Search for: finite-element-method
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    Discrete formulation for two-dimensional multigroup neutron diffusion equations

    , Article Annals of Nuclear Energy ; Volume 31, Issue 3 , 2004 , Pages 231-253 ; 03064549 (ISSN) Vosoughi, N ; Salehi, A. A ; Shahriari, M ; Sharif University of Technology
    The objective of this paper is to introduce a new numerical method for neutronic calculation in a reactor core. This method can produce the final finite form of the neutron diffusion equation by classifying the neutronic variables and using two kinds of cell complexes without starting from the conventional differential form of the neutron diffusion equation. The method with linear interpolation produces the same convergence as the linear continuous finite element method. The quadratic interpolation is proven; the convergence order depends on the shape of the dual cell. The maximum convergence order is achieved by choosing the dual cell based on two Gauss' points. The accuracy of the method... 

    A modified upwind-biased strategy to calculate flow on structured- unstructured grid topologies

    , Article 42nd AIAA Aerospace Sciences Meeting and Exhibit, Reno, NV, 5 January 2004 through 8 January 2004 ; 2004 , Pages 685-694 Darbandi, M ; Schneider, G. E ; Vakilipour, S ; Sharif University of Technology
    American Institute of Aeronautics and Astronautics Inc  2004
    A numerical upwind-biased procedure which respects the essence of upwinding is suitably extended in order to reduce the false diffusion induced by a first-order approximation. In this regard, some arbitrarily first and second order gradient terms are added to the primary upwind approximation. The additional terms are then discretized using second-order schemes which essentially produce dispersive errors. The suitable choices for the weights of the new added terms result in lowering the dissipative role of the original upwind scheme. Additionally, the implicit appearance of the third-order terms, which are the consequences of second-order discretizations, helps to reduce the dissipative... 

    Thermal stress analysis of concrete arch dams due to enviromental action

    , Article 2004 ASME International Mechanical Engineering Congress and Exposition, IMECE, Anaheim, CA, 13 November 2004 through 19 November 2004 ; Volume 375, Issue 1 , 2004 , Pages 393-402 ; 02725673 (ISSN) Shelbany, F ; Ghaemian, M ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2004
    A three-dimensional finite element analysis was carried out to determine the annual variation of temperature and thermal stresses of a concrete arch dam. Appropriate heat transfer boundary conditions in the dam body were used for air and reservoir temperature as well as solar radiation variations. Karaj arch dam in Iran was used as a case study. The rate of convergence of the numerical solution is examined. Results of the finite element analysis show that probable cracks occur in a very narrow region of the downstream face. Thermal loads have the most significant effects for causing downstream cracks in comparison with self-weigh and hydrostatic loads. The cracked areas of downstream face... 

    Parallel computation of a mixed convection problem using fully-coupled and segregated algorithms

    , Article 2004 ASME International Mechanical Engineering Congress and Exposition, IMECE, Anaheim, CA, 13 November 2004 through 19 November 2004 ; Volume 375, Issue 1 , 2004 , Pages 313-322 ; 02725673 (ISSN) Darbandi, M ; Banaeizadeh, A ; Schneider, G. E ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2004
    In this work, parallel solution of the Navier-Stokes equations for a mixed convection heat problem is achieved using a finite-element-based finite-volume method in fully coupled and semi coupled algorithms. A major drawback with the implicit methods is the need for solving the huge set of linear algebraic equations in large scale problems. The current parallel computation is developed on distributed memory machines. The matrix decomposition and solution are carried out using PETSc library. In the fully coupled algorithm, there is a 36-diagonal global matrix for the two-dimensional governing equations. In order to reduce the computational time, the matrix is suitably broken in several... 

