Abstract
Offshore wind turbine blades are expected to remain in operation with minimal maintenance for 35 years. However, it is now estimated that up to £1.3 million is spent on each turbine during its lifetime due to leading edge erosion from the impact of rain droplets. Erosion can be reduced by limiting blade tip speeds, but with reduced restrictions offshore, the current trend is to increase the blade length and tip speeds to maximise the potential of wind turbine technology as a source of clean and renewable energy helping to tackle climate change.Current polyurethane/polyurea based coating solutions for offshore wind turbines typically fail prematurely, reducing the aerodynamic efficiency of blades and significantly decreasing energy capture. While lifetime prediction models are available, they are commonly only suitable for homogeneous materials that undergo brittle failure. However, state-of-the-art models cannot accurately predict the effect of rain erosion on the lifetime of highly viscoelastic materials that are currently being developed at industrial levels. This limitation is thought to be due to a lack of understanding of the failure mechanisms and an inability to measure key material properties using standard methods that have been shown to vary due to loading and environmental conditions.
This project aimed to address the challenge of capturing the viscoelastic behaviour of several commercial coating systems relating the results with measured rain erosion performance. This was achieved through the down selection and adaptation of a set of quasi-static and dynamic physiomechanical tests which were used to study the effect of strain rates, load, and temperature, on key material properties. In parallel, accelerated rain erosion testing was used to determine each materials' erosion performance, allowing for correlations to be made to the measured material parameters. The work included utilising a design of experiment approach, which allowed for the influence of individual and combinations of test parameters to be quantified and detailed the preliminary results of a bespoke thin film testing approach.
The main findings indicate that modern viscoelastic coating systems show considerable strain rate and temperature-dependent behaviour that affects both the quasi-static and dynamic material properties. As a result, modern prediction models need to be adapted to account for variations resulting from different loading and environmental conditions.
Overall this thesis combines several techniques into an overarching methodology to characterise modern coating materials and compare their viscoelastic characteristics. This allows for rapid, relevant, and cost-effective laboratory test methods for early erosion performance screening, reducing overall development time.
| Date of Award | 24 Jan 2023 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Carwyn Ward (Supervisor), Ian Hamerton (Supervisor) & Kirsten P Dyer (Supervisor) |