Triple diagram method for the prediction of wave height and period

Many formulations have been developed so far to predict the wave height and period from fetch length and wind blowing duration for a constant wind speed. This study aimed to predict wave parameters from fetch length and meteorological factors by using triple diagram methodology based on Kriging principles. Proposed model results were compared with Joint North Sea Wave Project (JONSWAP) model which is used so commonly in the ocean and coastal engineering studies. For the implementation of the methodology hourly wave and wind data were obtained from a buoy located in Lake Ontario. Numerical and graphical comparisons demonstrated that the proposed method outperforms the classical formulation.     

Bayesian inference for long-term prediction of significant wave height

This paper considers the problem of estimating long-term predictions of significant wave-height. A method which combines Bayesian methodology and extreme value techniques is adopted. Inferences are based on the Metropolis–Hastings algorithm implemented in an appropriate Markov Chain Monte Carlo scheme. The method is applied to obtain return values of extreme values of significant wave height collected on the northern North Sea. The results are compared with those obtained by Guedes Soares and Scotto [Guedes Soares, C. and Scotto, M.G., 2004. Application of the r-order statistics for long-term predictions of significant wave heights. Coastal Engineering, 51, 387–394].     

Modified Weibull distribution for maximum and significant wave height simulation and prediction

Calibration coefficients incorporated in the modified Weibull distribution are more effective for maximum wave height simulation. The parametric relations are derived there from to estimate various wave height statistics including extreme wave heights. The characteristic function of the Weibull distribution is derived. The Weibull distribution is suggested for the newly defined significant wave height simulation by the method of characteristic function. The statistical tools suggested and developed here for predicting the required wave height statistics are validated against the wave data (both deep and shallow) of eastern Arabian Sea comprising rough monsoon conditions also, giving reasonable accuracy.     

A performance test of nearshore wave height prediction with CLASH datasets

The CLASH database was analyzed for extraction of a set of data having the measured wave heights at both the deep station and the toe of the structure for wave overtopping tests, yielding 1214 data from 29 datasets. Wave heights in front of the toe of the structure were estimated with the Goda formulas and compared with the measured ones. Comparison yielded the overall mean of 1.106 with the standard deviation of 0.155 for the ratio of the estimated to the measured heights, which support the use of the Goda formulas for prediction of nearshore wave heights. Another set of 1215 data having the measured wave heights at the deep station and the wave heights calculated with the SWAN model was also extracted from the CLASH database. A comparative test of the SWAN model using the wave height estimated with the Goda formulas in lieu of the measured height indicated the performance of the SWAN model being similar to that of the Goda formulas, but a tendency of underestimation was noticed in shallow water on a beach of very gentle slope.     

一种利用浮标站资料改进海浪模式有效波高预报的方法

基于浮标站海浪历史数据,利用回归分析方法建立了海浪数值模式有效波高预报产品的一元二次回归方程订正统计模型。通过2017年7月1日-2018年10月10日期间业务试运行结果发现:订正方程能有效改善有效波高数值预报产品的预报精度,且预报时效越短订正效果越显著。其中,第6~11 h预报时效内的订正前后平均绝对误差值减小0.17~0. 241 m,第6~18 h预报时效内订正前后均方根误差减小幅度为0.103~0. 28 m。这说明应用订正统计模型对海浪模式输出产品进行订正,也是改进海浪模式预报准确率的一种有效途径。     

The limiting wave height in wind-induced wave trains

The vertical acceleration threshold concept has been applied to evaluate the limiting wave height in the train of wind-induced waves propagated over a horizontal bottom. This concept yields very simple computation of the probability of breaking for stochastic sea in deep and finite water depths. The computations confirmed the available field and laboratory observations that the limiting wave steepness in the deep water is lower than the steepness predicted by Stokes. For shallow water depth, the limiting wave height is smaller than 0.55h. This conclusion is consistent with field as well as wave tank observations.     

基于SWAN模式的全球有效波高数值预报结果之初步验证

利用国家海洋环境预报中心基于SWAN模式和NCEP预报风场模拟的全球海浪预报场,结合Jason-2卫星高度计和NDBC浮标资料对全球海浪场进行了自2013年7月到2014年6月为期1 a的统计检验。结果表明:预报波高与实测值吻合较好,24 h、48 h、72 h预报的均方根误差均小于0.6 m,偏差绝对值均小于0.1 m,相关系数均大于0.91。有效波高的预报精度随预报时效的增加而降低,预报误差在48 h内变化不大,而在48 h后明显增大。有效波高的预报偏差存在地域性差别,全球西风带和热带地区的偏差较大,而赤道无风带和副热带高压控制地区的偏差较小。     

