John Doyle
Ansys Employee

Modal and Harmonic Analysis are linear.

You can do a prestressed modal analysis and have nonlinear effects included in the upstream static structural, but the modal analysis is always going to be a linear analysis.
Frictional or frictionless contact, if present in the upstream static analysis, would be reduced to its linear equivalent for the modal run, depending on its status.  If the frictional contact is open at end of the run, it would be ignored in the modal run altogether.  There are options available to control how the modal interprets the contact (true status, force sticking, force bonded), but the modal will always be linear in the end. 

Harmonic analysis has same limitations.  It only makes sense to do harmonic if your loads are cyclic and you are interested in the cyclic response. (i.e. displacement vs frequency). 

Please refer to the online documentation for Linear Perturbation for more details. 

A prestressed modal might be a good place to start, to get an understanding of the natural frequencies of greatest interest.

Full transient dynamics in general, can account for all nonlinearities in real time, and would be most accurate, in theory, but can also be most expensive, in terms of run time.