Search for: hydrodynamics
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    Numerical study on the asymmetric water entry of a wedge section

    , Article China Ocean Engineering ; Volume 18, Issue 4 , 2004 , Pages 595-604 ; 08905487 (ISSN) Seif, M. S ; Mousaviraad, S. M ; Saddathosseini, S. H ; Sharif University of Technology
    The effect of the asymmetric water entry over a submerged part of a ship on the hydrodynamic impact is investigated numerically. A wedge body is considered and the problem is assumed to be two-dimensional. The results of symmetric and asymmetric impacts are compared. The effect is found significant in the numerical simulation. The maximum hydro-dynamic pressure at a heel angle of 10 degrees becomes about 95% more than that of the symmetric entry. The result of the present work proves the importance of asymmetrical hydrodynamic impact loading for structural design of a ship. Besides, the numerical procedure is not limited to a wedge type cross section and it is possible to apply it for any... 

    The effect of asymmetric water entry on the hydrodynamic impact

    , Article International Journal of Engineering, Transactions A: Basics ; Volume 17, Issue 2 , 2004 , Pages 205-212 ; 17281431 (ISSN) Seif, M. S ; Mousaviraad, S. M ; Sadathosseini, S. H ; Sharif University of Technology
    National Research Center of Medical Sciences  2004
    The effect of ihe asymmetric water entry over a submerged part of a ship on the hydrodynamic impact is investigated numerically. A wedge body is considered 10 study and the problem is assumed to be two-dimensional. The Results of symmetric and asymmetric impacts are compared together. The effect is found significant in the numerical simulation. The maximum hydrodynamic pressure at a heel angle of 10 degrees becomes about 95% more than that of the symmetric entry. The result of the present, work proves the importance of asymmetrical hydrodynamic impact leading for structural design of a ship. Besides, the numerical procedure is not limited to a wedge type cross section and it is possible to... 

    Polyelectrolytes polarization in nonuniform electric fields

    , Article International Journal of Modern Physics C ; Volume 25, Issue 12 , 2014 ; ISSN: 17936586 Farahpour, F ; Ejtehadi, M. R ; Varnik, F ; Sharif University of Technology
    Stretching dynamics of polymers in microfluidics is of particular interest for polymer scientists. As a charged polymer, a polyelectrolyte (PE) can be deformed from its coiled equilibrium configuration to an extended chain by applying uniform or nonuniform electric fields. By means of hybrid lattice Boltzmann (LB)-molecular dynamics (MD) simulations, we investigate how the condensed counterions (CIs) around the PE contribute to the polymer stretching in inhomogeneous fields. As an application, we discuss the translocation phenomena and entropic traps, when the driving force is an applied external electric field  

    Effect of concentration on hydrodynamic size of magnetite-based ferrofluid as a potential MRI contrast agent

    , Article Colloids and Surfaces A: Physicochemical and Engineering Aspects ; 2013 ; 09277757 (ISSN) Ahmadi, R ; Gu, N ; Sharif University of Technology
    In this work, ferrofluids containing dextran coated magnetite nanoparticles have been synthesized via co-precipitation method. FT-IR results verified presence of dextran molecules on the particles surface. TEM results showed that mean particle size is 7.23 nm, while mean hydrodynamic size determined via PCS technique varies between 39.8 and 125.8 nm depending on the ferrofluid concentration. The maximum hydrodynamic size was obtained in mid concentrations. To the best of our knowledge, effect of concentration on mean hydrodynamic size has not been systematically studied before. VSM results confirmed the superparamagnetic behavior of the synthesized nanoparticles with saturation magnetization... 

    Evaluation of water impact for symmetric wedge by experimental and numerical methods

    , Article International Journal of Applied Mechanics and Engineering ; Volume 24, Issue 1 , 2019 , Pages 221-230 ; 17344492 (ISSN) Nikfarjam, M ; Koto, J ; Yaakob, O. B ; Seif, M. S ; Aref, A ; Sharif University of Technology
    Sciendo  2019
    Evaluation of impact loads when a ship hull contacts the wave surface is one of the main issues for researchers who are going to design the structure of marine vehicles. In this paper, the results of experimental tests and numerical modeling of the distribution of pressure on different wedge-shaped models are reported and the effect of related parameters such as the deadrise angles, the weight and drop heights, is assessed. The output of analyses and the results can give appropriate approximations of the maximum impact pressures for the geometries that are similar to marine vehicle's hull sections to estimate the hydrodynamic impact loads in different sea-states. In addition, other effective... 

