Hi
It seems like the industrial standard approach to yaw misalignment is that if the wind is approaching your turbine from a slightly clockwise direction (when viewed from above) to where your turbine is facing then you have a positive yaw error. To correct the error, you would yaw clockwise, in a positive direction.
Sadly this doesn’t tie up with maths, which likes anti clockwise to be positive. I guess following the industrial standard, positive yaw moments would cause negative movements. I’ve had a quick rummage through the FAST manual, and it doesn’t explicitly say which approach is followed (maths vs industrial standard).
Please could you let me know which way is positive when yawing and would you consider adding a top down view of a turbine to the manual in the section where the coordinate systems are described?
Thanks
Alec
Dear Alec,
In FAST, the wind direction output (HorWndDir), nacelle yaw angle input/ouput (NacYaw) and nacelle yaw error output (NacYawErr) are all defined counter-clockwise when looking from above (this is a positive rotation about the z-axis, which points vertically upwards). In AeroDyn, the wind direction input (WindDir) is defined clockwise when looking from above (which is opposite to that of FAST). For example, in Test01 from the FAST CertTest, NacYaw = -15 degrees and WindDir = -HorWindDir = 30 degrees, which equals NacYawErr = -15 degrees.
I hope that helps.
Best regards,
Thanks Jason, yes it does.
Alec
Hi everyone,
I just want to make sure that I understood the explanation concerning FAST’s yaw convention right.
Would you be so kind to confirm that the picture I created is correct?
It’s supposed to show the turbine viewed from above. The black arrows point out the rotation direction of the blades.
Thanks – and kind regards,
Julia
Dear Julia,
Yes, your image is correct.
Best regards,
Dear Jason,
thanks a lot for the quick response!
Best regards,
Julia
RE: FASTV8.16
Are any of the yaw options possible with the newest versions of FAST?
Mark C
Dear Mark,
What yaw options are you referring to?
Regardless, the yaw functionality is virtually unchanged between FAST v8.16 and earlier versions.
Best regards,
forgot to look under elastodyn inputs. thanks. M
Dear @Jason.Jonkman
I’m preparing simulation for wind-wave misalignment under yaw error condition with steady wind & regular waves environment.
I will set sea environment as followings
- Wind direction = 0, 30, 60 degrees (Clockwise rotation from zero direction)
- Wave direction = 0 degrees (Fixed from zero direction)
- Yaw error = -8, 0, +8 degrees (Every wind direction)
If I understood above messages correctly, Is it proper input for simulation?
Here is my simulation environment parameters.
I also put images so that help you to understand much better.
Image source : Li, Xiuhe, et al. “Effects of the yaw error and the wind-wave misalignment on the dynamic characteristics of the floating offshore wind turbine.” Ocean Engineering 199 (2020)
Best regards,
Sangwon
Dear @Sangwon.Lee
Your approach makes sense to me.
Best regards,
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Dear @Jason.Jonkman
Thank you for your confirmation.
And also I appreciate for your quick response.
Best regards,
Sangwon
Dear @Jason.Jonkman, Dear @Sangwon.Lee
It seems that the positive direction of NacYaw defined in this Figure is not consistent with OpenFAST
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Dear @Baoxuan.Wang
Figure (left) is just an example to show the combination of yaw error and wind-wave misalignment visually.
Table (right) is the OpenFAST parameter values made by myself for research.
Best regards,
Sangwon
Okay, Sangwon. Thank you for your clarification.
Best regards,
Baoxuan
Dear @Jason.Jonkman,
I am currently studying the outputs of nacelle yaw motions in the ElastoDyn module of OpenFAST v3.5.3. My case parameters include a steady wind field at 20 m/s, with NacYaw = -PropagationDir = 20 and YawNeut = 0, and my turbine is the onshore NREL 5MW wind turbine. During this process, I have encountered the following 3 issues:
- The output nacelle yaw angle YawPzn is the angle between xn and xp axes, where xn and xp are the x-axes of the “nacelle and tower-top coordinate systems,” respectively. For example, I have output the values of YawPzn for the first three time instances and plotted the values for the first two. The xn axis (marked with a thick red line) also represents the rotor axis, as shown in the figure below. Is my understanding correct?
- For the output nacelle yaw angular velocity YawVzn, I calculated this value based on the YawPzn of the previous time. However, my calculated value M_YawVzn differs significantly from the output, as shown in the figure below . Please help me identify where I should be wrong.
- For the deflected tower, I have drawn both the “tower-top and local tower coordinate systems,” as shown in the figure below. The plan view is the same. Is my understanding correct?
Best regards,
Dear @Yangyang.Li,
Here are my responses to your questions:
- Yes, I agree with your drawing (assuming the view of the figure is from above, other than the fact that your
NacYaw = -PropagationDir angle looks more than 60 degrees than 20 degrees). Please note that the nacelle yaw is quickly snapping back towards zero because you’ve set YawNeut = 0, likely with a high yaw spring stiffness. If you want to keep the 20-degree yaw angle, set YawNeut = 20deg.
- I agree with your math (other than the fact that you wrote -28.48 instead of -23.48 in your expression for the yaw rate). The difference in yaw rate calculation is likely the result of the simpleness of your derivative calculation for such a large yaw rate (ElastoDyn uses an RK4 integrator for the first few steps to derive yaw rate from yaw acceleration, which takes substeps smaller than the 0.05 s time step).
- Yes, I agree with how you’ve drawn the coordinate systems (again assuming the view of the left figure is from above).
Best regards,
Dear @Jason.Jonkman,
Yes, I agree with all your points regarding the oversight of the wind direction appearing to be 60 degrees (actually 20 degrees), the typographical error of -28.38, and the prompts that all views are from above. I apologize for the confusion, and thank you once again!
Best regards,
