Multicamera measurement system to evaluate the dynamic response of utility‐scale wind turbine blades

Abstract

AbstractWind turbine blade certification requires static and fatigue testing at a large‐scale facility similar to the Wind Technology Testing Center (WTTC) located in Charlestown, Massachusetts. Usually, these tests are conducted by using wire‐based sensors such as strain gages, accelerometers, and string potentiometers. These systems are expensive, require a time‐consuming installation (e.g., up to 3 weeks and $35 k–$50 k for a strain gage system on a 55‐m‐long blade), are difficult to deploy on large‐sized structures, require additional instrumentations (e.g., power amplifiers and data acquisition systems), and produce results only at a handful of a discrete number of measurement points. In this study, a multicamera measurement system is implemented and experimentally evaluated to obtain full‐field displacement and strain over a ~12‐m‐long portion of a ~60‐m utility‐scale wind turbine blade. The proposed system has the potential to streamline the certification process by reducing the blade's preparation and sensor installation cost and time to a few hundreds of dollars (for painting equipment) and a few days for preparing the surface of the blade for the test. Furthermore, operational modal analysis was used in conjunction with the multicamera system to estimate the natural frequencies and mode shapes of the wind turbine blade. The obtained results have shown that the proposed approach can detect in‐plane displacement as low as 0.2 mm, mechanical strain with an error below 3% when compared with measurement performed using strain gages, and the first five natural frequencies with an error below 2% when compared with data recorded using traditional wire‐based accelerometers. This paper presents these results and provides a summary of the strengths and weaknesses of the proposed optical measurement approach in the context of streamlining the blade certification/testing process and performing vision‐based structural dynamic measurements on large‐scale structures.