Peak Wave Period Research Articles

Lidar Observations of the Swash Zone of a Low-Tide Terraced Tropical Beach under Variable Wave Conditions: The Nha Trang (Vietnam) COASTVAR Experiment

A field experiment was conducted at a tropical microtidal intermediate sandy beach with a low tide terrace (Nha Trang, Vietnam) to investigate the short-term swash-zone hydrodynamics and morphodynamics under variable wave conditions. Continuous 2D Lidar scanner observations of wave height at the lower foreshore, subsequent run-up and swash-induced topographic changes were obtained. These data were complemented by detailed real-time kinematic GPS topographic surveys. Variable wave and tide conditions were experienced during the field experiment with relatively large swell waves (offshore significant wave height, Hs = 0.9 m to 1.3 m; peak wave period, Tp = 8 to 12 s) concomitant with spring tides at the beginning of the period, followed by mild wind waves (offshore Hs under 0.5 m and Tp 5 s) and neap tides. This resulted in the following morphological sequence: berm erosion followed by rapid neap berm reformation and beach recovery within a few days. New insights into the link between intra-tidal swash dynamics and daily beach profile evolution were found using the Lidar dataset. While waves directly cause morphology changes on a wave-by-wave basis, tidal levels were found to be a key factor in determining the morphological wave-effect (accretive or erosive) due to modulated interaction between surf and swash hydro-morphodynamics.

The Downscaling Study for Typhoon-Induced Coastal Inundation

Typhoons can often cause inundation in lower coastal cities by inducing strong surges and waves. Being affected by typhoon annually, the coastal cities in South Korea are very vulnerable to typhoons. In 2016, a typhoon ‘CHABA’, with a maximum 10 min sustained wind speed of about 50 m/s and a minimum central pressure of 905 hPa, hit South Korea, suffering tremendous damage. In particular, ‘CHABA’-induced coastal inundation resulted in serious damage to the coastal area of Busan where a lot of high-rise buildings and residential areas are concentrated, and was caused by the combined effect of tide, surge, and wave. The typhoon-induced surge raised sea levels during high tide, and the strong wave with a long period of more than 10 s eventually led to the coastal inundation at the same time. The present research focuses a numerical downscaling considering the effects of tide, surge and wave for coastal inundation induced by Typhoon ‘CHABA’. This downscaling approach applied several numerical models, which are the Weather Research and Forecasting model (WRF) for typhoon simulation, the Finite Volume Community Ocean Model (FVCOM) for tide and surge simulation, and the Simulating WAve Nearshore (SWAN) for wave simulation. In a domain covering the Korean Peninsula, typhoon-induced surges and waves were simulated applying the results simulated by WRF as meteorological conditions. In the downscaled domain ranged near the coastal area of Busan, the coastal inundation was simulated blending a storm tide height and an irregular wave height obtained from the domain, in which each height has 1 s interval. The irregular wave height was calculated using the significant wave height and peak period. Through this downscaling study, the impact of storm tide and wave on coastal inundation was estimated.

Estimating wave energy flux from significant wave height and peak period

Optimum design and location of wave energy converters in the marine environment require accurate assessments of the spatio-temporal variability of the available wave energy flux. However, numerical hindcast databases (commonly exploited for these long-term evaluations) integrate a restricted number of parameters such as the significant wave height Hs or the peak period Tp. Computation of wave power density from hindcast database is thus conducted by relying on simplified formulations derived from approximations of the group velocity and the wave energy spectrum. The present investigation quantified the biases in wave power computation from two standard formulations, based on the energy period and the peak period, respectively. The analysis relied on NOAA observations in 17 locations of the North-West Atlantic, the Gulf of Mexico and the Caribbean Sea. Whereas the energy-period formulation was a very good approximation of the wave power density in deep waters, the peak-period formulation (with a default calibration coefficient α=0.9) overestimated locally, by more than 8%, the available wave energy flux. A refined distribution of α against classes of Hs and Tp was established to reduce these differences, decreasing the relative difference from 9.9% to 0.3% off the Greater Antilles.

