• Title/Summary/Keyword: 문풀

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해상상태별 2차원 문풀내 유동 특성에 관한 연구

  • Lee, Sang-Min;Im, Nam-Gyun
    • Proceedings of the Korean Institute of Navigation and Port Research Conference
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    • 2013.06a
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    • pp.127-129
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    • 2013
  • 문풀은 해저케이블선, 해저탐사선, 생산용 부선, 드릴쉽과 같은 여러 종류의 선박에 설비되어 해상에서 각 작업에 필요한 장비의 진수 및 작업공간으로 활용되고 있다. 이러한 문풀내 자유수면의 유동은 정수중 부유체의 이동으로 인한 것과 작업중인 부유체에 작용하는 입사파에 의해 기인하는 것으로 알려져 있다. 본 연구에서는 입사파에 의한 문풀내 유동 특성을 분석하기 위하여 다양한 해상상태, 즉 서로 다른 파고와 파장에서의 자유수면의 변화와 문풀에 작용하는 유체력 계산을 CFD에 의하여 수행하였다. 수치 계산 결과 문풀내 수면 상승 및 유체력은 파고 및 파장에 의해 크게 영향을 받고 이것은 보오텍스와 같은 비선형 현상에 의한 것임을 확인할 수 있었다.

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Effects of Scale Ratio on Flow Characteristics in Moonpool (축척비가 문풀 내부 유동 특성에 미치는 영향)

  • Lee, Sang Bong
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.22 no.1
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    • pp.118-122
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    • 2016
  • When a geometric size of moonpool and an inflow velocity are determined based on the similarity of Froude number, Reynolds number is depending on the scale ratio of moonpool geometry. It means that different characteristics of flow fluctuations in moonpool can be observed depending on the scale ratio of moonpool even though Froude number is the same. In the present study two dimensional numerical simulations were performed to investigate the influence of scale ratios on the flow characteristics inside the moonpool. The inflow velocity at several scale ratios was determined to keep Froude number constant. A periodic response was observed in a small size of moonpool while a large moonpool showed complicated fluctuations with various amplitudes and frequencies, which made it difficult to distinguish the statistical steady-state response from the temporal responses in the case of large moonpool. The similarity of Froude number gave rise to a spectral characteristic which was inversely proportional to the square root of scale ratios ($f_{0.5}{\approx}{\sqrt{2}}f_1{\approx}2f_{2.0}$) but a low frequent occurrence of strong vortex ($f_{2.0}=0.07$)which is observed inside the large moonpool was characterized depending on scale ratios.

CFD Analysis of Two-Dimensional Floating Body with Moon Pool under Forced Heave Motion (문풀을 가지는 2차원 부유체의 강제 상하동요에 대한 CFD 해석)

  • Heo, Jae-Kyung;Park, Jong-Chun;Kim, Moo-Hyun
    • Journal of Ocean Engineering and Technology
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    • v.25 no.2
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    • pp.36-46
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    • 2011
  • A two-dimensional floating body with a moon pool under forced heave motion, including a piston mode, is numerically simulated. A dynamic CFD simulation is carried out to thoroughly investigate the flow field around a two-dimensional moon pool over various heaving frequencies. The numerical results are compared with experimental results and a linear potential program by Faltinsen et al. (2007). The effects of vortex shedding and viscosity are investigated by changing the corner shapes of the floating body and solving the Euler equation, respectively. The flow fields, including the velocity, vorticity, and pressure fields, are discussed to understand and determine the mechanisms of wave elevation, damping, and sway force.

Flow Analysis of Two-Dimensional Floating Body with Moon Pool Using a Numerical Wave Tank (수치 파동 수조를 이용한 부유체의 문풀 (Moon Pool) 유동해석)

  • Koo, Weon-Cheol;Lee, Kyoung-Rok
    • Journal of the Society of Naval Architects of Korea
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    • v.48 no.2
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    • pp.107-112
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    • 2011
  • The aim of this study is to analyze the hydrodynamic properties of a 2D floating body with moon pool using a 2D fully nonlinear Numerical Wave Tank(NWT). This NWT was developed based on the Boundary Element Method(BEM) with potential theory and fully nonlinear free surface boundary conditions. Free surface elevations in the moon pool were calculated in the time domain for various frequencies of forced body motions. The added-mass and damping coefficients of the heaving body were also obtained. The present numerical results were compared with the analytic and experimental results and their accuracy was verified.

Thermal Distortion Analysis by Inconel Over-lay at Circular Moonpool Structures (인코넬 육성용접에 의한 원형 문풀구조 선체블록의 열변형해석)

  • Ha, Yun-Sok
    • Journal of the Society of Naval Architects of Korea
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    • v.49 no.4
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    • pp.304-311
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    • 2012
  • One of the main features of Drillship or FPSO is a moonpool structure. The moonpool structures have various accuracy tolerances according to their functions and targets. This study is mainly interested in roundness of a circular moonpool structure in FPSO. Because this structure needs abrasion-resistance at which bearing of machine touches on inner wall of moonpool, we should do over-lay welding widely and deeply by using Inconel weld material. But a general over-lay can cause a severe distortion at ship block structure. If we can analyze the roundness by thermal distortion under Inconel over-lay, we can establish a special erection policy by the results. In this study, we designed stress-strain curve for strain-boundary condition analysis by an elasto-plastic material property. The results made us to decide an appropriate ship-block size and policy of crane manipulation will follow for its capacity. If a structure that needs over-lay is not large, solid elements also are not a bad choice for FEM modeling. Therefore we also developed a standard of using strain-boundary method that shell elements are used as over-lay on solid element modeling.

