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The present study aims to extend the applicability of the static-boundary absorption method in phase-resolving CFD simulations outside the conventional shallow-water waves limit. Even though this method was originally formulated for shallow-water waves based on the conventional piston type wavemaker, extending its use to deeper water conditions provides a more practical and computationally cost efficient solution compared to other available numerical wave absorption alternatives. For this sake, absorption of unidirectional monochromatic waves in a semi-infinite flume by means of a static wall is investigated theoretically and numerically. Moreover, implementation to a practical wave-structure interaction application is investigated numerically and experimentally. A phase-resolving numerical model based on the Reynold-averaged Navier-Stokes (RANS) equations is implemented using the open source C++ toolbox OpenFOAM. The study presents the performance of the static-boundary method, in a dimensionless manner, by limiting the depth at which the active-absorption conventional-piston velocity profile is introduced; as a function of incident wave conditions. Moreover, it is shown that the performance of the static-boundary method can be significantly enhanced where wave reflection was reduced to about half of that of the conventional setup in deep-water conditions. Furthermore, the absorption depth is correlated to the incident wave conditions; providing an optimization framework for the selection of the proper dimensions of an absorbing wall. Finally, wave-structure interaction experimental tests were conducted to validate the numerical model performance; which shows an acceptable agreement between the model and the experimental observations. The proposed limiter is straight forward to be applied in pre-existing wave-structure interaction CFD solvers, without the need of code modifications., Comment: 23 pages, 17 figures, 5 tables

The CO2 gas transfer velocity (KCO2) at air-water interface in a wind-wave flume was estimated at the circumstance of wave breaking. Three types of dynamic processes in the flume were created: monochromatic waves generated by wavemaker, mechanically-generated monochromatic waves with superimposed wind forcing, pure wind waves with 10-meter wind speed ranging from 4.5 m/s to 15.5 m/s. Without wind forcing, KCO2 correlated with the wave breaking probability, wave height of breakers and energy loss due to wave breaking. With superimposed wind, wind speed was found to influence KCO2 both in the coupled wind/mechanical wave experiments and in pure wind waves, but wave breaking still played a significant role in CO2 gas exchange. Therefore, wave properties should be considered directly in parameterization of KCO2. A non-dimensional empirical formula was established in which KCO2 is expressed as a function of wave breaking probability, a modified Reynolds number and an enhancement factor to account for wind speed., Comment: 10 pages, 5 figures

Solitons and breathers are nonlinear modes that exist in a wide range of physical systems. They are fundamental solutions of a number of nonlinear wave evolution equations, including the uni-directional nonlinear Schr\"odinger equation (NLSE). We report the observation of slanted solitons and breathers propagating at an angle with respect to the direction of propagation of the wave field. As the coherence is diagonal, the scale in the crest direction becomes finite, consequently, a beam dynamics forms. Spatio-temporal measurements of the water surface elevation are obtained by stereo-reconstructing the positions of the floating markers placed on a regular lattice and recorded with two synchronized high-speed cameras. Experimental results, based on the predictions obtained from the (2D+1) hyperbolic NLSE equation, are in excellent agreement with the theory. Our study proves the existence of such unique and coherent wave packets and has serious implications for practical applications in optical sciences and physical oceanography. Moreover, unstable wave fields in this geometry may explain the formation of directional large amplitude rogue waves with a finite crest length within a wide range of nonlinear dispersive media, such as Bose-Einstein condensates, plasma, hydrodynamics and optics.

The paper by Beya et al. (2012, hereinafter BPB) has a general title of Turbulence Beneath Finite Amplitude Water Waves, but is solely dedicated to discussing the experiment by Babanin and Haus (2009, hereinafter BH) who conducted measurements of wave-induced non-breaking turbulence by particle image velocimetry (PIV). The authors of BPB conclude that their observations contradict those of BH. Here we argue that the outcomes of BPB do not contradict BH. In addition, although the main conclusion of BPB is that there is no turbulence observed in their experiment, it actually is observed., Comment: 10 pages, 1 figure

A stochastic second-order wave model is applied to assess the statistical properties of wave orbital velocity in random sea states below the water surface. Directional spreading effects as well as the dependency of the water depth are investigated by means of a Monte-Carlo approach. Unlike for the surface elevation, sub-harmonics dominate the second-order contribution to orbital velocity. We show that a notable set-down occurs for the most energetic and steepest groups. This engenders a negative skewness in the temporal evolution of the orbital velocity. A substantial deviation of the upper and lower tails of the probability density function from the Gaussian distribution is noticed, velocities are faster below the wave trough and slower below the wave crest when compared with linear theory predictions. Second-order nonlinearity effects strengthen with reducing the water depth, while weaken with the broadening of the wave spectrum. The results are confirmed by laboratory data. Corresponding experiments have been conducted in a large wave basin taking into account the directionality of the wave field. As shown, laboratory data are in very good agreement with the numerical prediction., Comment: 13 pages, 8 figures