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gomar--kazem
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, M.Sc. Thesis Sharif University of Technology ; Borgheei, Mahmoud (Supervisor)
Abstract
Air entering in to the water supply systems and occurrence of two-phase flow makes several problems in design and operation of these systems by damaging the structures and making indefinite and complicated conditions. Existence of some singularities like contractions in pipelines makes the conditions more indefinite. So an experimental study is performed in order to investigate the two-phase flow hydraulic properties in a rectangular channel in presence of an area contraction. The contraction ratio is σ=0.44, whereby the test section is included two different rectangular channels from 60 × 100 mm to 40 × 67 mm. Four series of experiments are performed using four types of transitions with...
Discriminative Articulatory Models for Spoken Term Detection in Low-Resource Conditions
, M.Sc. Thesis Sharif University of Technology ; Sameti, Hossein (Supervisor)
Abstract
This thesis is focused on the spoken term detection system based on speech recognition in low resources conditions. A spoken term detection system is composed of two parts: speech recognition and search. In search of words, the method of proxy words is used as a basic approache to overcome the problem of OOV words. The main challenge in this thesis in the context of low resources, is poor training acoustic and language models and the small lexicon in speech recognition. Small lexicon increases the number of OOV words. In this thesis, two innovation has been proposed to improve the basic system. The first is training a bottleneck neural network for extraction the articulatory features of...
A transient fully coupled thermo-poroelastic finite element analysis of wellbore stability
, Article Arabian Journal of Geosciences ; Volume 8, Issue 6 , 2014 , Pages 3855-3865 ; ISSN: 18667511 ; Goodarznia, I ; Shadizadeh, S. R ; Sharif University of Technology
2014
Abstract
Stress variations around wellbores and in the reservoirs are of much interest in subsequent drilling operations, future production, and petroleum reservoir development. Stress variations induced by in situ stresses, pore pressure, and temperature changes during drilling operations may lead to various modes of instabilities in forms of induced fractures and borehole breakouts. Previous studies of thermally induced stresses were primarily based on either assumptions of heat conduction through rock matrix or heat convection, in this case, without considering the effect of solid grain thermal conductivity. To analyze wellbore stability, in the present work, a thermo-poro-mechanical model that is...
Fully coupled analysis of interaction between the borehole and pre-existing fractures
, Article International Journal of Rock Mechanics and Mining Sciences ; Volume 89 , 2016 , Pages 151-164 ; 13651609 (ISSN) ; Goodarznia, I ; Shadizadeh, S. R ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
The coupling of rock and thermal stresses along with fluid pressure are particularly important in fractured rock masses, since stress-induced changes in permeability can be large and irreversible under perturbations resulting from various natural and induced activities. A new method is presented to model fracture permeability changes during drilling in fractured rocks. The approach includes finite element method (FEM) for fully coupled thermo-poroelastic analysis of stress distribution around borehole and displacement discontinuity method (DDM) to model fracture deformation. Three cases of overbalanced, underbalanced, and balanced drilling fluid pressure conditions are employed. The...
Coupled thermo-poroelastic analysis of drilling induced mechanical damage in fractured rocks
, Article Journal of Petroleum Science and Engineering ; Volume 146 , 2016 , Pages 601-616 ; 09204105 (ISSN) ; Goodarznia, I ; Shadizadeh, S. R ; Sharif University of Technology
Elsevier
2016
Abstract
The wellbore represents one of the most crucial components in the hydrocarbon and geothermal reservoir system, as it is the sole conduit to the reservoir for fluid production or injection. Therefore, predicting and controlling of the permeability variations close to the wellbore has been one of the most challenging issues in geothermal and petroleum reservoir systems. A new method is presented to model fracture permeability changes during drilling in fractured rocks. The approach includes finite element method (FEM) for fully coupled thermo-poroelastic analysis of stress distribution around borehole and displacement discontinuity method (DDM) to model fracture deformation. Four models of...
