L.; Oliveira, Rodrigo P.; Conde, Daniel

    2016-04-01

    On the 20th February 2010, heavy rainfall was registered at Madeira Island, North Atlantic. Stony debris flows, mudflows and mudslides ensued causing severe property loss, 1.5 m thick sediment deposits at downtown Funchal including 16th century monuments, and a death toll of 47 lives. Debris-flow fronts propagated downstream while carrying very high concentrations of solid material. These two-phase solid-fluid flows were responsible for most of the infrastructural damage across the island, due to their significantly increased mass and momentum. The objective of the present modelling work is to validate a 2DH model for torrential flows featuring the transport and interaction of several size fractions of a poorly-sorted granular mixture typical of stony debris flow in Madeira. The module for the transport of poorly-sorted material was included in STAV-2D (CERIS-IST), a shallow-water and morphology solver based on a finite-volume method using a flux-splitting technique featuring a reviewed Roe-Riemann solver, with appropriate source-term formulations to ensure full conservativeness. STAV-2D also includes formulations of flow resistance and bedload transport adequate for debris-flows with natural mobile beds (Ferreira et al., 2009) and has been validated with both theoretical solutions and laboratory data (Soares-Frazão et al., 2012; Canelas et al., 2013). The modelling of the existing natural and built environment is fully explicit. All buildings, streets and channels are accurately represented within the mesh geometry. Such detail is relevant for the reliability of the validation using field data, since the major sedimentary deposits within the urban meshwork of Funchal were identified and characterized in terms of volume and grain size distribution during the aftermath of the 20th February of 2010 event. Indeed, the measure of the quality of the numerical results is the agreement between simulated and estimated volume of deposited sediment and between estimated and

  20. Transport analogy for segregation and granular rheology

    Science.gov (United States)

    Liu, Siying; McCarthy, Joseph J.

    2017-08-01

    Here, we show a direct connection between density-based segregation and granular rheology that can lead to insight into both problems. Our results exhibit a transition in the rate of segregation during simple shear that occurs at I ˜0.5 and mimics a coincident regime change in flow rheology. We propose scaling arguments that support a packing fraction criterion for this transition that can both explain our segregation results as well as unify existing literature studies of granular rheology. By recasting a segregation model in terms of rheological parameters, we establish an approach that not only collapses results for a wide range of conditions, but also yields a direct relationship between the coordination number z and the segregation velocity. Moreover, our approach predicts the precise location of the observed regime change or saturation. This suggests that it is possible to rationally design process operating conditions that lead to significantly lower segregation extents. These observations can have a profound impact on both the study of granular flow or mixing as well as industrial practice.

  1. Accretion Dynamics on Wet Granular Materials.

    Science.gov (United States)

    Saingier, Guillaume; Sauret, Alban; Jop, Pierre

    2017-05-19

    Wet granular aggregates are common precursors of construction materials, food, and health care products. The physical mechanisms involved in the mixing of dry grains with a wet substrate are not well understood and difficult to control. Here, we study experimentally the accretion of dry grains on a wet granular substrate by measuring the growth dynamics of the wet aggregate. We show that this aggregate is fully saturated and its cohesion is ensured by the capillary depression at the air-liquid interface. The growth dynamics is controlled by the liquid fraction at the surface of the aggregate and exhibits two regimes. In the viscous regime, the growth dynamics is limited by the capillary-driven flow of liquid through the granular packing to the surface of the aggregate. In the capture regime, the capture probability depends on the availability of the liquid at the saturated interface, which is controlled by the hydrostatic depression in the material. We propose a model that rationalizes our observations and captures both dynamics based on the evolution of the capture probability with the hydrostatic depression.

  2. Small solar system bodies as granular systems

    Science.gov (United States)

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

    2017-06-01

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

  3. Small solar system bodies as granular systems

    Directory of Open Access Journals (Sweden)

    Hestroffer Daniel

    2017-01-01

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

  4. Seismic wave propagation in granular media

    Science.gov (United States)

    Tancredi, Gonzalo; López, Francisco; Gallot, Thomas; Ginares, Alejandro; Ortega, Henry; Sanchís, Johnny; Agriela, Adrián; Weatherley, Dion

    2016-10-01

    Asteroids and small bodies of the Solar System are thought to be agglomerates of irregular boulders, therefore cataloged as granular media. It is a consensus that many asteroids might be considered as rubble or gravel piles.Impacts on their surface could produce seismic waves which propagate in the interior of these bodies, thus causing modifications in the internal distribution of rocks and ejections of particles and dust, resulting in a cometary-type comma.We present experimental and numerical results on the study of propagation of impact-induced seismic waves in granular media, with special focus on behavior changes by increasing compression.For the experiment, we use an acrylic box filled with granular materials such as sand, gravel and glass spheres. Pressure inside the box is controlled by a movable side wall and measured with sensors. Impacts are created on the upper face of the box through a hole, ranging from free-falling spheres to gunshots. We put high-speed cameras outside the box to record the impact as well as piezoelectic sensors and accelerometers placed at several depths in the granular material to detect the seismic wave.Numerical simulations are performed with ESyS-Particle, a software that implements the Discrete Element Method. The experimental setting is reproduced in the numerical simulations using both individual spherical particles and agglomerates of spherical particles shaped as irregular boulders, according to rock models obtained with a 3D scanner. The numerical experiments also reproduces the force loading on one of the wall to vary the pressure inside the box.We are interested in the velocity, attenuation and energy transmission of the waves. These quantities are measured in the experiments and in the simulations. We study the dependance of these three parameters with characteristics like: impact speed, properties of the target material and the pressure in the media.These results are relevant to understand the outcomes of impacts in

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

    Science.gov (United States)

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

    2015-03-09

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

  6. Modelação da perda de carga na filtração direta ascendente em meio granular de areia grossa e pedregulho Modeling of the head loss in up flow coarse sand and gravel direct filtration

    Directory of Open Access Journals (Sweden)

    Alexandre Botari

    2009-06-01

    Full Text Available Compreender e quantificar os mecanismos relacionados à perda de carga e à remoção de partículas em um meio filtrante granular é de importância fundamental para o estudo do processo da filtração. Este trabalho apresenta o desenvolvimento dos modelos de perda de carga na filtração em meios porosos e a proposição da modelação matemática semiempírica da perda de carga para meios filtrantes limpos e do desenvolvimento do perfil de perda de carga ao longo do tempo de filtração a partir da equação de Ergun. Objetivou-se a determinação dos valores das constantes da equação de Ergun para meio granular de areia grossa e pedregulho. Alguns exemplos de aplicação dessa modelação matemática são também apresentados e discutidos pelos autores com base em dados experimentais obtidos em uma estação piloto de dupla filtração.To understand and to quantify the head loss due to the particles removal in a porous medium has primary importance to filtration process study. This paper presents the development of the models of head loss used in the filtration in porous media and proposes a mathematical semi-empiric model for head loss in clean beds and head loss increasing profile during the filtration run length, by means of the Ergun equation. The goal was the determination of Ergun’s equation coefficients for granular material constituted of coarse sand and gravel. Examples of application of these mathematical modeling are also presented and discussed by the authors based on experimental data obtained in a double filtration pilot plant.

  7. Nonlinear time series modelling: an introduction

    OpenAIRE

    Simon M. Potter

    1999-01-01

    Recent developments in nonlinear time series modelling are reviewed. Three main types of nonlinear models are discussed: Markov Switching, Threshold Autoregression and Smooth Transition Autoregression. Classical and Bayesian estimation techniques are described for each model. Parametric tests for nonlinearity are reviewed with examples from the three types of models. Finally, forecasting and impulse response analysis is developed.

  8. Uni-axial compaction of a granular material

    Science.gov (United States)

    Morland, L. W.; Sawicki, A.; Milne, P. C.

