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Feature or improvement description
Adds 12 new output channels to BD:

  • RootAppliedF[xyzr]r - all loads applied to distributed mesh, mapped to root, F[xyz] in root frame
  • RootAppliedM[xyz]r - all loads applied to distributed mesh, mapped to root, M[xyz] in root frame
  • RootAppliedF[xyz]g - all loads applied to distributed mesh, mapped to root, F[xyz] in global inertial frame
  • RootAppliedM[xyz]g - all loads applied to distributed mesh, mapped to root, M[xyz] in global inertial frame

This was requested by @ndevelder for validating CFD coupling to OpenFAST with FSI (fluid-structure interaction)

Related issue, if one exists
None

Impacted areas of the software
New output channels in BD, nothing else affected.

Test results, if applicable
No test results change.

Verification of implementation
The 5MW_Land_BD_DLL_WTurb regression test was modified with:

  • no tower aero
  • no shaft tilt
  • no cone
  • 20 mps steady wind, no shear
  • rigid tower and drivetrain
  • blade pitch: 16 degree for all blades
  • rotor speed: 12 rpm
  • gravity turned off

Screenshot 2025-05-14 at 2 59 26 PM
Figure 1: root forces in x. B1RootFxr is the reaction load at the root for the entire beam (includes gravity and beam distortion reactions -- shows large oscillations as the blade deforms and vibrates initially). B1RootAppliedFxr compares well with B1RootFxr after initial oscillations damp out (very small difference due to blade deformation coupling to B1rootAppliedFyr and B1RootAppliedFzr terms). B1RootAppliedFxg is equal to B1RootAppliedFxr * sin(blade_pitch) as expected.

Screenshot 2025-05-14 at 3 30 23 PM
Figure 2: root forces in y. B1RootFyr includes gyroscopic terms as well reaction forces against the blade deformation. The B1RootAppliedFyg is in the global frame, so this oscillates as the blade changes azimuth

Screenshot 2025-05-14 at 3 37 37 PM
Figure 3: root forces in z. Note the dominance of the centrifugal loads in B1RootFzr. The B1RootAppliedFzr term is slightly offset from zero due to blade deformation, and B1RootAppliedFzg is comparable to the B1RootAppliedFyg trace offset by 90 degrees with azimuth phase.

Screenshot 2025-05-14 at 3 42 48 PM
Figure 4: Root moments B1RootMxr and B1RootMyr include reaction loads to blade distortion and centrifugal loading. The global frame loads are not shown to keep the figure legible.

@andrew-platt andrew-platt self-assigned this May 14, 2025
@andrew-platt andrew-platt requested a review from deslaughter May 14, 2025 21:48
@andrew-platt andrew-platt added this to the 4.0.5 milestone May 15, 2025
@andrew-platt andrew-platt merged commit f5ff4b8 into OpenFAST:rc-4.0.5 May 15, 2025
22 checks passed
@andrew-platt andrew-platt deleted the f/BD_ApplLoadsAtRoot branch May 23, 2025 19:57
@andrew-platt andrew-platt mentioned this pull request Jun 11, 2025
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2 participants