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    Study on microstructural events during hot rod rolling of steels using mathematical modelling

    , Article Ironmaking and Steelmaking ; Volume 35, Issue 2 , 2008 , Pages 115-123 ; 03019233 (ISSN) Serajzadeh, S ; Mirbagheri, S. M. H ; Sharif University of Technology
    In this paper, a mathematical model is employed to evaluate the kinetics of recrystallisation in the hot rod rolling process. To reach this goal it is required to accurately assess the temperature and the velocity fields within the metal being deformed. These parameters are evaluated by solving the governing equations of heat conduction and plastic deformation. In addition, a neural network model is coupled with finite element analysis to calculate the flow stress of deforming metal as a function of deformation parameters. To verify the validity of the employed model, the predictions and the measured surface temperatures after each pass are compared and a good agreement is observed. © 2008... 

    Investigation of transient response of erbium-doped fiber lasers by semi-classical theory

    , Article Journal of Optical Communications ; Volume 28, Issue 4 , 2007 , Pages 248-251 ; 01734911 (ISSN) Bahrampour, A. R ; Mahjoei, M ; Jamali, P ; Sharif University of Technology
    Fachverlag Schiele und Sohn GmbH  2007
    The transient response of all optical gain clamped multi channel erbium doped fiber amplifiers (EDFA's) and optical fiber inverter is studied by a semi-classical model. Using the semi-classical theory, the electric field interacting with mater is considered classical and the medium is quantized according to the equations of motion for density matrix. The rate equations and "self consistency" equations, which yield amplitude and phase of the electric fields of oscillator and amplifying channels are derived by considering Maxwell's equations and equation of motion of density matrix. The governing equations form a system of coupled partial differential equations. The relaxation oscillation... 

    A continuous vibration theory for rotors with an open edge crack

    , Article Journal of Sound and Vibration ; Volume 333, Issue 15 , 21 July 2014 , Pages 3522–3535 Ebrahimi, A ; Heydari, M ; Behzad, M ; Sharif University of Technology
    In this paper a new continuous model for flexural vibration of rotors with an open edge crack has been developed. The cracked rotor is considered in the rotating coordinate system attached to it. Therefore, the rotor bending can be decomposed in two perpendicular directions. Two quasi-linear displacement fields are assumed for these two directions and the strain and stress fields are calculated in each direction. Then the final displacement and stress fields are obtained by composing the displacement and stress fields in the two directions. The governing equation of motion for the rotor has been obtained using the Hamilton principle and solved using a modified Galerkin method. The free... 

    Gaseous slip-flow mixed convection through ordered microcylinders

    , Article Journal of Thermophysics and Heat Transfer ; Vol. 28, issue. 1 , 2014 , p. 105-117 Sadeghi, M ; Sadeghi, A ; Saidi, M. H ; Sharif University of Technology
    The fully developed longitudinal slip-flow mixed convection between a periodic bunch of vertical microcylinders arrangedin regular arraysis investigated inthe present work. The two axially constant heat flux boundary conditions of H1 and H2 are considered in the analysis. The rarefaction effects are taken into consideration using first-order slip velocity and temperature jump boundary conditions. The method considered is mainly analytical, in that the governing equations and three of the boundary conditions are exactly satisfied. The remaining symmetry condition on the right-hand boundary of the typical element is applied to the solution through the point-matching technique. The results... 

    The intra-cavity mode competition and laser absorption spectroscopy with CO2 laser

    , Article Optik ; Vol. 125, issue. 10 , 2014 , p. 2248-2255 Fuladvand, H ; Salehi, A ; Daneshfar, N ; Bahrampour, A ; Moghaddam, R. F ; Sharif University of Technology
    A mathematical model is developed for analysis the dynamics of an intra-cavity laser spectroscopy and mode competition using the CO2 laser as the coherent source. The governing equations of system are derived and effect of the absorbing material on the laser modes, as a time-dependent term is considered. Thus, the application of the CO2 laser for intra-cavity laser spectroscopy with considering an inhomogeneous medium and effect of the absorbing material is investigated  

