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Breaking‐wave induced bioluminescence is a critical component of the biogeochemical process in the ocean. Understanding bioluminescence is important for monitoring red tides caused by bioluminescent microorganisms. In this study, we present the first numerical effort to quantify bioluminescent light intensity based on high‐fidelity direct numerical simulations of breaking waves and a quantitative bioluminescent model. The dynamics of breaking waves are extensively validated through comparison with existing studies. We find that the time‐averaged and Lagrangian‐averaged shear stress saturates as surface tension effects decrease and wave steepness increases. The spatial distribution of light intensity correlates with the wave crest overturning and air bubbles generated in plunging breakers. Furthermore, we observe that the maximum light intensity asymptotically approaches the emission of single cells, suggesting the potential for cost‐effective prediction models in future studies. Plain Language Summary: Marine microorganisms, such as dinoflagellates, flash when stimulated by mechanical forces caused by breaking waves. Understanding this phenomenon, also known as the 'blue tears' of ocean, is helpful for predicting 'red tides', a hazardous algal blooms caused by dinoflagellates. We use computer simulations to determine how much light is emitted when breaking waves stimulates bioluminescence. Our analysis show that there is an upper limit for the level of the mechanical force in breaking waves. We also find that the maximum bioluminescence light intensity is similar to that emitted by a single cell. Key Points: A numerical framework is developed to quantify bioluminescence stimulated by ocean surface breaking wavesThe time‐averaged and Lagrangian‐averaged shear stress saturates as surface tension effects decrease and wave steepness increasesMaximum bioluminescent light intensity asymptotically approaches single cell emission at the time of flashing [ABSTRACT FROM AUTHOR]

In the present work, the conservative phase-field lattice Boltzmann model is applied to simulate plunging breakers in shallow waters. The solver is computationally efficient as it is explicit in time stepping and does not require a solution for the pressure Poisson equation. Nevertheless, the solver can simultaneously handle a large Reynolds number ( $ =10^4 $ = 10 4 ) and a high-density ratio of 1000. Simulations are performed by varying initial steepness and dispersion parameters, which influence the nonlinearity degree of wave (or the growth speed of instability) and the oscillatory motion (limited by the bottom) on the breaking characteristics. Detailed analyses of kinematics, air entrainment, vorticity, and energy dissipation are presented. [ABSTRACT FROM AUTHOR]

Semi-enclosed, fetch-limited waters create unique conditions for wind wave development and breaking. Parameters of breaking waves influence bubble entrainment depth and associated noise, which is why they differ in semi-enclosed sea compared to open waters. While the established noise-wind speed relationship holds in oceanic conditions, it differs in land-constrained basins like the Baltic Sea. To explore noise level, bubble entrainment depth and wind speed relationships, we conducted noise and sub-surface bubble measurements, coupled with wind observations, in the selected area of the Baltic Sea during two consecutive summers. A novel method was employed to estimate bubble entrainment depth under conditions of strong backscatter. Model data of wave field parameters were employed to assess their influence on noise level and bubble entrainment depth. Results suggest stronger connections between noise level and wind speed, as well as wave height, compared to wave age and wind sea steepness. The same patterns hold true for the correlation between bubble entrainment depth and both wind speed and wave field parameters. The parameterized noise level-wind speed relationship differs from that obtained for oceanic conditions and also varies across measurement periods. Observed differences were shaped by varying wind-wave conditions, notably differences in wind speed, direction, wave height, and the presence of swell. The noise level-bubble entrainment depth relation is reported for the first time for Baltic Sea conditions. For a thorough analysis of the influence of these factors on noise and bubbles, longer measurements under diverse wind-wave conditions are required to account for site-specific wave field characteristics.

A numerical model for the simulation of the performance of an oscillating water column (OWC) subjected to non-breaking and breaking waves is proposed in this paper. The numerical model consists of a hydrodynamic model specifically designed to simulate breaking waves and a pneumatic model that takes into account the air compressibility. The proposed numerical model was applied to evaluate the potential mean annual energy production from the waves of two coastal sites characterized by different hydrodynamic conditions: a deep-water condition, where the OWC interacts with non-breaking waves, and a shallow-water condition, where the OWC is subjected to breaking waves. The numerical results show that the effects of the air compressibility can be considered negligible only in numerical simulations of the performances of reduced-scale OWC devices, such as those used in laboratory experiments. We demonstrated that in real-scale simulations, the effect of the air compressibility within the OWC chamber significantly reduces its ability to extract energy from waves. The numerical results show that the effect of the air compressibility is even more significant in the case of a real-scale OWC located in the surf zone, where it interacts with breaking waves. [ABSTRACT FROM AUTHOR]

