The scope of this collaborative research & development project 'O&O Parkwind' is dealing with 'monitoring and asset management of offshore foundations' for Parkwind, which is a leading Belgian company in the field of developing, building an running offshore wind farms (references are Belwind, Northwind, Belwind 2,...).
When it comes to offshore foundations, dynamic behaviour, scouring, corrosion, reduction in grout and foundation integrity over time, can be problematic. Therefore, OWI-lab installed foundation-monitoring systems at several turbines. A first monitoring system, which is installed on a monopile foundation of a 3 MW Vestas turbine at the Belwind wind farm, has now been running for almost two years.
Recently two additional monitoring systems were installed at the Northwind wind farm. The motivation is gaining the insights that are necessary to minimize the installations and O&M costs of the future planned wind turbines at the Belwind 2 concession.
Approach
The purpose of the R&D projects at the Belwind farm and the Northwind farm is to gain a precise view on how the structure of the foundation of an offshore foundation is changing over time, and what causes the changing behaviour. It has been decided that the following parameters should be monitored:
- Loads, displacements, strains and local temperatures in the grouted connection: those parameters are necessary to see if the grouted connection is deteriorating. In one turbine the displacements and loads are measured. In two additional turbines also the strains in the grouted connection are monitored. The temperature distribution is needed to correct the stain measurements.
- Vibration and strain levels on tower and foundation: those parameters are needed to calculate the resonance frequencies and the damping values of the offshore structure. Additionally they give information on the correlations between scour and the vibration levels.
- Resonance frequencies, damping values and mode shapes of the offshore structure: With this information it is possible to track potential scour. This information also can be used to update the remaining life-time estimates by applying a modal expansion method and calculating the stresses at the critical locations.
- Oxygen levels and corrosion rates inside the monopile: corrosion will have an influence on the remaining life time of the foundation. Therefore, both the cause (oxygen levels) and the effect (corrosion rate) are monitored.
- Water ingress in the grouted connection: this parameter can be linked with potential damage of the grouted connection. Therefore, also the water ingress is monitored.
Link to conference posters:
- EWEA 2014 conference: "Foundation monitoring systems: analysis of 2 years of monitoring at the North Sea"
- Design verification of offshore wind turbines for foundation optimization and scour monitoring
- Damping of an offshore wind turbine: classification and comparison between simulations and measurements
- Monitoring of offshore turbines for design and O&M: an overview of the activities of OWI-Lab
