• 대한기계학회논문집A
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• 제36권12호
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• pp.1489-1495
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• 2012

본 논문에서는 부유식 플랫폼의 동적 거동을 고려하여 해상 풍력 발전기 타워의 구조 해석을 수행하였다. 풍력 발전기는 플랫폼, 타워, 낫셀, 허브 그리고 3 개의 블레이드로 구성된다. 타워는 3 차원 빔 요소를 사용하여 탄성체로 모델링하여 탄성 다물체계 동역학을 기반으로 한 운동 방정식을 구성하였다. 회전하는 블레이드에는 블레이드 요소 운동량 이론에 따라 계산된 공기역학적 힘이 적용되었고, 부유식 플랫폼에는 유체정역학적 힘, 유체동역학적 힘 그리고 계류력이 적용되었다. 타워의 구조 동역학적 거동을 수치적으로 시뮬레이션하였다. 시뮬레이션 결과를 이용하여 굽힘 모멘트와 응력을 산출하고 허용치와 비교하였다.

• International Journal of Ocean System Engineering
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• 제3권4호
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• pp.209-217
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• 2013

This paper presents a mooring design procedure for a floating offshore wind turbine. Offshore environmental data for Jeju are taken from KHOA (Korea Hydrographic and Oceanographic Administration) and used for the environmental conditions in numerical analyses. A semi-submersible-type floating wind system with a 5-MW-class wind turbine studied by the DeepCwind Consortium is applied. Catenary mooring with a studless chain is chosen as the mooring system. Design deliverables such as the nominal sizes of chain and length of the mooring line are decided by considering the long-term prediction of the breaking strength of the mooring lines where a 100-year return period is used. The designed mooring system is verified using a fatigue calculation based on rain-flow cycle counting, an S-N curve, and a Miner's damage summation of rule. The mooring tension process is obtained from time-domain motion analyses using ANSYS/AQWA.

• 풍력에너지저널
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• 제14권1호
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• pp.5-13
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• 2023

The commercialization has been of great importance to the clean energy research sector for investing the wind farm development, but it would be difficult to reach a social consensus on the need to expand the economic feasibility of renewable energy due to the lack of reliable and continuous information on levelized cost of Energy (LCOE). Regarding this fact, this paper presents the evaluation of LCOE, focusing on Ulsan offshore region targeting to build the first floating offshore wind farm. Energy production is estimated by the meteorology data combined with the Leanwind Project power curve of an exemplar wind turbine. This work aims to analyze the costs of the Capex depending on site-specific variables. The cost of final LCOE was estimated by using Monte-Carlo method, and it became an average range 297,090 KRW/MWh, a minimum of 251,080 KRW/MWh, and a maximum of 341,910 KRW/MWh. In the year 2021, the SMP (system marginal price) and 4.5 REC (renewable energy certificate) can be paid if 1 MWh of electricity is generated by renewable energy. Considering current SMP and REC price, the floating platform industry, which can earn around 502,000 KRW/MWh, can be finally estimated highly competitive in the Korean market.

• 풍력에너지저널
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• 제14권1호
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• pp.29-36
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• 2023

The analysis of the floating offshore wind turbine platform is based on the procedures provided by the IEC including the International Classification Society, which recommends the analysis in the time domain. But time-domain simulation requires a lot of time and resources to solve tens of thousands of DLCs. This acts as a barrier in terms of floating structure development. For final verification, it requires very precise analysis in the time domain, but from an initial design point of view, a simplified verification procedure to predict the quantity of materials quickly and achieve relatively accurate results is crucial. In this study, a structural design procedure using a design wave applied in the oil and gas industries is presented combined with a conservative turbine load. With this method, a quick design spiral can be rotated, and it is possible to review FOWTs of various shapes and sizes. Consequently, a KRISO Semi-Submersible FOWT platform was developed using a simplified design procedure in frequency-domain analysis.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권1호
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• pp.9-20
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• 2018

Due to integrated stochastic wind and wave loads, the supporting platform of a Floating Offshore Wind Turbine (FOWT) has to bear six Degrees of Freedom (DOF) motion, which makes the random cyclic loads acting on the structural components, for instance the tower base, more complicated than those on bottom-fixed or land-based wind turbines. These cyclic loads may cause unexpected fatigue damages on a FOWT. This paper presents a study on short-term fatigue damage at the tower base of a 5 MW FOWT with a spar-type platform. Fully coupled time-domain simulations code FAST is used and realistic environment conditions are considered to obtain the loads and structural stresses at the tower base. Then the cumulative fatigue damage is calculated based on rainflow counting method and Miner's rule. Moreover, the effects of the simulation length, the wind-wave misalignment, the wind-only condition and the wave-only condition on the fatigue damage are investigated. It is found that the wind and wave induced loads affect the tower base's axial stress separately and in a decoupled way, and the wave-induced fatigue damage is greater than that induced by the wind loads. Under the environment conditions with rated wind speed, the tower base experiences the highest fatigue damage when the joint probability of the wind and wave is included in the calculation. Moreover, it is also found that 1 h simulation length is sufficient to give an appropriate fatigue damage estimated life for FOWT.