    1993-11-01

    S HEARING OF GRANULAR materials causes rearrangement of the granular structure which induces irreversible volume decrease and shear strain, in addition to reversible strain. The model adopted describes the reversible compression and shear by hypoelastic laws, and the irreversible compaction and shear by evolutionary laws. The latter are differential relations defining the progress of irreversible strain as an appropriate time-independent monotonie loading parameter increases, which incorporate dependence on the current state, and which prescribe a direction for the irreversible shear strain increment. The model is described by four material functions and two material constants, and has been shown to determine valid initial response to applied shear stress. We apply the model to the compaction of a granular material in uni-axial strain, which is described by two simultaneous differential equations for the axial stress and compaction with the axial strain as independent variable, together with algebraic relations for the pressure and lateral stress. The equation forms for loading-increasing axial stress—and unloading—decreasing axial stress-are distinct. Reformulation as differential equations for the pressure and the principal stress difference shows that the pressure derivative depends only on two of the material functions and one constant. The axial strain and lateral stress measured during a complete load-unload cycle on a sand determine the pressure and stress difference derivatives which are correlated directly with the model differential relations. Two material functions and one constant are determined by an optimization procedure from the complete loadunload ressure data, then the remaining two functions and constant from the stress difference data. Solution of the resulting model differential equations reproduces accurately the axial strain and lateral stress variations during the experimental loading cycle. In addition, model predictions for load

  9. Granular Superconductors and Gravity

    Science.gov (United States)

    Noever, David; Koczor, Ron

    1999-01-01

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

  10. A Simple Fuzzy Time Series Forecasting Model

    DEFF Research Database (Denmark)

    Ortiz-Arroyo, Daniel

    2016-01-01

    In this paper we describe a new first order fuzzy time series forecasting model. We show that our automatic fuzzy partitioning method provides an accurate approximation to the time series that when combined with rule forecasting and an OWA operator improves forecasting accuracy. Our model does...... not attempt to provide the best results in comparison with other forecasting methods but to show how to improve first order models using simple techniques. However, we show that our first order model is still capable of outperforming some more complex higher order fuzzy time series models....

  11. Time series modeling, computation, and inference

    CERN Document Server

    Prado, Raquel

    2010-01-01

    The authors systematically develop a state-of-the-art analysis and modeling of time series. … this book is well organized and well written. The authors present various statistical models for engineers to solve problems in time series analysis. Readers no doubt will learn state-of-the-art techniques from this book.-Hsun-Hsien Chang, Computing Reviews, March 2012My favorite chapters were on dynamic linear models and vector AR and vector ARMA models.-William Seaver, Technometrics, August 2011… a very modern entry to the field of time-series modelling, with a rich reference list of the current lit

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

    Science.gov (United States)

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

    2012-05-01

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

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

    Science.gov (United States)

    Goldman, Daniel I.

    2014-07-01

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

  14. Interaction of Polybrominated Diphenyl Ethers and Aerobic Granular Sludge: Biosorption and Microbial Degradation

    Directory of Open Access Journals (Sweden)

    Shou-Qing Ni

    2014-01-01

    Full Text Available As a new category of persistent organic pollutants, polybrominated diphenyl ethers (PBDEs have become ubiquitous global environmental contaminants. No literature is available on the aerobic biotransformation of decabromodiphenyl ether (BDE-209. Herein, we investigated the interaction of PBDEs with aerobic granular sludge. The results show that the removal of BDE-209 from wastewater is mainly via biosorption onto aerobic granular sludge. The uptake capacity increased when temperature, contact time, and sludge dosage increased or solution pH dropped. Ionic strength had a negative influence on BDE-209 adsorption. The modified pseudo first-order kinetic model was appropriate to describe the adsorption kinetics. Microbial debromination of BDE-209 did not occur during the first 30 days of operation. Further study found that aerobic microbial degradation of 4,4′-dibromodiphenyl ether happened with the production of lower BDE congeners.

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

    Science.gov (United States)

    Lacaze, Laurent; Kerswell, Rich R.

    2009-03-01

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

  16. Evolution of the Granular Dynamics and Energy Transport

    Science.gov (United States)

    Nesis, A.; Hammer, R.; Schleicher, H.

    2003-05-01

    Based on series of excellent spectrograms taken at the German Vacuum Tower Telescope (VTT) at the Observatorio del Teide (Tenerife), we study the temporal evolution of the granular dynamics and the energy transport in the photospheric layers. We consider the ensemble of the granules cut by the spectrograph slit as a complex system. We describe this ensemble by the rms of the fluctuations of the granular observables along the slit: continuum intensity I, Doppler velocity v, and line width w. The history of the rms of the observables v and w reflects the dynamical change of the system over the 20 minutes observation time. We find for both observables a quasi-periodical change. However, the history of the cross-correlation between I and v remains virtually constant, with the exception of two gaps. We measure the rms of v in the deep photospheric layers for six lines of different strength included in the spectrograms. Using a model velocity variation based on our previous publications, we assign photospheric heights to the velocity measurements. These heights agree with those calculated by other means. On the basis of this v variation we calculate the kinetic energy flux as a function of the height in the photosphere for different times during the observation. The form of the variation with height turns out to be constant in time. The convective energy flux, finally, is calculated from the measured velocity and the temperature variations of our earlier models. Again we find practically the same variation form over the time of the observation. Taken together, these results quantify the different roles that the lower and higher photospheric layers play for the energetics of the convective overshoot at the upper boundary of the superadiabatic region of the Sun. A.N. acknowledges travel support from the German science foundation DFG.

  17. Fluctuations of the dissipated energy in a granular system

    Science.gov (United States)

    Lasanta, Antonio; Hurtado, Pablo I.; Garrido, Pedro L.; Brey, J. Javier

    2011-03-01

    Large fluctuations, play an important role in many fields of science as they crucially determine the fate of a system. The statistics of these fluctuations encodes essential information on the physics of the system at hand. This is particularly important in systems far from equilibrium, where no general theory exists up to date capable of predicting macroscopic and fluctuating behavior in terms of microscopic physics.The study of fluctuations far from equilibrium may open the door to such general theory. In this work we follow this path by studying the fluctuations of the dissipated energy in an oversimplified model of a granular system. The model, first proposed and solved by Levanony and Levine [1], is a simple one dimensional diffusive lattice system which includes energy dissipation as a main ingredient. When subject to boundary heat baths, the system reaches an steady state characterized by a highly nonlinear temperature profile and a nonzero average energy dissipation. For long but finite times, the time-averaged dissipated energy fluctuates, obeying a large deviation principle. We study the large deviation function (LDF) of the dissipated energy by means of advanced Monte Carlo techniques [2], arriving to the following results: (i) the LDF of the dissipated energy has only a positive branch, meaning that for long times only positive dissipation is expected, (ii) as a result of microscopic time-irreversibility, the LDF does not obeys the Gallavotti-Cohen fluctuation theorem, (iii) the LDF is Gaussian around the average dissipation, but non-Gaussian, asymmetric tails quickly develop away from the average, and (iv) the granular system adopts a precise optimal profile in order to facilitate a given dissipation fluctuation, different from the steady profile. We compare our numerical results with predictions based on hydrodynamic fluctuation theory [3], finding good agreement.

  18. Self-assembled granular towers

    Science.gov (United States)

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

    2013-03-01

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

  19. Delivery Time Reliability Model of Logistics Network

    OpenAIRE

    Liusan Wu; Qingmei Tan; Yuehui Zhang

    2013-01-01

    Natural disasters like earthquake and flood will surely destroy the existing traffic network, usually accompanied by delivery delay or even network collapse. A logistics-network-related delivery time reliability model defined by a shortest-time entropy is proposed as a means to estimate the actual delivery time reliability. The less the entropy is, the stronger the delivery time reliability remains, and vice versa. The shortest delivery time is computed separately based on two different assum...

  20. Continuous-Time Modeling with Spatial Dependence

    NARCIS (Netherlands)

    Oud, J.H.L.; Folmer, H.; Patuelli, R.; Nijkamp, P.

    2012-01-01

    (Spatial) panel data are routinely modeled in discrete time (DT). However, compelling arguments exist for continuous-time (CT) modeling of (spatial) panel data. Particularly, most social processes evolve in CT, so that statistical analysis in DT is an oversimplification, gives an incomplete

  1. Continuous-Time Modeling with Spatial Dependence

    NARCIS (Netherlands)

    Oud, J.; Folmer, H.; Patuelli, R.; Nijkamp, P.

    (Spatial) panel data are routinely modeled in discrete time (DT). However, compelling arguments exist for continuous-time (CT) modeling of (spatial) panel data. Particularly, most social processes evolve in CT, so that statistical analysis in DT is an oversimplification, gives an incomplete

  2. Bayesian inference for pulsar timing models

    CERN Document Server

    Vigeland, Sarah J

    2013-01-01

    The extremely regular, periodic radio emission from millisecond pulsars make them useful tools for studying neutron star astrophysics, general relativity, and low-frequency gravitational waves. These studies require that the observed pulse time of arrivals are fit to complicated timing models that describe numerous effects such as the astrometry of the source, the evolution of the pulsar's spin, the presence of a binary companion, and the propagation of the pulses through the interstellar medium. In this paper, we discuss the benefits of using Bayesian inference to obtain these timing solutions. These include the validation of linearized least-squares model fits when they are correct, and the proper characterization of parameter uncertainties when they are not; the incorporation of prior parameter information and of models of correlated noise; and the Bayesian comparison of alternative timing models. We describe our computational setup, which combines the timing models of tempo2 with the nested-sampling integ...

