Experimental and theoretical studies of after flow load effects on the hull girder damage in underwater explosion

The after flow induced by underwater explosion (UNDEX) plays an important role on the damage of ship structures, particularly in the near-field explosion. In this paper, the damage experiments of the hull girder were conducted at detonation distances of R/R0 = 6, 10, and 17, and a dynamic model was established to study the hull girder deformation considering the after flow. It shows that the numerical simulations have a good agreement with the experimental results of the hull girder deformation, which increases nonlinearly as the distance decreases due to the contribution of the after flow to the nonlinear growth of structural damage. It further demonstrates that the after flow has the most pronounced influence on the overall deformation at the closest distance (R/R0 = 6), with the after flow caused by bubble expansion playing a dominant role. Critically, due to the most contribution of the after flow to the total wall pressure and its continuous energy input, the after flow increases the maximum deformation by 79.3% compared with the numerical results that exclude it at this distance. Notably, the after flow caused by bubble expansion alone accounts for an additional 87.1% final deformation increment. This research provides significant insights into the structural damage mechanism caused by near-field UNDEX loads.