Tower Eigenfrequencies of NREL 5MW Turbine

Discuss theory and modeling of wind-turbine structures.

Moderator: Bonnie.Jonkman

Michael.Harte
Posts: 12
Joined: Thu Jan 28, 2010 7:27 am

Re: Tower Eigenfrequencies of NREL 5MW Turbine

Postby Michael.Harte » Tue Aug 28, 2012 12:58 pm

Hi Dr Jonkman
First off thanks very much for your response and the attached document.

You are right when I disable the RNA DOFs, (and only have a 4 DOF system two tower modes in the s-s and f-a direction) I get the natural frequencies
0.27585 Hz
0.27768 Hz
1.654 Hz
1.8623 Hz
Which correspond very well to the natural frequencies recorded from Bmodes (given in my last post)

When the RNA DOFs are enabled in FAST the coupling does indeed produces different natural frequencies (for the tower) than those give by BModes
(again given in my last post) which is reasonable,
there seem to be a lot of coupling in the second tower s-s mode,
driving it up to 2.7Hz or so,
originally I just thought this seemed a bit high and assumed i was doing something wrong especially when i compared it to the tower natural frequencies given by NRELOffshrBsline5MW_Tower_Monopile_RF.dat,

Thanks from again for your response i think im using Bmodes correctly now.

Regards
Michael

Mark.Spring
Posts: 45
Joined: Fri Aug 03, 2012 3:45 am
Organization: Lloyd's Register Group
Location: United Kingdom
Location: Bristol, United Kingdom

Re: Tower Eigenfrequencies of NREL 5MW Turbine

Postby Mark.Spring » Wed Nov 14, 2012 8:11 am

I am about to try to build a monopile on which to put a 6.2MW wind turbine. We will need to build a completely new model of a wind turbine soon for certification of a commercial project. I would like to make sure that I understand how the tower modes are calculated and how the mean sea level is defined. I am also testing a modified version of FAST, including tower wind loads. The external aerodynamic loads ought to be applied only to the part of the tower between the mean sea level and the yaw bearing (!!). The model I have tested my new code on so far is the NREL 5MW onshore machine.

I am re-reading this forum to try to glean what I need to know about how such a model may be build, representing a wind turbine on an offshore monopile foundation.

Please can you tell me where I can get a copy of the following paper, which describes the contruction of a model of the NREL 5MW wind turbine on an offshore monopile foundation?

Jonkman, J., Butterfield, S., Passon, P., Larsen, T., Camp, T., Nichols, J., Azcona, J., and Martinez, A., “Offshore Code Comparison Collaboration within IEA Wind Annex XXIII: Phase II Results Regarding Monopile Foundation Modeling,” 2007 European Offshore Wind Conference & Exhibition, 4–6 December 2007, Berlin, Germany [online proceedings], BT2.1, URL: http://www.eow2007proceedings.info/allfiles2/ 206_Eow2007fullpaper.pdf

reference made from the following document
http://www.nrel.gov/docs/fy09osti/38060.pdf

Kind Regards,

Mark Spring (Lloyd's Register - Renewables Team)

Jason.Jonkman
Posts: 5071
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: Tower Eigenfrequencies of NREL 5MW Turbine

Postby Jason.Jonkman » Wed Nov 14, 2012 9:04 am

Dear Mark,

Here is a link to the NREL-published version of that paper: http://www.nrel.gov/docs/fy08osti/42471.pdf.

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

Mark.Spring
Posts: 45
Joined: Fri Aug 03, 2012 3:45 am
Organization: Lloyd's Register Group
Location: United Kingdom
Location: Bristol, United Kingdom

Re: Tower Eigenfrequencies of NREL 5MW Turbine

Postby Mark.Spring » Mon Nov 26, 2012 4:50 am

Dear All,

There has been mention in this forum about incorporating the functionality of BModes into FAST itself. At the beginning of a simulation, FAST could calculate (or recalculate) the structural modes (tower and blades separately) and incorporate new mode shapes and frequencies in the subsequent simulation.

Has this been done?
Is it still planned (given the modularisation program under way)?
Should we still be setting the logical inputs (CalcBMode and CalcTMode) always to FALSE?

Many thanks for an update on this issue.

Kind Regards,

Mark

Jason.Jonkman
Posts: 5071
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: Tower Eigenfrequencies of NREL 5MW Turbine

Postby Jason.Jonkman » Mon Nov 26, 2012 7:35 am

Dear Mark,

We are currently working at NREL to develop a new module for FAST with nonlinear beam finite elements (FE) for improved blade modeling. This module is based on the geometrically exact beam theory (GEBT) instead of BModes. We will also include an option to derive mode shapes from this FE model for use in an improved modal method (including, e.g., torsion). More information will be forthcoming.

In the current version of FAST, "yes," you should always set logic inputs CalcBMode and CalcTMode to False.

