An Experimental Study of the Effect of Global Solid Fraction and Surface Material on Couette Granular Flow

2009 ◽  
Author(s):  
Martin C. Marinack ◽  
Venkata K. Jasti ◽  
C. Fred Higgs
Keyword(s):  
Solid Fraction ◽  
Granular Flow ◽  
Granular Flows ◽  
Two Dimensional ◽  
Shear Cell ◽  
Natural Processes ◽  
Parametric Studies ◽  
Driving Wheel ◽  
The Subject ◽  
Multiphase Behavior

The flow of solid granular material has been proposed as an alternative lubricant to conventional liquid lubricants. Since granular flows are also in numerous industrial and natural processes, they have been the subject of numerous studies. However, it has been a challenge to understand them because of their non-linear and multiphase behavior. There have been several past experiments, which have gained insight into granular flows. For example, previous work by the authors sheared grains in a two-dimensional annular shear cell by varying the velocity and roughness [1]. The present experimental work attempts to further insights from the previous work by specifically studying the interaction between rough surfaces and granular flows when the global solid fraction and grain materials are varied. A two dimensional annular (granular) shear cell, with a stationary outer ring and inner driving wheel, was used for this work. Digital particle tracking velocimetry was used to obtain local granular flow data such as velocity, local solid fraction, and granular temperature. Slip between the driving wall and first layer of granules is also extracted. This slip can be interpreted as momentum transfer or traction performance in granular systems such as wheel-terrain interaction. Parametric studies of global solid fraction and the material of the rough driving surface, attempt to show how these parameters affect the local granular flow properties.

Including Friction and Spin Rules in the Lattice-Based Cellular Automata Approach to Model Granular Flows

2009 ◽  
Author(s):  
Martin C. Marinack ◽  
Venkata K. Jasti ◽  
C. Fred Higgs
Keyword(s):  
Cellular Automata ◽  
Computational Efficiency ◽  
Granular Flow ◽  
Extreme Temperature ◽  
Granular Flows ◽  
Friction Modeling ◽  
Model Collision ◽  
Ca Model ◽  
Granular Behavior ◽  
Multiphase Behavior

Granular flows have been proposed as an alternative lubrication mechanism to conventional liquid lubricants in sliding contacts due to their ability to carry loads and accommodate surface velocities. Their load carrying capacity has been demonstrated in the experiments of Yu and Tichy [1]. Alternate lubrication techniques are becoming necessary due to the failure of conventional liquid lubricants in extreme temperature environments, and their promotion of stiction in micro-/nanoscale environments. Yet, understanding granular behavior has been difficult due to its non-linear and multiphase behavior. Cellular Automata (CA) has been shown to be a viable first order approach to modeling some complex aspects of granular flow. Previous work by the authors successfully modeled granular shear with a CA model [2]. Additional work combined CA computational efficiency with particle dynamics to effectively model collision events. This work builds upon and modifies the prior CA modeling approaches by adding friction modeling and spin of particles. This modification maintains the computational efficiency of CA, while increasing accuracy of the predicted granular flow properties, such as speed, solid fraction, and granular temperature. The current work compares the CA model with friction and spin physics relations to the authors’ prior CA model which neglected friction. Both CA models are also evaluated against experimental data to quantify the benefits of including friction and spin in the CA modeling approach for granular flows.

Granular Flow Lubrication: A Lattice-Based Cellular Automata Modeling Approach

2005 ◽  
Author(s):  
V. K. Jasti ◽  
C. F. Higgs
Keyword(s):  
Cellular Automata ◽  
Granular Flow ◽  
Solid Lubricant ◽  
Granular Flows ◽  
Complex Flows ◽  
Shear Cell ◽  
Modeling Approach ◽  
Ca Model ◽  
Model Benchmark ◽  
Good Agreement

Liquid lubricants break down at extreme temperatures and promote stiction in micro/nano-scale environments. Consequently, using flows of solid granular particles as a “dry” lubrication mechanism in sliding contacts was proposed, because of their ability to carry loads and accommodate surface velocities. Granular flows are highly complex flows that in many ways act similar to fluids, yet are difficult to predict because they are not well understood. Granular flows are composed of discrete particles which display fluid and solid lubricant behavior with time. This work describes the usefulness of employing lattice-based cellular automata (CA) as a tool for modeling granular flows in tribological contacts. The granular kinetic lubrication (GKL) continuum modeling approach has been successful at predicting trends gleaned from experiments conducted with granules in a couette shear cell. These results are used as a benchmark for determining the effectiveness of the CA modeling results. While the CA model was constructed entirely from rule-based mathematics, velocity and solid fraction results from the simulations were in good agreement with those from the GKL model benchmark results.

