Higher Significant Wave Height Research Articles

Accuracy and Resolution of SWOT Altimetry: Foundation Seamounts

AbstractWe assess the accuracy and spatial resolution of the surface water and ocean topography (SWOT) swath altimeter for deriving marine gravity anomalies. The analysis is performed at the Foundation Seamounts in the South Pacific where we developed a highly accurate gravity field by combining the long‐wavelength (>40 km) gravity field derived from previous nadir altimeters with the shorter wavelength gravity field from the seafloor topography as constrained by the ship gravity. In this region, the sea surface slope (SSS) of the ocean variability is 50–100 times smaller than the slope signal of the seamounts so can be ignored in the analysis. Each SWOT cycle can deliver SSS accurately with a standard deviation of 2.6 µrad and a spatial resolution of 14 km at typical sea state (significant wave height 4 m), with accuracy diminishing at high significant wave heights (e.g., exceeds 6 m). Averaging repeated SWOT measurements improves the accuracy and resolution. For example, we expect that averaging just 10 repeats (7 months) results in accuracy/resolution that matches the best marine gravity maps based on 230 months of nadir altimetry. With a mission lasting over a year, SWOT promises a substantial leap in marine gravity accuracy and resolution, uncovering previously uncharted details of the seafloor, including thousands of uncharted seamounts.

A Sea State Dependent Gas Transfer Velocity for CO2 Unifying Theory, Model, and Field Data

AbstractWave breaking induced bubbles contribute a significant part of air‐sea gas fluxes. Recent modeling of the sea state dependent CO2 flux found that bubbles contribute up to ∼40% of the total CO2 air‐sea fluxes (Reichl & Deike, 2020, https://doi.org/10.1029/2020gl087267). In this study, we implement the sea state dependent bubble gas transfer formulation of Deike and Melville (2018, https://doi.org/10.1029/2018gl078758) into a spectral wave model (WAVEWATCH III) incorporating the spectral modeling of the wave breaking distribution from Romero (2019, https://doi.org/10.1029/2019gl083408). We evaluate the accuracy of the sea state dependent gas transfer parameterization against available measurements of CO2 gas transfer velocity from 9 data sets (11 research cruises, see Yang et al. (2022, https://doi.org/10.3389/fmars.2022.826421)). The sea state dependent parameterization for CO2 gas transfer velocity is consistent with observations, while the traditional wind‐only parameterization used in most global models slightly underestimates the observations of gas transfer velocity. We produce a climatology of the sea state dependent gas transfer velocity using reanalysis wind and wave data spanning 1980–2017. The climatology shows that the enhanced gas transfer velocity occurs frequently in regions with developed sea states (with strong wave breaking and high significant wave height). The present study provides a general sea state dependent parameterization for gas transfer, which can be implemented in global coupled models.

Validation of the Ocean Wave Spectrum from the Remote Sensing Data of the Chinese–French Oceanography Satellite

