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Controlling bifurcations in high-speed rotors utilizing active gas foil bearings

Papadopoulos Anastasios, Gavalas Ioannis, Chasalevris Athanasios

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2023

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Vol. 71, nr 6

art. no. e146796

EN

High-speed rotors on gas foil bearings (GFBs) are applications of increasing interest due to their potential to increase the 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 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.

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Investigation of gas foil bearings with an adaptive and non-linear structure

Żywica Grzegorz, Bagiński Paweł

Acta Mechanica et Automatica

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2019

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Vol. 13, no. 1

5--10

EN

The article discusses the results of simulation-based and experimental research carried out on gas foil bearings. Owing to the use of a set of flexible thin foils in such bearings, they exhibit certain beneficial features that cannot be found in other types of bearings. They have nonlinear operational characteristics and allow the dissipation of excess energy, thus reducing the vibration level. Moreover, gas foil bearings can self-adapt themselves to the current operating conditions by changing the shape of the lubrication gap. Therefore, they can be used to improve the dynamic performance of rotors, in particular, those operating at very high rotational speeds. This article explains the mechanisms for changes of stiffness and vibration damping in compliant components of a foil bearing. The results of the analysis of the bearing’s subassemblies using advanced numerical models are presented. They are followed by conclusions that were drawn not only from these results but also from the results of the experimental research. It has been proven that the rotor supported on carefully designed foil bearings is capable of maintaining a low vibration level, even if it operates at a high rotational speed.

3

Modelowanie rozkładu naprężeń i odkształceń rotorów szybkoobrotowych metodą elementów skończonych

Pawelski K., Grothaus R., Kosmol J.

Prace Naukowe Katedry Budowy Maszyn / Politechnika Śląska

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2001

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nr 2

11-22

PL

W artykule przedstawiono wyniki badań hybrydowych rotorów szybkoobrotowych metodą elementów skończonych. Przedmiotem badań był dobór wstępnego napięcia pomiędzy stalowym korpusem rotora i bandażami wykonanymi w technologii kompozytu polimerowego. Przedstawiono rozkład naprężeń powstających w wyniku napięcia wstępnego oraz wpływ tego napięcia na stan naprężeń podczas pracy rotora.

EN

Some results of simulation by means of Finite Element Method of high speed rotors are presented in the paper. The main gool of the investigation was to tight the hybride rotor, to be made up of a steels sleeve and polymer's bandage. Distribution of stresses and displacements and their influence on the rotor are results of our simulation.