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Modelling of Turbulence and Chemistry Interaction Using an Optimized Conditional Source-term Estimation Approach
, M.Sc. Thesis Sharif University of Technology ; Salehi, Mohammad Mahdi (Supervisor)
Abstract
The purpose of this study is to evaluate the performance of the optimized conditional source-term estimation approach. This model was first implemented in a computational fluid dynamics code, and then the Bernstein expansion was used to optimize it. For validation, two pre-mixed turbulent flames with different turbulence intensity and equivalence ratios were modeled with the optimized and RANS model. The results were obtained for mass fraction of the main and intermediate species, velocity and temperature examined in different sections. In the first flame, the turbulence intensity is low, and the flame is in the flamelet regimes; As a result, the results obtained with the optimized model are...
Turbulent Premixed Combustion Modeling Using the Linear Eddy Model
, M.Sc. Thesis Sharif University of Technology ; Salehi, Mohammad Mahdi (Supervisor)
Abstract
It is difficult and time-consuming to calculate the reaction rate directly. For turbulence modeling methods such as RANS or LES, various statistical methods are used to model turbulence-kinetics interactions. The purpose of this study is to implement the linear eddy model in CANTERA open source-code. This code instantly simulates one-dimensional, quasi-one-dimensional laminar flames with different chemical kinetics in which the effects of viscosity and molecular diffusion are implemented like a laminar flame. The effects of turbulence are simulated by a series of stochastic processes called triple maps. This research can provide a linear eddy model in different types of one-dimensional...
Flamelet Generated Manifolds Combined with Neural Networks
, M.Sc. Thesis Sharif University of Technology ; Salehi, Mohammad Mahdi (Supervisor)
Abstract
Reduced mechanisms are widely used in the numerical simulation of turbulent combustion, motivated by the need to reduce computational costs. Tabulation is widely used in turbulent and reacting flow simulations. Still, the need for a huge memory, the high cost of searching and interpolating among the data, and the development of artificial neural networks have created a situation for combining these two sciences. In this research, to model the chemistry of a methane premixed flame, we produced several training databases using the flamelet generated manifold, the best of which is the database with five degrees of freedom. We used these data to train individual neural networks for the...
Order Flow Imbalance Effect on Price Movement in Tehran Stock Exchange
, M.Sc. Thesis Sharif University of Technology ; Barakchian, Mahdi (Supervisor)
Abstract
We investigate order book events impacts on price movement, using the 31 stocks from the Tehran Stock Exchange. We show that in a low-depth market the mid-price change is explained mainly by a linear relationship with our proposed explanatory variable, modified order flow imbalance that represents the depth-adjusted differences of first level orders volumes in different sides of order book. Our results shows that the bid and ask spread has a negative effect on the power of events to move the price
Turbulence Equation-of-State Interaction Modeling in Large Eddy Simulation
, M.Sc. Thesis Sharif University of Technology ; Salehi, Mohammad Mahdi (Supervisor)
Abstract
In most real combustion systems, flow is turbulent (e.g., diesel engines). Therefore, a reliable turbulence modeling approach is necessary to design and analyze a system with turbulent flow. Direct numerical simulation (DNS), Large eddy simulation (LES), and Reynolds-averaged Navier-Stokes (RANS) are the three most mature Computational fluid dynamics (CFD) methods for turbulent flow simulations. Because of LES’s good accuracy and acceptable computational cost. In this project, LES is chosen to simulate the turbulent flow field.Modeled turbulence subgrid scales' interaction with nonlinear flow parameters, needs modeling. In supercritical and transcritical conditions, Equation-of-state is a...
Simulation of Turbulent Premixed Flame using Laminar Flamelet Decomposition Method
, M.Sc. Thesis Sharif University of Technology ; Salehi, Mohammad Mahdi (Supervisor)
Abstract
The purpose of this study is to simulate a turbulent premixed flame with the help of the Laminar Flamelet Decomposition method. Numerical simulation is considered the main approach for studying this flame. A Bunsen-type premixed burner, which has a novel approach to making different levels of turbulence, has been used for modeling the premixed flame. To reduce the cost of numerical calculations, the Reynolds-averaged Navier-Stokes approach has been chosen for the CFD simulation. In this study, the Laminar Flamelet Decomposition model is the main combustion model for analyzing the turbulent premixed flame and with this method, the rate of reactions for all the reaction species will be...
Numerical Investigation of Soot Formation in Laminar and Turbulent Diffusion Flames
, M.Sc. Thesis Sharif University of Technology ; Salehi, Mohammad Mahdi (Supervisor)
Abstract
In this study, the performance of the Moss-Brooks semi-empirical model in estimating soot for six different diffusion flames with methane, ethylene, and kerosene fuels in laminar and turbulent regimes has been investigated. The results show that the model with the default constants in the laminar ethylene flame has relatively acceptable performance, but in the turbulent ethylene flame as well as the laminar and turbulent flames of methane, has a significant error. In this regard, inspired by past research and performing sensitivity analysis, the constants of oxidation and coagulation sub-models were reviewed and Improved. The results of soot volume fraction were evaluated for values of 0.015...
