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finite-difference-method
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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...
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...
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...
Open-and short-circuit switch fault diagnosis for nonisolated DC-DC converters using field programmable gate array
, Article IEEE Transactions on Industrial Electronics ; Volume 60, Issue 9 , October , 2013 , Pages 4136-4146 ; 02780046 (ISSN) ; Jamshidpour, E ; Poure, P ; Saadate, S ; Zolghadri, M. R ; Sharif University of Technology
2013
Abstract
Fault detection (FD) in power electronic converters is necessary in embedded and safety critical applications to prevent further damage. Fast FD is a mandatory step in order to make a suitable response to a fault in one of the semiconductor devices. The aim of this study is to present a fast yet robust method for fault diagnosis in nonisolated dc-dc converters. FD is based on time and current criteria which observe the slope of the inductor current over the time. It is realized by using a hybrid structure via coordinated operation of two FD subsystems that work in parallel. No additional sensors, which increase system cost and reduce reliability, are required for this detection method. For...
The dynamic pull-in instability and snap-through behavior of initially curved microbeams
, Article Mechanics of Advanced Materials and Structures ; Volume 19, Issue 6 , Jul , 2012 , Pages 485-491 ; 15376494 (ISSN) ; Sharif University of Technology
T&F
2012
Abstract
In this study, dynamic pull-in instability and snap-through buckling of initially curved microbeams are investigated. The microbeams are actuated by suddenly applied electrostatic force. A finite element model is developed to discretize the governing equations, and Newmark time discretization is employed to solve the discretized equations. The static pull-in behavior is investigated to validate the model. The results of the finite element model are compared with finite difference solutions and their convergence is examined. In addition, the influence of different parameters on dynamic pull-in instability and snap-through buckling is explored
Upwind compact implicit and explicit high-order finite difference schemes for level set technique
, Article International Journal of Computational Methods in Engineering Science and Mechanics ; Volume 13, Issue 4 , 2012 , Pages 308-318 ; 15502287 (ISSN) ; Kebriaee, A ; Sharif University of Technology
2012
Abstract
This paper investigates implementation of upwind compact implicit and explicit high-order finite difference schemes for solution of the level set equation. The upwind compact implicit and explicit high-order finite difference schemes are well-known techniques to descritize spatial derivatives for convection term in hyperbolic equations. Applying of upwind high-order schemes on the level set equation leads to less error and CPU time reduction compared to essential non-oscillatory (ENO), weighted essential non-oscillatory schemes (WENO), and even different particle level set methods. The results indicate the error based on area loss decreases drastically with applying high-order upwind,...
Effect of pressure on heat transfer coefficient at the metal/mold interface of A356 aluminum alloy
, Article International Communications in Heat and Mass Transfer ; Volume 39, Issue 5 , 2012 , Pages 705-712 ; 07351933 (ISSN) ; Jabbari, M ; Davami, P ; Sharif University of Technology
Abstract
The aim of this paper is to correlate interfacial heat transfer coefficient (IHTC) to applied external pressure, in which IHTC at the interface between A356 aluminum alloy and metallic mold during the solidification of casting under different pressures were obtained using the inverse heat conduction problem (IHCP) method. The method covers the expedient of comparing theoretical and experimental thermal histories. Temperature profiles obtained from thermocouples were used in a finite difference heat flow program to estimate the transient heat transfer coefficients. The new simple formula was presented for correlation between external pressure and heat transfer coefficient. Acceptable...
