Dear all,
I have a problem when simulating a 15MW FOWT using OpenFast. I used the UMaineSemi sample files downloaded from IEA-15-240-RWT/OpenFAST at master · IEAWindTask37/IEA-15-240-RWT · GitHub and changed the platform to my new designed model ( input files to HydroDyn, ElastoDyn and MoorDyn modules modified).
The simulation was carried out with parked turbine, still water and no wind with all the other settings were set accordingly, the total simulating time was 500 s and DT was 0.025 s. It ran well at about the first 300 s and the results shows that the model was physically stable. Then the following error messages came out and the program aborted:
FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption1:ED_HD_InputOutputSolve:HydroDyn_CalcOutp
ut: Angles in GetSmllRotAngs() are larger than 0.4 radians.
HydroDyn_CalcOutput:HDOut_MapOutputs: Angles in GetSmllRotAngs() are larger than 0.4 radians.
ED_HD_InputOutputSolve:HydroDyn_CalcOutput: Angles in GetSmllRotAngs() are larger than 0.4
radians.
To solve this problem, I’ve made the following attemps:
- To reduce/increase the time step, but it didn’t work.
- To disable the platform yaw DOF (PtfmYDOF = False) in ElastoDyn, this solved the problem, but the platform yaw motions were missed, which may affect the results in other DOFs.
- To disable AeroDyn module (with PtfmYDOF = True) , this solved the problem as well.
- To adjust the settings in AeroDyn input file, such as set TwrAero = 0, TwrShadow = 0 or change the DTAero and MaxIter, but this not worked.
I would appreciate if you could give any advice to solve this issue.
Yajun
Dear @Yajun.Ren,
Can you clarify what you mean when you say you parked the rotor? Is GenDOF disabled in ElastoDyn? Is Is ServoDyn disabled (CompServo = 0 in the OpenFAST driver) with all of the blades feathered (BlPitch = 90deg in ElastoDyn)? Have you disabled induction (WakeMod = 0) and unsteady airfoil aerodynamics (AFAeroMod = 1) in AeroDyn?
Best regards,
Dear Dr Jonkman,
Thanks for your reply. Yes those parameters were properly set (in .fst file: CompServo = 0, CompInflow = 0, in ElastoDyn file: GenDOF deisbled, BldPitch = 90, RotSpeed = 0, in AeroDyn file: WakeMod = 0 and AFAeroMod = 1).
Best wishes,
Yajun
Dear @Yajun.Ren,
Is the nacelle-yaw DOF disabled in your ElastoDyn model (YawDOF = False)? This would be important because ServoDyn is disabled and the nacelle would otherwise be in a free-yaw condition.
You mention that you receive the small angle violation warning about 300 s into the simulation. Are the deflections / displacements slowly building up over time or is the growth sudden at about 300 s?
Best regards,
Dear Dr Jonkman,
Yes, YawDOF was disabled in the ElastoDyn model.
The deflections/displacements suddenly changed as illustrated below.
Best regards,
Yajun
从 Windows 版邮件发送
Dear @Yajun.Ren,
How do other DOFs look such as platform sway and roll, tower deflection, and blade deflection?
Best regards,
Dear Dr Jonkman,
Please see the platform sway, roll, blade deflections and nacelle accelerations attached below. The output file is also attached if you would like to check some other channels.
Best regards,
Yajun
从 Windows 版邮件发送
(Attachment IEA15MW_UMaineSemi.out is missing)
It seems that the file could not be uploaded, please just let me know if you would like to look at other output data. Thank you very much.
Dear @Yajun.Ren,
I’m not sure why, but the system response seems to change at around 200 s into the simulation, where platform, sway, roll, and yaw start to diverge. I would likely have to review the input files and run the model myself to understand why.
Best regards,
Dear Jonkman,
I would really appreciate if you could help to check the input files in the onedrive link below:
https://1drv.ms/u/s!AsS3yLav-aS5jwUdshXyhKURu9kL?e=h4zdeV
Best regards,
Yajun
从 Windows 版邮件发送
Dear @Yajun.Ren
I took a brief look at your input files and reproduced the problem you are showing. My guess is that your model is unstable in the platform sway, roll, and/or yaw modes. Without wind and unidirectional waves, the excitation is two dimensional–with motion only in surge, heave, and pitch (with some tower and blade deflection as well). That is, except that the wave-induced motion causes some very small side-side aerodynamic forces due the pitched but parked blades in still air, which causes a small mount of sway, roll, and yaw motion. Eventually the sway, roll, or yaw motion becomes significant enough to trigger the instability.
BTW: I see two other issues with your model: (1) you changed the water depth to 100 m in HydroDyn, but the mooring system in MoorDyn is still set up for 200 m and (2) the mean heave is about -0.7 m whereas we recommend to always set up a floating wind turbine model to have a mean heave of zero.
Best regards,
