Nonlinear Vibrations of Vertical Asymmetrically-Supported Rotors Under Fluid Confinement: Theoretical Results

Moreira, Miguel; Pina, H.; Antunes, J.

http://hdl.handle.net/10400.26/4589

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Authors

Moreira, Miguel

Pina, H.

Antunes, J.

Abstract(s)

This paper is concerned about vertical rotors immersed in fluid annulus of moderate confinement. Such rotors are subjected to the dynamical effects of the fluctuating co-rotating flows. For high enough spinning velocities, the fluid-elastic forces become significant, and often lead to unstable dynamical regimes. These depend on the fluid gap and density, on the rotor eccentricity and spinning velocity, as well as structural properties. We developed an improved linear model for rotors under moderate fluid confinement as well as an exact model for the corresponding nonlinear rotordynamics. Recently a symbolic-numerical formulation based on a spectral/Galerkin approach was also developed by the authors. Numerical results showed a quite good agreement between exact solutions and these formulations and experimental validation of the theoretical model has been provided for symmetrically-supported rotors. Numerical simulations carried over immersed rotor configurations maintained by non-isotropic supports show that the rotor stability is affected by support stiffness-asymmetry. In this paper, we briefly summarize the theoretical approaches used in the numerical simulations and present an analysis of the linear rotor-dynamics, as a function of the support stiffness-asymmetry and of the rotor eccentricity. Theoretical stability domains are computed from the eigenvalues of the linearized model. Finally, we present time-domain numerical simulations of some stable solutions and nonlinear limit-cycles which stem from linearly-unstable solutions.