Numerical Modelling of a Monopile for Estimating the Natural Frequency of an Offshore Wind Turbine

Monopiles are the most common foundation system for supporting Offshore Wind Turbines (OWT’s), accounting for more than 80% of all OWT substructures installed in Europe to date [1]. Significant reductions in the cost of developing OWTs have been realized over the past few years, to the point where offshore wind can now be developed subsidy free in favorable locations. Optimizing the engineering design of these structures has played a key role in ensuring these cost reductions are possible. The largest uncertainty with respect to modelling the dynamic response of an OWT often relates to the geotechnical design. This paper examines the influence of soil-structure interaction on the dynamic response of an OWT structure. The below ground pile-soil behavior was modelled using (i) a conventional DNV (De Norske Veritas) ‘p-y’ approach and (ii) an advanced in-situ calibrated 3D FE geotechnical design approach. The results for the soil-structure interaction were inputted into a separate dynamic wind turbine model and the dynamic response using the two separate SSI approaches were compared.