Simulation error small wind turbine

Wind & Water Computer-Aided Engineering Software Tools
1

Hello,

I am using FAST to make the certification analysis of a small wind turbine (Rotor diameter=1.7m) which has a full GM15 airfoil with a low Reynolds (0.1million), in order to find the bending moments and tip deflection. I’m using Test09 from the CertTest examples as this is also a downwind turbine. I’ve run tests with Elastodyn and Aerodyn active, ServoDyn inactive and InflowWind file from Test09, nevertheless I get the following error.

Command Prompt
FAST_Solution:FAST_AdvanceStates:ED_ABM4:ED_AB4:ED_RK4: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.
Additional debugging message from SUBROUTINE SmllRotTrans(): 1.50000E-03 s

I’ve read through several posts and the most useful one was this NREL 5MW controls (DLL interface)
I’ve tried the suggested approaches, when I reduced the time step DT to 0.001 the simulation works but all the output values are NaN. Then I tried to reach the root of the problem and I thought it could be the stiffness. I made the blade much more stiffer and got the new mode shapes but the problem remained. Then I thought the problem could be the extrapolation of the airfoil data (angle of attack, cl, cd, cm) but I also tried the Test09 using GM15 airfoil and it worked with good numerical results.

Now I’m wondering if the problem is due to the size of the turbine, since the rotor diameter is very small and I’m not aware of FAST boundaries to validate a simulation. I followed the IEC standard and already performed the simplified loading calculations but now we would like to test the turbine under turbulence and specific cases due to the high centrifugal forces that the rotor experiences (the rotational speed is 540 rpm with direct drive generator).

I finally looked and did some trials using Test17 as is the smallest rotor in FAST (5.8m) but also got NaN values or didn’t run because of the previous error.

Thanks in advance,

Lizet Ramirez
MSc SET student
L.R.RamirezGonzalez@student.tudelft.nl

2

Dear Lizet,

From what you describe, I would guess that your model is going numerically unstable because of too large of a time step. The smaller and stiffer the turbine, the smaller the time step requirement is. I would try a time step of 0.0001 s or 0.00001 s to see if you can get the model to run. Obviously, you want to choose as large of time step as possible while keeping the solution numerically stable. My rule of thumb for selecting the time step for the structural module is given in the following forum topic: FAST Integrator, step size & precision - #3 by Jason.Jonkman.

Best regards,

3

Dear Jason,

After having read some threads in the FAST forum, I would like to ask you for your help since I am unable to perform the simulations. Like Lizet’s model, my model is also a small Wind Turbine, mounted on TLP, and I am considering the surge and 1st fore-aft tower DoF. What can I see here in the error message,


 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: AAUETLP, Edited by Jesper Kirkegaard Jensen, Kasper Laugesen, Kasper
   Jessen & Signe Mortensen

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

 Running HydroDyn (v2.05.01, 27-Jul-2016).
 Generating incident wave kinematics and current time history.
 Reading in WAMIT output with root name ".\TLP/HydroData/TLP".
 Computing radiation impulse response functions and wave diffraction forces.

 Running FEAMooring (v1.02.01, 23-Jul-2016).
 Heading of the FEAMooring input file: AAUTLP, Edited by Jesper Kirkegaard Jensen, Kasper
 Laugesen, Kasper Jessen & Signe Mortensen. #rho=998; WtrDpth=1.92
Number of iterations without Seabed :1
Number of final iterations          :1
 Timestep: 10 of 60 seconds. Estimated final completion at 17:16:33.

FAST_Solution:FAST_AdvanceStates:ED_ABM4:ED_CalcContStateDeriv:SetCoordSy:Small angle assumption
violated in SUBROUTINE SmllRotTrans() due to a large tower deflection (ElastoDyn SetCoordSy). The
solution may be inaccurate. Simulation continuing, but future warnings from SmllRotTrans() will
be suppressed.
 Additional debugging message from SUBROUTINE SmllRotTrans(): 12.812 s


FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption1:ED_HD_InputOutputSolve:LAPACK_SGETRF:
U(           1,           1)=0. Factor U is exactly singular.

