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Discussing the Behavior of the Boundary Theory Caused by Kalb-Ramond Field Perturbation in the Bulk, Using AdS/CFT Correspondence
, M.Sc. Thesis Sharif University of Technology ; Arfaei, Hessamaddin (Supervisor)
Abstract
In this thesis we have used the low energy effective action of the string theory to find an asymptotic Anti-de sitter metric with a non-vanishing H field. Then we have used the AdS/CFT correspondence to study the effects of the added Kalb_Ramond field on two calculations in the boundary theory. The first one was the calculation of the drag force exerted on a moving quark in the quark-gluon plasma. In the second calculation we observed the effect of the added field on the confinement-de confinement phase transition
Utilising flags to reduce drag around a short finite circular cylinder
, Article Journal of Turbulence ; Volume 19, Issue 3 , 2018 , Pages 229-251 ; 14685248 (ISSN) ; Kiani, F ; Tahaye Abadi, M ; Sharif University of Technology
Taylor and Francis Ltd
2018
Abstract
This paper utilises flags to decrease the drag around a short finite circular cylinder. Wall-adapted large eddy simulation and two-way fluid–structure interaction methods were applied to resolve unsteady turbulent flow structure. The far-field Reynolds number of the current configuration based on the cylinder diameter was chosen to be 20,000. In addition, the length-to-diameter ratio of the cylinder was assumed to be L/D = 2 whereas the flexible flag had a width-to-diameter ratio of W/D = 1.5. The results were compared with the regular short finite circular cylinder and the rigid flagged cylinder in our previous work. The results indicate that utilising flags inside the near-wake region of...
Response spectrum method for extreme wave loading with higher order components of drag force
, Article Journal of Marine Science and Application ; Volume 16, Issue 1 , 2017 , Pages 27-32 ; 16719433 (ISSN) ; Dezfouli, Mani, F ; Dastan Diznab, M. A ; Mohajernasab, S ; Seif, S. M ; Sharif University of Technology
Abstract
Response spectra of fixed offshore structures impacted by extreme waves are investigated based on the higher order components of the nonlinear drag force. In this way, steel jacket platforms are simplified as a mass attached to a light cantilever cylinder and their corresponding deformation response spectra are estimated by utilizing a generalized single degree of freedom system. Based on the wave data recorded in the Persian Gulf region, extreme wave loading conditions corresponding to different return periods are exerted on the offshore structures. Accordingly, the effect of the higher order components of the drag force is considered and compared to the linearized state for different sea...
Experimental analysis of cavitaion effects on drag force and back pressure of circular cylinder with free turbulence
, Article Scientia Iranica ; Volume 16, Issue 4 B , 2009 , Pages 344-353 ; 10263098 (ISSN) ; Rad, M ; Sharif University of Technology
2009
Abstract
The characteristics of a cavitation water tunnel test setup and the experiments of cavitation around a circular cylinder with free stream turbulence are presented in this paper. The Reynolds number of flow is limited in the range of 1.26 × 105 to 3 × 105 and the far upstream flow has free turbulence. Drag force, back pressure, location of cavitation inception, length of cavity and appearance of cavitation are measured or observed and their results are presented here. It was found that the cavitation effects on the boundary layer and separation of flow over the cylinder and drag force become minimum at the cavitation number of 1.94. The cavitation inception occurs in the sub-layer and at an...
Molecular Dynamics Simulation of Nano-Robot Motion in Nano-Scale Flows
, M.Sc. Thesis Sharif University of Technology ; Abbaspour, Madjid (Supervisor) ; Darbandi, Massoud (Supervisor)
Abstract
There is a need to achieve a capability for detailed modeling of the physical processes nano-robots at nano-scales that is driven by the growing demands of nanotechnology.. This is regime where behavior runs contrary to the familiar macroscopic world; optimized engineering design may well benefit from insight gained by emulating some of the multitude of architectures and mechanisms to be found in the biological world. Despite the fact that micro-robotics has long captured the imagination, practical implementations are only now starting to become feasible. One class of nano-robot with potential medical applications was considered that made of single wall carbon nanotube; however, long before...
