Year

1995

Degree Name

Doctor of Philosophy

Department

Department of Mechanical Engineering

Abstract

(1) Three different numerical methods are developed to calculate the static and dynamic characteristics of circular journal bearings with different slenderness ratios and different geometries. The Reynolds equation with Reynolds boundary condition is solved by the finite difference method and finite element method. The bearing oil film force coefficients are calculated by the finite perturbation method and the infinitesimal perturbation. The calculated results agree well with data from available literature.

Static and dynamic characteristics of grooved and ungrooved bearings with 5 different slenderness ratios are presented in 13 tables.

The relation of eight linear force coefficients of journal bearing with the perturbation amplitudes is also studied. The m a x i m u m perturbation amplitudes for different coefficient variations are also presented.

(2) The oil whirl property and stability of the rotor bearing system is studied. The dynamic performances of the rotor-bearing system under the impulse excitation, position perturbation, unbalance excitation and harmonic excitation, are simulated considering both linear and non-linear bearing forces. The linear scope in which the linear force coefficients can be used is determined.

(3) The misalignment effects on all bearing characteristics, including static characteristics, bearing force coefficients, critical stable speed and whirl frequency, are studied.

(4) Three different experimental methods are proposed to estimate force coefficients of journal bearings from harmonic, impact and unbalance responses.

For the harmonic excitation method, the traditional data process technique, which can only identify 8 bearing force coefficients of one journal bearing, is extended to identify 16 bearing force coefficients of two asymmetric journal bearings. Two different data processing techniques are developed for the separated excitation and combined excitation procedures.

For the impact excitation method, an explicit coefficient estimator on least-square-estimation is developed on the transfer functions of the impulse responses to the impact forces, all 16 bearing coefficients can be calculated through one operation. A new unbalance excitation method is proposed and is successfully used to identify 16 force coefficients of two practical journal bearings. From the unbalance responses under two or more sets of trial unbalance masses, all bearing coefficients can be calculated by solving a set of simultaneous linear equations.

The impact and the unbalance methods can be conveniently applied to estimate the coefficients of large journal bearings on-site, without relying on the expensive excitation equipment to apply large dynamic forces to excite the rotor as required by previous methods.

All the three experimental methods are thoroughly simulated on computers.

(5) To perform the proposed experimental methods two bearing test rigs are modified. Two eccentric-mass vibrators are firstly used to excite the rotor-bearing system. The dynamic coefficients of two grooved bearings and two ungrooved bearings under different loads are estimated. The estimated coefficients correlated well with the theory especially when the misalignments are considered in the theoretical calculation. The experimental results verify that the misalignment can improve the stability of the rotor-bearing system.

The sensitivity and uncertainty of the estimated coefficients to the measurement errors are analysed.

(6) Applicable experimental procedures, data processing techniques for all three excitation methods are proposed and performed on different test rigs.

A data re-sampling technique is used to avoid the alias of frequency characteristics and reduce the noise affection.

A data pre-processing method is developed to remove outliers and other unreasonable data from the experimental signal without changing its phase.

(7) More than 210 figures and 33 tables on theoretical and experimental results are presented. One hundred and sixty-three references are listed.

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