A novel FEM-based mass conserving nonlinear hydrodynamic interface element for EHL simulations of reciprocating rod seals

In the study of hydraulic reciprocating rod seals, the prediction of their sealing performance presents challenges in solving the soft elastohydrodynamic lubrication (EHL) problems due to the strong coupling between the hydrodynamic lubrication of the fluid and the finite deformation of the seal, as well as the nonlinear behaviors of the fluid. This paper develops a novel FEM-based mass conserving nonlinear hydrodynamic interface element (MCNL-HIE) to resolve the strongly coupled EHL problems through a monolithic finite element framework. The mass conservation and nonlinear properties of fluid are taken into account to accurately capture the hydrodynamic lubrication behavior of the fluid. In contrast to existing HIEs, no additional nodes or degrees of freedom are introduced in the proposed HIE, thus reducing memory requirements and improving the computation efficiency. Moreover, when dealing with the fluid cavitation problem, no artificial regularization parameters are required, thereby enabling accurate calculation of flow rates. In numerical examples, comparison studies are conducted to demonstrate the accuracy and efficiency of the proposed HIE. EHL simulations of a step-combined rod seal are performed to investigate the influence of fluid cavitation, compressibility and piezoviscous effects on lubrication characteristics and flow rates. Results indicate that unreasonable simulation results are generated when the fluid mass conservation cavitation model is not considered. The seal leakage could be underestimated under high-pressure conditions when fluid compressibility and piezoviscosity are not taken into consideration.