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Wind Energy Science The interactive open-access journal of the European Academy of Wind Energy
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Discussion papers
https://doi.org/10.5194/wes-2019-20
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wes-2019-20
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research articles 14 May 2019

Research articles | 14 May 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Wind Energy Science (WES).

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

Freddy J. Madsen, Antonio Pegalajar-Jurado, and Henrik Bredmose Freddy J. Madsen et al.
  • Department of Wind Energy, Technical University of Denmark, Nils Koppels Allé, Building 403, DK-2800 Kgs. Lyngby, Denmark

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 DTU 10MW Reference Wind Turbine mounted on the LIFES50+ OO-Star Wind Floater Semi 10MW 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 speed up relative to the state-of-the-art model. The comparative study is based on the planar version of design load cases (DLC) 1.2, 1.3, 1.6, 2.1 and 6.1 and the overall analysis shows that the simplified model is generally very 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, a perfect match in tower base bending moments between the two models is found. The nacelle acceleration, however, is generally under-predicted, which is likely due 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 remarkable 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 the QuLAF model in the preliminary design phase.

Freddy J. Madsen et al.
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Status: final response (author comments only)
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Freddy J. Madsen et al.
Freddy J. Madsen et al.
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Latest update: 23 Jul 2019
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Short summary
This paper presents a comparison study of the simplified model QuLAF (Quick Load Analysis of Floating wind turbines) and FAST for the planar version of various design load cases, in order to investigate how accurate results can be obtained from this simplified model. The overall analysis shows that QuLAF is generally very good at estimating the bending moment at the tower base and the floater motions, whereas the nacelle acceleration is generally under-predicted.
This paper presents a comparison study of the simplified model QuLAF (Quick Load Analysis of...
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