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    A different approach to estimate the process parameters in tube hydroforming

    , Article International Journal of Material Forming ; Volume 8, Issue 3 , July , 2015 , pp 355-366 ; ISSN: 19606206 Hashemi, R ; Shirin, M. B ; Einolghozati, M ; Assempour, A ; Sharif University of Technology
    Abstract
    An enhanced unfolding inverse finite element method (IFEM) has been used together with an extended strain-based forming limit diagram (FLD) to develop a fast approach to predict the feasibility of tube hydroforming process of concept part and determine where the failure or defects can occur. In tube hydroforming, the inverse IFEM has been used for estimating the initial length of tube, axial feeding and fluid pressure. The already developed IFEM algorithm used in this study is based on the total deformation theory of plasticity. Although the nature of tube hydroforming is three-dimensional deformation, in this article a modeling technique has been used to perform the computations in... 

    Development of an inverse finite element method with an initial guess of linear unfolding

    , Article Finite Elements in Analysis and Design ; Vol. 79, issue , 2014 , p. 1-8 Kankarani Farahani, M ; Bostan Shirin, M ; Assempour, A ; Sharif University of Technology
    Abstract
    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. In the inverse method the nodal coordinates in the final shape are known and their corresponding positions on the initial blank should be determined. The developed method deals with logarithmic large strains of membrane triangular elements, 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. The... 

    Modeling of Uplift and Impact with Finite Element and Generalized Finite Element Methods

    , M.Sc. Thesis Sharif University of Technology Eslahi, Reza (Author) ; Khoei, Amir Reza (Advisor)
    Abstract
    One of the most important issues in modeling natural phenomena that always takes into consideration is the problem of contact and collision between objects. Finite element method is known as the most basic and commonly used in numerical modeling techniques to simulate the above phenomenon.This method has specific problems such as dependency of this approach to the domain mesh especially near the contact region. Due to the dynamic and complex nature of impact problems in which drastic changes occur in short duration that often deals with large deformations, one of the perennial concerns, is the weaknesses of methods applied to enforce contact constrains, and so it is essential to use an... 

    Two Phase Fluid Flow Modeling in Deforming Porous Media Using XFEM Technique

    , M.Sc. Thesis Sharif University of Technology Farrokhpour, Leila (Author) ; Khoei, Amir Reza (Advisor)
    Abstract
    Geotechnical problems behavior depends on their interaction with existed fluid phases in their voids. In this research three phase porous media is introduced and it’s governing equations is presented. For solving this set of fully coupled dynamic equations finite element method is applied using elements with displacement and pressure degrees of freedom. Essential drawback of FEM method is in discontinuities modeling. In solid mechanic problems, discontinuity may occur in displacement field, such as crack or contact problems, or in their derivatives, such as multi-material problems. Major soil structures include some internal regions that there are some meshing problems during their FEM... 

    Development of 3D neutron noise simulator based on GFEM with unstructured tetrahedron elements

    , Article Annals of Nuclear Energy ; Volume 97 , 2016 , Pages 132-141 ; 03064549 (ISSN) Hosseini, S. A ; Vosoughi, N ; Sharif University of Technology
    Elsevier Ltd 
    Abstract
    In the present study, the neutron noise, i.e. the stationary fluctuation of the neutron flux around its mean value is calculated based on the 2G, 3D neutron diffusion theory. To this end, the static neutron calculation is performed at the first stage. The spatial discretization of the neutron diffusion equation is performed based on linear approximation of Galerkin Finite Element Method (GFEM) using unstructured tetrahedron elements. Using power iteration method, neutron flux and corresponding eigen-value are obtained. The results are then benchmarked against the valid results for VVER-1000 (3D) benchmark problem. In the second stage, the neutron noise equation is solved using GFEM and... 

    Effects of higher oscillation modes on TM-AFM measurements

    , Article Ultramicroscopy ; Volume 111, Issue 2, January 2011, Pages 107–116 Nejat Pishkenari, H ; Meghdari, A. (Ali) ; Sharif University of Technology
    Abstract
    The finite element method and molecular dynamics simulations are used for modeling the AFM microcantilever dynamics and the tip–sample interaction forces, respectively. Molecular dynamics simulations are conducted to calculate the tip–sample force data as a function of tip height at different lateral positions of the tip with respect to the sample. The results demonstrate that in the presence of nonlinear interaction forces, higher eigenmodes of the microcantilever are excited and play a significant role in the tip and sample elastic deformations. Using comparisons between the results of FEM and lumped models, how some aspects of the system behavior can be hidden when the point-mass model is... 

