• Journal of Ocean Engineering and Technology
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• v.11 no.3
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• pp.107-115
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• 1997

비성형 동력학계로 모델링된 부유수송체의 동적응답을 조사하고 그 운동의 안정성을 해석하였다. 종동요 모우드의 고유주파수가 횡동요 모우드의 고유주파수의 두배가 되는, 즉, 2:1 내부공진 혹은 자기계수공진인 조건하에서, 이부유수송체는 한 운동 모우드의 직접가진에 의해 간접가진된 다른 모우드가 대진폭 응답을 보일 수 있음을 밝혔다. 또항, 종동요 모우드의 감쇠력은 비교적 넓은 범위의 운동에 대해 선형적임에 반해, 횡동요 모우드의 감쇠력은 점성의 영향이 대단히 커서 비선형성이 대단히 강한 것으로 알려져 왔다. 이 문제를 수학적으로 모델링하기 위하여, 종동요 모우드의 운동방정식에는 선형및 제곱형의 합의 형태인 감쇠력 모형을 사용하였다. 다중척도법을 사용하여 이 두가지 운동 모우드의 주기적 응답및 그의 안정성에 미치는 제곱형 비선형 횡동요 감쇠력의 영향을 밝혔다. 조우주기가 횡동요 모우드의 고유주기와 근사한 경우에 대하여 이 비선형계의 응답을 구하고 주파수-응답 곡선으로 나타내었다.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.7
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• pp.956-964
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• 2017

This study contributes to deepening understand of the characteristics of fishing vessel rolling motions to improve the development of capsizing alarm systems. A time domain rolling motion simulation was performed. In order to verify capsizing alarm systems, it is necessary to carry out experiments assuming a capsizing situation and perform actual fishing vessel measurements, but these tasks are impossible due to the danger of such a situation. However, in many capsizing accidents, a close connection with rolling motion was found. Accordingly, the rolling motion of a fishing boat, which is the core of a fishing vessel capsizing alarm system, has been accurately measured and a time domain based on a rolling motion simulation has been performed. This information was used to verify the algorithm for a capsizing alarm system. Firstly, the characteristics of rolling motion were measured through a motion experiment. For small vessels such as fishing vessels, it was difficult to interpret viscosity due to analytical methods including CFD and potential codes. Therefore, an experiment was carried out focusing on rolling motion and a rolling mode RAO was derived.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.7
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• pp.1244-1251
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• 2022

Marine accidents due to a loss of stability, have been gradually increasing over the last decade. Measures must be taken on the roll reduction of a ship. Amongst the measures, building an anti-roll tank in a ship is recognized as the most simple and effective way to reduce the roll motion. Therefore, this study aims to develop a computational model for a U-tube type anti-roll tank and to validate it by experiment. In particular, to validate the developed computational model, the height of the free surface in the tank was measured in the experiment. To develop a computational model, the mesh dependency test was carried out. Further, the effects of a turbulence model, time step size, and the number of iterations on the numerical solution were analyzed. In summary, a U-tube type anti-roll tank simulation had to be performed accurately with conditions of a realizable k-𝜖 turbulence model, 10^-2s time step size, and 15 iterations. In validation, the two cases of measured data from the experiment were compared with the numerical results. In the present study, STAR-CCM+ (ver. 17.02), a RANS-based commercial solver was used.

• Bulletin of the Society of Naval Architects of Korea
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• v.17 no.4
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• pp.39-45
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• 1980

내항성이 우수한 선형을 개발하기 위해서는 초기설계단계에서 이미 그 배의 해상에서의 거동을 예측할 수 있어야만 한다. 이 보고서에서는 임의의 입사각을 갖는 규칙파중을 항주하는 선박이 겪게 되는 동요중에서 횡동요, 수평동요 그리고 선수동요의 연성운동방정식의 해를 Tassi-Takaki가 수정한 스트립이론을 적용하여 해석하였다. 제15차 ITTC의 내항성 위원회의 보고서에서 발표된 콘테이너선형에 대한 결과와 똑같이 선형에 대해 본 프로그램을 사용하여 계산한 수평동요, 횡동요 그리고 선수동요의 운동응답을 비교하여 보았으며, 상당히 만족스러운 결과를 얻었다.

