Modeling of linear foundation for onshore turbine

Discuss theory and modeling of wind-turbine structures.

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Jens.Geisler
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Modeling of linear foundation for onshore turbine

Postby Jens.Geisler » Sun Jan 19, 2020 11:48 pm

Hi everybody,
I am trying to convert a model from Bladed to OpenFAST as accurate as possible. In Bladed the tower base can be either coupled to the inertial frame or to a specified mass/inertia via a single linear spring per DOF with specified stiffness. I would like to reproduce the later option with OpenFAST.

In this post (https://wind.nrel.gov/forum/wind/viewtopic.php?f=3&t=1227&hilit=foundation+stiffness#p5322) it is mentioned that this could be done using HydroDyn without the "hydro"-parts. Is that still the recommended way to go? If yes, could some one give me an example file? I am not sure how to set some of the parameters:
[*] Do WtrDens, WtrDpth and MSL2SWL have an effect, if WaveMod, CurrMod and PotMod are zero?
[*] Should the platform force flags be true or false?
[*] Can I set NAxCoef, NJoints, NPropSets, NCoefDpth, NMembers, NFillGroups to zero?
[*] What should I choose for the simple hydro dynamic coefficients (model 1)

Thanks already for you help!
Last edited by Jens.Geisler on Tue Jan 21, 2020 1:48 am, edited 1 time in total.

Jason.Jonkman
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Re: Modelling of linear foundation

Postby Jason.Jonkman » Mon Jan 20, 2020 8:55 am

Dear Jens,

I gather from your question that you are modeling a land-based wind turbine; is that correct? If so, the simplest solution may be to enable the user-specified external platform (ExtPtfm) by setting CompSub = 2 and CompHydro = 0, which is briefly documented here: https://openfast.readthedocs.io/en/mast ... nfast.html.

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

Jens.Geisler
Posts: 8
Joined: Fri Jan 17, 2020 7:12 am
Organization: self
Location: Germany

Re: Modelling of linear foundation

Postby Jens.Geisler » Tue Jan 21, 2020 1:47 am

Hi Jason,
thanks for the quick reply.
Indeed I am modeling an onshore turbine. I will edit the title accordingly.
Is the file format for the SubFile the same as when CompSub=1? Or is there any place I can find an example file (already looked in the matlab-toolbox and r-test repos)?

BR

Jason.Jonkman
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Re: Modeling of linear foundation for onshore turbine

Postby Jason.Jonkman » Tue Jan 21, 2020 6:08 am

Dear Jens,

Good question; no, the file format is specific to ExtPtfm. I looked a bit and can't seem to find a sample input file. But looking at ExtPtfm_MCKF.f90/ReadPrimaryFile(), the format of the input file looks quite clear:

Code: Select all

Lines  Description
1      File Header: External Platform MCKF Matrices
2      Section Header: Mass Matrix
3-8    PtfmAM
9      Section Header: Damping Matrix
10-15  Damp
16     Section Header: Stiffness Matrix
17-22  Stff
23     Section Header: Loads time-history
24     Loads time-history table channel names, i.e. Time PtfmFt_FX PtfmFT_FY PtfmFT_FZ PtfmFt_MX PtfmFT_MY PtfmFT_MZ
25     Loads time-history table channel units, i.e. (s)  (N)       (N)       (N)       (Nm)      (Nm)      (Nm)
26-end PtfmFt_t PtfmFt

I hope that helps.

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

Jens.Geisler
Posts: 8
Joined: Fri Jan 17, 2020 7:12 am
Organization: self
Location: Germany

Re: Modeling of linear foundation for onshore turbine

Postby Jens.Geisler » Tue Jan 21, 2020 6:19 am

Great, thanks I'll try this and report back how it works.

