Breaking Wave Height Research Articles

Experimental study of breaker index of normal and oblique incident unidirectional and multidirectional irregular waves on slope

Most studies of wave breaking on slopes to date have investigated regular waves or normal incident unidirectional waves. In this study, wave breakings of normal and oblique incident irregular waves and multidirectional irregular waves on a 1:15 slope were investigated. The breaking criteria of irregular waves based on significant wave height and individual wave height were determined. Firstly, breaker indexes calculated using significant wave heights at incipient breaking were analyzed; they were substantially lower than the breaker indexes of regular waves. The breaker index formulae of irregular waves are presented based on the referred formula of regular waves. Furthermore, the breaker indexes of oblique incident waves were larger than the breaker indexes of normal incident waves. However, wave directionality had little effect on breaker indexes under the present experimental conditions. Secondly, the breaker index (the ratio of significant wave height to water depth) in surf zone was analyzed. It increased with a decrease in relative water depth. Thirdly, information of individual waves in irregular wave trains was tracked by the wave-by-wave method. The breaker indexes derived by individual wave heights were larger than the incipient breaker indexes derived from significant wave heights. Based on previous empirical formulae, some relatively simple expressions are proposed to calculate individual breaking wave heights for unidirectional irregular waves.

NOISE CHARACTERISTICS OF SEA WAVES BASED ON ITS HEIGHT, PERIOD AND BREAKING WAVES

ABSTRACT
 Wave sound is one of the sources of ambient noise in the waters which causes the role of sound as a transmission medium of information and communication becomes disrupted. The characteristics of wave noise can be influenced by their parameters, such as height and period of the waves and breaking waves. The study aimed to determine the characteristics of noise (intensity, frequency, pulse duration and interval duration) of waves based on its height, periods and breaking waves. Data acquisition for sound wave is obtained by hydrophones, visual of wave from CCTV cameras, and wave parameters is determined from ADCP data. Sound characteristics based its height, period and breaking waves were analyzed by Kruskal-Wallis analysis. The intensity of noise is affected by all wave parameters, while the pulse duration is significantly influenced by the changes in height and wave period, and the breaking waves velocity. Frequency of noise is only impacted by the breaking wave height. Other noise characteristics, the interval duration is not significantly influenced by all wave parameters.

Field Measurements of a High-Energy Headland Deflection Rip Current: Tidal Modulation, Very Low Frequency Pulsation and Vertical Structure

Headland rips, sometimes referred to as boundary rips, are rip currents flowing against natural or artificial obstructions extending seaward from the beach, such as headland or groynes. They can be driven either by the deflection of the longshore current against the obstacle or by alongshore variation in breaking wave height due to wave shadowing in the lee of the obstacle. The driving mechanism therefore essentially depends on the angle of wave incidence with respect to the natural or artificial obstruction. We analyze 42 days of velocity profile measurements against a natural headland at the high-energy meso-macrotidal beach of Anglet, southwest France. Measurements were collected in 6.5–10.5-m depth as tide elevation varied, during the autumn–winter period with offshore significant wave height and period ranging 0.9–6 m and 8–16 s, respectively, and the angle of wave incidence ranging from −20 ∘ to 20 ∘ . Here we analyze deflection rip configurations, corresponding to approximately 24 days of measurements, for which the current meter was alternatively located in the rip neck, rip head or away from the rip as wave and tide conditions changed. Deflection rips were associated with large offshore-directed velocities (up to 0.6 m/s depth-averaged velocities) and tide modulation for low- to moderate-energy waves. The vertical profile of deflection rips was found to vary from depth-uniform in the rip neck to strongly depth-varying further offshore in the rip head with maximum velocities near the surface. Very low frequency motions of the rip were dramatic, ranging 10–60 min with a dominant peak period of approximately 40 min, i.e., with longer periods than commonly reported. The strong offshore-directed velocities measured well beyond the surf zone edge provide new insight into deflection rips as a dominant mechanism for water and sediment exchanges between embayed (or structurally-controlled) beaches and the inner-shelf and/or the adjacent embayments.

