Changes In Wave Height Research Articles

FIELD STUDY ON INFLUENCE OF TIDAL CURRENTS ON INTRA-WAVE SEDIMENT TRANSPORT

Sediment transport by currents and waves determines the evolution of shoals and channels on the ebb-tidal delta. The channels are an important conduit for shipping and are often dredged to maintain access at considerable cost. A better understanding of the sediment transport processes within the channels is the basis for a more cost-effective maintenance strategy. In the vicinity of ebb-tidal inlets, waves from offshore encounter tidal currents. Depending on the tidal phase, incoming waves face strong positive or negative current gradients. Besides changes in wave height, period and direction, the current gradients also affect the nonlinear wave shape and corresponding velocity profile.

WAVE CLIMATE VARIABILITY AND RELATED CLIMATE INDICES

Climate change is highly expected to give significant impact on coastal hazards and environment. The future projections of wave climate under global warming scenarios have been carried out and shows changes in wave heights depending on the regions (e.g., Hemer et al., 2013). Beside the long-term trends of wave climate, annual to decadal changes are also important to understand variability. For example, the North Atlantic Oscillation (NAO) is highly correlated to monthly mean wave height along the western European coast. However, variability of wave climate is not well understood over the globe, quantitatively. Additionally, the standard coastal engineers regard stationary process for wave environment for solving coastal problems. This study analyzes global wave climate variability for the last half century based on principal component analysis of atmospheric forcing (sea surface winds U10 and sea level pressure P) and wave hindcast.

Characteristics of beach erosion in headland bays due to wave action: Taking the Narrabeen beach in Australia as an example

The special cape-shaped topography of a headland sandy bay is the reason its shoreline varies differently than that of a straight-line coast. The Narrabeen embayment is located on the southeastern coastline of Australia approximately 20 km north of Sydney. The enclosed sandy beach is 3.6 km in length and is composed of fine to medium quartz sand overlying sandstone bedrock, with a median sand grain size D50 of 0.3 mm. Due to the prevalence of moderate to high wave energy conditions and the exposure of the central and northern portions of the beach to the prevailing south-southeastern swell waves. The morphodynamic responses of the Narrabeen beach are highly variable and rapid alongshore. The beach state was predominantly influenced by episodic storm events throughout the year when erosion and accretion can occur. This study analyzed measurements of cross-shore profiles of the Narrabeen headland sandy bay from 1997-1998. With reference to an atypical huge-wave event, this paper describes in detail the beach erosion caused by huge-waves and the beach restoration caused by small waves after the huge-wave event. It also details the relationship between shoreline variation and wave parameters (wave height and wave angle). To discuss the regulations and causes of beach rotation, the study selected six huge wave events that occurred in 1990–2000, all of which were followed by over eight months of small waves, and analyzed the alongshore variation. The results show that the morphodynamic responses of the Narrabeen beach are highly variable and rapid alongshore. During the huge wave events, the beach was eroded and the shoreline retreated. In the aftermath, the small waves restored the beach. The difference in the shoreline variation due to small waves exhibits a rotational pattern. Wave height is related to sand volume above mean sea level and sand accumulation was rapid and high after the big nearshore wave events. The Southern Oscillation Index (SOI) is closely related to the variability in the shoreline. Time-lagged cross-correlations between monthly beach shoreline positions and the SOI were calculated to investigate the presence of stronger cross-correlations between the beach shoreline and the SOI; the central profile (profile 4) is the most sensitive to the feedback of SOI change. The small waves after a huge-wave event make beach rotation periodic. Analysis of directional wave data and the SOI suggests that beach change is driven by changes in wave height (power) and a subtle change in wave direction, both of which are positively related to the SOl. The change in the SOI induces changes in the wave angles, which leads to sediment transport. This is the most important factor in beach rotation. These results reconfirm huge-wave and small waves subaerial morphology, in particular, these results confirm that the wave height and angle, which are induced by the SOI after a huge-wave event, are key drivers of alongshore variation in headland sandy bay coastlines. Under small wave conditions, the northern and mid beach profiles have negative correlations with SOI index, while the southern beach profiles have positive correlations with SOI index. This lead to sediment erosion in the north while sediment deposition in the south. And the shoreline thereby shows a rotational pattern. With the variation of the SOI index, the sediment movement changes in each beach profile, and the shorelines rotational pattern shows periodicity.

