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Cavitation passive control on immersed bodies
, Article Journal of Marine Science and Application ; Volume 16, Issue 1 , 2017 , Pages 33-41 ; 16719433 (ISSN) ; Dorostkar, M. M ; Katal, A ; Sharif University of Technology
Harbin Engineering University
2017
Abstract
This paper introduces a new idea of controlling cavitation around a hydrofoil through a passive cavitation controller called artificial cavitation bubble generator (ACG). Cyclic processes, namely, growth and implosion of bubbles around an immersed body, are the main reasons for the destruction and erosion of the said body. This paper aims to create a condition in which the cavitation bubbles reach a steady-state situation and prevent the occurrence of the cyclic processes. For this purpose, the ACG is placed on the surface of an immersed body, in particular, the suction surface of a 2D hydrofoil. A simulation was performed with an implicit finite volume scheme based on a SIMPLE algorithm...
Stability enhancement of supercavitating projectiles by unsteady air injection
, Article 24th International Conference on Offshore Mechanics and Arctic Engineering, 2005, Halkidiki, 12 June 2005 through 17 June 2005 ; Volume 2 , 2005 , Pages 457-466 ; Yazdani, M ; Sharif University of Technology
2005
Abstract
In this work, numerical simulation is used to study the stability enhancement of high speed supercavitating hydrofoils.Although supercavitation is known as one of the most effective methods for drag reduction, producing the cavity, either by ventilation or by cavitator at front of the body, may cause some instabilities on cavity surface and thus on the projectile's motion. Therefore removing these instabilities comes as an important point of discussion. First of all, we calculate the sources of instabilities and measure respective forces and then present some approaches that significantly reduce these instabilities. One of these methods that could produce more stable supercavities is...
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 ; Nakisa, M ; Golnezhad, G ; Askari, M ; Sharif University of Technology
2005
Abstract
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...
Influence of Control Elements in Numerical Simulation of Ship Motions
, M.Sc. Thesis Sharif University of Technology ; Seif, Mohammad Saeed (Supervisor)
Abstract
Ship motion is one of the most complicated problems in hydrodynamics. These motions accompany with non linear phenomena and their modeling is very difficult. Analytical solution for governing equations for such problems is not possible and experimental study is very expensive. In this state we need remarkable time for investigating of influences of environmental condition changes. In previous research done by Jahanbakhsh and Panahi,a software created that could solve fluid domain and rigid body equations. But the software needs to be developed in some aspects. Aim of this research is expanding of rigid body motion section of software. The software is capable of getting force or moment and...
The Effect of Control Surfaces on Longitudinal Motions of High Speed Catamaran Vessels
, Ph.D. Dissertation Sharif University of Technology ; Seif, Mohammad Saeed (Supervisor)
Abstract
The purpose of this study is extracting a dynamic model of longitudinal motions of high speed catamaran in regular and irregular waves, and then motion control of vessels by using of foil control elements and interceptor. For simulating longitudinal motions in regular waves, at first the longitudinal hydrodynamic coefficients of vessels should be extracted, then by substituting extracted coefficients in cumminz equation and using system identification methods, some equations are presented to estimate longitudinal two degree of freedom motions of high speed catamaran in waves. In this thesis the extraction of hydrodynamic coefficients is based on both numerical and experimental methods. ANSYS...
A Reduced Order Hydroelastic Analysis of 3D Hydrofoil Considering Partial Sheet Cavitation Effects
, Ph.D. Dissertation Sharif University of Technology ; Haddadpour, Hassan (Supervisor) ; Dehghani Firouz-abad, Roohallah (Co-Supervisor)
Abstract
In this Thesis hydroelastic analysis of 3D hydrofoil is investigated while partial sheet cavitation effects are considered. To this aim, first steady cavity boundary must be recognized.This region is calculated by means of conventional iterative procedure, stood upon potential flow theorem. In the second step, the reduced order fluid dynamics equations are derived based on potential flow theorem along with finite element method. This procedure is done in a way that real time system of equations are derived and iterative algorithm of conventional methods is omitted. To this aim, it is assumed that amplitude and frequency of the body oscillations are altered so that the cavity length in...
