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Study aims to reduce scour on wind turbine foundations

HR Wallingford has joined forces with Oxford University’s Department of Engineering Science and energy company Eon to examine scour remediation strategies for offshore wind turbine foundations.

The Foundation Response to Scour Protection research programme is examining different forms of scour protection to assure the stability of offshore wind turbine monopiles and look at the most effective for maintaining foundation performance.

The 10 week project is being funded by Eon and HR Wallingford and includes scale experiments at HR Wallingford’s physical laboratory test facilities.

According to HR Wallingford, all monopile founded wind turbine structures vibrate to some degree during operation, with the frequency of resonant vibration determined by the monopile, tower, nacelle and blade dimensions and interactions of the foundation with the soil. The design process addresses this system behaviour, and yields optimised installation depths for each monopile installation. Nonetheless, 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, leading to loss of revenue and potentially significant remediation costs.

University of Oxford professor of engineering science Byron Byrne said: Oxford University is applying its expertise in geotechnical engineering and structural analysis to this research for which we have appropriately scaled the monopile and turbine structure and exposed it to scour and erosion processes. In the experiments, we 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 75m long and 8m wide, can hold 1M.l of water, and can generate waves up to 1m high and flows of over 2m/s.

“We are using our Fast Flow Facility to test the response of a monopile foundation employing different scour protection measures including rock protection and tyre filled nets,” said HR Wallingford chief technical director of sediment dynamics Richard Whitehouse. “We have designed the local and global scour scenarios for the project with a fully mobile sediment bed model and worked closely with Oxford University to deliver world class experiments on the interaction between scour and structural response.”

Eon Climate and Renewables offshore foundations engineer Phillipa Cassie added: “By conducting this research, we are aiming to quantify the contribution of scour and scour protection measures in structural terms to inform proactive management of the operational fleet and designs on future projects.”

 

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