Predicting dynamic strain on wind turbine blade using digital image correlation techniques in conjunction with analytical expansion methodologies

Abstract

Wind turbine blades are often subjected to static and dynamic testing to identify the performance levels of the blades. In general, strain gages are employed to capture strain data at discrete points. Recent advances in digital image correlation (DIC) and digital photogrammetry have allowed for new opportunities for blade inspection and structural health monitoring. DIC allows for imaging techniques to measure displacement values at various points on the structure. This displacement data is then used in conjunction with a finite element model to apply modal expansion techniques to obtain displacement values at each finite element degree of freedom for each time step of dynamic transient data. This technique is used to predict strain values at any point on the structure. This paper presents results obtained from dynamic testing at limited measurement locations to predict the full field dynamic strain for two structures evaluated. A major benefit to this approach is that strain values can be found at locations that are not in the measurement field of view, including on surfaces that are contained within the structure. © The Society for Experimental Mechanics, Inc. 2013.