Modes Indicate Cracks in Wind Turbine Blades

Abstract

On-line surveillance of the structural integrity of wind turbines is a critical need in this currently fast growing industry. The structural integrity of the turbine blades themselves is critical to the continued operation of a wind turbine. It is well known that the resonant or modal properties of a mechanical structure are directly influenced by its physical properties. Hence, any change in the physical properties of a structure should cause a change in its modal parameters. One question is always apparent though; “Do structural faults cause significant changes in a structure’s modal parameters?” In this paper, we present test results from a wind turbine blade with different cracks induced in it. Each result shows that some of the modes of the blade are significantly affected by a crack, and that the modal parameters change more significantly with a more severe crack. Changes in modal frequency, damping, and mode shape are considered. Using changes in modal parameters to indicate physical damage to turbine blades should be implemented in the online continuous monitoring of wind turbines. In such a system, differences between monitored modal parameters and their base-line values could be compared to both absolute and percentage difference warning levels. Comparing changes between operating and baseline modal parameters with warning levels will indicate when the blades of a wind turbine have undergone physical damage.