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

Michael.Harte
Posts: 12
Joined: Thu Jan 28, 2010 7:27 am

Re: Tower Eigenfrequencies of NREL 5MW Turbine

Postby Michael.Harte » Wed Jan 09, 2013 11:40 am

Hi all,
I've a question regarding placing an infinitely stiff Coupled Spring (CS) foundation matrix into FAST

I'm solving FAST for the 5MW monopile turbine sited in sallow water,

First I solved for a fixed base (FB) foundation and I use the linearization function and then an Eigenvalue analysis to get the natural frequencis of the turbine.
These are listed below. (All DOF are turned on)

I then place the CS stiffness matrix for the OC3 pile foundation (given by Memorandum: ''Derivation and Description of the Soil-Pile-Interaction Models'')
K_H = 2.58E9, K_M = 2.64E11 and K_HM = -2.26E10
into UserPtfmLd in UserSubs recompile get an new .exe FAST file and resolve my turbine.
This gives a new set of natural frequencies (the tower natural frequencies are reduced due to the softening effect of the foundation) this is all fine.
These are listed below:

Now to test that everything is working ok what I usually do is put in a very stiff foundation (infinitely stiff)
and check that the tower natural frequency are unaffected by the foundation (as the foundation should now have no effect because its so stiff)
With this in mind i changed the foundation stiff to very high values (ie inf)
K_H = 2.58E20, K_M = 2.64E22 and K_HM = -2.26E21

Again I put this inf stiff foundation into UserPtfmLd in UserSubs recompiled and get a .exe FAST
and then I used this to compute new natural frequencies, I expected these to match the fixed base results but the first tower natural frequencies are off
My question is why is this happening?? I find this a bit worrying

(note i also included an intermediately inf stiff foundation, OC3 foundation xx10000)
All the natural frequencies are listed below they are not sorted and simply arranged in ascending order

Code: Select all

FB   OC3foundation   OC3foundationx10000   inf
0   0.00016268   9.62E-05   9.66E-05
0.27895   0.23066   0.26168   0.30512
0.28385   0.2546   0.27737   0.34903
0.74414   0.74307   0.74408   0.74428
0.95032   0.94145   0.95587   0.95587
0.95484   0.94593   0.9604   0.9604
1.1408   1.1355   1.1444   1.1444
1.1502   1.1443   1.1541   1.1541
1.6537   1.4673   1.6538   1.6526
2.0708   1.5103   2.0706   2.071
2.2868   1.8306   2.2838   2.2898
2.3706   2.0825   2.3897   2.3897
2.3749   2.3433   2.3944   2.3944
2.6736   2.3469   2.6749   2.666
3.9406   3.8395   3.9406   3.9398
5.8528   5.3148   5.8528   5.8527
-        5.5238   214.04   1.07E+05
-        5.8584   214.36   1.07E+05
-        18.347   1619.9   3.23E+06
-         18.61   1620.5   3.23E+06

 



Also just to note when I am using a foundation I also recomputed the tower mode shapes using Bmodes,
Bmodes also gives an output of the tower natural frequencies these are listed below
When the foundation is infinitely stiff Bmodes gives useable results so i just used tower mode shapes from the fixed base case.

Interestingly Bmodes converges for a stiff foundation (stiffness matrix *10000) but breaks down for a very stiff foundation (inf).
(Just to note ive just listed the first 6 natural frequencies given by Bmodes for the inf stiff foundation)

Bmodes First two tower mode

Code: Select all

            
         
            
        FB    OC3foundation   OC3foundationx1000          inf
SS 1st   0.273744   0.242353   0.273744   0.001384
FA 1st   0.276006   0.243885    0.276006   0.005458
SS 2nd   1.588980   1.317520   1.328890   0.871748
FA 2nd   1.867030   1.498520    1.867030   0.923020
                                            1.330810
                                             2.220860
 


Thanks
Michael
Last edited by Michael.Harte on Wed Jan 09, 2013 11:48 am, edited 1 time in total.

Jason.Jonkman
Posts: 5071
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: Tower Eigenfrequencies of NREL 5MW Turbine

Postby Jason.Jonkman » Mon Jan 14, 2013 5:01 pm

Dear Michael,

I'm guessing the incorrect frequencies resulting from the use of an extremely large stiffness is simply the result of numerical errors in the solution process. In FAST, for example, the linearized stiffness matrix is derived from the nonlinear model through a central-difference numerical perturbation method. With such a large stiffness, the perturbation method will involve taking differences between large numbers, which may lead to numerical errors in the floating point math. Instead of setting very large stiffness, it is always better to disable DOFs, which you've done.

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

Michael.Harte
Posts: 12
Joined: Thu Jan 28, 2010 7:27 am

Re: Tower Eigenfrequencies of NREL 5MW Turbine

Postby Michael.Harte » Tue Jan 15, 2013 4:28 am

Ok, That makes sense.
Thanks for the response.

