Dear All,
im using Mlife to calculate fatigue loads.
I would like to specify the distribution of the runs by myself so I need to create a file for the variable “DistribFile” in Mlife.
Can someone give an example how this file should look like?
Best regards,
Simon
UPDATE:
In the source dir that comes with the latest Mlife_archie there is a function write_joint_pdf.m with this function it is very easy to create needed binary distribution files.
Dear Simon,
Presumably you mean MLife input parameter “DistribName” rather than “DistribFile”.
Test28.mlif in the MLife CerTest provides an example with a user-defined distribution, with the user-supplied distribution table given in CertTest/Data/WindDistrib.dat. But this file is in binary format, and so, is not human readable. However, the format is described in the document, “User_Probability_Distributions.pdf” given in the Documentation directory.
I hope that helps.
Best regards,
Dear Jason,
thank you for clarifying!
In order to validate mlife against Bladed postprocessing I try to do a fatigue calculation with only one time series and one sensor. But Mlife is giving me following error:
I also included the mlife settings file.
Is there any error or misunderstanding?
Best regards,
Simon
UPDATE:
I compared the basis of my settings file (Test28.mlif) with others (e.g. Test01.mlif) and found some differences. Apart from some names that are defined different I can find the option for a user specified distribution in Test01.mlif.
Then I tried to run Test28.mlif with Mlife_win32.exe and got the same error as shown below.
Test01.mlif works.
Can you provide a working example of Mlife with user defined distribution?
UPDATE_2:
It seems, that the compiled Mlife in Version MLife_v1.01.00a_0 is not updated. Can you provide a compiled version of the latest version? I don’t have a needed Toolbox for Wind Speed binning (function wblcdf) in Matlab so I need to run Mlife as a compiled version.
Mlife_HC_fix_Mx.txt (6.85 KB)
Hello Simon,
Unfortunately, we do not have the resources to supported pre-compiled versions of MLife at this time. The good news is that you can still use MLife! You simply need to create your own version of the Weibull cumulative distribution function, wblcdf() function.
[url]https://www.mathworks.com/help/stats/wblcdf.html[/url]
I cannot vouch for the following, but here is an example:
[url]http://www.dynare.org/dynare-matlab-m2html/matlab/missing/stats/wblcdf.html[/url]
Best Regards,
Greg
Dear Greg,
thank you very much. I will use the binary File or replace the mentioned Matlab function.
Best regards,
Simon
Dear all,
has anyone made a comparison between Mlife and Bladed post processing for the rainflow counting algorithm (e.g. comparing calculated DELs without Weibull weighting)?
I validated, that both programs are counting the same amount of cycles.
No Goodman correction was used in Bladed and Mlife.
The best results I get for UCMult = 0.5.
Altough for some time series / sensors I got a ~0% difference and for some up to 12% difference in DEL.
I tried to find out which algorithm was used in Mlife and Bladed. In both references to papers were made :
Mlife:
Downing, S.D.; Socie, D.F. (1982). “Simple Rainflow Counting Algorithms.” International Journal of Fatigue; Vol. 4, [N.1], pp. 31 40.masters.donntu.org/2015/fimm/zin … icle11.pdf
Bladed:
Recommended Practices for Wind Turbine Testing and Evaluation, 3. Fatigue Loads, IEA, 2nd edition 1990
community.ieawind.org/viewdocum … 488ff4bd04
Can someone explain the difference between both approaches or has experience with both post processing programs when it comes to DEL?
Best regards,
Simon
Dear Dr.Jonkman:
I am analyzing wind turbine yaw bearing fatigue using MLife v1.01.00a-gjh for Test09.mlif with MATLAB. I have the following question which confused me a lot:
I think it isn’t the problem with the Input files as I also tried the original two with the same fatigue analysis, it showed the same problems. And I am thinking whether it is the problem with the Distribution section or the Fatigue section?
Here is the attachment of the MLife running file “Test09_10mps_1.txt”.
Could you please have a look at it？
Kind regards
Jianwen
Test09_10mps_1.txt (7.53 KB)
Hello Everyone,
I’m studying the effects of aerodynamic rotor imbalance in power production and fatigue of wind turbine components. While looking for some insights on how to choose reasonable LUlt values for the blades, low speed shaft e tower, I’ve found a few references to a discussion on the FAQ page: [url]National Wind Technology Center's Information Portal | Wind Research | NREL. Also, I’ve read in some of the posts that a possible way to find LUlt values would be by running MExtremes, which I tried to get on the page: wind.nrel.gov/designcodes/postpr … mes/alpha/.
Unfortunately, none of the pages are available at moment. Would it be possible to share the new links for the FAQ page and for the MExtremes download?
For the discussion on the FAQ page, in case it is not available anymore, is there a NREL report / paper that I could use as reference for my studies? For the MExtremes tool, could someone share it with me?
Kind Regards,
Bruno Mazetto
Dear Bruno,
Unfortunately, the NWTC Information Portal has crashed and is no longer available, and there is a bit of gap before the new website becomes live–see the following announcement for more information: Other News.
Regardless, here is what the old FAQ said regarding the question, “What values do I use for TypeLMF and LUlt in my MCrunch and MLife input files?”:
Until the new website becomes live, I’ve temporarily places the MExtremes (as well as MCrunch and MLife) download(s) here: wind.nrel.gov/public/jjonkman/M … MExtremes/.
Best regards,
Dear Jason,
Thank you for your help!
Dear Jason,
I couldn’t access the NREL tools MLife and MExtreme on the new website. The link you have previously attached in this thread is also not working. Is there any repository to access those tools? Can I use those tools without Matlab source as well?
