Cross-scale vibration analysis of offshore wind turbine blades using distributed fiber optic sensing and iso-geometric modelling

• Development of a cross-scale validation and analysis methodology from scaled plates to full-size blades. • Development of distributed fiber optic sensing and isogeometric analysis (IGA) for blade health monitoring. • High-precision prediction of higher-order frequency modes and local damage responses using IGA. Distributed fibre-optic sensing (DFOS) systems are used for the online monitoring of the structural health of critical infrastructure. In the rapidly growing offshore wind power, it is becoming increasingly important to assess distributed strain and temperature in structures, especially to measure these distributions over long distances in real time with high accuracy. In this study, DFOS technology is applied for the health monitoring of scaled-down glass fiber reinforced polymer plate models. By remotely measuring strain distribution, vibration characteristics, the monitoring performance of the DFOS system was validated. The results showed that the fundamental frequency of the intact plate with the averaged thickness of 19.95 mm is 4.2 Hz. The measured fundamental frequency of the locally delaminated plate with the averaged thickness of 19.39 mm is 3.8 Hz, which may be mainly influenced by the manufacturing induced variation in stiffness factors including thickness distribution, the material properties (Young’s modulus) and density distribution. The first-mode frequency estimated by the iso -geometric analysis (IGA) is 3.97 Hz, validating the accuracy of the DFOS system. IGA results indicated that local delamination influences the vibrations in higher-order modes, providing the hint for further development. Furthermore, comprehensive studies and comparisons of vibration characteristics were conducted for full-scale wind turbine blades using both IGA and finite element analysis (FEA), respectively, offering more reliable numerical evidence for assessing the structural condition. This study successfully achieved cross-scale vibration characteristic research from experimental plates to full-scale blades.