Statistical Analysis of the Spatial Evolution of the Stationary Wind Wave Field

Abstract Detailed investigation of wind-generated water waves in a 5-m-long wind wave flume facility is reported. Careful measurements were carried out at a large number of locations along the test section and at numerous airflow rates. The evolution of the wind wave field was investigated using appropriate dimensionless parameters. When possible, quantitative comparison with the results accumulated in field measurements and in larger laboratory facilities was performed. Particular attention was given to the evolution of wave frequency spectra along the tank, distinguishing between the frequency domain around the spectral peak and the high-frequency tail of the spectrum. Notable similarity between the parameters of the evolving wind wave field in the present facility and in field measurements was observed.

Download Full-text

Wind-induced growth of water waves

Journal of Fluid Mechanics ◽

10.1017/s0022112082003139 ◽

1982 ◽

Vol 123 ◽

pp. 425-442 ◽

Cited By ~ 90

Author(s):

H. Mitsuyasu ◽

T. Honda

Keyword(s):

Growth Rate ◽

Water Waves ◽

Friction Velocity ◽

Wind Wave ◽

Wind Waves ◽

Pure Water ◽

Wave Flume ◽

Wind Speeds ◽

Wind Profiles ◽

The Waves

Spatial growth of mechanically generated water waves under the action of wind has been measured in a laboratory wind-wave flume both for pure water and for water containing a surfactant (sodium lauryl sulphate, concentration 2.6 × 10−2%). I n the latter case, no wind waves develop on the surface of the mechanically generated waves as well as on the still water surface for wind speeds up to U10≈ 15 m/s, where U10 is the wind velocity at the height Z = 10 m. Therefore we can study the wind-induced growth of monochromatic waves without the effects of co-existing short wind waves. The mechanically generated waves grew exponentially under the action of the wind, with fetch in both cases. The measured growth rate β for the pure water can be fitted by β/f = 0.34(U*/C)2 0.1 [lsime ] U*/C [lsime ] 1.0, where f is the frequency of the waves, C is the corresponding phase velocity, and U, is the friction velocity obtained from vertical wind profiles. The effect of the wave steepness H/L on the dimensionless growth rate β/f is not clear, but seems to be small. For water containing the surfactant, the measured growth rate is smaller than that for pure water, but the friction velocity of the wind is also small, and the above relation between β/f and U*/C holds approximately if the measured friction velocity U* is used for the relation.

Download Full-text

Rogue Waves in Wind Seas: An Experimental Model in an Annular Wind-Wave Flume

Volume 3A: Structures, Safety and Reliability ◽

10.1115/omae2017-61156 ◽

2017 ◽

Author(s):

A. Toffoli ◽

D. Proment ◽

H. Salman ◽

J. Monbaliu ◽

E. Stramignoni ◽

...

Keyword(s):

Wave Field ◽

Cross Sections ◽

Wind Wave ◽

Rogue Waves ◽

Surface Elevation ◽

Order Moment ◽

Wave Flume ◽

Wind Speeds ◽

Resonant Wave ◽

Development Regime

The probability of occurrence of rogue waves in wind-generated fields is investigated experimentally in an annular wind-wave flume. Unlike many experiments on rogue waves, where waves are mechanically generated, here the wave field is forced naturally by wind as it is in the ocean. The peculiar geometry of the flume makes waves propagating circularly in an unlimited-fetch condition. Water surface elevation was measured at specific cross-sections under the effect of different wind speeds to monitor the temporal evolution of the wave field. Results show that the kurtosis of the surface elevation, the fourth order moment of the probability density function and a measure of the percentage of extremes in a wave record, gradually increases in time with the evolution of the wave field. Deviations from Normal statistics are observed to be a function of wind speed. The maximum departure from Normality resembled the one induced by quasi-resonant wave-wave interactions and it is observed at the final stage of wave growth and immediately before reaching the fully development regime.

