Characteristics Of Wind Waves Research Articles

Wind Waves in the Northwestern Black Sea

The study presents the results of long-term monitoring of wind waves was carried out on the offshore fixed gas production platform in the northwestern part of the Black Sea in 1995–2011. The analysis of more than 31000 wave records provided reliable statistical characteristics of wind waves in the analyzed region. It was found that the maximum wave height reached 4.8 m in summer and 8.76 m in winter. The maximum hourly wave height exceeds significant wave height by 1.9 times in the vast majority of cases. The method of annual maxima revealed that in the Karkinit Bay the maximum wave height with the return period of 50 years is equal to 9.2 m.

Study on the growth of wind wave frequency spectra generated by cold waves in the northern East China Sea

The growth of frequency spectra and spectral parameters of wind waves generated by cold waves, a kind of severe weather system, in the northern East China Sea is studied in this paper. Based on a third-generation wave action model (the Simulating WAves Nearshore model), simulations were developed to analyze the spatiotemporal characteristics of wind waves and to output spectral data. It is shown that the cold wave-induced spectra can be well described by the modified Joint North Sea Wave Project spectral form. The growth of wave spectra is comprehensively reflected by the evolution of the three characteristic parameters: peak frequency, spectral peak and wave energy. Besides, the approximations of dependences between spectral parameters and the three types of universal induced factors are obtained with the least squares method and compared systematically. Fetch and peak frequency turn out to be suitable parameters to describe the spectral parameters, while the dependences on the inverse wave age vary in different sea areas. In general, the derived relationships improve on results from previous studies for better practical application of the wind wave frequency spectrum in the northern East China Sea.

Wave transformation in the nearshore waters of Jeddah, west coast of Saudi Arabia

Many specific problems in the coastal zones require an accurate description of the wave field and knowledge of wave parameters. The studies on the spectral characteristics of wind-waves in the Red Sea are very much limited. In this study, the spectral characteristics of nearshore waves in the central Red Sea, specifically the Jeddah coast has been investigated utilizing a third generation spectral wave model, SWAN. The model results were validated against the available measured data. The seasonal and monthly characteristics and the diurnal variability of wave spectra were analysed and discussed. The wave transformation between deep, intermediate and shallow water depths were assessed at three transects – northern, central and southern regions off Jeddah. The results indicate that multi-directional swells are present in the Jeddah nearshore regions, which are propagated from the northern and southern Red Sea. The diurnal variability in the wave spectra is persistent throughout the year, although it fluctuates among the seasons according to the prevailing wind conditions. Significant attenuations in wave heights were identified in the intermediate and shallow waters, with the highest attenuation occurred in the central Jeddah coast.

Characteristics of Wind and Planetary Waves Based on FPI over Kelan of Chinaormalsize

利用中国岢岚站（38.7&#176;N，111.6&#176;W）法布里-珀罗干涉仪2013年7月至2014年11月的水平风场数据，对87，97，250km风场长期变化和行星波特征进行了研究.通过分析年振荡（AO）和半年振荡（SAO）振幅相位，将午夜风场与HWM07数据对比发现：87km和97km处FPI纬向风变化趋势与HWM07相近，而经向风相位落后于HWM07，从振幅上看，HWM07振幅偏大；250km处风场月变化大，FPI与HWM07差异大，HWM07模式的准确性需进一步考虑太阳活动和行星际磁场的影响.利用Lomb-Scargle功率谱以及最小二乘谐波拟合提取了三个高度的行星波振幅，其特征表明87km和97km处纬向风16日波秋季及冬春季活动强，而6.5日波最强振幅出现在春季和秋季，在中间层顶附近两种行星波活动均较弱；250km处经向行星波活动略强于纬向，经向风不同周期带的行星波最强振幅主要出现在5-9月，与电离层<i>f</i>₀F₂振荡特性的研究结果一致.

General Sea State and Drag Coefficient Observed near Shore in Taiwan Strait

The general characteristics of wind waves and drag coefficient are studied using the data from the buoy observation near shore in Taiwan Strait. An algorithm of the bulk aerodynamic method using 10-minute mean wind speed and the temperature difference between the air and sea surface was developed to calculate the equivalent wind speed at 10 m in height and the surface friction velocity. The observation shows that the sea states contains a wide range of wave ages driven by the synoptic wind systems, i.e. the strong northeast monsoon in winter and southwest monsoon in summer, mixed with the thermally diurnal variation across the sea-land boundaries. The large-scale winds generate a number of swells with long fetch and the mesoscale circulation perpendicular to the main streams causing wind and wave misalignments. The drag coefficients display considerable scattering around the linear growth formulation along with the increase of neutral wind speed. This is attributed to the dependence of surface roughness on wave ages. The present observation confirms that the drag coefficients are sensitive to the sea state described using the Charnock constant and hence the wave ages.

