NREL 5MW Blade Mode Shape

Discuss theory and modeling of wind-turbine structures.

Moderator: Bonnie.Jonkman

Xiao.Sun
Posts: 36
Joined: Fri Jul 12, 2013 2:59 pm
Organization: Michigan Technological University
Location: U.S. state

NREL 5MW Blade Mode Shape

Postby Xiao.Sun » Thu Mar 12, 2015 7:39 pm

Hello Everyone,

I am trying to incorporate a smart controlled flap to the NREL 5MW blades and analyze the structural response.
In order to do that, I have to compute the blade mode shape for the blade with flap.
I decided to use the BModes to calculate the mode shape for the original NREL 5MW blades at the beginning to validate my simulation procedure and calibrate some parameters.
However, when I was doing the calculation, the result doesn't match the values given in the CertTest "NRELOffshrBsline5MW_Blade.dat".

My input file for BModes is based on the report "Definition of a 5-MW Reference Wind Turbine for Offshore System Development"

And result:
flap mode 1 from the CertTest
0.0622 BldFl1Sh(2)
1.7254 BldFl1Sh(3)
-3.2452 BldFl1Sh(4)
4.7131 BldFl1Sh(5)
-2.2555 BldFl1Sh(6)

From BModes
-0.0732
2.8556
-6.5268
8.5360
-3.7916

If plot the polynomial, one can see that they are different.
I thought it might be due to the rotational speed. However, I tried several different speed and it didn't work out.

Can anyone help me?

Thanks

Code: Select all

======================   BModes v1.03 Main Input File  ==================
Original 5MW blade (output is space-delimited)

--------- General parameters ---------------------------------------------------------------------
False     Echo        Echo input file contents to *.echo file if true.
1         beam_type   1: blade, 2: tower (-)
12.1      romg:       rotor speed, automatically set to zero for tower modal analysis (rpm)
1.0       romg_mult:  rotor speed muliplicative factor (-)
63        radius:     rotor tip radius measured along coned blade axis OR tower height (m)
1.5       hub_rad:    hub radius measured along coned blade axis OR tower rigid-base height (m)
-2.5      precone:    built-in precone angle, automatically set to zero for a tower (deg)
0.        bl_thp:     blade pitch setting, automatically set to zero for a tower (deg)
1         hub_conn:   hub-to-blade connection [1: cantilevered; other options not yet available] (-)
20        modepr:     number of modes to be printed (-)
f         TabDelim    (true: tab-delimited output tables; false: space-delimited tables)
t         mid_node_tw  (true: output twist at mid-node of elements; false: no mid-node outputs)

--------- Blade-tip or tower-top mass properties --------------------------------------------
0.0        tip_mass    blade-tip or tower-top mass (kg)
0.0        cm_loc      tip-mass c.m. offset from the blade axis measured along the tip section y reference axis (m)
0.0        cm_axial    tip-mass c.m. offset tower tip measures axially along the z axis (m)
0.0        ixx_tip     blade lag mass moment of inertia about the tip-section x reference axis (kg-m^2)
0.0        iyy_tip     blade flap mass moment of inertia about the tip-section y reference axis (kg-m^2)
0.0        izz_tip     torsion mass moment of inertia about the tip-section z reference axis (kg-m^2)
0.0        ixy_tip     cross product of inertia about x and y reference axes(kg-m^2)
0.0        izx_tip     cross product of inertia about z and x reference axes(kg-m^2)
0.0        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]
'5MWblade_sec_props.dat' sec_props_file   name of beam section properties file (-)

Property scaling factors..............................
1.04536       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 --------------------------------------------------
48      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 0.00325 0.01951 0.03577 0.05203 0.06829 0.08455 0.10081 0.11707 0.13335 0.14959 0.16585 0.18211 0.19837 0.21465 0.23089 0.24715 0.26341 0.29595   
0.32846   0.36098   0.3935   0.42602   0.45855   0.49106   0.52358   0.5561   0.58862   0.62115   0.65366   0.68618   0.7187   0.75122   0.78376   0.81626   0.84878   0.8813   
0.89756   0.91382   0.93008   0.93821   0.94636   0.95447   0.9626   0.97073   0.97886   0.98699   0.99512   1      