We examine the dependence of the penetration depth and fractional surface area (e.g., whitecap coverage) of bubble plumes generated by breaking surface waves on various wind and wave parameters over a wide range of sea state conditions in the North Pacific Ocean, including storms with sustained winds up to 22 m s−1 and significant wave heights up to 10 m. Our observations include arrays of freely drifting SWIFT buoys together with shipboard systems, which enabled concurrent high‐resolution measurements of wind, waves, bubble plumes, and turbulence. We estimate bubble plume penetration depth from echograms extending to depths of more than 30 m in a surface‐following reference frame collected by downward‐looking echosounders integrated onboard the buoys. Our observations indicate that mean and maximum bubble plume penetration depths exceed 10 and 30 m beneath the surface during high winds, respectively, with plume residence times of many wave periods. They also establish strong correlations between bubble plume depths and wind speeds, spectral wave steepness, and whitecap coverage. Interestingly, we observe a robust linear correlation between plume depths, when scaled by the total significant wave height, and the inverse of wave age. However, scaled plume depths exhibit non‐monotonic variations with increasing wind speeds. Additionally, we explore the dependencies of the combined observations on various non‐dimensional predictors used for whitecap coverage estimation. This study provides the first field evidence of a direct relation between bubble plume penetration depth and whitecap coverage, suggesting that the volume of bubble plumes could be estimated by remote sensing. Plain Language Summary: Quantifying the statistics of bubble plumes generated during ocean surface wave breaking is essential to understanding the exchange between the ocean and the atmosphere. Bubble plumes also cause important variations in underwater acoustics and optics. Recent studies also suggest that the statistics of bubble plumes are skillful predictors for total energy loss during wave breaking, which is an essential quantity for accurate wave forecasting. In this study, we examine how these bubble plume statistics change with different wind and wave conditions, including during storms. We used echosounders on drifting buoys to detect the bubbles and estimate how deep they go in the ocean. We also used shipboard camera systems to measure the surface area of the bubble plumes. We successfully develop multiple empirical relationships that allow us to predict how bubble plume depth and surface area change as a function of simple wind and wave statistics. These statistics are readily available from existing forecast models or typical ocean buoys. Our findings reveal that bubble plume depth is correlated with its visible surface area. This intriguing correlation suggests that we might estimate the volume of bubble plumes simply by observing the ocean surface from above. Key Points: Bubble plumes generated during ocean surface wave breaking are observed with echosounders on drifting buoysBubble plume depths are well correlated with whitecap coverage, wind speed, and spectral wave steepnessBubble plumes persist for many wave periods and exceed the persistence of visible surface foam [ABSTRACT FROM AUTHOR]

Internal solitary waves (ISWs) resonate with meter-scale surface waves, which causes crests to overturn and waves to break strongly, generating many whitecaps. We analyze the polarized SAR characteristics of ISWs based on nonpolarized scattering theory and polarization decomposition theory. The surface breaking waves induced by ISWs generate short-scale waves carrying Bragg waves on the one hand, which enhances the polarized Bragg scattering (PD) contribution at the decimeter or centimeter scale and generate additional nonpolarized scattering (NP) contribution through specular scattering on the other hand. The copolarized scattering intensity in ISW regions is always higher than that in unperturbed sea surface under both L and C bands, with higher PD and NP contributions. The average PD is 1.3 (1.7) times higher than that of the unperturbed sea surface, and the average NP is approximately 82% (165%) higher than that of the sea surface. The PD and NP values associated with the convergent zones are always larger than those associated with the divergent zones, indicating that breaking waves mainly occur in convergence. The results of $\bm{HA}\alpha$ decomposition show that the scattering mechanism of ISWs is surface scattering with reduced scattering entropy and mean scattering angle. We construct compact polarization based on fully polarized SAR, and extract polarization parameters that indicate increased degree of polarization at ISWs, which supports our inference of enhanced specular scattering.

Air‐entraining whitecaps provide an important source of bubbles over the global oceans, yet the rate at which the associated air is entrained is not well known. This lack of understanding limits the ability to accurately parameterize bubble‐mediated gas exchange and sea spray aerosol flux. In this paper I present a model to predict the total volume of air entrained by individual whitecaps and extend it to estimate the rate at which air is entrained per unit sea surface area. The model agrees well with existing models and measurements and can be forced by the rate at which energy is dissipated by the wavefield which can be routinely provided by spectral wave models. I then use the model to present the first distributions of the estimated total volume of air entrained by individual whitecaps, as well as their rate of air entrainment and air degassing. Plain Language Summary: The amount of air in the oceans in the form of bubbles at any given time is not well known because of the difficulty associated with making in‐situ measurements. This lack of knowledge inhibits how well ocean‐atmosphere exchange processes that are driven by air and bubbles can be represented in climate models. In this paper, I present a new model to estimate the volume of air entrained by individual breaking waves called whitecaps, as well as how quickly the air is entrained into the oceans and how quickly it leaves the oceans when bubbles rise to the surface and burst. Key Points: A model for the entrainment of air by oceanic whitecaps is presented which agrees well with existing models and measurementsDistributions of the estimated volume of air entrained by individual oceanic whitecaps are presented for the first timeKey uncertainties in the air fraction and entrainment velocities of individual whitecaps remain due to a lack of measurements [ABSTRACT FROM AUTHOR]

