Sharif Digital Repository

At this project we proceed to aero elastic modelling of a flapping wing using unsteady aerodynamic approach. Solving this model according to aerodynamic and structure coupling needs to simultaneously solve of aerodynamic and wing structure. Left side and right side of wing, each on divided into 18 elements. each element is interacting with sides element in terms of structural force and moment. In this modeling aerodynamic was modeling with unsteady aerodynamic approach (using modify theodersen function), also structure is flexible in to direction, bending and twisting. In the following it is proved that with change in flapping pattern better performance can be achieved. the effect of change... 

Reliability modeling, analysis and computation of a Thrust Vector Control System (TVC) is investigated. In this respect, first the TVC subsystems including the jet vanes (JVs), sensors and actuators,... are identified and their pertinent Reliability Block Diagram (RBD) is depicted. Subsequently static reliability of a jet vane is calculated considering both structural and thermal loadings via related verified limit state functions. In addition, a sensitivity analysis is performed that identifies the key JVs design parameters from a reliability point of view. Next, knowing the structural and thermal reliability of the JVs, static reliability of the total TVC system is computed via utility of... 

The subject of systemic reliability assessment, allocation and optimization as well as structural reliability (SR) of a two stage solid fuel launch vehicle (LV) is investigated. In this regards, first the LV reliability block diagram is broken-down into appropriate subsystems. Subsequently the total LV system reliability is determined assuming the subsystems reliability. In addition, using a hybrid GA-PSO algorithm optimal subsystems redundancy levels, reliabilities as well their type are determined to simultaneously maximize the total reliability while minimizing the LV cost (weight) as a constraint. While the reliability and cost of subsystems are not precisely known, the total LV... 

The problem of attitude determination (AD) has always been a challenging issue for space missions that is of importance either independently or for attitude control purposes. The problem of AD is generally focused from two aspects: measurement mechanisms (sensoring) and determination algorithms. From the former point of view, there exists a variety of measuring systems such as the Sun sensors, magnetometers, gyroscopes, star and horizon sensors that have been separately or collaboratively utilized for AD. Integrative usage of sensors not only can bring about added advantages in terms of accuracy, but also provides for estimates of attitude during special times such as the Sun eclipse. The... 

An optimal trajectory for flight through Microburst wind shears is designed which minimizes the maximum deviation from desired trajectory With respect to optimal control methods. The suitable performance of airplane retrieval in abort landing and landing phases at microburst encounter is achieved by influence of mentioned design in worse case of wind fluctuation and variation. 3D Vicroy microburst model is selected to investigate its effects on 6 DOF jet engine aircraft EOMs. Above optimal control problem is solved using gradient method of SD . Furthermore, sensitivity of optimal trajectory to lateral and longitudinal location of microburst, microburst parameters, throttle setting and... 

In line with advances in science and technology in the areas of robotics, artificial intelligence, computer and control, unmanned vehicles are being more utilized and focused. On the other hand, development and further advances of these vehicles is highly dependent on the level of their autonomy. Motion planning is one of the most important issues in this regard. Due to high levels of autonomy required for unmanned air vehicles (UAV), the subject of motion planning is of valuable interest in aerospace applications. The goal of the motion planning problem, that is the subject of this research, is to extract an optimal trajectory for the UAV from an initial location toward its target point... 

This thesis deals with the attitude estimation based on low cost sensor for a micro satellite in a circular, low earth orbit (LEO) and sensor calibration. With two body problem theory and Quaternion formulation, rotational motion is modeled. In addition gravity gradient effect is considered on satellite orbital elements. Using a 3-axis MEMS-based magnetometer and a sun sensor as two measurement systems, low cost attitude estimation is proposed. Bias and Scale factor are presented to model deterministic sensor error and white Gaussian noise to model stochastic sensor error. It is shown that by sensor calibration the estimation accuracy will improve. Non-linear estimation methods EKF, SRUKF... 

The problem of quadrotors formation flying via optimal approach is investigated using the idea of cooperative and multi-level control. In this respect, a low level optimal control formulation of quadrotors is formulated for stability and tracking where the required tracking commands are generated via the high level controller over a simpler translational dynamics of quads. The idea of multi-level controllers enables one to develop formation keeping controls for complex dynamics systems, where varying agents in terms of dynamics and platform could be utilized. Due to inherent difficulties in implementing acceleration commands emanated out of the high level controller, an inverse dynamic... 

A carrier should be used a guidance system for reaching to the point of injection in an orbit. The main purpose of guidance system in the injection process is issuance of guidance commands to achieve the final desirable velocity and position. These velocity and position indicate the purpose orbit for injection. Carrier is a dynamic system which is described by mathematical terms. In general carrier guidance systems apply pitch angle or rate of pitch angle to reach specific path over injection process. Different methods are available for carrier guidance such that preset method. In this method, the guidance system addresses specific guidance commands and control system performs these... 

Multidisciplinary Design Optimization (MDO) has been considered by many researchers, especially in field of aerospace engineering during the last two decades. The goal of MDO is to achieve optimal design of systems considering a variety of disciplines. In this regard, selection of viable disciplines, their codification, structure and interactions, levels of integrity and the optimization approach to be utilized are of importance and challenging.
In this project, MDO external ballistic optimization of the conceptual design of a flying projectile is investigated. The key objectives to be met by optimal design were chosen to be maximizing the payload weight and the covered range. To this... 

Since the classical continuum theory fails to deal with the problems associated with defects, stress concentrators, and relevant deformation phenomena in solids, alternative approaches that can detect the atomistic nature of materials' fracture are required. The deficiency of the capture the size effect which yields delusively high values for some components of the stress field right on the edge of the stress concentrators, and its weakness in describing the complex interaction between small inhomogeneities, cracks and the like when they are only a few nanometers apart, are among some of the disadvantages of the classical approach. In recent years, however, atomistic methods are emerging to... 

Aluminum Bronzes have many applications in marine environments. These alloys suffer from both hot cracking and cold cracking. In order to overcome the hot cracking and cold cracking, Semisolid Stir Joining method and a proper thermal cycle was used respectively. Effects of temperature, stirring rate, and tool type were investigated in Semisolid Stir joining method. In this method, butt joint design was used in order to place specimens, and the specimens were heated up to specific temperatures (920, 925, 930°C). A stirrer (Cylindrical and Grooved tool) with three rotational speeds (800, 1200, 1600 RPM) was introduced into the stir weld seam. Welded specimens were cooled to the 900°C... 

The low female labor force participation rate in the Iranian labor market relative to the global average and even to countries that do not differ significantly from the socio-economic characteristics of our country is one of the important questions of the Iranian labor market. In this study, we seek to answer the question of whether the economic participation rate of married women will increase if the gender gaps in wages, job findings and job losses among women and men are eliminated in the Iranian labor market. To answer this question using household expenditure and income data and labor force data, we show that between the two categories of occupations, in terms of the share of women's... 

Shot peening is a cold-working process commonly used in industry to improve the fatigue performance, stress corrosion resistance and surface nano-crystallization of metallic parts. This process extends fatigue life via two mechanisms: Preventing the crack growth due to compressive residual stresses and, preventing the crack initiation because of increased material hardness. These mechanisms are the results of the bombardment of the component's surface with small spherical particles. In this research, an analytical model is developed for estimating the residual stress distribution induced by shot peening process. The modifications of the developed analytical model are related to...