Error with the FF wind array boundaries

Wind & Water Computer-Aided Engineering Software Tools
1

Hi, everyone.
It’s the first time that I write on this forum. I’m a engineering student in Korea, and a beginner of using FAST.
I have a problem that I cannot solve by myself well.
I want to simulate some cases with the “NRELOffshrBsline5MW_OC3Hywind” type.
I made my own wind files by using TurbSim, (mean V = 10ms, IECKAI type) and i use other factors with the files from the public directory folders. When I set the platform model to 0, it runs well, but when I set the platform model to 1 or 3, error is occurred. (Below)

////////////////////////////////////////////////////////////////////////
D:\NREL data\NRELOffshrBsline5MW_OC3Hywind>fast PLT_3.fst

Running FAST (v7.00.00a-bjj, 31-Mar-2010).
Linked with NWTC Subroutine Library (v1.02.00, 16-Mar-2010).

Heading of the FAST input file: NREL 5.0 MW Baseline Wind Turbine for Use in Of
fshore Analysis.

Aerodynamic loads calculated using AeroDyn (v13.00.00a-bjj, 31-Mar-2010).
Heading of the AeroDyn input file: NREL 5.0 MW offshore baseline aerodynamic in
put properties;
Compatible with AeroDyn v12.58.

No file extension found. Assuming Wind\10ms_IECKAI is a binary FF wind file wit
h a “.wnd”
extension.

Reading a 13x13 grid (180 m wide, 4.10004E-02 m to 177.34 m above ground) with
a characterstic
wind speed of 10 m/s.
Processed 13801 time steps of 100-Hz full-field data (138 seconds).

ADAMS dataset file ‘PLT_3_ADAMS.adm’ created.
ADAMS command file ‘PLT_3_ADAMS.acf’ created.

WARNING message from DISCON.dll:
Running with torque and pitch control of the NREL offshore 5MW baseline wind tur
bine from
DISCON.dll as written by J. Jonkman of NREL/NWTC for use in the IEA Annex XXIII
OC3 studies.
Includes modifications for the Hywind spar.
Timestep: 2 of 120 seconds. Estimated final completion at 14:20:10.
Error: FF wind array boundaries violated. Grid too small in Z direction (height
(Z=-0.32841 m)
is below the grid and no tower points are defined).
Error getting velocity in AeroDyn/AD_WindVelocityWithDisturbance().
Aborting FAST.

///////////////////////////////////////////////////////////////////////////////////////

I change some input values to correct the grid area. but it doesn’t work well. How can I solve this problem?

Thanks to your help
S.J.Baik

2

Dear Seung Joo Baik,

The error regarding FF wind array boundaries is telling you that the blade element has passed outside of the turbulence grid in the Z (vertical) direction. A value of Z < 0 means that the blade element is below the still water level. So, the real problem is not your wind turbulence grid size, but excessive turbine deflections.

Without knowing more about your simulation, it is hard to assess why your turbine is deflecting so much. When you set the PtfmModel = 3, are you specifying the floating system properties (such as platform mass/inertia and DOFs, mooring properties, WAMIT input, wave conditions) in the platform file?

Best regards,

3

I use the floating system properties which are in “NRELOffshrBsline5MW_OC3Hywind.zip” from the public directory folders.
I didn’t change the properties’ values. And also, I don’t have a right to use WAMIT, so I just use the given ‘spar1, 3, hst’ in the simulation now.

And, what is the meaning of the error (Grid is too small in Z direction), if the height Z > 0?

Best regards,

Seung-Joo Baik

4

Dear Seung-Joo Baik,

As I said in my prior post, the error is not that your grid is too small, but that Z < 0.

I looked at your original post and noticed that FAST is not telling you that it was, “Reading in WAMIT output with root name …,” which is a message that should be shown if HydroDyn is being initialized properly for a floating platform. I suspect HydroDyn is not being initialized properly, which means that your platform has no reaction loads and that the system is simply falling due to gravity. Is the value of input parameter PtfmLdMod in your FAST platform input file set to FltngPtfmLd? FltngPtfmLd is the keyword that is used to call the currently undocumented HydroDyn features of FAST.

Best regards,

5

Dear Jason.

Thanks for your kind answers. I can simulate the first case with the offshore condition by your favor.