    CFD modeling of gas-liquid hydrodynamics in a stirred tank reactor

    , Article Iranian Journal of Chemistry and Chemical Engineering ; Volume 26, Issue 2 , 2007 , Pages 85-96 ; 10219986 (ISSN) Gorji, M ; Bozorgmehry Bozzarjomehry, R ; Kazemeini, M ; Sharif University of Technology
    Multiphase impeller stirred tank reactors enhance mixing of reacting species used in a variety of chemical industries. These reactors have been studied based on Computational Fluid Dynamics (CFD) that can be used in the analysis, design and scale up of these reactors. Most of the researches done in this area are limited to single phase reactors, and a few remaining two phase flow investigations have been done based on MRF (Multi Reference Frame) and Snapshot approach. However, the MRF and snapshot approaches cannot be used in rigorous simulation of unsteady state problems. In order to simulate the unsteady state behavior of the multiphase stirred tank reactors we have used sliding mesh... 

    Dynamic response of a moored semisubmersible in short-crested wave fields

    , Article Scientia Iranica ; Volume 11, Issue 4 , 2004 , Pages 351-360 ; 10263098 (ISSN) Heidari, A. H ; Borghei, S. M ; Sohrabpour, M ; Sharif University of Technology
    Sharif University of Technology  2004
    Wind generated sea states are more accurately modeled by short-crested wave fields. Whether or not these short-crested waves can induce larger response amplitudes in floating offshore structures is of great concern to offshore engineers. In this paper, the hydrodynamics of a moored semisubmersible in short-crested wave fields is investigated. Morison-based motion equations with nonlinear damping terms are used to analyze the dynamic behavior of the structure. A generalized three-parameter short-crested wave field is introduced as the incident wave. The effect of transverse phase lag, wave propagation angle and different ratios of in-line and transverse wave numbers are studied on the force... 

    Oblique rectangular sharp-crested weir

    , Article Proceedings of the Institution of Civil Engineers: Water and Maritime Engineering ; Volume 156, Issue 2 , 2003 , Pages 185-191 ; 14724561 (ISSN) Borghei, S. M ; Vatannia, Z ; Ghodsian, M ; Jalili, M. R ; Sharif University of Technology
    ICE Publishing  2003
    Among discharge flowmeters, the rectangular sharp-crested weir is one of the most popular and accurate, as well as being easy to work with. Using the standard weir, with the help of the conventional weir equation and Rehbock's or a similar standard formula for the discharge coefficient (Cd), the flow can be easily calculated. In order to increase the efficiency of the weir, it can be placed obliquely to the flow, increasing the effective weir length (L) and, hence, increasing the discharge for the same water head with the same channel width (B). The results of a comprehensive set of tests for oblique weirs (1·14 ≤ L/B ≤ 2·26 or oblique angles from 29° to 64°) show that for L/B less than 1·41... 

    Hydrofoil attack angle effect on hydrodynamic resistance of semi-planning catamaran

    , Article 24th International Conference on Offshore Mechanics and Arctic Engineering, 2005, Halkidiki, 12 June 2005 through 17 June 2005 ; Volume 2 , 2005 , Pages 695-702 Rad, M ; Nakisa, M ; Golnezhad, G ; Askari, M ; Sharif University of Technology
    The present paper contains results of experimental study on a semi-planing catamaran. The aim of this study is to find the effect of hydrofoil usage on resistance of semi-planing catamaran and achieving optimal attack angle, arrangement of hydrofoils and displacement center of gravity. Tests have been done without and with hydrofoils in certain arrangement with different angles of attack then the results are compared. Results show that considerable resistance reduction obtained in semi-planing vessels which equipped with hydrofoil in optimized angle of attack in service speed range. Meanwhile the hydrofoils arrangement and the angle of attack are important so unsuitable design causes the... 

    An experimental investigation of hydrodynamic performance, cavitation, and noise of a normal skew B-series marine propeller in the cavitation tunnel

    , Article Ocean Engineering ; Volume 238 , 2021 ; 00298018 (ISSN) Ebrahimi, A ; Razaghian, A. H ; Tootian, A ; Seif, M. S ; Sharif University of Technology
    Elsevier Ltd  2021
    In this paper, the hydrodynamic performance, cavitation inception, and acoustic performance of a 5-bladed B-series propeller are experimentally investigated in the Sharif University of Technology cavitation tunnel. For hydrodynamic performance, thrust, torque, and efficiency of the propeller model were measured in open water tests. In the cavitation study, in addition to blade cavitation, tip vortex cavitation was also observed, and the cavitation bucket diagram was extracted in different advance coefficients. Finally, for the acoustic analysis of the propeller, the emitted noise in the cavitation tunnel was recorded using two hydrophones according to the recommended procedures of the... 

