Experimental modal analysis of a utility-scale wind turbine blade using a multi-camera approach

Abstract

Utility-scale wind turbine blades (WTBs) require proper certification to ensure that they meet the design specifications and for safe operation throughout their lifetime. Instrumentation during testing involves using wire-based sensors such as strain gauges and accelerometers. These systems are expensive, time-consuming to install, difficult to deploy on large-sized structures, require additional instrumentations (e.g., power amplifiers and data acquisitions), and produce results at only a discrete number of points. In this study, a multicamera based measurement system is implemented and experimentally evaluated to estimate the modal parameters of a ∼60-meter long utility-scale WTB. The measurement areas of the stereo-vision systems are limited based on the field of view (FOV) of the cameras. Therefore, two sets of cameras were used to increase the measurement area. The performance of the optical sensing system in identifying the modal parameters of the WTB was validated by using the multi-camera approach to measure the dynamic response of the blade subjected to impulse inputs (i.e., impacts). The multi-camera stereo vision system in conjunction with a data stitching algorithm enables the photogrammetry technique to cover larger areas for expanded measurements. From an analysis of processed data, it was observed that the multi-camera system allows for detecting the first five operating mode shapes with an error below 2% as compared with traditionally wired accelerometers. For higher order modes, an estimation is possible, but the accuracy of the system decreases and miscorrelation in the mode shapes up to ∼10% resulted.