DEM SIMULATION OF PARTICULATE FLOW USING MULTI-SCALE TIME STEPS

2012 ◽  
Vol 09 (01) ◽  
pp. 1240010 ◽  
Author(s):  
JUN HUANG ◽  
ANGELA DE LEEBEECK ◽  
OLE JØRGEN NYDAL
Keyword(s):  
Volume Fraction ◽  
High Volume ◽  
Particulate Flow ◽  
Time Step ◽  
Dem Simulation ◽  
Local Volume ◽  
Volume Fractions ◽  
Multi Scale ◽  
Low Volume ◽  
Discrete Element Methods

Event-driven method (EDM) and the time-driven method (TDM) are two main branches of discrete element methods (DEM) for the simulations of granular materials. A new algorithm is introduced in this paper where different models are used for different local volume fractions. TDM time step is used for the cases with high volume fractions and EDM time step is used for the cases with low volume fractions. Whether the local volume fraction is low or high is determined by the number of neighbors in the Verlet table. While the time step updating the Verlet table is the same as the time step for those particles without neighbors in the Verlet table.

A Hybrid Algorithm of Event-Driven and Time-Driven Methods for Simulations of Granular Flows

2011 ◽  
Vol 10 (4) ◽  
pp. 1027-1043 ◽  
Author(s):  
Jun Huang ◽  
Ole Jørgen Nydal
Keyword(s):  
Hybrid Algorithm ◽  
Granular Flows ◽  
High Volume ◽  
Multiple Objects ◽  
Time Step ◽  
Volume Fractions ◽  
Cpu Time ◽  
Event Driven ◽  
Element Approach ◽  
Low Volume

AbstractThe classical discrete element approach (DEM) based on Newtonian dynamics can be divided into two major groups, event-driven methods (EDM) and time-driven methods (TDM). Generally speaking, TDM simulations are suited for cases with high volume fractions where there are collisions between multiple objects. EDM simulations are suited for cases with low volume fractions from the viewpoint of CPU time. A method combining EDM and TDM called Hybrid Algorithm of event-driven and time-driven methods (HAET) is presented in this paper. The HAET method employs TDM for the areas with high volume fractions and EDM for the remaining areas with low volume fractions. It can decrease the CPU time for simulating granular flows with strongly non-uniform volume fractions. In addition, a modified EDM algorithm using a constant time as the lower time step limit is presented. Finally, an example is presented to demonstrate the hybrid algorithm.

scholarly journals Aggregation kinetics of irreversible patches coupled with reversible isotropic interaction leading to chains, bundles and globules

2018 ◽  
Vol 90 (6) ◽  
pp. 1085-1098 ◽  
Author(s):  
Isha Malhotra ◽  
Sujin B. Babu
Keyword(s):  
Self Assembly ◽  
Patch Size ◽  
Colloidal Particles ◽  
Volume Fraction ◽  
Interaction Strength ◽  
Colloidal System ◽  
Angle Distribution ◽  
Volume Fractions ◽  
Low Volume ◽  
A Chain

Abstract In the present study we are performing simulation of simple model of two patch colloidal particles undergoing irreversible diffusion limited cluster aggregation using patchy Brownian cluster dynamics. In addition to the irreversible aggregation of patches, the spheres are coupled with isotropic reversible aggregation through the Kern–Frenkel potential. Due to the presence of anisotropic and isotropic potential we have also defined three different kinds of clusters formed due to anisotropic potential and isotropic potential only as well as both the potentials together. We have investigated the effect of patch size on self-assembly under different solvent qualities for various volume fractions. We will show that at low volume fractions during aggregation process, we end up in a chain conformation for smaller patch size while in a globular conformation for bigger patch size. We also observed a chain to bundle transformation depending on the attractive interaction strength between the chains or in other words depending on the quality of the solvent. We will also show that bundling process is very similar to nucleation and growth phenomena observed in colloidal system with short range attraction. We have also studied the bond angle distribution for this system, where for small patches only two angles are more probable indicating chain formation, while for bundling at very low volume fraction a tail is developed in the distribution. While for the case of higher patch angle this distribution is broad compared to the case of low patch angles showing we have a more globular conformation. We are also proposing a model for the formation of bundles which are similar to amyloid fibers using two patch colloidal particles.