    Simulation of orthogonal micro-cutting of FCC materials based on rate-dependent crystal plasticity finite element model

    , Article Computational Materials Science ; Vol. 86, issue , April , 2014 , pp. 79-87 ; ISSN: 09270256 Tajalli, S. A ; Movahhedy, M. R ; Akbari, J ; Sharif University of Technology
    Abstract
    Micro-machining of face centered cubic (FCC) metallic materials is simulated via the theory of rate-dependent crystal plasticity. This approach accounts for slip systems and crystallographic orientations in its constitutive framework in order to accurately model the evolution of localized shear band formed during severe plastic deformation of crystalline materials. Through developing a user-defined subroutine in the ABAQUS/Explicit FE platform, the constitutive model is implemented and used to study the influence of workpiece crystallographic orientation on the cutting and thrust specific energies of the process. Due to the high rate of deformation, mechanical properties of texture can be... 

    Numerical solution of the nonlinear diffusivity equation in heterogeneous reservoirs with wellbore phase redistribution

    , Article Journal of Petroleum Science and Engineering ; Vol. 114 , 2014 , pp. 82-90 ; ISSN: 09204105 Khadivi, K ; Soltanieh, M ; Sharif University of Technology
    Abstract
    We consider the application of the Finite Element Method (FEM) for numerical pressure transient analysis under conditions where no reliable analytical solution is available. Pressure transient analysis is normally based on various analytical solutions of the linear one-dimensional diffusion equation under restrictive assumptions about the formation and its boundaries. For example, the formation is either assumed isotropic or a restrictive a priori assumption is made about its heterogeneity. The wellbore storage effect is also often considered without regard to the possibility of phase redistribution. In many practical situations such restrictions are not justified and analytical solutions do... 

    Time-Variant evaluation of electromagnetic forces on transformer windings during inrush current and short-circuit by FEM

    , Article Arabian Journal for Science and Engineering ; Volume 38, Issue 4 , 2013 , Pages 883-893 ; 13198025 (ISSN) Eslami, A ; Vakilian, M ; Sharif University of Technology
    2013
    Abstract
    Time-variant axial and radial electromagnetic for ces under inrush current and short-circuit current are calculated (by finite element method; FEM) and compared. A simplified analytic method is presented for computation of inrush current in transformer. The simulation results obtained by this method are compared with the measured values. A compact three-phase, core-type 132/20 KV, 30 MVA, power transformer is modeled, employing two-dimensional (2D) FEM, the different forces under short-circuit and inrush current conditions are evaluated as a function of time. The simulation results for this sample transformer show that the inrush current axial force is larger than clamping force (which is... 

    Application of differential quadrature method to investigate dynamics of a curved beam structure acted upon by a moving concentrated load

    , Article Indian Journal of Science and Technology ; Volume 5, Issue 8 , 2012 , Pages 3085-3089 ; 09746846 (ISSN) Nikkhoo, A ; Kananipour, H ; Chavoshi, H ; Zarfam, R ; Sharif University of Technology
    Abstract
    Application of curved beams in special structures requires a special analysis. In this study, the differential quadrature method (DQM) as a well-known numerical method is utilized in the dynamic analysis of the Euler-Bernoulli curved beam problem with a uniform cross section under a constant moving load. DQ approximation of the required partial derivatives is given by a weighted linear sum of the function values at all grid points. A prismatic semicircular arch with simply supported boundary conditions is assumed. The accuracy of the obtained results is corroborated by employing the Galerkin and finite element methods. Finally, the convergence rate of the DQM and Finite Element Method (FEM)... 

    Evaluation of Soil-Structure Interaction Effects in Seismic Behavior of 3D Models of Elevated Tanks, Using Absorbing Boundary Method

    , M.Sc. Thesis Sharif University of Technology Seyedpour Esmailzadeh, Saba (Author) ; Rahimzadeh Rofooei, Fayyaz (Advisor)
    Abstract
    Elevated tanks are typically used to store water for drinking as well as fire fighting purposes. The failure of these critical structures during earthquakes can potentially lead to shortage of drinking water, difficulty in putting out fires, and substantial economical losses. Due to the fact that a large number of water tanks with insufficient seismic resistance were extremely damaged or collapsed during past earthquakes, (e.g. the elevated tank of Rasht in 1989 Gilan's earthquake), the reliability of these structures against failure under seismic loads is of critical concern. Numerous studies have analyzed and investigated the dynamic behavior of fluid storage tanks; however, most of them... 

    The Modeling of Graspers Force-Behavior in Minimally Invasive Surgery

    , M.Sc. Thesis Sharif University of Technology Hortamani, Ramin (Author) ; Zabihollah, Abolghasem (Advisor)
    Abstract
    Minimally Invasive Surgery (MIS) is a modern surgical technique in which the operation is performed through small incisions in the body. Therefore, the surgeon looses his/her sense of touch which is of high importance in any medical operation. In the present work, a novel smart grasper is presented in which the surgeon can virtually acquire a feeling of force/momentum experienced by the organ/tissue. The smart grasper uses piezoelectric sensors bonded at desired locations to detect the applied force/momentum applied by surgeon and to measure the transmitted force/momentum to the tissue/organ. First, an accurate electro-mechanical model of the smart grasper is developed and the relations... 

