NREL 5MW Baseline Offshore Monopile Simulation

Dear Jason

I keep receiving the same error everytime I try to run FAST with InflowWind entry.

First, I tested with steady wind, it ran normally. Then I introduced the InflowWind input, when I started to get the following messages:

FAST_Solution:FAST_AdvanceStates:ED_ABM4:ED_CalcContStateDeriv:SetCoordSy:Small angle assumption
violated in SUBROUTINE SmllRotTrans() due to a large tower deflection (ElastoDyn SetCoordSy). The
solution may be inaccurate. Simulation continuing, but future warnings from SmllRotTrans() will
be suppressed.
Additional debugging message from SUBROUTINE SmllRotTrans(): 0.3875 s

WARNING: High VT velocity encountered during induction factor calculation.
Blade number 1, Element number 1
VNW = 8.9453, VT = -560.63
WARNING: High VT velocity encountered during induction factor calculation.
Blade number 1, Element number 2
VNW = 10.169, VT = -557.62
WARNING: High VT velocity encountered during induction factor calculation.
Blade number 1, Element number 3
VNW = 10.322, VT = -554.83
WARNING: High VT velocity encountered during induction factor calculation.
Blade number 1, Element number 4
VNW = 10.305, VT = -551.68
WARNING: High VT velocity encountered during induction factor calculation.
Blade number 1, Element number 5
VNW = 10.293, VT = -548.55
WARNING: Induced velocity warning written 5 times. The message will not be repeated, though
the condition may persist.

ACH: Blade #1 element #4 is supersonic! Other elements are likely supersonic as well. Supersonic
mach nos. will be set to 0.7 to attempt continuation.
AD14_CalcOutput:ELEMFRC:BeddoesModel:SEPAR: Angle of attack = 2.64230E+20 is outside table.
Angles in GetSmllRotAngs() are larger than 0.4 radians.
ED_SD_HD_BD_Orca_InputOutputSolve:HydroDyn_CalcOutput: Angles in GetSmllRotAngs() are larger than
0.4 radians.

FAST encountered an error at simulation time 0.3875 of 299.99 seconds.
Simulation error level: FATAL ERROR

Aborting FAST.

I am using NREL 5MW Baseline Offshore Monopile OC3 inputs.

What did I missed?


Dear Eduardo,

I’m not sure what you mean when you say that you “introduced the InflowWind input”; do you mean that you used turbulent wind data from TurbSim?

It looks like your model is going unstable for some reason. I’m assuming you are using Test19 from the FAST v8.16 CertTest. Did you change this model in some way e.g. the time step sizes or geometry/mass/stiffness? Have you set proper initial conditions in terms of rotor speed and blade-pitch angle based on the mean wind speed you are simulating?

Best regards,

Dear Jason

Sorry for the delayed response.

I was using a modified input file. When I changed to Test19 as input, it worked normally. After, I modified some parameters on Test19 to work with the Turbsim output that I have generated, and I had no more errors.

Now, I am trying to add output channels, but, I am getting an INVALID message on .SUM log.

           Col   Parameter  Units
           ----  ---------  -----
              0  Time       (s)       
              1  RtAeroFxh  (N)       
              2  RtAeroFyh  (N)       
              3  RtAeroFzh  (N)       
              4  TwN1VUndx  INVALID   
              5  RtAeroMxh  (N·m)     
              6  RtAeroMyh  (N·m)     
              7  RtAeroMzh  (N·m)     

This happens on ElastoDyn, AeroDyn, and every other module I try to add output channels.
Do you have any tip to make this work


Dear Eduardo,

I can’t speak to other output-related errors, but in your example from AeroDyn, I could foresee that you would get an invalid error for output TwN1VUndx if NTwOuts is not set to 1 or greater. What do you have NTwOuts set to in the primary AeroDyn input file?

Best regards,

Dear Jason ,
I am currently modeling the OC3 Hywind (NREL 5MW Baseline Offshore) wind turbine in extreme turbulent and wind phenomena.
I have made some changes in the geometry of the turbine (Platform ,Tower) and in the water depth. (Hub Height=75m , Water Depth=150m) .

The conditions of wind i am simulating are the following (600 seconds of simulation) :

Operational Modes
NTM A for Uhub 10, 15, 20, 25 m/s
NTM B for Uhub 10, 15, 20, 25 m/s
ETM Class IIIA for Uhub = 40 m/s
ETM Class IIIB for Uhub = 40 m/s

Parked Modes
ETM Class IA for U10 = 50 m/s (Uhub=66 m/s)
ETM Class IB for U10 = 50 m/s
ETM Class IIA for U10 = 42.5 m/s ( Uhub=56 m/s)
ETM Class IIB for U10 = 42.5 m/s
Turbulent EWM Class I and Class II with 50 yr return period

A total of 16 combinations.
However,for the ETM IIIA and IIIB (Operational) models i am facing these errors :

  • Mach number exceeds 0.3. Theory is invalid.
  • Turning of UA due to high angle of attack.
    -The BEM solution is being turned off due to low TSR (1,9987).

I would also like to point out that i am changing the pitch angle and the Hs ,Tp (Jonswap) respectively to the wind speed .In addition to that ,i think it is significant to clarify that when the wind speed is below 36 m/s the 3rd error (BEM solution) doesn’t occure .

Last but not least ,for the parked modes with wind speed 66 m/s ( ETM IA and IB ) i am receiving the following error :
-Small angle assumption in SUBROUTINE due to large blade deflection ( Around 380s into the simulation )

I tried to reduce the time step (DT) , but that doesn’t seem to solve the problem.

P.S 1) I am aware that in reality the cut-out speed of the turbine is around 25 m/s ,but i would like to test out some extreme occasions.
P.S 2) The other 12 wind models i simulate ,are running just fine with no errors.

Thanks in advance ,
Best regards

Dear Nikos,

Well, I can’t say I have every simulated the operational case at 40 m/s because, as you say, this condition is beyond the cut-out speed of the wind turbine. At very high wind speed, the blade pitch angles will be very large and the blades will deflected upwind; see a related discussion in the following forum topic: The TSR will also get quite low and likely in a condition that the aerodynamic model was not designed for.

For the parked case, have a you modeled an idling rotor with the blades feathered at 90 degrees and the wake and unsteady airfoil aerodynamics models disabled?

Best regards,