Inhomogeneous wave load effects on a long, straight and side-anchored floating pontoon bridge

In this paper, we present a numerical study on the hydroelastic response of a 4.6 km long fjord crossing floating bridge subjected to wave loads. The bridge is straight in design and supported by 35 pontoons along its full length. To limit the response to horizontal loads, four clusters of deep water mooring lines are engaged to increase the transverse stiffness of the bridge. Owing to the very large span across the fjord, inhomogeneity in the wave field exists. This study examines the various effects of inhomogeneous wave loads on the dynamic responses of the floating bridge. These include the spatial variations of the wave direction, significant wave height and peak period as well as the coherence and correlation of waves along the entire length of the floating bridge. For the purpose of comparison, the dynamic bridge responses under homogeneous wave load cases are also studied. In addition, the effects of wave load components and short-crestedness are presented and discussed.

A global analysis of austral summer ocean wave variability during SAM–ENSO phase combinations

Anticipating and mitigating wave-related hazards rely heavily on understanding wave variability drivers. Here, we describe wave conditions related to concurrent Southern Annular Mode (SAM) and El Nino–Southern Oscillation (ENSO) phases during the austral summer. To identify such conditions, significant wave height (Hs) and peak wave period (Tp) daily anomalies were composited during different SAM–ENSO phase combinations over the last four decades (1979–2018). Surface wind anomalies were also composited to assist in the interpretation of wave conditions. The composites show significant wave variability across all ocean basins and in several semi-enclosed seas throughout the different SAM–ENSO phase combinations. The Southern, Indian, and Pacific Oceans generally experience the strongest Tp anomalies during combinations of SAM phases with El Nino, and the weakest Tp anomalies during combinations of SAM phases with La Nina. The anomalously large waves observed in the south-western Pacific, Tasman Sea, and the Southern Ocean, previously ascribed to ENSO conditions, seem to be instead associated with the SAM variability. SAM-related atmospheric conditions are found to be able to modulate the intensity of ENSO-related winds over the South China Sea, which, in turn, alter the magnitude of waves in that region. These and other wave anomaly structures described here, especially those contrasting the behaviour expected for a given ENSO phase, such as the one found along the California coast, stress the importance of understanding relationships between wave parameters and climate patterns interactions.

Effects of modes of climate variability on wave power during boreal summer in the western North Pacific

This study investigates extremes of wave climate in the western North Pacific (WNP) as significant responses to modes of climate variability: the El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Few studies have explicitly investigated significant wave height in this context, and hence, the aim of the present study is to investigate and quantify the responses to a simulated wave data set over the WNP from 1979–2009 by focusing on the combined influences of the ENSO and PDO during the boreal summer. We conducted a composite analysis of sea surface temperatures, sea-level pressure, and extreme anomalies of wave power density (Pw) on different phase combinations of the ENSO and the PDO, and also analyzed the effects of a latitudinal shift of the ITCZ for composite samples with respect to simulated tropical storm (TS) activities. The results demonstrate that the ENSO played a primarily positive role in intensifying anomalous wave climate, while the PDO had the opposite effect. The responses of the peak wave-period were linked to a strengthened anomalous low-pressure and a cooling of sea surface temperature anomalies. The PDO played a significant role in strengthening or weakening of the effects of the ENSO on Pw, thus confirming the findings of previous studies. We found that responses were dependent on whether ENSO and PDO were in or out of phase. These responses can be described by a strengthening of the southeast trade winds that blow across the equator with respect to a latitudinal shift of the Intertropical Convergence Zone (ITCZ). Our findings contribute to the understanding of a relationship between modes of climate variability and TS activities with respect to the status of the ITCZ over the WNP, which can be relevant factors in the lifetime of wave power and related wave parameters in the WNP during the boreal summer.

