• 한국항해항만학회지
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• 제39권5호
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• pp.385-391
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• 2015

In offshore, various external forces such as wind force, tidal current and impulsive breaking wave force act on offshore wind tower. Among these forces, impulsive breaking wave force is especially more powerful than other forces. Therefore, various studies on impulsive breaking wave forces have been carried out, but the soil reaction are incomplete. In this study, the p-y curve is used to calculate the soil reaction acting on the offshore wind tower when an impulsive breaking wave force occurs by typhoon. The calculation of offshore wind tower against impulsive breaking wave force is applied for the multi-layered soil. The results obtained in this study show that although the same wave height is applied, the soil reaction generated by impulsive breaking wave force is greater than the soil reaction generated by wave force.

• Ocean Systems Engineering
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• 제6권3호
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• pp.233-244
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• 2016

Tension Leg Platform (TLP) is a floating structure that consists of four columns with large diameter. The diffraction theory is used to calculate the wave force of floating structures with large dimensions (TLP). In this study, the diffraction and Froude-Krylov wave forces of TLP for surge, sway and heave motions and wave force moment for roll, pitch degrees of freedom in different wave periods and three wave approach angles have been investigated. From the numerical results, it can be concluded that the wave force for different wave approach angle is different. There are some humps and hollows in the curve of wave forces and moment in different wave periods (different wavelengths). When wave incidents with angle 0 degree, the moment of diffraction force for pitch in high wave periods (low frequencies) is dominant. The diffraction force for heave in low wave periods (high wave frequencies) is dominant. The phase difference between Froude-Krylov and diffraction forces is important to obtain total wave force.

• 한국해안·해양공학회논문집
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• 제29권2호
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• pp.121-127
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• 2017

구조물에 작용하는 실제 파랑은 다방향 불규칙파로써 장대 구조물의 경우 파의 위상차로 인해 파력의 감소효과가 발생한다. 본 연구에서는 이러한 효과가 파괴확률에 기여하는 정도를 파악하고 기존의 모듈형 방파제에 비해 어느 정도의 안정성이 확보되는지 확인하고자 기존 방파제 및 파력감소계수를 이용한 장대케이슨 방파제의 활동 파괴모드에 대해 신뢰성해석을 수행하였다. 그 결과 기존의 모듈형 케이슨 방파제보다 장대케이슨 방파제의 신뢰도지수가 더 높게 나타났고, 설계변수 중 유의파고가 가장 높은 영향을 미치는 것으로 확인되었다. 추가로 파력감소계수의 산정에 사용되는 변수들의 평균값 변화에 따른 신뢰성해석을 수행하였으며, 해석 결과 각 변수 값과 파력감소계수의 관계에서 확인된 경향이 평균값 변화에 따른 신뢰도지수 결과의 경향에 나타나는 것을 확인할 수 있었다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제5권4호
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• pp.569-579
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• 2013

A steel-type breakwater that uses a submerged dual horizontal porous plate was originally proposed by Kweon et al. (2005), and its hydrodynamic characteristics and design methodology were investigated in a series of subsequent researches. In particular, Kweon et al. (2011) proposed a method of estimating the vertical uplift force that acts on the horizontal plate, applicable to the design of the pile uplift drag force. However, the difference between the method proposed by Kweon et al. (2011), and the wave force measured at a different time without a phase difference, have not yet been clearly analyzed. In this study, such difference according to the method of estimating the wave force was analyzed, by measuring the wave pressure acting on a breakwater model. The hydraulic model test was conducted in a two-dimensional wave flume of 60.0 m length, 1.5 m height and 1.0 m width. The steepness range of the selected waves is 0.01~0.03, with regular and random signals. 20 pressure gauges were used for the measurement. The analysis results showed that the wave force estimate in the method of Kweon et al. (2011) was smaller than the wave force calculated from the maximum pressure at individual points, under a random wave action. Meanwhile, the method of Goda (1974) that was applied to the horizontal plate produced a smaller wave force, than the method of Kweon et al. (2011). The method of Kweon (2011) was already verified in the real sea test of Kweon et al. (2012), where the safety factor of the pile uplift force was found to be greater than 2.0. Based on these results, it was concluded that the method of estimating the wave force by Kweon et al. (2011) can be satisfactorily used for estimating the uplift force of a pile.

