Hello, NREL community.
I’m trying to find edgewise/flapwise frequencies and modal masses of IEA 15MW and 22MW WT’s blades using BModes.
I know I need to create a BModes input file if I want to do structural analysis of the blades themselves. I also understand that this file calls another file for the blades properties if I’m not mistaken. Where could I find a .bmi baseline example file for the blades of the WT models mentioned above, along with their section properties files that are added to the following lines?
--------- Distributed-property identifiers --------------------------------------------------------
1 id_mat: material_type [1: isotropic; non-isotropic composites option not yet available]
‘CS_monopile_tower_secs.dat’ : sec_props_file name of beam section properties file (-)
Regarding edgewise frequencies and modal masses. How exactly could I calculate them if i add different TMD masses along the blade lenghts?
Thank you in advance!
Best regards.
Dear @Fanny.Callisaya,
I’m not aware that NREL has developed BModes models for the blades of the IEA Wind 15-MW or 22-MW reference wind turbines. I was not the one to develop these models, but I believe the mode shapes for these models were derived via Frame3DD rather than through BModes. That said, the inputs set in the beam section properties file of BModes are very similar to those of the ElastoDyn blade file, so, it should not be hard to create these files yourselves. For the columns in the beam section properties file of BModes not specified in ElastoDyn (e.g., flp_iner), see the guidance from the following forum topic: NREL 5MW Blade Mode Shape.
BModes does not have functionality to model TMDs. However, if you’ve already derived the mode shapes for ElastoDyn and are modeling the system in OpenFAST, you can see the effect of TMDs on the blade response through the OpenFAST results.
Best regards,
Dear @Jason.Jonkman ,
Thank you so much for your guidance. I actually did read through the forum and found a lot of help regarding BModes. So, finally I was able to generate my BModes input files for the IEA 15MW WT. However, I have some doubts about the results.
As you can see, the 1st edgewise frequency of the blades is about 0.73Hz, which I also confirmed from my free decay test results using OpenFAST. The problem is that the technical report of the IEA 15MW says that the 1st edgewise frequency for the blades is 0.642 Hz. There is a considerable difference between these results (0.642 Hz and 0.73 Hz). Do you happen to know why this could be? I will additionally attach my BModes files so that you can help me confirm I generated them correctly.
====================== BModes v3.00 Main Input File ==================
IEA15 blades
--------- General parameters ---------------------------------------------------------------------
False Echo Echo input file contents to *.echo file if true.
1 beam_type 1: blade, 2: tower (-)
0. romg: rotor speed, automatically set to zero for tower modal analysis (rpm)
1.0 romg_mult: rotor speed muliplicative factor (-)
120.97 radius: rotor tip radius measured along coned blade axis OR tower height (m)
3.97 hub_rad: hub radius measured along coned blade axis OR tower rigid-base height (m)
-4.0 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]
'IEA15MW_blades_prop.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
Blade section properties
50 n_secs: number of 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)
0.000000000000000e+00 0 0 3.189145281139312e+03 1.00E-10 1.00E-10 1.525338961805330e+11 1.524792338826398e+11 1.00E+20 1.00E+20 0 0 0
2.040816326530612e-02 0 0 2.848491671981893e+03 1.00E-10 1.00E-10 1.388018747118786e+11 1.376398889340311e+11 1.00E+20 1.00E+20 0 0 0