Experiment on Pressure Characteristics of Submerged Floating Tunnel with Different Section Types Under Wave Condition

Abstract Submerged floating tunnel (SFT for short) is a special underwater traffic structure, and wave load is one of the main environmental loads of SFT structure. In this paper, the 1:60 physical model test of three kinds of SFT in a two-dimensional wave flume is tested. The effects of random irregular waves on the SFT structure under different wave heights and periods are discussed. The study shows that: (1) Compared with circular and polygonal sections, there are multiple local peaks in the elliptical section during the period. with the increase of wave height, the number of local peaks also increases. It suggests that the rotational moment plays an important role in the elliptical section which has a relatively small depth-width ratio. (2) The position of the maximum and minimum pressure in the three kinds of SFT sections is consistent. Their vertical wave forces are all larger than their horizontal wave forces. The increase of vertical wave force relative to horizontal wave force in polygon section is larger than that in elliptical section, and the difference in the circular section is the smallest. (3) Under the same traffic condition, the wave force of the elliptical and polygon section is smaller, but they are more sensitive to the change of wave height, and the increase is obvious. The distribution of wave force in the circular section is more uniform.

Influence of the Seagrass, Zostera marina, on Wave Attenuation and Bed Shear Stress Within a Shallow Coastal Bay

Local effects of flow interaction with seagrass structure modify meadow scale hydrodynamics, resulting in lower current velocities and wave heights within a seagrass meadow. This attenuation promotes the deposition of suspended sediment, increasing the light available locally to benthic organisms. To elucidate the relationship between small-scale hydrodynamics that occur at the sea floor and the meadow scale effects of seagrass, high resolution velocity profiles were recorded adjacent to the sediment-water interface within a Zostera marina seagrass meadow in South Bay, Virginia. Additionally, instrumentation was deployed across the meadow to seasonally monitor corresponding changes in wave height across the seagrass meadow. Results show that wave height was reduced by 25 – 49% compared to an adjacent bare site, and by 13 – 38% compared to an analytical model of wave attenuation over an unvegetated seafloor with the same bathymetry. The greatest attenuation of wave height occurred during the spring and summer when seagrass biomass was greatest, while the lowest attenuation occurred in winter, corresponding to periods of minimal seagrass biomass. Significant wave height attenuation coefficients, αw, calculated for the meadow ranged from αw = 0.49 in spring to 0.19 during winter, but were highly dependent on wave conditions, with greater αw for larger wave heights and longer period waves. Within the seagrass meadow during summer, the highest measured bed shear stress was t_bed = 0.034±0.022 Pa, which occurred during peak wave conditions. This suggests that during high biomass conditions, the bed shear stress rarely exceeds the critical bed shear, t_crit = 0.04 Pa necessary to initiate sediment resuspension. This is in contrast to the bare site which showed elevated values of t_bed above the critical threshold across all seasons. These findings suggest the seagrass meadow does exert significant control over both wave heights and the hydrodynamic conditions at the sediment-water interface, and this control is due to the attenuation of wave motion by drag induced from the seagrass over the expanse of the meadow.

