Optical flow dynamic measurements with high-speed camera on a small-scale steel frame structure

The tremendous advances in high-resolution and high-speed cameras have allowed improving optical measurement techniques enabling extraction of dynamic characteristics of vibrating structures. These techniques turned out to be particularly useful for vibration observations as they are contactless, and they do not interfere with the structural response (as is the case of accelerometers installed on a light-weight set-up, with non-negligible additional masses). The paper reports the results of an experimental campaign, carried out to verify the accuracy of the dynamic displacements measurement obtained with a high-speed camera and the Hybrid Lagrangian Particle Tracking software, a software based on the solution of the Optical Flow equation. The experimental setup includes a 4-dof small-scale steel frame structure excited on a shaking table, a high-speed camera able to record images of the motion and five accelerometers. From images, a two-dimensional moving field is recorded, and the absolute and relative displacements are determined. Confidence in the novel developed measuring methodology is determined by direct comparison with acceleration measurements which confirm that the image analysis measurements turned out to be sufficiently accurate for damage identification purposes.