4.081632653061224e-02 0 0 2.506316641079376e+03 1.00E-10 1.00E-10 1.222825651460343e+11 1.231043838261023e+11 1.00E+20 1.00E+20 0 0 0
6.122448979591835e-02 0 0 2.126327323268820e+03 1.00E-10 1.00E-10 9.721429241691763e+10 1.030038838221780e+11 1.00E+20 1.00E+20 0 0 0
8.163265306122448e-02 0 0 1.774273076643545e+03 1.00E-10 1.00E-10 7.473181210448022e+10 8.415417285570142e+10 1.00E+20 1.00E+20 0 0 0
1.020408163265306e-01 0 0 1.675415347578921e+03 1.00E-10 1.00E-10 5.670713863723486e+10 7.500334758775418e+10 1.00E+20 1.00E+20 0 0 0
1.224489795918367e-01 0 0 1.375372123508623e+03 1.00E-10 1.00E-10 4.333119910067368e+10 6.386874980164800e+10 1.00E+20 1.00E+20 0 0 0
1.428571428571428e-01 0 0 1.126877435288510e+03 1.00E-10 1.00E-10 3.488129485677473e+10 5.587550052530811e+10 1.00E+20 1.00E+20 0 0 0
1.632653061224490e-01 0 0 9.166967416567660e+02 1.00E-10 1.00E-10 3.074062953585106e+10 4.850443135202483e+10 1.00E+20 1.00E+20 0 0 0
1.836734693877551e-01 0 0 7.581128920505105e+02 1.00E-10 1.00E-10 2.769326286737285e+10 4.229417836732529e+10 1.00E+20 1.00E+20 0 0 0
2.040816326530612e-01 0 0 6.498201551435592e+02 1.00E-10 1.00E-10 2.461968089847847e+10 3.778979262471266e+10 1.00E+20 1.00E+20 0 0 0
2.244897959183673e-01 0 0 5.816598121783463e+02 1.00E-10 1.00E-10 2.139033204354521e+10 3.460539129185500e+10 1.00E+20 1.00E+20 0 0 0
2.448979591836735e-01 0 0 5.388110041072538e+02 1.00E-10 1.00E-10 1.869243518353476e+10 3.222839700500914e+10 1.00E+20 1.00E+20 0 0 0
2.653061224489796e-01 0 0 5.093885171950960e+02 1.00E-10 1.00E-10 1.631285343544707e+10 3.032117609748821e+10 1.00E+20 1.00E+20 0 0 0
2.857142857142857e-01 0 0 4.927842041149214e+02 1.00E-10 1.00E-10 1.479141128967237e+10 2.866882577015823e+10 1.00E+20 1.00E+20 0 0 0
3.061224489795917e-01 0 0 4.867795863196560e+02 1.00E-10 1.00E-10 1.408157287855375e+10 2.719211554338738e+10 1.00E+20 1.00E+20 0 0 0
3.265306122448979e-01 0 0 4.822296506379602e+02 1.00E-10 1.00E-10 1.340519691354671e+10 2.562551820076299e+10 1.00E+20 1.00E+20 0 0 0
3.469387755102040e-01 0 0 4.761842241246758e+02 1.00E-10 1.00E-10 1.213013620583955e+10 2.406788400839622e+10 1.00E+20 1.00E+20 0 0 0
3.673469387755101e-01 0 0 4.677912755581858e+02 1.00E-10 1.00E-10 1.057564915543031e+10 2.263018568852713e+10 1.00E+20 1.00E+20 0 0 0
3.877551020408163e-01 0 0 4.591296592557296e+02 1.00E-10 1.00E-10 9.428937598688459e+09 2.140687114823070e+10 1.00E+20 1.00E+20 0 0 0
4.081632653061223e-01 0 0 4.508379097619292e+02 1.00E-10 1.00E-10 8.679373622305126e+09 2.030554785264042e+10 1.00E+20 1.00E+20 0 0 0
4.285714285714285e-01 0 0 4.421998847689325e+02 1.00E-10 1.00E-10 8.090790463396826e+09 1.925965509911081e+10 1.00E+20 1.00E+20 0 0 0
4.489795918367346e-01 0 0 4.326008561862743e+02 1.00E-10 1.00E-10 7.430721516569722e+09 1.925965509911081e+10 1.00E+20 1.00E+20 0 0 0
4.693877551020408e-01 0 0 4.219773745307401e+02 1.00E-10 1.00E-10 6.532916397780468e+09 1.716666216090269e+10 1.00E+20 1.00E+20 0 0 0
4.897959183673469e-01 0 0 4.112534584982077e+02 1.00E-10 1.00E-10 5.635458983738827e+09 1.616806219912397e+10 1.00E+20 1.00E+20 0 0 0
5.102040816326531e-01 0 0 4.012473583789823e+02 1.00E-10 1.00E-10 4.924729531561621e+09 1.522285575052025e+10 1.00E+20 1.00E+20 0 0 0
5.306122448979592e-01 0 0 3.920469572984427e+02 1.00E-10 1.00E-10 4.401845320349272e+09 1.433708564071317e+10 1.00E+20 1.00E+20 0 0 0
5.510204081632651e-01 0 0 3.826675398780939e+02 1.00E-10 1.00E-10 3.941076638277167e+09 1.344497171773862e+10 1.00E+20 1.00E+20 0 0 0
5.714285714285713e-01 0 0 3.612661153435752e+02 1.00E-10 1.00E-10 3.426333092367449e+09 1.138100415398959e+10 1.00E+20 1.00E+20 0 0 0
