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We delimit nearshore storm waves generated by category-5 Tropical Cyclone Winston in February 2016 on the northern Fijian island of Taveuni. Wave magnitudes (heights and flow velocities) are hindcast by inverse modelling, based on the characteristics of large carbonate boulders (maximum 33.8 m 3 , 60.9 metric tons) that were quarried from reef-front sources, transported and deposited on coral reef platforms during Winston and older extreme events. Results indicate that Winston's storm waves on the seaward-margin of reefs fringing the southeastern coasts of Taveuni reached over 10 m in height and generated flow velocities of 14 m s − 1 , thus coinciding with the scale of the biggest ancient storms as estimated from pre-existing boulder evidence. We conclude that although Winston tracked an uncommon path and was described as the most powerful storm on record to make landfall in the Fiji Islands, its coastal wave characteristics were not unprecedented on centennial timescales. At least seven events of comparable magnitude have occurred over the last 400 years. [ABSTRACT FROM AUTHOR]

The characteristics of a reef-top boulder field created by a local submarine landslide tsunami are presented for the first time. Our examination of large reef-derived boulders deposited by the 1953 tsunami near Suva City, Fiji, revealed that shorter-than-normal-period tsunami waves generated by submarine landslides can create a boulder field resembling a storm boulder field due to relatively short boulder transport distances. The boulder-inferred 1953 tsunami flow velocity is estimated at over 9 m s − 1 at the reef edge. Subsequent events, for example Cyclone Kina (1993), appear to have remobilised some large boulders. While prior research has demonstrated headward retreat of Suva Canyon in response to the repeated occurrence of earthquakes over the past few millennia, our results highlight the lingering vulnerability of the Fijian coastlines to high-energy waves generated both in the presence (tsunami) and absence (storm) of submarine failures and/or earthquakes. To explain the age discrepancies of U-Th dated coral comprising the deposited boulders, we introduce a conceptual model showing the role of repeated episodes of tsunamigenic submarine landslides in removing reef front sections through collapse. Subsequent high-energy wave events transport boulders from exposed older sections of the reef front onto the reef where they are deposited as ‘new’ boulders, alongside freshly detached sections of the living reef. In similar situations where anachronistic deposits complicate the deposition signal, age-dating of the coral boulders should not be used as a proxy for determining the timing of the submarine landslides or the tsunamis that generated them. [ABSTRACT FROM AUTHOR]

Since the introduction of the NewWave theory (Lindgren, 1970), focused wave groups are used in physical and numerical studies to investigate the interaction of marine structures and ships with extreme waves. The propagation of such wave groups is associated with high order nonlinearities that can cause considerable deviations from linear and 2 n d order predictions. Consequently, nonlinear numerical models or laboratory tests are needed to accurately describe the evolution of focused wave groups. In the present study, we validate a widely used two-phase Reynolds Averaged Navier-Stokes (RANS) solver realised in OpenFOAM with experimental results for the propagation of steep focused wave groups, using a newly developed methodology based on the separation of harmonics. This approach allows for accurate focusing of wave groups and in-detail examination of the individual evolution of the high order terms, as well as identifying the source of discrepancies between experiments and numerical models. The wave groups comprise long-crested broadbanded Gaussian spectra of increasing steepness propagating in intermediate water depth. The contribution of the nonlinear harmonics to the crest height and overall shape of the wave are also discussed, together with the effect of nonlinear wave interactions on the free-wave spectrum. The rapid growth of 3 r d and 4 t h harmonics near focusing as well as the evolution of the free-wave spectrum, cause departures of up to 29% and 22% from analytic linear and 2 n d order predictions. The present results demonstrate that RANS-VoF solvers constitute accurate models to propagate nearly breaking waves. [ABSTRACT FROM AUTHOR]

