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This paper aims to develop a mathematical model for investigating the nonlinear dynamic mixed friction behaviors, including hydrodynamic, contact, deformation, etc., of the novel coupled bearing lubricated with low-viscosity fluid. The model fully integrates the five-degrees-of-freedom (5-DOF) rotor dynamic model with the mixed elastohydrodynamic lubrication model of the novel coupled bearing, considering the unbalance and exciting forces/comments caused by the propeller rotor. A comparative analysis is carried out to validate the effectiveness of the present model. Through the numerical simulation, the dynamic nonlinear mixed friction behaviors of the novel coupled bearing under low-viscosity lubricant are revealed. Based on the established mathematical model, a series of parametric studies are conducted to explore the effect of the structural parameters on the nonlinear mixed friction behavior of the novel coupled bearing. Numerical results demonstrate that the exciting moments increase the range of the axis orbit, thereby generating the edge asperity contact for both the journal and thrust bearings. The angular displacement along the y-axis improves the transient mixed friction performances of the thrust bearing. Furthermore, numerical results reveal that the increasing length-diameter ratio of the journal bearing (the specific pressure remains constant) improves the nonlinear dynamic mixed friction behaviors of the thrust bearing. In addition, the nonlinear dynamic mixed friction performance of the journal bearing becomes better with the increase in the thrust bearing radius.

This study explores the effects of wear and shaft-shape error defects on the tribo-dynamic responses of water-lubricated bearings under nonlinear propeller disturbance using a numerical model. The model proposed in this paper is verified by comparing the results from experiments and simulations in published studies. Numerical simulation studies reveal the effects of nonlinear propeller disturbance on the dynamic behavior and lubrication performance, such as hydrodynamic force, contact force, and journal trajectory, of the water-lubricated bearings with wear and shaft-shape errors. In addition, the effects of the critical factors for wear and shaft-shape errors, including wear depth, deviation angle, magnitude, and waviness order, on the tribo-dynamic responses of water-lubricated bearings are identified. The results of numerical spectrum analyses show that the nonlinear disturbance significantly affects the dynamic behavior (shown as the fluctuation range of the journal trajectory increases), and reasonable wear parameters can improve the lubrication performance of the water-lubricated bearing. Moreover, the effects of shaft-shape errors on the transient hydrodynamic force, contact force, film thickness, pressure, and journal trajectory are greater than that of wear.

This study aims to reveal the role of the mass conversation cavitation boundary on the tribo-dynamic responses of five kinds of micro-groove water-lubricated bearing under mixed lubrication. By introducing the mass conservation boundary, the tribo-dynamic model of the water-lubricated micro-groove bearing is established and numerically solved by the control volume method. The accuracy of the developed model is verified by comparing the calculated results with the existing experimental and simulation results. The effects of cavitation under Reynolds and mass conservation boundary conditions on different micro-groove bearings were analyzed using the model, and the rotational speed and microgroove depth parameters were analyzed. The simulation results show that , regardless of the shape of the bottom of the microgroove, cavitation can stabilize the journal movement and enhance the dynamic pressure effect of the micro-grooves. The parameter analysis of rotational speed and micro-groove depth proves that rotational speed significantly influences the micro-groove cavitation zone and the dynamic pressure effect. Moreover, the greater the micro-groove depth, the smaller the enhancement effect of cavitation to dynamic pressure. The water-lubricated micro-groove bearing with the bottom shape of the left-triangle has the best lubricating performance during the whole analysis process.

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