Five-DOF nonlinear tribo-dynamic analysis for coupled bearings during start-up

The novelty of this study lies in its investigation of the transient coupling relationship between 5-Degrees-OfFreedom (5-DOF) nonlinear dynamics and mixed lubrication behaviors of a Coupled Journal and Thrust Water-Lubricated Bearing (CJTWLB) used in rim-driven propeller during start-up. A fully coupled tribo-dynamic model is established, in which 5-DOF nonlinear dynamic behaviors interact with the mixed lubrication performance. The model incorporates nonlinear external excitations, including realistic forces and moments generated by the propeller during start-up. The present numerical model is validated using available experimental and theoretical results from existing literature. Through numerical simulation, the transient nonlinear dynamic and mixed lubrication behaviors of the CJTWLB during start-up are revealed. Results indicate that the evolution of elastic-plastic contact behaviors with acceleration time differs from that of a single journal or thrust bearing. The exciting moments, especially for the moment along the x-axis, and common boundary condition are identified as crucial factors affecting the nonlinear tribo-dynamic performances during start-up in such bearings. Additionally, an interesting finding is that an increase in rotational speed hardly improves the transient mixed lubrication performance of the journal bearing part of the CJTWLB during start-up. Finally, the results demonstrate that a higher blade number is beneficial for improving the stability of the CJTWLB.