Wind data of the FAST certification tests

Hello,

I am doing some control experiments with the 5MW baseline model (NRELOffshrBsline5MW_Onshore) and I have tried to change the wind data using TurbSim to generate the .bts file.

I run some controllers implemented as GH Bladed-style DLLs with the default wind data in “Wind/90m_12mps_twr.bts” and everything is ok, but whenever I try to use one of the files I generate with TurbSim i get the error message “Grid too small in the Z direction”. I think I am using the same boundaries as those of the default wind data file, but I must be missing something.

One of the .inp files I have tried:

[code]
TurbSim Input File. Valid for TurbSim v1.06.00, 21-Sep-2012

---------Runtime Options-----------------------------------
2318573 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)
True 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)
True WrBLFF - Output full-field time-series data in BLADED/AeroDyn form? (Generates RootName.wnd)
False 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)
True 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-----------------------
31 NumGrid_Z - Vertical grid-point matrix dimension
31 NumGrid_Y - Horizontal grid-point matrix dimension
0.0125 TimeStep - Time step [seconds]
100 AnalysisTime - Length of analysis time series [seconds] (program will add time if necessary: AnalysisTime = MAX(AnalysisTime, UsableTime+GridWidth/MeanHHWS) )
60 UsableTime - Usable length of output time series [seconds] (program will add GridWidth/MeanHHWS seconds)
90 HubHt - Hub height [m] (should be > 0.5GridHeight)
140.0 GridHeight - Grid height [m]
140.0 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-------------------
“SMOOTH” TurbModel - Turbulence model (“IECKAI”=Kaimal, “IECVKM”=von Karman, “GP_LLJ”, “NWTCUP”, “SMOOTH”, “WF_UPW”, “WF_07D”, “WF_14D”, “TIDAL”, or “NONE”)
“1-ED3” IECstandard - Number of IEC 61400-x standard (x=1,2, or 3 with optional 61400-1 edition number (i.e. “1-Ed2”) )
“A” IECturbc - IEC turbulence characteristic (“A”, “B”, “C” or the turbulence intensity in percent) (“KHTEST” option with NWTCUP model, 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]
default WindProfileType - Wind profile type (“JET”;“LOG”=logarithmic;“PL”=power law;“H2L”=Log law for TIDAL spectral model;“IEC”=PL on rotor disk, LOG elsewhere; or “default”)
90.0 RefHt - Height of the reference wind speed [m]
15.0 URef - Mean (total) wind speed at the reference height [m/s] (or “default” for JET wind profile)
default ZJetMax - Jet height [m] (used only for JET wind profile, valid 70-490 m)
default 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 (or “default”)
default PC_UV - Hub mean u’v’ Reynolds stress (or “default”)
default PC_VW - Hub mean v’w’ Reynolds stress (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-------------------
“Test\eventdata” CTEventPath - Name of the path where event data files are located
“Random” CTEventFile - Type of event files (“LES”, “DNS”, or “RANDOM”)
true Randomize - Randomize the disturbance scale and locations? (true/false)
1.0 DistScl - Disturbance scale (ratio of wave height to rotor disk). (Ignored when Randomize = true.)
0.5 CTLy - Fractional location of tower centerline from right (looking downwind) to left side of the dataset. (Ignored when Randomize = true.)
0.5 CTLz - Fractional location of hub height from the bottom of the dataset. (Ignored when Randomize = true.)
30.0 CTStartTime - Minimum start time for coherent structures in RootName.cts [seconds]

==================================================
NOTE: Do not add or remove any lines in this file!
==================================================[/code]

Has anyone an idea of what I am missing? Alternatively, could anyone tell me with what parameters were wind data files in the certification tests generated?

Thanks

Dear Borja,

The grid dimensions in your TurbSim file look sufficient for the NREL 5-MW rotor, however, Test18 in the FAST CertTest (for the land-based NREL 5-MW turbine) is set up to compute drag loads on the tower, which requires wind to be created at points along the tower below the main rectangular grid. You must set WrADTWR to TRUE in the TurbSim input file to enable this feature. See the TurbSim User’s Guide for more information.

Best regards,

Thank you very much, will try that right away.

Edit: that was it. Thanks again

Dear Jason

I am analyzing the standard NREL 5 MW 61.5 m land based wind turbine from the NREL website. I have used TurbSim to create wind files (".bst) and executed FAST. I get below error.

Using InflowWind (v1.01.00b-bjj, 10-Aug-2012)
Assuming .\TurbSim.bts is a binary FF wind file.
Running NWTC Subroutine Library (v1.07.00b-mlb, 10-Jan-2013).
Reading a 10x10 grid (150 m wide, 15 m to 165 m above ground) with a characterstic wind speed of
5 m/s. This full-field file was generated by TurbSim (v1.06.00, 21-Sep-2012) on 03-Oct-2015 at 17:31:07.
Processed 660 time steps of 1-Hz full-field data (659 seconds).