    Analysis of micro-rotating disks based on the strain gradient elasticity

    , Article Acta Mechanica ; Vol. 225, issue. 7 , 2014 , pp. 1955-1965 ; ISSN: 00015970 Danesh, V ; Asghari, M ; Sharif University of Technology
    In this paper, the mechanical behavior of micro-rotating disks is investigated utilizing the strain gradient theory. The governing equation and boundary conditions are derived utilizing the variational method. The analytical solution for the derived equation is also presented. As a case study, some numerical results are presented to emphasize the importance of utilization of non-classical theories such as the strain gradient elasticity instead of the classical continuum theory in dealing with micro-rotating disks  

    Exact solutions for free vibrations and buckling of double tapered columns with elastic foundation and tip mass

    , Article Journal of Vibration and Acoustics, Transactions of the ASME ; Volume 135, Issue 5 , 2013 ; 10489002 (ISSN) Firouz Abadi, R. D ; Rahmanian, M ; Amabili, M ; Sharif University of Technology
    The present study aims at the free vibration analysis of double tapered columns. Foundation is assumed to be elastic and the effects of self-weight and tip mass with significant moment of inertia are considered. The governing equation of motion is obtained using the Hamilton principle, based on both the Euler-Bernoulli and Timoshenko beam models. Applying the power series method of Frobenius, the base solutions of the governing equations are obtained in the form of a power series via general recursive relations. Applying the boundary conditions, the natural frequencies of the beam/column are obtained using both models. The obtained results are compared with literature and a very good... 

    Stability analysis of joined isotropic conical shells under axial compression

    , Article Thin-Walled Structures ; Volume 72 , 2013 , Pages 20-27 ; 02638231 (ISSN) Shakouri, M ; Kouchakzadeh, M. A ; Sharif University of Technology
    In this study, the buckling of two joined isotropic conical shells under axial compression and simply supported boundary conditions is investigated. The governing equations are obtained using thin-walled shallow shell theory of Donnell-type and theorem of minimum potential energy. The continuity conditions at the joining section of the cones are appropriate expressions among stress resultants and deformations. The equations are solved by assuming trigonometric response in circumferential and series solution in meridional direction. The results are validated in comparison with the available results in the literature. Effects of semi-vertex angles and meridional lengths on the buckling load... 

    Whirling frequencies of thin spinning cylindrical shells surrounded by an elastic foundation

    , Article Acta Mechanica ; Volume 224, Issue 4 , 2013 , Pages 881-892 ; 00015970 (ISSN) Firouz Abadi, R. D ; Torkaman Asadi, M. A ; Rahmanian, M ; Sharif University of Technology
    In this paper, the whirling frequencies of simply supported and clamped rotating cylindrical shells surrounded by an elastic foundation are investigated. The Love's shell theory is used along with the Winkler foundation to obtain the governing equations of motion. An exact power series solution is obtained for arbitrary boundary conditions and the results are verified with the literature. Several case studies are performed, and the effect of spinning speed, foundation stiffness, and geometrical dimensions of the cylinder on the whirling frequencies are investigated  

    On free vibration of functionally graded euler-bernoulli beam models based on the non-local theory

    , Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) ; Volume 12 , 2012 , Pages 169-173 ; 9780791845288 (ISBN) Moheimani, R ; Ahmadian, M. T ; Sharif University of Technology
    In this paper, the governing equations and boundary conditions of a functionally graded Euler-Bernoulli beam are developed based on the non-local theory of elasticity. Afterward, the free vibration is investigated and the effects of the axial load, the non-local parameter and the power index on the natural frequency of a hinged-hinged beam is assessed. The results indicate that the non-local parameter has a decreasing effect on the frequency while the power index has an increasing effect. It is also noted that the effect of the axial load is increasing too  

    On the static pull-in of circular microplates under capillary force

    , Article ASME 2011 International Mechanical Engineering Congress and Exposition, IMECE 2011 ; Volume 11 , 2011 , Pages 401-405 ; 9780791854976 (ISBN) Kahrobaiyan, M. H ; Fallah, A ; Bozorgzadeh, S ; Firoozbakhsh, K ; Ahmadian, M. T ; Sharif University of Technology
    In this paper, the static pull-in phenomenon is investigated in circular micro-plates subjected to capillary force. The capillary force appears in micro-scale structures due to presence of a liquid bridge. The governing equation of a circular micro-plate subjected to capillary force is presented and the static deflection of a fully-clamped circular plate is evaluated. Moreover, the effect of the normalized adhesion tension caused due to the capillary force on the static pull-in of the micro-plate is assessed  

