Deformation Measurement Of Wind Turbine Blade Model Based On Three-dimensional Digital Image Correlation Method

With the large-scale development and utilization of wind energy,the number of wind turbines is increasing.Turbine blade as a key part,the safety of wind turbine blades is more and more valued by people.At present,some scholars have studied the test of wind turbine blades,most of which are contact,discrete,non-three-dimensional test methods.In order to overcome and reduce the deficiencies in the traditional wind turbine blade structure testing process,this paper uses three-dimensional digital image correlation method to measure the deformation of the wind turbine blade model.Three-dimensional digital image correlation method is a non-contact optical measurement method.It not only has the advantages of the two-dimensional digital image correlation method,such as full-field measurement,non-contact measurement,and relatively low requirements for the measurement environment.It also incorporates binocular stereo vision technology,which can obtain the three-dimensional deformation information of the whole area of the measured object,so the work of this article has research significance.This article mainly studies the key technologies of binocular vision measurement system calibration,image correlation matching and three-dimensional displacement calculation in three-dimensional digital image correlation methods.And set up a measuring system to carry out three-dimensional deformation measurement of the small wind turbine blade model and analyze the experimental measurement results.The main research work of this article is as follows:First of all,this paper describes the basic principles of binocular stereo vision technology,including the conversion relation between image pixel coordinate system,image physical coordinate system,camera coordinate system and world coordinate system,camera linear model,camera nonlinear model,binocular vision model and camera calibration model.Then,according to the basic principle of camera calibration,the corner detection of the black and white checkerboard calibration board was carried out based on Harris algorithm,and the corner detection of the calibration board was realized.On this basis,zhang Zhengyou calibration method was used to carry out calibration experiment of the measurement system,and the internal and external parameters of the binocular camera were solved,which laid a foundation for subsequent image matching and three-dimensional displacement calculation.In the process of image matching,surface fitting method is used to solve the sub-pixel coordinates of the matching points before and after deformation,Then,the nearest neighbor ratio method was used to solve the sub-pixel coordinates of the matching points in the left and right images,and RANSAC algorithm was used to eliminate the mismatches in the matching point pairs.Finally,the internal and external parameters of the two cameras are used to solve the three-dimensional coordinates before and after the deformation of the matching point based on the least square method.The difference value of the three-dimensional coordinates before and after the deformation of the matching point is the three-dimensional displacement.The translation experiment was carried out with the translation workbench,and the relative error between the XTPDIC measurement system and the measurement system in this paper was calculated,the relative error of the measurement system in this paper was within 2%,meet the measurement requirements.Finally,a set of digital image correlation measurement system based on binocular vision technology was built.The correlation measurement system was used to obtain the three-dimensional deformation information of the small wind turbine blade model under different load conditions,and the full field three-dimensional of the small wind blade model was effectively obtained Deformation information and analyze the results of experimental measurements.The measurement experiment of wind turbine blade model can provide some reference for load analysis of wind turbine blades in the future.