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    Investigation of Designing and Material Property Parameters in Mechanical Behavior of Balloonexpandable Stent in Coronary Artery by Finite Element Analysis

    , M.Sc. Thesis Sharif University of Technology Yousefan, Mohammad Mahdi (Author) ; Arghavani Hadi, Jamal (Supervisor)
    The coronary arteries of the heart are one of the most important arteries in the body's cardiovascular system, which carry oxygen and nutrients to the heart.Therefore, coronary heart disease is one of the most important causes of death in society. In this disease, when the adhesion of sediments and blood plugs to the walls of the arteries increase, the ducts become narrow and the circulatory system gets hard. As a result, the risk of heart attack and mortality increases.Due to the increase in mortality caused by coronary heart disease, working on treatment methods for this disease is important. Angioplasty and stent implantation in a vein are the latest treatments for this disease and have... 

    Simulation of Concrete Meso-Structure Within FEM/CDM Framework

    , M.Sc. Thesis Sharif University of Technology Yghoobi, Mohammad Reza (Author) ; Vafai, Abolhassan (Supervisor) ; Shahbeyk, Sharif (Supervisor)
    Various theoretical studies have been developed to obtain a deeper understanding of concrete behavior lead to the concrete constitutive models in the macroscale. In these models, however, the microstructure of the concrete and its effects on the concrete behavior has not been taken into account.Several numerical approaches have been incorporated to determine the effects of concrete mesostructure on the overall behavior of concrete. They may be classified at least in three main groups. In the first group, Continuum finite element methods (FEM) equipped with interface elements is incorporated. Second group is to incorporate more efficient elements, such as lattice or truss elements, instead of... 

    Design of Fillet Welds in Plastic State

    , M.Sc. Thesis Sharif University of Technology Yazdi, Mohammad Hassan (Author) ; Maleki, Shervin (Supervisor)
    Fillet welds are widely used in steel construction due to their high strength and economy. In the joints used in construction, eccentricity loads in complex weld stress. The current research involves 72 bending specimens and 16 torsion specimens being modeled to study different design code relationships regarding the plastic properties of welds. In line with an even comprehensive study, the previous experimental programs in this field have been added to the modeling results.Reliability analysis has been applied to examine code relationships more precisely. The analysis involved examination of various uncertainties which showed that applying elastic methods proves more conservative than other... 

    Modeling of the Behavior of Prestressed Concrete Column Confined by CFRP Composites

    , M.Sc. Thesis Sharif University of Technology Yazdani, Mohammad (Author) ; Kazemi, Mohammad Taghi (Supervisor)
    Because of mistakes in the design and calculation, incoherence between construction and design, structural changes, changes in loads and also damages caused by the passage of the time, concrete structures need to be improved and strengthened. Polymeric sheets reinforced by fibers (FRP), according to their appropriate characteristic, are more efficient for strengthening concrete structures. Most studies on confined columns refers to confined RC columns with FRP and less mentioned about prestressed columns. In this study, the behavior of prestressed columns is analyzed by modeling a case of prestressed column in a nonlinear analysis software. Samples of confined concrete columns with CFRP and... 

    Polygonal Finite Element Modeling of Fracture Mechanism and Crack Propagation

    , M.Sc. Thesis Sharif University of Technology Yasbolaghi, Reza (Author) ; Khoei, Amir Reza (Supervisor)
    Fracture is one of the most important engineering problems, and the lack of knowledge about this phenomenon will result in loss of life and property. Before the computer age, fracture mechanics has been studied by many analytical mechanics researchers; and after that, lots of attempts have been done to accurately model this phenomenon.
    Finite element method, one of the best methods in Computational Mechanics, is common in computational fracture mechanics. Polygonal finite element is a new concept which has been recently applied in finite element analysis. This research utilized this concept in com-putational fracture mechanics. In another word, the crack discontinuity and crack tip... 