Download Full-text

Water waves excited by near-impulsive wind forcing

Journal of Fluid Mechanics ◽

10.1017/jfm.2017.521 ◽

2017 ◽

Vol 828 ◽

pp. 459-495 ◽

Cited By ~ 7

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).

Download Full-text

Wind–wave coupling study using LES of wind and phase-resolved simulation of nonlinear waves

Journal of Fluid Mechanics ◽

10.1017/jfm.2019.444 ◽

2019 ◽

Vol 874 ◽

pp. 391-425 ◽

Cited By ~ 7

Author(s):

Xuanting Hao ◽

Lian Shen

Keyword(s):

Wave Field ◽

Water Waves ◽

Wind Wave ◽

Wave Spectrum ◽

High Order ◽

Band Spectrum ◽

Wave Growth ◽

Turbulent Wind ◽

Wind Turbulence ◽

The Waves

We present a study on the interaction between wind and water waves with a broad-band spectrum using wave-phase-resolved simulation with long-term wave field evolution. The wind turbulence is computed using large-eddy simulation and the wave field is simulated using a high-order spectral method. Numerical experiments are carried out for turbulent wind blowing over a wave field initialised using the Joint North Sea Wave Project spectrum, with various wind speeds considered. The results show that the waves, together with the mean wind flow and large turbulent eddies, have a significant impact on the wavenumber–frequency spectrum of the wind turbulence. It is found that the shear stress contributed by sweep events in turbulent wind is greatly enhanced as a result of the waves. The dependence of the wave growth rate on the wave age is consistent with the results in the literature. The probability density function and high-order statistics of the wave surface elevation deviate from the Gaussian distribution, manifesting the nonlinearity of the wave field. The shape of the change in the spectrum of wind-waves resembles that of the nonlinear wave–wave interactions, indicating the dominant role played by the nonlinear interactions in the evolution of the wave spectrum. The frequency downshift phenomenon is captured in our simulations wherein the wind-forced wave field evolves for $O(3000)$ peak wave periods. Using the numerical result, we compute the universal constant in a wave-growth law proposed in the literature, and substantiate the scaling of wind–wave growth based on intrinsic wave properties.

Download Full-text

A New Inversion Method to Obtain Upper-Ocean Current-Depth Profiles Using X-Band Observations of Deep-Water Waves

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-16-0120.1 ◽

2017 ◽

Vol 34 (5) ◽

pp. 957-970 ◽

Cited By ~ 11

Author(s):

Jeffrey Campana ◽

Eric J. Terrill ◽

Tony de Paolo

Keyword(s):

Wave Field ◽

Water Waves ◽

Wave Spectrum ◽

Field Measurements ◽

New Method ◽

Ocean Current ◽

Inversion Method ◽

Depth Profiles ◽

X Band ◽

Rms Error

AbstractA new method for estimating current-depth profiles from observations of wavenumber-dependent Doppler shifts of the overlying ocean wave field is presented. Consecutive scans of marine X-band backscatter provide wave field measurements in the time–space domain that transform into the directional wavenumber–frequency domain via a 3D fast Fourier transform (FFT). Subtracting the linear dispersion shell yields Doppler shift observations in the form of (kx, ky, Δω) triplets. A constrained linear regression technique is used to extract the wavenumber-dependent effective velocities, which represent a weighted depth average of the Eulerian currents (Stewart and Joy). This new method estimates these Eulerian currents from the effective velocities via the inversion of the integral relationship, which was first derived by Stewart and Joy. To test the effectiveness of the method, the inverted current profiles are compared to concurrent ADCP measurements. The inversion method is found to successfully predict current behavior, with a depth-average root-mean-square (RMS) error less than 0.1 m s−1 for wind speeds greater than 5 m s−1 and a broad wave spectrum. The ability of the inversion process to capture the vertical structure of the currents is assessed using a time-average RMS error during these favorable conditions. The time-averaged RMS error is found to be less than 0.1 m s−1 for depths shallower than 20 m, approximately twice the depth of existing methods of estimating current shear from wave field measurements.

