Turning off Unsteady aerodynamics and no valid value of phi.

Dhaneesh.Machavarapu · March 18, 2020, 9:31am

Sir,

I was working on monopile supported offshore wind turbine using FASTv8. When I was trying to run it FAST was aborting.

Running FAST (v8.16.00a-bjj, 27-Jul-2016), compiled as a 32-bit application using single
precision
linked with NWTC Subroutine Library (v2.09.00, 23-Jul-2016)

Heading of the FAST input file:
FAST Certification Test #19: NREL 5.0 MW Baseline Wind Turbine with OC3 Monopile RF
Configuration, for use in offshore analysis

Running ElastoDyn (v1.04.00a-bjj, 26-Jul-2016).

Running BeamDyn (v1.01.04, 26-Jul-2016).

Running AeroDyn (v15.03.00, 27-Jul-2016).

Running AirfoilInfo (v1.01.00a-bjj, 5-Apr-2016).

Running BEM (v1.02.00, 29-Jun-2016).
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. BladeNode = 1, Blade = 1
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. BladeNode = 2, Blade = 1
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. BladeNode = 3, Blade = 1
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. BladeNode = 4, Blade = 1
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. BladeNode = 1, Blade = 2
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. BladeNode = 2, Blade = 2
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. BladeNode = 3, Blade = 2
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. BladeNode = 4, Blade = 2
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. BladeNode = 1, Blade = 3
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. BladeNode = 2, Blade = 3
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. BladeNode = 3, Blade = 3
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. BladeNode = 4, Blade = 3

Running InflowWind (v3.03.00, 26-Jul-2016).
Opening InflowWind input file:
E:/softwares/Project/FAST/folder/5MW_Baseline/NRELOffshrBsline5MW_InflowWind_12mps.dat

Reading a 31x31 grid (145 m wide, 17.5 m to 162.5 m above ground) with a characteristic wind
speed of 11.4 m/s. This full-field file was generated by TurbSim (v1.06.00, 21-Sep-2012) on
18-Mar-2020 at 11:57:37.

Processed 12855 time steps of 20-Hz full-field data (642.7 seconds).

Running ServoDyn (v1.06.00a-bjj, 26-Jul-2016).

Running ServoDyn Interface for Bladed Controllers (using Intel Visual Fortran for Windows,
14-Oct-2015).

Running HydroDyn (v2.05.01, 27-Jul-2016).
Generating incident wave kinematics and current time history.
Calculating second order difference frequency wave kinematics.
Calculating second order sum frequency wave kinematics.

Running SubDyn (v1.03.00, 11-Apr-2016).
Calculating Internal Modal Eigenvectors
Timestep: 0 of 630 seconds.

FAST_Solution0:CalcOutputs_And_SolveForInputs:SolveOption2:SrvD_CalcOutput:Running with torque
and pitch control of the NREL offshore 5MW baseline wind turbine from DISCON.dll as written by J.
Jonkman of NREL/NWTC for use in the IEA Annex XXIII OC3 studies.

Warning: Turning off Unsteady Aerodynamics due to high angle-of-attack. BladeNode = 5, Blade = 1

FAST_Solution:FAST_AdvanceStates:AD_UpdateStates:BEMT_UpdateStates(node 5, blade
1):BEMT_UnCoupledSolve:DeterminePhiBounds:There is no valid value of phi for these operating
conditions! Vx = 6.6517, Vy = -37.919, rlocal = 11.743, theta = 0.22769

FAST encountered an error at simulation time 1.50000E-02 of 630 seconds.
Simulation error level: FATAL ERROR

Aborting FAST.

I am not able to understand what are all those warnings. I got these warnings and error even after I adjusted the blade pitch angle according to my mean wind speed ( 0 degree for 11.4 m/s). How can I rectify these warnings and error.

Thank you.