Thanks and reagrds
Abhinay Goga
Dear Abhinay,
As I announced here: Other News, the drive.google.com/drive/folders/ … sp=sharing.
Best regards,
Dear everyone,
I am currently new to the MLife and the DEL calculation. I tried to implement the MLife using Matlab, using the test examples given. I am interested to compare the DEL reduction before and after implementation of IPC. Which parameter is the appropriate to calculate the DEL,( RootFxc1 or RootMyc1).
I noticed from the excel file generated, that DEL value are calculated for RootFxc1 and OSTwrBsMxt. Also I see from the script that OSTwrBsMxt is a calculated variable not existing in the out file. Can you help me identify the parameter.
Thanks and Regards
Dear @Nitin.Sivakumar,
It is common to assess the effect of IPC on the blade root flapwise bending moment (RootMyb1) or the blade root out-of-plane bending moment (RootMyc1).
Regarding your question about a specific MLife example, which CertTest number are you referring to? (I’m not that familiar with each test.)
Best regards,
Dear sir,
I did not try all test files, I just tried with Test07. I did not find any index in the certTest folder, I selected Test07 because, Matlab script contained a section for it to calculate DEL from OUT files.
Dear @Nitin.Sivakumar,
Test07 is an example demonstrating how MLife can be called without an input file. Calculated channel OSTwrBsMxt is set within a MATLAB script instead. See the script mlife_certification_tests.m in the CertTest directory of the MLife archive.
Best regards
Hello everyone,
I have two questions regarding the Lult. I am trying to find the Lult for several load channels, and from what I have seen in different discussions I should consider the maximum moment for the tested load cases and multiply it by a factor, or find the Lult that makes the fatigue life coincide with the typical lifetime of wind turbines (20 years). If I take any of these approaches I will get several values for the Lult (one for each load channel).
The orientation of the bending moments changes with respect to the section throughout the year: the directions of the flapwise and edgewise bending moments change with respect to the root’s section for wind speeds above nominal speed for a variable pitch machine, and the foreaft and side-to-side also change direction with respect to the tower section for different wind directions.
To compute the DELs using Goodman’s correction, a Lult is defined that is different for different bending moments’ components (eg. flapwise and edgewise). How can we have a fixed Lult for each of these components, since the orientation of them will change with respect to the section? Shouldn’t the Lult be defined according to the section?
In order to compute the maximum DEL using load roses, should the sectors be defined with respect to the moment vectors or the section?
Best regards,
Miguel Pereira
Dear @Miguel.Pereira,
You may be able to calculate the value of LUlt for simple cross sections composed of an isotropic material, but to truly calculate it for a complex airfoil cross section composed of composite material, you’d have to use a sectional analysis tool. See related topics regarding LUlt on this forum for further discussion e.g.: Mlife - User Defined Distribution - #15 by Jason.Jonkman.
Best regards,
Dear Jason,
We are currently working on fatigue preliminary calculations for land-based wind turbines using MLife and DEL as a quantitative measurement. We have a few doubts that we would like to clarify if possible. Here are some of our questions:
1- Short-term DEL vs. lifetime DEL:
Based on the information we gathered from the “MLife Theory Manual” and this forum, it seems that short-term DEL is calculated based on a “single time-series,” while lifetime DEL is based on the “entire set of time-series data.” We are unsure about when it’s appropriate to use one or the other. For instance, should we obtain the short-term DEL of a specific channel if we want to analyze the DEL caused by a particular event (i.e., only one time-series with a wind gust included)?
2-Fatigue analysis simulations:
We are also seeking guidance on how to perform proper simulations for fatigue analysis. Is there any recommended reference for land-based wind turbines? We have been reading the report “Dynamics Modeling and Loads Analysis of an Offshore Floating Wind Turbine” by J.M. Jonkman, specifically chapter 5.
3- Weibull distribution in MLife:
Regarding the Weibull distribution used in MLife, are its default parameters taken from the input files? The “MLife Theory Manual” mentions that MLife models the wind with a Weibull distribution, but we are unsure if the default Weibull distribution parameters are taken from the time-series, since this wind distribution is place-dependent.
As you can see, probably some of these questions are trivial, but we want to know if we are in the correct path. This is what is planned for the preliminary fatigue analysis (in general, we have to select the channels, etc):
a) We intend to use OpenFast to generate six 10-minute simulations for each wind condition, ranging from 4 to 24 m/s, centered within bins of 2 m/s. This will result in a total of 66 simulations. Is it recommended/enough to use Turbsim for generating the wind profiles?
b) After generating the 66 .out files, we plan to use MLife for fatigue analysis.
We apologize if some of these questions seem trivial, but we want to ensure we are on the correct path for our analysis.
Best regards,
Dear @Ignacio.Lopez,
Here are my responses to your questions, but overall it sounds like you are following the correct path.
Your understanding of short-term and lifetime DELs is correct. Fatigue lifetime or lifetime fatigue damage are what matters to a real structure. But if you are not trying to compute that, e.g., by focusing only on a limited number of load cases important to fatigue, the short-term DEL can be useful, e.g., to compare one situation relative to another. To compute fatigue lifetime or lifetime fatigue damage requires that you consider the full range of situations (load cases) important to fatigue of the structure.
The IEC 61400-1 design standard dictates the requirements for land-based wind turbine fatigue analysis. Load case 1.2, involving normal operation from cut-in to cut-out wind speed tends to be most important, but other fatigue load cases can be important dependent on the turbine and site conditions.
The parameters of the Weibull distribution, such as shape and scale factors, are directly user-specified within the MLife input file; they are not derived from user-provided time series.
a/b) Yes, TurbSim is appropriate for this. What you describe sounds like the typical execution of load case 1.2 from IEC 61400-1.
Best regards,