--------- Properties of tension wires suporting the tower --------------------------------
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) (-)
0.e0 0.e0 wire_stfness:  wire spring constant in each set (see users' manual) (N/m)
0. 0.     th_wire:       angle of tension wires wrt the tower axis at each attachment point (deg)



Code: Select all

Blade section properties
49        n_secs:     number of blade 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)
0.00000   13.308   13.308   678.935   972.860   973.040   1.81100E+10   1.81136E+10   5.56440E+09   9.72948E+09   0.00017   0   0
0.00325   13.308   13.308   678.935   972.860   973.040   1.81100E+10   1.81136E+10   5.56440E+09   9.72948E+09   0.00017   0   0
0.01951   13.308   13.308   773.363   1091.520   1066.380   1.94249E+10   1.95586E+10   5.43159E+09   1.07895E+10   0.02309   0   0
0.03577   13.308   13.308   740.550   966.090   1047.360   1.74559E+10   1.94978E+10   4.99398E+09   1.00672E+10   0.00344   0   0
0.05203   13.308   13.308   740.042   873.810   1099.750   1.52874E+10   1.97888E+10   4.66659E+09   9.86778E+09   0.04345   0   0
0.06829   13.308   13.308   592.496   648.550   873.020   1.07824E+10   1.48585E+10   3.47471E+09   7.60786E+09   0.05893   0   0
0.08455   13.308   13.308   450.275   456.760   641.490   7.22972E+09   1.02206E+10   2.32354E+09   5.49126E+09   0.06494   0   0
0.10081   13.308   13.308   424.054   400.530   593.730   6.30954E+09   9.14470E+09   1.90787E+09   4.97130E+09   0.07718   0   0
0.11707   13.308   13.308   400.638   351.610   547.180   5.52836E+09   8.06316E+09   1.57036E+09   4.49395E+09   0.08394   0   0
0.13335   13.308   13.308   382.062   316.120   490.840   4.98006E+09   6.88444E+09   1.15826E+09   4.03480E+09   0.10174   0   0
0.14959   13.308   13.308   399.655   303.600   503.860   4.93684E+09   7.00918E+09   1.00212E+09   4.03729E+09   0.10758   0   0
0.16585   13.308   13.308   426.321   289.240   544.700   4.69166E+09   7.16768E+09   8.55900E+08   4.16972E+09   0.15829   0   0
0.18211   13.181   13.181   416.820   246.570   569.900   3.94946E+09   7.27166E+09   6.72270E+08   4.08235E+09   0.22235   0   0
0.19837   12.848   12.848   406.186   215.910   601.280   3.38652E+09   7.08170E+09   5.47490E+08   4.08597E+09   0.30756   0   0
0.21465   12.192   12.192   381.420   187.110   546.560   2.93374E+09   6.24453E+09   4.48840E+08   3.66834E+09   0.30386   0   0
0.23089   11.561   11.561   352.822   160.840   468.710   2.56896E+09   5.04896E+09   3.35920E+08   3.14776E+09   0.26519   0   0
0.24715   11.072   11.072   349.477   148.560   453.760   2.38865E+09   4.94849E+09   3.11350E+08   3.01158E+09   0.25941   0   0
0.26341   10.792   10.792   346.538   140.300   436.220   2.27199E+09   4.80802E+09   2.91940E+08   2.88262E+09   0.25007   0   0
0.29595   10.232   10.232   339.333   124.610   398.180   2.05005E+09   4.50140E+09   2.61000E+08   2.61397E+09   0.23155   0   0
0.32846   9.672   9.672   330.004   109.420   362.080   1.82825E+09   4.24407E+09   2.28820E+08   2.35748E+09   0.20382   0   0
0.36098   9.110   9.110   321.990   94.360   335.010   1.58871E+09   3.99528E+09   2.00750E+08   2.14686E+09   0.19934   0   0
0.39350   8.534   8.534   313.820   80.240   308.570   1.36193E+09   3.75076E+09   1.74380E+08   1.94409E+09   0.19323   0   0
