Tuozzo, Sara (2024) Wave overtopping of vertical seawalls in the surf zone. [Tesi di dottorato]

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Abstract

The present Thesis analyzed in depth the wave overtopping of vertical walls in the surf zone. Seawalls are evergreen solutions commonly adopted to protect assets from coastal risks, such as flooding. The wave overtopping, hence, is an essential phenomenon to account for in designing coastal structures to guarantee their efficacy in protecting coastal zones from flooding risks. However, even though wave overtopping is one of the main issues in the coastal scientific community, a critical review of the literature has revealed that our knowledge about the overtopping of seawalls in shallow water is still rough and unaccomplished. In particular, a few reliable data on the overtopping of vertical walls in the surf zone are available in the literature. The work, hence, moves from these shortcomings and aims to fill this gap through a combined analysis of experimental and numerical data. The study firstly analyzes the laboratory data of an experimental campaign carried out at the University of Naples Federico II that have been also numerically reproduced via the non-hydrostatic model, SWASH, and the CFD-RANS model, FLOW-3D. On one hand, such analysis has shown that the phase-resolving models can capture, to a good extent, the physical processes (despite different levels of accuracy) and, thus, they significantly contribute to extending our comprehension of the wave overtopping in the surf-zone. On the other hand, the joint laboratory and numerical analysis has shed some light on the hydraulic variables that influence the wave overtopping in the surf zone. Specifically, the results have revealed that, unlike the literature assumption, the wave overtopping process of vertical walls does not depend on the wave energy distribution in the frequency domain but on the wave displacement distribution at the toe of the wall. Therefore, a new hydraulic variable has been introduced, which expresses the influence of the upper tail of the distribution on wave overtopping. Consequently, the work has attempted to provide a new overtopping model based on this hydraulic variable. To this end, an extensive parametric study has been carried out via SWASH; indeed, using a numerical model allowed the experimental conditions to vary smoothly, thus creating a wide and varied dataset and avoiding the typical limitation of laboratory experiments. The numerical investigation has ensured the identification of the main variables involved in the wave overtopping process, and thus, a new overtopping parametrization has been proposed. According to the new parametrization, a predictive model has been inferred from the numerical data. Numerical findings have been verified against 270 laboratory data from different datasets, including 70 physical model tests performed in this work to examine the wave overtopping of seawalls with very and extremely shallow foreshores and fill the void found in the literature. According to the numerical findings, the laboratory data follow a unique trend and exhibit a uniform behavior, demonstrating the large explanatory power of the new parametrization introduced. Finally, the work provides a unique generalized formula for estimating the wave overtopping of seawalls in shallow water, valid for both breaking and non-breaking waves. The last phase of the work has investigated the wind effect on wave overtopping at vertical seawalls in shallow water. By gathering numerical and laboratory data provided by the literature, this study provides a new empirical formula to quantify the flow rate enhancement due to the presence of the wind.

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