# A Review of Progress and Hydrodynamic Design of Integrated Motor Pump-Jet Propulsion
## 6 Conclusions  
This paper analyzes the IMP thruster's working structure, major structural application technology, current hydrodynamic performance research, and important technologies that require further resolution. The IMP thruster completely embraces the principle of extensive electric modularization and integration, better reflecting the high power density, high efficiency, low radiation noise, and maneuverability of electric propulsion systems. As a result, integrated motor propulsion technology has gradually expanded its application areas to other rotating machinery such as pumps, turbines, and fans. However, there are still some uncertain issues with IMP thrusters, for example, that the output power is still in the megawatt range due to power loss at the intake. Furthermore, using IMPs in shallow water, especially around gravel, is exceedingly risky. To design an IMP, numerous critical technologies must be resolved. Because the stator of the motor in the IMP propeller is embedded in the duct, the rotor and the impeller blade are seamlessly connected. This structure thickens the duct and affects the entire flow field. In addition, it is necessary to ensure that the propeller motor has a large enough flow area by limiting the thickness of the stator yoke, rotor yoke, and the magnet of the motor. If the size is too thin, the electromagnetic field will saturate prematurely, further reducing the magnetic flux density of the motor, causing the motor to fail to work normally. In addition, as the IMP thruster eliminates the use of the drive shaft, bearings, and vibration isolation devices that support the traditional motor and reduce the internal noise of the hull, the thrust and torque generated by the thruster are directly coupled with the electromagnetic excitation force generated by the motor, which then increases the electromagnetic noise, hydrodynamic noise, etc. Therefore, the complexity and necessity of designing a high-power, low-vibration, low-noise, and high-performance motor are increased. If a nonaqueous lubricant is used for bearing lubrication, then the sealing devices must be considered. This will increase the complexity and design cost of the entire IMP propeller structure and, at the same time, may cause some other marine pollution problems. Therefore, the use of water-lubricated bearings can reduce the weight and complexity of the IMP thruster system to better reflect the advantages of the IMP thruster. However, due to the low viscosity of the water medium, the bearing capacity of the water film is not large enough, which means that the water-lubricated bearings experience a mixed-lubrication state. As a result, this will affect the bearing capacity and working performance of the bearing. In addition, the adaptability of the bearing material to water and the influence of different flow conditions on the dynamic pressure lubrication characteristics of the bearing will affect the load transfer in the bearing. Therefore, the load-bearing reliability characteristics and design optimization of the bearing should consider the above-mentioned series of issues. To obtain an IMP thruster with a high propulsion efficiency and high output power, the design method for these components must be very strict, because the degree of coupling between high-power thruster components must be higher. Therefore, hydrodynamic-electromagnetic-thermal-fluid-solid coupling research can effectively help us to understand the complex working conditions of the coupling between the internal components and the whole of the IMP thruster. Additionally, it can obtain the key influencing factors that affect the propulsion performance, which will provide technical support for the design of high-power IMP thrusters in the future. When the IMP propeller is working, as it is completely immersed in seawater, all impurities in the seawater will be sucked into the air gap of the propeller, which will then reduce the amount of flowing fluid in the air gap, affecting the cooling of the motor and ultimately reducing the efficiency of the motor.