Numerical Simulation of Turbulent Partially-Premixed Flames using Strained Flamelet Model
, M.Sc. Thesis Sharif University of Technology ; Salehi, Mohammad Mahdi (Supervisor)
Abstract
The aim of this thesis is to use the strained flamelet model to numerically investigate the turbulent partially-premixed flame to observe the strain effects in the flame. Calculations are based on averaged Reynolds equations based on a Bunsen burner geometry (for a premixed flame) and flame close to blow-off (for a partially-premixed flame). The simulation of the flame in this thesis is done by Fluent software. Since the Fluent software is not open source, the innovation in this research is the implementation of the flamelet model in the Fluent software. It is important to be able to apply strain effects to the flame correctly and with good accuracy. Fluent takes the strain into account...
A Priori Investigation of Laminar Flamelet Decomposition and Conditional Source-term Estimation Methods in Turbulent Premixed Flames
, M.Sc. Thesis Sharif University of Technology ; Salehi, Mohammad Mahdi (Supervisor)
Abstract
An a priori analysis is performed to assess the performances of Laminar Flamelet Decomposition (LFD) and Conditional Source-term Estimation (CSE) methods in predicting conditional and unconditional filtered production rates and mass fractions for turbulent premixed flames over a wide range of Karlovitz numbers, which is an indicator for the level of turbulence-chemistry interaction in premixed combustion.In LFD, it is assumed that a turbulent flame is composed of strained laminar flamelets. By presuming the functional form of the probability density function (PDF) of the progress variable and inverting the integral equation for the unconditional filtered mass fractions of one of the species,...
VLSI Architecture for Base Band Part of an Optical OFDM Transceiver
, M.Sc. Thesis Sharif University of Technology ; Shabany, Mahdi (Supervisor) ; Salehi, Javad (Supervisor)
Abstract
Optical Communication is a promising technology in access networks because of bandwidth hungry application like videos. So fiber Optic is an important candidate as a media in networks. There are different methods of modulation for transferring data through a channel. Among all, Orthogonal Frequency Division Multiplexing is a method which used in most wired and wireless systems. Recent researches show that OFDM is also a good approach for optical communication.
In this thesis we concentrate on hardware implementation of digital part of an Optical OFDM transceiver. In the first step we ignore the effect of optical channel and design and simulate the transmitter and receiver. After that we...
In this thesis we concentrate on hardware implementation of digital part of an Optical OFDM transceiver. In the first step we ignore the effect of optical channel and design and simulate the transmitter and receiver. After that we...
Improving the Measurement of the Chemiluminescence of Methylidyne (CH*)Species with the Help of Thermometry by Soot Pyrometry Method
, M.Sc. Thesis Sharif University of Technology ; Salehi, Mohammad Mahdi (Supervisor) ; Mardani, Amir (Supervisor)
Abstract
This research introduces temperature measurement by a non-intrusive pyrometric method of the ratio of two colors of soot. For pyrometry, the spectral sensitivity of the Nikon D7100 camera was obtained by developing a neural network based on the results of photographing colored papers and their spectrum, and this camera was used for temperature measurement. Based on the dependence of soot radiation on temperature and the spectral sensitivity of the camera, a calibration chart has been extracted on the ratio of the green channel to the red channel of the camera with the soot temperature, which is used to produce the temperature contour using the flame image. The temperature contour of...
Design and Development of a Turbulent Partially-Premixed Jet Burner
, M.Sc. Thesis Sharif University of Technology ; Salehi, Mohammad Mahdi (Supervisor) ; Mardani, Amir (Co-Supervisor)
Abstract
The burners studied in the combustion principles have different types due to the configuration of different types of flames, each of them studies a specific phenomenon of combustion, so researchers need to design burners with the ability to: create different types of combustion flow regimes, changing in mixing rate and performance at critical points are felt more and more. This document describes the process of designing and manufacturing a turbulent jet burner with variable mixing ratio and the ability to create a diverse range of flow regimes and different flame configurations. Mixing rate is the most important characteristic in the stability of premixed flames, so the distinctive feature...
Flamelet Modeling in Large-eddy Simulation of Turbulent Premixed
Flames
,
M.Sc. Thesis
Sharif University of Technology
;
Farshchi, Mohammad
(Supervisor)
;
Salehi, Mohammad Mahdi
(Co-Supervisor)
Abstract
The purpose of this study is to investigate the efficiency of a flamelet method along with the LES1 approach in the modeling of a turbulent premixed flame behind the bluff-body. In this flame ,because of the high turbulence intensity and fuel dilution, there is a significant interaction between the turbulence and chemical kinetics. In this study, first, the cold flow is modeled using LES and RANS2 approaches. Then, using the Flame-Generated Manifold (FGM) model and a presumed PDF model, the turbulent reacting flow is simulated.Comparison of the results of the LES and RANS showed that the accuracy of the LES method in simulating the physics of turbulent flow is much higher than RANS, but its...