 FAST encountered an error at simulation time 12.819 of 60 seconds.
 Simulation error level: FATAL ERROR

 Aborting FAST.

is that I am getting two different mistakes, one is mentioned in this topic and the other one is mentioned as I found here: https://forums.nrel.gov/t/error-in-calculating-tower-loads-of-an-offshore-wind-turbine/1800/37?u, the simulation is always being aborted at the same time (10 seconds) , and as you recommended in this and other topics, I have tuned the Elastodyn’s time step (0.0001 and 0.00001) in order to finish the simulation, by doing that the simulation is aborted with some extra time but is still being aborted before it should.
Do you have any idea what could be done to complete the simulation?

Thank you in advance,
Best wishes,

Álvaro Ponce de León
AAU

4

Dear @Alvaro.Ponce.

Can you clarify what changes in the results when you drop the time step? Are you just changing the ElastoDyn time step, or have you tried changing the time step in the OpenFAST primary (.fst) input file?

A similar error regarding a singularity was recently discussed in the following forum topic: Wind Veer Parameter - #4 by Andre.White (see the posts between Aug 30, 2022 and Sep 1, 2022). Perhaps your model is suffering the same problem that can be fixed by disabling YawDOF or setting nonzero PtfmYIner?

Best regards,

5

Dear @Jason.Jonkman

Thank you for your quick answer.
Before answering I would like to tell you that I am using FAST v8.16, and trying to simulate the response of a TLP when subjected to waves, and the wind Turbine is idle (no wind).
What changes when I drop the time step in Elastodyn is that the simulation time is being extended but the simulation is still aborted. I have also dropped the FAST primary input file time step, making the simulation take much longer time, so far the simulation is running for 3h and the timestep is 30 out of 60.
Regarding your suggestions, I had already disabled YawDOF and PtfmYIner was set to non-zero value before you suggested.
When I take the Elastodyn input file from another colleague from the university, which has different DoF and different Initial Conditions, the simulation is carried out without any issue. Do you mind if you have a look at my ED input files to see where the issue could be? This first file is running without any issue, but the second input file has the above-mentioned problem when running.

