OpenFast Error in simulations

Wind & Water
1

Dear @Jason.Jonkman
I was trying to run an OpenFast simulation and got the following error.

In the wind files and the .fst files and I couldn’t find the number 51.158m mentioned in the error.

image
image795×834 20.1 KB

2

Dear @Karthik.Prakash,

The AeroDyn module of OpenFAST needs to be able to access ambient wind data at all aerodynamic analysis nodes along the blades and tower at all time steps. The undisplaced/undeflected positions of each aerodynamic analysis node are specified in the AeroDyn input file(s), but these positions will change as a result of turbine displacement/deflection over time. It is this displaced/deflected position that is mentioned in the error. In your case, it looks like a node is below the grid.

Best regards,

3

Dear @Jason.Jonkman

Thanks a lot for getting back. Which parameter in which file should be changed to remove this error. Is it the below Grid height and Grid Width paramter in .inp file for creating Wind from Turbsim that has to be changed. (Below, I don’t know the shaft length, so I assumed a much higher number than rotor dia to cover the rotor). I took the rotor dia. (or radius from ElastoDyn file, 63 TipRad - The distance from the rotor apex to the blade tip (meters)).

     90   HubHt           - Hub height [m] (should be > 0.5*GridHeight)
     120   GridHeight      - Grid height [m]
     120   GridWidth       - Grid width [m] (should be >= 2*(RotorRadius+ShaftLength))
4

Dear @Karthik.Prakash,

Your GridHeight and GridWidth are too small for the NREL 5-MW baseline wind turbine, which has a rotor diameter of 63*2 = 126 m. I would typically use a 10% margin to account for displacement/deflection, so, I would suggest using about 140 m.

Best regards,

6

Hi @Jason.Jonkman

Thanks a lot for getting back. I made the Grid height and Width to 150, but got the below error. Should The grid width and height cover the tower also, for example Grid height or width = Rotor dia + hub height ?

image
image1191×342 26.5 KB

7

Dear @Karthik.Prakash,

If you have tower aerodynamics enabled, you likely have aerodynamic nodes that extend along the tower well below the rotor. You can generate wind there by setting GridHeight larger than GridWidth (see Figure 5 in the TurbSim documentation for more information: https://www.nrel.gov/wind/nwtc/assets/downloads/TurbSim/TurbSim_v2.00.pdf) or by outputting from TurbSim wind along the tower (WrADTWR = TRUE). You can also eliminate tower aerodynamic nodes that extend below the wind domain.

Best regards,

8

Dear @Jason.Jonkman ,

Thanks a lot for getting back. I have few queries:

  1. Which variable tells me if if tower aerodynamics is enabled and what are the benefits of enabling the tower aerodynamics.
  2. By setting GridHeight greater than GridWidth to capture the tower aerodynamics nodes, should the Grid height be set equal to at least Hub height + Rotor dia to capture the tower aerodynamic nodes OR it does not matter as long as my Gridheight>Gridwidth irrespective of the number and that covers the rotor dia.
  3. How can I eliminate the tower aerodynamic nodes the is below the wind domain
9

Dear @Karthik.Prakash,

Here are my responses:

  1. The tower section of the AeroDyn input file is used when TwrPotent > 0, TwrShadow > 0, or TwrAero = TRUE. TwrAero is likely not important during operational conditions, but is likely important during parked/idling conditions. TwrPotent is likely important for upwind rotors that are operational, TwrShadow is likely important for downwind rotors that are operational.

  2. It is up to you to make modeling choices that meet your needs. You must ensure that all aerodynamic analysis nodes, which are defined by you in the AeroDyn input file, fall within the wind domain, which is also defined by you.

  3. The aerodynamic nodes along the tower are located via input TwrElev in the tower section of the AeroDyn input file. The lowest value of TwrElev must be above the lowest boundary of the wind domain.

Best regards,