Confined-crest impact: Forces dimensional analysis and extension of the Goda's formulae to recurved parapets

In this paper, an extended numerical analysis of the "confined-crest impact" (hereinafter referred as "C-CI"), induced by non-breaking waves on recurved parapet walls, is presented to better understand the physics and characteristics of this impulsive wave phenomenon, which significantly depends on the geometry of the parapet (here made by a sector of circumference) as well as on non-breaking wave steepness. A dimensional analysis of the forces has been carried out and used to analyse the results obtained by numerical CFD computations. The numerical simulations, performed for different radii of curvature, opening angles and incoming wave characteristics (changing both the wave height H and wave period T), have shown that the maximum impulsive pressure: (i) takes place on the top of the recurved parapet and decreases moving towards the SWL, where it tends to vanish; (ii) tends to decrease as the radii of curvature and the incoming wave characteristics (wave height H and period T) increase. However, this reduction in the maximum pressure, is always accompanied by an increase of the forces acting on the recurved parapet and a decrease of the wave overtopping volumes. Moreover, the maximum wave induced pressures have been examined by means of regular and irregular wave conditions in order to analyse the possibility of schematising the effects (i.e. forces) of an irregular sea state with those of a regular one, providing an equivalent force and therefore saving computational time. Based on the new results, a schematization of the pressure diagram induced by the C-CI impact has been proposed, used to extend the Goda-Takahashi pressure diagrams, valid for vertical walls in non-breaking wave conditions, including recurved walls.