耿贝尔逻辑模型在极值风速和有效波高联合概率分布中的应用

首先介绍了耿贝尔逻辑模型，采用该模型对南海海域的涠州岛海洋站的风速和有效波高实测数据进行了分析，结果表明耿贝尔逻辑模型较好地描述了年极值风速和有效波高两随机变量的联合分布；采用得到的极值风浪联合概率分布推算了不同重现期的极值风速和波高，表明考虑风速和波高相关性对设计荷载的确定有显著影响。由于耿贝尔逻辑模型具有函数结构简单，参数估计方便，因此有望成为极值风速和波高联合分布的较理想概率模型。     

基于广义极值分布的设计波高推算

简介了广义极值分布函数及其3种参数估计方法,包括极大似然(ML)、线性矩(LM)和间隔最大积(MPS)估计的计算方法。使用广义极值分布函数推算了北部湾涠洲岛海域3个波向的年波高极值序列设计波高,并与Weibull分布、Gumbel分布和皮尔逊Ⅲ型分布的推算结果加以对比。分析表明,涠洲岛海域极值波高服从于广义极值Ⅲ型分布,拟合优度检验结果表明广义极值分布能更好地拟合极值波高;MPS方法是一种优良的参数估计法,推算的设计波高可作为海岸环境工程设计的首要参考值。     

基于Copula函数的波高与周期长期联合分布

基于二元copula函数构建波高与相应波周期的长期联合分布。以粤东汕尾海域最大波高与相应平均周期为研究实例,经分析获得以下结果:(1)经拟合优度检验优选的年最大波高与相应周期的边缘分布分别为皮尔逊三型分布和广义极值分布,二者之间的较优连接函数为Archimedean类的Gumbel-Hougaard copula函数;(2)同频率条件下年最大波高和相应周期联合概率分布的设计要素值高于单变量的设计值,其中波高设计值的差异略大于周期设计值;(3)同现重现期和联合重现期的设计值可作为海岸海洋工程建设中的设计波高和相应周期的上限和下限;(4)条件概率1表明,同频率下的年最大波高和相应周期的遭遇概率很高,其组合概率可作为工程建筑物损毁风险率。     

广东沿海的极值风速概率分布研究

简要论述了当前广泛使用的极值理论和极值分布理论3个概率分布模型——标准耿贝尔(SG)分布、广义极值(GEV)分布和广义帕累托分布(GPD).应用模型推算广东沿海9个站点的极值风速,对比分析结果表明:(1)3个模型都是推算极值风速的合适模型,但GPD模型可更充分地利用实际观测站点数据,风速拟合的PPCC和RMSE指标确定GPD是更优的概率模型; (2)选取的超阚值风速样本服从GPD-Ⅱ型分布,偏向于给出比SG模型和GEV模型更大的极值风速估计值; (3)从工程安全考虑,尤其在观测数据较少情况下推算工程设计风速可优先选用GPD模型.     

经略21世纪海上丝路之海洋环境特征:极值风速和极值波高

极值风速和极值波高是海洋工程、海洋能开发、防灾减灾等极为关注要素。文章基于来自欧洲中期天气预报中心(ECMWF)的ERA-interim海浪再分析资料、ERA阵风资料,计算了"21世纪海上丝绸之路"涉及海域的年极值风速、极值波高,并首次计算了不同季节的极值。结果表明:1南海的50年一遇年极值风速大于孟加拉湾,孟加拉湾大于阿拉伯海;极值波高的分布特征与极值风速大体一致。2南海的极值风速在各个季节都大于孟加拉湾,孟加拉湾大于阿拉伯海;南海-北印度洋的极值风速在JJA和SON期间明显大于MAM期间,DJF期间最小。3南海各个季节的极值波高都大于北印度洋,阿拉伯海的极值波高在MAM和JJA期间明显大于孟加拉湾;南海的极值波高在JJA和SON期间明显大于MAM和DJF期间;北印度洋的极值波高在JJA期间最大,MAM次之,DJF最小。     

设计波高推算的一种新模型

考虑台风影响海域的设计波高,结合复合极值理论和最大熵原则,构造了1种新型的具有4个待定参量和1个台风频次参量的poisson-最大熵分布函数模型,并推导出求解参数的方程组,参数的数值解可通过年极值实测数据的期望、方差、偏度和峰度得到.以黄海某观测站26 a极值波高的实测数据为例计算了新模型中4个待定参量和多年一遇设计波高,并与传统常用计算方法得到的结果进行比较.比较表明,新模型相比传统方法具有一定的优势.     

