PROCEDURE FOR INVESTIGATION OF THE EQUILIBRIUM POSITION STABILITY AND FOR THE NONLINEAR RESPOSE OF A ROTOR SUPPORTED BY FLUID FILM BEARINGS AND HAVING A DISC SUBMERGED IN INVISCOUS, INWETTABLE LIQUID

Abstract eng:
Lateral vibration of rotors is significantly influenced by their supports and by their interaction with the medium in the ambient space. If the disc of the rotor is submerged in a liquid and if it vibrates, the pressure field is induced and the liquid acts by a force on the wall of the disc. It is assumed that the disc performs oscillations only with small amplitudes and it enables to describe the produced pressure field by a Laplace's equation and by the relation for the boundary conditions. The liquid is inwettable and it means that it does not lean to the disc surface and therefore no tangential forces acting on the disc are produced. The resulting force is obtained by integration of the pressure distribution around the circumference and along the height of the submerged part of the disc. Its components are proportional to the disc accelerations and it implies that the negatively taken coefficients of proportionality can be considered as additional masses. As the bearing gap is very narrow, the pressure field in the oil film can be described by a Reynolds' equation. In the areas of a vapour cavitation the pressure is considered to be constant. Components of the bearing forces are obtained by integration of the pressure distribution in the oil layer around the circumference and along the length of the bearing. Lateral vibration of such rotor systems is governed by a nonlinear equation of motion. In the neighbourhood of the equilibrium position it can be linearized and this enables to judge its stability utilizing the natural frequencies of the rotor system. For solution of the equation of motion including the transient component a modified Newmark method has been chosen.

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