Mid-twenty-first century global wave climate projections: Results from a dynamic CMIP5 based ensemble

Abstract Ocean surface gravity waves are part of the climate system, regulating the exchange of energy and momentum at the atmosphere-ocean interface. Besides that, waves have a direct impact on coastal erosion and sediment transport, in ship routing and offshore/ship infrastructure design, as well as in coastal management. Most future wave climate projections point out to statistically significant changes in wave height conditions in the global ocean towards the end of the 21st century. In the present study, the near future impact of a warmer climate on the global ocean wave climate towards the mid-21st century (2031–2060) is investigated through a 4-member “coherent” ensemble of wave climate projections: single-model (wave model WAM), single-forcing (EC-Earth) and single-scenario (RCP8.5). The wave model WAM was forced by wind speed and ice coverage from four Coupled Model Intercomparison Project Phase 5 (CMIP5) EC-Earth projections. The ensemble historic climate reference period has been evaluated by comparison against wave reanalysis/hindcast data, and wave in-situ observations. Statistically significant increases in the global mean wind speed, wave height, wave period and wave energy flux are to be expected towards the mid-twenty first century, in less than 50 years, these changes being more striking in the mid-to-high latitudes of the Southern Hemisphere. Due to the propagation of swell to lower latitudes, statistically significant increases in wave heights, periods and energy fluxes are also projected to occur in equatorial areas, especially along the eastern side of the main ocean basins, during the Austral winter. Comparatively, the projected changes in wave heights and energy fluxes are expected to occur more intensely during the first half of the 21st century, in several areas of the global ocean.

Parametric study of a wave energy converter (Searaser) for Caspian Sea

Over the past decades, different types of energy converters have been invented because wave energy is a renewable energy source with high potential for extraction of considerable clean energy. Many numerical and experimental tests have been conducted to calculate the power generation of ocean waves, and these tests have demonstrated the significance of this energy. In this paper, the hydrodynamic performance of a new energy converter called "Searaser" has been evaluated using numerical simulation to study different aspects of this energy converter. Since previous studies have found ocean wave energy converters excellent for implementation in the Caspian Sea, the aim of this study is to investigate its performance for that sea, so this study presents a numerical simulation of Searaser inside an experimental wave tank using commercial software Flow-3D. To model the motion of the energy converter, Reynolds Averaged Navier-Stokes was coupled with a volume-of-fluid (VOF) model to generate three-dimensional numerical linear propagating waves for solving the fluid field. Grid independency was also carried out to determine the best mesh numbers for the original simulations. Finally, the Searaser hydrodynamic performance was numerically calculated for different wave heights, and some of the most important parameters of point absorbers were captured, including output flow rate in different seasons, extractable wave power, and output power. Accordingly, the obtained results indicate that the output flow rate and the power generation are significantly increased by incremental changes in wave height, and using this type of converter device has potential for practical and profitable use in industrial applications.

Comparison of Redox-Dependent H-Bonding in Simple, Electroactive Ureas Containing Either Ferrocene or Phenylenediamine Redox Couples – Similar Results with Different Mechanisms

