Journal of Hydrospace Technology
- 기계 ＞ 조선/해양시스템
Van, Suak-Ho;Kim, Hyoung-Tae 1
This paper presents the result of a computational study on the wake characteristics of two tanker models, i.e. HSVA and Mystery hull forms. The focus of the study is on the distributions of axial, radial and tangential velocities of the two hull forms in way of the propeller, especially over the propeller disk. The effect of bilge vortices on the velocity distribution is also concerned. For the computation of stern and wake flows of the two hull farms, the incompressible Reynolds-Averaged Wavier-Stokes(RANS) equations are numerically solved by the second order finite difference method, which employs a four stage Runge-Kutta scheme with a residual averaging technique and the Baldwin-Lomax model. The calculated pressure distributions on the hull surface and the axial, radial and tangential velocity distributions over the propeller disk are presented for the two hull forms. Finally, the result of wake analysis for the computed wake distribution over the propeller disk is given in comparison with those for the experimental wake distribution fur the both hull forms.
Kim, Wu-Joan;Shin, Myung-Soo 14
The Reynolds-averaged Navier-Stokes equations for turbulent flow around a two-dimensional foil section moving ova. a flat surface (roller plate) is solved. The numerical method utilized the finite-difference schemes in collocated grids and the Baldwin-Lomax model is employed for turbulence closure. Calculations are carried out for three foil sections of different mean-line shape with various height ratio. As a foil approaches the bottom surface, the lift is augmented, while there exist some differences in pitching moment due to mean-line shape. It was found that the S-shaped mean line deteriorates lift characteristics but increases pitching moment to restore the designed height.
Estimation of Manoeuvring Coefficients of a Submerged Body using Parameter Identification TechniquesKim, Chan-Ki;Rhee, Key-Pyo 24
This paper describes parameter identification techniques formulated for the estimation of maneuvering coefficients of a submerged body. The first part of this paper is concerned with the identifiability of the system parameters. The relationship between a stochastic linear time-invariant system and the equivalent dynamic system is investigated. The second is concerned with the development of the numerically stable identification technique. Two identification techniques are tested; one is the ma7mum likelihood (ML) methods using the Holder & Mead simplex search method and using the modified Newton-Raphson method, and the other is the modified extended Kalman filter (MEKF) method with a square-root algorithm, which can improve the numerical accuracy of the extended Kalman filter. As a results, it is said that the equations of motion for a submerged body have higher probability to generate simultaneous drift phenomenon compared to general state equations and only the ML method using the Holder & Mead simplex search method and the MEKF method with a square-root algorithm gives acceptable results.
Lee, Seung-Joon;Joo, Young-Ryeol 36
In this work, a panel method is described, which cart solve the flow field round a surface-piercing body that experiences lift and wave resistance. As the body boundary condition, a Dirichlet type is employed, and as the free surface boundary condition the Poisson type is implemented, while in its discretization Dawson's 4-point upwind difference scheme is utilized, and as the Kutta condition a Morino-Kuo type is chosen. As to the type of singularity, source panels are distributed on the free surface, and source and dipole panels on the body surface, and dipole panels on the wake surface. For a sample run, a catamaran of the parabolic Wigley hull is chosen, for which experimental data are available, and the predictions by the numerical means and by the experiment are compared for a wide range of parameters.
Kim, Gyeong-Hwan;Kim, Hyo-chul 44
The effects of the air on the reductions in resistance when supplied under the bottom of a semi-planing ship with a step are investigated in the present study. A 1.275m long FRP model is constructed and the pressure and viscous tangential stresses over the planing surface of the hull with and without air supply are measured through measuring holes carefully selected at the towing tank of Seoul National University. Locations of holes most suitable for air injection are surveyed in front of the planing surface of the model with careful examinations of the limiting streamlines and pressure distributions measured without air supply. At those locations, found to be just front of the step, air has been supplied into a wake region to form an air filled cavity of fixed type. Flow rates and pressure of the supplied air as well as the local pressure and shear stress distributions on the hull surface are measured to understand the physics involved as well as to determine the conditions most effective in resistance reduction at the design speed. It has been found that total resistance of the stepped semi-planing hull can be considerably reduced if an air cavity generated by an adequate air injection at the bottom of the hull near the step. After the cavity optimized at the given speed, air bubbles also have been generated right behind the point where dividing streamlines re-attach to further reduce the frictional resistance but found to be not so effective as the air cavity in resistance reductions.
Choi, Jung-Eun 57
The formulation for hybrid-QUICK scheme of convective transport terms in finite-volume calculation procedure is presented. Source terms are modified to apply the hybrid-QUICK scheme. Test calculations are performed for wall-driven cavity flow at Re=
$10_2$, $10_3$, and $10_4$. These include the evaluation of boundary conditions approximated by third-order finite difference scheme. The stable and converged solutions are obtained without unsteady terms in the momentum equations. The results using hybrid-QUICK scheme show no difference with those using hybrid scheme at low Re ( $=10_2$) and are better at higher Re ( $10_3$, and $10_4$).
Yang, Seung-Il;Shin, Myung-Soo;Park, Yong-Jea;Min, Keh-Sik;Kim, Jae-Shin;Kim, Hyo-chul;Hong, Sung-Wan;Lee, Seung-Hee;Lee, Young-Gill;Chung, Jung-Han 68
The present report describes the results of the cooperative experimental study organized by the High-Speed Marine Vehicle Committee of the Korea Towing Tank Conference. The study aims to improve model test technique and accuracy and to self-evaluate their own capabilities. The resistance tests of a 23m class planing hull were performed at the towing tanks of the Korea Research Institute of Ships and Ocean Engineering (KRISO), Hyundai Maritime Research Institute (HMRI), Seoul National University (SNU), Inha University (IU) and Pusan National University (PNU). In addition, the longitudinal wave cut was measured antral and analyzed at the KRISO. All the results of total resistance, trim and mean sinkage are presented in this report and the results show fairly good agreements comparing with the ITTC HSMV committee's report.
Shin, Jong-Gye;Lee, Jae-Yeul 80
A creep-buckling analysis is studied for a simply-supported viscoelastic column. The fluid-type four-parameter model is employed because of its general applicability to creep materials. Using the imperfection-based incremental approach, a nonlinear load deflection equation is derived. Safe load and critical (or life) time which characterize the stability of the viscoelastic column are obtained mathematically and interpreted physically. A finite difference algorithm is applied to solve the second-order differential equation of the viscoelastic stress-strain relation. Numerical calculation has been made and discussed far a SUS316 stainless steel column.