Investigation of underwater explosion near composite structures using a combined RKDG-FEM approach

Abstract

A combined RKDG-FEM approach, using the Runge-Kutta discontinuous Galerkin (RKDG) method [1,2] for fluid simulating and the finite element method (FEM) [3,4] for structure simulating, is developed to study the complex interactions between compressible multiphase flows and deformable steel and composite structures in near-field early-time underwater explosion (UNDEX). The level set method (LSM) [5,6] and the real ghost fluid method (RGFM) [7,8] are applied to capture and treat the moving gas-water interface, respectively. A GFM-based interface treating scheme [9,10] is adopted to treat the fluid-structure interface, achieving the coupling by solving simultaneously the fluid characteristic equation and the structure equation of motion at the material interface to satisfy the kinematic compatibility and pressure equilibrium conditions. The isentropic one-fluid cavitation model in [11] is employed to capture the transient flow cavitation. Accuracy and effectiveness of the combined RKDG-FEM approach are validated by five benchmark cases, and then it is applied to simulate early-time UNDEX problems near a submerged aluminum foam-cored sandwich plate and a monolithic steel plate of equivalent mass. Numerical results show that the sandwich plate has a higher underwater explosion load resistance through absorbing plastic energy by the foam core than the monolithic steel plate of equivalent mass, and that the foam core plays an important role in the fluid-structure interaction (FSI) and flow cavitation effects, which can be exploited to improve the UNDEX mitigation capability of composite sandwich structures.