FAST v8 AeroDyn v15 convergence problems for low-speed, high-turbulence

Provide feedback, request enhancements, and get help with wind-turbine computer-aided engineering tools.

Moderators: Bonnie.Jonkman, Jason.Jonkman

Austin.Herrema
Posts: 8
Joined: Mon Oct 03, 2016 9:40 am
Organization: Iowa State University
Location: Iowa

FAST v8 AeroDyn v15 convergence problems for low-speed, high-turbulence

Postby Austin.Herrema » Fri Jan 06, 2017 1:11 pm

Dear all,

I using FAST v8 with AeroDyn v15 to simulate the NREL 5MW turbine (with Sandia 5MW blade definition) in TurbSim-generated turbulence fields (normal and extreme turbulence) throughout the operating range. Simulation setup is based on Certification Test #18. I am using the steady airfoil aerodynamics model (AFAeroMod = 1), an uncoupled skewed wake correction model (SkewMod = 1), and I do not include tower aerodynamic effects.

For some wind conditions (extreme turbulence model at 3, 5, 7, and 9 m/s and normal turbulence model at 3 m/s), the BEM solution is failing well into the simulation (anywhere from 100 s to 1200 s in) with a negative Vx. For example:

Code: Select all

 FAST_Solution:FAST_AdvanceStates:AD_UpdateStates:BEMT_UpdateStates(node 7, blade
 3):BEMT_UnCoupledSolve:DeterminePhiBounds:There is no valid value of phi for these operating
 conditions!  Vx = -1.50015E-02, Vy = 14.886, rlocal = 19.936, theta = 0.17736

 FAST encountered an error at simulation time 154.6 of 200 seconds.
  Simulation error level: FATAL ERROR

Although I wouldn't expect these steps to be helpful in this case, I have tried adding a correction step, making DT smaller, and changing InterpOrder, all to no avail. I set the initial conditions according to the discussion here https://wind.nrel.gov/forum/wind/viewtopic.php?f=4&t=1728&p=8211#p8211 (that post had to do with simulations failing right away, which was solved by setting correct initial conditions--now the failure happens well into simulation). I understand that Vx is the relative wind speed (wind speed minus structural speed); the structural solution seems reasonable up until failure for my simulations.

Based on the discussion with Yannick in https://wind.nrel.gov/forum/wind/viewtopic.php?f=4&t=1514&p=7513&hilit=negative+vx#p7513 it appears that problems stemming from small/negative Vx may be a known issue. Is that the case? Is there anything else I might try? Otherwise I may try to see if there is any difference using AeroDyn v14.

Thank you,
Austin Herrema

Jason.Jonkman
Posts: 4933
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: FAST v8 AeroDyn v15 convergence problems for low-speed, high-turbulence

Postby Jason.Jonkman » Sat Jan 07, 2017 12:56 pm

Dear Austin,

The failure of the BEM algorithm of AeroDyn v15.00 - v15.03 when Vx goes negative is a known issue. Working in collaboration with Envision, we have found the algorithmic problem causing the issue. While we have not yet publicly released the updated code, you can find a version of AeroDyn v15 with issue resolved here: https://github.com/NWTC/AeroDyn. Reverting to the older AeroDyn v14 will also work.

Bets regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Austin.Herrema
Posts: 8
Joined: Mon Oct 03, 2016 9:40 am
Organization: Iowa State University
Location: Iowa

Re: FAST v8 AeroDyn v15 convergence problems for low-speed, high-turbulence

Postby Austin.Herrema » Mon Jan 09, 2017 7:39 am

Dear Dr. Jonkman,

Thank you for the response; it is good to know that this issue is already being addressed and that a solution has been made available. Thanks to the NREL team (and Envision) for their great work!

Kind regards,
Austin

Tohid.Bagherpour
Posts: 15
Joined: Wed Feb 08, 2017 8:28 pm
Organization: HUST
Location: China

Re: FAST v8 AeroDyn v15 convergence problems for low-speed, high-turbulence

Postby Tohid.Bagherpour » Sat Feb 11, 2017 3:12 am

Dear Dr. Jonkman,

I'm using FAST8.16-Beamdyn, Aerodyn15 to simulate my case. it works well when I set to CompElast=1,CompAer=2.
when I switch to CompElast=2, it appears an error like in snapshot.
I checked the Beamdyn Distributed properties and blade geometry files, it ran in Beamdyn Stand alone without any error.
Moreover I tried to change ElemOrder=8, and DT=0.000125.
BEMT Error.jpg
BEMT Error.jpg (193.67 KiB) Viewed 2759 times


Kind regards,
Tohid.

Jason.Jonkman
Posts: 4933
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: FAST v8 AeroDyn v15 convergence problems for low-speed, high-turbulence

Postby Jason.Jonkman » Mon Feb 13, 2017 7:10 am

Dear Tohid,

You asked a similar question in the following forum topic: viewtopic.php?f=4&t=1535&p=8549. I've responded there. Please don't post the same question in multiple forum topics.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Tohid.Bagherpour
Posts: 15
Joined: Wed Feb 08, 2017 8:28 pm
Organization: HUST
Location: China

Re: FAST v8 AeroDyn v15 convergence problems for low-speed, high-turbulence

Postby Tohid.Bagherpour » Mon Feb 13, 2017 7:27 pm

Dear Jason,

i appologize for the mistake. I will follow my question in aforementioned link.

Best regards,
Tohid.

Fiona.Luedecke
Posts: 8
Joined: Fri Aug 25, 2017 5:56 am
Organization: University of Stuttgart
Location: Germany

Re: FAST v8 AeroDyn v15 convergence problems for low-speed, high-turbulence

Postby Fiona.Luedecke » Tue Dec 12, 2017 12:15 am

Dear Jason,

I tried to simulate a full nacelle rotation with still wind using AeroDyn 15 and the yaw maneuver. As I know from the posts in this section the error I got, is a well known problem. So I tried to include the release of AeroDyn, you posted the link for, but unfotunatly I still get the error with the new compiled FAST version. My wind field is uniform with a constant speed of 0.5 m/s in horizontal direction and no shear.

I guess, I did not include the source code for the changed AeroDyn in a correct way.
Do you have a short manual how to include the changed AeroDyn into the FAST source code, especially concerning the correct libary NWTC?

Thank you in advance.
Best regards,
Fiona

Jason.Jonkman
Posts: 4933
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: FAST v8 AeroDyn v15 convergence problems for low-speed, high-turbulence

Postby Jason.Jonkman » Tue Dec 12, 2017 1:44 pm

Dear Fiona,

Compiling FAST v8.16 with AeroDyn v15.04 has been discussed in the following forum topic: viewtopic.php?f=4&t=1824&p=9119.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov


Return to “Computer-Aided Engineering Software Tools”

Who is online

Users browsing this forum: No registered users and 1 guest