ACTIVE CONTROL OF MULTIMODE ROTOR-BEARING SYSTEMS USING HSFDS

This paper summarizes the modeling and control of hybrid squeeze film dampers (HSFDs) for active control of vibration of rotors exhibiting m ultiple modes. In a recent paper (El-Shafei and Hathout, 1994), it was shown that the automatically controlled HSFD based on feedback on rot or speed can be a very efficient device for active control of rotor vi bration. It was shown that this closed-loop, on-off control strategy r esults in a much improved behavior of the rotor system. The previous i nvestigation was performed on a Jeffcott rotor model. The model was si mple and fluid inertia effects were not taken into consideration. In t his paper, major strides were made in both the modeling of the rotor a nd the HSFD. Modal analysis was implemented in the dynamic analysis of the squeeze film damper supported rotor in a novel and unique manner of performing modal analysis on nonlinear rotor systems. This allowed the modeling of arty number of modes using modal analysis and hence to verify the capability of the HSFD to control multiple modes. Also, fl uid inertia forces were considered in our model for the HSFD due to th eir direct influence in changing the behavior of the damper (El-Shafei and Crandall, 1991). A complete mathematical model of this open-loop system is developed and is implemented on a digital computer. Finally, based on the feedback on speed, the closed-loop behavior was studied from both steady-state and transient points of view and showed an over all enhanced behavior for the rotor system.