Wave-Turbulence Decomposition Methods Applied to Tidal Energy Site Assessment

High levels of turbulence have been proven to substantially increase the blade loadings on tidal turbines, outlining the need of properly characterizing turbulence parameters in tidal energy sites. The presence of long surface gravity waves may cause a significant bias on the estimation of these parameters, which requires wave-turbulence decomposition methods that are currently missing from guidelines. Here, three techniques of decomposing wave and turbulence are tested: the stopband filter (SB), moving average filter (MA), and synchrosqueezing wavelet transform (SWT). The study site, Banks Strait, Tasmania, is a 16 km wide channel that presents high potential for tidal energy generation. Wave peak periods at the study site were found to vary mostly between 7 and 12 s, with maximum exceeding 15 s. Turbulence intensities (TI), turbulent kinetic energy (TKE), and integral scales are quantified. Our results indicate differences between the estimates obtained from each method. The MA highly underestimates turbulence, resulting in TI values which were nearly 50% lower than those obtained from other decomposition methods. While TI and TKE estimated from the SB and the SWT techniques are quite similar, integral length scales are considerably underestimated by the SB. These findings reveal that the SWT is a more reliable method because of the more accurate estimates of turbulence parameters and indicate the need of establishing guidelines which address wave-turbulence decomposition in tidal stream energy site assessments. Despite having shown to be quite a versatile technique, further investigation of its applicability in data from other prospective tidal energy sites is necessary to fully assess the generality of the SWT technique.

A methodology for data gap filling in wave records using Artificial Neural Networks

Wave measuring equipment are subject to malfunction that can be caused by various reasons such as maintenance, navigation accidents, errors in communications and biofouling of sensors. This can eventually result in loss of valuable data before the equipment is fixed. A continuous data set is often critical for modelling and/or analysis of wave conditions. Data gaps in wave records can be filled using numerical modelling. This study presents an alternative method for filling missing data based on publicly available wind and wave information and artificial neural networks (ANN). The ANN developed in this study uses offshore hindcast wave and wind information (significant wave height, peak wave period and direction, wind speed and direction) from a data set publicly available for any region of the globe. The results of the application of this method to two one-week gaps in wave measurements are compared against a spectral wave model developed and implemented to estimate wave conditions at the measurement location. The ANN results for the validation period show slightly better statistical performance when compared to the wave model results in terms of the correlation coefficient, root mean square error, bias and scatter index. ANN are viable alternative methods to wave modelling for filling gaps in data and have several advantages since specific knowledge of wave models is not required, input data to feed the neural network is available for any region of the globe and the processing time is highly reduced when compared to numerical modelling.

A new wave spectrum resembling procedure based on ship motion analysis

A new wave spectrum resembling procedure, based on two subsequent steps, is developed to detect the sea state parameters, namely the wave peak period, the significant wave height and the wave spectrum shape parameter, based on the analysis of heave and pitch motion time series, obtained by onboard measurements. The outlined procedure is applied to the S175 containership, assumed as reference vessel, and a set of basic conditions, with different vessel speeds, heading angles and sea state parameters, is preliminarily investigated. In this respect, heave and pitch motion time histories were obtained by time-domain simulations, based on theoretical wave spectra, in order to systematically investigate the reliability of the proposed procedure. Subsequently, a wide benchmark study is carried out, based on random generation of wave peak periods, significant wave heights and vessel speeds at four heading angles, equally spaced from head to following seas, in order to investigate the incidence of time duration on resembled sea state parameters. Finally, the statistics of errors on wave peak periods and significant wave heights are analysed to select the proper time duration of onboard measurements that allows balancing the reliability of resembled data with the need of an almost real-time sea state monitoring.

Virtual hull monitoring of a naval vessel using hindcast data and reconstructed 2-D wave spectra

A novel virtual hull monitoring approach is assessed using full-scale measurements from a naval vessel trial to address two questions. First: Can this technique accurately reproduce stress spectra from measured strains? Second: Are responses calculated using reconstructed two-dimensional wave spectra from hindcast data more accurate than those using simpler wave representations? Stresses calculated using wave hindcast data, ship track information, and stress transfer functions compare favorably to those derived from strain gauge measurements at five structural locations. Wave conditions are represented using a spectrum model along with bulk spectral parameters (significant wave height, peak period, and primary direction) from hindcast datasets and by reconstructing two-dimensional spectra from hindcast partition data. Both approaches give good agreement with strain measurements but using the more-detailed reconstructed two-dimensional wave spectra yields better results. Results suggest that wave hindcast data are sufficient for accurate structural calculations, encouraging further study of virtual hull monitoring using wave hindcast data.

