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| Titel |
Model and case study for freak waves in crossing swell and wind sea |
| VerfasserIn |
Odin Gramstad, Jean-Michel Lefevre, Karsten Trulsen |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250049762
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| Zusammenfassung |
| So-called crossing sea states (sea states characterised by two wave systems separated in
frequency or direction) is a common situation in the oceans. It has been suggested that
crossing sea states may lead to larger probability of freak waves. One possible approach to
study the statistical properties of waves is the use of phase-resolving nonlinear wave models
in Monte–Carlo simulations. With respect to crossing seas, such a study was recently
performed by Gramstad & Trulsen (J. Fluid Mech., vol. 650, 2010, pp. 57–79), where we
derived a new modified nonlinear Schrödinger equation describing the evolution of short
wind waves affected by a much longer swell. Numerical Monte–Carlo simulations of this
equation showed that the presence of a swell may increase the number of freak waves by a
small amount.
In the present study we have analysed hindcast data from the Atlantic Ocean taken from
the time and location of the sinking of the Tanker “Prestige” in 2002. These data show that
the sea condition associated with this incident was characterised by two crossing wave
systems, however with a smaller separation in the frequency domain than assumed by e.g.
Gramstad & Trulsen (2010). In order to better describe the sea states provided by the hindcast
data, we have derived a set of two coupled fourth-order nonlinear Schrödinger equations
capable of describing the situation of two crossing wave systems that are separated, yet
quite close in the frequency domain, so that resonant and quasi-resonant four-wave
interactions are the dominant processes in the mutual interaction between the wave
systems. We have taken the perturbation analysis up to fourth order in wave steepness
and bandwidth in order to include important aspects of the nonlinear evolution of
a wave field which are not included in lower order models. We have shown that
our fourth-order equations conserve the total wave action and momentum of the
combined wave field. Stability analysis of two interacting uniform wave trains is also
reported.
We plan to carry out numerical Monte–Carlo simulations with the new equations in order
to study the probability or freak waves in the realistic crossing sea states provided by the
hindcast data. |
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