A comparative linear and nonlinear dynamic analysis of compliant cylindrical journal bearings

Dynamic behaviour of compliant cylindrical journal bearings is investigated using linear and nonlinear numerical approaches. Journal motion orbits based on linearized dynamic coefficients are compared to the journal trajectories obtained by the nonlinear transient analysis. Obtained results are presented in terms of orbit amplitude, shape and location. The influence of compliant liner thickness, viscoelastic properties and deformation model is also investigated. A linear model is found to deliver acceptable results at a relatively small shaft unbalance under low to average loads. However, with a journal amplitude motion greater than 37% of the bearing diametral clearance, the linear model should not be used to analyse journal transient motion. Plane strain hypothesis is found to be a proper substitute for a full deformation model when a compliant liner is thinner than 2 mm (for the bearing geometry used in this study). It was also shown that the liner viscoelasticity should be taken into account whenever a compliant liner is relatively thick (in our case, 2 mm). Viscoelasticity of the liner decreases journal amplitude compared to a pure elastic liner.

► Linear and nonlinear models agree well for small journal amplitudes.
► A plain strain hypothesis can be used when liner deformation is small.
► Viscoelasticity decreases journal orbit amplitude by reducing dynamic deformation.