On Long-Crested Ocean Rogue Waves Originating From Localized Amplitude and Frequency Modulations

TL;DR

This study experimentally investigates the formation of long-crested rogue waves, revealing that both nonlinear amplitude and phase-related frequency modulations contribute to extreme wave focusing in ocean conditions.

Contribution

It demonstrates that phase-related frequency modulation is a significant, yet less-studied, mechanism in rogue wave formation alongside amplitude focusing.

Findings

Nonlinear focusing mechanisms include amplitude and phase-related frequency modulations.

Frequency modulation occurs at lower probability but is still significant.

Over 200 extreme events analyzed to identify formation mechanisms.

Abstract

Rogue waves are known to occur on the ocean surface leading to significant damage to marine installations and compromising ship safety. Understanding the physical mechanisms responsible for extreme wave focusing is crucial in order to predict and prevent their formation and impact. Two intensively discussed wave amplification frameworks are the linear and nonlinear focusing mechanisms. These are also known as superposition principle and modulation instability, respectively. We report an experimental study investigating the formation mechanism in a unidirectional representative JONSWAP-type sea state and show that the nonlinear focusing mechanism can be sub-categorized into either a localized amplitude or a so far less-studied phase-related frequency modulation, or both being at play. The frequency modulation-type mechanism occurs at a lower probability, as suggested from the distribution of more than 200 extreme events, however, it cannot be underrated or disregarded.