• Ocean Systems Engineering
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• 제1권1호
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• pp.95-111
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• 2011

Increasing numbers of floating offshore wind turbines are planned and designed these days due to their high potential in massive generation of clean energy from water depth deeper than 50 m. In the present study, a numerical prediction tool has been developed for the fully-coupled dynamic analysis of FOWTs in time domain including aero-blade-tower dynamics and control, mooring dynamics, and platform motions. In particular, the focus of the present study is paid to the dynamic coupling between the rotor and floater and the coupled case is compared against the uncoupled case so that their dynamic coupling effects can be identified. For this purpose, a mono-column mini TLP with 1.5MW turbine for 80m water depth is selected as an example. The time histories and spectra of the FOWT motions and accelerations as well as tether top-tensions are presented for the given collinear wind-wave condition. When compared with the uncoupled analysis, both standard deviations and maximum values of the floater-responses/tower-accelerations and tether tensions are appreciably increased as a result of the rotor-floater dynamic coupling, which may influence the overall design including fatigue-life estimation especially when larger blades are to be used.

• 대한조선학회논문집
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• 제54권3호
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• pp.196-203
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• 2017

In general, the installation of offshore wind turbine have been carried out by a jack-up barge or wind turbine installation vessel. In case of using jack-up barge, an additional barge is required to transport offshore wind turbines. During the transportation, barge is affected by environmental conditions such as wave, wind etc. So, it is important to secure the static and dynamic stability of the barge. In this study, fundamental research was performed to evaluate the stability of barge due to use the guide frame. The analysis for static stability of barge was performed under the two loading conditions with or without wave and those results were evaluated according to the Ministry of Oceans and Fisheries rules. Also motion analysis was performed under the ITTC wave spectrum using buoy data and evaluated based on NORDFORSK guideline by using commercial software Maxsurf Motions.

• International Journal of Naval Architecture and Ocean Engineering
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• 제5권2호
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• pp.199-209
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• 2013

This paper presents the model test results of 3 new spar platforms which were developed based on the OC3-Hywind spar to support a 5-MW wind turbine. By changing the shape but keeping both volume and mass of OC3-Hywind spar platform, those platforms were expected to experience different hydrodynamic and hydrostatic loads. The scale models were built with a 1/128 scale ratio. The model tests were carried out in waves, including both rotating rotor effect and mean wind speed. The characteristic motions of the 3 new models were measured; Response Amplitude Operators (RAO) and significant motions were calculated and compared with those of OC3-Hywind.

• Ocean Systems Engineering
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• 제13권3호
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• pp.287-312
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• 2023

The global performance of a 15 MW floating offshore wind turbine, a newly designed semisubmersible floating foundation with multiple heave plates by CNOOC, is investigated with two independent turbine-floater-mooring coupled dynamic analysis programs CHARM3D-FAST and OrcaFlex. The semisubmersible platform hosts IEA 15 MW reference wind turbine modulated for VolturnUS-S and hybrid type (chain-wire-chain with clumps) 3×2 mooring lines targeting the water depth of 100 m. The numerical free-decay simulation results are compared with physical experiments with 1:64 scaled model in 3D wave basin, from which appropriate drag coefficients for heave plates were estimated. The tuned numerical simulation tools were then used for the feasibility and global performance analysis of the FOWT considering the 50-yr-storm condition and maximum operational condition. The effect of tower flexibility was investigated by comparing tower-base fore-aft bending moment and nacelle translational accelerations. It is found that the tower-base bending moment and nacelle accelerations can be appreciably increased due to the tower flexibility.

• 한국소음진동공학회논문집
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• 제23권5호
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• pp.407-413
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• 2013

This paper deals with the analysis of dynamic characteristics of mooring system of floating-type offshore wind turbine. A spar-type floating structure which consists of a nacelle, a tower and the platform excepting blades, is used to model the floating wind turbine and connect three catenary cables to substructure. The motion of floating structure is simulated when the mooring system is attached using irregular wave Pierson-Moskowitz model. The mooring system is analyzed by changing cable position of floating structure. The dynamic behavior characteristics of mooring system are investigated comparing with cable tension and 6-dof motion of floating structure. These characteristics are much useful to initial design of floating-type structure. From the simulation results, the optimized design parameter that is cable position of connect point of mooring cable can be obtained.