Running IEA-15-240-RWT with BeamDyn instead of Elastodyn

Wind & Water
1

I already made quite some computations with the IEA-15-240-RWT model with the ElastoDyn blade model, but did not succeed so far in using the BeamDyn blade model instead.
I was wondering what other changes are required (other than changing the switch and reducing the time step) to successfully run the BeamDyn model.

The error I receive is :

FAST_InitializeAll:InitModuleMappings:BD_2_AD_BladeMotion(1):MeshMapCreate:CreateMotionMap_L2_to_L
2:CreateMapping_ProjectToLine2:Found close value for node 1. (9.22863E-05 m)
InitModuleMappings:AD_2_BD_BladeLoad(1):MeshMapCreate:CreateLoadMap_L2_to_L2:CreateMapping_Project
ToLine2:Found close value for node 1. (9.22863E-05 m)
InitModuleMappings:BD_2_AD_BladeMotion(2):MeshMapCreate:CreateMotionMap_L2_to_L2:CreateMapping_Pro
jectToLine2:Found close value for node 1. (1.00418E-04 m)
InitModuleMappings:AD_2_BD_BladeLoad(2):MeshMapCreate:CreateLoadMap_L2_to_L2:CreateMapping_Project
ToLine2:Found close value for node 1. (1.00418E-04 m)
InitModuleMappings:BD_2_AD_BladeMotion(3):MeshMapCreate:CreateMotionMap_L2_to_L2:CreateMapping_Pro
jectToLine2:Found close value for node 1. (1.00333E-04 m)
InitModuleMappings:AD_2_BD_BladeLoad(3):MeshMapCreate:CreateLoadMap_L2_to_L2:CreateMapping_Project
ToLine2:Found close value for node 1. (1.00333E-04 m)

Time: 0 of 1200 seconds.

FAST_Solution:FAST_AdvanceStates:B1:BD_GA2:BD_DynamicSolutionGA2:Solution does not converge after
the maximum number of iterations
FAST_AdvanceStates:B3:BD_GA2:BD_DynamicSolutionGA2:Solution does not converge after the maximum
number of iterations

OpenFAST encountered an error at simulation time 0 of 1200 seconds.
Simulation error level: FATAL ERROR

Aborting OpenFAST.

Thanks in advance,
Duncan van der Heul

2

Hello Duncan,
What time step are you using? The model works for me with a time step of 0.2 ms (DT=0.0002). We’re well aware of the excessive computational costs caused by such tiny time step and we’re actively working on a new coupling scheme between ElastoDyn and BeamDyn (and SubDyn) that we hope we’ll substantially improve things.
Let me know.
Best regards,
Pietro Bortolotti

3

Dear Pietro,
Thank you for replying to my question.
I was indeed using a larger time step than you suggested and will try again with the timestep size you propose.

Kind regards,
Duncan van der Heul

4

Hello NREL support team,

I also try to run the IEA15MW with BeamDyn and get the following fatal error:

OpenFAST-v4.1.1
Compile Info:

  • Compiler: Intel(R) Fortran Compiler 2021
  • Architecture: 64 bit
  • Precision: single
  • OpenMP: No
  • Date: Jul 09 2025
  • Time: 00:54:24
    Execution Info:
  • Date: 09/01/2025
  • Time: 15:28:46+0200

OpenFAST input file heading:
IEA 15 MW offshore reference model monopile configuration

Running ElastoDyn.
Running BeamDyn.
Running BeamDyn.
Running BeamDyn.
Running InflowWind.
Running AeroDyn.
AeroDyn: projMod: 1
Projection: legacy (NoSweepPitchTwist), BEM: legacy (2D)

FAST_InitializeAll:ED_Init:ED_SetParameters:SetPrimaryParameters: AllBldNdOuts option not
available in ElastoDyn when BeamDyn is used. Turning off these outputs.
FAST_InitializeAll:AD_Init:Init_BEMTmodule:BEMT_Init:DBEMT_Init:DBEMT_ValidateInitInp: The
timestep size for DBEMT (interval) must be larger than sqrt(epsilon).

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

Aborting OpenFAST.

I set as a time step 0.2ms (DT=0.0002) and in the AeroDyn file I set a time step of DTAero = 0.001, which should be larger then the epsilon, but I still got the same error message.
Do you have any ideas, what I can do?

Thank you
Torben

5

Dear @Nils.Schaefer,

SQRT(episilon) in single precision is around 0.00035 s. It sounds like your DT is lower then this, but your DTAero is higher. Are you sure you haven’t set DTAero = “DEFAULT”, which would equal DT? Could you also try increasing DT to 0.00035 s?
Best regards,