On the interaction between the underwater explosion and the double-layer structure with an orifice on the outer plate

High-speed metal jets induced by shaped-charge warheads in underwater weapons may initially damage the bottom of a ship. Subsequently, the load from a subsequent underwater explosion (UNDEX) can lead to secondary impacts on the compromised structure. This study delved into the strong nonlinear fluid-structure interaction in this process through numerical investigation. Utilising the coupled Eulerian–Lagrangian method (CEL), a model was established by validating experimental data. The response of a double-layer structure with an orifice on the outer plate was analysed by varying the charge distance, orifice radius, and charge weight. Our findings indicated that: (1) Intermittent flooding water affects the inner plate with the pulsation of the UNDEX bubble; (2) The outer plate undergoes upward arch deformation due to the load from flooding water, while the inner plate demonstrates periodic oscillatory deformation; (3) Near-field explosions cause bubbles to adopt an inverted mushroom shape, splitting into two sub-bubbles during collapse, accompanied by the appearance of opposite jets; and (4) The impact of flooding water through the orifice is the primary factor causing deformation of the inner plate. Furthermore, the deformation of the plate exhibited nonlinear behavior with the orifice radius. This study offers insights into new damage patterns in double-layer structures of ships.