Good morning all,

I am trying to simulate one of the sub cases in DLC 22 for the NREL 5MW according to the DTU Design Load Cases definition, which is DLC22y - Power production with abnormal yaw error. The simulation parameters are 4-26 m/s in steps of 2 m/s, 1 turbulence seed with NTM model per wind speed and a yaw angle range of 15 deg to 345 deg in steps of 15 deg. In total there are 276 simulation files. However some of the simulations fail and the error message is shown below -

FAST_Solution:FAST_AdvanceStates:SolveOption2c_Inp2AD_SrvD:InflowWind_CalcOutput:CalcOutput:IfW_Bl

adedFFWind:CalcOutput [position=(-45.747, -29.214, 7.9952)]: FF wind array boundaries violated.

Grid too small in Z direction (height (Z=7.9952 m) is below the grid and no tower points are

defined).

FAST encountered an error at simulation time 93.844 of 700 seconds.

Simulation error level: FATAL ERROR

Aborting OpenFAST.

The TurbSim parameters I have used to create these wnd files are -

--------Turbine/Model Specifications-----------------------

31 NumGrid_Z - Vertical grid-point matrix dimension

31 NumGrid_Y - Horizontal grid-point matrix dimension

0.05 TimeStep - Time step [seconds]

700 AnalysisTime - Length of analysis time series [seconds] (program will add time if necessary: AnalysisTime = MAX(AnalysisTime, UsableTime+GridWidth/MeanHHWS) )

“ALL” UsableTime - Usable length of output time series [seconds] (program will add GridWidth/MeanHHWS seconds unless UsableTime is “ALL”)

90.0 HubHt - Hub height [m] (should be > 0.5*GridHeight)
170.0 GridHeight - Grid height [m]
180.0 GridWidth - Grid width [m] (should be >= 2*(RotorRadius+ShaftLength))

0 VFlowAng - Vertical mean flow (uptilt) angle [degrees]

0 HFlowAng - Horizontal mean flow (skew) angle [degrees]

In all the failed cases, the error message is the same, that the grid is too small in Z direction. Most of the failed cases have a high nacelle yaw angle (~100 deg). My question is, if the grid has the correct dimensions for the cases that ran successfully, how is it that turbine yaw causes the grid to become small in the Z direction for the failed cases? The turbine dimensions have not changed in the Z direction, just the nacelle has been given different yaw angles for each case.

It would be very helpful to get some guidance in this matter. Apologies if I have posted this in the wrong place.

Thanks in advance!

Best regards,

Vishal