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Long-term extreme response of an offshore turbine: How accurate are contour-based estimates?

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Title: Long-term extreme response of an offshore turbine: How accurate are contour-based estimates?
Authors: Haselsteiner, Andreas F.1 (AUTHOR) a.haselsteiner@uni-bremen.de, Frieling, Malte1 (AUTHOR) frieling@uni-bremen.de, Mackay, Ed2 (AUTHOR) e.mackay@exeter.ac.uk, Sander, Aljoscha1,3 (AUTHOR) aljoscha.sander@uni-bremen.de, Thoben, Klaus-Dieter1 (AUTHOR) thoben@uni-bremen.de
Source: Renewable Energy: An International Journal. Jan2022, Vol. 181, p945-965. 21p.
Subject Terms: *Wind power, *Water depth, *Wind turbines, Bending moment, Turbines, Structural design
Abstract: According to design standards, offshore wind turbines need to withstand environmental loads with a return period of 50 years. This work compares the extreme response along the 50-year environmental contour with the true 50-year wind turbine response. It was found that the environmental contour method that is currently described in the IEC design standard for offshore wind turbines can strongly under-predict the 50-year return value of response variables whose annual maxima typically occur during power production. The bias in the contour-based estimate of the 50-year response can be attributed to three sources: (1) the method used to construct the contour; (2) neglecting serial correlation in environmental conditions; and (3) neglecting the short-term variability in the response. In our analysis the 50-year maximum mudline overturning moment was underestimated by 4–8% by the contour-based approach that is currently recommended, whereas the bending moment at 10 m water depth was underestimated by 25–28%. This underestimation was mainly due to ignoring the short-term variability in the response. The bias associated with contour construction, an effect much discussed in recent publications, was of much smaller magnitude. • Long-term extreme response of an offshore wind turbine was estimated. • Estimates from contour methods were compared to true response. • Sources of bias of the contour-based estimates were quantified. • Bias is due to contour construction, serial correlation and short-term variability. • Applying contour method from IEC's standard can underestimate the extreme response. [ABSTRACT FROM AUTHOR]
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Database: GreenFILE
Description
Abstract:According to design standards, offshore wind turbines need to withstand environmental loads with a return period of 50 years. This work compares the extreme response along the 50-year environmental contour with the true 50-year wind turbine response. It was found that the environmental contour method that is currently described in the IEC design standard for offshore wind turbines can strongly under-predict the 50-year return value of response variables whose annual maxima typically occur during power production. The bias in the contour-based estimate of the 50-year response can be attributed to three sources: (1) the method used to construct the contour; (2) neglecting serial correlation in environmental conditions; and (3) neglecting the short-term variability in the response. In our analysis the 50-year maximum mudline overturning moment was underestimated by 4–8% by the contour-based approach that is currently recommended, whereas the bending moment at 10 m water depth was underestimated by 25–28%. This underestimation was mainly due to ignoring the short-term variability in the response. The bias associated with contour construction, an effect much discussed in recent publications, was of much smaller magnitude. • Long-term extreme response of an offshore wind turbine was estimated. • Estimates from contour methods were compared to true response. • Sources of bias of the contour-based estimates were quantified. • Bias is due to contour construction, serial correlation and short-term variability. • Applying contour method from IEC's standard can underestimate the extreme response. [ABSTRACT FROM AUTHOR]
ISSN:09601481
DOI:10.1016/j.renene.2021.09.077