Transient thermo-poroelastic analysis of drilling-induced mechanical damage in nonfractured rocks
, Article Arabian Journal of Geosciences ; Volume 8, Issue 12 , 2015 , Pages 10803-10818 ; 18667511 (ISSN) ; Goodarznia, I ; Shadizadeh, S. R ; Sharif University of Technology
Springer Verlag
2015
Abstract
Permeability variations in reservoirs and around boreholes are of great interest in petroleum engineering due to the fact that they can significantly affect reserve estimates, reservoir development, well production or injection rate, and the likely success of remedial actions of near-wellbore damage. A fully coupled transient thermo-poroelastic concept with and without rock mechanical damage models is employed to evaluate stress distribution and permeability variation around the boreholes and breakouts. The anisotropy concept is applied to permeability, rock modulus, and uniaxial compressive strength using Weibull distribution. The Mogi–Coulomb failure criterion is employed to model breakout...
Synthesis and Study of Catalytic Activity of Iron (III)-bis(2-oxazolinyl) Methane complex by Urea Hydrogen Peroxide in Oxidation of Sulfides
, M.Sc. Thesis Sharif University of Technology ; Bagherzadeh, Mojtaba (Supervisor)
Abstract
Considerable effort has been directed in recent years towards the transition metal complex catalyzed oxidation of organic compounds. Herein the synthsis of the iron complex of bis(oxazoline) ligand as a novel catalyst is reported, and the catalytic activity of this complex in oxidation of sulfides is investigated. Bis(2-oxazolynil)methane as ligand is prepared by condensation of diethylmalonate with 2-aminoethanole in 1:2 molar ratio and finally corresponding complex is synthesized by the reaction between FeCl3.6H2O and Bis(2-Oxazolynil)methane in 1:1 molar ratio. The complex is characterized by using IR, UV-Vis, cyclic voltametery, conductometery and elemental analysis data. Moreover,...
Numerical Solution of Two-dimensional Compressible Flow Using Immersed Boundary Method with Compact Finite Difference Scheme
, M.Sc. Thesis Sharif University of Technology ; 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...
Numerical Simulation of Compressible Magnetohydrodynamic Flow Using Spectral Difference Method on Quadrilateral Grids
, M.Sc. Thesis Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract
In the present work, the numerical solution of 2D inviscid compressible Magneto-hydrodynamic flow is performed by using the spectral difference (SD) method on quadrilateral grids. In this numerical method, similar to the discontinuous Galerkin (DG) and spectral volume (SV) methods, the concept of the discontinuous and high-order local representations is used to achieve conservation property and high-order accuracy. In the SD method, the test function or the surface integral is not involved and thus it has a simpler formulation than the DG and SV methods. In this numerical method, two sets of structured points, namely unknown points and flux points, are defined in each cell to support the...
Implementing Appropriate Numerical Filters in the Lattice Boltzmann Method for Solving Multiphase Incompressible Flows with Large Density Ratio
, M.Sc. Thesis Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract
In this study, two finite-difference lattice Boltzmann methods (FDLBM) are applied and assessed for the simulation of two-phase liquid-vapor flows with high density ratios. For this aim, the He-Shan-Doolen type lattice Boltzmann multiphase model is used and the spatial derivatives in the resulting system of equations are discretized by using the second-order central difference and modified Lax-Wendroff schemes. Suitable numerical dissipation terms and filters are applied to regularize the numerical solution and remove spurious waves generated by flow nonlinearities in smooth regions and at the same time to remove the numerical oscillations in the interface region of the two phases.Three...
Numerical Simulation of Shock-Disturbances Interaction in 2-D Compressible Flows Considering Real Gas Effects by Using WENO Method
, M.Sc. Thesis Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract
In the present study, the shock-disturbances interaction in hypersonic inviscid flows considering real gas effects is numerically studied by using a high-order WENO scheme. To account for real gas effects, the equilibrium air model is utilized. The strong conservative form of the two-dimensional unsteady Euler equations in the generalized curvilinear coordinates is considered as the governing equations and a shock-capturing technique is applied. The resulting system of equations is discretized by using the fifth-order WENO finite-difference scheme in space and the explicit third-order TVD Runge-Kutta scheme in time to provide a high-order accurate flow solver. The WENO scheme is a stable scheme...
