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    Effect of boundary conditions on dynamic behaviour of bridges

    , Article Proceedings of the Institution of Civil Engineers: Structures and Buildings ; Volume 169, Issue 2 , 2016 , Pages 121-140 ; 09650911 (ISSN) Samanipour, K ; Vafai, H ; Sharif University of Technology
    Thomas Telford Services Ltd 
    Abstract
    A moving vehicle, owing to its vibration and mass inertia, has significant effects on the dynamic response of structures. Most bridge codes define a factor called the dynamic load allowance, which is applied to the maximum static moment under static loading due to traffic load. This paper presents how to model an actual truck on bridges and how the maximum dynamic stresses of bridges change during the passage of moving vehicles. Furthermore, an algorithm to solve the governing equation of the bridge simultaneous with the equations of motion of an actual European truck is presented. Subsequently, 32 dynamic analyses of different bridges with different spans, road profiles and boundary... 

    New and simple equations for ultimate bearing capacity of strip footings on two-layered clays: Numerical study

    , Article International Journal of Geomechanics ; Volume 16, Issue 4 , 2016 ; 15323641 (ISSN) Danaei Ahmadi, M. M ; Mofarraj Kouchaki, B ; Sharif University of Technology
    American Society of Civil Engineers (ASCE) 
    Abstract
    In this paper, two very simple and accurate equations are introduced that enable geotechnical engineers to determine the undrained ultimate bearing capacity of shallow strip foundations resting on two-layered clays. Results of the analyses show that in the case of weak-overstrong clay, usually general shear failure occurs, and in the case of strong-over-weak clay, the soil will most likely experience punching failure with a large amount of plastic settlement before it reaches its ultimate bearing capacity. This study applied the finite-difference method using a computer program to evaluate the undrained bearing capacity for all cases analyzed. The Mohr-Coulomb failure criterion was used for... 

    Electrokinetic and aspect ratio effects on secondary flow of viscoelastic fluids in rectangular microchannels

    , Article Microfluidics and Nanofluidics ; Volume 20, Issue 8 , 2016 ; 16134982 (ISSN) Reshadi, M ; Saidi, M. H ; Firoozabadi, B ; Saidi, M. S ; Sharif University of Technology
    Springer Verlag  2016
    Abstract
    The secondary flow of PTT fluids in rectangular cross-sectional plane of microchannels under combined effects of electroosmotic and pressure driving forces is the subject of the present study. Employing second-order central finite difference method in a very refined grid network, we investigate the effect of electrokinetic and geometric parameters on the pattern, strength and the average of the secondary flow. In this regard, we try to illustrate the deformations of recirculating vortices due to change in the dimensionless Debye–Hückel and zeta potential parameters as well as channel aspect ratio. We demonstrate that, in the presence of thick electric double layers, significant alteration... 

    Simulation of the interaction between nonspherical particles within the CFD–DEM framework via multisphere approximation and rolling resistance method

    , Article Particulate Science and Technology ; Volume 34, Issue 4 , 2016 , Pages 381-391 ; 02726351 (ISSN) Akhshik, S ; Behzad, M ; Rajabi, M ; Sharif University of Technology
    Taylor and Francis Inc 
    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.... 

    A numerical study on the absorption of water vapor into a film of aqueous LiBr falling along a vertical plate

    , Article Heat and Mass Transfer/Waerme- und Stoffuebertragung ; Volume 46, Issue 2 , 2009 , Pages 197-207 ; 09477411 (ISSN) Karami, S ; Farhanieh, B ; Sharif University of Technology
    Abstract
    Absorber is an important component in absorption machines and its characteristics have significant effects on the overall efficiency of absorption machines. This article reports a model of simultaneous heat and mass transfer process in absorption of refrigerant vapor into a lithium bromide solution of water - cooled vertical plate absorber in the Reynolds number range of 5 < Re < 150. The boundary layer assumptions were used for the transport of mass, momentum and energy equations and the fully implicit finite difference method was employed to solve the governing equations in the film flow. Dependence of lithium bromide aqueous properties to the temperature and concentration and film... 

