Wind turbine fatigue damage evaluation based on a linear model and a spectral method

Abstract

Wind turbine multidisciplinary design optimization is currently the focus of several investigations because it has showed potential in reducing the cost of energy. This design approach requires fast methods to evaluate wind turbine loads with a sufficiently high level of fidelity. This paper presents a method to estimate wind turbine fatigue damage suited for optimization design applications. The method utilizes a high-order linear wind turbine model. The model comprehends a detailed description of the wind turbine and the controller. The fatigue is computed with a spectral method applied to power spectral densities of wind turbine sensor responses to turbulent wind. In this paper, the model is validated both in time domain and frequency domain with a nonlinear aeroservoelastic model. The approach is compared quantitatively against fatigue damage obtained from the power spectra of time series evaluated with nonlinear aeroservoelastic simulations and qualitatively against rainflow counting. Results are presented for three cases: load evaluation at normal operation in the full wind speed range, load change evaluation due to two different controller tunings at normal operation at three different wind speeds above rated and load dependency on the number of turbulence seeds used for their evaluation. For the full-range normal operation, the maximum difference between the two frequency domain-based estimates of the tower base lateral fatigue moments is 36%, whereas the differences for the other sensors are less than 15%. For the load variation evaluation, the maximum difference of the tower base longitudinal bending moment variation is 22%. Such large difference occurs only when the change in controller tuning has a low effect on the loads. Furthermore, results show that loads evaluated with the presented method are less dependent on the turbulent wind realization; therefore, less turbulence seeds are required compared with time-domain simulations to remove the dependency on the wind realization used to estimate loads. Copyright

Wind Turbine Loads Induced by Terrain and Wakes: An Experimental Study through Vibration Analysis and Computational Fluid Dynamics

“…This task has been recently attracting much interest in the scientific community dealing with wind energy: the expected lifetime of a component is gradually becoming a parameter depending on the history of the operation of a wind turbine, rather than an estimate provided at the design phase. This connects the present work to an important future development: the analysis and modeling of fatigue loads [41,42]. In the perspective that in the future, it could be possible to formulate and connect careful modelings of the rotor, drive-train and wind field for wake and non-waked operation, in order to build a theoretical framework from wind to gear and from gear to wind, it is certainly valuable to start from the experimental evidence, as has been done in this work.…”

Using Pretwist to Reduce Power Loss of Bend-Twist Coupled Blades

“…The power curve was multiplied with a Rayleigh probability density function, assuming a mean velocity of 10 m/s, and integrated to obtain the AEP. The damage equivalent load was estimated with a frequency-based method proposed by Tibaldi et al [8]. For each wind speed, the wind inputs U w (ω) in frequency domain along the blades are obtained from sampling of a time domain simulation in HAWC2 [16].…”

“…The power curve of the turbine was estimated from the steady states of the operational wind speed range and translated into AEP assuming a Rayleigh wind speed distribution with an mean wind speed of 10 m/s. The damage equivalent load was estimated using a frequency approach recently presented by Tibaldi et al [8].…”

Aero-elastic Wind Turbine Design with Active Flaps for AEP Maximization

“…The 20 loads are evaluated with reduced Design Load Cases (DLCs) ] which is a simplification of the full set of DLCs defined in [Hansen et al (2015)]. From this, various load constraints (e.g root flap-wise bending moment, tower top thrust, etc.)…”

“…An envelope of bending loads is generated for the whole blade and then passed to BECAS to evaluate material failure constraints. The framework evaluates the fatigue damage with a frequency domain model from HAWCStab2 [Tibaldi et al (2015)]. More details on the framework are given in [Zahle et al (2016)].…”