    A simultaneous method for phase identification and equilibrium calculations in reactive mixtures

    , Article Chemical Engineering Research and Design ; Volume 89, Issue 10 , 2011 , Pages 1901-1908 ; 02638762 (ISSN) Avami, A ; Saboohi, Y ; Sharif University of Technology
    Phase identification is an important aspect of flash calculations which can affect the phase and chemical equilibria. A new simultaneous approach for reactive mixtures, based on τ-method which relies on modification equation for mole fraction summation, is introduced in this paper. In the proposed methodology, phase identification and solution of governing equations can be performed simultaneously and effectively. In addition, prior knowledge of the number of phases in advance is not required. Present methodology has been verified with the help of case studies and results are discussed in the present paper. The results indicate that the present method gives us information about presence of... 

    Thermo acoustic study of carbon nanotubes in near and far field: Theory, simulation, and experiment

    , Article Journal of Applied Physics ; Volume 117, Issue 9 , 2015 ; 00218979 (ISSN) Asadzadeh, S. S ; Moosavi, A ; Huynh, C ; Saleki, O ; Sharif University of Technology
    American Institute of Physics Inc  2015
    Carbon nanotube webs exhibit interesting properties when used as thermo-acoustic projectors. This work studies thermo-acoustic effect of these sound sources both in near and far field regions. Based on two alternative forms of the energy equation, we have developed a straightforward formula for calculation of pressure field, which is consistent with experimental data in far field. Also we have solved full 3-D governing equations using numerical methods. Our three-dimensional simulation and experimental data show pressure waves are highly affected by dimensions of sound sources in near field due to interference effects. However, generation of sound waves in far field is independent of... 

    Transient growth of a micro-void in an infinite medium under thermal load with modified Zerilli–Armstrong model

    , Article Acta Mechanica ; Volume 227, Issue 4 , 2016 , Pages 943-953 ; 00015970 (ISSN) Baghani, M ; Eskandari, A. H ; Zakerzadeh, M. R ; Sharif University of Technology
    In this paper, the transient growth of a spherical micro-void under remote thermal load in an infinite medium is investigated. After developing the governing equations in the problem domain, the coupled nonlinear set of equations is solved through a numerical scheme. It is shown that a small cavity can grow rapidly as the temperature increases in a remote distance and may damage the material containing preexisting micro-voids. Conducting a transient thermal analysis simultaneously with a structural one reveals that the material may experience a peak in the radial stress distribution, which is five times larger compared to the steady-state one, and shows the importance of employing a... 

    An X-FEM implementation of hydro-fracture growth in naturally fractured saturated porous media

    , Article Poromechanics 2017 - Proceedings of the 6th Biot Conference on Poromechanics, 9 July 2017 through 13 July 2017 ; 2017 , Pages 2027-2034 ; 9780784480779 (ISBN) Vahab, M ; Khoei, A. R ; Khalili, N ; Sharif University of Technology
    In this paper, a coupled hydro-mechanical formulation is developed for the simulation of interaction between hydraulic fractures and natural discontinuities within saturated porous media. The momentum balance equation of the bulk together with the momentum balance and continuity equations of the fluid phase are employed to obtain the fully coupled set of governing equations. The hydro-fracture is modeled for fluid flow using the Darcy law. The natural discontinuity on the other hand is modeled for both opening and closing modes which induce fluid flow and/or contact behavior along the crack edges. The discontinuity in the displacement field is incorporated by using the Heaviside enrichment... 