  3. Mixed continuous/discrete time modelling with exact time adjustments

    NARCIS (Netherlands)

    Rovers, K.C.; Kuper, Jan; van de Burgwal, M.D.; Kokkeler, Andre B.J.; Smit, Gerardus Johannes Maria

    2011-01-01

    Many systems interact with their physical environment. Design of such systems need a modelling and simulation tool which can deal with both the continuous and discrete aspects. However, most current tools are not adequately able to do so, as they implement both continuous and discrete time signals

  4. Silo Collapse under Granular Discharge

    Science.gov (United States)

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

    2015-01-01

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

  5. Granular convection and its application to asteroidal resurfacing timescale

    Science.gov (United States)

    Yamada, Tomoya; Ando, Kosuke; Morota, Tomokatsu; Katsuragi, Hiroaki

    2016-04-01

    A model for the asteroid resurfacing resulting from regolith convection is built to estimate its timescale. The regolith convection by impact-induced global seismic shaking could be a possible reason for regolith migration and resultant segregated terrain which were found on the asteroids Itokawa [1]. Some recent studies [2, 3] experimentally investigated the convective velocity of the vibrated granular bed to discuss the feasibility of regolith convection under the microgravity condition such as small asteroids. These studies found that the granular convective velocity is almost proportional to the gravitational acceleration [2, 3]. Namely, the granular (regolith) convective velocity would be very low under the microgravity condition. Therefore, the timescale of resurfacing by regolith convection would become very long. In order to examine the feasibility of the resurfacing by regolith convection on asteroids, its timescale have to be compared with the surface age or the lifetime of asteroids. In this study, we aim at developing a model of asteroid resurfacing process induced by regolith convection. The model allows us to estimate the resurfacing timescale for various-sized asteroids covered with regolith. In the model, regolith convection is driven by the impact-induced global seismic shaking. The model consists of three phases, (i) Impact phase: An impactor intermittently collides with a target asteroid [4], (ii) Vibration phase: The collision results in a global seismic shaking [5], (iii) Convection phase: The global seismic shaking induces the regolith convection on the asteroid [3]. For the feasibility assessment of the resurfacing process driven by regolith convection, we estimate the regolith-convection-based resurfacing timescale T as a function of the size of a target asteroid Da. According to the estimated result, the resurfacing time scale is 40 Myr for the Itokawa-sized asteroid, and this value is shorter than the mean collisional lifetime of Itokawa

  6. A Terradynamics of Legged Locomotion on Granular Media

    CERN Document Server

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

    2013-01-01

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

  7. Discounting Models for Outcomes over Continuous Time

    DEFF Research Database (Denmark)

    Harvey, Charles M.; Østerdal, Lars Peter

    Events that occur over a period of time can be described either as sequences of outcomes at discrete times or as functions of outcomes in an interval of time. This paper presents discounting models for events of the latter type. Conditions on preferences are shown to be satisfied if and only if t...

  8. Selective Maintenance Model Considering Time Uncertainty

    OpenAIRE

    Le Chen; Zhengping Shu; Yuan Li; Xuezhi Lv

    2012-01-01

    This study proposes a selective maintenance model for weapon system during mission interval. First, it gives relevant definitions and operational process of material support system. Then, it introduces current research on selective maintenance modeling. Finally, it establishes numerical model for selecting corrective and preventive maintenance tasks, considering time uncertainty brought by unpredictability of maintenance procedure, indetermination of downtime for spares and difference of skil...

  9. Segregation induced fingering instabilities in granular avalanches

    Science.gov (United States)

    Woodhouse, Mark; Thornton, Anthony; Johnson, Chris; Kokelaar, Pete; Gray, Nico

    2013-04-01

    It is important to be able to predict the distance to which a hazardous natural granular flows (e.g. snow slab avalanches, debris-flows and pyroclastic flows) might travel, as this information is vital for accurate assessment of the risks posed by such events. In the high solids fraction regions of these flows the large particles commonly segregate to the surface, where they are transported to the margins to form bouldery flow fronts. In many natural flows these bouldery margins experience a much greater frictional force, leading to frontal instabilities. These instabilities create levees that channelize the flow vastly increasing the run-out distance. A similar effect can be observed in dry granular experiments, which use a combination of small round and large rough particles. When this mixture is poured down an inclined plane, particle size segregation causes the large particles to accumulate near the margins. Being rougher, the large particles experience a greater friction force and this configuration (rougher material in front of smoother) can be unstable. The instability causes the uniform flow front to break up into a series of fingers. A recent model for particle size-segregation has been coupled to existing avalanche models through a particle concentration dependent friction law. In this talk numerical solutions of this coupled system are presented and compared to both large scale experiments carried out at the USGS flume and more controlled small scale laboratory experiments. The coupled depth-averaged model captures the accumulation of large particles at the flow front. We show this large particle accumulation at the head of the flow can lead to the break-up of the initially uniform front into a series of fingers. However, we are unable to obtain a fully grid-resolved numerical solution; the width of the fingers decreases as the grid is refined. By considering the linear stability of a steady, fully-developed, bidisperse granular layer it is shown that

  10. Determination of contact parameters for discrete element method simulations of granular systems

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Both linear-spring-dashpot (LSD) and non-linear Hertzian-spring-dnshpot (HSD) contact models are commonly used for the calculation of contact forces in Discrete Element Method (DEM) simulations of granular systems.Despite the popularity of these models, determination of suitable values for the contact parameters of the simulated particles such as stiffness, damping coefficient, coefficient of restitution, and simulation time step,is not altogether obvious.In this work the relationships between these contact parameters for a model system where a particle impacts on a flat base are examined.Recommendations are made concerning the determination of these contact parameters for use in DEM simulations.

  11. Survey of time preference, delay discounting models

    Directory of Open Access Journals (Sweden)

    John R. Doyle

    2013-03-01

    Full Text Available The paper surveys over twenty models of delay discounting (also known as temporal discounting, time preference, time discounting, that psychologists and economists have put forward to explain the way people actually trade off time and money. Using little more than the basic algebra of powers and logarithms, I show how the models are derived, what assumptions they are based upon, and how different models relate to each other. Rather than concentrate only on discount functions themselves, I show how discount functions may be manipulated to isolate rate parameters for each model. This approach, consistently applied, helps focus attention on the three main components in any discounting model: subjectively perceived money; subjectively perceived time; and how these elements are combined. We group models by the number of parameters that have to be estimated, which means our exposition follows a trajectory of increasing complexity to the models. However, as the story unfolds it becomes clear that most models fall into a smaller number of families. We also show how new models may be constructed by combining elements of different models. The surveyed models are: Exponential; Hyperbolic; Arithmetic; Hyperboloid (Green and Myerson, Rachlin; Loewenstein and Prelec Generalized Hyperboloid; quasi-Hyperbolic (also known as beta-delta discounting; Benhabib et al's fixed cost; Benhabib et al's Exponential / Hyperbolic / quasi-Hyperbolic; Read's discounting fractions; Roelofsma's exponential time; Scholten and Read's discounting-by-intervals (DBI; Ebert and Prelec's constant sensitivity (CS; Bleichrodt et al.'s constant absolute decreasing impatience (CADI; Bleichrodt et al.'s constant relative decreasing impatience (CRDI; Green, Myerson, and Macaux's hyperboloid over intervals models; Killeen's additive utility; size-sensitive additive utility; Yi, Landes, and Bickel's memory trace models; McClure et al.'s two exponentials; and Scholten and Read's trade

  12. 倾斜推移体激发颗粒流的连续介质模型%A Continuum Model of Granular Flow Induced By Inclined Plane

    Institute of Scientific and Technical Information of China (English)

