I have to simulate buckling in case of a hydraulic piston rod. One end of the rod is fixed whereas the other end of the rod i.e the piston head is guided inside the cylinder tube. The force is applied axially on the piston.I tried using the cylindrical faces fixture under advanced fixtures but i am unable to understand what the values of x,y,z in that mean physically. My object can move only in the axial direction and changing the value of 'z' in the cylindrical face fixture gives very different results. What does the value of 'z' exactly signify here? I have tried various other types of fixtures on the piston head but none of the results are convincing. Also with a decrease in load my displacements increase which makes no sense at all. Can anyone please suggest what changes i can make to obtain a better result? Please find attached a screenshot of my simulation.