    Modelling the work-roll temperature variation at unsteady state condition

    , Article Modelling and Simulation in Materials Science and Engineering ; Volume 11, Issue 2 , 2003 , Pages 179-194 ; 09650393 (ISSN) Serajzadeh, S ; Mucciardi, F ; Sharif University of Technology
    In this paper, the unsteady state heat transfer equations with time dependent boundary conditions are coupled with a two-dimensional finite element method to predict the work-roll temperature distribution during the continuous hot slab rolling process. To achieve an accurate temperature field, the effects of various factors including the thermal relationship of the work-roll and the metal slab, the idling work-roll revolutions, the rolling speed, the slab/roll interfacial heat transfer coefficient, and the magnitude of the thickness reduction of the slab at each deformation pass are taken into account. Comparisons between the predicted and published experimental results are used to... 

    Development of constitutive equations for a high carbon steel using additivity rule

    , Article ISIJ International ; Volume 43, Issue 7 , 2003 , Pages 1050-1055 ; 09151559 (ISSN) Serajzadeh, S ; Sharif University of Technology
    Iron and Steel Institute of Japan  2003
    Flow behavior of a high carbon steel under hot deformation condition has been studied and a mathematical model for describing the flow stress under isothermal and constant strain rate as well as under non-isothermal and varied strain rates has been developed. For doing so, Bergstrom dislocation model together with the additivity rule for strain have been employed also, hot compression experiments at various temperatures and strain rates have been utilized to achieve the kinetics of dynamic recovery and recrystallization of the high carbon steel. The comparison between the predicted and experimental results under both isothermal and non-isothermal conditions verifies the validity of the... 

    Evaluation of hydraulic fracturing pressure in a porous medium by using the finite element method

    , Article Energy Sources ; Volume 24, Issue 8 , 2002 , Pages 715-724 ; 00908312 (ISSN) Nouri, A ; Panah, A. K ; Pak, A ; Vaziri, H ; Islam, M. R ; Sharif University of Technology
    Hydraulic fracturing is a complicated phenomenon in which deformation of the porous medium and fluid leak-off to the surrounding area take place simultaneously. Their interaction therefore must not be overlooked. Modeling of this phenomenon in isothermal conditions requires analysis of soil deformation and crack and pore fluid pressure interaction. In this paper, a numerical scheme is presented for analysis of soil stresses and deformations and fluid flow in a coupled manner. This scheme is also used to detect the fracture in the medium. Our model was used in simulating a set of hydraulic fracturing experiments. These experiments were performed on compacted hollow cylindrical specimens under... 

    An Investigation of Brittle Fracture of Composite Pressure Vessels with Metal Liner Using a Numerical Approach Based on XFEM

    , M.Sc. Thesis Sharif University of Technology Tavakkoli, Arash (Author) ; Hosseini Kordkhili, Ali (Supervisor)
    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... 

    Compositional Simulation of CO2 Injection Process by Using Higher Order Finite Element Methods

    , M.Sc. Thesis Sharif University of Technology Shakourifar, Nima (Author) ; Pishvaie, Mahmmoud Reza (Supervisor)
    In most of the commercial and academic multiphase flow simulators, the numerical method in use is based on finite difference methods which can lead the solution toward numerical dispersions or even oscillations. These methods are very sensitive to the size of computational grid blocks. Even if we change the numerical method from finite difference to linear finite element (hFEM), still there will be such problems and size of grid blocks will be crucial in getting proper results which can lead to millions of computational grid blocks. One way to deal with this problem is using nonlinear finite element methods (pFEM) also known as higher-order finite element methods, Also compositional... 

    Modeling Saturated Porous Media Using Extended Finite Element Method

    , M.Sc. Thesis Sharif University of Technology Haghighat, Ehsan (Author) ; Khoei, Amir Reza (Supervisor)
    Soil structures have important roles in civil engineering applications. The most important types of these structures are soil dams and foundations which their damages may cause huge loss. Thus, appropriate analysis of these structures under possible loading conditions is unavoidable. The real behavior of this media can be achieved from the solution of its coupled governing differential equations. In order to solve this set of equations in practical applications, appropriate numerical solutions should be used. The finite element method can be called as one of the most important numerical solutions of differential equations which have been used in analyzing different types of engineering... 

