Hi,

I am using the alpha version of Turbsim 2.0 to generate a wind field using the Kaimal spectral model as defined in IEC (3rd ed.) and the Davenport coherence model. I have specified the Davenport coherence model by using the general coherence model defined in Turbsim with CohExp=0 and b=0. With this setting (see example below), I get the following error message:

CalcFourierCoeffs: CalcFourierCoeffs_General:Error in Cholesky factorization: LAPACK_SPPTRF: Leading minor order 34 of A is not positive definite, so Cholesky factorization could not be completed.

It appears that b cannot be arbitrarily small, as the same error message appears if it is set sufficiently small, b<b_lim (where b_lim depends on the other specifications of the input file). However, using the IEC coherence model with b=0 is no problem.

Is there any way to get around this issue?

Here is an example file which will replicate the error message:

---------TurbSim v2.00.* Input File------------------------

Example input file for TurbSim.

---------Runtime Options-----------------------------------

False Echo - Echo input data to .ech (flag)

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)

False WrADHH - Output hub-height time-series data in AeroDyn form? (Generates RootName.hh)

False 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)

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-----------------------

5 NumGrid_Z - Vertical grid-point matrix dimension

20 NumGrid_Y - Horizontal grid-point matrix dimension

1.0 TimeStep - Time step [seconds]

12000 AnalysisTime - Length of analysis time series [seconds] (program will add time if necessary: AnalysisTime = MAX(AnalysisTime, UsableTime+GridWidth/MeanHHWS) )

11900 UsableTime - Usable length of output time series [seconds] (program will add GridWidth/MeanHHWS seconds unless UsableTime is “ALL”)

41.00 HubHt - Hub height [m] (should be > 0.5*GridHeight)
80.00 GridHeight - Grid height [m]
200.00 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”,“IECVKM”,“GP_LLJ”,“NWTCUP”,“SMOOTH”,“WF_UPW”,“WF_07D”,“WF_14D”,“TIDAL”,“API”,“USRINP”,“TIMESR”, or “NONE”)

“unused” UserFile - Name of the file that contains inputs for user-defined spectra or time series inputs (used only for “USRINP” and “TIMESR” models)

“1-Ed3” IECstandard - Number of IEC 61400-x standard (x=1,2, or 3 with optional 61400-1 edition number (i.e. “1-Ed2”) )

13.5 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]

“LOG” WindProfileType - Velocity profile type (“LOG”;“PL”=power law;“JET”;“H2L”=Log law for TIDAL model;“API”;“USR”;“TS”;“IEC”=PL on rotor disk, LOG elsewhere; or “default”)

“unused” ProfileFile - Name of the file that contains input profiles for WindProfileType=“USR” and/or TurbModel=“USRVKM” [-]

10.0 RefHt - Height of the reference velocity (URef) [m]

30.0 URef - Mean (total) velocity at the reference height [m/s] (or “default” for JET velocity profile) [must be 1-hr mean for API model; otherwise is the mean over AnalysisTime seconds]

default ZJetMax - Jet height [m] (used only for JET velocity profile, valid 70-490 m)

default PLExp - Power law exponent [-] (or “default”)

0.01 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^2/s^2] (or “default” or “none”)

default PC_UV - Hub mean u’v’ Reynolds stress [m^2/s^2] (or “default” or “none”)

default PC_VW - Hub mean v’w’ Reynolds stress [m^2/s^2] (or “default” or “none”)