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    Stochastic nature of series of waiting times

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 87, Issue 6 , 2013 ; 15393755 (ISSN) Anvari, M ; Aghamohammadi, C ; Dashti Naserabadi, H ; Salehi, E ; Behjat, E ; Qorbani, M ; Khazaei Nezhad, M ; Zirak, M ; Hadjihosseini, A ; Peinke, J ; Tabar, M. R. R ; Sharif University of Technology
    2013
    Abstract
    Although fluctuations in the waiting time series have been studied for a long time, some important issues such as its long-range memory and its stochastic features in the presence of nonstationarity have so far remained unstudied. Here we find that the "waiting times" series for a given increment level have long-range correlations with Hurst exponents belonging to the interval 1/2

    Hydroelastic Effects on Energy Harvesting of a Semi-active Flapping-foil Mechanism

    , M.Sc. Thesis Sharif University of Technology Jalali Zeidanlu, Mohammad (Author) ; Ebrahimi, Abbas (Supervisor)
    Abstract
    The purpose of this study is to investigate a flapping hydrofoil with semi-active kinematics for energy harvesting and evaluate the effect of different dynamic parameters and structures on its performance. The turbulent flow field with Re = 5 × 105 around a NACA 0015 hydrofoil is simulated by URANS method using commercial software and the dynamics of the oscillating hydrofoil is modeled as a mass-spring-damper set in combination with the fluid solver. The sliding mesh method is used for the pitching motion of the hydrofoil with a reduced frequency of 0.14 in combination with the dynamic mesh method for Transitional motion. Initially, the oscillating hydrofoil was considered as a single... 

    Levels of complexity in turbulent time series for weakly and high Reynolds number

    , Article Physica A: Statistical Mechanics and its Applications ; Volume 391, Issue 11 , 2012 , Pages 3151-3158 ; 03784371 (ISSN) Shayeganfar, F ; Sharif University of Technology
    2012
    Abstract
    We use the detrended fluctuation analysis (DFA), the detrended cross correlation analysis (DCCA) and the magnitude and sign decomposition analysis to study the fluctuations in the turbulent time series and to probe long-term nonlinear levels of complexity in weakly and high turbulent flow. The DFA analysis indicate that there is a time scaling region in the fluctuation function, segregating regimes with different scaling exponents. We discuss that this time scaling region is related to inertial range in turbulent flows. The DCCA exponent implies the presence of power-law cross correlations. In addition, we conclude its multifractality for high Reynold's number in inertial range. Further, we... 

    Numerical investigation of the inlet baffle, header geometry, and triangular fins effects on plate-fin heat exchangers performance

    , Article Heat Transfer Engineering ; Volume 36, Issue 16 , 2015 , Pages 1397-1408 ; 01457632 (ISSN) Salehi, S ; Afshin, H ; Farhanieh, B ; Sharif University of Technology
    Taylor and Francis Ltd  2015
    Abstract
    In this study, the optimal location of baffle in the header of air-to-air plate heat exchangers and the geometry of the header and the effects of triangular fins arrays on the effectiveness were numerically investigated for different flow rates and Reynolds numbers on different models. The main purpose of inlet baffle and geometry changes is to improve the pattern of flow distribution and assist flow uniformity. The investigations show that the optimal location of the inlet baffle with high Reynolds numbers has an insignificant effect on effectiveness, while with Reynolds numbers 250-3000, the effectiveness is affected significantly by baffle location. On the other hand, the reduction in... 

    Effects of depth variation of vegetation density on vertical mixing

    , Article Environmental Hydraulics - Proceedings of the 6th International Symposium on Environmental Hydraulics, 23 June 2010 through 25 June 2010 ; Volume 1 , June , 2010 , Pages 247-252 ; 9780415595452 (ISBN) Ghazvinizadeh, S ; Jamali, M ; Sharif University of Technology
    2010
    Abstract
    This paper discusses an experimental study of vertical mixing in an aquatic canopy. Vertical variation of physical characteristics of stems is fairly observed in the field and leads to variation in frontal area. This can affect both the flow and the mixing process.We experimentally investigated the effects of vertical density variation on both flow and vertical diffusion at high Reynolds numbers (turbulent flow range). Using rigid cylinders, we simulated step-like density variation in a flume. Vertical mixing coefficient was measured by recording vertical mixing of dye in the flume. The results indicate that vertical mixing coefficient decreases as density increases in depth. Velocity... 

