Sharif Digital Repository

One of the ways to optimize fuel consumption and improve aircraft performance can be realized by reducing drag, and a major part of this force is the lift-induced drag, which is reduced by increasing the wing span. On the other hand, increasing the wingspan has physical limitations on the allowed dimensions of the aircraft, increasing the weight and reducing the maneuverability of the aircraft, especially in the roll maneuver. Therefore, in order to benefit from the advantages of increasing the wing span and not facing the mentioned limitations, the idea of using a Folding Wing-Tip (FWT) has been proposed by aircraft manufacturing companies and experts. In this way, in normal flight such as... 

In this thesis, we investigate the theoretical and experimental vibrations of a cylindrical shell with an electrorheological core. Magnetorheological and electrorheological fluids are the most suitable materials used in smart structures and have various applications in the automotive, aerospace, civil engineering, medical engineering and robotics industries. We use starch particles and silicone oil to make electrorheological fluid. Then we make a sandwich beam with an ER core and extract the modal parameters of the structure using the modal test. Using the ASTM standard, we estimate the shear modulus of the fabricated ER fluid. In the following, based on the equations developed for the... 

Experimental determination of aircraft aerodynamic characteristics is of prim importance in evaluation of its trimability and stability requirements. One of the most common tools for experimental identification of aircraft is the wind tunnel equipped with aerodynamic force and moment balance system. Design and development of wind tunnel equipped with such system for measuring aerodynamic forces and moments can affect the accuracy and quality of identifying the aircraft dynamics. However, since procurement of such professional systems is very expensive, the primary goal of this project is focused on initial design of a tabletop wind tunnel with a force and moment balance system. In addition,... 

This thesis aims to provide a method for obtaining the dynamic properties, including stiffness and damping, of rolling bearings in radial and axial directions using an experimental approach. Experimental and laboratory methods such as modal testing, vibration testing, and static tests are recognized as practical approaches to obtain these properties. In this research, all three of these methods were employed to determine these properties. After studying the theoretical relationships governing bearing stiffness coefficients, a test setup was designed and constructed for conducting experiments. Subsequently, various tests were conducted, and data was collected, including shaft displacement... 

This research investigates the possibility of using the component mode synthesis (CMS) method in experimentation. It should be noted that the original idea for this project originated from an industrial problem. The main issue in this problem was the lack of sufficient equipment to conduct tests on very large structural modes and the high computational cost for their analysis. Therefore, a test platform was constructed using a scaled-down sample (approximately 1:25) with connections that closely resembled real connections. This assembly was then tested separately, and the results were compared with analytical analyses. After updating and correcting the model in several stages, the structure... 

In this thesis, a method is presented for improving the observability of the heading angle in a UAV when using the Visual-Inertial navigation algorithm MSCKF by adding a magnetometer sensor. The proposed algorithm serves as a complementary extension to the primary algorithm, and efforts have been made to seamlessly integrate the magnetometer sensor into the primary algorithm to allow for easy modifications to the sensor's characteristics and to observe the resulting output in system simulations. Improving the observability of the heading angle will lead to an enhancement in the overall system state estimation. To achieve this, a new update stage is added to the existing algorithm.... 

This thesis aims to provide a method to obtain the radial dynamic properties of rolling element bearing, including stiffness and damping by experimental test methods. Methods such as modal test, vibration test, and static tests were known as experimental methods to obtain these properties, and in this research, all three of these methods were used to obtain these properties. After studying the theoretical relations governing the stiffness coefficients of the bearings, a test bed platform was designed and built to conduct the tests After the construction of this platform, the test design stage was reached done and different parameters changed during these tests several tests were it is noted... 

Three dimensional analyses have been carried out for predicting the behavior of the jointed rock slope of the abutments of the bridge which is proposed to be constructed across the river Karun4 in Iran using 3DEC. The rock overall slope angle is approximately 60 to 70 degrees, composed of highly jointed rock mass and the joint spacing and orientation are varying at different locations. Since 3DEC is a three-dimensional numerical code, utilizes a Lagrangian calculation scheme to model large movements and deformations of a blocky system, allows for modeling of large movements and rotations, and including complete detachment of rigid or deformable discrete blocks has been utilized for the... 

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 thesis is sliding mode control of a roll-pitch seeker by considering the zenith pass problem. This problem takes place when the target appears in front of the seeker’s head. First, the mathematical model of the roll and pitch frames is obtained by the Newton-Euler equations of motion. Then, a MIMO sliding mode controller is designed. The performance of the controller is investigated in the presence of model uncertainties and seeker disturbances. The results indicate that the designed controller is robust enough and provides a suitable performance in the stabilization, tracking and guidance loops.
 

