scholarly journals On Evolution of Young Wind Waves in Time and Space

Atmosphere ◽  
2019 ◽  
Vol 10 (9) ◽  
pp. 562 ◽  
Author(s):  
Shemer
Keyword(s):  
Wave Field ◽  
Field Experiments ◽  
Wind Wave ◽  
Wind Waves ◽  
Wave Generation ◽  
Wind Forcing ◽  
Spatial And Temporal Variation ◽  
Extensive Discussion ◽  
Deterministic Theory ◽  
Theoretical Approaches

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.

scholarly journals Loop-Type Wave-Generation Method for Generating Wind Waves under Long-Fetch Conditions

2017 ◽  
Vol 34 (10) ◽  
pp. 2129-2139 ◽  
Author(s):  
Naohisa Takagaki ◽  
Satoru Komori ◽  
Mizuki Ishida ◽  
Koji Iwano ◽  
Ryoichi Kurose ◽  
...  
Keyword(s):  
Wind Wave ◽  
Wind Waves ◽  
Peak Frequency ◽  
Wave Generation ◽  
New Wave ◽  
Wave Tank ◽  
Irregular Wave ◽  
Wind Speeds ◽  
Type Wave ◽  
Wave Generator

AbstractIt is important to develop a wave-generation method for extending the fetch in laboratory experiments, because previous laboratory studies were limited to the fetch shorter than several dozen meters. A new wave-generation method is proposed for generating wind waves under long-fetch conditions in a wind-wave tank, using a programmable irregular-wave generator. This new method is named a loop-type wave-generation method (LTWGM), because the waves with wave characteristics close to the wind waves measured at the end of the tank are reproduced at the entrance of the tank by the programmable irregular-wave generator and the mechanical wave generation is repeated at the entrance in order to increase the fetch. Water-level fluctuation is measured at both normal and extremely high wind speeds using resistance-type wave gauges. The results show that, at both wind speeds, LTWGM can produce wind waves with long fetches exceeding the length of the wind-wave tank. It is observed that the spectrum of wind waves with a long fetch reproduced by a wave generator is consistent with that of pure wind-driven waves without a wave generator. The fetch laws between the significant wave height and the peak frequency are also confirmed for the wind waves under long-fetch conditions. This implies that the ideal wind waves under long-fetch conditions can be reproduced using LTWGM with the programmable irregular-wave generator.

scholarly journals Observations of Wind Wave Development in Mixed Seas and Unsteady Wind Forcing*

2011 ◽  
Vol 41 (12) ◽  
pp. 2343-2362 ◽  
Author(s):  
Paul A. Hwang ◽  
Héctor García-Nava ◽  
Francisco J. Ocampo-Torres
Keyword(s):  
Wind Wave ◽  
Wave Generation ◽  
Wind Forcing ◽  
Quiescent State ◽  
Empirical Observation ◽  
Continuous Growth ◽  
Wave Growth ◽  
Wave Measurements ◽  
Wave Development ◽  
The Ideal

Abstract Theoretical study and experimental verification of wind wave generation and evolution focus generally on ideal conditions of steady state and quiescent initial background, of which the ideal fetch-limited wind wave growth is an important benchmark. In nature, unsteady winds and swell presence are more common. Here, the observations of wind wave development in mixed seas under unsteady and quasi-steady wind forcing are presented. With reference to the ideal fetch-limited growth functions established under steady wind forcing in the absence of swell, the analysis shows that the wind-steadiness factor impacts wave growth. The wind wave variance in mixed sea is enhanced in both accelerating and decelerating phases of an unsteady wind event, with a larger enhancement in the accelerating phase than in the decelerating phase. Spatial and temporal wind wave measurements under similar environmental conditions are also compared; the quantifiable differences in the wave development are attributable to the wind-steadiness factor. Coupled with the empirical observation that the average wind stress is decreased in mixed sea, these results suggest that wind wave generation and development are more efficient in mixed sea than in wind sea. Possible causes include (i) oscillatory modulation of surface roughness increases air–sea exchanges, (ii) background surface motion reduces energy waste for cold start of wind wave generation from a quiescent state, and (iii) breaking of short waves redistributes wind input and allows more of the available wind power to be directed to the longer waves for their continuous growth.

scholarly journals Wind-Waves Characteristics in the International Port of Algiers: Comparison of ALADIN and AROME’s Wind Effect

2019 ◽  
Vol 2 (3) ◽  
Author(s):  
Sara CHIKHI ◽  
Mohamed El-Amine Slimani
Keyword(s):  
Wind Wave ◽  
Wind Waves ◽  
National Development ◽  
Wave Model ◽  
Wind Forcing ◽  
Wind Effect ◽  
Atmospheric Models ◽  
The Stability ◽  
Ocean Wind ◽  
The Mediterranean Basin

