It is essential for the launch of polar ocean detectors to study the water entry behavior of projectiles passing through underwater ice-holes. In this paper, numerical simulation combined with overlapping grid technology and a volume-of-fluid (VOF) model is used to study the cavity dynamics of projectiles passing through under-water ice-holes, and the variations of velocity circulation and the movement stability of the projectile are also studied. The results show that the cavity experiences the process of first shrinking and then expanding when the projectile passes through the underwater ice-hole, and unique "cavity splash crown " and "combined cavity " are generated. The presence of the hole affects the velocity circulation and vector around the projectile. The pa-rameters of the holes have a strong influence on the cavity dynamics. When a projectile passes through a large -sized underwater ice-hole, the cavity size inside the hole (hnr) increases, the cavity size at the upper border of the hole (hur) decreases, and the cavity length (hcr) after pinch-off increases; additionally, the amplitude of force and velocity fluctuations decreases, and the projectile's movement stability increases. The ability of the cavity at the top border of the hole to expand and contract is reduced when the hole is farther away from the free liquid surface, the area of the cavity that wraps the projectile after pinch-off is also reduced, and the trajectory of the projectile shows obvious deflection during this process.
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