Search for: velocity-profiles
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    Velocity distribution profile for robot arm motion using rational Frenet-Serret curves

    , Article Informatica ; Volume 17, Issue 1 , 2006 , Pages 69-84 ; 08684952 (ISSN) Ravani, R ; Meghdari, A ; Sharif University of Technology
    IOS Press  2006
    The aim of this paper is to demonstrate that the techniques of Computer Aided Geometric Design such as spatial rational curves and surfaces could be applied to Kinematics, Computer Animation and Robotics. For this purpose we represent a method which utilizes a special class of rational curves called Rational Frenet-Serret (RF) curves for robot trajectory planning. RF curves distinguished by the property that the motion of their Frenet-Serret frame is rational. We describe an algorithm for interpolation of positions by a rational Frenet-Serret motion. Further more we present an algorithm for tracking the constructed RF motion to achieve the desired velocity distribution profile of robot arm.... 

    Experimental investigation of the effect of obstacles on the behavior of turbidity currents

    , Article Canadian Journal of Civil Engineering ; Volume 40, Issue 4 , 2013 , Pages 343-352 ; 03151468 (ISSN) Oshaghi, M. R ; Afshin, H ; Firoozabadi, B ; Sharif University of Technology
    Turbidity current is produced when a particle-laden fluid flows under lighter ambient fresh fluid. The streaming of particle-laden fluid is called a turbidity current and this kind of current is an important mechanism for sediment transportation in lakes and oceans. In the present research, the main concentration is on the effect of obstacle with an isosceles right triangular cross section on the behavior of turbidity current. A series of laboratory experiments were carried out with various obstacle heights and different inlet densimetric Froude numbers. In each experiment, velocity profiles upstream and downstream of the obstacle were measured, using an acoustic Doppler velocimeter. Kaolin... 

    Experimental study of obstacle effect on sediment transport of turbidity currents

    , Article Journal of Hydraulic Research ; Volume 56, Issue 5 , 2018 , Pages 618-629 ; 00221686 (ISSN) Abhari, M. N ; Iranshahi, M ; Ghodsian, M ; Firoozabadi, B ; Sharif University of Technology
    Taylor and Francis Ltd  2018
    The effects of an obstacle on the suspended load transport rate of supercritical turbidity currents were investigated experimentally. A Vectrino velocity meter was used to measure velocity and sediment concentration profiles. The effects of important parameters including inlet discharge, mean inlet sediment concentration and obstacle height on suspended load transport rate were investigated. In the upstream velocity profiles, the obstacle generates the reflected and the interface regions in addition to the wall and the jet regions. The average amount of suspended load transport rate downstream of the obstacle decreases to about 92%. This confirms the depositional behaviour of turbidity... 

    Experimental investigation of unsteady wake behind a section of a wind turbine blade

    , Article 25th AIAA Applied Aerodynamics Conference, 2007, Miami, FL, 25 June 2007 through 28 June 2007 ; Volume 2 , 2007 , Pages 870-876 ; 10485953 (ISSN) ; 1563478986 (ISBN); 9781563478987 (ISBN) Soltani, M.R ; Mahmoudi, M ; Sharif University of Technology
    A series of experiments were carried out to study the unsteady wake phenomenon behind an oscillating airfoil. The airfoil is a section of a wind turbine blade oscillating in pitch about the quarter chord axis at various reduced frequencies, oscillation amplitude and mean angles of attack. Streamwise velocity profiles were obtained by real time and instantaneous measurements at 35 vertically aligned points behind the airfoil via two similar rakes. One of rakes has only static pressure probes and the other is equipped with total pressure ones. An estimation of the variation of linear momentum defect during the oscillation is obtained and has been compared with the corresponding static one. The... 

    Qualitative Study of the Dynamic Adsorption Layer by Bubble Rising Method

    , M.Sc. Thesis Sharif University of Technology Bahmani, Alireza (Author) ; Bastani, Dariush (Supervisor) ; Lotfi, marzieh (Co-Advisor)
    Surface phenomena and dynamic interfacial properties plays a significant role in multiphase gas-liquid & liquid-liquid processes applied in different industrial applications. However, current laboratory equipment and represented methods for dynamic and unsteady state condition caused by motivation of interface of two phases (like rising bubble), in purpose of qualitative investigation of interphase properties are not satisfying enough. Also, common modeling methods are represented with lots of modified assumptions which are not validated properly with experimental results. In current thesis, with development of laboratory tools and applying the “rising bubble method” for investigating the... 

