Wave Height Distribution Research Articles

Assessments of wave energy in the Bohai Sea, China

Wave fields in the Bohai Sea are continuously simulated by the third-generation wave model SWAN in order to determine the wave energy resources from 1985 to 2010. The wind parameters used to simulate waves are obtained by the Regional Atmospheric Modeling System (RAMS). Comparisons of significant wave heights between simulations and observations show good agreement. The spatial distributions of mean monthly and annual averaged significant wave height and wave power flux are presented. Wave energy roses and temporal variations of average wave power density at five typical points in the Bohai Sea are calculated. Furthermore, the correlations between significant wave height and wave energy period are studied in scatter and energy diagrams.

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.

Bivariate joint distribution modeling of wave climate data using a copula method

The bivariate joint distribution of the significant wave height and the wave period is of great importance in characterizing the wave climate at a wave energy converter test site. In this paper, we ...

Coastal Wave-Height Statistics during Hurricane Ike

AbstractThe statistical behavior of wave heights obtained from short-term (i.e., 30-min) wave records during Hurricane Ike was investigated. Spectral data from seven temporary pressure gauges and one National Data Buoy Center (NDBC) buoy moored off the coast of Texas, covering a 12-day period, were used. The wave heights, based on time series reconstructed from the spectra, showed a very good fit to the form of the Rayleigh distribution with Hrms as the parameter of the distribution, whereas the use of the spectrally derived parameter 8m0 led to overprediction of the wave heights. Incorporating the spectral band width (α) in the Rayleigh distribution reduced this overprediction. The empirical two-parameter Weibull distribution was also found to represent the wave-height distribution well, but with parameters different from a = 2.126 and b = 8.42. The Tayfun model, used as a representative of Rayleigh-like models, provided the best fit. When converting model-derived significant wave heights to other quanti...

Satellite-based wave data and wave energy resource assessment for South China Sea

Wave energy has the potential to valuably contribute to the coastal states renewable energy mix. However, lack of data sources hinders the effort to deliberately assess this resource. This paper presents an assessment of wave energy resources in the South China Sea (Malaysian Exclusive Economic Zone) using satellite altimeter. Radar Altimeter Database System (RADS) provides data of significant wave height and wind speed from several satellite altimeters. The data were extracted for a space resolution of 0.25° × 0.25°, and within the time range from January 2001 to December 2010 and space range of 1.5°N – 10.0°N, 95.0°E − 116.0°E. For this study, fifteen 2° × 2° zones were considered around the east coast of Peninsular Malaysia and the coast of East Malaysia. The 10-year-data were validated with buoy measurements and presented as the probability distribution of wave height and wave period. The results indicate that bulk of the waves had peak period between 5s and 7s and significant wave height between 0.5 m and 1.5 m. The data were then used to calculate the theoretical available wave energy and power in the study areas. The results show that the average wave energy density of Malaysian seas facing the South China Sea is in the range of 1.41 kW/m to 7.92 kW/m, while the energy storage varies from 7.10 MW h/m to 69.41 MW h/m. This study also demonstrates the ability of satellite altimeter to provide an accurate and reliable data for more comprehensive and realistic estimate of the energy potential. The ability of satellite altimeter to provide wave data for all sea zones will enable more accurate identification of potential locations for wave energy development in Malaysia.

Dispersion Effects on Tsunami Propagation in South China Sea

As the Manila Trench is becoming the most tsunami-hazardous, it is necessary to ascertain the wave height and arrival time in the South China Sea region through numerical simulation of tsunamis generated from potential earthquake source along the Manila subduction zone. The Okada model is employed to generate tsunami. The surface elevation and depth-averaged horizontal velocity at first 5 min, coming from the simulation of shallow water equations, are then interpolated in the weakly dispersive model (FUNWAVE) to calculate tsunami propagation and far-field impact. The characteristics of tsunami wave height distribution in South China Sea are analyzed for the assessment of tsunami hazard near coasts around South China Sea due to the hypothetical earthquakes with magnitude of [Formula: see text] and the worst case scenario ([Formula: see text]). The maximum wave height distribution computed by the Boussinesq equations is compared with that by the shallow water equations to investigate the dispersion effects on propagation of tsunami in South China Sea. It is found that the dispersion effects of the tsunami waves propagating in South China Sea are not significant if the earthquake magnitude is large enough.

