A Nonlinear Constitutive Model for Granular Materials: Application to Gravity Flow

1982 ◽  
Vol 49 (2) ◽  
pp. 291-296 ◽  
Author(s):  
D. F. McTigue
Keyword(s):  
Granular Materials ◽  
Volume Fraction ◽  
Lower Boundary ◽  
Gravity Flow ◽  
Momentum Exchange ◽  
Maximum Slope ◽  
Nonlinear Constitutive Model ◽  
Coulomb Failure ◽  
Coulomb Failure Criterion ◽  
Thermodynamic Pressure

The form of the dissipative part of the stress in flowing granular materials is motivated by considering momentum exchange due to intergranular collisions. Both shear and normal stresses are predicted that are quadratic in the rate of deformation. The equilibrium part of the stress is assumed to include a thermodynamic pressure and a term compatible with the Coulomb failure criterion in the limit of vanishing deformation. Solutions for the volume fraction and velocity fields in steady gravity flow down a slope are found. The volume fraction increases linearly downward through the shearing layer at a rate that decreases with increasing slope. The velocity profile develops an inflection near the lower boundary at smaller slopes, and becomes fully convex downstream as it approaches a critical maximum slope for steady flow. The results are in qualitative agreement with available experimental measurements.

Genetic Programming based Drag Model with Improved Prediction Accuracy for Fluidization Systems

2017 ◽  
Vol 15 (2) ◽  
Author(s):  
R. R. Sonolikar ◽  
M. P. Patil ◽  
R. B. Mankar ◽  
S. S. Tambe ◽  
B. D. Kulkarni
Keyword(s):  
Pressure Drop ◽  
Genetic Programming ◽  
Drag Coefficient ◽  
Prediction Accuracy ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Superior Performance ◽  
Momentum Exchange ◽  
Drag Model ◽  
Parameter Ranges

Abstract The drag coefficient plays a vital role in the modeling of gas-solid flows. Its knowledge is essential for understanding the momentum exchange between the gas and solid phases of a fluidization system, and correctly predicting the related hydrodynamics. There exists a number of models for predicting the magnitude of the drag coefficient. However, their major limitation is that they predict widely differing drag coefficient values over same parameter ranges. The parameter ranges over which models possess a good drag prediction accuracy are also not specified explicitly. Accordingly, the present investigation employs Geldart’s group B particles fluidization data from various studies covering wide ranges of Re and εs to propose a new unified drag coefficient model. A novel artificial intelligence based formalism namely genetic programming (GP) has been used to obtain this model. It is developed using the pressure drop approach, and its performance has been assessed rigorously for predicting the bed height, pressure drop, and solid volume fraction at different magnitudes of Reynolds number, by simulating a 3D bubbling fluidized bed. The new drag model has been found to possess better prediction accuracy and applicability over a much wider range of Re and εs than a number of existing models. Owing to the superior performance of the new drag model, it has a potential to gainfully replace the existing drag models in predicting the hydrodynamic behavior of fluidized beds.

Transport properties of concrete-like granular materials interacted by their microstructures and particle components

2018 ◽  
Vol 32 (18) ◽  
pp. 1840011 ◽  
Author(s):  
Wenxiang Xu ◽  
Hongguang Sun ◽  
Wen Chen ◽  
Huisu Chen
Keyword(s):  
Transport Properties ◽  
Granular Materials ◽  
Soft Matter ◽  
Volume Fraction ◽  
Structural Characteristics ◽  
Effective Diffusion ◽  
Nonspherical Particles ◽  
Structure Property ◽  
Engineering Structures ◽  
Component Structure

Granular materials as typical soft matter, their transport properties play significant roles in durability and service life in relevant practical engineering structures. Physico-mechanical properties of materials are generally dependent of their microstructures including interfacial and porous characteristics. The formation of such microstructures is directly related to particle components in granular materials. Understanding the interactive mechanism of particle components, microstructures, and transport properties is a problem of great interest in materials research community. The resulting rigorous component-structure-property relations are also valuable for material design and microstructure optimization. This review article describes state-of-the-art progresses on modeling particle components, interfacial and porous configurations and incorporating these internal structural characteristics into modeling transport properties of granular materials. We mainly focus on three issues involving the simulation for geometrical components, the quantitative characterization for interfacial and porous microstructures, and the modeling strategies for diffusive behaviors of granular materials. In the first aspect, in-depth reviews are presented to realize complex morphologies of geometrical particles, to detect the overlap between adjacent nonspherical particles, and to simulate the random packings of nonspherical particles. In the second aspect, we emphasize the development progresses on the interfacial thickness and porosity distribution, the interfacial volume fraction, and the continuum percolation of soft particles representing compliant interfaces and discrete pores. In the final aspect, a literature review is also provided on modeling of transport properties on the forefront of the effective diffusion and anomalous diffusion in multiphase granular materials. Finally, some conclusions and perspectives for future studies are provided.

scholarly journals Mixed Convection in Superposed Nanofluid and Porous Layers Inside Lid-Driven Square Cavity

2015 ◽  
Vol 10 (2) ◽  
Keyword(s):  
Mixed Convection ◽  
Porous Layer ◽  
Volume Fraction ◽  
Darcy Number ◽  
Momentum Exchange ◽  
Square Cavity ◽  
Porous Layers ◽  
Adverse Action ◽  
Nanoparticles Volume Fraction ◽  
The Right

