# Study on the Interference Process of Liquid Radial Reflux on the Stability of a Shaped Charge Jet
## 1 Introduction  
A thin-walled, liquid-filled structure will demonstrate large deformation, tearing, or even complete failure when impacted by a high-speed projectile. This phenomenon is called the water hammer effect [1] because the incoming projectile will transform its kinetic energy into deformation energy of the shell through the liquid, which can lead to shell deformation and failure, to achieve structural damage. The water hammer effect makes thin-walled liquid-filled structures, such as aircraft and ship tanks, become one of the main attack targets on the battlefield. However, recent studies have found that the liquid-filled structure can also be used to resist the impact of high-speed penetrators such as a shaped charge jet (SCJ), when the constraint is strong. The liquid-filled composite structure (LFCS), a new type of protective structure, has gradually attracted the attention of scholars in the field of impact protection. Scholars have conducted thorough theoretical studies, simulations, and tests on the dynamic response process of kinetic energy projectiles impacting liquid-filled structures, focusing on the velocity attenuation of the projectiles, cavitation dynamic characteristics, liquid pressure distribution, and energy-absorbing deformation of the shells. [PERSON] et al. [2, 3] studied the bubble and fluid dynamic characteristics of an oil tank under the impact of fragments through numerical simulation. [PERSON] [4] investigated the liquid pressure distribution and shell deformation of aluminum square tubes with different liquid level heights under the impact of spherical projectiles with different velocities. [PERSON] [5] analyzed the change in shock wave pressure, bubble drag pressure, and hole wall during penetration of a high-speed bullet in an open liquid container. [PERSON] [6] used the simulation method to analyze the container deformation, liquid dispersion, and residual velocity of the projectile when the liquid-filled container was affected by the impact. [PERSON] [7, 8] analyzed the liquid dispersion after projectile impact on an oil tank by using high-speed camera technology and studied the damage characteristics of the simulated oil tank under a shock waveafter a 12.7 mm tungsten ball impact. [PERSON] [9] investigated the characteristics of a liquid spurt caused by the hydrodynamic ram in an experiment, which revealed the impact of high-velocity fragments on a liquid-filled container. [PERSON] [10] compared the hydrodynamic ram caused by one and two spherical projectiles impacting water-filled containers by using a numerical model. The interaction between the projectile and the LFCS is the dynamic impact response of the projectile to the LFCS, while its opposite is the interference of the LFCS in the projectile. The interference modes of an LFCS in different projectiles vary. A kinetic energy projectile, such as a long-rod projectile, and the fragments in the liquid will be subjected to resistance caused by the pressure difference between the head and the tail of the projectile and the viscosity of the liquid; the kinetic energy of the projectile is converted into kinetic energy of the liquid and finally into its potential energy and the deformation energy of the shell [11]. The movement trajectory of the projectile will also be changed by the interference of the liquid. In contrast, the LFCS mainly causes lateral interference in the SCJ through the convergence and reflux of the liquid driven by the shock wave, which results in necking fracture of the jet, thus reducing its penetration capability and realization of a high protection level. The use of an LFCS to resist the SCJ can play the role of replacing the rigid with the soft and meet the lightweight requirement of a protective structure. Therefore, the interference process of the LFCS in the SCJ must be studied for the application of an LFCS in the field of protection engineering. In recent years, scholars have conducted studies on jet penetration in liquid or liquid-filled structures successively.