-------e ELASTODYN v1.03.* INPUT FILE -------------------------------------------
AAUETLP, Edited by Jesper Kirkegaard Jensen, Kasper Laugesen, Kasper Jessen & Signe Mortensen
---------------------- SIMULATION CONTROL --------------------------------------
False         Echo        - Echo input data to "<RootName>.ech" (flag)
          3   Method      - Integration method: {1: RK4, 2: AB4, or 3: ABM4} (-) 3
       0.001  DT          - Integration time step (s) "default" E-4 1.25E-03 hydro-elasto:0.020
---------------------- ENVIRONMENTAL CONDITION ---------------------------------
    9.81584   Gravity     - Gravitational acceleration (m/s^2)
---------------------- DEGREES OF FREEDOM --------------------------------------
False          FlapDOF1    - First flapwise blade mode DOF (flag) True
False          FlapDOF2    - Second flapwise blade mode DOF (flag) True
False          EdgeDOF     - First edgewise blade mode DOF (flag) True
False          TeetDOF     - Rotor-teeter DOF (flag) [unused for 3 blades]
False          DrTrDOF     - Drivetrain rotational-flexibility DOF (flag)
FALSE	       GenDOF      - Generator DOF (flag)
False          YawDOF      - Yaw DOF (flag)
FALSE           TwFADOF1    - First fore-aft tower bending-mode DOF (flag)
FALSE           TwFADOF2    - Second fore-aft tower bending-mode DOF (flag)
FALSE  	       TwSSDOF1    - First side-to-side tower bending-mode DOF (flag)
FALSE	       TwSSDOF2    - Second side-to-side tower bending-mode DOF (flag)
True	       PtfmSgDOF   - Platform horizontal surge translation DOF (flag)
True	       PtfmSwDOF   - Platform horizontal sway translation DOF (flag)
True           PtfmHvDOF   - Platform vertical heave translation DOF (flag)
True           PtfmRDOF    - Platform roll tilt rotation DOF (flag)
True           PtfmPDOF    - Platform pitch tilt rotation DOF (flag)
True           PtfmYDOF    - Platform yaw rotation DOF (flag)
---------------------- INITIAL CONDITIONS --------------------------------------
          0   OoPDefl     - Initial out-of-plane blade-tip displacement (meters)
		  0   IPDefl      - Initial in-plane blade-tip deflection (meters)	
		  0   BlPitch(1)  - Blade 1 initial pitch (degrees)
      	  0   BlPitch(2)  - Blade 2 initial pitch (degrees)
		  0   BlPitch(3)  - Blade 3 initial pitch (degrees) [unused for 2 blades]
          0   TeetDefl    - Initial or fixed teeter angle (degrees) [unused for 3 blades]
          0   Azimuth     - Initial azimuth angle for blade 1 (degrees)
		  0   RotSpeed    - Initial or fixed rotor speed (rpm)
          0   NacYaw      - Initial or fixed nacelle-yaw angle (degrees)
       0.00   TTDspFA     - Initial fore-aft tower-top displacement (meters) 0.0258 - coupledFreedecay:0.0085
          0   TTDspSS     - Initial side-to-side tower-top displacement (meters)
-2.442396e-5   PtfmSurge   - Initial or fixed horizontal surge translational displacement of platform (meters) freedecay: 0.094 CoupledFreedecay:0.0285
		  0   PtfmSway    - Initial or fixed horizontal sway translational displacement of platform (meters)
-1.6043356e-3   PtfmHeave   - Initial or fixed vertical heave translational displacement of platform (meters) : -2.5E-4
		  0   PtfmRoll    - Initial or fixed roll tilt rotational displacement of platform (degrees)
-1.9991282e-3  PtfmPitch   - Initial or fixed pitch tilt rotational displacement of platform (degrees) : -0.0236 coupledFreedecay:0.063
		  0	  PtfmYaw     - Initial or fixed yaw rotational displacement of platform (degrees)
---------------------- TURBINE CONFIGURATION -----------------------------------
          3   NumBl       - Number of blades (-) AAUETLP
     1.0671E-0   TipRad      - The distance from the rotor apex to the blade tip (meters)
     0.0771E-0   HubRad      - The distance from the rotor apex to the blade root (meters)
          0   PreCone(1)  - Blade 1 cone angle (degrees)
          0   PreCone(2)  - Blade 2 cone angle (degrees)
          0   PreCone(3)  - Blade 3 cone angle (degrees) [unused for 2 blades]
          0   HubCM       - Distance from rotor apex to hub mass [positive downwind] (meters)
          0   UndSling    - Undersling length [distance from teeter pin to the rotor apex] (meters) [unused for 3 blades]
          0   Delta3      - Delta-3 angle for teetering rotors (degrees) [unused for 3 blades]
