A comparative study on water entry and water walking events of elastic spheres

This paper presents a comparative study on water entry and water walking events of elastic spheres using a fluid-structure interaction method. The sphere displacements, cavity formations, and hydrodynamic characteristics during the water entry and water walking events are investigated. When the impact angle decreases, an obliquely impacting elastic sphere on the water surface can undergo a transition from water entry events to water walking events. Based on the morphological classification of the cavity opening, the shapes of cavity openings formed by elastic spheres can be roughly predicted from material properties and impact conditions. Furthermore, the water walking event is characterized by three typical stages: impact below the surface, walking across the surface, and skipping from the surface. Each stage is analyzed in terms of sphere displacements and hydrodynamic characteristics. The results also show that the vertical hydrodynamic forces acting on elastic spheres are not always smaller than those acting on rigid spheres at all impact angles. The critical impact angle that results in an equivalent vertical hydrodynamic force acting on both elastic and rigid spheres can be predicted from the material properties and impact conditions of the elastic sphere.