A Study on the Influence of Bush Surface Waviness and Wear on the Tribo-Dynamic Behavior During the Start-Up Process of Water-Lubricated Bearings

The start-up process of water-lubricated bearings (WLBs) exhibits strong nonlinearity and is highly sensitive to the surface topography of both the bush and the journal. However, due to machining errors and operational wear in practical manufacturing and service, the bush inevitably develops surface waviness and wear, which significantly influence its start-up behavior. This issue is particularly critical in high-speed underwater unmanned vehicles, where lightweight design precludes the use of oil lubrication systems, making WLBs a more economically favorable and reliable alternative. To address this, the present study establishes a start-up tribo-dynamic model that comprehensively incorporates both bush surface waviness and wear to systematically investigate their coupled effects on the tribo-dynamic behavior during WLB start-up. The research findings indicate that axial surface waviness reduces the hydrodynamic effect during the start-up phase. Consequently, a higher rotational speed is needed to generate the necessary hydrodynamic pressure for the WLB to start up successfully. The significance of the influence exerted by circumferential surface waviness on start-up behavior is determined by its frequency number, m. A larger m leads to greater fluctuations in both hydrodynamic pressure and contact pressure. Furthermore, when wear occurs, the amplitude of bush surface waviness mediates the influence of wear depth on start-up performance, thereby modifying the optimal wear depth previously established for smooth bearings. These findings highlight the importance of controlling circumferential waviness frequency during machining and manufacturing processes to optimize WLB start-up reliability and service life.