This paper aims to evaluate the impact of both regular and irregular breaking waves on elevated houses with various freeboard levels. Computational fluid dynamic (CFD) analysis was utilized, and numerical outputs were validated based on available experimental tests. The validated CFD results in terms of vertical impact forces were compared with existing empirical formulas to better understand the applicability and accuracy of current methods. Turbulence sensitivity analysis shows that buoyancy-modified k - ω shear stress transport ( SST) model can accurately predict breaking wave characteristics in terms of the water surface elevation and surface pressures. The CFD model can predict front and bottom positive pressures for all freeboard levels as well as high bottom negative pressures and subsequent negative vertical forces for the elevated house model with zero freeboard. Regarding regular breaking waves, for the house with zero freeboard, the maximum discrepancies between the experimental and numerical results for the maximum positive and negative pressures are about 8% and 14%, respectively. Regarding irregular breaking waves, horizontal and vertical forces agree well with experimental results, in which the minimum and maximum discrepancies are − 5% and + 18% associated with forces at 1/3 significant level ( F 1 / 3 ) and the mean level ( F mean ), respectively. However, existing empirical formulas cannot accurately predict the vertical impact forces acting on elevated buildings, which highlights the need for the development of new empirical formulas to account for uncertainty in the wave field and structural characteristics. The results of this study can not only help predict accurate horizontal and particularly vertical breaking wave loads, but the outcomes also assist in developing accurate theoretical fragility curves for elevated coastal buildings. [ABSTRACT FROM AUTHOR]

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The use of convolutional neural networks (CNNs) in image classification has become the standard method of approaching many computer vision problems. Here we apply pre-trained networks to classify images of non-breaking, plunging and spilling breaking waves. The CNNs are used as basic feature extractors and a classifier is then trained on top of these networks. The dynamic nature of breaking waves is exploited by using image sequences extracted from videos to gain extra information and improve the classification results. We also see improved classification performance by using pre-computed image features such as the Optical Flow (OF) between image pairs to create new models in combination with infra-red images with reduction in errors of up to 60%. The inclusion of this dynamic information improves the classification between breaking wave classes. We also provide corrections to a methodology in the literature from which the data originates to achieve a more accurate assessment of model performance. [ABSTRACT FROM AUTHOR]

Multidirectional irregular breaking wave is the most prominent feature of the ocean surface and bears tremendous amounts of sustainable high‐entropy energy. However, the commercial utilization and harvesting efficiency are very limited low due to its low‐frequency and low‐amplitude. Here, a swing self‐regulated triboelectric nanogenerator (SSR‐TENG) is proposed, which can convert collected low‐grade breaking waves energy into electrical energy by regulating the oscillation frequency and resonance effect. Benefiting from simple and efficient structural strategy, SSR‐TENG outputs a peak power of 0.14 mW under wave height range of 6–11 cm, that the open‐circuit voltage, short‐circuit current and transferred charge increases is 5.8, 4, and 3.7 times compared to without self‐regulated design, respectively. This work gives a practical solution to the problems faced by harvesting high‐entropy ocean breaking waves energy, which exhibits large potential for building the self‐powered ocean assessment and meteorology system in the future. [ABSTRACT FROM AUTHOR]

ABSTRACTThe use of convolutional neural networks (CNNs) in image classification has become the standard method of approaching many computer vision problems. Here we apply pre-trained networks to classify images of non-breaking, plunging and spilling breaking waves. The CNNs are used as basic feature extractors and a classifier is then trained on top of these networks. The dynamic nature of breaking waves is exploited by using image sequences extracted from videos to gain extra information and improve the classification results. We also see improved classification performance by using pre-computed image features such as the Optical Flow (OF) between image pairs to create new models in combination with infra-red images with reduction in errors of up to 60%. The inclusion of this dynamic information improves the classification between breaking wave classes. We also provide corrections to a methodology in the literature from which the data originates to achieve a more accurate assessment of model performance.

A numerical model for the simulation of the performance of an oscillating water column (OWC) subjected to non-breaking and breaking waves is proposed in this paper. The numerical model consists of a hydrodynamic model specifically designed to simulate breaking waves and a pneumatic model that takes into account the air compressibility. The proposed numerical model was applied to evaluate the potential mean annual energy production from the waves of two coastal sites characterized by different hydrodynamic conditions: a deep-water condition, where the OWC interacts with non-breaking waves, and a shallow-water condition, where the OWC is subjected to breaking waves. The numerical results show that the effects of the air compressibility can be considered negligible only in numerical simulations of the performances of reduced-scale OWC devices, such as those used in laboratory experiments. We demonstrated that in real-scale simulations, the effect of the air compressibility within the OWC chamber significantly reduces its ability to extract energy from waves. The numerical results show that the effect of the air compressibility is even more significant in the case of a real-scale OWC located in the surf zone, where it interacts with breaking waves.