Wave pressure acting on V-shaped floating breakwater in random seas

Wave pressure on the wet surface of a V-shaped floating breakwater in random seas is investigated. Considering the diffraction effect, the unit velocity potential caused by the single regular waves around the breakwater is solved using the finite-depth Green function and boundary element method, in which the Green function is solved by integral method. The Response-Amplitude Operator (RAO) of wave pressure is acquired according to the Longuet-Higgins' wave model and the linear Bernoulli equation. Furthermore, the wave pressure's response spectrum is calculated according to the wave spectrum by discretizing the frequency domain. The wave pressure's characteristic value corresponding to certain cumulative probability is determined according to the Rayleigh distribution of wave heights. The numerical results and field test results are compared, which indicates that the wave pressure calculated in random seas agrees with that of field measurements. It is found that the bigger angle between legs will cause the bigger pressure response, while the increase in leg length does not influence the pressure significantly. The pressure at the side of head sea is larger than that of back waves. When the incident wave angle changes from 0A degrees to 90A degrees, the pressure at the side of back waves decreases clearly, while at the side of head sea, the situation is more complicated and there seems no obvious tendency. The concentration of wave energy around low frequency (long wavelength) will induce bigger wave pressure, and more attention should be paid to this situation for the structure safety.

Study of the foundation design for a linear generator wave energy converter using stochastic methods

This paper presents design studies of the gravity-based foundation for a linear generator wave energy converter. The wave energy converter is based on a direct driven generator mounted on the gravity-based foundation located at the seabed. The linear generator is connected to a point absorbing buoy on the sea surface via a connection rope. Such a device, developed at Uppsala University, has been in operation on the Swedish west coast since 2006. Study is focused on the analysis of the impact from undesirable motions of the gravity-based foundation, particularly the study of the tip and lifts phenomena with regard to the heave and surge forces. Long-term extreme significant wave heights are extrapolated from the statistical analysis of the measured wave climate data in the test site where the wave energy converter is deployed. The joint distribution of the significant wave height and the zero-crossing period from the measured wave climate is also analyzed to estimate the associated periods with respect to the long-term extreme significant wave height. The 25 years return extreme significant wave height 4.8 m which is associated with its mean zero-crossing period 8.25 s from the joint distribution is chosen to determine the characteristics of the possible maximum wave for the Lysekil test site. The estimated maximum wave 9.2 m is used to estimate the extreme values of the heave and surge forces on the wave energy converter and the gravity-based foundation. The results with respect to the foundation of a new generation wave energy converter about 35 tons with the presented methodology indicate that a heavier foundation which is about 70 tons needs to be designed in terms of considering the stability of the mooring foundation for long term real sea operation. The purpose of this paper is to propose a reliable approach to estimate the appropriate dimensions for gravity-based foundation of the linear generator wave energy converter and provides a theoretical reference to the construction of the gravity-based foundation.

Application of Probabilistic Tsunami Hazard Analysis for the Nuclear Power Plant Site

The tsunami hazard analysis is performed for testing the application of probabilistic tsunami hazard analysis to nuclear power plant sites in the Korean Peninsula. Tsunami hazard analysis is based on the seismic hazard analysis. Probabilistic method is adopted for considering the uncertainties caused by insufficient information of tsunamigenic fault sources. Logic tree approach is used. Uljin nuclear power plant (NPP) site is selected for this study. The tsunamigenic fault sources in the western part of Japan (East Sea) are used for this study because those are well known fault sources in the East Sea and had several records of tsunami hazards. We have performed numerical simulations of tsunami propagation for those fault sources in the previous study. Therefore we use the wave parameters obtained from the previous study. We follow the method of probabilistic tsunami hazard analysis (PTHA) suggested by the atomic energy society of Japan (AESJ). Annual exceedance probabilities for wave height level are calculated for the site by using the information about the recurrence interval, the magnitude range, the wave parameters, the truncation of lognormal distribution of wave height, and the deviation based on the difference between simulation and record. Effects of each parameters on tsunami hazard are tested by the sensitivity analysis, which shows that the recurrence interval and the deviation dominantly affects the annual exceedance probability and the wave heigh level, respectively.

