Image based vs vibration based analysis of a research scale wind turbine blade

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The objective of this study was to validate modal analysis and system identification of an operating, small-scale, wind turbine system in the laboratory. In general, wind turbine blades were instrumented with accelerometers and strain gages, and data acquisition was achieved using a prototype wireless sensing system. In this study, an experiment was designed to control the rotation of wind turbine blades in the lab. In order to control the excitation (rotation of the wind blade), a motor was used to spin the blades at controlled angular velocities. Sensors were installed onto two different representative and metallic wind blades (i.e., damaged versus undamaged blade). Data measured by the contact sensors (accelerometers and strain gages) and the photographic images (camera) were recorded while the blade was operated at different speeds. First, to analyze the displacement/motion of the turbine blade, a photogrammetric approach was used. After 3D calibration of the imaging system, 3D positions are calculated using a stereo triangulation technique and digital images taken to track the 3D motion of the blade. Image measurement error induced by image analysis error and camera synchronization error was discussed. Second, the dynamic characteristics of the rotating blade were investigated. The Rodrigues’ rotation was applied to the data to extract the vibration signal due to rotation. Separation of the turbine blade natural frequencies and the rotating frequency can successfully be carried out. From which the residual signal can be used to identify the dynamic characteristics of turbine blade. Dynamic characteristic of undamaged and damage turbine blade was investigated.