DIFFUSING VOID MODEL FOR GRANULAR FLOW

1992 ◽  
Vol 06 (13) ◽  
pp. 761-771 ◽  
Author(s):  
H. S. CARAM ◽  
D. C. HONG
Keyword(s):  
Free Surface ◽  
Velocity Profile ◽  
Flow Pattern ◽  
Granular Flow ◽  
Granular Media ◽  
Three Dimensional ◽  
Granular Flows ◽  
Two Dimensional ◽  
Upward Motion ◽  
Gravitational Flow

The gravitational flow pattern of granular media in a confined geometry is assumed to be caused by the upward motion of voids generated at the discharge orifices. The model describes some well known and unique features of granular flows such as the deformation of the free surface, the formation of dead zones, the flow around obstacles with its companion void regions and the formation of cascading zones. It also predicts an unexpected velocity profile in a flow expansion as well as the propagation of dilation waves whose scaling solutions are presented. These thin two-dimensional beds are also found to behave very differently from three-dimensional beds.

Modeling Segregation in Granular Flows

2019 ◽  
Vol 10 (1) ◽  
pp. 129-153 ◽  
Author(s):  
Paul B. Umbanhowar ◽  
Richard M. Lueptow ◽  
Julio M. Ottino
Keyword(s):  
Computer Simulations ◽  
Granular Flow ◽  
Granular Flows ◽  
Continuum Models ◽  
Large Space ◽  
Driving Mechanisms ◽  
Advection Diffusion ◽  
Parametric Studies ◽  
Discrete Element Methods ◽  
Dense Granular Flows

Accurate continuum models of flow and segregation of dense granular flows are now possible. This is the result of extensive comparisons, over the last several years, of computer simulations of increasing accuracy and scale, experiments, and continuum models, in a variety of flows and for a variety of mixtures. Computer simulations—discrete element methods (DEM)—yield remarkably detailed views of granular flow and segregation. Conti-nuum models, however, offer the best possibility for parametric studies of outcomes in what could be a prohibitively large space resulting from the competition between three distinct driving mechanisms: advection, diffusion, and segregation. We present a continuum transport equation–based framework, informed by phenomenological constitutive equations, that accurately predicts segregation in many settings, both industrial and natural. Three-way comparisons among experiments, DEM, and theory are offered wherever possible to validate the approach. In addition to the flows and mixtures described here, many straightforward extensions of the framework appear possible.

Boundary interactions for two-dimensional granular flows. Part 2. Roughened boundaries

1993 ◽  
Vol 247 ◽  
pp. 137-156 ◽  
Author(s):  
Charles S. Campbell
Keyword(s):  
Computer Simulation ◽  
Flow Field ◽  
Simulation Study ◽  
Granular Flow ◽  
Granular Flows ◽  
Microscopic Level ◽  
Two Dimensional ◽  
Computer Simulation Study ◽  
Global Behaviour ◽  
Roughness Elements

The global behaviour of a granular flow is critically dependent on its interaction with whatever solid boundaries with which it comes into contact, whether they be used to drive, retard or simply bound the flow field. This paper describes the results of a computer simulation study of the effects of roughening boundaries by ‘gluing’ particles to the surfaces. Roughness is commonly used in experimental devices as a way of approximating a no-slip condition between a granular material and the driving surfaces. On a microscopic level, this produces a boundary that extends out into the flow field to the limit of the roughness elements. This has a strong effect on the way that forces, and, in particular, torque, is transmitted to the particles in the neighbourhood of the boundary.

scholarly journals Self-diffusion scalings in dense granular flows

Soft Matter ◽  
2021 ◽  
Author(s):  
Riccardo Artoni ◽  
Michele Larcher ◽  
James T. Jenkins ◽  
Patrick Richard
Keyword(s):  
Shear Rate ◽  
Solid Fraction ◽  
Granular Flows ◽  
The Self ◽  
Granular Temperature ◽  
Restitution Coefficient ◽  
Self Diffusion ◽  
Diffusivity Tensor ◽  
Dense Granular Flows

