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finite-difference-methods
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Total 169 records
Lattice Approximation for Stochastic Partial Differential Equations
, M.Sc. Thesis Sharif University of Technology ; Zohuri Zangeneh, Bijan (Supervisor)Numerical Solution Of One-Dimensional Non-Fourier Bioheat Transfer Through Skin Tissue
, M.Sc. Thesis Sharif University of Technology ; 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 ; 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...
A Monte Carlo Method for Neutron Noise Calculation in the Frequency Domain
, M.Sc. Thesis Sharif University of Technology ; Vosoughi, Naser (Supervisor)
Abstract
Neutron noise equations, which are obtained by assuming small perturbations of macroscopic cross sections around a steady-state neutron field and by subsequently taking the Fourier transform in the frequency domain, have been usually solved by analytical techniques or by resorting to diffusion theory, but in this thesis, in order to increase of accuracy of neutron noise calculation, has been used transport approximation for neutron noise calculation and the Monte Carlo method has been used to solve transport equation of the neutron noise in the frequency domain. Since the transport equation of the neutron noise is a complex equation, a new Monte Carlo technique for treating complex-valued...
Numerical Simulation Cavitating Flows Using Compact Finite-difference Scheme
, M.Sc. Thesis Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract
In the study, the simulation of two-dimensional cavitating flows is performed by applying a high-order accurate numerical method to the preconditioned, homogenous, multiphase Navier-Stokes equations. The baseline differential equations system is comprised of the mixture volume, mixture momentum and constituent volume fraction equations. A coordinate transformation is applied and the resulting system of governing equations in curvilinear coordinates is discretized using a fourth-order compact finite-difference scheme. The high-order accurate numerical scheme employing the suitable linear and nonlinear filters to account for density jumps across the cavity interface is shown to yield an...
Development of Compact Finite-Difference Lattice Boltzmann Method for Solving Two-Phase Flows
, Ph.D. Dissertation Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract
In the present thesis, a high-order compact finite-difference lattice Boltzmann method (CFDLBM) is proposed and applied for an accurate and efficient numerical simulation of liquid-vapor two-phase flows. At first, the stability of the fourth-order CFDLBM is performed by using the von Neumann stability analysis for the D2Q7 and D2Q9 lattices. The stability analysis indicates that the CFDLBM proposed is stable and thus suitable for the simulation of high Reynolds number flows. The high-order CFDLBM is then developed and applied to accurately compute 2-D and 3-D incompressible flows in the Cartesian coordinates. Herein, the spatial derivatives in the lattice Boltzmann equation are discretized...
Numerical Simulation of 2D Compressible Cavitation Flow Using Compact Finite-Difference Method
, M.Sc. Thesis Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract
In the present study, the numerical simulation of 2D inviscid compressible cavitation flow is performed by using the compact finite-difference method. The problem formulation is based on the multiphase compressible Euler equations with the assumption of the homogeneous equilibrium model and the system of baseline differential equations is comprised of the continuity, momentum and energy equations for the vapor-liquid mixture. To complete the system of governing equations, the ideal gas relation is used for the vapor phase and the Tait relation is applied for the liquid phase, and therefore, the compressibility effects are considered for both the vapor and liquid phases. To analyze the flow...
Nonlinear Dynamic Analysis of Earth and Rockfill Dams Using the Finite Difference Method Considering the Effect of Vertical Earthquake Component
, M.Sc. Thesis Sharif University of Technology ; Haeri, Mohsen (Supervisor)
Abstract
Earth and rockfill dams are enormous three-dimensional structures constructed from earth and rockfill materials. They are mainly built for water supply, agricultural land irrigation, electricity generation, and flood control. Earthquake is one of the most significant natural hazards affecting the stability of these dams. Nowadays, with the development of computers and software, the seismic behavior of most dams are assessed by dynamic analysis. In a considerable part of technical literature, dynamic analysis of earth and rockfill dams have been performed by applying only the horizontal component of the earthquakes, and the effects of vertical component of the earthquakes have often been...
Numerical Study of Bearing Capacity of Shallow Foundations on Two-Layer Soils
, M.Sc. Thesis Sharif University of Technology ; Ahmadi, Mohammad Mahdi (Supervisor)
Abstract
The purpose of designing the foundation is to transfer the load of the structure to the subsoil without creating shear failure and additional settlement in the soil. Therefore, choosing the appropriate bearing capacity is an important point that should be considered in any project. Determining the bearing capacity of foundations is one of the topics that has long been considered by researchers and geotechnical engineering designers. For this reason, its design is not considered a new issue, but the application of new methods and the development of computers, raises new perspectives on this issue that justifies new studies.Most of the recent study, which have done so far on bearing capacity,...
