Confined-Crest Impact: The Influence of the Toe Berm on the Impulsive Forces

Abstract

The primary function of composite vertical breakwaters is to shield harbor basins from incoming waves and currents. To ensure high hydraulic efficiency, recurved parapets are commonly employed to mitigate the wave overtopping phenomenon. However, these breakwaters are typically used in locations characterized by high water depth. In such settings, nonbreaking waves form on the seaward side of the structure, leading to a phenomenon known as “Confined-Crest Impact” (referred to as “C-CI” hereafter). This phenomenon arises from the interaction between nonbreaking waves and overhanging structures. As presented in previous research works, the same author showed a method for considering the pressure increment induced by the “C-CI” using empirical relationships. However, these tools were unable to predict pressure increments in the presence of submerged berms. Nevertheless, vertical breakwaters commonly feature a berm designed primarily for seabed leveling. Particularly in areas with deep seabeds, the berm serves the purpose of diminishing the caisson height. The presence of the berm amplifies shoaling effects, leading to an increase in free surface velocity and, consequently, a rise in excess pressure induced by the “C-CI” in the presence of a recurved parapet. For this reason, this research specifically focuses on investigating the influence of the toe berm on “C-CI.” A series of computational fluid dynamics (CFD) numerical simulations have been conducted to analyze how changing the height of the toe berm affects the loading conditions on the recurved parapet. The geometrical configuration of the toe berm has been selected based on the “Parameter Map” outlined in the PROVERBS manual. As a main result, the intensity of “C-CI” tends to increase as the height of the toe berm increases. This is mainly due to the shoaling effect induced by the berm, as the steepness of the waves increases. A new empirical formula has been developed, with the purpose of determining the coefficient required to apply in Goda’s formulas, enabling the estimation of pressure distribution along the structure in presence of berms.