Prospects and Economics of Offshore Wind Turbine Systems

Thi Quynh Mai Pham,Sungwoo Im,Joonmo Choung 한국해양공학회 2021 韓國海洋工學會誌 Vol.35 No.5

In recent years, floating offshore wind turbines have attracted more attention as a new renewable energy resource while bottom-fixed offshore wind turbines reach their limit of water depth. Various projects have been proposed with the rapid increase in installed floating wind power capacity, but the economic aspect remains as a biggest issue. To figure out sensible approaches for saving costs, a comparison analysis of the levelized cost of electricity (LCOE) between floating and bottom-fixed offshore wind turbines was carried out. The LCOE was reviewed from a social perspective and a cost breakdown and a literature review analysis were used to itemize the costs into its various components in each level of power plant and system integration. The results show that the highest proportion in capital expenditure of a floating offshore wind turbine results in the substructure part, which is the main difference from a bottom-fixed wind turbine. A floating offshore wind turbine was found to have several advantages over a bottom-fixed wind turbine. Although a similarity in operation and maintenance cost structure is revealed, a floating wind turbine still has the benefit of being able to be maintained at a seaport. After emphasizing the cost-reduction advantages of a floating wind turbine, its LCOE outlook is provided to give a brief overview in the following years. Finally, some estimated cost drivers, such as economics of scale, wind turbine rating, a floater with mooring system, and grid connection cost, are outlined as proposals for floating wind LCOE reduction.

타워와 블레이드의 탄성효과를 고려한 부유식 해상풍력발전기의 동적거동해석

정혜영(Hye Young Jung),손정현(Jeong Hyun Sohn) 대한기계학회 2012 大韓機械學會論文集A Vol.36 No.8

부유식 해상풍력발전기의 시뮬레이션을 위해서 본 연구에서는 2㎿ 육상 풍력발전기에 부유구조물인 Tension Leg Platform(TLP) 구조를 추가하였다. 기상청 관측데이터와 해수면으로부터의 높이에 대해 풍속을 정의하는 지수법칙을 이용하여 풍하중을 산출하고 블레이드와 타워에 일정한 높이간격으로 적용하였다. 상대모리슨 방정식을 이용하여 파랑하중을 모델링하였다. 블레이드의 회전속도를 정격속도인 18rpm 으로 고려하고, 풍하중과 파랑하중 작용 시 2㎿ 의 부유식 해상풍력기의 동적거동 해석을 수행하였다. 파랑하중에 대한 해상풍력기의 공진특성을 조사하기 위해 타워와 블레이드의 탄성체 모델을 구성하여 해상풍력기의 고유진동수를 계산하였다. 타워와 블레이드의 탄성효과가 해상풍력기의 거동에 미치는 영향을 분석하기 위해 타워만 탄성체로 구성된 탄성타워모델과 타워와 블레이드가 탄성체로 고려된 탄성타워 블레이드모델을 각각 강체 모델과 비교하였다. To establish a floating offshore wind turbine simulation model, a tension leg platform is added to an onshore wind turbine. The wind load is calculated by using meteorological administration data and a power law that defines the wind velocity according to the height from the sea surface. The wind load is applied to the blade and wind tower at a regular distance. The relative Morison equation is employed to generate the wave load. The rated rotor speed (18 rpm) is applied to the hub as a motion. The dynamic behavior of a 2-㎿ floating offshore wind turbine subjected to the wave excitation and wind load is analyzed. The flexible effects of the wind tower and the blade are analyzed. The flexible model of the wind tower and blade is established to examine the natural frequency of the TLP-type offshore wind turbine. To study the effect of the flexible tower and blade on the floating offshore wind turbine, we modeled the flexible tower model and flexible tower-blade model and compared it with a rigid model.

Simultaneous out-of-plane and in-plane vibration mitigations of offshore monopile wind turbines by tuned mass dampers

Haoran Zuo,Kaiming Bi,Hong Hao 국제구조공학회 2020 Smart Structures and Systems, An International Jou Vol.26 No.4

To effectively extract the vast wind resource, offshore wind turbines are designed with large rotor and slender tower, which makes them vulnerable to external vibration sources such as wind and wave loads. Substantial research efforts have been devoted to mitigate the unwanted vibrations of offshore wind turbines to ensure their serviceability and safety in the normal working condition. However, most previous studies investigated the vibration control of wind turbines in one direction only, i.e., either the out-of-plane or in-plane direction. In reality, wind turbines inevitably vibrate in both directions when they are subjected to the external excitations. The studies on both the in-plane and out-of-plane vibration control of wind turbines are, however, scarce. In the present study, the NREL 5 MW wind turbine is taken as an example, a detailed three-dimensional (3D) Finite Element (FE) model of the wind turbine is developed in ABAQUS. To simultaneously control the in-plane and out-of-plane vibrations induced by the combined wind and wave loads, another carefully designed (i.e., tuned) spring and dashpot are added to the perpendicular direction of each Tuned Mass Damper (TMD) system that is used to control the vibrations of the tower and blades in one particular direction. With this simple modification, a bi-directional TMD system is formed and the vibrations in both the out-of-plane and in-plane directions are simultaneously suppressed. To examine the control effectiveness, the responses of the wind turbine without control, with separate TMD system and the proposed bi-directional TMD system are calculated and compared. Numerical results show that the bi-directional TMD system can simultaneously control the out-of-plane and in-plane vibrations of the wind turbine without changing too much of the conventional design of the control system. The bi-directional control system therefore could be a cost-effective solution to mitigate the bi-directional vibrations of offshore wind turbines.