Best regards,

6

Hi, everyone.
This is the first time I am posting on this forum. I’m a PhD student in NITK, Surthakal, INDIA and a beginner of using FAST.
I have a problem that I am not getting the result for V-Shaped Semi-submersible floating platform please help me with this errors.

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 #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 characteristic 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.

Running MoorDyn (v1.01.02F, 8-Apr-2016).
Creating mooring system. 3 fairleads, 3 anchors, 0 connects.
Finalizing ICs using dynamic relaxation.
t=2 FairTen 1: 1.15192E+06, 0, 0
t=3.9999 FairTen 1: 1.12661E+06, 1.15192E+06, 0
t=5.9997 FairTen 1: 1.19640E+06, 1.12661E+06, 1.15192E+06
t=7.9996 FairTen 1: 1.24175E+06, 1.19640E+06, 1.12661E+06
t=10 FairTen 1: 1.26622E+06, 1.24175E+06, 1.19640E+06
t=12.001 FairTen 1: 1.27184E+06, 1.26622E+06, 1.24175E+06
t=14.002 FairTen 1: 1.27073E+06, 1.27184E+06, 1.26622E+06

Fairlead tensions converged to 1% after 14.002 seconds.
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 modifications for the
Hywind spar.

Timestep: 1 of 3600 seconds. Estimated final completion at 11:32:21.

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:InflowWind_CalcOutput:
CalcOutput:IfW_TSF
FWind_CalcOutput [position=(10.844, -80.826, 109.75) in wind-file coordinates]:
FF wind array
boundaries violated: Grid too small in Y direction. Y=-80.826; Y boundaries = [-
72.5, 72.5]

FAST encountered an error at simulation time 1.3875 of 3600 seconds.
Simulation error level: FATAL ERROR

Aborting FAST.

7

Dear Nayak,

I’m not sure how you’ve defined your FAST model, but it appears that an aerodynamic analysis node is located at (X,Y,Z) = (10.844, -80.826, 109.75) m, but the Y-range of the turbulent wind data file is only -72.5 - 72.5 m. You must ensure that the wind data file encompasses the entire domain where you expect to have aerodynamic analysis nodes.

Best regards,

8

Dear Jason

I am trying to run Test24 of FAST (OC3 Hywind) with HAWC Format wind files. My input in the InflowWind file for the relevant section is as shown below:

----------------------------------------Parameters for HAWC-format binary files [Only used with WindType = 5] =====================
“wasp\Output\dummyu.bin” FileName_u - name of the file containing the u-component fluctuating wind (.bin)
“wasp\Output\dummyv.bin” FileName_v - name of the file containing the v-component fluctuating wind (.bin)
“wasp\Output\dummyw.bin” FileName_w - name of the file containing the w-component fluctuating wind (.bin)
16384 nx - number of grids in the x direction (in the 3 files above) (-)
32 ny - number of grids in the y direction (in the 3 files above) (-)
32 nz - number of grids in the z direction (in the 3 files above) (-)
3.076171875 dx - distance (in meters) between points in the x direction (m)
4.6875 dy - distance (in meters) between points in the y direction (m)
4.6875 dz - distance (in meters) between points in the z direction (m)
90 RefHt - reference height; the height (in meters) of the vertical center of the grid (m)

However, my FAST simulation terminates with the following error:

Reading HAWC wind files with grids of 16384 x 32 x 32 points.

FAST_Solution0:CalcOutputs_And_SolveForInputs:SolveOption2:InflowWind_CalcOutput:CalcOutput:IfW_HA
WCWind_CalcOutput [position=(0, 0, 10) in wind-file coordinates]: FF wind array boundaries
violated. Grid too small in Z direction (Z=10 m is below the grid).

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. Includes modifications for the Hywind spar.

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

Aborting FAST.

My understanding is that the centre of the grid is at (0,0,10) and that the point z=10 falls below the grid. Shouldn’t the centre of the grid coincide with RefHt, in the vertical direction? I’m not sure I understand how the value (0,0,10) comes into play. Could you please help me with this error?

Abhinav K A

9

Dear Abhinav,

The location (0,0,10) m is coming from the aerodynamic analysis node at the tower base used for the tower aerodynamic load calculation in Test24. (See the AeroDyn v15 primary input file of Test24 for details.)