As global climate warms and sea level rises, coastal areas will be subject to more frequent extreme flooding and hurricanes. Geologic evidence for extreme coastal storms during past warm periods has the potential to provide fundamental insights into their future intensity. Recent studies argue that during the Last Interglacial (MIS 5e, ~128-116 ka) tropical and extratropical North Atlantic cyclones may have been more intense than at present, and may have produced waves larger than those observed historically. Such strong swells are inferred to have created a number of geologic features that can be observed today along the coastlines of Bermuda and the Bahamas. In this paper, we investigate the most iconic among these features: massive boulders atop a cliff in North Eleuthera, Bahamas. We combine geologic field surveys, wave models, and boulder transport equations to test the hypothesis that such boulders must have been emplaced by storms of greater-than-historical intensity. By contrast, our results suggest that with the higher relative sea level (RSL) estimated for the Bahamas during MIS 5e, boulders of this size could have been transported by waves generated by storms of historical intensity. Thus, while the megaboulders of Eleuthera cannot be used as geologic proof for past "superstorms," they do show that with rising sea levels, cliffs and coastal barriers will be subject to significantly greater erosional energy, even without changes in storm intensity. [ABSTRACT FROM AUTHOR]

Wave tank tests often involve simulating extreme wave conditions as they enable the maximum expected loads to be inferred: a vital parameter for structural design. The definition, and simulation of, extreme conditions are often fairly simplistic, which can result in conditions and associated loads that are not representative of those that would be observed at the deployment location. Here we present a method of defining, simulating at scale, and validating realistic site-specific extreme wave conditions for survival testing of wave energy converters. Bivariate inverse-first order reliability method (I-FORM) environmental contours define extreme pairs of significant wave height and energy period (Hm0-TE), while observed extreme conditions are used to define realistic frequency and directional distributions. These sea states are scaled, simulated and validated at the FloWave Ocean Energy Research Facility to demonstrate that the site-specific extreme wave conditions can be re-created with accuracy. The presented approach enables greater realism to be incorporated into tank testing with survival sea states. The techniques outlined and explored here can provide further and more realistic insight into the response of offshore structures and devices, and can help make important design decisions prior to full-scale deployment. [ABSTRACT FROM AUTHOR]

Extreme waves in random seas are usually breaking or close to breaking. Understanding the kinematics and evolution of such waves is important for determining loads on offshore structures. Controlled repeatable generation of realistic breaking waves in wave flume experiments is a difficult but important task. It is rather easy to generate an arbitrary breaking wave, but to the authors' knowledge there is no methodology for accurate generation of a wave group with a pre-defined spectrum related to a modelled sea state with spilling breaking at a prescribed position. Such waves can be used to model extreme breaking waves in a random sea and their interaction with structures. This paper offers such a methodology. The key feature of the method is the application of an iterative focussing procedure to a linearised amplitude spectrum rather than to a full nonlinear spectrum. The linearised spectrum is obtained using a harmonics separation technique and the general derivation of the method is given for an arbitrary number of components. The procedure is applied to generate focussed wave groups with amplitudes increased in small steps until local crest breaking occurs. As a result, the highest non-breaking waves and weakly breaking waves are generated for otherwise identical conditions. The methodology is applied for four different wave spectra of the same peak frequency: JONSWAP, Pierson-Moskowitz, wide and narrow band Gaussian. It is found that steepness of the limiting breaking wave depends strongly on the choice of wave group spectrum. The results demonstrate that neglecting spectral properties of design waves may lead to misrepresentation of their breaking behaviour. [ABSTRACT FROM AUTHOR]

Model tests were conducted to investigate the global response of a conventional tension leg platform (TLP) due to wave-in-deck loads associated with extreme wave events in irregular long-crested waves of a cyclonic sea state. The experimental setup was designed to allow for the simultaneous measurement of wave surface elevations, rigid body motions, tendon tensions, as well as the pressure distribution at the model's deck underside. The obtained results demonstrated the variability of all the measurements and provided insights into the effect of wave-in-deck loads on the platform behaviour, tendon tensions and slamming pressures and showed qualitative correlations between these parameters. Based on the repeated tests in several events with different wave parameters, general observations and conclusions were made with respect to the platform dynamics during the deck impact, tendon tensions, slack tendon situations, tendon ringing and local impact pressures. The results of this study could be used for calibrating computational fluid dynamics (CFD) tools. [ABSTRACT FROM AUTHOR]

