Fatigue load reduction of bldae

This forum if for discussing controls. Questions about how to implement controls in FAST are more appropriate to the CAE Tools forum.

Moderator: Bonnie.Jonkman

Jason.Jonkman
Posts: 5082
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

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
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 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

Jason.Jonkman
Posts: 5082
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

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

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
psd1.PNG
psd1.PNG (45.75 KiB) Viewed 620 times
psd2.PNG
psd2.PNG (61.31 KiB) Viewed 620 times
psd3.PNG
psd3.PNG (53.86 KiB) Viewed 620 times

Jason.Jonkman
Posts: 5082
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

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


Return to “Controls”

Who is online

Users browsing this forum: No registered users and 1 guest