Structural Change Identification at a Wind Turbine Blade using Model Updating

In this paper, a damage and ice accretion localization method based on finite element model updating is tested using the example of a wind turbine blade. Both eigenfrequencies in combination with mode shapes and a new comparison technique based on transmissibility functions are employed in order to define measures for a quantification of the difference between numerical and measured results. Results of these quantifications are used to define an optimization problem, minimizing the deviation between model and measurement by variations of the numerical model using a combination of a global and a local optimization method. A full-scale rotor blade was tested in a rotor blade test facility in order to test those structural health monitoring methods. During the test, additional masses were installed on the structure in order to emulate ice accretion. Afterwards, the blade was driven to damage using an edgewise fatigue test. In this test a crack occurs at the trailing edge of the rotor blade. The model updating algorithm is applied to locate and quantify both structural changes with the two different measures. Though shown to be successful in a numerical study, both measures return incorrect damage locations when applied to real measurement data. On the other hand, ice localization is successful using eigenfrequencies and mode shapes, even quantification is possible. If transmissibility functions are applied, the localization is not possible.