Abstract Structural fatigue is a design driver for offshore wind turbines (OWT). In particular, the substructures, like jackets, are strongly affected by fatigue. Monitoring the fatigue progression in the welds is vital for the maintenance and a potential lifetime extension. However, inspections of critical locations are costly due to the limited accessibility of the mostly submerged jacket. Considering the high number of potentially critical welds, it is regarded as economically unfeasible to equip all fatigue hot spots with sensors. Thus, an indirect method to monitor the fatigue progress of the structure and point out critical locations is desirable. For a consistent support of ongoing maintenance, it has to yield reliable results for varying operational and environmental conditions. This paper applies a virtual sensing approach to jacket substructures. From a small set of sensors on the tower, fatigue at every desired location of the jacket is estimated using dual-band modal expansion. Simulations using the OC4 jacket design are performed to show potentials and limitations of the method. Namely fatigue progress on leg welds of K-joints is predicted with high accuracy over a wide range of load cases. However, some difficulties in fatigue prediction of X-joints due to the occurrence of local modes and limitations in the extrapolation of wave loading have to be resolved in future work.

中文翻译：

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使用双频带模态扩展的带有导管架子结构的海上风力涡轮机的应变估计

摘要 结构疲劳是海上风力涡轮机 (OWT) 的设计驱动因素。特别是子结构，如夹克，受疲劳的影响很大。监测焊缝中的疲劳进展对于维护和潜在的使用寿命延长至关重要。然而，由于大部分浸入式导管架的可达性有限，对关键位置的检查成本很高。考虑到大量潜在的关键焊缝，为所有疲劳热点配备传感器在经济上是不可行的。因此，需要一种间接方法来监控结构的疲劳进程并指出关键位置。为了持续支持持续维护，它必须针对不同的操作和环境条件产生可靠的结果。本文将虚拟传感方法应用于导管架子结构。从塔上的一小组传感器，使用双波段模态扩展估计导管架每个所需位置的疲劳。使用 OC4 套管设计进行模拟以显示该方法的潜力和局限性。即，在各种载荷情况下高精度地预测 K 型接头腿焊缝的疲劳进程。然而，由于局部模态的出现和波浪载荷外推的局限性，X 接头疲劳预测中的一些困难必须在未来的工作中解决。即，在各种载荷情况下高精度地预测 K 型接头腿焊缝的疲劳进程。然而，由于局部模态的出现和波浪载荷外推的局限性，X 接头疲劳预测中的一些困难必须在未来的工作中解决。即，在各种载荷情况下高精度地预测 K 型接头腿焊缝的疲劳进程。然而，由于局部模态的出现和波浪载荷外推的局限性，X 接头疲劳预测中的一些困难必须在未来的工作中解决。