The directional spectrum of ocean waves, and processes of wave generation

1962 ◽  
Vol 265 (1322) ◽  
pp. 286-315 ◽  
Keyword(s):  
Pressure Fluctuations ◽  
Wave Spectrum ◽  
Ocean Waves ◽  
Wave Generation ◽  
Air Pressure ◽  
Sea Surface ◽  
Shear Instability ◽  
Main Stage ◽  
Sea Waves ◽  
Directional Spectrum

This paper describes some recent observations of the directional spectrum of sea waves and of air pressure fluctuations at the sea surface, and discusses their implications for theories of wave generation. The angular spread of the wave energy in the generating area is found to be comparable with the ‘resonance angle’ sec -1 ( σU/g ) ( σ = wave frequency, U = wind speed) but lies slightly below it in the middle range of frequencies. The best fit to the directional spectrum F ( σ, ɸ ) is shown to be a cosine-power law: F ( σ, ɸ ) ∝ cos 2s (1/2 ɸ ), where s decreases as σ in ­ creases. At the higher frequencies the total spectrum satisfies the equilibrium law: F ( σ ) ∝ σ -5 . The initial stages of wave generation are attributed to turbulence in the air stream, and the main stage of growth to the shear instability mechanism described by Miles. At the highest frequencies the form of the spectrum suggests that wave breaking plays a predominant part, as proposed by Phillips. The broadening of the angular distribution at the highest frequencies may also be due partly to third-order ‘resonant’ interactions among components of the wave spectrum . The air-pressure fluctuations are nearly in phase with the vertical displacement of the sea surface (over most of the frequency range) and are consistent with the shear-flow model proposed by Miles. The turbulent component of the air pressure is much smaller than was previously supposed.

scholarly journals The directional spectrum of ocean waves: an experimental investigation of certain predictions of the Miles–Phillips theory of wave generation

1966 ◽  
Vol 25 (4) ◽  
pp. 795-816 ◽  
Author(s):  
A. W. R. Gilchrist
Keyword(s):  
Wave Train ◽  
Pressure Fluctuations ◽  
Ocean Waves ◽  
Bimodal Distribution ◽  
Wave Generation ◽  
Low Frequencies ◽  
Directional Spectrum ◽  
Theoretical Predictions ◽  
Atmospheric Pressure Fluctuations ◽  
The Waves

The directional spectrum of wind-driven surface waves has been measured under conditions of limited fetch, in order to check the predictions of the Phillips–Miles theory of wave generation (Miles 1960). The expression obtained for the directional spectrum in this theory involves the spectrum of the atmospheric pressure fluctuations, but it is possible to obtain theoretical estimates of the major features of the directional spectrum without knowledge of the pressures. Specifically, it is possible to predict the frequency at which the power spectrum should peak, and, for the higher frequencies, the range of azimuth over which high spectral values should be observed; for the lower frequencies the theory indicates a bimodal distribution in azimuth (Phillips's resonance waves), and gives the angle of travel relative to the wind as a function of frequency.The results of the measurements are in fairly good agreement with the theoretical predictions for the higher frequencies. The asymmetry of the fetch results in the prediction that the waves will travel at an angle to the wind which varies with frequency, and this was observed. The range of azimuth over which the spectral density is high is also close to the theoretical prediction. For the low frequencies the bimodal distribution was not observed: the waves were found to have a single predominant direction of travel at each frequency. However, this direction conformed closely to that of one of the two wave trains predicted by Phillips, and its variation with frequency was also that given by the theory. There is reason to suppose that the peculiarities of the experimental site may be responsible for the absence of the second wave train, especially as it would be difficult to account for the observed effects on any basis other than that of Phillips's theory.

scholarly journals In situ measurements of directional wave spectra from an unmanned aerial system

2021 ◽  
Author(s):  
Clarence Collins ◽  
Katherine Brodie
Keyword(s):  
Single Point ◽  
Field Research ◽  
Ocean Waves ◽  
Adaptive Method ◽  
Technical Note ◽  
Sea Surface ◽  
Unmanned Aerial System ◽  
Frequency Spectra ◽  
Directional Spectrum ◽  
Data Adaptive

