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| Modified form of the unsteady oil-film force formula of short bearing by variational approach |
| Revised:December 18, 2001 |
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| DOI：10.7511/jslx20034085 |
| KeyWord:hydrodynamic bearing,unsteady oil-film forces,var iational method |
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| Abstract: |
| In linear rotor dynamics, the oil-film forces of bearing s are generally treated as the well-known model of eight dynamic coefficients at the equilibrium state. This linear and steady model fails to analyze the nonlin ear dynamic behaviors of a rotor-bearing system. So short bearing model is frequent ly used in the nonlinear rotor-bearing system because of its concise form. Howe ver, the error may be significant when the length to diameter ratio of the beari ng is not small enough. Thus if we want to analyze the nonlinear phenomena of a rotating machine correct ly the hydrodynamic forces of the bearing has to be solved numerically. That is, Reynolds equation needs to be solved by the discrete methods such as the finite dif ference method or the finite element method step by step following the nonlinear dynamic analysis process of rotor-bearing system. In this paper, the oil-film p ressure solution of the short bearing is improved to be a new form with few of p arameters. The formulae of these parameters are obtained by the variational meth od. Thus, a modified form of the unsteady oil-film force of the short bearing i s obtained. The modified formulae not only hold the concise form of the short bea ring, but also adapt to the bearings with the large length to diameter ratio. Th ese formulae of oil-film forces have a high precision even the journal motions larg ely in the bearing. Compared with the finite differential method (set-zero algo rith m), the error of the results computed by the short bearing formula is as high as 200% when the length to diameter ratio of the bearing equals to 0.6, however th is error decreases to only about 5% if the modified formulae are used. So the mo dified method of this paper is sure an effective way for the nonlinear analysis of a rotor-bearing system, since it improves the oil-film force precision of s hort bearing model greatly and still has the concise analytical form. |
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