Investigation of the vibration reduction of a flexibly supported Jeffcott rotor damped by semiactive elements working on the principle of squeezing thin layers of normal and magnetorheological oils

摘要

Unbalance of rotating parts and time varying loading are the principal sources of lateral vibration of rotors and of increase of the forces transmitted into the stationary part. This oscillation and force effects can be considerably reduced if damping devices are added to the coupling elements placed between the rotor and its casing. The theoretical studies confirmed by practical experience show that if the rotor is flexible and is flexibly mounted with the stationary part, then its critical speed is not constant but depends on damping in the supports. Therefore, this damping effect must be controllable to be achieved the optimum performance of the rotating machine. For this purpose a new semiactive damping element has been proposed. Its design is based on the idea that some amount of damping should be continuously produced and if needed it should be possible to increase its magnitude. This leads to a concept of a combination of classical and magnetorheological dampers. As resistance against the flow of magnetorheological fluid depends on magnetic induction, the change of electric current generating the magnetic field can be used to control the damping force. In the developed mathematical model the rotor is represented by a flexibly supported Jeffcott rotor and the normal and magnetorheological oils in the proposed damping device are modelled by newtonian liquid and Bingham material whose yield shear stress depends on magnetic induction. The magnetorheological part of the proposed damping element can be used as an auxiliary damper. Such a design solution minimizes consumption of the magnetorheological oil, which is more expensive than normal lubricants. The carried out computational simulations show that the suitably proposed damping effect in dependence on the speed of the rotor rotation can significantly reduce maximum amplitude of the vibration and minimize the force transmitted between the rotor and its casing.