Experimental evaluation of wind turbine rotor tower structural dynamic interaction

Load characterization for wind turbines has been a major area of study with growing interest due to the upcoming extremely long and flexible turbine blades and towers. it is perhaps the most important task posed to a structural dynamics engineer in the wind energy generation field. What is currently requested by the engineering community are validated methods to evaluate dynamic responses of a wind turbine tower when coupled to an operating wind turbine rotor subjected to typical operational conditions. Such methods can provide insight into the structural health and behavior of a wind turbine system through varying operating conditions, information of paramount importance when it comes to condition based monitoring assessments. Toward this goal the dynamic characterization of an operating small 5kW wind turbine installed on a free-standing lattice tower was carried out by extracting natural frequencies, Operationally Deflected Shapes (ODS) and rotor speed information from data collected, at few discrete tower locations, during field measurements. The in-situ monitoring is used to identify and understand how integer harmonics of the rotor speed (nP), produce harmonic forcing affecting the wind turbine system natural frequencies. The proposed approach is also used to develop wind turbine dynamic characterization techniques which have the potentials to be employed in condition monitoring (CM) system.