Fatigue load reduction of bldae

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Jason.Jonkman
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Re: Fatigue load reduction of bldae

Postby Jason.Jonkman » Wed Mar 18, 2020 12:38 pm

Dear Cheng,

The mooring loads would be related to the platform motion based on the mooring configuration and line properties. I don't know what FAST model you are using (or if you made your own), so, I can't really comment on that.

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
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Cheng.Zhang
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Re: Fatigue load reduction of bldae

Postby Cheng.Zhang » Wed Mar 18, 2020 1:12 pm

Dear Jason,

I used the NRELOffshrBsline5MW_OC3Hywind model.
The _MAP.dat file is as following

Code: Select all

---------------------- LINE DICTIONARY ---------------------------------------
LineType     Diam     MassDenInAir    EA        CB    CIntDamp   Ca   Cdn   Cdt
(-)          (m)      (kg/m)         (N)       (-)     (Pa-s)    (-)  (-)   (-)
Material     0.09      77.7066      384.243E6   0.001   1.0E8    0.6  -1.0  0.05
---------------------- NODE PROPERTIES ---------------------------------------
Node Type       X     Y     Z     M     B     FX    FY    FZ
(-)  (-)       (m)   (m)   (m)   (kg)  (mˆ3)  (N)   (N)   (N)
1    fix     853.87   0    depth   0     0     #     #     #
2    Vessel    5.2    0    -70.0   0     0     #     #     #
---------------------- LINE PROPERTIES ---------------------------------------
Line    LineType  UnstrLen    NodeAnch  NodeFair  Flags
(-)      (-)       (m)         (-)       (-)       (-)
1       Material   902.2        1         2        tension_fair tension_anch
---------------------- SOLVER OPTIONS-----------------------------------------
Option
(-)
repeat 240 120


Best regards,
Cheng

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Re: Fatigue load reduction of bldae

Postby Jason.Jonkman » Wed Mar 18, 2020 2:49 pm

Dear Cheng,

Given that the platform rotations you are showing are small are not too different between the controllers, I would guess the difference in mooring loads are not related to the platform rotations; rather they are probably more related to surge and sway translations. Plotting those may help explain why the mooring loads differ.

By the way: MAP++ generally provides mooring reactions that enable calculation of floating wind turbine response, but mooring line loads tend to oscillate much more when using a dynamic mooring model, e.g. MoorDyn. (That is, MAP++ generally captures mean and low-frequency effects, whereas MoorDyn will capture those as well as high-frequency oscillations.) I would suggest using MoorDyn if your goal is to calculate loading of the mooring lines.

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

Cheng.Zhang
Posts: 66
Joined: Tue Nov 14, 2017 6:50 am
Organization: ECN
Location: france

Re: Fatigue load reduction of bldae

Postby Cheng.Zhang » Wed Mar 18, 2020 3:02 pm

Dear Jason,

Thank you very much for your patience and answers, it is very helpful for me!

Best regards,
Cheng

Cheng.Zhang
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Organization: ECN
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Re: Fatigue load reduction of bldae

Postby Cheng.Zhang » Thu Apr 02, 2020 4:16 pm

Dear Jason,

I used individual blade pitch (IBP) control reduced the 1p load of blade root flap-wise moment, and plotted its PSD as you see in Figure 1 and Figure 2.
The simulations are made by FAST OC3Hywind model with all DOFs enabled, Figure 1 shows the PSD results of constant wind and no wave; Figure 2 shows the PSD results of stochastic wind with the irregular wave;

I found that in the literature, only the 1p load is reduced, the load under or higher than 1p frequency is almost the same as collective blade pitch (CBP) control, for example, the PSD in Figure 3, the CBP and IBP controllers have almost coincident trajectories except for the 1p frequency.

Concerning my simulation results, my question is,

1, In Figure 1, the 1p load of IBP is reduced, but the low-frequency load (lower than 1p) of IBP is also smaller than CBP, is it normal? Should it be the same as CBP control?
2, Do you think the result of Figure 2 is OK?

I'm not a specialist of load analyzing, I want to make sure my results are reliable, could you give me some comment?
Thank you in advance!

Best regards,
Cheng
Attachments
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psd3.PNG
psd3.PNG (53.86 KiB) Viewed 1466 times

Jason.Jonkman
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Re: Fatigue load reduction of bldae

Postby Jason.Jonkman » Thu Apr 02, 2020 4:32 pm

Dear Cheng,

I'm not surprised by these results. The decrease in response outside of the 1P peak is not much different; the difference is exaggerated by the log scale on the y-axis. I would suggest plotting with linear scales to better see the true physical differences.

