Structural design of a slotted wrapping buffer head cap of vehicles and its load reduction performance

In order to solve the problems of structural damage and ballistic runaway caused by huge impact loads suffered by air-drop vehicles and rocket-assisted vehicles during high-speed water-entry, a slotted wrapping buffer head cap was proposed to guarantee the structural safety of the vehicles during water entry. Firstly, the structural composition and detailed parameters of the head cap were given, and a numerical model for the high-speed water-entry of the vehicles was established based on the arbitrary Lagrangian-Eulerian (ALE) algorithm. The Lagrangian viewpoint was used to solve the small deformation of the vehicle and the head cap, and the Eulerian viewpoint was used to capture the large deformation of the free surface such as water and air, thereby overcoming the problems that the Eulerian mesh was not accurate enough to solve the structural deformation and the numerical oscillation caused by mesh distortion in solving large deformation problems by the Lagrangian mesh. On this basis, the evolution processes of the cavity and flow field around the vehicle entering the water with the head cap at different angles were studied by numerical simulation, and the interaction process between the head cap and the water was given. Furthermore, the distribution of effective stress of the buffer was analyzed when it entering the water vertically and obliquely. Finally, the load reduction performances of the head cap when the vehicle entered the water at different velocities and angles were investigated. The results show that the cavities obtained by the simulation are basically consistent with the experimental images, and the change trends of impact acceleration are basically consistent with the experimental results. The relative error of the axial peak acceleration between the numerical simulation and experiment is 6.72%, and the relative error of the radial peak acceleration is 7.52%. The ratio of axial load reduction is 22.17% when the vehicle enters the water vertically with a head cap at 300 m/s. At the same time, the ratio of axial load reduction is 31.83% and the ratio of radial load reduction is 66.80% when the vehicle with a head cap enters the water at 100 m/s and 60°. So this research has a certain guiding role in the design of new load-reduction structure. © 2022 Explosion and Shock Waves. All rights reserved.