NREL 5MW OC3-Hywind (Test 24) Questions

Discuss theory and modeling of wind-turbine structures.

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Jason.Jonkman
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Re: NREL 5MW OC3-Hywind (Test 24) Questions

Postby Jason.Jonkman » Wed Mar 24, 2021 7:03 am

Dear Matthew,

The values of BlPitch specified in the ElastoDyn input file are the initial blade-pitch angles used at the start of the simulation. With active blade-pitch control enabled, these really are just initial conditions and the actual blade-pitch angles will change throughout the simulation. But it is often important to specify the initial conditions to their expected mean value for a given mean wind speed to ensure that the overall time-domain solution is reasonable. I can't tell from your forum post whether the response you are obtaining is expected or not.

You may get high angle of attack warnings at the inner-most nodes of a blade, which are typically not aerodynamically optimally designed. But I would not expect that you'd receive these warnings at most nodes along the blade. Can you confirm what nodes you receiving this error for?

My understanding is that the IEA Wind 15-MW reference turbine can experience high Mach numbers (exceeding 0.3) due to the high tip-speed ratio it is designed for. This was discussed on our forum here: viewtopic.php?f=2&t=2581&p=15459.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Matthew.Lee
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Re: NREL 5MW OC3-Hywind (Test 24) Questions

Postby Matthew.Lee » Mon Apr 05, 2021 7:58 am

Dear Jason,

I am analyzing the impact various wind and wave loads have on the tower base (at mudline) of the 15MW turbine. In particular I am looking at the fore-aft moment (ReactMXss) and the side-to-side moment (ReactMYss), assuming these are the correct parameters which represent the moments?

The following images are results I have from MLife.

TowerBaseSidetoSide_windwave.JPG
TowerBaseSidetoSide_windwave.JPG (99.58 KiB) Viewed 127 times
TowerBaseForeAft_windwave.JPG
TowerBaseForeAft_windwave.JPG (116.21 KiB) Viewed 127 times


I was under the impression that the fore-aft moment would produce larger DELs than the side-to-side DEL as shown in the following document (https://iopscience.iop.org/article/10.1 ... 052052/pdf).

However my results show the opposite, that the side-to-side moment have much larger DELs than the fore-aft moment.

Please could you offer a reason for this? And if I have made an error how best I can correct it?


Thanks as always for your help.
Regards,
Matthew

Jason.Jonkman
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Re: NREL 5MW OC3-Hywind (Test 24) Questions

Postby Jason.Jonkman » Mon Apr 05, 2021 8:12 am

Dear Matthew,

You have the labels reversed. ReactMXss is the side-to-side moment (i.e., the moment about X caused by side-to-side forces along Y) and ReactMYss is the fore-aft moment (i.e., the moment about Y caused by fore-aft forces along X).

That said, I'm not sure I understand the results you are showing, which don't seem to show clear trends. I would expect smoother curves if the results are converged.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Matthew.Lee
Posts: 15
Joined: Mon Nov 16, 2020 6:21 am
Organization: Trinity College Dublin
Location: Ireland

Re: NREL 5MW OC3-Hywind (Test 24) Questions

Postby Matthew.Lee » Mon Apr 05, 2021 8:34 am

Dear Jason,

Thank you for your quick reply.

That makes sense regarding the moments, thank you for clearing that up.

The reason for the non smooth curve which produces spikes is the limited dataset (only 240 input cases).

Also the input cases have varying wind wave misalignment and peak spectral period which may also cause the non smooth curve.

Best regards,
Matthew


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