5.918367346938775e-01 0 0 3.398659172619289e+02 1.00E-10 1.00E-10 2.966680532868500e+09 9.471654091893534e+09 1.00E+20 1.00E+20 0 0 0
6.122448979591835e-01 0 0 3.173247964654917e+02 1.00E-10 1.00E-10 2.598972931031398e+09 7.598070333791522e+09 1.00E+20 1.00E+20 0 0 0
6.326530612244897e-01 0 0 2.941148966103120e+02 1.00E-10 1.00E-10 2.299604180699598e+09 5.805653973761759e+09 1.00E+20 1.00E+20 0 0 0
6.530612244897959e-01 0 0 2.719321532357653e+02 1.00E-10 1.00E-10 2.026456858897451e+09 4.285716699307380e+09 1.00E+20 1.00E+20 0 0 0
6.734693877551020e-01 0 0 2.563144169585100e+02 1.00E-10 1.00E-10 1.750494448194900e+09 3.539638690389050e+09 1.00E+20 1.00E+20 0 0 0
6.938775510204080e-01 0 0 2.393766504954643e+02 1.00E-10 1.00E-10 1.480634479348676e+09 2.858341744436661e+09 1.00E+20 1.00E+20 0 0 0
7.142857142857143e-01 0 0 2.221564960620647e+02 1.00E-10 1.00E-10 1.225755456624930e+09 2.411448232374817e+09 1.00E+20 1.00E+20 0 0 0
7.346938775510203e-01 0 0 2.021377424119976e+02 1.00E-10 1.00E-10 9.915617242298139e+08 2.059272895765558e+09 1.00E+20 1.00E+20 0 0 0
7.551020408163265e-01 0 0 1.805543988230305e+02 1.00E-10 1.00E-10 7.965115478517663e+08 1.711553935321545e+09 1.00E+20 1.00E+20 0 0 0
7.755102040816326e-01 0 0 1.576606284996616e+02 1.00E-10 1.00E-10 6.379451447840538e+08 1.344077335734445e+09 1.00E+20 1.00E+20 0 0 0
7.959183673469387e-01 0 0 1.354839722001807e+02 1.00E-10 1.00E-10 5.016030937142348e+08 1.013798041821079e+09 1.00E+20 1.00E+20 0 0 0
8.163265306122449e-01 0 0 1.120816430883252e+02 1.00E-10 1.00E-10 3.837872963500269e+08 7.818269647609487e+08 1.00E+20 1.00E+20 0 0 0
8.367346938775508e-01 0 0 9.428716335486106e+01 1.00E-10 1.00E-10 2.922152544706123e+08 6.257356863909814e+08 1.00E+20 1.00E+20 0 0 0
8.571428571428570e-01 0 0 7.800953847011847e+01 1.00E-10 1.00E-10 2.234419323778142e+08 4.853089503492516e+08 1.00E+20 1.00E+20 0 0 0
8.775510204081634e-01 0 0 6.432912305900471e+01 1.00E-10 1.00E-10 1.655441909972637e+08 3.752666314364563e+08 1.00E+20 1.00E+20 0 0 0
8.979591836734692e-01 0 0 5.344190109844552e+01 1.00E-10 1.00E-10 1.178503801821035e+08 2.918966298394187e+08 1.00E+20 1.00E+20 0 0 0
9.183673469387755e-01 0 0 4.450335078883321e+01 1.00E-10 1.00E-10 7.916644695614292e+07 2.239967950809962e+08 1.00E+20 1.00E+20 0 0 0
9.387755102040815e-01 0 0 3.669679320964971e+01 1.00E-10 1.00E-10 4.921992371612750e+07 1.631692262693548e+08 1.00E+20 1.00E+20 0 0 0
9.591836734693876e-01 0 0 2.687365619764821e+01 1.00E-10 1.00E-10 2.743282717773140e+07 1.064318616320310e+08 1.00E+20 1.00E+20 0 0 0
9.795918367346939e-01 0 0 2.157201084316552e+01 1.00E-10 1.00E-10 1.296677095760643e+07 6.715371720843673e+07 1.00E+20 1.00E+20 0 0 0
1.000000000000000e+00 0 0 5.767382468564499e+00 1.00E-10 1.00E-10 1.862011072702549e+05 1.663313892259768e+06 1.00E+20 1.00E+20 0 0 0
Thank you in advance!
Dear @Fanny.Callisaya,
Your BeamDyn input files look good to me. You may want to reduce tor_stff and axial_stff a bit just to see if there is any issue in the eigensolver of BModes when using such high values (using values for tor_stff and axial_stff that are a few orders of magnitude larger than flap_stff and edge_stff should be sufficiently stiff).
Regarding the difference in natural frequency of the first edgewise model, perhaps this is related to setting the structural twist (str_tw) equal to zero? Setting str_tw to zero is recommended when generating blade mode shapes for ElastoDyn, but this may have some effect on the resulting natural frequencies calculated by BModes. But if the results are not too different from what you are seeing from OpenFAST, I wouldn’t be too concerned either.
Best regards,
