WEBINAR: Condition Monitoring of Floating Wind Turbine Moorings

A webinar by the IMarEST's Offshore Renewable Special Interest Group

About this Event

Fugro, AS Mosley and the University of Strathclyde formed a consortium to develop a cost-effective condition monitoring system for Floating Offshore Wind Turbine (FOWT) mooring lines for the Carbon Trust’s Floating Wind Technology Acceleration Competition.

In this project we developed a cost-effective condition monitoring system for mooring lines of floating wind turbine assets that tracks fatigue and can also be used to detect the occurrence of various events or failure modes. Using such a system we intend will reduce or eliminate visual inspection by ROVs or divers thereby realising a significant cost saving.

Technical Overview

Each floating structure is fitted with instrumentation to record motion and position. The motions are recorded using an inertial sensor package consisting of accelerometers and gyroscopes recording all six degrees of freedom. Position would use a differential GPS receiver. The advantage of using these instruments is that they are easy to attach to the structure and can be located inside the structure, which protects them from weather. The GPS antenna, of course, must be located externally with a clear view of the sky.

The motion data will record the dynamic response of the structure to wave and wind loading typically in the frequency range 0.05 Hz to 5 Hz. The motion signals would first be used to ensure that the dynamic response was matched to the predictions of the simulation model. However, the primary outcome is a knowledge of the stress cycles applied to each mooring line. A knowledge of the stress cycles determines damage accumulation in the mooring lines from fatigue. Advanced modelling techniques of these damage scenarios was implemented to track the condition of various subsea components (i.e. anchors; mooring chains and ropes, and their attachment point to the floating structure). What physical inspection of the mooring lines that proves necessary will be guided by the condition indicated as output from the instrumentation system and subsequent data processing. The objective is to perform site inspection (i.e. visual inspection by ROV or divers) only as often as necessary. This will reduce costs and exposure to safety risks. It is envisaged that a continuously monitored structure, where condition is actively assessed, will require far fewer inspections than a structure with no fatigue tracking.

The motion and position data will be interpreted by a simulation model of the floating structure. The model can be tailored to the as-built geometry of each of its mooring lines obtained via a postinstallation seabed survey. Based on the observed motions and positions of the floating structure, the tension cycles in each mooring line is calculated. This information is key to assessing the accumulated fatigue damage sustained throughout the life of the asset.

For the purpose of this study, the model will represent a spar-type floating wind turbine. A high quality, validated model based on Hywind Scotland is available, and given that this is the design is currently the most developed in Scottish waters, we focused on this. Nonetheless, the approach developed is equally applicable to all types of floating wind structures.

About the Speaker:

Stuart Killbourn

Holding a PhD in Physics from Glasgow University, Stuart Killbourn is a specialist in instrumentation and data analysis for offshore structures including oil & gas platforms, wind turbines and long-span suspension bridges.

He is the lead consultant for Fugro’s subsea wellhead monitoring service which provides real-time performance data to the well management team to ensure on-going wellhead integrity and utilised fatigue life during drilling or work-over operations. This technology has been transformational for enhancing safety and environmental protection.

Currently, Stuart is applying the structural monitoring techniques developed for oil & gas platforms and refocussing them within the offshore renewable industry. He is excited by the challenge of improving safety and the economic business case of offshore wind turbines through condition monitoring and service life extension.

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