Dynamic structural health monitoring of a model wind turbine tower using distributed acoustic sensing (DAS)

Abstract

Maintenance of wind turbine towers is currently a manual process that requires visual inspection and bolt tightening yearly. This process is costly to energy companies and its necessity is not well-defined. In this study, two Rayleigh-based distributed fiber optic sensing technologies are evaluated and compared for their ability to monitor the dynamic structural behavior of a model wind turbine tower subject to free and forced vibration. They are further tested for their ability to detect structural phenomena associated with loose bolts and material damage within the tower. The two technologies examined are optical frequency domain reflectometry (OFDR) and phase-based optical time domain reflectometry ($$\phi$$ ϕ -OTDR), which is a technology used in distributed acoustic sensing (DAS). OFDR is a tested and proven strain measurement technology commonly used for structural health monitoring but can only make strain measurements over short distances (10 s of meters). OFDR was used to validate the measurements made with $$\phi$$ ϕ -OTDR which can measure over much longer distances (several kilometers). Due to its sensing distance capability, $$\phi$$ ϕ -OTDR is a promising technology for monitoring many wind turbines networked together with a single fiber optic cable. This study presents a first-of-its-kind use of $$\phi$$ ϕ -OTDR for structural health monitoring to demonstrate its capabilities.

Scientific Applications of Distributed Acoustic Sensing: State-of-the-Art Review and Perspective

“…Another application is related to wind generators where a φ-OTDR makes it possible to measure the natural frequencies of the tower oscillations. Based on their amplitude, it is possible to draw conclusions about the reliability of the fastening (losses and breakages of bolts are possible) [ 111 ].…”

A Novel Sensor for Undrained Shear Strength Measurement in Very Soft to Soft Marine Sediments Based on Optical Frequency Domain Reflectometry Technology

“…The specification of the OFDR interrogator and optical fibers is listed in Table 2 . Although OFDR technology has been used for dynamic measurement [ 25 ], the OFDR interrogator used in this study is for static measurement only with a measuring rate of 1/3 Hz.…”

Watching the Cryosphere Thaw: Seismic Monitoring of Permafrost Degradation Using Distributed Acoustic Sensing During a Controlled Heating Experiment

“…DAS utilizes short pulses of laser light to interferometrically measure minute extensional strains (or strain rates) over spatially continuous intervals along an optical fiber (Hartog, 2017) with spatial resolutions down to the meter scale, linear extents from 10s to 100s of km, and bandwidth from the kHz range to quasi‐static depending on interrogator unit and measurement parameters (Lindsey et al., 2020; Paitz et al., 2021). Standard telecommunications‐grade optical fiber has been used successfully as the sensing element for infrastructure monitoring (Hubbard et al., 2021; Liu et al., 2016) and urban near‐surface seismic monitoring (Ajo‐Franklin et al., 2019; Dou, Lindsey, et al., 2017; Fang et al., 2020), but this technique has yet to be tested in permafrost environments where hazards to infrastructure are arguably greater.…”