    郭鸿; 骆亚生; 程大伟; 陈茜; 陈栋梁

    2015-01-01

    岩土工程中的土方推移等属于颗粒体的倾斜推移问题,探索了倾斜推移体在颗粒中平动推移时所受的阻力和升力。应用惯性数的理念,确定了流态类型,提出了适合非准静态流的广义摩擦系数。在此基础上,用基于改进的库伦被动土压力理论,通过基于二维颗粒离散元的位移场分析,建立了预测推移阻力和升力的楔体模型。结果表明,在其他条件相同时,推移阻力不随推移体的倾角变化,但是升力随倾角的增大而显著减小。升力和阻力分别是作用在推移体上合力的竖直分量和水平分量,且阻力和升力的比值为推移体倾角的正切值。广义摩擦角是推移速度和倾角的二次函数。所建立的模型可以预测不同倾角和推移速度时推移阻力和升力的大小。%Soils moving is one of the geotechnical problems, which can be described as a granular flow induced by inclined plane.This work aims to investigate the drag and lift forces acting on the inclined in-truder.By using the inertial number concept to confirm the flow regime, a parameter named dynamic fric-tion coefficient is induced to this non-quasi-static flow.By improving the Coulomb model, the displace-ment field is obtained by two dimensional discrete element method, and the wedge model for drag and lift forces is built.The results show that drag force is dependent of the inclined angle when the other condi-tions are the same, but the lift force is decreasing with the inclined angle.Drag and lift forces are the horizontal and vertical components of the total force, respectively.And the ratio of drag and lift forces is just equal to the tangent value of the inclined angle.The dynamic friction angle is the quadratic function of velocity and inclined angle.This model can predict different case in different inclined angle and veloci-ty.

  13. Spatiotemporal patterns in reaction-diffusion system and in a vibrated granular bed

    Energy Technology Data Exchange (ETDEWEB)

    Swinney, H.L.; Lee, K.J.; McCormick, W.D. [Univ. of Texas, Austin, TX (United States)

    1995-12-31

    Experiments on a quasi-two-dimensional reaction-diffusion system reveal transitions from a uniform state to stationary hexagonal, striped, and rhombic spatial patterns. For other reactor conditions lamellae and self-replicating spot patterns are observed. These patterns form in continuously fed thin gel reactors that can be maintained indefinitely in well-defined nonequilibrium states. Reaction-diffusion models with two chemical species yield patterns similar to those observed in the experiments. Pattern formation is also being examined in vertically oscillated thin granular layers (typically 3-30 particle diameters deep). For small acceleration amplitudes, a granular layer is flat, but above a well-defined critical acceleration amplitude, spatial patterns spontaneously form. Disordered time-dependent granular patterns are observed as well as regular patterns of squares, stripes, and hexagons. A one-dimensional model consisting of a completely inelastic ball colliding with a sinusoidally oscillating platform provides a semi-quantitative description of most of the observed bifurcations between the different spatiotemporal regimes.

  14. Model Epidemi Sirs Dengan Time Delay

    OpenAIRE

    Sinuhaji, Ferdinand

    2016-01-01

    The epidemic is an outbreak of an infectious disease situation in the population at a place that exceeds the normal approximation in a short period. When the disease is always contained in any place as well as with the causes, it is called endemic. This study discusses decrease SIRS epidemic models with time delay through a mathematical model based on the model of SIRS epidemic (Susceptible, Infective, Recovered, Susceptible). SIRS models used in this study with the assumption ...

  15. Nickel and cobalt sorption on anaerobic granular sludges: kinetic and equilibrium studies

    NARCIS (Netherlands)

    Hullebusch, van E.D.; Zandvoort, M.H.; Lens, P.N.L.

    2004-01-01

    The kinetics and equilibria of sorption of the divalent metal ions cobalt and nickel onto anaerobic granular sludge are described. Single component and binary equimolar systems were studied at different pH values (pH 6, 7 and 8). The kinetic modelling of metal sorption by anaerobic granular sludge h

  16. Multi-Scale Dynamics, Control, and Simulation of Granular Spacecraft

    Science.gov (United States)

    Quadrelli, Marco B.; Basinger, Scott; Swartzlander, Grover

    2013-01-01

    In this paper, we present some ideas regarding the modeling, dynamics and control aspects of granular spacecraft. Granular spacecraft are complex multibody systems composed of a spatially disordered distribution of a large number of elements, for instance a cloud of grains in orbit. An example of application is a spaceborne observatory for exoplanet imaging, where the primary aperture is a cloud instead of a monolithic aperture. A model is proposed of a multi-scale dynamics of the grains and cloud in orbit, as well as a control approach for cloud shape maintenance and alignment, and preliminary simulation studies are carried out for the representative imaging system.

  17. Granular cell ameloblastoma of mandible.

    Science.gov (United States)

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

    2014-01-01

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

  18. Ultrascale simulations of non-smooth granular dynamics

    Science.gov (United States)

    Preclik, Tobias; Rüde, Ulrich

    2015-06-01

    This article presents new algorithms for massively parallel granular dynamics simulations on distributed memory architectures using a domain partitioning approach. Collisions are modelled with hard contacts in order to hide their micro-dynamics and thus to extend the time and length scales that can be simulated. The global multi-contact problem is solved using a non-linear block Gauss-Seidel method that is conforming to the subdomain structure. The parallel algorithms employ a sophisticated protocol between processors that delegate algorithmic tasks such as contact treatment and position integration uniquely and robustly to the processors. Communication overhead is minimized through aggressive message aggregation, leading to excellent strong and weak scaling. The robustness and scalability is assessed on three clusters including two peta-scale supercomputers with up to 458,752 processor cores. The simulations can reach unprecedented resolution of up to ten billion () non-spherical particles and contacts.

  19. Ultrascale Simulations of Non-smooth Granular Dynamics

    CERN Document Server

    Preclik, Tobias

    2015-01-01

    This article presents new algorithms for massively parallel granular dynamics simulations on distributed memory architectures using a domain partitioning approach. Collisions are modelled with hard contacts in order to hide their micro-dynamics and thus to extend the time and length scales that can be simulated. The multi-contact problem is solved using a non-linear block Gauss-Seidel method that is conforming to the subdomain structure. The parallel algorithms employ a sophisticated protocol between processors that delegate algorithmic tasks such as contact treatment and position integration uniquely and robustly to the processors. Communication overhead is minimized through aggressive message aggregation, leading to excellent strong and weak scaling. The robustness and scalability is assessed on three clusters including two peta-scale supercomputers with up to 458752 processor cores. The simulations can reach unprecedented resolution of up to ten billion non-spherical particles and contacts.

  20. Delivery Time Reliability Model of Logistics Network

    Directory of Open Access Journals (Sweden)

    Liusan Wu

    2013-01-01

    Full Text Available Natural disasters like earthquake and flood will surely destroy the existing traffic network, usually accompanied by delivery delay or even network collapse. A logistics-network-related delivery time reliability model defined by a shortest-time entropy is proposed as a means to estimate the actual delivery time reliability. The less the entropy is, the stronger the delivery time reliability remains, and vice versa. The shortest delivery time is computed separately based on two different assumptions. If a path is concerned without capacity restriction, the shortest delivery time is positively related to the length of the shortest path, and if a path is concerned with capacity restriction, a minimax programming model is built to figure up the shortest delivery time. Finally, an example is utilized to confirm the validity and practicality of the proposed approach.

  1. Building Chaotic Model From Incomplete Time Series

    Science.gov (United States)

    Siek, Michael; Solomatine, Dimitri

    2010-05-01

    This paper presents a number of novel techniques for building a predictive chaotic model from incomplete time series. A predictive chaotic model is built by reconstructing the time-delayed phase space from observed time series and the prediction is made by a global model or adaptive local models based on the dynamical neighbors found in the reconstructed phase space. In general, the building of any data-driven models depends on the completeness and quality of the data itself. However, the completeness of the data availability can not always be guaranteed since the measurement or data transmission is intermittently not working properly due to some reasons. We propose two main solutions dealing with incomplete time series: using imputing and non-imputing methods. For imputing methods, we utilized the interpolation methods (weighted sum of linear interpolations, Bayesian principle component analysis and cubic spline interpolation) and predictive models (neural network, kernel machine, chaotic model) for estimating the missing values. After imputing the missing values, the phase space reconstruction and chaotic model prediction are executed as a standard procedure. For non-imputing methods, we reconstructed the time-delayed phase space from observed time series with missing values. This reconstruction results in non-continuous trajectories. However, the local model prediction can still be made from the other dynamical neighbors reconstructed from non-missing values. We implemented and tested these methods to construct a chaotic model for predicting storm surges at Hoek van Holland as the entrance of Rotterdam Port. The hourly surge time series is available for duration of 1990-1996. For measuring the performance of the proposed methods, a synthetic time series with missing values generated by a particular random variable to the original (complete) time series is utilized. There exist two main performance measures used in this work: (1) error measures between the actual

  2. Phase Diagram of Vertically Shaken Granular Matter

    CERN Document Server

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

    2006-01-01

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

  3. Multi-model Cross Pollination in Time

    CERN Document Server

    Du, Hailiang

    2016-01-01

    Predictive skill of complex models is often not uniform in model-state space; in weather forecasting models, for example, the skill of the model can be greater in populated regions of interest than in "remote" regions of the globe. Given a collection of models, a multi-model forecast system using the cross pollination in time approach can be generalised to take advantage of instances where some models produce systematically more accurate forecast of some components of the model-state. This generalisation is stated and then successfully demonstrated in a moderate ~40 dimensional nonlinear dynamical system suggested by Lorenz. In this demonstration four imperfect models, each with similar global forecast skill, are used. Future applications in weather forecasting and in economic forecasting are discussed. The demonstration establishes that cross pollinating forecast trajectories to enrich the collection of simulations upon which the forecast is built can yield a new forecast system with significantly more skill...

