Multi-level structural modeling of an offshore wind turbine

Offshore wind turbines are complex structural and mechanical systems located in a highly demanding environment. In this paper, a multi-level system approach is proposed for studying the structural behavior of the support structure of an offshore wind turbine. In accordance with this approach, a proper numerical modeling requires the adoption of a suitable technique in order to organize the qualitative and quantitative assessment in various sub-problems, which can be solved by means of sub-models at different level of detail, both for the structural behavior and for the simulation of loads. Consequently, in a first place, the effects on the structural response induced by the uncertainty of the parameters used to describe the environmental actions and the finite element model of the structure are inquired. The relevance of the various uncertain parameters is assessed by evaluating the structural risk, expressed by the probabilities of exceeding threshold values of the peak across-wind and along-wind displacements at the hub height. After that, a meso-level FEM model of the blade is adopted in order to obtain the detailed load stress on the blade/hub connection.