Key Takeaways & Executive Findings
- •• Preset bubbles on projectile trajectory induce secondary water-entry impact loads, altering penetration dynamics. • Rarefaction waves from bubble surface attenuate initial impact pressure peak by 68.8% and total specific impulse by 48.6%. • Larger bubbles and higher projectile velocities enhance global deformation attenuation (over 80%) but reduce local rear-wall protection. • Compressibility of bubbles is key to mitigating HRAM loads, but trade-offs exist for rear-wall perforation severity.
Abstract
In this paper, the failure caused by HRAM loads which were generated by high-speed projectile penetration, and protection technology of the fluid-filled structure were explored. A bubble was preset on the projectile trajectory in a fluid-filled structure. Based on the reflection and transmission phenomena of pressure waves at the gas-liquid interface and the compressibility characteristics of gases, a numerical analysis was conducted on the influence of preset bubble on projectile penetration and structural failure characteristics. The results indicate that the secondary water-entry impact phenomenon occurs when a preset bubble exists on the projectile trajectory, leading to the secondary water entry impact loads. The rarefaction waves reflected on the surface of the preset bubble cause the attenuation ratio of the initial impact pressure peak to reach 68.8% and the total specific impulse attenuation ratio to reach 48.6%. Furthermore, the larger the bubble, the faster the projectile, and the more obvious the attenuation effect. Moreover, due to the compressibility of the bubble, the global deformation attenuation ratio of the front and rear walls can reach over 80%. However, the larger the bubble size, the faster the projectile velocity, the smaller the local deformation attenuation effect of the rear wall, and the more severe the failure at the perforation of the rear wall.
1. Introduction
The impact and penetration of projectiles into fluid-filled structures may cause catastrophic consequences. There are many scenarios such as the impact and penetration of high-speed fragments into aircraft fuel tanks [1], the impact and penetration of spacecraft pressure vessels by space debris [2], and shooting of flammable or toxic liquid storage tanks [3] by terrorists. The impact and penetration of the projectile will generate a hydrodynamic ram (HRAM) effect in a fluid-filled structure, forming strong pressure waves and liquid flow. This effect, combined with the projectile’s effect, will cause large-scale fractures or bursts in the structure. Effectively controlling or alleviating the HRAM loads formed by high-speed projectile penetration while ensuring the integrity of fluid-filled structures has become an important direction of aircraft fuel tanks and other fluid-filled structures in the projectile resistance and protection design.
There are two main mechanisms for attenuating the HRAM effect in fluid-filled structures: impediment and load-off. Impediment refers to setting rigid bodies and energy-absorbing structures that disturb pressure waves along the transmission path. These bodies impede the direct action of HRAM loads on the inner wall of the fluid-filled structures, achieving attenuation and dissipation of HRAM loads. Disimile et al [4] installed four different geometries of triangular bars in the fluid-filled structure to reflect the shock wave and thus alleviate its failure effect on the subsequent structure. The experimental results showed that the peak pressure on the rear wall of the fluid-filled structure with the pressure mitigation system was reduced by 60% compared to that in the absence of the shock mitigating members. Wang et al [5] and Artero-Guerrero et al [6] conducted penetration experiments on novel perforated lattice fluid-filled structures and honeycomb aluminum structures, and found that the core layer's deformation and energy absorption process weakened the HRAM loads and reduced the bulging deformation of the outer wall of the fluid-filled structures. On this basis, Xu et al [7] embedded aramid fiber tubes in the honeycomb aluminum structure. The HRAM energy was simultaneously absorbed by the aramid tubes and honeycomb aluminum structure. Thereby, the HRAM loads were further weakened, and the ability of penetration resistance was enhanced.
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WU Meng-meng, HOU Hai-liang, LI Dian, LI Yong-qing, XIA Wei-xue, YANG Shao-hong (2025). Numerical Analysis on Influence of Preset Bubble in a Fluid-filled Structure on the Characteristics of Projectile Penetration and Structural Failure. SinoTechIntel Verified Research. https://doi.org/10.3969/j.issn.1007-7294.2025.06.007
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Frequently Asked Questions
What is the purpose of the preset bubble in the fluid-filled structure?
The preset bubble is placed on the projectile trajectory to attenuate the hydrodynamic ram (HRAM) loads generated during high-speed projectile penetration. It leverages gas-liquid interface wave reflection and gas compressibility to reduce pressure peaks and structural deformation.
How does the preset bubble affect the initial impact pressure?
The preset bubble causes rarefaction waves that reflect from its surface, leading to a 68.8% attenuation of the initial impact pressure peak and a 48.6% reduction in total specific impulse.
What are the trade-offs of using larger bubbles?
Larger bubbles enhance global deformation attenuation (over 80%) but reduce the local deformation attenuation effect on the rear wall, leading to more severe failure at the perforation of the rear wall.
What is the secondary water-entry impact phenomenon?
When a preset bubble exists on the projectile trajectory, the projectile may experience a secondary water-entry impact as it passes through the bubble, generating additional impact loads that influence the penetration and failure characteristics.
What is the significance of this research for protective design?
This research provides insights into using preset bubbles as a passive mitigation strategy for HRAM loads in fluid-filled structures, such as aircraft fuel tanks, to enhance their resistance to projectile penetration and reduce catastrophic failures.
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