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

KennethPaul.Dsouza
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Re: Fatigue load reduction of bldae

Postby KennethPaul.Dsouza » Thu Mar 11, 2021 10:49 pm

Dear Jason,

I am trying to use an IPC to reduce low frequency loading on the rotor blades. I am interested in the blade root out of plane bending moment, so i plotted the PSD of the out of plane root bending moment using Mcrunch. I have attached the plot below. It is showing peaks at much lower values than the expected 1P(~0.2Hz).

I am running the Fastv8 Test18 Certification case.

Can u clarify why are the peaks lower than expected?

Regards,
Kenneth Dsouza

untitled.tif
untitled.tif (351.88 KiB) Viewed 427 times

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Re: Fatigue load reduction of bldae

Postby Jason.Jonkman » Fri Mar 12, 2021 7:29 am

Dear Kenneth,

I would expect that you'd see peaks in the PSD of the blade-root moments at 1P, 2P, 3P, etc. I don't know why you are not seeing this. What does the time series look like; do you see a strong 1P oscillation in that?

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

KennethPaul.Dsouza
Posts: 12
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Organization: Indian Institute of Technology, Madras
Location: India

Re: Fatigue load reduction of bldae

Postby KennethPaul.Dsouza » Mon Mar 15, 2021 12:10 am

Thanks for the quick reply Jason.

There was a slight error in the time series data for which the previous PSD were calculated. So I ran simulations again this time with turbulent wind conditions. The PSDs still don't show peaks corresponding to 1P or higher frequencies. I have attached the PSD and time series data for out of pane root moment.

Also I am wondering whether there is any error in the Mcrunch Input file that i have used. So I have attached the input of PSD portion of Mcrunch as well. All other modules of Mcrunch are set to false.
Attachments
Screenshot 2021-03-15 113900.jpg
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roottomesnap.jpg
roottomesnap.jpg (124.56 KiB) Viewed 395 times
rootpsd.jpg
rootpsd.jpg (14.15 KiB) Viewed 395 times

Jason.Jonkman
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Re: Fatigue load reduction of bldae

Postby Jason.Jonkman » Mon Mar 15, 2021 9:14 am

Dear Kenneth,

Your MCrunch input data looks OK to me.

I think the biggest problem may be that Test18 from the FAST v8 CertTest is only run for 60 s, which does not provide a lot of resolution at low frequencies. I would suggest rerunning this simulation for at least 600 s

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

KennethPaul.Dsouza
Posts: 12
Joined: Mon Oct 28, 2019 5:30 am
Organization: Indian Institute of Technology, Madras
Location: India

Re: Fatigue load reduction of bldae

Postby KennethPaul.Dsouza » Wed Mar 17, 2021 10:31 pm

Dear Jason,

I followed your suggestion and ran simulation for 600s using 15m/s uniform wind speed. The PSD now show definitive peaks, but the 1P frequency is still shown as 0.25Hz compared to the 0.2Hz actual value. Can you provide any suggestion as to why this maybe happening.

Regards,
Kenneth
Attachments
Screenshot 2021-03-18 095832.jpg
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Jason.Jonkman
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Re: Fatigue load reduction of bldae

Postby Jason.Jonkman » Thu Mar 18, 2021 9:59 am

Dear Kenneth,

I would first suggest confirming that the rotor speed output from OpenFAST is what you expect it to be. 0.25 Hz = 15 rpm.

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

KennethPaul.Dsouza
Posts: 12
Joined: Mon Oct 28, 2019 5:30 am
Organization: Indian Institute of Technology, Madras
Location: India

Re: Fatigue load reduction of bldae

Postby KennethPaul.Dsouza » Fri Mar 19, 2021 5:26 am

Dear Jason,

The simulations were run at 15m/s uniform wind speed. The rotor speed was 12.1 rpm which should correspond to ~0.2Hz 1P frequency, but it is not the case.

Note:- I am using FAST v8 for running the simulations.

Regards,
Kenneth

Jason.Jonkman
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Re: Fatigue load reduction of bldae

Postby Jason.Jonkman » Fri Mar 19, 2021 7:03 am

Dear Kenneth,

Can you share the times-series output file used to generate this?

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

KennethPaul.Dsouza
Posts: 12
Joined: Mon Oct 28, 2019 5:30 am
Organization: Indian Institute of Technology, Madras
Location: India

Re: Fatigue load reduction of bldae

Postby KennethPaul.Dsouza » Fri Mar 19, 2021 11:06 pm

Dear Jason,

The time series data File is too large to be uploaded in the forum even after compression(97MB). Is there any other way I can send it to you?

Regards,
Kenneth


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