Jens.Geisler
Posts: 8
Joined: Fri Jan 17, 2020 7:12 am
Organization: self
Location: Germany

Re: Modeling of linear foundation for onshore turbine

Postby Jens.Geisler » Fri Jan 31, 2020 3:08 am

Here is my promised report. From what I saw so far it seems to work as expected.
In the main fst file I set:

Code: Select all

          2   CompSub         - Compute sub-structural dynamics (switch) {0=None; 1=SubDyn; 2=External Platform

and

Code: Select all

"sub_file_path"      SubFile         - Name of file containing sub-structural input parameters (quoted string)


In the ED file I set, e.g.

Code: Select all

True         PtfmSgDOF   - Platform horizontal surge translation DOF (flag)
True         PtfmSwDOF   - Platform horizontal sway translation DOF (flag)


and I have a SubExtPtfm file like this:

Code: Select all

------- External Platform MCKF Matrices INPUT FILE -----------------------------
------- MASS MATRIX ------------------------------------------------------------
    1.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00
    0.000000E+00     1.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00
    0.000000E+00     0.000000E+00     1.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00
    0.000000E+00     0.000000E+00     0.000000E+00     1.300000E+07     0.000000E+00     0.000000E+00
    0.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00     1.300000E+07     0.000000E+00
    0.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00     1.000000E+00
------- DAMPING MATRIX ---------------------------------------------------------
    1.000000E-02     0.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00
    0.000000E+00     1.000000E-02     0.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00
    0.000000E+00     0.000000E+00     1.000000E-02     0.000000E+00     0.000000E+00     0.000000E+00
    0.000000E+00     0.000000E+00     0.000000E+00     7.211103E+06     0.000000E+00     0.000000E+00
    0.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00     7.211103E+06     0.000000E+00
    0.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00     1.000000E-02
------- STIFFNESS MATRIX -------------------------------------------------------
    1.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00
    0.000000E+00     1.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00
    0.000000E+00     0.000000E+00     1.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00
    0.000000E+00     0.000000E+00     0.000000E+00     4.000000E+10     0.000000E+00     0.000000E+00
    0.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00     4.000000E+10     0.000000E+00
    0.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00     0.000000E+00     1.000000E+00
------- LOADS TIME HISTORY -----------------------------------------------------
Time PtfmFt_FX PtfmFT_FY PtfmFT_FZ PtfmFt_MX PtfmFT_MY PtfmFT_MZ
 (s)  (N)       (N)       (N)       (Nm)      (Nm)      (Nm)
 


This is written by a MATLAB function which essentially looks like this:

Code: Select all

M= diag([m m 1 I1 I2 1]);
K= diag([K_trans K_trans 1 K_rot K_rot 1]);
D= diag(0.005*2*sqrt(diag(K).*diag(M)));


fprintf(fid, '------- External Platform MCKF Matrices INPUT FILE -----------------------------\n');
fprintf(fid, '------- MASS MATRIX ------------------------------------------------------------\n');
for row= 1:6
    for col= 1:6
        fprintf(fid, '   % 12.6E ', M(row, col));
    end
    fprintf(fid, '\n');
end
fprintf(fid, '------- DAMPING MATRIX ---------------------------------------------------------\n');
for row= 1:6
    for col= 1:6
        fprintf(fid, '   % 12.6E ', D(row, col));
    end
    fprintf(fid, '\n');
end
fprintf(fid, '------- STIFFNESS MATRIX -------------------------------------------------------\n');
for row= 1:6
    for col= 1:6
        fprintf(fid, '   % 12.6E ', K(row, col));
    end
    fprintf(fid, '\n');
end
fprintf(fid, '------- LOADS TIME HISTORY -----------------------------------------------------\n');
fprintf(fid, 'Time PtfmFt_FX PtfmFT_FY PtfmFT_FZ PtfmFt_MX PtfmFT_MY PtfmFT_MZ\n');
fprintf(fid, ' (s)  (N)       (N)       (N)       (Nm)      (Nm)      (Nm)\n');

Jason.Jonkman
Posts: 4539
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
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Re: Modeling of linear foundation for onshore turbine

Postby Jason.Jonkman » Fri Jan 31, 2020 6:31 am

Thanks!
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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