Sharif Digital Repository

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... 

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... 

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  

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... 

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... 

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... 

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... 

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,... 

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... 

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... 

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... 

The integration of radar and communication functionalities into a unified Joint Radar-Communication (JRC) system offers enhanced spectral efficiency and reduced hardware complexity. Recognized as a key enabler for next-generation wireless networks, JRC systems require a careful balance between radar and communication demands, where waveform design plays a pivotal role in achieving this equilibrium. Although waveform design has been extensively studied separately in radar and communication domains, the requirements of modern networks necessitate a unified approach that simultaneously addresses the needs of both systems. This thesis advances waveform design methodologies for JRC systems,... 

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 dissertation, the application of frequency and space diversities in radar target parameter estimation are investigated. On this basis, multi-frequency signal is used to improve the range resolution, array structure is used to increase the angle estimation accuracy and the merger of the multi-frequency signal and array structure are used to increase the maximum number of targets that can be uniquely identified.Considering the desirable properties of multi-frequency signals such as high bandwidth efficiency, high range resolution achievement without chip length decrease and …, there has been increased interest in the vast area of research on the design of such signals that has... 

Target recognition techniques based on micro Doppler phenomenon are popular because they are applicable even on low resolution radars, in contrast to other techniques such as High Resolution Range Profile (HRRP) which need high resolution in range or angle. Usually, main purpose of such techniques is generating robust features against target initial state, velocity, aspect angle, etc. rather than features which exactly identify a target. Main approaches in the literature are based on time-frequency transforms (TFT) such as spectrogram in order to generate features to classify targets, but in this thesis, we propose a totally different method using Recurrence Plot for generating features... 

In this research with Finite Element Methods in ABAQUS, numerical modeling has done in three-dimensions, which can be used to determine the effect of different factors on the surface settlement. Also, various factors such as geotechnical conditions, tunnel diameter,tunnel depth, the impact of the thickness of the segments and the amount of eccentricity of the structure relative to the longitudinal axis of the tunnel considered in this study. Face Pressure Supports, and Grout Injection Pressures are taken into account, too.Tunnel drilling causes a change in the displacement area and creates a changing zone around the tunnel. In this regard, not only adjacent buildings will be affected by... 

Main aim of this work was to obtain the harder zinc coating and increasing the anti corrosive properties by mean of adding SiO2 particles by electrophoretic method.
The coating was applied on the substrate surface by mean of electro co-deposition technique in three different electrolytes ethanol, methanol and water. The morphology of the coating in each electrolyte studied by scanning electron microscope (SEM).For the Zn/SiO2 coatings achieved in ethanol solvent the polarization and EIS tests was took place and found that for the Zn/SiO2 coating contain less than 10% SiO2 the corrosion rate decreased but for the coatings contains more than 10% SiO2 the paradox occurred because of the... 

Validation is an important enterprise especially when the test to be validated is a high-stakes one the results of which bring about life-changing implications for the candidates (Roever, 2001). Messick’s (1988) notion of construct irrelevant factors is pertinent in test validation. Demographic variables like gender, field of study and age can affect test results and interpretations. A fair test needs to be neutral when it comes to construct irrelevant factors such as gender. Differential Item Functioning is a way of making sure that the test does not favor one group of test takers over the others. The current study investigated differential item functioning (DIF) in terms of gender in the... 

The present study was conducted to examine the effect of explicit and implicit teaching of the speech acts of apologies and requests with 40 students. They were given a discourse completion test (DCT) which was designed by the researcher. The students came up with situations that embodied apologies and requests. After exemplar generation and likelihood investigation some 16 items were retained and used with students. The participants of the study consisted of two groups of implicit and explicit. The two groups were intact and randomization was not a possibility. The design was quasi-experimental. To investigate the relationship between grammatical competence and pragmatic competence, the... 

The present study was conducted to explore the effect of strategy based instruction and task based teaching on EFL learners’ production of apology and request speech acts and also to investigate the relationship between grammatical competence and speech act performance. To this end, 35 intermediate English language students that comprised two intact classes in a language institute participated in this study. A standard English proficiency test for intermediate level and a discourse completion task (DCT) were used to measure students’ grammatical competence and speech act production. DCT was used at the beginning of the study to ensure that the two classes were homogenous in terms of apology...