    Simulation of 2-D dam break using improved incompressible smoothed particle hydrodynamics based on projection method

    , Article Applied Mechanics and Materials ; Volume 390 , 2013 , Pages 81-85 ; 16609336 (ISSN) ; 9783037858332 (ISBN) Pourabdian, M ; Qate, M ; Javareshkian, A ; Farzbod, A ; Sharif University of Technology
    This paper deals with numerical modeling of water flow which is generated by the break of a dam. The problem is solved by applying a new Incompressible Smoothed Particle Hydrodynamics (ISPH) algorithm based on projection method. The proposed ISPH model has two steps. In the first step, the incompressibility of fluid is maintained regarding to the changes of intermediate and initial particles densities at the first half-time step (stability step). In the second step, by computing the divergence of the intermediate secondary velocity at the second half-time step (accuracy step), the incompressibility is satisfied completely. In fact, by using this method both stability and accuracy are... 

    An experimental study of interceptor's effectiveness on hydrodynamic performance of high-speed planing crafts

    , Article Polish Maritime Research ; Volume 20, Issue 2 , 2013 , Pages 21-29 ; 12332585 (ISSN) Karimi, M. H ; Seif, M. S ; Abbaspoor, M ; Sharif University of Technology
    Trim control mechanisms such as interceptors and trim flaps have been widely used in recent years in highspeed crafts for ride and trim control. In spite of their extensive application, a few studies investigating the impact of interceptors on planing craft performance, have been published. In the present study, the impact of interceptors on planing crafts hydrodynamic quality is investigated through application of an experimental method. Two scaled-down models of high-speed planing mono-hull and catamaran are tested with and without interceptors in calm water at different heights of the interceptors to investigate the effect of interceptors on drag reduction of the models. The first one is... 

    Error estimation in smoothed particle hydrodynamics and a new scheme for second derivatives

    , Article Computers and Mathematics with Applications ; Volume 61, Issue 2 , 2011 , Pages 482-498 ; 08981221 (ISSN) Fatehi, R ; Manzari, M. T ; Sharif University of Technology
    Several schemes for discretization of first and second derivatives are available in Smoothed Particle Hydrodynamics (SPH). Here, four schemes for approximation of the first derivative and three schemes for the second derivative are examined using a theoretical analysis based on Taylor series expansion both for regular and irregular particle distributions. Estimation of terms in the truncation errors shows that only the renormalized (the first-order consistent) scheme has acceptable convergence properties to approximate the first derivative. None of the second derivative schemes has the first-order consistency. Therefore, they converge only when the particle spacing decreases much faster than... 

    Hydrodynamic stress correlations in fluid films driven by stochastic surface forcing

    , Article Physical Review Fluids ; Volume 3, Issue 6 , 29 June , 2018 ; 2469990X (ISSN) Mohammadi Arzanagh, M ; Mahdisoltani, S ; Podgornik, R ; Naji, A ; Sharif University of Technology
    American Physical Society  2018
    We study hydrodynamic fluctuations in a compressible and viscous fluid film confined between two rigid, no-slip, parallel plates, where one of the plates is kept fixed while the other one is driven in small-amplitude, translational displacements around its reference position. This jiggling motion is assumed to be driven by a stochastic, external, surface forcing of zero mean and finite variance. Thus, while the transverse (shear) and longitudinal (compressional) hydrodynamic stresses produced in the film vanish on average on either of the plates, these stresses exhibit fluctuations that can be quantified through their equal-time, two-point, correlation functions. For transverse stresses, we... 

    Investigation of Mass Transfer in Liquid-Liquid System in the Presence of Nanosized Particles

    , M.Sc. Thesis Sharif University of Technology Nakhaeipour, Fahimeh (Author) ; Bastani, Dariush (Supervisor)
    The main objective of this project is to study the effect of the presence of nanoparticles on mass transfer in liquid-liquid systems. To do this research, TiO2/water, Al2O3/water, CNTs/water and CNTs/toluene have been used as nanofluids. The experiments of TiO2/water nanofluid were been carried out in water-acetone-toluene system at two weigh percents of TiO2 nanoparticles. The result showed that mass transfer decreased in 0.5wt% of TiO2, compared to base fluid, and it increase in 1 %wt. Also in 0.5%wt the decrease in interfacial tension decreased diameter of drops and as a result mass transfer decreased too. In 1%wt the increase in viscosity increased the diameter of drops and then the... 

