Effect of directionality on extreme wave formation during nonlinear shoaling

TL;DR

This study experimentally investigates how wave directionality influences extreme wave formation during nonlinear shoaling, revealing that incidence direction significantly impacts non-equilibrium wave statistics.

Contribution

It provides new experimental insights into the role of wave directionality on depth-induced non-equilibrium wave behavior, an area previously limited to numerical studies.

Findings

Directional spreading has a minor effect on statistical moments.

Incidence direction significantly affects non-equilibrium wave response.

Effective bottom slope influences wave non-equilibrium dynamics.

Abstract

Recent studies have shown that, in coastal waters where water depth decreases significantly due to rapid bathymetric changes, the non-equilibrium dynamics (NED) substantially increases the occurrence probability of extreme (rogue) waves. Nevertheless, research on depth-induced NED has been predominantly confined to unidirectional irregular waves, while the role of directionality remains largely unexplored. The scarce studies on multidirectional waves mainly rely on numerical simulations and have yielded conflicting results. In this work, we report on an experimental investigation of wave directionality on the depth-induced non-equilibrium wave statistics. High-order statistical moments, skewness and kurtosis, are used as proxies for the non-equilibrium wave response. Our results indicate that the directional spreading has a minor effect on decreasing the maximum values of these statistical moments. In contrast, the incidence direction plays a significant role in the non-equilibrium wave response, which is attributed to the effective bottom slope.