Jason.Jonkman · March 18, 2020, 2:50pm

Dear Dhaneesh,

The error regarding “no valid value of phi” has been discussed several times on this forum. In summary, upgrading from AeroDyn v15.03 in FAST 8.16 to AeroDyn v15.04 or upgrading from FAST v8.16 to OpenFAST will solve the problem.

Best regards,

Dhaneesh.Machavarapu · March 19, 2020, 6:04pm

sir,

when I was trying to run FAST by using Aerodyn v15.04 FAST was aborting.

FAST (v8.16.00a-bjj, 27-Jul-2016)

This program comes with ABSOLUTELY NO WARRANTY. See the “license.txt” file distributed with this
software for details.

Running FAST (v8.16.00a-bjj, 27-Jul-2016), compiled as a 32-bit application using single
precision
linked with NWTC Subroutine Library (v2.09.00, 23-Jul-2016)

Heading of the FAST input file:
FAST Certification Test #19: NREL 5.0 MW Baseline Wind Turbine with OC3 Monopile RF
Configuration, for use in offshore analysis

Running ElastoDyn (v1.04.00a-bjj, 26-Jul-2016).

Running BeamDyn (v1.01.04, 26-Jul-2016).

Running AeroDyn (v15.03.00, 27-Jul-2016).

FAST_InitializeAll:AD_Init:ReadInputFiles:ReadPrimaryFile:Invalid numerical input for file
“E:/softwares/Project/FAST/folder/5MW_Baseline/NRELOffshrBsline5MW_OC3Monopile_AeroDyn15.dat”
occurred while trying to read AirDens.

FAST encountered an error during module initialization.
Simulation error level: FATAL ERROR

Aborting FAST.

Can I get some help regarding where I am doing wrong?

Jason.Jonkman · March 19, 2020, 6:14pm

Dear Dhaneesh,

From your command window, it says, “Running AeroDyn (v15.03.00, 27-Jul-2016).” So, it looks like you are using AeroDyn v15.03, not AeroDyn v15.04.

Regardless, from the error message, it doesn’t look like your AeroDyn input file is formatted properly. As with any input file format problem, I suggest that you use the Echo option from the input file to debug errors in the input-file processing.

Best regards,

Dhaneesh.Machavarapu · March 20, 2020, 5:53am

Sir,

When you told me to upgrade my input file to aerodyn v15.04. what I did was I copied Aerodyn v15.04 input file and its Airfoils and Aerodyn blade data files from Aerodyn module to my test folder and mentioned its Path in my Test 19 fst file. And I think that was not the correct way. Because the echo file I got was incomplete. I think the reason was I haven’t given source code for this version of input file. Is this the reason ?

If not, can I get some help where I was going wrong. I was attaching the echo file which I got when FAST was aborting.
New Microsoft Excel Worksheet (3).xlsx (8.74 KB)

Jason.Jonkman · March 20, 2020, 1:36pm

Dear Dhaneesh,

Correct, you’ll need to recompile FAST with the updated source code for AeroDyn v15.04 before using AeroDyn v15.04-formatted input files. Or you can upgrade from FAST v8.16 to OpenFAST.

Best regards,

Felipe.Alcantara · March 30, 2020, 1:45pm

Dear sir/madame,

I was having no problem running some analysis with diferent environmental conditions on the 5MW_Baseline offshore monopile wind turbine that i got when i donwloaded the FAST v8.16 files.

However, once i changed the tower and substructure properties, in the ElastoDyn, AeroDyn, SubDyn and HydroDyn files, the simulation started aborting with the following error message: “There is no valid value of phi for these operating conditions! Vx = -0.48585, Vy = 15.936, rlocal = 11.744, theta = 0.23227”

Therefore, after reading some of the questions in this forum, i decided to update from FAST v8.16 to OpenFAST, because then i would be able to use the Aerodyn 15.04, what could fix this issue. The problem is that, even after the upgrade, the simulation continued aborting, even though Vx wasn’t negative. The error messages i’ve been receiving for diffente blades and blade nodes are the following:

“Warning: Turning off Unsteady Aerodynamics due to high angle-of-attack. BladeNode = 10, Blade = 1”

“BEMT_UpdateStates(node 7, blade 2):BEMT_UnCoupledSolve:There is no valid value of phi for these operating conditions: Vx = 0.71932, Vy = -35.142, rlocal = 19.941, theta = 0.17731, geometric phi = 3.1211
BEMT_UpdateStates(node 8, blade 2):BEMT_UnCoupledSolve:There is no valid value of phi for these operating conditions: Vx = 1.682, Vy = -27.2, rlocal = 24.039, theta = 0.15718, geometric phi = 3.0798”

I think the problem is somehow related to big deflections of the blades, but i don’t understand why i started having this problem after i changed the tower and substructure properties and i don’t know how to fix it.

Jason.Jonkman · March 30, 2020, 1:59pm

Dear Felipe,

After upgrading to AeroDyn v15.04 or newer, you may still get a warning about “no valid value of phi”, but this will not trigger an abort. The warning should say, “This warning will not be repeated though the condition may persist” and the simulation should continue. Are you sure you are using OpenFAST?

Best regards,

Felipe.Alcantara · March 30, 2020, 2:12pm

Dear Jason,

Thank you for answering so quickly.

Yes, i am pretty sure i am using OpenFAST. In order to upgrade from FAST v8.16 to OpenFAST, i replaced the AeroDyn 15.03 inpute file by the Aerodyn 15.04 input file and ran the .fst file with the OpenFAST_x64.exe.

Is there something else i should have done?

I attached a text file with the messages i received when trying to run this simulation.
Error - OpenFAST.txt (15.1 KB)

Jason.Jonkman · March 30, 2020, 4:23pm

Dear Felipe,

Well, it is hard for me to guess what the problem is; I see many warnings that there is “no valid value of phi” with a large range of conditions and “Turning off Unsteady Aerodynamics due to high angle-of-attack”. Regardless, these warnings are not themselves triggering the fatal error in OpenFAST. Unfortunately, the true error message is hidden because the warning messages take up so much space (each write screen line length is limited and the last message ends abruptly with “…rlocal = 28.137, thet”; the actual error message would have happened after these warning messages). My guess is the actual error is that the turbine deflections are so large that an aerodynamic analysis node has left the wind field domain, but this is just a guess. I would suggest plotting other things like rotor speed, blade pitch, blade deflection, and tower deflection to get a better sense of what is happening before the simulation aborts. Simplifying the model by disabling features is likely needed to debug the problem.

Best regards,

Felipe.Alcantara · March 30, 2020, 5:34pm

Dear Jason,

I followed your advice and turned off the computation of aerodynamic loads.

Then i received the following message:

“FAST_Solution:FAST_AdvanceStates:ED_ABM4:ED_CalcContStateDeriv:SetCoordSy:Small angle assumption
violated in SUBROUTINE SmllRotTrans() due to a large blade deflection (ElastoDyn SetCoordSy). The
solution may be inaccurate. Simulation continuing, but future warnings from SmllRotTrans() will
be suppressed.”

Do you know how i can fix this problem?

I said earlier that i started having these problems after i changed the properties of the tower and substructure. Do you think that the structure that was introduced is not stiff enought, resulting in big deflections?

What intrigues me is that i haven’t changed the blades structural properties.

Jason.Jonkman · March 30, 2020, 6:06pm

Dear Felipe,

The “large blade deflection” warning has been discussed many times on this forum.

I’m not sure how you changed the tower and substructure properties, but could the structural model have gotten stiffer (higher natural frequencies) with your changes? If so, using a smaller time step would probably solve the problem. Use “Search…” in the upper-right to find similar questions and answers.

Best regards,

Felipe.Alcantara · March 30, 2020, 9:26pm

Dear Jason,

I looked at some posts related to “large blade deflection” and i decided to reduce the time step, it worked. I stoped receiving the warnings and the simulation ran normally.