Numerical Simulation of Natural Convection Using Smoothed Particle Hydrodynamics with Artificial Compressibility Method
, M.Sc. Thesis Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract
In this research, the numerical simulation of the natural convection is performed by using the smoothed particle hydrodynamics based on the artificial compressibility method. For this aim, the formulation of the artificial compressibility method in the Eulerian reference frame for the mass and momentum equations is written in the Lagragian reference frame and the Lagrangin form of the energy equation is also considered to compute the thermal effects. The benefit of the artificial compressibility-based incompressible SPH (ACISPH) method over the weakly compressible SPH (WCSPH) method for computing the natural convection is that there is no need in the formulation considered here to use any...
Development of Characteristic Boundary Conditions with Artificial Compressibility Method by Compact Finite-Difference Discretization
, Ph.D. Dissertation Sharif University of Technology ; 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...
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...
Modeling of Mechanical Damage in Fractured Rocks During Drilling
, Ph.D. Dissertation Sharif University of Technology ; Goodarznia, Iraj (Supervisor) ; Shadizadeh, Reza (Supervisor) ; Massihi, Mohsen (Co-Advisor)
Abstract
Effective stress variation is one of the main issues in petroleum and gheothermal reservoir development. These stress variation could cause formation damage, sand production, sloughing shale and various modes of borehole instability like induced fractures and borehole wall shearing. In petroleum engineering, drilling a borehole is the first step in reservoir development. The wellbores are implemented to produce or inject fluids such as water, oil, gas and chemical fluids used during secondary and tertiary recovery processes. Upon drilling a borehole, reservoir pore pressure, rock and fluid temperature and mechanical stresses change which induces borehole instability and variations in rock...
Aerodynamic Analysis of Dual Rotors Using Potential Method and Free Wake Modeling
, M.Sc. Thesis Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract
Potential flow solvers simplify the mathematical formulation and achieve efficient solutions. The prediction of aerodynamic of dual rotor systems using computational fluid dynamic methods is difficult task due to the interference effects between the wakes shed from the rotors. In the present work, a free wake vortex lattice method is used to predict the vertical wake and blade loading of dual rotors in hover. In this approach the blades are modeled as flat plates with zero thickness and ring vortices are distributed on the surface of each blade. When the blades rotate, vortices are shed into the wake and freely move with a local velocity induced by the effects of the vortices on the blades...
Numerical Solution of Hypersonic Axisymmetric Flows Including Real Gas Effects Using Compact Finite-Difference Scheme
, M.Sc. Thesis Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract
The numerical solution of the parabolized Navier-Stokes (PNS) equations for accurate computation of hypersonic axisymmetric flowfield with real gas effects is obtained by using the fourth-order compact finite-difference method. The PNS 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 the compact PNS scheme to obtain accurate solutions in the vicinity of the shock. To stabilize the numerical solution, numerical dissipation term and filters are used. The main advantage of the present formulation is that the basic flow variables...
The numerical solution of the parabolized Navier-Stokes (PNS) equations for accurate computation of hypersonic axisymmetric flowfield with real gas effects is obtained by using the fourth-order compact finite-difference method. The PNS 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 the compact PNS scheme to obtain accurate solutions in the vicinity of the shock. To stabilize the numerical solution, numerical dissipation term and filters are used. The main advantage of the present formulation is that the basic flow variables...
Numerical Simulation of 2D Inviscid Compressible Magnetohydrodynamic Flows by Spectal Difference Method
, M.Sc. Thesis Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract
In the present study, the numerical solution of 2D inviscid compressible ideal magnetohydrodynamic (MHD) flows by using the spectral difference (SD) method on unstructured meshes is performed. The SD method combines the most desirable features of structured and unstructured grid methods to have computational efficiency and geometric flexibility to accurately compute flow over complex geometries. In the SD method, two sets of structured points, namely “unknown points” and “flux points”, are defined in each cell to support the reconstruction of given order of accuracy. The differential form of the conservation laws is satisfied at nodal unknown points while the flux derivatives expressed in...
Developing a Compact Finite Difference Method for Solving Fluid - Solid Interaction in Incompressible Flow
, M.Sc. Thesis Sharif University of Technology ; 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...
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...