A Comparison of Soil Structure Interaction Models for Dynamic Analysis of Offshore Wind Turbines

Abstract

This paper compares the dynamic response of an OWT structure where the below ground pile-soil behaviour is modelled using (i) the conventional API ‘p-y’ approach and (ii) the ‘PISA’ approach. A nonlinear aero-elastic code is used to model the structural dynamics of the OWT and coupled to the geotechnical model. The dynamic behaviour (natural frequencies) and fatigue loads of the turbine tower and monopile are estimated and compared using both the API and PISA approaches. A limited number of load cases were considered in the dynamic analysis with varied met-ocean conditions. It was found that the stiffer springs estimated by the PISA approach reduce the mean displacement of the tower in both the fore-aft and side-to-side directions. However, the increased monopile stiffness leads to a slightly increased amplitude of oscillations, particularly in the lightly damped side-to-side direction.