Shock Spectral Analysis of Elastic System Impacting on the Water Surface

In this paper, the hydrodynamic and elastic forces arising in simple discrete and continuous systems impacting on the water surface are investigated. Both the impact of a single rigid wedge and the case of two elastically coupled bodies, where the lower one is 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 a continuous flexural system. By an envelope analysis of the displacement response, related to the hydrodynamic force spectrum, a slamming shock spectral expansion is introduced. This model is able to provide some insight into 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.