Laboratory study of temporal and spatial evolution of waves excited on water surface initially at rest by impulsive wind forcing

Evolution of waves excited by wind that varies in time is not yet understood sufficiently well. In the present study, waves generated from rest by an effectively impulsive wind forcing are studied in a small laboratory wind-wave tank. Multiple parameters characterizing evolution of the wave field in time as well as in space are presented. Measurements of the variation with time of the instantaneous surface elevation were performed simultaneously with determination of two components of the instantaneous surface slope at a number of fetches along the test section. For each wind forcing conditions, numerous independent realizations were recorded. Thus, sufficient data were collected for computation of statistically reliable ensemble-averaged values of parameters characterizing the evolving random wind-wave field as a function of time elapsed since the initiation of wind. In each realization, data acquisition started when the water surface was calm, and lasted until statistically steady random wave field conditions were attained. The analysis of the ensemble-averaged wind-wave characteristics indicated that distinct stages in the wind-waves evolution could be identified. These stages were compared with the predictions based on the viscous instability theory and on the random resonant wind-waves generation model.

Use of the Phenomenon of Total Internal Light Reflection for Diagnostics of Sea Wind Waves

We develop a mathematical model for the formation of underwater images of a perturbed sea surface. On the basis of this model, a method for determination of statistical spatio-temporal characteristics of wind waves, which uses the phenomenon of total internal light reflection at the water—air interface, is proposed.

An Approximation to the Statistical Characteristics of Wind Waves in Front and from the Toe of the Structure to the Toe of the Crown of Nonovertopped Breakwaters

According to the main recommendations and technical criteria along the world, the design project of a breakwater must address the verification of the different failure modes that can affect the breakwater stability. This research focuses on the estimation of the statistical characteristics of the wind waves interacting with different breakwater types and their evolution from the toe of the structure to the toe of the crown. This knowledge is essential to calculate the reliability of the structure in its useful life. Partial standing wave patterns are likely to occur in front and along the section of the breakwater depending on their typology. Based on Rice's theory of envelope amplitude, we present an approximate solution of the total wave height distribution in front of the breakwater. The experimental results in 2D confirmed that the incident, the reflected and the total wave height in front of the breakwater followed a Rayleigh distribution in which the parameter is the root-mean-square total wave height. Its value depends on the modulus and phase of the reflection coefficient. The probability density function of the total wave height evolves from a Rayleigh to a Weibull distribution, whose scale and shape parameters vary from the toe to the crown of the structure, and depend on the breakwater type, the relative grain diameter, and the relative water depth. The largest deviation from the Rayleigh distribution occurs at the toe of the crown. These findings are weakly dependent on the incident wave steepness, and are valid for narrow-banded incident wave trains, impinging perpendicularly on nonovertopped breakwaters with a steep frontface, which ensures the rapid evolution of the wave train. Then, each mode of failure that might occur in the breakwater section can be formally checked against the same incident wave height, but verified (calculated) with the actual wave height, locally transformed by the specific typology.

Numerical Simulation of Wave Characteristics off Kulasekharapatnam, Southeast Coast of India

