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|Title:||Effects of a steady nonuniform current on the characteristics of surface gravity waves|
|Authors:||Texas A & M University|
Hales, Lyndell Z.
Herbich, John B.
|Publisher:||Hydraulics Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Miscellaneous paper (U.S. Army Engineer Waterways Experiment Station) ; H-74-11.|
Abstract: When surface gravity waves propagate from a region of still water into a region of streaming water, changes occur in their characteristics. These wave characteristics have a direct implication regarding such physical phenomena as sediment movement in the near shore and coastal zone areas, energy propagation through tidal inlets into bays and estuaries, and safety to navigation as strong ebb currents can be created by channel dredging and jetty construction. The velocity field of the wave motion interacts with the velocity distribution of the current pattern and it has previously been shown analytically that the rate of energy propagation occurs at the group celerity of the wave motion and the current velocity plus additional terms produced by this interaction. An experimental study was conducted at the U. S. Army, Corps of Engineers, Waterways Experiment Station, Vicksburg, Mississippi, into the manner in which nonuniform currents affect the characteristics of a superimposed surface gravity wave train. The work was conducted in a three-dimensional wave basin in which was simulated a tidal inlet through which could be created nonuniform currents in both an ebb and flood direction. The current was required to build up on its own accord from essentially zero velocity in the ocean, reach a maximum value in the inlet throat and decay to essentially zero velocity in the bay region, for the flood condition. The ebb condition was similar except the current opposed the direction of the wave motion. For a variety of steady-state flow conditions through the facility, a range of wave trains with initial characteristics representative of those found in nature were superimposed. Measurements of velocity, wave height, and wave length were determined at selected points along the axis of the facility. Pertinent photographic documentation aided in understanding the phenomena of wave energy losses occurring in the ocean region. Spectral analyses of the generated wave form justified the assumption of constancy of the wave period; hence, theoretically the change in wave length was expected to vary with a current parameter in a linear fashion. Previous analytical investigations determined that the change in wave height should occur with the current parameter in a nonlinear manner of specific form. Multiple regression analysis of the experimental data indicated that in addition to the current parameter, the relative depth and initial wave steepness were statistically highly significant parameters affecting the changes in both wave length and wave height. The regression curves are displayed in graphical form for selected values of relative depth and initial wave steepness. The effect of the nonuniform current on the rate of energy propagation through the inlet was investigated by combining the results of these critical experiments with previously developed theoretical work. It was found that under certain specific conditions both flood and ebb currents enabled the waves to propagate more energy through the inlet than in the absence of a current, as a result of the interaction of the two velocity fields. NOTE: This file is very large. Allow your browser several minutes to download the file.
|Rights:||Approved for public release; distribution is unlimited.|
|Appears in Collections:||Miscellaneous Paper|
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|MP-H-74-11.pdf||24.76 MB||Adobe PDF|