Wave Conditions Research Articles

Nearshore Flow Dynamics Over Shore‐Oblique Bathymetric Features During Storm Wave Conditions

AbstractShore‐oblique bathymetric features occur around the world and have been statistically correlated with enhanced shoreline retreat on sandy beaches. However, the physical mechanisms that explain a causal relationship are not well understood. In this study, radar remote sensing observations and results from a phase‐resolved numerical model explore how complex morphology alters nearshore hydrodynamics. Observations at selected times during high‐energy storm events as well as a suite of idealized simulations indicate that shore‐oblique features induce strong spatial variations in the water surface elevation, wave breaking patterns, and mean current pathways. Re‐emergent offshore flows and longshore current accelerations occur near the shoreward apex of the oblique nearshore features. The results suggest that complex bathymetric morphology exerts a powerful control on nearshore hydrodynamics and increases the potential for enhanced cross‐shore and alongshore sediment transport.

Quality Enhancement of MIROS Wave Radar Data at Ieodo Ocean Research Station Using ANN

Remote sensing wave observation data are crucial when analyzing ocean waves, the main external force of coastal disasters. Nevertheless, it has limitations in accuracy when used in low-wind environments. Therefore, this study collected the raw data from MIROS Wave and Current Radar (MWR) and wave radar at the Ieodo Ocean Research Station (IORS) and applied the optimal filter by combining filters provided by MIROS software. The data were validated by a comparison with South Jeju ocean buoy data. The results showed it maintained accuracy for significant wave height, but errors were observed in significant wave periods and extreme waves. Hence, this study used an artificial neural network (ANN) to improve these errors. The ANN was generalized by separating the data into training and test datasets through stratified sampling, and the optimal model structure was derived by adjusting the hyperparameters. The application of ANN effectively improved the accuracy in significant wave periods and high wave conditions. Consequently, this study reproduced past wave data by enhancing the reliability of the MWR, contributing to understanding wave generation and propagation in storm conditions, and improving the accuracy of wave prediction. On the other hand, errors persisted under high wave conditions because of wave shadow effects, necessitating more data collection and future research.

Laboratory investigations of wave-induced transport of plastic debris over a rippled bottom

Laboratory experiments are conducted in a wave flume to investigate the effect of water waves on the transport of plastic pellets over a rippled bottom. The horizontal velocities of plastic debris are analyzed over the rippled bottom for different wave conditions and plastic elements with different properties. Laboratory investigations determined the characteristic transport patterns of wave-induced plastic debris with a density of ∼2.0g/cm3 moving along the rippled bottom. In the first, swing-type motion, the grains move only in the ripple trough with velocities lower than 0.10 m/s. For sliding-type movement, the grains move along the entire rippled surface with velocities in the range of 0.10–0.13 m/s. For higher velocities in the range of 0.15–0.20 m/s, a saltation-type motion becomes dominant. The results show that plastic grains may move up to 2–3 cm above the ripple crest depending on hydrodynamic conditions. The analysis shows that for velocity-skewed flows, sliding-type motion and onshore transport dominate. For acceleration-skewed flows, saltation-type motion and offshore transport dominate, which is attributed to higher boundary layer thickness and phase lag effects. The analysis of the relationship between the particle Reynolds number and the thickness of the turbulent boundary layer reveals that for values of Rep≥1000 and a boundary layer thicknessδ≥50 mm saltation-type motion becomes dominant. The direction of transport is affected not only by the density of the sediment and the wave skewness coefficients but also by the dimensions of the bottom ripples. The laboratory investigations also provide insight into the hydrodynamic conditions affecting the transport of plastic debris along the bottom covered with ripples in oscillating nonlinear water flows.