Since the launch of CFOSAT on 29 October 2018, more than three years of observational data of ocean wave spectra with a frequency range of 0.02–0.26 Hz and a horizontal resolution of 70–90 km have been obtained. This study compares wave spectra retrieved from 6°, 8°, and 10° incidence angle beams and their combination provided by CFOSAT with corresponding data from 98 buoys from the National Data Buoy Center (NDBC) in order to validate the remote sensing wave spectral accuracy from 1 January 2020 to 31 December 2022. The correlation coefficient of frequency spectra (Rs) between CFOSAT and buoys is used to represent the accuracy of the spectral form; the root mean square (RMS) of the significant wave height (SWH) is used to represent the accuracy of the total energy. The results indicate that CFOSAT can retrieve reliable wave frequency spectral forms with a high significant wave height (Rs > 0.8 when SWH > 3 m; RS < 0.4 when SWH < 1 m). The low-frequency noise in the swell part causes the main error, the RMS of the swell height is 0.4 m whereas the RMS of wind wave height is 0.24 m, and the mask filter used for spectral partitioned provided by CFOSAT can eliminate the low-frequency noise and improve the Rs of 10° beam wave spectra from 0.59 to 0.64. For the wind wave spectra, the correct spectra have been achieved and the mask filter cannot improve the accuracy. The wave spectra from the 10° beam without mask filtering provides the best estimation of total energy, the RMS of SWH is 0.23 m, after the mask filtering, the best estimation of spectral form can be achieved, the Rs is 0.64. The novelty of this study is that we found the strong correlation between SWH and Rs, where the scatter of SWH and Rs can be fitted as: Rs = 1 − exp(−0.89·SWH + 0.20); according to this approximate formula, we can estimate the reliability of wave spectra provided by CFOSAT according to the SWH in any region, which is important for wave spectral assimilation in the numerical model. The validation of wave direction indicates that the accuracy of wave spectra in the directional component is poor; further research is needed on the causes of directional errors. Generally, this study is not only an evaluation of the quality of the CFOSAT spectral data, but also an important reference for a series of research requiring the CFOSAT spectral data.

The Feasibility of the ERA5 Forced Numerical Wave Model in Fetch-Limited Basins

Numerical wave models are critical in hindcasting reliable long-term time series of significant wave heights, which play a crucial role in coastal and ocean engineering activities. Although wind fields are an important input to numerical wave models, few studies have investigated the feasibility of the widely used ERA5 wind reanalysis dataset in fetch-limited basins. In this work, we investigated the feasibility of the ERA5 forced numerical wave model (SWAN) in fetch-limited basins. ERA5 wind velocities were first compared to ground-based meteorological stations, showing poorer accuracy compared to finer gridded ALADIN wind data. Subsequently, the white-capping coefficient Cds in the Janssen white-capping formulation was calibrated separately using a surrogate model when establishing the ERA5 and ALADIN forced wave models. The calibrated ERA5 forced model showed a similar agreement to wave buoy data as the calibrated ALADIN forced wave model during the calibration period and even superior accuracy in the validation period. Overall, these results show that the wave model calibration procedure mitigates the effect of the poorer accuracy of the ERA5 wind data on the significant wave height results. Nevertheless, both ERA5 and ALADIN forced wave models showed an alarming overprediction for high simulated significant wave heights.

Regional wave model climate projections for coastal impact assessments under a high greenhouse gas emission scenario

In the future, shifts in wind storms across the North and Baltic Seas are highly unpredictable, challenging the projection of wave conditions for managing coastal hazards. Moreover, regional sea level rise (SLR), with very large uncertainty, complicates the situation for stakeholders seeking recommendations for climate adaptation plans. The purpose of this study is to examine the change of the storm surge and wind wave components of the water level due to climate change in a low tidal range Køge Bay near the entrance of the Baltic Sea. Under a high greenhouse gas emission scenario RCP8.5, we employed a regional climate model (HIRHAM) forced wave model (WAM) and focused on the wave model results during the “storm surge conditions” (exceeding 20 years storm surge events) and “stormy conditions” (exceeding 90th percentile of wave heights). We find that the change in both wave height and period in the future is negligible under “stormy conditions”. Nevertheless, under “storm surge conditions” when considering SLR, the simulated wave height is projected to double in the near future (mid-century) under RCP 8.5, and the wave period may also increase by about 1.5 seconds. This is because some high significant wave height events in the future are associated with the storm surge events when considering SLR. The findings suggest that the combined effects of mean sea level rise, storm surge and waves are likely to increase the risk to a bay with geography and exposure comparable to Køge Bay. As a result, the future plan for climate engineering protection should place a premium on the additional wave energy protection associated with storm surges.