An important goal in supramolecular chemistry is the design of stimuli-responsive supramolecular systems in which binding between components can be controlled by external signals. Supramolecular chemistry research in our group focuses in particular on using electron transfer to control the strength of H-Bonding interactions. In this presentation the redox-dependent H-bonding behavior of two simple phenylureas containing either a phenylenediamine redox couple, Figure 1a, or a ferrocene redox couple, FcUHH, Figure 1b, will be compared. The urea functional group provides two good H-donors (a DD array) which can be paired with two good H-acceptors (an AA array) in the PZD guest. Oxidation of either the ferrocene or phenylenediamine would be expected to increase the acidity of the attached urea NH, increasing the H-Bonding strength to PZD. Experimentally, this should result in a negative shift in the E1/2 of the cyclic voltammetric wave upon addition of PZD, with little change in wave shape or height. This behavior is indeed observed for both ureas in 0.1 M NBu4PF6/CH2Cl2. Plots of the ΔE1/2 of FcUHH vs [PZD] are fit well using a 1:1 binding isotherm, with initial results giving estimates of the binding constants to the oxidized and reduced forms as Kred = 80 M−1 and Kox = 500 M−1. The same type of experiments have been run with the phenylenediamine urea, UHH. The data also fits well to a simple 1:1 binding isotherm and gives similar values for the binding constants, Kred = 30 M−1 and Kox = 700 M−1. This is interesting because from our previous work1 we know that the electrochemistry is quite a bit more complex for UHH than FcUHH. In the former case the reversible, apparent 1 e− cyclic voltammetric (CV) wave observed in CH2Cl2 actually corresponds to 2 e− oxidation of half of the UHH’s to a quinoidal cation accompanied by proton transfer and electro-deactivation of the other half, Figure 1a. Given this, it is somewhat surprising that any potential shift is observed upon addition of PZD, since the oxidation product can only form a single H-bond with PZD. However, the key realization was that the other product, the protonated urea, can still form a 2 H-bond complex, and that should be stronger than the one formed with the starting urea due to the increased acidity of one of the urea NH’s. From this perspective, it is not surprising that we see such similar behavior between FcUHH and UHH. In the former, oxidation creates a +1 charge on one side of the urea (ferrocenium), Figure 1b, and, in the latter, proton transfer creates +1 charge, Figure 1a. This conclusion suggests an entirely new strategy to perturb H-bonding through electron transfer. Rather than doing this directly through oxidation/reduction introduced charges, it can also be done indirectly through oxidation-reduction induced proton transfer! 1 L. A. Clare, A. T. Pham, F. Magdaleno, J. Acosta, J. E. Woods and D. K. Smith, Journal of the American Chemical Society 2013, 135, 18930-18941. Figure 1

The impact of climate change on the wave climate in the Gulf of St. Lawrence

The purpose of this study is to investigate possible local changes in the wave climate for the coastal waters off eastern Canada, particularly in the Gulf of St. Lawrence (GSL) related to changes in marine winds, storm and the sea ice climate, due to climate change. These analyses are based on application of a dynamical downscaling approach whereby a regional climate model is driven by climate change estimates from the Canadian Global Climate Model (CGCM3) to provide relatively high resolution winds to drive a wave model. The CGCM3 simulation follows the A1B climate change scenario of the Special Report on Emission Scenarios from the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC AR4, 2007). The analyses of the wave climate are based on simulations of the waves from a third-generation wave model, WAVEWATCHIII™, and the downscaled winds obtained from the Canadian Regional (atmospheric) Climate Model (CRCM). We show that the significant wave heights in the Gulf of St. Lawrence (hereafter GSL) and neighboring coastal waters will slightly increase in the winter and decrease in the summer, in response to changes in storms and sea ice in the future climate (2040–2069) compared to the present wave climate, represented as 1970–1999. This time period is denoted as the “historical” wave climate in this study. In summer, the changes in significant wave heights (Hs) are associated with estimated decreases in the frequency of the occurrence of the cyclones. Projected changes in return values for summer extremes in the wave climate are consistent with the associated changes in the maximum Hs values. In winter, the projected increases in return values are mostly concentrated in the St. Lawrence Estuary, the northern and southwestern GSL, consistent with changes in the maximum waves in these regions. An important factor related to change in the winter wave climate is change in the sea ice.

Exploring changes in Caribbean hurricane-induced wave heights

During recent decades there has been open debate about a possible increase in the number and magnitude of more energetic hurricanes in the Atlantic, including their causes and implications. In this work, changes in extreme wave heights induced by hurricanes in the Caribbean Sea are analyzed. A non-stationary model is employed to study possible changes in the frequency of occurrence and magnitude of extreme waves from an hourly time series during the period of 1979–2012. The results indicate an increase in the occurrence of extreme wave events in the eastern and central Caribbean, and consequently, a positive long-term trend for 30yr return values. The zone of the highest trends is observed in the western basin in the middle of the Caribbean Sea towards the Gulf of Mexico. A final rate of approximately 2 events/year for 2012 is found throughout the Yucatan basin.