    Numerical Modeling of Fretting Fatigue Crack Nucleation using Finite Element Method

    , M.Sc. Thesis Sharif University of Technology Goharzay, Hamed (Author) ; Adibnazari, Saeed (Supervisor)
    Fretting fatigue damage occurs in contacting components while they are subjected to fluctuating loads and relatively small movement at the same time. In this condition some micro-cracks are created in these components. These micro-cracks will be propagated and cause sudden failure which is accompanied by great human and economic loss. There are many practical applications that are subjected to fretting fatigue, such as bolted and riveted connections, bearing shafts, blade-disk attachment in gas turbines, aero-engine splined couplings, cable connections and etc. Fretting fatigue failure process can be divided into two portions of crack initiation and propagation. It is very difficult, to... 

    Prediction of Deformation Field And Temperature Distribution in Extrusion of Composite AA6061-10%SiC(p)

    , M.Sc. Thesis Sharif University of Technology Goodarzi Hosseinabadi, Hossein (Author) ; Serajzadeh, Siamak (Supervisor)
    In this research, the extrusion of composite AA6061-SiC has been investigated and the temperature distribution field and energy required for the process has been predicted. In this regard, to predict the flow behavior of material, hot extrusion tests conformed at various ranges of temperatures and strain rates. Afterward, the finite element method coupled with the upper bound technique to calculate the temperature distribution and energy required during hot extrusion. This model has also used for wire drawing and cold extrusion processes. The present model is capable of considering various process parameters such as speed of extrusion, reduction and the initial billet/die temperature on the... 

    Simulation of Two Phase flow in 2D Hydrocarbon Reservoirs Using Reduced Order Modeling Based on Proper Orthogonal Decomposition Technique

    , M.Sc. Thesis Sharif University of Technology Goodarzi, Mahdi (Author) ; Taghizadeh Manzari, Mehrdad (Supervisor) ; Kazemzadeh Hannani, Siamak (Supervisor)
    The objective of this thesis is to use proper orthogonal decomposition (POD) method in numerical simulation of a hydrocarbon reservoir to decrease computational time.The algorithm basically consists of two projection steps: (1) projecting the governing equations onto a subspace spanned by a low number of global empirical basis functions extracted from previous time step solutions, and (2) solving the governing equations in this reduced space and projecting the solution back on the original, high dimensional one. After projection of governing equations to new subspace, because of much less dimensions of this subspace, the computational cost of numerical solution of the equations, which mostly... 

    Analysis, Design and Manufacturing of Custom Osteotomy Implants Forming Machine

    , M.Sc. Thesis Sharif University of Technology Gomari, Behnam (Author) ; Farahmand, Farzam (Supervisor) ; Farkhondeh, Hassan (Supervisor)
    Knee arthritis is a painful disease from which millions of people around the world are suffering. One of the main causes of osteoarthritis and joint damage that starts from a young age, is that bones around the knee are not in a straight line. As a result, this situation causes additional pressure to the knee. This should be corrected with surgery. There are two procedures for this operation, a conventional method and a customized method. In conventional method, surgical planning is based on 2d X-ray images and plates are formed and fixed approximately at the desired location. This method is not precise enough and may cause problems for the patient. A new developing method, is that all the... 

    Modeling of Mechanical Damage in Fractured Rocks During Drilling

    , Ph.D. Dissertation Sharif University of Technology Gomar, Mostafa (Author) ; Goodarznia, Iraj (Supervisor) ; Shadizadeh, Reza (Supervisor) ; Massihi, Mohsen (Co-Advisor)
    Effective stress variation is one of the main issues in petroleum and gheothermal reservoir development. These stress variation could cause formation damage, sand production, sloughing shale and various modes of borehole instability like induced fractures and borehole wall shearing. In petroleum engineering, drilling a borehole is the first step in reservoir development. The wellbores are implemented to produce or inject fluids such as water, oil, gas and chemical fluids used during secondary and tertiary recovery processes. Upon drilling a borehole, reservoir pore pressure, rock and fluid temperature and mechanical stresses change which induces borehole instability and variations in rock... 

