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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.

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The purpose of this study is to investigate the role of the misalignment journal, caused by journal elastic deformation, on the transient wear and mixed lubrication performances using a numerical model. In the numerical model, the transient geometry lubrication clearance considering the journal misalignment, the transient elastic deformation and the transient wear depth are incorporated to evaluate the transient film thickness during wear process. The evolutions, under different external loads, of the wear depth, wear rate, elastic deformation, film thickness, fluid pressure and contact pressure are calculated by the numerical model. Furthermore, the calculated results of the misaligned journal bearing are compared with those of the aligned journal bearing. The results show that the distributions of the wear depth, film pressure and elastic deformation are asymmetric along the axial direction and the peak values of them shift toward the back end when the journal misalignment is considered. The maximum wear depth, maximum fluid pressure, maximum contact pressure and maximum elastic deformation of the misaligned journal condition are significantly larger than those of the aligned journal condition.

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