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    A new parallel Gauss-Seidel method based on alternating group explicit method and domain decomposition method

    , Article Applied Mathematics and Computation ; Volume 188, Issue 1 , 2007 , Pages 713-719 ; 00963003 (ISSN) Tavakoli, R ; Davami, P ; Sharif University of Technology
    2007
    Abstract
    A new parallel Gauss-Seidel method is presented for solution of system of linear equations related to finite difference discretization of partial differential equations. This method is based on domain decomposition method and local coupling between interfaces of neighbor sub-domains, same as alternating group explicit method. This method is convergent and number of iterations for achieving convergence criteria is near the original Gauss-Seidel method (sometimes better and sometimes worse but difference is very small). The convergence theory is discussed in details. Numerical results are given to justify the convergence and performance of the proposed iterative method. © 2006 Elsevier Inc.... 

    A higher-order Boussinesq-type model with moving bottom boundary: Applications to submarine landslide tsunami waves

    , Article International Journal for Numerical Methods in Fluids ; Volume 53, Issue 6 , 2007 , Pages 1019-1048 ; 02712091 (ISSN) Ataie Ashtiani, B ; Najafi Jilani, A ; Sharif University of Technology
    2007
    Abstract
    A two-dimensional depth-integrated numerical model is developed using a fourth-order Boussinesq approximation for an arbitrary time-variable bottom boundary and is applied for submarine-landslide-generated waves. The mathematical formulation of model is an extension of (4,4) Padé approximant for moving bottom boundary. The mathematical formulations are derived based on a higher-order perturbation analysis using the expanded form of velocity components. A sixth-order multi-step finite difference method is applied for spatial discretization and a sixth-order Runge-Kutta method is applied for temporal discretization of the higher-order depth-integrated governing equations and boundary... 

    Implementation of high-order compact schemes to the iterative parabolized Navier-Stokes equations

    , Article 25th Congress of the International Council of the Aeronautical Sciences 2006, Hamburg, 3 September 2006 through 8 September 2006 ; Volume 3 , 2006 , Pages 1628-1643 Esfahanian, V ; Hejranfar, K ; Darian, H. M ; Sharif University of Technology
    Curran Associates Inc  2006
    Abstract
    The numerical solution of 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 the 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... 

    BEM modeling of surface water wave motion with laminar boundary layers

    , Article Engineering Analysis with Boundary Elements ; Volume 30, Issue 1 , 2006 , Pages 14-21 ; 09557997 (ISSN) Jamali, M ; Sharif University of Technology
    2006
    Abstract
    This study is concerned with numerical modeling of viscous surface wave motion using boundary element method (BEM). The equations of motion for thin boundary layers at the solid surfaces are coupled with the potential flow in the bulk of the fluid, and a mixed BEM-finite difference technique is used to obtain the viscosity-related quantities such as wave damping rate, shear stress, and velocity distribution inside the boundary layer. The technique is presented for standing surface wave motion. An excellent agreement is obtained between the numerical predictions and the previous results. The extension to other free surface problems is straightforward. © 2005 Elsevier Ltd. All rights reserved  

    Numerical simulation of liquid/gas phase flow during mold filling

    , Article Computer Methods in Applied Mechanics and Engineering ; Volume 196, Issue 1-3 , 2006 , Pages 697-713 ; 00457825 (ISSN) Tavakoli, R ; Babaei, R ; Varahram, N ; Davami, P ; Sharif University of Technology
    2006
    Abstract
    A numerical model for simulation of liquid/gas phase flow during mold filling is presented. The incompressible Navier-Stokes equations are discretized on a fixed Cartesian mesh with finite difference method. The fractional-step scheme is employed for enforcing incompressibility constraint. The free surface effects are calculated using the volume of fluid method based on the piecewise-linear interface reconstruction and split Lagrangian advection of volume fraction field. Adding limited compressibility to the gas phase led to improvement in convergence rate of Poisson equation solver (about 2-fold). This new concept permits simulation of two-phase incompressible free surface flow during mold... 