基于浮标资料的中国东部海域最大波高特征分析

利用原国家海洋局2010—2015年的浮标资料,计算渤、黄、东海有效波高和最大波高的线性关系,并通过1992—2011年共20 a的数值模拟有效波高资料计算中国东部海域各月的2.5 m、4 m、6 m以上最大波高频率和最大波高月极值分布。结果发现:中国东部海域由北至南,最大波高与有效波高的比值逐渐增大;最大波高频率和最大波高月极值空间分布均由渤海、黄海至东海逐渐增大,最大波高频率的极值12月最大,4或5月最小,最大波高月极值9月最大,4月最小。其时空分布表明:受不同天气系统影响,夏秋季台风较多,容易出现极值较大的最大波高;秋冬季冷空气较强,虽然最大波高极值相对较小,但大浪持续时间长、频率大、影响范围广。     

海洋重现期波高统一化计算方法

重现期波高是港口海岸及海洋工程设计中不可回避的一个重要设计参数,尤其对深水海港、海上平台、海底油气管道、沿海核电站等重大涉海工程设计具有巨大的经济价值和深远的社会效益。但是,现有重现期波高推算缺乏统一的计算方法,导致计算结果相差悬殊。研究重现期波高的统一化计算方法,分析重现期波高计算中存在的各种不确定因素,提出减少这些不确定因素的新方法,建立误差小、应用方便、方法统一的重现期波高计算方法。基于澳大利亚悉尼站的长期连续观测波浪数据,研究发现:广义帕累托函数(generalized Pareto distribution III,GPD-III)和威布尔(Weibull)是重现期波高计算的最佳候选极值分布函数,新推导的函数形状参数计算公式较好提高重现期波高的计算精度,极值波高数据的分析方法和样本大小是影响重现期波高计算精确度的两个重要因素,短期波浪资料和年极值法可能高估重现期波高值。逐个风暴的极值波高数据分析法及最佳候选极值分布函数GPD-III和Weibull建议应用于涉海工程设计的重现期波高推算。     

江苏滨海海域海上风电场的极值波高推算

为了给江苏滨海海域海上风电场的结构设计提供更为合理的设计参数,本文利用定量分析法对比分析了采用不同推算方法推算得到的工程海域极值波高,讨论了不同推算方法的差异及影响。结果表明：采用年极值法、条件极值法（包括风暴统计法、阈值上限法）和组合法推算出的工程海域极值波高受理论频率曲线、热带风暴年均频次、极端设计风速和特定水位的影响较大。其中,热带风暴年均频次主要影响风暴统计法推算的结果,当热带风暴年均频次不小于1时,推算的结果趋于稳定,相对偏差小于5%;极端设计风速和特定水位主要影响组合法推算的结果,极端设计风速的选择主要影响极值波高在各个方向上的分布,特定水位的叠加主要影响极值波高的幅值;对于非特定水位下的极值波高,利用条件极值法中的风暴统计法推算的结果最大,为6.55 m;利用年极值法中P-Ⅲ型曲线推算的结果最小,为5.48 m;两者相对偏差约20%;对于特定水位下的极值波高,利用组合法推算出的NW—SE方向极值波高与水位呈正相关,即叠加正水位时,极值波高增大,叠加负水位时,极值波高减小,幅值变化可达±15%;且极值波高的方向分布与所采用的极端设计风速的方向分布相同,利用极值波高对应的设计...     

确定海上极值波高的一种方法

本文介绍了海上极值波高设计值的确定方法,在数学原理上,该方法主要是通过波高的理论分布,或者由实测资料得出的波高经验概率分布,推求海上极值波高的众值和具有一定保证率的设计值。对于实测波高经验分布的模拟,本文采用F(x)=1-exp[-αx~bexp(-cx~d)]形式的拟合函数,并用非线性最小二乘法原理确定拟合函数中的非线性参数。实践证明,本方法计算简便,效果良好,可供实际工程设计时使用。     