This Coastal and Hydraulics Engineering Technical Note (CHETN) describes the ability to measure the directional-frequency spectrum of sea surface waves based on the motion of a floating unmanned aerial system (UAS). The UAS used in this effort was custom built and designed to land on and take off from the sea surface. It was deployed in the vicinity of an operational wave sensor, the 8 m* array, at the US Army Engineer Research and Development Center (ERDC), Field Research Facility (FRF) in Duck, NC. While on the sea surface, an inertial navigation system (INS) recorded the response of the UAS to the incoming ocean waves. Two different INS signals were used to calculate one-dimensional (1D) frequency spectra and compared against the 8 m array. Two-dimensional (2D) directional-frequency spectra were calculated from INS data using traditional single-point-triplet analysis and a data adaptive method. The directional spectrum compared favorably against the 8 m array.

scholarly journals DIRECTIONAL SPECTRA OF OCEAN SURFACE WAVES

1976 ◽  
Vol 1 (15) ◽  
pp. 18 ◽  
Author(s):  
H. Mitsuyasu ◽  
S. Mizuno
Keyword(s):  
Angular Distribution ◽  
Frequency Spectrum ◽  
Wind Waves ◽  
Wave Spectrum ◽  
Ocean Waves ◽  
Peak Frequency ◽  
Spectral Peak ◽  
Energy Concentration ◽  
Spectral Energy ◽  
Directional Spectrum

From 1971-74 seven cruises were made to measure the directional spectrum of ocean waves by using a cloverleaf buoy. Typical sets of wave data measured both in open seas and in a bay under relatively simple conditions have been analyzed to clarify the fundamental properties of the directional spectrum of ocean waves in deep water. It is shown that the directional wave spectrum can be approximated by the product of the frequency spectrum and a unimodal angular distribution with mean direction approximately equal to that of the wind. The normalized forms of the frequency spectrum show various forms lying between the Pierson-Moskowitz spectrum and the spectrum of laboratory wind wave which has a very sharp energy concentration near the spectral peak frequency. The form of the JONSWAP spectrum is very close to that of laboratory wind waves. The concentration of the spectral energy near the spectral peak frequency seems to decrease with increasing the dimensionless fetch and the spectral form finally approaches to the Pierson-Moskowitz spectrum which can be considered as the spectrum with the least concentration of the normalized spectral energy. However, the definite relation between the shape of the normalized spectrum and the dimensionless fetch has not been obtained. Concerning the angular distribution, it is shown that the shape of angular distribution of the single-peaked wave spectrum in a generating area can be approximated by the function G(6,f) = G'(s) | cos (6-6)/2 | ** proposed originally by Longuet=Higgins et al. (1963). Here G'(s) is a normalizing function, 6 is the mean direction of the spectral component, and s is a parameter which controls the concentration of the angular distribution function.

scholarly journals Transformation of Water Wave Spectra into Time Series of Surface Elevation

Earth ◽  
2021 ◽  
Vol 2 (4) ◽  
pp. 997-1005
Author(s):  
Phelype Haron Oleinik ◽  
Gabriel Pereira Tavares ◽  
Bianca Neves Machado ◽  
Liércio André Isoldi
Keyword(s):  
Time Series ◽  
Time Domain ◽  
Water Surface ◽  
Large Scale ◽  
Wave Spectrum ◽  
Ocean Waves ◽  
Surface Elevation ◽  
Sea Waves ◽  
Water Surface Elevation ◽  
Input Spectrum

Spectral wave modelling is widely used to simulate large-scale wind–wave processes due to its low computation cost and relatively simpler formulation, in comparison to phase-resolving or hydrodynamic models. However, some applications require a time-domain representation of sea waves. This article proposes a methodology to transform the wave spectrum into a time series of water surface elevation for applications that require a time-domain representation of ocean waves. The proposed method uses a generated phase spectrum and the inverse Fourier transform to turn the wave spectrum into a time series of water surface elevation. The consistency of the methodology is then verified. The results show that it is capable of correctly transforming the wave spectrum, and the significant wave height of the resulting time series is within 5% of that of the input spectrum.

Directional spectrum of wind-generated ocean waves

1964 ◽  
Vol 19 (3) ◽  
pp. 452-464
Author(s):  
Mahinder S. Uberoi
Keyword(s):  
North Atlantic ◽  
Digital Computer ◽  
Ocean Waves ◽  
Sea Surface ◽  
Published Data ◽  
Directional Spectrum ◽  
Empirical Prediction ◽  
The North ◽  
Optical Computer ◽  
The North Atlantic

Two sets of published data on an area 2700ft. by 1800ft. of sea surface in the North Atlantic are analysed by an optical computer which gives directly the directional spectrum. The results are compared with (i) those of other investigators obtained laboriously by using a digital computer, (ii) the frequency spectrum, and (iii) an empirical prediction.