Simulating Phase Coarsening of Ultra-High Volume Fractions

2010 ◽  
Vol 638-642 ◽  
pp. 3925-3930 ◽  
Author(s):  
K.G. Wang ◽  
X. Ding
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Volume Fraction ◽  
High Volume ◽  
Triple Junctions ◽  
Ginzburg Landau ◽  
Volume Fractions ◽  
Phase Coarsening ◽  
Kinetics Of

The dynamics of phase coarsening at ultra-high volume fractions is studied based on two-dimensional phase-field simulations by numerically solving the time-dependent Ginzburg-Landau and Cahn-Hilliard equations. The kinetics of phase coarsening at ultra-high volume fractions is discovered. The microstructural evolutions for different ultra-high volume fractions are shown. The scaled particle size distribution as functions of the dispersoid volume fraction is presented. The particle size distribution derived from our simulation at ultra-high volume fractions is close to Wagner's particle size distribution due to interface-controlled ripening rather than Hillert's grain size distribution in grain growth. The changes of shapes of particles are carefully studied with increase of volume fraction. It is found that more liquid-filled triple junctions are formed as a result of particle shape accommodation with increase of volume fraction at the regime of ultra-high volume fraction.

Multi-Scale Approach for Nonhomogeneous Microstructural Effects on Damage in Particulate Composites

2003 ◽  
Author(s):  
W. M. Cho ◽  
Y. W. Kwon ◽  
C. T. Liu
Keyword(s):  
Volume Fraction ◽  
Global Analysis ◽  
Particle Volume Fraction ◽  
Crack Tip ◽  
Particulate Composites ◽  
Local Analysis ◽  
Particle Volume ◽  
Damage Initiation ◽  
Volume Fractions ◽  
Multi Scale

This study investigated the effects of random and non-uniform particle distributions on the damage initiation and growth in particulate composites. Numerical specimens with either no crack or an existing crack were examined. For the cases with no crack, the effect of sizes of the representative area for non-uniform particle volume fractions was studied on the overall stress-strain curves and the results were compared with that of the specimen with uniform particle volume fractions. Other studies considered cracked specimens, either single edge crack or a center crack. The global-local approach was used along with multi-scale technique. The global analysis determined the deformations around the crack tip. Then, the local analysis evaluated the damage progress at the crack tip using the solution of the global analysis as boundary conditions. The results showed non-uniformed particle volume fractions in particulate composites caused the crack growth at lower applied loads than the uniform particle volume fraction. Statistical data were also plotted for the non-uniform particle volume fraction cases.

scholarly journals Permittivity of SiC ceramic matrix compositesin Ku band

2021 ◽  
Vol 229 ◽  
pp. 01012
Author(s):  
Youssef Ouhassan ◽  
Seddik Bri ◽  
My Chrif El boubakraoui ◽  
Mohamed Habibi
Keyword(s):  
Imaginary Part ◽  
Volume Fraction ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
High Volume ◽  
Matrix Composites ◽  
Frequency Increase ◽  
Volume Fractions ◽  
Sic Ceramic ◽  
Ku Band

The objective of this work is to determine the dielectric permittivity of two SiC ceramic matrix composites. These composites are reinforced with NicalonSiCfibers and SCS6SiC fibers (SiCf / SiC) and have different volume fractions. The results obtained show that the dielectric property depends on the volume fraction and the frequency. Composites with high volume fractions have better dielectric properties than others. The values of the real and imaginary part of the complex permittivity decrease with frequency increase in the Ku-band. Moreover, the imaginary part takes negative values.

