Structural monitoring for lifetime extension of offshore wind monopiles: verification of strain-based load extrapolation algorithm

Lisa Ziegler, Nicolai Cosack, Athanasios Kolios, Michael Muskulus

Research output: Contribution to journalArticle

Abstract

Lifetime extension needs low-cost assessments that can identify the remaining useful life of offshore wind monopiles. A novel concept for load monitoring was developed that only needs strain gauges installed at one level of the support structure. Damage equivalent loads were calculated from strain measurements and extrapolated along a monopile using a regression algorithm. In this paper, the assumptions behind the load extrapolation algorithm were verified with two consecutive months of measurement data from an offshore wind park. The verification was performed separately for two offshore wind turbines. Both turbines had strain gauges installed at a distance of approximately 15 m and 25 m. Results show that monthly damage equivalent loads can be predicted with errors smaller than 4% based on measurement data only. Prediction using linear regression resulted in similar results for the total fatigue damage as a nonlinear k-nearest neighbor approach, but individual 10-min damage equivalent loads showed larger differences than for the more robust k-nearest neighbor algorithm, especially for small loads. These results are very promising and should motivate further research.

LanguageEnglish
Pages154-163
Number of pages10
JournalMarine Structures
Volume66
Early online date24 Apr 2019
DOIs
Publication statusPublished - 31 Jul 2019

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Extrapolation
Loads (forces)
Strain gages
Monitoring
Offshore wind turbines
Strain measurement
Fatigue damage
Linear regression
Turbines
Costs

Keywords

  • fatigue
  • k-nearest neighbor
  • lifetime extension
  • load monitoring
  • monopile
  • offshore wind turbine
  • strain gauge

Cite this

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abstract = "Lifetime extension needs low-cost assessments that can identify the remaining useful life of offshore wind monopiles. A novel concept for load monitoring was developed that only needs strain gauges installed at one level of the support structure. Damage equivalent loads were calculated from strain measurements and extrapolated along a monopile using a regression algorithm. In this paper, the assumptions behind the load extrapolation algorithm were verified with two consecutive months of measurement data from an offshore wind park. The verification was performed separately for two offshore wind turbines. Both turbines had strain gauges installed at a distance of approximately 15 m and 25 m. Results show that monthly damage equivalent loads can be predicted with errors smaller than 4{\%} based on measurement data only. Prediction using linear regression resulted in similar results for the total fatigue damage as a nonlinear k-nearest neighbor approach, but individual 10-min damage equivalent loads showed larger differences than for the more robust k-nearest neighbor algorithm, especially for small loads. These results are very promising and should motivate further research.",
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Structural monitoring for lifetime extension of offshore wind monopiles : verification of strain-based load extrapolation algorithm. / Ziegler, Lisa; Cosack, Nicolai; Kolios, Athanasios; Muskulus, Michael.

In: Marine Structures, Vol. 66, 31.07.2019, p. 154-163.

Research output: Contribution to journalArticle

TY - JOUR

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T2 - Marine Structures

AU - Ziegler, Lisa

AU - Cosack, Nicolai

AU - Kolios, Athanasios

AU - Muskulus, Michael

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