Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session D14: Waves: Internal and Interfacial Waves |
Hide Abstracts |
Chair: T. R. Akylas, MIT Room: C125-126 |
Sunday, November 20, 2016 2:57PM - 3:10PM |
D14.00001: 3D instability of internal gravity wave beams T. R. Akylas, Takeshi Kataoka, Boyu Fan The stability of isolated and interacting internal gravity wave beams (IGWB) to 3D perturbations is studied, based on the beam--mean-flow equations derived in Kataoka & Akylas (2015). Depending on the beam profile and amplitude, a single uniform IGWB as well as two interacting IGWB which propagate in the same or opposite directions, can be subject to 3D modulational instability brought about by a purely inviscid nonlinear mechanism. Moreover, for moderate viscous dissipation, the mean flow induced by a mechanism analogous to acoustic streaming can cause significant distortion, leading to breakdown, of forced IGWB with small lateral amplitude variations. These findings suggest that modulational and streaming instabilities are central to 3D IGWB dynamics, in contrast to the widely-studied PSI of sinusoidal wavetrains, which is most relevant to beams with nearly monochromatic profile only. [Preview Abstract] |
Sunday, November 20, 2016 3:10PM - 3:23PM |
D14.00002: Effect of background rotation on the evolution of 3D internal gravity wave beams Boyu Fan, T. R. Akylas The effect of background rotation on the 3D propagation of internal gravity wave beams (IGWB) is studied, assuming that variations in the along-beam and transverse directions are of long length scale relative to the beam width. The present study generalizes the asymptotic model of KA (Kataoka & Akylas 2015) who considered the analogous problem in the absence of rotation. It is shown that the role of mean vertical vorticity in the earlier analysis is now taken by the flow mean potential vorticity (MPV). Specifically, 3D variations enable resonant transfer of energy to the flow MPV, resulting in strong nonlinear coupling between a 3D IGWB and its induced mean flow. This coupling mechanism is governed by a system of two nonlinear equations of the same form as those derived in KA. Accordingly, the induced mean flow features a purely inviscid modulational component, as well as a viscous one akin to acoustic streaming; the latter grows linearly with time for a quasi-steady IGWB. On the other hand, owing to background rotation, the induced mean flow in the vicinity of the IGWB is no longer purely horizontal and develops an asymmetric behavior. [Preview Abstract] |
Sunday, November 20, 2016 3:23PM - 3:36PM |
D14.00003: Harmonic generation by nonlinear refraction of a single internal wave mode with rotation Scott Wunsch Weakly nonlinear theory is used to explore the dynamics of a mode-1 internal tide in variable stratification with rotation. Nonlinear refraction at the pycnocline generates a perturbation which is forced with double the original frequency and wavenumber. The dynamics of the perturbation are analogous to a forced harmonic oscillator, with the steady state solution matching the forcing frequency and wavenumber. The perturbation exhibits resonance when its frequency is close to a natural frequency of the system. Enhanced dissipation due to the harmonic occurs near resonance, and its contribution to ocean tidal dissipation may be significant in some environments. The results are relevant to recent observations of harmonics of the diurnal tide in the South China Sea. More generally, nonlinear refraction may contribute to the dissipation of oceanic internal tides and the transfer of energy to smaller scales. [Preview Abstract] |
Sunday, November 20, 2016 3:36PM - 3:49PM |
D14.00004: An experimental investigation of energy transmission from an evanescent to a propagating region. Allison Lee, Julie Crockett Tidal flow over oceanic~bathymetry~is a well known generator of internal waves. However, in the deep ocean there are many~regions of weak stratification and the tides will~generate only evanescent waves~which decay exponentially as they propagate away from their source. In locations where stronger stratification exists above the weak, evanescent waves can form~propagating internal waves as they approach a depth with a stratification corresponding to their frequency (turning depth). An experimental study of the energy transfer from evanescent regions to propagating regions due to evanescent waves passing through a turning depth~is presented.~The effects of varying exponential stratification profiles and single and multi-peak topographical features are described and results are compared with linear theory approximations.~ [Preview Abstract] |