Evolution of microstructure and phases in in situ processed Ti–TiB composites containing high volume fractions of TiB whiskers

1999 ◽  
Vol 14 (11) ◽  
pp. 4214-4223 ◽  
Author(s):  
S. S. Sahay ◽  
K. S. Ravichandran ◽  
R. Atri ◽  
B. Chen ◽  
J. Rubin
Keyword(s):  
Volume Fraction ◽  
High Volume ◽  
Comparison Method ◽  
Relative Volume ◽  
X Ray Diffraction ◽  
Volume Fractions ◽  
Structure Factors ◽  
Integrated Intensities ◽  
Evolution Of Microstructure

A series of titanium composites, with varying volume fractions of titanium monoboride (TiB) whiskers, were made by mixing various proportions of titanium (Ti) and titanium diboride (TiB2) powders followed by hot pressing. The phases present were identified by x-ray diffraction. Microstructural examination revealed three different types of TiB whisker morphologies: (i) long and needle-shaped TiB whiskers that are isolated and randomly oriented in the Ti matrix at relatively low volume fractions (0.3), (ii) colonies of refined and densely packed TiB whiskers from intermediatevolume (0.55) to high volume (0.73 and 0.86) fractions, and (iii) coarse and elongated TiB particles with a few needle-shaped whiskers at the highest volume fraction (0.92). In all the composites, TiB was found to be the predominant reinforcement. However, in Ti–TiB composites with 0.86 and 0.92 volume fractions of TiB, a significant amount of TiB2 was also present. The relative volume fractions of Ti, TiB, and TiB2 phases were estimated from the integrated intensities of diffraction peaks by the direct comparison method employing the calculated structure factors and Lorentz polarization factors. The composite microstructure, as well as the evolution of different morphologies, of TiB whiskers is discussed.

scholarly journals Viscosity of nanofluids-A Review

2020 ◽  
Vol 7 (2) ◽  
Author(s):  
A.K. Patra ◽  
M.K. Nayak ◽  
A. Misra
Keyword(s):  
Carbon Nanotubes ◽  
Volume Fraction ◽  
Ph Value ◽  
Solid Volume Fraction ◽  
High Volume ◽  
Experimental Investigations ◽  
Fluid Viscosity ◽  
Shear Rates ◽  
Volume Fractions ◽  
Newtonian Behavior

In the present study a comprehensive review on rheological characteristics of nanofluids for their advanced heat transfer applications has been conducted and presented. The present article critically summarizes the recent research developments regarding the theoretical and experimental investigations about viscosity of different nanofluids. In addition, different reasonably attractive theoretical models and experimental correlations are explored and well discussed. Moreover, the current study analyzes several factors those strongly influencing viscosity of nanofluids include solid volume fraction, temperature, particle size, particle shape, different base fluids, surfactants addition, ultrasonication, nanoclustering and pH value. Important theoretical and experimental results from many researchers and predictions from a number of viscosity models are compared and discussed with appropriate justification. Most results reveal that the viscosity of nanofluid upsurges due to an increase in particle concentration while that belittles with diminishing temperature. Augmentation of nano-additives size leads to decreasing/increasing of nanofluid fluid viscosity. For the most nanofluids, Newtonian behavior is observed for low volume fractions, shear rates, concentrations and viscosity while non-Newtonian behavior is visualized for high volume fractions, shear rates, concentrations and viscosity. Nanofluids used carbon nanotubes are almost non-Newtonian in nature while nanofluids not involving carbon nanotubes are mostly Newtonian. Finally, the research challenges and needs in this important area of nanofluids are also highlighted.

A numerical study of the shearing motion of emulsions and foams

1995 ◽  
Vol 286 ◽  
pp. 379-404 ◽  
Author(s):  
Xiaofan Li ◽  
Hua Zhou ◽  
C. Pozrikidis
Keyword(s):  
Rheological Properties ◽  
Volume Fraction ◽  
Numerical Study ◽  
High Volume ◽  
Summation Method ◽  
Boundary Integral ◽  
Simple Shear Flow ◽  
Ewald Summation ◽  
Shearing Flow ◽  
Volume Fractions

