Browsing by Author "Kuo, YY"

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A study of bispectra in relation to the adequacy of wave spectral model
(1997-01-01)
Kuo, YY
;
Chien, CC
;
Yim, JY
;
土木工程學系
;
Department of Civil Engineering
In this paper, the characteristics of laboratory wind waves under various wind speeds and water depths are studied. It is found that either the real or the imaginary part of the bispectrum can be related to the asymmetry of the wave profile, and the bicoherence is related to the ratio of nonlinear to linear wave component. Occasionally, these two categories of nonlinear index lead to opposite inferences, because each of them has its own significance and functions. The applicability of linear wave spectral model in ocean waves becomes questionable only when strong nonlinearity is indicated by both of these two indexes, The linear spectral representation of wave fields does not necessarily become inadequate as water depth decreases, and its appropriateness can be examined through the characteristics of the bispectrum.
A study of bispectra in relation to the adequacy of wave spectral model
(1997-01-01)
Kuo, YY
;
Chien, CC
;
Yim, JY
;
土木工程學系
;
Department of Civil Engineering
In this paper, the characteristics of laboratory wind waves under various wind speeds and water depths are studied. It is found that either the real or the imaginary part of the bispectrum can be related to the asymmetry of the wave profile, and the bicoherence is related to the ratio of nonlinear to linear wave component. Occasionally, these two categories of nonlinear index lead to opposite inferences, because each of them has its own significance and functions. The applicability of linear wave spectral model in ocean waves becomes questionable only when strong nonlinearity is indicated by both of these two indexes, The linear spectral representation of wave fields does not necessarily become inadequate as water depth decreases, and its appropriateness can be examined through the characteristics of the bispectrum.
Directional spectrum analysis and statistics obtained from ERS-1 SAR wave images
(1999-11-01)
Kuo, YY
;
Leu, LG
;
Kao, IL
;
土木工程學系
;
Department of Civil Engineering
This work examines ERS-1 (the first European Remote Sensing Satellite) SAR (Synthetic Aperture Radar) water surface wave images over Hualien of Taiwan, indicating that the variation of SAR signals in space domain is similar to in situ wave data's in time domain. Some statistical properties of SAR data are investigated. The Rayleigh distribution function closely corresponds with the histogram of wave heights, but the Gaussian one cannot for water surface displacements. Evidence reveals that SAR wave signals do not respond well to actual ocean waves effectively. As wave spectral analysis of available SAR data reveals, the appropriate sample size of SAR wave image, sampling average, and moving average should be taken carefully to accurately confirm directional power spectra. Moreover, SAR spectra are compared with in situ ones, confirming that peak frequencies correlate well and wave directions approximately agree with each other. Some differences between both spectral shapes remain somewhat unclear and require further study. Nevertheless, in this study, ERS-1 SAR power spectra verified the feasibility of deriving an appropriate dominant wave direction and peak frequency. (C) 1998 Elsevier Science Ltd. All rights reserved.
Estimation of water particle velocities by empirical transfer function
(1997-01-01)
Chiu, YF
;
Kuo, YY
;
土木工程學系
;
Department of Civil Engineering
In previous and this studies it appears that the linear and nonlinear wave theory-can not accurately and easily predict the water particle velocities: Therefore, different from the theoretical considerations, in this study we have attempted to determine the transfer function empirically. Laboratory experiments were performed under various wave conditions. The empirical formulas of the transfer function of the wave height, angular frequency and water particle velocity were obtained on the basis of these test data by dimensional analysis and regression analysis. In intermediate and deep water depth conditions, the transfer function was only a function of a nondimensional parameter which is composed of the angular frequency, the depth of the velocity gauge under the still water level, water depth and the acceleration of gravity. Finally, the empirical formulas were compared with experimental data and observational data form present and Cavaleri's (1978) studies. The empirical formulas were found to be in sufficient correltion with these data.
Estimation of water particle velocities by empirical transfer function
(1997-01-01)
Chiu, YF
;
Kuo, YY
;
土木工程學系
;
Department of Civil Engineering
In previous and this studies it appears that the linear and nonlinear wave theory-can not accurately and easily predict the water particle velocities: Therefore, different from the theoretical considerations, in this study we have attempted to determine the transfer function empirically. Laboratory experiments were performed under various wave conditions. The empirical formulas of the transfer function of the wave height, angular frequency and water particle velocity were obtained on the basis of these test data by dimensional analysis and regression analysis. In intermediate and deep water depth conditions, the transfer function was only a function of a nondimensional parameter which is composed of the angular frequency, the depth of the velocity gauge under the still water level, water depth and the acceleration of gravity. Finally, the empirical formulas were compared with experimental data and observational data form present and Cavaleri's (1978) studies. The empirical formulas were found to be in sufficient correltion with these data.