I’m interested in examining blade structural responses. I created a simple test case, using the IEA-15-240-RWT-UMaineSemi files as a starting point. I made the following minor modifications:
- Fixed all platform motions, to allow me focus purely on the blades/tower (PtfmSgDOF etc. = False)
- Preventing the rotor from spinning, to keep things simple, no changes in relative wind velocity due to blade rotation (GenDOF=False, RotSpeed=0). Rotor facing wind (YawDOF=False).
- Blade pitch fixed at 30degs (BlPitch(1) etc. =30).
- Disabled ServoDyn (CompServo=0), to simulate steady conditions without any modifications stemming from control.
- Because rotor is not spinning, I disabled wake induction (WakeMod=0) and selected steady aerodynamics (AFAeroMod=1).
I am running OpenFAST V2.6.0.
I realise the case is somewhat artificial as in reality the rotor would be spinning for wind speeds above cut-in. Regardless:
- When a steady wind of 10m/s is applied, blade tip deflections quickly settle to steady state.
- For higher wind speeds (e.g. 20m/s), there seems to be some high frequency noise in the tip deflections. Suggests the blade is vibrating at high frequency.
Just wondering is this expected behaviour? I’ve seen a similar pattern in a more complicated model, this test case is designed to demonstrate the issue in a simple way. Perhaps I’m missing something, like structural damping. Do you have any suggestions?
PS: the plots are presented in an external tool but the data is taken from the OpenFAST out file.