• 한국구조물진단유지관리공학회 논문집
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• 제22권4호
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• pp.42-51
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• 2018

해상풍력 지지구조물은 설치과정에서 수직도 오차가 발생하여 풍력발전기 전체 구조의 안전성이 저하될 수 있다. 따라서, 본 논문에서는 콘크리트 중력식 해상풍력 연결부에서 PS 앵커와 앵커체결구 그라우트를 사용하여 수직도를 조정할 수 있는 방안에 대한 연구를 수행하였다. 연결부는 5MW급 해상풍력 지지구조물에서 발생한 수직도 오차를 최대 $0.5^{\circ}$까지 보정하는 것을 목표로 하였다. 우선, 수직도 조정이 가능한 해상풍력 연결부에 대해 주요 부재별 설계안과 설계절차를 제안하고, 제주도 해상지역을 대상으로 설계 제원을 산출하였다. 그 후, 설계 제원에 대해 비선형 3차원 유한요소해석을 수행하여 설계안의 적정성을 검토하였다. 검토 결과, 하중 전달 메커니즘과 연결부 발생 응력 확인을 통해 제안 설계안은 $0.5^{\circ}$의 수직도 오차를 보정하여도 안전하다고 판단하였다.

• Earthquakes and Structures
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• 제10권5호
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• pp.1143-1179
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• 2016

Offshore wind turbines are considered as a fundamental part to develop substantial, alternative energy sources. In this highly flexible structures, monopiles are usually used as support foundations. Since the monopiles are large diameter (3.5 to 7 m) deep foundations, they result in extremely stiff short monopiles where the slenderness (length to diameter) may range between 5 and 10. Consequently, their elastic deformation patterns under lateral loading differ from those of small diameter monopiles usually employed for supporting structures in offshore oil and gas industry. For this reason, design recommendations (API and DNV) are not appropriate for designing foundations for offshore wind turbine structures as they have been established on the basis of full-scale load tests on long, slender and flexible piles. Furthermore, as these facilities are very sensitive to rotations and dynamic changes in the soil-pile system, the accurate prediction of monopile head displacement and rotation constitutes a design criterion of paramount importance. In this paper, the Fourier Series Aided Finite Element Method (FSAFEM) is employed for the determination of static impedance functions of monopiles for OWT subjected to horizontal force and/or to an overturning moment, where a non-homogeneous soil profile has been considered. On the basis of an extensive parametric study, and in order to address the problem of head stiffness of short monopiles, approximate analytical formulae are obtained for lateral stiffness $K_L$, rotational stiffness $K_R$ and cross coupling stiffness $K_{LR}$ for both rough and smooth interfaces. Theses expressions which depend only on the values of the monopile slenderness $L/D_p$ rather than the relative soil/monopile rigidity $E_p/E_s$ usually found in the offshore platforms designing codes (DNV code for example) have been incorporated in the expressions of the OWT natural frequency of four wind farm sites. Excellent agreement has been found between the computed and the measured natural frequencies.

• 한국산업융합학회 논문집
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• 제23권2_2호
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• pp.343-349
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• 2020

As global warming accelerates due to global climate change, the International Maritime Organization(IMO) has set up Emission Control Area(ECA) and encourages the use of Liquefied Natural Gas(LNG). For this reason, as the demand for LNG increases, the demand and research of related equipment also increases. In this study, one of them, the vent mast for the discharge of LNG was studied. In general, vent mast receives various loads such as wind load, earthquake load and dead load during operation. Accordingly, consideration of these loads is essential for structural design and safety evaluation of the vent mast. In this study, the structural safety of the vent mast is evaluated by performing finite element analysis. As a result, the structural safety evaluation results were analyzed based on the database of materials of the vent mast, and the stress level was analyzed to provide a design guide.

• Wind and Structures
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• 제21권6호
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• pp.597-607
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• 2015

With an increasing demand of a renewable energy, new offshore wind turbine farms are being planned in some parts of the world. Foundation installation asks a significant cost of the total budget of offshore wind turbine (OWT) projects. Hence, a cost reduction from foundation parts is a key element when a cost-efficient designing of OWT budget. Mono-piles have been largely used, accounting about 78% of existing OWT foundations, because they are considered as a most economical alternative with a relatively shallow-water, less than 30 m of seawater depth. OWT design standards such as IEC, GL, DNV, API, and Eurocode are being developed in a form of reliability based limit state design method. In this paper, reliability analysis using the response surface method (RSM) and numerical simulation technique for an OWT mono-pile foundation were performed to investigate the sensitivities of mono-pile design parameters, and to find practical implications of RSM reliability analysis.

• 풍력에너지저널
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• 제5권1호
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• pp.22-32
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• 2014

The structural design of a wind turbine must show the verification of the structural integrity of all load-carrying components. Also, design load calculations shall be performed using appropriate and accurate methods. In this study, advanced numerical approach for the calculation of design loads based on unsteady computational fluid dynamics (CFD) is presented considering extreme design load conditions such as the extreme coherent gust (ECG) and the 50 year extreme operating gust (EOG). Unsteady aerodynamic loads are calculated based on Reynolds average Navier-Stokes (RANS) equations with shear-stress transport k-ω(SST k-ω) turbulent model. A full three-dimensional 5 MW offshore wind-turbine model with rotating blades, hub, nacelle, and tower configuration is practically considered and its aerodynamic interference effect among blades, nacelle, and tower is also accurately considered herein. Calculated blade loads based on unsteady CFD method with respect to blade azimuth angle are compared with those by NREL FAST code and physically investigated in detail.