    Determination of Eddy Current Losses in Power Transformer Tank and Analysis of Methods for Reduction of These Losses

    , M.Sc. Thesis Sharif University of Technology Motalleb, Mehdi (Author) ; Abbaspour Tehranifard, Ali (Advisor) ; Vakilian, Mehdi (Advisor)
    Abstract
    The leads with heavy current passing through the covering plates, and the winding in a transformer, are sources of eddy current losses. Due to this loss some regions of tank wall are subject to serious local overheating. It affects the safety and reliability of this expensive bject and power delivery.Heavy current in large power transformers and special type transformers give rise to a concentrated passage of eddy currents which in turn cause high local losses and overheating in the metallic parts especially in the steel tank walls of transformer.This local overheating is dangerous for transformer oil and the solid insulations. Therefore the calculation of losses and proper design of... 

    Modeling of Spleen Tissue for Analyzing it Sinteraction with Alaparoscopic Surgery Instrument

    , M.Sc. Thesis Sharif University of Technology Tirehdast, Mojdeh (Author) ; Farahmand, Farzam (Advisor) ; Asghari, Mohsen (Advisor)
    Abstract
    In the recent years, medical application of robots has been widely developed. Transforming open surgeries to close surgeries has distinguished this novel method to decrease limitations in this type of surgery. In this procedure, two or three small incisions on the skin are used as guides for robotic instruments to enter the cavity, to improve the surgeon’s manipulation and function in surgery. One of challenges in this field is surgeon’s training for laparoscopic surgery. Surgical simulators are used to solve this problem. Lack of instrument for large organs gripping and tissue palpation loss are existing difficulties in available surgical simulators in such a manner that surgeons has no... 

    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 (Advisor)
    Abstract
    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... 

    Simulation of Concrete Meso-Structure Within FEM/CDM Framework

    , M.Sc. Thesis Sharif University of Technology Yghoobi, Mohammad Reza (Author) ; Vafai, Abolhassan (Advisor) ; Shahbeyk, Sharif (Advisor)
    Abstract
    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... 

    Mechanical Properties of the Carbon Graphene Sheets with FEM

    , M.Sc. Thesis Sharif University of Technology Moshrefzde Sani, Hadi (Author) ; Hosseini Kordkheili, Ali (Advisor)
    Abstract
    In this research, molecular structural mechanics method is employed to calculate the Young’s modules of a two-layered carbon graphene sheet. For this purpose, covalent bonds are modeled using non-linear beam elements and van der Waals interactions are replaced by nonlinear truss elements. Morse potential and Lennard-Jones potential equations are used to simulate the covalent bonds and van der Waals interactions, respectively. For each atom, van der Waals forces are considered from all other atoms located in its cut-off radius. Young’s modulus, bending modules and Poisson’s ratio of single and two-layered graphene sheets were calculated and the results revealed that Young’s modulus decreases... 

    Numerical Calculation of Bearing Capacity of Foundations Near or on the Slopes

    , M.Sc. Thesis Sharif University of Technology Mohammadi, Amir Hossein (Author) ; Ahmadi, Mohammad Mehdi (Advisor)
    Abstract
    Bearing capacity of foundations is one of the most controversial issues in foundation engineering. In this study regarding to the previous researches which has done by the other researchers the bearing capacity factors of a footing has calculatedusing finite element method. On the next step of this study some footings has modeled on different positions near slopes with different angles and bearing capacity of them has calculated, then some strip foundation has modeled and bearing capacity of them has calculated and compared with the values of the footings in this study and strip foundations of the other researches. Furthermore some foundations have modeled on the solpe and bearing capacity... 

    Simulation of Chip Segmentation in Metal Cutting Using ALE Finite Element Method

    , M.Sc. Thesis Sharif University of Technology Rakhshan Haghighifard, Pedram (Author) ; Movahhedy, Mohammad Reza (Advisor)
    Abstract
    Since it is important to obtain the suitable cutting conditions for machining and investigate the effect of various parameters on this process, the simulation of this process has been developed extensively by using the finite element method in recent years. Due to very large plastic deformation and also continuous chip flow, one of the most appropriate techniques in modeling chip formation is the arbitrary Lagrangian-Eulerian (ALE) finite element method which has been used in several papers using some traditional codes like ABAQUS or personal codes in recent years. However, one of the limitations in this method is the use of a continuous mesh retains with no change in connectivities which is... 

    XFEM Analysis of Non-Linear Thermomechanical Problems

    , M.Sc. Thesis Sharif University of Technology Alipour, Kamran (Author) ; Kouchakzadeh, Mohammad Ali (Advisor)
    Abstract
    In this thesis a nonlinear thermomechanical model based on Lagrangian-extended finite element method is proposed to simulate discontinuities under thermal and mechanical loads. At first, a geometrically nonlinear model is presented for large deformation problems and then the model is completed by considering thermomechanical aspects. In extended finite element method, different enrichment functions are stated and also using analytical methods, a new set of functions are introduced to enrich the temperature filed around biomaterial crack tips. For numerical simulations, an object oriented code is created in C++. The results of numerical simulations are verified by the use of ABAQUS