Assessment of the use of scatterometer wind data to force wave models in the North Atlantic Ocean

The present work uses for the first time scatterometer wind fields to force a wave model and compares the accuracy of the resulting wave conditions with the ones obtained when using two different sources of hindcast wind fields forcing the same wave spectral model in the Atlantic Ocean. For this purpose, a 5-year hindcast (2010–2014) is performed with the wave spectral model SWAN for the Madeira and Azores archipelagos. The model uses as input the bathymetry from GEBCO, the wave boundary conditions from the WAVEWATCH III wave model provided by Ifremer and winds from the ERA-Interim and ERA5 databases, and remotely sensed winds from scatterometers. A quantitative analysis of the results is performed, and the numerical results are validated against altimeter data and buoy measurements. Globally, ERA-Interim, ERA5 and scatterometer wind data provided similar accuracy of the generated wave fields, as expressed in the error statistics, which are very close to each other, but in the case of extreme events, the scatterometer data reveals more intense winds and consequently lead to sea states with higher significant wave height. This is more visible in the Azores area than in Madeira. The results demonstrate that, in general, the significant wave height is well reproduced by SWAN.

Statistics of Simulated Storm Waves over Bathymetry

This paper shows simulations of high waves over different bathymetries to collect statistical information, particularly kurtosis and crest exceedance, that quantifies the occurrence of exceptionally extreme waves. This knowledge is especially pertinent for the design and operation of marine structures, safe ship trafficking, and mooring strategies for ships near the coast. Taking advantage of the flexibility to perform numerical simulations with HAWASSI software, with the aim of investigating the physical and statistical properties for these cases, this paper investigates the change in wave statistics related to changes in depth, breaking and differences between long- and short-crested waves. Three different types of bathymetry are considered: run-up to the coast with slope 1/20, waves over a shoal, and deep open-water waves. Simulations show good agreement in the examined cases compared with the available experimental data and simulations. Then predictive simulations for cases with a higher significant wave height illustrate the changes that may occur during storm events.

Asymmetric Wave Distributions of Tropical Cyclones Based on CFOSAT Observations

AbstractObservations of the China‐France oceanography satellite are used to investigate the wave distribution's asymmetry during tropical cyclone (TC) from August 2019 to August 2020. The spatial distribution of TC waves is analyzed based on an individual case, six ocean basins, and TCs categories. A study of super typhoon Hagibis shows that the highest significant wave height (SWH) appears on the typhoon track's right side. Further analysis reveals that the highest SWH is located on the right (left) side of TC tracks in the Northern Hemisphere (Southern Hemisphere). In the Western North Pacific, North Atlantic, Eastern North Pacific, and North Indian Ocean, the highest SWH is on the right side of TCs of 251, 260, 130, and 118 km, respectively. In the South Pacific and South Indian Ocean, the highest SWH is on the left side of 70 and 128 km. According to the TC categories, the largest (smallest) departure happens during the weakest (strongest) TC. The intensifying of TC favors the wavefield's growth and reduces the asymmetry of the wave height's distribution. Both the asymmetric wind fields and the land's orographic effects impact the TC wave's distribution. In the Eastern North Pacific, the TC wind is the weakest, but the departure is not the smallest, probably due to the left continent bounding the wave energy's propagation.

The Effect of the Difference in Intensity and Track of Tropical Cyclone on Significant Wave Height and Wave Direction in the Southeast Indian Ocean.

This study aims to analyze the effect of the differences in intensity and track of tropical cyclones upon significant wave heights and direction of ocean waves in the southeast Indian Ocean. We used the tropical cyclone data from Japan Aerospace Exploration Agency (JAXA) starting from December 1997 to November 2017. The significant wave height and wave direction data are reanalysis data from Copernicus Marine Environment Monitoring Service (CMEMS), and the mean sea level pressure, surface wind speed, and wind direction data are reanalysis data from European Center for Medium-Range Weather Forecasts (ECMWF) from December 1997 to November 2017. The results show that the significant wave height increases with the increasing intensity of tropical cyclones. Meanwhile, the direction of the waves is influenced by the presence of tropical cyclones when tropical cyclones enter the categories of 3, 4, and 5. Tropical cyclones that move far from land tend to have higher significant wave height and wider affected areas compared to tropical cyclones that move near the mainland following the coastline

