Sharif Digital Repository

Cardiovascular diseases are the major cause of death worldwide. Atherosclerosis is one of the major types of cardiovascular diseases in which fibrous and fatty materials, called plaque, build up inside the artery and cause partial or total occlusion of the artery. Intravascular balloon angioplasty with or without stenting is the most common treatment of this disease. In 2010, approximately 954000 stent implantations were performed in the United States. The major issue associated with stenting is reclosure or renarrowing of the transverse section of the artery termed in-stent restenosis (ISR). Unfortunately, nearly one–third of the patients
who receive stent implantation require further... 

Rotary equipment are being used in many industries over a wide range of applications, such as gas turbine. Due to the nature of the operating conditions, gas turbines are subjected to variety of damages especially crack propagation of a blade. The Cracks propagation may lead to catastrophic failure during operation. Therefore, detection of the crack presence and its propagation is very important and may reduce possible significant cost of the whole system failure. The thesis aims to investigate the cracks presence and their propagation effects on vibration of a turbine blade which is located at the National Iranian South Oilfields. First, theoretical study is calculated to validate an... 

Most engineering components must be manufactured so they are safe to use and are ‘‘fit for purpose’’. However despite all the efforts, cracking of the engineering components is inevitable. Residual stresses play an important role in either increasing or decreasing the possibility of failure. For instance, enhancement in apparent toughness following pre-loading arises principally because of the creation of local crack tip compressive residual stresses. Introducing compressive residual stresses can also slow the fatigue crack growth. Yet, the dilemma is choosing an efficient method growth to introduce such stresses for retardation of fatigue crack growth. There are many methods available in... 

Isogeometric Analysis method is a newly introduced method for the analysis of problems governed by partial differential equations.The major difference between classic finite element method and isogeometric method is that FEA uses piecewise polynomial shape functions for analysis while the Non-Uniform Rational B-Splines (NURBS) functions are applied as basis function in isogeometric method. To model strong discontinuities like cracks in classical finite element method , very fine mesh near the crack tip must be used. Application of eXtended Finite Element Method (X-FEM) avoid making very fine mesh near crack tip which is a time consuming task. In the extended finite element method , a... 

Isogeometric Analysis method is a newly introduced method for the analysis of problems governed by partial differential equations. The method has some features in common with the finite element method and some in common with the mesh-less methods. This method uses the Non-Uniform Rational B-Splines (NURBS) functions as basis function for analysis. With this basis functions, the refinement procedure is much easier than the classical finite element method by eliminating the need to communicate with the CAD model. Modeling cracks in classical finite element method requires very fine mesh near the crack tip. One can model crack propagation by means of classical finite element, using an updating... 

According to human needs and in line with the development of advanced technologies, different biomedical Engineering fields like hard tissue implants are growing rapidly. Despite significant biotechnology Developments in recent years, some problems to the recognition of implants related osseointegration phenomena persist. The deficient osseointegration and implant-associated infections are key issues for the long-term clinical success of titanium and titanium alloy implants, while development of multifunctional surfaces that can simultaneously overcome these problems remains highly challenging. Therefore, the ultimate goal of this paper was to improve bone cell attachment and simultaneously... 

Titanium trisulfide (TiS3), a transition metal chalcogenide, bears the potential to replace silicon, when taking the form of nanoflakes, due to its favorable band gap and optical response. In this work, first we investigate the response of TiS3 nanoflakes to gas detection through a careful quantum computational approach and a few succinct measurements. The computations are benchmarked and compared with a relevant experiment at each step, where their results/conclusions are discussed. The most stable surface of TiS3 particles is determined to (001), in agreement with the literature. The adsorption of 5 gas molecules is characterized through formulating and estimating their adsorption... 

In this project, two types of graphene obtained from chemical and chemical vapor deposition (CVD) methods were studied for gas/vapor sensing applications . In chemical method, oxidation and exfoliation of graphite was performed in liquid phase. AFM, XPS, Raman spectroscopy and Uv-visible spectroscopy were indicated that single layers synthesis of graphene oxide (GO) sheets was formed successfully. Reduction of the GO to reduced graphene oxide (RGO) was chemically done by hydrazine as a conventional reducing agent and melatonin as a green alternative. Photocatalytic reduction and hybridization of GO with TiO2 was also studied. TEM, SEM and AFM analyses confirmed nucleation and growth of TiO2... 

Polycaprolactone (PCL) scaffolds and its composites containing bioactive glass particles (45S5) and TiO2 nanostructures with pre-defined and controlled external and internal architecture were prepared via an indirect three-dimensional (3D) printing process. The scaffolds had an interconnected structure with macro- (400-500 μm) and micro- (~25 μm) pores. Bioactivity, mechanical behavior and kinetics of tissue growth in 3D scaffolds were studied. The size effect of biogactive glass particles (6 μm, 250 nm, <100 nm) and morphology of titania nanostructures (spherical, tube, leaf-like, and flower-like particles) were elaborated. The biogactive glass particles with different sizes were prepared... 

Facing the two challenges of the recession and rising requirement to reduce carbon emissions have led countries around the world to look for ways to promote economic productivity and reduce greenhouse gas emissions. In the meantime, the appearance of renewable energies has the potential to grow and diversify the economy, in addition to providing an effective solution to meet the growing demand for energy. The impact of development of the renewables industry on the economy for each country and each type of renewables can be examined separately. The purpose of this study is to evaluate the development role of wind energy industry as the motive engine of industry and specifically answer two... 

