Short Term Variability of Pressure Distribution on Vertical Breakwaters using WCSPH

Slamming loads on vertical breakwaters may cause severe damages on such kind of structures as occurred for instance in several circumstances in Italy after the second world war. Extreme wave impact loadings might determine high pressure peaks (tens or even hundreds of atmospheres), stressing the structure, despite their small duration. As the impact process take place, the pressure distribution change non linearly as function of the celerity of perturbations and fluid compressibility. As reference timescale may be considered the ratio between the water depth of the approaching wave and the celerity. Experimental and theoretical assessment on the matter seems to be not completely satisfying due to the intrinsic limits of transducers in the first case and to drastic simplifications leading to static or quasi-static theories in the latter case. In order to detect further insights, in the present work the authors have carried out numerical simulations of violent wave impact onto a vertical wall by means of a Lagrangian based code. The technique adopted is the Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH). As set up, a quickly approaching mass of fluid, discretized by a finite collection of pseudo-particles, is here assumed. Results have shown how pressure distribution on the wall increase abruptly from the bottom to the free surface, reaching values of tens of atmospheres as order of magnitude, in good agreement with the Allievi formula, yielding the overpressure in the case of abrupt variation of velocity. After this initial phase – lasting around the above introduced timescale – streamlines become to curve near the wall, determining the formation of a jet like, moving vertically.