A Comparative Study of Wave Height Estimation base on X-band Radar

This paper presents a comparative study of wave height estimation method that was used for signal to noise ratio and shadowing ratio based on X-band marine radar. If the signal to noise ratio, and is widely used as a method for estimating an wave height, a new method is presented for shadowing ratio. In the case of radar images used in this study it is measuring the data from the coast of Ulsan Jujeon, compared with marine meteorological information from the Meteorological Agency measured a light beacon. We compared the measured data for about 34 days, the typhoon was measured, incluidng a period in the East Sea, and verify the results for various distribution of wave height. For estimate wave height using a shadowing ratio analysis, it does not require calibration and real-time advantages of this part, coming confirmed the possibility of the measurement, the cause detection error for radar image was caused due to determine.

Random wave-induced current on mild slopes

This paper provides a simple analytical method for calculating the wave-induced current due to long-crested random waves on mild slopes. The approach is based on assuming the waves to be a stationary random process, adopting the Battjes and Groenendijk (2000) wave height distribution for mild slopes. An example is included to demonstrate the application of the analytical method for practical purposes using data typical for field conditions; the significant values of the surface Stokes drift and the volume Stokes transport are calculated. The present results can be used to make assessment of the random wave-induced current based on available wave statistics.

Short-term statistics of waves measured off Ratnagiri, eastern Arabian Sea

The short-term wave characteristics are required for design and operation of industrial facilities within the coastal areas. Water surface displacement measured using waverider buoy moored at 13m water depth in the eastern Arabian Sea off the west coast of India have been analyzed to study the short-term statistics of waves covering full one year period. The study indicates that the values of the observed maximum wave height as a function of duration are not consistent with the theoretical expected value. There is significant variation (1.29–2.19) in the ratio between highest 1% wave and significant wave height compared to the theoretical value of 1.67. The data recorded at 13m water depth indicates that the significant wave height is ∼8% lower than that predicted by the conventional Rayleigh distribution. The theoretical bivariate log-normal distribution represents the joint distributions of wave heights and periods for the study area.

Observation of Extreme Sea Waves in a Space–Time Ensemble

AbstractIn this paper, an observational space–time ensemble of sea surface elevations is investigated in search of the highest waves of the sea state. Wave data were gathered by means of a stereo camera system, which was installed on top of a fixed oceanographic platform located in the Adriatic Sea (Italy). Waves were measured during a mature sea state with an average wind speed of 11 m s−1. By examining the space–time ensemble, the 3D wave groups have been isolated while evolving in the 2D space and grabbed “when and where” they have been close to the apex of their development, thus exhibiting large surface displacements. The authors have selected the groups displaying maximal crest height exceeding the threshold adopted to define rogue waves in a time record, that is, 1.25 times the significant wave height (Hs). The records at the spatial positions where such large crests occurred have been analyzed to derive the empirical distributions of crest and wave heights, which have been compared against standard statistical linear and nonlinear models. Here, the maximal observed wave crests have resulted to be outliers of the standard statistics, behaving as isolated members of the sample, apparently uncorrelated with other waves of the record. However, this study has found that these unexpectedly large wave crests are better approximated by a space–time model for extreme crest heights. The space–time model performance has been improved, deriving a second-order approximation of the linear model, which has provided a fair agreement with the empirical maxima. The present investigation suggests that very large waves may be more numerous than generally expected.

위상을 포함한 다방향 불규칙파 조건에서의 이안류 수치모의

Recently, Choi et al.(2015) showed that a numerical simulation of the SandyDuck experiment under a directional random wave environment agreed well with the experimental data including the wave height distribution of the random waves, the well-developed longshore current and its energetic fluctuation. Based on the Boussinesq modeling, this study investigates the effect of the alongshore variations, which are induced by not only the field topography but also the phase interaction of multidirectional random waves in the surf zone wave field, on the rip currents. As a result, transient rip currents as well as topographical rip currents cause the complicated surfzone circulation and mixing process due to their interactions in a multi-directional random wave condition while the topographical rip currents are dominant in a monochromatic wave condition. 핵심용어: SandyDuck experiment, rip current, directional random waves, Boussinesq modeling, FUNWAVE, SandyDuck 실험, 이안류, 다방향 불규칙파, ë¹„ì„ í˜• Boussinesq ë°©ì •ì‹

Comparison of Distributions of Wave Heights From Nonlinear Schröedinger Equation Simulations and Laboratory Experiments

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.