    Experimental Investigation of Three Dimensional Turbidity Current

    , M.Sc. Thesis Sharif University of Technology Sheikhi Ahangarkolaei, Javad (Author) ; Firoozabadi, Bahar (Supervisor)
    Dense underflows are continuous currents which move down slope due to the fact that their density is heavier than ambient water. Driven by density differences between the inflow and clear water in the reservoirs, the density current plunges the clear water and moves on the bed. While density currents flowing on a sloping bed, the vertical spreading due to water entrainment plays an important role in determining the propagation rate in the longitudinal direction. These currents are similar to wall-jet currents according to structure of the flows but are complicated relative to wall-jet currents due to the existence of density difference. Characteristics of the density current sometimes are... 

    Experimental Study on Behavior of Turbidity Currents with Obstacle

    , M.Sc. Thesis Sharif University of Technology Oshaghi, Mohammad Reza (Author) ; Afshin, Hossein (Supervisor) ; Firoozabadi, Bahar (Co-Advisor)
    Turbidity currents are produced when a particle laden fluid flows under the lighter ambient fresh fluid. The streaming of particle laden fluid is called turbidity current and this kind of currents is the major mechanism for sediment transportations in lakes and oceans. In the present research, the main concentration is on the effect of obstacle on the behavior of turbidity current. A series of laboratory experiments were carried out with various obstacle heights, shapes and different inlet densimetric Froude numbers. In each experiment, velocity profiles upstream and downstream of the obstacle were measured, using an ADV (Acoustic Doppler Velocimeter). Kaolin was used as the suspended... 

    The Design of Ventricular Assist Devices and Analysis of Blood Flow Within them

    , M.Sc. Thesis Sharif University of Technology Tabrizchi, Zahra (Author) ; Ahmadian, Mohammad Taghi (Supervisor) ; Afshin, Hossein (Supervisor)
    Heart is a muscular organ, which pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste to the lungs. Heart is sort of like a pump, or two pumps in one. The right side of heart receives blood from the body and pumps it to the lungs. The left side of the heart does the exact opposite: It receives blood from the lungs and pumps it out to the body. However, in end-stage heart failure, the heart can no longer pump enough blood to meet the body’s needs, in which case implantable left ventricular assist devices provide support for patients at risk of death from end-stage heart failure.Centrimag... 

    Long-lived and unstable modes of Brownian suspensions in microchannels

    , Article Journal of Fluid Mechanics ; Volume 701 , 2012 , Pages 407-418 ; 00221120 (ISSN) Khoshnood, A ; Jalali, M. A ; Sharif University of Technology
    We investigate the stability of the pressure-driven, low-Reynolds-number flow of Brownian suspensions with spherical particles in microchannels. We find two general families of stable/unstable modes: (i) degenerate modes with symmetric and antisymmetric patterns; (ii) single modes that are either symmetric or antisymmetric. The concentration profiles of degenerate modes have strong peaks near the channel walls, while single modes diminish there. Once excited, both families would be detectable through high-speed imaging. We find that unstable modes occur in concentrated suspensions whose velocity profiles are sufficiently flattened near the channel centreline. The patterns of growing unstable... 

    A general methodology for bearing design in non-symmetric T-shaped sections in extrusion process

    , Article Journal of Materials Processing Technology ; Volume 212, Issue 1 , 2012 , Pages 249-261 ; 09240136 (ISSN) Meybodi, A. K ; Assempour, A ; Farahani, S ; Sharif University of Technology
    In this study, a general methodology has been developed to design the proper bearing in order to eliminate the curvature of the final product in extrusion process. Three smooth curved (advanced-surface) dies with non-symmetric T-shaped sections and different off-centricities have been studied. For each die, the proper bearing has been designed and physical and numerical modeling have been performed to validate the design. The design procedure is as follows: A formulation, based on Bezier curves, has been used to determine the exit velocity profile. Since the result of Bezier method is different from the actual velocity profile, the Chitkara corrective function has been modified and applied... 