The self-diffusivity tensor in homogeneously sheared dense granular flows is anisotropic. We show how its components depend on solid fraction, restitution coefficient, shear rate, and granular temperature.

scholarly journals Stress level effect on mobility of dry granular flows of angular rock fragments

Landslides ◽  
2021 ◽  
Author(s):  
B. Cagnoli
Keyword(s):  
Stress Level ◽  
Granular Flow ◽  
High Stress ◽  
Granular Flows ◽  
Flow Dynamics ◽  
Small Scale ◽  
Flow Volume ◽  
Rock Fragments ◽  
Rock Avalanches ◽  
Flow Mobility

AbstractGranular flows of angular rock fragments such as rock avalanches and dense pyroclastic flows are simulated numerically by means of the discrete element method. Since large-scale flows generate stresses that are larger than those generated by small-scale flows, the purpose of these simulations is to understand the effect that the stress level has on flow mobility. The results show that granular flows that slide en mass have a flow mobility that is not influenced by the stress level. On the contrary, the stress level governs flow mobility when granular flow dynamics is affected by clast agitation and collisions. This second case occurs on a relatively rougher subsurface where an increase of the stress level causes an increase of flow mobility. The results show also that as the stress level increases, the effect that an increase of flow volume has on flow mobility switches sign from causing a decrease of mobility at low stress level to causing an increase of mobility at high stress level. This latter volume effect corresponds to the famous Heim’s mobility increase with the increase of the volume of large rock avalanches detected so far only in the field and for this reason considered inexplicable without resorting to extraordinary mechanisms. Granular flow dynamics is described in terms of dimensionless scaling parameters in three different granular flow regimes. This paper illustrates for each regime the functional relationship of flow mobility with stress level, flow volume, grain size, channel width, and basal friction.

A Convex Complementarity Approach for Simulating Large Granular Flows

2010 ◽  
Vol 5 (3) ◽  
Author(s):  
Alessandro Tasora ◽  
Mihai Anitescu
Keyword(s):  
Granular Flow ◽  
Complementarity Problems ◽  
Particle Interaction ◽  
Granular Flows ◽  
Rigid Bodies ◽  
Integration Time ◽  
Frictional Contacts ◽  
Physical Experiments ◽  
Dense Granular Flow ◽  
Number Of Particles

Aiming at the simulation of dense granular flows, we propose and test a numerical method based on successive convex complementarity problems. This approach originates from a multibody description of the granular flow: all the particles are simulated as rigid bodies with arbitrary shapes and frictional contacts. Unlike the discrete element method (DEM), the proposed approach does not require small integration time steps typical of stiff particle interaction; this fact, together with the development of optimized algorithms that can run also on parallel computing architectures, allows an efficient application of the proposed methodology to granular flows with a large number of particles. We present an application to the analysis of the refueling flow in pebble-bed nuclear reactors. Extensive validation of our method against both DEM and physical experiments results indicates that essential collective characteristics of dense granular flow are accurately predicted.

Numerical Analysis of Bridge Expansion-Induced Rail Deformation of Ballast Truck

2014 ◽  
Vol 580-583 ◽  
pp. 3208-3214 ◽  
Author(s):  
Zhen Wei Xiong ◽  
Xin Ling Liang ◽  
Xian Xing Dai ◽  
Ping Wang
Keyword(s):  
Granular Flow ◽  
Element Model ◽  
Discrete Element Model ◽  
Board Structure ◽  
Vertical Deformation ◽  
Two Dimensional ◽  
Running Safety ◽  
Bridge Plate ◽  
Ballast Track ◽  
The Relationship

when the ballast track stretch with the bridge, ballast which is near expansion joint will move confusedly. As a result, rail produced vertical deformation. The deformation will affect the running safety and comfortability of train. At present, there are two kinds of treatments which are cover board structure and baffle structure to deal ballast’s movement. Aiming at the different modes of stretching when the two kinds of structures and different arrangement condition of bridge plate are applied, the rail-sleeper-ballast discrete element model is developed by the method of two-dimensional granular flow. The relationship between rail deformation and bridge expansion is analyzed on the foundation of the model. Results show as flows: when bridge extends or shortens, rail always produced upwarp deformation. Bridge plate should arrange asymmetrically. Like this, the rail deformation decrease by 40%. And adopting the baffle structure can effectively reduce the influence of bridge expansion in ballast truck.

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