The center of the turbulence grid is (0,0,90) m based on your setting of RefHt in InflowWind. However, I see that your grid is only (32-1)*4.6875 = 145.3125 m tall, and so, extends from 17.34375 to 162.65625 m above MSL. So, the tower aerodynamic analysis nodes clearly extend below the grid. The solution is to (1) disable tower aerodynamic loads by setting TwrAero = False in the AeroDyn v15 primary input file, (2) increase the elevation of the lowest tower aerodynamic nodes in the AeroDyn v15 primary input file so that all nodes lie within the grid, or (3) change the size/location of the turbulence grid so that all aerodynamic analysis nodes lie within the grid.

Best regards,

1 Like
10

Dear Jason

Thank you for the explanation

Sincerely

Abhinav

11

Dear Dr. Jason,

I am trying to run the simulation for the Power production 1.3 DLC AND turb.= EMT. while running the simulation I am getting error like as below in my OpenFAST.

"FAST_Solution0:CalcOutputs_And_SolveForInputs:SolveOption2:InflowWind_CalcOutput
:CalcOutput:IfW_TS
FFWind_CalcOutput [position=(-5.0765, 0.57484, 173.84) in wind-file coordinates]
: FF wind array
boundaries violated. Grid too small in Z direction (Z=173.84 m is above the grid
).

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

Aborting OpenFAST."

Could you please explain me why I am getting this error.
I Have to tried to use try and error method with changing some data in the turbsim file but I am still getting the same error.

I have attached my input Turbsim file as below and I am working with DTU 10MW ref. Wind Turbine with Spar-buoy structure.

I hope you will give me reply as soon as possible.

Thanks a lot

Best regards
Mitesh Ramani
TurbSim.rtf (6.15 KB)

12

Dear Mitesh,

It looks like your TurbSim file would create a turbulent wind data file that extends well beyond Z=173.84 m in height. Are you sure you have referenced the correct TurbSim-generated *.bts file from your InflowWind module?

Best regards,

13

Dear Dr. jason,

Thank you for your speedy reply,

Yes,I am sure I gave the reference *.bts file in the InflowWind.I am using DTU 10 MW reference Wind Turbine,
I have attached my InflowWind file as below.
My Reference height for horizontal wind speed is around 129m because I am using the Spar-Buoy.

I hope you can find a solution as soon as possible.

Thank you very much

Best regards
Mitesh Ramani
INflowWind.rtf (5.97 KB)

14

Dear Mitesh,

I still don’t really see any problem.

Are you sure your path is to the correct .bts file? You can check the z-coordinates of your TurbSim.bts file using the readfile_BTS.m script in the MATLAB Toolbox (github.com/OpenFAST/matlab-tool … file_BTS.m). This call will return the z-coordinates of the wind data points:

[~, ~, ~, z] = readfile_BTS(‘C:\Users\mitesh\Desktop\10_MW_Spar_Buoy_WT\Simulation26\TurbSim.bts’)

Best regards,

15

Dear Dr. Jason,

Thank you so much for your guidance.

I was getting that error because I have not generated *.bts file. I have solved that problem by using generated original *.bts file so now simulation is running well by your favor.

Thank you for sending me the MATLAB Toolbox script link.

Best Regards,
Mitesh Ramani

16

Hello,

I’m doing a simulation with OC3Hywind and for some DLC I have the error: “Grid too small in Z direction”. I tried to increase the grid height in the turbsim file, but it only change the inferior limit of the grid. Even if I change the grid size, the higher point of the grid continues on 172.5 m. Can anyone help me?

OpenFAST

Copyright (C) National Renewable Energy Laboratory
Copyright (C) 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-v2.0.0-dirty
Compile Info:

  • Architecture: 64 bit
  • Precision: single
  • Date: Dec 06 2018
  • Time: 10:09:59
    Execution Info:
  • Date: 04/28/2019
  • Time: 21:03:02-0300

OpenFAST input file heading:
FAST Certification Test #19: NREL 5.0 MW Baseline Wind Turbine with OC3 Monopile RF
Configuration, for use in offshore analysis

Running ElastoDyn.
Running AeroDyn.
Running AirfoilInfo.
Running BEM.
Running InflowWind.

Reading a 20x20 grid (165 m wide, 2.5 m to 172.5 m above ground) with a characteristic wind
speed of 39 m/s. This full-field file was generated by TurbSim (v1.06.00, 21-Sep-2012) on
28-Apr-2019 at 20:58:24.

