Study of dynamic coefficients of water film in marine stern tube bearing considering roughness and deformation

Dynamic analysis of water-lubricated marine stern tube bearing is incompatible with that of ordinary oil-lubricated bearing due to the deformation of compliant bushes and non-negligible roughness effects. A modified bearing dynamic analysis model embracing roughness and dynamic characteristics of a non-metal bush is proposed. Based on the model, Reynolds equations of perturbed pressures of water film considering roughness, deformation, and misalignment simultaneously are derived for the first time and solved by coupling the finite difference method and the finite-element method. The results show that dynamic coefficients are enhanced due to roughness when the minimum film thickness ratio exceeds a threshold around 2. The roughness effect is debilitated but the valid range of roughness is extended when bush deformation is considered. Additionally, dynamic coefficients of rougher bearing become obviously smaller than those of smoother bearing as the misalignment angle grows.