# Research on a Strategy for Prediction Methods of Submarine Self-Propulsion Hydrodynamic Performance
## 6 Conclusions  
Based on the steady Motion Reference Frame (MRF) method and the unsteady Rigid Body Motion (RBM) method, we used the RANS method to conduct numerical simulations of the self-propulsion hydrodynamic performance of a submarine model using four different calculation strategies: submarine with propeller, submarine first and propeller second, and propeller rotational speed iteration. The main conclusions are as follows:  
* By comparing the submarine resistance, propeller hydrodynamic performance, and total solver actual runtime for the four different calculation strategies, it was found that the steady MRF method provided the highest computational efficiency for a submarine with propeller self-propulsion simulations. Compared to the other three strategies, the errors in submarine resistance, propeller thrust, and torque were controlled within 0.1% and 0.8%, respectively. Therefore, the steady-state MRF method is recommended for tasks such as obtaining the self-propulsion point propeller rotational speed, analyzing propeller hydrodynamic performance, and conducting power matching studies during the self-propulsion state in the submarine model and propeller optimization design. * By comparing the submarine resistance, propeller hydrodynamic performance, and total solver actual runtime for the four different calculation strategies, it is evident that while the differences in submarine resistance and propeller hydrodynamic performance among the strategies are minor, the total solver actual runtime varies signif \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Method** & **Point 1 (BPF)** & **Point 2 (BPF)** & **Point 3 (BPF)** & **Point 4 (BPF)** \\ \hline strategy 1 & 7.578 & 8.457 & 7.827 & 8.102 \\ strategy 2 & 7.886 & 8.487 & 7.968 & 8.100 \\ strategy 3 & 7.632 & 8.479 & 7.947 & 8.110 \\ strategy 4 & 7.669 & 8.386 & 7.851 & 8.050 \\ \hline \hline \end{tabular}
\end{table} 
Table 16: Comparative analysis of the BPF amplitudes at four monitoring points under different strategies. icantly. When determining the propeller rotational speed corresponding to the self-propulsion point of the submarine model, the total solver actual runtime comparison shows that unsteady-state calculations (submarine with propeller) > unsteady-state calculations (submarine first, then propeller) > sequential unsteady-state calculations with propeller rotational speed iteration (submarine first, then propeller) > integrated steady-state and unsteady-state calculations (submarine with propeller). * Conducting self-propulsion hydrodynamic performance numerical simulations using the steady-state MRF method for the submarine-propeller system, followed by unsteady-state RBM simulations after hydrodynamic loads have converged, results in smaller errors in the fluctuating amplitudes of propeller unsteady-state bearing forces and induced fluctuating pressures compared to the other three calculation strategies. This approach is effective for analyzing propeller excitation forces during the submarine's self-propulsion state. * In the self-propulsion state of a submarine, although the mean lateral force (Y-direction) and vertical force (Z-direction) of the propeller are much smaller than the axial force, their fluctuation amplitudes are higher than or equal to those of the axial force and torque. The difference in fluctuation amplitude is more pronounced in individual blades. The primary fluctuating frequency of the propeller's thrust and torque in all three directions is BPF, while the primary fluctuating frequency of the blade's thrust and torque in all three directions is APF and four times the APF. * In the self-propulsion state of a submarine, the amplitude of the propeller-induced fluctuating pressure is highest at BPF. A broadband spectral characteristic appears between 3 BPF and 6 BPF, and the amplitude of the pulsations within this broadband spectrum cannot be ignored. Additionally, due to space limitations, the impact of different strategies on propeller noise has not been compared in this paper.