Performance-Based Design of Offshore Wind Turbines

The optimal design of complex structures exposed to a high demanding environment has to be carried out in the framework of Performance-Based Design (PBD). Recently a huge research effort has been devoted at applying PBD concepts to wind engineering, and a general framework of Performance-Based Wind Engineering (PBWE) has been developed. The procedure of risk assessment has to be developed in probabilistic terms, considering the different sources of uncertainty characterizing both the actions and the structural properties: moreover the effects of the interaction between the wind field and the structure has to be properly considered. The problem is more complex in case of offshore structures, where the interaction between the wind field, the waves and the sea currents introduces additional sources of uncertainty. In the paper, the uncertainty characterizing the wind-fluid-structure interaction is discussed, and an analytical formulation of the problem of risk assessment of offshore wind turbines is proposed. The procedure, developed in the framework of PBWE, is based on the solution of a probabilistic relation between the stochastic parameters characterizing both the input and the structural response. It is applied to an example case: an offshore wind turbine with a jacket support structure.