Dynamic characteristics of a complex rotor system supported on active dry friction dampers considering friction-stiffening effects

Active dry friction dampers (ADFDs) are promising in rotor vibration suppression. The normal force of ADFD is commonly designed by minimizing responses at a given axial position or maximizing damping ratios. These methods emphasize the maximization of local damping effects while the influences of stiffening effects on system dynamics are ignored. By analyzing the dynamic characteristics of a complex rotor-ADFDs system, this paper intends to disclose the existence of some phenomena due to friction-stiffening effects, which may make the optimization results of those local-damping-oriented methods unsatisfactory. The harmonic balance method is combined with an equivalent linearization technique to relate the unbalance responses with the damper's friction-stiffening effects. After model validation, the effects of rotational speeds, normal forces, and ADFD's installation positions on unbalance responses and ADFD's stiffness coefficients were studied. The results show that the friction-stiffening effects will cause discrepancies in unbalance responses at different positions. Due to the ADFD's stiffening effects, the response variation trends at different positions may differ after the stick-slip transition. An optimum ADFD's normal force exists to minimize rotor unbalance response, though the optimum result could vary for responses at different positions due to friction-stiffening effects. Using the ADFD's stiffening effects, better vibration suppression performance may be achieved at multiple positions even if the damping level of the friction damper is lower.