Dynamics & Control of Rotors via Active Fluid Film Bearings - An Overview

Dynamics & Control of Rotors via Active Fluid Film Bearings - An Overview

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Seminar talk by Ilmar Ferreira Santos, Department of Mechanical Engineering, Technical University of Denmark, Denmark.

Hydrodynamic and aerodynamic lubrication regimes in its controllable form have been intensively investigated over the last two decades. With the aim of reducing friction and improving thermal, static and dynamic characteristics of sliding bearings different types of electro-mechanical actuators have been coupled to such bearings. Depending on i) the actuator type, ii) the actuation principle, i.e. hydraulic, pneumatic, piezoelectric or magnetic among others, and iii) how such an actuator is coupled to the sliding bearings, different regulation and control actions of fluid film pressure and lubricant flow can be obtained. The most common actions are: a) the control of the injection pressure to modify the fluid film pressure statically as well as dynamically; b) the adjustment of the angle and direction of injection flow (mostly passive action); c) the control of the sliding bearing gap and its preload via movable and compliant sliding surfaces; and d) the control of the lubricant viscosity. All four parameters, i.e. pressure, flow (velocity profiles), gap and viscosity, are explicit parameters in the modified form of Reynolds’ equations for active lubrication. In this framework the lecture gives four original contributions to the state-of-art of sliding bearings and controllable lubrication: I) a comprehensive overview about the different types of controllable sliding bearings and principles used by several authors; II) how the sliding bearing properties – independent of the action principle – can be linked to and described by the modified Reynolds’ equation for active lubrication;  III) the correct use of the modified Reynolds’s equation for active lubrication and a challenge to be overcome: the discharge coefficients; IV) a large amount of data obtained from a specially-designed test rig to aid the validation of multi-physical models for sliding bearings under several lubrication regimes. In this test rig all state-variables – pressures, flows, temperatures, gaps, resultant forces, journal lateral movements, journal angular velocity and angular positions, actuator positions – are monitored by sensors, facilitating the model validation process. The lecture ends with some conclusive remarks about advantages and drawbacks of the different design solutions for controllable sliding bearings and the main challenges to be overcome towards industrial applications.

Keywords: active bearings, actuators, holistic design, multi-physical modelling, mechatronics. 

Professor Dr.-Ing.dr.techn. livre-docente Ilmar Santos
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