0.42602   7.932   7.932   294.734   62.670   263.870   1.10238E+09   3.44714E+09   1.44470E+08   1.63270E+09   0.14994   0   0
0.45855   7.321   7.321   287.120   49.420   237.060   8.75800E+08   3.13907E+09   1.19980E+08   1.43240E+09   0.15421   0   0
0.49106   6.711   6.711   263.343   37.340   196.410   6.81300E+08   2.73424E+09   8.11900E+07   1.16876E+09   0.13252   0   0
0.52358   6.122   6.122   253.207   29.140   180.340   5.34720E+08   2.55487E+09   6.90900E+07   1.04743E+09   0.13313   0   0
0.55610   5.546   5.546   241.666   22.160   162.430   4.08900E+08   2.33403E+09   5.74500E+07   9.22950E+08   0.14035   0   0
0.58862   4.971   4.971   220.638   17.330   134.830   3.14540E+08   1.82873E+09   4.59200E+07   7.60820E+08   0.1395   0   0
0.62115   4.401   4.401   200.293   13.300   116.300   2.38630E+08   1.58410E+09   3.59800E+07   6.48030E+08   0.15134   0   0
0.65366   3.834   3.834   179.404   9.960   97.980   1.75880E+08   1.32336E+09   2.74400E+07   5.39700E+08   0.17418   0   0
0.68618   3.332   3.332   165.094   7.300   98.930   1.26010E+08   1.18368E+09   2.09000E+07   5.31150E+08   0.24922   0   0
0.71870   2.890   2.890   154.411   6.220   85.780   1.07260E+08   1.02016E+09   1.85400E+07   4.60010E+08   0.26022   0   0
0.75122   2.503   2.503   138.935   5.190   69.960   9.08800E+07   7.97810E+08   1.62800E+07   3.75750E+08   0.22554   0   0
0.78376   2.116   2.116   129.555   4.360   61.410   7.63100E+07   7.09610E+08   1.45300E+07   3.28890E+08   0.22795   0   0
0.81626   1.730   1.730   107.264   3.360   45.440   6.10500E+07   5.18190E+08   9.07000E+06   2.44040E+08   0.206   0   0
0.84878   1.342   1.342   98.776   2.750   39.570   4.94800E+07   4.54870E+08   8.06000E+06   2.11600E+08   0.21662   0   0
0.88130   0.954   0.954   90.248   2.210   34.090   3.93600E+07   3.95120E+08   7.08000E+06   1.81520E+08   0.22784   0   0
0.89756   0.760   0.760   83.001   1.930   30.120   3.46700E+07   3.53720E+08   6.09000E+06   1.60250E+08   0.23124   0   0
0.91382   0.574   0.574   72.906   1.690   20.150   3.04100E+07   3.04730E+08   5.75000E+06   1.09230E+08   0.14826   0   0
0.93008   0.404   0.404   68.772   1.490   18.530   2.65200E+07   2.81420E+08   5.33000E+06   1.00080E+08   0.15346   0   0
0.93821   0.319   0.319   66.264   1.340   17.110   2.38400E+07   2.61710E+08   4.94000E+06   9.22400E+07   0.15382   0   0
0.94636   0.253   0.253   59.340   1.100   11.550   1.96300E+07   1.58810E+08   4.24000E+06   6.32300E+07   0.0947   0   0
0.95447   0.216   0.216   55.914   0.890   9.770   1.60000E+07   1.37880E+08   3.66000E+06   5.33200E+07   0.09018   0   0
0.96260   0.178   0.178   52.484   0.710   8.190   1.28300E+07   1.18790E+08   3.13000E+06   4.45300E+07   0.08561   0   0
0.97073   0.140   0.140   49.114   0.560   6.820   1.00800E+07   1.01630E+08   2.64000E+06   3.69000E+07   0.08035   0   0
0.97886   0.101   0.101   45.818   0.420   5.570   7.55000E+06   8.50700E+07   2.17000E+06   2.99200E+07   0.07096   0   0
0.98699   0.062   0.062   41.669   0.250   4.010   4.60000E+06   6.42600E+07   1.58000E+06   2.13100E+07   0.05424   0   0
0.99512   0.023   0.023   11.453   0.040   0.940   2.50000E+05   6.61000E+06   2.50000E+05   4.85000E+06   0.05387   0   0
1.00000   0.000   0.000   10.319   0.020   0.680   1.70000E+05   5.01000E+06   1.90000E+05   3.53000E+06   0.05181   0   0



