Structural integrity of composite tidal turbine blades

The global push for affordable, sustainable energy has accelerated the deployment of renewable technologies, with tidal stream energy emerging as a promising option due to its predictability and low environmental impact. Over the past two decades, significant strides have been made in developing commercially viable tidal stream power projects, advancing global sustainability objectives. By the end of 2023, Europe had deployed 30.5 MW of tidal stream technology, primarily through small and medium-sized enterprises. However, with only 1% of the 1000 GW of potential energy in shallow waters utilised, a vast opportunity for growth remains untapped. The efficiency and durability of tidal stream energy systems, in particular the turbine blades, are critical to their success. These blades are designed with a hydrodynamic profile that optimises energy capture but are subjected to severe cyclic fatigue due to tidal loads and water-induced degradation, making their structural integrity a key aspect of the technology. Therefore, this study aims to overcome these challenges by developing advanced methodologies, cutting-edge measurement tools, and modern testing strategies for the structural assessment of tidal turbine blades in line with industry standards, including DNV-ST-0164 and IEC TS 62600-3. Through a prototype testing program conducted as a case study under controlled conditions at the Large Structures Testing Laboratory at the University of Galway, this research focused to mitigate risks in a novel helical shape tidal turbine foil design and validate its long term reliability. One of the key approaches of this study is the use of advanced measurement tools and techniques to enhance the testing and validation process of tidal turbine blades. Therefore, to facilitate structural testing of the selected tidal turbine foil, advanced instrumentations were employed, including laser scanning vibrometers, digital image correlation systems, infrared thermal cameras, fibre Bragg grating systems, and laser displacement sensors. These technologies not only improved the precision and reliability of data recording but also accelerated data processing compared to conventional methods. Furthermore, a novel unbalanced rotating mass system was used to expedite fatigue testing, achieving a record-setting application of more than 1.3 million fatigue cycles on a single tidal turbine foil. This new approach significantly accelerated the fatigue testing process, while increasing the reliability and effectiveness of data recording and post processing. A finite element (FE) model was developed and validated the experimental results, revealing a consistent strain distribution with static testing data along the spanwise direction of the tidal foil. This underscores the potential of FE modelling to replicate physical testing methods in future studies, reducing dependence on expensive physical testing while ensuring accurate structural assessments. At the same time, a new knowledge base was developed to highlight the operating guidelines of using advanced measuring tools for enhancing the reliability, quality and accuracy of data recording and processing. The de-risking process of tidal turbine blades is complex, time-consuming, and costly. Therefore, developing efficient, cost-effective methods to predict their structural integrity and lifespan is essential. Within this framework, this study focused to formulate two novel approaches for developing vulnerability curves for tidal turbine blades and considered one approach as a case study. This method applied Miner’s rule to evaluate damage accumulation and estimate the remaining life expectancy of blades during operational stages. Moreover, the strategy for developing a vulnerability curve involved combining FE analysis, fatigue testing results of accelerated aged glass fibre powder epoxy composite materials, and loading conditions derived from the open source AeroDyn program within the FAST software package. Additionally, the process further highlights the parameters required to improve the quality and reliability of vulnerability curves for future applications, ensuring these methodologies grow alongside advancements in tidal turbine blade design and materials science for marine structures. By integrating modern measurement techniques, innovative testing strategies, and FE modelling, this research streamlines the de-risking process for tidal turbine blades, reducing costs and time while ensuring structural reliability. The strategy of combining FE modelling with fatigue testing of accelerated aged composite materials to develop vulnerability curves facilitates the prediction of the lifespan of tidal turbine blades during the operational phases. By contributing to lower levelised costs of energy, these innovations support the growth of tidal energy projects and align with the UN Sustainable Development Goal of "Affordable and Clean Energy." As the sector grows, these methodologies will drive further innovation and the broader adoption of tidal energy as a sustainable power source.

Funder

University of Galway

Publisher

University of Galway

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CC BY-NC-ND

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University of Galway Theses (PhD Theses)