    An approximated solution to the 2D incompressible Navier-Stokes equations via Adomian Decomposition Method

    , Article WSEAS Transactions on Mathematics ; Volume 5, Issue 7 , 2006 , Pages 878-885 ; 11092769 (ISSN) Najafi, M ; Taeibi Rahni, M ; Aavani, K ; Sharif University of Technology
    2006
    Abstract
    The Adomian Decomposition Method (ADM) for solving the highly non-linear vorticity-stream function formulation of 2D incompressible Navier-Stokes equations has been implemented. The analysis is accompanied by numerical boundary conditions. Also, numerical simulation, using finite difference method (FDM), is performed for comparison purposes. The obtained results only for few terms of the expansion are presented. Because present software such as Mathematica/Maple can not calculate many terms (for example: up to 10 terms) of solution and then ADM approach of this problem is an open problem case  

    A study on mutual interaction between atomistic and macroscopic phenomena during electrochemical processes using FD-KMC model: Application to CV test in simple copper sulfate bath

    , Article Journal of Electroanalytical Chemistry ; Volume 592, Issue 1 , 2006 , Pages 95-102 ; 15726657 (ISSN) Saedi, A ; Sharif University of Technology
    Elsevier  2006
    Abstract
    A multiscale FD-KMC model has been developed to simulate the cyclic voltammetry test of a copper electrode in simple copper sulfate bath. In this coupled model, the FD code provides the cupric ion concentration on OHP for KMC code, while the KMC code provides the electrochemical properties of the copper electrode (surface activity and rate constants of redox reactions) as an input data for FD code. The changes in the electrode properties due to the atomistic phenomena (deposition dissolution and surface diffusion) have been studied for the present potentiodynamic system. The results showed that the CV process consists of some distinct stages, so that the electrode exhibits a specific... 

    A coupled boundary element-finite difference model of surface wave motion over a wall turbulent flow

    , Article International Journal for Numerical Methods in Fluids ; Volume 51, Issue 4 , 2006 , Pages 371-383 ; 02712091 (ISSN) Jamali, M ; Sharif University of Technology
    2006
    Abstract
    An effective numerical technique is presented to model turbulent motion of a standing surface wave in a tank. The equations of motion for turbulent boundary layers at the solid surfaces are coupled with the potential flow in the bulk of the fluid, and a mixed BEM-finite difference technique is used to model the wave motion and the corresponding boundary layer flow. A mixing-length theory is used for turbulence modelling. The model results are in good agreement with previous physical and numerical experiments. Although the technique is presented for a standing surface wave, it can be easily applied to other free surface problems. Copyright © 2005 John Wiley & Sons, Ltd  

    A novel numerical solution to the diffraction term in the KZK nonlinear wave equation

    , Article Proceedings of the 38th Annual Symposium of Ultrasonic Industry Association, UIA 2009, 23 March 2009 through 25 March 2009, Vancouver, BC ; 2009 ; 9781424464296 (ISBN) Hajihasani, M ; Farjami, Y ; Gharibzadeh, S ; Tavakkoli, J ; Sharif University of Technology
    Abstract
    Nonlinear ultrasound modeling is finding an increasing number of applications in both medical and industrial areas where due to high pressure amplitudes the effects of nonlinear propagation are no longer negligible. Taking nonlinear effects into account makes the ultrasound beam analysis more accurate in these applications. One of the most widely used nonlinear models for propagation of 3D diffractive sound beams in dissipative media is the KZK (Khokhlov, Kuznetsov, Zabolotskaya) parabolic nonlinear wave equation. Various numerical algorithms have been developed to solve the KZK equation. Generally, these algorithms fall into one of three main categories: frequency domain, time domain and... 

    Modeling and Characterizing Transient Behavior of Distillation Columns with Travelling Wave Theory

    , M.Sc. Thesis Sharif University of Technology Hemmati Alam, Narjes (Author) ; Pishvaie, Mahmoud Reza (Supervisor)
    Abstract
    Simulation and controlling nonlinear process is one of the challenging problems in academic and industrial research. Saving data for keeping history of process or arising number of calculation for optimization in control design, is forcing to decrease number of equation or order of system. One of the methods to decrease the order of distillation process is using the travelling wave theory. This solution shows god accuracy for simulation the behavior of distillation column. On the other hand finite difference method as a solver for distillation equation takes some time to converge to steady state condition and the numbers of calculation in this method are high. Finite difference method is... 

