Decoupled simulations of offshore wind turbines with reduced rotor loads and aerodynamic damping

Schafhirt, Sebastian; Muskulus, Michael

doi:10.5194/wes-3-25-2018

Cited by 19 publications

(8 citation statements)

References 24 publications

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“…This means that for every step to a new wind speed, the structure decays to a new equilibrium position. These "decays" allow an equivalent linear damping ratio to be extracted and the principle is based on the work done by Schløer et al (2016) and Schløer et al (2018). Schafhirt and Muskulus (2018) made a detailed analysis of this approach and found that although the aero-elastic damping process is not linear, it can be successfully modelled by a linear damping model.…”

Section: The Simplified Model: Qulafmentioning

confidence: 99%

Performance study of the QuLAF pre-design model for a 10 MW floating wind turbine

2019

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Abstract. This paper presents a comparison study of the simplified model QuLAF (Quick Load Analysis of Floating wind turbines) and a FAST model of the Technical University of Denmark (DTU) 10 MW reference wind turbine mounted on the LIFES50+ OO-Star Wind Floater Semi 10 MW floating substructure. The purpose is to investigate how accurate results can be obtained from this simplified model for different load cases. The two models are briefly presented and the limitations of QuLAF are discussed. These are (a) an under-prediction of the wave excitation loads for large sea states; (b) a simplified representation of the rotor-induced forcing and damping; (c) an over-predicted aerodynamic damping for the tower mode motion and (d) restriction to planar motion. All the limitations are linked to approximations applied for achieving the substantial model speedup relative to the state-of-the-art model. The comparative study is based on the planar version of design load cases (DLCs) 1.2, 1.3, 1.6, 2.1 and 6.1, and the overall analysis shows that the simplified model is generally good at estimating the bending moment at the tower base and the floater motions in heave and pitch. The largest tower-base bending moments are slightly over-predicted, but it is observed that while stronger wind leads to an over-prediction, stronger waves lead to an under-prediction. Thus, in DLC 1.6, where the largest load was obtained at 10.3 m s−1, a good match in tower-base bending moments between the two models is found. The nacelle acceleration, however, is generally under-predicted, which is linked to an over-prediction of the aerodynamic damping on the tower mode. Furthermore, the floater response in large sea states is influenced by the omission of viscous hydrodynamic drag forcing, which leads to an under-prediction of the wave excitation loads. A further investigation of the model limitations confirms these findings with respect to the tower mode damping and viscous drag loads, while the simplified approach to rotor-induced loads is found to provide remarkably accurate forcing results. Although a full design load basis evaluation with a state-of-the-art model must be carried out for the final design, the present results show the potential of applying simplified models in the preliminary design phase.

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Section: The Simplified Model: Qulafmentioning

confidence: 99%

Performance study of the QuLAF pre-design model for a 10 MW floating wind turbine

2019

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Section: The Simplified Model: Qulafmentioning

confidence: 99%

Reply to referee #1

Madsen¹

2019

Preprint

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“…Ref. [17] compared results obtained from a fully integrated simulation and those of a decoupled system accounting for linear aerodynamic damping. The results showed that even if the aerodynamic damping is nonlinear, it is possible to match the results of a fully coupled-or integrated-simulation if optimization of the damping ratios for different wind speeds is performed.…”

Section: Introductionmentioning

confidence: 99%

“…Both [16,17] focused on the decoupling of the wind turbine rotor from the support structure. However, that is not the only component of an offshore wind turbine that could be decoupled.…”

Section: Introductionmentioning

confidence: 99%

Decoupled Modelling Approaches for Environmental Interactions with Monopile-Based Offshore Wind Support Structures

2020

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To meet the political goals regarding renewable energy production, offshore wind keeps expanding to waters with larger depths and harsher conditions, while the turbine size continues to grow and ever-larger foundation structures are required. This development can only be successful if further cuts in the levelized cost of energy are established. Regarding the design of the foundation structures, a particular challenge in this respect relates to the reduction of the total computational time required for the design. For both practical and commercial reasons, the decoupled modelling of offshore wind support structures finds a common application, especially during the preliminary design stage. This modelling approach aims at capturing the relevant characteristics of the different environment-structure interactions, while reducing the complexity as much as possible. This paper presents a comprehensive review of the state-of-the-art modelling approaches of environmental interactions with offshore wind support structures. In this respect, the primary focus is on the monopile foundation, as this concept is expected to remain the prominent solution in the years to come. Current challenges in the field are identified, considering as well the engineering practice and the insights obtained from code comparison studies and experimental validations. It is concluded that the decoupled analysis provides valuable modelling perspectives, in particular for the preliminary design stage. In the further development of the different modelling strategies, however, the trade-off with computational costs should always be kept in mind.

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Decoupled simulations of offshore wind turbines with reduced rotor loads and aerodynamic damping

Cited by 19 publications

References 24 publications

Performance study of the QuLAF pre-design model for a 10 MW floating wind turbine

Performance study of the QuLAF pre-design model for a 10 MW floating wind turbine

Reply to referee #1

Decoupled Modelling Approaches for Environmental Interactions with Monopile-Based Offshore Wind Support Structures

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