Modulation of short wind waves by a long surface wave: a mechanism for feedback with an air flow

1997 ◽  
Vol 8 (5) ◽  
pp. 305-327
Author(s):  
V. N. Kudryavtsev ◽  
K. Mastenbroek ◽  
V. K. Makin
Keyword(s):  
Surface Wave ◽  
Wind Waves ◽  
Air Flow

On the interaction of surface and internal waves

1972 ◽  
Vol 52 (1) ◽  
pp. 179-191 ◽  
Author(s):  
A. E. Gargettt ◽  
B. A. Hughes
Keyword(s):  
Surface Wave ◽  
Internal Wave ◽  
Surface Waves ◽  
Internal Waves ◽  
Wind Waves ◽  
Phase Speed ◽  
Surface Current ◽  
Propagation Direction ◽  
Wave Crest ◽  
Critical Position

The steady-state interaction between surface waves and long internal waves is investigated theoretically using the radiation stress concepts derived by Longuet-Higgins & Stewart (1964) (or Phillips 1966). It is shown that, over internal wave crests, those surface waves for which cg0cosϕ0 > ci experience a change in direction of propagation towards the line of propagation of the internal waves and their amplitudes are increased. Here cg0 is the surface-wave group speed at U = 0, ϕ0 is the angle between the propagation direction of the surface waves at U = 0 and the propagation direction of the internal waves, and ci is the phase speed of the internal waves. If cg0cos ϕ0 < ci the direction of the surface waves is turned away and their amplitudes are decreased. Over troughs the opposite effects occur.At positions where the local velocity of surface-wave energy transmission measured relative to the internal wave phase velocity is zero, i.e. cg + U − ci = 0, there is a singularity in the energy of the surface waves with resulting infinite amplitudes. It is shown that at these critical positions two wavenumbers which were real and distinct on one side coalesce and become complex on the other. The critical positions are thus shown to be barriers to the propagation of those wave-numbers. It is also shown that there is a critical position representing the coalescence of three wavenumbers. Surface-wave crest configurations are shown for three numerical examples. The frequency and direction of propagation of surface waves that exhibit critical positions somewhere in an internal wave field are shown as a function of the maximum horizontal surface current. This is compared with measurements of wind waves that have been reported elsewhere.

scholarly journals A NOTE ON THE DEVELOPMENT OF WIND WAVES IN AN EXPERIMENT

1966 ◽  
Vol 1 (10) ◽  
pp. 5
Author(s):  
Tokuichi Hamada ◽  
Akihiko Shibayama ◽  
Hajime Kato
Keyword(s):  
Boundary Condition ◽  
Tangential Stress ◽  
Water Surface ◽  
Physical Mechanism ◽  
Wind Waves ◽  
Air Flow ◽  
Wave Momentum

This is a note paper of experiment in an air-water experimental waterway. Two cases of the uniform depth of water 50 cm and of the uniform depth of water 15 cm are examined. The boundary condition for air flow is not changed. In a condition of almost the same discharge of air flow on the water surface, the development of wind waves is investigated. The properties of wind waves are slightly different in each case, but the analysis of physical mechanism of the development suggests that almost the same mechanism is active throughout both cases. Stillmore the portion of tangential stress, which is apparently transfered to wave momentum, is numerically obtained, and it is not so different in both cases of depth of water.

scholarly journals Occurrence Frequency of Air-flow Separation over Wind Waves

2009 ◽  
Vol 65 (1) ◽  
pp. 76-80
Author(s):  
Natsuki MIZUTANI ◽  
Cowen Edwin A. ◽  
Masahiro MIYAJIMA
Keyword(s):  
Flow Separation ◽  
Wind Waves ◽  
Air Flow ◽  
Occurrence Frequency

scholarly journals Observing Surface Wave Directional Spectra under Typhoon Megi 2010 using Subsurface EM-APEX Floats