Experimental and Analytical Investigation of Cavitation Phenomenon around Cylinder and Hydrofoil and its Effect on Drag Force
, Ph.D. Dissertation Sharif University of Technology ; Rad, Manouchehr (Supervisor)
Abstract
Cavitation phenomenon is defined as the process of rupturing of liquid by a decrease in pressure at nearly constant temperature and it is a very complex non- linear phenomenon. Therefore the theoretical and numerical analysis of cavitation is very difficult and even impossible. A high speed cavitation tunnel is designed and manufactured for experimental understanding of cavitation. The effects of cavitation on drag force of several models such as circular cylinder, hydrofoil and wedge with after body were studied. There was a sufficient turbulence provided at upstream flow, during the tests of circular cylinder and hydrofoil within Reynolds number 105 to .Boundary layer on the cylinder is...
Energy Loss of a Heavy Quark Moving Through Quark-Gluon Plasma
, Ph.D. Dissertation Sharif University of Technology ; Arfaei, Hessamaddin (Supervisor) ; Davody, Ali (Co-Advisor)
Abstract
One of the approaches to study the plasma phase of quantum chromodynamics is to investigate the motion of probes in the quark-gluon plasma. In the case of a moving heavy quark, the medium affects the quark by exerting a drag force on it. Since we finally detect hadron jets in detectors, the goal is to compute the darg force formula in a form compatible with the espectrum of final hadrons. On the other hand due to strong coupling, perturbative methods fail in the medium. So a nonperturbative method is needed. We use gauge gravity duality and compute the drag force exerted on a heavy quark in the hydrodynamic regime, up to first order in derivative expansion
Fabrication of Superhydrophobic Surfaces to Decrease Pressure Drop through the Galvanized Pipe and Study about Feasibility of the Fabricated Surface to Use for Non-newtonian Fluid
, M.Sc. Thesis Sharif University of Technology ; Mousavi, Ali (Supervisor) ; Nouri boroojerdi, Ali (Supervisor)
Abstract
Nowdays, one of the most important concerns for scientists is increasing CO2 emmisions and global warming. To overcome this problem, a large number of studies have been carried out to improve energy system performance and reducing the overall energy consumption. One solution to this problem is using the superhydrophobic surfaces with contact angle larger than 150°.In this study, we try to reduce the pressure drop through the galvanized pipes. So, by reducing the pressure drop, power required for pumps can be reduced. To this end, two different coatings by silica nano-particles which were modified with first hydrophobic agent are used. In first coating which is named as PS coating, stearic...
Modeling and CFD simulation of a mixed-convection flow of regular fluids and nanofluids in vertical porous and regular channels
, Article Heat Transfer - Asian Research ; Vol. 43, issue. 3 , May , 2014 , pp. 243-269 ; ISSN: 1523-1496 ; Dehkordi, A. M ; Sharif University of Technology
Abstract
In this article, the problem of combined forced and free convection in vertical porous and regular channels for both regular fluids and nanofluids has been solved using the CFD technique in the entrance regions of momentum and heat transfer taking into account the influences of viscous heating and inertial force. In this regard, various types of viscous dissipation models reported in the literature such as the Darcy model, the power of the drag force model, and the clear fluid-compatible model were applied. In the case of nanofluid flow, both the Brownian and thermophoresis molecular transfer mechanisms were considered. The dimensionless distributions of velocity, temperature, and the volume...
Drag reduction ability of slippery liquid-infused surfaces: A review
, Article Progress in Organic Coatings ; Volume 170 , 2022 ; 03009440 (ISSN) ; Nouri Borujerdi, A ; Moosavi, A ; Sharif University of Technology
Elsevier B.V
2022
Abstract
Devising effective methods to reduce drag forces is of great interest as these methods could prevent the wastage of fuel and decrease carbon emission and the global warming rate. Since the invention of Liquid-Infused Surfaces (LISs) in 2011, numerous investigations have been conducted to study their capability in various applications. Due to recirculation or drawing of the penetrated liquid within the surface structure, these surfaces acquire a slippiness property. The conducted investigations showed that these slippery surfaces have great potential for reducing drag forces, whether in a laminar or turbulent flow. In the present work, we first briefly elucidate common drag reduction methods,...
