OpenFAST warnings

Dear @Jason.Jonkman

My name is Ivan Fernandez and currently, I am working on my final master’s thesis, however, I have had several problems running OpenFAST.

A few days ago I tried to run the test case for the 15 MW reference wind turbine installed on the Volturn-S semisubmersible platform using OpenFAST 3.2.1 version.

Link (IEA-15-240-RWT/OpenFAST at master · IEAWindTask37/IEA-15-240-RWT · GitHub)

The program terminates normally but several warnings appear on the command prompt. Output message attached below

I have treated each warning individually at the end of this message and would be helpful if you could help me to clarify the reason why they appear.


**************************************************************************************************
OpenFAST

Copyright (C) 2022 National Renewable Energy Laboratory
Copyright (C) 2022 Envision Energy USA LTD

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-v3.2.1
Compile Info:
 - Compiler: Intel(R) Fortran Compiler 1900
 - Architecture: 64 bit
 - Precision: single
 - OpenMP: No
 - Date: Aug 01 2022
 - Time: 11:40:35
Execution Info:
 - Date: 10/05/2022
 - Time: 11:27:21+0200

OpenFAST input file heading:
    IEA 15 MW offshore reference model on UMaine VolturnUS-S semi-submersible floating platform

Running ElastoDyn.
Running AeroDyn.
Warning: Turning off Unsteady Aerodynamics because UA parameters are not included in airfoil
(airfoil has likely has constant polars). (node 1, blade 1)
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. (node 2, blade 1)
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. (node 4, blade 1)
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. (node 5, blade 1)
Warning: Turning off Unsteady Aerodynamics because UA parameters are not included in airfoil
(airfoil has likely has constant polars). (node 1, blade 2)
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. (node 2, blade 2)
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. (node 4, blade 2)
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. (node 5, blade 2)
Warning: Turning off Unsteady Aerodynamics because UA parameters are not included in airfoil
(airfoil has likely has constant polars). (node 1, blade 3)
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. (node 2, blade 3)
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. (node 4, blade 3)
Warning: Turning off Unsteady Aerodynamics because C_nalpha is 0. (node 5, blade 3)
Running InflowWind.
Running HydroDyn.
  WARNING:  The requested output channel is invalid: WavesF1xi
  WARNING:  The requested output channel is invalid: WavesF1zi
  WARNING:  The requested output channel is invalid: WavesM1yi
  WARNING:  The requested output channel is invalid: WavesF2xi
  WARNING:  The requested output channel is invalid: WavesF2zi
  WARNING:  The requested output channel is invalid: WavesM2yi
  WARNING:  The requested output channel is invalid: WavesF2xi
  WARNING:  The requested output channel is invalid: WavesF2yi
  WARNING:  The requested output channel is invalid: WavesF2zi
  WARNING:  The requested output channel is invalid: WavesM2xi
  WARNING:  The requested output channel is invalid: WavesM2yi
  WARNING:  The requested output channel is invalid: WavesM2zi
 Generating incident wave kinematics and current time history.
 Calculating second order difference frequency wave kinematics.
 Calculating second order sum frequency wave kinematics.
 Reading in WAMIT output with root name ".\HydroData/IEA-15-240-RWT-UMaineSemi".
 Computing radiation impulse response functions and wave diffraction forces.
 Calculating second order difference-frequency force using the full quadratic transfer function.
Running MoorDyn.
  MD_Init: Opening MoorDyn input file:  .\IEA-15-240-RWT-UMaineSemi_MoorDyn.dat
Warning: invalid output specifier FX.  Starting character must be C or L.
Warning: invalid output specifier FY.  Starting character must be C or L.
Warning: invalid output specifier FZ.  Starting character must be C or L.
   Creating mooring system.   3 fairleads, 3 anchors, 0 connects.
   Finalizing ICs using dynamic relaxation.
   t=60  FairTen 1: 2.43587E+06, 2.44120E+06, 2.43677E+06
   Fairlead tensions did not converge within TMaxIC=60 seconds.
Running ServoDyn.
Running ServoDyn Interface for Bladed Controllers (using Intel Visual Fortran for Windows).
Using legacy Bladed DLL interface.

