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Purpose: Fragment impact is one of the main threats for the safety of storage tank in aircraft. This study aims to investigate the influence of inserted baffle on hydrodynamic ram (HRAM) and damage of storage tank to optimize the protective performance of storage tank under fragment impact. Design/methodology/approach: The characteristics of initial shock wave, cavity evolution, velocity attenuation of fragment and anti-penetration performance of baffle-inserted tanks were evaluated by experimental and numerical methods. Findings: Results indicated that the inserted baffle in tank could significantly increase the velocity attenuation rate of fragment in water. The volume of the second cavity caused by the inserted baffle rapidly decreased with the baffle position moving backward. For the baffle-inserted tank, the deformation of the front and rear walls was substantially weakened, and the alleviating effect for front wall was more significant. Comparing with the ordinary storage tank, the inserted baffle at normalized position 0.25, 0.5 and 0.75 in tank made the ballistic limit velocity of storage tank increasing by 118.3%, 20.0% and 54.0%, respectively. Originality/value: The findings of this work illustrating the HRAM history and damage map of storage tanks after inserted baffle could provide a convenient approach to improve the anti-penetration performance of storage tanks effectively. [ABSTRACT FROM AUTHOR]

In this investigation, a series of experiments were carried out by using aluminum, steel and tungsten spherical projectiles to vertically impact a water-filled tank at a speed of 448.5–1018.2 m/s. The effects of impact velocity and sphere density on cavity, shock wave and motion characteristics of spheres were studied based on the shadowgraph visualization technology and digital image processing. Experimental results showed that for the same density of the sphere, as impact velocity increases, the time of surface closure gets longer and the cavity size becomes larger. In particular, the depth where the maximum cavity diameter occurs and the average velocity of cavity wall section are not significantly affected by the impact velocity. The higher the impact velocity is, the larger the peak pressure of the initial shock wave gets, the longer the penetration distance is, and the greater the velocity decay becomes. Additionally, when the impact velocity of the sphere is fixed, with the increase of sphere density, the time of surface closure gets longer and the cavity size becomes larger. It is worth noting that the deeper the maximum cavity diameter appears, the slower the average cavity wall velocity changes. The sphere of greater density produces relatively larger peak pressure of the initial shock wave, and undergoes longer entry distance and less velocity decay for the same entry time. Furthermore, an analytical model of cavity evolution was developed and good agreement was found between the experimental results and model predictions. • A shadowgraph visualization system is designed to visualize the shock wave front. • The methods of experimental date processing for vertical water entry are proposed. • The effects of impact velocity and sphere density on water entry are analyzed. • An analytical model of cavity evolution is developed and verified its validity. [ABSTRACT FROM AUTHOR]

Hydrodynamic ram (HRAM) is a phenomenon that occurs when a high-speed projectile penetrates a fluid-filled tank, where the energy transferred to the liquid could result in a catastrophic failure and excessive structural damage. It is essential to take physical comprehension of the hydrodynamic effects that occur during an HRAM event in the civilian domain as well as for the military aircraft design, which would in fact contribute to design better structures with respect to this particular threat. For this present work, the HRAM due to cavity evolution in confined vessels under ballistic impact by projectiles was investigated through theoretical analysis combined with experimental results. Taking the confinement effects due to the limited size of the fluid-filled vessel and corresponding structure deformation into account, a model is proposed to describe the pressure between the liquid and vessel wall along the penetration trajectory based on cavity dynamics analysis. By studying relevant parameters, changes of wall pressure, non-dimensional disturbance range and energy of two extreme containers, (namely, non-pressure resistance containers and rigid containers without deformation) were examined. The results show that the cavitation pressure has less intense peak but much greater temporal extent compared with the pressure generated during the shock stage, thereby the cavity pressure impulse induced by cavity evolution is a non-negligible factor affecting the deformation and failure of a fluid-filled vessel. The aim of the present work is to reveal the mechanism of the pressure acting on the container wall caused by cavity evolution rather than the initial shock wave in an HRAM event, which will help to study the nature of hydrodynamic ram and understand the role of the cavitation pressure in the damage or deformation of liquid-filled vessels under projectile impact. • Considering the vessel deformation, an energy conservation equation is built. • A model is proposed to describe the wall pressure induced by cavity evolution. • The cavitation pressure distribution along the penetration trajectory is studied. • Energy distribution along the penetration trajectory is studied. • Vessel size confinement effect on cavity evolution is analyzed. [ABSTRACT FROM AUTHOR]

To provide a general view of how the shock waves propagate and multi-reflect in a water-filled tank, a discrete method for the propagation of shock waves produced by high-speed projectile water entry was proposed based on the law of reflection in this present study. This method was employed to analyze the composition of shock wave fronts at typical moments, the reflection history of any point on the reflected wave front, and the reflection history of points on the arc of a continuous reflected wave front without inflection. Meanwhile, a shadowgraph visualization system for shock waves induced by high-speed projectile water entry was designed and used to capture the shock wave front propagation in the water-filled tank. So that, the images and the wave fronts obtained by the discrete method were combined to analyze the propagation characteristics of the shock wave produced by projectile water entry. Good agreements were found between the theoretical predictions and experimental results. • A discrete method for shock wave propagation in a water-filled tank was proposed. • The composition and reflection history of shock wave fronts were analyzed. • A shadowgraph visualization system for shock waves was designed. • Good agreements were found between the theoretical and experimental results. [ABSTRACT FROM AUTHOR]

As the main defense component of the ship against the attack of external damage sources, the liquid cabin will inevitably suffer some damage like holes or cracks in the battle because of the explosion fragments or the penetration of high-speed projectiles. The research on the rest capacity and dynamic response of the cabin with different damage cracks due to the underwater explosions is of great significance to the improvement of the protection design of cabin structures and the development of the fluid-solid coupling theory. For the sake of simplicity, an aluminum thin-walled plate with central prefabricated crack was adopted to solve the problem on coupling loads induced by underwater explosion, and an underwater shock wave tube was used to substitute an underwater explosion load to generate the shock loading on thin-walled aluminum plate. The shock wave pressures in the underwater explosion tube and the dynamic deformation responses of aluminum thin-walled plates with central prefabricated crack were recorded by three pressure sensors and two high-speed cameras, respectively. By analyzing experimental results, the history characteristics of the dynamic increase of plastic bulge height and the crack propagation of the aluminum plates were obtained. The results show that the time of the crack growth and the bulge increasing are not synchronized in the dynamic response of thin-walled plate; in addition, the effects of the crack shape and size on the bulge and the crack growth in dynamic response of target plate can be attributed to the trade-off between the energy leakage and the bending stiffness of the target plate. Finally, according to the velocity and acceleration on the target and based on a plastic-rigid material model, we obtain that the target bending angle sine is linear with the radial distance, and the conclusion was well validated by experimental target bending angle data. • Pre-cracked plate's shock impact is a good experimental method to study the explosion coupling loads. • DIC displacement results, and the kinetic derived parameters are valuable to research the dynamic responses of pre-cracked plates. • In the final plastic shapes of thin-walled cracked plates, the bending deviation angle's sine is linear with the radial distance. [ABSTRACT FROM AUTHOR]