###### Abstract  
As an important part of the turbomachinery, the rotor-bearing system has been upgraded to provide a high rotating speed in order to meet the demand of high power production. With increasing demand for stability, the squeeze film damper (SFD) has been widely used in industrial machinery because it can reduce the vibration amplitude and suppress the external force. Usually, it shows inadaptability under the different working conditions where the SFD parameters didn't change appropriately. Therefore, the reasonable choice of operational parameters of SFD is the key solution that can provide viscous damping effectively and restrain the nonlinear vibration generated by faults. In this paper, the mathematical model of a rotor-ball bearing-SFD system considering the misalignment fault and misalignment-rubbing coupling fault is built first. Then the dynamic characteristics under typical working conditions (\(\omega\) = 1000 rad/s) of the faulted rotor are discussed. The vibration attenuation effects of the SFD parameters selected by using the multi-objective optimization method on the dynamic responses are analyzed. The results show that when the rotor system operates under different states, the value and the sensitivity of optimization parameters are altered. With no fault, the amplitude of fundamental frequency decrease 23%. With the misalignment fault, the amplitude of the fundamental frequency decreases by 43.4%, the amplitude of 2\(\times\) fundamental frequency decreases by 27.5%, and the amplitude of 3\(\times\) fundamental frequency decreases by 66.7%. With the misalignment-rubbing coupling fault, the amplitude of fundamental frequency reduces by 7.4%, the amplitude of 2\(\times\) fundamental frequency drops by 51.5%, and the amplitude of 3\(\times\) fundamental frequency drops by 16.8%. Overall, the feasibility of the optimization method of the variable-structured SFD operational parameters for the faulted rotor system is verified. These parametric analyses are very helpful in the development of a high-speed rotor system and provide a theoretical reference for the vibration control and optimal design of rotating machinery.  
Keywords:rotor; SFD; misalignment rubbing coupling faults; multi-objective optimization +
Footnote †: journal: Applied Soft  
Wang [5] studied a controllable SFD for a rotor system and revealed its effect mechanism. [PERSON] [6; 7; 8] analyzed the dynamic behavior of a hybrid SFD-mounted gear-bearing system based on the typical unbalance approximation and discussed the rotating speed and damping effects. [PERSON] [9; 10] presented the dynamic analysis of a flexible rotor mounted in SFD with and without retaining springs independently, and the results showed that the onset of bifurcation increased with the stiffness of the retainer spring, which provided insights into the effect of the design parameters of SFD on the rotor response. [PERSON] [11] derived the dynamic equations of the single-disk rotor -SFD system under the elastic support and studied the nonlinear characteristics of the vibration responses. Consequently, there is no doubt that the application of SFD in rotor system can enhance the operational stability to a large extent. However, the improvement not only depends on the advanced structure design but also relates to the correlation of SFD parameters and the real condition of the rotor system. In other words, it is important to find out a suitable parameter set of SFD to prevent system instability due to fault occurrence as well as to facilitate product design and vibration control.  
In this paper, a dynamic system model of the fault rotor system with SFD is established first. Then the dynamic characteristics under typical working conditions of the faulted rotor are discussed. And the vibration attenuation effects of the oil film gap (\(C_{\text{S}}\)), elastic support stiffness (\(K_{\text{a}}\)) and the lubricating oil viscosity (\(\mu_{\text{s}}\)) of SFD selected by using the multi-objective optimization method on the dynamic responses are analyzed.