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    Dynamic mesh adaptation for two-dimensional unsteady flow

    , Article Iranian Journal of Science and Technology, Transaction B: Technology ; Volume 24, Issue 3 , 2000 , Pages 228-229 ; 03601307 (ISSN) Mazaherf, K ; Lessani, B ; Sharif University of Technology
    2000
    Abstract
    A method for adaptive refinement of a triangular mesh for solution of the steady and unsteady Euler equations is presented. An upwind, finite volume based on Roe's flux difference splitting method is used to discretize the equations. By using advancing front method an initial regular Delaunay triangulation has been made. The adaptation procedures involve mesh enrichment and mesh coarsening to either add points in high gradient regions of the flow or remove points where they are not needed, respectively, to produce solutions of high spatial accuracy at minimal cost. Steady transonic results are shown to be of high spatial accuracy, primarily in that the shock waves are very sharply captured.... 

    Assessment of characteristic boundary conditions based on the artificial compressibility method in generalized curvilinear coordinates for solution of the euler equations

    , Article Computational Methods in Applied Mathematics ; 2017 ; 16094840 (ISSN) Parseh, K ; Hejranfar, K ; Sharif University of Technology
    Abstract
    The characteristic boundary conditions are applied and assessed for the solution of incompressible inviscid flows. The two-dimensional incompressible Euler equations based on the artificial compressibility method are considered and then the characteristic boundary conditions are formulated in the generalized curvilinear coordinates and implemented on both the far-field and wall boundaries. A fourth-order compact finite-difference scheme is used to discretize the resulting system of equations. The solution methodology adopted is more suitable for this assessment because the Euler equations and the high-accurate numerical scheme applied are quite sensitive to the treatment of boundary... 

    Simulation of chatter vibrations in reaming

    , Article ASME International Mechanical Engineering Congress and Exposition, IMECE 2007, Seattle, WA, 11 November 2007 through 15 November 2007 ; Volume 3 , 2008 , Pages 441-447 ; 0791842975 (ISBN); 9780791842973 (ISBN) Sajjadi, M ; Movahhedy, M. R ; Sharif University of Technology
    2008
    Abstract
    A time domain approach is used to study the cutting conditions in reaming process that leads the system to regenerative chatter vibrations. The dynamic analysis of the system includes inertia of the tool, centripetal and Coriolis terms, damping and the first mode bending of reamer. A model of cutting forces proportional to chip cross sectional area and process damping proportional to cutting speed is considered. Numerical simulation based on the Euler integration scheme is carried out to obtain time domain solution of the equation. Despite linearization in force modelling, the model is nonlinear due to the change in the tool engagement area. Another nonlinearity included in the model jumping... 

    On the objective corotational rates of eulerian strain measures

    , Article Journal of Elasticity ; Volume 90, Issue 2 , 2008 , Pages 175-207 ; 03743535 (ISSN) Asghari, M ; Naghdabadi, R ; Sharif University of Technology
    2008
    Abstract
    In the present paper, some new basis-free expressions for an arbitrary objective corotational rate of the general Eulerian strain measures are provided which are in compact form. Moreover, a complete discussion on the requirements for the continuity of the objective corotational rates are presented. © 2008 Springer Science+Business Media B.V  

    A robust finite volume model to simulate granular flows

    , Article Computers and Geotechnics ; Volume 66 , May , 2015 , Pages 96-112 ; 0266352X (ISSN) Yavari Ramshe, S ; Ataie Ashtiani, B ; Sanders, B. F ; Sharif University of Technology
    Elsevier Ltd  2015
    Abstract
    This paper introduces a well-balanced second-order finite volume scheme, based on the Q-scheme of Roe, for simulating granular type flows. The proposed method is applied to solve the incompressible Euler equations under Savage-Hutter assumptions. The model is derived in a local coordinate system along a non-erodible bed to take its curvature into account. Moreover, simultaneous appearance of flowing/static regions is simulated by considering a basal friction resistance which keeps the granular flow from moving when the angle of granular flow is less than the angle of repose. The proposed scheme preserves stationary solutions up to second order and deals with different situations of wet/dry... 

