The phase characteristics of stiffness increase phenomena of rub-impact rotor

The phase characteristics of stiffness increase phenomena of a rubbing rotor were investigated. It was assumed that the full annular contact will be maintained for a wide speed range even though the rotor has passed through its critical speed. It was verified that for stationary rub, the phase has an inherent characteristic, that is, the phase difference between the response and the excitation approaches to π/2 gradually along with the increase of rotor speed; the phase difference will jump to π after it exceeds π/2 with a small increment, and then non-rub motion starts. The analytically and numerical results explain the mechanism of stiffness increase. The phase characteristics of non-stationary rub motions after Hopf bifurcation was also numerically analyzed.