Fatigue Assessment of Wind Turbine Towers: Review of Processing Strategies with Illustrative Case Study

Abstract

Wind turbines are structures predominantly subjected to dynamic loads throughout their period of life. In that sense, fatigue design plays a central role. Particularly, support structure design might be conservative with respect to fatigue, which may lead to a real fatigue life of considerably more than 20 years. For these reasons, the implementation of a fatigue monitoring system can be an important advantage for the management of wind farms, providing the following outputs: (i) estimation of the evolution of real fatigue condition; (ii) since the real condition of fatigue damage is known, these results could be an essential element for a decision about extending the lifespan of the structure and the possibility of repowering or overpowering; and (iii) the results of the instrumented wind turbines can be extrapolated to other wind turbines of the same wind farm. This paper reviews the procedures for calculating the fatigue damage of wind turbine towers using strain measurements. The applicability of the described procedures is demonstrated with experimental data acquired in an extensive experimental campaign developed at Tocha Wind Farm, an onshore wind farm located in Portugal, exploring the impact of several user-defined parameters on the fatigue results. The paper also includes the description of the data processing needed to convert raw measurements into bending moments and several validation and calibration steps.

Effect of curtailment scenarios on the loads and lifetime of offshore wind turbine generator support structures

“…A recommendation which has been confirmed in various other research on this topic, e.g. [10][13] [15].…”

“…section 3.1). A commonly applied representative value per bin in a research context is the mean value [15]. For the purpose of the present work, an engineering judgement based on the quantile values per bin was performed.…”

“…This updated model-driven simulations have been subject of research and industrial applications [3][4]. While the use of monitoring data is also recommended in current guidelines, the actual use-cases of data-driven fatigue assessments with load monitoring data are mainly found in a research context [5] [15]. The present work aims to investigate the potential of using load monitoring data in data-driven fatigue assessments methodology to evaluate the impact of curtailment scenarios on structural lifetime.…”

Farm‐wide interface fatigue loads estimation: A data‐driven approach based on accelerometers

“…As the turbine yaws to follow the wind directions FA and SS, loads get distributed along the entire circumference. In order to get the full cross‐section fatigue profile, further decomposition of the FA and SS components into a specific heading is required 10 . While outside of the current scope, it is planned in future work to use the derived FA and SS DELs to quantify localized fatigue loads as a function of observed environmental conditions.…”

“…Based on substructure strain measurements, the fatigue damage might then be extrapolated into the future and open the doors for lifetime quantification. [18][19][20] However, to measure mechanical stress by instrumenting all turbines of a given wind farm with strain gauges and maintaining these is not economically viable. The authors have observed that, as a result, in real-world scenarios, fewer than 10% of turbines in a farm are equipped with a SHM system that incorporates strain gauges.…”