Waves are important driving forces that have significant implications in deep and shallow waters. To achieve further understanding of the characteristics of wind waves in the Gulf of Mannar, an attempt is made based on the measured data off Kulasekharapatnam for the period from January 2006 to May 2007. The integrated third-generation ocean wave models, WAM and SWAN, are implemented to simulate the significant wave parameters. Simulations were carried out using ECMWF ERA-Interim winds over the deep waters (30°E–120°E; 70°S–30°N and 76°E–80°E; 6°N–10°N) domains. Comparison of the ECMWF ERA-Interim wind data against the field measured data demonstrates that the overall trend and dominant directions are consistent with the observational data. The validation of significant wave parameters exhibited very high correlation (R > 0.9) at the study location. Wave heights are high in the Gulf of Mannar during the southwest monsoon period and the waves are from south-southwest. The study also shows that swells are predominant (24%) in the Gulf of Mannar during non-monsoon period and during rest of the year, wind sea (75.9%) dominates. The study also demonstrates the sensitivity of the SWAN model towards different GEN3 physics options and bottom friction formulations by forcing the model with QuikSCAT/NCEP Blended winds off Kulasekharapatnam. The simulations obtained using different GEN3 physics options and bottom friction formulations have been compared with the buoy data. The study indicates that the SWAN model with Janssen and Komen physics options simulates the significant wave height and mean wave period, respectively, with a fairly high degree of accuracy. Similarly, the JONSWAP formulation for bottom friction reproduced the buoy signals at the study location with good accuracy for both significant wave height and mean wave period. The study demonstrates that the simulations are sensitive to the choice of GEN3 physics and bottom friction formulations off Kulasekharapatnam, and hence effective for obtaining more accurate wave predictions.

Remote Sensing Studies of Suspended Sediment Concentration Variations in a Coastal Bay During the Passages of Atmospheric Cold Fronts

Mississippi River, the largest river in North America, carries a significant amount of sediment into the northern Gulf of Mexico coastal waters. In this region, recurring wind events associated with atmospheric cold fronts between fall and the following spring dominate resuspension and transport of the sediment. In this paper, based on a time series of the moderate-resolution imaging spectroradiometer satellite images with a moderate spatial resolution of 250 m during the passages of three atmospheric cold fronts in March 2013, considering the entire process of cold fronts, the distribution and variation of total suspended sediment (TSS) concentration and underlying hydrodynamic mechanism were analyzed. The TSS concentration distribution and sediment transport in the Atchafalaya Bay within the Mississippi River estuary were found to be positively correlated with the magnitude of local winds and waves, and negatively correlated with bathymetry. During the prefrontal stage, concentrations in the offshore water always decreased as a result of the wind-induced landward sediment transport. In the shallower water, the variations of TSS concentration are dominated by the intensity of wind stress. In the postfrontal period, the variations of TSS were controlled by wind-driven currents, resuspension, and vertical mixing. Although there were some exceptional situations due to the variations of the characteristics of wind and wind-induce wave, in general, the TSS concentration decreased in the entire region.

Assessment of extreme hydrological conditions in the Bothnian Bay, Baltic Sea, and the impact of the nuclear power plant “Hanhikivi-1” on the local thermal regime

Abstract. The results of the study aimed to assess the influence of future nuclear power plant Hanhikivi-1 upon the local thermal conditions in the Bothnian Bay in the Baltic Sea are presented. A number of experiments with different numerical models were also carried out in order to estimate the extreme hydro-meteorological conditions in the area of the construction. The numerical experiments were fulfilled both with analytically specified external forcing and with real external forcing for 2 years: a cold year (2010) and a warm year (2014). The study has shown that the extreme values of sea level and water temperature and the characteristics of wind waves and sea ice in the vicinity of the future nuclear power plant can be significant and sometimes catastrophic. Permanent release of heat into the marine environment from an operating nuclear power plant will lead to a strong increase in temperature and the disappearance of ice cover within a 2 km vicinity of the station. These effects should be taken into account when assessing local climate changes in the future.

Global historical archive of wind waves based on Voluntary Observing Ship data

A new global archive of wind wave characteristics has been developed based on Voluntary Observing Ship (VOS) data for the period of 1888–2015. In addition to the basic meteorological variables, we have derived the records of visually observed heights, periods, and wind sea and swell directions. The main parameters have been supplemented by significant wave height and dominant period estimates, as well as wave geometry characteristics: steepness, wave age, and wavelength. Multistage quality control has been applied to correct or eliminate spurious values. Data are presented as individual records for every month and as original monthly means fields for every parameter. Easy access and use, along with representative data, make the new archive particularly special and applicable in different ways without any additional preprocessing. Visual wave observations assimilated in the new archive can be used to develop global and regional climatologies, estimate extreme wave characteristics and long-term trends in wave climate, verify and compare them with satellite measurements and model analysis, and test the theoretical laws of ocean wave development and propagation.

