Deformation and Vibration Measurement and Data Evaluation on Large Structures Employing Optical Measurement Techniques

Abstract

Deformation and vibration measurements and frequency analysis are part of complex product development cycles, typically performed during component development and testing phases. Optical measuring systems have become important tools in industrial testing processes, reducing the time frame for preparation, testing and evaluation of components and structures. Optical measuring systems rapidly deliver comprehensive operator-independent results and contribute to development and testing time optimization for deformation and vibration measurement procedures. This paper focuses on one recent trend in the field of optical measurements, application to large areas from 3-4 meters up to more than 100 meters. Point tracking videogrametry systems measure the 3D coordinates and derive measurement results for 3D displacements, velocities and accelerations of a large amount of applied point targets at the same time and replaces the time consuming application of displacement sensors (LVDT’s) and accelerometers. By transforming the measurement results into the frequency domain, an easy and fast evaluation of the frequency response of structures and components under various excitation load conditions, even for large measuring areas and small amplitudes, is enabled. With the full-field digital image correlation system, 3D coordinates are measured and 3D displacements, velocities and also strain distributions for thousands of points on the surface of the test object are derived. Therefore shape information is intrinsically obtained, and the application of strain gauges can be replaced. Measurement examples that are presented for large structures include single wind turbine blades, complete full scale wind turbines, and airplane wings. Detailed evaluation of the measurement results provides a better understanding of the deformation and vibration response of standard test specimens, components and structures.