Wavelength selection and symmetry breaking in orbital wave ripples
Nienhuis, Jaap H.
Perron, J. Taylor
Kao, Justin C. T.
Myrow, Paul M.
MetadataShow full item record
KeywordOrbital wave ripple; Separation zone; Wavelength selection; Wave ripple adjustment; Wave tank experiments; Lattice Boltzmann method
Sand ripples formed by waves have a uniform wavelength while at equilibrium and develop defects while adjusting to changes in the flow. These patterns arise from the interaction of the flow with the bed topography, but the specific mechanisms have not been fully explained. We use numerical flow models and laboratory wave tank experiments to explore the origins of these patterns. The wavelength of “orbital” wave ripples (λ) is directly proportional to the oscillating flow's orbital diameter (d), with many experimental and field studies finding λ/d ≈ 0.65. We demonstrate a coupling that selects this ratio: the maximum length of the flow separation zone downstream of a ripple crest equals λ when λ/d ≈ 0.65. We show that this condition maximizes the growth rate of ripples. Ripples adjusting to changed flow conditions develop defects that break the bed's symmetry. When d is shortened sufficiently, two new incipient crests appear in every trough, but only one grows into a full-sized crest. Experiments have shown that the same side (right or left) wins in every trough. We find that this occurs because incipient secondary crests slow the flow and encourage the growth of crests on the next flank. Experiments have also shown that when d is lengthened, ripple crests become increasingly sinuous and eventually break up. We find that this occurs because crests migrate preferentially toward the nearest adjacent crest, amplifying any initial sinuosity. Our results reveal the mechanisms that form common wave ripple patterns and highlight interactions among unsteady flows, sediment transport, and bed topography.
Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Earth Surface 119 (2014): 2239–2257, doi:10.1002/2014JF003158.
Suggested CitationArticle: Nienhuis, Jaap H., Perron, J. Taylor, Kao, Justin C. T., Myrow, Paul M., "Wavelength selection and symmetry breaking in orbital wave ripples", Journal of Geophysical Research: Earth Surface 119 (2014): 2239–2257, DOI:10.1002/2014JF003158, https://hdl.handle.net/1912/7017
Showing items related by title, author, creator and subject.
Mayer, Larry A.; Raymond, Richard; Glang, Gerd; Richardson, Michael D.; Traykovski, Peter A.; Trembanis, Arthur C. (IEEE, 2007-01)High-resolution multibeam sonar and state-of-the- art data processing and visualization techniques have been used to quantify the evolution of seafloor morphology and the degree of burial of instrumented mines and mine-shapes ...
Bowers, Colleen Marie (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2006-09)Recent studies have shown that the presence of sand ripples on the seabed improves sonar detection of buried mines at sub-critical angles. Sidescan sonar data of ripples on the west Florida shelf were collected as part ...
Traykovski, Peter A. (American Geophysical Union, 2007-06-30)Measurements of seafloor ripples under wave-dominated conditions from the LEO15 site and the Martha’s Vineyard coastal observatory were used to develop a time-dependent model for ripple geometry. The measurements consisted ...