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Title: Damping in monopile-supported offshore wind turbines
Author: Chen, Chao
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2020
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Vibration damping in offshore wind turbines (OWTs) is a key parameter to predict reliably the dynamic response and fatigue life of these systems. However, a comprehensive review of damping in OWTs identified the difficulties in quantifying the individual contributions from different damping sources that lead to considerable variation in the recommended values. First-principle models were developed to quantify the damping contributions from aerodynamics, hydrodynamics, and soil-structure interaction. Results from these models were systemically compared to published values and where appropriate with simulation results from the software package FAST. The range of values obtained for aerodynamic damping confirmed those available in the literature. The modelling of hydrodynamic damping showed that this damping is much smaller than usually recommended for large-size OWTs. Soil damping strongly depends on the soil specific nonlinear behaviour. Then the study focused on the aerodynamic damping in operating wind turbines. It is evident that even for the simplest free vibration test, conventional damping ratios assigned separately in the fore-aft (FA) and side-side (SS) directions cannot correctly characterise the vibration of wind turbines. A new aerodynamic damping model was developed to account for this coupling. This model is based on blade element momentum (BEM) theory and a linearisation of the aerodynamic forces, resulting in an aerodynamic damping matrix providing a new description of aerodynamic damping. The derivation of the aerodynamic damping matrix initially assumes that the inflow wind field is constant and uniformly distributed in the rotor plane. Then a turbulent and non-uniform wind field was considered. The aerodynamic damping model was successfully verified against FAST. In practice, the identification of damping from measured data is required. A novel approach based on the measurement of frequency response functions was developed to identify the aforementioned aerodynamic damping matrix. Numerical simulations confirmed the potential of this identification approach.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available