Investigation of 3D flow in Typical Body and Decrease its Drag Coefficient at Hight Reynolds
, M.Sc. Thesis Sharif University of Technology ; Abbaspoor, Majid (Supervisor) ; Rad, Manoochehr (Co-Advisor)
Abstract
Rapid growth in energy consumption and environmental concerns over conventional power generation technologies has increased the need for alternative energy sources. Kinetic hydropower has been available for decades, however, despite its minimal environmental impact, commercialization has been limited. The main purpose of the first part of this thesis is investigation of flow properties near the convergent-divergent nozzles with various geometries. Two parameters that studied include variation of drag force on body and mean velocity of water flow in middle cross section. In the second part, we studied a horizontal marine current turbine (which its geometry is taken from a NREL wind...
Evaluation of Exerted Drag Force on Alkane Saturated Air Bubbles in Aqueous Solutions by Experimental Studies
, M.Sc. Thesis Sharif University of Technology ; Bastani, Dariush (Supervisor) ; Lotfi, Marzieh (Supervisor)
Abstract
Interfacial phenomena and properties of interphase surfaces in dynamic mode play an important role in industrial processes that include gas-liquid and liquid-liquid multiphase flows. As well as, interface knowledge leads to better understanding of natural and fundamental phenomena. The present study has been performed for understanding about dynamic behavior of interphase surfaces in the presence of nanoparticles and hexane vapor in gas-liquid dispersion systems. In this research, rising bubble method has been used as one of the most conventional techniques. Accordingly, aqueous solutions of nanosilica were prepared in concentrations of 50, 100, 200, 400 and 1200 ppm as continuous phase...
Boundary drag force acting on an impenetrable nano-particle
, Article ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, ESDA2010, 12 July 2010 through 14 July 2010, Istanbul ; Volume 3 , 2010 , Pages 469-473 ; 9780791849170 (ISBN) ; Kebriai, M. H ; Meigounpoury, M. R ; Sharif University of Technology
2010
Abstract
Flow over nano spheres is a fundamental problem encountered in many engineering technical problems and the motion of nano-particles is important in many technical areas, for example nano-organizms motion in aqueous media, super hydrophobic spray for coating materials, nano-capsules for detecting cancer, and additive nano-particles in oil and fuel for automotive engines. In this paper computations are performed to determine the steady flow forces acting on the stationary nano-tube for Reynolds numbers in the range of 0.1
Experimental investigation of drag and lift forces on microparticles in low reynolds number poiseuille flow in microchannel
, Article Journal of Dispersion Science and Technology ; Volume 37, Issue 12 , 2016 , Pages 1767-1777 ; 01932691 (ISSN) ; Saidi, M. H ; Sharif University of Technology
Taylor and Francis Inc
Abstract
In this paper, the hydrodynamic drag and lift forces on microparticles in a dilute suspension in low Reynolds number Poiseuille flow in a microchannel is experimentally investigated using microscopic image analysis. An effective technique is applied to manipulate single-particle tracking in order to determine the velocity field and hydrodynamic forces on microparticles with diameter-to-channel height ratio of 0.1 (Formula presented.) in microchannels. The results show that there is a distance near the walls of the channel in which the hydrodynamic coupling between the particles and channel walls is considerable. Also, the magnitude of drag force that is imposed on the particles with...
