Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session D05: Surface Waves I |
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Chair: Lian Shen, University of Minnesota, Twin Cities Room: Georgia World Congress Center B207 |
Sunday, November 18, 2018 2:30PM - 2:43PM |
D05.00001: Overtaking and runup of double solitary waves on a gentle slope Hua Liu The overtaking interaction of the double solitary waves over a plane slope is studied experimentally. The slope of the plane beach is 1:20. For the cases of the double solitary waves of different amplitude ratios and different relative wave crest distances, the time series of the surface elevation and waterline movement are measured by wave gauges and recorded by high-speed cameras respectively. Three categories of overtaking solitary wave interactions are reproduced in the wave flume. Analyzing the measured runups, it turns out that the maximum runup amplification coefficient, defined as the ratio of the maximum runup to the larger amplitude of the double solitary waves, is dependent of the relative distance between two peaks of the incident waves. There is a peak in the curve of the maximum runup amplification coefficient versus the relative distance. The mechanism of generating the peak value is that the violent plunging breaking does not appear by the overtaking collision of two solitary waves near the breaking point on the slope. |
Sunday, November 18, 2018 2:43PM - 2:56PM |
D05.00002: Wind-Induced Changes to Wave Shape Thomas Zdyrski, Falk Feddersen Wave shape (eg. skewness and asymmetry) plays an important role in beach morphology evolution and microwave backscatter. Past experiments have demonstrated that wind forcing can change wave shape; however, most analyses that couple wind and waves are phase-averaged and cannot predict the wave shape. Here, a wind-induced surface pressure is prescribed and a multiple-scale analysis is used to obtain solutions for periodic progressive waves. In the absence of wind, solutions reduce to deep water Stokes waves with zero asymmetry. Jeffreys- and Miles-types forcings, as well as a generalized Miles-type forcing, are considered at various orders in the perturbation expansion. The Miles-type forcing gives zero asymmetry identically, while the Jeffreys-type and generalized Miles-type each produce asymmetry that depends on the non-dimensional growth rate. |
Sunday, November 18, 2018 2:56PM - 3:09PM |
D05.00003: Measurements of the Turbulent Stress over Wind-Driven Surface Waves in the Wave-Boundary Layer Kianoosh Yousefi, Fabrice Veron, Marc P. Buckley, Nyla Husain, Tetsu Hara Wind-driven surface waves and the wave-modulated turbulence on both sides of the interface play an essential role in linking the air and sea. Although the effects of surface waves on the air-sea momentum flux have been the subject of several studies, the current understanding is still insufficient. We are presenting detailed quantitative velocity measurements over wind waves acquired in the large wind-wave tunnel facility using a combination of particle image velocimetry (PIV) and laser-induced fluorescence (LIF) techniques for wind speeds varying from 0.86 to 16.63 m s^{-1}. The mean, wave, and turbulent velocity fields were then obtained by a linear triple decomposition in wave-following coordinates. The turbulent stress can be therefore directly calculated. The contribution of the turbulent stress to the total momentum flux, for example, increases with increasing wind speed. The presence of the surface waves leads to wave-phase coherent variations in the turbulent stress within the so-called wave boundary layer. The distribution of the turbulent stress presents a pattern of along-wave asymmetry near the surface with a separation-induced maximum above the downwind of wave crests. Experimental results will be compared to LES results obtained for similar wind and wave conditions. |
Sunday, November 18, 2018 3:09PM - 3:22PM |
D05.00004: Simulation-based study of surface wave dynamics at the initial stage of wind-wave generation process Tianyi Li, Lian Shen How wind generates waves is of great interest over decades, while the mechanism of wave development at the initial stage still lacks detailed study. We performed direct numerical simulation (DNS) of turbulent wind over calm water. Navier-Stokes equations are solved on a curvilinear wave surface fitted grid, where fully-nonlinear kinematic and dynamic boundary conditions at the free surface are implemented. We focus on the initial development of wave patterns, which refers to the Phillips’ theory (1957). Results show that the temporal behaviors of surface wave fluctuations transit from power law growth ⟨η^{2} ⟩~t^{4} to linear growth ⟨η^{2} ⟩~t, and the corresponding mechanism is proposed based on the modification of Phillips’ framework. Contributions of both turbulent air pressure and turbulent air shear stress, acting on the water surface, to the wave temporal growth behavior are quantified. Detailed analysis of the feedback of surface deformation to the turbulent airflow is also presented. It is found that the space-time correlation of turbulent air pressure on the water surface also characterizes the linear growth rate of wave fluctuations. |
Sunday, November 18, 2018 3:22PM - 3:35PM |
