Just how do offshore wind turbines structures behave when they're exposed to the hostile operating conditions of their working environment? What are the degradation mechanisms present? And how does each degradation mechanism affect the structure's response?
Answers to questions like these were needed by a TWI Industrial Member client, interested in developing a structural monitoring system for wind turbine structures. At the start of the project, TWI was supported by the Industrial Member Client, who provided key industry information. TWI then carried our a literature review and six degradation mechanisms relevant to wind turbine towers and foundation structures were identified, as well as four condition monitoring systems that were potentially appropriate for such structures.
But would such systems be able to detect the relevant degradation mechanisms and would they be sensitive enough? For the answers to its client's questions, TWI turned to finite element analysis to simulate the change of response of the wind turbine structure with and without defects.
In a nutshell TWI's work involved four objectives:
- It was asked to perform FEA simulations of a monopile wind turbine tower and foundation to predict the response of a damaged structure and compare the response to that of a similar intact structure.
- It needed to determine the minimum defect size required to produce a change in natural frequency/ mode shape/ amplitude of strain or displacement.
- It had to compare the magnitude of the structural response due to this minimum defect size with the minimum measurable response of the condition monitoring systems, the aim being to determine whether defects of this size could be detected.
- Lastly it needed to compare the minimum detectable defect size to the maximum tolerable defect size (from fracture mechanics analysis available in the literature). This was required to determine whether the condition monitoring systems would be capable of detecting defects before they reached the critical size which could cause catastrophic failure of the wind turbine structure.
In compliance with TWI's confidentiality policy, the results and conclusions of this work remain client confidential. However it was able to conclude that the finite element model of the wind tower could be used to predict the effect of various damage mechanisms on the structural response of the tower under wind and wave loading.
TWI's final report was able to inform its client about on the feasibility of these potential new condition monitoring systems which would allow the structural response of offshore wind turbine towers to be understood.
To learn more about conditioning monitoring for wind turbine towers and foundations, and indeed finite element modelling please
contact us.
