Using Mlife for a lifetime fatigue estimation

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Julius.Scherf
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Using Mlife for a lifetime fatigue estimation

Postby Julius.Scherf » Thu Jun 18, 2020 10:11 am

Hi everyone,

I want to use MLife to determine the fatigue lifetime for the 5MW NREL
turbine.
So far, I have run test 18 without problems. After reading up in the forum,
I've to download MLife to do fatigue estimations, but I can't find the
corresponding link.
Can somebody help me?

Thanks and best wishes,
Julius

Jason.Jonkman
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Re: Using Mlife for a lifetime fatigue estimation

Postby Jason.Jonkman » Thu Jun 18, 2020 11:47 am

Dear Julius,

A similar question was asked and answered in my post dated Jun 17, 2020 in the following forum topic: viewtopic.php?f=4&t=805&start=30.

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

Julius.Scherf
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Organization: TU Darmstadt
Location: Germany

Re: Using Mlife for a lifetime fatigue estimation

Postby Julius.Scherf » Thu Jun 18, 2020 1:25 pm

Thank you for your quick reply. That helps a lot.

Best wishes,
Julius

Julius.Scherf
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Re: Using Mlife for a lifetime fatigue estimation

Postby Julius.Scherf » Fri Jul 03, 2020 5:54 am

Hi Jason,

I managed to run the mlife_certification_test file provided by mlife.
Now I want to adjust the input files in such a manner that I can determine the lifetime of the 5MW NREL turbine for all three cases specified in the IEC-61400 standard.
1. To do so, do I have to modify the DLC data files, or do I have to import the data files from FAST?
2. I'm wondering how I can plot the corresponding Wöhler curve?

Best wishes,
Julius Scherf

Jason.Jonkman
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Re: Using Mlife for a lifetime fatigue estimation

Postby Jason.Jonkman » Fri Jul 03, 2020 8:58 am

Hi Julius,

I'm not sure what you mean by "DLC data files". Are you referring to the FAST time-series output files?

MLife will not plot the S-N curve for you, but you can plot it yourself using the values of L_Ult, L_MF, and m using equation (2) from the MLife Theory Manual: https://drive.google.com/file/d/1d7uWya ... sp=sharing.

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

Julius.Scherf
Posts: 9
Joined: Thu Jun 18, 2020 6:10 am
Organization: TU Darmstadt
Location: Germany

Re: Using Mlife for a lifetime fatigue estimation

Postby Julius.Scherf » Mon Jul 06, 2020 4:12 am

Hi Jason,

thank you for your quick reply.
The Problem concerning the DLC files solved itself.
But regarding the S-N curve, I have a question. I understand that I can calculate the number of cycles using equation (2) with L_Ult and L_MF provided by MLife, but I'm not sure about L_i^RF. Can I understand it as such that it represents the standard deviation from each load case?


Best wishes,
Julius Scherf

Jason.Jonkman
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Re: Using Mlife for a lifetime fatigue estimation

Postby Jason.Jonkman » Mon Jul 06, 2020 6:56 am

Dear Julius,

L^RF_i is the cycles load range about a fixed mean value. The S-N curve is a plot of L^RF_i (S) versus N_i (N).

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

Julius.Scherf
Posts: 9
Joined: Thu Jun 18, 2020 6:10 am
Organization: TU Darmstadt
Location: Germany

Re: Using Mlife for a lifetime fatigue estimation

Postby Julius.Scherf » Tue Jul 07, 2020 3:12 pm

Dear Jason,

thank you. I appreciate your effort.

Best wishes,
Julius

Julius.Scherf
Posts: 9
Joined: Thu Jun 18, 2020 6:10 am
Organization: TU Darmstadt
Location: Germany

Re: Using Mlife for a lifetime fatigue estimation

Postby Julius.Scherf » Fri Jul 17, 2020 11:02 am

Dear Jason,

I set the Weibull-Shape factor to 2, so I can assume a Rayleigh wind distribution. Further, I want to determine the lifetime damage for three different mean wind speed values (7.5; 8.5; 10 m/s). The strange thing that I observe is that the ultimate load decreases from 8.5 to 10 m/s. Is there a fundamental error I don't see. Do you have any ideas?


Best wishes,
Julius

Julius.Scherf
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Location: Germany

Re: Using Mlife for a lifetime fatigue estimation

Postby Julius.Scherf » Fri Jul 17, 2020 11:10 am

Dear Jason,

I'm sorry, I forget to tell you that the ultimate load for the lifetime damage was calculated for RootMMxy1, which was determined as described in the MLife manual.


Best wishes,
Julius

Jason.Jonkman
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Re: Using Mlife for a lifetime fatigue estimation

Postby Jason.Jonkman » Mon Jul 20, 2020 7:02 am

Dear Julius,

I'm sorry, but I'm not sure I understand. How are you arriving at the ultimate load for RootMMxy1?

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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Organization: Trinity College Dublin
Location: Ireland

Re: Using Mlife for a lifetime fatigue estimation

Postby Matthew.Lee » Mon Mar 15, 2021 7:52 am

Hi Jason,

I wasn't sure where exactly to post this but it is regarding L_Ult and the use of MLife.

I am wondering what values I should insert for L_Ult in the .mlif file for MLife? The turbine I am using is the 15MW offshore wind turbine. Please let me know what you think.


Thanks and best regards,
Matthew
Attachments
L_Ult.JPG
L_Ult.JPG (65.97 KiB) Viewed 1050 times

Jason.Jonkman
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Re: Using Mlife for a lifetime fatigue estimation

Postby Jason.Jonkman » Mon Mar 15, 2021 10:14 am

Dear Matthew,

LUlt has been discussed many times on our forum, e.g. see:

viewtopic.php?f=4&t=805&p=14747
viewtopic.php?f=4&t=2201&p=14310

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: Using Mlife for a lifetime fatigue estimation

Postby Matthew.Lee » Tue Mar 16, 2021 4:32 am

Dear Jason,

Thanks for your quick reply. I found the links very useful.

Best regards,
Matthew

Andriana.Vassiliou
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Organization: liverpool john moores university
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Re: Using Mlife for a lifetime fatigue estimation

Postby Andriana.Vassiliou » Thu Apr 01, 2021 11:53 am

Dear Jason,

I am wanting to perform a mooring fatigue life analysis using my tests from FAST V8, I have used Map++ in my simulations and wanting to know how to use mlife to process these results and work out the fatigue life.

Best regards,
Andriana.


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