**Note: If the above data represents TOWER properties, the following are overwritten:
  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


Xiao.Sun
Posts: 36
Joined: Fri Jul 12, 2013 2:59 pm
Organization: Michigan Technological University
Location: U.S. state

Re: NREL 5MW Blade Mode Shape

Postby Xiao.Sun » Mon Mar 16, 2015 1:39 pm

Problem solved. Set the rotation speed to zero

Jason.Jonkman
Posts: 5763
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: NREL 5MW Blade Mode Shape

Postby Jason.Jonkman » Wed Mar 18, 2015 6:32 pm

Dear Xiao,

It sounds like you've now obtained satisfactory results, but I thought I'd provide a few comments.

First, when the NREL 5-MW turbine FAST models were first made, BModes was not yet available. Instead, we used the old Modes tool to derive the blade mode shapes; I would expect some differences between the resulting mode shapes between Modes and BModes (with BModes being more accurate).

Second, we typically derive mode shapes for FAST based on nominal operating conditions--e.g. rotor speed and pitch angle at rated speed, although you could check the sensitivity of the mode shapes for different operating conditions.

Third, the blade structural model in FAST v7 and the ElastoDyn module of FAST v8 only takes into account flapwise and edgewise bending (with no axial, torsional, or shear DOFs) for a straight beam of isotropic material with no mass or elastic offsets, and coupling arising only from structural pretwist. Moreover, the coupling due to structural pretwist is introduced in the model at runtime, but the specified mode shapes are expected to be entered separately for flap and edge. You are using BModes to derive mode shapes for FAST, so, you want the BModes model to be consistent with FAST. I suggest the following values in BModes when deriving blade mode shapes for FAST:

str_tw = 0 (to uncouple the derived flapwise and edgewise modes, which are then coupled through the structural pretwist specified in FAST)
tw_iner = 0
flp_iner = very small number (you can't specify exactly zero for this input in BModes)
edge_iner = very small number
tor_stff = very high number (BModes won't allow infinite; just set it high enough that it doesn't impact the BModes results for the modes you care about)
axial_stff = very high number
cg_offst = 0
sc_offst = 0
tc_offst = 0

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

Xiao.Sun
Posts: 36
Joined: Fri Jul 12, 2013 2:59 pm
Organization: Michigan Technological University
Location: U.S. state

Re: NREL 5MW Blade Mode Shape

Postby Xiao.Sun » Thu Mar 19, 2015 3:08 pm

Dear Jason,

Thank you for you explanation.
I found that the mode shape from BMode is very similar for the different rotational speed. Maybe it is due to the range for my case is very narrow, from 0 to 12.1 rpm.
However, the natural frequencies are very sensitive to the rotor speed.
Only when the rotor speed is zero, the result of 5MW blades can match the frequencies from the CertTest.
However, it is not realistic case. For my case, I want to set it to rated rotor speed and rated wind speed.
I didn't see FAST using these frequencies during the run time.
Does it affect the simulation results?