  4. Segregation mechanisms in granular systems: role of gravity and velocity fluctuations

    Science.gov (United States)

    Staron, Lydie

    2016-04-01

    Size segregation patterns are often observed in natural granular systems: dune fields, debris flow deposits, river beds, asteroids surface... Identifying the underlying mechanisms and dynamics would be a significant progress towards understanding the evolution of these systems: discrimationsbetween different processes, relevant time-scales, history of the mechanical solicitation. In the case of the surface of asteroids exhibiting a granular nature, such as Itokawa, the origin of sorting patterns following grain size may have different origins. It can occur as a result of periodic changes in the gravity field, or seismic-shaking due to impacts, or be the signature of re-deposition of ejected material after impacts. It may also be related to size-dependent thermal weathering or impact bouncing dynamics, rather than mechanical segregation. It is thus crucial to explore the different candidate mechanisms and address their likeliness in spatial context. In this contribution, we use a discrete simulation model to reproduce the collective behaviour of rigid, frictional grains exhibiting different sizes. Segregation dynamics is obtained during gravity-driven flows, allowing for the detailed investigation of the micro-mechanical signature of segregation. In particular, we evidence the asymetry of the stress state induced by the different grain sizes. Discriminating between contacts stresses and kinematic stresses, we are able to discuss the respective role of gravity and velocity fluctuations in the segregation process. References L. Staron and J. C. Phillips, Stress partition and micro-structure in size-segregating granular flows, Phys. Rev. E 92 022210 (2015) L. Staron and J. C. Phillips, Segregation time-scales in bi-disperse granular flows, Phys. Fluids 26 (3), 033302 (2014)

  5. Pion showers in highly granular calorimeters

    Indian Academy of Sciences (India)

    Jaroslav Cvach; on behalf of the CALICE Collaboration

    2012-10-01

    New results on properties of hadron showers created by pion beam at 8–80 GeV in high granular electromagnetic and hadron calorimeters are presented. Data were used for the first time to investigate the separation of the neutral and charged hadron showers. The result is important to verify the prediction of the PFA algorithm based up to now on the simulated data only. Next, the properties of hadron showers were compared to different physics lists of GEANT4 version 9.3.

  6. Speckle visibility spectroscopy and variable granular fluidization.

    Science.gov (United States)

    Dixon, P K; Durian, D J

    2003-05-09

    We introduce a dynamic light scattering technique capable of resolving motion that changes systematically, and rapidly, with time. It is based on the visibility of a speckle pattern for a given exposure duration. Applying this to a vibrated layer of glass beads, we measure the granular temperature and its variation with phase in the oscillation cycle. We observe several transitions involving jammed states, where the grains are at rest during some portion of the cycle. We also observe a two-step decay of the temperature on approach to jamming.

  7. Archimedes' principle in fluidized granular systems.

    Science.gov (United States)

    Huerta, D A; Sosa, Victor; Vargas, M C; Ruiz-Suárez, J C

    2005-09-01

    We fluidize a granular bed in a rectangular container by injecting energy through the lateral walls with high-frequency sinusoidal horizontal vibrations. In this way, the bed is brought to a steady state with no convection. We measured buoyancy forces on light spheres immersed in the bed and found that they obey Archimedes' principle. The buoyancy forces decrease when we reduce the injected energy. By measuring ascension velocities as a function of gamma, we can evaluate the frictional drag of the bed; its exponential dependence agrees very well with previous findings. Rising times of the intruders ascending through the bed were also measured, they increase monotonically as we increase the density.

  8. Longitudinal Viscous Flow in Granular Gases

    OpenAIRE

    Santos, Andres

    2008-01-01

    The flow characterized by a linear longitudinal velocity field $u_x(x,t)=a(t)x$, where $a(t)={a_0}/({1+a_0t})$, a uniform density $n(t)\\propto a(t)$, and a uniform temperature $T(t)$ is analyzed for dilute granular gases by means of a BGK-like model kinetic equation in $d$ dimensions. For a given value of the coefficient of normal restitution $\\alpha$, the relevant control parameter of the problem is the reduced deformation rate $a^*(t)=a(t)/\

  9. Brine Transport Experiments in Granular Salt

    Energy Technology Data Exchange (ETDEWEB)

    Jordan, Amy B. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Boukhalfa, Hakim [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Caporuscio, Florie Andre [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Stauffer, Philip H. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-06-06

    To gain confidence in the predictive capability of numerical models, experimental validation must be performed to ensure that parameters and processes are correctly simulated. The laboratory investigations presented herein aim to address knowledge gaps for heat-generating nuclear waste (HGNW) disposal in bedded salt that remain after examination of prior field and laboratory test data. Primarily, we are interested in better constraining the thermal, hydrological, and physicochemical behavior of brine, water vapor, and salt when moist salt is heated. The target of this work is to use run-of-mine (RoM) salt; however during FY2015 progress was made using high-purity, granular sodium chloride.

  10. Uphill solitary waves in granular flows

    Science.gov (United States)

    Martínez, E.; Pérez-Penichet, C.; Sotolongo-Costa, O.; Ramos, O.; Måløy, K. J.; Douady, S.; Altshuler, E.

    2007-03-01

    We have experimentally observed uphill solitary waves in the surface flow on a granular material. A heap is constructed by injecting sand between two vertical glass plates separated by a distance much larger than the average grain size, with an open boundary. As the heap reaches the open boundary, solitary fluctuations appear on the flowing layer and move “up the hill” (i.e., against the direction of the flow). We explain the phenomenon in the context of stop-and-go traffic models.

  11. An experimental study of low velocity impacts into granular material in reduced gravity

    Science.gov (United States)

    Murdoch, Naomi; Avila Martinez, Iris; Sunday, Cecily; Cherrier, Olivier; Zenou, Emanuel; Janin, Tristan; Cadu, Alexandre; Gourinat, Yves; Mimoun, David

    2016-04-01

    The granular nature of asteroid surfaces, in combination with the low surface gravity, makes it difficult to predict lander - surface interactions from existing theoretical models. Nonetheless, an understanding of such interactions is particularly important for the deployment of a lander package. This was demonstrated by the Philae lander, which bounced before coming to rest roughly 1 kilometer away from its intended landing site on the surface of comet 67P/Churyumov-Gerasimenko before coming to rest (Biele et al., 2015). In addition to being important for planning the initial deployment, information about the acceleration profile upon impact is also important in the choice of scientific payloads that want to exploit the initial landing to study the asteroid surface mechanical properties (e.g., Murdoch et al., 2016). Using the ISAE-SUPAERO drop tower, we have performed a series of low-velocity collisions into granular material in low gravity. Reduced-gravity is simulated by releasing a free-falling projectile into a surface container with a downward acceleration less than that of Earth's gravity. The acceleration of the surface is controlled through the use an Atwood machine, or a system of pulleys and counterweights. In reducing the effective surface acceleration of the granular material, the confining pressure will be reduced, and the properties of the granular material will become more representative of those on an asteroid's surface. In addition, since both the surface and projectile are falling, the projectile requires a minimum amount of time to catch the surface before the collision begins. This extended free-fall increases the experiment duration, making it easier to use accelerometers and high-speed cameras for data collection. The experiment is built into an existing 5.5 m drop-tower frame and has required the custom design of all components, including the projectile, surface sample container, release mechanism and deceleration system (Sunday et al., 2016

