Hello,
What are the numbers of scaling inputs in CampbellDiagram (which is downloaded from forum) for Drive Train DoF and Nacelle Yaw DoF? Are these 1/(2*pi)?
Thanks,
Dear Lingling Yin,
The “Scaling” parameter within CampbellDiagram.xls is used as a unit conversion because some FAST DOFs have the units of radians while others have the units of meters. That is, the platform-translation, tower-bending, and blade-bending DOFs in FAST all have units of meters; the rest of the DOFs (e.g., drivetrain rotation) have the units of radians. To ensure that the eigenvectors have consistent units, the “Scaling” parameter can be used to scale different elements of the eigenvectors. The CampbellDiagram.xls spreadsheet recommends specific values of the “Scaling” parameter for the platform-translation, tower-bending, and blade-bending DOFs (effectively converting translational displacements in meters to slopes in radians); if these are used, you can set the “Scaling” parameter for the remaining DOFs to 1.0 (unity).
Please note that the “Scaling” parameter need not be used, but sometimes it helps to specify the recommended values to interpret the full-system modes correctly.
Best regards,
Dear Jason,
Thank you so much! But till now, I still can not distinguish the whole structural Natural Frequencies using FAST Linearization outputs, MBC3 codes and CampbellDiagram.xls.
I have attached one of my FAST linearization outputs and my CampbellDiagram.xls. In this model, 13 DoFs are turned on. And can you help me to check whether I am doing the right thing? There are still two modes can not be distinguished.
Another question is, can I use FAST Linearization outputs and MBC3 outputs to draw the modal displacement curves which are shown in the paper “nrel/cp-500-43045” by using BModes outputs.
Also, in that paper. How did you correlate the Natural Frequencies from ADAMS outputs with different modes?
Thank you so much!
1.xls (12 KB)
CampbellDiagram_twr.xls (259 KB)
Dear Lingling Yin,
Here’s how I interepret your linearization output:
Mode → Description
1 → 1st Tower Side-to-Side
2 → 1st Tower Fore-Aft
3 → 1st Blade Flap Asymmetric
4 → 1st Blade Flap Asymmetric
5 → 1st Blade Flap Collective
6 → 1st Blade Edgewise Collective
7 → 1st Blade Edgewise Asymmetric
8 → 1st Blade Edgewise Asymmetric
9 → 2nd Blade Flap Asymmetric
10 → 2nd Blade Flap Asymmetric
11 → 2nd Blade Flap Collective
12 → 2nd Tower Fore-Aft
13 → 2nd Tower Side-to-Side
Is that what you got?
The mode shapes of an individual tower or blade as a function of distance along the beam – as shown in NREL/CP-500-43045 – are inputs to FAST, not outputs from FAST. What the FAST linearization output provides is the full-system modes; that is, how the various DOFs get coupled together in the FAST representation of the full wind turbine system (blades, drivetrain, nacelle, tower, platform).
In NREL/CP-500-43045, we’ve compared the results from the FAST linearization analysis with the results from a linearization analysis from ADAMS, where the ADAMS model was built through the FAST-to-ADAMS preprocessor.
I hope that helps.
Best regards,
Dear Jason,
Thanks so much, but there are still some points need to be verified:
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Before running FAST and MBC3, it is necessary to run BModes or other FEM codes to obtain the normal mode shapes since we already turned on the DoFs in FAST simulations. But for no wind loads and 0rpm, it is not necessary to do that. In this case FAST just did static calculation to find the linearized matrixes.
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Either FAST or ADAMS cannot be used to output the mode shapes of an individual tower or blades as a function of distance along them.
Regarding the use of FAST, MBC3 and CampbellDiagram, I list the steps below since I still cannot distinguish the modes of 2nd Tower Fore-Aft and Side-to-Side from blades modes. Please once again help me to check.
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I turned on 13 DoFs in .fst input and simulated it using FAST-Linearization. I got the output .lin file after simulation.
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I downloaded MBC3 codes from wind.nrel.gov/designcodes/postpr … mbc/alpha/ and I copied the six .m file from the MBC/Source to the .lin location.
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I opened MATLAB and located to .lin file. I commanded GetMats in MATLAB command window, and then I command the name of .lin file, and then mbc3.
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After that, I open CampbellDiagram.xls Eigenanalysis FAST - #2 by Jason.Jonkman I copied DescStates, MBC_ModeShapeMagnitude, MBC_ModeShapePhaseDeg, MBC_DampingRatio, MBC_DampedFrequencyHz, MBC_NaturalFrequencyHz from MATLAB MBC3 outputs respectively to the 6 gray cells marked with comments. The Scaling inputs were set as 1. And I did not change other cells.
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There are 13 columns and 13 rows containing the information of Natural Frequencies, Magnitude and Phase in my sheet since my model owns 13 DoFs. Each column owns two sub-columns – Magnitude and Phase. In each column of the 13s, there is one row being red bolded which is used for me to interpret the associated mode (correlate with the column – States) with the Natural (Undamped) Frequency showing in the top of the column.
I have attached the CampbellDiagram.xls once again. Thank you so much about that!
CampbellDiagram.xls (256 KB)
1 Like
Dear Lingling,
Before turning on tower or blade DOFs in FAST (regardless of if the turbine is operating or not), you should always obtain good tower or blade mode shapes and specify these within FAST.
You can’t use FAST to find mode shapes as a function of distance along the tower or blade; these mode shapes are inputs to FAST. However, you can find mode shapes as a function of distance along the tower or blade using ADAMS.
Your process of running FAST and MBC3 sounds correct.
Isn’t your attachment from May 27 identical to your attachment from May 26?
It takes a bit of experience to interpret eigenvalues/eigenvectors correctly. Here is some general guidance:
*The tower fore-aft and side-to-side modes typically have fairly close natural frequencies.
*The blade flapwise modes for a 3-bladed turbine typically come in groups of 3 quite similar natural frequenices.
*Without the generator or drivetrain DOF, the blade edgewise modes for 3-bladed turbine also come in a group of 3 quite similar natural frequencies.
In your results, all but the two 2nd tower-bending modes were easy to spot. These remaining two can be found by the process of elimination and then picking which has the higher fore-aft and side-to-side contributions.
Best regards,
Dear Jason,
Great!
The two .xls are the same, but I just tried twice. Based on what I have tried, I strongly agree with your suggestions.
Thanks so much.
Can somebody tell me how to use ADAMS to get the mode shapes as a function of distance along the tower or blade?
Thanks,
Best regards,
Dear Lingling,
When you run an ADAMS linearization analysis, you can quite easily visualize the mode shapes within ADAMS/View. If you need numerical values of these, you can find fairly coarse information about the eigenvectors that are written to the *.out file generated by the ADAMS linaearization process (this is not given in a very convenient format, but we’ve used it before). If you need finer resolution output of the eigenvectors, you’ll have to ask MSC technical support for help.
Best regards,
Dear Jason,
Could you please explain that, why FAST-linearization could not give us the mode shapes of each DoFs while ADAMS can? It is obvious if we do eigenvalue analysis we can have modal frequencies and modal shapes of the system.
Really appreciate!
Best regards,
Dear Lingling,
The FAST linearization feature can be used to derive the coupled mode shapes of the full wind turbine system; that is, how the various DOFs are coupled together in full-system models (tower-blade coupling, etc). These coupled modes are the outcome of eigenanalysis on the FAST linearization output. What FAST can’t do is calculate mode shapes of isolated blades and towers (due to the distribution of mass and stiffnes along the member); these are inputs to FAST, not outputs.
Best regards,