Figure 2 Laser Doppler vibrometer Figure 3 Reflection of the laser beam from the blade. Since it is very difficult to keep the laser on the same marker while the turbine is rotating, LDV was only used for standstill measurements. A more detailed description of these measurements and the corresponding data analyses can be found in (3). The second measurement technique was based on photogrammetry which is a proven technology based on determination of the 3D coordinates of the points on an object by using two or more images taken from different positions. Although the several applications of photogrammetric measurements are currently in use and demonstrated to provide very accurate measurements for a wide variety of disciplines, its use is usually limited to small measurement volumes and experiments that are performed in laboratories or similar controllable environments. Within this small measurement volume it can be efficiently used for different purposes such as; - 3D shape determination, modeling and reverse engineering (4), (5), (6) - Static or dynamic deformation measurements (7),(8),(9), (10), (11), (12), (13) ,(14),(15) - Modal analysis and system identification (16), (17), (18), (19), (20), (21) This technology was for the first time applied on a MW scale wind turbine within the scope of this work. The 3D dynamic response of the rotor was captured at 33 different locations 259
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