Probabilistic distribution of the maximum wave height

A new method of treating maximum wave height as a random variable in reliability analysis of breakwater caissons is proposed. The maximum wave height is expressed as the significant wave height multiplied by the so-called wave height ratio.The proposed wave height ratio is a type of transfer function from the significant wave height to the maximum wave height.Under the condition of a breaking wave, the ratio is intrinsically nonlinear. Therefore, the probability density function for the     

The parameterisation and prediction of wave height and wind speed persistence statistics for oil industry operational planning purposes

This study sets out to define the basic forms in which wind speed and wave height persistence statistics may be defined for offshore engineering applications, and describes the development of a mathematical persistence model.The model incorporates some of the principles laid down by other workers, but it is fundamentally based on a new concept for parameterising persistence statistics, linking wind speed and sea state percentage probability of exceedance with the persistence average duration.North Sea measured wind and wave data have been used to calibrate and test the model. During the course of these test runs it proved necessary to fine tune the basic Weibull equation of the model, but following these adjustments the model runs were found to correlate well with the measured data.It is concluded that the model may be used to predict wind speed and wave height persistence statistics with acceptable accuracy for preliminary stage oil industry planning purposes and that the calibrated model has particular application for those areas where little measured data are currently available.     

Assessment of the uncertainty in visual observations of wave height

Visual observations of wave height are still the main source of statistical information available for the prediction of extreme wave conditions to be used in the design of ship structures. However, the observations need to be calibrated with measurements. This work examines previous calibration studies and after joining the old with more recent data sets a reanalysis of the complete data sets is performed leading to updated regression equations.     

Determination of wave energy dissipation factor and numerical simulation of wave height in the surf zone

Based on the time-dependent mild slope equation including the effect of wave energy dissipation, an expression for the energy dissipation factor is derived in conjunction with the wave energy balance equation. The wave height of regular and irregular waves is numerically simulated by use of the parabolic mild slope equation considering the energy dissipation due to wave breaking. Comparison of numerical results with experimental data shows that the expression for the energy dissipation factor is reasonable. The effects of the wave breaking coefficient on the breaking point and the distribution of wave height after breaking are discussed through the study of a specific experimental topography.     

Extreme significant wave height climate in the Gulf of Guinea

This article investigates spatio-temporal trends for different return periods of extreme significant wave height (SWH) in the Gulf of Guinea (GG), northeastern tropical Atlantic Ocean, based on a 37-year (1980–2016) wave hindcast. High-resolution reanalysis windfield datasets were used to force the spectral wave model WAVEWATCH III. The wave hindcast information was validated using data gathered from the US National Data Buoy Center. The model performance was adequate. In a spatial analysis, the trends were less than 0.3 m decade^?1 in all parts of the GG, and were increasingly positive westwards, extending to the far western part of the GG; trends below 0.01 m decade^?1 dominated in the eastern part and some areas of the northern part of the gulf. Temporal analysis showed that the trends were negative in all cases. Spatio-temporal trends in the return periods for the 99th-percentile wave height were generally weak. Also, trends in the yearly, seasonal and monthly means of extreme SWH all generally increased from east to west in the GG. Furthermore, temporal trend analysis showed that extreme SWH exhibited an increasing trend of 0.0041 m y^–1 throughout the 37-year period; by season, it exhibited a declining trend of ?0.0005 m y^–1 in winter, and an increasing trend of 0.0048 m y^?1 in summer. The observed increasing positive trend of extreme SWH westward in the GG, however, suggests an increasing storminess towards the western part of the gulf, with potential implications for coastal flooding and erosion, and consequences for coastal structures.     

On the largest wave height in water of constant depth

Experimental evidence of the fact that, both in the laboratory and in the field, the largest wave height to water depth ratio realisable for oscillatory waves propagating in water of constant depth is about 0.55, has been published recently (Nelson, 1985); (Nelson, 1987); (Nelson, 1994). This paper presents various theoretical approaches to estimate this maximum value. In particular, the higher approximations of the Stokes and cnoidal theories give a much higher limiting wave height, close to 0.78 h, which is commonly used in engineering practice.However, the inclusion of higher harmonics, generated by a wave-maker paddle, into the analysis provides maximum wave height less than ≈ 0.6 h, which is in good agreement with observations.     

