In the field of naval hydrodynamics, the slamming phenomenon is very widespread. The objective is to develop models that reproduce as faithfully as possible what is happening in reality, to be able to determine with the most accuracy the slamming loads suffered by the naval structures. To be able to increase the lifetime of ships and to avoid the damages due to the high pressures and the high forces induced during an impact. This impact occurs when the lower part of a ship hits the surface of the sea (free surface).

To do this, several methods have been used, such as the analytical models of [VonKarman, 1929] which linearize the wet surface but does not take into account the deformation or the free surface elevation. A few years later, [Wagner, 1932] suggest an asymptotic solution that considers the free surface as a flat disk delimited by the intersection between the wetted surface and the disturbed free surface. Subsequently [Zhao et al, 1996] generalizes the work of Wagner, he considers the nonlinear wet surface. The dynamic free surface condition is applied to a line from the point of contact between the wetted surface and the deformed free surface. In this method the jet formed during the primary impact is neglected in the calculations and therefore the formation of the air cavity and the secondary impact are neglected. Works using this method have been conducted by [Faltinsen, 2002], [Malleron and Scolan, 2008] and [Mei et al, 1999]. However, the vast majority of simplified models can only solve two-dimensional problems. Really three-dimensional analytical solutions of impact problems are rare. [Scolan and Korobkin, 2001] have developed an inverse method for three-dimensional problems.

To solve more complex phenomena and geometry, we use CFD (Computational Fluid Dynamics) numerical methods. The VOF method (Volume of Fluid) is one of the most used, see [Aquelet et al, 2006] and [Fleefsman et al, 2005].

On the experimental side, many tests have been made to observe slamming and to validate numerical models. [Greenhow, 1988] performs an experiment that consists in dropping a cylinder above the free surface and confirms the existence of flow separation and free surface elevation during the impact. Following this, many investigations have been carried out, such as the work of [Monroy et al, 2016] on a bow geometry with bulb that allows the formation of secondary impact on the upper parts after flow separation.

The study consists of determining the hydrodynamic loads suffered by the model during water entry of a bow flare section at constant velocity .The geometry is inclined with a constant roll angle that we have modified for each configuration. The roll angle allows us to generate a free surface elevation that impacts the top of the geometry to create a secondary impact. A numerical approach has been conducted with the VOF method using the Euler-Lagrange Coupling (CEL) widely used for fluid-structure interactions. The volume fraction is used to study the evolution of the free surface during the simulation. An experimental campaign was carried out using the hydraulic impact machine from ENSTA Bretagne, to validate numerical models. The interest is to visualize in real conditions the flow separation and the secondary impact and evaluate the gap between models and reality.