Best Regards,
Xiao

Paul.Feja
Posts: 16
Joined: Thu Aug 03, 2017 6:00 am
Organization: Fraunhofer IWES
Location: Germany

Re: NREL 5MW Blade Mode Shape

Postby Paul.Feja » Mon Jul 16, 2018 3:16 am

Jason.Jonkman wrote:I suggest the following values in BModes when deriving blade mode shapes for FAST:

str_tw = 0 (to uncouple the derived flapwise and edgewise modes, which are then coupled through the structural pretwist specified in FAST)
tw_iner = 0
flp_iner = very small number (you can't specify exactly zero for this input in BModes)
edge_iner = very small number
tor_stff = very high number (BModes won't allow infinite; just set it high enough that it doesn't impact the BModes results for the modes you care about)
axial_stff = very high number
cg_offst = 0
sc_offst = 0
tc_offst = 0


Hi Jason,

after reading also viewtopic.php?f=4&t=1657&p=7733&hilit=elastodyn+shapes#p7733 I have a question why you would recommend setting both flap and edge inertias to zero for mode shape determination. In my understanding the proper combination of mass and stiffness would lead to the correct eigenfrequencies and mode shapes, so I am a bit confused why you suggest setting the inertias to (almost) zero. Or will the mode shape purely be calculated out of the mass distribution?

There is another thing that just came to my mind: you said that you usually use rated rotation speed for mode shape determination, but in the thread referenced above Xiao Sun stated:

Xiao.Sun wrote:I found that the mode shape from BMode is very similar for the different rotational speed. Maybe it is due to the range for my case is very narrow, from 0 to 12.1 rpm.
However, the natural frequencies are very sensitive to the rotor speed.
Only when the rotor speed is zero, the result of 5MW blades can match the frequencies from the CertTest.
However, it is not realistic case. For my case, I want to set it to rated rotor speed and rated wind speed.
I didn't see FAST using these frequencies during the run time.
Does it affect the simulation results?


which hasn't been answered yet. So would you advise to use rated rotor speed or zero rotor speed for the mode shape determination with BModes? Considering that mode shapes match best at zero rpm while the frequencies might be more accurate at rated rotor speed...

Best
Paul

Jason.Jonkman
Posts: 5763
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: NREL 5MW Blade Mode Shape

Postby Jason.Jonkman » Mon Jul 16, 2018 11:05 pm

Dear Paul,

I recommended that the flapwise and edgewise inertias be very small so that BModes and FAST/ElastoDyn are modeling the same thing (i.e. FAST/ElastoDyn neglect the flapwise and edgewise inertias; the effect of the inertias on the mode shapes and dynamic response should be negligible for high-aspect ratio beams).

Xiao.Sun mentioned that the natural frequencies match best at zero rpm, but that the mode shapes where not much effected by rotational speed. It is certainly true that the blade natural frequencies are strongly effected by the rotor rotational speed. I'm not sure I understand Xiao.Sun's question about frequencies, as these are not actually input to FAST. However, FAST certainly considers the impact of rotor rotational speed on natural frequencies. I would still recommend to derive mode shapes at the rated rotor speed, but you could always perform a sensitivity analysis on the impact of mode shapes derived from different rotational speeds on the dynamic response of FAST.

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

Paul.Feja
Posts: 16
Joined: Thu Aug 03, 2017 6:00 am
Organization: Fraunhofer IWES
Location: Germany

Re: NREL 5MW Blade Mode Shape

Postby Paul.Feja » Tue Jul 17, 2018 5:35 am

Hi Jason,

thank you for the quick answer. You're right, the only output from BModes to FAST would be the mode shapes, so it doesn't really matter what frequency BModes calculates, at least not in this case. I haven't thought about this when asking my question.