The lack of wave measurements is a reality when making marine engineering designs in Chile. Recent extreme wave events such as 3 July 2013 and 8 August 2015, left considerable structural damage and put into evidence the need for a continuous and long-term wave monitoring programme in order to adequately estimate the frequency of occurrence of these events. Presently, the frequency analysis relies on global wave reanalysis databases of unknown quality for this purpose. This contribution attempts to quantify the uncertainty in the extreme waves frequency analysis. An extreme wave frequency analysis was carried out for different available wave databases. There are differences of the order of hundred years in the significant wave height return values for recent events. The quality of the information of these databases was evaluated by comparing them with the 10% highest values of the significant wave height measured by satellite in 8 areas along Chile. The uncertainty in the 50 year return period spectral significant wave heights tends to increase from north to south, with differences between databases ranging from 2.3 to 6.7 m. The parameters used in the comparison with satellite measurements show, in general, better model skills in the north than in the south except for the R2 parameter. Correlations are very low with values of R2 near 0 for points in the north. The best correlation is found for IFREMER database in front of Golfo Coronados with R2 = 0.66. Biases are generally negative indicating underestimates near 1 m for the highest significant wave heights. [ABSTRACT FROM AUTHOR]

A detailed climatology of extreme wave events for New Zealand waters is presented, in addition to estimates of significant wave height (Hs) for up to a 100-year return period. Extreme events were explored using 44 years (1958–2001) of wave hindcast data. Comparisons to buoy data at three locations around New Zealand showed negative biases in the model, which nevertheless provided a suitable basis for trends, spatial distribution, and frequency analyses. Results indicate some similarities to patterns previously shown in the mean wave climate, with the largest waves found in southern New Zealand, and the smallest ones observed in areas sheltered from southwesterly swells. The number of extreme events varies substantially throughout the year, while the differences in intensity are more consistent. Events occur more/less frequently in winter/summer months. The greatest mean annual variability of extreme Hs is found on the north coasts of both the North and South Islands, where more locally-generated storms drive the extremes. The interannual variability is largest along the north coast of the country and on the east coast of the South Island, suggesting relationships with La Niña-like effects and the Southern Annular Mode, respectively, which past work showed to be important drivers in these regions. Moreover, the known trend for a more positive Southern Annular Mode may explain the increasing number of extreme events shown in our study. [ABSTRACT FROM AUTHOR]

The focus of this paper is the survivability of wave energy converters (WECs) in extreme waves and tsunamis, using realistic WEC parameters. The impact of a generator damping factor has been studied, and the peak forces plotted as a function of wave height. The paper shows that an increased damping decreases the force in the endstop hit, which is in agreement with earlier studies. However, when analyzing this in more detail, we can show that friction damping and velocity dependent generator damping affect the performance of the device differently, and that friction can have a latching effect on devices in tsunami waves, leading to higher peak forces. In addition, we study the impact of different line lengths, and find that longer line lengths reduce the endstop forces in extreme regular waves, but on the contrary increase the forces in tsunami waves due to the different fluid velocity fields. [ABSTRACT FROM AUTHOR]

To generate projections of wave climate associated to tropical cyclones is a challenge due to their short historical record of events, their low occurrence, and the poor wind field resolution in General Circulation Models. Hence, synthetic tropical cyclones provide an alternative to overcome such limitations, improving robust statistics under both present and future climates. We use synthetic events to characterize present and future wave climate associated with tropical cyclones in the Gulf of Mexico. The NCEP/NCAR atmospheric reanalysis and the Coupled Model Intercomparison Project Phase 5 models NOAA/GFDL CM3 and UK Met Office HADGEM2-ES, were used to derive present and future wave climate under RCPs 4.5 and 8.5 scenarios. The GFDL model shows less bias in the present climate with respect to NCEP/NCAR results. Furthermore, the numerical results suggest an increase in wave activity for the future climate in the Caribbean Sea and Northern Gulf of Mexico, whereas some areas are expected to decrease the wave energy, as the stretch of the Gulf of Mexico between Yucatan and Southern Texas. The results have practical implications on the design of offshore structures. The 100-year design wave based on the present climate might result in under/over design of structures, owing to the lifespan of a structure that is within the future wave climate period. [ABSTRACT FROM AUTHOR]