When a radar detects marine targets, the radar echo is influenced by the shape, size and dielectric properties of the targets, as well as the sea surface under different sea conditions and the coupling scattering between them. This paper presents a composite backscattering model of the sea surface and conductive and dielectric ships under different sea conditions. The ship scattering is calculated using the equivalent edge electromagnetic current (EEC) theory. The scattering of the sea surface with wedge-like breaking waves is calculated using the capillary wave phase perturbation method combined with the multi-path scattering method. The coupling scattering between ship and sea surface is obtained using the modified four-path model. The results reveal that the backscattering RCS of the dielectric target is significantly reduced compared with the conducting target. Furthermore, the composite backscattering of the sea surface and ship increases significantly in both HH and VV polarizations when considering the effect of breaking waves under high sea conditions at low grazing angles in the upwind direction, especially for HH polarization. This research offers valuable insights into optimizing radar detection of marine targets in varying sea conditions. [ABSTRACT FROM AUTHOR]

Pile groups are extensively utilized as supports for many coastal structures, such as bridges, jetties, and oil production platforms. The problem of understanding the interaction effects within pile groups and predicting the breaking wave forces on them is considered in this paper, using experimental tests and machine learning-based predictive modeling. The restriction of previous studies on this important engineering problem is that the pile group arrangements considered are limited. Prediction methods are therefore developed only for specific pile group arrangements and do not incorporate the effect of the incident wave direction. In this study, to partially overcome this limitation, an extensive experimental investigation is conducted on 70 different pile group arrangements under six breaking wave conditions. Three pile group coefficients, characterized by the total, quasi-static, and dynamic forces, are introduced for a thorough assessment of the interaction effects within the pile group. First, the pile group coefficients for three basic arrangements (tandem, side-by-side, and staggered) are evaluated. The results reveal a sheltering effect in the tandem arrangement and an amplification effect in the side-by-side arrangement. However, the forces on the measured pile in the staggered arrangement resemble those on the isolated pile, with neither significant sheltering nor amplification effects observed. Then, the results for all arrangements highlight the significant effect of wave direction on the pile group coefficients for small inter-pile spacing. Finally, different machine learning algorithms are adopted to develop predictive models for the group coefficients. The XGBoost model demonstrates superior accuracy for predicting the total and quasi-static force coefficients, while the dynamic force coefficient remains challenging to predict accurately due to its stochastic nature. • Breaking wave forces on pile groups with various arrangements are studied experimentally. • Pile group coefficients are analyzed for both total, quasi-static, and dynamic forces. • New predictive models for the pile group coefficients are developed based on machine learning algorithms. • The superior accuracy of XGBoost in predicting total and quasi-static force coefficients is demonstrated. [ABSTRACT FROM AUTHOR]

In the present paper, a hydrodynamic model test of the monopile of the NREL 5-MW offshore wind turbine is carried out, and relevant data are presented. The effects of highly non-linear breaking waves were measured in terms of the wave run-up and wave loads around the offshore wind turbine monopile. The wave run-up and the interaction between the non-linear wave load and the monopile were analyzed at different positions around the monopile. The wave run-up around the monopile for the wave breaking conditions is quantified approximately twice the amplitude of the incident wave height. For specific examined wave breaking conditions, the wave height in front of the monopile is lower than behind the monopile. Empirical calculations are also used to verify the experimental results. The wave breaking forces calculated using the empirical formulas are conservative compared with the experimental data, although the experimentally measured maximum wave breaking force is smaller than that calculated one using relevant analytical methods. The present paper gives an insight into the design of monopile foundations for specific wave breaking conditions. [ABSTRACT FROM AUTHOR]

Wave slamming is an important phenomenon due to its destructive power, and with the rapid development of offshore wind turbines, wave slamming on vertical cylinders has garnered lots of attention. However, the phenomenon of wave slamming on vertical cylinders is very complicated due to both the intrinsic complexity of breaking waves and that of slamming forces. The objective of this paper is to provide a general review of research related to this problem, including theoretical methods, experimental studies, numerical simulations, and full-scale measurements. Based on these approaches, the momentum theory/pressure impulse theory, spatial distribution characteristics of impacts to various breaking waves, wave generation methods, analysis methods for measured forces under structure response, scale effects in experiments, and in-situ measurements have been introduced and discussed. Results show that simplifications in existing models for wave impacting such as wave characteristics and structural response reduce its applicability and should be studied further both in theoretical, experimental and numerical researches. [ABSTRACT FROM AUTHOR]

In this study, we developed a fiber-optic sensing system with an eight-probe array for measuring the spatial distributions of air volume (void) fractions in bubbly flows. Initially, we performed calibration experiments in a cylindrical tank by using a fiber-optic sensing system with a single probe to determine the relationship between the time fraction ratio of bubble signals and void fractions. A high correlation coefficient was obtained between the time fraction ratio and the void fraction, suggesting that the proposed fiber-optic sensing system can measure local void fractions of up to 18%. Subsequently, we used the proposed fiber-optic sensing system with the eight-probe array to measure the spatial distribution of air volume fractions in a bubbly flow caused by breaking waves near a submerged breakwater. The effects of different variables, including the incident wave height, period, and width of the breakwater, on the spatial distribution of the void fraction on the lee side of the breakwater were systematically studied. The results demonstrated that the proposed fiber-optic sensing system can be used to determine the spatial distribution of air volume fractions in bubbly flows. [ABSTRACT FROM AUTHOR]

