• Title/Summary/Keyword: Transom stern

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Topological View of Viscous Flow behind Transom Stern (트랜섬 선미 후방의 점성 유동장 Topology 관찰)

  • Kim, Wu-Joan;Park, Il-Ryong
    • Journal of the Society of Naval Architects of Korea
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    • v.42 no.4 s.142
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    • pp.322-329
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    • 2005
  • Viscous flows behind transom stern are analyzed based on CFD simulation results. Stern wave pattern is often complicated due to the abrupt change of stern surface curvature and flow separation at transom. When a ship advances at high speed, whole transom stern is exposed out of water, resulting in the so-called 'dry transom'. However, in the moderate speed regime, stern wave development in conjunction of flow separation makes unstable wavy surface partially covering transom surface, i.e., the so-called 'wetted transom'. Transom wave formation is usually affecting the resistance characteristics of a ship, since the pressure contribution on transom surface as well as the wave-making resistance is changed. Flow modeling for 'wetted transom' is difficult, while the 'dry transom modeling' is often applied for the high-speed vessels. In the present study CFD results from the RANS equation solver using a finite volume method with level-set treatment are utilized to assess the topology of transom flow pattern for a destroyer model (DTMB5415) and a container ship (KCS). It is found that transom flow patterns are quite different for the two ships, in conformity to the shape of submerged transom. Furthermore, the existence of free surface seems to after the flow topology in case of KCS.

A Numerical Method for a High-Speed Ship with a Transom Stern

  • Kyoung Jo-Hyun;Bai Kwang-June
    • Journal of Ship and Ocean Technology
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    • v.8 no.3
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    • pp.8-17
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    • 2004
  • A numerical method is developed for computing the free surface flows around a transom stern of a ship at a high Froude number. At high speed, the flow may be detached from the flat transom stern. In the limit of the high Froude number, the problem becomes a planning problem. In the present study, we make the finite-element computations for a transom stern flows around a wedge-shaped floating ship. The numerical method is based on the Hamilton's principle. The problem is formulated as an initial value problem with nonlinear free surface conditions. In the numerical procedures, the domain was discretized into a set of finite elements and the numerical quadrature was used for the functional equation. The time integrations of the nonlinear free surface condition are made iteratively at each time step. A set of large algebraic equations is solved by GMRES(Generalized Minimal RESidual, Saad and Schultz 1986) method which is proven very efficient. The computed results are compared with previous numerical results obtained by others.

A Study on the Speed Effects of Afterbody Appendage for the Container Carrier (컨테이너 운반선의 선미부가물에 의한 속도성능 향상에 대한 연구)

  • Lim, Chae-Seong;Park, Dong-Woo
    • Special Issue of the Society of Naval Architects of Korea
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    • 2007.09a
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    • pp.32-42
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    • 2007
  • Container vessels are required to have a large KMT to load many containers which requires a wide transom stern form. The wide transom stern generates large stern waves particularly at the scantling draft. This means that reducing the stern wave leads to resistance reduction. Numerical analyses and Model tests for duck-tail of the stern part have been performed to reduce the resistance of the container vessel having the wide transom on the scantling draft and optimize the form of duck-tail with the change of the design parameter i.e. length and edge height. The optimized duck-tail increases the speed by 0.8 % at scantling draft.

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Potential How Analysis for a Hull with the Transom Stern (트랜섬 선미를 가지는 선형의 포텐셜 유동해석)

  • 최희종;전호환
    • Journal of Ocean Engineering and Technology
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    • v.15 no.1
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    • pp.1-6
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    • 2001
  • This study focuses on the potential flow analysis for a hull with the transom stern. The method is based on a low order panel method. The Kelvin type free-surface boundary condition which is known to better fit experimental data for a high speed is applied. To treat a dry transom stern effect a special treatment for the free-surface boundary condition is adopted at the free-surface region after the transom stern. Trim and sinkage, which are important in high speed ships, are considered by an iterative method. Pressure and momentum approaches are used to calculate the wave resistance. Numerical calculations are performed for Athena hull and these results are compared with the experimental data and also other computational results.

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A Preliminary Study about the Stern Hull Form Design of Ship with Transom Stern (트랜섬 선미를 가지는 선박의 선미선형 설계에 관한 기초적 연구)

  • Lee Young-Gill;Kim Kyu-Seok;Kang Dae-Sun;Jeong Kwang-Leol
    • Journal of Ocean Engineering and Technology
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    • v.20 no.3 s.70
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    • pp.88-95
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    • 2006
  • The resistance characteristics of a trimaran are studied, varying the bottom profile and transom stern of the main hull. The bottom profile is varied in three cases (convex, flat, concave). Using the experimental and numerical methods, the resistance performance of each hull form is compared. The experiments are carried out in ship model basin, and the numerical simulations are performed by a finite-difference method, based on the Marker and Cell scheme. Euler and continuity equationsare used for the governing equations of the flaw field around a trimaran with transom stern. The agreement of both results is good. The optimal bottom profiles for transom stern are presented for law-speed and high-speed regions, respectively.

