FAST Tail Furling Convention Clarification

Wind & Water Computer-Aided Engineering Software Tools
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Dear Mike,

Here are my answers to your questions:

  1. Yes, when TFrlTilt = 90deg, the tail furl axis will be vertical (or at least, parallel to the tower centerline at the tower top).
  2. Yes, TFrlSkew is drawn in the positive sense. Please note, however, that when TFrlTilt = 90deg, the value of TFrlSkew doesn’t matter. This is because TFrlSkew determines the projection of the tail-furl axis in the nominally horizontal plane and when the tail-furl axis is vertical, there is no horizontal component.
  3. I’m not sure what you are asking here. The input parameters related to the tail-furl geometry are defined with respect to a tail-furl angle of zero, regardless of the initial condition of the tail-furl angle. See the last paragraph of the “Tail-Furl” section of the “Model Description” chapter of the FAST User’s Guide for more information. When TFrlTilt = 90deg, positive tail-furl rotations occur counter-clockwise when viewed from above.
  4. Yes, the tail-furl stop spring and damper angles are defined relative to a tail-furl angle of zero.
  5. I’m not sure what you are asking here. The tail-furl stop spring and damper angles determine the tail-furl angles beyond which spring and damping moments apply.

By the way, I suggest you set the tail-furl Coulomb-friction damping, TFrlCDmp, to zero. The present implementation may lead to numerical problems with the solution.

I hope that helps.

Best regards,