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transition-flow
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Markovian approach to tackle the interaction of simultaneous diseases
, Article Physical Review E ; Volume 100, Issue 6 , 2019 ; 24700045 (ISSN) ; Ghanbarnejad, F ; Meloni, S ; Gomez Gardenes, J ; Sharif University of Technology
American Physical Society
2019
Abstract
The simultaneous emergence of several abrupt disease outbreaks or the extinction of some serotypes of multistrain diseases are fingerprints of the interaction between pathogens spreading within the same population. Here, we propose a general and versatile benchmark to address the unfolding of both cooperative and competitive interacting diseases. We characterize the explosive transitions between the disease-free and the epidemic regimes arising from the cooperation between pathogens and show the critical degree of cooperation needed for the onset of such abrupt transitions. For the competing diseases, we characterize the mutually exclusive case and derive analytically the transition point...
Prediction of transition point on an oscillating airfoil using Neural network
, Article 2007 5th Joint ASME/JSME Fluids Engineering Summer Conference, FEDSM 2007, San Diego, CA, 30 July 2007 through 2 August 2007 ; Volume 2 FORA, Issue PART A , July , 2007 , Pages 33-39 ; 0791842886 (ISBN); 9780791842881 (ISBN) ; Seddighi, M ; Masdari, M ; Sharif University of Technology
2007
Abstract
Dynamic Neural network was used to minimize the amount of data required to predict the location of transition point on a 2-D oscillatory wing. For this purpose, various experimental tests were carried out on a section of a 660kw wind turbine blade. A multi layer non linear perceptrons network was trained using the output signals of four hot films attached on the upper surface of the model. Results show that using only 50% of the test data, the trained network was able to the transition point with an acceptable accuracy. Moreover, the method can predict the transition points at any position of the wing surface for different Reynolds numbers, amplitudes and initial angles of oscillation, and...
Simulation of Transient Flow in Deformable Pipes and Networks
, M.Sc. Thesis Sharif University of Technology ; Borghei, Mahmoud (Supervisor)
Abstract
Water hammer is a pressure surge or wave resulting when a pressurized fluid in motion is forced to stop or change direction suddenly. This phenomenon can cause great amount of damage to the system and should be considered in designing of pipe systems. So, researchers have derived and proposed numerous models using different approaches. In this study a one-dimensional model using Time Splitting Method (TSM) and Double Sweep Method (DSM) are proposed to simulate transient flow in deformable pipes in networks. To solve the equations of momentum and continuity TSM is applied. In addition Brunone model is used to study the effect of unsteady friction on water hammer wave shape and attenuation. To...
Numerical Modeling of Linear and Nonlinear Flow in Saturated Fractured Porous Media
,
M.Sc. Thesis
Sharif University of Technology
;
Pak, Ali
(Supervisor)
Abstract
Study of fluid flow through the porous fractured media is used in many branches of science such as oil production, environment, water resources, geotechnics and mining, and the results of these researches are useful for industries.The porous fractured media consist of two main parts each having different roles. The first is the fracture networks that act as channels to conduct the fluid in the media, and the second is the porous media that act as a storage space for the fluid. The differences of dimensions and ability of fluid conduction between these two parts would cause the flow analysis to be performed in a heterogeneous and non-isotropic media. Moreover, the irregular networks of...
Detail study on improving micro/nano gas mixer performances in slip and transitional flow regimes
, Article Sensors and Actuators, B: Chemical ; Volume 218 , October , 2015 , Pages 78-88 ; 09254005 (ISSN) ; Sabouri, M ; Sharif University of Technology
Elsevier
2015
Abstract
The mixer geometry has substantial effect on mixing performance of different micro/nanomixers. Despite past numerous studies dedicated to mixing of liquid flow streams, there are less efforts to investigate the geometry effects on gas mixing performances. In this work, we focus on gas-gas mixing through different micro/nanoscale mixers under slip and transitional flow regimes. We use the direct simulation Monte Carlo (DSMC) method to provide accurate and reliable results in such flow regimes. To extend our study, we implement different geometrical parameters in our consideration including the mixer size, the impact angle between two incoming gas streams, and the contraction height located in...
