I've a question regarding getting a linearized model of the 5MW wind turbine.
I want to get a linearized model of the wind turbine in Region 3. and I've used the 5MW baseline wind turbine model, with the settings as indicated in FAST user manual. here is a summary of these settings
AnalMode = 2
YCMode = 0
TMax = 1000
PCMode = 0
GenTiStr = True
GenTiStp = True
TimGenOn = 0.0
TimGenOf = 9999.9
THSSBrDp = 9999.9
TiDynBrk = 9999.9
TTpBrDp(i) = 9999.9
TYawManS = 9999.9
TPitManS(i) = 9999.9
TBDepISp(i) = 9999.9
StallMod = STEADY
InfModel = EQUIL
Wind: 16m/s hub higher steady wind (No turbulence, no shear)
Enabled DOF: GenDOF, TwFADOF1, TwSSDOF1
CompAero = True
RotSpeed = 12.1
CalcStdy = True
TrimCase = 3 (As indicated in FAST Manual for Variable Speed, Region 3 Linearization)
DispTol = 0.0001
VelTol = 0.00001
NAzimStep = 36
NInputs = 4
CntrlInpt = 3,5,6,7
NDisturbs = 1
Disturbnc = 1
Also, For variable speed the following settings as indicated by FAST Manual.
VSContrl = 1
VS_RtGnSp = 9999.9E-9
VS_RtTq = 43093.55
VS_Rgn2K = 9999.9E-9
VS_SlPc = 9999.9E-9
Linearization works fine, FAST converge after 65 steps (time=322 secs).
As I don't have any rotating states, I've used the "cce.m" code to get the Average natural frequencies. and I get the following results.
AvgNaturalFrequencyHz
0.32616
0.32143
0.026794
1.1223e-006
AvgDampingRatio
0.05819
0.0056572
Inf
Inf
AvgModeShapeMagnitude
0.43576 0.026631 0.03308 2.8578e-006
0.04902 0.44285 0.001757 3.0813e-006
0.0049679 0.0080601 0.98557 1
AvgModeShapePhaseDeg
86.664 107.26 180 180
102.33 -90.324 180 180
-172.64 91.204 180 0
Now my Question is: I know that the first two natural frequencies (0.32616, 0.32143) are related to tower first fore-aft and side-to-side modes, as I get similar values if I run the same Linearization but this time setting GenDOF to false so I get (0.32665, 0.31636). but what about the other two natural frequencies, and their corresponding damping ratios and mode shapes. how could I interpret them.
Best Regards
Rannam Chaaban.