# Questions about wind turbine tower base moment

Hi everyone,

I am now doing the simulation of OC3Hywind wind turbine and wanna calculate the stress on the tower base. However, I feel confused with some questions:

1. I have set the directions of wind and waves for 0 degree that means along the X axis. But I find that the output of the wind speed does not equal to 0 (for Y and Z directions). I used kaimal spectrum to generate the wind files.
2. The bending moment of tower base for X direction does not equal to 0. (I think if wind and waves are aligned with X axis, the bending moment for X axis should be 0)

Many thanks
Jerome

Dear Jerome,

1. By “Kaimal spectrum”, I assume you mean that you are using TurbSim. Even if the mean wind speed propagates along the global X-axis, TurbSim will include lateral wind fluctuations (horizontal and vertical), whose mean is zero, but whose variations are not.
2. The lateral wind fluctuations will bring about tower-base bending moments about the x-axis. Moreover, the torque generated by the rotor will result in tower-base bending moments about the x axis (including a nonzero mean).

Best regards,

Hi Jason,

Thanks for your kindly help. I just did another simulation. I have set the wind type for steady with a very small wind speed (0.00001m/s) and I also changed the wave file for the still water. Then I got a figure for the x axis bending moment which is attached in the topic. Do you think it is feasible for the tendency of the bending moment? why does the bending moment not equal to a constant?

Many Thanks
Jerome

Dear Jerome,

I can’t seem to view your image, so, I can’t really comment.

Best regards,

Hi Jason,

I mean is it possible to change the wind speed to 0m/s to investigate the wave induced stress on the wind turbine?

Kind Regards
Junyi

Dear Junyi,

If you don’t want aerodynamic loads, it is better to disable the aerodynamics calculations all together by setting CompAero to 0 in the FAST primary input file, rather than by setting the wind speed to zero.

Best regards,