Water-entry behavior of projectiles under the protection of polyurethane buffer head

The water entry behaviors of projectiles with cylindrical buffer head were studied experimentally and theoretically, focusing on projectile dynamics and impact reduction. Based on the elastic, perfectly plastic, strain rate dependent, compacting model, the equation of motion was developed for the projectiles to describe their motion before compaction of the buffer. The validity of the equation was proven both experimentally and numerically. The peak deceleration of the projectiles was investigated by numerical simulations in LS-DYNA using Lagrange–Euler coupling, and an empirical formula was proposed to accurately describe the impact reduction based on the experimental and numerical results. When the impact velocity and buffer dimension were held constant, an optimum buffer density existed for the reduction of impact by the buffer head. At a constant buffer density, the impact was larger when the initial velocity increased or when the buffer had a larger cross section compared with its length. Good agreements were observed between the analytical and experimental results.