With the development of green tribology in the shipping industry, the application of water lubrication gradually replaces oil lubrication in stern bearings and thrust bearings. In terms of large-scale and high-speed ships, water-lubricated bearings with high performance are more strictly required. However, due to the lubricating medium, water-lubricated bearings have many problems such as friction, wear, vibration, noise, etc. This review focuses on the performance of marine water-lubricated bearings and their failure prevention mechanism. Furthermore, the research of marine water-lubricated bearings is reviewed by discussing its lubrication principle, test technology, friction and wear mechanism, and friction noise generation mechanism. The performance enhancement methods have been overviewed from structure optimization and material modification. Finally, the potential problems and the perspective of water-lubricated bearings are given in detail.

Take a dual-winding permanent magnet fault tolerant motor (FTPMM) in the ship shaftless rim-driven thruster (RDT) as the research object, the position sensorless control algorithm based on high frequency (HF) current injection is presented to estimate the rotor position and the rotor position signal is extracted from the voltage. In order to reduce influences of proportional-integral (PI) controller, current regulators and voltage calculation errors, the generalized second-order integrator (SOGI) is discussed along with how to combine with the low-speed sensorless control. And the current vector fault-tolerant control strategy is applied to compensate for the faulty phase current with other healthy phase currents. The rotor position at low speed is estimated under healthy as well as open-circuit faulty conditions by using the HF current injection algorithm based on SOGI (HF-SOGI). After simulation in Matlab/Simulink, the experimental results further demonstrate the feasibility of the HF-SOGI strategy by the FTPMM experimental setup. It can be calculated that the rotor speed ripple is decreased obviously after fault-tolerant control strategy is applied. It can be concluded that the HF-SOGI strategy can estimate the position accurately, which can further improve the reliability and application scope of FTPMM and the RDT system.

The water-lubricated thrust bearings of the marine rim-driven thruster (RDT) are usually composed of polymer composites, which are prone to serious wear under harsh working conditions. Ultrasonic is an excellent non-destructive monitoring technology, but polymer materials are characterized by viscoelasticity, heterogeneity, and large acoustic attenuation, making it challenging to extract ultrasonic echo signals. Therefore, this paper proposes a wear monitoring method based on the amplitude spectrum of the ultrasonic reflection coefficient. The effects of bearing parameters, objective function, and algorithm parameters on the identification results are simulated and analyzed. Taking the correlation coefficient and root mean square error as the matching parameters, the thickness, sound velocity, density, and attenuation factor of the bearing are inversed simultaneously by utilizing the differential evolution algorithm (DEA), and the wear measurement system is constructed. In order to verify the identification accuracy of this method, an accelerated wear test under heavy load was executed on a multi-functional vertical water lubrication test rig with poly-ether-ether-ketone (PEEK) fixed pad and stainless-steel thrust collar as the object. The thickness of pad was measured using the high-precision spiral micrometer and ultrasonic testing system, respectively. Ultimately, the results demonstrate that the thickness identification error of this method is approximately 1%, andin-situmonitoring ability will be realized in the future, which is of great significance to the life prediction of bearings.