• 한국소음진동공학회논문집
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• 제23권7호
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• pp.662-668
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• 2013

In this paper, possibility of controlling motion of a floating structure using a tuned liquid damper (TLD) is numerically investigated. A TLD is a tank partially filled with liquid. Sloshing motion of liquid inside a tank is known to suppress movement of the tank subject to external excitations at specific frequency. The effects of sloshing phenomena inside a rectangular floating body on its surge motion are investigated by varying external excitation frequency. First, a grid-refinement study is carried out to ensure validity of grid independent numerical solutions using present numerical techniques. Then, surge motion of the floating body subjected to external wave is simulated for five different excitation frequencies of which the center frequency equals to the natural frequency of internal liquid sloshing. The normalized amplitudes of surge motion of the target floating body are compared according to the excitation frequency, for the cases with and without water inside the floating body. It is shown that the motion of the floating body can be minimized by matching the sloshing natural frequency to the excitation frequency.

• 한국해안해양공학회지
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• 제1권1호
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• pp.81-86
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• 1989

본 논문에서는 선형포텐셜 이론을 이용하여 항만에 계류된 선박의 운동해석을 수행하였다. 해양에서 입사되는 장파의 진동수와 항만의 고유진동수가 일치될 때 항만공진이 발생하며, 항만공진은 선박의 운동을 크게 야기시킨다. 해석 방법으로는 정합점근전개법 (Matched Asymptotic Expansion)을 사용하였다. 이 방법을 적용하기 위하여 선박은 세장선으로 가정하였고, 항만입구의 폭이 좁은 직사각형 항만을 계산 모델로 삼았다. 대칭운동(Surge, Heave, Pitch)에 대하여 수치계산을 수행한 결과 항만내의 위치에 따라 야기되는 선박운동모드가 크게 차이남을 밝혔다.

• Nuclear Engineering and Technology
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• 제54권10호
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• pp.3732-3744
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• 2022

To investigate the effects of ocean conditions on the thermal stress and deformation caused by thermal stratification of a pressurizer surge line in a floating nuclear power plant (FNPP), the finite element simulation platform ANSYS Workbench is utilized to conduct the fluid-solid-thermal coupling transient analysis of the surge line under normal "wave-out" condition (no motion) and under ocean conditions (rolling and pitching), generating the transient response characteristics of temperature distribution, thermal stress and thermal deformation inside the surge line. By comparing the calculated results for the three motion conditions, it is found that ocean conditions can significantly improve the thermal stratification phenomenon within the surge line, but may also result in periodic oscillations in the temperature, thermal stress, and thermal deformation of the surge line. Parts of the surge line that are more susceptible to thermal fatigue damage or failure are determined. According to calculation results, the improvements are recommended for pipeline structure to reduce the effects of thermal oscillation caused by ocean conditions. The analysis method used in this study is beneficial for designing and optimizing the pipeline structure of a floating nuclear power plant, as well as for increasing its safety.

• 한국해양공학회지
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• 제27권6호
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• pp.56-64
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• 2013

Crabbing motion is the pure sway motion of a ship without surge velocity. Thus, it can be applied to a berthing operation. Crabbing motion is induced by a peculiar operation method called the push-pull mode. The push-pull mode is induced by using a combination of the main propeller and side thruster. Two propellers generating the same amounts of thrust and rotating in opposite directions produce some yawing moment on a vessel but do not induce longitudinal motion. With the additional operation of side thrusters, the push-pull mode is used to induce a large amount of lateral force. In this paper, three-degree-of-freedom equations of motion such as for the surge, sway, and yaw are constructed for the crabbing motion. Based on these equations of motion, a feedback linearization control method is applied to auto-berthing control for a twin-screw ship with side thrusters. The controller can deal with the nonlinearity of a system, which is present in the berthing maneuver of a twin screw ship. A simulation of the auto-berthing of a ship is performed to validate the performance of the designed controller.

• 한국해양공학회지
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• 제19권2호
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• pp.12-18
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• 2005

Typhoon Maemi landed on the southeast coast of Korea and caused a severe storm surge in Jinhae Bay and Masan Bay. The tide gage in Masan Port recorded the storm surge of a maximum of more than 2m and the area of more than 700m from the Seo Hang Wharf was flooded by the storm surge. They had not met such an extremely severe storm surge since the opening of the port. Then storm surge was hindcasted with a numerical model. The typhoon pressure was approximated by Myers' empirical model and super gradient wind around the typhoon eye wall was considered in the wind estimation. The land topography surrounding Jinhae Bay and Masan Bay is so complex that the computed wind field was modified with the 3D-MASCON model. The motion of seawater due to the atmospheric forces was simulated using a one-layer model based on non-linear long wave approximation. The Janssen's wave age dependent drag coefficient on the sea surface was calculated in the wave prediction model WAM cycle 4 and the coefficient was inputted to the storm surge model. The result shows that the storm surge hindcasted by the numerical model was in good agreement with the observed one.