Methylidyne (CH*)Chemiluminescence Measurement in Sooting Flames
, M.Sc. Thesis Sharif University of Technology ; Salehi, Mohammad Mahdi (Supervisor) ; Mardani, Amir (Supervisor)
Abstract
In this study, using a non-interference experimental method, the chemical luminosity of CH* in co-flow diffusion flames with soot and using natural gas hydrocarbon in a laminar flow regime has been investigated. In addition to experimental research, in current research, numerical simulation has been used to extract information such as temperature field, mass fraction of species, and flow structure and comparison and validation with experimental results. Numerical simulation has been used to simulate the mechanism of CH* species formation. Two different mechanisms have been used. In addition, the Soot simulation model from the Moss-Brookes model and radiation heat transfer mechanism...
Investigation of the continuum-rarefied flow and isotope separation using a hybrid CFD-DSMC simulation for UF6 in a gas centrifuge
, Article Annals of Nuclear Energy ; 2020 ; Akbar Salehi, A ; Reza Keshtkar, A ; Mahdi Shadman, M ; Hossein Askari, M ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
UF6 gas flow in the total regions of a rotor with the radius of 0.1 m and the length of 1 m in axisymmetric and steady states was simulated using a new hybrid CFD-DSMC method in the OpenFOAM framework. Implicit coupled density-based scheme was performed for CFD method, and Variable Hard Sphere (VHS) and diffuse model were employed in DSMC method. Also, as an initial estimation, the local Knudsen number was applied to determine the interface location between the continuum-rarefied regions (r = 0.0855 m). Then it was modified (r = 0.084 m) to reduce the computational cost. The comparison results of pure CFD and CFD-DSMC methods illustrated that there were large differences between the flow...
Investigation of the continuum-rarefied flow and isotope separation using a hybrid CFD-DSMC simulation for UF6 in a gas centrifuge
, Article Annals of Nuclear Energy ; Volume 152 , 2021 ; 03064549 (ISSN) ; Akbar Salehi, A ; Reza Keshtkar, A ; Mahdi Shadman, M ; Hossein Askari, M ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
UF6 gas flow in the total regions of a rotor with the radius of 0.1 m and the length of 1 m in axisymmetric and steady states was simulated using a new hybrid CFD-DSMC method in the OpenFOAM framework. Implicit coupled density-based scheme was performed for CFD method, and Variable Hard Sphere (VHS) and diffuse model were employed in DSMC method. Also, as an initial estimation, the local Knudsen number was applied to determine the interface location between the continuum-rarefied regions (r = 0.0855 m). Then it was modified (r = 0.084 m) to reduce the computational cost. The comparison results of pure CFD and CFD-DSMC methods illustrated that there were large differences between the flow...
Emerging OCDMA communication systems and data networks [electronic resource]
, Article Journal of Optical Networking ; Volume 6, Issue 9, 1 September 2007, Pages 1138-1178 ; Sharif University Of Technology
Abstract
I present an in-depth review of the trends and the directions taken by researchers worldwide in optical code-division multiple-access (OCDMA) systems. I highlight those trends and features that I believe are essential to the successful introduction of various OCDMA techniques in communication systems and data networks in the near future. In particular I begin by giving a comprehensive review of the construction of optical orthogonal codes (OOCs). Specifically I discuss the recently developed algorithms that are based on matrix algebra, which simplify and enhance the efficiencies of algorithms in OOC generation. In communication systems studies I first focus on and discuss various OCDMA...
Electroplating and characterization of Cr–Al2O3 nanocomposite film from a trivalent chromium bath [electronic resource]
, Article Anti-Corrosion Methods and Materials ; Vol 61, No 4, 2014, 205-214 ; Sadrnezhaad, Khatiboleslam ; Salehi Doolabi, Davood ; Sharif University of Technology
Abstract
The main aim of this study was to improve current efficiency and to obtain thicker coatings via aluminum oxide (Al2O3) addition to the chromium (Cr) (III) bath. Design/methodology/approach ‐ Pure Cr and nanocomposite Cr–Al2O3 coatings were electrodeposited from Cr (III) bath onto cathode copper substrates by conventional method. Dependence of current efficiency to current density, Al2O3 content and particle size were investigated. Findings ‐ Current efficiency increased with Al2O3 amount and decreased with Al2O3 particle size. Maximum current efficiency was achieved at 25 A/dm2 for pure Cr and 30 A/dm2 for composite coatings. Al2O3 bath content, current density and stirring rate increased...
MBBR and MBR Reactor Configuration for Better Performance
, M.Sc. Thesis Sharif University of Technology ; Borgheei, Mahdi (Supervisor)
Abstract
Membrane bioreactors (MBRs) which are commonly understood as the combination of membrane filtration and biological treatment using activated sludge have several advantages, but membrane fouling reduces the membrane efficiency, permeability and lifetime. An alternative is replacing a moving bed biofilm reactor (MBBR) with the activated sludge system which may reduce the effect of membrane fouling. The sludge produced in MBBRs has poor settling characteristics, therefore, their efficiency is limited by the sedimentation tank performance and they require a larger settling surface. The combination of moving bed biofilm reactors and membrane bioreactors can compensate for the drawbacks of both of...