Ramboll has designed more offshore wind turbine foundations than any other company in the world due to our 30 years' experience with anchoring oil and gas rigs at sea. We have also been involved in the Burbo Bank wind farm project offshore the UK.
Our ability to deal with the challenges of the sea environment in this connection has successfully been adapted to wind farms. Offshore wind farms are more difficult to design, construct and maintain compared to those on land. For this reason they are more expensive, but at the same time wind speeds across the open water are generally higher and more reliable - and offshore turbines are also less obtrusive.
Burbo Offshore Wind Farm consists of 25 Siemens 3.6 MW wind turbines connected to shore by three buried submarine cables. The wind farm is constructed at a water depth of 3.5-7.5 metres on Burbo Flats in Liverpool Bay, 4 miles from the Sefton coast line.
Pile installation challenges
The foundation structures are monopiles with grouted transition pieces made ready for mounting of the WTG tower structures once installed. At most positions the monopiles were driven, however, for a few positions, where the pile tip is below bedrock level, the piles were driven and drilled.
Cost-efficient design solutions
The design was carried out as 25 individual foundation designs based on the actual site conditions at the individual positions, i.e. the actual soil profile and water depth at each location. In comparison with the tender design based on five standardised foundation types, the detailed design of the monopile and transition pieces as well as the grouted joint included a number of design innovations and advanced analyses, which lead to an overall weight reduction as well as substantial savings on steel and grout material quality.
The advantage of 3D design
For this project 3D modelling was used to design the foundations of the wind turbines. The use of 3D enables our engineers to prepare detailed models of the foundations so that we are able to provide precise work drawings as well as an estimation of the amount of materials necessary to our clients.
The services by Ramboll included:
- Project manager for the detailed design of offshore wind turbine foundations
- Design briefs for certification and certification of the design
- Detailed design of secondary steel for foundations such as boat landing, external and internal platforms, J-tubes and annodes (DDPS)
- FEM analysis of grouted connection between the transition pieces and the monopiles