Cyclones cause significant loss of life and damage to properties, ecosystems and marine facilities. To address such issues, Royal HaskoningDHV (RHDHV) has developed regional tidal hydrodynamic and wave models covering the Northern Arabian Sea. A total of 29 major cyclones were identified in the Arabian Sea since 1945. However, as less information is available on Cyclone Nilofar (2014), this paper has concentrated on this event to illustrate the use of numerical modelling to simulate waves and surge generated by cyclones. Sample results from the modelling study are presented in this paper. The methodology described in this paper for modelling cyclone waves and surges in the Arabian Sea could be applied to simulate such natural hazards at other sites around the world. [ABSTRACT FROM AUTHOR]

The main objective of this investigation is to modify endurance wave analysis (EWA) based on New-wave theory for convenient assessment of offshore structures under extreme waves. EWA is a novel time history based approach to evaluate structural performance in various excitation levels of wave loading by intensifying wave records. In this article, modifications are proposed to determine appropriate time duration and intensifying trend for reliable and practical assessment of offshore structures. In this way, a simplified model of a real jacket platform is utilised to investigate the application of this approach under extreme wave conditions in the Persian Gulf and results are compared with typical three hour random wave simulations. It is shown that in extreme waves, except resonance states, proposed method can estimate the structural response with acceptable accuracy and very low computational costs. [ABSTRACT FROM AUTHOR]

This paper concerns the description of surface water waves, specifically nonlinear changes in the directionality. Supporting calculations are provided to establish the best method of directional wave generation, the preferred method of directional analysis and the inputs on which such a method should be based. These calculations show that a random directional method, in which the phasing, amplitude and direction of propagation of individual wave components are chosen randomly, has benefits in achieving the required ergodicity. In terms of analysis procedures, the extended maximum entropy principle, with inputs based upon vector quantities, produces the best description of directionality. With laboratory data describing the water surface elevation and the two horizontal velocity components at a single point, several steep sea states are considered. The results confirm that, as the steepness of a sea state increases, the overall directionality of the sea state reduces. More importantly, it is also shown that the largest waves become less spread or more unidirectional than the sea state as a whole. This provides an important link to earlier descriptions of deterministic wave groups produced by frequency focusing, helps to explain recent field observations and has important practical implications for the design of marine structures and vessels. [ABSTRACT FROM AUTHOR]

Insight is provided into focused wave group runup on a plane beach by means of laboratory wave flume experiments and numerical simulations. A focused wave group is presented as an alternative to an empirical description of the wave conditions leading to extreme runup. Second-order correction to the laboratory wavemaker generation signal is observed to remove about 60% of the sub-harmonic error wave that would otherwise contaminate coastal response experiments. Laboratory measurements of the wave runup time history are obtained using inclined resistance-type wires and copper strips attached to the beach surface. The numerical wave runup model is based on hybrid Boussinesq-Nonlinear Shallow Water equations, empirical parameters for wave breaking and bed friction, and a wetting and drying algorithm. After calibration against experimental runup data, the numerical model reproduces satisfactorily the propagation, shoaling and runup of focused wave groups over the entire length of the wave flume. Results from a comprehensive parametric study show that both measured and predicted maximum runup elevations exhibit strong dependence on the linear focus amplitude of the wave group (linked to its probability of occurrence), the focus location, and the phase of the wave group at focus. The results also demonstrate that extreme runup events owing to focused wave incidence cannot be characterised using spectral parameters alone. The optimal band of focus locations shifts onshore as linear focus amplitude of the incident wave group increases. Optimisation of phase and focus location leads to a maximum runup elevation at each linear amplitude, and, when generated using second-order corrected paddle signals, the maximum runup appears to approach saturation at very large focused wave amplitudes. This study therefore moves beyond simple wave focusing, and presents a focused wave group as a tool for investigating the relationship between extremes within an incident wave field and extreme wave runup. [ABSTRACT FROM AUTHOR]

A series of physical experiments were conducted to investigate the characteristics of extreme wave groups over a shoal. An improved method for detecting wave groups based on instantaneous energy was verified, which can identify wave groups reasonably and effectively. As a result, it was found that a linear relationship exists between the wave group energy and group time length on the logarithmic coordinate diagram, and the same tendency holds for extreme wave groups. Moreover, a steeper slope of the linear curve was observed for larger significant wave heights, indicating that the significant wave height significantly affects the wave heights and energy levels of extreme wave groups. The research also found that the average energy of the identified extreme wave group is approximately twice the average energy of the recorded data, thereby supporting the hypothesis that the wave group plays an important role in the generation of extreme waves. • A method for detecting wave groups was improved and verified, which can identify wave groups reasonably and effectively. • The wave groupiness factor can satisfactorily reflect the mean wave group energy. • A larger significant wave height tends to generate more energetic extreme waves. • The mean energy of an extreme wave group is approximately twice that of the entire data series. [ABSTRACT FROM AUTHOR]

