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.