However, I was looking at the YawBrFxp time series and i am not sure if it is how it’s supposed to be. There force oscilates a lot, assuming even some negative values sometimes.

My guess is that this is caused by ressoance on the tower structure, but i want your opinion about it.

I attached the YawBrFxp and Wind1VelX time series.

Kind regards.

Jason.Jonkman · March 30, 2020, 9:37pm

Dear Felipe,

I see some strong oscillations, but it is hard for me to say whether this is expected or not. How does this compare to the same simulation ran with the original model where you didn’t change the substructure? It would also be useful to plot other outputs (e.g. tower-top deflection and tower-base moment), as well as look at the statistics and power spectra density of the time series.

Best regards,

Dhaneesh.Machavarapu · April 4, 2020, 8:32am

Sir,

Sorry for my late reply. Thank you for your earlier suggestion. As per your earlier suggestion I have upgraded from FASTv8.16 to OPENFAST. But when I was trying to run my 5MW_OC3Mnpl_DLL_WTurb_WavesIrr fst File I was getting these errors.

C:\Users\Bhargav>E:\softwares\Project\openfast\offshore\5MW_OC3Mnpl_DLL_WTurb_WavesIrr\OpenFAST_x64.exe E:\softwares\Project\openfast\offshore\5MW_OC3Mnpl_DLL_WTurb_WavesIrr\5MW_OC3Mnpl_DLL_WTurb_WavesIrr.fst

OpenFAST

Copyright (C) National Renewable Energy Laboratory

This program is licensed under Apache License Version 2.0 and comes with ABSOLUTELY NO WARRANTY.
See the “LICENSE” file distributed with this software for details.

OpenFAST-v1.0.0
Compile Info:

Architecture: 64 bit
Precision: single
Execution Info:
Date: 04/04/2020
Time: 13:48:16+0530

OpenFAST input file heading:
FAST Certification Test #19: NREL 5.0 MW Baseline Wind Turbine with OC3 Monopile RF
Configuration, for use in offshore analysis

Running ElastoDyn.
Running AeroDyn.

FAST_InitializeAll:AD_Init:ReadInputFiles:ReadPrimaryFile:Invalid logical input for file
“E:/softwares/Project/openfast/offshore/5MW_OC3Mnpl_DLL_WTurb_WavesIrr/NRELOffshrBsline5MW_OC3Mono
pile_AeroDyn15.dat” occurred while trying to read TipLoss.
ReadPrimaryFile:Invalid numerical input for file
“E:/softwares/Project/openfast/offshore/5MW_OC3Mnpl_DLL_WTurb_WavesIrr/NRELOffshrBsline5MW_OC3Mono
pile_AeroDyn15.dat” occurred while trying to read IndToler.
ReadPrimaryFile:Invalid numerical input for file
“E:/softwares/Project/openfast/offshore/5MW_OC3Mnpl_DLL_WTurb_WavesIrr/NRELOffshrBsline5MW_OC3Mono
pile_AeroDyn15.dat” occurred while trying to read MaxIter.

FAST encountered an error during module initialization.
Simulation error level: FATAL ERROR

Aborting OpenFAST.

But I haven’t done any changes to Tiploss, IndToler, MaxIter parameters in aerodyn input file. Can I get some help regarding this?

Jason.Jonkman · April 6, 2020, 12:54pm

Dear Dhaneesh,

The AeroDyn input file format changed between FAST v8.16 and OpenFAST v1.0. You can review what in the input has changed in the OpenFAST documentation–see: openfast.readthedocs.io/en/mast … hange.html. You can also use the Echo option from the AeroDyn input file to debug errors in the input-file processing.

Best regards,

Dhaneesh.Machavarapu · April 6, 2020, 7:33pm

Sir,

As per your suggestion I used echo option in aerodyn input file. And the echo file I got was this.

This file of echoed input was generated by AeroDyn on 07-Apr-2020 at 00:34:50.

