Special Issue "Advances in the Dynamics of Granular Materials"

Guest Editor
Prof. Dr. Hayley H. Shen
Department of Civil and Environmental Engineering, Clarkson University, Potsdam, NY 13699-5710, USA
Website: http://people.clarkson.edu/~hhshen
E-Mail:
Phone: +1-315-268-6614
Fax: +1-315-268-7985
Interests: granular media; constitutive relations; transitional flows; internal structures; ice formation in a wave field; water wave propagation through a pancake ice field

Dear Colleagues,

Stationary or quasi-static granular mechanics have been a part of the traditional soil mechanics for centuries. In contrast, moving granular materials has not received comparable scientific attention until much later. An intense growth of research in the dynamics of granular materials has been observed in the past several decades. The field has now become truly multi-disciplinary, including all engineering disciplines and physics, with recent interactions with chemical, biological, and human sciences. Due to the dissipative nature of grain interactions, the dynamics of granular materials display many surprising characteristics. Flowing granular materials act like a fluid. However, without external excitation, this fluid “freezes” to become a solid. The transition between phases, unlike ordinary materials, eludes a description based on currently available thermodynamic. Likewise, moving granular materials display rich mixing/de-mixing that has no observed analogues in ordinary fluids. The above phenomena are known for the simplest granular flows where the grains only exert contact forces to each other. When compounded with long range, such as electrostatic and magnetic, forces, the richness and complexity of phenomena drastically increase. The field of dynamic granular materials may provide a platform for a dialog amongst all researchers in studying discrete systems with complex interactions.

Prof. Dr. Hayley H. Shen
Guest Editor

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• granular
• dynamics
• micromechanics
• discrete systems

Title: Flow of a Granular Material along a Rotating Wall: The Rolling Transition
Author: Francois Rioual and Goodarz Ahmadi
Affiliation: Cemagref Clermont-Ferrand, domaine des Palaquins, 03150 Varennes-sur-Allier, France; E-Mail: francois.rioual@cemagref.fr
Abstract: The dynamics of granular materials is far from being well understood on a general point of view and still demonstrates unexpected properties compared to classical fluids. For dry granular flows under gravity, the continuum formalism of Saint-Venant has been shown to be very useful because it does not require in principle any knowledge of the constitutive law of the considered material. In particular, the coulomb like friction coefficient is supposed to model the dissipation of energy in the entire flow. It seems that the ignorance of the physical processes at the scale of the microstructure might constitute an obstacle to progress in these approaches in particular for more and more complex granular materials (polydisperse for instance). We will present here some properties of a granular flow of spherical particles along a rotating wall by the discrete element method. In particular, we will present the apparition of a rolling transition: In this new regime, the particles of the flow  can roll without any sliding at their contacts above a certain critical friction coefficient. We show also that this regime may represent an optimum for the flow in terms of energetics.

Title: The Streamwise Solid Fraction Variation of a Gravity-driven Granular Flow with a Granular Hydraulic Jump
Authors: Li-Tsung Sheng ¹, San-Yu Chiu ¹, Chih-Yu Kuo ², Yih-Chin Tai ³ and Shu-San Hsiau ¹
Affiliations: ¹ Department of Mechanical Engineering, National Central University, No.300, Jhongda Road, Jhongli City, Taoyuan County 32001, Taiwan
² Research Center for Applied Sciences, Academia Sinica, No.128 Academia Road, Section 2, Nankang, New Taipei City 115, Taiwan;
E-Mail: cykuo06@gate.sinica.edu.tw
³ Department of Hydraulic and Ocean Engineering, National Cheng Kung University, No.1, University Road, Tainan City 701, Taiwan
Abstract: We describe the streamwise flux-averaged solid fractions of steady gravity-driven dry granular flows moving over semi-circular cylinder obstacles by using an indirect measurement method. In the method, the volume flux is inferred by the velocity profile along the perimeter cross-section, combined with knowledge of the constant mass flow rate. In the flow, there is a granular hydraulic jump, which produces a strong variation of the solid fraction. The chute has a width of 5 cm wide, a length of 150 cm long, and is inclined at 30°. It is found that the perturbations in the solid fraction caused by the obstacle back-propagate into the upstream for a certain distance. The effect of the obstacle size as well as its influences on the flow height and velocity is reported. To explain the solid fraction variation, we propose a continuum mixture model which contains one solid and one interstitial fluid phases. It is demonstrated that the simulation is in qualitative agreements with the experimental measurements.

Title: Granular Fingering Instability in Vibrated Glass Beads
Authors: Piroz Zamankhan ¹ and Goodarz Ahmadi ²
Affiliations: ¹ Faculty of Industrial -, Mechanical Engineering and Computer Sciences, University of Iceland, Hjardarhagi 2-6, IS- 107 Reykjavik, Iceland; E-Mail: piroz@hi.is
² Mechanical and Aeronautical Engineering, Clarkson University, PO Box 5725, Potsdam, NY 13699-5725, USA; E-Mail: ahmadi@clarkson.edu
Abstract: A series of experiments are described in which bubbles are produced in a bed of airimmersed glass beads in a thin annulus that is exposed to vertical sinusoidal oscillations. In addition, three-dimensional simulations of the aforementioned systems are performed on a graphics processing unit (GPU). This study combines the Eulerian (grid-based) and the Lagrangian (particle-based) methods (Eu-La) to achieve a unification of solid body and fluid simulations. The simulation results show that two regions can be distinguished in a bubbling regime. The one of weakly connected aggregates where nucleation dominates aggregation and the other one of strongly connected aggregates where aggregation dominates nucleation. The dispersion of the tagged particles of weakly connected aggregates is found to increase more rapidly than self diffusion. This observation suggests that an interaction between self and turbulent diffusion occurs that causes acceleration of the granular dispersion. The accelerated granular dispersion leads to the formation of fractal like structures at the air-grain interfaces. In the regions of strongly connected aggregates, the self-diffusion coefficient approaches a very low value, which indicates structural arrest.