# Numerical Study of Wave Effect on Aircraft Water-Landing Performance
## 5 Conclusions  
The aircraft wave-landing performance is essentially different from the calm-water-landing situation. This paper studied the wave effect on the water-landing process of an amphibious aircraft. Several case studies are undertaken to evaluate the difference between calm water and regular wave and to explore the effect of wave height on regular wave-landing performance. The following conclusions can be drawn from the obtained results. (1) In the aircraft regular wave-landing event, there are several distinctive features compared with the calm-water-landing case. First, a more rapid oscillation in aircraft overload time-history is presented due to the dramatic air-water mix in the rear-fuselage region. Second, the aircraft experienced three unique stages. In the rear-fuselage impacting and front-fuselage on-flight stages, because of the wave shape, the main part of the fuselage is not impacted on the wave surface. Therefore, the aircraft overloads are mainly determined by aerodynamic characteristics in these two stages. Third, the pitch-down angular acceleration generated by the rear-fuselage makes the front-fuselage of aircraft heavily slammed on the wave surface at beginning of the second impacting stage. That results in a large hydrodynamic impact load. Therefore, the maximum overload in this stage is obviously higher than that of the calm-water-landing case. (2) The correlation between the acceleration of aircraft and the wave height is different in time and changes from negative to positive during the second impacting stage. Overall, as the wave height increases from 0.5 m to 2.0 m, the maximum acceleration of the aircraft increases. On the other hand, comparing with the calm-water-landing case, the safety of crews and aircraft structures is higher in the wave-landing situation when the wave height is less than 1.0 m. The reasons for these features are the wave surface slope and wave particle velocity. Generally, as the wave height increases with a fixed wave length, the wave steepness, wave slope and wave particle velocity both monotonously increase which could  
Figure 19: Vertical wave velocity of water field when aircraft landing on wave surface with \(H=2\) m at \(t=0.45\) s.  
Figure 18: Comparison of free surface and pressure distribution of aircraft landing with different wave heights at \(t=0.526\) s.  
result in the variations of the impacting area and position of the aircraft and the effective impacting velocity between the aircraft and free surface. Limited by the numerical simulation resource, the performance of the aircraft irregular wave-landing is not analyzed in the present study. In future studies, improvements will be made to the numerical simulation conditions, and the influence of significant height and mean period of the irregular wave on aircraft landing characteristics will be explored. Due to the temporal-spatial irregularity of wave surface, the aircraft irregular-wave landing process is more complicated thus the longer simulation time will be performed. Furthermore, the deformation of the fuselage in the air-water two-phase flows will be considered in the next step of this study. Conceptualization, methodology, formal analysis, investigation, visualization, writing--original draft preparation, J.C. and T.X. ; software, validation, resources, data curation, M.W. and Y.L. ; writing--review and editing, T.X. and M.T. ; supervision, project administration, M.T. All authors have read and agreed to the published version of the manuscript. This work was supported by the grants from Aeronautical Science Foundation of China (No. 20182352015 and 201928052009) and Nanjing University of Aeronautics and Astronautics (No. 180603 DF01). Not applicable. The data presented in this study are available on request from the first author. The authors would like to thank Nanjing Jiangbei New Area BPS (Biopharmaceutical Public Service Platform) HPC for the technical supports. The authors also thank [PERSON], [PERSON], [PERSON], and [PERSON] for the useful discussions.