Sharif Digital Repository

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... 

Orbit perturbations are most important environmental factors that affecting performance of satellites. These effects mainly in two ways affect the satellite. Through the first, perturbing acceleration, change the orbital elements and the second, moments due to perturbations, couple the dynamics and attitude equations. Various studies regarding how the resources of major perturbations such as direct solar radiation, atmosphere and the third body attractions have been done. However, effects a significant number of other perturbations, such as solar, rotation of the atmosphere, reflected solar radiations, earth oblateness with high order of earth harmonics consideration and small forces (such... 

Using a Lithium Selective Ion Sieve is one of the most advanced processes for Extraction of lithium from Brines. The ability to Extract Lithium selectively from brines make the ion sieve suitable for brines with low concentrations of lithium. In this study brines samples from Urmia Lake with lithium concentration of 30 ppm was used. The main objective of this study was to find the best condition for lithium adsorption and desorption using the synthesized titanium dioxide ion sieve. In this study lithium selective ion sieve with nanotube morphology and Diameter of 81 nm was synthesized. Study on pH of synthesized solution containing lithium ions was carried out and pH=12 was concluded the... 

Upwind methods for forward time marching integration of compressible flow equations, suffer low accuracy and convergence rate for very low mach numbers. Here we have used a preconditioning scheme to address this challenge. A preconditioner matrix is multiplied in the Euler flow equations. First we investigate subsonic flow around an airfoil to validate the numerical scheme used here, and to show grid independence of our solutions. Then very low mach numbers between 0.1 and 0.001 is solved and increase in accuracy and convergence rate is demonstrated. The proposed algorithm has flow parameters, which are studied here to find their effect on accuracy and convergence rate. The found results are... 

The main subject of this thesis is to improve conventional CFD algorithms applied in numerical simulation of inviscid unsteady flows around moving boundaries with large relative motions, on unstructured grids. All challenges in this regard are reviewed, and appropriate efficient schemes are introduced to address them. A new scheme is presented for valid grid generation during grid movement and is implemented for 2D and 3D problems. Customary three dimensional convergence acceleration techniques such as implicit time stepping and multigriding have been applied. For implicit solution of the flow equations a new algorithm is used. Via a special renumbering algorithm, the approximate... 

In this thesis, a method developed for producing technology roadmap to identify technologies needed in design, construction and testing of turbofan engines. In the first phase and in scoping step, 10 years’ time horizon is determined. Then project organization and the role required are intended and after that the second phase that is technology roadmap formation is begun. Market identification, product identification by key success factors forms and experts are steps of this phase and determination of three generations of engine are results of product identification step. After that, the technology identification step is begun but simultaneously the technology mapping drawing steps for... 

Ramjets have many applications and in the speed range of Mach numbers 2 to 5 show the best performance in terms of specific fuel consumption. In many applications, including some anti-air missiles, cannon and mortars, solid fuel ramjet can be used to improve the system performance.
In this thesis, two activities are performed:
A) One dimensional simulation of the internal flow field of solid fuel ramjet by development of available softwares.
B) Optimization of design parameters of a specific ramjet motor based on the above simulation.
The main target of this thesis is simulation of internal ballistics, design and optimization of a solid fuel ramjet for a particular... 

Flapping wing vehicles produce aerodynamic lift and thrust through the flapping motion of their wings. The dynamic performance of a flexible membrane flapping wing is experimentally investigated here. To investigate aeroelastic effects of flexible wings (specifically, wing’s twisting stiffness) on hovering and cruising aerodynamic performance, a flapping-wing system and an experimental setup were designed and built. This system measures the unsteady aerodynamic and inertial forces, power usage and angular speed of the flapping wing motion for different flapping frequencies, angles of attack, various wind tunnel velocities up to 12 m/s and for various wings with different chordwise... 

In the present study, design and manufacturing of a connected pipe liquid fuel ramjet test platform is implemented for performance investigation of a research liquid fuel ramjet burner in the thermodynamic flight conditions. Design and manufacturing of platform systems include: the hot air supply system, the liquid fuel system and the square cross-sectional combustion chamber with the v-gutter shape flame holder. In order to determine the performance range of subsystems, calibration process has been carried out. Calibration process of the hot air supply system includes: determining of the burner inlet velocity and temperature. Also, calibration of the liquid fuel system includes: determining... 

This study develops an aerodynamic shape optimization code using parallel processing capability based on a gradient-based adjoint method. Calculation of the gradient of the objective function with respect to design variables is the most costly part of the gradient-based optimization algorithms. Applying adjoint methods, gradients can be calculated with solving some additional equations known as the "adjoint equations", instead of direct calculation. In this study, the blade shape optimization is performed by inverse design method and using steepest descent optimization algorithm. The objective function of inverse design problem is the desired blade surface pressure distribution. In each... 

In this study, aerodynamic shape optimization of axial compressors is considered. In order to optimization, one of the gradient based optimization algorithms, namely Adjoint method, is used. Recently, Adjoint method has been emerged as one of the reliable gradient based optimization algorithms in turbomahineries applications. Because this method is a gradient method of optimization, similar to the other entire gradient based algorithms, adjoint method also has a better convergence than non-gradient based optimization algorithms. In this work, aerodynamic shape optimization of two-dimensional cross section through a transonic axial compressor is studied. The process is considered for midspan... 

