beamdyn monitor point spanwsie position check

[QB-Lin]

In OpenFAST's IEA 15MW model, the beamdyn module records the blade displacement time histories to 51 points at different locations, such as

"B1N001_TDyr	B1N002_TDyr	B1N003_TDyr	B1N004_TDyr	B1N005_TDyr	B1N006_TDyr	B1N007_TDyr	B1N008_TDyr	B1N009_TDyr	B1N010_TDyr	B1N011_TDyr	B1N012_TDyr	B1N013_TDyr	B1N014_TDyr	B1N015_TDyr	B1N016_TDyr	B1N017_TDyr	B1N018_TDyr	B1N019_TDyr	B1N020_TDyr	B1N021_TDyr	B1N022_TDyr	B1N023_TDyr	B1N024_TDyr	B1N025_TDyr	B1N026_TDyr	B1N027_TDyr	B1N028_TDyr	B1N029_TDyr	B1N030_TDyr	B1N031_TDyr	B1N032_TDyr	B1N033_TDyr	B1N034_TDyr	B1N035_TDyr	B1N036_TDyr	B1N037_TDyr	B1N038_TDyr	B1N039_TDyr	B1N040_TDyr	B1N041_TDyr	B1N042_TDyr	B1N043_TDyr	B1N044_TDyr	B1N045_TDyr	B1N046_TDyr	B1N047_TDyr	B1N048_TDyr	B1N049_TDyr	B1N050_TDyr	B1N051_TDyr

I want to know the exact spanwise positions of these monitor points.
ChatGPT said I could set SumPrint from False to True in IEA-15-240-RWT_BeamDyn.dat. Then run OpenFAST, the program will generate IEA-15-240-RWT-UMaineSemi.BD1.sum.yaml. In this file, the third column (Z) is the spanwise position of B1N0XXX.

