Dynamic analysis of rotor–bearing systems lubricated with electrorheological fluids

Abstract

Smart machines are defined here as machines with properties adaptable to measurements of some external situations. In this paper, a rotor supported by two or more journal bearings is considered as a rotating system. As an external situation the magnitude of the rotor vibrations is considered here, and the smartness of the system is the possibility to change the dynamic characteristics of the journal bearings using electrorheological fluids as lubricant. These lubricants are known to alter their viscosity and consequently their flow properties, when an electric field of some kV/mm is imposed on them and is expected to alter the dynamic stiffness and damping coefficients, thus giving the possibility to alter the rotor dynamics. The finite element method is used to model the rotating shaft on journal bearings that are considered as stiffness and damping coefficients having controllable values. The gyroscopic effect is taken into consideration, as it influences the system dynamics, particularly at high angular velocities and large mass moments of inertia of the disks included. The Reynolds equation has been numerically solved using also the finite element method in order to calculate the stiffness and damping dynamic coefficients of the journal bearing as functions of the applied electric field. The free response of the complex system is firstly considered rewriting its equations in state-space form. The eigenmodes of the vibration have been also calculated and presented. The comparison of the results for both conventional and electrorheological fluid lubricants show the control possibility of the smart journal bearings thus resulting in a smart rotor-bearing system. Finally, the forced vibration problem of Kikuchi rotor-bearing system is implemented, showing the ability for amplitude and frequency alteration due to electric field.