Fatigue analysis of tripods and jackets for offshore wind turbines

It is common understanding that large offshore wind farms may supply an increasing portion of the energy demand in the next years. To minimize the visual impact, future offshore wind energy projects are planned in deeper water than in most of the current sites. For these purposes, tripod or jacket structures must be generally resorted to. At present a considerable theoretical and experimental research effort is devoted to assess whether a tripod or a jacket structure may be the preferable option in deeper water. In general, the choice should take into account technical and economical aspects but up to now no consensus has been reached on the preferable option. In an attempt to contribute to the research effort in this field, this paper carries out a comparative study of the structural performances under fatigue. A Mediterranean site at a water depth of 45 m is considered as a reference site. The tripod and jacket structures are conceived according to typical current design. The fatigue behaviour is assessed in the time domain under combined stochastic wind and wave loading and results are compared in terms of lifetime damage equivalent load.