• 대한조선학회논문집
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• 제52권6호
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• pp.460-470
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• 2015

In general ships and FPSOs, roll damping is very small and consequently roll motion is very large at the roll resonance frequency. Proper evaluation of the roll damping coefficient at the resonance frequency is an important task in the study of roll motion and usually it is done by the analysis of free roll decay tests. The relative decrement method based on energy relation has been used mainly for the evaluation of roll damping coefficient from the roll decay test so far. As another method, the logarithmic decrement method based on equivalent linear decay assumption can be used for the same purpose and it is relatively simple. In this paper, both of the relative decrement method and the logarithmic decrement method are used for the evaluation of roll damping coefficient including quadratic damping from the free roll decay tests, and their results are cross-checked for verifying the obtained damping coefficients. Through applications to a box-type floating body equiped with bilge keels, it is shown that the two methods give almost the same damping coefficients in a practical view point and the cross-check of their results is to be a good tool to prevent a possible error. And also the quantitative effects of the bilge keels on the roll damping of box-type floating body are shown and discussed.

• Journal of Advanced Marine Engineering and Technology
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• 제40권9호
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• pp.791-798
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• 2016

본 연구에서는 상용 점성 유동 해석 소프트웨어인 Star-CCM+를 이용하여 110m급 해양작업지원선의 빌지킬 효과에 따른 횡동요 성능에 관한 연구를 수행하였다. 해양작업지원선에 관한 연구에 앞서 DTMB 5512 선형에 대한 수치 시뮬레이션을 통해 실험과 비교 검증하였다. 검증된 결과를 바탕으로 빌지킬 유무에 따른 해양작업지원선의 자유 횡동요 시뮬레이션을 수행하였으며, 이를 통해 각각의 무차원 감쇠 계수와 횡동요 응답진폭함수를 산출하였다.

• 대한조선학회논문집
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• 제56권6호
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• pp.550-558
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• 2019

The roll motion of a general vessel, which is more influenced by resonance as compared to other motions, adversely affects the passenger and hull. Therefore, reducing the roll motion through an anti-rolling system is critical, and most ships use various devices such as anti-rolling tanks, bilge keels, and fin stabilizers to accomplish this. In this study, a simplified model is developed for the application of an anti-rolling device for unmanned semi-submersible vessels. The applied anti-rolling device is installed on the stern and stem of a ship using a pair of servo motors with added weight, and the motor is controlled through the Arduino. The moment of the motor is designed and implemented based on a mathematical model such that it is calculated through the restoring force according to the heel angle of the ship. The performance of the proposed system was verified by utilizing the roll damping coefficient calculated by the free-roll decay test and logarithmic decrement method and was validated by a towing tank test. The system is expected to be used for unmanned vessels to perform sustainable missions.

• 대한조선학회논문집
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• 제49권1호
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• pp.52-59
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• 2012

Among many factors to be considered for higher safety level requirements, the hull stability in intact and damaged conditions in seaways is of utmost importance. Since the assessment of a damaged ship is complicated due to the highly non-linear behavior, it is widely acknowledged that computational fluid dynamics (CFD) methods are one of the most feasible approaches. Although many research activities are being reported on the damaged ship stability recently, most of them are not designed for validation of CFD studies. In this study, well-designed model tests were performed to build a CFD validation database, which is essential in developing better CFD methods for the damage stability assessment. The geometry of the damaged compartment and test conditions were determined based on preliminary CFD simulations. Free roll decay tests in calm water with both intact and damaged ships were performed and the roll motion characteristics were compared. The damaged ship showed a larger roll damping coefficient and more rapid decrease of roll amplitude than the intact ship. The primary reason of these efforts can be explained by the movement of the flooded water.

• 한국해양공학회지
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• 제33권4호
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• pp.322-329
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• 2019

The magnitude of the roll motion of a floating structure depends on the roll damping acting on the body. In other words, the roll damping of a floating structure must be accurately obtained in order to precisely evaluate the roll motion. Various methods are used to evaluate the roll damping of a floating structure, such as the linear potential theory, computational fluid dynamics (CFD), and model tests. However, it is difficult to evaluate the roll motion of a floating structure with appendages such as a bilge keel and riser slot due to the limitation of ignoring the viscous effects in the linear potential theory. Among these methods, a model test based on a free decay test and harmonic excited roll motion (HERM) is known to be the most reliable method to estimate the roll damping of the floating structures. In this study, model tests using free decay and HERM techniques were performed in the Ocean Engineering Basin (OEB) of KRISO with various types of midship sections. The roll damping results were estimated based on post-processing methods using both techniques, and the roll damping results were compared.

• 한국항해항만학회지
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• 제41권6호
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• pp.365-372
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• 2017

부유체의 횡동요는 승조원의 피로를 누적시키고, 심지어 구조물 전체를 전복시키기까지 하고, 또 선체에 반복적인 외력을 가하는 등 부유체의 안정성과 구조물의 안전에 심대한 영향을 끼친다. 그래서 거의 모든 선박의 경우에는 빌지킬을 설치하여 횡동요를 감소시키고 있고, 특수한 경우에는 안티롤링 탱크나 핀 스태빌라이저나 자이로스코프 등을 설치하여 횡동요를 줄이고 있다. 그러나 안티롤링 탱크는 설치하는데 용적을 많이 차지하고, 핀 스태빌라이저나 자이로스코프는 설치비와 유지 관리비가 많이 든다. 저자들은 안티롤링진자를 이용한 부유체의 롤링저감에 대한 연구를 하여 실험과 Runge-Kutta 해석에 의하여 그 유효성을 보인 바 있다. 여기에서는 선박에 안티 롤링 진자를 설치한 모델을 2자유도 점성감쇠계로 선형화하여 시스템을 해석하고 실험과 비교하여 수학 모델의 정당성을 보이고, 수학 모델의 정당성을 바탕으로 최적의 안티 롤링 진자를 제안한다. 7.7kg의 모형선의 경우 모형선 질량의 0.26%인 20g의 안티롤링 진자가 가장 효율이 좋음을 보였다. 또 안티 롤링 진자의 질량이 다른 몇 가지 경우에 대하여서 자유 롤링 실험을 하여 안티 롤링 진자의 유효성을 보인다.