Monitoring substructures – a long term experience
As of 2011 OWI-lab, in co-operation with the Vrije Universiteit, Brussels (VUB), has been conducting a long term structural monitoring campaign at all Belgian offshore wind farms. The measurements focus on the structural health of the substructure (SHM) rather than the wind turbine itself. PES is pleased to share this important research, which is sure to have an impact on future wind farm monitoring.
This different focus was motivated by the operators of offshore wind farms. While the correct operation of the wind turbine is typically covered under a service level agreement with the turbine OEM, other vital components such as the substructure, foundation and cables along with the offshore high voltage station and grid infrastructure, fall under the responsibility of the operator. It was from their concerns that OWI-lab started to research and develop tailored monitoring solutions and search for decision support tools towards the substructure.
Dealing with operators’ concerns
One particular concern posed by the operators is the development of scour around the foundation. During scouring the seabed around the foundation is eroded, reducing the embedded length of the foundation. This has a direct effect on the structural properties. With the development of a scour hole, the exposed length increases and the resonance frequencies of the structure will reduce. This reduction in resonance frequencies can lead to an increased dynamic amplification of the wave loads and consequently a decreased fatigue life.