    Implementation of translational motion dynamics for INS data fusion in DVL outage in underwater navigation

    , Article IEEE Sensors Journal ; Volume 21, Issue 5 , 2021 , Pages 6652-6659 ; 1530437X (ISSN) Karmozdi, A ; Hashemi, M ; Salarieh, H ; Alasty, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2021
    Abstract
    Underwater navigation is generally accomplished through the data fusion of INS (Inertial Navigation System) and auxiliary sensors such as DVL (Doppler Velocity Logger) sensor. However, because of the possibility of DVL outage, alternative low-cost solutions are attractive. Among these, one is using vehicle kinetic model information extracted by the Newton-Euler equation to improve INS performance, which is called model-aided navigation. In this paper, only the vehicle translational motion dynamics are used to replace DVL in underwater navigation in DVL outage. The vehicle 3D translational dynamics has been obtained by using general Newton-Euler equations. Integrating these dynamics leads to... 

    Non-steady burning effect on solid rocket motor performance

    , Article 45th AIAA Aerospace Sciences Meeting 2007, Reno, NV, 8 January 2007 through 11 January 2007 ; Volume 14 , 2007 , Pages 9531-9536 ; 1563478900 (ISBN); 9781563478901 (ISBN) Tahsini, A. M ; Sharif University of Technology
    American Institute of Aeronautics and Astronautics Inc  2007
    Abstract
    Solid rocket performance during rapid pressure excursions differs greatly from predictions based on steady state burning rate data. Rapid pressurization following a chamber filling interval produces indicated burning rate overshoots. Transient internal ballistics of a solid propellant rocket motor during rapid pressurization part of chamber filling phase has been considered in this work. Quasi one-dimensional unsteady Euler equations with a transient propellant burning model that accounts for the effects of time rate of change of the chamber pressure on the burning rate have been used to simulate the internal ballistics of rocket motors. The compressible convective flow solver used in this... 

    A comparative study of two preconditioners for solving 3D inviscid low speed flows

    , Article Applied Mechanics and Materials ; Volume 110-116 , 2012 , Pages 423-430 ; 16609336 (ISSN) ; 9783037852620 (ISBN) Hejranfar, K ; Moghadam, R. K ; Sharif University of Technology
    2012
    Abstract
    In the present study, two preconditioners proposed by Eriksson, and Choi and Merkel are implemented on a 3D upwind Euler flow solver on unstructured meshes. The mathematical formulations of these preconditioning schemes for the set of primitive variables Q→p 1=[ρ u v , w p] T are drawn and their eigenvalues and eigenvectors are compared with each others. A cell-centered finite volume Roe's method is used for discretization of the 3D preconditioned Euler equations. The accuracy and performance of these preconditioning schemes are examined by computing low Mach number flows over the ONERA M6 wing for different conditions  

    A Direct Design Method Based on the 3-Dimensional Euler Equations with Application in Internal Subsonic and Supersonic Flows

    , M.Sc. Thesis Sharif University of Technology Nejati, Ashkan (Author) ; Taeibi-Rahni, Mohammad (Supervisor) ; Ghadak, Farhad (Supervisor)
    Abstract
    In this work, a direct design approach for designing a surface shape (inverse design problem) has been developed in which both the target surface pressure and the unknown nodal coordinates appear explicitly in the formulations. The final discretized form of the governing equations (unified formulation) can be used for both analysis and shape design problems. Shape design problems in the context of the steady inviscid and compressible flow, based on the three-dimensional Euler equations, were directly solved to achieve a prescribed pressure along the solid boundaries. The AUSM+ scheme was used to discretize the flux terms in the Euler equations, in which the inviscid flux is splitted into... 

    Numerical Simulation of Two-dimensional Sonoluminescence Phenomenon, Using Front Tracking/Ghost Fluid Method

    , M.Sc. Thesis Sharif University of Technology Moezzi Rafie, Hamid (Author) ; Tayyebi Rahni, Mohammad (Supervisor)
    Abstract
    Sonoluminescence is a unique phenomenon in physics, which is known as the process of converting sound into light. By applying sound to a volume of liquid, with a specific geometrical shape (such as sphere) and forming standing waves around an existing bubble, the bubble first expands to a maximum radius and then gets extremely small leading to its supersonic collapse. During the collapse, the resulting shock wave approches the center of the bubble, causing extreme increase in the pressure and temperature at the center of the bubble. This causes flashing of light during small time scales (pico-seconds). This phenomenon is used in many fields, such as treatment of cancer. Also, the energy... 