In this thesis, the mechanical properties of collagen hydrogels were characterized using Finite Element method and the collagen content effect on the mechanical properties of hydrogels were investigated. Hydrogels samples with different collagen content were assessed which caused diverse mechanical behaviors. Due to the nonlinear behavior of hydrogels, using numerical methods and simulation softwars can be helpful to determine the mechanical properties of these material and save agreat deal of time. Finite Viscoelaticity theory was exploited for a UMAT Subroutine in Abaqus and an special Starin Energy Function was selected to extract the formulations. The agreement between simulation results... 

In the present study, the nonlinear vibrations of the rotor on the nonlinear bearing have been studied by the multiple scale method. To achieve this goal, Jeffcott models, two degrees of freedom and rotating Euler-Bernoulli beam have been used as rotors and insulators and nonlinear tilting-bearing bearings have been used as supports.To better understand the importance of the supports in the analysis of rotating systems, the rotor joints with isolates with high static stiffness and low dynamic stiffness have been considered and the dynamic behavior of the system has been studied using the multiple scale method. The results of this study showed that this type of nonlinear isolator has a good... 

A simple control system contains at least an actuator, a controlled link, and a foundation. These structures are not ideally rigid, this flexibility can appear willingly or unwillingly in any parts of the system or the connections between them. As a consequence of this flexibility, the movement of the controlled part will fluctuate unintentionally. In this thesis, a control system with rigid controller and flexible torsional base is investigated and controllers are designed and compared to reduce these unwanted vibrations. Finally, by implementing the controllers on the constructed system, the experimental results are obtained and compared with the analytical results.To fabricate the... 

The present study aims to achieve two major objectives in the field of Rotordynamics. The first one is to investigate the frequency response function by considering rubbing between fixed and rotating components of the system and also the presence of nonlinear support such as tiling-pad bearings using analytical approach and the second one is to study the stability of the system using both analytical and numerical methods. In first step, by using assumptions and laws of physics, a model for dealing with the rubbing phenomenon and the friction force between fixed and rotating components of the system is presented. In the next step, the rubbing force is modeled. Then using the Jeffcott rotor... 

The current research is devoted to the design and optimization of a Blended Wing Body aircraft configuration in the conceptual design phase. In this respect, two objective functions with eight design variables have been considered within the optimization process in order to reach to a desired design. The key objective functions include the aerodynamic efficiency as well as the aircraft empty weight alongside the longitudinal stability requirement that are accounted for within the Genetic algorithm optimization loop. In this regard, some analytical and semi-empirical relations are utilized to determine the aerodynamic and structural characteristics of different designs alongside the numerical... 

In this dissertation, the buckling and postbuckling analysis of lattice conical shells are presented. The outer skins of the shell may be reinforced by cross-ply laminated composites. The shell is subjected to uniform axial compression and the boundary conditions are simply supported. This problem is solved using two different approaches. At first approach, the main priority is high speed calculations, which is investigated in static and dynamic types of loadings. In the case of static loads, the equilibrium equations are formulated based on the classical theory and von Karman type of nonlinearity. The equations are solved by Galerkin method and a closed-form relation is derived. In the case... 

One of the steps toward applying artificial intelligence in the field of unmanned aerial vehicles, as they are extending is the development of the controller unit and expansion of the basis of its implementation. In the beginning, one of the targets of this research is to offer an intelligent controller that utilizes an RBF neural network. Second, in order to physical parameters estimation in case of real-time system identification, an Augmented Extended Kalman Filter (AEKF) has been purposed which is capable of filtering the noise of sensors in addition to estimate some of the physical parameters. Furthermore, to check the generalization ability of the structure, three different cases of... 

The main purpose of this dissertation is to investigate and improve the efficiency of Sparse Reconstruction method for structural health monitoring application in order to solve the challenges including; finding multiple simultaneous damages, damage detection and location in anisotropic structures and real engineering complex structures. The main approach of this research is based on presenting theoretical concepts and developing practical methods based on the presented concepts, as well as evaluating and implementing the developed methods using numerical simulations and experimental tests. In this work, the finite element method is used for numerical simulation. In the experimental test,... 

The purpose of the current study is to design an optimal trajectory and control for an aircraft to perform a microgravity maneuver automatically. This subject is by itself an important research topic that has not yet been attempted via optimal control formulation and modelling. Space stations are commonly utilized to conduct long-term microgravity research. Unfortunately utility of space stations to perform space based microgravity experiments is expensive and inaccessible for many researchers and scientific institutions. However, since many experiments requiring microgravity conditions can be performed in short time intervals, there is a possibility to meet their demand via optimal... 

The problem of concurrent attitude and orbit estimation (CAOE) of satellite using its surface thermal data is studied and investigated in the present dissertation. Considering various uncertainties associated with the satellite system and its surrounding with regards to thermal issues, the dissertation subject and its application to CAOE is challenging and of importance. To this aim, the space thermal model for low Earth orbiting (LEO) satellite is initially reviewed and presented. Since the Sun and the Earth are considered as significant sources of radiation for near Earth space systems, the view factor is a key parameter for orbit observability and estimation via surface thermal data....