Studies of the nonlinear Schrödinger (NLS) equation indicate that surface gravity waves traveling against currents of increasing strength gain energy and steepness in the process, and this can be a mechanism for rogue wave formation. Likewise, experimental studies have shown that stable wavetrains traveling against adverse currents can give rise to extreme waves. We studied this phenomenon by using computational fluid dynamics (CFD) tools, whereby the non-hydrostatic Euler equations were solved utilizing the finite volume method. Waveforms based on a JONSWAP spectrum were generated in a numerical wave tank and were made to travel against current gradients of known strength, and wave characteristics were monitored in the process. We verified that waves gain energy from the underlying flow field as they travel against current gradients, and the simulated level of energy increase was comparable to that predicted by earlier studies of the NLS equation. The computed significant wave height, H s , increased substantially, and there were strong indications that the current gradients induced nonlinear wave instabilities. The simulations were used to determine a new empirical relationship that correlates changes in the current velocity to changes in the Benjamin⁻Feir Index (BFI). The empirical relationship allows for seafaring entities to predict increased risk of rogue waves ahead, based on wave and current conditions.

The bearing connection between the bridge girder and substructure plays a crucial role in resisting wave forces. Previous works pointed out that the box-girder bridge with laminated rubber bearings is susceptible to unseating, sliding, and overturning under extreme waves. This study develops a tension-compression (TC) bearing system to enhance the structural resistance against wave impact. A three-dimensional (3D) finite element (FE) model considering the nonlinear rubber material is established for investigating the dynamic behavior of coastal box-girder bridges, where the wave forces are imported from the computational fluid dynamics (CFD) simulations. By tracking the time histories of the reaction forces and efficient stress, four damage status levels are identified to assess the vulnerability of coastal bridges. To improve calculation efficiency, the Kriging-based surrogate model is adopted for the fragility analysis of coastal box-girder bridges under extreme waves. The results indicate that the lower plate of the bearing on the seaward side (R1) is more prone to yield under the uplifting wave forces, while the upper plate of the bearing on the landward side (R2) is more sensitive to the horizontal forces. The vertical wave force is the key influential factor of bridge damage under extreme waves. In addition, the structural capacity of the bridge with the proposed bearing system is enhanced compared with the one using the traditional laminated rubber bearing. • A tension-compression bearing system is developed for coastal box-girder bridges. • A precision FE model of the box-girder bridge with bearings is established. • Kriging-based surrogate model is proposed to consider wave uncertainties. • Fragility assessment of coastal bridges with bearings is carried out. [ABSTRACT FROM AUTHOR]

In the complex marine environment, coastal bridges are vulnerable to damage under extreme wave action, and researchers have focused on taking effective measures to reduce structural damage and extreme wave forces in recent years. In this study, a wave-structure coupling method was utilized to numerically investigate the focused wave forces on the two-dimensional coastal bridge with a box-girder superstructure under the influence of the pile-restrained floating breakwater. After a series of validations in the focused wave generation and wave-structure interactions, the effectiveness of floating breakwaters in protecting the box-girder superstructure from extreme wave damage and the influence of control parameters of floating breakwaters on extreme wave forces were conducted. The numerical results demonstrate that the focused wave forces on the box-girder superstructure are effectively reduced after the installation of the pile-restrained floating breakwater. Compared with the floating breakwater with linear stiffness, the maximum horizontal and vertical wave forces are reduced more significantly by the floating breakwater with the displacement constraint. According to the wave parameters of the coastal bridge site, the appropriate size of the pile-restrained floating breakwater and the distance between the breakwater and the superstructure are suggested to improve the reduction effect of focused wave forces on the box-girder superstructure. [ABSTRACT FROM AUTHOR]

