Error Message

Wind & Water General
1

Dear all,
I am working on the topic of the multi-risk assessment of on-shore 5MW HAWT against the combined effect of wind and seismic actions.
In particular, I wish using FAST in order to carry out the aerodynamic response of an Onshore 5MW HAWT of NREL, subjected to a turbulent wind field, aim to evaluation of the rotor thrust time-history.
First, I have calibrated my numerical model starting from the certified test 18.
Then, I set the TurbModel to "IECVKM " with a 10% of Turbulence intensity creating an output full-field time-series data in TurbSim/AeroDyn form. In this case, I faced some problems when the GridHeight parameter was set to a value lower than two times of the hub height. However, this problem seems to be exceeded.
Finally when I run the FAST, I get this error.

D:\fast_Alberto\bin>fast_x64 D:\fast_Alberto\CertTest\Test18_2.fst

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

Copyright (C) 2016 National Renewable Energy Laboratory

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 64-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 #18: NREL 5.0 MW Baseline Wind Turbine (Onshore)

 Running ElastoDyn (v1.04.00a-bjj, 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:
 D:\fast_Alberto\CertTest\5MW_Baseline/NRELOffshrBsline5MW_InflowWind_12_1mps.dat

   Reading a 21x21 grid (175.19 m wide, 5.00488E-03 m to 175.2 m above ground) with a
   characteristic wind speed of 12 m/s. This full-field file was generated by TurbSim
   (v2.00.07a-bjj, 14-Jun-2016) on 08-Nov-2016 at 18:42:32.

   Processed 12000 time steps of 20-Hz full-field data (period of 600 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).
 Timestep: 0 of 600 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 = 15, Blade = 1

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:AD_CalcOutput:BEMT_CalcOutput(node 11,
blade 1):Compute_UA_AirfoilCoefs:UA_CalcOutput:Mach number exceeds 1.0. Equations cannot be
evaluated.

 FAST encountered an error at simulation time 0.2 of 600 seconds.
 Simulation error level: FATAL ERROR

 Aborting FAST.

Could you help me to overcome this problem?
Thanks in advance for your support

Best regards,
Alberto Maria Avossa

P.S.: I attached to this message the text files of the input parameters setting for the wind field generation in TurbSim and for the carry out of the aerodynamic analysis in FAST.
NRELOffshrBsline5MW_InflowWind_12_1mps.dat.txt (5.39 KB)
Test18_2.fst.txt (5.8 KB)
TurbSim.inp.txt (6.97 KB)

2

Dear Alberto,

From my quick look at your FAST primary input (*.fst) file, it looks like you increased the time step (DT) quite a bit. Unless you’ve disabled many of the structural degrees of freedom in the ElastoDyn module, my guess is that the model is going numerically unstable, which is leading to large deflection/high speed blade motion and triggering the error regarding a high Mach number.

Best regards,

3

Thanks a lot for you previous answer.

Now, I have a new question.
As in the previous stage I wish using FAST to carry out the aerodynamic response of an Onshore 5MW HAWT of NREL, subjected to a turbulent wind field, aiming to evaluation of the rotor thrust time-history. Can you support me to set Elastodyn parameters to develop a simulation in these specific conditions:

  • Turbulent Wind Field generated by Turbsim with a mean wind speed higher than one related to the cut-out condition (25 m/s);
  • Angular velocity of the rotor equal to 0 (rotor off);
  • Pitch angle equal to 23.25 degrees (reproducing an almost stall condition).

Could you help me to overcome this problem?
Thanks in advance for your support

Best regards,
Alberto Maria Avossa

4

Dear Alberto,

NREL does not have the resources to offer detailed step-by-step guidance. There should be no problem setting up the model as you require. Hopefully the provided documentation is sufficient for your needs.

Best regards,