Three methods for studying wave groups and their main parameters for describing wave groupiness are reviewed in this paper. Then they are analyzed and compared combined with field data from both aspects of group heigh...Three methods for studying wave groups and their main parameters for describing wave groupiness are reviewed in this paper. Then they are analyzed and compared combined with field data from both aspects of group height and group length. A method and two parameters that can describe wave groupiness are suggested. The groupiness parameters of sea waves at three field stations are given. The effects of groupiness on both distributions of the wave height and the phase of component waves are investigated. The effects of datum length on the calculated value of grouping parameters are also discussed.展开更多
Theoretical studies so far on random wave groups have all been in Linear ways. Methods to simulate random wave groups, an important subject in ocean engineering, also employ relationship resulting from a Gaussian proc...Theoretical studies so far on random wave groups have all been in Linear ways. Methods to simulate random wave groups, an important subject in ocean engineering, also employ relationship resulting from a Gaussian process. Many filed measurements have shown that the real sea surface displacement deviates somewhat from Gaussian distribution. Tayfun et al, have further depicted in theory that the envelope spectral peak frequency is constantly zero for a Gaussian process which means that the groupiness factors will be constants, too. In this paper, the effect of nonlinearity on groupiness of a random wave field is examined via the theoretical results derived by Tayfun et al. from an expression of amplitude-modulated Stokes waves. When the surface displacement is treated as a non-Gaussian process, it is found that the group height factors GF(1) and GF(2) proposed by Zhao et al. and Yu et al., respectively, depend on a nonlinearity factor as well as a spectrum-bandwidth factor, deferring from the case of a Gaussion process. Comparison between the theoretical results and the field data shows a favorable agreement in consideration of errors from instrumentation and measuring means. The significance of the results is also discussed.展开更多
Waves with the same wave parameters, such as significant wave height and period, but with different wave groupiness factors are simulated, to study the motion behavior of a moored ship under the action of waves with d...Waves with the same wave parameters, such as significant wave height and period, but with different wave groupiness factors are simulated, to study the motion behavior of a moored ship under the action of waves with different Groupiness Factors of Height （GFH） and Group Length Factors （GLF）. The numerical results show that both the sway and heave motions increase with an increase in GFH. In contrast, the influence of GLF on the motions of a moored ship is weak.展开更多
A new method using group-induced second-order long waves (GSLW) to describe wave groups is presented in this paper on the basis of the GSLW theory by Longuet- Higgins and Steward (1964) . In the method , the parabolic...A new method using group-induced second-order long waves (GSLW) to describe wave groups is presented in this paper on the basis of the GSLW theory by Longuet- Higgins and Steward (1964) . In the method , the parabolic relationship between GSLW and the wave envelope is first deduced , and then the distribution function of GSLW amplitude is derived . Thus, the formulae in terms of the moments of GSLW and short wave spectra for the average time duration and the mean length of runs of wave heights exceeding a certain level can be derived . A new groupiness factor equivalent to half the mean wave number in wave groups is defined by taking into account the widths of spectra of GSLW and short waves . Compared with theoretical results of others , ours are closer to measured wave data .展开更多
The physical simulation method of wave groups in a wave flume is proposed and verified by the exper- iments. The experimental results demonstrate that random waves with desired wave groupiness, which simultaneously in...The physical simulation method of wave groups in a wave flume is proposed and verified by the exper- iments. The experimental results demonstrate that random waves with desired wave groupiness, which simultaneously includes the wave group height and length, can be generated satisfactorily at the specified position in a wave flume using the proposed method. Furthermore, the transformation properties of the wave groupiness along the fiat-bottomed wave flume are investigated based on the physically simulated waves. Associated proposals with the physical simulation of wave groups are given.展开更多
文摘Three methods for studying wave groups and their main parameters for describing wave groupiness are reviewed in this paper. Then they are analyzed and compared combined with field data from both aspects of group height and group length. A method and two parameters that can describe wave groupiness are suggested. The groupiness parameters of sea waves at three field stations are given. The effects of groupiness on both distributions of the wave height and the phase of component waves are investigated. The effects of datum length on the calculated value of grouping parameters are also discussed.
基金National Natural Science Foundation of China(Grant No.49706067)Natural Science Foundation of Shandong Province(Y98E05076)
文摘Theoretical studies so far on random wave groups have all been in Linear ways. Methods to simulate random wave groups, an important subject in ocean engineering, also employ relationship resulting from a Gaussian process. Many filed measurements have shown that the real sea surface displacement deviates somewhat from Gaussian distribution. Tayfun et al, have further depicted in theory that the envelope spectral peak frequency is constantly zero for a Gaussian process which means that the groupiness factors will be constants, too. In this paper, the effect of nonlinearity on groupiness of a random wave field is examined via the theoretical results derived by Tayfun et al. from an expression of amplitude-modulated Stokes waves. When the surface displacement is treated as a non-Gaussian process, it is found that the group height factors GF(1) and GF(2) proposed by Zhao et al. and Yu et al., respectively, depend on a nonlinearity factor as well as a spectrum-bandwidth factor, deferring from the case of a Gaussion process. Comparison between the theoretical results and the field data shows a favorable agreement in consideration of errors from instrumentation and measuring means. The significance of the results is also discussed.
基金Project supported by the National Natural Science Foundation of China (Grant No. 50921001)the Ministry of Communications of China (Grant No. 200632800003-01)
文摘Waves with the same wave parameters, such as significant wave height and period, but with different wave groupiness factors are simulated, to study the motion behavior of a moored ship under the action of waves with different Groupiness Factors of Height （GFH） and Group Length Factors （GLF）. The numerical results show that both the sway and heave motions increase with an increase in GFH. In contrast, the influence of GLF on the motions of a moored ship is weak.
基金This project was funded by the National Natural Science Foundation of China
文摘A new method using group-induced second-order long waves (GSLW) to describe wave groups is presented in this paper on the basis of the GSLW theory by Longuet- Higgins and Steward (1964) . In the method , the parabolic relationship between GSLW and the wave envelope is first deduced , and then the distribution function of GSLW amplitude is derived . Thus, the formulae in terms of the moments of GSLW and short wave spectra for the average time duration and the mean length of runs of wave heights exceeding a certain level can be derived . A new groupiness factor equivalent to half the mean wave number in wave groups is defined by taking into account the widths of spectra of GSLW and short waves . Compared with theoretical results of others , ours are closer to measured wave data .
基金The National High Technology Research and Development Program of China under contract No.2012AA052602the National Natural Science Foundation of China under contract Nos 51079023 and 50921001
文摘The physical simulation method of wave groups in a wave flume is proposed and verified by the exper- iments. The experimental results demonstrate that random waves with desired wave groupiness, which simultaneously includes the wave group height and length, can be generated satisfactorily at the specified position in a wave flume using the proposed method. Furthermore, the transformation properties of the wave groupiness along the fiat-bottomed wave flume are investigated based on the physically simulated waves. Associated proposals with the physical simulation of wave groups are given.