    Experimental observation of the flow structure of turbidity currents

    , Article Journal of Hydraulic Research ; Volume 49, Issue 2 , 2011 , Pages 168-177 ; 00221686 (ISSN) Nourmohammadi, Z ; Afshin, H ; Firoozabadi, B ; Sharif University of Technology
    The structure of turbidity currents released on a sloping bed below fresh water is investigated. Kaolin is used as a suspended material. Laboratory observations indicate that if a dense layer moves through the channel, the current thickness increases due to a hydraulic jump. This phenomenon occurs under special inlet conditions and has a significant effect on the current structure including velocity profile, current height and bed shear stress. Flows with different inlet Froude numbers based on various inlet concentrations behave more distinctly than those based on different inlet opening heights. Laboratory experiments indicate that an increase in the inlet Froude number causes an increase... 

    Dynamics of Rear Stagnant Cap formation at the surface of spherical bubbles rising in surfactant solutions at large Reynolds numbers under conditions of small Marangoni number and slow sorption kinetics

    , Article Advances in Colloid and Interface Science ; Volume 222 , 2015 , Pages 260-274 ; 00018686 (ISSN) Dukhin, S. S ; Kovalchuk, V. I ; Gochev, G. G ; Lotfi, M ; Krzan, M ; Malysa, K ; Miller, R ; Sharif University of Technology
    Elsevier  2015
    On the surface of bubbles rising in a surfactant solution the adsorption process proceeds and leads to the formation of a so called Rear Stagnant Cap (RSC). The larger this RSC is the stronger is the retardation of the rising velocity. The theory of a steady RSC and steady retarded rising velocity, which sets in after a transient stage, has been generally accepted. However, a non-steady process of bubble rising starting from the initial zero velocity represents an important portion of the trajectory of rising, characterized by a local velocity profile (LVP). As there is no theory of RSC growth for large Reynolds numbers Re « 1 so far, the interpretation of LVPs measured in this regime was... 

    Numerical Simulation of Saccardo Ventilation System in Tunnel Fire Scenarios

    , M.Sc. Thesis Sharif University of Technology Ganjiazad, Rouhollah (Author) ; Afshin, Hossein (Supervisor) ; Farhanieh, Bijan (Supervisor)
    While the population of the cities all over the world is increasing, more and more tunnels and underground transportation passages are being constructed. So, there is an urgent need for designing an appropriate ventilation system for these passages, not only in normal conditions but also for emergency scenarios especially in fire incidents.In the present research, the operation of Saccardo ventilation system, especially in emergency fire scenarios is investigated using computational fluid dynamics methods. Studies conducted in this research are classified into five parts.In the first part, the effect of tunnel ventilation flow rate (due to Saccardo system operation) and its interaction with... 

    Numerical and One Dimensional Modeling of Cardiovascular System

    , M.Sc. Thesis Sharif University of Technology Molaei, Mehdi (Author) ; Saeedi, Mohammad Saeed (Supervisor) ; Firoozabadi, Bahar (Supervisor)
    Cardiovascular diseases are most common causes of deaths in the whole world. Nowadays, engineers and scientists in various fields become intent on finding solutions for prevention and recovery of these diseases. In this way, it is very important to know about the blood flow in arterial systems and its changes in various diseases. Numerical simulation of the blood flow beside of experimental studies could be very useful in this way. One dimensional simulation among various methods of numerical simulation was chosen to simulate a cardiovascular system since it has smaller computational cost and ability to modeling of whole arterial systems. It also is useful in extraction of medical indexes.... 

    Role of Non-Dimensional Numbers in Density Current Stability

    , M.Sc. Thesis Sharif University of Technology Nourmohammadi, Zahra (Author) ; Firoozabadi, Bahar (Supervisor)
    Density currents are occurred as a result of the intrusion of a dense fluid into a fluid with a different density. Density differences are typically caused by the difference in temperature, existence of solution or insoluble material and suspended solids. A special kind of density current is called a turbidity current which is a sediment-laden density current. This is a kind of flow which is driven by the force of gravity on suspended sediment particles that causes an excess fractional density with respect to the surrounding ambient fluid. In this work, the 2-D sediment-laden density current on a sloping surface of the channel is investigated through experiments. The channel is 12 m long,... 

