FAST.Farm Error: "GF wind array was exhausted" – Time Synchronization Issue with TurbSim

Wind & Water
1

Dear FAST.Farm and TurbSim community,

I am encountering an error when running a FAST.Farm simulation with turbulent inflow generated by TurbSim. The error messages indicate that FAST.Farm is trying to access wind data at negative time steps, which is outside the range of the generated wind field. Here are the details:

Farm_Initialize:AWAE_Init:AWAE_UpdateStates:InflowWind_CalcOutput:CalculateOutput:IfW_FlowField_GetVelAcc:Grid3DField_GetCell:
Error: GF wind array was exhausted at 0.1 seconds (trying to access data at -0.48498 seconds). IT_Lo=-4, IT_HI=-3

Configuration Details:

TurbSim Input File:

  • GridWidth = 240 m

  • GridHeight = 204 m

  • AnalysisTime = 7800 s

  • UsableTime = "ALL"

  • TimeStep = 0.1 s

FAST.Farm Input File:

  • TMax = 3900 s

  • DT_Low = 0.1 s

  • DT_High = 0.1 s

  • Mod_AmbWind = 3 (multiple instances of InflowWind)

  • NY_High = 37, dY_High = 6.4864 m, Y0_High = -120 m (for both turbines)

I’ve tried different configuration :

Grid Alignment:

  • Adjusted Y0_High and dY_High to ensure the high-resolution grid is entirely within the TurbSim flow field (GridWidth = 240 m).

  • Confirmed that the grid extends from -120 m to ~120 m, which is within the TurbSim limits.

Time Synchronization:

  • Verified that DT_Low and DT_High in FAST.Farm match the TimeStep in TurbSim (0.1 s).

  • Ensured TMax in FAST.Farm (3900 s) is less than AnalysisTime in TurbSim (7800 s

Simulation Start Time:

  • Confirmed that the simulation should start at t = 0 s (no negative start time is specified).

Question :

  1. Why is FAST.Farm trying to access wind data at negative time steps (-0.48498 s, -46.211 s)?

  2. Are there any hidden parameters or delays in FAST.Farm or TurbSim that could cause this issue?

  3. Could the issue be related to the InflowWind module configuration or the way FAST.Farm initializes the wind field?

Any insights or suggestions would be greatly appreciated!

Thank you in advance,

2

Dear @Tom.Salic,

I suspect you are running into the same issue reported in the OpenFAST GitHub repository: FAST.Farm Outside the grid Type: Usage question · Issue #3183 · OpenFAST/openfast · GitHub, which we isolated to a bug in FAST.Farm. My understanding is a fix is forthcoming soon.

Best regards,

1 Like
3

Ok thank you for the quick response. I’m waiting for the updates soon.