Strongly Nonlinear Phenomena in Extreme Waves

In this paper the breaking of steep free surface waves is investigated by a two-fluid numerical approach. The study is focused at providing estimates of the energy dissipation and the variations to the spectrum associated to the breaking process. The simulations make available a highly refined description of the flow in both air and water which is also important for the estimates of load in severe conditions. Two different approaches are used to produce steep waves. A first approach exploits the classical Benjamin-Feir instability which generates extreme waves through the modulational instability process. In a second application a more realistic, narrow-banded, JONSWAP spectrum is used. Results are presented in terms of free surface dynamics and energy, separated in kinetic and potential components. The changes operated by the breaking occurrence on the spectrum are also discussed.