    Modeling the Dynamic Contact with Large Deformations Using the G-ALE-FEM Method

    , M.Sc. Thesis Sharif University of Technology Mohajeri, Sina (Author) ; Khoei, Amir Reza (Supervisor)
    Contact between different parts of a system and their interactions on each other is one of the most important phenomena that we face in modeling a variety of mechanical issues which should be carefully considered. Sometimes, this phenomenon occurs between different components in a phase and some other times between several phases, which, causes changes in the performance and response of the system. Therefore, in order to investigate its effect in particular on dynamic problems that are subject to severe changes over a short period of time, and to provide more effective methods for dealing with it, the subject of this research has been devoted to dynamic contact modeling with large... 

    Modeling of Arbitrary Interfaces with Extended Finite Element (XFEM)in Pressure-Sensitive Materials

    , M.Sc. Thesis Sharif University of Technology RafieeRaad, Maryam (Author) ; Khoei, Amir Reza (Supervisor)
    There are various physical phenomena involving discontinuities and interfaces. The finite element method (FEM) has become the most popular and influential analytical tool for solving these physical phenomena. In the analysis of progressive failures because of discontinuities and interfaces, the mesh adaptive refinement in diverse stages of process is of great importance and, at each stage the mesh conforming to the shape of the interfaces is not inconsiderable. Consequently, the requirement of mesh adaption may necessitate high expenses of time and capacity. In contrast, the extended finite element method (XFEM) has been developed to efficiently perform modeling of problems including... 

    A Thermo-Mechanical Multi-Scale Simulation for the Compaction Process of the Oxide-Coated Aluminum Nano-Powders

    , M.Sc. Thesis Sharif University of Technology Orvati Movaffagh, Amir Mohammad (Author) ; Khoei, Amir Reza (Supervisor)
    This research introduces a novel thermo-mechanical multiscale technique, utilizing machine learning, for simulating the compaction process of aluminum nanopowders with surface oxidation at various temperatures. The methodology employed involves the utilization of nonlinear thermo-mechanical Finite Element Method (FEM) for macro scale analysis, while employing the Molecular Dynamics (MD) method to calculate the mechanical and thermal characteristics of aluminum nanopowders at the nano-scale. The first part of the research presents a comprehensive study on the thermal conductivity of alumina-coated aluminum nanopowders, which is a crucial property for their application in powder metallurgy,... 

    Some improvements on the unfolding inverse finite element method for simulation of deep drawing process

    , Article International Journal of Advanced Manufacturing Technology ; Vol. 72, issue. 1-4 , 2014 , pp. 447-456 ; ISSN: 02683768 Bostan Shirin, M ; Assempour, A ; Sharif University of Technology
    The linear unfolding inverse finite element method (IFEM) has been modified and enhanced by implementing large deformation relations. The method is helpful to predict forming severity of the part that should be deep drawn as well as its blank shape and strain distribution in preliminary design stage. The approach deals with minimization of potential energy and large deformation relations with membrane elements. To reduce the computation time, the part is unfolded properly on the flat sheet and treated as 2D problem. Moreover, the nonlinear stress-strain relationship of plastic material properties has been considered to increase the accuracy of the results. An experiment set up has been... 

    Analysis of an endlessly single-mode penrose-tiling photonic quasicrystal fiber

    , Article Mediterranean Photonics Conference, MePhoCo (3rd :2014:Trani ) ; May , 2014 , 1 - 3 Bahrampour, A ; Iadicicco, A ; Foomezhi, E ; Momeni, S ; Bhrampour, A. R ; Sharif University of Technology
    We propose a 10-fold photonic quasicrystal(QC)pattern as the cladding of modified index guiding quasi crystal fiber. We have studied the single-mode operation regime of the fiber by analyzing the effective V parameter. In this case it is presented an endlessly single mode regime due to V-parameter, and the result is in agreement with finite element method (FEM) simulation result. We present birefringence and electromagnetic field profiles using finite element method  

    Modelling and analysis of the effect of angular velocity and acceleration on brain strain field in traumatic brain injury

    , Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) ; Volume 3 A , 2013 ; 9780791856215 (ISBN) Hoursan, H ; Ahmadian, M. T ; Barari, A ; Beidokhti, H. N ; Sharif University of Technology
    Traumatic brain injury (TBI) has long been known as one of the most anonymous reasons for death around the world. A presentation of a model of what happens in the process has been under study for many years; and yet it remains a question due to physiological, geometrical and computational complications. Although the facilities for soft tissue modeling have improved and the precise CT-imaging of human head has revealed novel details of brain, skull and the interface (the meninges), a comprehensive FEM model of TBI is still being studied. This study aims to present an optimized model of human head including the brain, skull, and the meninges after a comprehensive study of the previous models.... 

