Error in calculating tower loads of an offshore wind turbine

Dear Jason,

I am attaching the fresh platform input file here Platform_Monopile.txt (6.1 KB). I am still having this uploading error issue. However, I have sent you an email on your official emailing address with subject “Error in calculating tower loads of an offshore wind turbine”. I have attached the graphs of platform motion with that email.

Kindly have a look at them suggest what to change in my model so that system behave as desired.

Dear Syed,

Why do you want to enable platform DOFs without providing any reaction loads on the platform? For a fixed-bottom monopile (with a rigid foundation), I would disable all platform DOFs (PtfmSgDOF = PtfmSwDOF = PtfmHvDOF = PtfmRDOF = PtfmPDOF = PtfmYDOF = False) in FAST v7.

Best regards,

Dear Jason,
sorry to bother you with my naive questions.

My confusion is, If I want to calculate hydrodynamic loads on wind turbine for a fixed-bottom monopile (with a rigid foundation). In that case, should I disable all platform DOFs (PtfmSgDOF = PtfmSwDOF = PtfmHvDOF = PtfmRDOF = PtfmPDOF = PtfmYDOF = False) in FAST v7 as well?

Yes, that’s correct.

Best regards,

Dear Jason,

Thank you for your help.

I have two questions in my mind.

1: In FAST v8 if I want to calculate hydrodynamic loads on wind turbine for a fixed-bottom monopile (with a rigid foundation), in that case, should I disable all platform DOFs (PtfmSgDOF = PtfmSwDOF = PtfmHvDOF = PtfmRDOF = PtfmPDOF = PtfmYDOF = False) while turning on the CompHydro = CompSub = 1 in main FAST input file??

2: In your 2nd last post, you mentioned “reaction loads on the platform”, how to set them here in FAST v7 platform monopile file ??

---------------------- MASS AND INERTIA (CONT) ---------------------------------
0 PtfmMass - Platform mass (kg)
0 PtfmRIner - Platform inertia for roll tilt rotation about the platform CM (kg m^2)
0 PtfmPIner - Platform inertia for pitch tilt rotation about the platform CM (kg m^2)
0 PtfmYIner - Platfrom inertia for yaw rotation about the platform CM (kg m^2)
---------------------- PLATFORM (CONT) -----------------------------------------
0 PtfmLdMod - Platform loading model {0: none, 1: user-defined from routine UserPtfmLd} (switch)
---------------------- TOWER (CONT) --------------------------------------------
0 TwrLdMod - Tower loading model {0: none, 1: Morison’s equation, 2: user-defined from routine UserTwrLd} (switch)
0 TwrDiam - Tower diameter in Morison’s equation (meters) [used only when TwrLdMod=1]
0 TwrCA - Normalized hydrodynamic added mass coefficient in Morison’s equation (-) [used only when TwrLdMod=1] [determines TwrCM=1+TwrCA]
0 TwrCD - Normalized hydrodynamic viscous drag coefficient in Morison’s equation (-) [used only when TwrLdMod=1]

Dear Syed,

Here are my answers to your questions:

  1. In FAST v7, the monopile structure is modeled as an extension of the tower structure, so the platform (at the tower base) is located at the “seabed”. In FAST v8, the tower structure is modeled in ElastoDyn and the monopile structure is modeled in SubDyn, so, the platform (at the tower base) is located at the transition between the tower and monopile. So to model a monopile with rigid foundation in FAST v7 requires you to disable all platform DOFs. To model a monopile with rigid foundation in FAST v8 requires to enable all platform DOFs (to enable a proper coupling between ElastoDyn and SubDyn) and constrain a node at the seabed within SubDyn.

  2. If the platform DOFs are disabled in FAST v7, the reaction loads will be calculated directly by FAST to ensure that the platform does not accelerate. If the platform DOFs are disabled, you must calculate your own reaction loads in the user-defined routine UserPtfmLd(), which requires that you set PtfmLdMod = 1 and implement your own userPtfmLd() routine and recompile FAST.

