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    Development of a 2-D 2-group neutron noise simulator for hexagonal geometries

    , Article Annals of Nuclear Energy ; Volume 37, Issue 8 , 2010 , Pages 1089-1100 ; 03064549 (ISSN) Malmir, H ; Vosoughi, N ; Zahedinejad, E ; Sharif University of Technology
    Abstract
    In this paper, the development of a neutron noise simulator for hexagonal-structured reactor cores using both the forward and the adjoint methods is reported. The spatial discretisation of both 2-D 2-group static and dynamic equations is based on a developed box-scheme finite difference method for hexagonal mesh boxes. Using the power iteration method for the static calculations, the 2-group neutron flux and its adjoint with the corresponding eigenvalues are obtained by the developed static simulator. The results are then benchmarked against the well-known CITATION computer code. The dynamic calculations are performed in the frequency domain which leads to discarding of the time... 

    Enhanced finite difference scheme for the neutron diffusion equation using the importance function

    , Article Annals of Nuclear Energy ; Volume 96 , 2016 , Pages 412-421 ; 03064549 (ISSN) Vagheian, M ; Vosoughi, N ; Gharib, M ; Sharif University of Technology
    Elsevier Ltd  2016
    Abstract
    Mesh point positions in Finite Difference Method (FDM) of discretization for the neutron diffusion equation can remarkably affect the averaged neutron fluxes as well as the effective multiplication factor. In this study, by aid of improving the mesh point positions, an enhanced finite difference scheme for the neutron diffusion equation is proposed based on the neutron importance function. In order to determine the neutron importance function, the adjoint (backward) neutron diffusion calculations are performed in the same procedure as for the forward calculations. Considering the neutron importance function, the mesh points can be improved through the entire reactor core. Accordingly, in... 

    Comparison of finite difference schemes for water flow in unsaturated soils

    , Article World Academy of Science, Engineering and Technology ; Volume 40 , 2009 , Pages 21-25 ; 2010376X (ISSN) Taheri Shahraiyni, H ; Ataie Ashtiani, B ; Sharif University of Technology
    2009
    Abstract
    Flow movement in unsaturated soil can be expressed by a partial differential equation, named Richards equation. The objective of this study is the finding of an appropriate implicit numerical solution for head based Richards equation. Some of the well known finite difference schemes (fully implicit, Crank Nicolson and Runge-Kutta) have been utilized in this study. In addition, the effects of different approximations of moisture capacity function, convergence criteria and time stepping methods were evaluated. Two different infiltration problems were solved to investigate the performance of different schemes. These problems include of vertical water flow in a wet and very dry soils. The... 

    Revealing electrical stresses acting on the surface of protoplast cells under electric field

    , Article European Journal of Mechanics, B/Fluids ; Volume 76 , 2019 , Pages 292-302 ; 09977546 (ISSN) Dastani, K ; Moghimi Zand, M ; Hadi, A ; Sharif University of Technology
    Elsevier Ltd  2019
    Abstract
    When cells exposed to an electric field, localized changes in the distribution of the electric field will be induced and these changes in turn lead to electrical stresses on cell surface. The electrical stresses play a key role in the cell membrane structural changes which leads to important phenomena like hydrophilic pores formation on the cell membrane resulting in the cell permeability. In this work, protoplast cell interaction with direct current (DC) electric field is investigated. The electrical stresses acted on the cell membrane in the presence of electric field are investigated numerically by a modified finite difference method, fast Immersed Interface Method (IIM). Exact solution... 

