Preprints
https://doi.org/10.5194/wes-2022-15
https://doi.org/10.5194/wes-2022-15
 
30 Mar 2022
30 Mar 2022
Status: this preprint is currently under review for the journal WES.

Probabilistic Temporal Extrapolation of Fatigue Damage of Offshore Wind Turbine Substructures Based on Strain Measurements

Clemens Hübler and Raimund Rolfes Clemens Hübler and Raimund Rolfes
  • Leibniz Universität Hannover, Institute of Structural Analysis, ForWind, Appelstr. 9a, D-30167 Hannover, Germany

Abstract. Substructures of offshore wind turbines are becoming older and beginning to reach their design lifetimes. Hence, lifetime extensions for offshore wind turbines are becoming not only an interesting research topic, but also a relevant option for industry. To make well-founded decisions on possible lifetime extensions, precise fatigue damage predictions are required. In contrast to the design phase, fatigue damage predictions cannot only be based on aero-elastic simulations but also on strain measurements. Nonetheless, strain measurement-based fatigue damage assessments for lifetime extensions have been rarely conducted so far. Simulation-based approaches are much more common, although current standards explicitly recommend the use of measurement-based approaches as well. For measurement-based approaches, the main challenge is that strain data are limited. This means that measurements are only available for a limited period and only at some specific hot-spot locations. Hence, spatial and temporal extrapolations are required. Available procedures are not yet standardised and in most cases not validated. This work focuses on extrapolations in time. Several methods for the extrapolation of fatigue damage are assessed. The methods are intended to extrapolate fatigue damage calculated for a limited time period using strain measurement data to a longer time period, or another time period, where no such data are available. This could be, for example, a future period, a period prior to the installation of strain gauges or a period after some sensors have failed. The methods are validated using several years of strain measurement data from the German offshore wind farm Alpha Ventus. The performance and user friendliness of the various methods are compared. It is shown that fatigue damage can be predicted accurately and reliably for periods where no strain data are available. Best results are achieved if wind speed correlations are taken into account by applying a binning approach, and if a least some winter months of strain data are available.

Clemens Hübler and Raimund Rolfes

Status: open (until 24 May 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on wes-2022-15', Anonymous Referee #1, 05 May 2022 reply
  • RC2: 'Comment on wes-2022-15', Anonymous Referee #2, 15 May 2022 reply

Clemens Hübler and Raimund Rolfes

Clemens Hübler and Raimund Rolfes

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Short summary
Offshore wind turbines are beginning to reach their design lifetimes. Hence, lifetime extensions are becoming relevant. To make well-founded decisions on possible lifetime extensions, fatigue damage predictions are required. Measurement-based assessments instead of simulation-based analyses are rarely conducted so far, since data are limited. Therefore, this work focuses on the temporal extrapolation of measurement-data. It is shown that fatigue damage can be extrapolated accurately.