    Investigation of flow dynamics in porous media using computer simulation

    , Article 20th European Simulation and Modelling Conference, ESM 2006, Toulouse, 23 October 2006 through 25 October 2006 ; 2006 , Pages 157-163 Jafari, A ; Zamankhan, P ; Mousavi, S. M ; Pietarinen, K ; Sarkomaa, P ; Sharif University of Technology
    EUROSIS  2006
    Abstract
    The aim of this work is to investigate flow hydrodynamics in porous media. Random non-overlapping spherical particles in a cylindrical geometry were produced as a porous media. Navier-Stokes equations in three-dimensional porous packed bed have been solved and dimensionless pressure drop has been studied for a fluid flow through the porous media at different Reynolds numbers (based on pore permeability and interstitial fluid velocity). The numerical results are in good agreement with those reported by Macdonald (1979) in the range of Reynolds numbers studied. At higher Reynolds numbers turbulent models such as large eddy simulation (LES) and Reynolds stress model (RSM) also have been... 

    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 Hejranfar, K ; 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... 

    Investigation of particle dispersion and deposition in a channel with elliptic obstructions using lattice Boltzmann method

    , Article 2012 7th IEEE International Conference on Nano/Micro Engineered and Molecular Systems, NEMS 2012, 5 March 2012 through 8 March 2012 ; March , 2012 , Pages 523-528 ; 9781467311243 (ISBN) Tehrani, A ; Moosavi, A ; Sharif University of Technology
    2012
    Abstract
    Particle transport and deposition in a channel flow with elliptic obstruction is studied. Numerical simulation of fluid flow is performed using two-dimensional lattice Boltzmann method, while one-way coupling Lagrangian method for particle tracking is used. Standard particles are injected in the inlet of the channel. Gravity, Drag force, Brownian forces, and the Saffman lift are considered in equation of particle motion. The influence of geometrical parameter, ellipse aspect ratio, is studied on dispersion and deposition of particles as well as the flow parameters, such as Reynolds number. In addition, the effect of particles size -particles of 0.01-10μm in diameter- on dispersion and... 

    Solution of burgers' equation using a local-rbf meshless method

    , Article International Journal of Computational Methods in Engineering Science and Mechanics ; Volume 12, Issue 1 , Feb , 2011 , Pages 44-58 ; 15502287 (ISSN) Hosseini, B ; Hashemi, R ; Sharif University of Technology
    2011
    Abstract
    A local radial basis function (RBF) meshless method is applied for solution of the Burgers' equation with different initial and boundary conditions of various complexities. Local-RBF collocation is employed for discretization in space, whilst the unsteady term is handled via a simple explicit time discretization. Moreover, in case of non-smooth initial conditions with high Reynolds numbers, a treatment is proposed for inability of local-RBF methods to solve such problems. The scheme is validated over a variety of benchmark problems and very good agreement is found with existing analytical and numerical solutions  

    Hydrodynamics of secondary settling tanks and increasing their performance using baffles

    , Article Journal of Environmental Engineering ; Volume 136, Issue 1 , 2010 , Pages 32-39 ; 07339372 (ISSN) Tamayol, A ; Firoozabadi, B ; Ashjari, M. A ; Sharif University of Technology
    Abstract
    Generally, the flow in settling tanks is stratified, but the effect of buoyancy force on the flow field depends on the inlet concentration of particles and flow bulk velocity. A common approach for increasing settling tanks performance is to use baffles which can reduce effects of the unfavorable phenomena such as short circuiting between inlet and outlet and density currents in primary and secondary settling tanks, respectively. The suitable position of the baffles is related to the importance of buoyancy force. As a result, effects of inlet Reynolds and Froude numbers on the strength of buoyancy force are studied for a secondary settling tank and the results show that neither Reynolds nor... 

