Offshore monopile in the southern North Sea: Part II, simulated hydrodynamics and loading

This paper examines two methods for determining the local wave particle kinematics and hydrodynamic forces on an idealised wind turbine monopile in the southern North Sea using sea state data at Teesside Offshore Wind farm. An assessment of local flow hydrodynamics is important with regard to safe access of personnel from a crew transfer vessel to a monopile. The hydrodynamic behaviour is calculated using an analytical solution from linear diffraction theory and numerical predictions using OpenFOAM, with both slip and no-slip cylinder boundary conditions. Provided the underlying sea state is unidirectional, it is found that close agreement is obtained between analytical and numerical spectra derived from the time series of local free surface elevation, water particle velocity components, and in-line wave force loading on the monopile. Less satisfactory agreement is achieved with sea-states possessing a bimodal spectrum, largely because possible wave directionality, exhibited in the field data set at various frequencies, is not taken into account.