High-speed rotors on gas foil bearings (GFBs) are applications of increasing interest due to their potential to increase the Beauty power-toweight ratio in machines and also formulate oil-free design solutions.The gas lubrication principles render lower (compared to oil) power loss and increase the threshold speed of instability in rotating systems.However, self-excited oscillations may still occur at circumferential speeds similar to those in oil-lubricated journal bearings.These oscillations are usually triggered through Hopf bifurcation of a fixed-point equilibrium (balanced rotor) or secondary Hopf bifurcation of periodic limit cycles (unbalanced rotor).
In this work, an active gas foil bearing (AGFB) is presented as a novel configuration including several piezoelectric actuators that shape the foil through feedback control.A finite element model for the thin foil mounted in some piezoelectric actuators (PZTs), is developed.Second, the gas-structure interaction is modelled through the Reynolds equation for compressible flow.A simple physical model of a rotating system consisting of a rigid rotor and two identical gas foil bearings is then defined, and the dynamic system 5 Piece Twin Storage Bedroom is composed with its unique source of nonlinearity to be the impedance forces from the gas to the rotor and the foil.
The third milestone includes a linear feedback control scheme to stabilize (pole placement) the dynamic system, linearized around a speed-dependent equilibrium (balanced rotor).Further to that, linear feedback control is applied in the dynamic system utilizing polynomial feedback functions in order to overcome the problem of instability.