Study on water entry of a 3D torpedo based on the improved smooth particle hydrodynamics method

Abstract

Abstract The water entry of a torpedo is a complex nonlinear problem, involving transient impact, free surface deformation, droplet splashing, and fluid-solid coupling, which poses severe challenges to traditional mesh methods. The meshless smooth particle hydrodynamics (SPH) method shows unique advantages in capturing the complex features of the water entry of the torpedo. However, it still suffers from some inherent shortcomings, such as low surface discretization accuracy, poor discretization flexibility, and low calculation efficiency. In this study, an improved adaptive SPH algorithm is proposed to accurately and efficiently investigate the water entry of the torpedo. This method integrates meshless point generation and adaptive techniques simultaneously. Numerical results demonstrate that when the torpedo vertically enters the water at different velocities, the induced impact loads acting on the head of the torpedo fluctuate significantly with two peak values at the initial stage and thereafter stabilize at a later stage. The impact load acting on the torpedo, the entry depth of the torpedo, the splash height of the droplets, and the size of the cavity generated around the torpedo increase with the increment of the entry velocity. When the torpedo enters the water at different enter angles under the same initial enter velocity, both the vertical and the horizontal movements of the torpedo are observed, which results in more complex variations of parameters along the x- and y-axes. The findings and the corresponding numerical method in this study can provide a certain basis for the future designs of the entry trajectory and the structural bearing capacity of torpedoes.