Regards
Michael

Rebecca.Sykes
Posts: 12
Joined: Tue Jan 10, 2012 3:08 am
Organization: Lloyd's Register
Location: United Kingdom

Re: Tower Eigenfrequencies of NREL 5MW Turbine

Postby Rebecca.Sykes » Fri Jan 18, 2013 7:51 am

Jason,

Can you tell me what the difference between BModes hosted on your site at http://wind.nrel.gov/public/jjonkman/BModes/ (JJ) and on the design codes website http://wind.nrel.gov/designcodes/ (DC) is.

Having looked at the source code for the design codes website and testing that hosted on JJ, it seems there is a difference in the options for tow_support. JJ allows 0 or 1, where 1 enables the read in of the platform properties and, I presume, the tension wires. The DC site allows 0, 1 for tension wires and 2 for the platform properties.

When testing the NREL 5MW monopile file CS_Monopile.bmi also hosted on your site with tow-support is 1 for JJ and tow_support is 2 for DC but all other parameters unchanged, the displacements caused by the first two modes (SS1 and FS1) are practically the same, but there is a difference in the mode shapes for the next two which are torsion/s-s modes, from one of which you would need to take the second s-s mode.

I have included comparison plots in the attached file.

All the best, Rebecca

JJ version

Code: Select all

 ******** modal analysis results **********

     eigenvalue(  1) =  0.211357D+11        mode  1 frequency =      0.242302
     eigenvalue(  2) =  0.214035D+11        mode  2 frequency =      0.243832
     eigenvalue(  3) =  0.628000D+12        mode  3 frequency =      1.320774
     eigenvalue(  4) =  0.674696D+12        mode  4 frequency =      1.368998
     eigenvalue(  5) =  0.835069D+12        mode  5 frequency =      1.523035
     eigenvalue(  6) =  0.288383D+13        mode  6 frequency =      2.830309
     eigenvalue(  7) =  0.375475D+13        mode  7 frequency =      3.229530
     eigenvalue(  8) =  0.133352D+14        mode  8 frequency =      6.086242
     eigenvalue(  9) =  0.143371D+14        mode  9 frequency =      6.310724
     eigenvalue( 10) =  0.180019D+14        mode 10 frequency =      7.071443
     eigenvalue( 11) =  0.506911D+14        mode 11 frequency =     11.866286
     eigenvalue( 12) =  0.517176D+14        mode 12 frequency =     11.985830
     eigenvalue( 13) =  0.917630D+14        mode 13 frequency =     15.965505
     eigenvalue( 14) =  0.138548D+15        mode 14 frequency =     19.617754
     eigenvalue( 15) =  0.139579D+15        mode 15 frequency =     19.690570
     eigenvalue( 16) =  0.258782D+15        mode 16 frequency =     26.811162
     eigenvalue( 17) =  0.287978D+15        mode 17 frequency =     28.283179
     eigenvalue( 18) =  0.311704D+15        mode 18 frequency =     29.425219
     eigenvalue( 19) =  0.312880D+15        mode 19 frequency =     29.480713
     eigenvalue( 20) =  0.617526D+15        mode 20 frequency =     41.416786


DC version

Code: Select all

 mode   1  frequency (hz) =      0.249
 mode   2  frequency (hz) =      0.250
 mode   3  frequency (hz) =      1.322
 mode   4  frequency (hz) =      1.375
 mode   5  frequency (hz) =      1.544
 mode   6  frequency (hz) =      2.781
 mode   7  frequency (hz) =      3.124
 mode   8  frequency (hz) =      6.039
 mode   9  frequency (hz) =      6.143
 mode  10  frequency (hz) =      7.292
 mode  11  frequency (hz) =     11.833
 mode  12  frequency (hz) =     11.911
 mode  13  frequency (hz) =     15.965
 mode  14  frequency (hz) =     19.594
 mode  15  frequency (hz) =     19.631
 mode  16  frequency (hz) =     26.877
 mode  17  frequency (hz) =     28.283
 mode  18  frequency (hz) =     29.405
 mode  19  frequency (hz) =     29.431
 mode  20  frequency (hz) =     41.417
Attachments
BMODESwebvsBmodesJJ.xls
(462 KiB) Downloaded 2904 times

Jason.Jonkman
Posts: 5071
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: Tower Eigenfrequencies of NREL 5MW Turbine

Postby Jason.Jonkman » Mon Jan 21, 2013 7:07 am

Dear Rebecca,

The version of BModes on http://wind.nrel.gov/public/jjonkman/BModes/ (JJ) is an unfinished version Gunjit Bir was working before he left NREL. The version was being developed to work for flexible foundations, offshore monopiles, and offshore floating wind turbines. More information is available in the forum post found here: viewtopic.php?f=4&t=541. Unfortunately, because it was unfinished, I am unsure of the all the differences between this version and the version uploaded to http://wind.nrel.gov/designcodes/preprocessors/bmodes/ (DC).