FAST_InitializeAll: HydroDyn_Init: HydroDynInput_ProcessInitData: A requested output channel is
invalid

------------------------------------------------------------------------------
Running ROSCO-v2.5.0
A wind turbine controller framework for public use in the scientific field
Developed in collaboration: National Renewable Energy Laboratory
                            Delft University of Technology, The Netherlands
------------------------------------------------------------------------------

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:RotCalcOutput:BEMT_CalcOutput(node 3,
blade 3):UA_CalcOutput:UA_BlendSteady:Temporarily turning off UA due to high angle of attack or
low relative velocity. This warning will not be repeated though the condition may persist.

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:RotCalcOutput:BEMT_CalcOutput(node 50,
blade 2):UA_CalcOutput:Mach number exceeds 0.3. Theory is invalid. This warning will not be
repeated though the condition may persist.
Generator speed:    5.7 RPM, Pitch angle:   0.0 deg, Power:  8168.8 kW, Est. wind Speed:   8.2 m/s

 Total Real Time:       6.421 seconds
 Total CPU Time:        6.1562 seconds
 Simulation CPU Time:   2.7656 seconds
 Simulated Time:        10 seconds
 Time Ratio (Sim/CPU):  3.6158

 OpenFAST terminated normally.

Reasoning

• AeroDyn Warnings: In my opinion, those blade nodes belong to the cylindrical section of the blade. Nevertheless, I have not been able to figure out why C_nalpha is set to 0.

• HydroDyn Warnings: Requested outputs are not specified correctly

• MoorDyn Warnings:

  1. Requested outputs are not specified correctly
  2. Simulation time is not enough or the convergence rate is too small

• Servodyn: I have not been able to figure out the reason for these warnings

Thanks beforehand

Regards

Ivan

Dear @Ivan.Fernandez,

Here are my responses:

AeroDyn Warnings: In my opinion, those blade nodes belong to the cylindrical section of the blade. Nevertheless, I have not been able to figure out why C_nalpha is set to 0.

Cylindrical sections do not have lift, so, C_nalpha should be zero.

HydroDyn Warnings: Requested outputs are not specified correctly

The names of HydroDyn’s wave-excitation load outputs from the potential-flow solution changed in OpenFAST v2.6 and newer. See the updated names here: https://openfast.readthedocs.io/en/main/_downloads/3f19498a5dc774461e022b671ff01ec6/OutListParameters.xlsx.

MoorDyn Warnings:

Requested outputs are not specified correctly
Simulation time is not enough or the convergence rate is too small

I agree. Proper MoorDyn output names are documented here: MoorDyn Usage — MoorDyn 1.01.01 documentation.

Servodyn: I have not been able to figure out the reason for these warnings

I’m not sure what ServoDyn warnings you are referring too. I don’t see any ServoDyn warnings listed.

Regardless, it sounds like these OpenFAST input files from the IEA Wind 15-MW reference wind turbine repository need some updating.

Best regards,

Dear @Jason.Jonkman

Thanks for your rapid response. Regarding ServoDyn, you are right I did not reference warnings properly.

I was trying to point out the following messages:

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:RotCalcOutput:BEMT_CalcOutput(node 3,
blade 3):UA_CalcOutput:UA_BlendSteady:Temporarily turning off UA due to high angle of attack or
low relative velocity. This warning will not be repeated though the condition may persist.

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:RotCalcOutput:BEMT_CalcOutput(node 50,
blade 2):UA_CalcOutput:Mach number exceeds 0.3. Theory is invalid. This warning will not be
repeated though the condition may persist.
Generator speed:    5.7 RPM, Pitch angle:   0.0 deg, Power:  8168.8 kW, Est. wind Speed:   8.2 m/s

Dear @Ivan.Fernandez,

Are you initial conditions for rotor speed and blade pitch set properly for the wind you are using (i.e., are the initial rotor speed and pitch set equal to their expected mean value for the given mean wind speed you are using)? If not, these warnings could be tied to that.

Best regards,

Dear @Jason.Jonkman

I have modified the initial conditions and it seems to work now.

Thanks for your help.

Best regards.

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