    Essays on Explaining the Household Consumption Smoothing

    , Ph.D. Dissertation Sharif University of Technology Einian, Majid (Author) ; Nili, Masoud (Supervisor)
    Abstract
    This dissertation studies the intertemporal decisions on private consumption and its relationship with financial markets. The main focus here is on using micro-data and heterogeneities. The first chapter gives a brief review on the literature. In the second chapter, we present estimates of the Elasticity of Intertemporal Substitution (EIS) for Iranian households using synthetic cohort panels based on household micro-data. Results show significant difference with the common values used in Dynamic Stochastic General Equilibrium (DSGE) models which are originally based on estimated values for developed countries. We show that this difference has important theoretical and practical implications.... 

    Gas Turbine Simulator Design for Dynamic Modeling

    , M.Sc. Thesis Sharif University of Technology Baghaee, Zohreh (Author) ;
    Abstract
    In order to observe natural gas turbine phenomena and predicting engine behavior, we need to have a comprehensive simulator in every engine phase of design and analysis. Because of the high cost of manufacturing and prototype experimental tests, it's beneficial to access a gas turbine engine simulator. As well it's hard to make change in a manufactured engine, while we can change a simulator easily.Gas turbine is simulating in zero, one, two and three dimensions. In this project, we have studied previous researches and according to problem, among all simulations, we have studied the ATEC simulation and its assumptions in this thesis. Of these, zero and one dimensional simulations are simpler... 

    An assessment of shock-disturbances interaction considering real gas effects

    , Article Journal of Fluids Engineering, Transactions of the ASME ; Volume 141, Issue 1 , 2019 ; 00982202 (ISSN) Hejranfar, K ; Rahmani, S ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2019
    Abstract
    In this study, a theoretical analysis is performed to assess the interaction of freestream disturbances with a plane normal shock considering real gas effects. Such effects are important in a field with high velocities and high temperatures. To perform the theoretical analysis, the downstream disturbances field is expressed as a mathematical function of the upstream one by incorporating real gas effects in the formulation. Here, the linearized one-dimensional perturbed unsteady Euler equations are used for the classification of the downstream/upstream disturbances field and the linearized one-dimensional perturbed Rankine-Hugoniot equations are applied to provide a relationship between the... 

    An extended arbitrary Lagrangian-Eulerian finite element method for large deformation of solid mechanics

    , Article Finite Elements in Analysis and Design ; Volume 44, Issue 6-7 , 2008 , Pages 401-416 ; 0168874X (ISSN) Khoei, A. R ; Anahid, M ; Shahim, K ; Sharif University of Technology
    2008
    Abstract
    In this paper, a new computational technique is presented based on the eXtended arbitrary Lagrangian-Eulerian finite element method (X-ALE-FEM) for large deformation of solid mechanic problems. An arbitrary Lagrangian-Eulerian (ALE) technique is employed to capture the advantages of both Lagrangian and Eulerian methods and alleviate the drawbacks of the mesh distortion in Lagrangian formulation. The X-FEM procedure is implemented to capture the discontinuities independently of element boundaries. The process is accomplished by performing a splitting operator to separate the material (Lagrangian) phase from convective (Eulerian) phase, and partitioning the Lagrangian and relocated meshes with... 

    Arbitrary Lagrangian-Eulerian method in plasticity of pressure-sensitive material: Application to powder forming processes

    , Article Computational Mechanics ; Volume 42, Issue 1 , 2008 , Pages 13-38 ; 01787675 (ISSN) Khoei, A. R ; Anahid, M ; Shahim, K ; DorMohammadi, H ; Sharif University of Technology
    Springer Verlag  2008
    Abstract
    In this paper, an application of Arbitrary Lagrangian-Eulerian (ALE) method is presented in plasticity behavior of pressure-sensitive material, with special reference to large deformation analysis of powder compaction process. In ALE technique, the reference configuration is used for describing the motion, instead of material configuration in Lagrangian, and spatial configuration in Eulerian formulation. The convective term is used to reflect the relative motion between the mesh and the material. Each time-step is divided into the Lagrangian phase and Eulerian phase. The convection term is neglected in the material phase, which is identical to a time-step in a standard Lagrangian analysis.... 