Best regards,
Paul

Soeren.Link
Posts: 3
Joined: Sat Jan 09, 2021 1:00 pm
Organization: Flensburg University of Applied Sciences
Location: Deutschland

Re: NREL 5MW Blade Mode Shape

Postby Soeren.Link » Mon Mar 08, 2021 2:56 pm

Hi,

I am pretty new in using BModes and am trying to get the modes shapes for blades to insert them to the ElastoDyn module but the output of the mode shapes computed by BModes are (for me) looking strange since they are not fitting the typical mode shapes and their zero crossing of higher modes. The following is the content of my output file:

-------- Mode No. 1 (freq = 0.79631E+00 Hz)

span_loc flap disp flap slope lag disp lag slope twist

0.0000 0.000000 0.000000 0.000000 0.000000 0.000000
0.0800 0.000025 0.000634 -0.000206 -0.005170 0.000000
0.1600 0.000108 0.001482 -0.000856 -0.011350 0.000000
0.2400 0.000292 0.003120 -0.002138 -0.021304 0.000000
0.3200 0.000603 0.004715 -0.004320 -0.034302 0.000000
0.4000 0.001120 0.008294 -0.008537 -0.072570 0.000000
0.4800 0.001925 0.011973 -0.016339 -0.125417 0.000000
0.5600 0.003009 0.015505 -0.028988 -0.195628 0.000000
0.6400 0.004333 0.018100 -0.047274 -0.269040 0.000000
0.7200 0.005825 0.019851 -0.071925 -0.356602 0.000000
0.8000 0.007414 0.020766 -0.102888 -0.429997 0.000000
0.9000 0.009465 0.021194 -0.147754 -0.480274 0.000000
1.0000 0.011534 0.021243 -0.195399 -0.491675 0.000000


-------- Mode No. 2 (freq = 0.19677E+01 Hz)

span_loc flap disp flap slope lag disp lag slope twist

0.0000 0.000000 0.000000 0.000000 0.000000 0.000000
0.0800 0.000877 0.022058 -0.000128 -0.003279 0.000000
0.1600 0.003647 0.048372 -0.000552 -0.007511 0.000000
0.2400 0.008161 0.066647 -0.001559 -0.017255 0.000000
0.3200 0.014153 0.086264 -0.003243 -0.024891 0.000000
0.4000 0.022581 0.128204 -0.005707 -0.036139 0.000000
0.4800 0.034637 0.178740 -0.008651 -0.036696 0.000000
0.5600 0.050899 0.235462 -0.010900 -0.018994 0.000000
0.6400 0.071422 0.287744 -0.010993 0.017577 0.000000
0.7200 0.095901 0.336427 -0.007008 0.083275 0.000000
0.8000 0.123665 0.371958 0.002402 0.153048 0.000000
0.9000 0.161260 0.394696 0.020579 0.209816 0.000000
1.0000 0.200067 0.399262 0.042098 0.224575 0.000000

I already tried the settings Jason suggested in this chat before but they did not effect the output in a way that the mode shapes "improved". I will also attach the settings and input files for BModes - maybe my problem is with a chosen setting or values (probably something obvious).
Thanks in advance.

Sören

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)
0.00E+00 9.50E+00 0.00E+00 1.21E+03 5.73E+02 2.65E+02 1.29E+10 6.52E+09 1.13E+09 2.74E+10 0.00E+00 0.00E+00 0.00E+00
1.07E-01 1.20E+01 0.00E+00 8.01E+02 4.29E+02 2.35E+02 9.65E+09 5.54E+09 1.10E+09 1.76E+10 0.00E+00 0.00E+00 0.00E+00
1.59E-01 1.28E+01 0.00E+00 4.22E+02 2.53E+02 6.36E+01 5.58E+09 1.42E+09 3.28E+08 8.94E+09 0.00E+00 0.00E+00 0.00E+00
2.25E-01 9.50E+00 0.00E+00 1.03E+03 7.38E+02 1.47E+02 1.51E+10 3.02E+09 1.15E+09 2.08E+10 0.00E+00 0.00E+00 0.00E+00
3.20E-01 6.37E+00 0.00E+00 3.20E+02 1.76E+02 2.43E+01 3.76E+09 5.41E+08 1.58E+08 6.70E+09 0.00E+00 0.00E+00 0.00E+00
4.76E-01 3.28E+00 0.00E+00 1.96E+02 7.76E+01 8.04E+00 1.55E+09 1.76E+08 5.74E+07 4.03E+09 0.00E+00 0.00E+00 0.00E+00
6.99E-01 6.65E-01 0.00E+00 1.31E+02 3.55E+01 2.35E+00 6.95E+08 4.81E+07 2.10E+07 2.54E+09 0.00E+00 0.00E+00 0.00E+00
1.00E+00 -1.43E-01 0.00E+00 9.09E+01 1.70E+01 8.31E-01 3.15E+08 1.64E+07 7.78E+06 1.73E+09 0.00E+00 0.00E+00 0.00E+00