    Development of a Computer Code for Thermo Hydraulics Analysis of Prismatic High Temperature Gas Cooled Reactors

    , M.Sc. Thesis Sharif University of Technology Naderi, Mohammad Hossein (Author) ; Ghofrani, Mohammad Bagher (Supervisor) ; Jafari, Jalil (Supervisor)
    Abstract
    A prismatic high temperature gas-cooled reactor (HTGR), which is a graphite moderated, helium-cooled reactor, is a promising candidate for next generation nuclear power plant in that it enables applications, such as hydrogen production or process heat for petrochemical by supplying heat with core outlet temperatures as high as 1000°C. A Thermal Hydraulic Analysis Code (THAC) for gas-cooled reactors has been developed. THAC implicitly solves heat transfer equation of fuel, graphite block and helium. Three types of fuel pins were considered; solid fuel pin, fuel pins with inside holes and annular fuels with coolant flow from its inside and outside surfaces. THAC predicts axial and radial... 

    Design and Implementation of Near Field Excitation System for Spectroscopy of Biological Species

    , Ph.D. Dissertation Sharif University of Technology Sasanpour, Pezhman (Author) ; Rashidian, Bizhan (Supervisor) ; Vossoughi, Manouchehr (Supervisor) ; Shahrokhian, Saeed (Co-Advisor)
    Abstract
    The main goal of this project is analysis, design and implementation of scanning near field optical system for detection of biological species. The activities fall in two main category. Theoretical and experimental. In theoretical part, after studying different models describing near field interaction, we have developed software for computationally analysis of nonlinear interaction of light with nanostructures, considering third order nonlinear susceptibility and dispersion behavior of permittivity for metallic nanostructures. The software implements three dimensional finite difference time domain (FDTD) method for analysis of interaction of electromagnetic wave with matter. In developed... 

    Development of a Computer Code for Thermal Hydraulic Design of a High Temperature Gas Cooled Reactor Core

    , M.Sc. Thesis Sharif University of Technology Khosravi Mirzaee, Morteza (Author) ; Ghofrani, Mohammad Bagher (Supervisor) ; Jafari, Jalil (Supervisor)
    Abstract
    High temperature gas cooled reactors (HTGR) are one of the most promising reactors in the new generation of world commercial reactors. They are divided into two main categories: Prismatic gas cooled reactors and pebble bed gas cooled reactors. These reactors have many advantages, such as inherent safety, high thermodynamic efficiency and the possibility of producing hydrogen. One of the most important challenges in developing these reactors is providing appropriate codes in design and simulating their performance. Two codes have been developed in this thesis. The first, THFAM, is a steady state thermal hydraulic code which helps in analyzing a fuel assembly. The second, named THCM is... 

    Modeling of Liquid-Vapor Two Phase Flow through Nozzle

    , M.Sc. Thesis Sharif University of Technology Varzideh, Mohammad (Author) ; Nouri Borujerdi, Ali (Supervisor)
    Abstract
    This thesis is about modeling of liquid-vapor two phase flows through nozzle. Liquid-vapor two phase flow is very applicable in industries such as boilers, expansion valves, refrigeration and sudden failures in pipelines. Two models are used for modeling of fluid flow through nozzle, transient and steady state. In Both model the solution field is considered as saturated liquid and vapor and the mass, momentum and energy equations as well as equation of state is used for describing of fluid flow properties. Homogeneous equilibrium model is used and for complete modeling of fluid flow heat transfer and friction force is also considered.
    Numerical solutions are used for solving of the... 

    An Investigation on the Effects of Liquefaction-Induced Lateral Spreading on Deep Foundations Using Finite Difference Method

    , M.Sc. Thesis Sharif University of Technology Afzal Soltani, Sina (Author) ; Haeri, Mohsen (Supervisor)
    Abstract
    Liquefaction is an important phenomenon in geotechnical engineering which can cause severe damages to structures. Liquefaction-induced lateral spreading is defined as the lateral displacement in mild slopes or level grounds ending in free faces (such as quay walls) triggered by liquefaction in subsurface soil layers. During recent years, extensive studies have been conducted around the world documenting liquefaction induced lateral spreading and its effects on deep foundations. In the present study, a series of shaking table experiments which were previously conducted at Sharif University of Technology are numerically simulated using the three dimensional finite difference based program,... 

