Short-term fatigue analysis for tower base of a spar-type wind turbine under stochastic wind-wave loads

摘要

AbstractDue to integrated stochastic wind and wave loads, the supporting platform of a Floating Offshore Wind Turbine (FOWT) has to bear six Degrees of Freedom (DOF) motion, which makes the random cyclic loads acting on the structural components, for instance the tower base, more complicated than those on bottom-fixed or land-based wind turbines. These cyclic loads may cause unexpected fatigue damages on a FOWT. This paper presents a study on short-term fatigue damage at the tower base of a 5?MW FOWT with a spar-type platform. Fully coupled time-domain simulations codeFASTis used and realistic environment conditions are considered to obtain the loads and structural stresses at the tower base. Then the cumulative fatigue damage is calculated based on rainflow counting method and Miner's rule. Moreover, the effects of the simulation length, the wind-wave misalignment, the wind-only condition and the wave-only condition on the fatigue damage are investigated. It is found that the wind and wave induced loads affect the tower base's axial stress separately and in a decoupled way, and the wave-induced fatigue damage is greater than that induced by the wind loads. Under the environment conditions with rated wind speed, the tower base experiences the highest fatigue damage when the joint probability of the wind and wave is included in the calculation. Moreover, it is also found that 1?h simulation length is sufficient to give an appropriate fatigue damage estimated life for FOWT.Highlights?The response spectra and statistical properties of axial stress at different tower base positions are compared.?The comparisons of fatigue damage at different tower base positions under different environment conditions are studied.?The effects of simulation length on the results of FOWT fatigue analysis are investigated.?The influences of misaligned wind and wave conditions on fatigue damage of the tower base are researched.?The fatigue damages of different tower base positions under wind-only and wave-only are compared.