Potential-flow multisection approach for the vertical water entry of elongated bodies

The present paper introduces a potential-flow multisection approach for analyzing the hydrodynamics of the vertical water impact of elongated bodies. In these cases the derivatives in the longitudinal direction are much smaller than those in the transverse plane and therefore the slender body approximation can be profitably exploited. The original 3D water entry problem is then approximated in a series of 2D problem, in an earth-fixed frame of reference, of the body cross section which are solved by using a fully non-linear potential-flow model. The multisection procedure here proposed, exploits a 2D fully non-linear potential-flow solver, based on a Hybrid BEM-FEM (HBF) approach, in which a Boundary Element Method (BEM) is coupled with a Finite Element Method (FEM) to compute the hydrodynamics of water impact problems. The model is developed and applied to the vertical water entry of aircraft fuselages for which experimental data are available. The evolution of the free surface at different sections and the associated pressure distribution are presented. Particular attention is paid at the integration of loads computed at the different sections in order to provide a prediction of the 3D hydrodynamic force acting on the entering fuselage. Comparisons with available experimental data are presented.