## 3 DDMM for Impact Resistance Calculation
### Analysis of Impact Response Results  
The DDAM calculation yields the maximum impact response values of the propulsion shaft system after being subjected to an impact. In the finite element post-processing module, the impact displacement response and impact stress response results for each direction and each shaft segment can be extracted, as shown in Figures 11-14, which depict the impact displacement response and stress response cloud diagrams for typical shaft segments in each direction of the propulsion shaft system. Additionally, the impact displacement or impact stress response at key sections defined during the modeling process can be extracted for verification against impact calculation results based on different equipment and different locations, as shown in Table 5 for the impact displacement response and impact stress response at key sections. Figure 11: Stern shaft impact displacement cloud diagram: (**a**) longitudinal impact displacement; (**b**) vertical impact displacement; (**c**) transverse impact displacement. Figure 12: Stern shaft impact stress cloud diagram: (**a**) longitudinal impact stress; (**b**) vertical impact stress; (**c**) transverse impact stress. Figure 13: Motor shaft impact displacement cloud diagram: (**a**) longitudinal impact displacement; (**b**) vertical impact displacement; (**c**) transverse impact displacement. As can be seen from Figures 11 and 12, it can be observed that the maximum impact displacement and maximum impact stress experienced by the tail shaft occur when subjected to vertical loading. The maximum impact displacement is 15.1 mm, and the maximum impact stress is 210.6 MPa. There are likely two contributing factors to the larger impact response between the tail shaft segments. Firstly, the tail shaft is directly connected to the propeller shaft, which, due to its short length and connection to the propeller, has a larger mass. This increases the force experienced by the latter half of the tail shaft. This can be directly observed from the propulsion shaft system's straight-line state bearing load table in Section 2.3, which shows a relatively high load on the after-tail bearing. Secondly, the span between the after-tail bearing and the forward-tail bearing is relatively large, and the distance is further, which may result in a larger impact displacement response in the mid-to-rear end. Figure 14: Motor shaft impact stress cloud diagram: (**a**) longitudinal impact stress; (**b**) vertical impact stress; (**c**) transverse impact stress. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Location**} & \multicolumn{2}{c}{**Maximum Transient Displacement (mm)**} & \multicolumn{2}{c}{**Maximum Instantaneous Stress (MPa)**} \\ \cline{2-7}  & **Longitudinal** & **Vertical** & **Transverse** & **Longitudinal** & **Vertical** & **Transverse** \\ \hline center of gravity of the propeller & 2.38 & 10.90 & 7.99 & 44.71 & 47.82 & 43.07 \\ after stern bearing support point & 2.89 & 2.16 & 1.57 & 14.55 & 160.21 & 123.08 \\ before the stern bearing support point & 1.34 & 1.12 & 0.79 & 23.38 & 151.95 & 137.52 \\ thrust bearing support point & 1.10 & 7.70 & 5.77 & 7.92 & 252.67 & 174.22 \\ high-elasticity coupling rear end & 0.97 & 11.91 & 7.70 & 7.55 & 31.7 & 19.14 \\ high-elasticity coupling front end & 4.23 & 22.47 & 11.72 & 5.86 & 10.8 & 9.19 \\ motor 1\# bearing support point & 4.04 & 19.39 & 6.41 & 4.29 & 111.98 & 78.22 \\ motor 2\# bearing support point & 5.95 & 19.41 & 6.16 & 0.77 & 196.28 & 205.64 \\ \hline \hline \end{tabular}  
* Motor 1\#: the motor located at the front; Motor 2\#: the motor situated at the rear.  
\end{table} 
Table 5: The propulsion shaft system key section impact response. As can be seen from Figures 13 and 14, when the motor shaft is subjected to a vertical impact, the impact displacement and impact stress represented on the impact response cloud diagram are relatively large.