Omnidirectional multi-view high-speed-camera-based full-field 3D modal identification

Abstract

Structures with complex geometries often exhibit elaborate spatial responses to a dynamic excitation. Traditional point-wise vibration measurement techniques, such as accelerometer measurements, provide reliable results usually lacking spatial resolution. In contrast, image-based displacement identification methods provide full-field non-contact measurement capabilities at the cost of a lower dynamic range. Furthermore, 3D digital image correlation is able to reconstruct the geometry and spatial displacements of structures, but require multi-camera setups to work. In the case of omnidirectional experimental modal analysis, frequency-domain stitching is required. This research builds on the recently introduced, multi-view, frequency-domain-triangulation method, that provides a framework for the extraction of full-field 3D operating deflection shapes with a high dynamic range. The existing method is based on sequential high-speed recordings of the vibrating structure made from different views; however, to work it requires prior knowledge of the structure’s geometry. In this research, following an initial camera calibration, a 3D surface mesh is extracted using a photogrammetric geometry reconstruction approach. Displacements of the vibrating object are then recorded and extracted from a large number of views and full-field 3D operating deflection shapes are extracted using frequency-domain triangulation. In the final step, the deflection shapes are magnified and mapped to the reconstructed 3D surface mesh to visualize the vibrational behavior of the test subject. The results of the introduced method for the extraction and visualization of full-field 3D deflection shapes do not require any prior knowledge regarding the geometric or dynamic properties of the studied object. The considerable over-determination in the frequency domain of measurement data obtained from the large number of viewpoints leads to a larger dynamic range and a better reconstruction.