I hope that helps.

Best regards,

Dear Jason,

Thank you for your help.

So, for FAST v8 If the water depth is 50m, how do one can constrain a node at the seabed within SubDyn??
Actually, I didn’t understand what you mean by this in your previous reply?

Dear Syed,

In FAST v8, the monopile substructure is modeled in SubDyn. Within SubDyn, the joint at the base of the monopile (seabed) should be identified as a fixed base reaction joint by setting RctTDXss = RctTDYss = RctTDZss = RctRDXss = RctRDYss = RctRDZss = 1. More information on SubDyn can be found in the draft SubDyn User’s Guide and Theory Manual: wind.nrel.gov/nwtc/docs/SubDyn_Manual.pdf.

Best regards,

Dear Jason,

Thank you for your help.
For FAST v8, If the water depth is 50m, then

1: As you said in you previous post that I should mention the joint which lies on sea bed via RJointID?

For example, if my first joint is at height = -50 then I should define RJointID = 1?

2: I would like to ask that how to set “NInterf” if I don’t know the length of Transition Piece, for a fixed-bottom monopile (with a rigid foundation)??

3: For the case mentioned above, how to set “Jointzi” in HydroDyn file?

Dear Syed,

Here are my answers to your questions:

  1. Correct.

  2. NInterf is the number of SubDyn joints that will be rigidly connected to the platform in ElastoDyn. For a monopile, I would expect NInterf = 1.

  3. For a monopile, I would expect the first joint in HydroDyn to be located just below the seabed e.g. -50.1 m in your case. (Joints placed right at the seabed will have buoyancy loads applied; joints placed below the seabed will not have buoyancy). See the draft HydroDyn User’s Guide and Theory Manual for more information: wind.nrel.gov/nwtc/docs/HydroDyn_Manual.pdf.

Best regards,

Dear Jason,
When I set parameters as you suggested, i.e.,

JointID JointXss JointYss JointZss [Coordinates of Member joints in SS-Coordinate System]
(-) (m) (m) (m)
1 0.00000 0.00000 -50.00000
2 0.00000 0.00000 -40.10000
3 0.00000 0.00000 -30.00000
4 0.00000 0.00000 -26.00000
5 0.00000 0.00000 -22.00000
6 0.00000 0.00000 -18.00000
7 0.00000 0.00000 -14.00000
8 0.00000 0.00000 -10.00000
9 0.00000 0.00000 -8.00000
10 0.00000 0.00000 -6.00000
11 0.00000 0.00000 -4.00000
12 0.00000 0.00000 -2.00000
13 0.00000 0.00000 0.00000
14 0.00000 0.00000 2.00000
15 0.00000 0.00000 4.00000
16 0.00000 0.00000 6.00000
17 0.00000 0.00000 8.00000
18 0.00000 0.00000 10.00000
------------------- BASE REACTION JOINTS: 1/0 for Locked/Free DOF @ each Reaction Node ---------------------
1 NReact - Number of Joints with reaction forces; be sure to remove all rigid motion DOFs of the structure (else det([K])=[0])
RJointID RctTDXss RctTDYss RctTDZss RctRDXss RctRDYss RctRDZss [Global Coordinate System]
(-) (flag) (flag) (flag) (flag) (flag) (flag)
1 1 1 1 1 1 1 “”
------- INTERFACE JOINTS: 1/0 for Locked (to the TP)/Free DOF @each Interface Joint (only Locked-to-TP implemented thus far (=rigid TP)) ---------
1 NInterf - Number of interface joints locked to the Transition Piece (TP): be sure to remove all rigid motion dofs
IJointID ItfTDXss ItfTDYss ItfTDZss ItfRDXss ItfRDYss ItfRDZss [Global Coordinate System]
(-) (flag) (flag) (flag) (flag) (flag) (flag)
1 1 1 1 1 1 1

then the following error appears:

FAST_InitializeAll:SD_Init:Craig_Bampton:SetIndexArrays: IDL or p%DOFL are the incorrect size.