풍동시험을 활용한 10 MW급 부유식 해상풍력터빈 운송 및 설치 시 풍하중 예측

심인환 한국풍력에너지학회 2024 풍력에너지저널 Vol.15 No.1

As the generation capacity of floating offshore wind turbines increases, the wind load applied to each turbine increases. Due to such a high wind load, the capacity of transport equipment (such as tugboats or cranes) required in the transportation and installation phases must be much larger than that of previous small-capacity wind power generation systems. However, for such an important wind load prediction method, the simple formula proposed by the classification society is generally used, and prediction through wind tunnel tests or Computational Fluid Dynamics (CFD) is rarely used, especially for a concept or initial design stages. In this study, the wind load of a 10 MW class floating offshore wind turbine was predicted by a simplified formula and compared with results of wind tunnel tests. In addition, the wind load coefficients at each stage of fabrication, transportation, and installation are presented so that it can be used during a concept or initial design stages for similar floating offshore wind turbines.

Sensitivity Analysis of Offshore Wind Turbine Tower Caused by the External Force

김남형,진정운 대한토목학회 2013 KSCE JOURNAL OF CIVIL ENGINEERING Vol.17 No.5

Generally, faster wind speeds are observed in coastal areas than in inland areas. Therefore, for the development of offshore wind energy, more electricity is expected to be generated using wind turbines. This also solves environmental obstacles such as the selection and acquisition of land for a site and the need to protect surrounding sites from noise problems. In this paper, a numerical analysis on the external forces that affects a wind turbine tower is performed, when the wind turbine is installed in a coastal area. To calculate the extreme wind and wave forces, the maximum wind speed is assumed to be 55 m/s, which is observed 10 minutes as the mean maximum wind speed of typhoon Maemi in 2003. During the calculation procedure, the wind force is calculated according to the Korea Building Code 2009. The significant wave height and period are estimated by using the Sverdrup-Munk-Bretschneider (SMB) method. The result data obtained using the SMB method are applied to Morison’s equation to compute the wave force. The blade of the wind turbine is designed based on the Blade Element Momentum Theory, and the thrust force of the blade is computed. The diameters of the wind turbine tower are assumed to be 3 m, 4.5 m, and 6 m. The results of this numerical analysis show that wave force acting on the wind turbine tower is increased according to the diameter of the tower and the wind speed.

Analysis of Dynamic Response Characteristics for 5 MW Jacket-type Fixed Offshore Wind Turbine

Jaewook Kim,Sanghwan Heo,WeonCheol Koo 한국해양공학회 2021 韓國海洋工學會誌 Vol.35 No.5

This study aims to evaluate the dynamic responses of the jacket-type offshore wind turbine using FAST software (Fatigue, Aerodynamics, Structures, and Turbulence). A systematic series of simulation cases of a 5 MW jacket-type offshore wind turbine, including wind-only, wave-only, wind & wave load cases are conducted. The dynamic responses of the wind turbine structure are obtained, including the structure displacement, rotor speed, thrust force, nacelle acceleration, bending moment at the tower bottom, and shear force on the jacket leg. The calculated time-domain results are transformed to frequency domain results using FFT and the environmental load with more impact on each dynamic response is identified. It is confirmed that the dynamic displacements of the wind turbine are dominant in the wave frequency under the incident wave alone condition, and the rotor thrust, nacelle acceleration, and bending moment at the bottom of the tower exhibit high responses in the natural frequency band of the wind turbine. In the wind only condition, all responses except the vertical displacement of the wind turbine are dominant at three times the rotor rotation frequency (considering the number of blades) generated by the wind. In a combined external force with wind and waves, it was observed that the horizontal displacement is dominant by the wind load. Additionally, the bending moment on the tower base is highly affected by the wind. The shear force of the jacket leg is basically influenced by the wave loads, but it can be affected by both the wind and wave loads especially under the turbulent wind and irregular wave conditions.

