I intended to model a structure with a hydraulic to move it up and in addition I want to use that model to do a vibration analysis using either Ansys or Abaqus. However, I wonder, How I must model the jack to make sure that the result is reliable?!
There are a couple of things to be sure of before modeling a mechanism in commercial 3D FEM tools. The modeling and simulation process depends whether you are considering a rigid body simulation or a multibody dynamic simulation with flexible bodies.
If you have made a note of that, then you can just use a translation type joint between the two cylindrical surfaces i.e. outer surface of the piston and the internal surface of the cylinder. If you have all other constraints set up properly, then this should work.