Dynamic Soil-Structure Interaction issues in designing offshore wind turbines

 Choosing appropriate foundations for supporting offshore wind turbines is one of the uncertainties in the future rounds of offshore wind power development. Offshore wind turbines are dynamically sensitive structures as the global natural frequency of the whole system is very close to the forcing frequencies (due to the environmental loads and the associated frequencies due to the rotor). This particular aspect is important for designing foundations for Round 2 and Round 3 offshore wind farms in the UK. It must be mentioned here that monopile foundations have been commonly used to support offshore wind turbine generators (WTGs), but this type of foundation encounters economic and technical limitations for larger WTGs in water depths exceeding 30m. Therefore offshore wind farm projects are increasingly turning to alternative multipod foundations (for example tetrapod, jacket, tripods) or on shallow foundations to reduce the environmental effects of piling noise. However the characteristics of these foundations under dynamic loading or long term cyclic wind turbine loading are not fully understood. This keynote lecture summarizes the results from a series of scaled model tests of the overall wind turbine system (including the foundations).