IEA 15MW RWT Extreme Events_ DLC 6.1

Dear NREL team

Thanks for your efforts on 15MW reference wind turbine in advance.

I simulate the 15-MW monopile wind turbine under extreme wind conditions according to DLC 6.1 by comparing the results on page 32 of the IEA Wind TCP Task 37 report, “Definition of the IEA Wind 15-Megawatt Offshore Reference Wind Turbine”, published in March 2020, as I could not obtain concrete validation results for this case, and I am not sure if you can give me some comments on my settings in the attached input files.

I have been following this thread for DLC 6.3 as below for more suggestions (FAST - Warning: tower model/possible tower strike - #28 by Satish.Jawalageri), and I was able to validate results for ULS well by comparing Tower base moments side-side which gave an accuracy of 5% deviation. However, when I tried to do the validation for DLC 6.1, I had a much lower amplitude in both Tower base bending moments including side-side and fore-aft (around 25% deviation).

As what I knew is that the only difference between DLC 6.1 and DLC 6.3 comes from extreme winds speed with a 50-year return period and a 1 year return period as well as different yaw angles (±8/±20 degrees), respectively. I am wondering if I missed some considerations for 6.1 so I could not get the right results for validation. (Like the water levels? structural critical damping ratios? values for hydrodynamic coefficients?)

Also, I would like to check the further followings doubts with you as well.

  1. What does the water levels be considered for this monopile wind turbine system? where could I set up the water levels in the HydroDyn?
  2. Did you include the wave stretching into account?

Thanks a lot for your consideration and kind help. I really appreciated what you have done for this research.

Best regards
Shuo-Ting Chiang
DLC 6.1.zip (32.9 KB)

Hello Shuo-Ting,

Thank you for your interest in the IEA Wind 15-MW reference wind turbine. I am not surprised that you could not match the results in the original publication exactly. This is due to a few reasons:

  • The underlying model has changed slightly since the original publication and release. There were some bugs related to incorrect model parameters and inconsistencies across the model input decks. A more significant set of bug fixes are pending in the “openfast_develop” branch of the 15-MW Github repository. The bug fixes are intended to bring the publicly released model closer to the original design intent.
  • OpenFAST has gone through a few releases, some of which are major upgrades, that could also contribute to the differences.
  • Due to employee transitions, we no longer have access to the set of OpenFAST input-output files that were shown in the original report.

If you can match some of the results but not all, I would say you are using the model correctly. If you have questions regarding proper implementation of DLC 6.3 in OpenFAST, that would be best posed in a new forum thread.

With regards to your other questions:

Cheers,
Garrett