Probabilistic analysis of blade fatigue in exposed tidal sites.

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Andrew Clarke, Jimmy Murphy

Tuesday 30 june 2015

15:05 - 15:20h at Antarctica (level 0)

Themes: (T) Special session, (ST) Marine renewable energy

Parallel session: 6D. Special session: Marine Renewable Energy

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Horizontal axis tidal turbines, when in operation, are subject to cyclical loading as a result of the vertical velocity profile and particle velocity from wave orbitals. In ideal sites wave heights are limited by geographical boundaries i.e. the narrow inlet at Strangford Lough, however more often than not sites are exposed to the open ocean i.e. off the coast of Northern Ireland/ Scotland. At these sites the effects of waves in particular can have a significant effect on increasing the number of fatigue loading cycles for a turbine blade which in turn reduces the blade’s operational lifetime. This paper outlines the effects of wave conditions and current speed through the use of probabilistic and computational methods. The analysis involves computing the occurrence of wave conditions and current speed, determining applicable loading conditions and the likelihood of those conditions occurring. These loading conditions are simulated and a rainflow analysis is performed on each loading cycle. The contribution of these cycles to the cumulative fatigue damage can then be calculated and applied to a fatigue loading cycle curve. These analyses are used to determine the influence of environmental conditions on blade loadings and the effects an exposed site can have on the blades operational lifetime. A comparison is performed between the predicted lifetime of the turbine blades under the same current conditions both with and without the influence of wave conditions.