Modelling damping sources in monopile‐supported offshore wind turbines

Abstract

Vibration damping in offshore wind turbines is a key parameter to predict reliably the dynamic response and fatigue life of these systems. Damping in an offshore wind turbine originates from different sources, mainly, aerodynamic, structural, hydrodynamic, and soil dampings. The difficulties in identifying the individual contribution from each damping source have led to considerable uncertainty and variation in the values recommended. This paper proposes simplified but direct modelling approaches to quantify the damping contributions from the aerodynamic, hydrodynamic, and soil interactions. Results from these models were systemically compared to published values and when appropriate with simulation results from the software package FAST.The range of values obtained for aerodynamic damping confirmed those available in the literature, and blade element modelling theory was shown to provide good results relatively efficiently. The influence of couplings between fore-aft and side-side directions on the aerodynamic damping contribution was highlighted. The modelling of hydrodynamic damping showed that this damping is much smaller than usually recommended and could be safely ignored for offshore wind turbines. Soil damping strongly depends on the soil specific nonlinear behaviour.

Mechanics‐based model updating for identification and virtual sensing of an offshore wind turbine using sparse measurements

“…For the considered OWT, the structural damping was estimated as 0.8% of critical damping in a previous study using an emergency brake test 24 . Aerodynamic damping is mainly caused by an air drag on the rotating blades 37 . There are several studies in the literature on estimation of aerodynamic damping analytically 38,39 and experimentally 40 .…”

“…The aerodynamic damping forces in this study are lumped in the input force applied at the top of tower. Hydrodynamic damping is generated by wave radiation and hydrodynamic drag and can be neglected in shallow waters 37 . In Blyth farm, 24 hydrodynamic damping can be neglected compared to other sources of damping 37 .…”

“…Hydrodynamic damping is generated by wave radiation and hydrodynamic drag and can be neglected in shallow waters 37 . In Blyth farm, 24 hydrodynamic damping can be neglected compared to other sources of damping 37 . In this study, structural damping ratio is considered to be 0.8% for the first two modes and modeled using Rayleigh model.…”

Reliability-based design optimization of offshore wind turbine support structures using analytical sensitivities and factorized uncertainty modeling

“…For the uncertainty in global damping, the two main contributions are assumed to come from aerodynamic damping and soil damping. Expected ranges of the damping coefficients corresponding to these two sources can be obtained from Chen and Duffour (2018) as [4.0, 8.0] for aerodynamic damping (in the fore-aft direction for operational conditions) and [0.17, 1.30] for soil damping, both given as percentages of critical damping. Assuming, as above, that these ranges correspond to 98 % confidence intervals and that the uncertainty can be modeled (for lack of better knowledge) as following a normal distribution, then we obtain θ damp,aero ∼ N (6, 0.86) and θ damp,soil ∼ N (0.735, 0.243).…”

Modelling wind turbine tower-rotor interaction through an aerodynamic damping matrix

“…Dong et al [20] and Dai et al [21] applied similar modified SSI methods to identify the frequency and damping in operating turbines, and the modification improves classic SSI when the excitation contains harmonic forces. More detailed discussion of damping identification in operating wind turbines can be found in [22]. Aerodynamic damping has also been calculated directly.…”