    Rapid depressurization dynamics of solid propellant rocket motors

    , Article 43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference, Cincinnati, OH, 8 July 2007 through 11 July 2007 ; Volume 8 , 2007 , Pages 7871-7879 ; 1563479036 (ISBN); 9781563479038 (ISBN) Tahsini, A. M ; Farshchi, M ; Sharif University of Technology
    American Institute of Aeronautics and Astronautics Inc  2007
    Abstract
    Transient internal ballistics of a solid propellant rocket motor during rapid depressurization due to opening of an auxiliary nozzle for active thrust termination has been considered in this work. Prediction of thrust termination and reversing dynamics is required for successful stage separation in multi-stage rockets. Quasi one-dimensional unsteady Euler equation with a transient propellant burning model that accounts for the effects of time rate of change of the chamber pressure on the burning rate have been used to simulate the internal ballistics of a rocket motor. The compressible convective flow solver used in this study is based on Roe's scheme. The effects of rapid chamber pressure... 

    A coupled prescribed wake-Euler solver for efficient computing helicopter rotor flows in hover

    , Article 25th Congress of the International Council of the Aeronautical Sciences 2006, Hamburg, 3 September 2006 through 8 September 2006 ; Volume 3 , 2006 , Pages 1670-1681 Hejranfar, K ; Mohammadi, M ; Sharif University of Technology
    Curran Associates Inc  2006
    Abstract
    A numerical solution technique is developed to simulate the flowfield of hovering helicopter rotor. The present method uses a coupled prescribed wake-Euler solver to efficiently allow the vortical wake effects. The threedimensional Euler equations written in a rotating coordinate frame are solved by using a cell-centered finite volume scheme that is based on the Roe's flux-difference splitting on unstructured meshes. High-order accuracy is achieved via the reconstruction of flow variables using the MUSCL interpolation technique. Calculations are carried out for an isolated rotor in hover for two operating conditions of subsonic and transonic tip Mach numbers, Mtip = 0.44 and Mtip = 0.877 ,... 

    Assessment of three preconditioning schemes for solution of the two-dimensional Euler equations at low Mach number flows

    , Article International Journal for Numerical Methods in Engineering ; Volume 89, Issue 1 , 2012 , Pages 20-52 ; 00295981 (ISSN) Hejranfar, K ; Kamali Moghadam, R ; Sharif University of Technology
    Abstract
    Three preconditioners proposed by Eriksson, Choi and Merkel, and Turkel are implemented in a 2D upwind Euler flow solver on unstructured meshes. The mathematical formulations of these preconditioning schemes for different sets of primitive variables are drawn, and their eigenvalues and eigenvectors are compared with each other. For this purpose, these preconditioning schemes are expressed in a unified formulation. A cell-centered finite volume Roe's method is used for the discretization of the preconditioned Euler equations. The accuracy and performance of these preconditioning schemes are examined by computing steady low Mach number flows over a NACA0012 airfoil and a two-element... 

    Assessment of a central difference finite volume scheme for modeling of cavitating flows using preconditioned multiphase Euler equations

    , Article Journal of Hydrodynamics ; Volume 23, Issue 3 , 2011 , Pages 302-313 ; 10016058 (ISSN) Hejranfar, K ; Fattah Hesary, K ; Sharif University of Technology
    Abstract
    A numerical treatment for the prediction of cavitating flows is presented and assessed. The algorithm uses the preconditioned multiphase Euler equations with appropriate mass transfer terms. A central difference finite volume scheme with suitable dissipation terms to account for density jumps across the cavity interface is shown to yield an effective method for solving the multiphase Euler equations. The Euler equations are utilized herein for the cavitation modeling, because some certain characteristics of cavitating flows can be obtained using the solution of this system of equations with relative low computational effort. In addition, the Euler equations are appropriate for the assessment... 

    Implementation of translational motion dynamics for INS data fusion in DVL outage in underwater navigation

    , Article IEEE Sensors Journal ; 2020 Karmozdi, A ; Hashemi, M ; Salarieh, H ; Alasty, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2020
    Abstract
    Underwater navigation is generally accomplished through the data fusion of INS (Inertial Navigation System) and auxiliary sensors such as DVL (Doppler Velocity Logger) sensor. However, because of the possibility of DVL outage, alternative low-cost solutions are attractive. Among these, one is using vehicle kinetic model information extracted by the Newton-Euler equation to improve INS performance, which is called model-aided navigation. In this paper, only the vehicle translational motion dynamics are used to replace DVL in underwater navigation in DVL outage. The vehicle 3D translational dynamics has been obtained by using general Newton-Euler equations. Integrating these dynamics leads to...