Experimental analysis of post-overtopping flows on composite vertical breakwaters with retreated wave walls: mapping of the hydrodynamic parameters

Retreated wave walls are often used to improve the hydrodynamic performance of composite vertical breakwaters placed in relatively deep-water conditions. The wall retreat changes significantly the dynamics of wave-structure interaction, making the current design criteria not adequate for such structures. Previous experimental findings highlight that these processes are governed by the complex hydrodynamics driven by the characteristics of post-overtopping flows occurring on the superstructure between the seaward edge of the caisson trunk and the wave wall. In this article a new 2D experimental campaign has been carried out to explore the hydrodynamics of post-overtopping flows on composite vertical breakwaters with retreated wave wall. To improve the overall understanding of the phenomena, these flows have been analyzed and classified into three distinct types, based on wave characteristics and structural parameters, namely: Dam break (DB), Plunging-Dam break (PDB), and Hammer-Fist (HF). Then, the characteristics of each event type have been studied as a function of the wave wall retreat position. To this end, an advanced image-clustering analysis technique has been applied to visualize the process and estimate those quantities which are difficult to measure with direct measurement techniques (e.g., air content). Moreover, wave-induced loads on the wall and downfall pressures have been measured, allowing to explore how different flow types, wall retreats, and aeration levels could affect impact loads and flow dynamics. The detailed analysis of the post-overtopping flows dynamics, combined with the measurements of the forces acting on the wave wall, allowed to obtain a comprehensive parameters map, based on the flows classification and geometrical dimensions, which contributes to the development of practical design tools for such structures.

A special acknowledgment is due to the master’s student Matteo Scaramozzino for the help provided during the experimental campaign.