Experimental Study of the Statistical Properties of Directionally Spread Ocean Waves Measured by Buoys

AbstractWave-following buoys are used to provide measurements of free surface elevation across the oceans. The measurements they produce are widely used to derive wave-averaged parameters such as significant wave height and peak period, alongside wave-by-wave statistics such as crest height distributions. Particularly concerning the measurement of extreme wave crests, these measurements are often perceived to be less accurate. We directly assess this through a side-by-side laboratory comparison of measurements made using Eulerian wave gauges and model wave-following buoys for randomly generated directionally spread irregular waves representative of extreme conditions on deep water. This study builds on the recent work of McAllister and van den Bremer (2019, https://doi.org/10.1175/JPO-D-19-0170.1), in which buoy measurements of steep directionally spread focused waves groups were considered. Our experiments confirm that the motion of a wave-following buoy should not significantly affect the measured wave crest statistics or spectral parameters and that the discrepancies observed for in situ buoy data are most likely a result of filtering. This filtering occurs when accelerations that are measured by the sensors within a buoy are converted to displacements. We present an approximate means of correcting the resulting measured crest height distributions, which is shown to be effective using our experimental data.

Stochastic response of a cable-stayed bridge under non-stationary winds and waves using different surrogate models

The prediction of the structural stochastic response under strong winds and waves is important in the design of cross-sea bridges with longer spans, while the non-stationary characteristics of winds and waves may affect the accuracy. This paper investigates the effects of non-stationary winds and waves on the stochastic response of a cable-stayed bridge based on a wind-wave-bridge (WWB) system. In order to improve the computational efficiency, three surrogate models, i.e., the support vector regression (SVR), the BP neural network (BPN), and the Gaussian process regression (GPR), are established by correlating the environmental parameters with the bridge response. A comparison among the three models is conducted to find the optimal one, and the effects of the mean wind speed, the significant wave height, and the peak wave period on the bridge response are further investigated. The bridge responses of the stationary wind and wave fields are 0.05%–16% larger than those of the non-stationary wind and wave fields. Different surrogate models are applicable to different parts of the bridge. The SVR, BPN, and GPR models are recommended for predicting the response of the tower, the foundation, and the girder, respectively, and the sensitivity analysis reveals the effects of non-stationary winds and waves.

A classification system for global wave energy resources based on multivariate clustering

Better understanding of the global wave climate is required to inform wave energy device design and large-scale deployment. Spatial variability in the global wave climate is analysed here to provide a range of characteristic design wave climates. K-means clustering was used to split the global wave resource into 6 classes in a device agnostic, data-driven method using data from the ECMWF ERA5 reanalysis product. Classification using two sets of input data were considered: a simple set (based on significant wave height and peak wave period) and a comprehensive set including a wide range of relevant wave climate parameters. Both classifications gave resource classes with similar characteristics; 55% of tested locations were assigned to the same class. Two classes were low energy, found in enclosed seas and sheltered regions. Two classes were moderate wave energy classes; one swell dominated and the other in areas with wave action often generated by more local storms. Of the two higher energy classes; one was more often found in the northern hemisphere and the other, most energetic, predominantly on the tips of continents in the southern hemisphere. These classes match existing regional understanding of resource. Consideration of publicly available device power matrices showed good performance was primarily realised for the two highest energy resource classes (25–30% of potential deployment locations); it is suggested that effort should focus on optimising devices for additional resource classes. The authors hypothesise that the low-risk, low variability, swell dominated moderate wave energy class would be most suitable for future exploitation.

Evaluation of the convertible offshore wave energy capacity of the southern strip of the Caspian Sea

The wave energy can be a critical solution for growing international renewable energy demand. The present study demonstrates the wave potential of the southern side of the Caspian Sea. In this regard, the mathematical equation of the wave energy was presented. Moreover, the wave energy simulation was performed using the wind data from ECMWF within 2011–2015 by implementing the MIKE software. For this reason, nine nominated stations were presented and the wave height characteristics and the maximum wave potential were evaluated in order to validate the results of the simulation, Amirabad and Neka stations were selected and the results were compared and good agreement was observed. Moreover, a mesh structure was presented to demonstrate the depth variation of the Caspian Sea. The results of the simulation were achieved for nine stations and the wave height and peak wave period was demonstrated. The wave power contours were revealed for every station. The result showed that the May (0.9 kW per meter) and December (3.6 kW per meter) have the lowest and highest wave energy potential for selected stations.

