The coupling of wind and internal waves: modulation and friction mechanisms

1994 ◽  
Vol 278 ◽  
pp. 33-62 ◽  
Author(s):  
V. N. Kudryavtsev
Keyword(s):  
Random Field ◽  
Internal Waves ◽  
Joint Action ◽  
Friction Mechanisms ◽  
Wind Waves ◽  
Spontaneous Generation ◽  
Inertial Oscillations ◽  
Feedback Mechanisms ◽  
Strong Winds ◽  
Ekman Current

The interaction between internal waves (IW) and wind waves (WW) is studied. Three types of interaction are considered: spontaneous IW generation by a random field of WWs, and two feedback mechanisms - modulation and friction.The latter mechanism has not been studied before. Its influence on the IW-WW coupling is of primary importance. The modulation and friction mechanisms result in exponential attenuation of the IWs. Attenuation of IWs propagating against wind is the strongest. The IW attenuation has a dimensionless decrement of order 10-3, whereas for storm winds it attains the value of 10-2. Joint action of the spontaneous generation of IWs and their attenuation due to feedback mechanisms permits a stationary ‘wind-IW’ spectrum to exist. For strong winds the ‘wind-IW’ energy is of order 105 erg cm-2. The effect of IWs on currents in the ocean's upper layer is considered. Momentum and energy lost by IWs due to their interaction with WWs generates inertial oscillations. Under the attenuation of intensive IWs, the amplitude of inertial oscillations may be compared with the background Ekman current.

On the energy spectra of a random field of internal waves

Tellus ◽  
1972 ◽  
Vol 24 (2) ◽  
pp. 161-163 ◽  
Author(s):  
Jacques C. J. Nihoul
Keyword(s):  
Random Field ◽  
Internal Waves ◽  
Energy Spectra

scholarly journals Strong Modulation of Short Wind Waves and Ka-Band Radar Return Due to Internal Waves in the Presence of Surface Films. Theory and Experiment

2021 ◽  
Vol 13 (13) ◽  
pp. 2462
Author(s):  
Stanislav A. Ermakov ◽  
Irina A. Sergievskaya ◽  
Ivan A. Kapustin
Keyword(s):  
Phase Velocity ◽  
Internal Waves ◽  
Wind Waves ◽  
Strong Increase ◽  
Small Scale ◽  
Surface Films ◽  
Ka Band ◽  
Steady Current ◽  
Backscatter Modulation ◽  
Resonance Surface

Strong variability of Ka-band radar backscattering from short wind waves on the surface of water covered with surfactant films in the presence of internal waves (IW) was studied in wave tank experiments. It has been demonstrated that modulation of Ka-band radar return due to IW strongly depends on the relationship between the phase velocity of IW and the velocity of drifting surfactant films. An effect of the strong increase in surfactant concentration was revealed in convergent zones, associated with IW orbital velocities in the presence of a “resonance” surface steady current, the velocity of which was close to the IW phase velocity. A phenomenological model of suppression and modulations in the spectrum of small-scale wind waves due to films and IW was elaborated. It has been shown that backscatter modulation could not be explained by the modulation of free (linear) millimeter-scale Bragg waves, but was associated with the modulation of bound (parasitic) capillary ripples generated by longer, cm–dm-scale waves—a “cascade” modulation mechanism. Theoretical analysis based on the developed model was found to be consistent with experiments. Field observations which qualitatively illustrated the effect of strong modulation of Ka-band radar backscatter due to IW in the presence of resonance drift of surfactant films are presented.

scholarly journals Brief communication: Modulation instability of internal waves in a smoothly stratified shallow fluid with a constant buoyancy frequency

2019 ◽  
Vol 19 (3) ◽  
pp. 583-587 ◽  
Author(s):  
Kwok Wing Chow ◽  
Hiu Ning Chan ◽  
Roger H. J. Grimshaw
Keyword(s):  
Numerical Simulation ◽  
Surface Wave ◽  
Internal Waves ◽  
Modulation Instability ◽  
Rogue Waves ◽  
Buoyancy Frequency ◽  
Spontaneous Generation ◽  
Large Displacements ◽  
Analytical Treatment ◽  
Intermediate Depth