    Nonlinear free and forced vibrations of graphene nanoplatelet reinforced microbeams with geometrical imperfection

    , Article Microsystem Technologies ; Volume 25, Issue 8 , 2019 , Pages 3137-3150 ; 09467076 (ISSN) Mirjavadi, S. S ; Mohasel Afshari, B ; Barati, M. R ; Hamouda, A. M. S ; Sharif University of Technology
    Springer Verlag  2019
    Nonlinear free/forced vibration of a functionally graded graphene nanoplatelet (GNP) reinforced microbeam having geometrical imperfection which is rested on a non-linear elastic substrate have been studied in the present research. Graphene Platelets have been uniformly and non-uniformly scattered in the cross section area of the microbeam. Non-uniform distribution of GNPs is considered to be linear or non-linear type. Geometric imperfection is considered similar to the first vibration mode of microbeam. Size effects due to micro-rotations are captured in this study by means of modified couple stress elasticity. In the case of forced vibration, a uniform harmonic load is exerted to the top... 

    The moment method for fiber raman amplifier gain ripple minimization

    , Article Optics Communications ; Volume 281, Issue 14 , 2008 , Pages 3673-3680 ; 00304018 (ISSN) Bahrampour, A. R ; Farman, F ; Ghasempour, A ; Sharif University of Technology
    We aim to propose a novel fiber Raman amplifier modeling based on the moment method, which is previously introduced for modeling the inhomogeneous Erbium doped fiber amplifiers and recently employed to analyze the fiber Raman amplifier with continuous pump spectrum. In this model, the number of governing equations is independent of the number of signals and according to the degree of accuracy it is proportional to the number of pumps. This method is employed to analyze the Raman fiber amplifiers with an arbitrary input signal line shape and to minimize the gain ripple of the fiber Raman amplifier with respect to the pump powers and pump frequencies. © 2008 Elsevier B.V. All rights reserved  

    Stress distribtuion on open-ended carbon nanotubes

    , Article 2008 Proceedings of the ASME - 2nd International Conference on Integration and Commercialization of Micro and Nanosystems, MicroNano 2008, 3 June 2008 through 5 June 2008, Kowloon ; 2008 , Pages 343-351 ; 0791842940 (ISBN); 9780791842942 (ISBN) Momeni, K ; Alasty, A ; Sharif University of Technology
    The stress distribution on open-ended Carbon Nanotubes (CNTs) embedded in a composite material is considered in this work and an analytical solution for the stress distribution has been obtained. The effects of CNT's thickness and CNT's length on the distribution of stress have been investigated. To find the governing relations, continuity equations of the axisymmetric problem in cylindrical coordinate (r,o,z) are used. Under some assumptions, the governing equations are solved and by using constitutive equations and applying the boundary conditions, an equation which relates the stress applied to the representative volume element with the stress distribution on the CNT, has been found. The... 

    Nonlinear free vibration of nanobeams with surface effects considerations

    , Article Proceedings of the ASME Design Engineering Technical Conference, 28 August 2011 through 31 August 2011 ; Volume 7 , August , 2011 , Pages 191-196 ; 9780791854846 (ISBN) Fallah, A ; Firoozbakhsh, K ; Kahrobaiyan, M. H ; Pasharavesh, A ; Sharif University of Technology
    In this paper, simple analytical expressions are presented for geometrically non-linear vibration analysis of thin nanobeams with both simply supported and clamped boundary conditions. Gurtin-Murdoch surface elasticity together with Euler-Bernoulli beam theory is used to obtain the governing equations of motions of the nanobeam with surface effects consideration. The governing nonlinear partial differential equation is reduced to a single nonlinear ordinary differential equation using Galerkin technique. He's variational approach is employed to obtain analytical solution for the resulted nonlinear governing equation. The effects of different parameters such as vibration amplitude, boundary... 

    Modeling Saturated Porous Media Using Extended Finite Element Method

    , M.Sc. Thesis Sharif University of Technology Haghighat, Ehsan (Author) ; Khoei, Amir Reza (Supervisor)
    Soil structures have important roles in civil engineering applications. The most important types of these structures are soil dams and foundations which their damages may cause huge loss. Thus, appropriate analysis of these structures under possible loading conditions is unavoidable. The real behavior of this media can be achieved from the solution of its coupled governing differential equations. In order to solve this set of equations in practical applications, appropriate numerical solutions should be used. The finite element method can be called as one of the most important numerical solutions of differential equations which have been used in analyzing different types of engineering...