    Implementation of high-order compact finite-difference method to parabolized Navier-Stokes schemes

    , Article International Journal for Numerical Methods in Fluids ; Volume 58, Issue 6 , 2008 , Pages 659-685 ; 02712091 (ISSN) Esfahanian, V ; Hejranfar, K ; Mahmoodi Darian, H ; Sharif University of Technology
    2008
    Abstract
    The numerical solution to the parabolized Navier-Stokes (PNS) and globally iterated PNS (IPNS) equations for accurate computation of hypersonic axisymmetric flowfields is obtained by using the fourth-order compact finite-difference method. The PNS and IPNS equations in the general curvilinear coordinates are solved by using the implicit finite-difference algorithm of Beam and Warming type with a high-order compact accuracy. A shock-fitting procedure is utilized in both compact PNS and IPNS schemes to obtain accurate solutions in the vicinity of the shock. The main advantage of the present formulation is that the basic flow variables and their first and second derivatives are simultaneously... 

    Numerical Analysis of Stresses and Steady State Creep Strain Rates Fields of a Short Fibre Composite

    , M.Sc. Thesis Sharif University of Technology Ghavami, Ali (Author) ; Abedian, Ali (Supervisor)
    Abstract
    A finite difference technique is developed to predict the second stage creep displacement rates and stress analysis of a short fiber metal matrix composite subjecting to a constant axial load. The exponential law is adopted to describe the matrix creep behavior. Also, a method for prediction of interfacial debonding at fiber/matrix interface is developed using a stress based method. The obtained results could greatly help to better understand the flow pattern of matrix material and the load transfer mechanism between fiber and matrix. The stress components and strain rates are also validated by the available FEM and experimental results  

    Localization of a Postulated Noise in VVER-1000 Reactor Core Using Neutron Noise Analysis Methods

    , M.Sc. Thesis Sharif University of Technology Malmir, Hessam (Author) ; Vosoughi, Naser (Supervisor)
    Abstract
    In this thesis, localization of a postulated noise from limited neutron detectors sparsely distributed throughout the core of a typical VVER-1000 reactor is investigated. For this purpose, developing a 2-D neutron noise simulator for hexagonal geometries based on the 2-group diffusion approximation, the reactor dynamic transfer function is calculated. The box-scheme finite difference method is first developed for hexagonal geometries, to be used for spatial discretisation of both 2-D 2-group static and noise diffusion equations. Using the discretised static equations, a 2-D 2-group static simulator (HEXDIF-2) is developed which its results are benchmarked against the well-known CITATION... 

    Development of a model for Hydro-Mechanical Deep Drawing Process to Analyze the Effects of Assumptions and Parameters

    , M.Sc. Thesis Sharif University of Technology Taghipour, Ehsan (Author) ; Assempour, Ahmad (Supervisor)
    Abstract
    It is the goal of this thesis to develop an analytical model for the hydro-mechanical deep drawing (HDD) process of an axisymmetric sheet metal with the fixed gap method to evaluate the effects of some assumptions such as: proportional loading, plane stress, and constant thickness conditions. The effect of parameters on the HDD process is also studied. The main model is developed with considering the normal stress and part thickness change, non-proportional loading, bending and unbending effects at the top of the cup wall. The interrelationships between geometrical and mechanical variables are obtained in the finite difference form based on the incremental strain theory, thereby being solved... 

    Developing a Compact Finite Difference Method for Solving Fluid - Solid Interaction in Incompressible Flow

    , M.Sc. Thesis Sharif University of Technology Parseh, Kaveh (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In this study, fluid-solid interaction (FSI) is simulated computationally by using a high-order accurate numerical method. The two-dimensional incompressible viscous flows are considered in the fluid domain. The primary problem with solutions of the incompressible Navier–Stokes equations is the difficulty of coupling changes in the velocity field with changes in the pressure field while satisfying the continuity equation. Herein, the artificial compressibility method is used to overcome this difficulty. Preconditioning is implemented to reduce the stiffness of the system of equations to increase the convergence rate of the solution. Using preconditioning, physical solutions even at low... 

