Sharif Digital Repository

In the class of unmanned air vehicles (UAV), there is a class entitled as Quad-rotor that engineers pay much attention due to specific features to them. Main applications of this class are because of vertical take-off and landing capability and high controllability. This class has high controllability in environments with high barriers because of the inherent imbalance. All of the Quad-rotors have already studied, had a fixed structure. So the designer's main focus was on improving the guidance and control systems and almost all forms of linear and nonlinear control methods and fuzzy, adaptive and robust control have been investigated. In this study variable structure is examined instead... 

In high-performance liquid fuel motors and space thrusters, the combustion chamber and nozzle walls are in contact with the gases caused by high temperature and pressure combustion, making severe thermal loads on the walls. Therefore, these systems require cooling mechanisms. The most common way of cooling in space thrusters is film cooling. This study is a numerical simulation of film cooling in the liquid fuel space thrusters. Numerical and empirical studies have been reviewed in this area and evaluated while conducting studies and results to select an appropriate model for ongoing project studies. Along this path, various fuel and oxidizing thrusters, including oxygen and hydrogen,... 

This project investigates the effect of plasma on diffusion flame. A Dielectric Barrier Discharge (DBD) plasma actuator has been used to generate plasma, which converts fuel-air non-premixed mixtures into plasma. Then, the effect of plasma on the shape and stability of the diffusion flame composed of fuel and air mixture has been evaluated. This study investigates the laminar flow regime for low calorific value fuels. For this purpose, natural gas fuel (urban methane) has been diluted with N2 and CO2 gases to reduce its calorific value. Then, the diffusion flame is formed from the fuel and air mixture in a laboratory stand. This stand consists of two coaxial tubes made of quartz, fuel flows... 

The problem of launching a satellite to low earth orbit has been considered. Preliminary concepts such as satellite orbits, launcher missiles and their equations of motion, and traditional methods for guidance of launchers are reviewed first. Then a new method for optimizing the launch trajectory under non-ideal conditions is introduced in which the solution of a known ideal trajectory optimization problem is used as an initial guess for the actual optimization problem. Several methods for guiding a launcher to place a satellite in Earth orbit are presented next; they have been titled as (1) launch path re-computation outside the atmosphere, (2) prediction error minimization, and (3) output... 

Presently, a wide range of devices operate at supercritical condition. In fact, supercritical condition refers to a condition in which both temperature and pressure of injected fluid exceed the critical point. In the case of modern internal combustion engine, the temperature and pressure of combustion chamber is high enough that can be considered as supercritical condition, whilst the fuel injected may be subcritical or transcritical.It has been widely accepted that in supercritical state, vaporization enthalpy is vanished and there is no distinction between gas and liquid. Hence, only a single state will remain which is neither liquid nor gas and referred to as fluid. Moreover, many... 

This study investigates the effect of changes in natural gas and diesel prices on 〖CO 〗_2 emissions from power plants in Iran. We use annual data of fuel prices (including natural gas, diesel, and fuel oil), efficiency, amount of fuel consumed, and emissions of GHG (mainly carbon dioxide) of all thermal power plants from 1997 to 2023. To find the effect of fuel price fluctuations on emissions, gas and diesel price changes are used on two types of gas power plants (gas and diesel consumers) and diesel power plants (diesel consumers). First, a difference-in-difference (DiD) model is used to evaluate the causal effect of fuel price changes on gas power plant's efficiency and emission intensity... 

The present work is concerned with numerical simulation of spray flame for rocket combustor (MASCOTTE A-10 test case at 10 bar pressure) based on cryogen gaseous hydrogen and liquid oxygen at specific condition. This liquid oxygen and gaseous hydrogen single element combustor experiment has been the focus of many numerical studies which is representative of combustion in rocket combustion chamber condition. The purposed strategy relies on hybrid Eulerian-Lagrangian framework that continuous phase is evaluated by Reynolds average Navier-stokes (RANS) equation with quick discretization method and dispersed phase of combustion chamber atmosphere is evaluated by discrete phase method (DPM). To... 

Formation and detachment of drops are of fundamental importance in studying two-phase flows, such as ink jet printing, emulsion, and spray. Drops are formed under the effects of surface tension forces. After formation, forces like gravity detach the drop from the rest of the fluid. The flow rate is varied from dripping to jetting regime. In this project, formation and detachment of drops were simulated, using LBM with phase field model, which can simulate flows with high-density ratios and is a robust method for applying wetting condition on the walls. Results were validated using single-phase and two-phase flows. After code validation, the oscillations caused by formation and detachment of... 

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... 

In this study, numerical simulations of a Dielectric-Barrier Discharge (DBD) plasma actuator are performed to predict its output chemical composition. The plasma actuator is cylindrical, with two coaxial electrodes and a quartz dielectric. The electrical discharge occurs in a pulsed manner around the quartz wall. This device is utilized for methane conversion in plasma-assisted combustion applications. The effects of voltage, frequency, temperature, and relative permeability parameters on methane conversion and some selected species concentrations were investigated. The results show that plasma discharging converts methane to hydrogen and heavier hydrocarbons such as C2H3, C2H4,C2H5, C2H6,... 

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... 

In this thesis, consider three important questions in the Iranian Wholesale Electricity Market (IWEM) and answer its. The first one is whether the bidding behavior of the firms in the IWEM has been ex-post optimal? The results of the research show that, on average, the firm’s bidding behavior didn’t optimal in the IWEM, and therefore the bidding strategy of them could be improved. This issue is importance from the regulatory viewpoint in terms of assessing market efficiency and market power of firms, as well as from the firm’s point of view to improve the bidding strategy and increase its profits. The second issue is the assessment of the firm’s ability to exercise unilateral market power by... 

The present study focus is on finding a new solution to control laminar separation bubble phenomenon by combustion actuators in micro scale, which is investigated in flows with low Reynolds number surface effect and free flows. The main parameters in this problem are classified in three groups of formation location of laminar separation bubble, its length, and transition from laminar to turbulent around airfoil SD8020 in attack angle of 5 and 8 degree. Following that, the new combustion actuators in micro scale method the comparison it with cold (and hot) air jet injection is introduced to control boundary layer flow with separation bubble point of view. Some mechanisms are identified in...