          0   AzimB1Up    - Azimuth value to use for I/O when blade 1 points up (degrees) 0.22
      -0.05E-0   OverHang    - Distance from yaw axis to rotor apex [3 blades] or teeter pin [2 blades] (meters) (AAUETLP: -0.258)
       0.10E-0   ShftGagL    - Distance from rotor apex [3 blades] or teeter pin [2 blades] to shaft strain gages [positive for upwind rotors] (meters)
        0.0   ShftTilt    - Rotor shaft tilt angle (degrees)
     0.0146E-0   NacCMxn     - Downwind distance from the tower-top to the nacelle CM (meters) 1.9
          0   NacCMyn     - Lateral  distance from the tower-top to the nacelle CM (meters) 0
     0.1176E-0   NacCMzn     - Vertical distance from the tower-top to the nacelle CM (meters) 1.75
          0   NcIMUxn     - Downwind distance from the tower-top to the nacelle IMU (meters)
          0   NcIMUyn     - Lateral  distance from the tower-top to the nacelle IMU (meters)
        0.0   NcIMUzn     - Vertical distance from the tower-top to the nacelle IMU (meters)
     0.0520   Twr2Shft    - Vertical distance from the tower-top to the rotor shaft (meters)
       2.11E-0   TowerHt     - Height of tower above ground level [onshore] or MSL [offshore] (meters)
        0.3E-0   TowerBsHt   - Height of tower base above ground level [onshore] or MSL [offshore] (meters)
          0   PtfmCMxt    - Downwind distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)
          0   PtfmCMyt    - Lateral distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)
      -0.06E-0   PtfmCMzt    - Vertical distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)
       0.00   PtfmRefzt   - Vertical distance from the ground level [onshore] or MSL [offshore] to the platform reference point (meters)
---------------------- MASS AND INERTIA ----------------------------------------
          0   TipMass(1)  - Tip-brake mass, blade 1 (kg)
          0   TipMass(2)  - Tip-brake mass, blade 2 (kg)
          0   TipMass(3)  - Tip-brake mass, blade 3 (kg) [unused for 2 blades]
     4.5583E-0   HubMass     - Hub mass (kg) 56780
	 4.1E-3   HubIner     - Hub inertia about rotor axis [3 blades] or teeter axis [2 blades] (kg m^2)
	  1E-05   GenIner     - Generator inertia about HSS (kg m^2)
      7.406E-0   NacMass     - Nacelle mass (kg) 7.406
0.878296922E-0   NacYIner    - Nacelle inertia about yaw axis (kg m^2)
          0   YawBrMass   - Yaw bearing mass (kg)
    121.217   PtfmMass    - Platform mass (kg)													114.0000
    20.6080   PtfmRIner   - Platform inertia for roll tilt rotation about the platform CM (kg m^2)	14.25419862
    20.6080   PtfmPIner   - Platform inertia for pitch tilt rotation about the platform CM (kg m^2)	14.25419862
    19.2342   PtfmYIner   - Platform inertia for yaw rotation about the platform CM (kg m^2)		9.352674144
---------------------- BLADE ---------------------------------------------------
         1   BldNodes    - Number of blade nodes (per blade) used for analysis (-)
"TLP_Blade.dat"    BldFile(1)  - Name of file containing properties for blade 1 (quoted string)
"TLP_Blade.dat"    BldFile(2)  - Name of file containing properties for blade 2 (quoted string)
"TLP_Blade.dat"    BldFile(3)  - Name of file containing properties for blade 3 (quoted string) [unused for 2 blades]
---------------------- ROTOR-TEETER --------------------------------------------
          0   TeetMod     - Rotor-teeter spring/damper model {0: none, 1: standard, 2: user-defined from routine UserTeet} (switch) [unused for 3 blades] Not used for AAUE-TLP
          0   TeetDmpP    - Rotor-teeter damper position (degrees) [used only for 2 blades and when TeetMod=1]
          0   TeetDmp     - Rotor-teeter damping constant (N-m/(rad/s)) [used only for 2 blades and when TeetMod=1]
          0   TeetCDmp    - Rotor-teeter rate-independent Coulomb-damping moment (N-m) [used only for 2 blades and when TeetMod=1]
          0   TeetSStP    - Rotor-teeter soft-stop position (degrees) [used only for 2 blades and when TeetMod=1]
          0   TeetHStP    - Rotor-teeter hard-stop position (degrees) [used only for 2 blades and when TeetMod=1]
          0   TeetSSSp    - Rotor-teeter soft-stop linear-spring constant (N-m/rad) [used only for 2 blades and when TeetMod=1]
