Shape estimation and health monitoring of wind turbine tower using a FBG sensor array

This paper introduces a high-speed fiber Bragg grating (FBG) sensor system for use in shape estimation of wind turbine tower under dynamic loads. A fiber Bragg grating interrogator was developed with a spectrometer-type demodulator based on a linear photo detector. In the high-speed demodulation mode, up to six arrayed FBGs can conduct 40 kHz sampling per each channel simultaneously, and in the low-speed demodulation mode, the system can be effectively used for the dynamic strain monitoring of large structures that require many sensors, by expansion of the sensing channels. Real-time shape estimation of the wind turbine tower structure was accomplished using strain data gathered by surface mounted fiber Bragg grating sensors. The finite element model of the wind turbine tower was created and a displacement-strain transformation based on a modal approach was applied to find the displacement-strain transformation (DST) matrix. The estimated shapes measured by ten Bragg grating sensors are analyzed for two operational load cases of wind turbine. The results show very close agreement showing the potentials of the proposed shape estimation technique based on displacement-strain transformation using Bragg grating sensors.