On Evolution of Young Wind Waves in Time and Space

Abstract

The mechanisms governing the evolution of the wind-wave field in time and in space are not yet fully understood. Various theoretical approaches have been offered to model wind-wave generation. To examine their validity, detailed and accurate experiments under controlled conditions have to be carried out. Since it is next to impossible to get the required control of the governing parameters and to accumulate detailed data in field experiments, laboratory studies are needed. Extensive previously unavailable results on the spatial and temporal variation of wind waves accumulated in our laboratory under a variety of wind-forcing conditions and using diverse measuring techniques are reviewed. The spatial characteristics of the wind-wave field were determined using stereo video imaging. The turbulent airflow above wind waves was investigated using an X-hot film. The wave field under steady wind forcing as well as evolving from rest under impulsive loading was studied. An extensive discussion of the various aspects of wind waves is presented from a single consistent viewpoint. The advantages of the stochastic approach suggested by Phillips over the deterministic theory of wind-wave generation introduced by Miles are demonstrated. Essential differences between the spatial and the temporal analyses of wind waves’ evolution are discussed, leading to examination of the applicability of possible approaches to wind-wave modeling.

Spatial evolution of young wind waves: numerical modelling verified by experiments

“…The wind input modelling adopted here originates from the theory by Miles (1957, 1959), which is linear and deterministic, and thus predicts exponential growth in time. These features were retained in later developments of the theory – for more details, see Shemer (2019). However, experiments on wind-wave growth under impulsive forcing by Zavadsky & Shemer (2017 b ) demonstrate that the exponential growth stage is extremely short, and is followed by stages with growth that is essentially linear in time.…”

“…Note that an attempt by Liberzon & Shemer (2011) to determine experimentally the spatial growth rate coefficient of narrow band-pass filtered surface elevation records, defined as , revealed notable deviations from the exponential growth calculated using (3.1). Those deviations may be attributed to the effects of nonlinearity and dissipation (Shemer 2019).…”

“…Wind waves in the laboratory are often steeper than in the ocean under regular conditions; nonlinear effects are thus more essential. Nevertheless, as discussed in Shemer (2019), small-scale experiments provide valuable insight into the main processes associated with wind-wave evolution. In spite of their intrinsic limitations, a better understanding of the details of wave evolution under different wind forcing conditions gained in such experiments may significantly advance understanding of the interaction of wind waves, and in this way to contribute to wave modelling.…”

Self- and Inter-Crossover Points of Jasons’ Missions as New Essential Add-on of Satellite Altimetry in the Sub-Arctic Seas and the Southern Ocean

“…The appearance of gradient of H s in the basic relationship (2) is associated with two important features of the physical model [20]. First, the fetch-limited scenario of wind-wave evolution is considered as the most adequate to the dynamics of wind-driven sea [65][66][67]. It allows to relate variations of wave height with spectral flux of energy which is documented by instantaneous sea state parameters: wave height and wave period.…”

Effect of a weak current on wind-generated waves in the wrinkle regime

“…In this work, we account for the effect of a weak sheared current in the liquid, either longitudinal or transverse, by introducing a modified Doppler-shifted dispersion relation to lowest order in viscosity and current in the spectral theory previously derived by Perrard et al [J. Fluid Mech. 873, 1020(2019]. This theory describes the simplified one-way problem of surface deformations excited by a prescribed turbulent forcing, thereby neglecting the retroaction of waves on turbulence in the air.…”