۱٫ Introduction

۲٫ Numerical model description

۳٫ Aerodynamic and sea wave loadings

۴٫ Fragility analysis of wind turbine

۵٫ Conclusions

Acknowledgements

References

Abstract

To more effectively extract the vast wind energy in marine areas, offshore wind turbines have been constructed with slender tower and large rotor. External vibration sources such as aerodynamic, sea wave and seismic loadings can threaten the safety of these energy infrastructures. It is important to evaluate the reliability of offshore wind turbines subjected to external vibration sources. Previous research works on the wind turbine fragility analyses only considered the fragility of the tower by assuming the wind turbine was in the parked condition with the blade mass lumped at the top of the tower. The study of the fragility of the blade which is one of the most important components of a wind turbine has not been reported. In the present study, a detailed three-dimensional (3D) finite element (FE) model of the NREL 5 MW wind turbine is developed in ABAQUS, and the tower and blades are explicitly modelled to realistically estimate the aerodynamic loads and structural behaviours of the wind turbine. The uncertainties of the structural mass, stiffness and damping are taken into account to develop the probabilistic wind-induced demand models for the tower and blades. The dynamic behaviours of the wind turbine subjected to the simultaneous aerodynamic and sea wave loadings are investigated in a probabilistic frame and the fragility curves for both the tower and blades under the parked and operating conditions are derived and discussed.

Introduction

Wind energy as one of the renewable energies is becoming a main contributor to the new electricity generation. The growth and expansion of wind farms increased rapidly in the past decade. As reported by the Global Wind Energy Council (GWEC), the worldwide installed capacity of wind power at the end of 2018 reached 591 GW, with an increase of 9.6% compared to that at the end of 2017 [1]. Due to the fact that the power generated by the wind turbine is proportional to the rotor area and cube of wind speed, multi-megawatt wind turbines with slender tower and large rotor are widely constructed in the state-of-the-art designs. These wind turbines are very flexible and lightly damped 38 since they are normally manufactured by the light-weight high-strength materials. They are thus susceptible to external vibration sources such as aerodynamic and sea wave loadings, which are experienced constantly during the whole lifetimes by offshore wind turbines. Moreover, many wind farms are located in the regions of high seismic activities such as western of United States, Japan and China [2], seismic loading is another possible vibration source during their lifetimes in these regions. The excessive vibrations may slow down the conversion of wind energy to electricity, reduce the 44 fatigue life of the structural components or even lead to the structural collapse in extreme conditions.