====================== BModes Main Input File ==================
Sample non-uniform blade (output is space-delimited)

--------- General parameters ---------------------------------------------------------------------
True Echo Echo input file contents to *.echo file if true.
1 beam_type 1: blade, 2: tower (-)
13. romg: rotor speed, automatically set to zero for tower modal analysis (rpm)
1.0 romg_mult: rotor speed muliplicative factor (-)
44.868 radius: rotor tip radius measured along coned blade axis OR tower height (m)
1.132 hub_rad: hub radius measured along coned blade axis OR tower rigid-base height (m)
3.5 precone: built-in precone angle, automatically set to zero for a tower (deg)
0. bl_thp: blade pitch setting, automatically set to zero for a tower (deg)
1 hub_conn: hub-to-blade connection [1: cantilevered; other options not yet available] (-)
4 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 --------------------------------------------
0.0 tip_mass blade-tip or tower-top mass (see users' manual) (kg)
0.0 cm_loc tip-mass c.m. offset from the blade axis measured along the tip section y reference axis (m)
0.0 cm_axial tip-mass c.m. offset tower tip measures axially along the z axis (m)
0.0 ixx_tip blade lag mass moment of inertia about the tip-section x reference axis (kg-m^2)
0.0 iyy_tip blade flap mass moment of inertia about the tip-section y reference axis (kg-m^2)
0.0 izz_tip torsion mass moment of inertia about the tip-section z reference axis (kg-m^2)
0.0 ixy_tip cross product of inertia about x and y reference axes(kg-m^2)
0.0 izx_tip cross product of inertia about z and x reference axes(kg-m^2)
0.0 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]
'blade_sec_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 --------------------------------------------------
12 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. 0.08 0.16 0.24 0.32 0.40 0.48 0.56 0.64 0.72 0.80 0.90 1.0

--------- Properties of tension wires suporting the tower --------------------------------
0 n_attachments: no of wire-attachment locations on tower, maxm allowable is 2; 0: no tension-wire support (-)
0 0 n_wires: no of wires attached at each location (must be 3 or higher) (-)
0 0 node_attach: node numbers of attacments location (node number must be more than 1 and less than nselt+2) (-)
0.e0 0.e0 wire_stfness: wire sifnness in each set (see users' manual) (N/m)
0. 0. th_wire: angle of tension wires wrt the tower axis at each attachment point (deg)

END of Main Input File Data *********************************************************************
*************************************************************************************************

Jason.Jonkman
Posts: 5763
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: NREL 5MW Blade Mode Shape

Postby Jason.Jonkman » Mon Mar 08, 2021 3:14 pm

Hi Soeren,

From my brief review of your files, I see the following:
  • The flap stiffness is higher than the edge stiffness, which is a bit odd.
  • Because of the previous point, the first mode is the edge mode and the second mode is the flap mode.
  • However, the modes are coupled a bit because the structural twist has not been zeroed.
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

Soeren.Link
Posts: 3
Joined: Sat Jan 09, 2021 1:00 pm
Organization: Flensburg University of Applied Sciences
Location: Deutschland

Re: NREL 5MW Blade Mode Shape

Postby Soeren.Link » Mon Mar 08, 2021 5:51 pm

Hi Jason,

yes this is helping me a lot, thanks!

Best regards,
Soeren


Return to “Structural Analysis”

Who is online

Users browsing this forum: No registered users and 1 guest