In your comparison between the two, how were you able to simulate the CS_Monopile.bmi in DC? Inputs such as "Draft" and "ref_msl" are available in JJ but not in DC and will certainly impact the results.

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

Rebecca.Sykes
Posts: 12
Joined: Tue Jan 10, 2012 3:08 am
Organization: Lloyd's Register
Location: United Kingdom

Re: Tower Eigenfrequencies of NREL 5MW Turbine

Postby Rebecca.Sykes » Tue Jan 22, 2013 9:25 am

Thanks for your reply Jason.

You made me question myself but I downloaded a new copy of the DC version from the website http://wind.nrel.gov/designcodes/preprocessors/bmodes/ to be sure. The additional supports section including draft etc. is included in the design codes website version. Line 590 onwards in bmodes.f90 are:

Code: Select all

  if ( tow_support == 2 ) then
   
 ! platform data
 
     CALL ReadVar ( UnIn, InFile, draft, 'draft', 'depth of tower base from the MSL (mean sea level) (m)'  )
     CALL ReadVar ( UnIn, InFile, cm_pform, 'cm_pform', 'distance of platform c.m. below the MSL (m)'      )
     CALL ReadVar ( UnIn, InFile, mass_pform, 'mass_pform', 'platform mass (kg)' )


Here is the header from the .out file for CS_monopile.bmi:

Code: Select all

Results generated by BModes (v3.00.00, 20-Mar-2008, compiled using double precision) on 22-Jan-2013 at 16:17:20.
NREL 5MW Tower   


and here is the echo file:

Code: Select all

            T  Echo           - Echo input file contents to *.echo file if true
            2  beam_type      - beam type, 1: blade; 2: tower
   0.0000E+00  rot_rpm        - rotor speed (rpm)
   1.0000E+00  rpm_mult       - rotor speed multiplicative factor
   8.7600E+01  radius         - rotor tip radius or tower height above ground (m)
   0.0000E+00  rroot          - hub radius or tower-base height (m)
   0.0000E+00  btp            - precone (deg)
   0.0000E+00  bl_thp         - blade pitch setting (deg)
            3  hub_conn       - hub-to-blade connectivity identifier
           20  modepr         - number of modes to be printed
            T  TabDelim       - output format (t: std; f: tab-delimited)
            F  mid_node_tw    - t: output twist at mid nodes; f: do otherwise
                                                                                                                                                                                                       
--------- Blade-tip or tower-top mass properties --------------------------------------------                                                                                                           
   3.5000E+05  tip_mass       - tip mass
  -4.1378E-01  cm_loc         - tip-mass c.m. location wrt the reference axis
   1.9670E+00  cm_axial       - tip-mass c.m. axial offset wrt tip
   4.3700E+07  ixx_tip        - mass moment of inertia about x axis (wt-specific)
   2.3530E+07  iyy_tip        - mass moment of inertia about y axis
   2.5420E+07  izz_tip        - mass moment of inertia about z axis
   0.0000E+00  ixy_tip        - cross product of inertia
   1.1690E+06  izx_tip        - cross product of inertia
   0.0000E+00  iyz_tip        - cross product of inertia
                                                                                                                                                                                                       
--------- Distributed-property identifiers --------------------------------------------------------                                                                                                     
            1  id_mat         - material isotropy identifier (not used; use later)
               sec_props_file - name of beam section properties file (-)
  "CS_monopile_tower_secs.dat"
                                                                                                                                                                                                       
Property scaling factors..............................                                                                                                                                                 
   1.0000E+00  sec_mass_mult  - mass density multiplier (-)
   1.0000E+00  flp_iner_mult  - blade flap or tower f-a inertia multiplier (-)
   1.0000E+00  lag_iner_mult  - blade lag or tower s-s inertia multiplier (-)
   1.0000E+00  flp_stff_mult  - blade flap or tower f-a bending stiffness multiplier (-)
   1.0000E+00  edge_stff_mult - blade lag or tower s-s bending stiffness multiplier (-)
   1.0000E+00  tor_stff_mult  - torsion stiffness multiplier (-)
   1.0000E+00  axial_stff_mul - axial stiffness multiplier (-)
   1.0000E+00  cg_offst_mult  - cg offset multiplier (-)
   1.0000E+00  sc_offst_mult  - shear center multiplier (-)
   1.0000E+00  tc_offst_mult  - tension center multiplier (-)
                                                                                                                                                                                                       
