Peak Wave Period Research Articles

Feasibility of Wave Simulation in Typhoon Using WAVEWATCH-III Forced by Remote-Sensed Wind

The purpose of our work was to assess the feasibility of hindcasting waves using WAVEWATCH-III (WW3) in a typhoon by assembling winds from multiple remote-sensed products. During the typhoon season in 2021–2022, the swath wind products in the Western Pacific Ocean were collected from scatterometers and radiometers. Cyclonic winds with a spatial resolution of 0.125° at intervals of 6 h were obtained by assembling the remote-sensed winds from those satellites. The maximum wind speeds, Vmax, were verified using the reanalysis data from the National Hurricane Center (NHC), yielding a root-mean-squared error (RMSE) of 4.79 m/s and a scatter index (SI) value of 0.2. The simulated wave spectrum was compared with the measurements from Surface Waves Investigation and Monitoring (SWIM) carried out on the Chinese–French Oceanography Satellite (CFOSAT), yielding a correlation coefficient (Cor) of 0.80, squared error (Err) of 0.49, RMSE of significant wave height (SWH) of 0.48 m with an SI of 0.25, and an RMSE of the peak wave period (PWP) of 0.95 s with an SI of 0.10. The bias of wave (WW3 minus European Centre for Medium-Range Weather Forecasts (ECMWFs) reanalysis (ERA-5)) concerning the bias of wind (assembling minus ERA-5) showed that the WW3-simulated SWH with the assembling wind forcing was significantly higher than that with the ERA-5 wind forcing. Moreover, the bias of SWH gradually increased with an increasing bias of wind speed; i.e., the bias of SWH increased up to 4 m as the bias of wind speed reached 30 m/s. It was concluded that the assembling wind from multiple scatterometers and radiometers is a promising source for wave simulations via WW3 in typhoons.

Numerical study on self-power supply of large marine monitoring buoys: Wave-excited vibration energy harvesting and harvester optimization

With the diversification of marine monitoring buoy functions, limited onboard batteries have been unable to meet the energy demand of multifarious carrying sensors. Finding a self-sustained power supply for marine monitoring buoys is an urgent problem, while wave energy is an ideal and promising option to address that problem. In this study, two wave-excited vibration energy harvesters (WVEHs) are proposed, which can be installed inside large buoys to provide a sustainable power supply. A full-coupled wave-to-wire model is developed to investigate the influence of blocks’ mass, geometric size of buoys, mooring system and WVEH’s quantity on the electric power performance of harvesters in realistic sea states. Parametric studies based on the Taguchi method imply that the sea state and the WVEH’s quantity have a significant effect on the device’s electric power performance. Numerical results indicate that the optimized two harvesters can produce a mean electric power of 777.50 W and 747.43 W, respectively, under a sea state with a peak wave period of 7 s and a significant wave height of 1.6 m. A high wave-to-wire efficiency of 2.60% is obtained for a specific system parameter combination. Furthermore, more electric power generation can be achieved by installing multiple harvesting units.

Sea surface reconstruction from marine radar images using deep convolutional neural networks

The sea surface reconstructed from radar images provides valuable information for marine operations and maritime transport. The standard reconstruction method relies on the three-dimensional fast Fourier transform (3D-FFT), which introduces empirical parameters and modulation transfer function (MTF) to correct the modulation effects that may cause errors. In light of the convolutional neural networks’ (CNN) success in computer vision tasks, this paper proposes a novel sea surface reconstruction method from marine radar images based on an end-to-end CNN model with the U-Net architecture. Synthetic radar images and sea surface elevation maps were used for training and testing. Compared to the standard reconstruction method, the CNN-based model achieved higher accuracy on the same data set, with an improved correlation coefficient between reconstructed and actual wave fields of up to 0.96-0.97, and a decreased non-dimensional root mean square error (NDRMSE) of around 0.06. The influence of training data on the deep learning model was also studied. Additionally, the impact of the significant wave height and peak period on the CNN model’s accuracy was investigated. It has been demonstrated that the accuracy will fluctuate as the wave steepness increases, but the correlation coefficient remains above 0.90, and the NDRMSE remains less than 0.11.

