FATIGUE DESIGN OF SUPPORT STRUCTURES FOROFFSHORE WIND ENERGY CONVERTERS

摘要

Support structures of Offshore Wind Energy Converters (OWECs) are exposed to combined loadingrnfrom wind and waves. Therefore, to gain adequate design methods for OWECs the establishedrndesign concepts for offshore platforms and onshore wind energy structures have to be improved.rnTraditional concepts for fatigue design vary from deterministic design methods, which can be used inrnspecial conditions for oil and gas platforms, to calculations in the time domain, which are applied tornthe actual generation of multi megawatt onshore wind energy converters.rnFor tripod structures the structural stress approach is likely to be adapted for fatigue assessment ofrntubular joints. This method requires the determination of stress concentration factors. Differentrnanalytical methods for determining the stress concentration factors have been compared to numericalrnmethods.rnBecause of the great differences in the amount of computing time, it is important for the designingrnprocess to evaluate the quality of the fatigue damage prediction using different design methods. Therninvestigations are focussed on wave loading. Results of comparative calculations in the frequencyrndomain and with deterministic single waves show the influence of site specific environmentalrnconditions. The fatigue damage is predicted using Dirliks-formula in the frequency domain.