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Okenyi, VA 
ORCID: https://orcid.org/0000-0001-6489-2675,
2024.
Prediction and assessment of corrosion-fatigue in offshore wind turbines.
PhD, Nottingham Trent University.
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Abstract
Offshore wind energy has seen substantial growth globally as part of a shift towards net zero. Offshore wind turbines with predominant fixed-bottom monopile support structures are near their end of service life, necessitating assessments of their remaining life. The sector confronts fatigue challenges, environmental concerns such as corrosion from harsh conditions as they expand into deep seas, damage assessment challenges, and design optimisation challenges.
This study aimed to develop a novel corrosion-fatigue damage theory for predicting corrosion-fatigue damage and remaining life in monopile-supported horizontal-axis offshore wind turbines.
The research methodology involved experimental investigations, analytical estimations, and computational modelling. The experimental work involved the fabrication of structural steel plates, mechanical tests, fatigue tests, and corrosion characterisation analyses. Analytical methods were applied using the beam theory, linear wave theory, and blade element momentum approach. Computational modelling involved applying finite element analysis in stress analysis for uniform corrosion and soil-structure interaction and assessing residual stress.
The results showed that the splash zone may accumulate the most damage over time owing to monopile thickness reduction and local pits. The fatigue life of materials appeared less influenced by thickness effects and more by a combination of stress concentration, residual stress, axial misalignment, and angular distortion. An S-N curve for corrosion-fatigue assessment applying a corrosion-based fatigue prediction model was developed. These results were integrated into a corrosion-fatigue damage theory applied to operational loads for predicting the remaining life of offshore wind turbines. In conclusion, the developed theory showed great promise for assisting engineers and stakeholders with vital information for corrosion-fatigue assessment of offshore wind turbines necessary for effective maintenance, decommissioning, and life extension.
| Item Type: | Thesis |
|---|---|
| Creators: | Okenyi, V.A. |
| Contributors: | Name Role NTU ID ORCID |
| Date: | June 2024 |
| Rights: | The author owns the copyright for this material. You're allowed to reproduce a maximum of 5% of this content for personal study or non-commercial research. If you utilise any part of this document, please cite it properly, including details like the author's name, title, affiliated university, degree level, and page numbers. For any other purposes, or if you need a significant portion, please contact the author directly. |
| Divisions: | Schools > School of Science and Technology |
| Record created by: | Laura Ward |
| Date Added: | 23 Aug 2024 10:05 |
| Last Modified: | 23 Aug 2024 10:05 |
| URI: | https://irep.ntu.ac.uk/id/eprint/52078 |
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