• 한국해안·해양공학회논문집
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• 제20권4호
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• pp.413-420
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• 2008

파랑하중은 연약지반을 굴착 치환시킨 후에 축조된 사석경사식 방파제의 안정에 직접적인 영향을 주는 요소이다. 특히 일부 침하를 허용하는 굴착치환 사석경사 방파제에서 침하를 유발하는 주요인으로 지목되었으나, 설계 시 파랑하중에 의한 방파제의 침하에 대한 영향을 검토하여 반영하는 사례가 전무한 상태이다. 따라서 본 연구에서는 파랑하중에 의한 방파제 침하의 영향을 설계에 직접 반영할 수 있도록 수치모형실험을 실시하여 방파제 침하량을 계산한 후 현장계측자료와 비교하였다. 계산값과 실측값은 양호한 일치를 보이는 것으로 나타났다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.367-375
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• 2020

This paper presents an integrated analysis about dynamic performance of a Floating Offshore Wind Turbine (FOWT) OC4 DeepCwind with semi-submersible platform under real sea environment. The emphasis of this paper is to investigate how the wave mean drift force and slow-drift wave excitation load (Quadratic transfer function, namely QTF) influence the platform motions, mooring line tension and tower base bending moments. Second order potential theory is being used for computing linear and nonlinear wave effects, including first order wave force, mean drift force and slow-drift excitation loads. Morison model is utilized to account the viscous effect from fluid. This approach considers floating wind turbine as an integrated coupled system. Two time-domain solvers, SIMA (SIMO/RIFLEX/AERODYN) and FAST are being chosen to analyze the global response of the integrated coupled system under small, moderate and severe sea condition. Results show that second order mean drift force and slow-drift force will drift the floater away along wave propagation direction. At the same time, slow-drift force has larger effect than mean drift force. Also tension of the mooring line at fairlead and tower base loads are increased accordingly in all sea conditions under investigation.

• 센서학회지
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• 제27권4호
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• pp.259-263
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• 2018

A radial artery pulse wave is measured while pressing an artery with constant force. However, pulse waveform measurements vary depending on pressing force and direction. Accurate pulse waveform measurements are important for analysis. Thus, it is necessary to define the measurement range of the permissible force and direction from which a correct pulse waveform is derived. In this study, pulse waves were generated by a pulse wave generator for accurate control. The pulse waves generated for different angles and pressing forces were analyzed. The augmentation index (AIx), which is the most commonly used index for evaluating vascular stiffness, was analyzed. The AIx was measured within ${\pm}6^{\circ}$ of the vessel direction and within ${\pm}8^{\circ}$ perpendicular to the vessel direction with a force that was 25% or more of the pressing force at which the maximum pressure wave was generated. We identified the applicable pressing force and angle range by analyzing the effect of pressing angle on the pulse wave. The AIx analysis performed using the pulse wave measurement device is reliable and reproducible.

• 한국해양공학회지
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• 제36권6호
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• pp.390-402
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• 2022

Offshore wind energy has become a major energy source, and various studies are underway to increase the economic feasibility of floating offshore wind turbines (FOWT). In this study, the characteristics of wave-induced motion of a combined wind-wave energy platform were analyzed to reduce the variability of energy extraction. A user subroutine was developed, and numerical analysis was performed in connection with the ANSYS-AQWA hydrodynamic program in the time domain. A platform combining the TLP-type FOWT and the Wavestar-type wave energy converter (WEC) was proposed. Each motion response of the platform on the second-order wave load, the effect of WEC attachment and Power take-off (PTO) force were analyzed. The mooring line tension according to the installation location was also analyzed. The vertical motion of a single FOWT was increased approximately three times due to the second-order sum-frequency wave load. The PTO force of the WEC played as a vertical motion damper for the combined platform. The tension of the mooring lines in front of the incident wave direction was dominantly affected by the pitch of the platform, and the mooring lines located at the side of the platform were mainly affected by the heave of the platform.

• 대한조선학회논문집
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• 제55권2호
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• pp.103-115
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• 2018

This paper performs a numerical computation of ship maneuvering performance in waves. For this purpose, modular-type model (MMG (Mathematical Modeling Group) model) is adopted for maneuvering simulation and wave drift force is included in the equation of maneuvering motion. In order to compute wave drift force, two different seakeeping programs are used: AdFLOW based on Wave Green function method and SWAN based on Rankine panel method. When wave drift force is calculated using SWAN program, not only ship forward speed but also ship lateral speed are considered. By doing this, effects of lateral speed on wave drift force and maneuvering performance in waves are confirmed. The developed method is validated by comparing turning test results in regular waves with existing experimental data. Sensitivities of wave drift force on maneuvering performance are, also, checked.

• 한국해양공학회지
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• 제20권2호
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• pp.22-28
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• 2006

The motion and wave drift forces of floating BBDB (backward-bent duct buoy) wave energy absorbers in regular waves are calculated, taking account of the oscillating surface-pressure due to the pressure drop in the air chamber above the oscillating water column, within the scope of the linear wave theory. A series of model tests has been conducted in order to order to verify the motion and time mean wave drift force reponses in regular waves at the ocean engineering basin, MOERI/KORDI. The pneumatic damping through an orifice-type duct for the BBDB wave energy device are deducted from experimental research. Numerical simulation for motion and drift force responses of the BBDB wave energy device, considering pneumatic damping coefficients, has been carried out, and the results are compared with those of model tests.