## 5 Discussion  
In the finite element model simulation calculations of the propulsion shafting system containing an equivalent model of a high-elasticity coupling, the dynamic design analysis method and the time-history method for impact input loads are based on GJB1060.1-91 and BV043/85, respectively. The impact load value of the dynamic design analysis method is related to the modal mass of the propulsion shafting system; the time-history method, on the other hand, is a time-history curve derived from the equipment's mass combined with the standard impact spectrum. A comparative analysis of the results from the impact resistance calculations of the propulsion shafting system using both the dynamic design analysis method and the time-history method indicates that the trends and patterns of the impact responses are essentially the same, although the degrees of response vary. Moreover, the vertical vibration amplitudes of the impact displacement and impact stress are generally larger than those in the axial and transverse directions. To compare the results of the two calculation methods, the impact stress response and displacement response of different vertical shaft sections of the propulsion shafting system are compared, as shown in Figure 22, which compares the maximum displacement and maximum equivalent stress results at different sections in the vertical direction of the propulsion shafting system.  
Figure 22 indicates that the trends of the computational results from both the dynamic design analysis method and the time-history method are generally similar, although they differ in amplitude of vibration. However, there are noticeable differences in the stern and bow bearing support cross-sections. From the displacement response comparison chart, Section 1, which is the propeller position, exhibits a larger displacement response. The dynamic design analysis method calculates a displacement of 10.9 mm, while the time-history method also yields a significant displacement of 8.5 mm. The trend of displacement response then decreases, primarily due to the proximity to the stern bearing. Additionally, Section 17, which is the driven end of the high-elasticity coupling, shows the maximum impact displacement calculated by the dynamic design analysis method, reaching up to 22.47 mm. This is mainly attributed to the lower radial stiffness of the thrust bearing, resulting in a larger vertical impact displacement response. Sections 18 and 19 correspond to the simplified motor bearing support points, where the vertical displacement response is also larger due to the larger mass of the motor rotor and the lower radial stiffness of the motor bearing. From the stress response comparison chart, it is observed that the stress levels at each bearing support point are relatively high, especially at the thrust bearing  
Figure 22: Comparison chart of impact response at key cross-sections of the propulsion shafting system: (**a**) impact displacement curve; (**b**) impact stress curve.  
support point where the impact stress is notably higher, while the impact stress levels of the motor bearing, stern bearing, and bow bearing are slightly lower. Through a comparative analysis of the results from the two methods, it is evident that in the impact resistance calculations for the propulsion shafting system, the results from the dynamic design method are slightly greater than those from the time-history method, with the former's results being more conservative.