A Renewable Source of Hydroelectricity

2013 ◽  
Vol 310 ◽  
pp. 399-402
Author(s):  
Saleh A. Aboukhres ◽  
Ali S. Zayed ◽  
Hisham A. Ayad ◽  
S. Ganesan
Keyword(s):  
Kinetic Energy ◽  
Mechanical Energy ◽  
Pressure Fluctuations ◽  
Ocean Waves ◽  
Wave Power ◽  
Sea Waves ◽  
Power Devices ◽  
Regular Form ◽  
The World ◽  
Different Parts

The Sea-waves, as a kinetic energy, is one of the renewable sources of energy which can be harnessed to generate electricity. Wave power devices extract energy directly from the surface motion of sea (ocean) waves or from pressure fluctuations below the surface. A variety of technologies have been proposed to capture the energy from waves and some of the more promising designs are undergoing demonstration testing at economical scales. In this research, the irregular kinetic energy in sea waves is to be converted to a stored potential energy and used in a regular form, with conversion once again to mechanical energy, for driving a turbine which to be connected to an electricity generator through a gear box. Wave power varies considerably in different parts of the world and wave energy cannot be harnessed effectively everywhere. Because sea waves may become ineffective for a period of time, this research is concerned with the storage of energy in one of its forms.

The Southern Ocean Waves Experiment. Part III: Sea Surface Slope Statistics and Near-Nadir Remote Sensing

2008 ◽  
Vol 38 (3) ◽  
pp. 670-685 ◽  
Author(s):  
E. J. Walsh ◽  
C. W. Wright ◽  
M. L. Banner ◽  
D. C. Vandemark ◽  
B. Chapron ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Incidence Angle ◽  
Wave Spectrum ◽  
Ocean Waves ◽  
Sea Surface ◽  
Radar Altimeter ◽  
Ka Band ◽  
Wide Range ◽  
Non Gaussian

Abstract During the Southern Ocean Waves Experiment (SOWEX), registered ocean wave topography and backscattered power data at Ka band (36 GHz) were collected with the NASA Scanning Radar Altimeter (SRA) off the coast of Tasmania under a wide range of wind and sea conditions, from quiescent to gale-force winds with 9-m significant wave height. Collection altitude varied from 35 m to over 1 km, allowing determination of the sea surface mean square slope (mss), the directional wave spectrum, and the detailed variation of backscattered power with incidence angle, which deviated from a simple Gaussian scattering model. The non-Gaussian characteristics of the backscatter increased systematically with the mss, suggesting that a global model to characterize Ka-band radar backscatter from the sea surface within 25° of nadir might be possible.

scholarly journals Booms and Busts in the Deep

2010 ◽  
Vol 40 (9) ◽  
pp. 2159-2169 ◽  
Author(s):  
W. E. Farrell ◽  
Walter Munk
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Gravity Waves ◽  
Deep Sea ◽  
Acoustic Radiation ◽  
Wave Spectrum ◽  
Sea Surface ◽  
Directional Spectrum ◽  
Distinct Band ◽  
Strong Winds

Abstract Deep sea (5 km) pressure and velocity at the Hawaii-2 Observatory (H2O), midway between Hawaii and California, exhibit a number of remarkable features that are interpreted using the Longuet–Higgins theory of acoustic radiation from oppositely directed surface waves. A change in the slope of the bottom spectra near 5 Hz can be associated with a transition near 2.5 Hz (25-cm wavelength) of the surface wave spectrum from the classical κ−4 saturated (wind independent) Phillips spectrum to a distinct band of ultragravity waves. Bottom spectra are remarkably stable. Occasional 15-dB busts in the gravities and booms in the ultragravities are prominent features in the bottom records and can be associated with calms and storms at the sea surface. For strong winds, two broad lobes in the directional spectrum of the gravity waves are nearly perpendicular to the wind; as the wind drops, the lobes become narrower and more nearly aligned with the wind, leading to busts.

scholarly journals A Review of Wave Spectrum Models as Applied to the Problem of Radar Probing of the Sea Surface

2019 ◽  
Vol 124 (10) ◽  
pp. 7104-7134 ◽  
Author(s):  
M. Ryabkova ◽  
V. Karaev ◽  
J. Guo ◽  
Yu. Titchenko
Keyword(s):  
Wave Spectrum ◽  
Sea Surface
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