tower buckling moment of floating wind turbins

Dear Jason:
Now I am using the FAST software to calculate the tower bending buckling moment of offshore floating wind turbines (such as SPAR type, semi-submerisble type). However, the only output signals avaliable for analysising the tower bending buckling moment are “TwrBsMxt (x-components)” and “TwrBsMyt” (y- components), as I read them in the users’ guide as far. So my idea is :a )the two signals (TwrBsMxt and TwrBsMyt) consider the tower buckling moments induced by the aerodynamics force on the feathered blades. b) Other tower bending buckling moments should be esitmated by us using other empirical functions (to calculate the wind loads on the nacelle or tower) when we need obtain the whole tower bending buckling moments.
My question is:
1):
I don’t know how to calculate the buckling moments produced by the wave loads. I wonder if the wo signals (TwrBsMxt and TwrBsMyt) have covered the hydrodynamics force on the tower base (if We enable the hydrodynamic module).

2):
I just do this kind of research for the first time and I am not sure this is the right idea to obtain the moments using the FAST. Could you please give me some suggestions ? Thank you very much!

Best regards,
Yichau. Liu

Dear Yichau,

The tower-base loads output by FAST include the effects of both the applied loads (aerodynamic and hydrodynamic) and the gravity/inertia loads (mass/inertia times acceleration). I’m not sure which version of FAST you are using (v7 or v8) or what features of the model you’ve enabled, but direct wind loading on the tower is a feature available in FAST v8. (You are correct that direct wind loading on the nacelle is not available, but this can often be neglected.)

I hope that helps.

Best regards,

Dear Jason:
Thanks for your help. In fact, I am using the FAST v8 to simulate the tower buckling and the enabled features including a) ElastoDyn, b)InflowWind, c)AeroDyn v15 and d)CompHydro. And the details of tower-base loads are not described in the users’ guide. So it is still confused for me to do the simulations.
As you stated in your response, the tower-base loads cover the effects of both the aerodynamic, hydrodynamic and the grabity/inertia loads. So is it means that the our required effect of wind loading on the most part of floaring wind turbines, especially the blades, the tower, has been included in the tower-base loads(“TwrBsMxt (x-components)” and “TwrBsMyt” (y- components)) in FAST v8? and if we neglect the wind loading on the nacelle, the tower buckling could be modelled using the only variable, tower-base load (“TwrBsMxt (x-components)” and “TwrBsMyt” (y- components))? Thank you very much.

Best regards,

Dear Yichau,

Yes, I agree.

Just FYI: Whether or not your model includes wind loading on the tower depends on whether you’ve enabled that model in AeroDyn v15 (TwrAero = True). Normally, however, the aerodynamic loads on the rotor dominate the tower loads when the rotor is in operation; the direct wind loading on the tower is most important when considering cases where the rotor is parked or idling.

Best regards,