Dear Enes,
I’m sorry, but I don’t understand your question. If you are doing any further code development, I suggest starting with FAST v8.
Best regards,
Dear Jason,
For now, I need linearization functionality for the offshore system. But I will take your kind advice about using FAST8 as soon as possible.
Best regards
Hello Jason,
is it possible to give out the rotational velocities and accelerations as well as the translational acceleration of the nacelle, when the Nacelle Yaw DOF is enabled? I am not sure you answered that question in the beginning of this topic already but as I understand the Outputs you list there only apply for the case of disabled Nacelle Yaw DOF, is that right?
The orientation of the nacelle’s motion is not too important to me, so I would be happy about either the motion in nacelle orientation or in the inertial frame orientation. So according to the TMD manual, the values I am looking for are either
omega_N_O_N ; alpha_N_O_N and rddot_P_O_N
or
omega_N_O_G ; alpha_N_O_G and rddot_P_O_G.
Thank you very much in advance
Best regards
Laurin
Dear Laurin,
My answer from my posted dated Jul 02, 2012 above applied to both systems with and without the nacelle-yaw DOF enabled (I clarify how the nacelle-yaw will effect the nacelle motion in the second paragraph).
My understanding is that you want the absolute (global) angular velocity and absolute (global) angular acceleration of the nacelle expressed in either the nacelle or global coordinate system…is that correct? If so, the most relevant ElastoDyn outputs are NcIMURVxs, NcIMURVys, NcIMURVzs for angular velocities and NcIMURAxs, NcIMURAys, and NcIMURAzs for angular accelerations, but these are output in the shaft coordinate system rather than the nacelle coordinate system. You could easily transform from the shaft to the nacelle coordinate system by applying a transformation involving the fixed shaft-tilt angle.
Best regards,
Dear Jason,
thank you for your quick as always answer. You are right, I am looking for the absolute global angular velocity, angular acceleration and translational acceleration of the nacelle. The way I understand your reply (and also to my logical understanding), is it right, that the shaft coordinate system is always twisted by the constant shaft tilt angle against the nacelle coordinate system? So in case of the 5MW wind turbine the only difference between the orientation of the nacelle system and the shaft system would be the 5 degree angle called ‘ShftTilt’ around the ys- or yn-axis?
Best regards
Laurin
Dear Laurin,
Yes, your understanding is correct.
Best regards,
Dear Jason,
I am trying to do a reliability analysis (for the onshore NREL 5MW turbine), using the tower top rotation as the failure criteria. As I understand, FAST outputs the tower top rotation using the channels TTDspRoll and TTDspPtch, about the xt and yt axes at the tower base.
Could you please tell me if there is a limiting maximum value for the tower top rotation? The DNV (2016) standard Support Structures for Wind Turbines specifies a maximum value of 0.25 degrees, but I believe this is at the mudline.
I have attached a sample plot for 13 m/s for your reference.
Sincerely
Abhinav
Dear @Abhinav.Abeendranath,
This doesn’t mean that DNV hasn’t published something, but I’m not personally aware of specific limits on maximum tower-top rotation. I’ve certainly heard of specific limits on maximum tower-top (or nacelle) acceleration, e.g., 1/3*gravity is a typical limit.
Best regards,
Dear Jason,
Thank you for the reply. I will look into the limit on tower top acceleration.
Also, I have just noticed a couple of works in literature (https://doi.org/10.1016/j.finel.2016.06.006 and Energies | Free Full-Text | Seismic Fragility Analysis of Monopile Offshore Wind Turbines under Different Operational Conditions) making use of 5 degrees and 2.5 degrees (equal to the precone of the rotor) respectively, as limiting values for seismic analysis of the NREL 5 MW wind turbine.
Sincerely
Abhinav