Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session G1: Geophysical Flows: Oceanography II |
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Chair: Alan Brandt, JHU Applied Physics Laboratory Room: 301 |
Monday, November 21, 2011 8:00AM - 8:13AM |
G1.00001: Mass Transport by Large Amplitude Internal Solitary Waves Alan Brandt, Kara Blaine Mode-2 internal solitary waves (ISW) (symmetric ``bulge'' waves) have been observed on pycnocline interfaces in the coastal ocean. Mode-2 ISW with sufficiently large amplitudes can have closed streamlines and regions of internal recirculation resulting in entrainment and transport of mass. To investigate the extent of mass transport, a series of laboratory experiments was conducted in a two-layer stratified channel by releasing a volume of fluid at a density equal to that of the interface. The released fluid formed a series (one to three) of large amplitude mode-2 ISW that propagated along the interface. The extent of mass transport was determined by measuring the volume of the initially dyed release fluid contained within the ISW. It was found that the ISW mass transport was governed by the entrainment of external fluid and leakage from the trailing edge. These effects resulted in the larger amplitude ISW having a smaller mass transport decay rate with distance. [Preview Abstract] |
Monday, November 21, 2011 8:13AM - 8:26AM |
G1.00002: Internal wave driven transport of fluid away from the boundary of a lake Chris Rehmann, Danielle Wain, Michael Kohn, Joshua Scanlon A field study was conducted at West Okoboji Lake near Arnolds Park, Iowa to study transport of fluid resulting from wind forcing on summer stratification. A tracer was injected at the boundary of the lake and surveyed on four separate occasions over a period of three days. Although the Lake number was below 10 in two sustained periods, no elevated mixing occurred near the boundary. Nevertheless, dye injected at the boundary moved almost 950 m into the interior in 29 h. Advection by internal waves accounts for much of the transport, and shear dispersion from the spatially varying velocities in the internal wave field may explain at least some of the rest. [Preview Abstract] |
Monday, November 21, 2011 8:26AM - 8:39AM |
G1.00003: Propagating and evanescent internal gravity waves in the deep ocean Matthew S. Paoletti, M.C. Drake, Harry L. Swinney We present experimental and numerical studies on internal gravity waves in a stably stratified fluid designed to model the deep ocean. Internal gravity waves generated by tidal flow over ocean topography are responsible for much of the energy transfer in the ocean. King et al. recently found that there exist regions in the deep ocean where the density gradient becomes so small that the buoyancy frequency (proportional to the square root of the density gradient) becomes smaller than the tidal frequency; below such (previously unknown) ``turning points'' the internal gravity waves become evanescent. The present experiments and simulations examine internal wave reflection and energy transfer at turning points. Further, we study internal wave generation for tidal flow over a ridge on the ocean bottom, and we examine how the evanescent and propagating internal wave intensities depend on the height of the ridge relative to the turning point depth. [Preview Abstract] |
Monday, November 21, 2011 8:39AM - 8:52AM |
G1.00004: Large amplitude internal waves in weakly stratified oceans Wooyoung Choi, Roxana Tiron, Roberto Camassa We consider large amplitude internal waves in weakly stratified fluids and obtain the nonlinear evolution equations, which generalize the strongly nonlinear model for a system of two constant density layers. After the linear dispersion relation of the new model is compared with that of the linearized Euler equations, the solitary wave and conjugate state solutions of the model are obtained and compared with other theoretical solutions and field data. [Preview Abstract] |
Monday, November 21, 2011 8:52AM - 9:05AM |
G1.00005: Internal wave--vorticity coupling for an oscillating disk Bruno Voisin, Sylvain Joubaud, Thierry Dauxois In a density-stratified fluid, viscosity couples internal waves with vertical vorticity. So far this coupling used to be neglected in analytical studies and only the viscous attenuation and spreading of the waves was taken into account, except in a very recent study of the oscillations of a horizontal circular disk.\footnote{A. M. J. Davis \& S. G. Llewellyn Smith, J. Fluid Mech. \textbf{656}, 342--359 (2010).} We investigate the relations between the previous analytical approaches of the disk, considering either inviscid or viscous propagation of the waves and either free- or no-slip conditions at the disk, and compare their output with an original approach based on the boundary integral method. In particular, the role of the Stokes number is clarified. The analytical predictions are compared with contact measurements for vertical oscillations\footnote{R. N. Bardakov, A. Yu. Vasil'ev \& Yu. D. Chashechkin, Fluid Dyn. \textbf{42}, 612--616 (2007).} and with original PIV measurements and visualizations for both vertical and horizontal oscillations. [Preview Abstract] |
