Rotor vibration due to collision with annular guard during passage through critical speed

This paper deals with a nonstationary vibration of a rotor due to its collision with a guard during passage through a critical speed. An unbalanced rigid rotor supported by springs and dampers is accelerated at a constant angular acceleration and collides with an annular guard supported by springs and dampers, This dynamic process is calculated by the Runge-Kutta method, and effects of system-parameters the process are discussed. The collision phenomenon is analyzed through two different theories. In the collision theory, the law of conservation of momentum and the coefficient of restitution are used in order to obtain rotor and guard velocities after collision. The impulse of the force induced by collision is assumed to be equal to the momentum change before and after collision. In the contact force theory, the contact force is assumed to be proportional to the overlapped displacement of the two bodies. Few differences are observed between the calculated responses based on the two theories, In some cases, the rotor executes a diverging backward whirl due to the friction force that occurs during collision with the guard and can not pass through the critical speed The criteria maps for nonoccurrence of the backward whirl are shown.