Investigation typhoon induced storm surge and high wave in Vietnam using coupled Delft3d-FLOW – WAVE models combined with weather research forecast (WRF) output wind field

Introduction: Typhoon-induced disasters including storm surge and high wave are obvious threats to coastal areas in Vietnam. Thus, many researchers have paid their attention to this issue. The approaching methods are varied, including statistical methods and also numerical methods. This study suggests the coupled models Delft3D-FLOW and WAVE, using the meteorological output data from the Weather Research Forecast (WRF) for investigating the typhoon induced disasters in the coastal areas in Viet Nam. Method: WRF is run in multiple domains with different grid resolutions simultaneously and there is an interaction between them to reproduce the wind field during the typhoon events. Delft3D-FLOW is coupled with Delft3D-WAVE (SWAN) through a dynamic interaction, in which the FLOW module considers the received radiation stresses calculated by the wave module. On the other side, the updated water depth including the contribution of the storm surge will be used by the WAVE module. Both Delft3D-FLOW and Delft3D-WAVE models used wind fields from the WRF simulation output as the meteorological input data. The total surge level includes the storm surge, wave-induced setup and the tidal level. Results: The case of extreme weather event Typhoon Kaemi (2000) was used to validate the wind field and the wave height. The calibration process of the the storm surge level was based on the observed data during Typhoon Xangsane (2006), while Typhoon Durian (2006) were used to validate the coupled models. The comparisons show the good agreement between simulated results and observed data, especially in terms of the peak water level and highest significant wave height, which mainly governed by the typhoon wind field. The simulated results reveal that the surge height durring Typhoon Durrian period along its path was ranged from 1.2 to more than 1.4m, which can be considered to pose the greatest risk to low-lying coastal areas of the Mekong Delta. Conclusion: The suggested coupled models can be used to investigate the impact of typhoon induced disasters.

Application of the Saffir-Simpson Hurricane Wind Scale to Assess Sand Dune Response to Tropical Storms

Over one-third of the Earth’s population resides or works within 200 km of the coast. The increasing threat of coastal hazards with predicted climate change will impact many global citizens. Coastal dune systems serve as a natural first line of defense against rising sea levels and coastal storms. This study investigated the volumetric changes of two dune systems on Isle of Palms, South Carolina, USA prior to and following Hurricanes Irma (2017) and Florence (2018), which impacted the island as tropical storms with different characteristics. Irma had relatively high significant wave heights and precipitation, resulting in an average 39% volumetric dune loss. During Florence, a storm where precipitation was low and winds were moderate, net volumetric dune loss averaged 3%. The primary driving force causing dune change during Irma was water (precipitation and storm surge), and during Florence, it was wind (aeolian transport). We suggest that the application of the Saffir-Simpson Hurricane Wind Scale classifications should be reconsidered because different geomorphic responses were measured, despite Irma and Florence both being designated as tropical storms. Site-specific pre- and post-storm studies of the dune morphology and site-specific meteorological measurements of the storm (wind characteristics, storm surge, precipitation) are critically needed.

Analysis of Typhoon-Induced Waves along Typhoon Tracks in the Western North Pacific Ocean, 1998–2017

