Some insights into slamming forces: compressible and incompressible phases

In the present paper the slamming force occurring in the free-fall impact of cylindrical bodies over the water surface is analysed in both compressible and incompressible stages. In the compressible phase the hydrodynamic analysis is carried out by the acoustic approximation and a closed-form expression for the impact force is recovered. The incompressible stage is approached through an unsteady boundary element method to compute the free surface evolution and the slamming force on the body. In both cases the hydrodynamic force is coupled to the rigid body motion to update the entry velocity of the body. The combined effect of the increasing wetted area and the reducing entry velocity leads to a maximum in the impact force that depends on the body mass. A parametric investigation shows that in the impact of a wedge section, if the maximum is reached either in the compressible or in the incompressible stages, a similar square root trend characterizes the dependence of this maximum on a non-dimensional mass parameter.