Sharif Digital Repository

This work investigates adsorption and possible dissociation of a number of small molecules on small clusters and carbonic surface. Theoretical study of carbon monoxide adsorption on SixGe4_x(x=0–4) nano-clusters has been carried out using MPW1B95 density functional. The geometry, adsorption energy, charge distribution, and vibrational frequency of CO adsorption on all possible structures were investigated. The maximum vibrational frequency changes occur in the bridge structures while the most stable structures occur when CO adsorbs on one silicon atom in a flat surface. Adsorption energies of CO on one Si atom are by far more negative than the corresponding value for on Ge atom. Theoretical... 

Progress aerodynamic and structural applications has lead to solid-fluid interaction (SFI) engineering. One major application of SFI is to improve of aerodynamic characteristics of airplanes. One option is to use elastic shells.this field of study is so novel and a challenge for future researches. This what current thesis is focused on We use numerical simulation in both fluid and solid parts.In other word, we employ the finite –element method to solve the solid mechanics governing equation and the finite volume element method to treat the fluid dynamics governing equations. The fluid governing equations are 2D navier- stokes equations and the solid part is the 1D Euler – Bernoulli equations... 

With the rapid development of mico-nano propulsion systems in micro-spacecrafts and micro-sattelites, precise investigation of flow field in these devices has become necessary. Micro propulsion systems usually have a thrust in order of mili Newton, and they can be used for maneuvers of spacecrafts with mass of less than 10 kg. Micro propulsion systems are usually classified according to their thrust generation mechanism to different classes like cold gas, and chemical propulsion systems. Cold gas micro propulsion systems obtain their energy from thermodynamic expansion of gas and not by combustion. If the flow fiel dimensionare comparable to mean free path, rarefaction effects are observed... 

Novel manufacturing technologies in micro scales, such as micro machining, guide us through constructing micro scale systems known as MEMS. These systems have a wide range of applications, from fabrication of electrostatic, magnetic, pneumatic sensors and actuators to micro mechanical gears and motors. Also, MEMS applications involve the manipulation of one or more fluids, known as microfluids. Simulation of flow through microchannels over nano particles has important applications in solid particles transport. In this flow, the rarefaction phenomenon will affect the flow behavior and its subsequent impacts such as aerodynamic drag forces. In this work, we use the Lattice Boltzmann method... 

Analysis and design of power systems are challenging due to ever increasing dimension of the system and also the nonlinearities involved in the system. The conventional approach is to use linear analysis tools and then investigate the nonlinear impacts by the means of computer simulations. This requires great deal of trial and error and it is not always a timely approach. In this project, we initiate a comprehensive nonlinear analysis for a single-machine infinite-bus system by studying a Hopf bifurcation in its dynamics. We use results of our nonlinear analysis to study how a capacitive compensation such as TCSC works. Subsequently, we design a nonlinear controller for a PSS to have... 

To investigate boiling heat transfer characteristics of nanofluids, transient quenching¬ experiments of a high temperature silver sphere in water-based nanofluids with Ag and TiO2 nanoparticles were performed. A silver sphere of 10 mm in diameter at the initial temperature of 700o C was quenched in the nanofluids at the temperature of 90o C. The results showed considerable reduction in the quenching ability of nanofluids compared to that of pure water. The presence of nanoparticles in water caused film boiling mode to vanish at lower temperatures depending on the mixture concentration. Computed heat transfer rates in nanofluids were lower than those in pure water. In the quenching... 

It is well known that the most rigorous method to assess the performance and to predict the seismic demands of a structure subjected to earthquake is nonlinear time history analysis. However, this technique is accompanied by complexities and difficulties in evaluating the seismic demands of structures and requires superior knowledge and skill. As a result, in recent years, nonlinear static analysis has been proposed in performance based design procedures. One of the primary assumptions of nonlinear static procedures is that the behavior of a structure with multiple degrees of freedom (MDOF) subjected to seismic ground motion can be estimated from the response of an oscillator with a single... 

Hydrogen fuel cell is one important choice to supply energy for vehicles in near future. The lack of a safe but inexpensive technology to store hydrogen in a vehicle tank is a serious challenge to commercialize the application of fuel cells. Past experiments have shown that carbon nanostructures, especially single walled carbon nanotubes, have considerable capacity to boost up hydrogen storage. Therefore, many studies have been performed to investigate the possibility of higher hydrogen storage capability using nanostructures for the past decade. Molecular dynamics method which is considered as one of the most important tools in studying nanostructures has shown vast applications in these... 

In this research, a structural lateral bracing system called ‘Chevron Knee Bracing’ (CKB) on reinforced frames is investigated. This new form of framing system is constructed through the knee and the diagonal brace elements. The diagonal brace component provides the required level of lateral stiffness and stays in the elastic range without buckling at any time. However, the knee part is a fuse-like component that dissipates energy by the formation of plastic flexural and/or shear hinges at its ends and mid-span, when the building is subjected to severe lateral loads. For this purpose, first, by elastic studying of the system, three new and practical parameters are established. Then, the best... 

Nanotechnology is an efficient method suitable for fabrication and production of minimal single dimensional nanometric structures. Such materials and systems can be logically designed that lead to new and optimized biological, chemical and physical properties and characteristics due to their size. Nucleation and growth –appearance of a new phase out of an old phase – is a ubiquitous phenomenon in nature. Fundamental understanding of nanoparticles nucleation and growth mechanism allows more control on form, size and composition and allows tuning of the above said properties easily with use of different reactive conditions as a result of this ability . Nanoparticles of titania are one of... 

Base plate is one of the important and sensitive elements of a structure which roles as a connector of force and moment in column to foundation joint and prevents from stress concentration in the joint area. As until now there has been several numerical and experimental researches conducted about base plate connections, but in practice for design, base plate is considered as a cantilever beam which undertakes compressive force and bending moment. In this method of design many important factors such as separation and deflection of base plate, interaction of base plate with bolts and foundation aren’t taken into consideration. Therefore there is an urgent need to design base plates considering... 

Polymeric membranes based on polyaniline and PVDF were prepared by using cast-solvent film method. The effects of various parameters including polyaniline synthesis temparature, thickness of the PANI/PVDF films and feed pressure were investigated. The results obtained from exprimental data showed increasing permeability with reducing the thickness of the film and increasing feed pressure. Increasing polyaniline synthesis temprature increased the permeability of PANI/PVDF films. Reducing the films thikcness and increasing the feed pressure decreased the selectivity of films for the , and . The results showed increasing selectivity for PANI/PVDF films by using PANI produced at 10°C....