共查询到10条相似文献，搜索用时 125 毫秒
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In this paper, we define a time-domain pressure transfer function calculated from SIWEH (smoothed instantaneous wave energy history) transforms, and a time-frequency domain pressure transfer function calculated from wavelet transforms, of synchronized wave and pressure data. It is our objective to study whether the time-domain pressure transfer function and the time-frequency domain pressure transfer function can provide new interpretation of wind wave behaviors. The detail structure of local time-frequency pressure transfer function in three-dimensional plot from wavelet transform is not employed due to its large variations, instead the time-integral wavelet spectral pressure transfer function and frequency-integral wavelet SIWEH pressure transfer function are used. These two averaged pressure transfer functions are smooth approximations of frequency-domain Fourier and time-domain SIWEH pressure transfer functions, respectively.Application to real ocean waves reveals that in frequency-domain the measured Fourier and wavelet spectral pressure transfer functions can be approximated by the linear pressure transfer function in the dominant wave range. In time-domain, the wavelet SIWEH pressure transfer function is a better indicator of wind wave behaviors than the SIWEH pressure transfer function. A value higher than 0.5 for the wavelet SIWEH pressure transfer function is a good discriminator of relative shallow-water long waves and wave groups are mostly composed of relative low frequency long waves. 相似文献
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Analysis of freak wave measurements in the Sea of Japan 总被引：3，自引：0，他引：3
This paper presents an analysis of a set of available freak wave measurements gathered from several periods of continuous wave recordings made in the Sea of Japan during 1986–1990 by the Ship Research Institute of Japan. The analysis provides an ideal opportunity to catch a glimpse of the statistics of freak waves in the ocean. The results show that a well-defined freak wave may occur in the developed wind–wave condition: S(f)∝f−4, with single-peak directional spectra. The crest and trough amplitude distributions of the observed sea waves including freak waves are different from the Rayleigh distribution, although the wave height distribution tends to agree with the Rayleigh distribution. Freak waves can be readily identified from the wavelet spectrum where a strong energy density occurs in the spectrum, and is instantly surged and seemingly carried over to the high-frequency components at the instant the freak wave occurs. 相似文献
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Wave interaction with T-type breakwaters 总被引：1，自引：0，他引：1
The wave transmission, reflection and energy dissipation characteristics of partially submerged ‘T'-type breakwaters (Fig. 1) were studied using physical models. Regular and random waves, with wide ranges of wave heights and periods and a constant water depth were used. Five different depths of immersions of the ‘T'-type breakwater were selected. The coefficient of transmission, Kt, coefficient reflection, Kr, were obtained from the measurements and the coefficient of energy loss, Kl is calculated using the law of conservation of energy. It is found that the coefficient of transmission generally reduces with increased wave steepness and increased relative water depth, d/L. This breakwater is found to be effective closer to deep-water conditions. Kt values less than 0.35 is obtained for both normal and high input wave energy levels, when the horizontal barrier of the T type breakwater is immersed to about 7% of the water depth. This breakwater is also found to be very efficient in dissipating the incident wave energy to an extent of about 65% (i.e. Kl>0.8), especially for high input wave energy levels. The wave climate in front of the breakwater is also measured and studied.
Fig. 1. Schematic view of the T-type breakwater. 相似文献
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Li Luping 《海洋学报(英文版)》1997,16(1):45-56
In this paper, it is held that the universal relationships of wave growth in fetch-limited conditions , i. e.,(f|~) p=A(x|~)-Band (m|~)0= C(x|~) Dshould satisfy the Toba 3/2 power law and the wave energy balance equation. In the ideal generation situation, theoretically it can be derived that the ideal fetch-limited wave growth relationship should have D=3B and D B =1, (i.e., B = 0.25, D = 0.75 ) and A3C=2. 1×l(T4C~(1/2)_d , where Cd is the drag coefficient. The 3/2 power law, the wave energy balance equation and the decrease of wave steepness with increasing fetch have became three requirements which should be satisfied by fetch-limited wave growth algorithms. A semi-empirical and semi-theoretical model for fetch-limited wave growth is presented. In the application to the slanting wind situation an un(?)ersal relationship of dimensionless wave energy vs dimensionless peak frequency is presented and the comparisons show that the model is in good agreement with observations. 相似文献
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A parametric study was carried out to investigate the hydrodynamics of a cylindrical wave energy absorber. Established methods of hydrodynamic analysis were applied to the case of a damped vertically oriented cylinder pivoted near the sea floor in intermediate depth water. The simple geometry provides a canonical reference for more complex structure shapes and configurations that may be considered for either wave energy conversion or wave energy absorption. The study makes use of the relative velocity Morison equation, with force coefficients derived from radiation and diffraction theory. Viscous effects were accounted for by including a drag term with an empirically derived coefficient, CD. A non-linear first-order formulation was used to calculate the cylinder motion response in regular waves. It was found that the non-linear drag term, which is often neglected in studies on wave energy conversion, has a large effect on performance. Results from the study suggest a set of design criteria based on Keulegan–Carpenter (KC) number, ratio of cylinder radius to water depth (a/h), and ratio of water depth to wavelength (h/L). Respectively, these parameters account for viscous, wave radiation, and water depth effects, and optimal ranges are provided. 相似文献
