# Numerical Study of Wave Effect on Aircraft Water-Landing Performance
###### Abstract
In 2002, Airbus A321 calm water ditching simulation was performed by [PERSON] et al. [13]. Later, [PERSON] and [PERSON] [14] employed ALE-FE method to simulate a full-scale WG30 helicopter impacting on calm water with a vertical velocity. They concluded that the over-estimated pressure and acceleration are partly caused by that the air layer between the fuselage and water surface is not modelled in the simulation. The well-approved point from [PERSON]. [15; 16; 17] is that the ALE technique is an efficient formulation for both vertical impact and landing simulations, but difficult to accurately capture air-water-structure interface, the SPH method provides accurate results of ditching simulation due to free mesh strategy and high-resolution water spray but may suffers from huge computational cost. Recently, [PERSON] et al. [18] developed an in-house SPH code and successfully applied it to predict calm water ditching process of capsule [19] and helicopter [20]. The influences of the initial pitch angle on overload, kinematic dynamics and pressure distribution were detailed. Their results show that the initial pitch angle has a noticeable effect on the load of the aircraft, the splashing jet generated from the belly is regarded as the strong interaction of the aircraft with water surface, and the pitch motion of the aircraft is caused by the hydrodynamic overpressure and suction. In fact, as presented in this study, the aerodynamic characteristic plays a non-negligible role in the aircraft water-landing/ditching process. Therefore, the FVM approach might be the reasonable choice for the aircraft landing/ditching simulation due to the outstanding advantages in capturing the complex air-water mixing phenomenons. Early confidence of numerical results through FVM approach was gained by [PERSON] et al. [21] and [PERSON] et al. [22]. [PERSON] et al. [21] studied the effect of initial drop velocity on an unmanned air vehicle (UAV) vertical drop performance. The simulated behaviour of the pressure time-histories was in good agreement with experimentally measured values. [PERSON] et al. [22] used the non-deforming mesh strategy to compute the path of the aircraft fuselage landing on calm-water surface and the numerical results were comparable with the test data. They concluded that the high pressure in the front part of the fuselage and the negative pressure at the rear part lead to upward and downward forces, which result in the deceleration and pitch-up motions of the aircraft model. Further study, carried out by [PERSON] et al. [23], numerically simulated the planned landing of a transport airplane on the calm water and summarized that as the pitching angle increases, the maximal normal force and the pitching motion becomes much gentler. [PERSON] et al. [24] proposed a new global-moving-mesh (GMM) method based on [PERSON]'s work, and studied the ditching characteristics of transport aircraft (NACA2929 model). By using GMM method, [PERSON] et al. [4] further detailed the effects of initial pitching angle and initial descent velocity on the performance of aircraft water-landing in calm water. They concluded that the pressure distribution on the fuselage in the water region plays a decisive role in the water-landing process, the negative pressure around the rear part of the fuselage is attributed to the Coanda effect and can create a nose-up pitch motion, a larger initial pitching angle is recommended to improve safety due to that the larger initial pitch angle can lead to a smaller horizontal and vertical loads, and with the increase in the initial descent velocity, the impact peak value of the vertical load is of larger magnitude. Most aforementioned publications are limited to the calm water surface and mainly focus on the effects of the initial parameters on the aircraft and helicopter water-landing and ditching performance, including initial velocity and pitch angle. Recently, the aircraft wave-landing problem was gain attention by few researchers in the literature. In 2019, by using the SPH method, [PERSON] et al.