Based on the Navier-Stokes (RANS) equations, a three-dimensional (3-D) mathematical model for the hydrodynamics and structural dynamics of a floating point-absorbing wave energy converter (WEC) with a stroke control system in irregular and extreme waves is presented. The model is validated by a comparison of the numerical results with the wave tank experiment results of other researchers. The validated model is then utilized to examine the effect of wave height on structure displacements and connection rope tension. In the examined cases, the differences in WEC’s performance exhibited by an inviscid fluid and a viscous fluid can be neglected. Our results also reveal that the differences in behavior predicted by boundary element method (BEM) and the RANS-based method can be significant and vary considerably, depending on wave height. [ABSTRACT FROM AUTHOR]

It is demonstrated that the greatest influence of the variations in the groupiness of storm waves in the Baltic Sea concerns the highest waves. The variations in the height of less high waves are defined by wind speed. It is revealed that the height of 3% of the highest waves depends on their bandwidth: higher and lower waves are characterized by the larger and smaller set of frequencies, respectively. The significant wave height does not almost depend on the bandwidth. It is found that the spectrum of storm waves in the southwestern part of the Baltic Sea has a multi-peak structure which reflects the complex structure of waves consisting of several wave systems. Envelopes and individual waves of different frequency ranges superimpose, and extreme waves are generated. The probability of occurrence of extreme waves is maximum at the moments of the maximum development of wave groupiness. [ABSTRACT FROM AUTHOR]

Wave characteristic assessments of wave energy test sites provide a greater understanding of prevailing wave conditions and are therefore extremely important to both wave energy test site operators and clients as they can inform wave energy converter design, optimisation, deployment, operation and maintenance. This research presents an assessment of the wave resource at the Atlantic Marine Energy Test Site (AMETS) on the west coast of Ireland based on 12-years of modelled data from January 2004 to December 2015. The primary aim is to provide an assessment of annual and seasonal wave characteristics and resource variability at the two deployment berths which comprise the site. A nested model has been developed using Simulating WAves Nearshore (SWAN) to replicate wave propagations from regional to local scale with a 0.05° resolution model covering the northeast Atlantic and a 0.0027° resolution model covering AMETS. The coarse and fine models have been extensively validated against available measured data within Irish waters. 12-year model outputs from the high resolution model were analysed to determine mean and maximum conditions and operational, high and extreme event conditions for significant wave height, energy period and power. Annual and seasonal analyses are presented. The 12-year annual mean P were 68 kW/m at Berth A (BA) and 57 kW/m at Berth B (BB). The resource shows strong seasonal and annual variations and the winter mean power levels were found to be strongly correlated with the North Atlantic Oscillation (NAO). [ABSTRACT FROM AUTHOR]

This paper investigates the experimental and numerical vertical bending moments induced by abnormal waves on two ships, namely, a bulk carrier and a Roll-on/Roll-off. The experimental data was obtained by seakeeping tests with scaled models in head waves at two Froude numbers. The wave traces were predefined and corresponding to wave records measured during storms in the North Sea. These wave records are particularly interesting because each of them includes one abnormal wave. The ship models, which are similar in length but different in their geometry, were tested in the same predefined wave conditions. The objective is to investigate the hull geometry influence on vertical bending moment under extreme sea conditions. Some conclusions are made by comparing directly the measured responses from the two models. The experimental data is also used as benchmark to validate the predictions by a partially nonlinear time domain seakeeping numerical model. The numerical model is then used to generalize the comparative analysis between the two ships. [ABSTRACT FROM AUTHOR]

The Gulf of Guinea in West Africa is dominated by swells, extreme waves are also characterized by this kind of wave, and it is different from that along the China coast for which extreme waves are induced by typhoon. When determining the design wave parameters for such sea areas that dominated by swells, study approaches for the typhoon waves are not suitable. In order to provide methods as reference for the calculation of nearshore extreme wave along swell-dominated coasts, two of the most used methods are summarized according to the wave study reports performed by DHI for ports in West Africa, and then finally the average of the calculated values from these two methods is recommended for designs. [ABSTRACT FROM AUTHOR]