--------- Finite element discretization --------------------------------------------------                                                                                                             
           61  nselt          - number of blade or tower elements (-)
Distance of element boundary nodes from blade or flexible-tower root (normalized wrt blade or tower length), el_loc()                                                                                   
   0.0000E+00  el_loc         - array of normalized element locations (-)
   3.4819E-03  el_loc         - array of normalized element locations (-)
   1.0446E-02  el_loc         - array of normalized element locations (-)
   1.7409E-02  el_loc         - array of normalized element locations (-)
   2.4373E-02  el_loc         - array of normalized element locations (-)
   3.1337E-02  el_loc         - array of normalized element locations (-)
   3.8301E-02  el_loc         - array of normalized element locations (-)
   4.5265E-02  el_loc         - array of normalized element locations (-)
   5.2228E-02  el_loc         - array of normalized element locations (-)
   5.9192E-02  el_loc         - array of normalized element locations (-)
   6.6156E-02  el_loc         - array of normalized element locations (-)
   7.3120E-02  el_loc         - array of normalized element locations (-)
   8.0084E-02  el_loc         - array of normalized element locations (-)
   8.7047E-02  el_loc         - array of normalized element locations (-)
   9.4011E-02  el_loc         - array of normalized element locations (-)
   1.0097E-01  el_loc         - array of normalized element locations (-)
   1.0794E-01  el_loc         - array of normalized element locations (-)
   1.1490E-01  el_loc         - array of normalized element locations (-)
   1.2187E-01  el_loc         - array of normalized element locations (-)
   1.2883E-01  el_loc         - array of normalized element locations (-)
   1.3579E-01  el_loc         - array of normalized element locations (-)
   1.3990E-01  el_loc         - array of normalized element locations (-)
   1.4972E-01  el_loc         - array of normalized element locations (-)
   1.5669E-01  el_loc         - array of normalized element locations (-)
   1.6365E-01  el_loc         - array of normalized element locations (-)
   1.7061E-01  el_loc         - array of normalized element locations (-)
   1.7758E-01  el_loc         - array of normalized element locations (-)
   1.8454E-01  el_loc         - array of normalized element locations (-)
   1.9150E-01  el_loc         - array of normalized element locations (-)
   1.9847E-01  el_loc         - array of normalized element locations (-)
   2.0543E-01  el_loc         - array of normalized element locations (-)
   2.1240E-01  el_loc         - array of normalized element locations (-)
   2.1936E-01  el_loc         - array of normalized element locations (-)
   2.2632E-01  el_loc         - array of normalized element locations (-)
   2.3329E-01  el_loc         - array of normalized element locations (-)
   2.4025E-01  el_loc         - array of normalized element locations (-)
   2.4721E-01  el_loc         - array of normalized element locations (-)
   2.5070E-01  el_loc         - array of normalized element locations (-)
   3.2033E-01  el_loc         - array of normalized element locations (-)
   3.7971E-01  el_loc         - array of normalized element locations (-)
   4.2479E-01  el_loc         - array of normalized element locations (-)
   4.5961E-01  el_loc         - array of normalized element locations (-)
   4.8663E-01  el_loc         - array of normalized element locations (-)
   5.1366E-01  el_loc         - array of normalized element locations (-)
   5.4068E-01  el_loc         - array of normalized element locations (-)
   5.6770E-01  el_loc         - array of normalized element locations (-)
   5.9471E-01  el_loc         - array of normalized element locations (-)
   6.2173E-01  el_loc         - array of normalized element locations (-)
   6.4875E-01  el_loc         - array of normalized element locations (-)
   6.7577E-01  el_loc         - array of normalized element locations (-)
   7.0279E-01  el_loc         - array of normalized element locations (-)
   7.2981E-01  el_loc         - array of normalized element locations (-)
   7.5683E-01  el_loc         - array of normalized element locations (-)
   7.8385E-01  el_loc         - array of normalized element locations (-)
   8.1087E-01  el_loc         - array of normalized element locations (-)
   8.3789E-01  el_loc         - array of normalized element locations (-)
   8.6491E-01  el_loc         - array of normalized element locations (-)
   8.9192E-01  el_loc         - array of normalized element locations (-)
   9.1894E-01  el_loc         - array of normalized element locations (-)
   9.4596E-01  el_loc         - array of normalized element locations (-)
   9.7298E-01  el_loc         - array of normalized element locations (-)
   1.0000E+00  el_loc         - array of normalized element locations (-)
                                                                                                                                                                                                       