    Numerical solution of non-fourier heat transfer during laser irradiation on tooth layers

    , Article Journal of Mechanical Science and Technology ; Volume 31, Issue 12 , 2017 , Pages 6085-6092 ; 1738494X (ISSN) Falahatkar, S ; Nouri Borujerdi, A ; Najafi, M ; Mohammadzadeh, A ; Sharif University of Technology
    Abstract
    This study reports on the simulation of temperature distribution of human tooth under a laser beam based on non-Fourier models. The temperature in the tooth depth that directly results from the conduction heat transfer process is caused by the lengthy thermal relaxation time in the tooth layers. A detailed tooth composed of enamel, dentin, and pulp with unstructured shape, uneven boundaries, and realistic thicknesses was considered. A finite difference scheme was separately adopted to solve time-dependent equations in solid layers and soft tissue of the tooth. In this study, a dual-phase-lag non-Fourier heat conduction model was applied to evaluate temperature distribution induced by laser... 

    The size-dependent electromechanical instability of double-sided and paddle-type actuators in centrifugal and Casimir force fields

    , Article Scientia Iranica ; Volume 24, Issue 3 , 2017 , Pages 1077-1090 ; 10263098 (ISSN) Mokhtari, J ; Farahani, M ; Kanani, A ; Rach, R ; Keivani, M ; Abadyan, M ; Sharif University of Technology
    Sharif University of Technology  2017
    Abstract
    The present research is devoted to theoretical study of the pull-in performance of double-sided and paddle-type NEMS actuators fabricated from cylindrical nanowire operating in the Casimir regime and in the presence of the centrifugal force. D'Alembert's principle was used to transform the angular velocity into an equivalent static, centrifugal force. Using the couple stress theory, the constitutive equations of the actuators were derived. The equivalent boundary condition technique was applied to obtain the governing equation of the paddle-type actuator. Three distinct approaches, the Duan-Adomian Method (DAM), Finite Difference Method (FDM), and Lumped Parameter Model (LPM), were applied... 

    Pure axial flow of viscoelastic fluids in rectangular microchannels under combined effects of electro-osmosis and hydrodynamics

    , Article Theoretical and Computational Fluid Dynamics ; 2017 , Pages 1-21 ; 09354964 (ISSN) Reshadi, M ; Saidi, M. H ; Ebrahimi, A ; Sharif University of Technology
    Abstract
    This paper presents an analysis of the combined electro-osmotic and pressure-driven axial flows of viscoelastic fluids in a rectangular microchannel with arbitrary aspect ratios. The rheological behavior of the fluid is described by the complete form of Phan-Thien–Tanner (PTT) model with the Gordon–Schowalter convected derivative which covers the upper convected Maxwell, Johnson–Segalman and FENE-P models. Our numerical simulation is based on the computation of 2D Poisson–Boltzmann, Cauchy momentum and PTT constitutive equations. The solution of these governing nonlinear coupled set of equations is obtained by using the second-order central finite difference method in a non-uniform grid... 

    Simultaneous measurement of refractive index and thickness of multilayer systems using Fourier domain optical coherence tomography, part 2: Implementation

    , Article Journal of Biomedical Optics ; Volume 22, Issue 1 , 2017 ; 10833668 (ISSN) Rajai, P ; Schriemer, H ; Amjadi, A ; Munger, R ; Sharif University of Technology
    SPIE  2017
    Abstract
    We introduce a theoretical method for simultaneous measurement of refractive index and thickness of multilayer systems using Fourier domain optical coherence tomography (FD-OCT) without any auxiliary arrangement. The input data to the formalism are the FD-OCT measured optical path lengths (OPLs) and properly selected spectral components of FD-OCT interference spectrum. The outputs of the formalism can be affected significantly by uncertainty in measuring the OPLs. An optimization method is introduced to deal with the relatively large amount of uncertainty in measured OPLs and enhance the final results. Simulation result shows that by using the optimization method, indices can be extracted... 

    Simultaneous measurement of refractive index and thickness of multilayer systems using fourier domain optical coherence tomography, part 1: theory

    , Article Journal of Biomedical Optics ; Volume 22, Issue 1 , 2017 ; 10833668 (ISSN) Rajai, P ; Schriemer, H ; Amjadi, A ; Munger, R ; Sharif University of Technology
    Abstract
    We introduce a theoretical framework for simultaneous refractive index and thickness measurement of multilayer systems using the Fourier domain optical coherence tomography (FD-OCT) system without any previous information about the item under investigation. The input data to the new formalism are the FD-OCT measured optical path lengths and properly selected spectral components of the FD-OCT interference spectrum. No additional arrangement, reference reflector, or mechanical scanning is needed in this approach. Simulation results show that the accuracy of the extracted parameters depends on the index contrast of the sample while it is insensitive to the sample's thickness profile. For... 