A substantial part of the energy of wake waves from high-speedships sailing in shallow water is concentrated in nonlinear componentswhich at times have a solitonic nature. Recent results of investigationsinto solitonic wave interactions within the framework of theKadomtsev-Petviashvili equation and their implications for roguewave theory are reviewed. A surface elevation four times as highas the counterparts occurs if the properties of the interactingwaves are specifically balanced. The slope of the water surfacemay increase eightfold. The resulting structure may persist fora long time. Nonlinear wake components may exert a considerableinfluence on the marine ecosystem in coastal areas

This paper deals with the reproduction of unidirectional extreme events in a numerical wave basin. From a rogue wave measurement at a given location, experiments or numerical simulations are conducted with the same wave profiles using reproduction procedures. Although it is recognized that many different physical mechanisms may be at play in freak wave formation, reproduction procedures generally use frequency focusing to generate these high waves. This paper intends to assess the validity of this approach. In particular, it will focus on the relationship between an accurate reproduction of the free surface elevation and the accuracy of the corresponding wave kinematics inside the fluid domain. A highly nonlinear model is used to compute the occurrence of unidirectional freak waves in large periodic domain, which are reproduced in a 2-D numerical wave tank and compared. The study presents an advanced reproduction procedure that deals with rogue waves embedded in an irregular sea state. It shows that, using the appropriate reproduction procedure, it is possible to accurately reproduce free surface elevation as well as kinematics induced by this extreme event. [ABSTRACT FROM AUTHOR]

This research presents an assessment of wave characteristics at the 1/4 scale wave energy test site in Galway Bay based on (1) data from a waverider buoy from 2009 to 2013 and (2) data from a high frequency radar system (CODAR) from 2011 to 2013. The main objective of this research is to provide an assessment of annual and seasonal wave characteristics and resource variability at a wave energy site. Such assessments are extremely important for wave energy test sites so as to inform the design, optimisation and maintenance of wave energy converters. An approach for classifying operational, high and extreme wave events is presented. The approach is based on percentage of occurrences of particular wave events and can be applied to any site and any wave parameter. In the present research it is separately applied to wave height and wave power. An additional objective is the validation of CODAR wave data for use in assessment of wave height characteristics; this was achieved by comparing CODAR data with waverider data. The research shows that the authors characterisation methodology is easy to apply and unambiguous to interpret. Due to the significant variation in wave parameters at the site from season to season and year to year, operational, high and extreme conditions are presented for the 5-year measurement period, individual years and individual seasons. The research also shows that wave heights determined from CODAR show good agreement with those from a waverider buoy and may be relied upon for accurate site characterisation. [ABSTRACT FROM AUTHOR]

The wave endurance time method is a novel dynamic approach to conveniently estimate structural performance under various extreme wave conditions. In this method, offshore structures are subjected to a gradually intensifying sea surface profile called wave function, and their performance is assessed in different sea state conditions by a single time history analysis. From a wave endurance time analysis perspective, structural behavior is judged based on the maximum time duration that a structure can withstand the wave function. In this study, a description of the wave endurance time concept is presented, and generation of the initial type of wave functions is thoroughly addressed. In addition, the evaluation of a simplified model of a realistic jacket platform under extreme wave conditions is viewed through the lens of a wave endurance time study. The accuracy of this approach is investigated by a comparative study between the wave endurance time approach and typical 3-h time history analyses. The results indicate that the wave endurance time approach is capable of estimating the results of 3-h simulations with acceptable accuracy and less computational effort. [ABSTRACT FROM AUTHOR]

You, Z.J., Yin, B.S., Ji, Z.Z., and Hu, C., 2016. Minimisation of Uncertainty in Estimation of Extreme Waves. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1277 - 1281. Coconut Creek (Florida), ISSN 0749-0208. Accurate information on extreme wave conditions is often required for inshore and offshore structure designs, coastal inundation and erosion hazard studies, coastal construction planning, and coastal port operations. Estimates of extreme wave heights are commonly extrapolated from historical wave records based on extreme-value theory. Although a large number of studies have been undertaken to develop and improve methodologies in extreme wave analysis, there still exists much uncertainty in estimates of extreme waves. This study is to investigate main causes of this uncertainty based on historical wave buoy data collected off the NSW coast of Australia. It is found that the uncertainty is caused mainly by short wave record, missing storm wave data, different methods for generation of return wave height data, too low/high POT thresholds, subjective plotting positions, unsuitable distribution functions, different distribution parameter estimators, and ad-hoc criteria on selection of the best-fit function. The likelihood errors of the uncertainty are evaluated and the detail on how to minimise the uncertainty is also proposed. [ABSTRACT FROM AUTHOR]