--------- Properties of tower support subsystem (read only if beam_type is 2) ------------                                                                                                             
            2  tow_support    - aditional tower support (-)
   2.0000E+01  draft          - depth of tower base from the MSL (mean sea level) (m)
   0.0000E+00  cm_pform       - distance of platform c.m. below the MSL (m)
   0.0000E+00  mass_pform     - platform mass (kg)
Platform mass inertia 3X3 matrix (i_matrix_pform):                                                                                                                                                     
   0.0000E+00  i_matrix_pform - platform inertia matrix-row1
   0.0000E+00  i_matrix_pform - platform inertia matrix-row1
   0.0000E+00  i_matrix_pform - platform inertia matrix-row1
   0.0000E+00  i_matrix_pform - platform inertia matrix-row2
   0.0000E+00  i_matrix_pform - platform inertia matrix-row2
   0.0000E+00  i_matrix_pform - platform inertia matrix-row2
   0.0000E+00  i_matrix_pform - platform inertia matrix-row3
   0.0000E+00  i_matrix_pform - platform inertia matrix-row3
   0.0000E+00  i_matrix_pform - platform inertia matrix-row3
   2.0000E+01  ref_msl        - distance of platform reference point below the MSL (m)
Platform-reference-point-referred hydrodynamic 6X6 matrix (hydro_M):                                                                                                                                   
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
   0.0000E+00  hydro_M        - platform added-mass inertia matrix
Platform-reference-point-referred hydrodynamic 6X6 stiffness matrix (hydro_K):                                                                                                                         
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
   0.0000E+00  hydro_K        - platform hydrodynamic stiffness matrix
Mooring-system 6X6 stiffness matrix (mooring_K):                                                                                                                                                       
   2.5748E+09  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
  -2.2532E+10  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   2.5748E+09  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   2.2532E+10  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   2.2532E+10  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   2.6291E+11  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
  -2.2532E+10  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   2.6291E+11  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
   0.0000E+00  mooring_K      - platform mooring-system stiffness matrix
                                                                                                                                                                                                       
Distributed (hydrodynamic) added-mass per unit length along a flexible portion of the tower length:                                                                                                     
            0  n_secs_m_distr - number of points at which added mass per unit length is specified (-)
                                                                                                                                                                                                       
Distributed elastic stiffness per unit length along a flexible portion of the tower length:                                                                                                             
            0  n_secs_k_distr - number of points at which distributed stiffness per unit length is specified (-)
Tower section properties                                                                                                                                                                               
           13  n_secs         - number of blade or tower sections (-)
                                                                                                                                                                                                       
sec_loc  str_tw  tw_iner   mass_den  flp_iner  edge_iner  flp_stff   edge_stff   tor_stff   axial_stff  cg_offst  sc_offst tc_offst                                                                     
(-)      (deg)    (deg)    (kg/m)     (kg-m)    (kg-m)     (Nm^2)     (Nm^2)      (Nm^2)       (N)        (m)       (m)      (m)                                                                       
0.00000     0.000     0.000  9517.140 41979.200 41979.200  1.04E+12  1.04E+12  7.98E+11  2.35E+11     0.000     0.000     0.000
0.27881     0.000     0.000  9517.140 41979.200 41979.200  1.04E+12  1.04E+12  7.98E+11  2.35E+11     0.000     0.000     0.000
0.27882     0.000     0.000  4306.510 19205.600 19205.600  4.74E+11  4.74E+11  3.65E+11  1.06E+11     0.000     0.000     0.000
0.35094     0.000     0.000  4030.440 16720.000 16720.000  4.13E+11  4.13E+11  3.18E+11  9.96E+10     0.000     0.000     0.000
0.42306     0.000     0.000  3763.450 14483.400 14483.400  3.58E+11  3.58E+11  2.75E+11  9.30E+10     0.000     0.000     0.000
0.49517     0.000     0.000  3505.520 12478.700 12478.700  3.08E+11  3.08E+11  2.37E+11  8.66E+10     0.000     0.000     0.000
0.56729     0.000     0.000  3256.660 10689.200 10689.200  2.64E+11  2.64E+11  2.03E+11  8.05E+10     0.000     0.000     0.000
0.63941     0.000     0.000  3016.860  9098.900  9098.900  2.25E+11  2.25E+11  1.73E+11  7.45E+10     0.000     0.000     0.000
0.71153     0.000     0.000  2786.130  7692.700  7692.700  1.90E+11  1.90E+11  1.46E+11  6.88E+10     0.000     0.000     0.000
0.78365     0.000     0.000  2564.460  6455.700  6455.700  1.59E+11  1.59E+11  1.23E+11  6.34E+10     0.000     0.000     0.000
0.85576     0.000     0.000  2351.870  5373.900  5373.900  1.33E+11  1.33E+11  1.02E+11  5.81E+10     0.000     0.000     0.000
0.92788     0.000     0.000  2148.340  4433.600  4433.600  1.10E+11  1.10E+11  8.43E+10  5.31E+10     0.000     0.000     0.000
1.00000     0.000     0.000  1953.870  3622.100  3622.100  8.95E+10  8.95E+10  6.89E+10  4.83E+10     0.000     0.000     0.000


All the best,
Rebecca

Jason.Jonkman
Posts: 5071
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: Tower Eigenfrequencies of NREL 5MW Turbine

Postby Jason.Jonkman » Tue Jan 22, 2013 11:43 am

Dear Rebecca,

OK, I was unaware that those inputs even existed in the DC version (v3.00.00) of BModes. None of the sample models in the BModes CertTest have those inputs. It is difficult to support BModes now that the developer has left NREL.

