Risø–R–1181(EN) Modal Analysis of Wind

Abstract Modal analysis has been used to identify natural frequencies, damp-ing characteristics and mode shapes of wind turbine blades. Different experimental procedures have been considered and the most appropri-ate of these has been selected. Although the comparison is based on measurements on a LM19 m blade, the recommendations given are believed to be valid for other types of wind turbine blades as well. The reliability of the selected experimental analysis has been quantified by es-timating the unsystematic variations in the experimental findings. Satisfactory results have been obtained for natural frequencies, damping characteristics and for the dominating deflection direction of the investigated mode shapes. For non-dominating deflection directions of the investigated mode shapes, however, the observed experimental uncertainty may be considerable – especially for the tor-sional deflection. The experimental analysis of the LM19 m blade has been compared with results from a FE-modeling of the same blade. For some of the higher modes substantia