基于Copula函数的海岸增水高度与相应风速的遭遇概率分析

简要论述了Copula理论与几种常用的二维Archimedean Copula函数的性质和适用性。以粤东汕头海域妈屿历年最高增水高度与相应风速的遭遇为研究实例,在分别采用3个三参数的概率分布模式:广义极值分布(GEV)、Weibull分布(WBL)和皮尔逊Ⅲ型(P-Ⅲ)分布对两个边缘分布(年最高增水高度与相应风速)拟合优度检验基础上构建了两变量联合概率分布模型。主要结果如下:(1) 年最大增水高度与相应风速的边缘分布分别服从Weibull分布和P-Ⅲ型分布;(2) 拟合优度检验指标表明二者的最优连接函数为Archimedean Copula类的Gumbel-Hougaard Copula;(3) 重现期介于2~200 a之间的边缘分布与同频率的联合分布的重现水平相对差值大约介于6.7%~22.2%之间;(4) 特定风速设计频率条件下,随年最大增水设计频率的减小,二者的遭遇概率也随之迅速减小;反之,特定增水设计频率随风速条件频率的减小,二者的遭遇概率随之明显增大。     

利用TOPEX卫星高度计资料分析东中国海的风、浪场特征

利用TOPEX卫星高度计和日本气象厅浮标观测资料,对东中国海的有效波高和风速进行比较,分析了卫星高度计资料的有效性。利用有效波高和风速的3种概率密度函数分布,结合TOPEX卫星高度计资料,并采用最大似然方法对统计分布参数进行估计,结果表明,有效波高的对数-正态概率密度分布与观测资料的直方图在有效波高的整个范围内符合较好,风速的直方图与Weibul概率密度分布符合较好。同时,分析了有效波高大于4 m的巨浪在东中国海的时空分布特征,表明巨浪多出现在冬、秋两季,平均有效波高最大值出现在夏季,且主要分布在东中国海东南部。     

欧洲北海海域波高区间分布概率研究

为了研究欧洲北海海域的波高全区域概率分布情况,从而为海洋平台等海洋浮式结构物的选址和结构设计提供依据。首先基于Global Waves Statistics(GWS)提供的实测数据,确定典型计算工况的发生概率;同时考虑实测数据中极端波浪环境下的数据缺失导致大波高分布概率偏小的问题,利用三参数Weibull分布确定不同重现期下的极值风速,作为典型计算工况的补充。以不同风速、风向的定常风场为输入项,利用第三代海浪数值模型SWAN模型,对北海全区域波高进行数值模拟。将数值模拟的稳态形式依照各工况的发生概率进行归一化累加处理,认为其结果可以表征全区域的波高概率分布情况。以波高概率分布的计算结果为依据,分析北海海域波浪环境的统计学特征,发现有效波高为7 m以上的大波高频发区在北海北部区域有大范围分布;有效波高4～5 m为北海东北区域的多发海况,极端海况下的有效波高主要分布于7～14 m区间,在地形突变区域的波高发生显著变化。     

基于Copula函数的联合概率法在海洋工程中的应用

本文介绍了Copula函数的定义、属性和几种特殊的Copula函数.将Copula函数应用到近海工程中,用其建立了最大有效波高和最大风速的联合分布函数并检验,结果表明:Copula函数能够比较好的模拟实际的联合概率分布。通过Copula方法,可以由边缘分布和一个连接它们的Copula函数来得出联合分布函数,发挥其描述相关性尤其是尾部相关性的优势。该方法在近海工程的工程可靠度、设计标准和失效概率的计算中具有广泛的应用前景。     

Intermittency of wind wave group breaking

Knowledge on intermittency of wave breaking is so far limited to a few summary statistics, while the probability distribution of time interval between breaking events can provide a full view of intermittency. Based on a series of experiments on wind wave breaking, such probability distributions are investigated. Breaking waves within a wave group were taken as a single breaking event according to recent studies. Interval between successive wave groups with breaker is the focus of this paper. For intervals in our experiments with different fetch and wind conditions, their distributions are all skewed and weighted on small intervals. Results of Kolmogorov-Smirnov tests on time series of these intervals indicate that they all follow gamma distribution, and some are even exponential type. Average breaking-group-interval decreases with friction velocity and significant steepness until the wind is strong enough;most of them are more than 10 times the dominant wave period. Group breaking probability proposed by Babanin recently and the average number of breaking waves in wave groups are also discussed, and they are seemingly more reasonable and sensitive than traditional breaking probability defined in terms of single wave.     

