Universality of Sea Wave Growth and Its Physical Roots

Modern day studies of wind-driven sea waves are usually focused on wind forcing rather than on the effect of resonant nonlinear wave interactions. The authors assume that these effects are dominating and propose a simple relationship between instant wave steepness and time or fetch of wave development expressed in wave periods or lengths. This law does not contain wind speed explicitly and relies upon this asymptotic theory. The validity of this law is illustrated by results of numerical simulations, in situ measurements of growing wind seas and wind wave tank experiments. The impact of the new vision of sea wave physics is discussed in the context of conventional approaches to wave modeling and forecasting.Comment: submitted to Journal of Fluid Mechanics 24-Sep-2014, 34 pages, 10 figure

Laboratory modelling of the wind-wave interaction with modified PIV-method

Laboratory experiments on studying the structure of the turbulent air boundary layer over waves were carried out at the Wind-Wave Flume of the Large Thermostratified Tank of the Institute of Applied Physics, Russian Academy of Sciences (IAP RAS), in conditions modeling the near water boundary layer of the atmosphere under strong and hurricane winds and the equivalent wind velocities from 10 to 48 m/s at the standard height of 10 m. A modified technique of Particle Image Velocimetry (PIV) was used to obtain turbulent pulsation averaged velocity fields of the air flow over the water surface curved by a wave and average profiles of the wind velocity. The main modifications are: 1) the use of high-speed video recording (1000-10000 frames/sec) with continuous laser illumination helps to obtain ensemble of the velocity fields in all phases of the wavy surface for subsequent statistical processing; 2) the development and application of special algorithms for obtaining form of the curvilinear wavy surface of the images for the conditions of parasitic images of the particles and the droplets in the air side close to the surface; 3) adaptive cross-correlation image processing to finding the velocity fields on a curved grid, caused by wave boarder; 4) using Hilbert transform to detect the phase of the wave in which the measured velocity field for subsequent appropriate binning within procedure obtaining the average characteristics

La génération des vagues par le vent: est-ce un problème résolu à l'heure actuelle?

séminair

Experimental study of microbreaking and breaking wind wave properties

Macro and micro-scale wave breaking generates at the air-sea interface high surface slope and curvature roughness which in turn affects significantly momentum transfer from wind to waves, leads to the formation of vortical structures in water and modifies deeply electromagnetic and acoustic wave reflectivity at the water surface. The geometric properties of the parasitic capillaries or the plunging jet formed when steady monochromatic waves break have been rather well described over the last decades, both experimentally and by means of numerical simulations. However, owing to their variability, the basic features of wind wave field breakers of various scales as observed at sea or even in laboratory are far from being identified up to now. In the present work, we report the first results of an experimental investigation of the breaking wind wave surface motions as observed in the large IRPHE-Luminy wind wave tank for a wide range of wind speeds. Visualizations of gravity-capillary to gravity-scale wave breaker profiles were made simultaneously with single-point wave elevation and slope measurements. It is shown that microscale breakers exhibit a characteristic signature in slope suggesting the formation of a bulge on the forward face of the wave crest but parasitic ripples are not systematically generated ahead. Such breakers are observed for a wide range of wave steepness and wave slope skewness thus weakly dependent on wavelength and wind forcing. In comparison, short gravity-scale breaking waves present a much more complex shape. A number of their geometric properties are then analysed statistically as function of wind speed

Characteristic slopes and curvatures of wind waves observed in laboratory

Séminair