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| Titel |
Evolution of boundary layers on beaches |
| VerfasserIn |
E. K. Lindstrøm, G. Pedersen, A. Jensen, A. Bertelsen |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250060666
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| Zusammenfassung |
| The understanding of wave runup on beaches is crucial for the prediction
of coastal impact of tsunamis, storm surge and swells. There exists a
number of theoretical models based on inviscid theory on this subject and
the models are usually validated by experiments. Experiments are
generally performed in wave tanks with depths ranging from 10 cm to 50 cm. For
depths of this order the runup might be scale dependent since the swash
tongues are very thin and the flow might be influenced of viscosity and
surface tension, and one should be aware of these effects. This presentation
addresses discrepancies between experimental and theoretical runup heights
on an inclined plane. Recently we have performed experiments
in a wave tank with 20
cm water depth and a beach of 10 degrees inclination. Five incident solitary
waves of different amplitudes are generated. Detailed observations are made
for the shoreline motion and velocity profiles during runup. Both viscous and
capillary boundary layers are detected and the flow behavior depends on the
amplitude of the incident wave and the location on the beach. Comparison
with numerical simulations reveals that the experimental runup heights are
markedly smaller than predictions from inviscid theory. Findings suggest
that laminar bed friction is important in the runup experiments and may be
a main reason for the over-prediction of runup by inviscid models.
Moreover, the smaller incident waves yield stable, laminar boundary layers on
the beach, while the higher amplitudes give instabilities at
some locations. Hence, corresponding experiments with a water depth markedly
larger than 20 cm will presumably yield transitional or turbulent
boundary layers. |
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