In this study, Version 5.16 of the WAVEWATCH-III (WW3) model is used to simulate parameters of typhoon-generated wave fields in the Western North Pacific Ocean during the period 1998–2017. From a database of more than 300 typhoons, typhoon tracks are partitioned into six groups by their direction of motion and longitude of recurvature track. For typhoons that recurve east of 140° E, or track toward mainland Asia, regions of high significant wave height (SWH) values are separated by a minimum in SWH near 30° N. Partitioning SWH into wind sea and swell components demonstrates that variations in typhoon tracks produce a much stronger signal in the wind sea component of the wave system. Empirical orthogonal function (EOF) analysis is used to compute the four leading modes of variation in average SWH simulated by the WW3 model. The first EOF mode contributes to 17.3% of the total variance; all other modes contribute less than 10%. The first EOF mode also oscillates on an approximately 1-year cycle during the period 1998–2017. Overall, typhoon-induced wave energy dominates north of 30° N. Temporal analysis of the leading principal component of SWH indicates that (a) the intensity of the wave pattern produced by westward-tracking typhoons decreased during the last 20 years, and (b) typhoons that recurve east of 140° E and those that track westward toward southeast Asia are largely responsible for the decadal variability of typhoon-induced wave distribution.

Impact of 2019 Tropical Storm (Pabuk) on Beach Morphology, Terengganu Coast (Malaysia)

Shariful, F.; Sedrati, M.; Ariffin, E.H.; Md Shubri, S., and Akhir, M.F., 2020. Impact of 2019 tropical storm (Pabuk) on beach morphology, Terengganu coast (Malaysia). In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 346-350. Coconut Creek (Florida), ISSN 0749-0208.Occurrences of tropical storms, including cyclone and typhoon, across the Southeast Asia region are uncommon despite being highly prone to monsoon storm. Nevertheless, Thailand was recently hit by a cyclone called Pabuk, which had affected several parts of Malaysia with a significant impact along the Terengganu coastal area, particularly its infrastructure erected along the coastal line. This Pabuk storm was associated with the direction of waves, along with intense current velocities and strong winds, in comparison to a normal monsoon storm. The Pabuk storm had struck the Terengganu coastal area precisely in January 2019, which was during the Northeast monsoon storm that commonly occurs between November and January with heavy rainfall and strong wind. Interestingly, in November and December 2018, the rainfall was minimal to only a few drops, while the weather was hot and dry. In order to comprehend the variances between seasonal monsoon and the Pabuk storm, beach profile surveys were conducted during monsoon seasons, including the Southwest monsoon (June 2018), the transition monsoon (October 2018), the Northeast monsoon (December 2018), and after the Pabuk storm. In particular, during the Northeast monsoon season, erosion was absent along the beach, except for some discovery in the anthropogenic area, while the beach volume decreased from the beach dune and foreshore areas after the Pabuk storm. This study revealed that the highest significant wave height from numerical model (MIKE-21) during the Pabuk storm inflicted a significant morphological change onto the beach dune. Since the recovery of beach dune varies depending on the availability of sediment source, the recovery process may take a longer period in the anthropogenic areas. Such findings are integral for coastal managers involved in repairing and rebuilding activities on the adversely affected coastal infrastructures along the coastal line at the event of tropical storm.

Wave Energy Potential and Simulation on the Andaman Sea Coast of Thailand

Ocean wave energy is an interesting renewable energy because it will never run out and can be available all the time. If the wave energy is to be used, then the feasibility study of localized wave potential has to be studied. This goal is to study the potential of waves in the Andaman Sea. The Simulating WAves Nearshore (SWAN) model was used to calculate the significant wave heights, which were validated with the measurement data of the Jason-2 satellite. The coastal area of Phuket and Phang Nga provinces are suitable locations for studying wave energy converters because they have high significant wave height. Moreover, this study used computational fluid dynamics (CFD) for the simulation of wave behavior in accordance with wave parameters from the SWAN model. The wave height simulated from CFD was validated with linear wave theory. The results found that it was in good agreement with linear wave theory. It can be applied for a simulation of the wave energy converter.