Effect of Sea Level Rise and Offshore Wave Height Change on Nearshore Waves and Coastal Structures

In 1994, Townend proposed a method to calculate the relative changes in various wave characteristics and structure-related parameters due to sea level rise for regular waves. The method was extended to irregular waves by Cheon and Suh in 2016. In this study, this method is further extended to include the effect of future change in offshore wave height and the sea level rise. The relative changes in wavelength, refraction coefficient, shoaling coefficient, and wave height in nearshore area are presented as functions of the relative changes in water depth and offshore wave height. The calculated relative changes in wave characteristics are then used to estimate the effect of sea level rise and offshore wave height change on coastal structures by calculating the relative changes in wave run-up height, overtopping discharge, crest freeboard, and armor weight of the structures. The relative changes in wave characteristics and structure-related parameters are all expressed as a function of the relative water depth for various combinations of the relative changes in water depth and offshore wave height.

The impact of wave energy converter arrays on wave-induced forcing in the surf zone

An alternative metric for assessing nearshore hydrodynamic impact due to Wave Energy Converter (WEC) arrays is presented that is based on the modeled changes in alongshore radiation stress gradients in the lee of the array. The metric is developed using a previously observed relationship between measured radiation stresses and alongshore current magnitudes. Next, a parametric study is conducted using the spectral model SWAN to analyze the nearshore impact of different WEC array designs. A realistic range of array configurations, locations, and incident wave conditions are examined and conditions that generate alongshore radiation stress gradients exceeding a chosen impact threshold on a uniform beach are identified. Finally, the methodology is applied to two permitted WEC test sites to assess the applicability of the results to sites with more realistic bathymetries. For these sites, the overall trends seen in the changes in wave height, direction, and radiation stress gradients in the lee of the array are similar to those seen in the parametric study. However, interactions between the wave field and real bathymetry induce additional alongshore variability in wave-induced forcing. Results indicate that array-induced changes can exceed the natural variability up to 15% of the time with certain array designs and locations.

Effectiveness of a compound defense system of sea embankment and coastal forest against a tsunami

The Great East Japan tsunami revealed the limits of using only a sea embankment for defense. Therefore, a compound defense system combining a coastal forest and sea embankment for a tsunami overflowing the embankment is proposed to mitigate damage. This study was conducted to clarify the changes in overflow volume from an embankment due to the location and thickness of a coastal forest. The effect of tree overturning was also investigated in relation to changes in wave height. A flume with a gate quickly lifted by air pressure to create an unsteady tsunami-like bore was used to investigate the changes in overflow volume and the reflection characteristics of various compound-defense models. The results show that a landward forest has the advantage of decreasing the fluid force behind the forest, and seaward forest can reduce overflow volume landward. Even when the sea-side forest is thin, the change in flow pattern in front of the embankment increases its total reflection and decreases the overflow volume by approximately 10%, although the forest itself does not increase the reflection. A thin seaward and overturned forest also decreases the overflow volume when the approaching tsunami height was less than the embankment height.

Long-Term Changes in the Extreme Significant Wave Heights on the Western North Pacific: Impacts of Tropical Cyclone Activity and ENSO

Seasonal extreme wave statistics were reproduced by using the 25-km-grid global wave model of WAVEWATCH-III. The results showed that the simulated wave dataset for the present climate (1979-2009) was similar to Climate Forecast System Reanalysis (CFSR) wave data. Statistics such as the root mean squared error (RMSE) and correlation coefficient (CC) over the western North Pacific (WNP) basin were 0.5 m and 0.69 over the analysis domain. The largest trends and standard deviation were around the southern coast of Japan and western edge of the WNP. Linear regression analysis was employed to identify the relationship between the leading principal components (PCs) of significant wave heights (SWHs) in the peak season of July to September and sea surface temperature (SST) anomalies in the equatorial Pacific. The results indicated that the inter-annual variability of SWH can be associated with the El Nino-Southern Oscillation in the peak season. The CC between the first PC of the SWH and anomalies in the Nino 3.4 SST index was also significant at a 99% confidence level. Significant variations in the SWH are affected by tropical cyclones (TCs) caused by increased SST anomalies. The genesis and development of simulated TCs can be important to the variation in SWHs for the WNP in the peak season. Therefore, we can project the variability of SWHs through TC activity based on changes in SST conditions for the equatorial Pacific in the future.

