An experimental study of weakly three-dimensional non-breaking and breaking waves
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Abstract A spectral framework for quantifying the geometric/kinematic and dynamic/energetic properties of breaking ocean waves was proposed by Phillips in 1985. Phillips assumed a constant breaking strength coefficient to link the kinematic/geometric breaking crest properties to the associated excess energy and momentum fluxes from the waves to the upper ocean. However, a scale-dependent (spectral) breaking strength coefficient is needed, but is unavailable from measurements. In this paper, the feasibility of a parametric mean effective breaking strength coefficient valid for a wide range of sea states is investigated. All available ocean breaking wave datasets were analyzed and complemented with wave model behavior. Robust evidence is found supporting a single linear parameter relationship between the effective breaking strength and wave age or significant wave steepness. Envisaged applications for the effective breaking strength are described.
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The aim of this paper is to investigate experimentally and numerically the breaking limit, breaking and post-breaking wave deformation due to three different types of submerged structures such as bottom-seated, non-bottomseated fixed and tautly-moored structures. Based on laboratory experiments, the breaking limits have been formulated for three different types of the submerged structures. Moreover, a modified SOLA-VOF method with the nonreflective wave generation method has been proposed and found to be very effective in evaluating the wave breaking process and post-breaking wave characteristics.
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The paper presents an attempt to estimate short wave generation by wave breaking. A breaking wave crest disturbs the surface and generates sub‐surface turbulence. The locally disturbed area further disperses and feeds short wave energy to the surroundings. The total short wave energy results from summing up the effect of wave breaking events randomly distributed over the sea surface. The rate of short wave generation is determined by the frequency of wavebreaking events per unit area. The source of short wave energy is isotropic, thus it generates waves at cross and opposite wind directions. The model qualitatively reproduces observed directional property of short wind wave spectra and mean square slope.
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The groupness is a significant feature of wind wave breaking.Recent studies have shown that the analysis of wind wave breaking should base on wave group instead of single waves.Based on a series of wind wave breaking experiments,this paper investigates distinguishing characteristic indexes of breaking wave group which are quite different from those of non-breaking wave groups.Breaking wave groups were determined by multi-breaking criteria and mark signal recorded in situ simultaneously.The statistical distributions of 28 indexes on breaking and non-breaking wave groups was discussed,including indexes of wave groups,geometric indexes of single waves,local breaking criteria indexes,geometric indexes of wave envelope and indexes represent wave group energy structure.The results show that for wave steepness,crest front steepness,instantaneous wave slope,index in kinematic and dynamic breaking criteria,few overlaps can be found in their distributions on breaking and non-breaking wave groups,especially for the last two indexes,which in kinematics and dynamic breaking criterion.They are distinguishing characteristic indexes of breaking wave group.Other indexes can't be used to distinguish breaking and non-breaking wave groups owing to varying degree overlap of their distributions on breaking and non-breaking wave groups.
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PROBLEM: Waves propagating into a tidal inlet will shoal and break because of changes in water depth, focusing by shoals, and interactions with an opposing (ebb) current. On an ebb current, waves steepen because their height increases and length decreases. The wave steepening can intensify wave breaking, causing a navigation hazard and inducing a wave-driven current and sediment transport. Most wave-breaking criteria are based on a maximum ratio of wave height to water depth. But, in regions where waves break because of steepening on an ebb current, the height-to-depth criterion may significantly underestimate wave breaking and overestimate wave height. CETN IV-9 (Smith 1997) describes the process of wave-current interaction in one dimension and gives the equations for calculating wave-height transformation on an ebb (opposing) or flood (following) current. Extending the discussion in CETN IV-9, the present CETN provides guidance on estimating wave breaking that may occur as waves transform on an opposing current. Before the method for calculating breaking is described, the governing equation, wave-action conservation, is reviewed (see also CETN IV-9), and wave shoaling on a current is discussed. CONSERVATION OF WAVE ACTION: Wave height in the presence of a current is governed by the conservation of wave action (Jonsson 1990, and others). The one-dimensional conservation of wave action equation is given by:
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This paper presents the experimental study on the multi-directional focusing waves and breaking waves,which are generated in wave basin by using focusing wave method with two different spectrums(constant wave amplitude spectrum and constant wave steepness spectrum) and two different water depths.For the breaking wave,the wave surface characteristics,the breaking criteria and the spectral variation during the wave packet propagation were studied.The results show that spectral distribution,water depth and wave directionality affect the breaking wave characteristics.The wave spectra in high frequency range are distinctly changing during the packet propagation,and the shift of higher frequencies can be distinctly observed.Energy losses during wave breaking are mainly from higher frequency wave band.
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Wave energy dissipation and energy transfer among wave components during the directional wave breaking are investigated experimentally. Directional breaking waves in deep water were simulated by focusing the multi-frequency and multi-directional wave components at a designed location based on constant wave amplitude and constant wave steepness frequency spectrum. The incipient and plunging breakers with the same spectral characteristics were generated by applying the different scale factors on wave amplitude. The time series of surface wave elevation were measured around the wave focusing point using a wave gauge array to examine the variation of directional spreading function. The free wave components of a directional wave train are separated from bound wave components by nonlinear decomposition based on directional hybrid wave model accurate up to second order. The local free wave components derived from nonlinear decomposition still include directional dispersion effect. A spatial variation of free wave packet due to directional dispersion is estimated by comparing incipient breaking wave packets at corresponding locations. When the bound wave components and directional dispersion effect are removed from the plunging breaking wave train, a variation of the directional wave spectrum of resultant free wave components before and after the wave breaking is solely responsible to wave energy dissipation and transfer between free wave components. By comparing free wave components of a plunging breaking wave packet before and after the wave breaking, the characteristics of energy dissipation and energy transfer caused by wave breaking are investigated and their dependences on frequency are analyzed.
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The aim of this paper is to investigate experimentally and numerically the breaking limit, breaking and post-breaking wave deformation due to three different types of submerged structures such as bottom-seated, non-bottom-seated fixed and tautly-moored structures. Based on laboratory experiments, the breaking limits have been formulated for three different types of the submerged structures. Moreover, a modified SOLA-VOF method with the non-reflective wave generation method has been proposed and found to be very effective in evaluating the wave breaking process and post-breaking wave characteristics.
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Both the modulation of short wind wave breaking in the long surface wave field and the occurrence of breaking in the presence of a long wave were investigated in wind-wave tank. Short wind waves were generated by the air flow at various speeds, the long surface wave at various frequency and amplitude were generated by wave maker. Data of X- and Ka-band scatterometers, string wave recorder placed in the probing area, and web camera making video records of the probing area were synchronously recorded in the experiment. It is shown that at relatively weak wind long surface wave causes short wind wave breaking, and at high wind speeds - breaking intensification. Wind wave breaking is mainly observed on the front slope of the long wave, the breaking observation area extends with increasing wind speed.
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