Dear Aina,
The eigenvectors resulting from a FAST linearization analysis represent the mode shapes for the full system (including coupling between the blades, drivetrain, nacelle, tower, and platform). Most mode shapes have coupling between these system components. The relative magnitude of each DOF in an eigenvector determines the amount of coupling that DOF contributes to a mode. For example, the first tower fore-aft mode typically includes coupling with the 1st flap modes of each blade. The phasing of each DOF in an eigenvector determines the phase of the coupling (two DOFs with the same angle are in phase and angles that are 180 degrees apart are out of phase). It is difficult to explain the mode shape interpretation more without seeing the eigenvectors.
When CalcStdy is set to False, it is likely that the solution will not be in static equilibrium before linearizing (unless the initial conditions from which the model is linearized about correctly define the static equilibrium condition). An operating point that is not in equilibrium will introduce an “effective stiffness”, which may make interpretation of the linearized model difficult, as explained in this forum topic: FAST: Model linearization. In general, it is better to linearize a model with CalcStdy set to True. With CalcStdy set to True, FAST will search for an equilibrium condition before linearizing.
I hope that helps.
Best regards,