Proper Orthogonal Decomposition of Pressure Fluctuations in Moonpool (문풀 내 압력 변동에 대한 POD 분석)

  • Lee, Sang Bong;Woo, Bum;Park, Dong Woo;Ahn, You Won;Go, Seok Cheon;Seo, Heung Won
    • Journal of the Society of Naval Architects of Korea
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    • v.49 no.6
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    • pp.484-490
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    • 2012
  • Experiments of circulating water channel and two dimensional numerical simulations were performed to investigate the fluctuating characteristics of pressure in moonpool. Based on the quasi-two dimensional characteristics of pressure fluctuations disclosed by the spatial cross-correlations, the numerical results showed qualitatively good agreement with experimental data. Proper orthogonal decomposition was employed to the spatial distributions of pressure fluctuations in order to find the first and second modes of fluctuations. The first mode of pressure fluctuations showed that the fluctuating characteristics of pressure were related to the behaviors of vortical structures. The velocity fluctuations were conditionally averaged to make clear that the coherent structures were responsible for the pressure fluctuations in moonpool.

Welding Deformation and Its Correction of Cylindrical Moon Pool Structure (원통형 문풀 구조물의 탑재 시 변형과 수정)

  • Seong, Woo-Jae;Chun, Kwang-San
    • Journal of the Society of Naval Architects of Korea
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    • v.56 no.5
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    • pp.389-395
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    • 2019
  • Turret mooring type Floating Production Storage and Offloading (FPSO) is designed to rotate the hull around a turret system. The system is mounted inside a cylindrical moon-pool structure of the ship hull structure. The upper part of the moon-pool structure called Bogie Support Structure (BSS) is supported on ring type rail structure (bogie), so high roundness is required at the top of the structure. In this study, the deformation measured during BSS installation was compared with the predicted values through the thermal elasto-plastic analysis, and the causes of deformation were analyzed. Deformation behavior of cylindrical structure with a very large diameter compared to the thickness was investigated. In addition, a proper welding sequence and correction method for the deformed structure were proposed. This study can be an example of the solution to the tolerance problem of large cylindrical structures.

Reduction of Added Resistance by Internal Flow Control in the Moonpool of a Drillship (시추선 문풀의 내부 유동제어에 의한 부가저항 저감)

  • Choi, Si-Young;Lee, Young-Gill;Jeong, Kwang-Leol;Ha, Yoon-Jin
    • Journal of the Society of Naval Architects of Korea
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    • v.48 no.6
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    • pp.544-551
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    • 2011
  • The internal flows of moonpool usually causes huge added resistance on drillships, and those are very complex to analyze. Therefore, not only experimental approaches but also numerical simulations are required for better investigations when dealing with the hydrodynamic problems of moonpool. In the present research, numerical simulations are used to find out why the resistance increases by moonpool on a running drillship. That is, the three-dimensional numerical simulations and model tests are carried out to examine the characteristics of internal flow and added resistance by changing the section of the moonpool in both longitudinal and transverse directions. Finally, based on the present studies, an optimized shape of the moonpool is suggested, which effectively reduces added resistance, and that is confirmed with three-dimensional numerical simulations and model tests.

Repair Procedure and Structural Strength Analysis to Damage of Moon-Pool Structure for Drillship During Construction (드릴쉽 건조 중 문풀 구조 수정 작업 및 구조적 안정성 검토)

  • Yoo, In-Sang;Sohn, Sang-Young;Baek, Seung-Jung;Choi, Young-Lack;Yoo, Hae-Kun;Yoon, Ki-Jeong
    • Special Issue of the Society of Naval Architects of Korea
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    • 2011.09a
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    • pp.12-16
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    • 2011
  • During the shipbuilding construction, the repair works will be occurred by various reasons such as the natural disaster, mistakes of engineers or workers, defect of material, and so on. The one of the engineer's responsibilities is to design considering every possibility and to prevent the repair works due to the mistakes during construction stages, but actually it is very difficult and impossible to avoid every mistake. However, it is also the responsibility of engineers to find the best solution for the unavoidable mistakes which is to maintain the capacity of vessel and guarantee the safety for the repair works considering the construction schedules and economic cost. In this paper, it will be introduced the brief of repair works to the structural damage of the moon-pool structure in drillship which is built in our shipyard. For the verification of the structural strength, the fatigue analysis has been carried out based on the guide of Classification society. Furthermore, the modifications of structure design and welding procedure have been applied to avoid the stress concentration in the moon-pool structure.

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