Linear and Nonlinear Performance Analysis of Hydrodynamic Journal Bearings with Different Geometries

Abstract

In rotor dynamics, a traditional way of representing the dynamics of hydrodynamic bearings is using stiffness/damping coefficients. It is thus necessary to carry out a linearization of hydrodynamic forces around the shaft’s equilibrium position. However, hydrodynamic bearings have highly nonlinear nature, depending on operating conditions. Therefore, this paper discusses the applicability of these linear/nonlinear approaches using a computational model of the rotating system, where the finite element method is used for rotor modelling and the finite volume method for bearing calculation. The main goal is to investigate the boundaries for linear approximation of the hydrodynamic forces present in lobed hydrodynamic bearings, with the system operating under high loading conditions. Several numerical simulations were performed varying preload parameter and rotating speed. A comparison of the system’s responses, in time domain (shaft orbits) and frequency domain (full spectrum), is made for linear and nonlinear models. Results showed that trilobed bearings are more susceptible to nonlinearities, even in situations of smaller vibration amplitudes, while elliptical bearings are sensitive only under larger vibration amplitudes. These analyses are of great importance for mapping the influence of nonlinearities in different types of lobed hydrodynamic bearings with fixed geometry, varying the preload parameter to verify the influence on the system’s dynamic response. This study is important and serves as the basis for cases of monitoring and fault diagnosis (in the field of structural health monitoring) since it is crucial to distinguish what would be a fault signature or a standard nonlinear effect created by the use of hydrodynamic bearings.

Effect of wear on the dynamic characteristics of a rigid rotor supported by journal bearings

“…In rotor dynamics, the dynamics of hydrodynamic bearings are tradiotionally represented using stiffness and damping coefficients. Therefore, a linearization of hydrodynamic forces around the shaft’s equilibrium position is required 6 . For that purpose, it is important to determine the forces created by the fluid flow to obtain precise estimates of the dynamics of the journal bearings.…”

“…Kim et al 21 presented a review that summarized the previous studies done on journal bearing induced nonlinear, rotordynamic forces, and responses. Viana et al 6 investigated the boundaries for linear approximation of the hydrodynamic forces present in lobed hydrodynamic bearings in highly loaded operating conditions.…”

Optimization of Control Parameters of Magnetorheological Squeeze Film Dampers to Minimize the Vibration Amplitude of Rotors Passing the Critical Speed

“…Wu and Pfeiffer [12] reported on an active journal bearing, the stiffness of which is controlled by the change in the oil influx into the bearing gap. The effect of different geometries on the performance of hydrodynamic bearings was investigated by Viana et al [13]. The modeling of a controllable bearing with three flexible sleeves can be found in [14].…”