A new approximate method for evaluating oil-film force acting on a finite journal bearing with unsteady and larger perturbed motion is presented． The nonlinear dynamic analysis of rotor supported by finite oil-film bearings is carried out by the new oil-film force model． Form the numerical results the following conclusions are obtained： 1．At very low speed， oil-film force can be ignored， the motion is synchronous whirl due to unbalance response． 2．At very high speed or with large eccentricity the influence of unbalance force prevails over that of oil-film force． The motion is also synchronous and stable． 3．In the middle interval of speed， oil-film force and unbalance force have the same order of magnitude， or oil-film force plays the main role and the motion is much complex． The nonlinear properties appear obviously． The operating danger of the rotor would be happened in this runing interval．%根据文献［1］提出的非稳态非线性油膜力基本表达式，导出了有限长轴承非稳态油膜力近似公式。应用该公式，采用数值模拟，对有限长油膜轴承支撑的刚性Jeffcott转子进行了不平衡力下油膜振荡的非线性分析，得出了与文献［13］的结论相类似的分岔和混沌特性。
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