Error with the FF wind array boundaries

Dear Carol,

I would not expect changing the initial azimuth angle to have any effect on the stability of the OpenFAST solution. I suggest doing a file comparisons between the files you are using and those for the OC3-Hywind spar test from the r-test to see if you inadvertently changed other input settings.

Best regards,

Hello, everyone
This is the first time I am posting in this forum. I am a Masters student from India and I am a beginner in FAST. So I have been trying to model a DeepCWind with point absorbers configuration around the DeepCWind. While running fast, I encountered this error. Please help me out.

[b]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 Hywind 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.dat

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 for 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/dcw_pa_528”.
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=16.003 FairTen 1: 9.96023E+05, 1.00412E+06, 1.00178E+06
Fairlead tensions converged to 1% after 16.003 seconds.
Timestep: 0 of 3600 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.
Timestep: 41 of 3600 seconds. Estimated final completion at 07:26:55.

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:InflowWind_CalcOutput:CalcOutput:IfW_TSF
FWind_CalcOutput [position=(6.7564, -80.164, 87.43) in wind-file coordinates]: FF wind array
boundaries violated: Grid too small in Y direction. Y=-80.164; Y boundaries = [-72.5, 72.5]

FAST encountered an error at simulation time 41.113 of 3600 seconds.
Simulation error level: FATAL ERROR

Aborting FAST.

[/b]

I have tried changing the grid dimensions in the Turbsim File, but every time I increase the grid dimensions, the position in the wind file coordinates becomes even larger resulting in the FF wind array boundaries violation. And also I face a new error which is:

ED_HD_InputOutputSolve: HydroDyn_CalcOutput: Angles in GetSmllRotAngs() are larger than 0.4 radians
FAST encountered an error at simulation time 41.113 of 3600 seconds.
Simulation error level: FATAL ERROR

Aborting FAST.

How do I solve this?

Reeti
M.Tech

Dear Reeti.Rajan,

If you are receiving an error regarding large angles in HydroDyn, this likely means that your model has gone numerically unstable. You say you are running “DeepCWind with point absorbers configuration”, but the heading your input file refers to the “OC3-Hywind [spar] configuration”. Are you running one of the sample models provided with the FAST v8 archive? If so, what did you change in the input file(s)?

Best regards,

Hello, Dr. Jonkman
I have changed only the HydroDyn.DAT file in which I have done the following changes
-Changed the additional stiffness matrix with reference from the FAST manual
-Added additional member joints for the point absorbers. (I have taken 3 conical point absorbers in a circular arrangement around the DeepCWind)
-Added member cross-sectional properties and hydrodynamic coefficients
-Added additional members.

I have noticed that the program runs without errors when I keep the PtfmPitch as ‘FALSE’ in the ElastoDyn file. Also, the program runs without errors when I use a different ‘.gdf’ file (in which the point absorbers are a little closer to the platform) to obtain .1, .3, .hst.

But in my original design of the platform where the point absorbers are a little further away from the DeepCWind, I encounter this error of the GetSmllRotAngs() larger than 0.4. Is there anyway I can rectify this error?

With Regards
Reeti

Dear Reeti,

Did you change the pitch stiffness? If so, did you decrease or increase it?

I would guess that either the pitch stiffness has reduced and the platform is no longer hydrostatically stable or the pitch stiffness has increased, introducing a high frequency in the model that requires a smaller time step. You could first check if reducing the time step solves the problem.

Best regards,

Dear Jason
I’m having some problems generating wind data for farm simulation using turbsim. The first is the first setting:

--------Turbine/Model Specifications-----------------------
       45   NumGrid_Z       - Vertical grid-point matrix dimension
      250   NumGrid_Y       - Horizontal grid-point matrix dimension
     0.05   TimeStep        - Time step [seconds]
    1800.0  AnalysisTime    - Length of analysis time series [seconds] (program will add time if necessary: AnalysisTime = MAX(AnalysisTime, UsableTime+GridWidth/MeanHHWS) )
    "ALL"   UsableTime      - Usable length of output time series [seconds] (program will add GridWidth/MeanHHWS seconds unless UsableTime is "ALL")
      95    HubHt           - Hub height [m] (should be > 0.5*GridHeight)
      180   GridHeight      - Grid height [m]
     1000   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]

The error message is shown in the figure.


