Coupled hydrodynamic lubrication and unbalanced magnetic force analysis in water-lubricated bearings for rim-driven thrusters

During the operation of rim-driven thrusters (RDTs), eccentricity between the journal and water-lubricated bearing (WLB), as well as between the motor's stator and rotor, is commonly observed. This eccentricity generates both hydrodynamic force (HF) and unbalanced magnetic pull (UMP), which interact in a coupled manner, complicating the accurate evaluation of the hydrodynamic performance of the WLB. This paper proposes a coupled model that integrates the HF and UMP. The HF is derived from the Reynolds equation, while the UMP is calculated using the magnetic potential and air gap reluctance. These forces are then coupled to determine the bearing's equilibrium position and hydrodynamic performance in the RDT. This paper demonstrates the necessity of considering UMP in the hydrodynamic lubrication analysis of WLBs working in RDTs. Additionally, the impact of motor parameters on the WLB is investigated under both fixed and varying operating conditions. It is found that the bearing's hydrodynamic performance is significantly affected by the length of the permanent magnet and the air gap.