Data from AeroDyn primary input file “E:/softwares/Project/openfast/offshore/5MW_OC3Mnpl_DLL_WTurb_WavesIrr/NRELOffshrBsline5MW_OC3Monopile_AeroDyn15.dat”:

           FTitle         - File Header: File Description (line 2)

“NREL 5.0 MW offshore baseline aerodynamic input properties, with OC3 Monopile tower”

        T  Echo           - Echo flag
           DTAero         - Time interval for aerodynamic calculations {or default} (s)

“default”
1 WakeMod - Type of wake/induction model {0=none, 1=BEMT} (-)
2 AFAeroMod - Type of airfoil aerodynamics model {1=steady model, 2=Beddoes-Leishman unsteady model} (-)
1 TwrPotent - Type tower influence on wind based on potential flow around the tower {0=none, 1=baseline potential flow, 2=potential flow with Bak correction} (-)
F TwrShadow - Calculate tower influence on wind based on downstream tower shadow? (flag)
T TwrAero - Calculate tower aerodynamic loads? (flag)
F FrozenWake - Assume frozen wake during linearization? (flag)
F CavitCheck - Perform cavitation check? (flag)

1.2250E+00 AirDens - Air density (kg/m^3)
1.4640E-05 KinVisc - Kinematic air viscosity (m^2/s)
3.3500E+02 SpdSound - Speed of sound (m/s)
1.0350E+05 Patm - Atmospheric pressure ¶
1.7000E+03 Pvap - Vapour pressure of fluid ¶
5.0000E-01 FluidDepth - Water depth above mid-hub height (MHK only, for cavitation check) (m)

        2  SkewMod        - Type of skewed-wake correction model {1=uncoupled, 2=Pitt/Peters, 3=coupled} [used only when WakeMod=1] (-)
        T  HubLoss        - Use the Prandtl hub-loss model? [used only when WakeMod=1] (flag)
        T  TanInd         - Include tangential induction in BEMT calculations? [used only when WakeMod=1] (flag)
        T  AIDrag         - Include the drag term in the axial-induction calculation? [used only when WakeMod=1] (flag)
        F  TIDrag         - Include the drag term in the tangential-induction calculation? [used only when WakeMod=1 and TanInd=TRUE] (flag)
           IndToler       - Convergence tolerance for BEM induction factors [used only when WakeMod=1] (-)

“False”

I got glue codes for OPENFAST form github.com/openfast/r-test. In that there was no source F90 files like in previous versions of FAST. Was it the reason?
If it is can I get some help where I can get that.

Jason.Jonkman · April 6, 2020, 8:26pm

Dear Dhaneesh,

The Echo file can be used to check that data read into OpenFAST matches what you specified in the input file(s) so as to debug errors in the input file formatting. Are the values you showing matching what you specified in the input file? I’m not sure why, but I don’t see TipLoss in you Echo file. Do you copy/paste the contents of the whole echo file? It also looks like IndToler is set to “False”, instead of a “DEFAULT” or a number, which doesn’t look right.

In FAST v8, the archive contained the source code, compiled executable, and sample models (CertTest). In OpenFAST, the source code is contained in: github.com/OpenFAST/openfast/releases.

Best regards,

Dhaneesh.Machavarapu · April 13, 2020, 11:24am

Sir,

I have downloaded r-test files and compiled executables and made a copy of my work files(5MW_Baseline and 5MW_OC3Mnpl_DLL_WTurb_WavesIrr)
in seperate folder and tried to run it in command prompt then it was showing that there was a installation problem. Is openfast have a installation procedure or is it similar to that of FAST v8.16 . Because when I tried to run it like before it was not working .

Jason.Jonkman · April 13, 2020, 1:02pm

Dear Dhaneesh,

What do you mean by “installation problem”. What error are you receiving?

Best regards,

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Turning off Unsteady aerodynamics and no valid value of phi.

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