Investigation of turbulent flow past a flagged short finite circular cylinder
, Article Journal of Turbulence ; Volume 17, Issue 4 , 2016 , Pages 400-419 ; 14685248 (ISSN) ; Javadi, K ; Sharif University of Technology
Taylor and Francis Ltd
Abstract
This study was conducted to investigate the flow structures of turbulent flow passing over a short finite cylinder in which a rigid flag is attached to the rear of the cylinder, in wake region. The length-to-diameter ratio of the cylinder was chosen to be L/D = 2, whereas the rigid flag had a width-to-diameter ratio of W/D = 1.5. Wall-adapted large-eddy simulation (LES-WALE) was used to resolve unsteady turbulent flow structures. The far field Reynolds number based on cylinder diameter was chosen to be 20,000. The results were compared with the regular case wherein no flag was attached to the cylinder. Results revealed that the flow pattern behind the cylinder with flag was totally different...
Influence of afterbody and boundary layer on cavitating flow
, Article International Journal of Engineering, Transactions B: Applications ; Volume 22, Issue 2 , August , 2009 , Pages 185-196 ; 1728-144X (ISSN) ; Rad, M ; Sharif University of Technology
Materials and Energy Research Center
2009
Abstract
The characteristics of a cavitation water tunnel test setup and the experiments of cavitation around different models are given in this paper. Models of test are formed from combination of head and variable length afterbody. The experiments are performed initially with the smooth head and then with the roughened head. Cavitation initiates both in the wake and after the head. If the nose of models is roughened then cavitation initiates at the lower cavitation numbers. The cavitation inception is a function of the model geometry, nose condition and upstream flow characteristics. During the measuring process of drag force from non-cavitating flow regions to supercavitation case, only the tunnel...
Flexible polymeric tail for micro robot drag reduction bioinspired by the nature microorganisms
, Article Physics of Fluids ; Volume 34, Issue 11 , 2022 ; 10706631 (ISSN) ; Javadi, K ; Sharif University of Technology
American Institute of Physics Inc
2022
Abstract
In nature, most microorganisms have flexible micro/nanostructure tails, which help them create propulsion, reduce drag, or search for food. Previous studies investigated these flexible structures mostly from the propulsion creation perspective. However, the drag reduction and the underlying physical mechanisms of such tails are less known. This scientific gap is more significant when multi-polymeric/hierarchical structures are used. To fill the gap, we use the dissipative particle dynamics (DPD) method as a powerful fluid-polymer interaction technique to study the flexible tails' influences on drag reduction. Note that the flow regime for these microorganisms is in the range of laminar low...
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) ; 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...
Experimental and numerical investigation of drag force over tubular frustum
, Article Scientia Iranica ; Volume 18, Issue 5 , 2011 , Pages 1133-1137 ; 10263098 (ISSN) ; Rad, M ; Sharif University of Technology
Abstract
There are different ways in order to achieve higher velocity in underwater vehicles. One of these methods is using a body with special form. This paper presents a towing tank based experimental study on drag forces for different Reynolds Numbers of a special underwater model. This paper investigates drag force and drag coefficient in a different flow direction over the model. Obtained experimental results in towing tank are explained. Computational Fluid Dynamic (CFD) simulation also is performed using commercial CFD software package FLUENT 6.3.26. There is a significant decrease in drag coefficient of model moving with small diameter at upstream
Mixed-convection flow of nanofluids and regular fluids in vertical porous media with viscous heating
, Article Industrial and Engineering Chemistry Research ; Volume 50, Issue 15 , 2011 , Pages 9403-9414 ; 08885885 (ISSN) ; Golmakani, A ; Dehkordi, A. M ; Sharif University of Technology
2011
Abstract
In this article, the problem of combined forced and natural convection in a vertical porous channel for both regular fluids and nanofluids has been solved by perturbation and numerical methods, taking into account the influences of viscous heating and inertial force. In this regard, various types of viscous dissipation models, including the Darcy model, the power of drag force model, and the clear fluid compatible model, were considered to account for viscous heating. In addition, the mass flux of nanoparticles was also considered in terms of Brownian and thermophoresis mechanisms. The velocity and temperature distributions of both the regular fluid and nanofluid and the Nusselt number...