NREL 5MW Blade Mode Shape

Wind & Water Structural Analysis
1

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

======================   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)

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
2

Problem solved. Set the rotation speed to zero

3

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,

4

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

5

Hi Jason,

after reading also Blade mode shapes with BModes - #2 by Jason.Jonkman 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:

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

6

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,

7

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

8

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 *********************************************************************

9

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,

10

Hi Jason,

yes this is helping me a lot, thanks!

Best regards,
Soeren