The rehabilitation timing of a damaged rubble mound structure depends on the remaining capacity of the deteriorated structure. A laboratory experiment was conducted in a wave flume to measure the remaining capacity of a low-crested rubble mound inside the surf zone on a sand beach. The formation of a bar and trough feature modified wave conditions at the toe of the structure. Wave transmission over and through the structure increased with lowering of the mound crest. The mound with a double armor layer on smaller core stones was exposed to irregular wave action lasting 22.2 h. Some of the core stone was visible through holes of the thinned armor layer but remained in place. Crest lowering reduced the wave action on the damaged mound. On the other hand, the mound with a single armor layer did not stabilize itself because of core stone removal after 7.8 h. The rubble mound structure was resilient as long as the core stone was protected. [ABSTRACT FROM AUTHOR]

The topic of the present paper subscribes to one of the most challenging themes that are nowadays under the spotlight of the scientific community. It describes a substantiated method aimed not only at predicting accurately the consequences of the associated effects of navigation in waves but also at contributing to ruling the conditions in which the operation of a ship should be performed is presented. A series of multiple degrees of freedom (DOF hereafter) simulations of the MOERI (Korea Research Institute for Ships and Ocean Engineering) container ship (KCS hereafter) hull moving in regular waves are performed and thoroughly validated with the experimental data provided by the organizers of the Tokyo 2015 Workshop on CFD in Ship Hydrodynamics. A verification and validation (V&V hereafter) is performed for the calm water navigation case to prove the robustness of the theoretical approach. Several numerical innovations are proposed, and the solutions are discussed in every detail aimed at setting up a properly established methodology usable in further similar studies. Finally, a set of remarks will conclude the present research. [ABSTRACT FROM AUTHOR]

Dynamic responses of offshore wind turbines, particularly under extreme wave excitations, are crucial to structural design. Extreme waves, e.g. breaking waves, are random processes, which induce uncertainty in the estimation of dynamic responses. This type of uncertainty has been accommodated through a safety of factor which is conservative and thus leads to cost inflation. To reduce the cost and enable economically viable development of offshore wind, it is essential to understand the dynamic process of offshore wind turbines under extreme wave excitation scenarios. However, it is challenging to predict these dynamic responses through numerical simulations, due to the nonlinearity and randomness in such a complex process. To overcome these challenges, this study conducted a series of physical model testing to better capture the extreme wave induced loads on a monopile, which are then served as input for numerical modelling. Through this hybrid model, different vibration mechanisms are revealed, which shed lights on further cost reduction in the design of offshore wind turbines. • There is a pressing need to reduce the costs associated with offshore wind energy. • A series of experiments and computations have been conducted, focusing on extreme wave loads. • Different vibration mechanisms of the monopile vibration responses induced by extreme waves are revealed. • Insights into design optimization and cost reduction are shed. [ABSTRACT FROM AUTHOR]

We experimentally investigate the depth distributions and dynamics of air bubbles entrained by breaking waves in a wind‐wave channel over a range of breaking wave conditions using high‐resolution imaging and three‐dimensional bubble tracking. Below the wave troughs, the bubble concentration decays exponentially with depth. Patches of entrained bubbles are identified for each breaking wave, and statistics describing the horizontal and vertical transport are presented. Aggregating our results, we find a stream‐wise transport faster than the associated Stokes drift and modified Stokes drift for buoyant particles, which is an effect not accounted for in current models of bubble transport. This enhancement in transport is attributed to the flow field induced by the breaking waves and is relevant for the transport of bubbles, oil droplets, and microplastics at the ocean surface. Plain Language Summary: Air bubbles are produced when waves break at the ocean surface. The additional air‐water surface area they introduce enhances the global transfer of gases such as carbon dioxide and oxygen from the atmosphere to the ocean. Understanding the dynamics of these air bubbles, in particular their residence time under water, is necessary to improve bubble‐mediated gas transfer models. Such knowledge is also critical in predicting the dispersion of oil spills and the transport of buoyant particles like microplastics in the turbulent environment created by breaking waves. We use three‐dimensional measurements of air bubbles produced by breaking waves in a laboratory experiment to show that bubbles typically move in the direction of the wave faster than they would under linear waves due to the effects of wave breaking, and that the bubbles are typically injected to a depth underwater that is related to the height of the wave that breaks. Key Points: We perform three‐dimensional measurements of the trajectories of air bubbles entrained by breaking wavesThe concentration of bubbles decays exponentially below the wave troughsBubbles are transported downstream significantly faster than the Stokes drift during their first wave period underwater [ABSTRACT FROM AUTHOR]