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

Aborting FAST.

Kindly advice.

Dear Syed,

You must set IJointID = 18 to properly connect the top of the monopile to the platform in ElastoDyn.

Best regards,

Dear Jason,

After setting IJointID = 18 as you suggested, following error appears:

Timestep: 10 of 100 seconds.

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:AD14_CalcOutput:ELEMFRC:Beddoes Model:ATTACH: Blade #2 element #36 is supersonic! Other elements are likely supersonic as well.
Supersonic mach nos. will be set to 0.7 to attempt continuation.
AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Supersonic condition has subsided with Blade #3 element #4.

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Blade #2 element #36 is supersonic! Other elements are likely supersonic as well.
Supersonic mach nos. will be set to 0.7 to attempt continuation.
AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Supersonic condition has subsided with Blade #3 element #4.

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Blade #2 element #34 is supersonic! Other elements are likely supersonic as well.
Supersonic mach nos. will be set to 0.7 to attempt continuation.
AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Supersonic condition has subsided with Blade #3 element #4.

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Blade #2 element #34 is supersonic! Other elements are likely supersonic as well.
Supersonic mach nos. will be set to 0.7 to attempt continuation.
AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Supersonic condition has subsided with Blade #3 element #4.

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Blade #2 element #35 is supersonic! Other elements are likely supersonic as well.
Supersonic mach nos. will be set to 0.7 to attempt continuation.
AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Supersonic condition has subsided with Blade #3 element #4.

WARNING: High VT velocity encountered during induction factor calculation.

Blade number 2, Element number 37
VNW = 18.14, VT = 403.88

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Blade #2 element #33 is supersonic! Other elements are likely supersonic as well.
Supersonic mach nos. will be set to 0.7 to attempt continuation.
AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Supersonic condition has subsided with Blade #3 element #4.

WARNING: High VT velocity encountered during induction factor calculation.
Blade number 2, Element number 36
VNW = 18.112, VT = 404.17
WARNING: High VT velocity encountered during induction factor calculation.
Blade number 2, Element number 37
VNW = 18.115, VT = 412.83

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:AD14_CalcOutput:ELEMFR
C:BeddoesModel:ATTACH: Blade #2 element #32 is supersonic! Other elements are likely supersonic a
s well.
Supersonic mach nos. will be set to 0.7 to attempt continuation.AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Supersonic condition has subsided with Blade #3 element #4.

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Blade #2 element #33 is supersonic! Other elements are likely supersonic as well.
Supersonic mach nos. will be set to 0.7 to attempt continuation.
AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Supersonic condition has subsided with Blade #3 element #4.

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Blade #2 element #33 is supersonic! Other elements are likely supersonic as well.
Supersonic mach nos. will be set to 0.7 to attempt continuation.
AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Supersonic condition has subsided with Blade #3 element #4.

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Blade #2 element #34 is supersonic! Other elements are likely supersonic as well.
Supersonic mach nos. will be set to 0.7 to attempt continuation.
AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Supersonic condition has subsided with Blade #3 element #4.

WARNING: High VT velocity encountered during induction factor calculation.
Blade number 2, Element number 27
VNW = 17.984, VT = 406.33
WARNING: High VT velocity encountered during induction factor calculation.
Blade number 2, Element number 28
VNW = 17.985, VT = 442.44
WARNING: Induced velocity warning written 5 times. The message will not be repeated, though the condition may persist.

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Blade #2 element #26 is supersonic! Other elements are likely supersonic as well.
Supersonic mach nos. will be set to 0.7 to attempt continuation.
AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Supersonic condition has subsided with Blade #3 element #4.

FAST_Solution:CalcOutputs_And_SolveForInputs:ED_CalcContStateDeriv:SetCoordSy:Sm
all angle assumption violated in SUBROUTINE SmllRotTrans() due to a large platform displac
ement (ElastoDyn SetCoordSy). The solution may be inaccurate. Simulation continuing, but future w
arnings from SmllRotTrans() will be suppressed.