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This paper discusses wave grouping of wind waves observed at Lake Biwa from the physical viewpoint of wave modulational instability. Amplitude modulation periods obtained from the smoothed instantaneous wave energy history (SIWEH) of the observed data proposed by Funke and Mansard are compared with the values predicted by the modulational instability theory using the Zakharov equation for a finite constant water depth derived by Stiassnie and Shemer. The modulation period normalized by the typical wave period corresponds to the length of total run. It is shown that the amplitude modulation periods of the observed data agree satisfactorily with the predicted values. Thus, it is concluded that the modulational instability is a hydrodynamical cause of grouping of high waves. 相似文献
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Canopy-forming algae occur across of range of energy environments (i.e., wave sheltered to exposed coasts) where disturbances are frequent (i.e., gap formation) and benthic patterns largely reflect variation in post-disturbance processes. Disturbances vary in extent (area affected) and intensity (degree of damage), and this may affect recolonisation at local scales. On an open oceanic coast, we tested whether habitat structure (patches of canopy algae) differed between heavy and relatively lighter wave exposure (sheltered vs. exposed sides of islands), and whether wave exposure affected the response of prominent habitat-formers to varying disturbance regimes (different sizes of partial and complete canopy removal). Observations of naturally occurring patterns showed sheltered coasts to be characterised by small patches of fucoids, whereas exposed coasts were characterised by large patches of kelp. Canopy-gaps were larger at exposed than sheltered coasts, and mixed canopies constituted > 24% of the subtidal rocky habitat independently of wave exposure. Experimental disturbances showed the local density of kelps to affect recovery through greater recruitment to partial clearings (80% canopy removal). Fucalean algae, on the other hand, mainly recruited into complete clearings (100% removal), but when their recruits were abundant, they also recruited into partial clearings. The covers of filamentous, turf-forming algae increased in all clearings, and more so at exposed than sheltered sites. Extent of disturbance had no detectable effect on recolonisation by canopy-forming algae across the scales examined (i.e., 1.5 m, 3 m diameter loss of canopy). Recolonisation varied among islands kilometres apart, and correlations (r > 0.85) between cover of canopies and cover of their recruits in clearings at the scale of sites, suggested that differences in propagule supply could account for variation in patterns of recolonisation at scales of kilometres. There was no evidence to suggest that the effect of disturbance depended on wave exposure within the range of exposures tested in this study (i.e. open coasts). We recognise that wave exposure can be fundamental to habitat structure of subtidal rocky coasts, but we suggest that its influence may be mediated by the biological setting (e.g., canopy composition). 相似文献
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The variations in the quantity of wave power available to a wave energy converter by filtering out short-period waves have been examined in this paper. Ocean wave data recorded at three different locations and water depths around northern Europe are used for this purpose along with numerically synthesized wave time series. A wave power ratio, defined as the ratio between the wave power for the filtered and unfiltered data, is calculated for each data set, and the variation of this quantity with the degree of filtering is investigated. Two new parameters namely, R and S are defined to quantify the effect of this filtering on the variation of wave-to-wave period and height. It is shown that removing the shorter period waves has little effect upon the power available for extraction but may significantly reduce the rate at which the wave energy converter must retune to achieve optimum power conversion. 相似文献
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The wave transmission, reflection and energy dissipation characteristics of ‘’-type breakwaters were studied using physical models. Regular and random waves in a wide range of wave heights and periods and a constant water depth were used. Five different depths of immersion (two emerged, one surface flushing and two submerged conditions) of this breakwater were selected. The coefficient of transmission, Kt, and coefficient of reflection, Kr, were obtained from the measurements, and the coefficient of energy loss, Kl was calculated using the law of balance of energy. It was found that the wave transmission is significantly reduced with increased relative water depth, d/L, whether the vertical barrier of the breakwater is surface piercing or submerged, where ‘d’ is the water depth and ‘L’ is the wave length. The wave reflection decreases and energy loss increases with increased wave steepness, especially when the top tip of the vertical barrier of this breakwater is kept at still water level (SWL). For any incident wave climate (moderate or storm waves), the wave transmission consistently decreases and the reflection increases with increased relative depth of immersion, Δ/d from −0.142 to 0.142. Kt values less than 0.3 can be easily obtained for the case of Δ/d=+0.071 and 0.142, where Δ is the height of exposure (+ve) or depth of immersion (−ve) of the top tip of the vertical barrier. This breakwater is capable of dissipating wave energy to an extent of 50–80%. The overall performance of this breakwater was found to be better in the random wave fields than in the regular waves. A comparison of the hydrodynamic performance of ‘’-type and ‘T’-type shows that ‘T’-type breakwater is better than ‘’-type by about 20–30% under identical conditions. 相似文献