Bottom sediment resuspension in the easternmost Gulf of Finland in the Baltic Sea: A case study based on three–dimensional modeling

A three-dimensional model of the Neva Bay, located in the eastern part of the Baltic Sea, was used to simulate the bottom sediment resuspension. The model takes into account the non-linear interaction of current-related and wave-related bed shear stress, sediment cohesion and packing effects, variable fall velocity of suspended particles due to hindered settling and flocculation, and also the influence of suspended particles upon the total stratification of the water column. Three main types of sediments in the Neva Bay were considered: gravel, sand and silt. The model SWAN was used to calculate the characteristics of wind waves. Satellite data was used to calibrate and validate the model. The present study has revealed that for the Neva Bay it is necessary to consider both current-related and wave-related bed shear stresses and spatial distribution of sediments, and also that taking into account the influence of suspended particles upon the total stratification in the Neva Bay leads to the damping of vertical turbulent mixing. The results have demonstrated that the model correctly simulates the patterns of high-turbidity events in the Neva Bay. Model runs for ice-free periods of 2004, 2008 and 2013 years have shown that significant sediment resuspension happened along the whole coastline from the town of Sestroretsk to the estuary of the Neva River and at the river sand bars during strong west and south-west winds. Sediment resuspension occurred most intensively during autumn months, with the peak of intensity being observed in November.

Wind wave characteristics based on visual Observations and satellite altimetry

Joint analysis of wind wave characteristics derived from the Voluntary Observing Ship data (VOS) and satellite altimetry is presented as the first step of the synthesis of different data sources. Global distributions of significant wave heights and periods along with wind speed are constructed using various techniques and empirical parameterizations. Good qualitative and quantitative agreement of VOS and satellite altimetry is found especially for regions with high spatio-temporal density of observations. The problems and prospects of the further development of the study are discussed in the context of global wave climatology and marine safety.

Wave spectra partitioning and long term statistical distribution

A new method is presented for a physically based statistical description of wind wave climatology. The method applies spectral partitioning to identify individual wave systems (partitions) in time series of 2D-wave spectra, followed by computing the probability of occurrence of their (peak) position in frequency–direction space. This distribution can be considered as a spectral density function to which another round of partitioning is applied to obtain spectral domains, each representing a typical wave system or population in a statistical sense. This two-step partitioning procedure allows identifying aggregate wave systems without the need to discuss specific characteristics as wind sea and swell systems. We suggest that each of these aggregate wave systems (populations) is linked to a specific generation pattern opening the way to dedicated analyses.Each population (of partitions) can be subjected to further analyses to add dimension carrying information based on integrated wave parameters of each partition, such as significant wave height, wave age, mean wave period and direction, among others. The new method is illustrated by analysing model spectra from a numerical wave prediction model and measured spectra from a directional wave buoy located in the Southern North Sea. It is shown that these two sources of information yield consistent results. Examples are given of computing the statistical distribution of significant wave height, spectral energy distribution and the spatial variation of wind wave characteristics along a north–south transect in the North Sea. Wind or wave age information can be included as an extra attribute of the members of a population to label them as wind sea or swell systems. Finally, suggestions are given for further applications of this new method.

Identification of support structure damping of a full scale offshore wind turbine in normal operation

The support structure damping of a 3.6 MW pitch controlled variable speed offshore wind turbine on a monopile foundation is estimated both in standstill conditions and in normal operation. The net substructure damping is identified from the parameters of an exponential curve fitted to the relative maxima of an impulse response caused by a boat impact. The result is used in the verification of the non aerodynamic damping in normal operation for low wind speeds. The auto-correlation function technique for damping estimation of a structure under ambient excitation was validated against the identified damping from the decaying time series. The Enhanced Frequency Domain Decomposition (EFDD) method was applied to the wind turbine response under ambient excitation, for estimation of the damping in normal operation. The aero-servo-hydro-elastic tool HAWC2 is validated with offshore foundation load measurements. The model was tuned to the damping values obtained from the boat impact to match the measured loads. Wind turbulence intensity and wave characteristics used in the simulations are based on site measurements. A flexible soil model is included in the analysis. The importance of the correctly simulated damping in the model is stressed for accurate load prediction. Differences in the identified damping between the model and the wind turbine are detailed and explained. Discrepancies between simulated and measured loads are discussed.

