Shock mitigation effects of cellular cladding on submersible hull subjected to deep underwater explosion

Highlights

• Shock resistance of coated submersible hull under deep water blast is investigated.

• Cellular claddings are very effective on mitigating shock damage of pressure hull.

• Stress enhancement appears when the cladding is fully densified.

• The effects of hydrostatic pressure on system response are discussed.

Abstract

Warships and submarines can be severely damaged by underwater explosion (UNDEX) shock loadings, so improving shock resistance ability of such weapons is of great importance. However, studies on the shock resistance ability of submersible hull subjected to deep UNDEX shock wave are rare. In this paper, the transient response of bare/coated submersible hull subjected to combined loads of hydrostatic pressure and shock wave is analyzed numerically by Abaqus, with special attention on shock mitigation capability of cellular cladding coated on the pressure hull. The local cavitation in water and transient response of bare and coated hulls are obtained. Additionally, the effects of the initially applied hydrostatic pressure on the system response are discussed. The results indicate that the cellular cladding coated on the pressure hull is very effective on reducing hull deformation, velocity and acceleration response, and the soft cladding is more effective than the strong cladding if the cladding is not fully densified. Otherwise, the stress enhancement appears which can amplify the local response of coated hull. The research results are useful in designing surface shields for submersible hull so as to enhance its resistance to underwater shock damage.

Introduction

Surface ships and submarines are routinely exposed to threats of underwater explosion (UNDEX). The transient response of ships/submarines subjected to UNDEX is a very complicated problem since it involves shock wave propagation, cavitation, fluid–structure interaction and nonlinear dynamic behavior of structure. To enhance shock resistance ability of such structures, we need to accurately predict the transient response of ships/submarines subjected to underwater shock loading and improve the strength of ship hull or design effective surface shields to protect the warships. In the past, there have been many studies to investigate the dynamic response of warships subjected to primary shock wave (Gong and Lam, 1999, Liang and Tai, 2006), bubble pulse load (Zhang et al., 2011, Zhang et al., 2014) and the combined loads of these two (Hung et al., 2009, Jin and Ding, 2011, Wang et al., 2014). Their studies demonstrated that such explosive loads can lead to large plastic deformation, overall damage of the ship and even break offs.

In recent years, researches on how to enhance naval vessels’ shock resistance ability attract more and more researchers’ interests. Two possible methods exist to enhance the shock resistance ability of warships: one is to improve the strength of the ship hull itself and the other is to design effective surface shields. Improving material or adding stiffeners can strengthen the ship hull. Kalavalapally et al. (2009) demonstrated that the stiffened torpedo performed better than the unstiffened torpedo under explosive pressure loads. Gong and Lam (1998) found that the composite hull surpassed over the steel hull in amortizing the effects of underwater shock wave. Recently, Gong and Khoo (2015) studied the transient response of composite and steel hull subjected to the bubble pulse and revealed that composite hull outperformed the steel hull. Fathallah et al. (2015) investigated the dynamic behavior of optimized composite elliptical submersible pressure hull to non-contact UNDEX. Surface shields are also proved to be effective in attenuating shock wave. Chen et al. (2009) experimentally demonstrated that a rubber sandwich layer coated on the metal box was efficient in mitigating water blast. Kim and Shin (2013) researched different surface shields and verified their shock resistance ability. LeBlanc et al. (2013) and LeBlanc and Shukla (2014) used a conical shock tube facility to explore the underwater blast response of polyurea coated composite plates. They found that the shock resistance ability of the composite plates is improved when coated by polyurea. Later, LeBlanc et al. (2015) experimentally studied the same structure subjected to near field underwater explosion and drew similar conclusions. Additionally, sandwich structures with cellular material cores possess a superior energy absorption capability and are widely used in resistance of shock/impact loadings (Xue and Hutchinson, 2004, Deshpande and Fleck, 2005, Liang et al., 2007, Schiffer and Tagarielli, 2014, Avachat and Zhou, 2015a, Avachat and Zhou, 2015b, Avachat and Zhou, 2013). Both mentioned above dealt with only the shock resistance ability of the shield itself or for simple structures, such as beam and plate. Literatures dealt with transient response of a submersible hull as well as shock resistance ability of sacrificial claddings coated on the pressure hull subjected to combined loads of hydrostatic pressure and shock wave, however, are limited.

Due to complicated physical phenomena involved in UNDEX, analytical method is extremely difficult and full-ship trials are costly and limited by environment. Therefore, numerical simulation is unavoidable for practical structures. The present paper aims to numerically study the transient response of bare/coated submersible hull subjected to deep UNDEX. The local cavitation in water, deformation mode of hull, pressure at the fluid–structure interface, velocity and plastic deformation of hull are presented. Specially, the shock mitigation effects of cellular cladding coated on the pressure hull are discussed in detail. In addition, the effects of initially applied hydrostatic pressure on the response of system is examined. The results are useful for designing effective surface shields for submersible hull to enhance its resistance to underwater shock damage. All analyses are performed by the non-linear finite element code Abaqus. The incident pressure from the explosive charge is obtained from the empirical equation of Cole (1948). Both initially applied hydrostatic pressure and UNDEX shock wave are taken into consideration.

An outline of this paper is as follows. In Section 2, the formulations of UNDEX load and fluid–structure interaction equations are described. Then the numerical model is validated in Section 3. In Section 4, the geometry characteristics, material properties and loading conditions of bare/coated submersible hull analyzed in this paper are presented. Section 5 provides comparisons and discussions on the typical transient response and shock resistance ability of bare/coated submersible hull subjected to the combined loads of hydrostatic pressure and shock loading. Finally, conclusions are presented in Section 6.