          0   TeetHSSp    - Rotor-teeter hard-stop linear-spring constant (N-m/rad) [used only for 2 blades and when TeetMod=1]
---------------------- DRIVETRAIN ----------------------------------------------
        100   GBoxEff     - Gearbox efficiency (%)
          1   GBRatio     - Gearbox ratio (-)
8.67637E+08   DTTorSpr    - Drivetrain torsional spring (N-m/rad)
  6.215E+06   DTTorDmp    - Drivetrain torsional damper (N-m/(rad/s))
---------------------- FURLING -------------------------------------------------
False         Furling     - Read in additional model properties for furling turbine (flag) [must currently be FALSE)  Not used for AAU-ETLP
"unused"      FurlFile    - Name of file containing furling properties (quoted string) [unused when Furling=False]
---------------------- TOWER ---------------------------------------------------
         2   TwrNodes    - Number of tower nodes used for analysis (-)
"TLP_ElastoDyn_Tower.dat"    TwrFile     - Name of file containing tower properties (quoted string)
---------------------- OUTPUT --------------------------------------------------
False         SumPrint    - Print summary data to "<RootName>.sum" (flag)
          1   OutFile     - Switch to determine where output will be placed: {1: in module output file only; 2: in glue code output file only; 3: both} (currently unused)
True          TabDelim    - Use tab delimiters in text tabular output file? (flag) (currently unused)
"ES10.3E2"    OutFmt      - Format used for text tabular output (except time).  Resulting field should be 10 characters. (quoted string) (currently unused)
         30   TStart      - Time to begin tabular output (s) (currently unused)
          1   DecFact     - Decimation factor for tabular output {1: output every time step} (-) (currently unused)
          0   NTwGages    - Number of tower nodes that have strain gages for output [0 to 9] (-)
		 15   TwrGagNd    - List of tower nodes that have strain gages [1 to TwrNodes] (-) [unused if NTwGages=0]
          0   NBlGages    - Number of blade nodes that have strain gages for output [0 to 9] (-)
          9   BldGagNd    - List of blade nodes that have strain gages [1 to BldNodes] (-) [unused if NBlGages=0]
              OutList     - The next line(s) contains a list of output parameters.  See OutListParameters.xlsx for a listing of available output channels, (-)
"PtfmSurge"               - Platform translational surge, sway, and heave displacements (m)
"PtfmSway"                - Platform translational surge, sway, and heave displacements (m)
"PtfmHeave"               - Platform translational surge, sway, and heave displacements (m)
"PtfmRoll"                - Platform rotational roll, pitch and yaw displacements (deg)
"PtfmPitch"               - Platform rotational roll, pitch and yaw displacements (deg)
"PtfmYaw"                 - Platform rotational roll, pitch and yaw displacements (deg)
"PtfmTVxi" 				  - Platform horizontal surge (translational) velocity Directed along the xi-axis (m/sec)
"PtfmTVyi" 				  - Platform horizontal sway (translational) velocity Directed along the yi-axis (m/sec)
"PtfmTVzi"			      - Platform vertical heave (translational) velocity Directed along the zi-axis (m/sec)
"PtfmRVxi" 				  - Platform roll tilt angular (rotational) velocity About the xi-axis (deg/sec)
"PtfmRVyi" 			 	  - Platform pitch tilt angular (rotational) velocity About the yi-axis (deg/sec)
"PtfmRVzi" 				  - Platform yaw angular (rotational) velocity About the zi-axis (deg/sec)
"PtfmTAxi" 				  - Platform horizontal surge (translational) acceleration Directed along the xi-axis (m/sec^2)
"PtfmTAyi" 				  - Platform horizontal sway (translational) acceleration Directed along the yi-axis (m/sec^2)
"PtfmTAzi" 				  - Platform vertical heave (translational) acceleration Directed along the zi-axis (m/sec^2)
"PtfmRAxi" 				  - Platform roll tilt angular (rotational) acceleration About the xi-axis (deg/sec^2)
"PtfmRAyi" 				  - Platform pitch tilt angular (rotational) acceleration About the yi-axis (deg/sec^2)
"PtfmRAzi" 				  - Platform yaw angular (rotational) acceleration About the zi-axis (deg/sec^2)
END of input file (the word "END" must appear in the first 3 columns of this last OutList line)
---------------------------------------------------------------------------------------