A numerical study is presented of the motion of two-dimensional, doubly periodic, dilute and concentrated emulsions of liquid drops with constant surface tension, subject to a simple shear flow. The numerical method is based on a boundary integral formulation that employs a Green's function for doubly periodic Stokes flow, computed using the Ewald summation method. Under the assumption that the viscosity of the drops is equal to that of the ambient fluid, the motion is examined in a broad range of capillary numbers, volume fractions, and initial geometrical configurations. The latter include square and hexagonal lattices of circular and closely packed hexagonal drops with rounded corners. Based on the nature of the asymptotic motion at large times, a phase diagram is constructed separating regions where periodic motion is established, or the emulsion is destabilized due to continued elongation or coalescence of intercepting drops. Comparisons with previous computations for bounded systems illustrate the significance of the walls on the evolution and rheological properties of an emulsion. It is shown that the shearing flow is able to stabilize a concentrated emulsion against the tendency of the drops to become circular and coalesce, thereby allowing for periodic evolution even when the volume fraction of the suspended phase might be close to that for dry foam. This suggests that the imposed shearing flow plays a role similar to that of the disjoining pressure for stationary foam. At high volume fractions, the geometry of the microstructure and flow at the Plateau borders and within the thin films separating adjacent drops are illustrated and discussed with reference to the predictions of the quasi-steady theory of foam. Although the accuracy of certain fundamental assumptions underlying the quasi-steady theory is not confirmed by the numerical results, we find qualitative agreement regarding the basic geometrical features of the evolving microstructure and effective rheological properties of the emulsion.

Pore-size effects on thermal conductivity of SiO2 quartz using non-equilibrium molecular dynamics simulations

2018 ◽  
Vol 17 (01) ◽  
pp. 1850010
Author(s):  
Jin Hyeok Cha ◽  
Woongpyo Hong ◽  
Sujung Noh ◽  
Shinhu Cho
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Porous Materials ◽  
Thermal Conduction ◽  
Volume Fraction ◽  
Nonequilibrium Molecular Dynamics ◽  
Volume Fractions ◽  
Low Volume ◽  
Dynamics Simulations

Porous materials are commonly used to decrease or regulate thermal transport in insulating materials due to the very low thermal conductivity of the pores. More pores can achieve a better insulating effect; however, this can also be a shortcoming when the materials are directly involved in physical movement with friction, such as an interior wall of a cylinder in an automobile engine intended to prevent heat loss. Thus, it is important to clarify the mechanisms of the pore-dependent thermal properties of porous materials. In this study, the effects of the number and size of pores in silica quartz on thermal conductivity were investigated using nonequilibrium molecular dynamics simulations. The results revealed that the thermal conductivity of porous silica quartz decreased in all cases with an increase in the volume fraction of pores. A lower number of pores in the system showed higher thermal conductivity in the range of low volume fractions. We also showed that the interstitial distance between pores mostly governs thermal conduction at low volume fractions [Formula: see text] vol.%. Additionally, the mechanism of thermal conduction was assessed with respect to several theoretical models.

Morphology, Distribution and Identification of Micro-Constituents Along Grain Boundaries in Nickel-Base Alloys

1973 ◽  
Vol 31 ◽  
pp. 176-177
Author(s):  
D. E. Fornwalt ◽  
A. R. Geary ◽  
B. H. Kear
Keyword(s):  
Electron Microscope ◽  
Grain Boundaries ◽  
Volume Fraction ◽  
Rupture Life ◽  
Stress Rupture ◽  
High Volume ◽  
Precipitate Morphology ◽  
Stress Rupture Life ◽  
Nickel Base ◽  
Scanning Electron

A systematic study has been made of the effects of various heat treatments on the microstructures of several experimental high volume fraction γ’ precipitation hardened nickel-base alloys, after doping with ∼2 w/o Hf so as to improve the stress rupture life and ductility. The most significant microstructural chan§e brought about by prolonged aging at temperatures in the range 1600°-1900°F was the decoration of grain boundaries with precipitate particles.Precipitation along the grain boundaries was first detected by optical microscopy, but it was necessary to use the scanning electron microscope to reveal the details of the precipitate morphology. Figure 1(a) shows the grain boundary precipitates in relief, after partial dissolution of the surrounding γ + γ’ matrix.

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