AeroDyn v15 convergence issues

Jason,

Yes exactly, this is when I get the error. I run a large set of tests at different wind speeds in the context of a fatigue analysis. The error occurred in most of the cases with a 5m/s average and class A turbulence, and some cases with a 7m/s average and class A turbulence.
It rarely happened for higher wind speeds, or lower turbulence, as you guessed.

Best regards,
Yannick

Dear Yannick,

OK, it is good to know what is triggering the error. But I doubt this issue will be easy to solve. The AeroDyn source code already has logic to prevent the code from throwing an error for the case where Vx equals zero; perhaps the tolerance around zero needs to be expanded? I’ll report this as a known issue, but I can’t promise an immediate solution.

Best regards,

Dear Jason,

I have a problem when using AD15.ipt instead of AD.ipt as the AeroDyn inputs.
I ran the FAST Test04 example after changing the inputs “AeroFile” and “CompAero” in the Test04.fst file into “AWT27/Test04_AD15.ipt” and “2” {2=AeroDyn v15}, I got the following errors:


How can I fix the errors? Thanks a lot in advance.

Yingyi Liu

Dear Yingyi Liu,

It appears that we forgot to update the AeroDyn v15 input file for Test04, when converting from AeroDyn v15.02 to v15.03 in FAST v8.16. To resolve this error, simply add the following line after line for input TwrAero:

See the draft AeroDyn v15 User’s Guide and Theory Manual for more information: wind.nrel.gov/nwtc/docs/AeroDyn_Manual.pdf.

We’ll fix this in the next release of FAST.

Best regards,

Dear Jason,

Many thanks. It works. Yet here comes another error, see below screenshot:


I tried to enlarge the grid size to even GridHeight=80.0 and GridWidth=100.0 in the file of 42m_12mps.inp, and then run by using Turbsim v1.06.00. However, the resulting new 42m_12mps.wnd file still cannot resolve the above error. Do you know the possible reason?

Best regards,
Yingyi Liu

Dear Yingyi Liu,

Looking at the AWT27/Test04_AD15.ipt file, I see that the downwind tower shadow model is enabled (TwrShadow = True), with tower analysis nodes starting at ground level (TwrElev = 0). To run this model, you must use wind with data starting at the ground level.

Best regards,

Dear Jason,

Thank you for you advice, they are very helpful.
Now the problem is solved. FAST can run freely with this Test04 example.

Best Regards,
Yingyi Liu

Dear Jason,

I refer to your post:

Is it possible to fix this issue in the source code in AeroDyn? May you instruct me to do this?

Thank you very much.

Best regards,
René

Dear Rene,

As first reported here: http://forums.nrel.gov/t/fast-v8-aerodyn-v15-convergence-problems-for-low-speed-high-turbulence/1532/2, working in collaboration with Envision Energy, we have found the algorithmic problem causing the convergence issues in AeroDyn v15.00 - v15.03 when Vx goes negative. While we have not yet publicly released an update to FAST with this version of AeroDyn, you can find AeroDyn v15.04 with this issue resolved here: nwtc.nrel.gov/AeroDyn.

Bets regards,

Dear Hongbo,

I agree that you won’t receive an error regarding “no valid value of phi” if you switch from CompAero = 2 (AeroDyn v15) to CompAero = 1 (AeroDyn v14). To avoid the issue with CompAero = 2 will require you to recompile with the newer version of AeroDyn v15, as discussed in my previous post above.

I don’t know why your Linux compilation does not allow CompAero = 2.

The error you are receiving from ElastoDyn is caused because you’ve changed to CompAero = 1, but you didn’t change the format of the AeroDyn primary input file to that compatible with AeroDyn v14.

Best regards,

Dear Jason

I am facing the AeroDyn v.15 convergence issue for Vx value <0. I understand it has been corrected in AeroDyn v15.04. How do I get the FAST version I am using (v8.16.00a) to run with AeroDyn v15.04, instead of v15?

Sincerely

Abhinav

Dear Abhinav,

I don’t have a compiled Windows executable of FAST v8 linked with AeroDyn v15.04. However, I suggest that you simply upgrade to OpenFAST v1.0.0, which includes the AeroDyn v15.04 changes, as well as a few other more minor improvements to the FAST source code relative to v8.16. You can read about the changes and download a 64-bit Windows executable of OpenFAST v1.0.0 here: nwtc.nrel.gov/OpenFAST.