Sunday, November 20, 2016 3:49PM - 4:02PM |
D14.00005: Effect of pycnocline thickness on internal wave bolus transport Michael Allshouse, Harry Swinney Internal waves shoaling on a continental slope can produce boluses, which are vortices that develop and travel upslope with the shoaling internal wave. In contrast to propagating solitary waves, boluses can trap and transport nutrient rich water upslope. Past laboratory investigations of bolus generation and transport have examined systems that have two layers of uniform density. The present laboratory experiment examines bolus formation and transport as a function of the thickness of a model pyncnocline where there is a continuous variation in density between two regions of constant density. Our dye based measurements for transition layers varying in thickness from 2 to 30 cm demonstrate that fluid transport by boluses exhibits a maximum as the thickness of the transition layer is varied. Complementary Navier-Stokes direct numerical simulations, analyzed using Lagrangian coherent structure techniques, compare well with the laboratory observations. [Preview Abstract] |
Sunday, November 20, 2016 4:02PM - 4:15PM |
D14.00006: Internal Wave Scattering in Idealized and Realistic Continental Slope Canyons Robert Nazarian, Sonya Legg When internal waves interact with topography, such as continental slopes, they can deposit their energy to local dissipation and mixing. Submarine canyons comprise about ten percent of global continental slopes, and can enhance the local dissipation of internal wave energy, yet parameterizations of canyon mixing processes are currently missing from ocean models. As a first step in developing such parameterizations, a parameter space study of M2 tidal-frequency, low-mode internal waves interacting with idealized canyon topographies was conducted. A two-pronged approach was employed in which a suite of MITgcm simulations was compared with a novel, analytical ray tracing scheme. The most noticeable result was that, as the ratio of the canyon mouth width to canyon length decreased, there was a marked increase in the relative energy loss. This energy loss also increased as the canyon sidewall steepness increased. Processes leading to this increased energy loss include increased energy focusing, increasing vertical wavenumber via multiple reflections for non-vertical sidewalls and the presence of arrested lee waves for vertical sidewalls. To test the robustness of these results, we model the energy lost from remotely-generated M2 internal tides in three realistic canyons with very different geometries: Veatch, La Jolla and Eel Canyons, comparing results with both idealized simulations and microstructure data taken from these locations. We also discuss how current parameterizations of tidally-driven diapycnal mixing can be extended to include the effects of continental slope canyons. [Preview Abstract] |
Sunday, November 20, 2016 4:15PM - 4:28PM |
D14.00007: Generation of realistic tsunami waves using a bottom-tilting wave maker Yong Sung Park, Jin Hwan Hwang Tsunamis have caused more than 260,000 human losses and {\$}250 billion in damage worldwide in the last ten years. Observations made during 2011 Japan Tohoku Tsunami revealed that the commonly used waves (solitary waves) to model tsunamis are at least an order-of-magnitude shorter than the real tsunamis, which calls for re-evaluation of the current understanding of tsunamis. To prompt the required paradigm shift, a new wave generator, namely the bottom-tilting wave generator, has been developed at the University of Dundee. The wave tank is fitted with an adjustable slope and a bottom flap hinged at the beginning of the slope. By moving the bottom flap up and down, we can generate very long waves. Here we will report characteristics of waves generated by simple bottom motions, either moving it upward or downward from an initial displacement ending it being horizontal. Two parameters, namely the initial displacement of the bottom and the speed of the motion, determine characteristics of the generated waves. Wave amplitudes scale well with the volume flux of the displaced water. On the other hand, due to combined effects of nonlinearity and dispersion, wavelengths show more complicated relationship with the two bottom motion parameters. We will also demonstrate that by combining simple up and down motions, it is possible to generate waves resembling the one measured during 2011 tsunami. [Preview Abstract] |