Wave modeling of a reef-sheltered coastal zone in the Red Sea

The coastal areas of the Red Sea are characterized by shallow banks of fringing and barrier reefs that provide protection against coastal hazards and erosion by dissipating wave energy. This study investigates the wave climate and extremes of a reef-protected coastal zone in the Red Sea using a high-resolution coupled wave and circulation model, ADCIRC + SWAN, configured on an unstructured grid forced with the meteorological fields from high-resolution regional atmospheric model. Our simulations suggest that the relatively narrow offshore reefs with steep fore-reef slopes dissipate 40–50% of the wave energy propagating towards the shoreline, and this is more pronounced during extremes. The impact of the coupling on determining the wave climate is negligible, but is significant for storms with ~10 cm higher significant wave height (Hs) during the observed period. The back-reef wave climatology computed from 30-year model simulations shows that the mean Hs distribution is uniform throughout the year, and extremes occur more often from February to May. Different return levels of Hs in the sheltered areas are estimated using extreme value analysis. Our results emphasize that preserving the complex offshore reefs is crucial for mitigating the coastal hazards of high-energy waves which are projected to increase with climate change.

Spatio-Temporal Distribution and Variability of High Threshold Wind Speed and Significant Wave Height for the Indian Ocean

Space-borne satellites provide extensive coverage of measuring sea surface wind field and wave heights on a global scale. The present study provides a comprehensive assessment of distribution of extreme wind and wave fields over the Indian Ocean (IO) utilizing satellite-based scatterometer and altimeter datasets. Merged scatterometer data from ERS-1/2, QuikSCAT, and ASCAT for a period of 27 years produced continuous record of wind speed, whereas the calibrated altimeter data for different satellite missions provided information on the significant wave height. A comparison study between merged scatterometer and calibrated altimeter derived long-term maximum wind speed shows an overestimation of altimeter product by an average measure of 3 m/s and higher as compared to the scatterometer winds in 92.8% of the total observational points considered. A decadal variability was observed in the inter-annual spatial distribution of the 90th and 95th percentile winds for the study region. Interestingly, the study reveals a declining trend in the dispersion of higher waves (90th, 95th, and 99th percentiles) in the entire IO except the South China Sea. Further, 2011 onwards there is an increasing trend in the annual distribution of extreme winds and waves for the Extra-tropical South Indian Ocean having implications on the generation of swell wave fields.

The characteristics of wind waves in Lake Chaohu in 2018

基于实测数据，利用验证良好的SWAN风浪模型开展了2018年巢湖风浪变化及分布特征研究.巢湖2018年平均有效波高和波周期分别为0.16 m和1.22 s，整体春季风浪大，秋季风浪小.月均最大值出现在4月，分别为0.22 m和1.36 s，月均最小值出现在11月，分别为0.11 m和1.06 s，变化幅度分别为最大值的52%和22%.月均值整体中巢湖最大，东巢湖次之，西巢湖最小.巢湖月最大有效波高和波周期主要出现在东巢湖或中巢湖，各值月间差异显著，最大变化幅度分别为最大值的61%和27%.不同湖区计算的月均有效波高和波周期较大值分布范围所占湖区的比例不同，中巢湖与东巢湖较大，西巢湖最小.不同月份及湖区较大有效波高出现的时间占比是不一致的，9-11月份时间占比较小，将有利于蓝藻水华的出现.;In this study, the wind-wave model SWAN was used to simulate the characteristics of variations and distributions of wind waves in Lake Chaohu for the year 2018. The model was calibrated and evaluated using observational data. Results suggest that the annual mean significant wave height and wave period of Lake Chaohu during 2018 were 0.16 m and 1.26 s, respectively. The wind wave was strong in spring and weak in autumn. The monthly mean values exhibit great variations. The largest monthly values of 0.22 m and 1.36 s were obtained in April, while these values were 0.11 m and 1.06 s in November, which were the lowest during 2018 and whose variation ranges were 52% and 22% of the maximum values, respectively. Among different lake basins, monthly mean wave height in the east basin and central basin were the highest, followed by the west basin. The highest value of monthly maximum significant wave height and wave period appeared in the east basin or the central basin. The values of monthly maximum significant wave height and wave period varied significantly during different months, whose variation ranges were 61% and 27% of the maximum values, respectively. The distribution ratio of the high values of monthly significant wave height and wave period computed by model in different lake zones were large in the east basin or central basin, but it was small in the west basin. The proportion of time when the high significant wave height appeared was different during different months in different lake zones, and it was small from September to November, which would be beneficial to the emergence of cyanobacteria blooms.

