###### Abstract  
Squeeze film dampers are often used to suppress vibration in turbine engines and play an important role in rotor systems. In this paper, the nonlinear dynamic characteristics of an industrial turbine engine fitted with squeeze film dampers are investigated with the static eccentricity of the SFDs. A recently developed time domain technique that combines the finite element method and the fixed interface modal synthesis method is applied to predict the nonlinear unbalance response of the industrial turbine engine under different unbalanced and static eccentricity configurations. By comparing the results obtained using SFDs with and without static eccentricity, it can be concluded that increasing the static eccentricity of the SFDs promotes non-periodic motion, while an increase in the unbalance level promotes the jump phenomenon. The efficiency of the rotor system would improve with an appropriate amount of unbalance applied to compressor IV, resulting in a reduction in the vibration level. If static sprung eccentricity occurs, the center of the journal orbit would be offset from the SFD center, rendering it inefficient or even leading to rub impact. Therefore, it is crucial to control the static eccentricity of the SFDs for optimal performance. The time domain technique is verified by the experimental results reported in the literature. nonlinear vibration; SFD; modal synthesis method; eccentric; finite element method Article  
The Nonlinear Dynamic Characteristics of an Industrial Turbine Engine with Eccentric Squeeze Film Dampers  
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on the effects of cavitation and found that cavitation might be beneficial in preventing excessive vibration of the shaft. Recent experimental investigations [5] showed that the critical speed of the rotor system might increase due to the static eccentricity of the squeeze film damper, and the theoretical prediction based on short bearing approximation showed some consistency with the experimental data. [PERSON] et al. [6] developed a non-contact method to identify the unbalanced mass of a rotor system in 3D space. In comparison with sensor methods, the relative error of the proposed method decreased from 30.6% and 41.3% to 2.2%. Although much work has been conducted, it can be seen that most of the studies were conducted with rigid rotor systems or simple flexible rotor systems. Additionally, to alleviate the computational burden, most of the theoretical investigations adopted frequency domain techniques, such as the harmonic balance method or trigonometric collocation method. However, as stated in Reference [4], these techniques might yield results that disagree with the numerical integration method due to a loss of periodicity. In comparison, time domain techniques yield the actual steady-state response after the initial transients have died out. All these facts necessitate that more effort should be made to improve the efficiency of the time domain techniques and thus enable more detailed models of a flexible rotor system mounted with sprung eccentric squeeze film dampers to be established and analyzed. The time domain methods for the nonlinear unbalance response of rotor systems have been extensively investigated. [PERSON] [7] employed the fixed interface modal synthesis method to reduce the size of the rotor system to obtain better computational efficiency. In References [8; 9], the transfer matrix method was adopted. [PERSON], [PERSON] [10] improved the free interface modal synthesis method to analyze the dynamic characteristics of a multi-rotor system. [PERSON] [11] established a dual-rotor system with the finite element method to investigate the influences of the speed ratio of the rotor system. [PERSON] [12] analyzed the vibration attenuation effects of the SFD parameters selected by using the multi-objective optimization method on the dynamic response.