    The role of ion partitioning in electrohydrodynamic characteristics of soft nanofluidics: Inclusion of EDL overlap and steric effects

    , Article Chemical Engineering Science ; Volume 190 , 2018 , Pages 443-458 ; 00092509 (ISSN) Reshadi, M ; Saidi, M. H ; Sharif University of Technology
    Elsevier Ltd  2018
    Abstract
    In this paper, we aim to account for the partitioning of finite sized ions and electric double layer (EDL) overlapping effects on the electrostatics and hydrodynamics of soft nanofluidics by stablishing a modified Poisson-Boltzmann (MPB) equation enjoying mean field approach. The application of the present MPB equation enables us to describe the interaction between the steric effect and electrostatic repulsion of EDL ions due to permittivity difference of polyelectrolyte layer (PEL) and electrolyte solution. Utilizing the Debye-Hückel approximation pertinent to low surface potentials, we analytically derive the solutions of electric potential and velocity profiles of mixed electroosmotic and... 

    Development of a high-order compact finite-difference total Lagrangian method for nonlinear structural dynamic analysis

    , Article Applied Mathematical Modelling ; Volume 63 , 2018 , Pages 179-202 ; 0307904X (ISSN) Parseh, K ; Hejranfar, K ; Sharif University of Technology
    Elsevier Inc  2018
    Abstract
    A high-order compact finite-difference total Lagrangian method (CFDTLM) is developed and applied to nonlinear structural dynamic analysis. The two-dimensional simulation of thermo-elastodynamics is numerically performed in generalized curvilinear coordinates by taking into account the geometric and material nonlinearities. The spatial discretization is carried out by a fourth-order compact finite-difference scheme and an implicit second-order accurate dual time-stepping method is applied for the time integration. The accuracy and capability of the proposed solution methodology for the nonlinear structural analysis is investigated through simulating different static and dynamic benchmark... 

    Preconditioned WENO finite-difference lattice Boltzmann method for simulation of incompressible turbulent flows

    , Article Computers and Mathematics with Applications ; Volume 76, Issue 6 , 2018 , Pages 1427-1446 ; 08981221 (ISSN) Hejranfar, K ; Saadat, M. H ; Sharif University of Technology
    Elsevier Ltd  2018
    Abstract
    In this work, a preconditioned high-order weighted essentially non-oscillatory (WENO) finite-difference lattice Boltzmann method (WENO-LBM) is applied to deal with the incompressible turbulent flows. Two different turbulence models namely, the Spalart–Allmaras (SA) and k−ωSST models are used and applied in the solution method for this aim. The spatial derivatives of the two-dimensional (2D) preconditioned LB equation in the generalized curvilinear coordinates are discretized by using the fifth-order WENO finite-difference scheme and an implicit–explicit Runge–Kutta scheme is adopted for the time discretization. For the convective and diffusive terms of the turbulence transport equations, the... 

    Prediction of fluid flow and acoustic field of a supersonic jet using vorticity confinement

    , Article Journal of the Acoustical Society of America ; Volume 144, Issue 3 , 2018 , Pages 1521-1527 ; 00014966 (ISSN) Sadri, M ; Hejranfar, K ; Ebrahimi, M ; Sharif University of Technology
    Acoustical Society of America  2018
    Abstract
    In this study, the numerical simulation of the fluid flow and acoustic field of a supersonic jet is performed by using high-order discretization and the vorticity confinement (VC) method on coarse grids. The three-dimensional Navier-Stokes equations are considered in the generalized curvilinear coordinate system and the high-order compact finite-difference scheme is applied for the space discretization, and the time integration is performed by the fourth-order Runge-Kutta scheme. A low-pass high-order filter is applied to stabilize the numerical solution. The non-reflecting boundary conditions are adopted for all the free boundaries, and the Kirchhoff surface integration is utilized to... 

    Non-isothermal simulation of the behavior of unsaturated soils using a novel EFG-based three dimensional model

    , Article Computers and Geotechnics ; Volume 99 , 2018 , Pages 93-103 ; 0266352X (ISSN) Iranmanesh, M. A ; Pak, A ; Samimi, S ; Sharif University of Technology
    Elsevier Ltd  2018
    Abstract
    In this paper, a three-dimensional simulation of fully coupled multiphase fluid flow and heat transfer through deforming porous media is presented in the context of EFG mesh-less method. Spatial discretization of the system of governing equations is performed using EFG and a fully implicit finite difference scheme is employed for temporal discretization. Penalty method is used for imposition of essential boundary conditions. The developed numerical tool is employed to simulate two problems of nuclear waste disposal and CO2 sequestration in deep underground strata. The obtained results demonstrate the capability and robustness of the developed EFG code. © 2018 Elsevier Ltd  

