FAST - Warning: tower model/possible tower strike

Wind & Water Computer-Aided Engineering Software Tools
21

Dear Satish,

I generally agree with how you’ve set your idling wind turbine, except that you’ve engaged the Thevenin-equivalent induction generator at time zero in ServoDyn. You should disable the generator / torque controller altogether by setting GenTIStr = TRUE with TimGenOn > TMax.

Best regards,

22

Dear Jason,

Thanks for your reply.

I am getting the same error even if I change the above suggested (attached the servodyn input file).

[code]FAST_InitializeAll:FAST_Init:FAST_ReadPrimaryFile:1/VTK_fps is not an integer multiple of DT.
FAST will output VTK information at 15.385 fps, the closest rate possible.
FAST_InitializeAll: IfW_Init:IfW_UniformWind_Init: Only 1 line in uniform wind file. Steady,
horizontal wind speed at the hub height is 56 m/s.

Time: 0 of 90 seconds.

FAST_Solution:FAST_AdvanceStates:ED_ABM4:ED_CalcContStateDeriv:SetCoordSy:Small angle assumption
violated in SUBROUTINE SmllRotTrans() due to a large blade deflection (ElastoDyn SetCoordSy). The
solution may be inaccurate. Simulation continuing, but future warnings from SmllRotTrans() will
be suppressed.
Additional debugging message from SUBROUTINE SmllRotTrans(): 6.00000E-02 s

FAST_Solution:FAST_AdvanceStates:SolveOption2c_Inp2AD_SrvD:InflowWind_CalcOutput:CalcOutput:IfW_Un
iformWind_CalcOutput:GetWindSpeed:Height must not be negative. Error calculating the wind speed
at position (-55.591, 143.81, -127.53) in the wind-file coordinates

FAST encountered an error at simulation time 6.00000E-02 of 90 seconds.
Simulation error level: FATAL ERROR

Aborting OpenFAST.[/code]

Thanks,
Satish J
IEA-15-240-RWT-Monopile_ServoDyn.rtf (11.9 KB)

23

Dear Satish,

I also noticed that you’ve set the initial nacelle-yaw angle to NacYaw = 8deg in ElastoDyn, but you’ve set the neutral yaw position in ServoDyn to be YawNeut = 0deg. This will cause the nacelle-yaw angle to quickly snap back to 0deg and result in unrealistic loads and deflections. If you want to keep the nacelle at 8deg and keep the nacelle-yaw DOF enabled (YawDOF = TRUE), then set YawNeut = 8deg as well.

Best regards,

24

Dear Jason,

Thanks for your reply.

  1. Still I am getting error after changing.

[code]FAST_InitializeAll:FAST_Init:FAST_ReadPrimaryFile:1/VTK_fps is not an integer multiple of DT.
FAST will output VTK information at 15.385 fps, the closest rate possible.
FAST_InitializeAll: IfW_Init:IfW_UniformWind_Init: Only 1 line in uniform wind file. Steady,
horizontal wind speed at the hub height is 56 m/s.

Time: 0 of 90 seconds.

FAST_Solution:FAST_AdvanceStates:SolveOption2c_Inp2AD_SrvD:InflowWind_CalcOutput:CalcOutput:IfW_Un
iformWind_CalcOutput:GetWindSpeed:Height must not be negative. Error calculating the wind speed
at position (51.995, -161.71, -2.6111) in the wind-file coordinates

FAST encountered an error at simulation time 7.00000E-02 of 90 seconds.
Simulation error level: FATAL ERROR

Aborting OpenFAST.[/code]

  1. As I am running DLC 6.3, instead of using the IECWind, I used Turbisim, but I am still getting following error and I have attached the turbsim and inflow file.

[code]FAST_Solution:FAST_AdvanceStates:ED_ABM4:ED_CalcContStateDeriv:SetCoordSy:Small angle assumption
violated in SUBROUTINE SmllRotTrans() due to a large blade deflection (ElastoDyn SetCoordSy). The
solution may be inaccurate. Simulation continuing, but future warnings from SmllRotTrans() will
be suppressed.
Additional debugging message from SUBROUTINE SmllRotTrans(): 6.50000E-02 s

FAST_Solution:FAST_AdvanceStates:SolveOption2c_Inp2AD_SrvD:InflowWind_CalcOutput:CalcOutput:IfW_TS
FFWind_CalcOutput [position=(-1040.4, 3272.6, -874.5) in wind-file coordinates]: FF wind array
boundaries violated. Grid too small in Z direction (height (Z=-874.5 m) is below the grid and no
tower points are defined).

FAST encountered an error at simulation time 6.50000E-02 of 90 seconds.
Simulation error level: FATAL ERROR

Aborting OpenFAST.[/code]

Thanks and regards,
Satish J
IEA-15-240-RWT_InflowFile_Turbsim.zip (4.13 KB)

25

Dear Satish,

Well, clearly your model is going numerically unstable very quickly. You’ve changed the input file a couple times no, so, it may be useful to share what you are running now. Regardless, something is clearly not set up correctly and I would suggest simplifying the model to debug. Does the model run if you disable aerodynamics altogether? How about if you disable structural degrees of freedom? Or reduce the time step?

Best regards,

26

Dear Jason,

Thanks for the reply.

It is working well when I reduce the time step, thanks a lot! Could I know what might be the reason for running normally when I reduce the time step.

Thanks,
Satish J

27

Dear Satish,

Typically the time step requirements are dictated by the structural properties (mass, stiffness, or geometry) (see related forum topics on this subject). Again, I’m not sure I understand everything you’ve changed in the model.

Best regards,

28

Dear Jason,

Thanks for your reply.

I have attached the input files for IEC DLC case 6.3 with -20deg yaw misalignment. Could you please advice on whether I have changed everything correct or not.

Thanks,
Satish J
IEA-15-240-RWT-Monopile_Ip.zip (13.3 KB)

29

Dear Satish,

Yes, your simulation set-up looks good to me.

Best regards,