Hydro-Elastic Contributions to Fatigue Damage on a Large Monopile

The present work identifies the qualitative hydro-elastic contributions to fatigue damage on large volume monopiles intended for use in the offshore wind energy industry. Although aerodynamic effects cannot be neglected in a complete dynamic analysis of the structure, the scope of this work is limited to wave loads and soil effects on a turbine in simplified operational conditions. As the rotors are scaled up to improve effciency and reduce the overall costs in wind farms, the foundation and support structure dimensions are increased. As a result, the fluid-structure interaction becomes important for wave-lengths comparable to the characteristic size of the structure. The importance of including diffraction effects is present in the results. Also, the contributions from ringing type response in a fatigue-limit sea-state is investigated by applying the third order Faltinsen, Newman, Vinje (FNV) formulation. Hydrodynamic loading is applied as particle velocities in a spatial time variant grid for first and second order wave theories in long crested irregular waves. Additionally, the second order diffraction forces are calculated using an internationally recognized panel code for second order sum-frequency diffraction forces.