Flow and skin friction over natural rough beds
MetadataShow full item record
KeywordCurrent ripples; Skin-friction patterns; Sedimentary tails; Roughness length; Rough turbulent boundary layers; Ocean bottom; Marine sediments; Frictional resistance (Hydrodynamics)
The first of two sets of data reported here, measured over two-dimensional immobile current ripples, comprises skin-friction time series at four streamwise positions and velocity profiles measured to within a few mm of the bed. The velocity profiles cannot be linked to the local mean skin friction through the law of the wall, so they do not represent an internal boundary layer growing downstream of reattachment. Rather the velocity field is the sum of a spatially averaged rotational profile and a locally inviscid perturbation. Normalized skin-friction spectra are independent of position, but skin-friction probabilty density functions show strong increases in skewness and kurtosis near reattachment. The second set of data comprises measurements of the skin-friction vector field around isolated hemispheres with and without model sedimentary tails, and skinfriction and velocity measurements on arrays of hemispheres with and without tails. The skin-friction field around an isolated hemisphere is not consistent with formation of growth of a sedimentary tail more than about two obstacle heights long. The skin-friction field in a hemisphere array of areal density 0.02 is significantly distorted from the isolated-element case, and the roughness length in arrays of two areal densities is not altered by addition of tails.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution.
Showing items related by title, author, creator and subject.
Walsh, Joseph B.; Zhu, Wenlu (American Geophysical Union, 2004-05-19)Sliding of a rough surface having a range of asperity heights is a gradual process, starting at contacts under relatively low normal shear load and spreading until the surface slides as a unit. We analyze this process ...
Estimating hydrodynamic roughness in a wave-dominated environment with a high-resolution acoustic Doppler profiler Lacy, Jessica R.; Sherwood, Christopher R.; Wilson, Douglas J.; Chisholm, Thomas A.; Gelfenbaum, Guy R. (American Geophysical Union, 2005-06-30)Hydrodynamic roughness is a critical parameter for characterizing bottom drag in boundary layers, and it varies both spatially and temporally due to variation in grain size, bedforms, and saltating sediment. In this paper ...
Results of research on surface waves of the western North Atlantic. I. Investigation of bottom pressure fluctuations and surface waves. II. Results of sea surface roughness determinations in the vicinity of Woods Hole, Mass., and Bermuda Seiwell, Harry Richard (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1948-08)Part I: It is to be expected that in the future, measurements of pressure fluctuations beneath the ocean surface will provide basic data for solution of many practical problems on the state of the sea. As a result of the ...