Free fall motion of a floating body: Bubble formation and its effect

The hydrodynamic problem of a floating body moving downwards into water with prescribed velocity or in free fall motion is solved based on the incompressible velocity potential theory through the boundary element method in the time domain. In particular, the focus is on the whole process of flow detachment, the formation of an open cavity, closure of the cavity or formation of entrapped air bubble, collision of the inner jet with the body surface and jet impact with free surface. The whole problem is divided into several stages and methodology is introduced to resolve the numerical challenge at each stage. In particular the dual coordinate system method is adopted to resolve the local sharp spatial and temporal variation in the impact zone, and the domain decomposition method with Riemann second sheet is adopted to resolve domain overlapping. An auxiliary function method is used to decouple the nonlinear mutual dependence of fluid loading, body motion and bubble deformation. Simulations are undertaken for a floating body moving into water at constant velocity or constant acceleration, and in free motion, respectively. Detailed results for pressure, free surface profile, bubble deformation and body motion are provided, and their physical implications are discussed. (C) 2019 Elsevier Masson SAS. All rights reserved.