Every day, an offshore wind turbine blade faces the full force of the ocean weather, enduring winds up to hurricane force. Regular inspection is vital to ensure that the smooth operation of the turbine is maintained. Today, these checks are carried out once or twice a year by engineers who use rope access techniques to physically inspect the blade, a process that can be challenging, time-consuming and expensive.
The BOHEM (Blade Optical HEalth Monitoring) project aimed to develop a cost effective early warning system to flag up blade structural failures. The system works by tracking the position of reflective markers inside the blade – any substantial change in the movement of the markers at a given wind speed could indicate that structural failures have occurred. This enables the turbine to be de-rated until maintenance can be scheduled.
After conceiving the idea of an optical blade health monitoring system, the Catapult approached Wideblue Ltd to develop the idea further.
Wideblue is a Glasgow-based SME, formerly Polaroid’s R&D lab, who develop optical solutions to a wide variety of problems. Its expertise in product development, optics, and software development made the firm an ideal partner to develop BOHEM.
The BOHEM system consists of three main components: A series of reflective strips which are placed around the inside of the blade at a series of points around the critical ‘max chord’ area, a bright LED light to illuminate the reflective strips, and a machine vision camera which films the position of the markers.
The system works by comparing the position of the markers at any given moment to the position in a ‘reference’ configuration with the blade undeformed. Initially, the system has been trialled in the Catapult’s blade test facility to validate whether the deformations detected using the BOHEM system correspond to those measured by a laser, but the long-term goal for the project is to use the system in-field to monitor the cross-sectional deformation and detect if it is starting to change over time, which would indicate that a structural failure has occurred.
The BOHEM project aimed to a low-cost, optimised, optical blade condition monitoring solution for deployment during the development of new designs, and in the operational field.
The combination of the camera system and image acquisition software developed by Wideblue and image processing software developed by the Catapult has been validated against laser measurements during a full scale static blade test. It was shown that BOHEM allows accurate measurement of blade cross sectional deformations; next steps will involve developing the BOHEM into a standalone product that can be deployed in a turbine blade in the field.
