Nonlinear modeling and analysis of rotors supported by magnetorheological squeeze film journal bearings
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MODELLING AND ANALYSIS OF MECHANICAL SYSTEMS DYNAMICS
Nonlinear modeling and analysis of rotors supported by magnetorheological squeeze film journal bearings Airton Nabarrete
. Gustavo de Freitas Fonseca
Received: 2 April 2020 / Accepted: 15 September 2020 Ó Springer Nature B.V. 2020
Abstract The driver coupled to a driven system through mechanical couplings is very common in rotating machinery. These couplings can present angular and parallel misalignments with more or less degree due to manufacturing tolerances or maintenance proceedings. Theoretical and experimental analyses have been published demonstrating the effects of rotor misalignment and the vibration stability of rotor systems. In this work the nonlinear formulation of a magnetorheological fluid journal bearing is included in the finite element model that evaluates the nonlinear responses of a complete rotor system subject to rigid coupling misalignment. The modified Reynolds equations for Bingham viscoplastic materials are implemented in the finite element procedures to evaluate the nonlinear hydrodynamic reaction forces acting on the bearing positions. The finite element formulation for the shaft-line and mechanical couplings is based on the Timoshenko beam theory. Misalignment forces are calculated and included in the equations of motion. The nonlinear dynamic responses are calculated by the modified Newmark method incorporating the Newton–Raphson iteration method to find the equilibrium position at
A. Nabarrete (&) G. de Freitas Fonseca Aerospace Engineering, Aeronautics Institute of Technology (ITA), Prac¸a Marechal Eduardo Gomes, 50 Vila das Aca´cias, Sa˜o Jose´ dos Campos, SP 12228-900, Brazil e-mail: [email protected]
each time step. Bifurcation analysis demonstrates the influence of misalignment to obtain periodic and period-doubling orbit for the center position of the rotor. Results are demonstrated through displacements versus time and frequency responses. Keywords Rotor misalignment Nonlinear rotordynamics Magnetorheological squeeze film Modified Newmark method Bifurcation
1 Introduction Misalignment and unbalance are common disturbance sources in rotating machines that promote anticipated faults in oil-film journal bearings. While the misalignment comes from the mechanical assembly of rotating shafts, like the coupling of a driver to a driven rotating system, the unbalance is always present after the machine turning or milling of a manufactured rotating part. Both defects can generate oscillations of the shaft inside the oil-film journal bearing resulting in variations of the pressure distribution and consequently in bearing reaction forces and moments. Recently magnetorheological (MR) fluids have been developed to be incorporated in journal bearings with the promise of controlling these rotor oscillations by changing stiffness and damping coefficients with an applied external magnetic field.
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Meccanica
It is important to take in account the nonlinear phenomena caused by
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