| Автор | Agrawal, Y. C. |
| Автор | Aubrey, D. G. |
| Дата выпуска | 1992 |
| dc.description | Velocity observations are reported in a plane across a regular nonmigrating ripple in 2.5 m of water depth. The forcing was weak, primarily wave‐induced near‐bed orbital motion. The data were acquired using a two‐axis submerged laser Doppler velocimeter. Synchronous records of pressure below the surface were also obtained. The instrumentation is described. The pressure information was used to separate wave‐coherent and turbulence motion in the observed velocity. Turbulent kinetic energy and dissipation rates are obtained over a range of distances above the bed from 1.5 mm above the ripple to 10 cm. Velocity time series are smooth except at high‐velocity magnitudes, indicating the formation of a lee vortex during peak velocities only. The data show convective acceleration of the flow over the ripple and a lack of significant shear in the rms horizontal motion farther from the bed. Velocity spectra at one location, 1.5 mm from the bed show second and third harmonics of the incident wave, which are interpreted to be due to convective acceleration over the ripple and vortex shedding. High‐frequency velocity spectra show uniformly decreasing turbulence intensity away from the bed. We conclude that the boundary layer observed here was transitional, i.e., laminar through small velocity periods, becoming turbulent for short periods during which the breakup of the vortex shed by the ripples occurred. Laminar estimates of maximum bottom friction are consistent with the threshold for initiation of motion criterion for 0.2 mm sand and the observed ripple steepness. |
| Формат | application.pdf |
| Копирайт | Copyright 1992 by the American Geophysical Union. |
| Тема | BIOGEOSCIENCES |
| Тема | Estuarine and nearshore processes |
| Тема | NONLINEAR GEOPHYSICS |
| Тема | Turbulence |
| Тема | OCEANOGRAPHY: GENERAL |
| Тема | Benthic boundary layers |
| Тема | Estuarine processes |
| Тема | OCEANOGRAPHY: PHYSICAL |
| Тема | Instruments and techniques |
| Тема | Turbulence, diffusion, and mixing processes |
| Название | Velocity observations above a rippled bed using laser Doppler velocimetry |
| Тип | article |
| DOI | 10.1029/92JC01797 |
| Electronic ISSN | 2156-2202 |
| Print ISSN | 0148-0227 |
| Журнал | Journal of Geophysical Research: Oceans |
| Том | 97 |
| Первая страница | 20249 |
| Последняя страница | 20259 |
| Выпуск | C12 |
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