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

Wystan.Carswell
Posts: 4
Joined: Wed Mar 13, 2013 6:24 am
Organization: University of Massachusetts Amherst
Location: Massachusetts

Re: Tower Eigenfrequencies of NREL 5MW Turbine

Postby Wystan.Carswell » Fri Mar 15, 2013 7:20 am

Hello,
My question regards BModes vs. Modes. I understand that BModes is the currently recommended pre-processor for obtaining FAST-input mode shapes. However, when I used Table 6-1 from the Definition of a 5MW Reference Turbine report for the inputs to BModes and Modes, my results indicated Modes was closer to the NREL distributed mode shapes/frequencies than the results from BModes. As an example, the fore-aft frequency result for Mode 2 from BModes was 2.2416 Hz vs. Modes 2.9405 Hz vs. NREL (from Table 9-1 in "Definition") 2.8590.

Perhaps I've entered something incorrectly in my BModes input file to cause this discrepancy?
Here are my tower sections:

Code: Select all

[size=85]Tower section properties (NREL 5MW Onshore Reference Turbine)
11        n_secs:     number of blade or tower sections at which properties are specified (-)

sec_loc  str_tw  tw_iner  mass_den flp_iner  edge_iner  flp_stff    edge_stff     tor_stff    axial_stff  cg_offst  sc_offst tc_offst
(-)      (deg)    (deg)   (kg/m)    (kg-m)    (kg-m)     (Nm^2)      (Nm^2)        (Nm^2)        (N)         (m)       (m)     (m)
0       0   0   5590.87     24866.3   24866.3   6.14E+11   6.14E+11   4.73E+11   1.38E+11   0   0   0
0.1     0   0   5232.43    21647.5   21647.5   5.35E+11   5.35E+11   4.12E+11   1.29E+11   0   0   0
0.2     0   0   4885.76    18751.3   18751.3   4.63E+11   4.63E+11   3.56E+11   1.21E+11   0   0   0
0.3     0   0   4550.87     16155.3   16155.3   3.99E+11   3.99E+11   3.07E+11   1.12E+11   0   0   0
0.4    0   0   4227.75     13838.1   13838.1   3.42E+11   3.42E+11   2.63E+11   1.04E+11   0   0   0
0.5    0   0   3916.41    11779   11779   2.91E+11   2.91E+11   2.24E+11   9.68E+10   0   0   0
0.6     0   0   3616.83     9958.2   9958.2   2.46E+11   2.46E+11   1.89E+11   8.94E+10   0   0   0
0.7     0   0   3329.03     8356.6   8356.6   2.06E+11   2.06E+11   1.59E+11   8.22E+10   0   0   0
0.8     0   0   3053.01     6955.9   6955.9   1.72E+11   1.72E+11   1.32E+11   7.54E+10   0   0   0
0.9     0   0   2788.75     5738.6   5738.6   1.42E+11   1.42E+11   1.09E+11   6.89E+10   0   0   0
1       0   0   2536.27     4688   4688   1.16E+11   1.16E+11   8.91E+10   6.27E+10   0   0   0

**Note: If this file is for a TOWER, the following section properties are read but overwritten as follows:
  str_tw is set to zero
  tw_iner is set to zero
  cg_offst is set to zero
  sc_offst is set to zero
  tc_offst is set to zero
  edge_iner is set equal to flp_iner
  edge_stff is set equal to flp_stff[/size]


And here is my .bmi input file (I copied the tower top mass properties from the CS_Monopile .dat-file).

Code: Select all

[size=85]======================   BModes v1.03 Main Input File  ==================
Modes of ORT tower (89.6 m) with tip mass 350e3 kg

--------- General parameters ---------------------------------------------------------------------
False     Echo        Echo input file contents to *.echo file if true.
2         beam_type   1: blade, 2: tower (-)
0.        romg:       rotor speed (rpm), automatically set to zero for tower modal analysis
1.0       romg_mult:  rotor speed muliplicative factor (-)
87.6      radius:     rotor tip radius measured along coned blade axis OR tower height (m)
0.        hub_rad:    hub radius measured along coned blade axis OR tower rigid-base height (m)
0.        precone:    built-in precone angle (deg), automatically set to zero for a tower
0.        bl_thp:     blade pitch setting (deg), automatically set to zero for a tower
1         hub_conn:   hub-to-blade connection [1: cantilevered; other options not yet available]
7         modepr:     number of modes to be printed (-)
f         TabDelim    (true: tab-delimited output tables; false: space-delimited tables)
f         mid_node_tw  (true: output twist at mid-node of elements; false: no mid-node outputs)

--------- Blade-tip or tower-top mass properties --------------------------------------------
3.500003109E+005   tip_mass    blade-tip or tower-top mass (kg)
-0.4137754432      cm_loc      tip-mass c.m. offset from the tower axis measured along x-tower axis (m)
1.9669893542       cm_axial    tip-mass c.m. offset tower tip measures axially along the z axis (m)
4.370E7            ixx_tip     blade lag mass moment of inertia about the tip-section x reference axis (kg-m^2)
2.353E7            iyy_tip     blade flap mass moment of inertia about the tip-section y reference axis (kg-m^2)
2.542E7            izz_tip     torsion mass moment of inertia about the tip-section z reference axis (kg-m^2)
0.                 ixy_tip     cross product of inertia about x and y reference axes(kg-m^2)
1.169E6            izx_tip     cross product of inertia about z and x reference axes(kg-m^2)
0.                 iyz_tip     cross product of inertia about y and z reference axes(kg-m^2)