• Journal of KSNVE
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• v.7 no.5
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• pp.765-772
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• 1997

This paper presents the swing motion analysis of the container crane headblock with the passive control device using hydraulic motors and anti-swing ropes. The device hauls at the headblock to opposite direction of its swing motion using the tension difference between anti-swing ropes connected to the headblock. To consider this control mechanism, the headblock is modelled as the rigid bar suspended by two hoist ropes at the overhead trolley and its non-linear equation of motion is derived using Lagrange's equation. Some numerical experiments using the equation are carried out to investigate the swing motion characteristics of the headblock under the variation of geometric relation among the cargo handling components and to evaluate the performance of the anti-swing device.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.6
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• pp.832-838
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• 2021

Recently, reports of marine accidents of small fishing vessels less than 10 tons have been increasing. In this study, the characteristics of the motion response in regular waves were analyzed using computations for these ships. Small vessels less than 10 tons are classified by size and used for marine accident investigations. Therefore, the motion response analysis was performed on three small fishing vessels of different sizes. In the case of the head sea, it was confirmed that as the speed of the vessel increased in the long wavelength region, the motion responses of heave and pitch became large. The motion response of the smallest 3-ton fishing vessel was greater than that of the other sizes of fishing vessels. The maximum value of the roll motion shifted to the long wavelength region as the speed gradually increased in the bow sea, regardless of the size of the ship. In all the three small fishing vessels, it was found that the roll motion was the greatest at 15 knots, the highest speed in both bow and beam seas. When sailing in the head sea and bow sea conditions, lowering the speed is one of the effective approaches to reduce the effects of the vertical and lateral plane motions. The roll motion caused by the beam wave showed a tendency to increase rapidly only at a specific wavelength regardless of the speed and the size of the vessel. It was confirmed that the roll motion was significantly reduced with forward speed in the stern wave compared to the bow wave. As there is a specific region where the maximum value of the hull motion response appears depending on the size and speed of the ship, an operation method that can minimize the effect of this motion should be considered and implemented.

• Journal of Navigation and Port Research
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• v.45 no.1
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• pp.16-25
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• 2021

Hydrodynamic coefficients should be accurately estimated to predict the maneuverability of underwater vehicles. Various captive model tests have been performed as part of estimation methods for these coefficients. Estimating hydrodynamic coefficients related to roll motion is important because underwater vehicles are sensitive to changes of roll moment. In this research, a pure roll motion equipment was newly designed to simply estimate hydrodynamic coefficients with respect to roll motion. Roll motion was implemented through a brief mechanical mechanism. The principle of operation, application process, and system identification of the equipment are described. An analysis method of the pure roll test is also suggested. Repeated tests of the newly equipment were carried out to check its reproducibility.

• Journal of the Society of Naval Architects of Korea
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• v.32 no.1
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• pp.37-41
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• 1995

In order to analyze the rolling motion of a ship in random beam waves we use the partial stochastic linearization method. The quadratic damping and the nonlinear restoring moments given by the odd polynomials up to the 11th order are added to a single degree of freedom linear equation of roll motion. The irregular excitation moment is assumed to be the Gaussian white noise. The statistical characteristics of the response by the partial stochastic linearization method is compared with results by the equivalent linearization method and Monte Carlo simulation. It is fecund that the partial stochastic linearization method is not necessarily superior to the equivalent linearization method.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.9
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• pp.791-798
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• 2016

In this study, numerical simulations on the effects of bilge keel on roll motion were conducted. The numerical simulations were performed on a 110 m class PSV using the commercial viscous flow analysis software Star-CCM+. Before conducting the study on the 110 m class PSV, an additional simulation of DTMB 5512 was performed and compared with the experimental results to validate the feasibility of the numerical simulation. In the simulation on PSV, a nondimensional damping coefficient was calculated using a free roll decay simulation, and the response amplitude operator (RAO) for the roll motion was calculated with a nondimensional damping coefficient at two conditions (with/without bilge keel).

• Journal of the Society of Naval Architects of Korea
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• v.49 no.1
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• pp.60-67
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• 2012

This study considers the numerical analysis on parametric roll for container ships. As a method of numerical simulation, an impulse-response-function approach is applied in time domain. A systematic study is carried out for the parametric roll of two container ships, particularly observing the sensitivity of computational results to some parameters which can affect the analysis of parametric roll. The parameters to be considered are metacentric height (GM), simulation time window, and the discretization of wave spectrum. Based on the result of parametric roll simulation, numerical sensitivity and uncertainty in computational analysis are discussed.