Coupled lattice boltzmann - Discrete element method for numerical modelling of sand production
, Article Particle-Based Methods II - Fundamentals and Applications, 26 October 2011 through 28 October 2011 ; 2011 , Pages 371-382 ; 9788489925670 (ISBN) ; Pak, A ; Sharif University of Technology
Abstract
In this study, a coupled numerical approach based on Lattice Boltzmann Method (LBM) and Discrete Element Method (DEM) is employed for 2D simulation of fluid flow in porous media comprising of movable circular particles. The developed model is used for simulation of sand production which is one of the important problems in petroleum industry. The numerical tool has proved to have the capability of investigating the mechanisms involved in sand production problem. The results show that the rate of sand production is strongly affected by flow rate and confining pressure
Numerical modeling of incline plate LiBr absorber
, Article Heat and Mass Transfer/Waerme- und Stoffuebertragung ; Volume 47, Issue 3 , November , 2011 , Pages 259-267 ; 09477411 (ISSN) ; Farhanieh, B ; Sharif University of Technology
2011
Abstract
Among major components of LiBr-H 2O absorption chillers is the absorber, which has a direct effect on the chillier size and whose characteristics have significant effects on the overall efficiency of absorption machines. In this article, heat and mass transfer process in absorption of refrigerant vapor into a lithium bromide solution of water-cooled incline plate absorber in the Reynolds number range of 5
Simulation of the interaction between nonspherical particles within the CFD–DEM framework via multisphere approximation and rolling resistance method
, Article Particulate Science and Technology ; 2015 , Pages 1-11 ; 02726351 (ISSN) ; Behzad, M ; Rajabi, M ; Sharif University of Technology
Taylor and Francis Inc
2015
Abstract
The particle shape is an important factor playing critical role in evaluation of the interactions between particles in high-concentration particle-fluid flows. In this paper, the well-known multisphere (MS) approximation approach and the novel rolling resistance approach are utilized to examine their performance in order to simplify the generalized shaped particle’s interactions within the framework of discrete element method (DEM) and computational fluid dynamics (CFD). The performance of two approaches are compared with the perfect particle’s shape geometry, for the limited cases of cubic-shaped and disk-shaped particle flows in a horizontal well drilling process as a reference scenario....
Simulation of two-phase liquid-vapor flows using a high-order compact finite-difference lattice Boltzmann method
, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 92, Issue 5 , November , 2015 ; 15393755 (ISSN) ; Ezzatneshan, E ; Sharif University of Technology
American Physical Society
2015
Abstract
A high-order compact finite-difference lattice Boltzmann method (CFDLBM) is extended and applied to accurately simulate two-phase liquid-vapor flows with high density ratios. Herein, the He-Shan-Doolen-type lattice Boltzmann multiphase model is used and the spatial derivatives in the resulting equations are discretized by using the fourth-order compact finite-difference scheme and the temporal term is discretized with the fourth-order Runge-Kutta scheme to provide an accurate and efficient two-phase flow solver. A high-order spectral-type low-pass compact nonlinear filter is used to regularize the numerical solution and remove spurious waves generated by flow nonlinearities in smooth regions...
Numerical simulation of sand production experiment using a coupled Lattice Boltzmann-Discrete Element Method
, Article Journal of Petroleum Science and Engineering ; Volume 135 , November , 2015 , Pages 218-231 ; 09204105 (ISSN) ; Pak, A ; Sharif University of Technology
Elsevier
2015
Abstract
In this study, a coupled numerical approach based on Lattice Boltzmann Method (LBM) and Discrete Element Method (DEM) is employed for two-dimensional simulation of fluid flow in deformable particulate media comprising of movable circular particles. The developed LB-DE code is validated against the results of a bi-axial shear test as well as two well-known benchmark problems including settling of a circular particle under gravity force inside a viscous fluid, and motion of a neutrally buoyant particle released in a Poiseuille flow. The verified code is then utilized for simulation of "Sand Production" phenomenon which is of importance for oil producing wells in weakly cemented sandstone...
Congestion effect on maximum dynamic stresses of bridges
, Article Structural Engineering and Mechanics ; Volume 55, Issue 1 , 2015 , Pages 111-135 ; 12254568 (ISSN) ; Vafaia, H ; Sharif University of Technology
Techno Press
2015
Abstract
Bridge behavior under passing traffic loads has been studied for the past 50 years. This paper presents how to model congestion on bridges and how the maximum dynamic stress of bridges change during the passing of moving vehicles. Most current research is based on mid-span dynamic effects due to traffic load and most bridge codes define a factor called the dynamic load allowance (DLA), which is applied to the maximum static moment under static loading. This paper presents an algorithm to solve the governing equation of the bridge as well as the equations of motions of two real European trucks with different speeds, simultaneously. It will be shown, considering congestion in eight case...