Context

Tidal turbines are among the most advanced ORE technologies. The lack of knowledge regarding the characteristics of fluid loadings at different tidal sites leads to certain limitations in the methodology used for fatigue estimation of mobile components such as blades and rotors. Nevertheless, the prediction of fatigue life is a critical parameter that influences the LCOE, and in particular the strategies in the operational and maintenance phases.

Indeed, an accurate prediction of the life expectancy of components is necessary to complete the planning of planned maintenance operations. Based on this schedule, a feedback loop can be applied to the design of the components in order to optimise the necessary maintenance and the associated high costs. The structural definition of each component can also be revised accordingly and new materials can be incorporated if the expected durability is insufficient. Consequently, the accuracy of fatigue prediction is a critical issue to tidal turbine deployment.

Objective

To improve the identification of complex fluid loads in an open tidal environment (waves + current) in order to improve performance prediction and fatigue design of mobile components.

Main achievements

• Description of flow dynamics at the Alderney Race high-potential tidal energy site.
• Proposal of formulations to take into account fluctuating hydrodynamic loads used in fatigue calculations.
• Improvement of numerical models to accurately simulate complex flows.
• Proposal of recommendations in relation to the specifications for tank tests.

Conclusion

Current velocity measurements collected by 2 acoustic profilers coupled to 4 beams have allowed to characterise the turbulence in 3D over the entire water column in the Alderney Race. Assuming a tidal turbine aligned with the direction of the prevailing current, MUSCATTS showed that the main parameters likely to affect the structure are: turbulence intensity in the longitudinal direction, shear stress, normal stress and the vertical integral length scale. The turbulence intensity associated with the longitudinal direction was found to be higher than that estimated at other tidal sites around the world. The size of the most energetic vortices associated with the vertical direction is of the order of 10 m.

Resources

Fact sheet (PDF)

Partners and funding

This project was led by France Energies Marines.

The total project budget was €76K.

This project received funding from Brittany.

Photo credit: France Energies Marines