Period and length of high surface gravity waves measured in the coastal waters of eastern Arabian Sea and its variations in 10 years

Information on the period and length of waves is required for the planning and design of marine facilities and wave energy converters. In this article, the period and length of the waves measured during the peak monsoon (June–July) in the coastal waters of the eastern Arabian Sea for 10 years are examined. The most typical wave periods (T) are within 3.9 s and 5.5 s and about 25 % are above 9 s. The peak wave period (Tp) indicates that during the peak monsoon months, long-period waves dominate the eastern Arabian Sea. Significant wave period and integral wave period show a good linear relationship with energy wave period with a slope value close to 1. There are inter-annual variations of up to 15 % in the 90-percentile value of the Tp. From 2010 to 2019, the average wavelength during peak monsoon varied from 61.3 m to 67.6 m and the maximum wavelength from 216.6 m to 248.8 m. Interannual variations in the 90-percentile values for wavelength corresponding to maximum wave height is only 7 %.

Analysis of the North Atlantic offshore energy flux from different reanalysis and hindcasts

To date there is a wide range of wave reanalysis and hindcasts available to the scientific and engineering community which are commonly used for different applications, including downscaling or the estimation of the wave energy resource (Morim et al., 2022). These long datasets have been created using different combinations of forcing fields, physical parameterizations, and numerical choices (like spatial and spectral resolution). All these elements have a direct effect on the accuracy of the wave models’ output (e.g., Alday et al., 2021) and thus, they are one of the main reasons for the differences between these products. In the present study we analyze the significant wave heights and peak periods characteristics from a selection of global datasets. We additionally include results from a hindcast created using the WAVEWATCH III model, with adjustments specially aimed to reduce uncertainties of the wave energy resource along the Atlantic coasts of Europe. Models’ output is compared with buoys and altimeter data from the latest ESA (European Space Agency) CCI Sea State V3 product. Preliminary validation of the hindcast we have generated for the North Atlantic already show an important bias reduction for wave heights in the 2.5 to 11.5 range compared to ERA5 wave product. Using the relevant wave parameters, we estimate the power density and quantify the differences between databases. Then, based on scatter diagrams obtained from the joint distributions of significant wave height and peak period, the differences in the power captured by wave energy converters (WEC) related to different wave data sources will be quantified (e.g., Babarit et al., 2011; Henriques et al., 2016).

WAVE TRANSFORMATION OVER PALM BEACH REEF

Ocean wave parameters are influenced by shallowing water depth and varying bottom topography. Modelling and in-situ studies have found that as waves propagate over a reef, interaction in the form of friction with the shallower reef can alter wave height, wave spectra, wavelength, and wave direction. Quantifying wave transformation over submerged structures will inform and aid in the design of future coastal protection. The natural reef at Palm Beach on the Gold Coast, Queensland, Australia is a rock-based reef that extends seaward, surrounded by sand bottom. The seaward reef edge is 10 to 16 metres deep while the shore edge is 5 to 9 metres deep, hence the reef shallows towards the shore. The reef is generally exposed to a dominant south easterly swell but Point Danger to the south offers some protection. Waverider buoys were deployed at four strategic locations at the Palm Beach reef and used to determine how the reef influences wave characteristics as waves travel over the reef. Wave transformation occurs, with the presence of Palm Beach reef having an observable influence on wave height and wave direction. Windward to leeward of the reef significant wave height was reduced by up to 12.7 per cent, wave direction changed by up to 13.9 degrees depending on how the measurement station was aligned with propagation over the reef, peak wave period was not changed significantly.

AN EFFICIENT HYBRID IMPACT SWELL INUNDATION SYSTEM FOR SMALL ISLANDS

Coastal flooding events generated by the combination of different simultaneous Meteorological and Oceanographic processes that occur at different spatial and temporal scales, are a big concern for Pacific nations. Although for many applications, the full wave directional spectra aggregated into its bulk parameters (i.e., significant wave height, peak period and mean or peak direction) is used, this is especially unsuitable for islands located in large ocean basins where concurrent seas and swells approaching from every direction are common and including the directional complexity of the full spectrum becomes crucial. Moreover, when attempting to assess coastal flooding, it is imperative to analyze the setup and the energy released by infragravity waves at the coast in a high spatial and temporal resolution in order to generate the adequate conditions to force a flooding model. However, dynamically simulating the propagation of wave spectral energy to the coast in order to obtain setup and infragravity waves to feed a flooding model is a very computationally expensive task, particularly for Small Island Developing States (SIDS) where computational resources are often limited. For this reason, we propose the use of metamodels that combine statistical and numerical modeling to efficiently downscale waves and obtain the flooding extents needed to assess the impact associated to a particular event.

