In this paper hydrodynamic and elastic forces arising in simple discrete and continuous systems impacting on the water surface are investigated. Resuming some previous work, both the impact of a single rigid wedge and then the case of two elastically coupled bodies, where the lower one is a wedge directly plunging the water, are studied. The analysis is performed by a simplified theoretical model and by a numerical simulation of the fluid-structure interaction. The concepts of residual and overall shock spectrum of the slamming force are introduced. The attention is then addressed to the case of an impacting continuous flexural system. By an envelope analysis of the displacement response, related to the slamming force spectrum, a slamming shock spectral expansion is introduced. This model is able to provide some insights on the structural response during the impact. The characteristic maxima in the time histories of the elastic deformation are theoretically evaluated in terms of the impact quantities, such as the deadrise angle of the wedge, the entry velocity and the structural parameters. Results obtained by numerical simulations validate the theoretical predictions.
The design of modern high speed vessels requires an extreme care to fluid-structure interaction problems. In particular dangerous impact phenomena occur in fast marine vehicles, leading to severe pressure load conditions of the hull structure. The prediction of pressure and structural stress is of paramount importance, providing the tools for a better safety in ship design. Nevertheless some basic phenomena occurring during the impact process are well known. Simple considerations show that, even though the water is usually treated as incompressible, water compressibility effects are of some importance in the early stage of the contact. Actually, the intersection between the body and the free surface moves 440 with a velocity that depends strongly on the body shape.