# Quadrature points position and rotation vectors
#              X                  Y                  Z                WM_x               WM_y               WM_z       
#      -----------------  -----------------  -----------------  -----------------  -----------------  -----------------
# Element number:    1
Init_QP_E1: # 51 x 6
  - [       0.00000E+00,       0.00000E+00,       0.00000E+00,      -2.17344E-03,       1.58721E-02,      -2.72594E-01]
  - [       9.15106E-03,       0.00000E+00,       5.85000E-01,      -2.09383E-03,       1.52725E-02,      -2.73098E-01]
  - [       1.79612E-02,       0.00000E+00,       1.17000E+00,      -2.01735E-03,       1.47120E-02,      -2.73238E-01]
  - [       2.64528E-02,       0.00000E+00,       1.75500E+00,      -1.94395E-03,       1.41883E-02,      -2.73035E-01]
  - [       3.46468E-02,       0.00000E+00,       2.34000E+00,      -1.87358E-03,       1.36995E-02,      -2.72508E-01]
  - [       4.25630E-02,       0.00000E+00,       2.92500E+00,      -1.80616E-03,       1.32436E-02,      -2.71676E-01]
  - [       5.02203E-02,       0.00000E+00,       3.51000E+00,      -1.74161E-03,       1.28187E-02,      -2.70556E-01]
  - [       5.76362E-02,       0.00000E+00,       4.09500E+00,      -1.67983E-03,       1.24228E-02,      -2.69167E-01]
  - [       6.48271E-02,       0.00000E+00,       4.68000E+00,      -1.62071E-03,       1.20541E-02,      -2.67526E-01]
  - [       7.18087E-02,       0.00000E+00,       5.26500E+00,      -1.56412E-03,       1.17109E-02,      -2.65649E-01]
  - [       7.85952E-02,       0.00000E+00,       5.85000E+00,      -1.50995E-03,       1.13914E-02,      -2.63552E-01]
  - [       9.47936E-02,       0.00000E+00,       7.31250E+00,      -1.38426E-03,       1.06853E-02,      -2.57447E-01]
  - [       1.10037E-01,       0.00000E+00,       8.77500E+00,      -1.27085E-03,       1.00916E-02,      -2.50285E-01]
  - [       1.24473E-01,       0.00000E+00,       1.02375E+01,      -1.16774E-03,       9.58663E-03,      -2.42270E-01]
  - [       1.38216E-01,       0.00000E+00,       1.17000E+01,      -1.07306E-03,       9.14866E-03,      -2.33587E-01]
  - [       1.63927E-01,       0.00000E+00,       1.46250E+01,      -9.02527E-04,       8.39455E-03,      -2.14860E-01]
  - [       1.87511E-01,       0.00000E+00,       1.75500E+01,      -7.48528E-04,       7.68695E-03,      -1.95226E-01]
  - [       2.08931E-01,       0.00000E+00,       2.04750E+01,      -6.04087E-04,       6.90782E-03,      -1.75559E-01]
  - [       2.27836E-01,       0.00000E+00,       2.34000E+01,      -4.65576E-04,       5.96181E-03,      -1.56516E-01]
  - [       2.43626E-01,       0.00000E+00,       2.63250E+01,      -3.31960E-04,       4.77458E-03,      -1.38566E-01]
  - [       2.55513E-01,       0.00000E+00,       2.92500E+01,      -2.03922E-04,       3.29118E-03,      -1.22016E-01]
  - [       2.62574E-01,       0.00000E+00,       3.21750E+01,      -8.30521E-05,       1.47447E-03,      -1.07038E-01]
  - [       2.63802E-01,       0.00000E+00,       3.51000E+01,       2.87958E-05,      -6.96548E-04,      -9.36921E-02]
  - [       2.58147E-01,       0.00000E+00,       3.80250E+01,       1.29936E-04,      -3.22827E-03,      -8.19469E-02]
  - [       2.44564E-01,       0.00000E+00,       4.09500E+01,       2.19066E-04,      -6.11410E-03,      -7.17011E-02]
  - [       2.22040E-01,       0.00000E+00,       4.38750E+01,       2.95288E-04,      -9.33602E-03,      -6.28014E-02]
  - [       1.89632E-01,       0.00000E+00,       4.68000E+01,       3.57995E-04,      -1.28661E-02,      -5.50588E-02]
  - [       1.46488E-01,       0.00000E+00,       4.97250E+01,       4.06662E-04,      -1.66684E-02,      -4.82640E-02]
  - [       9.18727E-02,       0.00000E+00,       5.26500E+01,       4.40627E-04,      -2.06999E-02,      -4.22011E-02]
  - [       2.51838E-02,       0.00000E+00,       5.55750E+01,       4.58886E-04,      -2.49130E-02,      -3.66589E-02]
  - [      -5.40376E-02,       0.00000E+00,       5.85000E+01,       4.59984E-04,      -2.92563E-02,      -3.14416E-02]
  - [      -1.46098E-01,       0.00000E+00,       6.14250E+01,       4.42007E-04,      -3.36767E-02,      -2.63770E-02]
  - [      -2.51148E-01,       0.00000E+00,       6.43500E+01,       4.02712E-04,      -3.81211E-02,      -2.13243E-02]
  - [      -3.69186E-01,       0.00000E+00,       6.72750E+01,       3.39786E-04,      -4.25375E-02,      -1.61786E-02]
  - [      -5.00062E-01,       0.00000E+00,       7.02000E+01,       2.51215E-04,      -4.68772E-02,      -1.08755E-02]
  - [      -6.43490E-01,       0.00000E+00,       7.31250E+01,       1.35741E-04,      -5.10961E-02,      -5.39287E-03]
  - [      -7.99064E-01,       0.00000E+00,       7.60500E+01,      -6.66132E-06,      -5.51563E-02,       2.48708E-04]
  - [      -9.66278E-01,       0.00000E+00,       7.89750E+01,      -1.74336E-04,      -5.90277E-02,       5.98669E-03]
  - [      -1.14455E+00,       0.00000E+00,       8.19000E+01,      -3.63589E-04,      -6.26899E-02,       1.17195E-02]
  - [      -1.33326E+00,       0.00000E+00,       8.48250E+01,      -5.68499E-04,      -6.61331E-02,       1.73109E-02]
  - [      -1.53176E+00,       0.00000E+00,       8.77500E+01,      -7.80944E-04,      -6.93604E-02,       2.25957E-02]
  - [      -1.73945E+00,       0.00000E+00,       9.06750E+01,      -9.90894E-04,      -7.23887E-02,       2.73879E-02]
  - [      -1.95579E+00,       0.00000E+00,       9.36000E+01,      -1.18697E-03,      -7.52508E-02,       3.14889E-02]
  - [      -2.18036E+00,       0.00000E+00,       9.65250E+01,      -1.35727E-03,      -7.79968E-02,       3.46993E-02]
  - [      -2.41292E+00,       0.00000E+00,       9.94500E+01,      -1.49034E-03,      -8.06953E-02,       3.68305E-02]
  - [      -2.65347E+00,       0.00000E+00,       1.02375E+02,      -1.57628E-03,      -8.34356E-02,       3.77192E-02]
  - [      -2.90228E+00,       0.00000E+00,       1.05300E+02,      -1.60755E-03,      -8.63286E-02,       3.72425E-02]
  - [      -3.16000E+00,       0.00000E+00,       1.08225E+02,      -1.57938E-03,      -8.95087E-02,       3.53358E-02]
  - [      -3.42770E+00,       0.00000E+00,       1.11150E+02,      -1.48934E-03,      -9.31350E-02,       3.20112E-02]
  - [      -3.70698E+00,       0.00000E+00,       1.14075E+02,      -1.33527E-03,      -9.73926E-02,       2.73790E-02]
  - [      -4.00000E+00,       0.00000E+00,       1.17000E+02,      -1.11127E-03,      -1.02493E-01,       2.16698E-02]

