Damage equivalent wind-wave correlations on basis of damage contour lines for the fatigue design of offshore wind turbines

An adequate representation of the site-specific wind-wave joint distribution is essential for cost-efficient and reliable designs of offshore wind turbines. Therefore, the wind and wave climates are subjected to a correlation of wind and wave parameters for design purposes. These correlations are often based on a lumping of the directional wave climate and subsequent association of the lumped wave climate to the directional wind climate. Preservation of the hydrodynamic fatigue distribution from the full wave climate is an important aspect in the wind-wave correlation process which requires an adequate consideration of the dynamics from the offshore wind turbine. However, only a few wind-wave correlation methods exist for the fatigue design of offshore wind turbines and none of them take the dynamics of the full structure adequately into account. In this study a new wind-wave correlation method has been developed and introduced. The new method is based on the establishment of damage contour lines which are used to determine the sea-state parameters that ensure simultaneous compliance with damage equivalency criterions at different locations within the offshore wind turbine. This simultaneous damage equivalency throughout the structure together with the straightforward derivation of the corresponding damage equivalent sea-state parameters constitutes the novelty of the presented wind-wave correlation method.