ABSTRACT When the hydrostatic and the hydrodynamic lubrication are simultaneously combined in a journal bearing, with the aim of reducing wear between rotating and stationary parts, one refers to the hybrid lubrication, which offers the advantages of both lubrication mechanisms. When part of the hydrostatic pressure is also dynamically modified by means of hydraulic control systems, one refers to the active lubrication. By the combination of fluid power, electronics and control theory, the active lubrication makes feasible the reduction of wear and the attenuation of rotor instabilities. Significant reduction of resonance peaks is demonstrated in a test rig, specially designed with the aim of experimentally exploring the potential of the active lubrication. Experiments are led in the frequency domain. INTRODUCTION High efficiency rotating machines, working at severe pressure and flow conditions, demand continuous monitoring and control of vibration levels. One of the ways of reducing vibration amplitudes in rotating machines is the use of hydrodynamic bearings. Among the hydrodynamic bearings, the tilting-pad bearings are those which show the best stability properties. Nevertheless, in many cases, due to aerodynamic excitations (crosscoupling effect) instabilities can occur, if the amount of bearing damping (at full load condition, i.e. high maximum continuous speed) is not enough to ensure a reasonable stability margin. One of the ways of improving this stability margin is by applying ac
