Two-way fluid–structure interaction in elastohydrodynamic lubrication of the piston/cylinder interface in deep-sea axial piston pumps

Fluid–structure interaction (FSI) of the piston/cylinder interface critically affects the lubrication performance of axial piston pumps, yet its role under deep-sea conditions remains insufficiently understood. This study proposes an elastohydrodynamic (EHD) lubrication model for the piston/cylinder interface under deep-sea conditions, in which two-way FSI is realized through dynamic nodal data exchange. The proposed model integrates finite volume discretization of the Reynolds equation with finite element analysis of bushing deformation, and resolves the interdependence among film geometry, pressure distribution, and structural deformation by coupling piston dynamics with oil film lubrication equations within an iterative framework. The evolution of interfacial lubrication fields is characterized, and the effects of structural and operating parameters on energy consumption are quantified by comparing the EHD and hydrodynamic (HD) lubrication models. The results show that elastic deformation of the bushing under deep-sea conditions increases the leakage flow rate while reducing the viscous friction power loss. More importantly, although the leakage flow rate increases substantially with clearance, the EHD model reveals a non-monotonic dependence of viscous friction power loss on clearance, in contrast to the monotonic trend observed in the HD model. These findings provide useful guidance for the design and optimization of deep-sea axial piston pumps.