Additional debugging message from SUBROUTINE SmllRotTrans(): 11.795 s
ED_CalcContStateDeriv:LAPACK_DGETRF: U( 10, 10)=0. Factor U is exactly singular.
CalcOutputs_And_SolveForInputs:SolveOption2:AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Blade #2 element #22 is supersonic!
Other elements are likely supersonic as well. Supersonic mach nos.
will be set to 0.7 to attempt continuation.
AD14_CalcOutput:ELEMFRC:BeddoesModel:ATTACH: Supersonic condition has subsided with Blade #3 element #4.

CalcOutputs_And_SolveForInputs:SolveOption1:ED_SD_HD_BD_Orca_InputOutputSolve:ED_CalcContStateDeriv:LAPACK_DGETRF: U( 10, 10)=0.
Factor U is exactly singular.

FAST encountered an error at simulation time 11.79 of 100 seconds.
Simulation error level: FATAL ERROR
Aborting FAST.

Kindly advice.

Dear Syed,

From the error message you’ve received, I would guess that your model has suffered a numerical instability due to the use of a time step that is too large. (Enabling the platform DOFs with a SubDyn-modeled substructure likely introduced higher natural frequencies in your structural model.) I suggest that you drop the time step and try running the simulation again.

Furthermore, have you followed the modeling guidance section 5 of the draft SubDyn User’s Guide and Theory manual (wind.nrel.gov/nwtc/docs/SubDyn_Manual.pdf)?

Best regards,

Dear Jason,

Thank you for your help.
I solved the problem by reducing the time step.

Hello,

I have a problem by running FASTv8 using Test18. This error appearsFAST (v8.15.00a-bjj, 12-Apr-2016)

Copyright (C) 2016 National Renewable Energy Laboratory

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



Running FAST (v8.15.00a-bjj, 12-Apr-2016), compiled as a 32-bit application usi
ng single
precision
linked with NWTC Subroutine Library (v2.08.00, 5-Apr-2016)

Heading of the FAST input file:
FAST Certification Test #24: NREL 5.0 MW Baseline Wind Turbine with OC3 Hywin
d Configuration,
for use in offshore analysis

Running ElastoDyn (v1.03.02a-bjj, 8-Apr-2016).

Running AeroDyn (v15.02.03, 12-Apr-2016).

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

Running BEM (v1.01.00a, 12-Apr-2016).

Running InflowWind (v3.02.00a-bjj, 11-Apr-2016).
Opening InflowWind input file: .\5MW_Baseline/NRELOffshrBsline5MW_InflowWind.d
at

Reading a 20x20 grid (145 m wide, 17.5 m to 162.5 m above ground) with a char
acteristic wind
speed of 12 m/s. This full-field file was generated by TurbSim (v1.50, 25-Sep
-2009) on
01-Jun-2017 at 19:14:57.

Processed 72242 time steps of 20-Hz full-field data (3612.1 seconds).

Running ServoDyn (v1.05.00a-bjj, 11-Mar-2016).

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

Running HydroDyn (v2.05.00, 15-Mar-2016).
Generating incident wave kinematics and current time history.
Reading in WAMIT output with root name “.\5MW_Baseline/HydroData/ssv”.
Computing radiation impulse response functions and wave diffraction forces.

FAST_InitializeAll:MAP_Init:Cannot read the MAP input file.

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

Aborting FAST.

I:\SURAJ-PhD\FAST\FASTV8-Program\dcw1>FAST_win32 DeepCwind.fst



FAST (v8.15.00a-bjj, 12-Apr-2016)

Copyright (C) 2016 National Renewable Energy Laboratory

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



Running FAST (v8.15.00a-bjj, 12-Apr-2016), compiled as a 32-bit application usi
ng single
precision
linked with NWTC Subroutine Library (v2.08.00, 5-Apr-2016)

Heading of the FAST input file:
FAST Certification Test #24: NREL 5.0 MW Baseline Wind Turbine with OC3 Hywin
d Configuration,
for use in offshore analysis

Running ElastoDyn (v1.03.02a-bjj, 8-Apr-2016).

