Research On Modal Identification Method And Vibration Characteristics Of Wind Turbine Blade Based On Binocular Camera

Vibration testing is an important method for power mechanical structure design and equipment fault diagnosis.Modal parameters are significant content of wind turbine blade performance and quality detecting,and provide important guidance data for structural design and quality monitoring.In response to the large-scale and complex measurement requirements of the vibration structure,compared with the traditional data collection system,the binocular stereo photogrammetry method proposed in this paper can not only achieve full-field measurement,but also meet the requirements of the test environment and other measurement technologies that are not feasible.Its high durability has great application value for establishing the geometric model of the vibration structure,multi-point and multi-target dynamic tracking,and realizing the structure vibration data collection and analysis under the excitation state.The paper uses digital images to extract the geometric shape,displacement and deformation of the structure,effectively measures high displacement and low-frequency vibration.Proposing an imaging model with distortion,matching image which based on the feature edge and energy optimization of the optimal parallax in the image system,and utilizing the algorithm to track the structure pasted with coded targets,and finally the coded targets in multiple images are captured to interpret and determine the three-dimensional coordinate information.Based on the principle of stereo vision,two cameras are manually synchronizing and continuously collecting with marked points of vibration structure images from different orientations,pre-processing smoothly eliminates irrelevant information,and the images are segmented by adaptive thresholds,then the gray scale of the characteristic area with the fastest jump is used as the edge,after that the two-dimensional orthogonal polynomial method is further used to fit the edge.Finally,the gray square weighted centroid method is used to obtain the subpixel center coordinates of the marked targets in the continuous frame image.Realizing data acquisition by the methods of feature points matching,tracking and modal parameter identification,which have the advantages of non-contact,fast,multi-point testing,high accuracy,and low sensitivity to the test environment.Through building a binocular photogrammetry platform combined with image processing to obtain the spatial position information of the measuring point and the vibration information of the collected targets.A complete image acquisition and analysis system is formed,which has good practicability,and is especially suitable for the modal identification and vibration characteristics research of large vibration structures.In this study,the first four modal frequencies of a wind turbine blade are successfully identified by binocular camera measurement technique.The results are compared with other measurement techniques(such as Laser Doppler Vibration measurement and Acceleration Sensor measurement)and numerical analysis methods(such as FEM)used in structural dynamics,which controls the dependability and potency of the binocular photogrammetry method.The comparison results show that the modal frequency error obtained by the binocular photogrammetry method is only less than 5%,which has certain engineering application value,and provides theoretical method and technical reference for modal identification of large wind turbine blades.