  12. Energy Content & Spectral Energy Representation of Wave Propagation in a Granular Chain

    Science.gov (United States)

    Shrivastava, Rohit; Luding, Stefan

    2017-04-01

    A mechanical wave is propagation of vibration with transfer of energy and momentum. Studying the energy as well as spectral energy characteristics of a propagating wave through disordered granular media can assist in understanding the overall properties of wave propagation through materials like soil. The study of these properties is aimed at modeling wave propagation for oil, mineral or gas exploration (seismic prospecting) or non-destructive testing for the study of internal structure of solids. Wave propagation through granular materials is often accompanied by energy attenuation which is quantified by Quality factor and this parameter has often been used to characterize material properties, hence, determining the Quality factor (energy attenuation parameter) can also help in determining the properties of the material [3], studied experimentally in [2]. The study of Energy content (Kinetic, Potential and Total Energy) of a pulse propagating through an idealized one-dimensional discrete particle system like a mass disordered granular chain can assist in understanding the energy attenuation due to disorder as a function of propagation distance. The spectral analysis of the energy signal can assist in understanding dispersion as well as attenuation due to scattering in different frequencies (scattering attenuation). The selection of one-dimensional granular chain also helps in studying only the P-wave attributes of the wave and removing the influence of shear or rotational waves. Granular chains with different mass distributions have been studied, by randomly selecting masses from normal, binary and uniform distributions and the standard deviation of the distribution is considered as the disorder parameter, higher standard deviation means higher disorder and lower standard deviation means lower disorder [1]. For obtaining macroscopic/continuum properties, ensemble averaging has been invoked. Instead of analyzing deformation-, velocity- or stress

  13. The NIST Real-Time Control System (RCS): A Reference Model Architecture for Computational Intelligence

    Science.gov (United States)

    Albus, James S.

    1996-01-01

    The Real-time Control System (RCS) developed at NIST and elsewhere over the past two decades defines a reference model architecture for design and analysis of complex intelligent control systems. The RCS architecture consists of a hierarchically layered set of functional processing modules connected by a network of communication pathways. The primary distinguishing feature of the layers is the bandwidth of the control loops. The characteristic bandwidth of each level is determined by the spatial and temporal integration window of filters, the temporal frequency of signals and events, the spatial frequency of patterns, and the planning horizon and granularity of the planners that operate at each level. At each level, tasks are decomposed into sequential subtasks, to be performed by cooperating sets of subordinate agents. At each level, signals from sensors are filtered and correlated with spatial and temporal features that are relevant to the control function being implemented at that level.

  14. Feature Matching in Time Series Modelling

    CERN Document Server

    Xia, Yingcun

    2011-01-01

    Using a time series model to mimic an observed time series has a long history. However, with regard to this objective, conventional estimation methods for discrete-time dynamical models are frequently found to be wanting. In the absence of a true model, we prefer an alternative approach to conventional model fitting that typically involves one-step-ahead prediction errors. Our primary aim is to match the joint probability distribution of the observable time series, including long-term features of the dynamics that underpin the data, such as cycles, long memory and others, rather than short-term prediction. For want of a better name, we call this specific aim {\\it feature matching}. The challenges of model mis-specification, measurement errors and the scarcity of data are forever present in real time series modelling. In this paper, by synthesizing earlier attempts into an extended-likelihood, we develop a systematic approach to empirical time series analysis to address these challenges and to aim at achieving...

  15. Modeling noisy time series Physiological tremor

    CERN Document Server

    Timmer, J

    1998-01-01

    Empirical time series often contain observational noise. We investigate the effect of this noise on the estimated parameters of models fitted to the data. For data of physiological tremor, i.e. a small amplitude oscillation of the outstretched hand of healthy subjects, we compare the results for a linear model that explicitly includes additional observational noise to one that ignores this noise. We discuss problems and possible solutions for nonlinear deterministic as well as nonlinear stochastic processes. Especially we discuss the state space model applicable for modeling noisy stochastic systems and Bock's algorithm capable for modeling noisy deterministic systems.

  16. Modeling discrete time-to-event data

    CERN Document Server

    Tutz, Gerhard

    2016-01-01

    This book focuses on statistical methods for the analysis of discrete failure times. Failure time analysis is one of the most important fields in statistical research, with applications affecting a wide range of disciplines, in particular, demography, econometrics, epidemiology and clinical research. Although there are a large variety of statistical methods for failure time analysis, many techniques are designed for failure times that are measured on a continuous scale. In empirical studies, however, failure times are often discrete, either because they have been measured in intervals (e.g., quarterly or yearly) or because they have been rounded or grouped. The book covers well-established methods like life-table analysis and discrete hazard regression models, but also introduces state-of-the art techniques for model evaluation, nonparametric estimation and variable selection. Throughout, the methods are illustrated by real life applications, and relationships to survival analysis in continuous time are expla...

  17. Estimating High-Dimensional Time Series Models

    DEFF Research Database (Denmark)

    Medeiros, Marcelo C.; Mendes, Eduardo F.

    We study the asymptotic properties of the Adaptive LASSO (adaLASSO) in sparse, high-dimensional, linear time-series models. We assume both the number of covariates in the model and candidate variables can increase with the number of observations and the number of candidate variables is, possibly...

  18. Forecasting with periodic autoregressive time series models

    NARCIS (Netherlands)

    Ph.H.B.F. Franses (Philip Hans); R. Paap (Richard)

    1999-01-01

    textabstractThis paper is concerned with forecasting univariate seasonal time series data using periodic autoregressive models. We show how one should account for unit roots and deterministic terms when generating out-of-sample forecasts. We illustrate the models for various quarterly UK consumption

  19. Forecasting with periodic autoregressive time series models

    NARCIS (Netherlands)

    Ph.H.B.F. Franses (Philip Hans); R. Paap (Richard)

    1999-01-01

    textabstractThis paper is concerned with forecasting univariate seasonal time series data using periodic autoregressive models. We show how one should account for unit roots and deterministic terms when generating out-of-sample forecasts. We illustrate the models for various quarterly UK consumption

  20. Assessing continuum postulates in simulations of granular flow

    Energy Technology Data Exchange (ETDEWEB)

    Rycroft, Chris; Kamrin, Ken; Bazant, Martin

    2008-08-26

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

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

    Science.gov (United States)

    Blumenfeld, Raphael

    2010-05-01

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

  2. Flexible boosting of accelerated failure time models

    Directory of Open Access Journals (Sweden)

    Hothorn Torsten

    2008-06-01

    Full Text Available Abstract Background When boosting algorithms are used for building survival models from high-dimensional data, it is common to fit a Cox proportional hazards model or to use least squares techniques for fitting semiparametric accelerated failure time models. There are cases, however, where fitting a fully parametric accelerated failure time model is a good alternative to these methods, especially when the proportional hazards assumption is not justified. Boosting algorithms for the estimation of parametric accelerated failure time models have not been developed so far, since these models require the estimation of a model-specific scale parameter which traditional boosting algorithms are not able to deal with. Results We introduce a new boosting algorithm for censored time-to-event data which is suitable for fitting parametric accelerated failure time models. Estimation of the predictor function is carried out simultaneously with the estimation of the scale parameter, so that the negative log likelihood of the survival distribution can be used as a loss function for the boosting algorithm. The estimation of the scale parameter does not affect the favorable properties of boosting with respect to variable selection. Conclusion The analysis of a high-dimensional set of microarray data demonstrates that the new algorithm is able to outperform boosting with the Cox partial likelihood when the proportional hazards assumption is questionable. In low-dimensional settings, i.e., when classical likelihood estimation of a parametric accelerated failure time model is possible, simulations show that the new boosting algorithm closely approximates the estimates obtained from the maximum likelihood method.

  3. Discrete-time modelling of musical instruments

    Science.gov (United States)

    Välimäki, Vesa; Pakarinen, Jyri; Erkut, Cumhur; Karjalainen, Matti

    2006-01-01

    This article describes physical modelling techniques that can be used for simulating musical instruments. The methods are closely related to digital signal processing. They discretize the system with respect to time, because the aim is to run the simulation using a computer. The physics-based modelling methods can be classified as mass-spring, modal, wave digital, finite difference, digital waveguide and source-filter models. We present the basic theory and a discussion on possible extensions for each modelling technique. For some methods, a simple model example is chosen from the existing literature demonstrating a typical use of the method. For instance, in the case of the digital waveguide modelling technique a vibrating string model is discussed, and in the case of the wave digital filter technique we present a classical piano hammer model. We tackle some nonlinear and time-varying models and include new results on the digital waveguide modelling of a nonlinear string. Current trends and future directions in physical modelling of musical instruments are discussed.

