Questions regarding InflowWind grid boundary error and Tower Strike in NREL 5MW TLP simulation

[benwys957]

[benwys957]

Dear @jjonkman,

Sorry to bother you again—I have been posting quite a bit on GitHub recently regarding various OpenFAST simulation issues as I work through my model setups. I really appreciate all the support and guidance you provide to the community!

I am currently running OpenFAST simulations for the NREL 5MW TLP model. During my runs, I encountered an InflowWind grid boundary error as well as a Tower Strike warning/abort. Below, I have detailed these two issues and would greatly appreciate your insights and guidance.

Issue 1: InflowWind Grid Boundary Error
When running OpenFAST, I encountered the following error message:

Some of my key simulation settings in Turbsim.inp, InflowFile.dat, Input.fst, AeroDyn.dat are shown below:
Turbsim.inp:

InflowFile.dat:

Input.fst:

AeroDyn.dat:

Could this be because TwrElev in the "Tower Influence and Aerodynamics" section of the AeroDyn.dat starts at 0.0? When TwrAero = True, TwrShadow = 1, and TwrPotent = 1, does OpenFAST require wind speed information near the tower base to calculate the tower aerodynamic loads and the tower influence on the wind field based on potential flow? In fact, the simulation runs normally without aborting only when I set TwrAero = False, TwrShadow = 0, and TwrPotent = 0. I would like to confirm whether my understanding of this mechanism is correct.

Issue 2: Tower Strike Warning
For the same 5MW TLP model, my simulation setup in Input.fst, InflowFile.dat, ElastoDyn,dat, AeroDyn.dat, Seastate.dat are as follows:
Input.fst:

InflowFile.dat:

ElastoDyn,dat:

AeroDyn.dat:

Seastate.dat:

I am performing misaligned wind-wave simulations with a wind speed of 23 m/s. In the InflowWind file, PropagationDir = 180, and in SeaState.dat, WaveDir = 150. Additionally, to simulate a fixed Nacyaw condition, I set YawDOF = False and NacYaw = 172 (which creates an 8° yaw misalignment relative to the incoming wind direction). During the simulation, I encountered warnings and an abort due to "Tower Strike". Could you kindly advise if there are any unreasonable parameters or potential issues with this setup?

Thank you very much for your time and helpful guidance!

Best regards,

[jjonkman]

Dear @benwys957,

Regarding (1), yes, I agree that is the issue. The aerodynamic analysis nodes in AeroDyn must remain within the wind domain during the simulation. In your case, your TurbSim wind field extends vertically from 2.5 m to 177.5 m; however, your lowest tower aerodynamic analysis node is located at ground level. I would suggest defining the lowest tower aerodynamic analysis node to be above 2.5 m, e.g. TwrElev(1) = 5 m.

Regarding (2), my guess is the tower strike is driven by your use of poor initial conditions. At a minimum, we generally recommend setting the initial rotor speed (RotSpeed) and initial blade-pitch angles (BlPitch) in ElastoDyn to their expected (mean) values conditioned on the the mean hub-height wind speed you are simulating. At 23 m/s for the NREL 5-MW baseline wind turbine, these should be RotSpeed = 12.1 rpm and BlPitch = 21.2 deg (in your case, RotSpeed is correct, but BlPitch is not). For other wind speeds, see Figure 9-1 of the NREL 5-MW specifications report: https://docs.nlr.gov/docs/fy09osti/38060.pdf.

Best regards,