Sharif Digital Repository

In this work we simulate SIRS1 model on homogeneous networks by means of simulation, then we drove meanfield equations for this model and compared the solution of these equations to the simulations results on the network. To obtain a new model closer to the reality, we modified the SIRS model and introduce history to the convenient model. After simulation of this model we redrove the equations with history and found that this model can show bifurcation so we found the phase diagram for this model. And in the last part we introduced history to a meanfield model with pair approximation and drove the equations and try to solve
them numerically.
 

The surge phenomenon, as the most important aerodynamic instability, has caused a severe drop in efficiency and performance in centrifugal compressors, and its prevention and control is considered one of the main concerns of industrialists. The purpose of this study is to design and develop a surge control system in order to improve the stability and safety of the system under the effect of surge. In this research, after simulating the existing control system and working line in Borzouyeh Petrochemical Industry, by designing and adding the piston surge active control system to the above centrifugal compressor and using the combined control system, the flow rate of the bypass path has been... 

In recent decade, pollution reduction is one of challenges in front of engineers. Nowadays accurate prediction of temperature and harmful Pollutants is vital, this leads to various models for turbulent combustion to predict combustion-generated pollutants. One of the most widely used models for simulating turbulent combustion is Flamelet because of separating the chemical reactions and the turbulent flow field. The unsteady state assumption of Flamelet model is capable of reasonably predict complicated phenomenon such as slow chemical reaction and radiation. The purpose of this study is to calculate combustion-generated emissions by Flamelet model and reduce these emissions by engineering... 

In the present study an air supply system of a connected-pipe ramjet test facility for liquid fuel ramjet engine in theoretical and numerical base designed and optimized that the purpose is for performance test of a ramjet engine combustor in flight condition. The flight condition gained from previous assessment that is 1.5 kg air in 10 bars and 550 K. Air supply subsystems consist of air tanks, compressors, valves, regulators, preheater, and fuel and oxygen systems that are designed in a preliminary process and then valves, orifices, and fuel and oxygen systems optimized by HYSYS program. In the last step preheater that is a gas turbine combustor investigated and possible changes made by... 

In the present research, a test stand for investigating the behavior of an injected jet in cross flow, is established. In All experiments water and air was used as injected jet and cross flow respectively. At the beginning, with help of dimensional analysis, non-dimensional parameters are introduced and their effect of these parameter on the jet behavior, as the most important goal of this research, is investigated. In order to inject the fluid in the cross flow, two injector with 0.58 mm and 1.08 mm exit diameter and 10 mm exit length was used, and jet speed varies from 2 m/s to 12 m/s. The cross section of the wind tunnel was a 8cm-edge-square and the air speed was adjustable in the range... 

In chis chcsis we consider a work by Dmitry Dolg:opyat and Raphac) Kriko­ rian (on Simulcanoous Lincariwtion of Diffcomorphisms of Sphere) and a recent preprint by Jonathan Dc\Vitt (Simulrn.ncous Lincarization of Diffco­ morphisms of Isotropic Manifolds). Suppasc /1,h,...,J.. arc pcrturbacions of rotations R1, R2 , ...,Rn of the sphere which generate SOd+I (d 2). \\Tc c". plian how it can be shown that all /; can besimn)tancously conjugated to some new rotations when all the Lyapunov cxponcms of the rcndom walk a.,:;.,sociatc to {/;}arc zero. This rcsn1t is applied to obtain stable ergodicity when d is even.The idea is co translate al1 the information co a linear setting and approach chc... 

Bluff bodies are commonly used to stabilize flames in many high-speed flow applications. V-gutters are one of the most common bluff bodies that are mainly used in ramjet combustors and turbojet or turbofan afterburners for flameholding. Aerodynamic characteristics of flow behind V-gutter has crucial effect on mechanism of flame stabilization, therefore more experimental investigations still seem to be necessary in this area. Particle Image Velocimetry technique which has high temporal and spatial resolution has been used in this research in order to better investigate the structure and dynamics of this unsteady and complex flow filed. Experiments were done on a reference V-gutter in... 

Since the beginning of industrial age the concentration of the greenhouse gases in the atmosphere has increased significantly. This is due to using fossil fuels (oil, gas and coal) exceedingly, leading to higher average temperature of earth and many environmental problems. The critical solution of controlling greenhouse gas emission is replacing other energy resources (for example; solar energy, wind energy and nuclear energy), while considering energy infrastructures shows this is a far solution. An early way for decreasing emission of greenhouse gases in atmosphere is injection of CO2 in geological formations. Moreover, in reservoir and environmental engineering, CO2 injection has been... 

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...