Effect of flap angle on transom stern flow of a High speed displacement Surface combatant

  • Hemanth Kumar, Y.;Vijayakumar, R.
    • Ocean Systems Engineering
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    • v.10 no.1
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    • pp.1-23
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    • 2020
  • Hydrodynamic Drag of Surface combatants pose significant challenges with regard to fuel efficiency and exhaust emissions. Stern flaps have been used widely as an energy saving device, particularly by the US Navy (Hemanth et al. 2018a, Hemanth Kumar and Vijayakumar 2018b). In the present investigation the effect of flap turning angle on drag reduction is numerically and experimentally studied for a high-speed displacement surface combatant fitted with a stern flap in the Froude number range of 0.17-0.48. Parametric investigations are undertaken for constant chord length & span and varying turning angles of 5° 10° & 15°. Experimental resistance values in towing tank tests were validated with CFD. Investigations revealed that pressure increased as the flow velocity decreased with an increase in flap turning angle which was due to the centrifugal action of the flow caused by the induced concave curvature under the flap. There was no significant change in stern wave height but there was a gradual increase in the stern wave steepness with flap angle. Effective length of the vessel increased by lengthening of transom hollow. In low Froude number regime, flow was not influenced by flap curvature effects and pressure recovery was marginal. In the intermediate and high Froude number regimes pressure recovery increased with the flap turning angle and flow velocity.

A Study on the Turbulent Flow Characteristics in the Wake of Transom Sterns using PIV Method (동일입자추적기법을 이용한 트랜섬선미 후류 난류유동특성에 관한 연구)

  • Lee, Gyoung-Woo;Gim, Ok-Sok
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.18 no.4
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    • pp.352-359
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    • 2012
  • An experiment was carried out to figure out the turbulence flow characteristics in the wake of the transom stern's 2-dimensional section by 2-frame grey level cross correlation PIV method at Re= $3.5{\times}10^3$, Re= $7.0{\times}10^3$. The angles of transom stern are $45^{\circ}$(Model "A"), $90^{\circ}$(Model "B") and $135^{\circ}$(Model "C") respectively. The depth of wetted surface is 40mm from free surface. Strong turbulence intensity appears at the interaction between the flow separation of the bottom of a model and the free surface. This study provides statistic flow information such as turbulence intensity, Reynolds stress and turbulence kinetic energy. Model C type (Raked transom) has low Reynolds stress and turbulence kinetic energy.

A Note on the Strip Methods associated with Ship Motion Problems (선체운동(船體運動)에 관(關)한 Strip Method의 일고찰(一考察))

  • Y.J.,Kwon;J.H.,Hwang
    • Bulletin of the Society of Naval Architects of Korea
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    • v.8 no.1
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    • pp.17-28
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    • 1971
  • The coefficients of equations of heave, pitch and coupled motion are evaluated for the small typical fishing boat(KIST-MARK Fishing Boat) with transom stern in regular head sea. And the results of computations based on eight models of strip theory are compared one another for the forward speed Froude number 0.30. There are some distinctive differences among those theories for the hydrodynamic and coupling coefficients. The former seems to be caused by the effects of the transom stern and the latter of the foward speed.

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Nonlinear Potential Flow Analysis for the Hull with a Transom Stern (트랜섬 선미를 가지는 선형의 비선형 포텐셜 유동해석)

  • Choi, Hee-Jong;Lee, Gyoung-Woo;Chang, Yong-Chai
    • Journal of Navigation and Port Research
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    • v.30 no.8 s.114
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    • pp.631-636
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    • 2006
  • In this paper, the wave pattern around the hull with the transom stern advancing on the free surface with a constant speed was taken into consideration. To solve the problem the numerical analysis program was developed using Rankine source panel method based on potential flow analysis technique. The non-linearity of the free surface boundary conditions was fully satisfied. To verify the validity of the developed program the numerical calculations for Athena hull and KCS(KRISO container ship) hull was performed. The results of the numerical computation was compared with the ones of the model test experiment.

PIV Measurement of Viscous Flow Field in the Wake of Transom Stern (PIV기법을 이용한 트랜섬 선미 후류 점성유동장 계측)

  • Lee, Gyoung-Woo;Gim, Ok-Sok
    • Journal of Navigation and Port Research
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    • v.35 no.10
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    • pp.805-810
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    • 2011
  • An experiment was carried out to figure out the instantaneous flow characteristics in the wake of the transom stern's 2-dimensional section by 2-frame grey level cross correlation PIV method at $Re=3.5{\times}103$, $Re=7.0{\times}103$. The stern angles of models were learning at $45^{\circ}$(Model "A"), $90^{\circ}$(Model "B") and $135^{\circ}$(Model "C") respectively based on the survey results of real ships. The depth of wetted surface is 40mm from free surface. As Reynolds number increases, vortices increase in volume and move their way to the downstream. Flow separation appeared at the end of model's bottom.