    Numerical Modeling of Fracture Mechanics in Isotropic/ Orthotropic FGMs by XFEM

    , M.Sc. Thesis Sharif University of Technology Goli, Elyas (Author) ; Kazemi, Mohammad Taghi (Supervisor)
    Nowadays, regarding to knowledge progresses in various fields,advanced materials for which have acceptable performance in sensitive and special conditions must be used. Functionally graded materials are advanced multiphase composite materials that are characterized by continues spatial variations in mechanical and thermal properties. Clearly, studying on fracture mechanics of FGMs is important because they are used in igh-tech and sensitive applications.In this research, numerical modeling of fracture mechanics in isotropic/orthotropic/ transversely isotropic FGMs via interaction integral method is performed. Both incompatible and non-equilibrium formulations of interaction integral are... 

    Measuring Limb Darkening of Distant Stars Using Microlensing Events by Finite Element Method

    , Ph.D. Dissertation Sharif University of Technology Golchin, Laya (Author) ; Rahvar, Sohrab (Supervisor)
    The finite-size effect in gravitational microlensing provides a possibility to measure the variation of surface brightness of stars from centre to limb which is called limb darkening profile. Measuring limb darkening profile provides information about star atmosphere. It is also useful in other fields of astrophysics. In this thesis we develop a numerical method to recover limb darkening of source stars from single lens microlensing light curves with finite source effect in which the lens transits the source disk. We use the Finite Element Method (FEM) as an inversion tool for discretization and inversion of the finite source effect integral equation. This method makes no explicit assumption... 

    Temperature-dependent Multi Scale Large Deformation Simulation of Heterogeneous Crystals

    , M.Sc. Thesis Sharif University of Technology Gordan, Ali (Author) ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Co-Advisor)
    In this study, a novel and unprecedented multi-scale hierarchical molecular dynamics (MD) – finite element (FE) coupling method is proposed to demonstrate the influence of temperature on mechanical properties of heterogeneous Nano-crystalline structures. The embedded-atom method (EAM) many-body interatomic potential is implemented to consider pairwise interactions between atoms in the metallic alloys with face-centered-cubic (FCC) lattice structure at different temperatures. In addition, the Nose-Hoover thermostat is employed to adjust the fluctuation of temperature. In order to calculate the equivalent lattice parameter, a weight average between the lattice parameters of atomic structures... 

    Numerical Study of Flow and Heat Transfer Around a Rotor

    , M.Sc. Thesis Sharif University of Technology Gerami, Mohammad (Author) ; Nouri Borujerdi, Ali (Supervisor)
    The purpose of this study is to investigate the distribution of air flow and temperature in electric machines. The fluid flow equations are solved by using the characteristic Galerkin. The unsteady equations of the air flow and heat transfer between the rotor, stator and radial cooling channels of the generator are solved by finite element method. Tetrahedral elements are used, but hexahedral elements can also be used. The upwind method is used to discretize the convection terms, but the central difference for the diffusion parts, that is equal to Petrov-Galerkin method in steady state situation. Due to the large number of channels and specific geometry, to reduce the computation costs, the... 

    Finite Element Analysis of Reinforced Concrete Waffle Slabs in Steel Structures Service Conditions

    , M.Sc. Thesis Sharif University of Technology Keihanian, Pedram (Author) ; Eskandari, Morteza (Supervisor) ; Kazemi, Mohammad Taghi (Supervisor)
    Since the main weight of structures comes from the weight of floor systems, it is desirable to use tin and light floor system in order to reduce gravity and seismic force induced in the structure. However architectural aspects limit the application of short spans in the structural system. The objective of this work was to analyze the adequacy of a design method widely used in the modeling of waffle slabs interaction with steel columns as its supports in steel frames, and to verify if it represents the slab behavior satisfactorily. A real scale waffle slab was laid on a steel column and submitted to service loads. Subsequently it was analyzed with FE method for measuring specific stress,... 