Laboratory experiments were conducted to evaluate the feasibility of profiling and characterizing subsurface bubble plumes following a breaking wave event from an above-water Light Detection and Ranging (LiDAR) system. Measurements of LiDAR backscatter profiles of bubble plumes under mechanically generated breaking waves in a wave tank were collected and analyzed. After onset of wave breaking, the LiDAR backscatter increases rapidly by injected bubble plumes of active wave breaking. This intensification reaches a depth of one wave height within one wave period. After active wave breaking, the LiDAR backscatter from dissipated bubble plumes in the upper layer of water column decreases very slowly. The temporal variations of LiDAR backscatter are comparable to the collocated in-water measurements of optical backscatter at 850 nm wavelength and acoustic backscatter at 2000 kHz frequency. The decay rate of LiDAR backscatter of dissipated bubble plumes follows a power-law function consistent with decay rate of void fraction measurements in previous studies. This study demonstrates the viability and potential of using above-water LiDAR remote sensing to characterize subsurface bubble plumes. [ABSTRACT FROM AUTHOR]

The aim of this paper is to study the water wave problem for uneven bottoms in a highly nonlinear regime. It is well known that, for such regimes, a generalization of the KdV equation called the Camassa–Holm equation can be derived and justified when the bottom is variable (Israwi in Esaim: M2AN 44:347–370, 2010). In this work, new asymptotic models are derived so that they have the same accuracy as the standard equations. We solve explicitly the new simple models and we validate numerically the results. [ABSTRACT FROM AUTHOR]

Emerging as powerful open-source software in recent years, "DualSPHysics" is receiving increased attention for its ability to simulate large-scale flow fields. In the context of applying open-source software, the differences in the numerical results due to different model parameters need to be investigated in detail. In this study, some benchmark problems have been solved with DualSPHysics to validate the estimation of wave impact pressure with violent breaking waves. We have demonstrated three main results: (i) as an alternative to the artificial viscosity traditionally used in DualSPHysics, a laminar viscosity model can also well reproduce the solutions to the existing benchmark problems in a violent flow field with the modified dynamic boundary condition; (ii) the dynamics of the gas phase is essential in the calculation of wave breaking with rapid gate opening; and (iii) if the density diffusion parameter is too large, the impact pressure may be underestimated. The practical contribution by this study is to find that DualSPHysics well reproduces complex breaking waves, including multi-phase gas-liquid flows, and that the wave impact pressure is accurate by comparison with existing experimental results. This allows us to understand the complex behavior of fluid-structure interactions in coastal engineering by means of DualSPHysics. [ABSTRACT FROM AUTHOR]

Wind-wave interaction affects the wind-wave fields and the combined loading on structures. This study aims to characterize turbulent airflow over non-breaking and breaking waves using a high-fidelity two-phase model in OpenFOAM. The volume of fluid method is utilized to model the complex air–water interface. Wind turbulence is considered via prescribing it at the inlet boundary. The model is validated against experimental data, and a numerical case study is conducted to simulate extreme wind and wave-plunging conditions. Results reveal that non-breaking waves induce wind turbulence and affect averaged wind velocity. For wave steepness exceeding 0.35, extreme wind forces amplify the turbulence by over 100% at wave crests. The amplified turbulence region extends to about 0. 6 λ in height. When waves plunge, an overturning jet propels the wind forward, generates a counterclockwise vortex, and enhances wind turbulence. Averaged wind speeds increase by over 20% above wave crests, with the enhanced region extending to a height of around 0. 2 λ for old waves. Maximum turbulence kinetic energy transiently increases by around 0. 1 C p 2 and maximum kinematic energy of wave-coherent velocity increases and subsequently decreases during wave plunging. • An LES-based two-phase model is developed to simulate coupled turbulent wind-wave flows. • Simulated wind-wave flow characteristics agree well with the experimental data. • Over non-breaking waves, the wave generated wind turbulence depends on wave ages. • Over plunging waves, a counterclockwise vortex forms, enhancing wind turbulence. • Wave breaking has a significant impact on the pattern of phase-averaged wind speed. [ABSTRACT FROM AUTHOR]

Proper recognition of the coastal area helps to make better use of this area. Due to high risk conditions and wide variations in the coastal area, studies of this area usually cost a lot. In this research, the relationships among the breaking wave height, the width of the breaking zone, and number of breakings have been investigated as visual assessment and processing of video images taken by conventional and UAV cameras. Study of correlation between these parameters indicates the possibility of estimating the target parameter from the available parameters data using the relationships provided. The breaking zone width and the height of first breaking wave are directly correlated with coefficient of 0.92 and the correlation coefficient between the number of breaking and the breaking zone width is 0.86. The maximum, minimum, and averages of breaking zone width are 100, 0 and 27 meters, respectively.

Abstract There are few high‐resolution field observations of the water surface during breaking owing to the difficulty of collecting spatially dense measurements in the surf zone, and thus the factors influencing breaking‐wave shape in field conditions remain poorly understood. Here, the shape and evolution of plunging breakers is analyzed quantitatively using three‐dimensional scans of the water surface collected at high spatial and temporal resolution with a multi‐beam terrestrial lidar scanner. The observed internal void shapes in plunging breakers agree well with previously developed theoretical shapes at the onset of breaking, and become more elongated and less steep as breaking progresses. The normalized void area increases as the local bottom slope steepens and as the breaking depth decreases. The void shape becomes more circular as the local bottom slope and the ratio of breaking water depth to wavelength increase, as well as in conditions with opposing winds.

