Nonlinear Oil-film Force Research Articles

Dynamic analysis of hydrodynamic bearing–rotor system based on neural network

Feed-forward neural network is employed to model the nonlinear oil-film force database of a finite-length hydrodynamic journal bearing, which is constructed by continuous transformation of Reynolds equation. Neural network models trained are utilized to investigate motion characteristics of a rigid unbalanced rotor supported on elliptical bearings in 300 MW steam turbine generator set. There exist various forms of periodic, quasi-periodic and chaotic motions at different rotating speeds. Periodic doubling bifurcation and quasi-periodic routes to chaos may be found when rotating speed is used as the control parameter. Computational results show that there exist similar motion behaviors between neural networks and numerical method. It is available for neural network models of oil-film forces to research nonlinear dynamic problems of rotating machinery.

Stability and response analysis of symmetrical single-disk flexible rotor-bearing system

The motion equations have been established for symmetrical single-disk flexible rotor-bearing system, and non-linear oil-film forces of finite journal bearings are calculated. The rotor's stiffness and damping are considered. The motions of journal and disk have been simulated with fourth-rank Runge-kutta method. The threshold speed of the system based on linear oil-film forces has been derived. Non-linear transient simulation and unbalanced responses are investigated. Moreover, linear oil-film forces are used for computing unbalanced responses, and the feasibility is discussed.

Dynamic Response of a Hydrodynamic Thrust Bearing-Mounted Rotor

For investigating the dynamic response of a hydrodynamic thrust bearing-mounted flexible rotor, the dynamic characteristic data of thrust bearings for high surface velocities are applied for constructing the equation of motion for the rotor system, which is modeled with the finite element method. Based on the short bearing approximation and the π film cavitation model of the nonlinear oil-film forces, the dynamic responses are investigated using direct numerical integration with a variable order solver based on the numerical differentiation formulas. Harmonic, quasi-periodic, and chaotic motions are predicted for a range of spin speeds of the rotor. Poincare´ maps of predicted rotor trajectories are also examined. It shows that spin speeds of the rotor and the oil film force coefficient might promote undesirable nonsynchronous vibrations.

Vibration analysis of cracked rotor sliding bearing system with rotor–stator rubbing by harmonic wavelet transform

In this paper, the vibration of a cracked rotor sliding bearing system with rotor–stator rubbing is investigated using harmonic wavelet transform (HWT). Three non-linear factors, non-linear oil film forces, rotor–stator rubbing and the presence of crack, are taken into account. So the non-linear behavior of the rotor will be much more complex. According to Newmark method, the dynamic response of the rotor is calculated. Using HWT method, the effect of these non-linear factors is analyzed simultaneously in both time and frequency domain. The numerical simulated result shows that HWT will be available to analyze this multi-non-linear factors rotor effectively and can reveal the exact fault characteristics in detail.

Numerical and Experimental Studies on Nonlinear Dynamic Behaviors of a Rotor-Fluid Film Bearing System With Squeeze Film Dampers

In this paper, the nonlinear oil film forces of bearings and dampers with free boundary conditions are determined by the finite element method (FEM) and the complementary solution for variational inequalities. The mode synthesis technique is used to reduce the linear degrees of the high order finite element model. The periodic solution of the system and its stability are determined by the Poincare´ mapping method and the Floquet theory, respectively. The results of experiment show that squeeze film dampers (SFDs) can effectively prevent subsynchronous and nonsynchronous vibrations and some structural parameters have significant effects on the dynamic behaviors of the system. Comparing the numerical results with those of experiment, it is shown that the above theories and schemes are feasible and efficient in analyzing nonlinear behaviors of the high-order dynamic system with local nonlinearities.

Modeling of Nonlinear Oil-Film Force Acting on a Journal with Unsteady Motion and Nonlinear Instability Analysis under the Model

Modeling of Nonlinear Oil-Film Force Acting on a Journal with Unsteady Motion and Nonlinear Instability Analysis under the Model

Numerical Simulation of Nonlinear Oil Film Forces ofTilting‐Pad Guide Bearing in Large Hydro‐unit

A new numerical method is proposed for predicting the nonlinearity of tilting‐pad guide bearing oilfilm force in the rotor‐bearing system in a large hydro‐unit. Nonlinear displacement and velocity of the journal center, as well as nonlinear tilting angles and angular velocities of the pads in non‐stationary Reynolds equation are taken into account. This method is also suited for other small rotor‐bearing system. As an example, the response due to a momentarily created unbalance is Calculated. The nonlinear motion patterns of the pad and journal whirling orbit are obtained. Finally, the nonlinear orbit is compared to the linear one that could be calculated from linear stiffness and damping coefficients. It is shown that there are important differences between those two orbits and that the nonlinear simulation is more accurate.

Stress analysis and life expectancy of rolling mill housings: Guo, R.-M. Iron Steel Eng. Aug. 1992 69, (8), 45–53

This study focuses on the nonlinear dynamic behavior of a marine rotor-bearing system coupled with vibration isolation structure under ship rolling motion. After considering the effect of the nonlinear oil film force and the ship rolling motion, a mathematical model is established based on Lagrange's equation. By employing a numerical method, the dynamic steady-state response of the system is analyzed, such as the orbits of the rotor and its Poincaré maps, spectrum waterfall diagram, and the displacements and frequency spectrum diagram of the raft frame. We also studied the effects of the rotor speed, the amplitude and frequency of ship rolling on the marine rotor-bearing system coupled with isolation structure under ship rolling motion. The results indicates that response of the rotor shows obvious nonlinear dynamic behaviors such as amplitude jumping, bifurcation and chaos due to the influence of the nonlinear oil film force and the ship rolling motion. As the rotor speed increases, the motion of the rotor experiences the process of quasi-periodic and chaos vibration. Both the amplitude and frequency of ship rolling have effects on the amplitude of the rotor and the raft frame. Moreover, the rotation angle of the raft frame is greatly influenced by the amplitude and frequency of ship rolling, and it is necessary to control the vibration attitude of the raft frame.