    An experimental and numerical prediction of marine propeller noise under cavitating and non-cavitating conditions

    , Article Brodogradnja ; Volume 66, Issue 2 , 2015 , Pages 29-45 ; 0007215X (ISSN) Bagheri, M. R ; Mehdigholi, H ; Seif, M ; Yaakob, O ; Sharif University of Technology
    Brodarski Institute  2015
    In this study, the hydrodynamics and noise prediction of a five blade marine propeller were analyzed through numerical and experimental methods under variety operational conditions. The hydrodynamics of the propeller was studied and the characteristic curves were presented in both numerical and experimental methods. Inception and development of sheet cavitation conditions are obtained in both numerical and experimental methods. The cavitation was started and developed by either increasing the propeller rotational speed in constant pressure or decreasing pressure, while the velocity was kept constant. Good agreements are observed between numerical and experimental results, qualitatively and... 

    Identification of underwater vehicle hydrodynamic coefficients using model tests

    , Article ASME 2010 International Mechanical Engineering Congress and Exposition, IMECE 2010, Vancouver, BC, 12 November 2010 through 18 November 2010 ; Volume 8, Issue PARTS A AND B , 2010 , Pages 165-173 ; 9780791844458 (ISBN) Sadeghzadeh, B ; Mehdigholi, H ; Sharif University of Technology
    Predicting the hydrodynamic coefficients of an autonomous underwater vehicle (AUV) is important during vehicle design. SUT-2 is an AUV. being developed by the Marine Engineering Research Center of Sharif University of Technology in Iran (MERC). Model tests are done in the marine engineering laboratory towing tank. In tins research, hydrodynamic coefficients are calculated using model test results of an autonomous underwater vehicle. Hydrodynamic forces are also analyzed. These coefficients are used for dynamic modeling and autonomous controller design  

    Rans simulation of hydrofoil effects on hydrodynamic coefficients of a planing catamaran

    , Article Brodogradnja ; Volume 67, Issue 1 , 2016 , Pages 43-66 ; 0007215X (ISSN) Najafi, A ; Seif, M. S ; Sharif University of Technology
    Brodarski Institute  2016
    Determination of high-speed crafts’ hydrodynamic coefficients will help to analyze the dynamics of these kinds of vessels and the factors affecting their dynamic stabilities. Also, it can be useful and effective in controlling the vessel instabilities. The main purpose of this study is to determine the coefficients of longitudinal motions of a planing catamaran with and without a hydrofoil using RANS method to evaluate the foil effects on them. Determination of hydrodynamic coefficients by experimental approach is costly, and requires meticulous laboratory equipment; therefore, utilizing numerical methods and developing a virtual laboratory seems highly efficient. In the present study, the... 

    Hydro-acoustic and hydrodynamic optimization of a marine propeller using genetic algorithm, boundary element method, and FW-H equations

    , Article Journal of Marine Science and Engineering ; Volume 7, Issue 9 , 2019 ; 20771312 (ISSN) Ebrahimi, A ; Seif, M. S ; Nouri Borujerdi, A ; Sharif University of Technology
    MDPI AG  2019
    Noise generated by ships is one of the most significant noises in seas, and the propeller has a significant impact on the noise of ships, which reducing it can significantly lower the noise of vessels. In this study, a genetic algorithm was used to optimize the hydro-acoustic and hydrodynamic performance of propellers. The main objectives of this optimization were to reduce the propeller noise and increase its hydrodynamic efficiency. Modifying the propeller geometry is one of the most effective methods for optimizing a propeller performance. One of the numerical methods for calculating propeller noise is the Ffowcs Williams and Hawkings (FW-H) Model. A numerical code was developed by... 

    Unstable modes of non-axisymmetric gaseous discs

    , Article Monthly Notices of the Royal Astronomical Society ; Volume 373, Issue 1 , 2006 , Pages 337-348 ; 00358711 (ISSN) Asghari, N. M ; Jalali, M. A ; Sharif University of Technology
    We present a perturbation theory for studying the instabilities of non-axisymmetric gaseous discs. We perturb the dynamical equations of self-gravitating fluids in the vicinity of a non-axisymmetric equilibrium, and expand the perturbed physical quantities in terms of a complete basis set and a small non-axisymmetry parameter e. We then derive a linear eigenvalue problem in matrix form, and determine the pattern speed, growth rate and mode shapes of the first three unstable modes. In non-axisymmetric discs, the amplitude and the phase angle of travelling waves are functions of both the radius R and the azimuthal angle φ. This is due to the interaction of different wave components in the...