Dynamic responses of a transversely isotropic poroelastic seabed subjected to nonlinear random waves with emphasis on liquefaction depth

Seabed instability is one of the important causes that lead to the failures of marine structures. Most previous works on seabed instability are limited to regular surface waves and linear random waves while nonlinear random waves are seldom touched. Hence, in this study, the hydrodynamic pressure of nonlinear random waves up to the second order is derived first. Then the analytical solutions of the dynamic responses of a transversely isotropic poroelastic seabed under the nonlinear hydrodynamic pressure are developed. The solutions are validated against analytical and experimental works in literature. The frequency response functions of pore water pressure, shear stress, vertical effective stress and horizontal effective stress are presented and discussed in the frequency domain. The influences of significant wave height, peak wave period and water depth on the dynamic responses and liquefaction depths of soil are analyzed in the time domain. The nonlinear random waves, linear random waves, linear regular waves and the second-order Stokes waves are compared in both time and frequency domains in terms of their influences on the dynamic responses and liquefaction depths of soil. The results reveal that the dynamic responses induced by second-order random waves are always greater than that induced by linear random waves, and much greater than that induced by equivalent linear waves and the second-order Stokes waves. The seabed may not liquefy under regular waves but does liquefy under random waves. Furthermore, the instantaneous liquefaction depths of soil caused by the second-order random waves are up to 23.5% larger than that induced by linear random waves. Therefore, the nonlinear random waves are recommended for the finite water depth use in engineering practice. In addition, the frequency-difference term plays an important role in soil liquefaction.

Spectral wave energy period and peak period statistics concomitant with maximum significant wave heights

Spectral wave energy period and peak period statistics concomitant with maximum significant wave heights

Wave forces and moments on concave and vertical front caissons supported on piles

ABSTRACT The present paper details the total wave-induced forces and moments on the circular cum parabola shape (CPS-PSB) and vertical front pile-supported breakwaters (VF-PSB) through a comprehensive experimental investigation under intermediate to deep water conditions. The model was subjected to the action of random waves with peak wave periods ranging from 1s to 2.6s. The total wave forces and moments were measured using a six-component force balance. VF-PSB experiences maximum wave force at lower submergence and the vertical force decreases exponentially as relative depth increases. In the case of CPS-PSB, the variation of vertical force with relative depth is similar to the energy loss. The horizontal wave forces on both PSB models decrease with their relative submergence as the wave exposure frontal area. The induced moments are higher for longer waves and higher submergence. CPS-PSB experiences lesser force and moment than VF-PSB.

Performance evaluation of a global CMIP6 single forcing, multi wave model ensemble of wave climate simulations

A performance evaluation is conducted for a state-of-the-art Coupled Model Intercomparison Project Phase 6 (CMIP6)-derived ensemble of global wave climate simulations. A single-model (forcing), single-scenario approach is considered to build the ensemble, where the differentiating factor between each member is the wave model or physics parameterization used to simulate waves. The 7-member ensemble is evaluated for the 1995-2014 historical period, highlighting the impact of the multiple source terms on its robustness. The ensemble’s ability to accurately represent the present wave climate is assessed through an extensive comparison with long-term ERA5 reanalysis and in-situ observational data. Relevant aspects such as the depiction of extremes and natural wave climate variability are analyzed, and inter-member uncertainties are quantified. Overall, the results indicate that the ensemble is able to accurately simulate the global wave climate, regarding the significant wave height (HS), mean and peak wave periods (Tm and Tp, respectively) and mean wave direction (MWD). However, we show that using multiple wave models and parameterizations should be cautiously considered when building ensembles, even under the same forcing conditions. Model-parameterization-induced ensemble spreads during the historical period are found to be high, compromising the robustness of projected changes in wave parameters towards the end of the 21st century across several areas of the global ocean.

Assimilation of peak period from video images in numerical wave models at a local scale

This paper presents an innovative methodology to assimilate peak period into wave models at a local scale. The proposed methodology estimates the peak period by processing time stack images from a video monitoring system for assimilation into a wave energy balance spectral model. Assimilation of the wave peak period is performed by correcting the boundary conditions and replacing the directional spectra prescribed by SWAN when using a nesting scheme. This methodology represents a new procedure for assimilating wave peak periods in coastal areas with video system infrastructures. The wave modelling is performed using a three-mesh nesting scheme where the finer domain coincides with the local scale and the proposed assimilation methodology is applied. The results show that the model improves the estimation of the peak period across the whole domain. The shape of the spectrum obtained changes significantly in the inner domain, mainly for low frequencies.

