Operational Modal Analysis Based On Videogrammetric Measurement

Modal analysis is widely used in the fields of aviation, aerospace, machinery, automobiles, high-speed rail, civil engineering, biological science and so on. It plays an important role in the structural dynamic analysis and optimization design, contributing to the reduction of noise and vibration, vibration control, structural health monitoring and the finite element model updating, etc.To generate the test model is usually time-consuming. For the flexible and lightweight structures, the traditional contact sensors bring great additional-mass effect, as a result, it is not easy to realize direct measurement. To solve these problems, videogrammetric technique, which is easy-to-use, non-intrusive and high-precision, is studied to realize geometry modeling and dynamic measurement in this paper. The geometry model is set up by linking the spatial measurement points, which are identified from the video recorded with a camera in the stationary state of the tested structure. The dynamic displacement responses are extracted from the video that records the vibration of the tested structure. The movement of multiple measurement points are tracked by multi-object tracking techniques. The 3D displacements of each measurement point are calculated and optimized by using the camera imaging model and the bundle adjustment methods. In this sense, a measurement point can be taken as a micro three-axis displacement transducer, and the multi-object tracking of measurement points can be considered as synchronized multi-channel data acquisition. Based on the band-pass filter, Hilbert transform and piecewise linear fitting method, a method for operational modal analysis is also carried out to obtain the modal parameters of the structure. The method is compared with the classical Save Time Domain and Frequency and Spatial Domain Decomposition methods.Based on GUI programming technique, the measurement and multiple target tracking systems are established. Integrated with the modal analysis software, a complete video acquisition and analysis system is formed. It has good ability to show the structural dynamic characters in the spatial domain, especially suitable for the dynamic testing and analysis of flexible and low-frequency structures. The presented procedure is successfully applied to a small fan blade, various leaves, three pendulum system, a flexible cantilever beam and the wings of the model plane.