Abstract
With the structural parameters of the rotation machinery increased, the seal fluid induced force imposed on the rotor will significantly increase. Taking a cracked rotor-bearing-seal system as object the non-linear dynamic behaviours of the coupled system are investigated using numerical integration method. For the crack in shaft, the segmented switch function is applied to express the process of the crack’s opening and closing in rotation, and the cross stiffness originated from crack is considered. Various nonlinear phenomena compressing periodic, quasi-periodic and chaotic motions in the rotor system are analysed. The research results show that the unstable form of the rotor system is Hopf bifurcation when the crack depth is smaller. The influence to the response of the system increased along with the crack depth, the unstable form of the coupled system is period-doubling bifurcation. The seal clearance has an important impact on stability of the cracked rotor system. In other words, the fluid induced force can reduce the periodic responses of the rotor. It is indicated that this study can contribution to a further understanding of the nonlinear of such a rotor-bearing system with crack and seal.
Highlights
The demand for more powerful and efficient rotating machinery has led to higher operating speed and working pressure, which results in the need of reliable components such as bearings and seals
The model of rotor-bearing system is shown in Fig. 1, where O1 is the bearing center, O2 is the disk geometric center, O3 is the disk mass center, Fx and Fy are seal fluid forces, fx and fy are dimensionless oil forces, m1 is the bearing mass, m2 is the disk mass, c is the clearance of bearing, R is the radius of shaft, a is the crack depth in middle of shaft, k is the stiffness of the shaft without crack and δ is an initial clearance between the rotor and stator
Special attention is paid to the influence of the crack depth and seal clearance on the bifurcation of the system with rotation speed as a control parameter
Summary
The demand for more powerful and efficient rotating machinery has led to higher operating speed and working pressure, which results in the need of reliable components such as bearings and seals. With the increase in the rotating speed, the performances of the rotor system are significantly influenced by the characteristics of the seal [2]. Under these circumstances, the rotor is likely to develop one or more faults, e.g. crack, bow, etc. Many theoretical studies numerical calculations and measurements have been carried out to determine the influence of the dynamic vibration due to seal or crack. Under fatigue load operating conditions, the stiffness and dynamic behaviour of the rotor shaft will change greatly and these crack faults may cause huge failure and loss. An in-depth study investigating the vibration characteristic of a cracked rotor-bearing-seal system is the main objective of this paper
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