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

Amirafshari, Peyman and Brennan, Feargal and Kolios, Athanasios (2021) A fracture mechanics framework for optimising design and inspection of offshore wind turbine support structures against fatigue failure. Wind Energy Science, 6 (3). pp. 677-699. ISSN 2366-7451

[thumbnail of Amirafshari-etal-WES-2021-A-fracture-mechanics-framework-for-optimising-design-and-inspection-of-offshore-Wind-Turbine]
Preview
Text (Amirafshari-etal-WES-2021-A-fracture-mechanics-framework-for-optimising-design-and-inspection-of-offshore-Wind-Turbine)
Amirafshari_etal_WES_2021_A_fracture_mechanics_framework_for_optimising_design_and_inspection_of_offshore_Wind_Turbine.pdf
Final Published Version
License: Creative Commons Attribution 4.0 logo

Download (4MB)| Preview

    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 (stress-number of cycles) curve method has been used for the design of structures against fatigue failure. There are a number of limitations in the 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 and 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 (NDT) techniques can be optimised to reduce in-service inspection 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 a better capability to account for NDT reliability over a range of possible crack sizes as well as to provide 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 a better estimate of fatigue stress with a time-history analysis, the application of the framework to other types of support structures such as jackets and tripods, and integration of risk-based optimisation with a cost-benefit analysis.

    ORCID iDs

    Amirafshari, Peyman ORCID logoORCID: https://orcid.org/0000-0001-5394-9648, Brennan, Feargal ORCID logoORCID: https://orcid.org/0000-0003-0952-6167 and Kolios, Athanasios ORCID logoORCID: https://orcid.org/0000-0001-6711-641X;