Dynamic modeling of wind turbines. How to model flexibility into multibody modelling

This work is part of a research activity inserted into “Smart Optimazed Fault Tolerant WIND Turbines (SOFTWIND)” project of PRIN 2015, funded by the Italian Ministry of the University and Research (MIUR). The need to define a robust multibody modelling procedure to realistically characterize the dynamical behavior of a generic wind turbine and to have a reduced computational burden has pushed the authors to adopt a freeware software called Nrel-FAST, that is universally considered to be a reference in the field of aeroelastic wind turbine simulations. The lightness of this software is paid in terms of modelling simplicity, which makes the modelling of wind turbines with unconventional support structures (i.e. that con not directly outlined as a fixed-beam) difficult. In this paper, some methodologies to overcome this obstacle are presented, including the use of a more powerful multibody software which, on the other hand, entails higher simulation times. In particular, the authors present a methodology based on structure stiffness-matrix reconstruction that allows, under appropriate hypothesis, to reduce a complex wind turbine support frame to a simple fixed beam so that the simulations can be done directly in FAST environment, with low computational times. The results obtained from these different approaches are compared using as test-case a small wind turbine property of University of Perugia (UniPG).