Sunday, November 20, 2016 4:28PM - 4:41PM |
D14.00008: Cylindrical waves at the interface of viscous immiscible fluids Ratul Dasgupta, Palas Kumar Farsoiya We conduct Navier-Stokes simulations of cylindrical, axisymmetric standing gravity waves at the interface of radially unbounded, immiscible viscous fluids. The fluid motion generated by these oscillations are studied. Results from the numerical solutions are compared to the analytical solution of an integro-differential equation representing the amplitude of motion of the interface. Standing waves are initiated at the interface as zeroth order Bessel's mode at rest i.e. $h(r,0) = H_0\left( 1 + \epsilon J_0(kr)\right)$ where $H_0$ is the undisturbed fluid depth in the simulation, chosen to be large enough for deep water approximation to hold. For small initial amplitudes (compared to $2\pi k^{-1}$), we obtain good agreement with the analytical solution at early times. As we increase initial amplitude, the time period of the first oscillation is found to increase. Diffusion of vorticity from the interface is studied as a function of initial amplitude. We compare our results to the analytical solution obtained from the corresponding planar problem (Prosperetti, 1981). We will discuss these results in the framework of the viscous Cauchy-Poisson (initial-value) problem between two fluids, and also compare our results to the viscous, single fluid case (Miles, 1968). [Preview Abstract] |
Sunday, November 20, 2016 4:41PM - 4:54PM |
D14.00009: Study of downward annular pipe flow using combined laser-based approaches Jae Sik An, Andrey Cherdantsev, Ivan Zadrazil, Omar Matar, Christos Markides In downward annular flow, the liquid phase flows as a film along the pipe wall and the gas flows in the core of the pipe. The liquid free-surface is covered by a complex multiscale system of waves. The interaction dynamics of the interfacial waves with each other and with the gas stream exert a significant influence on the pressure drop, heat transfer and mass interchange between the phases. The complexity of the interface requires the application of measurement techniques with high spatiotemporal resolution. In this work, two approaches based on the principle of laser-induced fluorescence, namely planar LIF and brightness-based LIF, are applied simultaneously to study interfacial phenomena in these flows, while simultaneous LIF and PIV are used to obtain velocity field information in the liquid phase underneath the waves. Sources of measurement bias are then analysed: total internal reflection at the out-of-plane interface; steep longitudinal slopes and transverse wave curvature; presence of gas bubbles in the liquid film. Although each method has its own limitations, a combined technique can provide reliable spatiotemporal measurements of film thickness to accompany the velocity information. Finally, flow development is studied in a moving frame of reference over long lengths. [Preview Abstract] |
Sunday, November 20, 2016 4:54PM - 5:07PM |
D14.00010: Characterization of interfacial waves in horizontal core-annular flow SUMIT TRIPATHI, Amitabh Bhattacharya, Ramesh Singh, Rico F. Tabor In this work, we characterize interfacial waves in horizontal core annular flow (CAF) of fuel-oil and water. Experimental studies on CAF were performed in an acrylic pipe of 15.5mm internal diameter, and the time evolution of the oil-water interface shape was recorded with a high speed camera for a range of different flow-rates of oil ($Q_o$) and water ($Q_w$). The power spectrum of the interface shape shows a range of notable features. First, there is negligible energy in wavenumbers larger than $2\pi/a$, where $a$ is the thickness of the annulus. Second, for high $Q_o/Q_w$, there is no single dominant wavelength, as the flow in the confined annulus does not allow formation of a preferred mode. Third, for lower $Q_o/Q_w$, a dominant mode arises at a wavenumber of $2\pi/a$. We also observe that the power spectrum of the interface shape depends weakly on $Q_w$, and strongly on $Q_o$, perhaps because the net shear rate in the annulus appears to depend weakly on $Q_w$ as well. We also attempt to build a general empirical model for CAF by relating the interfacial stress (calculated via the mean pressure gradient) to the flow rate in the annulus, the annular thickness and the core velocity. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700