The uncertainties of continuum-based cfd solvers to perform microscale hot-wire anemometer simulations in flow fields close to transitional regime
, Article ASME 2016 5th International Conference on Micro/Nanoscale Heat and Mass Transfer, MNHMT 2016, 4 January 2016 through 6 January 2016 ; Volume 2 , 2016 ; 9780791849668 (ISBN) ; Ghorbani, M. R ; Darbandi, H ; Heat Transfer Division ; Sharif University of Technology
American Society of Mechanical Engineers
2016
Abstract
In this study, we simulate the flow and heat transfer during hot-wire anemometry and investigate its thermal behavior and physics using the Computational Fluid Dynamics (CFD) tool. In this regard, we use the finite-volume method and solve the compressible Navier-Stokes equations numerically in slightly non-continuum flow fields. We do not use any slip flow model to include the transitional flow physics in our simulations. Using the CFD method, we simulate the flow over hot-wire and evaluate the uncertainty of CFD in thermal simulation of hot-wire in low transitional flow regimes. The domain sizes and the mesh distributions are carefully chosen to avoid boundary condition error appearances....
A Unified Fve-Ale Approach to Solve Unsteady Laminar to Turbulent Flow on Moving Boundary Domains
, Ph.D. Dissertation Sharif University of Technology ; Darbandi, Masoud (Supervisor) ; Taeibi Rahni, Mohammad (Supervisor)
Abstract
In this study, an arbitrary Lagrangian-Eulerian (ALE) approach is incorporated with a mixed finite- volume-element (FVE) method to establish a novel moving boundary algorithm to simulate unsteady incompressible flow on non-stationary meshes. The method collects the advantages of both finite-volume and finite-element methods as well as the ALE approach in a unified algorithm capable of solving laminar, transient, and turbulent flows in fluid flow problems with moving boundaries. To enhance the robustness of the extended algorithm, we treat the convection terms at the cell faces using a physical influence upwinding scheme, while the diffusion terms are treated using bilinear finite-element...
Developing of Flow in Porous and Semi-Porous Channels with Different Interface Boundary Conditions
, M.Sc. Thesis Sharif University of Technology ; Nouri Borujerdi, Ali (Supervisor)
Abstract
In this study we solve the porous and semi-porous flow in the entrance region in a channel filled with porous material or partially filled with it. We present a semi-analytical method for solving the momentum equation in porous and semi-porous channel and pipes at the development and fully developed regions in order to acquire the entrance length and velocity profile and its dependence to the interface boundary conditions between the porous and fluid flow. For solving the equations of entrance region we utilize the definition of boundary layer and use integral solution. Subliminally we find the thickness of boundary layer at the walls and interface of regions in the porous layer. For fully...
An experimental investigation of transition point over a quasi-2D swept wing by using hot film
, Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 229, Issue 2 , February , 2015 , Pages 243-255 ; 09544100 (ISSN) ; Soltani, M. R ; Masdari, M ; Davari, A ; Sharif University of Technology
SAGE Publications Ltd
2015
Abstract
In this study, we performed experiments to investigate the effect of sweep angle on the transition location of laminar flow to turbulent flow. Three half wing models were used, each having a different sweep angle but with the same aspect ratio in various angles of attack. Two flat plates were used at the ends of the swept wing models to prevent the flow from rolling up over the wing. By simulating flow over infinity swept wing by eliminating tip vertices, the effect of sweep angle on flow transition phenomenon was investigated. The experiments included the study of transition flow via hot-film sensors, which were glued on the wing surface. We found that the small leading-edge radius and low...
DSMC solution of supersonic scale to choked subsonic flow in micro to nano channels
, Article 6th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM2008, Darmstadt, 23 June 2008 through 25 June 2008 ; Issue PART A , 2008 , Pages 985-993 ; 0791848345 (ISBN); 9780791848340 (ISBN) ; Darbandi, M ; Mirjalili, V ; ASME ; Sharif University of Technology
2008
Abstract
In this study, the supersonic and choked subsonic flows through micro/nano channels are investigated using direct simulation Monte Carlo (DSMC) method. The supersonic case is simulated at different Knudsen numbers covering slip to transition flow regimes, while the effects of inlet Mach and back pressure are studied in details. The inlet/outlet pressure boundary conditions are suitably implemented benefiting from the basics of characteristics theory. A behavior similar to the one predicted by the Fanno theory is observed here; i.e., the supersonic flow velocity decelerates up to a choking condition where any further increase in Knudsen number is impossible unless strong normal/oblique shocks...
