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.
Highlights
The computational simulation of rotating machines is an indispensable resource for engineers
Cavalini Jr. et al / Uncertainty analysis of a flexible rotor supported by fluid film bearings taking into account various subsystems, as follows: first, the subsystems that are defined by their geometry, as the shaft, drives and couplings; later, the gyroscopic effect; the subsystems that are frequency and/or state dependent, such as the hydrodynamic bearings
In this paper two uncertainty approaches were used to evaluate the dynamic responses of a flexible rotor supported by oil film bearings, namely fuzzy and stochastic analyses
Summary
The computational simulation of rotating machines is an indispensable resource for engineers. The hydrodynamic bearings represent an important component of rotating machinery due to their large use in the industry (Riul, 1988) In this case, the load is supported by a thin film of lubricant that separates the shaft from the bearing (i.e., there is no direct contact between metal parts). It is worth mentioning that due to the oil film, the damping effect on hydrodynamic bearings is more pronounced than in rolling bearings, which is beneficial in machines that go through critical speeds during startup and stop down procedures In this context, the analysis of uncertainties either in the geometry (e.g., radial clearance, due to the machining processes or damage) or in the operating conditions (e.g., oil temperature) that affect the performance of the hydrodynamic bearings is an important design issue. As the uncertainties are analyzed only in the bearings' parameters, the Monte Carlo simulation is directly applied to the deterministic finite element model of the rotor (Koroishi et al, 2012)
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