Sharif Digital Repository

A metal cylinder tank with composite coating is a pressure vessel which is made of a thin metal layer and a composite layer; like Graphite, and most of the loading is carried by the composite layer. In this study the penny-shaped cracks in cylindrical pressure vessels with composite coating is studied. These kinds of cracks are mostly initiated in manufacturing processes and they have crucial rule in fatigue life and load carrying of the structure. Although there are numerous analytical and numerical methods, they have shortcomings in the case of penny-shaped cracks problems. The strain discontinuity in the interfaces of materials along with discontinuity and singularity due to the crack are... 

Rotating shafts are widely used in various industries, especially aerospace industries such as engines, compressors and turbines. Due to the sensitivity of these shafts, considerable efforts have been made by researchers to investigate their dynamic behavior. In this thesis, the finite element numerical method has been used to analyze and investigate rotating shafts using a pipe elbow element. This element has four nodes and six degrees of freedom in each node, that is, three degrees for translation and three degrees for rotation relative to the general coordinate system and has a circular cross section. In the linear part of the dynamic formulation of the finite element for rotating axes... 

In this research, the reliability of time domain modal identification methods is studied. First three different MIMO time domain method are studied which are EITD, PRCE and ERA. The effectiveness and accuracy of the methods are evaluated for simulated mass-spring system and numerical cantilever beam in EMA (using time history data of impulse response directly) and OMA (using correlation function of random response of the structure) cases. Based on the results achived in this section, the most qualified method is identified (which was ERA) to continue the research. In order to evaluate the reliability of time domain OMA technique in case of repeated modes, first a numerical plate is studied... 

The increasing growth of composite materials in various industries and the use of these materials in the production of the main structures, recognized study and simulation of accurate behavior of these materials at different scales. On the other hand, the appearance of Nano-scale materials with amazing physical and mechanical properties and the use of these nanoparticles as reinforcement in the structure of polymer composites, further highlights the importance of simulating the behavior of polymer nanoparticles at different scales. One of the issues that is considered in various industries, especially in the airspace industry, is the phenomenon of fatigue. The complexity of the fatigue... 

Today using of microwave integrated circuits in commercial and military applications is paid attention too much, especially with emerging of monolithic microwave integrated circuits that prepares for us producing of amplifier with mass production, enough accuracy and proper cost. Power amplifiers that used in the end of transmitter path are paid attention in this field. However,in transmitter systems which require high power to create stable link with the receivers, fabrication process like CMOS are unable to provide such level of power. Thus, designers employ another group of integrated circuits which names MMIC that offers this capability to designers.MMIC is the abbreviation of Microwave... 

In this thesis, heterogenous catalysts based on poly(ionic liquids) were synthesized. These catalysts were prepared by polymerization of functionalized ionic liquid monomers in the presence of an ionic cross-linker. Several types of poly(ionic liquids) such as acidic ionic liquid, basic ionic liquid and their complexs with copper and palladium were prepared. Some of these polymers were coated onto the magnetic nanoparticles to produce a catalyst with magnetic prppertise with easy magnetic separation from the reaction medium. Such catalysts have high loading level and high thermal stability. Most of prepared catalysts have high loading level due to the macromolecular nature of polymer. At the... 

Ultralow phase noise microwave oscillators with high stability are one of the key components required for many applications. With recent advances in ultrapure microwave oscillators, optoelectronic oscillators (OEOs) culminated in the state-of-the-art ultralow phase noise microwave oscillators. In this thesis, a nonlinear analytical approach is used to predict the main oscillation mode power and spurious levels in ultrapure microwave OEOs. Our analytical predictions are verified by numerical simulations and experimental data. Performance of an intensity-modulation direct-detection (IMDD) microwave photonic link (MWPL) operating under nonlinear conditions when its input consists of a sum of... 

The impact of ownership concentration on competitive conditions and profitability of industries has been studied and analyzed for decades. By using the Herfindahl-Hirschman concentration index, a range for the level of concentration in the industry has been determined, and some countries implement anti-trust laws based on this range. The new literature that has been discussed recently is the concentration of the market directly and through the common ownership of corporations by large shareholders. In the sense that two or more apparently independent companies may have a common owner who practically regulates their behavior as a company. The structure of ownership in Iran is complex and... 

In this research a robotic fish was designed and fabricated. For this propose different types of manufactured robotic fish were investigated and this model was developed and made with a one-piece flexible tail with an actuator that creates lateral movement through cable strings attached to the tail. Proposed mechanism has a simple, low cost structure that facilitates the control of the robotic fish movement. To control this robotic fish, a four-channel radio controller with 40 kHz frequency, was used. Swimming mode of this robotic fish is categorized in Subcarangiform swimming mode which is faster and has better maneuverability compared to its counterparts. It should be noted that the... 

In this research, delamination in compound laminated materials under the I mode loading is studied. In this way, a Double Cantilever Beam is investigated, which is the only experiment to study delamination in standard compound laminated materials. At first, a survey and comprehension of the failure of these materials is performed and the major mode of failure, which is named Delamination Mode is understood. Next, a survey on the possible methods of investigating the delamination phenomena is presented. In the next chapter, possible numerical methods are analysed, and the better performance of Cohesive Zone Model and Virtual Crack Closure Technique is studied. In this research, using the... 