Validation of a 750 kW semi-submersible floating offshore wind turbine numerical model with model test data, part I: Model-I

Pham, Thanh Dam,Shin, Hyunkyoung The Society of Naval Architects of Korea 2019 International Journal of Naval Architecture and Oc Vol.11 No.2

This paper describes a model test and numerical simulation of a 750-kW-semi-submersible platform wind turbine under several wind and wave conditions for validation of the numerical simulation model. The semi-submersible platform was designed to support the 750-kW-wind turbine class and operate at a water depth of 50 m. The model tests were performed to estimate the performance characteristics of the wind turbine system in the wide tank of the University of Ulsan. Motions and loads of the wind turbine system under the wind and wave conditions were measured and analyzed. The NREL-FAST code was used to simulate the wind turbine system, and the results were compared with those of the test model. The results demonstrate that the numerical simulation captures noticeably the fully coupled floating wind turbine dynamic responses. Also, the model shows a good stability and small responses during waves, wind, and operation of the 750-kW-floating offshore wind turbine.

Validation of a 750 kW semi-submersible floating offshore wind turbine numerical model with model test data, part I: Model-I

Thanh Dam Pham,Hyun Kyoung Shin 대한조선학회 2019 International Journal of Naval Architecture and Oc Vol.11 No.2

This paper describes a model test and numerical simulation of a 750-kW-semi-submersible platform wind turbine under several wind and wave conditions for validation of the numerical simulation model. The semi-submersible platform was designed to support the 750-kW-wind turbine class and operate at a water depth of 50 m. The model tests were performed to estimate the performance characteristics of the wind turbine system in the wide tank of the University of Ulsan. Motions and loads of the wind turbine system under the wind and wave conditions were measured and analyzed. The NREL-FAST code was used to simulate the wind turbine system, and the results were compared with those of the test model. The results demonstrate that the numerical simulation captures noticeably the fully coupled floating wind turbine dynamic responses. Also, the model shows a good stability and small responses during waves, wind, and operation of the 750-kW-floating offshore wind turbine.

Performance changes of a floating offshore wind turbine with broken mooring line

Bae, Y.H.,Kim, M.H.,Kim, H.C. Elsevier 2017 RENEWABLE ENERGY Vol.101 No.-

<P><B>Abstract</B></P> <P>In the present study, a series of numerical simulations of the performance changes of a Floating Offshore Wind Turbine (FOWT) with broken mooring line was carried out. For this simulation, an aero-hydro-servo-elastic-mooring coupled dynamic analysis were carried out in the time domain. The OC4 DeepCwind semisubmersible with NREL's 5-MW baseline turbine was selected as a reference platform. One of the three mooring lines was intentionally disconnected from the floating platform at a certain time. The resulting transient/unsteady responses and steady-state responses after that, mooring line tensions, and turbine performance were checked. The accidental disconnection of one of the mooring lines changes the watch circle of the floating platform and the tensions of the remaining mooring lines. In addition, the changes in the platform orientation also cause nacelle yaw error, which is directly related to the power production and structural fatigue life. When horizontal offset becomes large, power-line is likely to be disconnected and its influence was also investigated. To ensure the sustainability of a series of FOWTs associated with farm development, the influence of mooring line failure and resulting changes to the turbine performance should be checked in advance. Otherwise, successive failure of neighboring FOWTs could take place.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We investigated the dynamic responses of the OC4 semi-submersible floating offshore wind turbine with broken mooring line. </LI> <LI> We developed the coupled dynamic analysis tool for FOWT with broken mooring lines and large-offset-position effects. </LI> <LI> We demonstrated the platform drifting route after one-mooring-line failure in wind-wave environment. </LI> <LI> We examined the platform motion and wind turbine responses after the disconnection of the specific mooring line. </LI> </UL> </P>

Monitoring system for the wind-induced dynamic motion of 1/100-scale spar-type floating offshore wind turbine

C.M. Kim,조진래,S.R. Kim,이연승 한국풍공학회 2017 Wind and Structures, An International Journal (WAS Vol.24 No.4

Differing from the fixed-type, the dynamic motion of floating-type offshore wind turbines is very sensitive to wind and wave excitations. Thus, the sensing and monitoring of its motion is important to evaluate the dynamic responses to the external excitation. In this context, a monitoring system for sensing and processing the wind-induced dynamic motion of spar-type floating offshore wind turbine is developed in this study. It is developed by integrating a 1/00 scale model of 2.5MW spar-type floating offshore wind turbine, water basin equipped with the wind generator, sensing and data acquisition systems, real-time CompactRIO controller and monitoring program. The scale model with the upper rotatable blades is installed within the basin by means of three mooring lines, and its translational and rotational motions are detected by 3-axis inclinometer and accelerometers and gyroscope. The detected motion signals are processed using a real-time controller CompactRIO to calculate the acceleration and tilting angle of nacelle and the attitude of floating platform. The developed monitoring system is demonstrated and validated by measuring and evaluating the time histories and trajectories of nacelle and platform motions for three different wind velocities and for eight different fairlead positions.