Research on leading-vehicle-based force reduction for main vehicle in vertical water entry

Crossing the air–water interface during water entry subjects vehicles to severe impact forces, posing significant risks such as structural vibration, large deformation, and motion instability. To mitigate these effects, this study proposes a tandem water entry strategy utilizing a perforated leading vehicle to reduce impact forces. The main vehicle vertically penetrates the cavity wall formed by the leading vehicle, thereby attenuating impact forces. The water entry process is simulated using the delta-smoothed particle hydrodynamics ($\delta$-SPH) method, whose convergence and accuracy are verified against experimental results. Analysis of main cavity evolution, pressure distribution, and water-jet impacts elucidates the force reduction mechanism of the tandem strategy. Furthermore, the influences of the leading vehicle’s initial velocity and attitude angle on the main vehicle’s impact forces are investigated. Results demonstrate a reduction in peak axial force of up to 90% while ensuring collision avoidance. Increasing the relative attitude angle between vehicles and the initial velocity ratio further minimizes collision risk. These findings offer valuable insights for developing efficient and operationally feasible impact force reduction techniques.