The Offshore wind turbine (OWT) is one. of the most important installations to harvest the wind source. However, the service environment of the OWT is very severe. Aiming to ensure the safety of the OWT and reduce unnecessary maintenance costs, the structural health monitoring (SHM) system can fulfil the requirements. Inverse Finite Element Method (iFEM) which is a state-of-the-art methodology can overtake the diagnosis task. In this thesis, iFEM is adopted for the tower and composite blade of the OWT under close-to-reality loading conditions. The results give an illustration that iQS4 elements can be utilized successfully for the health monitoring of the OWT even with the practical number of sensors. The provided number of sensors and their locations can also be applied to any scaled tower and blade of the OWT. Then a novel dent damage. identification parameter is introduced, which allows the iFEM with the ability to identify the location and shape. of the structural defects. Four cases with different damage locations and varying damage sizes are presented to verify the feasibility and accuracy of this new judgment criterion. Attention is also given to the creation of the general inverse plane elements and the major inverse plane crack tip (iPCT element. The accuracy of this type of element is tested with various numerical examples by estimating the SIF values. With the help of this iPCT element, the limitation of iFEM when dealing with cracked structures can be eliminated and the SIF around the crack tip can also be estimated. Although iFEM can be utilized during the diagnosis process, it would be much better to have another tool for the following prognosis process to establish a comprehensive SHM system for the OWT. Peridynamics (PD) which is very suitable for fracture analysis is chosen. The fatigue and fracture analysis of the triplate on the mooring lines of the OWT is performed. The damage initiation matches well with the expected analytic.al results and the complete process of the fatigue damage evolution can be captured. Afterward, the PD interaction force equation is updated with the thermal expansion coefficient. Combining with PD cubic polycrystalline model, the porosity effects on brittle fracture and thermally-induced fracture on the microscale are explored. With the increase in the number of grains and pores, the crack especially the newly generated crack will become more serious. But the distribution of the grains and pores will not strongly influence the fracture behaviors. The stronger the grain boundary, the fracture pattern will be willing to convert from intergranular to transgranular. In conclusion, the current study is the first time to apply iFEM and PD to the OWT components, it would be a critical step for the complete SHM system of the OWT, and it can also provide guidance for the real application of iFEM and PD.
| Date of Award | 8 Nov 2022 |
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| Original language | English |
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| Awarding Institution | - University Of Strathclyde
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| Sponsors | University of Strathclyde |
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| Supervisor | Erkan Oterkus (Supervisor) & Selda Oterkus (Supervisor) |
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