Winds and Waves in the Yellow and East China Seas: A Comparison of Spaceborne Altimeter Measurements and Model Results

Wind speed and wave height measured by satellite altimeters represent a good data source to the study of global and regional wind and wave conditions. In this paper, the TOPEX altimeter wind and wave measurements in the Yellow and East China Seas are analyzed. The results provide a glimpse on the statistical properties and the spatial distributions of the regional wind and wave conditions. These data are excellent for use in the validation and verification of numerical simulations on global and regional scales. The altimeter measurements are compared with model output of temporal statistics and spatial distributions. The results show that the model simulations are in good agreement with TOPEX measurements in terms of the local mean and standard deviation of the variables (wave height and wind speed). For the comparison of spatial distributions, the quality of agreement between numerical simulations and altimeter measurements varies significantly from cycle to cycle of altimeter passes. In many cases, trends in the spatial distributions of wave heights and wind speeds between simulations and measurements are opposite. The statistics of biases, rms differences, linear regression coefficients and correlation coefficients are presented. A rather large percentage (∼50%) of cases show poor agreement based on a combination of low correlation, large rms difference or bias, and poor regression coefficient. There are indications that wave age is a factor affecting the performance of wave modeling skills. Generally speaking, the error statistics in the wave field is correlated to the corresponding error statistics in the wind field under the condition of active wind-wave generation. The error statistics between the wave field and the wind field become less correlated for large wave ages. This revised version was published online in August 2006 with corrections to the Cover Date.     

Wave energy assessment based on trivariate distribution of significant wave height,mean period and direction

Based on the Vine copula theory, a trivariate statistical model of significant wave height, characterized wave period and mean wave direction was constructed. To maintain the properties of the different types of variables, a special copula function was derived from the model developed by Johnson and Wehrly based on the maximum entropy principle. It was then combined with the Archimedean copulas to construct the proposed model. An effective algorithm for generating corresponding joint pseudo-random numbers was also developed. Statistical analysis of hindcast data for the significant wave height, mean wave period, and direction, which were collected from an observation point in the North Atlantic every three hours from 1997 to 2001, was performed. The marginal distributions of the significant wave height and mean wave period were fitted by a modified maximum entropy distribution, and the mean wave direction was fitted by a mixture of von Mises distributions. It was shown that the proposed model is a good fit for the data. The seasonal wave energy resources in the target area were assessed using the model estimates. Histograms of the directional wave energy, wave energy roses, and scatter and energy diagrams were presented.     

Statistical Distribution of Depth-Integrated Local Horizontal Momentum for Second-Order Random Ocean Waves in Finite Water Depth

Based on the second-order random wave solutions of water wave equations in tinite water depth, statistical distributions of the depth-integrated local horizontal momentum components are derived by use of the characteristic function expansion method. The parameters involved in the distributions can be all detemained by the water depth and the wavenumber spectrum of ocean waves. As an illustrative example, a fully developed wind-generated sea is considered and the parameters are calculated for typical wind speeds and water depths by means of the Donelan and Pierson spectrum. The effects of nonlinearity and water depth on the distributions are also investigated.     

A Study on the Distribution of Wave Phases

Probability distributions of wave phases in association with distributions of surface elevations arestudied with wave records.Wave records of different nature are used for comparison.These are surface fluc-tuations acquired during wind wave flume experiments,representing wave generation under strong wind:andwave records measured in the northern part of Taiwan for waves in natural environments.Three probabilitymodels,the unifrom distribution,the beta distribution,and a model from Tayfun and Lo(1989)are adoptedto study the possible distributions of wave phases.It is found that when surface elevations become skewed,wave phases deviate from the usually assumed uniform distribution and a better model would be the beta dis-tribution.     

Application of MEP Method to the Study of Statistical Properties of Random Waves

—The maximum entropy principle(MEP)method and the corresponding probability evaluationmethod are introduced,and the maximum entropy probability distribution expression is deduced in mo-ment of the second order.Fully developed wave height distribution in deep water and wave height and peri-od distribution for different depths in wind wave channel experiment are obtained from the MEP method,and the results are compared with the distribution and the experimental histogram.The waveheight and period distribution for the Lianyungang port is also obtained by the MEP method,and the re-sults are compared with the Weibull distribution and the field histogram.