  4. Discrete-time modelling of musical instruments

    Energy Technology Data Exchange (ETDEWEB)

    Vaelimaeki, Vesa; Pakarinen, Jyri; Erkut, Cumhur; Karjalainen, Matti [Laboratory of Acoustics and Audio Signal Processing, Helsinki University of Technology, PO Box 3000, FI-02015 TKK, Espoo (Finland)

    2006-01-01

    This article describes physical modelling techniques that can be used for simulating musical instruments. The methods are closely related to digital signal processing. They discretize the system with respect to time, because the aim is to run the simulation using a computer. The physics-based modelling methods can be classified as mass-spring, modal, wave digital, finite difference, digital waveguide and source-filter models. We present the basic theory and a discussion on possible extensions for each modelling technique. For some methods, a simple model example is chosen from the existing literature demonstrating a typical use of the method. For instance, in the case of the digital waveguide modelling technique a vibrating string model is discussed, and in the case of the wave digital filter technique we present a classical piano hammer model. We tackle some nonlinear and time-varying models and include new results on the digital waveguide modelling of a nonlinear string. Current trends and future directions in physical modelling of musical instruments are discussed.

  5. The cerebellar Golgi cell and spatiotemporal organization of granular layer activity

    Directory of Open Access Journals (Sweden)

    Egidio eD‘Angelo

    2013-05-01

    Full Text Available The cerebellar granular layer has been suggested to perform a complex spatiotemporal reconfiguration of incoming mossy fiber signals. Central to this role is the inhibitory action exerted by Golgi cells over granule cells: Golgi cells inhibit granule cells through double feedforward and feedback inhibitory loops and generate a broad lateral inhibition that extends beyond the afferent synaptic field. This characteristic connectivity has recently been investigated in great detail and been correlated with specific functional properties of the neuron. These include theta-frequency pacemaking, network entrainment into coherent oscillations and phase resetting. Important advances have also been made in terms of determining the membrane and synaptic properties of the neuron, and clarifying the mechanisms of activation by input bursts. Moreover, voltage sensitive dye imaging and multi-electrode array recordings, combined with mathematical simulations based on realistic computational models, have improved our understanding of the impact of Golgi cell activity on granular layer circuit computations. These investigations have highlighted the critical role of Golgi cells in: generating dense clusters of granule cell activity organized in center-surround structures, implementing combinatorial operations on multiple mossy fiber inputs, regulating transmission gain and cut-off frequency, controlling spike timing and burst transmission, and determining the sign, intensity and extension of long-term synaptic plasticity at the mossy fiber-granule cell relay. This review considers recent advances in the field, highlighting the functional implications of Golgi cells for granular layer network computation and indicating new challenges for cerebellar research.

  6. Alternative time representation in dopamine models.

    Science.gov (United States)

    Rivest, François; Kalaska, John F; Bengio, Yoshua

    2010-02-01

    Dopaminergic neuron activity has been modeled during learning and appetitive behavior, most commonly using the temporal-difference (TD) algorithm. However, a proper representation of elapsed time and of the exact task is usually required for the model to work. Most models use timing elements such as delay-line representations of time that are not biologically realistic for intervals in the range of seconds. The interval-timing literature provides several alternatives. One of them is that timing could emerge from general network dynamics, instead of coming from a dedicated circuit. Here, we present a general rate-based learning model based on long short-term memory (LSTM) networks that learns a time representation when needed. Using a naïve network learning its environment in conjunction with TD, we reproduce dopamine activity in appetitive trace conditioning with a constant CS-US interval, including probe trials with unexpected delays. The proposed model learns a representation of the environment dynamics in an adaptive biologically plausible framework, without recourse to delay lines or other special-purpose circuits. Instead, the model predicts that the task-dependent representation of time is learned by experience, is encoded in ramp-like changes in single-neuron activity distributed across small neural networks, and reflects a temporal integration mechanism resulting from the inherent dynamics of recurrent loops within the network. The model also reproduces the known finding that trace conditioning is more difficult than delay conditioning and that the learned representation of the task can be highly dependent on the types of trials experienced during training. Finally, it suggests that the phasic dopaminergic signal could facilitate learning in the cortex.

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

    Science.gov (United States)

    Parker, D J

    2017-05-01

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

  8. Hard sphere dynamics for normal and granular fluids.

    Science.gov (United States)

    Dufty, James W; Baskaran, Aparna

    2005-06-01

    A fluid of N smooth, hard spheres is considered as a model for normal (elastic collision) and granular (inelastic collision) fluids. The potential energy is discontinuous for hard spheres so that the pairwise forces are singular and the usual forms of Newtonian and Hamiltonian mechanics do not apply. Nevertheless, particle trajectories in the N particle phase space are well defined and the generators for these trajectories can be identified. The first part of this presentation is a review of the generators for the dynamics of observables and probability densities. The new results presented in the second part refer to applications of these generators to the Liouville dynamics for granular fluids. A set of eigenvalues and eigenfunctions of the generator for this Liouville dynamics system is identified in a special stationary representation. This provides a class of exact solutions to the Liouville equation that are closely related to hydrodynamics for granular fluids.

  9. Shock front width and structure in supersonic granular flows.

    Science.gov (United States)

    Boudet, J F; Amarouchene, Y; Kellay, H

    2008-12-19

    The full structure of a shock front around a blunt body in a quasi-two-dimensional granular flow is studied. Two features, a large density gradient and a very small thickness of the front, characterize this shock and make it different from shocks in molecular gases. Both of these features can be understood using a modified version of the granular kinetic theory. Our model separates the particles into two subpopulations: fast particles having experienced no collisions and randomly moving particles. This separation is motivated by direct measurements of the particle velocities which show a bimodal distribution. Our results not only shed new light on the use of the granular kinetic theory under extreme conditions (shock formation) but bring new insight into the physics of shocks in general.

  10. Liquidity crisis, granularity of the order book and price fluctuations

    Science.gov (United States)

    Cristelli, M.; Alfi, V.; Pietronero, L.; Zaccaria, A.

    2010-01-01

    We introduce a microscopic model for the dynamics of the order book to study how the lack of liquidity influences price fluctuations. We use the average density of the stored orders (granularity g) as a proxy for liquidity. This leads to a Price Impact Surface which depends on both volume ω and g. The dependence on the volume (averaged over the granularity) of the Price Impact Surface is found to be a concave power law function g ˜ ωδ with δ ≈ 0.59. Instead the dependence on the granularity is φ(ω,g|ω) ˜ gα with α ≈ -1, showing a divergence of price fluctuations in the limit g → 0. Moreover, even in intermediate situations of finite liquidity, this effect can be very large and it is a natural candidate for understanding the origin of large price fluctuations.

  11. Magnetic avalanches in granular ferromagnets: thermal activated collective behavior

    Science.gov (United States)

    Chern, Gia-Wei

    2017-02-01

    We present a numerical study on the thermal activated avalanche dynamics in granular materials composed of ferromagnetic clusters embedded in a non-magnetic matrix. A microscopic dynamical simulation based on the reaction-diffusion process is developed to model the magnetization process of such systems. The large-scale simulations presented here explicitly demonstrate inter-granular collective behavior induced by thermal activation of spin tunneling. In particular, we observe an intriguing criticality controlled by the rate of energy dissipation. We show that thermal activated avalanches can be understood in the framework of continuum percolation and the emergent dissipation induced criticality is in the universality class of 3D percolation transition. Implications of these results to the phase-separated states of colossal magnetoresistance materials and other artificial granular magnetic systems are also discussed.

  12. An experimental study of the elastic theory for granular flows

    Science.gov (United States)

    Guo, Tongtong; Campbell, Charles S.

    2016-08-01

    This paper reports annular shear cell measurements granular flows with an eye towards experimentally confirming the flow regimes laid out in the elastic theory of granular flow. Tests were carried out on four different kinds of plastic spherical particles under both constant volume flows and constant applied stress flows. In particular, observations were made of the new regime in that model, the elastic-inertial regime, and the predicted transitions between the elastic-inertial and both the elastic-quasistatic and pure inertial regimes.