Effect of amplitude and mean angle-of-attack on the boundary layer of an oscillating aerofoil
, Article Aeronautical Journal ; Volume 112, Issue 1138 , 2008 , Pages 705-713 ; 00019240 (ISSN) ; Bakhshalipour, A ; Sharif University of Technology
Royal Aeronautical Society
2008
Abstract
Extensive experiments were conducted to study the effect of various parameters on the surface pressure distribution and transition point of an aerofoil section used in a wind turbine blade. In this paper details of the variation of transition point on the aforementioned aerofoil are presented. The aerofoil spanned the wind-tunnel test section and was oscillated sinusoidally in pitch about the quarter chord. The imposed variables of the experiments were free stream velocity, amplitude of motion, mean angle-of-attack, and oscillation frequency. The spatial-temporal progressions of the leading-edge transition point and the state of the unsteady boundary-layer were measured using eight...
Mass transfer during drop formation on the nozzle: New flow expansion model
, Article AIChE Journal ; Volume 52, Issue 3 , 2006 , Pages 895-910 ; 00011541 (ISSN) ; Bastani, D ; Taeibi Rahni, M ; Sharif University of Technology
2006
Abstract
An attempt was made to introduce a new approach for evaluating mass transfer during drop formation via definition of a parameter related to the extent of the convective mixing within the growing drop. For this purpose it was assumed that the entrance of the dispersed flow into the growing drop from the nozzle is analogous to the entrance of the flow from a smaller channel to a larger one. This transfer mechanism has been dubbed the "flow expansion." A global time-dependent Reynolds number of growing drop (Regd) was defined based on the equivalent diameter of growing drop as a length scale and also on a velocity scale, which is obtained using this flow expansion assumption. The results show...
Implementation of Time Splitting Projection Method in water hammer modeling in deformable pipes
, Article International Journal of Pressure Vessels and Piping ; Volume 98 , October , 2012 , Pages 30-42 ; 03080161 (ISSN) ; Borghei, S. M ; Bohluly, A ; Sharif University of Technology
Elsevier
2012
Abstract
In this paper Time Splitting Projection Method (TSPM) has been implemented to model transient flow in a deformable pipe. In addition a quasi-steady model and the Brunone unsteady model have been incorporated into the algorithm to consider the effect of static and dynamic friction on the shape and attenuation of pressure waves. The deformation of the cross section of the pipe due to the change of pressure has been considered using Hooke's Law of elasticity. Numerical results of the model have been compared with a simple analytical test and results of experimental measurements for water hammer problem with different Reynolds numbers in a simple pipeline system; besides, numerical stability...
Torque data on non-isothermal rarefied Cylindrical Couette flow
, Article Vacuum ; Volume 121 , November , 2015 , Pages 56-63 ; 0042207X (ISSN) ; Javadi, K ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
Abstract The torque exerted on the walls of a micro cylindrical Couette gas flow is studied using Direct Simulation Monte Carlo (DSMC) method and analytical solutions. An analytical solution for temperature filed under specified wall heat flux condition is proposed using a previously introduced power-law (PL) wall-scaling approach. The results of cylindrical Couette flow under specified wall heat flux condition are compared with those of isothermal flow. The effects of rarefaction, compressibility, tangential momentum accommodation coefficient (TMAC) and gas-surface heat exchange on the torque values are investigated for slip to free molecular flow regimes. The results indicate that the...
Numerical investigation of the forward and backward travelling waves through an undulating propulsor: performance and wake pattern
, Article Ships and Offshore Structures ; Apr , 2015 ; 17445302 (ISSN) ; Abbaspour, M ; Sharif University of Technology
Taylor and Francis Ltd
2015
Abstract
Recently, the mechanisms of natural undulatory locomotion of aquatic animal swimming have become one of the most significant issues for the researchers, swimmers and engineers. This study aims to elucidate and compare the propulsive vortical signature and performance of backward (negative undulation) and forward (positive undulation) travelling waves through a typical fishlike propulsor by a systematic numerical study. The numerical approach uses a pressure-based finite volume method solver to solve Navier–Stokes equations in an arbitrary Lagrangian–Eulerian framework domain containing a two-dimensional NACA 0012 foil moving with prescribed kinematics. Some of the important findings are: (1)...
