Fatigue load reduction of bldae

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Cheng.Zhang
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Fatigue load reduction of bldae

Postby Cheng.Zhang » Tue Oct 29, 2019 7:01 am

Dear all,

I have a question about the reduction of blade fatigue load.

As far as I know, I can use individual blade pitch control to reduce the blade load.
In order to design the controller, I need the information of blade flap-wise root moments.
The question is, if I want to reduce the fatigue load, I need to reduce the magnitude of moments or to reduce the variation of the moments.

Thank you!

Cheng

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Re: Fatigue load reduction of bldae

Postby Jason.Jonkman » Tue Oct 29, 2019 8:24 am

Dear Cheng,

Fatigue loads are oscillations about a mean value. Considering the Goodman criteria, the same oscillation about a higher mean load will result in increased fatigue. Thus, ideally you'd reduce both the amplitude of oscillation and the mean, but it is likely that IPC would be most useful at reducing the amplitude.

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: 57
Joined: Tue Nov 14, 2017 6:50 am
Organization: ECN
Location: france

Re: Fatigue load reduction of bldae

Postby Cheng.Zhang » Tue Oct 29, 2019 11:01 am

Dear Jason,
Thank you for your fast reply.
I remembered I asked you a similar question about the fatigue load evaluation in this forumhttps://wind.nrel.gov/forum/wind/viewtopic.php?f=30&t=2004&start=45.

I only have a single time series of results, you recommend me to use STD or RMS of moments to evaluate the fatigue load. However, just as you said, the same oscillation about a higher mean moments leads to same STD but higher RMS, I'm confused now, which performance index is better, STD or RMS.

Since I used STD to evaluate the fatigue load (of tower base and blade root) in my previous work, i.e., I want to get smaller oscillation. If I use IBP to reduce the amplitude of blade bending moments, I'm not sure I will get small STD of blade bending moments.

Best regards,
Cheng

Jason.Jonkman
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Re: Fatigue load reduction of bldae

Postby Jason.Jonkman » Tue Oct 29, 2019 11:56 am

Dear Cheng,

The "best" would be to calculate a damage-equivalent load (DEL), together with the Goodman correction to account for load means. RMS and STD are simplifications of this (with RMS better than STD).

Please note that a proper fatigue analysis would require many more than a single time series. It is standard practice to test your controller for a full range of operational conditions (from cut-in wind speed to cut-out) through many separate time-domain simulations. At the minimum, I would recommend using 2 m/s wind-speed bins and 6 turbulence seeds per bin.

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: 57
Joined: Tue Nov 14, 2017 6:50 am
Organization: ECN
Location: france

Re: Fatigue load reduction of bldae

Postby Cheng.Zhang » Wed Oct 30, 2019 3:49 am

Dear Jason.

Thank you.

Actually, no matter which index I use. I think the inputs of IBP controller have the following options, I don't know which one is better

1. The variation (with respect to an operating point) of the blade root moments; the control objective is to reduce such variation to zero.

2. The rate of change of blade root moments; It is similar to the 1st case, one can reduce the rate to zero such that reduce the variation.

3. The blade root moments; the control objective of to reduce the value of moments (same as you said, reduce the amplitude of moment). But the question is, the moments of the blade root (after the MBC transformation) are not varying around zero, I don't know if I want to reduce them, how can I fix my reference (in the previous cases, the reference is zero).

Best regards,
Cheng

Jason.Jonkman
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Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
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Re: Fatigue load reduction of bldae

Postby Jason.Jonkman » Wed Oct 30, 2019 6:58 am

Dear Cheng,

I'm not sure I understand your question, but I would suggest reviewing papers on independent blade-pitch control to see how others have defined the objective function. I'm not an expert on wind turbine control.

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: 57
Joined: Tue Nov 14, 2017 6:50 am
Organization: ECN
Location: france

Re: Fatigue load reduction of bldae

Postby Cheng.Zhang » Wed Oct 30, 2019 7:29 am

Dear Jason,

I appreciate your help, my last question is, is there any link between the FlapDOF1 and blade root flap-wise bending moment?

Best regards,
Cheng

Jason.Jonkman
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Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
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Re: Fatigue load reduction of bldae

Postby Jason.Jonkman » Wed Oct 30, 2019 7:45 am

Dear Cheng,

I would expect a strong correlation between the displacement of the flapwise degree of freedom and the flapwise bending moment, but there will not be perfect correlation (one is not a scaling of the other).

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


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