# A Review of Progress and Hydrodynamic Design of Integrated Motor Pump-Jet Propulsion
## 3 IMP Bearing and Hydrodynamic Design
### Hydrodynamic Design  
#### 3.2.1 Hydrodynamic Performance  
The hydrodynamic performance of an IMP thruster is the key to ensuring its thrust and power index, which directly affect the propulsion efficiency, vibration, and noise. With the continuous development of computer technology, numerical testing has gradually become an important means of keeping pace with and complementing physical testing in the research and development of the hydrodynamic performance of propulsion devices, as well as effectively promoting the research and development of propulsion devices in general. It is critical to match propeller hydrodynamic characteristics to specific factors to achieve efficient IMP. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Bearing Type** & **Year** & **Reference** & **Geometry of the Bearing** & **Performance** & **Problem** \\ \hline \hline \multirow{6}{*}{**Rolling bearing structure**} & & & & The test results of these prototypes were not ideal, mainly due to the low reliability of the ball bearings in the mud and sand environment and the excessive bearing wear; furthermore, due to bearing friction, the rotor could not reach the predetermined speed under rated voltage conditions. In addition, ball bearings also have inherent shortcomings in terms of vibration, noise, and load-carrying capacity. In high-power propellers, large axial thrust is required, and rolling bearings experience excessive strain under high loads. & The results of these prototypes were not ideal, mainly due to the low reliability of the ball bearings in the mud and sand environment and the excessive bearing wear; furthermore, due to bearing friction, the rotor could not reach the predetermined speed under rated voltage conditions. In addition, ball bearings also have inherent shortcomings in terms of vibration, noise, and load-carrying capacity. In high-power propellers, large axial thrust is required, and rolling bearings experience excessive strain under high loads. & The difficulty, complexity, and cost of the entire system is increased, and it is likely to cause water pollution. \\ \cline{2-5}  & \multirow{2}{*}{2017 bearings} & & & The bearing capacity and service life of oil-lubricated oil-lubricated bearings are higher than those of water-lubricated bearings. & The construction, on the other hand, is complex, with significant machining and installation requirements. Oil-leakage prevention and sealing systems must also be reliable. \\ \cline{2-5}  & \multirow{2}{*}{2017 [41]} & & & The thrust bearing supported by rubber pads uses rubber deformation to adjust the inclination of the pad, which has great potential for damping vibration. & To obtain a good hydrodynamic performance from the IMP propell, the thickness of the duct and the diameter of the hub must be as small as possible, which leads to the complexity of the bearing design. \\ \cline{2-5}  & \multirow{2}{*}{2016 thrust bearings} & & & Many units are also exploring the use of a support/thrust integrated structure which can bear both gravity and thrust loads. & The practicality has yet to be tested by engineering. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Types of bearings applicable to IMP. The most significant metric is the propeller pitch ratio. The hydrodynamic efficiency is further affected by the propeller's structural design, the form and size of the duct, the air-gap thickness, and other parameters. Computational analyses and experimental research on some IMP parameters are presented in this section to provide a clear picture and detailed explanation of IMP thrusters' hydrodynamic performance (see Table 3).