A high-resolution wave energy assessment of south-east Australia based on a 40-year hindcast

In this study, a third-generation ocean wave model (WAVEWATCH III; WW3) implemented on a high-resolution unstructured grid was developed to investigate wave energy in the south-east of Australia over the 40-year period from 1981 to 2020. The simulated wave power shows good agreement with values estimated from multiplatform satellite data. Thus, the modeled data were used to study statistics (mean conditions, seasonality, extremes, and long-term trends) of wave power in the domain, which show impacts of Southern Ocean swell and protection provided by the land mass of Tasmania. The results indicate increasing wave power trends, with the largest values in the southeastern part of the domain over the 40-year period. These positive trends are mainly a result of an increase in significant wave height rather than peak wave period. By utilizing the simulated wave properties, we estimated regional annual electric power at 14 coastal locations using 9 typical wave energy converters (WECs). To do so, we conducted a comprehensive analysis (seasonal variations, wave power roses, probability distributions, and bivariate probability distributions) at these locations. The results demonstrate that the western and southwestern coasts of the domain are promising generation sites but with large seasonal variability. The central and eastern coasts are protected by Tasmania, and exhibit more stable conditions but are far less energetic for electricity production. This study has critical implications for the region, which provides a benchmark for coastal WEC deployment.

Hydrodynamic and environmental modelling influence on numerical analysis of an innovative installation method for floating wind

This paper presents a numerical modelling methodology for an innovative installation method of floating wind turbines. The study analyses the influence of hydrodynamic and environmental modelling factors on the dynamics of a multibody system consisting of a catamaran with three wind turbines and a spar foundation with a mooring system. The research focuses on features such as viscous drag on the spar, hydrodynamic interaction between floating bodies, long- and short-crested waves, first- and second-order wave loads, wave directions, and wave peak periods. The study found that hydrodynamic modelling factors had a significant effect on the horizontal motion of the installation system but a negligible effect on vertical motion and mooring system tension. Therefore, it is recommended to consider viscous drag forces, hydrodynamic interaction, and first- and second-order wave forces when developing mechanical damping and control systems to reduce horizontal motion. The study also suggests using both long- and short-crested waves for numerical analysis when estimating the weather window for installation operability analysis. Overall, this study contributes to the development of an efficient and practical installation method for floating wind turbines by analysing the impact of hydrodynamic and environmental factors on the dynamics of the multibody system.

Field Investigation into Abrasion of Concrete at a Coastal Stepped Revetment: A U.K. Case Study

Although concrete abrasion damage is a major maintenance challenge for coastal structures fronted by beaches with hard coarse sediments, there are no readily available field studies that have measured abrasion damage of known concrete mixtures under defined exposure conditions. The objective of this investigation is to evaluate the abrasive exposure conditions of the concrete revetment armour units at Cleveleys on the Fylde coast of the U.K. and examine the feasibility of using terrestrial laser scanning (TLS) to measure concrete abrasion damage in field conditions. It was found that the concrete elements at Cleveleys are exposed to a macro-tidal environment, which experiences significant wave heights that vary from 0.42 to 1.92 m, whilst the peak wave periods range from 3.7 to 6.5 s. The beach sediments have a mean size of 26 mm and are moderately sorted. TLS provides a dense point cloud of abraded surfaces suitable for quantitative assessment of concrete abrasion in the field. Based on the measured abrasion depths and exposure durations, the peak concrete abrasion rates at the site varied from 3.5 to 4.5 mm/year, and severe abrasion was concentrated in the region between mean high-water springs and mean high-water neaps, wherein the highest beach levels were also found during the survey. Finally, the abraded surfaces exhibited a polished texture with no visible craters; thus, the mechanism of concrete material loss was by grinding/polishing due to rolling/sliding sediments.

Environmental contours based on imprecise probability distributions

Environmental contours are commonly applied in the design of marine structures to identify extreme environmental conditions that can give rise to extreme loads and responses. There are different methods to establish these contours, mainly the one based on the Rosenblatt transformation and the one based on Monte Carlo simulations, and in some cases significant differences can be obtained.In this paper, a method to determine environmental contours using imprecise probability models is proposed. The aim is incorporating the uncertainties that exist in the joint cumulative distribution function of the environmental variables. This is accomplishment through probability boxes defined by confidence intervals of the parameters of the joint cumulative distribution function of the environmental variables, which are proposed to be obtained with the maximum likelihood method. Furthermore, the dependence structure of the environmental variables is modeled using copulas.The proposed method is applied to obtain imprecise environmental contours for a site in the Gulf of Mexico, using extreme sea states defined by significant wave height and peak period. Then, such environmental contours are used to determine the imprecise most probable extreme response of a tension leg platform.

