HR Wallingford has completed a ten week project working with Oxford University’s Department of Engineering Science and E.ON, examining different forms of scour protection to assure the stability of offshore wind turbine monopiles.
Erosion around the foundation due to the process of seabed scour causes the exposed length of the monopile at the seabed to change, and can alter the frequency at which the system resonates. If the turbine structure begins to vibrate excessively due to this behaviour, it will need to be shut down.
Oxford University is applying its expertise in geotechnical engineering and structural analysis to this research for which they have appropriately scaled the monopile and turbine structure and exposed it to scour and erosion processes. In the experiments, they are measuring the structural dynamic responses, quantifying the amplification of the vibration as it changes with erosion at the base of the monopile, and for different scour protection systems. The physical modelling tests, at a scale of 1:20, are being carried out in HR Wallingford’s Fast Flow Facility, which at 75 m long and 8 m wide, can hold a million litres of water, and can generate waves up to 1 m high and flows of over 2 m/second. They used the Fast Flow Facility to test the response of a monopile foundation employing different scour protection measures including rock protection and tyre filled nets. They have designed local and global scour scenarios for the project with a fully mobile sediment bed model. For this project, Oxford University’s DEng student Russell Mayall is being co-supervised by the University, E.ON and HR Wallingford.