Grain Growth Simulation Based on Potts Model with Different Parameters

2005 ◽  
Vol 475-479 ◽  
pp. 3173-3176 ◽  
Author(s):  
Xiangge Qin ◽  
Guo Quan Liu
Keyword(s):  
Steady State ◽  
Grain Growth ◽  
Potts Model ◽  
Large Scale ◽  
Square Lattice ◽  
Small Scale ◽  
Weibull Function ◽  
Simulation Based ◽  
Log Normal ◽  
Large Scale Simulations

Potts model was often used to simulate grain growth without necessary evaluation of the effect of lattice scale and simulation temperature. It is found in this paper that such parameters may affect the simulation results markedly. The results show that simulations at zero temperature or on a small scale lattice (say, the number of sites on one edge of the square lattice L=1000) cannot reach the steady-state period of grain growth, while large-scale simulations (say, L=2000) at a much higher simulation temperature can. The steady-state grain size distribution so obtained may be well described by Weibull function other than log-normal or Rayleigh functions.

scholarly journals Experimental Characterization and Correlation Analysis of Indoor Channels at 15 GHz

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
Xin Zhou ◽  
Zhangdui Zhong ◽  
Bei Zhang ◽  
Ruisi He ◽  
Ke Guan ◽  
...  
Keyword(s):  
Large Scale ◽  
Small Scale ◽  
Delay Spread ◽  
Experimental Characterization ◽  
Wireless System ◽  
Normal Distributions ◽  
Indoor Radio ◽  
Log Normal ◽  
Wireless System Design ◽  
Correlation Properties

The indoor radio channels at 15 GHz are investigated based on measurements. The large- and small-scale fading behaviors as well as the delay dispersion characteristics are discussed. It is found that the large-scale fading, RiceanK-factor, and delay spread can be described by log-normal distributions. Furthermore, both autocorrelation and cross correlation properties of the above parameters are analyzed and modeled. These parameters characterize fading and delay behaviors as well as their mutual dependency and can be used as empirical values for future wireless system design and simulation in 15 GHz short-range indoor channels.

scholarly journals Wall-Normal Variation of Spanwise Streak Spacing in Turbulent Boundary Layer With Low-to-Moderate Reynolds Number

Entropy ◽  
2018 ◽  
Vol 21 (1) ◽  
pp. 24 ◽  
Author(s):  
Wenkang Wang ◽  
Chong Pan ◽  
Jinjun Wang
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Buffer Layer ◽  
Large Scale ◽  
Normal Growth ◽  
Small Scale ◽  
Piv Measurement ◽  
Moderate Reynolds Number ◽  
Scale Structures ◽  
Log Normal

Low-speed streaks in wall-bounded turbulence are the dominant structures in the near-wall turbulent self-sustaining cycle. Existing studies have well characterized their spanwise spacing in the buffer layer and below. Recent studies suggested the existence of these small-scale structures in the higher layer where large-scale structures usually receive more attention. The present study is thus devoted to extending the understanding of the streak spacing to the log layer. An analysis is taken on two-dimensional (2D) wall-parallel velocity fields in a smooth-wall turbulent boundary layer with Ret = 4402400, obtained via either 2D Particle Image Velocimetry (PIV) measurement taken here or public Direct Numerical Simulation (DNS). Morphological-based streak identification analysis yields a Re-independent log-normal distribution of the streak spacing till the upper bound of the log layer, based on which an empirical model is proposed to account for its wall-normal growth. The small-scale part of the spanwise spectra of the streamwise fluctuating velocity below y? = 100 is reasonably restored by a synthetic simulation that distributes elementary streak units based on the proposed empirical streak spacing model, which highlights the physical significance of streaks in shaping the small-scale part of the velocity spectra beyond the buffer layer.

scholarly journals Unmanned Aerial Vehicle Propagation Channel over Vegetation and Lake Areas: First- and Second-Order Statistical Analysis

Sensors ◽  
2021 ◽  
Vol 22 (1) ◽  
pp. 65
Author(s):  
Deyvid L. Leite ◽  
Pablo Javier Alsina ◽  
Millena M. de Medeiros Campos ◽  
Vicente A. de Sousa ◽  
Alvaro A. M. de Medeiros
Keyword(s):  
Secure Communication ◽  
Large Scale ◽  
Communication Channel ◽  
Channel Model ◽  
Path Loss ◽  
Doppler Frequency ◽  
Unmanned Aircraft ◽  
Small Scale ◽  
Log Normal