    IGBT open-circuit fault diagnosis in a Quasi-Z-source inverter

    , Article IEEE Transactions on Industrial Electronics ; Volume 66, Issue 4 , 2019 , Pages 2847-2856 ; 02780046 (ISSN) Yaghoubi, M ; Shokrollahi Moghani, J ; Noroozi, N ; Zolghadri, M. R ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2018
    Abstract
    In this paper, a fast and practical method is proposed for open-circuit (OC) fault diagnosis (FD) in a three-phase quasi-Z-source inverter (q-ZSI). Compared to the existing fast OC FD techniques in three-phase voltage-source inverters (VSIs), this method is more cost-effective since no ultra-fast processor or high-speed measurement is required. Additionally, the method is independent of the load condition. The proposed method is only applicable to Z-source family inverters and is based on observing the effect of shoot-through (SH) intervals on the system variables during switching periods. The proposed algorithm includes two consecutive stages: OC detection and fault location identification.... 

    On coarse grids simulation of compressible mixing layer flows using vorticity confinement

    , Article Journal of Fluids Engineering, Transactions of the ASME ; Volume 140, Issue 3 , 2018 ; 00982202 (ISSN) Hejranfar, K ; Ebrahimi, M ; Sadri, M ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2018
    Abstract
    In this work, the capability and performance of the vorticity confinement (VC) implemented in a high-order accurate flow solver in predicting two-dimensional (2D) compressible mixing layer flows on coarse grids are investigated. Here, the system of governing equations with incorporation of the VC in the formulation is numerically solved by the fourth-order compact finite difference scheme. To stabilize the numerical solution, a low-pass high-order filter is applied, and the nonreflective boundary conditions are used at the farfield and outflow boundaries to minimize the reflections. At first, the numerical results without applying the VC are validated by available direct numerical... 

    Application of a preconditioned high-order accurate artificial compressibility-based incompressible flow solver in wide range of Reynolds numbers

    , Article International Journal for Numerical Methods in Fluids ; Volume 86, Issue 1 , 2018 , Pages 46-77 ; 02712091 (ISSN) Hejranfar, K ; Parseh, K ; Sharif University of Technology
    John Wiley and Sons Ltd  2018
    Abstract
    In the present study, the preconditioned incompressible Navier-Stokes equations with the artificial compressibility 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 in a wide range of Reynolds numbers. A fourth-order compact finite-difference scheme is utilized to accurately discretize the spatial derivative terms of the governing equations, and the time integration is carried out based on the dual time-stepping method. The capability of the proposed solution methodology for the computations of the steady and unsteady incompressible... 

    Simulation of three-dimensional incompressible flows in generalized curvilinear coordinates using a high-order compact finite-difference lattice Boltzmann method

    , Article International Journal for Numerical Methods in Fluids ; 2018 ; 02712091 (ISSN) Ezzatneshan, E ; Hejranfar, K ; Sharif University of Technology
    John Wiley and Sons Ltd  2018
    Abstract
    In the present study, a high-order compact finite-difference lattice Boltzmann method is applied for accurately computing 3-D incompressible flows in the generalized curvilinear coordinates to handle practical and realistic geometries with curved boundaries and nonuniform grids. The incompressible form of the 3-D nineteen discrete velocity lattice Boltzmann method is transformed into the generalized curvilinear coordinates. Herein, a fourth-order compact finite-difference scheme and a fourth-order Runge-Kutta scheme are used for the discretization of the spatial derivatives and the temporal term, respectively, in the resulting 3-D nineteen discrete velocity lattice Boltzmann equation to... 

    Computational simulation of marangoni convection under microgravity condition

    , Article Scientia Iranica ; Volume 16, Issue 6 B , 2009 , Pages 513-524 ; 10263098 (ISSN) Saidi, M. H ; Taeibi Rahni, M ; Asadi, B ; Ahmadi, G ; Sharif University of Technology
    2009
    Abstract
    In this work, the rising of a single bubble in a quiescent liquid under microgravity condition was simulated. In addition to general studies of microgravity effects, the initiation of hydrodynamic convection, solely due to the variations of interface curvature (surface tension force) and thus the generation of shearing forces at the interfaces, was also studied. Then, the variation of surface tension due to the temperature gradient (Marangoni convection), which can initiate the onset of convection even in the absence of buoyancy, was studied. The related unsteady incompressible full Navier-Stokes equations were solved using a finite difference method with a structured staggered grid. The...