Monday, November 21, 2011 9:05AM - 9:18AM |
G1.00006: ABSTRACT WITHDRAWN |
Monday, November 21, 2011 9:18AM - 9:31AM |
G1.00007: Boluses leading the run up of shoaling internal waves of elevation Michelle E. Pede, Daniel T. Valentine Numerical solutions of the two-dimensional Navier-Stokes and convective-diffusion equations, to within the Boussinesq approximation, are presented. These solutions illustrate the mechanism of production, ejection and propagation of boluses, i.e., vortex projectiles, induced by shoaling internal solitary waves of elevation. They are the type of boluses observed in laboratory and field experiments reported in the geophysical fluid dynamics literature. The boluses predicted in this study are {\it not} a consequence of a breaking event. They are the shedding of a packet of fluid with concentrated vorticity that forms a vortex. This vortex is formed as the leading portion of the shoaling internal solitary wave of elevation steepens. The wave of elevation contains a significant concentration of vorticity. This vorticity is accumulated near the front of the wave by a combination of convection and production by enhancement of horizontal gradients of density as it shoals. The concentration of vorticity forms a vortex projectile. It interacts with its image on the other side of the shoal in the same way two vortices of opposite strength interact. The image vortex system propels the vortex projectile up the shoal a relatively large distance, even as part of the incident wave reflects and recedes offshore. The bolus leading the run-up process contains fluid that is heavier than the surrounding fluid and, hence, transports bottom layer fluid quite effectively to locations far up the sloped topography. [Preview Abstract] |
Monday, November 21, 2011 9:31AM - 9:44AM |
G1.00008: Exact solutions for waves over periodic topography of arbitrary shape and amplitude Jie Yu Understanding the interaction of wave and seabed topography is important, due to its relevance to sediment transport and wave transformation in coastal oceans. For periodic topography of large amplitude, exact theoretical solutions are few, even for linear waves. Recently, Howard and Yu (2007, J. Fluid Mech.) have developed an exact theory for linear waves over large amplitude bottom corrugations, using a conformal transformation. A complete set of Floquet-type solutions is given, which are analogous to the families of propagating and evanescent modes over the flat bottom. The corrugations considered in Howard and Yu have a shape which is approximately sinusoidal at small amplitude and becomes increasing cusp-like as the amplitude increases. Here, we have extended the theory of Howard and Yu to consider periodic topographies of arbitrary shape and amplitude. Examples are shown for purely sinusoidal, doubly sinusoidal bottom undulations, and square-wave like bottom topography. [Preview Abstract] |
Monday, November 21, 2011 9:44AM - 9:57AM |
G1.00009: The Effect of Wave Intensity on Fine Sediment Transport in Oscillatory Channel Celalettin Ozdemir, Tian-Jian Hsu, S. Balachandar Simulations on particle-laden flow in oscillatory channel are critical to further understand suspension and offshore delivery of fine terrestrial sediment in the coastal ocean. In an effort to understand these mechanisms, the degree of sediment induced density stratification quantified by Richardson number, Ri and settling velocity of particles, V$_{s}$, have been studied through turbulence resolving simulations with simplified Eulerian-Eulerian two phase model (Ozdemir et al. 2010, 2011). In these studies, moderately energetic wave field is considered given by Stokes Reynolds number, Re, of 1000 where all the scales of turbulence can be resolved. As a result, existence of four regimes of particle transport has been identified and presented in the parametric space defined by V$_{s}$ and Ri. From low to high Ri (or V$_{s})$, these regimes range from well-mixed condition to the formation of lutocline, and eventually a complete flow laminarization. Here, we further demonstrate the impact of lower wave intensity (Re) to the modes of sediment transport. Results show significant changes in the particle transport modes under variable V$_{s}$ and Ri. The culmination of the results so far yields a comprehensive picture on the nature of transitional turbulence due to different degree of sediment impact and the mode of mixing and transport in the oscillatory channel. [Preview Abstract] |
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