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Ann. Geophys., 26, 2131-2142, 2008
www.ann-geophys.net/26/2131/2008/
© European Geosciences Union 2008
Gas transfer under breaking waves: experiments and an improved vorticity-based model
V. K. Tsoukala and C. I. Moutzouris
Laboratory of Harbor Works (LHW), School of Civil Engineering, National Technical University of Athens (N.T.U.A.), 5 Iroon Polytechniou 157 80 Zografou, Greece
Abstract. In the present paper a modified vorticity-based model for gas transfer under
breaking waves in the absence of significant wind forcing is presented. A
theoretically valid and practically applicable mathematical expression is
suggested for the assessment of the oxygen transfer coefficient in the area
of wave-breaking. The proposed model is based on the theory of surface
renewal that expresses the oxygen transfer coefficient as a function of both
the wave vorticity and the Reynolds wave number for breaking waves.
Experimental data were collected in wave flumes of various scales: a)
small-scale experiments were carried out using both a sloping beach and a
rubble-mound breakwater in the wave flume of the Laboratory of Harbor Works,
NTUA, Greece; b) large-scale experiments were carried out with a sloping
beach in the wind-wave flume of Delft Hydraulics, the Netherlands, and with
a three-layer rubble mound breakwater in the Schneideberg Wave Flume of the
Franzius Institute, University of Hannover, Germany.
The experimental data acquired from both the small- and large-scale
experiments were in good agreement with the proposed model. Although the
apparent transfer coefficients from the large-scale experiments were lower
than those determined from the small-scale experiments, the actual oxygen
transfer coefficients, as calculated using a discretized form of the
transport equation, are in the same order of magnitude for both the small- and
large-scale experiments. The validity of the proposed model is compared to
experimental results from other researchers.
Although the results are encouraging, additional research is needed, to
incorporate the influence of bubble mediated gas exchange, before these
results are used for an environmental friendly design of harbor works, or for projects
involving waste disposal at sea.
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