Final Report 4.1

UPWIND
The amount of damping in a dynamic system, such as an offshore wind turbine, is difficult to
determine. There are different damping factors contributing to the total damping of the system,
which are:
� Aerodynamic damping
� Hydrodynamic damping
� Structural damping
� Soil damping
The single contributions of the different damping factors depend very much on the turbine type,
offshore site, materials and soil conditions. Previous studies by DONG Energy have shown that
a total damping of approximately 12 % of the logarithmic damping is possible for a typical 3.6
MW offshore design [9]. To determine these values, a turbine in the offshore wind farm Burbo
Banks [11] was stopped several times with an emergency stop to generate a decay curve in
nearly undisturbed operational conditions. The found values in total damping are shown in
Figure 2.7. They range between 10 to 20 % with a mean of approximately 12 % [9].
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Figure 2.7: Estimated logarithmic decrements from Burbo Banks [9]
The study by DONG Energy also tried to determine the different damping contributions from
aerodynamic, hydrodynamic, structural and soil damping. Due to the fact that the studied turbine
had a tower damper included with an unknown damping factor, a final distinction was difficult.
Further results of this study can be found in [12].
In the following the main damping contributions are again explained in more detail, especially in
their context to offshore support structures.