The flexible supports make it possible to decrease the forces transmitted between the working machines and their foundations. As rotating machinery, the hydrodynmic bearings exhibiting compliance and considerable damping together with high load capacity are ofen used for this purpose. Nevertheless, on certain operating conditions, the hydraulic forces produced in the thin oil film can destabilize the rotor equilibrion position, which consequently leads to development of the rotor self-excited vibration of large amplitude. There are several ways how to increase the critical speed of the rotor rotation at which the self-excited vibration starts. Recently, the attention was focused on increasing damping in the rotor supports or on modification of the bearings geometry. At present time there are available many active control devices working on various physical principles. In this paper the research of the concept based on controlled kinematic excitation of the bearings shells is carried out. The performed computer simulations prove that the investigated technique enables to reduce amplitude of the self-excited vibration and to increase the rotor angular speed of rotation, at which the self-excited vibration begins. Suppression of the rotor oscillation is always connected with increasing the force by which the turning rotor acts on its stationary part. The developed computational procedures and results of the performed analyses are intended for finding properties and behaviour of the active control devices for mitigation of excessive vibration of rotating machines and to contribute to their proper design in this way. and Obsahuje seznam literatury
A frequently used technological solution of reducing the time varying forces transmitted between the rotor and its casing is represented by application of a flexible suspension with damping devices added to the constraint elements. To achieve their optimum performance their damping effect must be controllable. For this purpose a concept of a hybrid damping device working on the principle of squeezing the layers of normal and magnetorheological oils have been developed. Here in this article, there is investigated influence of the proposed damping element on stabilty of the rotor vibrations induced by its imbalance during the steady state operating regimes. The stability is assessed by the evolutive method which is based on evaluation of eigenvalues of the system linearized in a small neighbourhood of the rotor phase trajectory and calculation of the corresponding damping ratio or logarithmic decrement. and Obsahuje seznam literatury