Nonlinear Hydrodynamics of Extreme Waves With Different Generation Mechanisms

Abstract Generation mechanism of ocean extreme waves has long been a mystery for scientists and engineers in the marine offshore community. Extremely large waves have been more frequently observed in the ocean in recent years under the circumstance of climate change, which attracts much research interest. However, the generation mechanism and nonlinear physics associated with those sea monsters and their prediction remain open questions. This study attempts to provide further insights into three possible explanations of the formation of ocean extremes waves, namely, linear focusing (enhanced with nonlinear effects), modulational instability and wave interaction with abrupt depth transition (ADT). Theories, experimental and numerical studies are briefly presented for each formation mechanism supported by our recent work. Spectral analysis is carried out to investigate the characteristics of elevations and nonlinear evolution for large waves. Harmonic decomposition technique is employed to separate higher harmonics in order to evaluation the importance of higher order components in the formation of extreme waves. Key findings regarding the three generation mechanisms are summarized. The results show that nonlinear effects play a significant role in the formation of the ocean extreme waves. More accurate and efficient nonlinear numerical models shall be developed to study these highly nonlinear waves. Further work regarding the generation mechanisms and nonlinear physics is also discussed.