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-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-OTDR which can measure over much longer distances (several kilometers). Due to its sensing distance capability, phi-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-OTDR for structural health monitoring to demonstrate its capabilities.
Highlights
Wind energy generation capacity worldwide increased from 24 GW in 2001 to 568 GW by the end of 2018 [1]
This study shows that the measurements made with -OTDR can be interpreted as dynamic strain and are useful for structural health monitoring (SHM)
The measurement distance limited but industry-accepted optical frequency domain reflectometry (OFDR) was used to validate the dynamic strain measurements made with -OTDR. -OTDR, known as distributed acoustic sensing (DAS), is a technology with a very large maximum sensing distance
Summary
Wind energy generation capacity worldwide increased from 24 GW in 2001 to 568 GW by the end of 2018 [1]. Wind power was responsible for 15% of the increase in electricity generating capability globally [2, 3]. O&M costs for land-based wind turbines fell by nearly 50% [4]. Procedure improvement and technology advancements have been the main cause for these cost decreases, and in turn have helped the growth of investments in wind energy.
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