Dynamic optical deformation measurements on wind turbines. Issue 2 (1st May 2022) - Helming, P
Abstract: Because of an increase in the size of wind turbines in recent years, efficient structural health monitoring of the turbine's structure has become critical. Wind turbine towers deform elastically as a result of the loads due to wind and inertial forces acting on the revolving rotor blades. To adequately assess these deformations, an earthbound device is desired that can measure the tower's movement in two directions from a very large working distance of over 150 m and a single site. For this task, a terrestrial laser scanner in line-scanning mode with horizontal alignment is used to measure the tower cross-section and to determine its axial (in the line of sight) and lateral (transverse to the line of sight) position using a least-squares fit. The method is validated by comparing the data obtained by the laser scanner with continuously measured wind speed data. To test its application, the method is then applied to two separate wind turbines with hub heights of 61.4 m and 128 m and the experimental results are compared with a reference video measurement that records the nacelle movement from below and determines the nacelle movement using point-tracking software. The results are compared for various operating circumstances, such as different wind speeds. The laser-based and the reference measurement have a strong correlation. The measurement uncertainty is determined to be 9.6 mm in the lateral direction and 10.3 mm in the axial direction at a measurement distance of 160 m, respectively. As a result, the proposed approach is identified as an effective tool for the in-process structural health monitoring of wind turbine towers.