There are few high‐resolution field observations of the water surface during breaking owing to the difficulty of collecting spatially dense measurements in the surf zone, and thus the factors influencing breaking‐wave shape in field conditions remain poorly understood. Here, the shape and evolution of plunging breakers is analyzed quantitatively using three‐dimensional scans of the water surface collected at high spatial and temporal resolution with a multi‐beam terrestrial lidar scanner. The observed internal void shapes in plunging breakers agree well with previously developed theoretical shapes at the onset of breaking, and become more elongated and less steep as breaking progresses. The normalized void area increases as the local bottom slope steepens and as the breaking depth decreases. The void shape becomes more circular as the local bottom slope and the ratio of breaking water depth to wavelength increase, as well as in conditions with opposing winds. Plain Language Summary: Breaking waves inject momentum into the surf zone that drives nearshore currents, raises water levels, and generates turbulence. However, there are few high‐resolution field observations of the water surface during breaking because of the difficulty of collecting spatially dense measurements of the water‐surface elevation at the location of wave breaking, leaving open questions related to the factors controlling the shape and properties of breaking waves. In this study, three‐dimensional scans of the water surface in the surf zone collected using a multi‐beam terrestrial lidar scanner are used to analyze quantitatively the shape and evolution of plunging breakers. The shape of the internal barrel (or void) created as the plunging lip intersects with the front face of the wave agrees well with theoretical void shapes at the start of the breaking process, and then becomes more elongated and less steep through the breaking process. The normalized area of the void is larger when waves break on steeper bottom slopes and in shallower water. The void is more circular when waves break on steeper bottom slopes and with larger ratios of breaking water depth to wavelength, and also when the wind is blowing in a direction opposing the direction of wave propagation. Key Points: Three‐dimensional lidar scans of the water surface allow for quantitative analyses of the shape and evolution of plunging breakersThe observed internal void shapes in plunging breakers agree well with theoretical void shapes at the onset of breakingThe internal void shape and normalized area are influenced by bathymetry, wave parameters, and cross‐crest wind stress [ABSTRACT FROM AUTHOR]

The topic of the present paper subscribes to one of the most challenging themes that are nowadays under the spotlight of the scientific community. It describes a substantiated method aimed not only at predicting accurately the consequences of the associated effects of navigation in waves but also at contributing to ruling the conditions in which the operation of a ship should be performed is presented. A series of multiple degrees of freedom (DOF hereafter) simulations of the MOERI (Korea Research Institute for Ships and Ocean Engineering) container ship (KCS hereafter) hull moving in regular waves are performed and thoroughly validated with the experimental data provided by the organizers of the Tokyo 2015 Workshop on CFD in Ship Hydrodynamics. A verification and validation (V&V hereafter) is performed for the calm water navigation case to prove the robustness of the theoretical approach. Several numerical innovations are proposed, and the solutions are discussed in every detail aimed at setting up a properly established methodology usable in further similar studies. Finally, a set of remarks will conclude the present research.

Bubbles bursting at the ocean surface are an important source of sea‐spray aerosol. We describe jet drop production, from ensembles of high fidelity numerical simulations of bubble bursting, validated against experimental results. The number of jet drops, their size, and velocity are controlled by the ratio of the bubble size, Rb, and the visco‐capillary length, lμ=ρwγRb/μw2, where γ is the surface tension, ρw, μw the water density and viscosity. The mean drop size follows 〈rd〉∝(Rb/lμ)5/4 and the ejected number of drops n∝(Rb/lμ)−1/3, accounting for temperature variations. We confirm that submicrons jet drops are produced by bubbles in the 10–40 microns range. We compute the distribution of jet drops formed by a range of bubbles present under a breaking wave which compares well against laboratory experiments. We discuss the applicability of the proposed formulation in the context of sea spray generation function. Plain Language Summary: Bubbles bursting at the ocean surface have long been recognized as an important source of sea spray aerosols. However, the description of sea spray production remains elusive in parts due to the large range of scales involved, from bubble bursting at the ocean surface to large scale breaking waves. We discuss the range of droplets that can be formed by bubble bursting, for bubble sizes typical of ocean conditions. We show that jet drops can have sizes from 0.5 to 500 microns, and propose theoretical relationships to describe their size and number, as a function of the bubble size, as well as water temperature and salinity. The results compare very well to laboratory experiments, and pave the way toward mechanistic formulation of sea spray, to be used in atmospheric and climate models. Key Points: We perform numerical simulations of the two‐phase Navier‐Stokes equations to resolve bubble bursting and jet drop productionWe describe the jet drop distribution for a wide range of bubble conditions, with droplet production from 0.5 to 500 micronsThe jet drop distribution from bubbles under breaking waves is compatible with laboratory measurements of drop distribution [ABSTRACT FROM AUTHOR]

