In the FAST,I simulate the static analysis by setting the Rotspeed=0,the wind file=“noshr_12.wnd”,WaveMod=0(still wave),I found the platform surge offset is 2.41, but when I set the constant Rotspeed =12.1(without control),other setting have no change,but the platform surge offset is about 25m.I think someting wrong happened.I don’t konw why!
I have another question about the simulation time to get the stable result in the offshore wind turbine,How long did it take to get the stable result for offshore turbine gerenally?
I’m sure that the change in platform surge is the result of a change in rotor thrust. The thrust of a wind turbine is strongly dependent on the rotor speed, wind speed, and blade-pitch angle. I’m not surprised you see a large change in thrust when changing the rotor speed.
Floating systems typically have long natural periods and low damping, so, start-up transients can last a long time if proper initial conditions are not set. Section 6.8.2 of the HydroDyn User’s Guide and Theory manual provides some guidance for choosing proper initial conditions to minimize start-up transients for floating wind systems.
As you say that The large offest (PlatformSurge=25m) is noraml ? But in the paper ‘Coupled Dynamic Modeling of Floating Wind Turbine Systems’ I find that the PaltformSurge is smaller than 25m when the wind speed is larger than rated speed,I have never saw so large offset.
Is it noraml?
The platform surge is dependent on the platform type. A displacement of 25 m may be reasonable for platform with very slack catenary mooring system. Are you modeling the same exact system from that paper?
I use the Test24.fst for 5MWwind turbine Offshore Hywind.Is it normal ?
Yes, such a large displacement is expected for the OC3-Hywind system at rated wind speed. See the plot below (taken from Lorenz Haid’s MS Thesis - University of Stuttgart, 2013) of the steady state response of the OC3-Hywind system dependent on wind speed (with still water), which was derived from FAST.