Maximum Wave Height Distribution in a Sea State: Effects of Record Length and Spectral Peakedness

Author(s):  
Germa´n Rodri´guez ◽  
Mercedes Pacheco ◽  
Carlos Guedes Soares

The probability distribution of the maximum wave height in a sea state is examined in terms of the spectral peakedness and the sea state duration. The study is based on the analysis of numerically simulated gaussian wave records with given target spectra to fulfill the long duration and stationarity jointly required conditions, seldom found in nature. Results indicate a clear dependence of the probability distribution structure and location on the record length and the spectral shape.

2005 ◽  
Vol 127 (4) ◽  
pp. 340-344 ◽  
Author(s):  
Germán Rodríguez ◽  
Mercedes Pacheco ◽  
C. Guedes Soares

The probability distribution of the maximum wave height in a sea state is examined in terms of the spectral peakedness and the sea state duration. The study is based on the analysis of numerically simulated Gaussian wave records with given target spectra to fulfill the long duration and stationarity jointly required conditions, seldom found in nature. Results indicate a clear dependence of the probability distribution structure and location on the record length and the spectral shape.


Author(s):  
Germán Rodríguez ◽  
Carlos Guedes Soares ◽  
José Carlos Nieto Borge

Location, dispersion, and asymmetry variability of the probability distribution of the maximum wave height from a set of N individual wave heights are examined in terms of the spectral peakedness and the duration of the sea states through the use of robust statistical parameters. The capability of various empirical and theoretical models to reproduce the observed features is also explored. The study is based on the analysis of numerically simulated Gaussian wave records with given target spectra to fulfill the long duration and stationarity jointly required conditions, seldom found in nature. Results indicate a clear dependence of the probability distribution structure and location on the record length and the spectral narrowness. Furthermore, it is observed that theoretical models based on the statistical independence of individual waves in a sea state and the knowledge of its population distribution assumptions are not able to characterize the structure and variations induced by these factors on the empirical distribution. However, the observed features can be reproduced by a simple empirical model depending on the sample quartiles.


Author(s):  
Huidong Zhang ◽  
Zhivelina Cherneva ◽  
C. Guedes Soares ◽  
Miguel Onorato

Numerical simulations of the nonlinear Schrödinger (NLS) equation are performed by using random initial wave conditions characterized by the JONSWAP spectrum and compared with four different sea states generated in the deep water wave basin of Marintek. The comparisons show that the numerical simulations have a high degree of agreement with the laboratory experiments although a little overestimation can be observed, especially in the severe sea state. Thus the simulations still catch the main characteristics of the extreme waves and provide an important physical insight into their generation. The coefficient of kurtosis λ40 presents a similar spatial evolution trend with the abnormal wave density and the nonlinear Gram-Charlier (GC) model is used to predict the wave height distribution. It is demonstrated again that the theoretical approximation based on the GC expansion can describe the larger wave heights reasonably well in most cases. However, if the sea state is severe, wave breaking can significantly decrease the tail of wave height distribution in reality and the discrepancy occurs comparing with the numerical simulation. Moreover, the number of waves also plays an important role on the prediction of extreme wave height.


Author(s):  
Huidong Zhang ◽  
Zhivelina Cherneva ◽  
Carlos Guedes Soares ◽  
Miguel Onorato

Numerical simulations of the nonlinear Schrödinger (NLS) equation are performed by imposing randomly synthesized free surface displacement at the wave maker characterized by the Joint North Sea Wave Project (JONSWAP) spectrum and compared with four different sea states generated in the deepwater wave basin of Marintek. The comparisons show that the numerical simulations have a high degree of agreement with the laboratory experiments although a little overestimation can be observed, especially in the severe sea state. Thus, the simulations still catch the main characteristics of extreme waves and provide an important physical insight into their generation. The coefficient of kurtosis λ40 presents a similar spatial evolution trend with the abnormal wave density, and the nonlinear Gram–Charlier (GC) model is used to predict the wave height distribution. It is demonstrated again that the theoretical approximation based on the GC expansion can describe large wave heights reasonably well in most cases. However, if the sea state is severe, wave breaking can significantly decrease the actual tail of wave height distribution, and discrepancy occurs when comparing with the numerical simulation. Moreover, the number of waves also plays an important role on the prediction of extreme wave height.