The use of unmanned aerial vehicles (UAV) to provide services such as the Internet, goods delivery, and air taxis has become a reality in recent years. The use of these aircraft requires a secure communication between the control station and the UAV, which demands the characterization of the communication channel. This paper aims to present a measurement setup using an unmanned aircraft to acquire data for the characterization of the radio frequency channel in a propagation environment with particular vegetation (Caatinga) and a lake. This paper presents the following contributions: identification of the communication channel model that best describes the characteristics of communication; characterization of the effects of large-scale fading, such as path loss and log-normal shadowing; characterization of small-scale fading (multipath and Doppler); and estimation of the aircraft speed from the identified Doppler frequency.

scholarly journals On the scale sizes of magnetosheath jets

2020 ◽  
Author(s):  
Ferdinand Plaschke ◽  
Heli Hietala
Keyword(s):  
Large Scale ◽  
Dynamic Pressure ◽  
Large Population ◽  
Small Scale ◽  
Size Distributions ◽  
Exponential Functions ◽  
Scale Size ◽  
Order Of Magnitude ◽  
Log Normal ◽  
Spacecraft Data

<p>The subsolar magnetosheath is oftentimes permeated by jets. These are localized entities of enhanced dynamic pressure with respect to the ambient plasma. Magnetosheath jets are thought to arise from bow shock ripples and/or foreshock structures. They can easily propagate through the entire magnetosheath and impact on the magnetopause, where they can cause large amplitude indentations, launch magnetopause surface waves, or modulate magnetopause reconnection. The scale size distributions of magnetosheath jets observed by single spacecraft are relatively well modeled by exponential functions with characteristic scales of 0.71 Earth radii (RE) and 1.34 RE in the directions parallel and perpendicular to the jet propagation direction, respectively. However, these functions do not represent the actual, true jet scale size distributions, because of two reasons: (1) Spacecraft are much more likely to observe large scale jets rather than small scale jets. Hence, the observed scale size distributions are biased towards larger scales. (2) The distributions modeled by exponential functions highly overestimate observation probabilities of jets of smallest scales (on the order of 0.1 RE). We overcome both shortcomings by replacing the exponential functions by log-normal functions, which can be corrected for the bias. By re-analyzing THEMIS multi-spacecraft data, we obtain, for the first time, unbiased, i.e., actual jet scale size distributions. Our results reveal a large population of jets of smallest scales that have not been accounted for, so far. Consequently, we find median scale sizes of jets to be about an order of magnitude smaller than previously thought: 0.15 and 0.12 RE in the parallel and perpendicular directions, respectively.</p>

scholarly journals Production and excitation of molecules by dissipation of two-dimensional turbulence

2020 ◽  
Vol 495 (1) ◽  
pp. 816-834
Author(s):  
P Lesaffre ◽  
P Todorov ◽  
F Levrier ◽  
V Valdivia ◽  
N Dzyurkevich ◽  
...  
Keyword(s):  
Large Scale ◽  
Energy Gap ◽  
Small Scale ◽  
Two Dimensional ◽  
One Dimensional ◽  
Infrared Telescope ◽  
High Resolution Mapping ◽  
Localized Heating ◽  
Resolution Mapping ◽  
Large Scale Simulations

ABSTRACT The interstellar medium (ISM) is typically a hostile environment: cold, dilute and irradiated. Nevertheless, it appears very fertile for molecules. The localized heating resulting from turbulence dissipation is a possible channel to produce and excite molecules. However, large-scale simulations cannot resolve the dissipative scales of the ISM. Here, we present two-dimensional small-scale simulations of decaying hydrodynamic turbulence using the chemses code, with fully resolved viscous dissipation, time-dependent heating, cooling, chemistry and excitation of a few rotational levels of H2. We show that molecules are produced and excited in the wake of strong dissipation ridges. We carefully identify shocks and we assess their statistics and contribution to the molecular yields and excitation. We find that the formation of molecules is strongly linked to increased density as a result of shock compression and to the opening of endothermic chemical routes because of higher temperatures. We identify a new channel for molecule production via H2 excitation, illustrated by CH+ yields in our simulations. Despite low temperatures and the absence of magnetic fields (favouring CH+ production through ion-neutral velocity drifts), the excitation of the first few rotational levels of H2 shrinks the energy gap to form CH+. The present study demonstrates how dissipative chemistry can be modelled by statistical collections of one-dimensional steady-state shocks. Thus, the excitation of higher J levels of H2 is likely to be a direct signature of turbulence dissipation, and an indirect probe for molecule formation. We hope these results will help to bring new tools and ideas for the interpretation of current observations of H2 rotational lines carried out using the Stratospheric Observatory for Infrared Astronomy (SOFIA), and pave the way for a better understanding of the high-resolution mapping of H2 emission by future instruments, such as theJames Webb Space Telescope and the Space Infrared Telescope for Cosmology and Astrophysics.

