Application of the Hopf bifurcation theory to limit cycle prediction of short journal bearings with isotropic roughness effects

On the basis of the Christensen stochastic theory, the effects of isotropic surface roughness upon the bifurcation behaviour of a short journal-bearing system are investigated. By applying the Hopf bifurcation theorem to the non-linear equations of motion of rough journal bearings, the steady-state performance, the linear characteristics, and the weakly non-linear bifurcationphenomenaarepresented. For the short bearing with length-to-diameter ratio l = 0. 5, the onset of oil-whirl rough bearing system can manifest a bifurcation behaviour exhibiting subcritical limit cycles or super-critical limit cycles for running speeds near the bifurcation point. For a particular system parameter, the effects of isotropic surface roughness are found to enlarge the size of sub-critical limit cycles and super-critical limit cycles when the Hopf bifurcation occurs. On the whole, the roughness effects of isotropic surface patterns upon the Hopf bifurcation phenomena of the short-bearing system are more pronounced for a smaller system parameter ( p = 0. 4 in the sub-critical region and Sp = 0. 05 in the super-critical region) and a higher roughness parameter (Λ = 0. 4).