Cross-scale modeling of storm surge, tide, and inundation in Mid-Atlantic Bight and New York City during Hurricane Sandy, 2012

Driven by high-resolution NAM (North America Mesoscale) and ECMWF (European Centre for Medium-Range Weather Forecasts) atmospheric fields, a 3-D unstructured grid SCHISM (Semi-implicit Cross-scale Hydroscience Integrated System Model) was applied to simulate total water level in the Mid-Atlantic Bight during Hurricane Sandy in 2012. The simulated storm surge, tide, significant wave height, and wave peak period results compared favorably with NOAA observations along US East Coast, Long Island Sound, and New York Harbor. The maximum total water level at The Battery in the New York Harbor was accurately simulated with an absolute error of less than 0.08 m (out of 2.9 m peak surge) and a timing difference less than 10 min, which includes the effects on the order of 0.1–0.3 m (5–10%) from the coastal setup induced by the surface waves. The scenario comparisons of (1) “NAM” versus “ECMWF”, (2) “2-D” versus “3-D”, and (3) “with” versus “without” wind wave model were examined. The 3-D barotropic model forced by ECMWF including the effects of wind waves performs the best, attributed to wave-induced radiation stress and reduction of bottom stress when the 3-D version is used. Simultaneously, the ELCIRC-Sub model, using a 5-m topography/bathymetry sub-grid and a regular 200-m resolution finite volume computational model grid, was developed to simulate the street-level inundation in New York City. The momentum and mass fluxes calculated by the coarser base grid model were effectively coupled with the sub-grid so that running a full-blown high-resolution base model is not required. The ELCIRC-Sub model uses MPI (Message Passing Interface) parallel computing to enlarge the coverage of the land surface and an efficient non-linear solver to improve the accuracy of the wetting-and-drying processes. The temporal comparisons of modeled water level with NOAA's tidal stations and USGS′ rapid-deployed gauges showed overall performance with an average error of 0.1 m. Particularly, ELCIRC-Sub captured the profile of the highest peak surge (3.9 m), which rose 2 m within 3 hour at Kings Point, NY. The spatial comparisons of the modeled peak water level at 80 surveyed locations showed an average error less than 0.13 m. The modeled maximum inundation extent also matched well with an 80% hit rate against FEMA's Hurricane Sandy maximum flooding extent.

What happens to the ocean surface gravity waves when ENSO and MJO phases combine during the extended boreal winter?

The safety of vulnerable coastal and offshore infrastructures requires an in-depth understanding of wave variability and climate drivers. We investigate the association of significant wave height (Hs) and peak wave period (Tp) with the co-occurrence of El Nino–Southern Oscillation (ENSO) and the Madden–Julian Oscillation (MJO) at the global scale. We calculate composites of daily anomalies in modelled Hs, Tp, and surface wind for periods of ENSO–MJO phase combinations. Calculations spanned November–March seasons over the period 1979–2018. Wave anomalies are widespread across the world’s oceans, with remarkable strength during several ENSO–MJO phase combinations, demonstrating strong tropic–tropic and tropic-extratropic teleconnections. Positive Hs anomalies are strongest in the Pacific Ocean during El Nino–MJO phase 8, in the Atlantic Ocean during ENSO-neutral-MJO phase 3, and in the Indian Ocean during ENSO-neutral-MJO phase 4. Positive Tp anomalies are strongest in the Pacific Ocean during La Nina–MJO phase 8, in the Atlantic Ocean during El Nino–MJO phase 1, and in the Indian Ocean during El Nino–MJO phase 8. In the Southern Ocean, the strongest Hs anomalies occur during El Nino–MJO phase 8, whereas in the Maritime Continent, they appear during ENSO-neutral-MJO phases 5–6. Despite previous studies finding low correlations of ENSO indices with wave parameters in the North Atlantic, our results suggest that ENSO-related conditions play a significant role in the area when combined with certain MJO-related conditions. This study also reveals that the wave anomalies associated with ENSO–MJO phase combinations can be twice as strong as those found in previous work, related only to the MJO. Therefore, considering multiple concurrent climate patterns in the analysis of wave anomalies is essential to developing more reliable coastal management plans.