Hydrodynamic Performance Assessment of Emerged, Alternatively Submerged and Submerged Semicircular Breakwater: An Experimental and Computational Study

Coastal protection structures are essential defenses against wave energy, safeguarding coastal communities. This study aims to refine coastal protection strategies by employing a semicircular breakwater (SBW) model. Through a combination of physical and computational models, the hydrodynamic properties of the SBW under regular wave conditions were thoroughly examined. The primary objectives included delineating the hydrodynamic characteristics of SBWs, developing a computational model to validate experimental findings. Hydrodynamic characteristics of the SBW model were scrutinized across various wave conditions. Experimental testing in a wave flume covered a range of relative water depths (d/h) from 0.667 to 1.667, wave steepness (Hi/L) spanning 0.02 to 0.06 and wave periods ranging from 0.8 to 2.5 s. Notably, analysis of an emerged SBW with d/h = 0.667 revealed superior wave reflection, while an alternative submerged SBW with d/h = 1.000 showed the highest energy loss. These findings are further corroborated by the validation of computational models against experimental outcomes for d/h = 0.667, 1.000, 1.333 and 1.667. Moreover, the investigation of forces revealed an inverse correlation between horizontal forces and wave height, while vertical forces showed nuanced variations, including a slightly decreasing average vertical force with greater relative wave period (B/L) for different immersion scenarios.

Optimization of Submerged Breakwaters for Maximum Power of a Point-Absorber Wave Energy Converter Using Bragg Resonance

This study focused on optimizing the power generation of a heaving point-absorber wave energy converter (HPA-WEC) by integrating submerged breakwaters. An optimization analysis was conducted based on a framework developed in the authors’ previous work, aiming to maximize the capture width ratio (CWR) by inducing Bragg resonance. Numerical simulations were conducted using a two-dimensional frequency domain boundary element method (FD-BEM) under irregular wave conditions. Advanced particle swarm optimization (PSO) was used for the optimization, with design variables that included the power take-off (PTO) damping coefficient, spring constant, and position and shape of the submerged breakwaters. The results showed that the CWR almost doubled when two breakwaters were used compared with the case without breakwaters. The CWR significantly increased, even with only one breakwater installed behind the WEC. A coastal stability analysis showed that installing two breakwaters provided the best performance, reducing the transmitted wave energy by approximately 25%. Furthermore, the CWR reached its maximum when the distance between the breakwater endpoints equaled the wavelength of the peak wave frequency, indicating the occurrence of Bragg resonance. This study underscores the potential of submerged breakwaters in enhancing power generation and coastal stability in the design of HPA-WECs.

Converting evanescent waves into propagating waves by hyper-hemi-microsphere

Hyper-hemi-microspheres (HHMS) have shown promise in enhancing super-resolution imaging when combined with conventional optical microscopy. To offer actionable guidance for optimizing HHMS and hold broad applicability in the field of super-resolution imaging, the mechanism underpinning the enhanced imaging facilitated by HHMS is revealed by deriving the conversion and transmission conditions for evanescent waves. This is achieved by elucidating the intricate interplay between evanescent wave conversion and factors including refractive index, thickness, and surroundings of HHMS. Using the finite-difference time-domain (FDTD) method, influences of various HHMS properties on the conversion and transmission process are analyzed in detail. To fully harness the potential of HHMS in super-resolution imaging, the immersion conditions are elucidated.

Hybrid Torque Coefficient Control of Average-to-Peak Ratio for Turbine Angular Velocity Reduction in Oscillating-Water-Column-Type Wave Energy Converter

Wave energy converters (WECs) have significant potential to meet the increasing energy demands and using an oscillating water column (OWC) is one of the most reliable ways to implement them. The OWC has a simple structure and excellent durability. However, control of the power take-off (PTO) system is difficult due to variability in the input wave energy. In particular, the design and control of the PTO system are complex, as the average-to-peak ratio of the output generation is large. Owing to the nature of the OWC, if the energy above the rating cannot be controlled, the power generated is inevitably reduced due to the decrease in operating time. We propose a method to reduce the angular speed of the turbine by dividing the section according to the input energy and correspondingly changing the torque coefficient, thereby increasing the operating time of the OWC. The control methods for the PTO system of OWC are verified through a 30 kW full-scale experimental device to be installed in a real sea area. The full-scale experimental device consists of an inverter that simulates the mechanical torque of an OWC based on the aerodynamic simulation of an impulse turbine, an induction motor, a permanent magnet synchronous generator, an AC/DC converter, and a battery for the energy storage system. The performance of conventional control methods and the proposed method are compared based on the results of numerical simulations and experiments. We show that the fluctuation in the turbine angular velocity in the proposed method is significantly reduced compared with that in the conventional control methods under regular and irregular wave conditions.