Seasonal and interannual changes of significant wave height in shelf seas around India during 1998–2012 based on wave hindcast

Present study examines the interannual changes of significant wave height (Hs) in shelf seas around Indian mainland based on the 15-year (1998–2012) wave hindcast data obtained from numerical model. Validation of the hindcast data with buoy-measured data shows that hindcast Hs is reasonably in good agreement with the observation (Pearson correlation coefficient values of 0.92–0.97). Annual average Hs varied from 0.9 to 1.4 m and the wave heights are higher (∼20%) in western shelf seas compared to eastern shelf seas. The analysis reveals seasonal fluctuations of wave climate, with a strong influence of Asian summer monsoon in the western shelf seas compared to the eastern shelf seas of India. Maximum Hs varied from 3.65 to 7.36 m and these maximum values were during the tropical cyclones. During 1998 to 2012, a statistically significant positive trend of 0.8–1.4 cm yr−1 in annual mean Hs is observed and the increasing trend is higher (∼0.7–2.5 cm yr−1) during the Asian summer monsoon period (June–September). The average trend of annual mean wind speed is also positive and is higher (∼1.67 cm s−1 yr−1) for the western shelf seas than that for eastern shelf seas (∼0.93 cm s−1 yr−1).

Do wave heights and water levels increase ocean lifeguard rescues?

ObjectiveTo investigate the association of wave height and tidal water level changes with the frequency of ocean lifeguard rescues. MethodsAll ocean lifeguard rescues recorded by Newport Beach Lifeguards in 2015 and 2016 were linked by time and location to weather and ocean variables contained in other historical databases. We performed separate multivariable analyses using mixed effects negative binomial regression to evaluate the total effects of wave height, mean water level (primarily set by tidal elevation), and rising vs. falling water level, on the frequency of ocean rescue in the study location, controlling for confounding variables. ResultsNewport Beach Lifeguards made 8046 rescues during the study period. In all areas of the beach, rescue frequency increased as waves got larger (IRR: 3.25; 95%CI: 2.91–3.79) but then decreased in large surf (IRR: 0.52; 95%CI: 0.37–0.73). In two sections of beach, lifeguards made more rescues during lower water levels, but in the third section of beach, made more rescues during higher water levels. Rescue frequency increased in two sections of beach with rising water levels, but did not in the other section. ConclusionsWave height, water level, and water level direction were associated with rescue frequency, but the environmental factors included in the analysis did not fully account for most variation in rescue frequency. Other factors need to be evaluated to identify major determinants of rescue frequency.

The 2004 Sumatra tsunami in the Southeastern Pacific Ocean: New Global Insight from Observations and Modeling