Optimization of Energy Harvesting from a Flapping Hydrofoil with Prescribed Pitch Profile
, M.Sc. Thesis Sharif University of Technology ; Ebrahimi, Abbas (Supervisor)
Abstract
In present research, a new system of energy extraction from water flow has been studied and optimized. This semi-active energy harvesting system consists of an airfoil that is connected to the generator by an arm. The passage of water causes the airfoil to move, so the hydrodynamic forces on the airfoil will cause the arm to move and finally the generator. In this research, complete dynamic modeling of this energy extraction system including generator, airfoil, controller and actuator modeling is presented and the governing dynamic equations are extracted using this modeling for dynamic simulation. Two dimensional fluid simulations have also been performed using fluent software. Finally, in...
An improved progressive preconditioning method for steady non-cavitating and sheet-cavitating flows
, Article International Journal for Numerical Methods in Fluids ; Volume 68, Issue 2 , December , 2012 , Pages 210-232 ; 02712091 (ISSN) ; Akbarzadeh, P ; Hejranfar, K ; Sharif University of Technology
2012
Abstract
An improved progressive preconditioning method for analyzing steady inviscid and laminar flows around fully wetted and sheet-cavitating hydrofoils is presented. The preconditioning matrix is adapted automatically from the pressure and/or velocity flow-field by a power-law relation. The cavitating calculations are based on a single fluid approach. In this approach, the liquid/vapour mixture is treated as a homogeneous fluid whose density is controlled by a barotropic state law. This physical model is integrated with a numerical resolution derived from the cell-centered Jameson's finite volume algorithm. The stabilization is achieved via the second-and fourth-order artificial dissipation...
Effects of boundary layer control method on hydrodynamic characteristics and tip vortex creation of a hydrofoil
, Article Polish Maritime Research ; Volume 24, Issue 2 , 2017 , Pages 27-39 ; 12332585 (ISSN) ; Tanha, A ; Kourabbasloo, N. N ; Tavakoli, S ; Sharif University of Technology
De Gruyter Open Ltd
2017
Abstract
There is currently a significant focus on using boundary layer control (BLC) approach for controlling the flow around bodies, especially the foil sections. In marine engineering this is done with the hope of increasing the lift - to - drag ratio and efficiency of the hydrofoils. In this paper, effects of the method on hydrodynamic characteristics and tip vortex formation of a hydrofoil are studied. Steady water injection at the tip of the hydrofoil is simulated in different conditions by using ANSYS-CFX commercial software. Validity of the proposed simulations is verified by comparing the obtained results against available experimental data. Effects of the injection on the lift, drag, and...
Hydroelastic analysis of two degree of freedom hydrofoil using a reduced-order hydrodynamic model considering unsteady partial sheet cavity flows
, Article Journal of Fluids and Structures ; Volume 81 , 2018 , Pages 116-130 ; 08899746 (ISSN) ; Haddadpour, H ; Dehghani Firouz Abadi, R ; Sharif University of Technology
Academic Press
2018
Abstract
In the present study a new, fast, precise algorithm for studying hydroelastic stability of a typical section with two degrees of freedom (2DOF) is proposed based on the finite element method (FEM), while the partial sheet cavitation effects are considered. For this means, the steady cavity boundary is calculated by some conventional iterative procedures, developed based on the potential flow simulation. Thereafter, assuming that the amplitude and the frequency of the body oscillations are altered so that the cavity length in unsteady flow remains unchanged, the simulation of the unsteady hydrodynamic flow is performed by imposing some velocity fluctuations over the rigid cavity boundary. For...
Optimal Design of Hydrofoil for Marine Current Turbine
, M.Sc. Thesis Sharif University of Technology ; Abbaspour, Majid (Supervisor)
Abstract
Marine current power has been utilized in recent years as one of the most foreseeable renewable energy sources. In this study a multi-objective hydrofoil optimal design is carried out for use in marine current turbine in order to improve hydrodynamic performance due to low speed current in Qeshm channel. A particle swarm optimization code using FORTRAN is developed and coupled with XFoil software as flow solver that is based on panel method. B-spline curve is used to parameterize the hydrofoil shape and the coordinates values of the control points are designated to act as optimization parameters. Validity of flow solver examined by comparison made between computed data against experimental...
Energy Extraction from Two Oscillating Airfoils in Tandem Configuration at Low-Reynolds-number Turbulent Flow
, M.Sc. Thesis Sharif University of Technology ; Ebrahimi, Abbas (Supervisor)
Abstract
In this study, the physic of an unsteady flow surrounding two oscillating airfoils in tandem configuration at low Reynolds-numbers has been simulated in a 2D manner by utilizing the Sliding-mesh approach and K-ω-SST turbulent model in Ansys-Fluent application. The first step in this study is selecting the decent numerical grid and flow solution scheme. After choosing the proper solution for this problem, next is to verify the methodology with respect to the references. In the next step, The tandem configuration and pitching motion of the airfoils is being implemented with existing tools and the flow structure, leading-edge and trailing-edge vortex shedding and blade-vortex interactions is...