Second ED input file:

------- ELASTODYN v1.03.* INPUT FILE -------------------------------------------
AAUETLP, Alvaro
---------------------- SIMULATION CONTROL --------------------------------------
True          Echo        - Echo input data to "<RootName>.ech" (flag)
          3   Method      - Integration method: {1: RK4, 2: AB4, or 3: ABM4} (-) 3
      0.0001  DT          - Integration time step (s) "default" E-4 1.25E-03 hydro-elasto:0.020, it was 0.001
---------------------- ENVIRONMENTAL CONDITION ---------------------------------
    9.81584   Gravity     - Gravitational acceleration (m/s^2)
---------------------- DEGREES OF FREEDOM --------------------------------------
False          FlapDOF1    - First flapwise blade mode DOF (flag) True
False          FlapDOF2    - Second flapwise blade mode DOF (flag) True
False          EdgeDOF     - First edgewise blade mode DOF (flag) True
False          TeetDOF     - Rotor-teeter DOF (flag) [unused for 3 blades]
False          DrTrDOF     - Drivetrain rotational-flexibility DOF (flag)
False	       GenDOF      - Generator DOF (flag)
False          YawDOF      - Yaw DOF (flag)
True           TwFADOF1    - First fore-aft tower bending-mode DOF (flag)
False          TwFADOF2    - Second fore-aft tower bending-mode DOF (flag)
False  	       TwSSDOF1    - First side-to-side tower bending-mode DOF (flag)
False	       TwSSDOF2    - Second side-to-side tower bending-mode DOF (flag)
True	       PtfmSgDOF   - Platform horizontal surge translation DOF (flag)
False          PtfmSwDOF   - Platform horizontal sway translation DOF (flag)
False          PtfmHvDOF   - Platform vertical heave translation DOF (flag)
False          PtfmRDOF    - Platform roll tilt rotation DOF (flag)
False          PtfmPDOF    - Platform pitch tilt rotation DOF (flag)
False          PtfmYDOF    - Platform yaw rotation DOF (flag)
---------------------- INITIAL CONDITIONS --------------------------------------
          0   OoPDefl     - Initial out-of-plane blade-tip displacement (meters)
	  0   IPDefl      - Initial in-plane blade-tip deflection (meters)	
	  0   BlPitch(1)  - Blade 1 initial pitch (degrees)
      	  0   BlPitch(2)  - Blade 2 initial pitch (degrees)
	  0   BlPitch(3)  - Blade 3 initial pitch (degrees) [unused for 2 blades]
          0   TeetDefl    - Initial or fixed teeter angle (degrees) [unused for 3 blades]
          0   Azimuth     - Initial azimuth angle for blade 1 (degrees)
	  0   RotSpeed    - Initial or fixed rotor speed (rpm)
          0   NacYaw      - Initial or fixed nacelle-yaw angle (degrees)
          0   TTDspFA     - Initial fore-aft tower-top displacement (meters) 0.0258 - coupledFreedecay:0.0085
          0   TTDspSS     - Initial side-to-side tower-top displacement (meters)
     0.0285   PtfmSurge   - Initial or fixed horizontal surge translational displacement of platform (meters) freedecay: 0.094 CoupledFreedecay:0.0285
	  0   PtfmSway    - Initial or fixed horizontal sway translational displacement of platform (meters)
          0   PtfmHeave   - Initial or fixed vertical heave translational displacement of platform (meters) : -2.5E-4
	  0   PtfmRoll    - Initial or fixed roll tilt rotational displacement of platform (degrees)
          0   PtfmPitch   - Initial or fixed pitch tilt rotational displacement of platform (degrees) : -0.0236 coupledFreedecay:0.063
	  0   PtfmYaw     - Initial or fixed yaw rotational displacement of platform (degrees)
---------------------- TURBINE CONFIGURATION -----------------------------------
          3   NumBl       - Number of blades (-) AAUETLP
  1.0671E-0   TipRad      - The distance from the rotor apex to the blade tip (meters)
  0.0771E-0   HubRad      - The distance from the rotor apex to the blade root (meters)
          0   PreCone(1)  - Blade 1 cone angle (degrees)
          0   PreCone(2)  - Blade 2 cone angle (degrees)
          0   PreCone(3)  - Blade 3 cone angle (degrees) [unused for 2 blades]
          0   HubCM       - Distance from rotor apex to hub mass [positive downwind] (meters)
          0   UndSling    - Undersling length [distance from teeter pin to the rotor apex] (meters) [unused for 3 blades]
          0   Delta3      - Delta-3 angle for teetering rotors (degrees) [unused for 3 blades]
          0   AzimB1Up    - Azimuth value to use for I/O when blade 1 points up (degrees) 0.22
   -0.05E-0   OverHang    - Distance from yaw axis to rotor apex [3 blades] or teeter pin [2 blades] (meters) (AAUETLP: -0.258)
    0.10E-0   ShftGagL    - Distance from rotor apex [3 blades] or teeter pin [2 blades] to shaft strain gages [positive for upwind rotors] (meters)
        0.0   ShftTilt    - Rotor shaft tilt angle (degrees)
  0.0146E-0   NacCMxn     - Downwind distance from the tower-top to the nacelle CM (meters) 1.9
          0   NacCMyn     - Lateral  distance from the tower-top to the nacelle CM (meters) 0
  0.1176E-0   NacCMzn     - Vertical distance from the tower-top to the nacelle CM (meters) 1.75
          0   NcIMUxn     - Downwind distance from the tower-top to the nacelle IMU (meters)
          0   NcIMUyn     - Lateral  distance from the tower-top to the nacelle IMU (meters)
        0.0   NcIMUzn     - Vertical distance from the tower-top to the nacelle IMU (meters)
     0.0520   Twr2Shft    - Vertical distance from the tower-top to the rotor shaft (meters)
    2.11E-0   TowerHt     - Height of tower above ground level [onshore] or MSL [offshore] (meters)
     0.3E-0   TowerBsHt   - Height of tower base above ground level [onshore] or MSL [offshore] (meters)
          0   PtfmCMxt    - Downwind distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)
          0   PtfmCMyt    - Lateral distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)