Recuperator Design of a 100kW Aviation Gas Turbine and its Integrated Performance Analysis with the Aircraft
, M.Sc. Thesis Sharif University of Technology ; Ghorbanian, Kaveh (Supervisor)
Abstract
The increasing need for more efficient and environmentally friendly microturbines necessitates the utilization of compact recuperators resulting in lower fuel consumption and emissions. The goal of this research is to determine the performance behavior of a primary surface recuperator to be incorporated in a 100 kW microturbine. Primary surface recuperator, known for relatively favorable characteristics in heat transfer, low weight, and high efficiency is considered as a candidate in aviation engines. In this research, a computational model for heat transfer and pressure losses is used for the design optimization of annular involute-profile cross wavy primary surface recuperators in...
Development of a Computer Code for Thermo Hydraulics Analysis of Prismatic High Temperature Gas Cooled Reactors
, M.Sc. Thesis Sharif University of Technology ; 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...
Development of a Computer Code for Thermal Hydraulic Design of a High Temperature Gas Cooled Reactor Core
, M.Sc. Thesis Sharif University of Technology ; 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...
Flow Simulation for Vacuum-assisted Resin Transfer Molding in Manufacturing of Composite Structures
, M.Sc. Thesis Sharif University of Technology ; Abedian, Ali (Supervisor)
Abstract
One of the common and efficient methods in the construction of large-scale structures from composites is the Vacuum Assisted Resin Transfer Molding (VARTM) method, which is widely used in the automotive industry, wind turbine blades, warships and pleasure boats, etc. VARTM is one of the liquid molding methods in which one side of the closed mold is replaced with a vacuum bag and the resin flows into the mold only with the help of air pressure (pressure of one atmosphere). One of the main challenges in the vacuum resin molding process is to be aware of the physics governing the flow motion in the porous mold so that the dry spots formed in the mold can be located accordingly. On the other...
Numerical Simulation of One-Dimensional Compressible Flow with Real Gas Effects by Solving Boltzmann Equation Using High-Order Accurate Finitedifference Method
, M.Sc. Thesis Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract
In this study, the Shokov-BGK model of the Boltzmann equation is reformulated and generalized to consider the real gas effects. At first, the formulation is performed to consider an arbitrary specific heats ratio and the correct Prandtl number for polyatomic gases. Here, the resulting equations of the present formulation are numerically solved by applying the high-order finite-difference weighted essentially non-oscillatory (WENO) scheme. The present solution method is tested by computing the one-dimension Reiman problem with different specific heats ratios for a wide range of the Knudsen numbers. The results are compared with the available gas-kinetic results which show good agreement. It...
Numerical Modeling of Cone Penetration Tests in Saturated Clayey Soil under Undrained Conditions
, M.Sc. Thesis Sharif University of Technology ; Ahmadi، Mohammad Mehdi (Supervisor)
Abstract
This study aims to numerical modeling of piezocone penetration test (CPTu) in saturated clayey soils under undrained conditions using FLAC-2D software. According to the available studies, measuring excess pore water pressure during the piezocone penetration test can play an important role in determining the characteristics and engineering parameters of clayey soils. In many geotechnical problems, the initial state of existing stresses in the ground and are an important parameter that must be known for designs and analysis. The relationship between vertical and horizontal effective stress under zero lateral deformation is usually expressed by the coefficient of lateral earth pressure at...
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 ; 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 ; 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...
Numerical solution of homogeneous double pipe heat exchanger: Dynamic modeling
, Article Scientia Iranica ; Volume 21, Issue 2 , 2014 , pp. 449-455 ; ISSN: 10263098 ; Kazemi, Y ; Fattahi, M ; Sharif University of Technology
Abstract
Dynamic modeling of a double-pipe heat exchanger is the subject of the current study. The basis of this study is the same velocity of vapor and liquid phases or, in other words, homogeneous phase, in the annulus part of the exchanger. The model can predict the temperature and vapor quality along the axial pipe from the pipe inlet up to a distance where steady state conditions are achieved. The simulation is conducted for two modes of co- and counter-flow in a one dimensional transient system. The physical properties of water are estimated from empirical correlation and a saturated vapor table with cubic spline interpolation. The exchanger model, which is a set of Ordinary Differential...
An experimental-based numerical simulation of two phase flow through porous media: A comparative study on finite element and finite difference schemes
, Article Petroleum Science and Technology ; Volume 31, Issue 18 , 2013 , Pages 1881-1890 ; 10916466 (ISSN) ; Kharrat, R ; Ghazanfari, M. H ; Sharif University of Technology
2013
Abstract
In this study, the nonlinear partial differential equations governing two phase flow through porous media are solved using two different methods, namely, finite difference and finite element. The capillary pressure term is considered in the mathematical model. The numerical results on a 2-D test case are then compared with the experimental drainage process and water flooding performed on a glass type micromodel. Based on the obtained results, finite difference technique needs less computational time for solving governing equations of two phase flow, but findings of this method show less agreement with the experimental data. The finite element scheme was found to be more adequate and its...
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) ; 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...