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In turbomachinery,such as ultra supercritical turbo-set,the requirement of high efficiency has leaded to reduced clearances between rotating and stator components.With tighter clearances,Rotor may physically contacts with stationary elements of a rotating machine,and the subsequent rubbing at the contact area is a serious malfunction in turbomachinery that may leads the machines catastrophic failure.Thus,the diagnosis and elimination of this type fault in an accurately and timely manner are crucially important for reliability and highly efficient operation of rotating machine.Determining the dynamic behavior of rotating machinery is needed.In the case of considering the shear effect and gyroscopic effect,a finite element model is developed to study the nonlinear and linear dynamic behavior of two rotor-three bearing system named N+1 configuration with rub-impact in this paper.The influence of rotational speed,eccentric condition and the stiffness of coupling on the dynamic behavior of N+1 configuration and the propagation of motion are discussed in detail.The linear rotordynamic analysis included an evaluation of rotor critical speeds and unbalance response.The results show that the critical speed and unbalance response of rotors are sensitive to coupling stiffness in N+1 configuration.In the nonlinear analysis,bifurcation diagrams,shaft-center trajectory,amplitude spectrum,Poincaré map are used to analyze the dynamic behavior of the system.The results of the research transpire that these parameters have the great effects on the dynamic behavior of the system.The response of the system with rub-impact shows abundant nonlinear phenomena.The system will exhibit synchronous periodic motion,multi-periodic motion,quasi-periodic motion and chaotic motion patterns under rotor-stator rub interaction conditions.The dynamic response is more complicated for flexible coupling and two mass eccentricities than that of system with rigid coupling and one mass eccentricity.The results of this paper are useful in identifying and understanding this type of undesirable behavior in rotating machinery.