Reliable ocean wave forecasts are critical for reducing the risk posed by extreme waves for ships and offshore infrastructure. Despite insights gained from theoretical investigations and constantly improving operational wave forecasting systems, the emergence of extreme waves remain unpredictable. In this article, the authors propose a data-driven modelling approach to generate high resolution wave forecasts for capturing individual waves, including rogue waves. To this end, a decomposition of the sea surface into a set of rapid oscillations and slowly varying amplitudes is utilized. The slow amplitude variations are subsequently forecasted by using universal, data-driven methods. In this approach, the extrapolation range of the data-driven techniques is extended by the slowness of the amplitude variations. The method's capabilities are demonstrated by using available measurements from an experimental wave tank and field data from ocean buoys. • Novel data-driven methodology for ocean wave forecasting. • Combination of physical modelling with data-driven techniques. • Extensive validation of the proposed methodology with experimental data and field measurements. • Accurate forecasts in real-time. • Prediction of rogue waves up to one minute in advance. [ABSTRACT FROM AUTHOR]

Experiments have been undertaken in a wave basin with the hinged attenuator-type wave energy converter M4 in a 6-float configuration with two hinges for power take off (PTO), moored to a single-point buoy. This follows previous experiments with inelastic cables giving very high snap loads. The PTO was disengaged for these tests. The aims are i) to use the elastic mooring cable to reduce the snap loads of the M4 system, with two elastic stiffnesses tested, and ii) to study the system's dynamic response with a basic mooring configuration under intermediate to large waves. Mooring loads at the fairlead and the bed, and relative pitch angle between floats were measured. Numerical simulations using two different models were carried out, and the results were compared against the experiment results. For very large waves, the floats showed occasional deck submergence (dunking) limiting relative angular motion as wave height increases, in effect providing a passive end stop. The largest peak relative angle was just less than 40°. The extreme snap loads were up to 1/6th of those with inelastic cables. Spectral analyses of relative pitch angle and mooring force were made and shown to be quite different and complex. • Elastic cables to mooring buoy for multi-float WEC in extreme waves investigated. • In very large waves overtopping limited relative pitch angular response to 40° • Elastic cables reduced snap force by factor up to about 6 below inelastic. • Increasing cable elasticity reduced snap forces. • Mooring force spectra showed peaks at pitch and peak wave frequencies. [ABSTRACT FROM AUTHOR]

Coastal box-girder bridges have wide applications in the near-shore transportation systems and many low-lying bridges are under serious threats from extreme waves. However, few researchers paid attention to the dynamic structural behaviors of coastal low-lying bridges under extreme wave conditions, which is crucial to the rational design of these bridges. In this study, a three-dimensional finite element model, including the local nonlinear bearing material model and wave loading importation from the computational fluid dynamics (CFD) simulations, is established to investigate the dynamic behavior of the bridge structure. Specifically, to provide a more scientific and precise evaluation for the dynamic behavior of coastal bridges, the laminated rubber bearing model is established at joints between the superstructure/box-girder and bent cap using solid elements. Three common failure modes, including the large lateral shear deformation of the rubber bearing, sliding between the girder and bearings, and overturning of the superstructure, are investigated in detail. To consider the uncertainty under different loading conditions, one surrogate model based on the support vector machine (SVM) is adopted to enhance the calculation efficiency of the vulnerability assessment for the coastal box-girder bridge. It is revealed that (a) The overturning and sliding failures are more likely to occur for the box-girder in submerged states, while the large lateral shear deformation for the bearing is prone to arise when the girder is elevated; (b) The wave height to water depth ratio has a significant influence on the safety of the bridge; and (c) The high failure probability indicates that appropriate countermeasures are necessary to improve the safety margin of the bridge. • A precision FE model of the box-girder with laminated rubber bearings is established. • The failure mechanism of box-girder coastal bridges under extreme waves is inclusively investigated. • SVM based surrogate model is adopted to consider uncertainties under different loading conditions. • Fragility assessment of coastal box-girder bridges under extreme waves is conducted. [ABSTRACT FROM AUTHOR]