Experimental and computational damping estimation of an offshore wind turbine on a monopile foundation

• Two sets of measurements, namely overspeed stop and ambient excitation, are performed on a monopole offshore Vestas V90-3MW wind turbine.
• Numerical simulations are implemented in HAWC2 and the simulation-parameters are chosen to be in agreement with the real measurement data.
• The different damping contributions of each source have been discussed and evaluated using the simulations combined with OMA techniques.
• PolyMAX approach is used to analyze both the experimental and simulation results in order to obtain reliable damping estimates.
• Overall damping ratio of the first for-aft (FA) mode has been evaluated and compared with the measurements.

In this study, Operational Modal Analysis (OMA) is used to identify the damping value of the fundamental for-aft (FA) mode of an Offshore Wind Turbine (OWT) using both real life measurements and simulations. Estimations of the total damping of an offshore wind turbine (taking into account the effects of the aerodynamic, hydrodynamic and soil loads) give a quantitative view of the stability characteristics of the wind turbine. Two different test cases including an overspeed stop and ambient excitation have been considered. The experimental data has been obtained during a measurement campaign on an offshore wind turbine in the Belgian North Sea and the results are compared with the numerical simulations which have been carried out in HAWC2.