A volume-adaptive smoothed particle hydrodynamics (SPH) model for underwater contact explosion

Underwater explosions can generate substantial dynamic loads, leading to damage or failure of solid structures such as submarine pipelines. This process involves the interaction of high-pressure explosion products, water, and solid structures, characterized by transience, multi-phase interaction, and large deformations. In this study, a Lagrange mesh-free method called Smoothed Particle Hydrodynamics (SPH) is employed to establish a fluid-solid interaction (FSI) model for underwater contact explosions. The SPH discrete equations of governing equations of continuum media including fluid and solid are constructed as anti-symmetric forms based on the particle approximation technique and kernel gradient correction scheme. The equation of state is presented to describe the material response in strong interactions for the explosive, water, and solid, respectively. To simulate solid plasticity, the Johnson-Cook constitutive models are integrated into the SPH procedure to capture the behavior of large deformation and damage of metal structures. To address the issue of drastic changes in particle spacing caused by suddenly expanding gas, a modified particle regeneration technique (M-PRT) is proposed to refresh SPH particles in the gas domain according to the volume change rate. The first-order Moving Least Squares (MLS) approach is used to update the variables of refreshed particles, thus the linear variation of field variables is reproduced. The accuracy of the model is verified through several examples, including free-field underwater explosions, near-wall underwater explosions, and underwater contact explosions.