• 한국항공우주학회지
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• 제46권5호
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• pp.368-375
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• 2018

본 연구에서는 부유식 플랫폼의 6자유도 방향으로의 주기 운동이 로터 공력 성능에 미치는 영향을 확인하기 위해 부유식 해상 풍력터빈에 대한 공력 해석이 수행되었다. 수치 해석을 위해 블레이드 요소 운동량 방법을 이용하였으며, 유동 박리와 후류 영향에 의한 비정상 공력 효과를 포착하기 위해 인디셜 응답 방법에 기반한 동적 실속 모델을 이용하였다. 로터에 의해 유도되는 내리 흐름은 운동량 이론과 난류 후류 상태에 대한 경험적 모델을 연계하여 계산하였다. heave, sway, surge 방향으로의 병진 운동과 roll, pitch, yaw 방향으로의 회전 운동을 포함한 플랫폼 주기 운동을 고려하였으며, 각각의 모션은 사인함수 형태로 적용되었다. 수치해석을 위한 대상 풍력터빈으로는 NREL 5MW 풍력터빈이 사용되었다. 해석 결과로부터 세 방향 병진 운동 모드 중, surge 운동 시 로터 공력 변화가 상대적으로 크게 나타났으며, 회전 운동 모드의 경우, pitch 운동에 의해 로터 공력이 크게 변화됨을 확인할 수 있었다.

• 대한조선학회지
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• 제18권1호
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• pp.19-27
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• 1981

The surge motion of a freely-floating sphere in a regular wave is studied within the framework of a linear potential theory. The fluid is assumed to be perfect and only the steady-state harmonic motion in a water of infinite depth is considered. A velocity potential describing the fluid motion is decomposed into three parts; the incident wave potential, the diffraction potential and the radiation potential. In this paper the diffraction potential and the radiation potential are analysed by using multipole expansion method. Upon calculating pressures over the immersed surface of the sphere, the hydrodynamic forces are evaluated in terms of Froude-Krylov, diffraction, added mass and damping forces as functions of the frequency of the incident wave. Finally the frequency dependence of two pertinent parameters, the amplitude ratio and the phase lag between the motion of the sphere and that of the incident wave is derived from the equation of motion. As for numerical results the general tendency of the present calculation shows good agreement with Kim's work who also treated this problem utilizing the Green's function method.

• 한국해안·해양공학회논문집
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• 제26권3호
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• pp.140-148
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• 2014

고조방파제는 폭풍해일이나, 대조시 창조류로부터 내부 해역을 보호하기 위하여 설계된 특수한 형태의 수문 구조물로, 홍수 방지 벽, 방조제 및 다른 구조물로 구성된다. 평상시 고조방파제는 해수 소통을 허용하지만, 폭풍해일이 예상되면 폐쇄된다. 폐쇄시키는 다양한 방법 중 본 연구에서는 이태리 모세프로젝트에 적용한 것과 같은 부유 플랩형 고조방파제를 마산만에 적용할 경우, 폭풍해일 및 파랑이 작용할 때의 고조방파제 거동특성을 3차원 유동해석프로그램인 FLOW-3D를 이용하여 살펴보았다. 수치해석결과, 고조차 2 m인 상태에서 파고 3 m 조건에서도 고조방파제로서의 기능을 발휘할 수 있는 것으로 평가되었다.

• 천문학회보
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• 제37권1호
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• pp.88.1-88.1
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• 2012

We observed a surge associated with an Ellerman bomb using the Fast Imaging Solar Spectrograph(FISS) of the New Solar Telescope at Big Bear Solar Observatory. The surge was seen in absorption and varied rapidly both in H alpha and Ca II 8542 line. It originated from the Ellerman bomb, and was impulsively accelerated to 20km/s of the blueshift(upward) motion. Then the gradual change from blueshift of 20km/s to redshift of 40km/s occurred in 20 minutes. Based on the measured line-of-sight velocities, we estimated the material reached up to about 5,000km height. We inferred physical parameters of the surge by adopting the cloud model, and found that the temperature of the surge material was about 25,000K and the non-thermal velocity was about 10km/s. Our results suggest that the surge might be heated intensely after it was ejected from the Ellerman bomb.

• 한국해양공학회지
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• 제31권2호
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• pp.81-90
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• 2017

The 1MW OTEC (Ocean Thermal Energy Conversion) platform was designed for application in equatorial seas. In this study, the OTEC platform was investigated using numerical and experimental methods. An octagon-shaped OTEC platform was investigated using the Ocean Engineering Basin of KRISO. These experiments included various tests of regular waves, irregular waves and irregular waves with current (wave+current). The responses of the platform in regular waves showed good agreement between the numerical and experimental results, including the motion RAO, wave run up, and mean drift force. The peak period of heave and pitch motions were observed around 0.5 rad/s, and the effect of the total reflection was found under short wave conditions. The standard deviation (STD) of the platform motion was checked in irregular waves of equatorial and Hawaiian seas. The STD of the pitch was less than $4^{\circ}$ different from the operability requirement under equatorial conditions and the surge STD of the wave frequency showed good agreement between the numerical and experimental results. The STD values of the surge and pitch were increased 66.6% and 92.8% by the current effects in irregular waves, but the pitch STD was less than $4^{\circ}$ under equatorial conditions. This study showed that the STD of the surge was affected by spring effects. Thus, the watch circle of the platform and tension of the mooring lines must be evaluated for a specific design in the future.