  13. Markov chain modeling of precipitation time series: Modeling waiting times between tipping bucket rain gauge tips

    DEFF Research Database (Denmark)

    Sørup, Hjalte Jomo Danielsen; Madsen, Henrik; Arnbjerg-Nielsen, Karsten

    2011-01-01

    A very fine temporal and volumetric resolution precipitation time series is modeled using Markov models. Both 1st and 2nd order Markov models as well as seasonal and diurnal models are investigated and evaluated using likelihood based techniques. The 2nd order Markov model is found to be insignif...

  14. Auger-type granular fertylizer distributor: matemathical model and dynamic simulation Dosador helicoidal de fertilizante granular: modelo matemático e simulação da dinâmica

    Directory of Open Access Journals (Sweden)

    Angel P. Garcia

    2012-02-01

    Full Text Available The objective of this study was to model mathematically and to simulate the dynamic behavior of an auger-type fertilizer applicator (AFA in order to use the variable-rate application (VRA and reduce the coefficient of variation (CV of the application, proposing an angular speed controller θ' for the motor drive shaft. The input model was θ' and the response was the fertilizer mass flow, due to the construction, density of fertilizer, fill factor and the end position of the auger. The model was used to simulate a control system in open loop, with an electric drive for AFA using an armature voltage (V A controller. By introducing a sinusoidal excitation signal in V A with amplitude and delay phase optimized and varying θ' during an operation cycle, it is obtained a reduction of 29.8% in the CV (constant V A to 11.4%. The development of the mathematical model was a first step towards the introduction of electric drive systems and closed loop control for the implementation of AFA with low CV in VRA.O objetivo deste trabalho foi modelar matematicamente e simular o comportamento dinâmico de um dosador helicoidal de fertilizantes (DHF a fim de utilizá-lo em aplicação a taxas variáveis (ATVe reduzir o coeficiente de variação (CV da aplicação, propondo uma forma de atuação na velocidade angular de acionamento θ' do seu eixo. A entrada do modelo foi θ' e a resposta foi a vazão mássica de fertilizante em função de suas características construtivas, densidade do fertilizante, fator de enchimento e posição do fim do helicoide. O modelo foi usado na simulação de um sistema de controle em malha aberta, com o acionamento do DHF feito por meio de um motor elétrico com atuação na tensão de armadura (V A. Introduzindo-se um sinal de excitação senoidal em V A com amplitude e defasagem otimizada, consequentemente variando-se θ' durante um ciclo de operação, obteve-se redução no CV de 29,8 % (V A constante para 11,4 %. O

  15. 准静态颗粒介质的弹性势能弛豫分析∗%Analysis of elastic energy relaxation pro cess for granular materials at quasi-static state

    Institute of Scientific and Technical Information of China (English)

    金鑫鑫; 金峰; 刘宁; 孙其诚

    2016-01-01

    . Then granular temperature rooted from gas kinetics is introduced to model the macroscopic behaviors. For loose and rapid granular flow, the kinetic granular temperature itself is the root to affect the flow process. While in a dense granular system, the granular temperature at a quasi-static state is referred to as elastic energy fluctuation. The structure can be kept stable when granular temperature exists on account of the mutual confinement among particles. And the granular temperature at a stable state is just a representation of internal structure of granular assembly. When the granular temperature stimulated by the external disturbance exceeds the stable value, the irreversible process happens and the difference between the excited state and stationary state is the driving force for evolution. The stress relaxations under different surface properties and confining pressures are simulated using non-equilibrium theory with new change for granular temperature. It can be found that the granular temperature difference triggers elastic relaxation and force chains reorganization. And the larger the temperature difference, the further away from the steady state the system is and the larger the stress change is. The more smooth the surface and the smaller the confining pressure, the lower resistance is generated, so that the initial granular temperature difference is larger and the stress change is larger during stress relaxation. The granular temperature decreases as time goes by because of its own relaxation. When the difference is equal to zero, the process of stress relaxation finishes and the system evolves into a global minimum of potential energy.

  16. From Discrete-Time Models to Continuous-Time, Asynchronous Models of Financial Markets

    NARCIS (Netherlands)

    K. Boer-Sorban (Katalin); U. Kaymak (Uzay); J. Spiering (Jaap)

    2006-01-01

    textabstractMost agent-based simulation models of financial markets are discrete-time in nature. In this paper, we investigate to what degree such models are extensible to continuous-time, asynchronous modelling of financial markets. We study the behaviour of a learning market maker in a market with

  17. From Discrete-Time Models to Continuous-Time, Asynchronous Models of Financial Markets

    NARCIS (Netherlands)

    K. Boer-Sorban (Katalin); U. Kaymak (Uzay); J. Spiering (Jaap)

    2006-01-01

    textabstractMost agent-based simulation models of financial markets are discrete-time in nature. In this paper, we investigate to what degree such models are extensible to continuous-time, asynchronous modelling of financial markets. We study the behaviour of a learning market maker in a market with

  18. Size segregation in a granular bore

    Science.gov (United States)

    Edwards, A. N.; Vriend, N. M.

    2016-10-01

    We investigate the effect of particle-size segregation in an upslope propagating granular bore. A bidisperse mixture of particles, initially normally graded, flows down an inclined chute and impacts with a closed end. This impact causes the formation of a shock in flow thickness, known as a granular bore, to travel upslope, leaving behind a thick deposit. This deposit imprints the local segregated state featuring both pure and mixed regions of particles as a function of downstream position. The particle-size distribution through the depth is characterized by a thin purely small-particle layer at the base, a significant linear transition region, and a thick constant mixed-particle layer below the surface, in contrast to previously observed S-shaped steady-state concentration profiles. The experimental observations agree with recent progress that upward and downward segregation of large and small particles respectively is asymmetric. We incorporate the three-layer, experimentally observed, size-distribution profile into a depth-averaged segregation model to modify it accordingly. Numerical solutions of this model are able to match our experimental results and therefore motivate the use of a more general particle-size distribution profile.

  19. Time-varying modeling of cerebral hemodynamics.

    Science.gov (United States)

    Marmarelis, Vasilis Z; Shin, Dae C; Orme, Melissa; Rong Zhang

    2014-03-01

    The scientific and clinical importance of cerebral hemodynamics has generated considerable interest in their quantitative understanding via computational modeling. In particular, two aspects of cerebral hemodynamics, cerebral flow autoregulation (CFA) and CO2 vasomotor reactivity (CVR), have attracted much attention because they are implicated in many important clinical conditions and pathologies (orthostatic intolerance, syncope, hypertension, stroke, vascular dementia, mild cognitive impairment, Alzheimer's disease, and other neurodegenerative diseases with cerebrovascular components). Both CFA and CVR are dynamic physiological processes by which cerebral blood flow is regulated in response to fluctuations in cerebral perfusion pressure and blood CO2 tension. Several modeling studies to date have analyzed beat-to-beat hemodynamic data in order to advance our quantitative understanding of CFA-CVR dynamics. A confounding factor in these studies is the fact that the dynamics of the CFA-CVR processes appear to vary with time (i.e., changes in cerebrovascular characteristics) due to neural, endocrine, and metabolic effects. This paper seeks to address this issue by tracking the changes in linear time-invariant models obtained from short successive segments of data from ten healthy human subjects. The results suggest that systemic variations exist but have stationary statistics and, therefore, the use of time-invariant modeling yields "time-averaged models" of physiological and clinical utility.

  20. Modeling of the time sharing for lecturers

    Directory of Open Access Journals (Sweden)

    E. Yu. Shakhova

    2017-01-01

    Full Text Available In the context of modernization of the Russian system of higher education, it is necessary to analyze the working time of the university lecturers, taking into account both basic job functions as the university lecturer, and others.The mathematical problem is presented for the optimal working time planning for the university lecturers. The review of the documents, native and foreign works on the study is made. Simulation conditions, based on analysis of the subject area, are defined. Models of optimal working time sharing of the university lecturers («the second half of the day» are developed and implemented in the system MathCAD. Optimal solutions have been obtained.Three problems have been solved:1 to find the optimal time sharing for «the second half of the day» in a certain position of the university lecturer;2 to find the optimal time sharing for «the second half of the day» for all positions of the university lecturers in view of the established model of the academic load differentiation;3 to find the volume value of the non-standardized part of time work in the department for the academic year, taking into account: the established model of an academic load differentiation, distribution of the Faculty number for the positions and the optimal time sharing «the second half of the day» for the university lecturers of the department.Examples are given of the analysis results. The practical application of the research: the developed models can be used when planning the working time of an individual professor in the preparation of the work plan of the university department for the academic year, as well as to conduct a comprehensive analysis of the administrative decisions in the development of local university regulations.