--------- Distributed-property identifiers --------------------------------------------------------
1         id_mat:     material_type [1: isotropic; non-isotropic composites option not yet available]
'ORT_props.dat' sec_props_file   name of beam section properties file (-)

Property scaling factors..............................
1.0       sec_mass_mult:   mass density multiplier (-)
1.0       flp_iner_mult:   blade flap or tower f-a inertia multiplier (-)
1.0       lag_iner_mult:   blade lag or tower s-s inertia multiplier (-)
1.0       flp_stff_mult:   blade flap or tower f-a bending stiffness multiplier (-)
1.0       edge_stff_mult:  blade lag or tower s-s bending stiffness multiplier (-)
1.0       tor_stff_mult:   torsion stiffness multiplier (-)
1.0       axial_stff_mult: axial stiffness multiplier (-)
1.0       cg_offst_mult:   cg offset multiplier (-)
1.0       sc_offst_mult:   shear center multiplier (-)
1.0       tc_offst_mult:   tension center multiplier (-)

--------- Finite element discretization --------------------------------------------------
61        nselt:     no of blade or tower elements (-)
Distance of element boundary nodes from blade or flexible-tower root (normalized wrt blade or tower length), el_loc()
0   0.003481894   0.010445682   0.017409471   0.024373259   0.031337047   0.038300836   0.045264624   0.052228412   0.059192201   0.066155989   0.073119777   0.080083565   0.087047354   0.094011142   0.10097493   0.107938719   0.114902507   0.121866295   0.128830084   0.135793872    0.13990   0.149721448   0.156685237   0.163649025   0.170612813   0.177576602   0.18454039   0.191504178   0.198467967   0.205431755   0.212395543   0.219359331   0.22632312   0.233286908   0.240250696   0.247214485   0.250696379   0.320334262    0.37971    0.424791072   0.45961   0.486635   0.51366   0.54068   0.5677   0.594715   0.62173   0.64875   0.67577   0.70279   0.72981   0.75683   0.78385   0.81087   0.83789   0.864905   0.89192   0.91894   0.94596   0.97298   1.0

--------- Properties of additional tower support subsystem (read only if beam_type is 2) ------------
0         tow_support: : additional tower support [0: no additional support; 1: Tension guy wires for land-based tower; 2: offshore turbine support: floating platform or monopile] (-)
Tension-wires data
0         n_attachments: no of wire-attachment locations on tower, maxm allowable is 2; 0: no tension-wire support (-)
3 3       n_wires:       no of wires attached at each location (must be 3 or higher) (-)
6 9       node_attach:   node numbers of attacments location (node number must be more than 1 and less than nselt+2) (-)
1.e8 1.e8 wire_stfness:  wire sifnness in each set (see users' manual) (N/m)
45. 45.   th_wire:       angle of tension wires (wrt a horizontal plane) at each attachment point (deg)
[/size]


Kind Regards,

Wystan Carswell

Jason.Jonkman
Posts: 5071
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: Tower Eigenfrequencies of NREL 5MW Turbine

Postby Jason.Jonkman » Fri Mar 15, 2013 10:07 am

Dear Wystan,

Your BModes input files look fine to me. For an explanation on why your BModes results are not matching the results from Table 9-1 for the 2nd tower fore-aft mode, please see my Aug 28, 2012 post in this forum topic above. My guess is if Modes is matching the results from Table 9-1 better than BModes, that this is only coincidental. In general, BModes will be more accurate than Modes.

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

Hamid.Hokmabady
Posts: 17
Joined: Wed Apr 17, 2013 2:10 am
Organization: University
Location: Iran

Re: Tower Eigenfrequencies of NREL 5MW Turbine

Postby Hamid.Hokmabady » Tue Oct 15, 2013 2:52 am

Hello everyone!

I'm new in this topic; I read most of posts of this topic and the others but I didn't get to my answer;
I'm working on a NREL 5MW offshore TLP; and in my research the first mode and frequency of the structure is necessary; I searched for this frequency and how I can get to that;
for using BMode I need an input file for 5MW TLP but I didn't find any! should I make one? or is there any?
and also I didn't find the frequency or modes in the output table of User Guide as a result of the BMode!! how can I get to this structures frequency?
After BMode is there something else that I have to do to get to the result?

Sincerely
Hamid
-----
Hamid Hokmabady
M.Sc Student of Civil Engineering
Tabriz University
Tabriz
Iran


Return to “Structural Analysis”

Who is online

Users browsing this forum: No registered users and 1 guest