    Development of Characteristic Boundary Conditions with Artificial Compressibility Method by Compact Finite-Difference Discretization

    , Ph.D. Dissertation Sharif University of Technology Parseh, Kaveh (Author) ; Hejranfar, Kazem (Supervisor)
    Abstract
    In the present study, the preconditioned incompressible Navier‐Stokes equations with the artificial compressibility (AC) method formulated in the generalized curvilinear coordinates are numerically solved by using a high‐order compact finite‐difference scheme for accurately and efficiently computing the incompressible flows. A fourth‐order compact finite‐difference scheme is utilized to discretize the spatial derivative terms of the resulting system of equations and the time integration is carried out based on the dual time‐stepping method. The capability of the proposed solution methodology for computing the steady and unsteady incompressible viscous flows in a wide range of Reynolds... 

    A Two-dimensional Modeling and Numerical Simulation of PEM Fuel Cell

    , M.Sc. Thesis Sharif University of Technology Bayat, Maziyar (Author) ; Taghizadeh Manzari, Mehrdad (Supervisor) ; Roshandel, Ramin (Supervisor)
    Abstract
    In this research, a simple yet efficient two-dimensional model of proton exchange membrane fuel cell (PEMFC) is developed using stream function-vorticity formulation. The model accounts for the fluid flow and masstransport processes in cathode gas channel and gas diffuser layer. The governing equations are decoupled and solved usingtwo efficient approaches, Alternating Direction Implicit (ADI) and False Transient Method (FTM) in a modified geometry to simulate the fully-developed condition consistently. An in-house code was developed to perform a parametric study of fuel cell performance. The results show the variations of important parameters along the cathode channel such as velocity... 

    A high-order compact finite-difference lattice Boltzmann method for simulation of steady and unsteady incompressible flows

    , Article International Journal for Numerical Methods in Fluids ; Vol. 75, Issue. 10 , 2014 , Pages 713-746 ; ISSN: 02712091 Hejranfar, K ; Ezzatneshan, E ; Sharif University of Technology
    Abstract
    A high-order compact finite-difference lattice Boltzmann method (CFDLBM) is proposed and applied to accurately compute steady and unsteady incompressible flows. Herein, the spatial derivatives in the lattice Boltzmann equation are discretized by using the fourth-order compact FD scheme, and the temporal term is discretized with the fourth-order Runge-Kutta scheme to provide an accurate and efficient incompressible flow solver. A high-order spectral-type low-pass compact filter is used to stabilize the numerical solution. An iterative initialization procedure is presented and applied to generate consistent initial conditions for the simulation of unsteady flows. A sensitivity study is also... 

    Mixed-convection flow of Al2O3-H2O nanofluid in a channel partially filled with porous metal foam: Experimental and numerical study

    , Article Experimental Thermal and Fluid Science ; Vol. 53 , February , 2014 , pp. 49-56 ; ISSN: 08941777 Hajipour, M ; Molaei Dehkordi, A ; Sharif University of Technology
    Abstract
    Mixed-convection flow of nanofluids inside a vertical rectangular channel partially filled with open-cell metal foam and subject to a constant wall-heat flux was investigated experimentally and numerically. Al2O3-water nanofluids with different concentrations were prepared and their stability was examined using UV-Vis spectroscopy. Dynamic light scattering method was used to determine particle size distribution of the nanofluid feedstock. The outlet temperature and pressure drop were measured for different nanofluid flow rates (i.e., Reynolds number values). In the numerical section, a two-dimensional volume-averaged form of the governing equations was used. The velocity and temperature... 

    FPGA-based fast detection with reduced sensor count for a fault-tolerant three-phase converter

    , Article IEEE Transactions on Industrial Informatics ; Volume 9, Issue 3 , 2013 , Pages 1343-1350 ; 15513203 (ISSN) Mahmoud, M ; Philippe, P ; Shahrokh, S ; Mohammad Reza, M. R ; Sharif University of Technology
    2013
    Abstract
    Fast fault detection (FD) and reconfiguration is necessary for fault tolerant power electronic converters in safety critical applications to prevent further damage and to make the continuity of service possible. The aim of this study is to minimize the number of the used additional voltage sensors in a fault tolerant three-phase converter. In this paper, first a practical implementation of a very fast FD scheme with reduced sensor number is discussed. Then, an optimization in this scheme is also presented to decrease the detection time. For FD, special time and voltage criterion are applied to observe the error in the estimated phase-to-phase voltages for a specific period of time. The...