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GLERL What's New: 1999
Great Lakes Environmental Research
Laboratory
Distinguished Scientist Seminar Series
"Instabilities and Nonlinear Evolution of Wave-Induced Longshore Currents
in the Surf Zone"
H. Tuba Ozkan-Haller
Naval Architechture and Marine Engineering
University of Michigan
Location: Great Lakes Environmental Research Laboratory
2205 Commonwealth Blvd.
Ann Arbor, MI 48105-2945
Date: Thursday, February 18th, 1999
Time: 10:00 am
Room: 105 (Main Conference Room)
ABSTRACT: Obliquely incident waves on open coastal beaches generate
a strong, longshore-directed jet confined between the mean shoreline position
and the outer edge of the surf zone. The resulting longshore current is
strongly sheared in the cross-shore direction. The profiles have an inflection
point on the seaward side of the profile and should be unstable to small
wavy perturbations in the longshore direction. Linear stability analysis
confirms this and predicts growing waves with maximum growth rates at the
frequencies on the order of 0.001 Hz. These waves have been given the moniker
"shear waves" in the coastal oceanography community.
In this study, we employ a pseudospectral solution of the nonlinear shallow water equations in order to study the long-time evolution of the instabilities. The results depend strongly on the nature of the beach profile studied and on the relative importance of frictional effects, with instabilities evolving to both regular and chaotic wave trains through pathways dominated by vortex pairing effects. Resulting longshore currents and spectra of shear wave fluctuations are compared to field data, and reasonable agreement is found. Additional documentation may be found in Ozkan-Haller and Kirby, (1999, to appear in the Journal of Geophysical Research), who examine a range of conditions during the 1986 Superduck experiment.
For further information, please contact:
Michael J. McCormick
NOAA Great Lakes Environmental Research Laboratory
2205 Commonwealth Blvd.
Ann Arbor, MI 48105-2945
734-741-2277
michael.mccormick@noaa.gov
Last update: September 19, 2002 mbl