Globally, the majority of fixed offshore wind installations reside in the North Sea and on continental shelves surrounding the UK due to extensive shallow water regions. However, these locations are subject to severe weather conditions with year-round storms prevalent. This environment places demands upon the offshore structures, and, as individual assets tend to become larger (with 12MW turbines now feasible), the benefits derived from monitoring to manage the structural condition over the lifetime of the assets’ operation are enhanced.
Motion measurements from two self-contained, portable data acquisition units installed on a fixed-bottom offshore wind turbine tower are analysed using modal analysis and advanced data-driven techniques to demonstrate the applicability and sensitivity of such methods to structural health monitoring. Motion measurements were made in six degrees of freedom using triaxial accelerometers and gyroscopes, thus recording displacements and rotations. The response of the turbine towers is characterised in response to ambient wave conditions, which were also recorded. As well as assessing the relative fatigue accumulation at different locations on the structure, the motion data is used to track on-going structural integrity – particularly that of the monopile foundation. The ability to detect cracks or other defects at an early stage is investigated. This would provide a clear advantage to the industry in terms of reduced maintenance costs, as opposed to progressive damage modes that become larger and more difficult to repair.
Presented at the 2nd International Conference on Structural Integrity for Offshore Energy Industry, 9-10 September 2019, Asranet, Aberdeen, UK