Sharif Digital Repository

Friction stir spot welding (fssw) is a newly-developed solid state joining technology. In this study, normal fssw is applied to join the AlMg6 aluminum alloy sheets with 3 mm thickness and then the effect of the rotational speed and dwell time on microstructure and mechanical properties is discussed. The hardness profile of the welds exhibited a W-shaped appearance and minimum hardness was measured in the HAZ. The results of tensile/shear tests indicate that the joint strength increases and after a special rotational speed it decreases. Also the strength increases and after a special dwell time it decreases . At the rotational speed of 1500 rpm and dwell time of 6 sec, the... 

In the past few decades, shaking tables are widely used to evaluate system response of structures under seismic excitations. These devices are used without any fundamental research performed on a shaking table system as an entity model. In most of these studies for simplicity, it is assumed that there exist no considerable vibration and displacement around the shaking tables, and no attention is paid to the peripheral substances such as soil settled under the foundation.
In this thesis, result of ambient vibration test on shaking table system (solid deck, concrete foundation and soil layer) has been presented. Precise sensors known as low frequency and high accuracy accelerometers have... 

This thesis aims to introduce a numerical method for investigating the appropriate arrangement of visco-pseudo-elastic dampers applicable to shell and plate structures under large deformation. These passive dampers are considered as viscoelastic layers and discrete shape memory alloy (SMA) wires in which this combination improves their overall efficiency and reduces their drawbacks. Also, the main advantages of these dampers are discussed during some illustrative problems. The current finite element formulation is based on an incremental updated Lagrangian (UL) approach along with the Newmark's integration technique. In the layerwise shell element, the Mindlin-Reissner theory is adopted in... 

In this thesis the effects of vibro absorbing coating on vibration behavior of an aluminum sheet and also on a stiffened aluminum panel are investigated using experimental approach. Since there wasn't any information available about the used coating, to find its viscoelastic material properties, the method mentioned in ASTM E756-05 standard is employed and corresponding tests are performed.
In the next step, an analytical solution developed for the aluminum sheet with viscoelastic coating and the obtained results compared with experimentation, in order to find its prediction accuracy for loss in “loss factor” of the system in presence of coating.
To study the effect of... 

This research aims to study fundamentals of design as a science for possible use in special structures. Special structures are referred to those structures that designers’ knowledge for which are insufficient. Designs of such structures are complex in the sense that we lack all necessary elements of design matrix; as well as proper steps to reach the unknowns. Introducing appropriate design strategy for such structures; we show how a design could be developed without specific needs for trial and errors. In this work, various design methodologies and especially “Axiomatic Design” have been examined. In addition, functional requirement and associated design parameters for structural design are... 

Dynamic analysis of deploying elastic arms of spacecrafts carrying tip mass has been presented. The research concentrates on the precise analytical simulation to reveal the phenomena which are usually eliminated in estimations. One of the most important factors which affect the dynamic response of such arms is rigid body dynamics of spacecraft. Considering this aspect of the problem the evolutionary analytical simulation has been developed through three steps. The first step focuses on the minute simulation of the arm deployment, in which a new mathematical approach called "elastic profile" has been developed which leads to semi-analytical solutions for the arm carrying tip mass.... 

Compressors are one of the most important components of gas turbines and turbomachinery processes. Thus some precise and quick tools are needed for design and analysis purposes. Despite of vast development of Computational Fluid Dynamics (CFD) tools, Through-Flow Streamline Curvature Methods (SCM) has retained their position. 2D and quasi-3D forms of SCM in combination with CFD results nowadays make more than 80% of turbomachinery design process of axial and radial compressors and turbines. In this thesis, the basics of developing a tool for axial-flow compressor analysis are introduced. As will be seen, this analysis tool can be used for design purposes too. The method that is chosen for... 

Axial compression systems are widely used in many aerodynamic applications. However, the operability of such systems is limited at low mass flow rates by fluid dynamic instabilities. These instabilities lead the compressor to rotating stall or surge. In some instances, a combination of rotating stall and surge, called modified surge, has also been observed. In this research Moore – Greitzer model that the principle of constant speed mode checks as a base case has been considered and the developed condition of this model in which the dynamic model of the shaft will also respect and shaft rotational speed as a basis for state shall consider, has been analyzed.
In this study the effect of... 

Currently, in the Islamic Republic of Iran, after aviation accidents and incidents, conversations between pilots and air traffic controllers are re-examined by the State Air Transport Organization of the Islamic Republic of Iran and turned into text. The Automatic Recognition System for Pilot-Air Traffic Service Units’ Communication helps in the implementation of speech recognition. Reducing the time and cost of converting conversations into texts and creating an aviation database in the country are other uses of this system. In this research, after collecting and refining the actual conversation between pilots and air traffic controllers and examining seven methods, we design a system that...