Date: 03/13/09

Speaker: A. Kalmikov

Title: Phase resolved modeling of wind-wave generation with High Order Spectral model

Abstract:
Gravity waves on the ocean surface are a powerful phenomenon of
central importance in ocean engineering. Surface waves are also a
major factor in ocean-atmosphere interaction, and have significant
implications on weather and climate dynamics. Mechanical energy
contained and dissipated in surface waves is the largest component in
the energetics of global oceans. Most of this energy is transferred to
waves by the action of the wind, and these waves are known as
wind-waves. The wind-waves are non-stationary, irregular and highly
nonlinear, which poses severe constraints on traditional wave modeling
approaches. A novel phase resolving nonlinear simulation of wind-wave
generation and evolution is developed with the High Order Spectral
(HOS) model. Wind forcing is assumed to be primarily a form drag
mechanism acting on the surface through a wave-induced distribution of
normal stress. The mechanism is parameterized in a linearized
framework of weakly interacting spectral components of the wave field,
and its magnitude is adjusted by the observed growth rates. The
effects of dissipation by wave breaking are accounted for by an
adaptive low-pass filter that also acts to stabilize the simulations.
Phase resolving simulations of wind forced regular periodic and
irregular random wave fields are examined. Linear and nonlinear
simulations are compared. The growth of regular waves is modulated by
bounded harmonics. The irregular broadband wave field evolves
nonlinearly, exhibiting peak frequency downshift on a time scale of
weak nonlinear mode coupling.