   -0.06E-0   PtfmCMzt    - Vertical distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)
       0.00   PtfmRefzt   - Vertical distance from the ground level [onshore] or MSL [offshore] to the platform reference point (meters)
---------------------- MASS AND INERTIA ----------------------------------------
          0   TipMass(1)  - Tip-brake mass, blade 1 (kg)
          0   TipMass(2)  - Tip-brake mass, blade 2 (kg)
          0   TipMass(3)  - Tip-brake mass, blade 3 (kg) [unused for 2 blades]
  4.5583E-0   HubMass     - Hub mass (kg) 56780                                                         2.023
     4.1E-3   HubIner     - Hub inertia about rotor axis [3 blades] or teeter axis [2 blades] (kg m^2)
      1E-05   GenIner     - Generator inertia about HSS (kg m^2)
   7.406E-0   NacMass     - Nacelle mass (kg)                                                           7.406
0.878296922E-0  NacYIner    - Nacelle inertia about yaw axis (kg m^2)
          0   YawBrMass   - Yaw bearing mass (kg)
    121.217   PtfmMass    - Platform mass (kg)								114.0000
    20.6080   PtfmRIner   - Platform inertia for roll tilt rotation about the platform CM (kg m^2)	14.25419862
    20.6080   PtfmPIner   - Platform inertia for pitch tilt rotation about the platform CM (kg m^2)	14.25419862
    19.2342   PtfmYIner   - Platform inertia for yaw rotation about the platform CM (kg m^2)		9.352674144
---------------------- BLADE ---------------------------------------------------
         1   BldNodes    - Number of blade nodes (per blade) used for analysis (-)
"TLP_Blade.dat"    BldFile(1)  - Name of file containing properties for blade 1 (quoted string)
"TLP_Blade.dat"    BldFile(2)  - Name of file containing properties for blade 2 (quoted string)
"TLP_Blade.dat"    BldFile(3)  - Name of file containing properties for blade 3 (quoted string) [unused for 2 blades]
---------------------- ROTOR-TEETER --------------------------------------------
          0   TeetMod     - Rotor-teeter spring/damper model {0: none, 1: standard, 2: user-defined from routine UserTeet} (switch) [unused for 3 blades] Not used for AAUE-TLP
          0   TeetDmpP    - Rotor-teeter damper position (degrees) [used only for 2 blades and when TeetMod=1]
          0   TeetDmp     - Rotor-teeter damping constant (N-m/(rad/s)) [used only for 2 blades and when TeetMod=1]
          0   TeetCDmp    - Rotor-teeter rate-independent Coulomb-damping moment (N-m) [used only for 2 blades and when TeetMod=1]
          0   TeetSStP    - Rotor-teeter soft-stop position (degrees) [used only for 2 blades and when TeetMod=1]
          0   TeetHStP    - Rotor-teeter hard-stop position (degrees) [used only for 2 blades and when TeetMod=1]
          0   TeetSSSp    - Rotor-teeter soft-stop linear-spring constant (N-m/rad) [used only for 2 blades and when TeetMod=1]
          0   TeetHSSp    - Rotor-teeter hard-stop linear-spring constant (N-m/rad) [used only for 2 blades and when TeetMod=1]
---------------------- DRIVETRAIN ----------------------------------------------
        100   GBoxEff     - Gearbox efficiency (%)
          1   GBRatio     - Gearbox ratio (-)
8.67637E+08   DTTorSpr    - Drivetrain torsional spring (N-m/rad)
  6.215E+06   DTTorDmp    - Drivetrain torsional damper (N-m/(rad/s))
---------------------- FURLING -------------------------------------------------
False         Furling     - Read in additional model properties for furling turbine (flag) [must currently be FALSE)  Not used for AAU-ETLP
"unused"      FurlFile    - Name of file containing furling properties (quoted string) [unused when Furling=False]
---------------------- TOWER ---------------------------------------------------
         2   TwrNodes    - Number of tower nodes used for analysis (-)
"TLP_ElastoDyn_Tower.dat"    TwrFile     - Name of file containing tower properties (quoted string)
---------------------- OUTPUT --------------------------------------------------
False         SumPrint    - Print summary data to "<RootName>.sum" (flag)
          1   OutFile     - Switch to determine where output will be placed: {1: in module output file only; 2: in glue code output file only; 3: both} (currently unused)
True          TabDelim    - Use tab delimiters in text tabular output file? (flag) (currently unused)
"ES10.3E2"    OutFmt      - Format used for text tabular output (except time).  Resulting field should be 10 characters. (quoted string) (currently unused)
         30   TStart      - Time to begin tabular output (s) (currently unused)
          1   DecFact     - Decimation factor for tabular output {1: output every time step} (-) (currently unused)
          0   NTwGages    - Number of tower nodes that have strain gages for output [0 to 9] (-)
	 15   TwrGagNd    - List of tower nodes that have strain gages [1 to TwrNodes] (-) [unused if NTwGages=0]
          0   NBlGages    - Number of blade nodes that have strain gages for output [0 to 9] (-)
          9   BldGagNd    - List of blade nodes that have strain gages [1 to BldNodes] (-) [unused if NBlGages=0]
              OutList     - The next line(s) contains a list of output parameters.  See OutListParameters.xlsx for a listing of available output channels, (-)
"PtfmSurge"               - Platform translational surge, sway, and heave displacements (m)
"PtfmTVxi" 		  - Platform horizontal surge (translational) velocity Directed along the xi-axis (m/sec)
"PtfmTAxi" 		  - Platform horizontal surge (translational) acceleration Directed along the xi-axis (m/sec^2)
"YawBrTAxp"		  - Tower-top / yaw bearing fore-aft (translational) acceleration (absolute) Directed along the xp-axis	(m/s^2)
"YawBrTDxp"		  - Tower-top / yaw bearing fore-aft (translational) deflection (relative to the undeflected position) Directed along the xp-axis (m)

