Multi-objective optimization of elliptical variable-section projectile for armor-piercing and penetration performance via NSGA-II

High-speed non-circular cross-section projectiles can effectively damage various targets，including semi-infinite concrete structures and thin-walled metal structures. Structural optimization design for such projectiles has become an important research direction in the field. For semi-infinite concrete structures, projectile penetration performance is mainly reflected by penetration depth; for thin-walled metal structures, it is indicated by anti-ballistic deflection capability. To improve the adaptability of elliptical variable-section projectiles to thin metal and semi-infinite concrete targets, this study optimizes their structural parameters. It uses an attitude deflection model for thin-layer metal targets and a penetration depth model for concrete targets to predict deflection angle and penetration depth, respectively. The NSGA-II algorithm is applied to optimize shape parameters, including caliber-radius-head (CRH), length-to-diameter ratio, major-to-minor axis ratio, and variable cross-section angle. The influences of impact velocity, initial oblique angle, and initial attack angle on optimization are also analyzed. Results show that anti-ballistic deflection and deep penetration capabilities compete with each other. A two-segment non-linear curve with a critical point exists between deflection angle and penetration depth. Higher initial velocity raises the upper limit of optimized performance, while larger absolute oblique and attack angles reduce it. Longer, sharper-nosed projectiles with smaller variable cross-section angles and flatter cross-sections have better penetration performance, and the opposite improves armor-piercing performance.