黄海海浪季节变化的数值模拟研究

利用第三代海浪数值模式SWAN,研究了黄海海浪有效波高的季节变化特征及相关的物理过程。结果表明,在黄海的大部分区域,混合浪有效波高的最大值出现在冬季,而最小值则基本出现在夏季。北黄海北部和山东半岛南岸的近海海域呈现稍微不同的季节变化,有效波高的最大值出现在春季。全年4个季节中混合浪有效波高的空间分布基本一致:均在济州岛西南最大,沿黄海中部区域向北和由中部区域向近岸区域逐渐减小。黄海海浪为风浪占主,涌浪有效波高远小于风浪有效波高。在黄海的大部分区域,白冠耗散和四波非线性相互作用对黄海海浪的季节变化均至关重要;对于外海区域,四波非线性相互作用更为重要,而对于近海区域,白冠耗散则影响更大。本研究旨在研究黄海海浪的季节变化特征及其物理过程,为进一步探讨该海域海浪在其他时间尺度上的变异特征和动力学过程提供研究基础。     

The long-term trend of the sea surface wind speed and the wave height (wind wave, swell, mixed wave)in global ocean during the last 44 a

Utilizing the 45 a European Centre for Medium-Range Weather Forecasts(ECMWF)reanalysis wave data(ERA-40),the long-term trend of the sea surface wind speed and(wind wave,swell,mixed wave)wave height in the global ocean at grid point 1.5×1.5 during the last 44 a is analyzed.It is discovered that a majority of global ocean swell wave height exhibits a significant linear increasing trend(2–8 cm/decade),the distribution of annual linear trend of the significant wave height(SWH)has good consistency with that of the swell wave height.The sea surface wind speed shows an annually linear increasing trend mainly concentrated in the most waters of Southern Hemisphere westerlies,high latitude of the North Pacific,Indian Ocean north of 30 S,the waters near the western equatorial Pacific and low latitudes of the Atlantic waters,and the annually linear decreasing mainly in central and eastern equator of the Pacific,Juan.Fernandez Archipelago,the waters near South Georgia Island in the Atlantic waters.The linear variational distribution characteristic of the wind wave height is similar to that of the sea surface wind speed.Another find is that the swell is dominant in the mixed wave,the swell index in the central ocean is generally greater than that in the offshore,and the swell index in the eastern ocean coast is greater than that in the western ocean inshore,and in year-round hemisphere westerlies the swell index is relatively low.     

元洪港设计波高参数的推算和分析

根据福建元洪港无长期海浪和风观测资料及该水域的多岛礁地形的特征，以邻近的平潭海洋站３０ａ实测海浪资料，采用考虑底摩擦效应的浅水波浪折射数值模式进行港区设计波高计算，并与港工程规范算法相比较，得出码头，航道口门和航道中段的设计波高参数。     

石岛海域海浪数值模拟及特征分析

本文基于SWAN(Simulating Waves Nearshore)模式研究了2001～2016年石岛海浪有效波高的季节和年际变化特征,评估了不同区域风场对其贡献,并探讨了其与ENSO的关系。结果表明,石岛有效波高受黄海季风系统的影响呈现显著的季节变化:12月份最大, 6月份最小, 1%大波有效波高季节变化不显著。石岛有效波高年际变化信号显著,其与风速年际变化之间的关系存在季节性差异:石岛有效波高和石岛、黄海区域平均风速不同月份的年际异常分别在7、10月份相关性较高,而石岛1%大波有效波高和石岛、黄海区域平均1%大风风速不同月份的年际异常则在8月份左右相关性最高。不同区域风场对石岛有效波高场的影响也呈现了季节性差异:夏季,黄海南部区域风场对石岛海浪的贡献较大,而石岛风场的贡献较小;冬季,石岛风场的贡献较大。ENSO(El Ni?o-Southern Oscillation)事件会对石岛有效波高的年际变化产生一定的影响,但影响比较小。本研究旨在对石岛海浪在季节和年际尺度上的变化特征以及风场等影响因素进行研究,对该海域海浪场进行了详细的认识,对了解该海域海浪有重要意义。     

A simplified model for wave height and set-up in the surf zone

Based upon a simple extension of the analytical solution by Dally et al., a closed form expression has been developed for the variation of long-crested regular wave heights in the surf zone including the effect of set-up. The expression predicts wave height and set-up values which compare favourably with experimental data.     

Modelling uncertainty in long-term predictions of significant wave height

This paper deals with the application of different methods to estimate the occurrences of high sea states. A case study of the Norwegian continental shelf is considered. The Annual Maxima Method and the Peak Over Threshold Method are used to obtain return values for 25, 50 and 100 years. Several parametric models are used to fit the long-term distribution of significant wave height and to obtain predictions of extremes values. It is shown that the prediction of these sea states depends very much on the tail behaviour of the fitted distribution.