• 한국태양에너지학회 논문집
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• 제32권3호
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• pp.33-41
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• 2012

As the wind farms in large scale demand enormous amount of construction cost, minimizing the economic burden is essential and also it is very important to measure the wind resources and forecast annual energy production correctly to judge the economic feasibility of the proposed site by way of installing a Met mast at or nearby the site. Wind resources were measured by installing a 80[m] high Met mast at WangdeungYeo Island to conduct the research incorporated in this paper and offshore wind farm was designed using WindPRO. Wind farm of 100[MW] was designed making use of 3 and 4.5[MW] wind generator at the place selected to compare their annual energy production and capacity factor applying the loss factor of 10[%] and 20[%] respectively to each farm. As a result, 336,599[MWh] was generated by applying 3[MW] wind generator while 358,565 [MWh] was produced by 4.5[MW] wind generator. Difference in the energy production by 3[MW] generator was 33,660 [MWh] according to the loss factor with the difference in its capacity factor by 3.8[%]. On the other hand, 23 units of 4.5 [MW] wind generators showed the difference of annual energy production by 35,857 [MWh] with 4.0[%] capacity factor difference.

• Wind and Structures
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• 제18권3호
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• pp.253-265
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• 2014

The platform and floating structure of spar type offshore wind turbine systems should be designed in order for the 6-DOF motions to be minimized, considering diverse loading environments such as the ocean wave, wind, and current conditions. The objective of this study is to optimally design the platform and substructure of a 3MW spar type wind turbine system with the maximum postural stability in 6-DOF motions as well as the minimum material cost. Therefore, design variables of the platform and substructure were first determined and then optimized by a hydrodynamic analysis. For the hydrodynamic analysis, the body weight of the system was considered, and the ocean wave conditions were quantified to the wave forces using the Morison's equation. Moreover, the minimal number of computation analysis models was generated by the Design of Experiments (DOE), and the design variables of the platform and substructure were finally optimized by using a genetic algorithm with a neural network approximation.

• 신재생에너지
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• 제6권3호
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• pp.47-54
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• 2010

Foundation plays an important role in the offshore wind turbine system. Different from conventional foundations, the suction caisson is proven to be economical and reliable. In this work, three-dimensional finite element method is used to check the suitability of suction caisson foundation. NREL 5MW wind turbine is chosen as a baseline model in our simulation. The maximum overturning moment and vertical load at the mudline are calculated using FAST and Bladed. Meanwhile the soil-structure interaction response from our simulation is also compared with the experiment data from Oxford university. The design parameter such as caisson length, diameter of skirt and spacing of multipod are investigated. Accordingly based on these parameters suggestions are given to use suction caisson foundations more efficiently.

• Ocean Systems Engineering
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• 제8권1호
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• pp.79-99
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• 2018

The effects of BPC (blade pitch control) on FOWT (floating offshore wind turbine) motions and generated power are investigated by using a fully-coupled turbine-floater-mooring simulation program. In this regard, two example FOWTs, OC4-5MW semi-submersible FOWT and KRISO four-3MW-units FOWT, are selected since the numerical simulations of those two FOWTs have been verified against experiments in authors' previous studies. Various simulations are performed changing BPC natural frequency (BPCNF), BPC damping ratio (BPCDR), and wind speeds. Through the numerical simulations, it was demonstrated that negative damping can happen for platform pitch motions and its influences are affected by BPCNF, BPCDR, and wind speeds. If BPCNF is significantly larger than platform-pitch natural frequency, the pitch resonance can be very serious due to the BPC-induced negative-damping effects, which should be avoided in the FOWT design. If wind speed is significantly higher than the rated wind velocity, the negative damping effects start to become reduced. Other important findings are also given through systematic sensitivity investigations.

• 한국전자통신학회논문지
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• 제17권5호
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• pp.1003-1012
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• 2022

풍력발전시스템의 터빈과 하부구조에 전달되는 수평방향의 에너지 전달은 시스템의 안전성 유지 측면에서 매우 중요한 요소이지만 지진, 태풍과 같은 대규모 연안재해에 취약할 수 밖에 없다. 연안 또는 먼 해상에 구축되는 풍력발전시스템은 연안재해에 취약한 지역에 설치 시 보다 견고한 설계가 요구되기 때문에 초기 투자비용의 증가로 사업의 경제성 측면에서 매우 불리하다. 본 연구에서는 연안재해의 리스크를 저감한다는 관점에서 풍력발전단지의 최적 부지를 선정하기 위해 GIS 기법을 사용하였다. 우리나라 서해와 남해의 지진 현황, 서해와 남해에 영향을 미치거나 통과하는 태풍의 이동경로와 강도도 복합적으로 분석하였다. 이에 연안재해 위험이 가장 낮은 최적의 해상풍력단지 부지를 선정했고, 향후 해당지역 해상풍력 프로젝트의 기초연구자료로 활용하고자 한다.