# Calculation of drag and moment due to wind turbine in Openfast

Dear Jason,

I am trying to calculate the wind loading on the whole wind turbine (Rotor, Nacelle and tower). The wind turbine is in parked-feathered condition

1. How do I calculate the wind drag due to the whole wind turbine system? Can I get this directly from Aerodyn ?
2. How do I calculate the moment due to the wind loading on the whole wind turbine about the centre of mass of a floating platform? Is RtAeroMxh calculated with respect to the CM of the platform?
3. Is it possible to get the moment due to wind blowing sideways (90 degrees with respect normal to the rotor plane) Does setting NacYaw to 90 deg in elastodyn work ? or should I change PropagationDir to 90 deg in the inflowwind file? Is there any other way ? Does this consider/calculate the wind load acting on the side of the nacelle ?

Regards,

Rahul.

Dear @Rahul.Ramachandran,

Here are my responses:

1. AeroDyn can compute the drag loads on the tower and blades for idling rotors, but AeroDyn does not currently consider drag loads on the nacelle or hub.
2. AeroDyn output `RtAeroMxh` is the total rotor aerodynamic moment (torque) about the shaft. This output includes the integral of the aerodynamic loads along all blades, but does not consider the tower loads or moment arm relative to the platform CM. While AeroDyn can output the distributed drag load at aerodynamic analysis nodes along the tower (as it can for the blades as well), AeroDyn does not currently output the integrated aerodynamic load along the tower. Of course, you could always integrate the distributed values in a post-processing step. More common, though, is to obtain the reaction loads from the structural solver (ElastoDyn), which includes the contribution of applied aerodynamic loads, as well as weight and inertia.
3. Both approaches are possible. Please note that if you set `NacYaw` = 90deg with the nacelle-yaw DOF enabled in ElastoDyn (`YawDOF` = True), you should also set `YawNeut` = 90deg in ServoDyn.

Best regards,

Thank you Jason.

If the wind is blowing in the X direction, then RtAeroFxh is the total wind loading on the on the rotor along the shaft axis ?

Just to be clear, If I disable servodyn, set YawDOF=False and PropagationDir = 90, then I get the wind loading on the the rotor that is facing X direction and wind coming from Y direction and It calculates the loads on the tower also with these settings?

Dear @Rahul.Ramachandran,

I would distinguish between different coordinate systems. Wind is defined in global coordinates. `PropagationDir` = 0 means wind propagating along global X; `PropagationDir` = 90 means wind propagating along global -Y. AeroDyn output `RtAeroFxh` is the aerodynamic thrust directed along shaft (in the hub coordinate system). This axis is nominally along global X when the yaw angle is zero and nominally along global Y when the yaw angle is 90deg (could be offset a bit due to turbine displacements/deflections).

Best regards,

Dear Jason,

If I turn off all the platform DOFs (PtfmSgDOF,PtfmSwDOF,PtfmHvDOF,PtfmRDOF,PtfmPDOF,PtfmYDOF) in Elastodyn and run the simulation, does the `RtAeroFxh` give the total thrust along the shaft in the X direction (The rotor plane is facing the wind). I have turned off Moordyn and the wind turbine is in parked-feathered condition. Basically, I am trying to get the wind loads on the turbine for a platform at the installation draught just before the mooring lines are attached.

Thank you.

Dear @Rahul.Ramachandran,

AeroDyn output `RtAeroFxh` is the aerodynamic thrust of the rotor along the shaft. I’m not exactly sure what you mean by “X direction”, but presumably you are referring to the global coordinate? AeroDyn output `RtAeroFxh` is the aerodynamic thrust of the rotor along the global X direction when the platform and nacelle yaw are zero, when platform pitch and tower fore-aft deflection are zero, and when the shaft tilt is zero.

Best regards,

That clears it. Yes I am referring to the global X coordinate. Thanks a lot Jason.