Pragmatic uncertainty bounds on modal parameters from an offshore wind turbine and its supporting structure

The modal parameters of civil structures, such as offshore wind turbines, are often influenced by notable
uncertainties. In the field of structural dynamics, numerous techniques for modal parameter estimation are
available but common for all is the struggle to obtain consistent damping estimates. This paper investigates
the uncertainty of modal parameters obtained from full-scale measurements of the dynamic behavior of an
offshore wind turbine in its operational environment. Pragmatic uncertainty bounds are established in order
to bound the random and bias errors of the total damping in a statistical confidence interval. This interval
represents a lower and a higher boundary for the damping estimates corresponding to each of the natural
modes identified in the field measurements collected from the offshore wind turbine structure. The validity
of this pragmatic principle for establishing uncertainty bounds is evaluated by comparing the experimentally
obtained damping estimates to a simulated model. Attaching a lower and higher boundary allows for a better
understanding of the uncertainties related to the damping estimates obtained through Operational Modal
Analysis.