Numerical modelling of the spatial distribution of wave overtopping water behind dikes under regular wave action using OpenFOAM

The spatial distribution of wave overtopping water behind dikes is a key parameter for assessing the safety zone behind dikes in coastal areas, and it is essential for the safety of pedestrians behind dikes and the placement of critical infrastructure. A 2D OpenFOAM numerical model is validated using experimental data for predicting overtopping discharges and the spatial distribution of wave overtopping water behind a dike. The influences of slope angle, berm, landward ground level, relative structure freeboard, and product of incident wave height and wavelength are studied using a validated numerical model. Numerical model outcomes indicate that the lower slope angle has a critical value that is to be determined by the breaker parameter. Tests were conducted for a range of breaker parameters, including structure freeboard, and empirical-based predictive equations were derived for overtopping events under different wave conditions. We also found that the extent of the hazard area due to wave overtopping is significantly reduced when the landward ground level is negative. The findings of this study provide data and predictive formulas for assessments of the hazard zones behind the dikes and indicate the capability of numerical models in the design and safety assessment of dikes.

Experimental study on wave-induced loads and nonlinear effects for pier-pile group foundations of sea-crossing bridges: Wave slamming and suction effect

Strong nonlinear effects, such as wave slamming, suction effects, and wave overtopping, may be induced during wave-bridge interaction. However, an accurate understanding of these nonlinear effects is still insufficient. This study comprehensively investigates the wave slamming and suction effects on pier-pile group foundations of sea-crossing bridges in a 1:50 scale laboratory experiment. Random and regular waves with different strengths are generated based on wave conditions at the bridge site. Five water depths with a 2 cm spacing are designed to simulate varying pile cap clearances. Various pile arrangements are also set up to explore the influence of piles. Results show that wave slamming is low-aeration and is triggered mainly on the cap bottom wall, whereas the wave action on the vertical wall of the pile cap is quasi-static. The suction effect is generally recorded in the quasi-static phase of pressures and depends on the water exit process and the wave crest height. Moreover, the pressure oscillation after the impact phase results from the flow separation and rotation at structure corners. The wave slamming enhances with the increasing wave frequency when the impact area is constant, otherwise, it depends on the impact area. On the cap bottom wall, the wave slamming on inter-pile areas is enhanced, but the suction effect is less affected by pile arrangements. The increase in pile cap clearances reduces vertical forces but has less effect on horizontal forces. Additionally, a sustained increase in the wave crest height may reduce the slamming force. An empirical method for predicting wave forces is finally proposed based on the water entry theory and experimental findings. This work enhances the physical understanding of nonlinear effects during wave-bridge interaction and aims to support the design of substructures for sea-crossing bridges.

A numerical study on a winglet floating breakwater: Enhancing wave dissipation performance

Box-type floating breakwaters (FBs), widely used for marine protection, face challenges in their wave dissipation capabilities. Although the effectiveness of the winglet-type floating breakwater in improving wave dissipation has been recognized, the specific mechanisms involved are not fully understood. This research presents an innovative winglet breakwater design, featuring three unique winglet configurations: 4-wings, Down-wings, and Up-wings. The study examines its performance against both regular and irregular waves using the Smooth Particle Hydrodynamics (SPH) method, taking into account factors such as the wave period, FB immersion depth, and FB relative density. Numerical simulations indicate a marked enhancement in wave dissipation for the FB equipped with four winglets compared to a baseline model without winglets. The Response Amplitude Operator (RAO) amplitude for the winglet-equipped FB is notably lower, approximately half that observed in the baseline scenario. Notably, the winglet FB's performance in irregular waves outperforms that in regular wave conditions. The insights gained from the design of these winglets provide significant contributions to practical engineering applications.

Enhancing Hydrodynamic Performance of Floating Breakwaters Using Wing Plates

Understanding the dynamic response of floating breakwaters to wave forces is essential for optimizing their design and improving coastal protection. The response amplitude operator serves as a key parameter in accurately predicting the structural response amplitudes at different frequencies and wave angles. By incorporating this knowledge, adjustments can be made to enhance the effectiveness of floating breakwaters. In this study, a comprehensive 3D model of the mooring system is developed to simulate its behavior under various wave and current conditions. The model takes into account critical design factors such as pontoon shapes, anchor types, placements, and configurations. Through simulations, valuable insights are obtained regarding the performance of the wing-plate floating breakwater mooring system across different operational settings. These findings contribute to the optimization of floating breakwaters and their ability to protect coastlines from wave impacts.

