Session: 09-02-07 Wind Energy: Fatigue Analysis

Submission Number: 177447

Transient Fatigue Analysis of a Reference Floating Wind Turbine During Curtailment Events 

Driven by grid overloads and negative market prices, wind farm operators must reduce the power production of wind turbines during so-called curtailment events. This de-rating can also be done voluntarily in order to participate in energy reserve markets. Extensive studies have covered the production in a de-rated steady-state and shown that fatigue damage accumulation is reduced compared to nominal production. However, the transition between these operational states is often overlooked in fatigue analyses, despite being characterized by high stress cycles. Indeed, the relatively fast reduction in thrust forces typically excites vibrations of the wind turbine in the fore-aft direction which, due to low damping in general, persist for a characteristic time. These transitions could significantly affect the project lifetime if the frequency of curtailment events increases in the future.

While there have been some analyses of this in onshore and fixed-bottom offshore turbines recently, we study this issue for a floating wind turbine, using numerical simulations. De-rating events have been simulated with a coupled aero-hydro-elastic model of the floating reference turbine IEA15MW and the UMaine VolturnUS-S semi-submersible platform. The fatigue analysis focussed on two critical locations, the blade root and the tower base, and was conducted to highlight the impact of the transitions during such curtailment events on damage accumulation. Cumulative damage and equivalent fatigue load are evaluated as functions of key control parameters, such as transition time. A threshold has been identified that provides a lower limit to prevent excessive damage to the tower base.

Specific wind loading, wave loading, and transition simulations were superposed and compared with combined simulations to quantify the contribution of each fatigue-inducing factor: wind loading, wave forcing, and transitional de-rating events, and to identify potential cancellation or amplification effects of these curtailment transition–induced fatigue cycles. A linear regression model was used to estimate the contributions and possible interactions between these three factors. This analysis has been performed across a wide range of wind conditions and sea states to identify favourable environmental conditions for curtailment operations and to lay the groundwork for developing lifetime-conscious curtailment control strategies.

Presenting Author: Paul Dupin Norwegian University of Science and Technology NTNU

Presenting Author Biography: Paul Dupin is a PhD candidate at the Norwegian University of Science and Technology (NTNU) within the Marie Skłodowska-Curie Doctoral Network TWEED. His research focuses on developing optimal strategies for lifetime-conscious power curtailment of wind energy systems. He holds a Master of Science degree in Mechanical Engineering from ENSTA Paris (France) and in Energy Engineering from KTH Royal Institute of Technology (Sweden), and Instituto Superior Técnico (Portugal).

Authors:

Paul Dupin Norwegian University of Science and Technology NTNU
Michael Muskulus Norwegian University of Science and Technology NTNU