This dissertation is a survey on linear and nonlinear dynamics of single-walled carbon nanotubes (SWNTs) conveying fluid with different boundary conditions. A detailed review on Some of the most important studies on free vibration and instability of CNTs conveying fluid is done. By employing the nonlocal continuum field theory of Eringen and Von Karman nonlinear strains, an analytical model are developed. In linear analysis the natural frequencies and critical flow velocities are discussed. In nonlinear analysis effect of nonlocal parameter on Nonlinear dynamics of cantilevered SWNTs conveying fluid investigated by bifurcation diagram, phase plane and Poincare map. The numerical results... 

In the beginning of the 90’s a new type of robot was introduced by Fukuda. The brachiation is a type of mobile robot that moves from branch to branch like a long-armed ape. Here, as a new innovation, optimal control is used to obtain the optimal trajectories for two different problems. The first problem is “Brachiation between fixed branches with different distance and height” and the second is “Brachiating and catching the moving target branch”. Theoretical results show that the control effort in the proposed method is reduced by 25% in comparison with the “Target Dynamics” method which was proposed in prior articles for this robot. The obtained optimal trajectory also minimizes the... 

The J-integral, as a powerful tool in fracture mechanics, is used to analysis of fracture behavior of materials. In order to, evaluate of three dimensional J-integral, an integral evaluation of line and surface is required. However, because surface integral evaluation requires the calculation of the second derivative of displacement field, an commercial finite element codes cannot calculate it.In this thesis, a method for computing 3D J-integral is presented using finite element analysis. In the analysis, the second derivative evaluation of displacement field is employed. In this method, error-minimal points for stress computation are not suitable for second derivative displacement... 

This thesis focuses on how the dimensions and location of piezoelectric patches affect thedynamic behavior of multi layered sandwich panels by the use of finite element method (FEM). To accomplish this objective the finite element formulation of the problem, including coupling of electrical and mechanical characteristic equations for piezoelectric patches is derived. Finite element modeling of sandwich panels is presented on the basis of classic theory and also first order shear displacement hypothesis for multi-layered plates. To perform finite element analysis, ABAQUS is utilized and the development procedure of a finite element model by this software is also introduced. After verifying... 

When vibration of the structure is unrecognized we call it random vibrations which their analysis is very important in space structures because these structures are exposed to acoustic forces or forces produced by turbulence of the atmosphere when a spacecraft is launched. Also in the aviation field, the random vibration analysis use to examine the response of the aircraft and missile structures to atmospheric turbulence and gust. In this research dominated equations of a truncated conical axisymmetric shell structure with linearized approximation of Love’s equations under uniform pressure is utilized. Considering displacements in the form of Frobenius series expansion the frequencies and... 

Today, for construction of UAV, designers are interested in and trying for substitution of composite material instead of metal. They would rather use composite structures due to lower costs of construction, availability, along with high ratio of strength to weight of this material, while metal structures are mainly rare and too expensive for construction of UAV. For instance, unavailability of aluminum metal and complicated methods of construction of aluminum wings with using of special tools, justifies using of composite with easier construction, abundant, and cheaper materials. The main goal of this project is redesign of aluminum wing of a jet engine UAV, In fact, by doing some structural... 

One of the most widely used methods in the study of the mechanical behavior of fiber-reinforced polymers is modeling and simulation of a unit cell behavior. According to the arrangement of composite materials, the unit cell is selected in order to include and represent actual constructions of the material. In this study a numerical self-consistence method is proposed to estimate effective properties of Carbon-epoxy composite materials. In this method, in addition of two main phases i.e. matrix and fiber, a phase of composite properties is also considered surrounding the unit cell. First using analytical and semi-empirical methods, the properties are calculated and are converged after... 

One of the important tasks of operation manager is keeping system in safe and reliable situation. There are many tools that supply safety in the power system. One of them is operation reserve. Operation reserve is any type of capacity being used to support active power balance. In this thesis, an approach for optimal determining reserve capacity with considering dynamic constraint is presented. This thesis describes a method for setting the optimum value of reserve capacity based on the cost of its provision, the benefit derived from its availability and Frequency stability. The method that used is D-SCRM algorithm. However, as the size of power systems increases, the current centralized... 

Composite structures are subjected to different kinds of loadings in different workspaces, and sometimes these load conditions can damage them. Delamination is a common damage in composites. In this research, the delamination effect on modal behavior of a laminated composite plate is studied. To investigate this effect, the frequency response method is used and piezoelectric patches are used as a sensor and an actuator for extracting the frequency response. The aim of this project is to investigte presence and severity of the delamination. To survey the frequency response method, an intact and some damaged plates with one sensor and actuator are modeled with abaqus software and frequency... 

In this study, the thermal buckling behavior of thin metal liner reinforced by composite shell in present of the initial imperfection is investigated. For this purpose, the Ryzener – Myndlyn shear-deformation theory & the virtual work method are used to extract equilibrium equations. In this work, the conical shell with c-c, s-s, c-f boundary conditions has been studied. The outer layer of reinforced composite is exposed to constant ambient temperature and iner layer is exposed to heat. Metal liner and reinforced composite shell are merged with together. In other words, the degrees of freedom at each node for both shells are assumed to be equal. Solution method is finite element method using...