Response Extremes of Floating Offshore Wind Turbine Based on Inverse Reliability and Environmental Contour Method

Floating structures are subject to complex marine conditions. To ensure their safety, reliability analysis needs to be conducted during the design phase. However, because of the complexity of traditional full long-term analysis, the environmental contour method (ECM) based on the inverse reliability method, which can combine accuracy and efficiency, is extensively used. Due to the unique environment in the South China Sea, the probabilistic characteristics of three-dimensional (3D) environmental parameters of wind, wave and current are investigated. The ECs of the target sea are established via the ECM based on both the inverse first-order reliability method (IFORM) and inverse second-order reliability method (ISORM). It is found that the sea state forecasted by ISORM is more extreme and may lead to a more conservative design than IFORM. Furthermore, the wind–wave–current combination coefficient matrixes developed using the 3D ECs are proposed for the design of FOWTs in the South China Sea. The validity and practicality of the contours and matrixes are tested by using a floating offshore wind turbine (FOWT) as a numerical example. Then, the short-term response of the structure under the combined wind, wave and current conditions is calculated, providing a theoretical reference for the design of FOWTs.

Seagrass as a nature-based solution for coastal protection

Our coasts are facing a growing threat from rising sea levels and detrimental storm events. Nature-based solutions are gaining interest for their potential to provide multiple ecosystem services, including coastal protection. Seagrass can influence coastal sediment transport and wave propagation, however, whether seagrass can be used as an effective intervention for coastal protection is unclear. Using the Delft3D model, this study looks at how seagrass affects coastal hydrodynamics in a macrotidal bay, under idealised scenarios that simulate a rise in sea level and storm wave heights, emulating projected sea conditions under climate change. Through the use of a habitat suitability model, a seagrass patch in Morecambe Bay was simulated, based on a location within the bay that is most suitable for seagrass species Zostera marina. Hydrodynamic simulations were run for a number of scenarios for a domain with and without a seagrass patch. Scenarios included variable boundary wave heights, sea levels and vegetation parameters, to test the influence of seagrass in future climates. Results show that there is a reduction in mean and maximum wave height inside and behind the seagrass patch, with the largest changes in wave dissipation observed during higher boundary wave conditions. In these conditions the maximum wave height reduced by over a half within the patch. Simulations examining the influence of seagrass density and canopy height found that a lower density seagrass patch reduced maximum wave height more substantially than higher density patches. Although alternative hard engineered solutions are able to attenuate wave energy more effectively than seagrass, these results demonstrate seagrass could play an important role in conjunction with salt marsh restoration or existing hard engineering solutions, helping to mitigate the risk of flooding and erosion, whilst providing additional ecosystem services such as carbon sequestration and habitat provision.

Impacts of regular head waves on thrust deduction at model self-propulsion point

The results obtained from the self-propulsion simulations using Computational Fluid Dynamics (CFD) in the current study, for a ship free to heave, pitch and surge with the means of a weak spring system, are combined with the formerly executed CFD results of the bare hull and propeller open water simulations to investigate the impacts of regular head waves on the propeller-hull interactions in comparison to calm water, at the self-propulsion point of the model. Despite a rather significant dependency of the nominal wake on the wave conditions, the Taylor wake fraction remains almost unchanged in different studied waves which is around 12% lower than the calm water value. The thrust deduction factor in waves is reduced (12.8%–26.1%) in comparison to the calm water value. The change of thrust deduction factor is found to be associated with the boundary layer contraction/expansion and vortical structure dynamics, originating from the wave orbital velocities as well as the significant shaft vertical motions and accelerations that resulted in a modified propeller action, and consequently diminished suction effect on the aft ship. The altered thrust deduction factor and wake fraction in waves in comparison to calm water underlines the significance of waves on the propulsive factors and propeller design.