D05.00005: Hydroelastic wake on a thin elastic sheet floating on water Jean-Christophe Ono-dit-Biot, Miguel Trejo, Elsie Loukiantcheko, Maximillian Lauch, Elie Raphael, Kari Dalnoki-Veress, Thomas Salez Waves can be formed at the surface of water by a moving disturbance. These waves are known as gravity-capillary waves and have been extensively studied both experimentally and theoretically. In this study, the surface of water is covered with a thin elastic film (hundreds of micrometers in thickness). A large tank filled with water is rotated at constant speed and a stationary air jet perturbs the surface of the covering film, thereby producing a hydroelastic wake. The waves are characterized as a function of the rotational speed of the tank using a high-resolution cross-correlation method. In particular, we experimentally probe the dispersion relation and compare to the theoretical expression. We find excellent agreement, revealing that gravity, tension and bending all contribute in our system. This study might have implications in geology, ice floes, as well as energy harvesting at the surface of the ocean. |
Sunday, November 18, 2018 3:35PM - 3:48PM |
D05.00006: A new method for determining near-surface shear current profiles from wave measurements Benjamin Smeltzer, Eirik Æsøy, Simen Å Ellingsen We present a new inversion method for finding the near-surface shear current profile from measurements of the wave spectrum. The method extracts wavelength-dependent Doppler shift velocities of the wave celerity due to the subsurface current, and assigns effective depths to the shifts using an iterative technique. The method gives an improvement over existing state-of-the-art techniques for most current profiles, and is less sensitive to experimental noise. We apply the method to laboratory experimental results of waves generated atop vertically-sheared currents of various depth-dependence, where particle image velocimetry (PIV) is used as ‘truth’ data. We also investigate the use of the method in cases where the current profile is known for deeper depths, which greatly reduces the error in the inferred current profiles. |
Sunday, November 18, 2018 3:48PM - 4:01PM |
D05.00007: Experimental study of surface wave phenomena on a vertically sheared current Benjamin K Smeltzer, Simen Å. Ellingsen We present an experimental study of surface waves on a sheared current. The experiments were performed in a newly built laboratory at the Norwegian University of Science and Technology. A shear current with a free surface is created in two different ways: with a curved mesh upstream, and in a region where an obstacle near the surface creates an area upstream of it where the surface is stagnant, and the sub-surface flow is strongly sheared. We present qualitative and quantitative observations of surface waves, wave dispersion and shear effects in the real and Fourier planes, and compare with theoretical results from a recently developed theoretical framework for initial waves on a current with arbitrary vertical shear. |
Sunday, November 18, 2018 4:01PM - 4:14PM |
D05.00008: Asynchronous shedding phenomena due to moving in-line double pressure sources on deep water Beomchan Park, Yeunwoo Cho Moving in-line double pressure sources move horizontally over the surface of deep water with speeds near the minimum phase speed c_{min}=23cm/s of gravity-capillary waves on deep water. Three different periodic shedding phenomena of 3-D depressions are observed according to the pressure-source speed near c_{min}; synchronous (in-phase) symmetric shedding of 3-D depressions behind each moving pressure source, asynchronous (out-of-phase) symmetric shedding of 3-D depressions behind each moving pressure source, and symmetric shedding of 3-D depressions behind the moving front pressure source along with the steady ‘V’-shaped wave pattern behind the moving rear pressure source. These experimental observations are compared with numerical results based on a model equation that admits gravity–capillary wave solutions near c_{min}. They agree with each other very well. |
Sunday, November 18, 2018 4:14PM - 4:27PM |
D05.00009: Stokes drift and ExB drift are the same thing. Paul W. Fontana Measurements of Lagrangian fluid particle drifts, such as Stokes drift, rarely match theoretical predictions. Because the classical prediction of Stokes drift is dependent on the wave model, it has been hard to identify what feature or features of the measured flows (e.g. reflux, vorticity, finite system size) violate the assumptions of the predictions to cause the discrepancy. It would therefore be desirable to understand if there is a general mechanism that produces drift that does not depend as particularly on the details of the model. In this talk, a technique for analyzing Lagrangian fluid particle kinematics is developed that models a particle trajectory as a circular gyration plus a steady drift, a path known as a "trochoid". We show that a particle undergoing such motion is experiencing in its frame a rotating centripetal acceleration proportional to its speed plus a constant cross-axis acceleration. This is exactly what happens in the ExB drift of charged particles, so that Stokes drift and ExB drift are special cases of the same phenomenon. In the case of Stokes drift we find that the cross-axis acceleration is connected with an upward Eulerian stress, suggesting that differences in that parameter may be why theory and experiment disagree. |
Sunday, November 18, 2018 4:27PM - 4:40PM |
D05.00010: Fantastic Fluted Films Matthew Jones, Nathan B Speirs, Mohammad Mansoor, Jesse L. Belden, Tadd Truscott When the rear end of a jet exits a pipe various beautiful shapes emerge. As the water flows through the pipe, the no-slip condition at the wall forms a thin boundary layer. Upon tube exit this slower moving fluid at the tube walls creates a thin tubular film, trailing behind the main water mass and connecting it to the tube exit. This film can morph into various shapes including fluted champagne glasses, bubbles, bells, jets, and crowns. We experimentally examine the regimes of this phenomenon and attempt to elucidate the physics behind how and why they occur. |
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