Modal analysis of wind turbine blade using machine vision

The Modal analysis is one of the applicable methods used to identify the dynamic characteristics of structures. Inspection of structures to avoid resonance conditions can be achieved by extracting vibration modes using modal analysis. Since every point of the vibrating structure has its own characteristics such as the displacement, speed and acceleration, therefore the measurement of these parameters in a specific time interval can be used to extract modal parameters. In this study, stereo vision as a non-contact measuring system is used to obtain the displacement of several points of the blade of a 2.5kW wind turbine with a length of 3m under the operational modal condition. At first, the camera calibration process is performed and then the three-dimensional data of the turbine blade are extracted from images recorded during the test. Consequently, modal parameters of the blade are calculated by analyzing the data. Finally, modal parameters obtained by three different methods including the stereo vision system, the finite element analysis and the testing accelerometer are compared. The results show that visually obtained data are sufficiently accurate to find the natural frequency of the first mode of the blade. The first natural frequency mode extracted by the stereo vision System shows a difference of 10.36% and 2.67% compared to the those obtained by finite element method and the accelerometer respectively.