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Wind Energy Science The interactive open-access journal of the European Academy of Wind Energy
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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  06 Apr 2020

06 Apr 2020

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This preprint is currently under review for the journal WES.

A fracture mechanics framework for optimising design and inspection of offshore Wind Turbine support structures against fatigue failure

Peyman Amirafshari, Feargal Brenan, and Athanasios Kolios Peyman Amirafshari et al.
  • Department of Naval Architecture, Ocean and Marine Engineering, University of Strathclyde, Glasgow, G4 0LZ, UK

Abstract. Offshore Wind Turbine (OWT) support structures need to be designed against fatigue failure under cyclic aerodynamic and wave loading. The fatigue failure can be accelerated in a corrosive sea environment. Traditionally, a stress-life approach called the S-N curve method has been used for design of structures against fatigue failure. There are a number of limitations in S-N approach related to welded structures which can be addressed by the fracture mechanics approach. In this paper the limitations of the S-N approach related to OWT support structure are addressed, a fatigue design framework based on fracture mechanics is developed. The application of the framework to a monopile OWT support structure is demonstrated and optimisation of in-service inspection of the structure is studied. It was found that both the design of the weld joint and Non-destructive testing techniques can be optimised to reduce In-service frequency. Furthermore, probabilistic fracture mechanics as a form of risk-based design is outlined and its application to the monopile support structure is studied. The probabilistic model showed to possess a better capability to account for NDT reliability over a range of possible crack sizes as well as providing a risk associated with the chosen inspection time which can be used in inspection cost benefit analysis. There are a number of areas for future research. including better estimate of fatigue stress with a time-history analysis, the application of framework to other types of support structures such as Jackets and Tripods, and integration of risk-based optimisation with a cost benefit analysis.

Peyman Amirafshari et al.

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Peyman Amirafshari et al.

Peyman Amirafshari et al.


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Latest update: 01 Dec 2020
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Short summary
One particular problem with structure operating in seas is the so-called fatigue phenomena. Cyclic loads imposed by waves and winds can cause structural failure after a number of cycles. The tradition method have some limitations. This paper presents a developed design framework based on Fracture Mechanics for offshore wind turbine support structures which enables the design engineer to make most of available inspection capabilities and optimise the design and inspection, simultaneously.
One particular problem with structure operating in seas is the so-called fatigue phenomena....