Aerodynamic shape optimization has been always of great importance in aerospace design. Recent advancements in computational algorithms and hardware, has made it feasible to have advanced optimization as a standard part of desing procedure. Here we have promoted aerodynamic optimization in three different applications, i. e., wing-body configuration, hydro propellers, and air propellers. First we have reviewed fluidic theoretical aspects, and have selected appropriate physical models or existing softwares. Accuracy of physical analysis or software is validated. Then different optimization algorithms are reviewed, and schemes used in this thesis are described and the softwares are validated. ... 

In this research, steady state and transient performance of a single spool axial turbojet engine (without afterburner) is studied. Performance maps of main components such as; compressor, combustor and turbine are extracted from a similarity (geometry independent) approach.Then using nested loops method, steady state model of the turbojet engine is developed and using shaft dynamics and volume packing equations, transient model of the turbojet engine is analyzed. Steady state and transient simulations results of an engine are validated by experimental data and then effect of changes on input parameters such as; polar moment of inertia, Mach number, fuel heating value, pressure and... 

Here we have used CFD to simulate the flow field around a DBD plasma active controller for flow control. Enhanced Electrostatic model is applied to model the plasma actuator, by solution of two elliptic equations to find electric field and charge density in whole flow field. So, it provided the body force by neglecting the magnetic forces in Lorentz equation. The body force is added to the momentum equation as a source term. A commercial software FLUENT is used for this simulation. To validate the algorithm, flow over a flat plate using DBD actuator is solved and results are compared with experimental and numerical results. Flow control around a cylinder with Reynolds number of 18,000 is... 

In this thesis all the information about different techniques and methods used in Local Area Network (LAN) are described and organized as follows:
Chapter 1: The network properties are described including Network definitions and different types of LAN and their relative applications
Chapter 2 :Different techniques and protocols of data transfer and switching methods are being described and compared.
Chapter 3 : Network technology consists of different topologies for physical connections and various transfer Medias are covered.
Chapter 4 :All network protocols are described including different methods of DATA access in LOOP, RING and BUS topologies and the ISO and IEEE... 

Shock control bump (SCB) and suction and blowing are flow control methods used to control the shock wave/boundary layer interaction (SWBLI) in order to reduce the resulting wave drag in transonic flows. A SCB uses a small local surface deformation to reduce the shock-wave strength, while suction decreases the boundary-layer thickness and blowing delays the flow separation. Here, a single-point, a multi-point, and a robust optimization method are used to find the optimum design of SCB and suction and blowing. The flow control methods are used separately or together on two transonic airfoils i.e.; RAE-2822 and NACA-64A010 for a wide range of off-design transonic Mach numbers. The RANS flow... 

Streamline Curvature method is one of the most commonly used methods by industry for prediction of axial flow compressors. This method analyze axial compressor by solving radial equations in the meridional plane to locate streamlines and also by using empirical models to predict total pressure loss. Despite growth of CFD models, Streamline Curvature method has been considered as most practical method for compressor preliminary design and performance assessment because of it’s high speed and good precision. In the current work a C++ code (SLC) has been developed using streamline curvature for axial flow compressor performance analysis. This code receives compressor geometry, properties of... 

Nowadays, the axial transonic compressors are used widely in aircraft engines, oil and gas industry and etc. because of higher pressure ratio and more efficiency than the other compressors. The Major part of losses in transonic compressors is due to shock waves. In this study the idea of using Shock Control Bump as a passive flow control method has been used for weakening the shock waves. The Shock Control Bump is modeled with the Hicks-Henne function and added to the suction side of a section of the NASA rotor 67 blade. Validation of flow solver is done in both two and three dimensions. Single-point and multi-point optimizations are performed in the design condition and in two off-design... 

In the current study, first, the presence history of dielectric barrier discharge (DBD) plasma actuator in flow control usages has been investigated. After recognizing the importance of plasma actuator in this branch of engineering, this active controller was modeled relying on computational fluid dynamics (CFD) knowledge to control flow separation. In order to model this actuator, physics based model called spilt-potential model and modifications done to improve it, were used. Using this model and solving two elliptic equations, electrical field and plasma charge density distribution are obtained in range of solution domain and body force from plasma actuator modeling in all computational... 

Control and reduction of gas turbines pollutants emissions are increasingly of major concern. Here we introduce and apply new algorithms for derivation of accurate and low cost skeletal chemical kinetics, optimization of global multi-step chemical kinetics, and optimization of geometry of Lean Premixed (LPM) dry low emission (DLE) combustors.A new reduction algorithm called SA-GEIE, based on sensitivity analysis of reaction mechanisms respect to ignition delay, flame temperature and pollutants concentration (NO and CO), is introduced. This algorithm is implemented to GRI-3.0 to produce a low cost methane oxidation skeletal mechanism with 118 reactions and 39 specie. The accuracy is assessed...