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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]

• Precise velocity fields solved by two-dimensional multi-physical coupling model. • A porous electrode layer to describe the mass transfer resistance. • Polarization current curves precisely reproduced under different rotation speeds. • An improved Tafel method to obtain more intrinsic transfer coefficient. Rotating disk electrodes with porous layers are commonly used to obtain the oxygen reduction reaction kinetic parameters. In this paper, to eliminate the severe error in the intrinsic reaction kinetic measurement of porous layers of the rotating disk electrode, a flow-electrochemical multi-physical model with porous electrode layer is developed for the detailed simulation of the mass transfer and electrochemistry reaction process. The multi-physical model is solved by finite element method, whose results are validated with the porous electrode layer generated by NGHMs. It turned out that the multi-physical model can reproduce the results of physical experiments by fitting the effective diffusion coefficient in the porous structure. Based on this model, the classical Tafel method is improved, so that it can be applied to porous electrodes and more accurate intrinsic reaction kinetic parameters can be obtained as a result. All of the above proves that the measurement accuracy of the electrocatalytic performance of porous rotating disk electrode can be greatly enhanced. [ABSTRACT FROM AUTHOR]

A numerical procedure that couples the Runge–Kutta discontinuous Galerkin method (RKDG), the boundary element method (BEM) and the finite element method (FEM) is developed to study the dynamics of an underwater explosion bubble near a sandwich structure efficiently and accurately. The numerical approach is validated by a near-field underwater explosion experiment. The numerical predicted bubble shape, cavitation and the free field pressure are in good agreement with the experimental results. The validated code is then used to determine the effects of the foam core strengths, the stand-off distances and the boundary condition of the back face sheet on the fluid response, the bubble behaviors, and the deformation of the sandwich structure. The results are beneficial for guiding the design of the protection structures. • Dynamics of an underwater explosion bubble near a sandwich structure is studied. • A numerical procedure that couples RKDG, BEM and FEM is developed. • Deformation of sandwich structures has significant effects on the bubble behaviors. [ABSTRACT FROM AUTHOR]

One-dimensional (1D) response of single/double-layer cellular claddings to water blast, including the core crushing, fluid-structure interaction (FSI) and cavitation phenomenon, is investigated by analytical approaches and finite element (FE) simulations. Analyses are focused on the shock mitigation mechanism of cellular cladding and optimization design of double-layer cladding (DLC) with particular interests in shortening cladding thickness without increasing the transmitted stress to the main structure. It is demonstrated that the actual incident wave impinged on the cladding and interface pressure at the wet face are highly dependent on the core crushing, FSI effects and cavitation phenomenon under identical incident wave. The actual incident wave will be enhanced due to the collapse of cavitation bubbles, especially for soft core. The total pressure at the wet face typically exhibits a rapid decline followed by a long pressure plateau whose value approximately equals to the quasi-static stress of the core being compressed. The high pressure loading incident on the cladding is converted into a lower magnitude load with much longer duration, which is beneficial for shock mitigation. Parametric analyses of the single-layer cladding (SLC) indicate that strong core cladding can largely shorten the total foam thickness needed to dissipate the shock energy. However, the transmitted stress to the main structure increases correspondingly. Therefore, a DLC with strong core being placed at the impinged end is proposed to shorten the foam thickness without increasing the transmitted stress. Comparisons of shock mitigation ability between the DLC and its single counterpart are conducted in terms of the total foam thickness, partial impulse imparted to the cladding and absorbed energy. The results reveal that the DLC can absorb more energy and reduce the total foam thickness when the face sheet of the soft core is properly designed. Finally, design guides for the DLC against water blast are presented. [ABSTRACT FROM AUTHOR]

In previous studies, the response of sandwich structures to water blast is solved by envisaging the plate adjacent to water as a rigid one, while the effects of the elasticity in the longitudinal direction of the plate are rarely studied. In this paper, a monolithic elastic coating with varying stiffness and thickness is investigated by a one-dimensional analytical approach, based on linear wave motion theory, to reveal the elastic effect of the plate on the incident wave. One side of the coating is loaded by a planar shock wave; on the opposite side, rigid boundary or air-backed boundary is imposed. The fluid–structure interaction (FSI), cavitation phenomenon and large deformation of the coating are taken into account. In particular, the initiation and evolution of cavitation, including the propagations of breaking fronts and closing fronts, as well as the pressure histories of radiated wave by the closing front, are examined. The analytical solution has been compared with finite element (FE) predictions. The results are found to be in excellent agreement for the propagation of breaking front and closing front, as well as the pressure and particle velocity histories at the wet face before the cavitation reaches the wet face. However, when the wet face cavitates, the predictions provided by the analytical method are less accurate and the analytically-computed particle velocity can only be compared in an average sense with the FE predictions. For air-backed case, Taylor׳s model prior to cavitation becomes a trivial case of the analytical model and the comparison also indicates the validity of the analytical model. The validated analytical model is used to determine the dependence of the peak pressure at the wet face and the impulse transmitted to the coating on the coating properties, including the wave impedance and thickness. [ABSTRACT FROM AUTHOR]