Alternative Environmental Contours for Marine Structural Design—A Comparison Study1

A new approach to estimate environmental contours in the original physical space by direct Monte Carlo simulations rather than applying the Rosenblatt transformation has recently been proposed. In this paper, the new and the traditional approach to estimating the contours are presented and the assumptions on which they are based are discussed. The different results given by these two methods are then compared in a number of case studies. Simultaneous probability density functions are fitted to the joint distribution of significant wave height and wave period for selected ocean locations and environmental contours are estimated for both methods. Thus, the practical consequences of the choice of approach are assessed. Particular attention is given to mixed sea systems. In these situations, the two approaches to environmental contours may be very different while for other wave conditions the contours are similar.

Bivariate distributions of significant wave height and mean wave period of combined sea states

This work presents the results of the fit of three bivariate models to twelve years of significant wave height and mean zero-crossing period data of swell, wind sea components, and combined sea states from Australia. The Conditional Modelling Approach defines the joint distribution from a marginal distribution of significant wave height and a set of distributions of mean zero-crossing period conditional on significant wave height. The second model fits the Plackett model to the data, and the last one applies the Box–Cox transformations to the data with the aim of making it approximately normal to fit a bivariate normal distribution to the transformed data. The conditional model with a lognormal distribution for the significant wave height and lognormal distributions for the zero-crossing period gave the best fit for the total sea states and for the wind component. In case of the swell component the conditional model with a Weibull distribution to the significant wave height and a lognormal distribution to the mean zero-crossing period gave a relatively close fit to the data.

On the distribution of significant wave height and associated peak periods

This study uses 21years (1958–1978) significant wave height and associated peak periods off Azores in the North Atlantic Ocean, extracted from 44years HIPOCAS database. Empirical average conditional exceedances of peak periods are executed. Plausibility of judging the distribution of the peak periods by modelling average conditional exceedance of peak periods by Erlang, generalized Pareto and three-parameter Weibull models is investigated and we also assessed certain peak period statistics predicted by the models. 50year gamma peak period quantiles are reasonably accurate when compared with 44year peak period quantiles (HIPOCAS). Erlang and generalized Pareto estimate of mean peak period are reasonable; whereas all the three models fairly evaluate the average of the one-third the highest peak periods. Weibull model derived parametric relation gauged the average of the one-tenth the highest peak periods. A general statistical formula is suggested for estimation of significant wave period. Average of one-third the highest peak period estimates by the parametric relation derived from generalized Pareto distribution using the general formula for significant wave period, provides reliably precise results. Significant wave period to mean wave period observational ratio of 1.2 is appropriately interpreted for both computed and estimated ratios of mean peak period of one-third the highest significant wave heights to mean peak periods.

Combined Method for Measuring 3D Wave Spectra. I. Algorithms to Transform the Optical-Brightness Field into the Wave-Height Distribution

Optical instruments for measuring surface-wave characteristics provide a better spatial and temporal resolution than other methods, but they face difficulties while converting the results of indirect measurements into absolute levels of the waves. We have solved this problem to some extent. In this paper, we propose an optical method for measuring the 3D power spectral density of the surface waves and spatio-temporal samples of the wave profiles. The method involves, first, synchronous recording of the brightness field over a patch of a rough surface and measurement of surface oscillations at one or more points and, second, filtering of the spatial image spectrum. Filter parameters are chosen to maximize the correlation of the surface oscillations recovered and measured at one or two points. In addition to the measurement procedure, the paper provides experimental results of measuring multidimensional spectra of roughness, which generally agree with theoretical expectations and the results of other authors.

Wave Height and Horizon Dip

A mariner who takes the height of the sun or a star to find his position at sea, must correct his observation for horizon dip. Throughout history, dip values have been tabulated based on the idealized assumption of a perfectly flat sea. Literature on wave height correction for dip is scarce, especially in the Western part of the world and suggested procedures are often conflicting or incorrect. We investigate the effect of wave height on the apparent horizon for realistic wave height distributions by optical ray tracing methods and show that there are two eye height corrections: one representing the apparent rise of the horizon itself and the second when sights are selectively taken from wave crests. Tables and formulas for dip and horizon distance taking wave height into account are presented. Copyright © 2015 Institute of Navigation.