Best regards,

Dear Jason

Thank you, for the reply. I will upgrade to OpenFAST.

Sincerely

Abhinav

Dear Jason
I hope you are doing well.
I have been working on Test #21,the OC4 jacket, for a while and after setting some more output requested parameters in output lists of each module of the FAST v.8 tried to run the code.In the FAST primary input file the computational flags were assigned as follows:
compElast=2,compInflow=1,compAero=2,compServo=1,compHydro=1,compSub=1,compMooring=0,compIce=0.
**The compElast was set to 2 as the purpose of my test is to investigate maximum effects due to external forces implied to the whole structure(piles,Jacket,Tower,RNA and Blades).But when I run the code some warnings due to unsteady airfoils and some errors are occured those I have not been able to get rid of them so far even though I managed to do whatever I thought could have likely related to this.I atteched the errors photos here and if you could help me I would be pleased.
Best regards,
Arsalan Shahmohammadi

Dear Arsalan,

Setting CompElast = 2 will enable BeamDyn, which is not really needed if you are still modeling the NREL 5-MW baseline wind turbine. I suggest setting CompElast = 1 to enable ElastoDyn to model the blade structural dynamics.

Best regards,

Dear Jason
I really appreciate for your quick answer as always.
Sincerely,
Arsalan

Dear Dr. Jonkman,

I am running test13 with the version v8.16 and AeroDyn v15.03. and I am using Turbsim to generate wind velocity time histories for mean wind speed at the range of 4, 6,8 …24m/s and wanna get structural response under these wind speeds. For simplicity, I did no any other changes. However, there seems exist the convergence problem in AeroDyn discussed above, but my problem seems to be more odd.

I almost read all the relevant posts on this forum. I know the adjustment of DT (my DT is 0.005s, so I think this is okay), but I did not change the initial condition as I do not know what better initial rotor speed value should be in this case?

So I think the main problems should lie in the parameters in the AeroDyn input file. I run the test13 with the AFAeroMod=UA and SkewMod=2, for the mean wind speed >14m/s, every time I will get this fatal error below:

Then, By referring to the previous posts, In my simulation, I change the AFAeroMod from UA to Steady model, SkewMod=1. The simulation results are: for the mean wind speed between 4m/s-14m/s, it can run successfully, above 14m/s FAST will give several types of fatal errors, shown in screensnaps below: the Vs, Vy and theta will be minus randomly, and occasionally FAST will give error saying FF wind array boundaries violated.


So with the results above, I would like to seek your suggestions, or do you know any info about how to make FAST work successfully for WP 1.5MW wind turbine. Or you think this convergence problem in AeroDyn v15.03 can not be fixed, the only choose is to using AeroDyn v14 or using the latest OpenFAST?

Looking forwards to your reply!

Best regards,
Charlie

Dear Charlie,

The AeroDyn convergence issues that were common in AeroDyn v15.03 of FAST v8.16 have been resolved in OpenFAST v1.0.0 (or newer), so, you could always upgrade to see if that solves your problem. However, I recall that the convergence issues happened most frequently at low wind speeds with high turbulence, which is not where you are seeing issues.

Otherwise, I see large deflection warnings in your simulation, which I would guess in your case are caused by the use of improper initial conditions. As discussed several times on this forum, it is important to set at a minimum the initial conditions of rotor speed and blade-pitch angle appropriate to each mean wind speed. It doesn’t sound like you’ve calculated/applied these for the WindPACT 1.5-MW turbine (and I don’t have them myself), but the process for calculating them has been discussed on our forum…e.g. here: http://forums.nrel.gov/t/wp-1-5-mw-turbine-pitch-angle/1026/2.

Best regards,

Dear Dr. Jonkman,

Appreciate your assistance. I really do not know so important the initial condition setting would be for FAST! I did the sensitivity analysis for WP 1.5 WM following your given post, now my model can run successfully.

Many thanks!
Charlie

Glad to hear it.

The initial conditions of rotor speed and blade-pitch angle are often important for the controller.

Best regards,