Assessing the impact of wave model calibration in the uncertainty of wave energy estimation

The accuracy of estimated sea conditions, specifically wave height and peak/average wave periods, affects the estimation of electrical energy production from wave energy converters. This study investigates the uncertainty in wave energy harvesting estimated by the SWAN wave model and determines possible improvements by adjusting the model's tunable parameters. Three different wave energy converters (OEBuoy, WaveBob, and Pontoon) and ten different locations along the Atlantic coast of the Iberian Peninsula are used in the study. The SWAN model is calibrated using the ST6 term package based on both wave height and peak period wave parameters. Different wave hindcast data produced by different model settings are used to estimate the wave energy produced by the wave energy converters at ten buoy locations and compared to wave energy produced estimated based on wave observations. The study finds that the physical settings of the SWAN model have a considerable influence on the uncertainty in the estimation of the power output produced by the device. The best-fitting calibrated model improved the mean energy output value of all locations compared to the SWAN default settings. The study concludes that adjusting the SWAN model parameters can improve the accuracy of the estimation of the energy output.

HyWaves: Hybrid downscaling of multimodal wave spectra to nearshore areas

Long-term and accurate wave hindcast databases are often required in different coastal engineering projects. The assessment of the nearshore wave climate is often accomplished by using downscaling techniques to translate offshore waves to coastal areas. However, dynamical downscaling approaches may incur huge computational cost. Additionally, the common use of bulk parameterizations are often not accurate for multidimensional waves. To overcome these limitations, we present a hybrid downscaling approach that combines mathematical algorithms (statistical downscaling) and numerical modeling (dynamical downscaling) over the individual spectral partitions. Every wave partition is downscaled and aggregated afterward by using principles of wave linear theory. By assuming linearity in the propagation of the wave celerity, the application of the method is limited from offshore to intermediate water depths. In addition, the method proposed uses a technique to simplify the spectral boundary conditions in complex domains. The methodology has been applied and validated in the island states of Samoa, American Samoa, Majuro, and Kwajalein, showing good skill at reproducing the spectral hourly time series of significant wave height, peak period, and peak direction. Moreover, an accurate representation of the observed energy spectrum was achieved. This study provides insight into the numerical approximation of the combined sea-swell states while improving the quality of fast spectral forecasting and early warning systems.

Short-term analysis of extreme wave-induced forces on the connections of a floating breakwater

In the design of floating breakwaters, assessment of the extreme wave-induced loads on the connections, their weakest element, is required to ensure structure survival. This case study provides guidelines for estimating the extreme wave-induced forces on the connections of a floating breakwater. A Boundary Element Method (BEM) solver was applied to obtain the time-domain response of an array of five pontoons anchored to the sea bottom with elastic mooring lines. The hydrodynamic behaviour of the structure was assessed for short-duration sea states with different wave peak periods and oblique wave directions. Two peak selection criteria were applied to obtain force distributions, and several different probability density functions (PDF) were fitted to the resulting data. The extreme wave-induced forces on every connection and sea state were estimated for two different exceedance levels during a typical 3-h sea state. Based on the results, combination of the Peaks Over Threshold (POT) method and generalized Pareto distribution results is proposed for estimating the wave-induced design forces on the connections of floating pontoon breakwaters.

Freak wave events in 2005–2021: statistics and analysis of favourable wave and wind conditions

Abstract. Freak or rogue waves are unexpectedly and abnormally large waves in seas and oceans, which can cause loss of human lives and damage to ships, oil platforms, and coastal structures. Evidence of such waves is widely spread around the globe. The present paper is devoted to analysis of the unified collection of freak wave events from different chronicles and catalogues from 2005 to 2021. The considered rogue waves are not measured in situ data, but their descriptions, which have been found in mass media sources and scientific articles, are the data used. All of them resulted in damage to ships or coastal/offshore structures and/or human losses. The collection accounts for 429 events. First, the analysis based on their characteristics taken from the descriptions of the events (including locations, water depth, damages) is carried out. Second, the analysis of wave parameters taken from the climate reanalysis ERA5 is performed. Thus, the most probable background wave parameters at the time of the freak event (including wind speed, gusts, significant wave height, maximum wave height, peak wave period, skewness, excess kurtosis, Benjamin–Feir instability (BFI), and wave spectral directional width) for each freak wave event are determined.