Developments in Large Wind Turbine Modal Analysis Using Point Tracking Videogrammetry

Abstract

Wind turbine installations are increasing significantly in numbers as well as capacity as part of the global demand for sustainable energy sources. This leads to stronger need for comprehensive dynamic test data to support reliable cost reductions while meeting safety requirements. The complete wind turbine structural mechanical response at different load conditions is of particular interest. Detailed analysis of the component operational resonances during loading, such as the interaction of the blade - and tower deformations is of basic engineering importance. A testing of the structure with traditional equipment would be quite extensive in sensor instrumentation, calibration and analysis effort. Dynamic field measurements were performed on a 500 kW Nordtank wind turbine at the Risoe DTU campus in Denmark using a customized Pontos point tracking photogrammetry system. Data was acquired at 100 Hz for 7 seconds from more than 50 targets within a 50 meter wide field of view. Practical aspects of the measurement setup including illumination requirements, blade and tower targeting, the ability to automatically track numerous targets through multiple rotations, rigid body correction (de-rotation), and the use of projected angles and trajectory analysis are discussed. Results include movies with animated vectors and associated time history plots for 3D directional and resultant displacements of all blades and the support tower, as well as trajectory plots.