    A Parametric Study on Application and Analysis of Beam to Column "Reversed Channel" Connection in Tubular Systems

    , M.Sc. Thesis Sharif University of Technology Kokabi, Sina (Author) ; Mofid, Massoud (Supervisor)
    Today steel tubular systems are used more than before, especially in recent years. A difficulty with this type of systems is making beam to column connections using bolts due to no access to holes of bolts from the inside of tube or hollow circular column. Reverse channel connection is devised and introduced to prevail this problem. Access to holes in this connection is from the inside of channel. In this connection, the web of the channel is connected to steel beam using bolts and the two legs of channel is welded to face of tube column.
    This type of connection does include some innovations; not too many researchers work on different versions of this connection. This thesis provides an... 

    Prediction of Strain Field in Strip and Work-Roll During Cold Rolling of a Low Carbon Steel

    , M.Sc. Thesis Sharif University of Technology Koohbor, Behrad (Author) ; Serajzadeh, Siamak (Supervisor)
    In this research, distribution of stress, strain and temperature fields in the strip and workroll were determined during steady state cold rolling process. To do this, first an initial guess based on the approach proposed by Hill for the velocity field was taken and accordingly, the real velocity distribution and then the strain rate and stress fields in the strip were calculated. Then, using the obtained stress and strain rate fields, the deformation power was determined and used as a boundary condition for solving the thermal behavior of the strip. By considering the Streamline Upwind Petrov-Galerkin method and solving the finite element relations, the temperature distribution within the... 

    Static and Dynamic Analysis of Micro-structures in Electric Field Using Newly Developed Strain Gradient Finite Elements

    , Ph.D. Dissertation Sharif University of Technology Kahrobaiyan, Mohammad Hossein (Author) ; Ahmadian, Mohammad Taghi (Supervisor) ; Asghari, Mohsen (Supervisor)
    Due to importance of micro electromechanical systems (MEMS), inability of the classical continuum theory to predict the mechanical behavior of micro-scale structures accurately, and vast applications of finite element method (FEM) in modeling of the MEMS, in this dissertation, the static and dynamic mechanical behavior of electrostatically actuated micro structures has been investigated using newly developed finite elements based on strain gradient continuum theory. The governing equations and boundary conditions have been developed for longitudinal and torsional behavior of microbars as well as flexural behavior of Euler-Bernoulli and Timoshenko microbeams based on strain gradient... 

    Development of a Nonlinear Inverse Finite Element Method in Strain Analysis of sheet metal forming

    , M.Sc. Thesis Sharif University of Technology Kangarani Farahani, Mohammad (Author) ; Assempour, Ahmad (Supervisor)
    An inverse finite element method (IFEM) has been developed for estimation of the blank size and prediction of the strain distribution in sheet metal forming. This approach deals with logarithmic large strains of membrane triangular elements, deformation theory of plasticity, virtual work principle and a new approach for friction modeling. This method leads to a system of nonlinear equations which is highly sensitive to the initial guess. In order to avoid the converging problems, especially in the quasi vertical walls, an appropriate initial guess is introduced. As well, the number of iterations in the nonlinear numerical solution is decreased by using this initial guess and the solution... 

    Nonlinear Seismic Response of Concrete Gravity Dams Due to Foundation Fault Movement

    , M.Sc. Thesis Sharif University of Technology Karimi, Zana (Author) ; Ghaemian, Mohsen (Supervisor)
    Generally concrete dams have not been sited at location where there were faults classified as active. However, there may be sites suitable for concrete dams where there is some possibility of fault displacement occurring underneath the dam. In addition, there may be situations where an existing dam was constructed over a fault thought to be inactive and later determined to be active, due to different approaches of classification of a fault whether it is active or not. Also some discontinuities may be observed during construction. For these cases nonlinear analysis and criteria will be required to assess the capability of concrete dams to safely withstand fault displacements. In this thesis,...