Processed 72685 time steps of 20-Hz full-field data (3634.2 seconds).
Running ServoDyn.
Running ServoDyn Interface for Bladed Controllers.
Running HydroDyn.
Generating incident wave kinematics and current time history.
Reading in WAMIT output with root name
“C:\Users\carol\Desktop\OC3Spar_OpenFast\OWT\model01\5MW_Baseline\HydroData\Spar”.
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] : 320.00
Vessel reference position [m] : 0.00 , 0.00 , 0.00

Time: 0 of 3630 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. Includes modifications for the
Hywind spar.

FAST_Solution:FAST_AdvanceStates:ED_ABM4: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(): 0.43 s

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:InflowWind_CalcOutput:CalcOutput:IfW_TSF
FWind_CalcOutput [position=(-2.7651, 1.1849, 177.22) in wind-file coordinates]: FF wind array
boundaries violated. Grid too small in Z direction (Z=177.22 m is above the grid).

FAST encountered an error at simulation time 0.765 of 3630 seconds.
Simulation error level: FATAL ERROR

Aborting OpenFAST.

Thanks

17

Hi Carol,

The error is telling you that an aerodynamic analysis node is above the grid where wind is defined. See the TurbSim User’s Guide (especially Figures 4 and 5 and the associated text) for information on how TurbSim defines the grid: nwtc.nrel.gov/system/files/TurbSim.pdf.

Best regards,

18

Hi Jason,

Thank you for your answer.

I understood that the error is due to the small grid in Z direction. In the example above, there is a Z=177,22 m that is above the grid which goes up to 172,5 m above the ground. The problem is that there is always a node above the grid defined. I listed some definition of grids that I have tried and the node which is above of it.

When I choose a GridHeight of 145 m, the grid goes from 17,5 m to 162,5 m above the ground. (16x16) - and there is a at Z=177,22 m

When I choose a GridHeight of 165 m, the grid goes from 2,5 m to 162,5 m above the ground. (16x16) - Z=177,22 m

When I choose a GridHeight of 170 m, the grid goes from 2,5 m to 172,5 m above the ground. (20x20) - Z=177,22 m

When I choose a GridHeight of 175 m, the grid goes from 2,5 m to 177,5 m above the ground. (20x20) - Z = 182,25 m

When I choose a GridHeight of 179 m, the grid goes from 0,5 m to 179,5 m above the ground. (20x20) - Z = 184,23 m

I don’t know if the problem is only with the definition of the grid or if there is something else that I’m not realizing.

My TurbSim Input File is below:

TurbSim Input File. Valid for TurbSim v1.50; 17-May-2010; Example file that can be used with simulations for the NREL 5MW Baseline Turbine; note that UsableTime has been decreased in this file so that the file distributed with the FAST CertTest isn’t as large

---------Runtime Options-----------------------------------
1 RandSeed1 - First random seed (-2147483648 to 2147483647)
RanLux RandSeed2 - Second random seed (-2147483648 to 2147483647) for intrinsic pRNG, or an alternative pRNG: “RanLux” or “RNSNLW”
False WrBHHTP - Output hub-height turbulence parameters in binary form? (Generates RootName.bin)
False WrFHHTP - Output hub-height turbulence parameters in formatted form? (Generates RootName.dat)
False WrADHH - Output hub-height time-series data in AeroDyn form? (Generates RootName.hh)
True WrADFF - Output full-field time-series data in TurbSim/AeroDyn form? (Generates RootName.bts)
False WrBLFF - Output full-field time-series data in BLADED/AeroDyn form? (Generates RootName.wnd)
True WrADTWR - Output tower time-series data? (Generates RootName.twr)
False WrFMTFF - Output full-field time-series data in formatted (readable) form? (Generates RootName.u, RootName.v, RootName.w)
False WrACT - Output coherent turbulence time steps in AeroDyn form? (Generates RootName.cts)
True Clockwise - Clockwise rotation looking downwind? (used only for full-field binary files - not necessary for AeroDyn)
0 ScaleIEC - Scale IEC turbulence models to exact target standard deviation? [0=no additional scaling; 1=use hub scale uniformly; 2=use individual scales]