The purpose of this research is developing an analytical and decision-making tool that examines the interactions between greenhouse energy demand and yield production. Greenhouseholders can use the analytical tool to design and operate existintg and newly built greenhouses in an optimal way. Becides, the decision making tool helps planners and policymakers to improve the performance of greenhouses and extend greenhouse cultivation with respect to their economic or environmental objectives.In order to develop this decision making tool, existing models for greenhouses have been investigated and various algorithms have been combined to develop an integrated energy demand-plant growth model. The... 

This research explored the corrosion effect of NaCl solution on the surface quality of AZ31 magnesium alloy. Cubic-shaped specimens were immersed in standard 3.5% NaCl solution for 1, 2, 3, and 4 hours. The size of corrosion pits, fatigue crack propagation area, and surface topology were characterized. Fatigue tests were carried out on pre-corroded AZ31 specimens under different stress amplitudes. The correlation between the corrosion time and the virtual crack size was obtained. The virtual crack size is a new parameter that can relate the corrosion to the fatigue life. A new model was proposed to map the surface topology on the virtual crack size of pre-corroded AZ31 magnesium alloy. The... 

In the present work, the beginning and progressive growth of delamination in laminated composites plates has been studied. Interlaminar stresses at free edge of laminate may give rise to edge delamination and result in failure of laminate. So we need to determine the exact interlaminar stresses to predict the failure of laminated composites. A computer code based on layerwise theory that can obtain the exact interlaminar stresses been developed. Comparison between the present study and finite element software result showed the good agreement.A fracture mechanics approach is used to analysis delamination propagation between layers of composites laminate. In this approach damage propagation... 

The number of GPS satellites, which are spent their life and work, have been increasingly on the rise. Hence with knowledge of debris numbers, we can get an estimate of collisions risk probability and functional interference of active satellites in the future time. In this study, by using three methods, least-squares, RBF and ANFIS and statistical data the growth pattern of retired satellite numbers has been expected in the future. Numbers estimated by curve fitting methods in 2014 have been compared to the number of satellites disabled and growth estimation error has been analyzed by two models. Solar activity, the sun's radiation incidence angle on the satellite solar panel and the Earth's... 

In this project, the structure of an aircraft and its sensitive areas has been studied for fatigue damages and then the design philosophies have been analyzed. Subsequently, relevant analysis and calculations have been conducted on a critically important part of the airframe (due to its location), which has suffered fatigue due to the age of the aircraft. This part belongs to the airframe of a Boeing 747, known as frame 360 in section 41 of the body of the aircraft, in which the numerous flight cycles have led to the creation and propagation of fatigue crack.
In the first stage of this project, the remaining life time of the frame has been estimated using theoretical relationships. In... 

In many mechanical components, contact loading has a major role in stress field analysis. In this thesis, a combination of crack growth simulation and unilateral contact problem was carried out numerically. The Finite Element Method provides a powerful numerical tool to analyze contact problems. In the traditional FEM discontinuities should not cross through elements, so crack will grow through boundaries of elements, therefore, the model should remesh in each step of crack growth in order to align the mesh along the boundaries of discontinuities. This limitation causes major errors and computational costs. To overcome this limitation, the extended Finite Element Method (XFEM) will be used... 

The first project ,paid to review and analysis types of crack and agents Also, was referred methods to control them in rail industry .
The wheel of Alestom train and UIC60 rail were simulated and stress analysis by software FEM (ANSYS and ABAQUS) , and effect of various parameters such as applied forces , train wheel diameter , contact position and rail inclination on stress values was studied . For comparision of results has been used analytic Hertz theory .
By using experimental data on the subsurface crack , those cracks were created in the wheel . For load on the modeling wheel and rail, ,assuming contact on the wheel rolling point , were used vertical load of wagon weight ( with... 

Building fast and economic space station requires systematic approach toward their design. This research serves to investigate such idea based on Bionic approach. Based on lengthy observations on plant growth we have been able to propose different types of polyhedrons which could help expedite the construction procedure. Different case studies show that how the objectives could be achieved. There are two differences in growth of the modern structures in space and plants. The first is inexistence of producer near the points of growth and Second difference is inexistence of fixed lines for transporting mass. The first difference is not solvable with today's technologies but for second... 

Studying the failure mechanics of FGM materials is inevitable due to the increasing use of these materials in various industries. Stress intensity factor and integral-J are important parameters in fracture mechanics. Due to the fragile nature of ceramic components in FGM During the processing of these types of composite materials, cracks are encouraged. Therefore, crack analysis is inevitable in optimizing the design, reliability and durability of FGM materials and structures in innovative engineering applications. In this research, transverse crack growth in beams made of FGM materials has been investigated. First, a MATLAB code was prepared to extract the mechanical properties of these... 

This paper develops a theoretical model based on economic misconceptions to explain the stylized facts of unsatisfactory long-term economic growth rates. Should the economic agents lack sufficient public understanding of economics, office-seeking politicians can take advantage of the situation and adopt populistic policies to get elected into office. Undermined economic growth is the price society pays for its ignorance. This mechanism is most relevant in democratic resource-abundant countries suffering from weak institutions. That is because natural resource price fluctuations make it more challenging to distinguish politicians’ performance and exogenous economic shocks, translating...