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| Titel |
Direct measurement of dispersion relation for directional random surface gravity waves |
| VerfasserIn |
Tore Magnus Arnesen Taklo, Karsten Trulsen, Harald Krogstad, José Carlos Nieto Borge |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250092255
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| Publikation (Nr.) |
 EGU/EGU2014-6586.pdf |
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| Zusammenfassung |
| Linear wave theory is widely used to model for instance response of ocean structures and
ships to water surface gravity waves and assumes that the water surface can be modeled as a
linear superposition of regular waves satisfying the linear dispersion relation. The linear
dispersion relation is often taken for granted for the interpretation of wave measurements.
The interpretation of nautical radar images currently depends on the linear dispersion
relation as a prerequisite, Nieto Borge et al. (J. Atmos. Ocean Tech., 2004, vol. 21, pp.
1291-1300).
Krogstad & Trulsen (Ocean Dynamics, 2010, vol. 60, pp. 973-991) carried out numerical
simulations in one horizontal dimension with the nonlinear Schrödinger equation NLS and
the modified nonlinear Schrödinger equation MNLS. From wavenumber-frequency
spectra obtained from the simulated unidirectional surfaces they found that nonlinear
evolution of unidirectional wave fields may cause deviation from the linear dispersion
relation.
Extending the work by Krogstad & Trulsen (2010) we carried out experiments with
unidirectional waves with fixed wave steepness and various bandwidths in a narrow wave
tank. These experiments verified the results obtained from the simulations with the (M)NLS
models and showed that the directly measured dispersion relation deviated from the linear
dispersion relation for sufficiently narrow bandwidths. For broad bandwidths, however, the
linear dispersion relation was satisfied, suggesting validity of linear wave theory. By further
analysis of the experimental data we suggest that the occurence of the deviation depends on
steepness and spectral bandwidth.
Recently we have extended the work by Krogstad & Trulsen (2010) to two horizontal
dimensions using the MNLS equation and simulated directional random surface gravity
waves with bandwidths ranging from narrow to relatively broad. The wavenumber-frequency
spectra obtained from these simulated directional surfaces also show deviation from the linear
dispersion relation for narrow bandwidths.
In the present study we have also analysed laboratory data from the MARIN wave basin
in the Netherlands. These experiments provide a unique set of data from three different wave
fields with different directional distributions. |
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