Uncertainty analysis of a flexible rotor supported by fluid film bearings

Abstract

This paper is dedicated to the analyses of the effect of uncertain parameters on the dynamic behavior of a flexible rotor containing two rigid discs and supported by two fluid film bearings. A stochastic method has been extensively used to model uncertain parameters, i.e., the so-called Monte Carlo simulation. However, in the present contribution, the inherent uncertainties of the bearings' parameters (i.e. the oil viscosity as a function of the oil temperature, and the radial clearance) are modeled by using a fuzzy dynamic analysis. This alternative methodology seems to be more appropriated when the stochastic process that models the uncertainties is unknown. The analysis procedure is confined to the time domain, being generated by the envelopes of the rotor orbits and the unbalance responses obtained from a run-down operating condition. The hydrodynamic supporting forces are determined by considering a nonlinear model, which is based on the solution of the dimensionless Reynolds' equation for cylindrical and short journal bearings. This numerical study illustrates the versatility and convenience of the mentioned fuzzy approach for uncertainty analysis. The results from the stochastic analysis are also presented for comparison purposes.

Sensitivity Analysis of Flexible Rotor Subjected to Interval Uncertainties

“…The uncertainty modeling and quantification of flexible rotors have been analyzed by applying different numerical approaches: stochastic finite element method (Koroishi et al 2012), polynomial chaos expansion (Didier et al 2012), fuzzy finite element method (Cavalini Jr et al 2015), and fuzzy-stochastic finite element method . In those contributions, the system responses were computed in the presence of parametric uncertainties and assessed for several uncertain scenarios in order to determine the influence of each uncertain parameter on the dynamic behavior of the system.…”

Kriging Metamodeling in Rotordynamics: Application for Predicting Critical Speeds and Vibrations of a Flexible Rotor

“…For example, some parameters may vary throughout the life of a rotating machinery or some uncertainties have to be taken into account during the manufacturing monitoring. All these facts can drastically affect the vibration responses of a rotor system (see, e.g., [5][6][7][8][9][10][11][12][13]). And therefore it complicates the approach to be put in place in order to propose a robust design.…”

Experimental Estimation of Journal Bearing Stiffness for Damage Detection in Large Hydrogenerators

“…The influence of the uncertainties in journal bearing operating conditions, like pads clearances, lubricant viscosity, and 2 Shock and Vibration shaft eccentricity, may be analyzed using stochastic modeling techniques [8,9]. However, for damage detection purposes, the experimental estimation of bearing dynamic coefficients may be used as an effective solution.…”

“…The lower bearing is a combined thrust and journal bearing, constituted by the generator lower shaft (4), the thrust block and pads (7), and the thrust bearing bracket (10). The turbine bearing is composed of the turbine shaft (5), pads (8), and turbine headcover (11). Table 1 presents the main data of these journal bearings [10].…”