Abstract. Unexpectedly large displacements in the interior of the oceans are studied through the dynamics of packets of internal waves, where the evolution of these displacements is governed by the nonlinear Schrödinger equation. In cases with a constant buoyancy frequency, analytical treatment can be performed. While modulation instability in surface wave packets only arises for sufficiently deep water, “rogue” internal waves may occur in shallow water and intermediate depth regimes. A dependence on the stratification parameter and the choice of internal modes can be demonstrated explicitly. The spontaneous generation of rogue waves is tested here via numerical simulation.

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 Brief communication: The occurrence of rogue waves in the interior of the oceans: A modelling and computational study

2018 ◽  
Author(s):  
Kwok Wing Chow ◽  
Hiu Ning Chan ◽  
Roger H. J. Grimshaw
Keyword(s):  
Numerical Simulations ◽  
Internal Waves ◽  
Deep Water ◽  
Modulation Instability ◽  
Computational Study ◽  
Rogue Waves ◽  
Buoyancy Frequency ◽  
Spontaneous Generation ◽  
Large Displacements ◽  
Analytical Treatment

Abstract. The occurrence of unexpectedly large displacements in the interior of the oceans is studied through the dynamics of packets of internal waves, where the evolution is governed by the nonlinear Schrödinger equation. The case of constant buoyancy frequency permits analytical treatment. While modulation instability for surface waves only arises for sufficiently deep water, rogue internal waves may occur if the fluid depth is shallow. The dependence on the stratification parameter and choice of internal modes can be demonstrated explicitly. The spontaneous generation of rogue waves is tested by numerical simulations.

Simultaneous Stochastic Model of Waves and Currents for Prediction of Structural Design Loads

2018 ◽  
Author(s):  
Kjersti Bruserud
Keyword(s):  
North Sea ◽  
Wind Waves ◽  
Current Data ◽  
Joint Models ◽  
Inertial Oscillations ◽  
Annual Variations ◽  
Precise Knowledge ◽  
Long Duration ◽  
Waves And Currents ◽  
Northern North Sea

Simultaneous data of metocean parameters, such as wind, waves and current, of sufficient quality and duration are necessary to establish reliable, joint models of metocean loads and load effects on marine structures. In lack of such joint models, the Norwegian design standard, NORSOK N-003, recommends combinations of metocean parameters for load estimations assumed to be conservative. However, the degree of conservatism is rather uncertain. The possible conservatism in NORSOK N-003 for combinations of wave and current conditions in the northern North Sea has been assessed. To perform such an assessment, precise knowledge about the wave and current conditions is required, as well as simultaneous wave and current data of high quality and long duration. Available measured wave and current data during nearly five years, at selected locations in the northern North Sea, are described. A thorough assessment of the current conditions at these locations is given, with the following important findings; (1) the quality of measured current data is poorer than anticipated, (2) the dominating current conditions at some locations is wind-generated inertial oscillations, (3) the seasonality of current conditions at these locations is very distinct due to the inertial oscillations and (4) significant inter-annual variations in current conditions is found. For waves in the northern North Sea, both measured and hindcast data are found to be of appropriate quality and duration for joint considerations, but neither current measurements nor hindcast have the required quality or duration. To generate adequate current data, a simple model for wind-generated inertial oscillations is applied and validated at one location in the northern North Sea. With that, simultaneous wave and current data of sufficient quality and duration for joint modelling are available and a joint conditional model for waves and currents is proposed. The anticipated conservatism in NORSOK N-003 for load estimations is assessed by a case study. A simplified model for a generic static load on a jacket, caused by waves and currents, is assumed. For the northern North Sea, metocean loads are estimated first according to the NORSOK N-003 recommendation, and then directly from a load times series. Comparison of the two different approaches gives a clear indication that the NORSOK recommendation is not necessarily conservative in the northern North Sea. Due to several simplifications in the steps leading up to the load estimations, this result is intended to be illustrative.

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