I guess the reason may be that the grid point spacing in the vertical direction (180/45=4) cannot be divisible by 5 (the bottom of the wind data). I don’t know if this understanding is correct? To verify, I redid the following settings:

--------Turbine/Model Specifications-----------------------
       35   NumGrid_Z       - Vertical grid-point matrix dimension
      250   NumGrid_Y       - Horizontal grid-point matrix dimension
     0.05   TimeStep        - Time step [seconds]
    1800.0  AnalysisTime    - Length of analysis time series [seconds] (program will add time if necessary: AnalysisTime = MAX(AnalysisTime, UsableTime+GridWidth/MeanHHWS) )
    "ALL"   UsableTime      - Usable length of output time series [seconds] (program will add GridWidth/MeanHHWS seconds unless UsableTime is "ALL")
      90    HubHt           - Hub height [m] (should be > 0.5*GridHeight)
      140   GridHeight      - Grid height [m]
     1000   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]

But still getting error:

although I got some help from previous post, I confirmed setting TwrAero = False in the AeroDyn v15 primary input file, I don’t know how to interpret it.

What surprises me is that the bts file I used before is the same except for the wind speed, and the farm operation can be performed smoothly, so where is the problem?
The settings in fstf are as follows:

--- AMBIENT WIND: INFLOWWIND MODULE --- [used only for Mod_AmbWind=2]
2.0                DT_Low                 Time step for low -resolution wind data interpolation; will be used as the global FAST.Farm time step (s) [>0.0]
0.3333333          DT_High            Time step for high-resolution wind data interpolation (s) [>0.0]
600                NX_Low             Number  of low -resolution spatial nodes in X direction for wind data interpolation (-) [>=2]
90                 NY_Low             Number  of low -resolution spatial nodes in Y direction for wind data interpolation (-) [>=2]
17                 NZ_Low             Number  of low -resolution spatial nodes in Z direction for wind data interpolation (-) [>=2]
0.0                X0_Low             Origin  of low -resolution spatial nodes in X direction for wind data interpolation (m)
-450.0             Y0_Low             Origin  of low -resolution spatial nodes in Y direction for wind data interpolation (m)
0.0                Z0_Low             Origin  of low -resolution spatial nodes in Z direction for wind data interpolation (m)
10.0               dX_Low             Spacing of low -resolution spatial nodes in X direction for wind data interpolation (m) [>0.0]
10.0               dY_Low             Spacing of low -resolution spatial nodes in Y direction for wind data interpolation (m) [>0.0]
10.0               dZ_Low             Spacing of low -resolution spatial nodes in Z direction for wind data interpolation (m) [>0.0]
100                NX_High            Number  of high-resolution spatial nodes in X direction for wind data interpolation (-) [>=2]
75                 NY_High            Number  of high-resolution spatial nodes in Y direction for wind data interpolation (-) [>=2]
80                 NZ_High            Number  of high-resolution spatial nodes in Z direction for wind data interpolation (-) [>=2]
"AmbWind\14m-006.dat"   InflowFile         Name of file containing InflowWind module input parameters (quoted string)
--- WIND TURBINES ---
1                  NumTurbines        Number of wind turbines (-) [>=1]   [last 6 columns used only for Mod_AmbWind=2]
WT_X   WT_Y   WT_Z   WT_FASTInFile                                        X0_High  Y0_High  Z0_High  dX_High  dY_High  dZ_High
(m)    (m)    (m)    (string)                                             (m)      (m)      (m)      (m)      (m)      (m)
1000.0  0.0    0.0    "OpenFAST\5MW_Land_DLL_WTurb_T1.fst"                  935.0    -70.5    0.0      2.0     2.0     2.0

Dear @Jundong.Wang,

The problem is that your TurbSim domain and FAST.Farm low- and high-resolution domains are not aligned. The TurbSim domain must fully encompass the low- and high-resolution domains defined within FAST.Farm (or better yet, the low- and high-resolution domains in FAST.Farm should be aligned with the TurbSim grid to avoid extra interpolations that will smooth out the ambient turbulence).

E.g., for the low-resolution domain in the Y direction, your domain extends from -450 to 440 m in steps of 10 m while your TurbSim domain extends from -500 to 500 m in steps of 4.016 m. This will not result in any warnings/errors, but the TurbSim domain is wider than it needs to be, and because the grid points are not aligned, the data will be interpolated, which will smooth out turbulence. For the low-resolution domain in the Z direction, your domain extends from 0 to 160 m in steps of 10 m while your TurbSim domain extends from 5 to 185 m (from your first TurbSim input file) in steps of 4.091 m. This will result in an error because your low-resolution domain is lower than your TurbSim domain, and again, the grid points are not aligned, resulting in smoothing of the inflow turbulence.

I recommend following the guidance for inflow wind generation found in the online FAST.Farm User’s Guide and Theory manual and to use the provided python scripts for generating inflow for FAST.Farm from TurbSim: 4.2.14.6. Modeling Guidance — OpenFAST v3.2.0 documentation.

Best regards,