Investigation and optimization of load characteristics of a multi-stage load-reduction structure for vehicles during high-speed vertical water entry

Abstract

Vehicles are subjected to intense impact loads during water entry at high speed, so some appropriate measures are taken to reduce the impact response of the structure. In this paper, a multi-stage load-reduction structure composed of foam aluminum and cavitation structure is designed to improve the load characteristics of high-speed vehicles. Its three-dimensional numerical model is established based on the Coupled Euler-Lagrange (CEL) method. The accuracy of the numerical simulation was verified by comparison with various experimental results of the sphere and AUV head section, and irrelevant grids were obtained. The simulation of a vehicle with and without a multi-stage load-reduction structure was carried out to study the load characteristics under the influence of different parameters such as vertical velocity and relative density of foam aluminum. Researches were also carried out to select the optimal parameters. The results show that the impact acceleration and the optimal density increase synchronously with the initial velocity. The installation of the multi-stage structure transforms the single impact of direct water entry into three reduced acceleration peaks, and finally realizes the load reduction. When the velocity is 100, 200 or 300 m/s, the load reduction rates under the optimum density are up to 84.6%, 83.7% and 79.3%.