AbstractThe 2004 Sumatra tsunami was an unprecedented global disaster measured throughout the world oceans. The present study focused on a region of the southeastern Pacific Ocean where the “westward” circumferentially propagating tsunami branch converged with the “eastward” branch, based on data from fortuitously placed Chilean DART 32401 and tide gauges along the coast of South America. By comparison of the tsunami and background spectra, we suppressed the influence of topography and reconstructed coastal “spectral ratios” that were in close agreement with a ratio at DART 32401 and spectral ratios in other oceans. Findings indicate that even remote tsunami records carry spectral source signatures (“birth‐marks”). The 2004 tsunami waves were found to occupy the broad frequency band of 0.25–10 cph with the prominent ratio peak at period of 40 min related to the southern fast‐slip source domain. This rupture “hot‐spot” of ∼350 km was responsible for the global impact of the 2004 tsunami. Data from DART 32401 provided validation of model results: the simulated maximum tsunami wave height of 2.25 cm was a conservative approximation to the measured height of 2.05 cm; the computed tsunami travel time of 25 h 35 min to DART 32401, although 20 min earlier than the actual travel time, provided a favorable result in comparison with 24 h 25 min estimated from classical kinematic theory. The numerical simulations consistently reproduced the wave height changes observed along the coast of South America, including local amplification of tsunami waves at the northern stations of Arica (72 cm) and Callao (67 cm).

Extreme coastal erosion enhanced by anomalous extratropical storm wave direction

Extratropical cyclones (ETCs) are the primary driver of large-scale episodic beach erosion along coastlines in temperate regions. However, key drivers of the magnitude and regional variability in rapid morphological changes caused by ETCs at the coast remain poorly understood. Here we analyze an unprecedented dataset of high-resolution regional-scale morphological response to an ETC that impacted southeast Australia, and evaluate the new observations within the context of an existing long-term coastal monitoring program. This ETC was characterized by moderate intensity (for this regional setting) deepwater wave heights, but an anomalous wave direction approximately 45 degrees more counter-clockwise than average. The magnitude of measured beach volume change was the largest in four decades at the long-term monitoring site and, at the regional scale, commensurate with that observed due to extreme North Atlantic hurricanes. Spatial variability in morphological response across the study region was predominantly controlled by alongshore gradients in storm wave energy flux and local coastline alignment relative to storm wave direction. We attribute the severity of coastal erosion observed due to this ETC primarily to its anomalous wave direction, and call for greater research on the impacts of changing storm wave directionality in addition to projected future changes in wave heights.

Simulating Wave Climate Fluctuation in the Bohai Sea Related to Oscillations in the East Asian Circulation Over a Sixty Year Period

ABSTRACT Huiru, R.; Guosheng, L.; Linlin, C.; Yue, Z., and Ninglei, O., 2017. Simulating wave climate fluctuation in the Bohai Sea related to oscillations in the East Asian circulation over a sixty year period. Wave climate in the Bohai Sea from 1950 to 2011 was simulated with the Simulating Waves Nearshore model. Results showed that the following: (1) The significant wave height decreased; wave direction and wave period all increased in the past 62 years; the average decrease in significant wave height was 0.3 cm/y, and the increase in the wave angle was 0.12°/y. (2) The abrupt change of significant wave height occurred around 1968; the abrupt change of wave direction occurred around 1960. The characteristics of wave climate were affected by a complicated long-term process of the East Asian circulation. Four patterns for the effects of the East Asian circulation on the wave climate in the Bohai Sea were found by analysing the variation in the summer significant wave height and correlations of the signifi...

Modelling of a flap‐type wave energy converter farm in a mild‐slope equation model for a wake effect assessment

It is expected that large farms of wave energy converters (WECs) will be installed and as part of the consenting process it will be necessary to quantify their impact on the local environment. The objective of this study is to assess the impact a WEC farm has on the incoming wave field through the use of a novel methodology. This methodology assesses the changes of the significant wave height surrounding a flap-type WEC farm with a special focus on the lee of the farm. A time-dependent mild-slope equation model is employed to solve the propagation of surface waves and their interaction with the devices. The model represents the devices as obstacle cells with attributed absorption coefficients tuned against near-fields obtained from a boundary element method (BEM) solver. The wake effect of the farm is determined by using a step-by-step approach starting first with an assessment of one device and progressively incrementing to a larger number of flaps. The effect of incident sea states, device separations and water depth changes on the wake effect of the farm is also investigated. This work shows the potential of a WEC farm to reduce significant wave heights on the leeside.