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Volume 14
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10.3390/jmse14020137
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This is an early access version, the complete PDF, HTML, and XML versions will be available soon.
Article

Effects of Aperture Ratio and Aspect Ratio on High-Speed Water-Entry Stability of Hollow Projectiles

by
Jianqiu Tu
1,2,
Yu Hou
3,*,
Haixin Chen
1,
Changjian Zhao
2,
Hairui Zhang
2 and
Xiaodong Na
4
1
School of Aerospace Engineering, Tsinghua University, Beijing 100084, China
2
China Academy of Launch Vehicle Technology, Beijing 100076, China
3
School of Electrical Engineering and Automation, Nantong University, Nantong 226019, China
4
National Key Laboratory of Transient Physics, Nanjing University of Science and Technology, Nanjing 210094, China
*
Author to whom correspondence should be addressed.
J. Mar. Sci. Eng. 2026, 14(2), 137; https://doi.org/10.3390/jmse14020137
Submission received: 14 November 2025 / Revised: 5 January 2026 / Accepted: 6 January 2026 / Published: 8 January 2026
(This article belongs to the Section Ocean Engineering)
Versions Notes

Abstract

The oblique water-entry stability of hollow projectiles with different aperture ratios (d/D) and aspect ratios (L/D) is investigated numerically in this study. The effects of aperture and aspect ratios on cavity evolution, hydrodynamic forces, and projectile motion are disclosed and discussed. When aperture ratios vary from 0.2 to 0.7, a larger aperture ratio results in a longer through-hole jet, earlier cavity closure, and a smaller cavity with less vapor. The best water-entry stability with minimal projectile deflection occurs at d/D = 0.3. For d/D > 0.4, the projectile tends to rotate clockwise and touch the surrounding cavity with a rapid increase in the lift, drag, and moment coefficients, accelerating the velocity decay. When aspect ratios vary from 2 to 7, the transition from stability to instability in the projectile motion is predicted at L/D = 2.75~3. A lower aspect ratio (L/D = 2) promotes stable motion with a steady drag coefficient (Cd ≈ 0.9) and negligible lift and moment. In contrast, the instability occurs at L/D = 3. However, when L/D > 3, the water-entry stability is enhanced with the increasing aspect ratio due to greater projectile mass. The inflection points in the hydrodynamic forces are also delayed and the hollow projectiles penetrate further.
Keywords: water-entry stability; hollow projectile; aperture ratio; aspect ratio; stability transition water-entry stability; hollow projectile; aperture ratio; aspect ratio; stability transition

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MDPI and ACS Style

Tu, J.; Hou, Y.; Chen, H.; Zhao, C.; Zhang, H.; Na, X. Effects of Aperture Ratio and Aspect Ratio on High-Speed Water-Entry Stability of Hollow Projectiles. J. Mar. Sci. Eng. 2026, 14, 137. https://doi.org/10.3390/jmse14020137

AMA Style

Tu J, Hou Y, Chen H, Zhao C, Zhang H, Na X. Effects of Aperture Ratio and Aspect Ratio on High-Speed Water-Entry Stability of Hollow Projectiles. Journal of Marine Science and Engineering. 2026; 14(2):137. https://doi.org/10.3390/jmse14020137

Chicago/Turabian Style

Tu, Jianqiu, Yu Hou, Haixin Chen, Changjian Zhao, Hairui Zhang, and Xiaodong Na. 2026. "Effects of Aperture Ratio and Aspect Ratio on High-Speed Water-Entry Stability of Hollow Projectiles" Journal of Marine Science and Engineering 14, no. 2: 137. https://doi.org/10.3390/jmse14020137

APA Style

Tu, J., Hou, Y., Chen, H., Zhao, C., Zhang, H., & Na, X. (2026). Effects of Aperture Ratio and Aspect Ratio on High-Speed Water-Entry Stability of Hollow Projectiles. Journal of Marine Science and Engineering, 14(2), 137. https://doi.org/10.3390/jmse14020137

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