Reynolds-averaged navier-stokes simulation of hydrofoil effects on hydrodynamic coefficients of a catamaran in forced oscillation
, Article Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment ; Volume 231, Issue 2 , 2017 , Pages 364-383 ; 14750902 (ISSN) ; Seif, M. S ; Sharif University of Technology
Abstract
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 Reynolds-averaged Navier-Stokes method to evaluate the foil effects on them. Determination of hydrodynamic coefficients by experimental approach is costly and requires meticulous laboratory equipment; therefore, utilizing the numerical methods and developing a virtual laboratory seem highly...
Investigation of the effect of cavitation passive control on the dynamics of unsteady cloud cavitation
, Article Applied Mathematical Modelling ; Volume 64 , 2018 , Pages 333-356 ; 0307904X (ISSN) ; Moctar, O. E ; Javadi, K ; Sharif University of Technology
Abstract
We present an efficient method to control the evolution of unsteady cloud cavitation around the CAV2003 benchmark hydrofoil using passive cavitation controllers so called cavitation-bubble generators (CGs). Cavitation control may be used in many engineering applications, particularly in the marine and turbo machinery field. We first simulated the unsteady cavitating flow around the hydrofoil without CGs using a Partially-averaged Navier–Stokes (PANS) method, and validated the acquired results against experimental data. We coupled the turbulence model with a mass transfer model and successfully implemented it in the open source toolbox OpenFOAM. Next, we studied the effect of different CGs on...
A reduced-order hydroelastic analysis of 2D hydrofoil considering supercavitation effects
, Article Ships and Offshore Structures ; Volume 13, Issue 6 , 2018 , Pages 584-593 ; 17445302 (ISSN) ; Haddadpour, H ; Firouz Abadi, R. D ; Sharif University of Technology
Taylor and Francis Ltd
2018
Abstract
An efficient two-dimensional reduced-order hydroelastic model for studying supercavitation phenomenonwith zero cavitation number is proposed. In order to compute fluid eigenmodes, unsteady hydrodynamic model is derived using the finite-element method along with the potential flow assumption. This model takes advantage of a new real time, direct algorithm to compute the pressure distribution around the hydrofoil, which avoids any iterative scheme to find cavity extent as like as conventional method. The present approach starts by specifying the steady cavitation domain for the zero cavitation number, then, it is assumed that unsteady cavitation flow around the steady-state leads to small...
Experimental and numerical investigation of marine propeller cavitation
, Article Scientia Iranica ; Volume 16, Issue 6 B , 2009 , Pages 525-533 ; 10263098 (ISSN) ; Hajilouy Benisi, A ; Farhanieh, B ; Sharif University of Technology
2009
Abstract
Cavitating flow is investigated around marine propellers, experimentally and numerically. Two different types of conventional model propellers are used for the study. The first one is a four bladed model propeller, so called model A, and the second one is a three bladed propeller, model B. Model A is tested in different cavitation regimes in a K23 cavitation tunnel. The results are presented in characteristic curves and related pictures. Finally, the results are discussed. Model B is investigated based on existing experimental results. In addition, model B is used for validation of the numerical solution prior to the testing of model A. The cavitation phenomenon is predicted numerically on a...
Stabilization of cloud cavitation instabilities using Cylindrical Cavitating-bubble Generators (CCGs)
, Article International Journal of Multiphase Flow ; Volume 115 , 2019 , Pages 108-125 ; 03019322 (ISSN) ; el Moctar, O ; Javadi, K ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
Unsteady cloud cavitation phenomenon is an important subject due to its undesirable effects in various applications such as ship propeller, rudder and hydraulic machinery systems. We present an efficient passive control method to control the cavitation instabilities which may be caused by the shedding of cavity structures in the vicinity of the solid surface of an immersible body. We proposed a passive control method so called Cylindrical Cavitating-bubble Generators (CCGs) on the surface of a benchmark hydrofoil and analyzed the effects of this passive controller on the dynamics of the unsteady cloud cavitation. First we modeled the unsteady cavitating flow around the hydrofoil without CCGs...