Running AeroDyn (v15.02.03, 12-Apr-2016).

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

Running BEM (v1.01.00a, 12-Apr-2016).

Running InflowWind (v3.02.00a-bjj, 11-Apr-2016).
Opening InflowWind input file: .\5MW_Baseline/NRELOffshrBsline5MW_InflowWind.d
at

Reading a 20x20 grid (145 m wide, 17.5 m to 162.5 m above ground) with a char
acteristic wind
speed of 12 m/s. This full-field file was generated by TurbSim (v1.50, 25-Sep
-2009) on
01-Jun-2017 at 19:14:57.

Processed 72242 time steps of 20-Hz full-field data (3612.1 seconds).

Running ServoDyn (v1.05.00a-bjj, 11-Mar-2016).

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

Running HydroDyn (v2.05.00, 15-Mar-2016).
Generating incident wave kinematics and current time history.
Reading in WAMIT output with root name “.\5MW_Baseline/HydroData/ssv”.
Computing radiation impulse response functions and wave diffraction forces.

MAP++ environment properties (set externally)…
Gravity constant [m/s^2] : 9.81
Sea density [kg/m^3] : 1025.00
Water depth [m] : 200.00
Vessel reference position [m] : 0.00 , 0.00 , 0.00

Timestep: 0 of 3600 seconds.

FAST_Solution0:CalcOutputs_And_SolveForInputs:SolveOption2:SrvD_CalcOutput:Runni
ng 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. Includes modif
ications for the
Hywind spar.
CalcOutputs_And_SolveForInputs:SolveOption1:ED_HD_InputOutputSolve:LAPACK_SGETRF
: U( 11,
11)=0. Factor U is exactly singular.

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

Aborting FAST.

Dear Nayak.Sooraj,

It appears that you are using some customized FAST model rather than one provided by NREL. You mention Test18, but based on the messages, the first simulation appears to be some modified form of Test24 (using a WAMIT output file named ssv) and the second simulation is using a primary FAST input file names DeepCwind.fst. What did you change in the input files from one of the FAST models provided?

The first simulation seems to have an error related to the format of the MAP input file. Hopefully you know what you changed in the MAP input file to know why this error is triggered.

The second simulation seems to have an error in the Jacobian set up in the glue code where the coupling between ElastoDyn and HydroDyn happens. I’m not sure what would trigger this error unless the platform mass/inertia in ElastoDyn are set to zero or the added mass is the opposite of the platform mass/inertia such that there sum is zero. Perhaps upgrading from FAST v8.15 to FAST v8.16 or OpenFAST v1.0.0 would also help?

Best regards,

Dear Jason,

I have used Test 25.fst data to run the program, I am getting the error like this can you help me out



FAST (v8.15.00a-bjj, 12-Apr-2016)

Copyright (C) 2016 National Renewable Energy Laboratory

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



Running FAST (v8.15.00a-bjj, 12-Apr-2016), compiled as a 32-bit application using single
precision linked with NWTC Subroutine Library (v2.08.00, 5-Apr-2016)

Heading of the FAST input file:
FAST Certification Test #25: NREL 5.0 MW Baseline Wind Turbine with OC4-DeepC
wind semi
configuration, for use in offshore analysis

FAST_InitializeAll:FAST_Init:FAST_ReadPrimaryFile:Invalid numerical input for file
“DeepCwind.fst” occurred while trying to read WrVTK.

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

Aborting FAST.

Dear Nayak,

Again, I would guess that you changed the input file in some way from what we provided as Test25.fst in the FAST v8.15 CertTest.

Regarding the runtime error you are receiving, I suggest that you use the Echo option from the primary FAST input file to debug errors in the input-file processing.

Best regards,