You are correct that the previous results I showed were without UA. Disabling the Pitt/Peters skewed-wake correction model did indeed allow the simulation to compute fully with seemingly reasonable results, so that’s great! I’ve shown the inflow-skew angle as well as Vx at the previously problematic node for both SkewMod = 1 and SkewMod = 2 for reference. These values, at least, seem to be comparable between the two cases before failure. The skew angle goes to a maximum of a bit under 80 degrees.
I’ll have to do a bit of reading to understand the implications of using a different skewed-wake correction model. Feel free to let me know if you think there is anything I should be aware of in that regard! (I’m using these simulations to extract loads for FEM blade design and analysis.) Overall, though, I’m happy to have the simulation running at this point. Thanks for your thorough support!
The Pitt and Peters skewed-wake model of AeroDyn v15 (SkewMod = 2) works well for small to moderate inflow-skew angles, but is invalid for large skew angles (much greater than 45 degrees). This is mentioned in section 6.4 of the draft AeroDyn v15 User’s Guide and Theory Manual: wind.nrel.gov/nwtc/docs/AeroDyn_Manual.pdf. From your plot, it looks like the inflow-skew angle exceeds 70 degrees; I recommend disabling the Pitt and Peters skewed-wake model at these extreme inflow-skew angles.
I’ve noticed the same issue for power production calculations with turbulent wind with high turbulences (e.g. for rated wind speed) without yaw error/direction change. I’ve solved the problem like Austin has done, but isn’t it poor to disable wake and unsteady aerodynamics in AeroDyn v15 under these conditions?
How valid is the model with these restrictions?
I have had the same problem as Austin with the Mach number, I have change AFAeroMod to 1 and solve that problem. Then, I couldn’t solve the problem with negative wind-speed Vx disabling the wake or unsteady airfoil aerodynamics calculation. So I decide to solve it with AeroDyn V14.
To use AeroDyn V14 I just need to change CompAero to 1 on the .fst file, Am I correct?
When I try to simulate with that change I have this error:
input for file
3Hywind_AeroDyn15.dat" occurred while trying to read Blade element line1.
How can I solve it? The main objetive is to simulate with AeroDyn14 to avoid the negative wind-speed Vx. Is it necessary to change anyhing else apart from the CompAero in the .fst?
Which version of FAST / OpenFAST are you using? As discussed above, there are two solutions:
(1) If you are using FAST v8.16, upgrade from AeroDyn v15.03 to AeroDyn v15.04 (or newer). If you are using OpenFAST, AeroDyn should already be updated.
(2) Switching to AeroDyn v14. However, the AeroDyn input files are very different between AeroDyn v14 and AeroDyn v15. So, when you change CompAero to 1, you must also switch to the AeroDyn v14 input file format. There are sample AeroDyn v14 input files for the NREL 5-MW baseline turbine in the archives of both FAST v8 and OpenFAST.
I’m using OpenFAST-v2.4.0. Thast’s why I don’t understand all this errors. I ve reading in this foro the errors have been solutioned in newest version. So I don’t understand why I am having them. This error may ocurr due to the desviation of the wind with the rotor (45 degrees aprox.).
I am simulating with SkewMod = 1 and AFAeroMod=1, as yo recomended in this post.
This is the error when I try to simulate with AFAeroMod=2 and SkewMod=2:
blade 2):Compute_UA_AirfoilCoefs:UA_CalcOutput:Mach number exceeds 1.0. Equations cannot be
CalcOutputs_And_SolveForInputs:SolveOption1:ED_HD_InputOutputSolve:HydroDyn_CalcOutput: Angles in
GetSmllRotAngs() are larger than 0.4 radians.
ED_HD_InputOutputSolve:HydroDyn_CalcOutput: Angles in GetSmllRotAngs() are larger than 0.4
FAST encountered an error at simulation time 123.62 of 300 seconds.
Simulation error level: FATAL ERROR
The problem with the GetSmllRotAngs() are larger than 0.4 radians, start before the simulation stop in every step time.
This is the error with AFAeroMod=1 and SkewMod=2 or SkewMod=1, it doesn’t change:
iformWind_CalcOutput:GetWindSpeed:Height must not be negative. Error calculating the wind speed
at position (43122, -34986, -61939) in the wind-file coordinates
FAST encountered an error at simulation time 123.8 of 300 seconds.
Simulation error level: FATAL ERROR
The problem with the GetSmllRotAngs() are larger than 0.4 radians, start before the simulation stop in every step time in this simulation too.
Well, it looks like your model has gone unstable in the platform. The exact error that aborts the simulation (whether it be high Mach number or a node passing the boundaries of the TurbSim grid) is determined by which features you’ve enabled in the model, but is probably irrelevant. It is the instability in the platform that needs to be fixed.
It appears that you are running a simulation of an offshore wind turbine. Is it fixed or floating? Are you running a model NREL has provided or one you made yourself? Does the model run stably in the absence of wind or wave excitation?
Well, I would suggest simplifying the model to debug.
If the problem is controller related, I would expect the model to run well if you disable the generator degree of freedom in ElastoDyn (GenDOF = False). Does it, or does setting GenDOF = False still result in large floater / platform motions?