A parametric study of the sensitivity of fatigue loading experienced by a tidal current turbine to the environment in which it operates is reported. The design tool GH Tidal Bladed is used to model a generic 2MW turbine operating in a range of flow turbulence and sea-state environments representative of the turbine’s lifetime. Time histories of the salient load component ‘blade root out-of-plane bending moment’ are rainflow cycle counted to provide lifetime damage equivalent loads as functions of both mean flow turbulence and significant wave height.
Fatigue load criticality is then assessed by comparing the resulting fatigue damage margins with the ultimate yield stress resulting from the 50-year extreme wave event. Although in this particular study it is found that the selected extreme load case drives the blade root design, fatigue stress margins are observed to fall as low as +8% under certain environmental conditions, suggesting that fatigue loading is still an important consideration in the overall design process -particularly for those projects where the severity of site conditions may exceed those considered in this study.
Generally, strong correlations are observed between turbine fatigue loading and levels of both turbulence and sea-state severity. This indicates the necessity of a detailed description of environmental conditions at a potential tidal turbine site, coupled with sophisticated, validated models of the complex interaction of this environment with the turbine’s operational behaviour, if more optimised, cost-effective design solutions are to be achieved in the future.