2021 ◽  
Author(s):  
Je-Yuan Hsu
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Current Velocity ◽  
Autonomous Vehicles ◽  
Wind Waves ◽  
Peak Frequency ◽  
Ocean Dynamics ◽  
Vertical Acceleration ◽  
Wave Direction ◽  
The Right

AbstractEM-APEX floats as autonomous vehicles have been used for profiling temperature, salinity and current velocity for more than a decade. In the traditional method for processing horizontal current velocity from float measurements, signals of surface wave motion are removed as residuals. Here, a new data processing method is proposed for deriving the horizontal velocity of surface waves at the floats. Combined with the vertical acceleration measurements of waves, surface wave directional spectra E(f,θ) can be computed. This method is applied to the float measurements on the right of Typhoon Megi’s track 2010. At 0.6 day before the passage of Megi’s eye to the floats, the fast-propagating swell may affect wind waves forced by the local storm wind. When the storm moves closer to the floats, the increasing wind speed and decreasing angle between wind and dominant wave direction may enhance the wind forcing and form a mono-modal spectrum E(f). The peak frequency fp ~ 0.08 Hz and significant wave height > 10 m are found near the eyewall. After the passage of the eye to the floats, the fp increases to > 0.1 Hz. Although E(f) still has a single spectral peak at the rear-right quadrant of Megi, E(f,θ) at frequencies from 0.08 to 0.12 Hz has waves propagating in three different directions as a tri-modal spectrum, partially due to the swell propagating from the rear-left quadrant. Enhancing the capability of EM-APEX floats to observe wave spectra is critical for exploring the roles of surface waves in the upper ocean dynamics in the future.

Linear dynamics of wind waves in coupled turbulent air—water flow. Part 1. Theory

1994 ◽  
Vol 271 ◽  
pp. 119-151 ◽  
Author(s):  
S. E. Belcher ◽  
J. A. Harris ◽  
R. L. Street
Keyword(s):  
Growth Rate ◽  
Water Flow ◽  
Water Waves ◽  
Wind Waves ◽  
Air Flow ◽  
Local Equilibrium ◽  
Outer Region ◽  
Wave Growth ◽  
Drift Current ◽  
The Waves

When air blows over water the wind exerts a stress at the interface thereby inducing in the water a sheared turbulent drift current. We present scaling arguments showing that, if a wind suddenly starts blowing, then the sheared drift current grows in depth on a timescale that is larger than the wave period, but smaller than a timescale for wave growth. This argument suggests that the drift current can influence growth of waves of wavelength λ that travel parallel to the wind at speed c.In narrow ‘inner’ regions either side of the interface, turbulence in the air and water flows is close to local equilibrium; whereas above and below, in ‘outer’ regions, the wave alters the turbulence through rapid distortion. The depth scale, la, of the inner region in the air flow increases with c/u*a (u*a is the unperturbed friction velocity in the wind). And so we classify the flow into different regimes according to the ratio la/λ. We show that different turbulence models are appropriate for the different flow regimes.When (u*a + c)/UB(λ) [Lt ] 1 (UB(z) is the unperturbed wind speed) la is much smaller than λ. In this limit, asymptotic solutions are constructed for the fully coupled turbulent flows in the air and water, thereby extending previous analyses of flow over irrotational water waves. The solutions show that, as in calculations of flow over irrotational waves, the air flow is asymmetrically displaced around the wave by a non-separated sheltering effect, which tends to make the waves grow. But coupling the air flow perturbations to the turbulent flow in the water reduces the growth rate of the waves by a factor of about two. This reduction is caused by two distinct mechanisms. Firstly, wave growth is inhibited because the turbulent water flow is also asymmetrically displaced around the wave by non-separated sheltering. According to our model, this first effect is numerically small, but much larger erroneous values can be obtained if the rapid-distortion mechanism is not accounted for in the outer region of the water flow. (For example, we show that if the mixing-length model is used in the outer region all waves decay!) Secondly, non-separated sheltering in the air flow (and hence the wave growth rate) is reduced by the additional perturbations needed to satisfy the boundary condition that shear stress is continuous across the interface.

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