    Comparison and Evaluation of the Performance of some Fundamental Models for Simulation of Naturally Fractured Hydrocarbon Reservoirs

    , M.Sc. Thesis Sharif University of Technology Mahmoudi, Siamak (Author) ; Taghizadeh Manzari, Mehrdad (Supervisor)
    Abstract
    Fractured reservoirs show a different behavior from common reservoirs because of the existence of a broad network of fractures. This phenomenon makes it necessary to apply special methods for fractured reservoirs in the procedure of reservoir simulation. Since twenty percent of petroleum content in the world is buried in fractured reservoirs, investigating these reservoirs is of great importance.
    The first step in simulation of these kinds of reservoirs is to come up with a geometrical model which can be used to take the fracture network influence into account. In the course for reaching such an objective, various models have been developed which are based on specific assumptions and in... 

    A Multiscale Moving Boundary Model For Cancer Invasion

    , M.Sc. Thesis Sharif University of Technology Mohammad Mirzaei, Navid (Author) ; Fotouhi Firoozabad, Morteza (Supervisor)
    Abstract
    Cancer invasion of tissue is a key aspect of the growth and spread of cancer and is crucial in the process of metastatic spread i.e. the growth of secondary cancers. Invasion consists in cancer cells secreting various matrix degrading enzymes (MDEs) which destroy the surronding tissue or extracellular matrix (ECM). Through a combination of proliferation and migration, the cancer cells then actively spread locally into the surrounding tissue. Thus processes occuring at the level of individual cells eventually give rise to processes occuring at the tissue level. In this thesis we introduce a new type of multiscale model describing the process of cancer invasion of tissue.Our multiscale model... 

    Development of WENO Finite Difference Lattice Boltzmann Method for Simulation of 2D Incompressible Laminar and Turbulent Flows

    , M.Sc. Thesis Sharif University of Technology Saadat, Mohammad Hossein (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In the present study, the numerical simulation of incompressible laminar and turbulent flows using a high-order finite difference lattice Boltzmann method is presented. To handle curved geometries with non uniform grids, the incompressible form of lattice Boltzmann equation is transformed into the generalized curvilinear coordinates and the spatial derivatives of the resulting equation are discretized using the fifth-order WENO scheme. The advantage of using the WENO-LBM developed is that it needs less number of grid points and remains stable even at high Reynolds number flows. For the temporal term, the fourth-order explicit Rung-Kutta scheme is adopted for laminar flow calculations and... 

    Investigation of Dynamic Behavior of Beams with Different Supports under Moving Vehicles

    , M.Sc. Thesis Sharif University of Technology Samanipour, Kianoosh (Author) ; Vafai, Abolhassan (Supervisor) ; Esmaeil Pourestekanchi, Homayun (Co-Advisor)
    Abstract
    With the transportation progress and appearance of transit industry, necessity of modern vehicles redounded to appearance of heavier trucks with higher speeds, moving on the roads. In addition, with the progress in mechanical engineering and automobile industry, appearance of such trucks is growing increasingly. So, bridges as one of the structures that civil engineers design and construct, nowadays are subjected to higher moving dynamic loads in comparison with the past. As a result, lots of investigation and researches in the universities and institutions all over the world are being conducting on the effects of the vehicle speeds on the dynamic stresses of the bridges. Bridge codes... 

    Soil-structure Interaction in Geothermal Foundations

    , M.Sc. Thesis Sharif University of Technology Moradshahi, Aria (Author) ; Khosravi, Ali (Supervisor)
    Abstract
    Regarding the issue that significant amount of energy consumption in the world is dedicated to heating and cooling of the buildings, by using traditional methods of heating and cooling, the environment is facing serious problems like green house gases. There were various techniques for decreasing the amount of contaminants stem from this process. Heat-exchanger energy piles are one of the most common methods that will result in economic usage of energy resources. Assessing the long-term behavior of the energy piles requires comprehensive understanding of the complex interaction between soil and pile subjected to mechanical and thermal loadings. Several numerical and analytical methods have... 