2019 ◽  
Vol 7 (3) ◽  
pp. 79 ◽  
Author(s):  
Stephen Orimoloye ◽  
Harshinie Karunarathna ◽  
Dominic Reeve

An understanding of the wave height distribution of a sea state is important in forecasting extreme wave height and lifetime fatigue predictions of marine structures. In bimodal seas, swell can be present at different percentages and different frequencies while the energy content of the sea state remains unaltered. This computational study investigates how the wave height distribution is affected by different swell percentages and long swell periods in an energy-conserved bimodal sea both near a wave maker and in shallow water. A formulated energy-conserved bimodal spectrum was created from unimodal sea states and converted into random waves time series using the Inverse Fast Fourier Transform (IFFT). The resulting time series was used to drive a Reynolds-Averaged Navier Stokes computational (RANS) model. Wave height values were then extracted from the model results (both away near and near the structure) using down-crossing analysis to inspect the non-linearity imposed by wave-wave interactions and through transformations as they propagate into shallow waters near the structure. It is concluded that the kurtosis and skewness of the wave height distribution very inversely with the swell percentage and peak periods. Non-linearities are greater in the unimodal seas compared to the bimodal seas with the same energy content. Also, non-linearities are greater structure side than at wave maker and are more dependent on the phases of the component waves at different frequencies.


1986 ◽  
Vol 1 (20) ◽  
pp. 26
Author(s):  
J.T. Juang

Due to the special bathymetry in Taiwan Strait, the waves off the western coast of Taiwan are considered to be composed of two-source wave system. One propagates from the central part of the Strait named main wave, and the other is generated by the local wind known as local wave which occurs along the shore. After the combination and the transformation procedure from these two-nonlinear-source wave system, the wave height distribution in Taiwan Strait should be modified. A comparison of the wave height distributions based on the present proposed method with the field data indicates that the present method yields a better result than other theorems. Furthermore, the result of application of two non-linear wave theorem to wave prediction are also presented.


1988 ◽  
Vol 1 (21) ◽  
pp. 48 ◽  
Author(s):  
Akira Kimura

The probability distribution of the maximum run of irregular wave height is introduced theoretically. Probability distributions for the 2nd maximum, 3rd maximum and further maximum runs are also introduced. Their statistical properties, including the means and their confidence regions, are applied to the verification of experiments with irregular waves in the realization of a "severe sea state" in the test.


2008 ◽  
Vol 17 ◽  
pp. 13-18 ◽  
Author(s):  
P. Lionello ◽  
M. B. Galati

Abstract. This study analyzes the link between the SWH (Significant Wave Height) distribution in the Mediterranean Sea during the second half of the 20th century and the Northern Hemisphere SLP (Sea Level Pressure) teleconnection patterns. The SWH distribution is computed using the WAM (WAve Model) forced by the surface wind fields provided by the ERA-40 reanalysis for the period 1958–2001. The time series of mid-latitude teleconnection patterns are downloaded from the NOAA web site. This study shows that several mid-latitude patterns are linked to the SWH field in the Mediterranean, especially in its western part during the cold season: East Atlantic Pattern (EA), Scandinavian Pattern (SCA), North Atlantic Oscillation (NAO), East Atlantic/West Russia Pattern (EA/WR) and East Pacific/ North Pacific Pattern (EP/NP). Though the East Atlantic pattern exerts the largest influence, it is not sufficient to characterize the dominant variability. NAO, though relevant, has an effect smaller than EA and comparable to other patterns. Some link results from possibly spurious structures. Patterns which have a very different global structure are associated to similar spatial features of the wave variability in the Mediterranean Sea. These two problems are, admittedly, shortcomings of this analysis, which shows the complexity of the response of the Mediterranean SWH to global scale SLP teleconnection patterns.


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