Abstract

Internal waves are three dimensional waves that occur in stratified fluids, where density increases with depth, such as the ocean and atmosphere. In the oceans, internal waves are continuously generated by tidal flow over subsea topography. The size and shape of the topography, as well as the stratification relative to the oscillation frequency influence the characteristics of the generated internal wave field. To advance the current understanding of how ridges on a subcritical topography changes the internal waves generated, four symmetric topographies are used with ridge numbers ranging from three to six. An additional single ridge topography is used, as well as a plateau topography representing the limit of infinite ridges. To examine the effects of the depth of the valleys between ridges, two more topographies are used wherein the valleys of the three and four ridge topographies are filled to the same depth as the six ridge topography. Three width series of eight topographies each are examined. Synthetic schlieren is used to image internal waves generated by oscillating the topographies in a linear density stratification. Experiments are analyzed using the Hilbert transform to isolate waves propagating directly from the topography and the kinetic energy spectrum is estimated. A transition is observed for increasing topography ridges. The three ridge topographies generate internal wave beams with multiple crests, but as the ridges increase the interior wave crests decay close to the topography yielding a wavefield similar to the plateau topographies such that additional ridges beyond five has negligible difference on the wavefield. Immediately beneath the multiple ridge topographies a region with constructive and destructive interference is seen, which suggests that while the far wavefield may appear similar between the six ridge and plateau topographies, the near wavefield region varies. Transect lines along the wave beam capture kinetic energy decay within the internal wave beam. Results show that farther from the topography, kinetic energy decreases and this is enhanced at higher wavenumbers. The normalized spatial decay depends on both wavenumber and distance from the topography.

Degree

College and Department

Ira A. Fulton College of Engineering; Mechanical Engineering

Rights

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