This paper presents a numerical experiment of single low-density sphere falling into the water from the air. A sphere with initial speed in the air was released above the water surface, splashes and waves will be generated when it touched the water; after that, it jumped above water because of buoyancy. The procedure is simulated by the Open source Field Operation and Manipulation (OpenFOAM) based on VOF method and dynamic mesh method. The result of time history of hydrodynamic forces and sphere's motion is given. Validations of grid and time convergence are performed in order to prove the correctness of this method. Results of the velocity field and the pressure distribution around the sphere are discussed.
The significance of research on water entry problem is the large damage impact force on ship and ocean structures. In rough sea, large motion of the ocean platforms or ship hulls can usually cause great damage to the structures when they touch and entry the water. This kind of damage sometimes can cause the sink of ocean structure, which will bring huge economic losses. The problem of sphere water entry is related to large amplitude motion of body in fluid with large free surface deformation. Although fast and easily accessible, these methods are not accurate enough and fail to deal with the large motion of body or waves. In this paper, water entry problem is solved by incompressible Navier-Stokes equations based on VOF surface capturing method and automatic deformation dynamic method. In recent decades, many methods were developed to solve these kinds of problems. Battistin(2003) used a boundary-element formulation with nonlinearities in the free-surface boundary conditions to investigate the water entry of two-dimensional bodies of arbitrary shape. Iafrati(2008) solved the flat plate impact problem by using method of matched asymptotic expansions.
