Experimental vibration analysis of large structures using 3D DIC technique with a novel calibration method

A novel calibration method is developed for calibrating stereo-camera-based digital image correlation (DIC) setup to overcome the difficult challenge of 3D vibration measurement of large structures using digital imaging techniques. The calibration method employs an IMU sensor for camera orientations, a laser sensor for camera positions, and a virtual stereovision approach for intrinsic parameters. This novel stereo-camera calibration method is validated using an ideal physical calibration method and then integrated with DIC technique for field experiments. The first field experiment is performed on a light tower of 10m height. The results showed that the developed technique can measure 3D displacements of the light tower under various excitation modes. It was also consistent in terms of natural frequency estimation which is validated using an accelerometer. With this success, the developed methodology is employed in the second field experiment where 3D vibration study is carried out on a utility-scale wind turbine. The developed DIC-calibration method is able to obtain the in-plane and out-of-plane displacements of the tower and rotor blade of the turbine. The method is also able to produce accurate values of natural frequencies validated using a ground-based microwave interferometer. It can be said that the present study established a stereo-camera-based DIC technique with a novel calibration method for 3D vibration analysis of various large-sized civil and aerospace structures.