Expression analysis of Hsp70 genes in the psychrophilic yeast, Glaciozyma antarctica PI12 as biomarkers for thermal stress during heat waves

Heat shock proteins 70 (Hsp70) are potential thermal stress markers as they play a pivotal role in safeguarding cells against heat shock-induced damage. The Hsp70s are present in several variants with each containing its peculiar importance due to their specific functions such as cell protection during elevated thermal stress. The present investigation evaluated the gene expression profiles of all Hsp70 genes in Glaciozyma antarctica PI12 during a heat wave condition. In this study, we exposed G. antarctica PI12 cells to a realistic heat wave to understand the impacts of the extraordinary, unprecedented heat waves that hit Antarctica at nearly 40°C above the average in 2022. The experiment was carried out through eight days where cells were exposed gradually at 0, 2, 4, 8, 12, 16, 20, 25 and 30°C. The gene expression profiles were obtained during the simulated heat wave along with non-stressed control treatments by real-time PCR. Out of the six Hsp70 genes in G. antarctica PI12, five were expressed under the conditions tested. Among the expressed genes, gahsp70-1, gahsp70-5, and gahsp70-6 showed significant upregulation. Specifically, their expression levels increased by five- to eightfold after exposure to heat shock at 4°C. Gene expression patterns at 20°C and 30°C also showed induction with the highest at 3.6 folds and 5.8 folds, respectively. These results indicate that the expression of Hsp70 genes in G. antarctica PI12 was inducible under thermal stress, indicating their importance in cells during the heat waves. These results conclude that the gene expression patterns of Hsp70 during heat waves contribute vital information on thermal adaptation in the Antarctic marine ecosystem under climate stress.

A self-powered smart wave energy converter for sustainable sea

Self-powered smart buoys are widely used in sustainable sea, such as marine environmental monitoring. The article designs a self-powered and self-sensing point-absorber wave energy converter based on the two-arm mechanism. The system consists of the wave energy capture module, the power take-off module, the generator module and the energy storage module. As the core component of the wave energy converter, the power take-off module is mainly composed of a two-arm mechanism, which can convert the oscillation heave motion into unidirectional rotary motion. To evaluate the power generation performance of the system, the kinematic and dynamic models of the wave energy converter with the flywheel are established, and the disengagement and engagement phenomena of the flywheel are analyzed. The effectiveness of the prototype in capturing wave energy is verified through dry experiments in lab and field tests. The dry experiment reveals that the maximum output power of the system is 5.67 W, and the maximum and average mechanical efficiency are 66.63 % and 48.35 %, respectively. Additionally, the field test demonstrates that the peak output power can reach 92 W. Meanwhile, the generated electrical signals can be processed by deep learning algorithms to accurately identify different wave states. This high performance confirms that the proposed wave energy converter can meet its own energy needs by capturing wave energy in the marine environment, while also achieving self-sensing for wave condition monitoring. The system has great potential for promoting the development of intelligent sustainable sea in the future.

Regulating flow to maximize riverine nitrogen removal by riparian zones downstream of reservoirs

Flood waves generated by reservoir discharge play a crucial role in the potential for riparian denitrification downstream. The efficiency of nitrogen (N) removal from river water by riparian zones is typically enhanced with greater wave amplitude (A) and duration (T). However, a knowledge gap exists with respect to the impact of flood waves on N removal when considering a fixed-value integral over time of flood waves (IOFW). This study explored N transport and transformation in the riparian zone downstream of the dammed Inbuk River, Korea under various wave conditions with a fixed IOFW. The results revealed a logarithmic enhancement in solute infiltration into the riverbank with an increasing wave amplitude/duration ratio (A/T ratio). The solute residence time within the riparian zone displays an initial increase followed by a decrease with the increment in the A/T ratio. We identified a threshold for the wave A/T ratio that maximizes riverine N removal by the riparian zone, a phenomenon observed across various dammed rivers. Our findings indicated that riparian denitrification is reaction time-limited when the wave A/T ratio exceeds the threshold; contrarily, it becomes transport capacity-limited. Additionally, we observed a significant relationship between the net nitrate removal and the return/infiltration time ratio of water (r2 = 0.93, p < 0.05). The research results contribute to a better understanding of the impact of water level fluctuations on the N cycle in riparian zones, and provide valuable insights for developing sustainable reservoir operation strategies.