The sea states numerical modeling has been developed for years, it used for very varied fields such as the sizing of coastal work, the safety of navigation, the study of the stability of the beaches or the water leisure.  The spectral third-generation ocean wind-wave model WAVEWATCH III (WW3) software was adopted and developed for simulating wave propagation in the Mediterranean basin.  In this study, a more detailed study was carried out on the port of Algiers. Two different atmospheric models have been used to get the wind forcing: ALADIN (Area Limited Dynamic Adaptation Inter National Development) with an 8 km resolution. And AROME (Application to Operational Research at Meso-scale) with a 3 km resolution. The results obtained using both of the atmospheric models have been compared and analyzed.

scholarly journals Stress above Wind-Plus-Paddle Waves: Modeling of a Laboratory Experiment

2007 ◽  
Vol 37 (12) ◽  
pp. 2824-2837 ◽  
Author(s):  
V. K. Makin ◽  
H. Branger ◽  
W. L. Peirson ◽  
J. P. Giovanangeli
Keyword(s):  
Stress Distribution ◽  
Laboratory Experiment ◽  
Wave Field ◽  
Stress Level ◽  
Surface Stress ◽  
Wind Wave ◽  
Wind Waves ◽  
Wave Steepness ◽  
Low Level ◽  
Level Characteristic

Abstract A model based on wind-over-waves coupling (WOWC) theory is used to simulate a laboratory experiment and to explain the observed peculiarities of the surface stress distribution above a combined wave field: wind-generated-plus-monochromatic-paddle waves. Observations show the systematic and significant decrease in the stress as the paddle wave is introduced into the pure wind-wave field. As the paddle-wave steepness is further increased, the stress level returns to the stress level characteristic of the pure wind waves. Further increase in the paddle-wave steepness augments the stress further. The WOWC model explains this peculiarity of the stress distribution by the fact that the paddle waves significantly damp the wind waves in the spectral peak. The stress supported by these dominant waves rapidly falls when the paddle wave is introduced, and this decrease is not compensated by the stress induced by the paddle wave. With further increase in the steepness of the paddle wave, the stress supported by dominant wind waves stays at a low level while the stress supported by the paddle waves continues to grow proportional to the square of the steepness, finally exceeding the stress level characteristic of the pure wind-wave field.

scholarly journals Numerical Investigation of Wind Waves in the Persian Gulf: Bathymetry Effects

2016 ◽  
Vol 33 (1) ◽  
pp. 17-31 ◽  
Author(s):  
Ying-Po Liao ◽  
James M. Kaihatu
Keyword(s):  
Persian Gulf ◽  
Wind Wave ◽  
Wind Waves ◽  
Peak Shift ◽  
Wave Generation ◽  
Seasonal Effects ◽  
Contour Maps ◽  
The North ◽  
Eastern Site ◽  
The Persian Gulf

AbstractThe effects of bathymetry on the process of wind-wave generation in the Persian Gulf have been investigated using a long-term hindcasting analysis. A 5-yr (2004–08) hindcasting procedure is first performed (denoted as origin) by using the Simulating Waves Nearshore (SWAN) model and COAMPS wind field data. Two alternative scenarios, in which wave breaking (noBrek) and depth-induced refraction (noRefc) are deactivated, are also generated. By comparing the results from alternative cases with those from the ordinary cases, a 5-yr total energy deviation (TED) is calculated and presented as seasonal contour maps depicting the sensitivity to bathymetry. The results show only ±2% TED found in noBrek, but up to ±20% TED found in noRefc, an order of magnitude larger than depth-induced breaking. Similarly, the seasonal effects of refraction on the nearshore wave-propagating directions can be investigated by comparison between origin and noRefc. The seasonal histograms of mean wave angle are plotted and discussed for three selected nearshore sites around Qatar, located at the western, northern, and eastern sides of the peninsula. The largest relative occurrence percentage and the largest peak shift ranging in 10°–20° can be found at the northern side, while the eastern side results in a weaker and more random distribution in the winter (the strong shamal season) due to the leeside location. The effect of fetch-limited wind-wave generation is also present at the eastern site, as remotely generated waves propagating eastward over a long fetch toward this site offset southward-propagating waves generated by dominant winds from the north over a limited fetch.

The influence of wave breaking on the surface pressure distribution in wind—wave interactions

1990 ◽  
Vol 211 ◽  
pp. 463-495 ◽  
Author(s):  
Michael L. Banner
Keyword(s):  
Pressure Distribution ◽  
Surface Pressure ◽  
Wave Breaking ◽  
Wind Wave ◽  
Wind Waves ◽  
Breaking Waves ◽  
Wind Forcing ◽  
Wave Interactions ◽  
Form Drag ◽  
Surface Pressure Distribution

