Internal wave excitation by a vertically oscillating elliptical cylinder

Abstract

Laboratory experiments are performed to measure the amplitude of internal waves generated by an elliptical cylinder oscillating vertically with different frequencies and amplitudes in a uniformly stratified fluid. The experimental results are compared with the theoretical predictions of Hurley and Keady ͑1997͒. Though in qualitatively good agreement with experiments, the theory underestimates the amplitude of low-frequency waves and overestimates the amplitude of high-frequency waves. The measured beam width is underestimated by theory, which neglects the dynamics of viscous boundary layers surrounding the cylinder. When the cylinder oscillates at a frequency less than half the buoyancy frequency, experiments reveal that two sets of waves beams are generated. The secondary set of waves have double the frequency of the primary waves and are excited due to nonlinear processes.

Parametric subharmonic instability of internal waves: locally confined beams versus monochromatic wavetrains

“…In contrast to sinusoidal wavetrains which are generally prone to PSI, however, no evidence of PSI in wave beams is reported in these studies. Moreover, the same is true for internal wave beams generated in several laboratory experiments by oscillating a body in a stratified fluid tank (see, for example, Mowbray & Rarity 1967;Sutherland et al 1999;Sutherland & Linden 2002).…”

Tangential oscillations of a circular disk in a viscous stratified fluid

“…These techniques are now accurate enough for the inclusion of viscous effects in theoretical calculations to be necessary for quantitative agreement between prediction and experiment, as shown by experiments on a variety of body shapes (e.g. Sutherland & Linden 2002;Ermanyuk & Gavrilov 2008). We examine the time-harmonic wave field generated by a horizontal disk moving at constant frequency.…”

The response of a continuously stratified fluid to an oscillating flow past an obstacle

“…From the u field we can see that the beams are thinnest adjacent to the critical points (white circles), widening slightly into the interior. We distinguish between the beam thickness, shown schematically in the image, which is much less than the diameter d and the beam separation (also shown) which is equal to d. Our terminology is thus different from that in Sutherland & Linden (2002) where what we call the beam separation is called the beam width. The beam thickness results from the competing effects of ray tube compression near the critical points and viscous smoothing.…”