Regional evaluation of simulated waves during tropical storm events in the Gulf of Mexico

High waves in the Gulf of Mexico are mainly originated in tropical cyclones and winter storms. The availability of accurate estimations of high wave characteristics is an essential prerequisite for marine spatial planning, coastal zone management, and marine developments over the Northeastern Gulf of Mexico (NeGoM). Moreover, accurate wave simulation relies upon accurate wind field estimations. The wind field data used as input for numerical wave models is typically obtained from global and regional atmospheric model outputs. However, these model outputs may exhibit higher bias relative to observations, especially during fast-traveling tropical weather events. This study evaluates wave sensitivity over the NeGoM to different input wind speed and direction sources using unstructured SWAN model simulations. Five wind data products were employed in this study from ECMWF and NCEP global and regional models to examine the impact of wind forcing on wave simulations. The quality of wind field input data from these sources was evaluated relative to available observations (wind speed and direction) at National Data Buoy Center stations. A detailed sensitivity analysis is carried out to determine optimal wave model configuration. The model's performance is evaluated by comparing its wave simulation results with observational data during selected periods, simultaneously assessing the quality and sufficiency of wind data inputs from various sources. Our study shows that wind fields from FNL and NAM datasets are better correlated with observational data, in terms of vector correlation. Simulations using ECMWF – Real-Time product, combined with Janssen white-capping scheme better estimate wave conditions over the NeGoM compared with the other wind forcings used in this study. Moreover, Janssen white-capping scheme seems to be more realistic for estimations during Hurricane Michael; while for Hurricane Ida, Janssen generation scheme tends to overestimate the wave heights and Komen provides more accurate results.

Calibration of wave-induced high-frequency dynamic response and its effects on the fatigue damage of floating offshore wind turbine

There is a demand to calibrate the high-frequency dynamic responses of semi-submersible floating offshore wind turbine (FOWT) induced by the second-order sum-frequency hydrodynamic loads in the numerical model and evaluate its effects on the fatigue damage of the FOWT. A modification approach for the calibration of the high-frequency dynamic responses of FOWT is proposed. In this approach, the effects of the viscous damping and additional restoring force on the second-order sum-frequency quadratic transfer functions (QTFs) are discussed in the frequency domain. The calibrated numerical model (CNM) is obtained with the tuned viscous damping, the second-order sum-frequency QTFs, and the structural damping, based on the measured data from the FOWT model test. The CNM is proved to accurately predict the high-frequency components of the strongly nonlinear responses, namely the pitch motion and tower-top shear force, with the proper prediction of the wave-frequency responses compared with the experimental model under regular wave conditions. The CNM is further applied to predict the high-frequency dynamic responses of the OUCwind under a typical sea state for an operational condition. It is found that the high-frequency component occupies a non-negligible part of the pitch motion, and dominates the tower-top shear force. The linear model (LM) cannot predict and the uncalibrated numerical model (UCNM) underpredicts the high-frequency components of responses. Furthermore, the fatigue damage of the CNM is 14 times greater than that of the LM after a 3 h sea state with a significant wave height of 3 m and a peak period of 6 s. It follows that the large frequency and intensity make the high-frequency tower-top shear force to be a huge risk to the safe operation of the wind turbine, which should attract the industry’s concern about the wave-induced high-frequency dynamic responses for the design of FOWTs.

Introducing bimodal sea-states in a hybrid model for nearshore wave processes

HySwash has been recently developed as a fast and effective hybrid method to predict nearshore wave processes under unimodal wave conditions. However, global wave climates, and especially those in the tropical regions where coral reefs are hosted, are usually exposed to multiple incoming wave systems, resulting in several energy peaks corresponding to coexisting swells and wind seas. Moreover, although the full distribution of wave runup can have a significant impact on the assessment of vulnerable low-lying tropical regions, predictive models of flooding usually synthesize wave runups to an extreme percentile value, overlooking its full distribution. To enhance the capabilities of HySwash, in the present work, the inclusion of bimodality, as well as the prediction of the complete wave runup distribution is presented. This involves adapting the sampling, selection, and interpolation algorithms together with the hydrodynamic modeling that constitutes the original HySwash methodology. The positive mathematical validation reinforces the applicability of HySwash for a variety of coastal applications. Furthermore, a comparison is conducted between extreme wave runups induced by bimodal sea states and unimodal sea states, providing insights into the impact of multimodality on wave runup extremes.