Analysis of the influence of human errors on the occurrence of coastal ship accidents in different wave conditions using Bayesian Belief Networks

The paper describes a study aiming to assess the human error contribution in ship accidents in different weather conditions and the contribution that high significant wave heights have in the occurrence of certain accident typologies. To this aim, a Bayesian Belief Network model is developed, which includes variables related to the maritime accident but also to the different wave conditions. For the quantification of the conditional probability tables the maritime accident database of the Portuguese Maritime Authority is used, which includes 857 validated accidents registered in the period 1997–2006. Similarly, several significant wave height databases are used to populate the node correspondent to this variable. The importance of accurate estimation of the significant wave height is also discussed. To substantiate this discussion a comparison between hard evidence (ε) and a soft one (μ,σ) is performed for the significant wave height node of the BBN model. The application of different combinations of evidence in the model allows the identification of patterns of influence of the human error cause in comparison with others, namely with the sea and weather one. The results show one apparent high-risk acceptance within the crews of the fishing vessels and low risk perception in the recreational vessels. Based on the results, are provided recommendations to decrease the risk associated to specific probable causes.

Uncertainties of the 50-year wave height estimation using generalized extreme value and generalized Pareto distributions in the Indian Shelf seas

Information about waves with specific return period in a region is essential for the safe design of marine facilities. In this study, significant wave height for 50-year return period is estimated using generalized extreme value (GEV) distribution and generalized Pareto distribution (GPD) based on the 15-year wave hindcast data. In order to realize the dependency of nature of the time series data on return value estimation, three types of data series: daily maxima (DM), monthly maxima (MM) and annual maxima (AM) are considered for GEV, whereas for GPD, threshold values are estimated from the parent data set at 6 h and the DM series. The GEV distribution shows that AM predicts higher significant wave height followed by MM and then DM. The large number (~ 50%) of smaller wave height value (< 1 m) in the DM leads to smaller estimate in wave height for 50-year return period for DM series compared to other data series. Among the locations studied, the maximum value of the significant wave height with 50-year return period by GEV with AM data series is 7.15 m in the western shelf seas and is 7.36 m for the eastern shelf seas, whereas the values based on GPD with peak over threshold are 6.94 and 7.42 m, respectively. Case studies are also done to know the influence of tropical cyclone on the estimated 50-year return value.

Lifting Wind Turbine Components From a Floating Vessel: A Review on Current Solutions and Open Problems

Offshore wind energy is experiencing rapid development and is expected to make up an even bigger part of the world's future energy mix. New installation concepts for offshore wind farms involve lifting operations of wind turbine components from floating vessels. These installation concepts will only be economic if the lifting operations are performed safely at sea states with high significant wave heights. In this paper, we give an overview of current technical solutions, which could be used to lift the components tower, nacelle, hub, and rotor blade from a floating vessel. We classify and analyze solutions found in patents and the academic literature and point out open problems, which need to be addressed to enable lifting operations at higher sea states than what is currently feasible. However, we restrict the paper to technical solutions concerning the interface between the vessel and the component as well as the interface between the component and the crane. Consequently, we analyze, classify, and discuss solutions for the seafastening, the lifting gear as well as motion compensation systems. We find that there exists a large number of solutions, which are specific for a single component, but few solutions, which are applicable to all components without major adaptations. Additionally, we miss hydraulic seafastening mechanisms, which are remotely controlled and synchronized with the lifting operation. Consequently, we argue that versatile interfaces between the component and the crane as well as remotely controlled and synchronized seafastening mechanisms are best suited to enhance the lifting process.