Australian blocking impacts on ocean surface waves

We assess the impact of split-flow blocking in the Australian region on global ocean wind waves using 30 years of high-resolution wave data from the CAWCR wave model hindcast. Statistically significant anomalies in significant wave height (Hs), peak wave period (Tp) and zonal wave energy flux (CgE) are found to covary with local variations in surface zonal wind induced by blocking at 140° E. Strong negative anomalies in these wave fields highlight the role of blocking in promoting calm wave conditions around the Australian coast. A relatively weak but notable remote signal also appears in the Northern Hemisphere extratropics, suggesting a link to the Australian region via tropical forcing. The occurrence of daily low (below the 5th percentile) and high (above the 95th percentile) wave conditions also varies contemporaneously with blocking at 140° E. Considering the ability of global circulation model forecasts to skilfully predict the blocking index out to at least 2 weeks lead time, our results point to blocking as a possible source of predictable wind-wave variability from sub-weekly to seasonal timescales.

Wave Height and Wave Period Derived from a Shipboard Coherent S-Band Wave Radar in the South China Sea

To expand the scope of ocean wave observations, a shipboard coherent S-band wave radar system was developed recently. The radar directly measures the wave orbital velocity from the Doppler shift of the received radar signal. The sources of this Doppler shift are analyzed. After removing the Doppler shifts caused by the ocean current and platform, the radial velocities of water particles of the surface gravity waves are retrieved. Subsequently, the wavenumber spectrum can be obtained based on linear wave theory. Later, the significant wave height and wave periods (including mean wave period and peak wave period) can be calculated from the wavenumber spectrum. This radar provides a calibration-free way to measure wave parameters and is a novel underway coherent microwave wave radar. From 9 September to 11 September, 2018, an experiment involving radar-derived and buoy-measured wave measurements was conducted in the South China Sea. The Doppler spectra obtained when the ship was in the state of navigation or mooring indicated that the quality of the radar echo was fairly good. The significant wave heights and wave periods measured using the radar are compared with those obtained from the wave buoy. The correlation coefficients of wave heights and mean wave periods between these two instruments both exceed 0.9 while the root mean square differences are respectively less than 0.15 m and 0.25 s, regardless of the state of motion of the ship. These results indicate that this radar has the capability to accurately measure ocean wave heights and wave periods.

An ocean wind-wave climatology for the Southern Brazilian Shelf. Part I: Problem presentation and model validation

Geomorphological features and sparse visual wave measurements, presented in previous works, point out to the possible existence of alongshore wave energy gradients over the Southern Brazilian Shelf (SBS). After describing the two numerical models utilized and the model grids and settings, the present study evaluated the proposed validation of the basin-scale results against orbital altimetry and the regional-scale results against the two available wave-buoy data, discussing the extent to which the model reproduced local reality. The basin-scale model results of significant wave height could be considered as in good agreement with observations, presenting remarkable similarities with observed altimetry. Regarding the regional-scale modeling, both significant wave height and peak wave periods were considered as in good agreement with observations. The peak wave directions, however, were classified as in poor agreement, once the ESE waves were erroneously reproduced as E. Increased spatial resolution certainly played a role, but it was the lowering of bottom friction that represented the major improvement in the coastal grid simulations.

Applications of an unstructured grid surface wave model (FVCOM-SWAVE) to the Arctic Ocean: The interaction between ocean waves and sea ice

Rapidly melting sea ice processes during the summer tend to enlarge the open water in the Arctic region. The resulting larger potential fetch for surface waves can allow significant wave generation and development in the region. The sea ice plays an energy dissipation role for waves propagating into the ice-covered sea. A spherical-coordinate surface wave model was established within the unstructured grid Finite-Volume Community Ocean Model (FVCOM) to examine the influence of ice-induced wave attenuation on waves propagating into the ice in the Arctic Ocean. Ice-induced wave attenuation parameterizations were implemented, with an effective methodology to reduce numerical dissipation during the energy advection in geographic space. Wave partition and source tracking methods were added to distinguish the windsea and swell, as well as to backtrack swell waves to their sources. The model-simulated significant wave heights and peak periods were compared with available buoy and Jason-2 satellite measurements. Results from a process-oriented model show that simulations of the surface waves in the Arctic region are improved when ice-induced attenuation is included in the model system. An empirical method is used to statistically estimate wave-induced ice breakage, based on the wave-induced internal ice strain, as waves penetrate into the ice zone. The simulation results support the ‘ice retreat-wave growth’ positive feedback mechanism.