--------Turbine/Model Specifications-----------------------
20 NumGrid_Z - Vertical grid-point matrix dimension
20 NumGrid_Y - Horizontal grid-point matrix dimension
0.05 TimeStep - Time step [seconds]
3630.0 AnalysisTime - Length of analysis time series [seconds]
3630.0 UsableTime - Usable length of output time series [seconds] (program will add GridWidth/MeanHHWS seconds) [bjj: was 630]
90.0 HubHt - Hub height [m] (should be > 0.5GridHeight)
179.0 GridHeight - Grid height [m]
179.0 GridWidth - Grid width [m] (should be >= 2(RotorRadius+ShaftLength))
0 VFlowAng - Vertical mean flow (uptilt) angle [degrees]
0 HFlowAng - Horizontal mean flow (skew) angle [degrees]

--------Meteorological Boundary Conditions-------------------
IECKAI TurbModel - Turbulence model (“IECKAI”=Kaimal, “IECVKM”=von Karman, “GP_LLJ”, “NWTCUP”, “SMOOTH”, “WF_UPW”, “WF_07D”, “WF_14D”, or “NONE”)
“3” IECstandard - Number of IEC 61400-x standard (x=1,2, or 3 with optional 61400-1 edition number (i.e. “1-Ed2”) )
11.0 IECturbc - IEC turbulence characteristic (“A”, “B”, “C” or the turbulence intensity in percent) (“KHTEST” option with NWTCUP, not used for other models)
NTM IEC_WindType - IEC turbulence type (“NTM”=normal, “xETM”=extreme turbulence, “xEWM1”=extreme 1-year wind, “xEWM50”=extreme 50-year wind, where x=wind turbine class 1, 2, or 3)
default ETMc - IEC Extreme turbulence model “c” parameter [m/s]
PL WindProfileType - Wind profile type (“JET”=Low-level jet,“LOG”=Logarithmic,“PL”=Power law, or “default”, or “USR”=User-defined)
90.0 RefHt - Height of the reference wind speed [m]
39.0 URef - Mean (total) wind speed at the reference height [m/s]
default ZJetMax - Jet height [m] (used only for JET wind profile, valid 70-490 m)
0.11 PLExp - Power law exponent [-] (or “default”)
default Z0 - Surface roughness length [m] (or “default”)

--------Non-IEC Meteorological Boundary Conditions------------
default Latitude - Site latitude [degrees] (or “default”)
0.05 RICH_NO - Gradient Richardson number
default UStar - Friction or shear velocity [m/s] (or “default”)
default ZI - Mixing layer depth [m] (or “default”)
default PC_UW - Hub mean u’w’ Reynolds stress [(m/s)^2] (or “default”)
default PC_UV - Hub mean u’v’ Reynolds stress [(m/s)^2] (or “default”)
default PC_VW - Hub mean v’w’ Reynolds stress [(m/s)^2] (or “default”)
default IncDec1 - u-component coherence parameters (e.g. “10.0 0.3e-3” in quotes) (or “default”)
default IncDec2 - v-component coherence parameters (e.g. “10.0 0.3e-3” in quotes) (or “default”)
default IncDec3 - w-component coherence parameters (e.g. “10.0 0.3e-3” in quotes) (or “default”)
default CohExp - Coherence exponent (or “default”)

--------Coherent Turbulence Scaling Parameters-------------------
“M:\coh_events\eventdata” CTEventPath - Name of the path where event data files are located
“Random” CTEventFile - Type of event files (“random”, “les” or “dns”)
true Randomize - Randomize disturbance scale and location? (true/false)
1.0 DistScl - Disturbance scale (ratio of dataset height to rotor disk).
0.5 CTLy - Fractional location of tower centerline from right (looking downwind) to left side of the dataset.
0.5 CTLz - Fractional location of hub height from the bottom of the dataset.
10.0 CTStartTime - Minimum start time for coherent structures in RootName.cts [seconds]

==================================================
NOTE: Do not add or remove any lines in this file!

Thanks

19

Dear Carol,

OK, it appears that you understand how TurbSim creates its grids.

You say you are using the OC3-Hywind model. Looking closer, I now see that you are receiving a “large blade deflection” warning, which has been discussed many times on this forum. Did you modify the OC3-Hywind model in some way e.g. changing the geometry, mass, stiffness, or time steps?

Best regards,

20

Hi !

I only have changed the azimuth to 180 due to another previous error in a different case. The rest is exactly like in the originals file.