In this study, analytical solutions and physical interpretations are presented for the Riemann wave equation (RWE), which has an important physical property in fluid dynamics. The solutions of the RWE, which models the formation, interaction and breaking of the waves that occur as a result of any external effect on the ocean surface, are examined using the generalized exponential rational function method (GERFM). Bright (nontopological) soliton, singular soliton and solitary wave solutions are produced with advantages of GERFM over other traditional exponential methods. The factors in which solitary wave solutions cause breaking of wave are examined. The effects of parameters on wavefunctions and the physical interpretations of these effects are discussed and supported by graphics and simulations. [ABSTRACT FROM AUTHOR]

In the present paper, the computational fluid dynamics method is used to investigate the effects of breaking wave loads on a 10-MW large-scale monopile offshore wind turbine under typical sea conditions in the eastern seas of China. Based on Fifth-Order Stokes wave theory a user-defined function is developed and used for wave numerical modeling, and a numerical wave tank with different bottom slopes is developed. The effects of different types of breaking waves, such as spilling and plunging waves, on the wave run-up, pressure distribution and horizontal wave force of a large diameter monopile are investigated. Different numerical and analytical methods for calculating the wave breaking loads are used and their results are compared with the relevant results of the developed computational fluid dynamics model and their respective scopes of application are discussed. With an increase in wave height, the change in the hydrodynamic performance of breaking waves observed through the transition from plunging to spilling waves is explored. The intensity of interactions occurring between the breaking waves and the monopile foundation depends mainly on the form of wave breaking involved and its relationship to wave steepness is weak. Analytical methods for calculating the breaking wave loads are preservative especially for plunging breaking wave loads.

This paper proposes an equation to calculate breaking wave induced wave set-up and set-down along reef flat. The mathematical equation was derived based on the theory of radiation stress and the conservation of wave energy. The equation is primarily determined by several physical variables including the breaking wave index, the stable wave index, the attenuation coefficient of wave energy flux, and the flow velocity in the re-stabilization zone. A series of laboratory experiments were carried out to calibrate the theoretical equations. Specifically, the breaking wave index, the stable wave index, and the velocity over the reef flat were measured in the laboratory. The attenuation coefficient of wave energy flux in our theoretical equation was determined by calibration by comparing with the laboratory measured wave height. Furthermore, it has been put forward that the velocity based on cnoidal wave theory could be used to determine the velocity over the reef flat if there is no velocity measurement available. Overall, the proposed equation can provide satisfactory prediction of wave set-up and set-down along the reef flat. [ABSTRACT FROM AUTHOR]

Accurate estimates of microwave radar returns based on theoretical electromagnetic scattering models are of great benefit to obtain insight into the microwave scattering mechanism at the ocean surface. In this study, quad‐polarized radar backscatters from the regular ocean surface (no breaking waves) are first simulated using a composite surface Bragg model and a second‐order small slope approximation model, using three different surface roughness spectral models. The copolarized and cross‐polarized radar backscatters, induced by breaking waves, are then quantitatively estimated using two recent empirical models, which are dependent on incidence angles, wind speeds, and wind directions. Model‐simulated total radar backscatters, from regular surface waves and breaking waves, are statistically compared with measurements from spaceborne C‐band quad‐polarization RADARSAT‐2 synthetic aperture radar and also calculations from copolarized and cross‐polarized geophysical model functions. Results show that simulations of quad‐polarization radar backscatter are significantly improved when the effects of breaking waves are incorporated, especially for HH and VH polarizations. Key Points: CB and SSA‐2 models underestimate HH‐ and VH‐polarization radar backscatters, especially in upwind and crosswind casesThe copolarized and cross‐polarized radar backscatters, induced by breaking waves, are quantitatively estimatedSimulations of quad‐polarization radar backscatter are significantly improved when the effects of breaking waves are incorporated [ABSTRACT FROM AUTHOR]

The two-phase flow generated by breaking ocean waves plays a crucial role in various geophysical processes, including dissipation of wave energy and atmospheric gas exchange. This paper presents a technique to measure the two-phase flow generated by breaking waves at prototype scale. We have demonstrated the validity and potential of this technique in the Large Wave Flume (Grosser Wellenkanal, GWK) facility in Hanover, Germany. Actively breaking, depth-limited waves were measured using an array of three downward-looking lidars mounted above the water surface and an upward-looking multibeam sonar below. This novel setup enabled the characterization of the complete upper boundary (free water surface and splash-up) and seaward lower boundary (entrained cavity and bubble plume) of the breaking wave. We have quantified the migration of the lower boundary as the cavity and plume are entrained in the water column—penetrating toward the seabed, moving onshore with the passage of the wave crest, and then rising as it is slowly advected offshore. We have also estimated the overall composition of the splash, cavity, and plume as the breaking wave evolves over time. Our observations are consistent with results from previous small-scale laboratory experiments and the suitability of the technique for experimentation at prototype scale has been demonstrated. [ABSTRACT FROM AUTHOR]