Search for: finite-element-method
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    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 
    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... 

    Position error calculation of linear resolver under mechanical fault conditions

    , Article IET Science, Measurement and Technology ; Volume 11, Issue 7 , 2017 , Pages 948-954 ; 17518822 (ISSN) Daniar, A ; Nasiri-Gheidari, Z ; Tootoonchian, F ; Sharif University of Technology
    Position sensors are inseparable part of motion control systems. Linear resolvers (LRs) are electromagnetic position sensors that are suitable for high vibration, polluted environments. The accuracy of their detected position can be affected by different mechanical faults. In this study, variety of possible mechanical faults along with their mathematical index in LRs is introduced. Static eccentricity, dynamic eccentricity, inclined mover and run out error are the presented mechanical faults that are discussed independently and simultaneously. Then, three-dimensional non-linear, time-stepping finite element method is employed to investigate the performance of the studied resolver under... 

    Analytical model for performance prediction of linear resolver

    , Article IET Electric Power Applications ; Volume 11, Issue 8 , 2017 , Pages 1457-1465 ; 17518660 (ISSN) Saneie, H ; Nasiri Gheidari, Z ; Tootoonchian, F ; Sharif University of Technology
    In this study an analytical model based on solving Maxwell equations in the machine layers is presented for linear resolver (LR). Anisotropy, field harmonics, slot effects, number of slots per pole per phase and the effect of tooth skewing are considered in the model. The proposed method is a design oriented technique that can be used for performance prediction and design optimisation of the LR due to its acceptable accuracy and fast computation time. Two- and three-dimensional time stepping finite element method (FEM) is employed to validate the results of the proposed model. Good correlations between the results obtained by the proposed method and the FEM confirm the superiority of the... 

    Influence of mechanical faults on the position error of an axial flux brushless resolver without rotor windings

    , Article IET Electric Power Applications ; Volume 11, Issue 4 , 2017 , Pages 613-621 ; 17518660 (ISSN) Nasiri Gheidari, Z ; Tootoonchian, F ; Sharif University of Technology
    Institution of Engineering and Technology  2017
    The axial flux brushless resolver without rotor windings is newly proposed resolver that has the advantages of variable reluctance (VR) resolvers for having no winding on rotor and also, its manufacturing process is much simpler than that of VR resolvers. The influence of different mechanical faults on the position error of the studied resolver is discussed. Different types of eccentricities, inclined rotor and run out error independently and simultaneously are studied using 3D time stepping finite-element method. The results show the maximum position error is related to the resolver under static eccentricity (SE), so an optimised rotor is proposed for the studied resolver to overcome this... 

    Twelve-slot two-saliency variable reluctance resolver with non-overlapping signal windings and axial flux excitation

    , Article IET Electric Power Applications ; Volume 11, Issue 1 , 2017 , Pages 49-62 ; 17518660 (ISSN) Tootoonchian, F ; Nasiri Gheidari, Z ; Sharif University of Technology
    Institution of Engineering and Technology  2017
    In this study, a new 12-slot two-saliency variable reluctance (VR) resolver with simple non-overlapping windings is proposed. The excitation winding in the proposed resolver is replaced with one axial coil that is perpendicular to the signal windings. Both distributed and non-overlapping concentric windings with uniform coil turns are used. The rotor has two upper and lower saliencies located in front of each other. The shape and width of each saliency are determined based on the optimisation. Compared with conventional 12-slot VR resolvers, the proposed resolver has a simpler rotor structure and the advantages of two-saliency resolvers against eccentricity, absolute output position, and... 

    Design oriented technique for mitigating position error due to shaft run-out in sinusoidal-rotor variable reluctance resolvers

    , Article IET Electric Power Applications ; 2017 , Pages 132-141 ; 17518660 (ISSN) Nasiri Gheidari, Z ; Tootoonchian, F ; Zare, F ; Sharif University of Technology
    Variable reluctance (VR) resolvers have some distinguish features over wounded rotor resolvers that make them suitable for industrial applications. Among different types of VR resolvers, sinusoidal-rotor resolvers are preferred due to simple structure and high performance under eccentricities. However, their accuracy is affected by inevitable run-out error. As they work based on sinusoidal variation of coupling area between stator and rotor and under run-out error the coupling area is impaired. Hence, in this study, a new disk shape configuration is proposed for sinusoidal-rotor resolver that is robust against run-out error. Geometrical dimensions are calculated based on optimisations to... 

    Developing new enrichment functions for crack simulation in orthotropic media by the extended finite element method

    , Article International Journal for Numerical Methods in Engineering ; Volume 69, Issue 10 , 2007 , Pages 2150-2172 ; 00295981 (ISSN) Asadpoure, A ; Mohammadi, S ; Sharif University of Technology
    New enrichment functions are proposed for crack modelling in orthotropic media using the extended finite element method (XFEM). In this method, Heaviside and near-tip functions are utilized in the framework of the partition of unity method for modelling discontinuities in the classical finite element method. In this procedure, by using meshless based ideas, elements containing a crack are not required to conform to crack edges. Therefore, mesh generation is directly performed ignoring the existence of any crack while the method remains capable of extending the crack without any remeshing requirement. Furthermore, the type of elements around the crack-tip remains the same as other parts of... 

    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 (Supervisor) ; Vakilian, Mehdi (Supervisor)
    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 (Supervisor) ; Asghari, Mohsen (Supervisor)
    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... 

    Compartion of Numerical Methods for Nonsymmetrical Contact Problem

    , M.Sc. Thesis Sharif University of Technology Mansoori, Hassan (Author) ; Adibnazari, Saeed (Supervisor)
    This thesis aims to discuss matters in the area of non-symmetrical contact. Problems have been solved by the use of different numerical methods and their precision has been determined. In most projects which have been conducted in regards with contact's studies, Indenter has been considered vertical on the other object and particles of two objects are moving in the vertical direction of the free surface. This matter has resulted in obtaining symmetrical functions relevant to the point of beginning contact which helps distributing contact pressure, stresses and movements. In addition, mostly profiles of two involved objects are considered symmetrical that this matter greatly contributes... 

    Thermal Local Buckling of Metal Truncated Conical Shells with Composite Rainforced Layers by Finite Element Method

    , M.Sc. Thesis Sharif University of Technology Merati, Ali (Author) ; Hosseini Kordkheili, Ali (Supervisor)
    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... 

    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... 

    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... 

    Mechanical Properties of the Carbon Graphene Sheets with FEM

    , M.Sc. Thesis Sharif University of Technology Moshrefzde Sani, Hadi (Author) ; Hosseini Kordkheili, Ali (Supervisor)
    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... 

    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 (Supervisor)
    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... 

    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 (Supervisor)
    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... 

    The Modeling of Graspers Force-Behavior in Minimally Invasive Surgery

    , M.Sc. Thesis Sharif University of Technology Hortamani, Ramin (Author) ; Zabihollah, Abolghasem (Supervisor)
    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... 

    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
    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
    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
    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...