WARNING: Small angle assumption violated in SUBROUTINE SmllRotTrans() due to a large blade
deflection. The solution may be inaccurate. Simulation continuing, but future warnings will be suppressed.
Additional debugging message from SUBROUTINE SmllRotTrans(): 5.00000E-02 s
WARNING: Blade #1 element #15 is supersonic! Other elements are likely supersonic as well.
Supersonic mach nos. will be set to 0.7 to attempt continuation.
WARNING: High VT velocity encountered during induction factor calculation.
Blade number 1, Element number 17
VNW = 5.2117, VT = 403.6
WARNING: Supersonic condition has subsided with Blade #2 element #4.
WARNING: Blade #2 element #15 is supersonic! Other elements are likely supersonic as well.
Supersonic mach nos. will be set to 0.7 to attempt continuation.
WARNING: High VT velocity encountered during induction factor calculation.
Blade number 2, Element number 17 VNW = 3.0739, VT = 405.11
WARNING: Supersonic condition has subsided with Blade #3 element #4.
WARNING: Blade #3 element #16 is supersonic! Other elements are likely supersonic as well.
Supersonic mach nos. will be set to 0.7 to attempt continuation.
WARNING: High VT velocity encountered during induction factor calculation.
Blade number 1, Element number 1 VNW = 5.0856, VT = 928.76
WARNING: High VT velocity encountered during induction factor calculation.
Blade number 1, Element number 2 VNW = 5.0938, VT = 1771.5
WARNING: High VT velocity encountered during induction factor calculation.
Blade number 1, Element number 3 VNW = 5.1267, VT = 2511.4
WARNING: Induced velocity warning written 5 times. The message will not be repeated, though the condition may persist.
Error: FF wind array boundaries violated. Grid too small in Z direction (Z=165.76 m is above the grid).
Error getting velocity in AeroDyn/AD_WindVelocityWithDisturbance().
Aborting FAST.

FAST Input file:-
primary.txt (22.7 KB)

TurbSim input file:
TurbSim.txt (6.17 KB)

Please help me to identify which parameters is causing the Grid to be small in Z direction and how can I resolve this error.

In addition, my AeroDyn input parameters are as per attached file

AeroDyn input file:
NRELOffshrBsline5MW_AeroDyn.txt (2.49 KB)

-Regards
Pravin

Dear Pravin,

I’m not sure what you are trying to do, but from your input files it looks like you’ve disabled the controller (PCMode = VSContrl = 0), enabled the simple induction generator model (GenModel = 1), but didn’t set any of the simple induction generator model settings (SIG_SlPc etc.). I wouldn’t expect the model to run with these inputs.

Do you need to use FAST v7 or can you use FAST v8? In FAST v7, the interface to the Bladed-style DLL controller used by the NREL 5-MW turbine was not a standard feature, but required a customized FAST executable. However, the interface to Bladed-style DLL controllers is standard in FAST v8. The land-based version of the NREL 5-MW turbine, including the controller, is available as Test18 in the FAST v8 Certest, available from here: nwtc.nrel.gov/FAST8. I suggest that you start with that.

Best regards,

Hi Jason

Thanks a lot for pointing to new version of FAST with which I can run the basic FAST analysis with Test18. I have further queries on how to deploy the output loads in FEA tool which I will put in another relevant forum

-Best Regards
Pravin

Hi Jason

I am trying to run FAST8 64bit for a small land based HAWT turbine with following parameters. When I run FAST8, I always get error as “Grid too small in Z direction” . Whatever options I try for the height of the grid such as 5 m to 45m above ground, the FF wind array is alway somewhat outside the grid such as Z=45.495 as you can see in attached image of the FAST command prompt, Also the input files are attached.
Requesting help to resolve this error.

TurbSim parameters
10 NumGrid_Z
10 NumGrid_Y
25 HubHt
40.00 GridHeight
40.00 GridWidth
25 RefHt
3.51 URef [m/s]

FAST8 AeroDyn parameters
45 HH

FAST8 ElastoDyn parameters
5.04 TipRad
0.1 HubRad
12.1 RotSpeed
44.5 TowerHt

FAST8 ServoDyn parameters
0 VSContrl
1 GenModel
ServoDyn.txt (10 KB)
AeroDyn_ElastoDyn.txt (21.3 KB)

Dear Pravin,

You set the hub-height in FAST equal to 45 m, which means a 5-m tip radius will lead to blade tips that exceed 50 m in elevation above the ground. You set the hub-height in TurbSim equal to 25 m, with the grid extending up to 45 m. So, clearly the blades will pass outside the wind grid; hence the error.

I also noticed that you have enabled the NREL 5-MW baseline controller DLL. Unless you’ve changed the parameters in this DLL, you should be aware that the DLL is only applicable to the NREL 5-MW turbine and won’t in general be valid for other turbines, especially turbines of drastically different size.

Best regards,

Thanks Jason for quick help.

Now when I change the parameters such that the TurbSim grid is 0.5 to 50.5 m above ground and change the FAST parameters such that

TurbSim

25.5 HubHt
50.00 GridHeight
50.00 GridWidth
25.5 RefHt

FAST8

20.5 TowerHt
21 HH

Then I get error as “Grid too small in Y direction. Y=30.305; Y boundaries = [-25, 25]”. Please see attached image. So now Y is going out of wind boundaries. I have disabled the bladed style controller discom.dll. Kindly help. What will be right parameters for a 5 mt radius blade?

-Regards
Pravin
error_Y_Dir.png

Dear Pravin,

Now it appears that the problem is not with the size of the turbulent wind field, but that there is a numerical instability in your model. Warnings regarding a “small angle approximation violation”, a simulation crash, or very large deflections that occur in the time series near the start of a simulation are good signs of a numerical instability. Please use “Search…” in the upper right of the forum to search for “small angle assumption” to see how others have solved similar problems in the past e.g. see my post dated Nov 04, 2010 in the following forum topic: http://forums.nrel.gov/t/error-in-fast-working-in-adams/298/3.

Best regards,