END of input file (the word "END" must appear in the first 3 columns of this last OutList line)
---------------------------------------------------------------------------------------

Thank you again for your time and consideration,

Best regards,
Álvaro

6

Dear @Alvaro.Ponce,

From my quick review of your input files, the only differences I see between these two ElastoDyn files are:

  • The time step is 0.001 s in (1) and 0.0001 s in (2)
  • The first tower fore-aft bending mode DOF is disabled in (1) and enabled in (2)
  • All platform DOFs are enabled in (1) while only surge is enabled in (2)
  • The initial conditions differ

I would not expect initial conditions to effect the stability of the solution, as long as the initial conditions are not unrealistic. And the first model has a larger time step and more DOFs enabled than the second. My guess is enabling the first tower fore-aft mode is causing the problem with the second model. (Presumably the second model would run fine if you enabled all platform DOFs but disabled the first tower fore-aft DOF.) Are the mode shapes you’ve specified for this tower mode consistent with the distributed tower mass, distributed tower stiffness, tower top mass/inertia, and floater boundary condition? Is the tower-bending frequency what you expect it should be?

I also notice that all of the geometry and mass values are quite small. It appears that you are simulating a wind turbine in model scale. Please note it is more common to simulate a model scale wind turbine at full scale and scale up experimental measurements to full scale rather than the other way around.

Best regards,