Download Full-text

An Inexpensive Method for Measurements of Static Pressure Fluctuations

Journal of Atmospheric and Oceanic Technology ◽

10.1175/2009jtecha1352.1 ◽

2010 ◽

Vol 27 (4) ◽

pp. 776-784 ◽

Cited By ~ 3

Author(s):

Dan Liberzon ◽

Lev Shemer

Keyword(s):

Water Waves ◽

Static Pressure ◽

Wind Wave ◽

Dynamic Pressure ◽

Pressure Fluctuations ◽

Pressure Probe ◽

Directional Sensitivity ◽

Inexpensive Method ◽

Wave Flume ◽

High Dynamic

Abstract An application of a commercially available and inexpensive pressure probe and transducer, originally designed for pressure drop measurements in air conditioning conduits, is suggested for accurate and reliable measurements of static pressure fluctuations in airflow, with a particular application to wind interaction with water waves. It is demonstrated that this static pressure probe is a robust instrument that offers efficient dynamic pressure elimination while having low directional sensitivity and sufficiently high dynamic response. A series of measurements in a wind-wave flume was carried out to validate the characteristics of the sensor and of the pressure transducer.

Download Full-text

On the separation of air flow over water waves

Journal of Fluid Mechanics ◽

10.1017/s0022112076002905 ◽

1976 ◽

Vol 77 (4) ◽

pp. 825-842 ◽

Cited By ~ 183

Author(s):

M. L. Banner ◽

W. K. Melville

Keyword(s):

Water Waves ◽

Wind Wave ◽

Air Flow ◽

Interfacial Shear Stress ◽

Breaking Wave ◽

Pressure Measurements ◽

Wave Flume ◽

Air Water Interface ◽

Interfacial Boundary ◽

Air Blowing

Conditions leading to the onset of air-flow separation over a mobile air-water interface are discussed. It is argued that, in a frame of reference in which the interfacial boundary assumes a steady shape, the occurrence of separation requires a stagnation point on the interface. In the case of air blowing over water waves, this corresponds to the onset of wave breaking. These arguments are strongly supported by flow visualization and pressure measurements carried out in a laboratory wind-wave flume. Furthermore, the pressure measurements show a greatly enhanced interfacial shear stress for a breaking wave compared with that over an unbroken wave of the same wavelength. The implications of these findings for wind-wave generation are discussed.

Download Full-text

Momentum and buoyancy transfer in atmospheric turbulent boundary layer over wavy water surface – Part 2: Wind–wave spectra

Nonlinear Processes in Geophysics ◽

10.5194/npg-20-841-2013 ◽

2013 ◽

Vol 20 (5) ◽

pp. 841-856 ◽

Cited By ~ 7

Author(s):

Yu. I. Troitskaya ◽

E. V. Ezhova ◽

D. A. Sergeev ◽

A. A. Kandaurov ◽

G. A. Baidakov ◽

...

Keyword(s):

High Frequency ◽

Wind Wave ◽

Wave Number ◽

Transfer Coefficients ◽

Experiment Data ◽

Mean Velocity ◽

Tropical Ocean ◽

Frequency Spectra ◽

Number Frequency ◽

Wave Induced

Abstract. Drag and mass exchange coefficients are calculated within a self-consistent problem for the wave-induced air perturbations and mean velocity and density fields using a quasi-linear model based on the Reynolds equations with down-gradient turbulence closure. This second part of the report is devoted to specification of the model elements: turbulent transfer coefficients and wave number-frequency spectra. It is shown that the theory agrees with laboratory and field experimental data well when turbulent mass and momentum transfer coefficients do not depend on the wave parameters. Among several model spectra better agreement of the theoretically calculated drag coefficients with TOGA (Tropical Ocean Global Atmosphere) COARE (Coupled Ocean–Atmosphere Response Experiment) data is achieved for the Hwang spectrum (Hwang, 2005) with the high frequency part completed by the Romeiser spectrum (Romeiser et al., 1997).

Download Full-text