Mixed convection in a lid-driven composite square cavity is studied numerically. The cavity is composed of two layers; a Cu–water nanofluid layer superposed a porous layer. The porous layer is saturated with the same nanofluid. The left and right walls of the cavity are thermally insulated. The bottom wall which is in contact with the porous layer is isothermally heated and being lid to the left, while the top wall is isothermally cooled and being lid to the right. Cavity walls are impermeable except the interface between the porous layer and the nanofluid. Maxwell-Brinkman model is invoked for the momentum exchange within the porous layer. Equations govern the conservation of mass, momentum, and energy within the two layers were modeled and solved numerically using under successive relaxation (USR) up- wind finite difference scheme. Four pertinent parameters are studied; nanoparticles volume fraction φ (0.0 - 0.05), porous layer thickness Wp (0.1 - 0.9), Darcy number Da (10-7 – 10-1), and Richardson number Ri (0.01 - 10). The results have showed that the existence of the porous layer in a specified value can enhance the convective heat transfer when Ri ≥ 1, while an adverse action of nanoparticles is recorded when Da ≥ 10-4.

scholarly journals Probabilistic landslide risk assessment: Case study of Bujumbura

2018 ◽  
Vol 251 ◽  
pp. 06011
Author(s):  
Gervais Shirambere ◽  
Maurice O. Nyadawa ◽  
Jean pierre Masekanya ◽  
Timothy Nyomboi
Keyword(s):  
Risk Assessment ◽  
Monte Carlo Simulation ◽  
Landslide Risk ◽  
Cell Level ◽  
Monte Carlo Simulation Technique ◽  
Mapping Model ◽  
Coulomb Failure ◽  
Landslide Risk Assessment ◽  
Coulomb Failure Criterion

A spatial probabilistic landslide risk assessment and mapping model has been applied in a data scare region. The probabilistic model is based on a physical model based on Mohr coulomb failure criterion. A Monte Carlo simulation technique is applied to field collected data. The results are integrated and a probability of landslide is obtained at each cell level. The results are compared to a prepared landslide inventory. The overall accuracy of the model is 79.69%.

scholarly journals A 2D Multiphase Model of Drop Behavior during Electroslag Remelting

Metals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 490
Author(s):  
Jérémy Chaulet ◽  
Abdellah Kharicha ◽  
Sylvain Charmond ◽  
Bernard Dussoubs ◽  
Stéphane Hans ◽  
...  
Keyword(s):  
Small Volume ◽  
Slag Phase ◽  
Volume Fraction ◽  
Liquid Pool ◽  
Electroslag Remelting ◽  
Multiphase Model ◽  
Momentum Exchange ◽  
Small Volume Fraction ◽  
Drag Law ◽  
Two Fluid

Electroslag remelting is a process extensively used to produce metallic ingots with high quality standards. During the remelting operation, liquid metal droplets fall from the electrode through the liquid slag before entering the liquid pool of the secondary ingot. To better understand the process and help to optimize the operating condition choice, a 2D axisymmetric multiphase model of the slag domain has been developed using a two fluid Eulerian approach. During their fall, droplets hydrodynamic interactions are calculated thanks to an appropriate drag law. Influence of droplets on the electromagnetic field and on the slag hydrodynamics is discussed, as well as their heat exchange with the slag. Even with a small volume fraction, the droplets influence is noticeable. The present investigation shows that small droplets have a large influence on the slag hydrodynamics, due to a great momentum exchange. However heat transfer is more influenced by large drops, which are found to be relatively far from the thermal equilibrium with the slag phase.

On a Spring-Network Model and Effective Elastic Moduli of Granular Materials

1999 ◽  
Vol 66 (1) ◽  
pp. 172-180 ◽  
Author(s):  
K. Alzebdeh ◽  
M. Ostoja-Starzewaski
Keyword(s):  
Granular Materials ◽  
Disordered Systems ◽  
Granular Media ◽  
Elastic Moduli ◽  
Volume Fraction ◽  
Effective Medium ◽  
Solid State Physics ◽  
Two Phase ◽  
Effective Medium Theories ◽  
The Individual

Two challenges in mechanics of granular media are taken up in this paper: (i) development of adequate numerical discrete element models of topologically disordered granular assemblies, and (ii) calculation of macroscopic elastic moduli of such materials using effective medium theories. Consideration of the first one leads to an adaptation of a spring-network (Kirkwood) model of solid-state physics to disordered systems, which is developed in the context of planar Delaunay networks. The model employs two linear springs: a normal one along an edge connecting two neighboring vertices (grain centers) which accounts for normal interactions between the grains, as well as an angular one which accounts for angle changes between two edges incident onto the same vertex; edges remain straight and grain rotations do not appear. This model is then used to predict elastic moduli of two-phase granular materials—random mixtures of soft and stiff grains —for high coordination numbers. It is found here that an effective Poisson’s ratio, νeff, of such a mixture is a convex function of the volume fraction, so that νeff may become negative when the individual Poisson’s ratios of both phases are both positive. Additionally, the usefulness of three effective medium theories—perfect disks, symmetric ellipses, and asymmetric ellipses—is tested.

Gravity flow of granular materials round obstacles—II

1985 ◽  
Vol 40 (3) ◽  
pp. 337-351 ◽  
Author(s):  
U. Tüzün ◽  
R.M. Nedderman
Keyword(s):  
Granular Materials ◽  
Gravity Flow
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