scholarly journals Comparative Study and Limits of Different Level-Set Formulations for the Modeling of Anisotropic Grain Growth

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 3883
Author(s):  
Brayan Murgas ◽  
Sebastian Florez ◽  
Nathalie Bozzolo ◽  
Julien Fausty ◽  
Marc Bernacki
Keyword(s):  
Grain Growth ◽  
Level Set ◽  
Large Scale ◽  
Mesoscopic Scale ◽  
Element Level ◽  
Mean Values ◽  
Grim Reaper ◽  
Polycrystalline Structures ◽  
First Time ◽  
Large Scale Simulations

In this study, four different finite element level-set (FE-LS) formulations are compared for the modeling of grain growth in the context of polycrystalline structures and, moreover, two of them are presented for the first time using anisotropic grain boundary (GB) energy and mobility. Mean values and distributions are compared using the four formulations. First, we present the strong and weak formulations for the different models and the crystallographic parameters used at the mesoscopic scale. Second, some Grim Reaper analytical cases are presented and compared with the simulation results, and the evolutions of individual multiple junctions are followed. Additionally, large-scale simulations are presented. Anisotropic GB energy and mobility are respectively defined as functions of the mis-orientation/inclination and disorientation. The evolution of the disorientation distribution function (DDF) is computed, and its evolution is in accordance with prior works. We found that the formulation called “Anisotropic” is the more physical one, but it could be replaced at the mesoscopic scale by an isotropic formulation for simple microstructures presenting an initial Mackenzie-type DDF.

scholarly journals Large Scale Statistics for Computational Verification of Grain Growth Simulations with Experiments

2002 ◽  
Vol 731 ◽  
Author(s):  
Melik C. Demirel ◽  
Andrew P. Kuprat ◽  
Denise C. George ◽  
Galen K. Straub ◽  
Amit Misra ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Growth ◽  
Large Scale ◽  
Three Dimensional ◽  
Interface Energy ◽  
Aluminum Film ◽  
Grain Structure ◽  
Small Scale ◽  
Microstructural Development ◽  
Electron Backscattered Diffraction

AbstractIt is known that by controlling microstructural development, desirable properties of materials can be achieved. The main objective of our research is to understand and control interface dominated material properties, and finally, to verify experimental results with computer simulations. We have previously showed a strong similarity between small-scale grain growth experiments and anisotropic three-dimensional simulations obtained from the Electron Backscattered Diffraction (EBSD) measurements [1]. Using the same technique, we obtained 5170-grain data from an Aluminum-film (120μm thick) with a columnar grain structure. Experimentally obtained starting microstructure and grain boundary properties are input for the three-dimensional grain growth simulation. In the computational model, minimization of the interface energy is the driving force for the grain boundary motion. The computed evolved microstructure is compared with the final experimental microstructure, after annealing at 550°C.

Simulation of Directed Nanocrack Patterns for the Fabrication of Nanowires [PowerPoint Submission]

2006 ◽  
Vol 978 ◽  
Author(s):  
David Salac ◽  
Wei Lu
Keyword(s):  
Level Set Method ◽  
Level Set ◽  
Large Scale ◽  
Scanning Tunneling ◽  
Small Scale ◽  
Crack Tips ◽  
Multiple Materials ◽  
Material Fracture ◽  
Recent Experimental Work ◽  
Large Scale Simulations

Abstract While material fracture is generally considered undesirable, recent experimental work has indicated that cracking can be utilized to create small scale nanowire structures with diameters of 100nm and smaller. Typical nanowire fabrication techniques include the use of a scanning tunneling microscope and electrochemical deposition. Compared to fracture fabricated nanowire structures current fabrication techniques are either extremely slow or require large amounts of post-processing. To become a viable nanowire fabrication technique the cracking of materials must be directed. We propose a computational model to predict propagation paths in large scale crack systems. We utilize the level set method to investigate the creation of nanoscale crack patterns. The level set method allows for large scale simulations of many crack tips while easily accommodating large scale deformations. Unlike traditional methods such as finite elements explicit modeling of the cracks is not needed. We show that the use of multiple materials and etched regions can effectively direct the cracking of a thin film. Using these patterns nanowire structures can be constructed which would be difficult to obtain otherwise.

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