    Numerical Solution of Two-dimensional Compressible Flow Using Immersed Boundary Method with Compact Finite Difference Scheme

    , M.Sc. Thesis Sharif University of Technology Mashayekh, Erfan (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In this study, the viscous compressible flow is simulated over two-dimensional geometries by using the immersed boundary method and applying a high-order accurate numerical scheme. A fourth-order compact finite-difference scheme is used to accurately discretize the spatial derivative terms of the governing equations and the time integration is performed by the fourth-order Runge–Kutta scheme. To regularize the numerical solution and eliminate spurious modes due to unresolved scales, nonlinearities and inaccuracies in implementing boundary conditions, high-order low-pass compact filters are applied. A uniform Cartesian grid that is not coincident with the body surface is used and the boundary... 

    A Parametric Study of Geosynthetic Reinforced Soil (GRS) Low Height Walls with Concrete Block Facing in FLAC Software

    , M.Sc. Thesis Sharif University of Technology Selseleh, Amin (Author) ; Pak, Ali (Supervisor)
    Abstract
    Because of seismic flexibility, aesthetics, economic advantage and rapid construction of reinforced soil walls, application of these walls has raised tremendously since 1970’s. The early reinforced soil retaining walls used metallic srips to reinforce the soil with precast concrete panels as facing, however, since 1990’s using of geosynthetics to reinforce these walls with modular concrete block facing have replaced the old fashion. In this study, a finite difference code was developed in FLAC software. After verification of the numerical modeling procedure, a wall with 3.6m height reinforced by geosynthetics was simulated. In the course of numerical simulations the stage of counstruction,... 

    Numerical Simulation of 2D Panel Flutter in Compressible Flow using Compact Finite-Difference Method

    , M.Sc. Thesis Sharif University of Technology Vafaei Sefti, Maryam (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In the present study, the numerical simulation of the panel flutter in compressible inviscid flow is performed by the compact finite difference method. For this purpose, the 2D compressible Euler equations written in the arbitrary Lagrange-Eulerian form are considered and the resulting system of equations in the generalized curvilinear coordinates is solved by the fourth-order compact finite-difference method. An appropriate nonlinear filter is applied for the shock capturing and for the solution to be stable. The governing equation for the panel is also numerically solved by using the fourth-order compact finite difference method. The time integration in the flow domain is made by the... 

    Lattice Approximation for Stochastic Partial Differential Equations

    , M.Sc. Thesis Sharif University of Technology Mohammadian, Sogol (Author) ; Zohuri Zangeneh, Bijan (Supervisor)

    Numerical Solution Of One-Dimensional Non-Fourier Bioheat Transfer Through Skin Tissue

    , M.Sc. Thesis Sharif University of Technology Fazel, Zeynab (Author) ; Taghizadeh Manzari, Mehrdad (Supervisor)
    Abstract
    Innovations in laser, microwaves, and similar technologies have significantly advanced thermal treatments for diseases or even injuries concerning skin tissue. For a thorough understanding in the underlying mechanisms of bioheat transfer behavior of skin,a1D unsteady non-dimensional hyperbolic model of heat transfer through this tissue with metabolic heat generation which is subject to specific boundary conditions, is solved numerically using the finite difference method. A thermal shock is generated at the base of the tissue, which moves forward with a finite speed. A Numerical solution for a simple one-layer skin tissue is obtained. Then, the effects of various parameters, time step,... 

    Development of Compact Finite Difference Boltzmann Method for Simulating Compressible Rarefied Gas Flow

    , M.Sc. Thesis Sharif University of Technology Alemi Arani, Ali (Author) ; Hejranfar, Kazem (Supervisor) ; Fouladi, Nematollah (Co-Supervisor)
    Abstract
    In this work, a high-order accurate gas kinetic scheme based on the compact finite-difference Boltzmann method (CFDBM) is developed and applied for simulating the compressible rarefied gas flows. Here, the Shakhov model of the Boltzmann equation is considered and the spatial derivative term in the resulting equation is discretized by using the fourth-order compact finite-difference method and the time integration is performed by using the third-order TVD Runge-Kutta method. A filtering procedure with three discontinuity-detecting sensors is applied and examined for the stabilization of the solution method especially for the problems involving the discontinuity regions such as the shock. The...