Extracting fatigue damage parts from the stress-time history of horizontal axis wind turbine blades

Abstract

Horizontal axis wind turbine (HAWT) blades are a critical component of wind turbines. Full-scale blade fatigue testing is required to verify that the blades possess the strength and service life specified in the design. Unfortunately. fatigue tests must be run for a long time period. which has led blade testing laboratories to seek ways of accelerating fatigue testing time and reducing the costs of tests. The objective of this article is to propose a concept of applying accumulative power spectral density (AccPSD) to identify fatigue damage events contained in the stress-time history of HAWT blades. Based on short time Fourier transform (STFT). a novel method called STFT-based fatigue damage part extracting method has been developed to extract fatigue damage parts from the stress-time history and to generate the edited stress-time history. It has been found that a STFT window size of 256 and an AccPSD level of 9800 Energy/Hz (cutoff level) provides the edited stress-time history having reduction of 15.38% in length with respect to the original length. whilst fatigue damage per repetition can be retained almost the same level as the original fatigue damage. In addition. an existing method. time correlated fatigue damage (TCFD). is used to validate the effectiveness of STFT-based fatigue damage part extracting method. The results suggest that not only does the STFT improve the accuracy of fatigue damage retained. but also it provides a shorter length of the edited stress-time history. To conclude. STFT is suggested as an alternative technique in fatigue durability study. especially for the field of wind turbine engineering