    X-FEM modeling of large plasticity deformation; A convergence study on various blending strategies for weak discontinuities

    , Article European Journal of Computational Mechanics ; Volume 24, Issue 3 , 2015 , Pages 79-106 ; 17797179 (ISSN) Khoei, A. R ; Vahab, M ; Ehsani, H ; Rafieerad, M ; Sharif University of Technology
    Taylor and Francis Ltd  2015
    In the extended finite element method (FEM), the transition elements between the enriched and standard elements, which are generally referred as the blending, or partially enriched elements, are often crucial for a good performance of the local partition of unity enrichments. In these elements, the enrichment function cannot be reproduced exactly due to the lack of a partition of unity, and blending elements produce unwanted terms into the approximation that cannot be compensated by the standard final element part of the approximation. In this paper, some optimal X-FEM-type methods reported in literature are employed to study the performance of blending elements in large plastic deformation... 

    An optimized axial flux variable reluctance resolver with concentric windings

    , Article 24th Iranian Conference on Electrical Engineering, ICEE 2016, 10 May 2016 through 12 May 2016 ; 2016 , Pages 1284-1290 ; 9781467387897 (ISBN) Tootoonchian, F ; Nasiri Gheidari, Z ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2016
    Radial flux variable reluctance resolvers (RFVR2s) are widely used in variety of applications. However, they suffer from an intrinsic error which is called static eccentricity (SE). Although most of the errors in the resolvers can be suppressed using electronic methods in resolver to digital (R/D) converters, static misalignment is an exception. In this paper an axial flux configuration is proposed for variable reluctance (VR) resolvers with concentric windings. Then the proposed structure is optimized to achieve the minimum sensitivity of accuracy against SE. The performance of the presented structure, so called axial flux variable reluctance resolver (AFVR2), is validated using 3-D time... 

    The effects of die geometry in tube channel pressing: Severe plastic deformation

    , Article Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications ; Volume 230, Issue 1 , 2016 , Pages 263-272 ; 14644207 (ISSN) Farshidi, MH ; Kazeminezhad, M ; Sharif University of Technology
    SAGE Publications Ltd 
    The effects of die geometry on the deformation behavior of aluminum 6061 alloy tube in a novel severe plastic deformation (SPD) process called tube channel pressing (TCP) were studied using the Abaqus 6.10 software. Using the optimized die geometry, 1 to 3 passes of TCP is imposed not only to validate the simulation results, but also to investigate the performance of TCP as a SPD process. The finite element method (FEM) simulation results show that the moderated plastic strain, the lower inhomogeneity in distribution of plastic strain, and the lower risk of fracture during process can be obtained using the proper die geometry. In addition, the imposed strain is a mixture of shear strain and... 

    Design, analysis, and prototyping of a new wound-rotor axial flux brushless resolver

    , Article IEEE Transactions on Energy Conversion ; Volume PP, Issue 99 , 2016 ; 08858969 (ISSN) Nasiri Gheidari, Z ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2016
    Resolvers are electromagnetic position sensors that are widely used in industrial applications. In this study, a new axial flux brushless resolver (AFBR) with a wound rotor is introduced. In the proposed resolver, the core of the rotary transformer (RT) is omitted, and an innovative design is used to supply the excitation winding of the resolver. The proposed resolver can be built with smaller dimensions, and its thermal stability and mechanical strength are increased compared with conventional AFBRs. The performance of the proposed structure is simulated and optimized by using a 3-D time-stepping finite element method. The effect of the leakage flux of the rotary transformer on the...