| 17 Jun 2025
Kriging meta-models for damage equivalent load assessment of idling offshore wind turbines
Abstract. Lifetime reassessments of offshore wind turbines are very time consuming due to the large number of required simulations. As a result, the use of meta-models as surrogate models of the aeroelastic simulation model could offer a suitable alternative to simulations in the time domain (e.g., Kriging, artificial neural networks, or polynomial chaos expansion). Meta-models for the approximation of fatigue loads, i.e., damage equivalent loads, of wind turbines in normal operation have been researched comprehensively in recent years. Especially for offshore wind turbines, however, the downtimes, i.e, the times when the wind turbine is idling, also have a significant impact on the lifetime. For this reason, the creation of meta-models, more precisely Kriging meta-models, for an idling offshore wind turbine is investigated comprehensively in this paper. To ensure that the fatigue loads for the training and test data are not influenced by the initial transients at the start of the simulation, the run-in times are determined first. The subsequent investigation of meta-modelling shows that for the approximation of the rotor blade root bending moments, two additional input parameters have to be considered in addition to the input parameters that are used for the creation of a meta-model for the same offshore wind turbine in normal operation. The comprehensive investigation of the Kriging meta-models shows that the meta-models trained with 2000 data points represent the simulation model with an acceptable approximation quality when choosing suitable Kriging settings.
Competing interests: R. Rolfes is a member of the editorial board of the journal.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
Dear authors, thank you for your submission entitled "Kriging meta-models for damage equivalent load assessment of idling offshore wind turbines". Your publication is well written and presents relevant work. I believe it should be published in this journal, and I only have minor suggestions that can hopefully improve the readability of your manuscript:
1. Abstract: I would have appreciated a slightly less technical abstract, where the reader gets a higher level overview of what your article is about. Also, some terms generated some confusion even in a technical expert like me. I later understood what they refer to, but I had to google to confirm what "lifetime reassessments" and "run-in times" referred to. I was more familiar with wording like "lifetime extension potential" and "initial transients". I would strongly recommend clearing these possible sources of confusion, especially from the abstract that will hopefully be read by many people.
2. Line 20: The load cases are lumped here. "here" where?
3. Line 42: lower occurring loads. Fatigue or peak loads?
4. Lines 42-47: a citation seems missing
5. Line 49: "of of", typo
6. Line 65: "known" typo
7. Line 71: I am more familiar with the wording "initial transients" rather than "run-in times"
8. Line 95: There is no action item here, but please note that FASTv8 is 10+ years old. I'd strongly recommend upgrading to the latest releases of OpenFAST to make your work more impactful
9. Line 255: I'd recommend referencing Table 1 here, it took me a while to understand what those forces and moments were