Time series analysis on marine wind-wave characteristics using chaos theory

This paper discusses an attempt to identify the chaotic behavior of the dynamic system of wind-wave characteristics including significant wave height, wave period and wave direction in southern, central and northern regions of the Caspian Sea. Surrogate data method and spectral analysis are utilized to detect the nonlinearity and aperiodicity of the time series. The delay embedding theorem of reconstructing the phase space is applied to identify characteristics of the time series dynamic system. The false nearest neighbor analysis along with the correlation dimension estimation indicate the presence of high dimensional chaotic behavior with dimensions of the chaotic attractors at the range of 5.91, 6.30 and 7.55 for the significant wave height series and 6.59, 7.64 and 7.87 for the wave period for the southern, central and northern parts of the Sea. Higher correlation dimension of the northern station could be related to the physical characteristics of the sea bathymetry. However, the estimated correlation dimension indicates the low choaticity of the wave direction set (3.65, 3.70 and 3.77). Positive Lyapunov exponents obtained for all 9 data series prove the exponential divergence of the trajectories which support the presence of chaos in the wind-wave characteristics.

Wind wave characteristics and engineering environment of the South China Sea

Wave simulation was conducted for the period 1976 to 2005 in the South China Sea (SCS) using the wave model, WAVEWATCH-III. Wave characteristics and engineering environment were studied in the region. The wind input data are from the objective reanalysis wind datasets, which assimilate meteorological data from several sources. Comparisons of significant wave heights between simulation and TOPEX/Poseidon altimeter and buoy data show a good agreement in general. By statistical analysis, the wave characteristics, such as significant wave heights, dominant wave directions, and their seasonal variations, were discussed. The largest significant wave heights are found in winter and the smallest in spring. The annual mean dominant wave direction is northeast (NE) along the southwest (SW)-NE axis, east northeast in the northwest (NW) part of SCS, and north northeast in the southeast (SE) part of SCS. The joint distributions of wave heights and wave periods (directions) were studied. The results show a single peak pattern for joint significant wave heights and periods, and a double peak pattern for joint significant wave heights and mean directions. Furthermore, the main wave extreme parameters and directional extreme values, particularly for the 100-year return period, were also investigated. The main extreme values of significant wave heights are larger in the northern part of SCS than in the southern part, with the maximum value occurring to the southeast of Hainan Island. The direction of large directional extreme H s values is focus in E in the northern and middle sea areas of SCS, while the direction of those is focus in N in the southeast sea areas of SCS.

Wave characteristics analysis in Bohai Sea based on ECMWF wind field

In order to achieve further understanding of the characteristics of wind waves in the Bohai Sea, the SWAN (Simulating Waves Nearshore) model is applied to investigate the wave characteristics in Bohai Sea for the period from 1993 to 2012. The SWAN model is driven by the wind data from ECMWF (European Center for Medium Range Weather Forecasts). Comparison of the ECMWF wind data against the field measured data shows that the ECMWF wind data underestimates wind speed over the Bohai Sea, though the overall trend and dominant directions are consistent with the observational data. Thus, the ECMWF wind data was corrected according to the filed measured data before it is input into the SWAN model. The SWAN model is calibrated using both the short-term and long-term field measured data, and the model results agree well with the measured data. The temporal and spatial distribution of wave height, averaged period and wave direction were analyzed. It shows that our results are generally agree with that of the previous studies. However, the previous studies overestimate the significant wave height by 10cm in three major bays in Bohai Sea and by 1–10cm in Bohai Center and the Bohai Strait.

Characteristics of the frequency spectra of wind-waves in Eastern Black Sea

Spectral information for wind-waves in the Black Sea is extremely limited. Knowledge on spectral characteristics of wind-waves would contribute to scientific, engineering, and operational coastal and marine activities in the Black Sea, and would allow a better understanding of the nature of the waves occurring in this enclosed basin. Frequency spectra obtained from the directional buoys deployed offshore Sinop and Hopa in Turkey, and Gelendzhik in Russia were utilized as the three sets of data to investigate characteristics of wind-waves frequency spectra for the Eastern Black Sea. Records were firstly analyzed to identify them as uni-modal or multi-modal spectra. Single-peaked spectra were then identified as belonging to fully arisen or developing sea states. Parameters of the JONSWAP and PM model spectra were estimated for the corresponding sea state by using a least square error method. Finally, the records of developing seas were further analyzed to select the ones belonging to stable wind conditions. ECMWF analysis wind fields were utilized as the wind information corresponding to the wave records. Fetch dependencies of non-dimensional spectral variables (variance and peak frequency) and α parameter of the JONSWAP model spectrum were investigated for this data sub-set.