Sharif Digital Repository

Aluminum alloys are used in many industries because of its high strength to weight ratio. Due to many problems of fusion welding of aluminum alloys, In the past decade, much attention of scientists and craftsman has been directed towards friction stir welding (FSW) as a solid-state welding process. In this study, joint strength of butt friction stir welded wrought 1050 aluminum alloy with the thickness of 4mm increased by inserting pure copper foil (100 µm), pure zinc foil (250 µm), brass foil (100.250.500 µm) with chemical composition of 60wt% Cu and 40 wt% Zn. FSW was conducted at a tool traverse speed of 25 mmmin−1 and a rotational speed of 1200, 1600 and 2000 rpm. Results showed... 

Foil gas bearings are compliant surface, self-acting hydrodynamic bearings that use ambient gas as their working fluid. They do not require external pressurization and are typically constructed from several layers of sheet metal foils. In high-speed, high-temperature applications the GFB’s have the advantage of developing higher load capacities than with fixed geometry gas bearings. Since GFB’s have a complex structure consisting of a spring-like substructure with an overlying flexible surface, there exists a great variety of permutations on any given design. At current work presents a 1D model for GFB with couple solving Reynolds and Euler-Bernoulli beam equation. This mean top foil assume to... 

In this project, a model which had been suggested for a lithium battery is used with the assumption of using C.N.T instead of activated carbon for the cathode. This battery include lithium foil, C.N.T and solution as anode, cathode and electrolyte. The electrolyte solution consist of lithium salt and a separator. The mathematical solving of the model consisted of using two CPM and DFM methods. In DFM method, a concentration gradient was considered as the driving force for diffusion and in the CPM method chemical potential as the driving force. Furthermore CPM method considered energy interaction between ions. Changing physical parameters of cathode and modification of model parameters... 

In present research, a new system of energy extraction from water flow has been studied and optimized. This semi-active energy harvesting system consists of an airfoil that is connected to the generator by an arm. The passage of water causes the airfoil to move, so the hydrodynamic forces on the airfoil will cause the arm to move and finally the generator. In this research, complete dynamic modeling of this energy extraction system including generator, airfoil, controller and actuator modeling is presented and the governing dynamic equations are extracted using this modeling for dynamic simulation. Two dimensional fluid simulations have also been performed using fluent software. Finally, in... 

One of the problems that affects the lifetime and cycle life of lithium ion batteries is the localized corrosion of aluminum current collector (during the storage and charging cycle). Since applying corrosion-resistant coating has always been one of the ways to reduce corrosion of materials in different environments, in the present project, this method has been used to prevent corrosion of aluminum in lithium-ion batteries. For this purpose, the graphene oxide coating, which has desirable anti-corrosion properties, was coated on aluminum by Electrophoretic deposition and doctor blade methods. linear polarization, cyclic voltammetry and electrochemical impedance spectroscopy were performed to... 

The purpose of this study is to investigate a flapping hydrofoil with semi-active kinematics for energy harvesting and evaluate the effect of different dynamic parameters and structures on its performance. The turbulent flow field with Re = 5 × 105 around a NACA 0015 hydrofoil is simulated by URANS method using commercial software and the dynamics of the oscillating hydrofoil is modeled as a mass-spring-damper set in combination with the fluid solver. The sliding mesh method is used for the pitching motion of the hydrofoil with a reduced frequency of 0.14 in combination with the dynamic mesh method for Transitional motion. Initially, the oscillating hydrofoil was considered as a single...