A study of energy transfer during water entry of solids using incompressible SPH simulations

Cavity formation during water entry of a solid corresponds to the deceleration experienced by the solid. Several experimental studies in the past have facilitated qualitative understanding of the relation between flow and impact properties and the type of cavity formed. The types of cavities formed are classified primarily based on the nature of the seal, such as (a) surface seal, (b) deep seal, (c) shallow seal and (d) quasi-static seal. The flow mechanism behind these features and their effects on the speed of the impacting solid require further quantitative understanding. A study of such phenomenon is difficult using the existing CFD techniques owing to the fact that the high density ratios between the two phases, namely water and air, bring in issues with respect to the convergence of the linear system used to solve for the pressure field for a divergence-free velocity field. Based on a free surface modeling method, we present Incompressible Smoothed Particle Hydrodynamics (ISPH) simulations of water entry of two-dimensional solids of different shapes, densities and initial angular momenta. From the velocity field of the fluid and shape of the cavity, we relate the transfer of kinetic energy from the solid to the fluid through different phases of the cavity formation. Finally, we present a three-dimensional simulation of water entry to assert the utility of the method for analysis of real life water entry scenarios.