Sharif Digital Repository

In the present work, the effect of different methods of melting, remelting and solidification conditions on the microstructural evolution of IN100 superalloy was investigated. For this purpose, the superalloy was solidified within steel and ceramic molds to provide different cooling rates. Furthermore, the re-melting processes using ESR in the water circulated copper mold and ceramic molds, VAR and combined ESR and VAR were considered. The microstructure of alloy under different casting and remelting conditions were studied by means of optical and SEM microscopy and ESD analysis. According to our results, the ingot which was cast in the ceramic molds, due to lower cooling rate during... 

Control and guidance of a vehicle is vital for it to do its mission correctly. Guidance system and decisional algorithms used in it need exact information of instantaneous position, velocity, and attitude of the guided vehicle to determine and issue proper guiding commands.
Estimation algorithms and navigation sensors are two necessary tools for navigation. In the first section of present study, the satellite equations of motion are derived and a 6-DOF simulation is done for it. In the second section, measurements of star tracker will be simulated using results of the first section. The third section appertains to development of navigation equations, attitude determination using UKF... 

In the current study, nonlinear vibration and stability of conical shells with both separate and concurrent internal and external flows are studied. External and internal flows are in the supersonic and subsonic regimes, respectively. The Krumhar’s aerodynamic piston theory is utilized to model the external loading on the structure as well as the compressible potential flow model to capture the internal fluid dynamics. The so-called compressible fluid model is obtained via simplification of the Navier-Stockes equations after applying the inviscid and irrotational assumptions. The nonlinear structural equations of motion are derived using the Hamiltonian dynamics approach and utilizing the... 

In this study, the modeling of shrink-fit connection was performed by considering the effect of friction on the connection. The behavior of a beam with shrink-fit connection was compared with the results of Adams software and the modeling accuracy was shown. Using both energy and Newton methods, the equations of motion of a rigid rotor consisting of two shafts connected by shrink-fit connection were obtained and the dynamic behavior of the rotor was investigated. Finally, the coupling parameters affecting the vibrations and stability of this rotor were introduced and the effect of each on the system behavior was shown.
 

Unmanned Aerial Vehicles have been used for different applications despite their short life. In last recent years, the developements in technology which leads to producing smaller electronical and electromechanical deveices, attract more attention to the researches in these fields. Among these vehicles, unmanned helicopters are more important because of their special abilities and capabilities. However there are some drawbacks which makes using them more difficult.
In this project, the first principle modeling of a RC helicopter has been accomplished and a parametric model including different sections effects has been created. This model has been implemented for a Trex600 CF helicopter.... 

The goal of this research is investigation and analysis of a surface consists of vertically aligned carbon nanotubes (VACNTs) using continuum mechanics modeling. Today these kinds of surfaces also known as the darkest material have a particular importance in industries. Knowing the properties of a material is one of the most important things in analysis and designing using that kind of material, so extraxting the stiffness matrix of a material could be a big step for starting analyzing it. In this thesis a lattice of VACNTs with two different layouts and several unique geometrics is simulated using molecular dynamics approach using the Lammps software. The general stiffness matrix of the... 

In the process of Additive manufacturing for metals, the ability to predict and control the microstructure can reduce the need for subsequent heat treatment and accelerate the component quality assessment process. The ability to predict and control the microstructure of materials in the laser deposition method needs to understand the thermal conditions during the solidification process. For this purpose, the present study investigated the relationship between cooling rate and temperature gradient during local solidification, and control parameters of the laser deposition process such as power, beam radius, scanning speed and strategy of laser, ambient temperature and preheating temperature.... 

With the emergence and expansion of social media in the societies, these media has become an integral part of modern society and the lives of citizens. These networks have improved communication facilities in the community and created an opportunity for politicians to use these media as a communication and marketing channel to communicate with citizens and use them to achieve their goals. Social media's ability to communicate has put politicians' relationship with citizens in a very strategic position. This has made it important to have a communication plan and, more generally, principled political marketing.Therefore, the main issue that this dissertation has investigated is the review of... 

Recently nanostructure materials have used in various technologies and hence an extensive part of research focused on preparing and optimization of growth of nanostructure materials. Usually common procedure is based on a two-step process. First, construction a pre-layer by means of different deposition methods and then formation a nanostructure with a thermal treatment which increases the cost of research. Hence with one step method such as glancing angle deposition (GLAD ( it is possible to form a desirable structure with low cost. In this research Nano columns of tungsten was deposited on Si(133) by means of GLAD-RF sputtering without any heat treatment at substrate rotational speed ( )... 

Microrobots (MRs) have attracted a lot of attention during recent years due to their promising biomedical applications. Due to their small size, these robots have limited capability to carry energy sources, sensors, or actuators, so researchers try to transfer energy from outside as much as possible. For this purpose, various actuation methods such as optical, acoustic, electric, and magnetic have been proposed. Magnetic field is the most used energy source. The current study deals with the design and implementation of a system for simultaneous independent control of multiple swimming magnetic MRs. The ability to control multiple MRs simultaneously and independently could lead to higher... 

In the problem of Distributed Multi¬User Secret Sharing (DMUSS), in which K users are connected through some error¬free links to N distinct storage nodes with the same size M information unit, the users desire to retrieve their corresponding secret message through an arbitrary set of accessible storage nodes. A trusted master node, which knows all of the secret messages transmits correctly and privately, the messages with a means of coding. The capacity of Distributed Multi¬User Secret Sharing is the supremum of all achievable schemes satisfying privacy and correctness conditions. In this thesis we have investigated two notions of privacy namely, individual and joint privacy. Individual... 

Unmanned Aerial Vehicles (UAVs) have attracted huge attention in recent years due to the technology improvements. Among them, Unmanned Helicopters (UHs) have great importance because of their special abilities. In this research, the problem of design and implementation of an actual flight control system for an unmanned helicopter is investigated. For this purpose, first a multi-level flight simulation environment is developed in Simulink software environment to model the helicopter flight dynamics. The system identification, control system design and implementation are successfully performed in this flight simulator. Next, the actual helicopter flight control system is designed and produced... 

With the epidemic of viral diseases in humans and animals, and their potential to cause irreparable economic damages, due to their recent noticeable changes in their structures followed by becoming antibiotic resistance, many researchers nowadays are focusing on the new antiviral Agents with least side effects. Influenza A virus is a common seasonal virus which can lead to sever infections. This type of influenza has the ability to transmit between humans and animals, and also by antigenic shifts can transform to new type of influenza which can cause a global disaster. While classical antiviral drugs are still in use for influenza patients, new influenza A subtypes become resistant to these...