NDLI: A Simplified and Consistent Nonlinear Transient Analysis Method for Gas Bearing: Extension to Flexible Rotors

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Hassini, Amine Arghir, Mihai
Copyright Year	2014
Abstract	A simplified, new method for evaluating the nonlinear fluid forces in air bearings was recently proposed in [1]. The method is based on approximating the frequency dependent linearized dynamic coefficients at several eccentricities, by second order rational functions. A set of ordinary differential equations is then obtained using the inverse of Laplace Transform linking the fluid forces components to the rotor displacements. Coupling these equations with the equations of motion of the rotor lead to a system of ordinary differential equations where displacements and velocities of the rotor and the fluid forces come as unknowns. The numerical results stemming from the proposed approach showed good agreement with the results obtained by solving the full nonlinear transient Reynolds equation coupled to the equation of motion of a point mass rotor. However the method [1] requires a special treatment to ensure continuity of the values of the fluid forces and their first derivatives. More recently, the same authors [2] showed the benefits of imposing the same set of stable poles to the rational functions approximating the impedances. These constrains simplified the expressions of the fluid forces and avoided the introduction of false poles. The method in [2] was applied in the frame of the small perturbation analysis for calculating Campbell and stability diagrams. This approach enhances also the consistency of the fluid forces approximated with the same set of poles because they become naturally continuous over the whole bearing clearance while their increments were not. The present paper shows how easily the new formulation may be applied to compute the nonlinear response of systems with multiple degrees of freedom such as a flexible rotor supported by two air bearings.
Sponsorship	International Gas Turbine Institute
File Format	PDF
ISBN	9780791845776
DOI	10.1115/GT2014-25955
Volume Number	Volume 7B: Structures and Dynamics
Conference Proceedings	ASME Turbo Expo 2014: Turbine Technical Conference and Exposition
Language	English
Publisher Date	2014-06-16
Publisher Place	Düsseldorf, Germany
Access Restriction	Subscribed
Subject Keyword	Degrees of freedom Stability Bearings Rotors Clearances (engineering) Air bearings Laplace transforms Equations of motion Transients (dynamics) Gas bearings Fluids Poles (building) Differential equations Transient analysis
Content Type	Text
Resource Type	Article

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