Load Evaluation for Tower Design of Large Floating Offshore Wind Turbine System According to Wave Conditions

Ahn, Hyeonjeong; Ha, Yoon-Jin; Kim, Kyong‐Hwan

doi:10.3390/en16041862

Cited by 4 publications

(4 citation statements)

References 19 publications

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“…To distribute the force applied to the heave spring element, the heave spring element was connected to all the nodes of each column bottom plate by a load coupling element. The stiffness of the heave spring, 𝑘 , is determined by Equation (12). Where 𝜌 , 𝑔 , and 𝐴 are the seawater density, gravitational acceleration, and water plane area at the draft, respectively.…”

Section: Loading and Boundary Conditionsmentioning

confidence: 99%

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Structural Design of the Substructure of a 10 MW Floating Offshore Wind Turbine System Using Dominant Load Parameters

Park

Choung

2023

JMSE

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Fully coupled integrated load analyses (ILAs) to evaluate not only the load response but also the structural integrity are required to design a floating offshore wind turbine, since there has been no firmly established approach for obtaining the structural responses of a FOWT substructure in the time domain. This study aimed to explore if a direct strength analysis (DSA) technique that has been widely used for ships and offshore structures can adequately evaluate the FOWT substructure. In this study, acceleration and nacelle thrust were used for the dominant load parameters for DSA. The turbine thrust corresponding to the 50-year return period was taken from the literature. The acceleration response amplitude operator (RAO) was obtained through frequency response hydrodynamic analysis. The short-term sea states defined by the wave scatter diagram (WSD) of the expected installation area was represented by the JONSWAP wave spectrum. To account for the multi-directionality of the short-crested waves, the 0th order moments of the wave spectrum were corrected. The probabilities of each short-term sea state and each wave incidence angle were applied to derive the long-term acceleration for each return period. DSA cases were generated by combining the long-term acceleration and nacelle thrust to maximize the forces in the surge, sway, and heave directions. Linear spring elements were placed under the three outer columns of the substructure to provide soft constraints for hive, roll, and pitch motions. Nonlinear spring elements with initial tension were placed on the three fairlead chain stoppers (FCSs) to simulate the station-keeping ability of the mooring lines; they provided initial tension in the slacked position and an increased tension in the taut position. The structural strength evaluation of the coarse mesh finite element model with an element size same as the stiffener spacing showed that high stresses exceeding the permissible stresses occurred in the unstable members of the substructure. The high stress areas were re-evaluated using a fine mesh finite element model with an element size of 50 mm × 50 mm. The scope of structural reinforcement was identified from the fine mesh analyses. It was found that the DSA can be properly utilized for the substructure strength assessment of a FOWT.

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Section: Loading and Boundary Conditionsmentioning

confidence: 99%

“…Li et al [11] investigated the motion and structural loads of the NREL 5 MW FOWT under a typhoon condition. Ahn et al [12] used OpenFAST to investigate the variation of the tower base moment. The effect of second-order hydrodynamics was investigated using Wamit [13] and Open-FAST [14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Structural Design of the Substructure of a 10 MW Floating Offshore Wind Turbine System Using Dominant Load Parameters

Park

Choung

2023

JMSE

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“…In this paper, the authors check how modes are modified by enabling and disabling different degrees of freedom (DOF). In [18], load evaluation is conducted according to time series and FFT results. The main findings of this study relate to the problem here addressed: first, in the correlation analysis, the tower-top deflection has the highest correlation, and this further affects nacelle acceleration.…”

Section: Related Workmentioning

confidence: 99%

Identification of Vibration Modes in Floating Offshore Wind Turbines

Serrano-Antoñanazas,

Sierra-Garcia,

Santos

et al. 2023

JMSE

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Compared to onshore turbines, floating offshore wind turbines (FOWTs) take advantage of the increased availability of offshore wind while causing less environmental impact. However, the strong winds, waves, and currents to which they are subjected trigger oscillations that can cause significant damage to the entire structural system and reduce its useful life. To reduce these loads, active tower damping techniques such as filter banks can be used. These filters must be carefully tuned to block specific vibration frequencies. Therefore, it is essential to analyze the nature of the oscillations in the FOWT and to understand how the frequencies vary in time. This topic is usually approached from a point of view very focused on a specific turbine. What is proposed here is a general method, which can be applied to any type of wind turbine, to automatically study the relationship between vibration frequencies and the degrees of freedom (DOF) of the turbine, which facilitates the design of structural control. Each frequency is associated with the DOF of the FOWT that produces it. This methodology has been successfully validated in simulation experiments with the NREL 5 MW ITI Barge FOWT. Under the wind conditions of the experiments, the main frequency found is 0.605 Hz. This frequency coincides with the 3P theoretical frequency of the FOWT. This proposal may help to design structural control systems able to damp these vibration frequencies with accuracy and efficiency.

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“…Xu Sheng et al employed the T-N curve to calculate the shortterm fatigue damage of point absorption wave energy devices [11]. Ahn et al investigated the loads on a 15 MW floating wind turbine tower based on wave conditions, which in turn analyzed the relationship between the pitching moments at the top and base of the tower with the wave conditions without regard to the effect of wave conditions on the mooring system [12]. Zhao et al analyzed the reliability of a floating wind turbine mooring system based on the environmental isoline method and studied the relationship between the extreme tension of the mooring line and environmental parameters [13].…”

Section: Introductionmentioning

confidence: 99%

Study on Mooring Design of 15 MW Floating Wind Turbines in South China Sea

Chen,

Jiang,

Zhang

et al. 2023

JMSE

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Wind turbines and floating platform upsizing are major trends in the current offshore wind development. However, harsh environmental conditions increase the risk of anchor dragging and mooring failure when deploying large offshore floating wind turbines. Therefore, it is necessary to design a mooring system for the specific deployment site. This study aims to perform the mooring system design of a floating offshore wind turbine (FOWT) operated in the South China Sea, which is a combination of the IEA 15 MW wind turbine and UMaine VolturnUS-S floating platform. Hydrodynamic coefficients were calculated based on the potential flow theory, considering the environmental loads in the South China Sea. Additionally, the hydrodynamic coefficients were imported into AQWA to calculate the time-domain mooring tension. The mooring design parameters, such as mooring line length, nominal sizes, and anchor point, were determined using the criterion of anchor uplift, maximum breaking strength, and fatigue life, respectively. The design criterion required that the anchor uplift is not more than the allowable value, the long-term breaking limit of mooring with a 100-year return period should be less than the maximum breaking limit, and the fatigue damage accumulation in 50 years should be safe. The mooring design procedure provides a reference for mooring system design and safe operation of large floating wind turbines in the South China Sea.

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Load Evaluation for Tower Design of Large Floating Offshore Wind Turbine System According to Wave Conditions

Cited by 4 publications

References 19 publications

Structural Design of the Substructure of a 10 MW Floating Offshore Wind Turbine System Using Dominant Load Parameters

Structural Design of the Substructure of a 10 MW Floating Offshore Wind Turbine System Using Dominant Load Parameters

Identification of Vibration Modes in Floating Offshore Wind Turbines

Study on Mooring Design of 15 MW Floating Wind Turbines in South China Sea

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