In reviewing the current status of our understanding of the mechanisms underlying wind-wave generation, it is apparent that existing theories and models are not applicable to situations where the sea surface is disturbed by breaking waves, and that the available experimental data on this question are sparse. In this context, this paper presents the results of a detailed study of the effects of wave breaking on the aerodynamic surface pressure distribution and consequent wave-coherent momentum flux, as well as its influence on the total wind stress.Two complementary experimental configurations were used to focus on the details and consequences of the pressure distribution over breaking waves under wind forcing. The first utilized a stationary breaking wave configuration and confirmed the presence of significant phase shifting, due to air flow separation effects, between the surface pressure and surface elevation (and slope) distributions over a range of wind speeds. The second configuration examined the pressure distribution, recorded at a fixed height above the mean water surface just above the crest level, over short mechanically triggered waves which were induced to break almost continuously under wind forcing. This allowed a very detailed comparison of the form drag for actively breaking waves and for waves of comparable steepness just prior to breaking (‘incipiently’ breaking waves). For these propagating steep-wave experiments, the pressure phase shifts and distributions closely paralleled the stationary configuration findings. Moreover, a large increase (typically 100%) in the total windstress was observed for the breaking waves, with the increase corresponding closely to the comparably enhanced form drag associated with the actively breaking waves.In addition to further elucidating some fundamental features of wind-wave interactions for very steep wind waves, this paper provides a useful data set for future model calculations of wind flow over breaking waves. The results also provide the basis for a parameterization of the wind input source function applicable for a wave field undergoing active breaking, an important result for numerical modelling of short wind waves.

Water waves excited by near-impulsive wind forcing

2017 ◽  
Vol 828 ◽  
pp. 459-495 ◽  
Author(s):  
Andrey Zavadsky ◽  
Lev Shemer
Keyword(s):  
Wave Field ◽  
Water Waves ◽  
Wind Wave ◽  
Wind Forcing ◽  
Wave Parameter ◽  
Small Scale ◽  
Detailed Knowledge ◽  
Limited Information ◽  
Statistical Parameters ◽  
Resonance Model

Only limited information is currently available on the evolution of waves generated by wind that varies in time, and in particular on the initial stages of wind–wave growth from rest under a suddenly applied wind forcing. The emerging wind–wave field varies in time as well as in space. Detailed knowledge of wave parameter distributions under those conditions contributes to a better understanding of the mechanisms of wind wave generation. In the present study, the instantaneous surface elevation and two components of the instantaneous surface slope were recorded at various fetches in a small-scale experimental facility under nearly impulsive wind forcing. Numerous independent realizations have been recorded for each selection of operational conditions. Sufficient data at a number of fetches were accumulated to calculate reliable ensemble-averaged statistical parameters of the evolving random wind–wave field as a function of the time elapsed from activation of wind forcing. Distinct stages in the wave evolution process from appearance of initial ripples to emergence of a quasi-steady wind–wave field were identified. The experimental results during each stage of evolution were analysed in view of the viscous instability theory by Kawai (J. Fluid Mech., vol. 93, 1979, pp. 661–703) and the resonance model by Phillips (J. Fluid Mech., vol. 2, 1957, pp. 417–445).

Modelling the Impact of Squall on Wind Waves with the Generalized Kinetic Equation

2015 ◽  
Vol 45 (3) ◽  
pp. 807-812 ◽  
Author(s):  
Sergei Annenkov ◽  
Victor Shrira
Keyword(s):  
Kinetic Equation ◽  
Wave Field ◽  
Wind Wave ◽  
Wind Waves ◽  
Qualitative Difference ◽  
Time Interval ◽  
Short Time Interval ◽  
Spectral Evolution ◽  
Generalized Kinetic Equation ◽  
The Impact

AbstractThis is a first study of short-lived transient sea states, arising from fast variations of wind fields. This study considers the response of a wind-wave field to a sharp increase of wind over a short time interval (a squall). Conventional wind-wave models based on the Hasselmann equation assume quasi stationarity of a random wave field and are a priori inapplicable for such transient states. To describe fast spectral changes, the authors use the generalized kinetic equation (GKE) derived without the quasi-stationarity assumption. A novel efficient highly parallelized algorithm for the numerical simulation of the GKE is presented. Simulations with the GKE and the Hasselmann equation are examined and compared. While under steady wind, the spectral evolution in both cases is shown to be practically identical, but after the squall the qualitative difference emerges: the GKE predicts formation of a transient sea state with a considerably narrower peak.

scholarly journals PROPAGATION OF WIND WAVES ON TIDES

1988 ◽  
Vol 1 (21) ◽  
pp. 36 ◽  
Author(s):  
Hendrick L. Tolman
Keyword(s):  
Wave Propagation ◽  
Wind Wave ◽  
Numerical Models ◽  
Wind Waves ◽  
Absolute Frequency ◽  
Shelf Seas ◽  
Shelf Sea

Effects of instationary depths and currents in tides on shelf seas on wind wave propagation are investigated using two numerical models in two academical situations representing shelf sea conditions. It is shown that changes in absolute frequency, which are induced by the instationarity of depth and current, are significant in contrast to what is usually assumed. If these changes are neglected large and unpredictable errors may occur in calculated changes of wavenumber and amplitude.

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