Vibrations of Flexible Multistage Rotor Systems Supported by Water-Lubricated Rubber Bearings

Este trabalho apresenta um procedimento computacional baseado no metodo de elementos finitos desenvolvido especialmente para predizer o comportamento dinâmico de sistemas rotativos apoiados em mancais hidrodinâmicos. O procedimento computacional proposto permite simular diferentes tipos de rotores compostos por eixo flexivel, discos massivos e mancais rigidos ou hidrodinâmicos, com perfis circulares ou elipticos. Sao usados elementos finitos de viga baseando-se na teoria de vigas de Timoshenko no modelo do eixo, o que permiteincluir os efeitos de deformacao por cisalhamento, inercia rotatoria e efeito giroscopico. Um procedimento baseado no metodo de elementos finitos e aplicado para resolver a equacao de Reynolds para fluidos incompressiveis, junto a um procedimento de perturbacao linear para secalcular os coeficientes dinâmicos de forca dos mancais cilindricos e elipticos. As equacoes de movimento para rotores desbalanceados apoiados em mancais hidrodinâmicos sao integradas usando-se o Metodo de Newmark para se obter a resposta no tempo. Os resultados sao validados pela comparacao com valores experimentais coletados em uma bancada de teste e tambem com valores publicados na literatura. Sao apresentadas algumas relacoes algebricas que permitempredizer os parâmetros de desempenho dos mancais e a resposta desbalanceada do sistema rotormancal em funcao dos parâmetros geometricos dos mancais, tais como pre-carga, razao de esbeltez, e folga radial. E identificada uma faixa operacional dos mancais onde estas relacoes algebricas apresentam uma boa aproximacao com os resultados computacionais. Os resultados deste trabalho servem de base para o projeto de maquinas rotativas, uma vez que permitempredizer seu comportamento dinâmico para diversas condicoes operacionais.

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Análise de rotores flexíveis apoiados em mancais radiais elípticos e cilíndricos utilizando o método de elementos finitos

Fixed-geometry hydrodynamic journal bearings are one of the best supporting systems for several applications of rotating machinery. Cylindrical journal bearings present excellent loadcarrying capacity and low manufacturing costs, but they are subjected to the oil-film instability at high speeds. An attempt of overcoming this instability problem has been the development of non-circular journal bearings. This work deals with an analysis of oil-lubricated elliptical journal bearings using the finite element method. Steadystate and dynamic performance characteristics of elliptical bearings are rendered by zerothand first-order lubrication equations obtained through a linearized perturbation method applied on the classical Reynolds equation. Four-node isoparametric rectangular finite elements are employed to model the bearing thin film flow. Curves of elliptical bearing load capacity and dynamic force coefficients are rendered at several operating conditions. The results presented in this work demonstrate the influence of the bearing ellipticity on its performance at different loading conditions. Keywords—Elliptical journal bearings, non-circular journal bearings, hydrodynamic bearings, finite element method.

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Finite Element Analysis of Oil-Lubricated Elliptical Journal Bearings

High power and speed are new demands for rotating machinery which needs the journal bearings with high dynamic characteristics. The critical speed of the rotor-bearing system is one of the most significant parameters to evaluate the dynamic characteristics. This paper aims to investigate the theoretical and experimental analysis of a rotor system supported by large diameter elliptical bearings.,To obtain the theoretical and experimental support for rotor-bearing system design, dynamic characteristics theoretical analysis based on the finite difference method is given and an experiment focuses on critical speed identification is carried out.,The theoretical calculation results indicate that the critical speed is near to 800 rpm and there is no large vibration amplitude round working speed (1,500 rpm). Using the test bench in the factory unit, vibration data including three experimental processes are obtained. According to the vibration data, the critical speed is identified which also indicates that it is stable when working at 1,500 rpm.,The design method for the rotor system supported by large diameter elliptical bearing can be obtained by the theoretical and experimental results shown in this paper.,The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-04-2020-0122/

Theoretical and experimental dynamics analysis of rotor-bearing system supported by elliptical bearings

Influence of thermal pressure and temperature profile approximations in thermohydrodynamic analysis of surface‐textured noncircular journal bearing

This paper presents the development of a finite element procedure for the dynamic analysis of flexible rotors supported on fluid-film elliptical journal bearings operating under several operating conditions. The rotating shaft is modeled by using Timoshenko beam theory and the coupled rotating components, such as disks and impellers, are modeled by using lumped masses. The modeling of the elliptical journal bearings is performed by solving the lubrication equations generated from the application of a linearized perturbation method on the classical Reynolds equation. The bearing carrying-load capacity and the linearized dynamic force coefficients can be predicted for elliptical bearings with different preloads and journal eccentricities. The rotor transient whirling unbalance response is estimated by performing the time integration of the finite element equations using Newmark method. Experimental whirling unbalance response of a rotating shaft supported at two identical journal bearings is used to validate the finite element procedure. A comparative analysis of the dynamic response of flexible rotors supported on both cylindrical and elliptical journal bearings is performed to show that some elliptical bearings are capable of attenuating the rotor unbalance response more efficiently than cylindrical bearings are.

W. M. Miranda

Papers

Lateral Vibration Analysis of Flexible Shafts Supported on Elliptical Journal Bearings