    On spatial filtering of flow variables in high-order finite volume methods

    , Article Computers and Fluids ; Volume 132 , 2016 , Pages 19-31 ; 00457930 (ISSN) Ghadimi, M ; Farshchi, M ; Hejranfar, K ; Sharif University of Technology
    Elsevier Ltd  2016
    Abstract
    A new method of spatial filtering in high-order finite volume methods is presented and assessed. The base of this method is to filter face-averaged variables (fluxes) and then the recovery of cell-averaged ones. Two kinds of filtering method are proposed. The first kind is highly dissipative and appropriate for the numerical regions that need high dissipation, e.g. sponge zones. The second kind, on the other hand, is a precise method and hence is suitable for applying the high-order finite difference filters to the finite volume methods. Applying high-order finite difference filters directly to the high-order finite volume methods without using the proposed method causes stability problems... 

    Effect of non-uniform magnetic field on heat transfer of swirling ferrofluid flow inside tube with twisted tapes

    , Article Chemical Engineering and Processing: Process Intensification ; Volume 117 , 2017 , Pages 70-79 ; 02552701 (ISSN) Mokhtari, M ; Hariri, S ; Barzegar Gerdroodbary, M ; Yeganeh, R ; Sharif University of Technology
    Abstract
    In this article, a three-dimensional numerical simulation is performed to investigate the effect of magnetic field on the heat transfer of ferrofluid inside a tube which is equipped with twisted tape. This work comprehensively focused on the flow feature and temperature distribution of ferrofluid in presence of non-uniform magnetic field while ferrofluid swirled inside a tube with twisted tape. In this study, it is assumed that the ferrofluid is single phase and laminar and constant heat flux is applied on the outside of the tube. The magnetic field is established by wire in parallel direction with the axis of the tube. The base fluid is water with 0.86 Vol% Nano particles (Fe3O4). The... 

    High-order weighted essentially nonoscillatory finite-difference formulation of the lattice boltzmann method in generalized curvilinear coordinates

    , Article Physical Review E ; Volume 95, Issue 2 , 2017 ; 24700045 (ISSN) Hejranfar, K ; Saadat, M. H ; Taheri, S ; Sharif University of Technology
    Abstract
    In this work, a high-order weighted essentially nonoscillatory (WENO) finite-difference lattice Boltzmann method (WENOLBM) is developed and assessed for an accurate simulation of incompressible flows. To handle curved geometries with nonuniform grids, the incompressible form of the discrete Boltzmann equation with the Bhatnagar-Gross-Krook (BGK) approximation is transformed into the generalized curvilinear coordinates and the spatial derivatives of the resulting lattice Boltzmann equation in the computational plane are solved using the fifth-order WENO scheme. The first-order implicit-explicit Runge-Kutta scheme and also the fourth-order Runge-Kutta explicit time integrating scheme are... 

    Numerical investigation of corner angle and wing number effects on fluid flow characteristics of a turbulent stellar jet

    , Article Heat and Mass Transfer/Waerme- und Stoffuebertragung ; Volume 46, Issue 1 , 2009 , Pages 25-37 ; 09477411 (ISSN) Faghani, E ; Saemi, S ; Maddahian, R ; Farhanieh, B ; Sharif University of Technology
    2009
    Abstract
    In this research the fluid dynamics characteristics of a stellar turbulent jet flow is studied numerically and the results of three dimensional jet issued from a stellar nozzle are presented. A numerical method based on control volume approach with collocated grid arrangement is employed. The turbulent stresses are approximated using k-ε and k-ω models with four different inlet conditions. The velocity field is presented and the rate of decay at jet centerline is noted. Special attention is drawn on the influence of corner angle and number of wings on mixing in stellar cross section jets. Stellar jets with three; four and five wings and 15-65° corner angles are studied. Also the effect of...