Experimental investigation of transition on a plunging airfoil
, Article Scientia Iranica ; Volume 17, Issue 6 B , NOVEMBER-DECEMBER , 2010 , Pages 468-479 ; 10263098 (ISSN) ; Rasi Marzabadi, F ; Sharif University of Technology
2010
Abstract
Extensive tests were carried out on a section of a wind turbine blade. The effect of reduced frequency on the boundary layer transition point of the model oscillating in plunge has been investigated. The spatial-temporal progressions of the transition point and the state of the unsteady boundary layer were measured using multiple hot-film sensors. The measurements showed that reduced frequency highly affects variations of the transition point and results in a hysteresis loop in the dynamic transition locations. The dominated frequencies of the boundary layer are found to be a function of the reduced frequency and mean angle of attack
Numerical investigation of the forward and backward travelling waves through an undulating propulsor: performance and wake pattern
, Article Ships and Offshore Structures ; Volume 11, Issue 5 , 2016 , Pages 517-539 ; 17445302 (ISSN) ; Abbaspour, M ; Sharif University of Technology
Taylor and Francis Ltd
2016
Abstract
Recently, the mechanisms of natural undulatory locomotion of aquatic animal swimming have become one of the most significant issues for the researchers, swimmers and engineers. This study aims to elucidate and compare the propulsive vortical signature and performance of backward (negative undulation) and forward (positive undulation) travelling waves through a typical fishlike propulsor by a systematic numerical study. The numerical approach uses a pressure-based finite volume method solver to solve Navier–Stokes equations in an arbitrary Lagrangian–Eulerian framework domain containing a two-dimensional NACA 0012 foil moving with prescribed kinematics. Some of the important findings are: (1)...
Investigation of the pressure distribution and transition point over a swept wing
, Article Scientia Iranica ; Volume 18, Issue 6 , December , 2011 , Pages 1277-1286 ; 10263098 (ISSN) ; Ghorbanian, K ; Masdari, M ; Sharif University of Technology
2011
Abstract
A series of wind tunnel tests are performed to examine the flow field over a swept wing under various conditions. The wing has a laminar flow airfoil section, similar to those of the NACA 6-series. Static pressure distributions over the upper surface of the wing, in both chordwise and spanwise directions, are measured at different angles of attack. The data is employed to predict the transition point at each chordwise section. The skewness parameter of the pressure data shows that this factor drops to zero in the transition region. A comparison of the calculated transition point on the wing surface with that obtained from the 2D computational method shows reasonable agreement over a portion...
Numerical study on boundary layer control using CH4[sbnd]H2[sbnd]air Micro-reacting jet
, Article International Journal of Hydrogen Energy ; Volume 41, Issue 47 , 2016 , Pages 22433-22452 ; 03603199 (ISSN) ; Yahyavi Koochaksarai, M ; Javadi, K ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
The focus of present numerical study is on assessment of control of laminar separation bubble phenomenon using Micro-scale combustion actuators in an airfoil with low Reynolds number under surface effect and free flows. In this way, the characteristics of laminar separation bubble such as its formation, geometry, and transition from laminar to turbulent around airfoil SD8020 in attack angles of 5 and 8° are investigated. Following that, the new combustion actuators in Micro-scale, cold, and hot air-jet injection are introduced to control boundary layer flow in terms of eliminating the separation bubble. Some mechanisms are identified for improvement of methane-air premixed flame...
Extending the Navier-stokes solutions to transition regime in two-dimensional micro- and nanochannel flows using information preservation scheme
, Article Physics of Fluids ; Volume 21, Issue 8 , 2009 ; 10706631 (ISSN) ; Darbandi, M ; Sharif University of Technology
2009
Abstract
The kinetic-theory-based numerical schemes, such as direct simulation Monte Carlo (DSMC) and information preservation (IP), can be readily used to solve transition flow regimes. However, their high computational cost still promotes the researchers to extend the Navier-Stokes (NS) equations beyond the slip flow and to the transition regime applications. Evidently, a suitable extension would accurately predict both the local velocity profiles and the mass flow rate magnitude as well as the streamwise pressure distribution. The second-order slip velocity model derived from kinetic theory can provide relatively accurate velocity profiles up to a Knudsen (Kn) number of around 0.5; however, its...