    Investigation on the Hydrodynamic Behavior of Spouted beds with Draft Tube

    , M.Sc. Thesis Sharif University of Technology Morad Soltani, Pooria (Author) ; Molaei Dehkordi, Asghar (Supervisor)
    Spouted beds are widely used in various process industries as an appropriate gas-solid contacting device. Thus, it is of great importance to study their hydrodynamics as a way of improving their design and efficiency. Furthermore, adding a draft tube to spouted beds considerably changes their hydrodynamic behavior. In this research work, the influences of different parameters involved in the simulation of spouted beds were examined to choose the appropriate ones that can reproduce the experimental data reported in the literature. In this regard, Wen and Yu drag model, Lun et al. radial distribution function, a restitution coefficient of 0.95, and a specularity coefficient of 0.02 were chosen... 

    High frequency oscillatory flow in micro channels

    , Article Colloids and Surfaces A: Physicochemical and Engineering Aspects ; Vol. 460 , 2014 , pp. 355-360 ; ISSN: 09277757 Karbaschi, M ; Javadi, A ; Bastani, D ; Miller, R ; Sharif University of Technology
    This paper deals with computational and experimental studies on the oscillatory flow at high frequencies up to 100. Hz performed with the Oscillating Drop and Bubble Analyzer (ODBA) setup based on the capillary pressure technique. The CFD results are validated considering pressure amplitude experimental data. The simulated results of phase shift between the generated oscillatory flow and the consequent pressure amplitudes show also good agreement with the experimental data. In absence of any compressibility and viscoelasticity effects and assumptions, a complex velocity field during oscillation is the main reason for the observation of a phase shift. The results of velocity profiles at the... 

    Mixed electroosmotically and pressure-driven flow with temperature- dependent properties

    , Article Journal of Thermophysics and Heat Transfer ; Volume 25, Issue 3 , Sep , 2011 , Pages 432-442 ; 08878722 (ISSN) Sadeghi, A ; Yavari, H ; Saidi, M. H ; Chakraborty, S ; Sharif University of Technology
    The present work reports the outcome of a comprehensive parametric study on mixed electroosmotically and pressure-driven flow in slit microchannels with constant wall heat fluxes. Special attention is given to disclose the applicability ranges of usual assumptions in simplified analyses. The governing equations for fully developed conditions are first made dimensionless and then solved by means of an implicit finite difference method. The results reveal that the assumption of constant thermophysical properties does not leadto significant errors in practical applications. Although the Debye-Huckel linearization may successfully be used to evaluate velocity profiles up to the zeta potentials... 

    Dissipative particle dynamics simulation of electroosmotic flow in nanoscale channels

    , Article 48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, Orlando, FL, 4 January 2010 through 7 January 2010 ; 2010 ; 9781600867392 (ISBN) Darbandi, M ; Zakeri, R ; Schneider, G. E ; Sharif University of Technology
    This Paper presents the simulation of electroosmotic flow in nanochannels using the dissipative particle dynamics (DPD) method. Most of the past electroosmotic phenomenon studies have been carried out using the continuum flow assumptions. However, there are many electroosmotic applications in nanoscales NEMS and microscales MEMS, which need to be treated using non-continuum flow assumptions. We simulate the electroosmotic flow within the mesoscopic scale using the DPD method. Contrary to the ordinary molecular dynamics method, the DPD method provides less computational costs. We will show that the current DPD results are in very good agreement with other available non-DPD results. To expand... 

    DPD simulation of electroosmotic flow in nanochannels and the evaluation of effective parameters

    , Article 10th AIAA/ASME Joint Thermophysics and Heat Transfer Conference, 28 June 2010 through 1 July 2010, Chicago, IL ; 2010 ; 9781600867453 (ISBN) Darbandi, M ; Zakeri, R ; Schneider, G. E ; Sharif University of Technology
    We provide the simulation of electroosmotic phenomenon in nanochannels using the Dissipative Particle Dynamics (DPD) method. We study the electroosmotic phenomenon for both newtonian and non-newtonian fluids. Literature shows that most of past electroosmotic studies have been concentrated on continuum newtonian fluids. However, there are many nano/microfluidic applications, which need to be treated as either non-newtonian fluids or non-continuum fluids. In this paper, we simulate the electroosmotic flow in nanochannel considering no limit if it is neither continuum nor non-nonewtonian. As is known, the DPD method has several important advantages compared with the classical molecular dynamics...