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• Underwater explosion induced cavitation near sacrificial coatings are studied. • RKDG-FE-GFM-IsenCav is developed to study the cavitation effects. • Five benchmark problems are studied. • Effects of geometrical and physical properties of the model are discussed. The load resulting from cavitation collapse is a major threat to structures exposed to underwater explosions. Protective structures for warships, such as sacrificial coatings, which are sandwich structures attached to the wet face of the ship hull. They have energy absorbing cores made of cellular or composite materials that can significantly influence the effects of cavitation. In this study, a physical model consisting of water, an explosion bubble, and a sacrificial coating is established to investigate the effects of cavitation near sacrificial coatings subjected to underwater explosions. A numerical method is developed that couples the Runge-Kutta discontinuous Galerkin method, the finite element method, a Ghost Fluid Method-based numerical technique, and an isentropic one-fluid cavitation model to capture the physical phenomena of shock wave propagation, cavitation inception, expansion and collapse, and explosion bubble expansion and contraction. To ensure the accuracy of the mathematical model, five benchmark problems and a convergence test of the numerical solution are studied. The study comprehensively discusses the influences of core strengths, face sheet thickness, stand-off distances, and structure curvature on the evolution of the cavitation region, pressure profiles near the structure, and structure responses. [ABSTRACT FROM AUTHOR]

• This work deals with the shock mitigation effects of sacrificial coatings plastered on the stiffened double cylindrical shell. • The physical experiments of a stiffened double cylindrical shell under non-contact underwater explosion are carried out. • The coating on the thin hull plays the key role to mitigate shock loadings while the coating on the pressure hull has limited effects. Underwater explosion shock loadings can seriously damage the vitality and fighting capacity of warships. Plastering a layer of sacrificial coating on the ship hull is one of effective strategies to isolate shock impulses and absorb shock energy. In this paper, the shock mitigation effects of sacrificial coatings plastered on a stiffened double cylindrical shell are analyzed numerically. The numerical models are validated by conducting a series of physical experiments of a stiffened double cylindrical shell under noncontact underwater explosion. Three different configurations are considered: both the pressure and thin hulls are plastered with sacrificial coatings; only the thin hull is plastered with sacrificial coatings; and only the pressure hull is plastered with sacrificial coatings. The total pressure field in water and the dynamic response of the stiffened double cylindrical shell are obtained. The results indicate that the deformation and motion of the sacrificial coatings can more easily generate rarefaction wave, which can decrease the total shock impulse acting on the structure. Among three configurations, the configuration of the coating plastered on the thin hull has a better capability of isolating the shock impulse and reducing the shock loadings transmitted to the pressure hull. The dynamic stress and velocity responses of the shell are effectively decreased. Comparisons between different configurations suggest that the coating on the thin hull plays a key role in mitigating shock loadings, while the coating on the pressure hull has limited effects. Moreover, comparison results between the bare hull and the equivalent model which increases the thickness of the thin or pressure hulls under the same mass conditions indicate that the method of using a sacrificial coating is more effective in improving the blast resistance of the structure. The research results are useful in guiding the shock resistance design of stiffened double cylindrical shells. [ABSTRACT FROM AUTHOR]

Near-field underwater explosions can cause serious local damage to ship hulls. A protective shield sticking on the outer surface of a ship hull can effectively attenuate the shock loadings from these explosions. The present paper aims to experimentally and numerically analyze the anti-shock effects of a protective shield, which consists of rigid polyurethane foam (R–PUF) with certain thickness, and thin rubber skin, coated onto a circular plate in a near-field underwater explosion. The underwater explosion experiment was conducted in a man-made lake for both the bare and coated circular plates. The experimental results indicate that the protective shield can reduce the overall deformation of the circular plate by 41.1% on average under the experimental conditions. Then a Eulerian compressible fluid model is developed and used in combination with Abaqus/Explicit software in a numerical simulation to explore the anti-shock effects of protective shields. The overall deformation, velocity and displacement of the circular plate, and the pressure and velocity of the fluid are calculated. Comparisons between the experimental results and numerical simulations indicate that the developed compressible fluid model can effectively calculate the fluid response and the overall deformation of the circular plate effectively. The simulated results illustrate that the protective shield can effectively mitigate the peak value and the duration of pressure on the wetted surface in the initial stage. Then, two situations are considered to deeply investigate the shock mitigation effects of the protective shield. When the protective shield is kept unchanged while the detonation distance is changed (situation I), it was found that softer protective shields are needed for far detonation distance while stronger protective shields are needed for near detonation distance. Moreover, when the shock environment remains unchanged and the mechanical properties of the protective shield are changed (situation II), it was found that the protective shield should be as soft as possible to generate a sufficient energy absorption capacity. These research results are useful in protective shield design for ship hulls subjected to near-field underwater explosions. • The anti-shock effects of rigid polyurethane foam to near-field underwater explosion are analyzed. • A compressible fluid model is developed to solve the near-field underwater explosion problem. • The matching between the strength of the protective shield and the shock environment has significant influences on the anti-shock effects. [ABSTRACT FROM AUTHOR]