# A Review of Progress and Hydrodynamic Design of Integrated Motor Pump-Jet Propulsion
## 5 Discussion  
### The Design of the IMP  
The lifting-line theory has significantly promoted the development of IMP propeller design technology. Many researchers have proposed a corresponding design theory, mainly focused on the design method and design object. In terms of design methods, the IMP propeller lifting-line theory was improved because of the defects of the heavy-duty propeller and the basic design theory under nondesign conditions. For IMP propellers with a side slope and pitch, the corresponding lifting-line design method is perfected. In recent years, scholars have combined the IMP propeller lifting-line theory with the panel method and the Reynolds-averaged Navier-Stokes (RANS) method to improve the accuracy and efficiency of IMP propeller performance prediction. In addition, it is combined with modern optimization design theory, and the performance optimization of an IMP propeller is considered in the design stage, which improves the design efficiency. In terms of the design objects, as the calculation speed increases, the lifting-line theory can be applied to the performance prediction and design of complex thrusters.  
The lifting-surface method is used by many studies to deal with the forward prediction of IMP propellers. The current research focuses include the shrinkage and curling of the wake vortex in the transition zone of the IMP propeller and the tip vortex separation model, which considers the trim and side slope, etc., establishing a model of the IMP propeller trailing vortex and tip vortex, and the separation vortex of the leading edge and corresponding improvement methods are also proposed. In addition, when the IMP propeller interacts with other components, the influence of the hub and the coupling panel method are introduced to consider the influence of other components to improve the accuracy of the performance prediction. Regarding the inverse problem of the lifting-surface design method, since the shape of the blade profile is closely related to its load form, efficiency, cavitation, and other hydrodynamic properties, the main research focus is the precise and rapid design of the vortex grid method to meet the given lift distribution, the design of the arcuate surface of the blade arch under the circulation distribution, and the three-dimensional refinement of the theoretical boundary value problem of the IMP propeller lifting surface. In addition, when considering the interaction between the hull and its appendages, ducts, and propellers, the lifting surface is coupled with other theories such as RANS for design, and the influence of other components is more accurately considered in the design stage to further improve the design accuracy and efficiency.  
At present, the lifting-line model is relatively mature and can solve the problems related to the calculation of the propeller thrust, torque, efficiency, and induced speed field behind the propeller; the calculation time required is relatively short, but it has certain  
Figure 12: Temperature distribution of stator and windings [86].  
limitations. Compared with the lifting-line method, whether it is a forward prediction problem or a reverse design problem, the lifting-surface method can fully consider the blade chord length, camber, and pitch distribution, which has great advantages. Regarding IMP propeller design issues, most of the past studies have focused on the deformation of the tail vortex, the effect of the hub, and the related lifting-surface design of the profile load distribution. It is particularly important to refine the design of some special propellers, such as ducted propellers and pump-jet propellers, to couple the lifting-line and lifting surface design methods with methods such as the surface element method or RANS, and to consider the interaction of the components. This aspect is worthy of further study.