He also said that the position of B1N0XXX correspond to the * * node / output grid * * of BeamDyn. In BeamDyn, * * key points ( kp _ total and kp _ zr in IEA-15-240-RWT _ BeamDyn.dat ), blade input stations, and FE / output nodes * * are three sets of discrete nodes that are independent of each other. The key points are only used to define the blade reference axis geometry and torsion ; 'order _ elem ' defines the finite element order of LSFE ; the section property is defined by ' station _ total ' in blade input file. OpenFAST / NREL 's instructions also clearly mentioned : key points only define geometry, and the number of FE nodes and stations can be different.

The reason why the IEA 15MW model outputs to * * N051 * * is not that 'kp _ total = 50 ', but that it uses * * trapezoidal quadrature * * and 'refine = 2 '. BeamDyn document shows that under trapezoidal quadrature, ' refine ' will subdivide the interval between two adjacent blade-input stations into ' refine ' segments. The ' station _ total = 26 ' in IEA 15MW ' IEA-15-240-RWT _ BeamDyn _ blade.dat '. So the number of output grid nodes can be press
[
N = ( station _ total-1 ) * refine + 1 = ( 26-1 )* 2 + 1 = 51
]

Is the statement of ChatGPT correct?

Besides, the section force (B1N0002_Mxr) only has 50 sections, as the tip does not have sectional force. Is my understanding correct?

[jjonkman]

Dar @QB-Lin,

I would say that the ChatGPT response to your prompt is close. I would clarify that key points in BeamDyn define the curved reference axis of the blade. When quadrature = 2 in BeamDyn (as is the case for the IEA Wind 15-MW RWT), the blade structural analysis nodes are determined by trapezoidal quadrature based on the stations (eta, representing the normalized distance along the curved reference axis) defined within the BeamDyn blade input file, and with refine = 2, there is an extra analysis node defined at the midpoint between each station. So, I agree with your calculation of N based on station_total and refine for this quadrature = 2 case, but the calculation would differ if Gaussian quadrature where used via quadrature = 1.

I agree that the reaction load would be zero exactly at the tip node because there is no structure outboard of that node.

Best regards,