Novel free surface boundary conditions for spilling breaking waves

The breaking of gravity water waves induces both strong turbulence near the free surface and air–water mixing, which are not captured in currently-available single-phase, non-hydrostatic Reynolds Averaged Navier Stokes (RANS) models. In order to account for such dynamics, the boundary conditions proposed by Brocchini (2002) have been implemented in a two-dimensional vertical (2DV) non-hydrostatic RANS numerical model. For the theoretical boundary conditions of Brocchini (2002) to be applicable in the numerical model, appropriate closures have been adopted and mathematical equations have been proposed to calculate the coefficients introduced in the mentioned boundary conditions. Navier Stokes equations along with different turbulence closure models have been solved using finite volume method and pressure correction technique. According to the new boundary conditions, the normal-to-mean surface gradient of the turbulent kinetic energy (TKE) differs from zero and is computed as a balance between production and dissipation of TKE within the air–water mixing layer. Also, the kinematic and dynamic boundary conditions have been modified accordingly, to account for the effects of the thin two-phase layer formed at the free surface. The modified kinematic boundary condition allows for the mass exchange between the two-phase layer and the main body of the water. For the first time it is demonstrated that the proposed simple analytical model of Brocchini (2002) leads to improvements in the prediction of incipient breaking and the wave characteristics in the surf zone. This opens the way to a new, accurate but numerically low cost, approach for the computation of the air–water mixing that characterizes breaking waves. All the many benchmarking tests run to verify the ability of the new model show that significant improvements are achieved. Improvements are specifically observed in the prediction of: (I) breaking point and the breaking wave height, (II) the consequent dissipation of the wave energy observed in the form of the crest level distribution throughout the surf zone, (III) the magnitude of the horizontal velocity near the free surface, and (IV) the TKE distribution in depth. Notably, the novel numerical model does not use any parametric criteria for detecting the inception of breaking, thus it does not need calibration for different flow circumstances. Also, since no special treatments, such as hydrostatic pressure assumptions at the front face of the breaking waves are considered, the new model well captures the breaking-induced dissipation while giving a more accurate estimation of the dynamic pressure.

Breaking Wave Height Estimation from Timex Images: Two Methods for Coastal Video Monitoring Systems

The breaking wave height is a crucial parameter for coastal studies but direct measurements constitute a difficult task due to logistical and technical constraints. This paper presents two new practical methods for estimating the breaking wave height from digital images collected by shore-based video monitoring systems. Both methods use time-exposure (Timex) images and exploit the cross-shore length ( L H s ) of the typical time-averaged signature of breaking wave foam. The first method ( H s b , v ) combines L H s and a series of video-derived parameters with the beach profile elevation to obtain the breaking wave height through an empirical formulation. The second method ( H s b , v 24 ) is based on the empirical finding that L H s can be associated with the local water depth at breaking, thus it can be used to estimate the breaking wave height without the requirement of local bathymetry. Both methods were applied and verified against field data collected at the Portuguese Atlantic coast over two days using video acquired by an online-streaming surfcam. Furthermore, H s b , v 24 was applied on coastal images acquired at four additional field sites during distinct hydrodynamic conditions, and the results were compared to a series of different wave sources. Achievements suggest that H s b , v method represents a good alternative to numerical hydrodynamic modeling when local bathymetry is available. In fact, the differences against modeled breaking wave height, ranging from 1 to 3 m at the case study, returned a root-mean-square-error of 0.2 m. The H s b , v 24 method, when applied on video data collected at five sites, assessed a normalized root-mean-square-error of 18% on average, for dataset of about 900 records and breaking wave height ranging between 0.1 and 3.8 m. These differences demonstrate the potential of H s b , v 24 in estimating breaking wave height merely using Timex images, with the main advantage of not requiring the beach profile. Both methods can be easily implemented as cost-effective tools for hydrodynamic applications in the operational coastal video systems worldwide. In addition, the methods have the potential to be coupled to the numerous other Timex applications for morphodynamic studies.

Modulational Stability of Nonlinear Saturated Gravity Waves

Abstract Stationary gravity waves, such as mountain lee waves, are effectively described by Grimshaw’s dissipative modulation equations even in high altitudes where they become nonlinear due to their large amplitudes. In this theoretical study, a wave-Reynolds number is introduced to characterize general solutions to these modulation equations. This nondimensional number relates the vertical linear group velocity with wavenumber, pressure scale height, and kinematic molecular/eddy viscosity. It is demonstrated by analytic and numerical methods that Lindzen-type waves in the saturation region, that is, where the wave-Reynolds number is of order unity, destabilize by transient perturbations. It is proposed that this mechanism may be a generator for secondary waves due to direct wave–mean-flow interaction. By assumption, the primary waves are exactly such that altitudinal amplitude growth and viscous damping are balanced and by that the amplitude is maximized. Implications of these results on the relation between mean-flow acceleration and wave breaking heights are discussed.

Experimental study of wave propagation characteristics on a simplified coral reef

The wave transformation over slope topography is widely studied, but most of studies are for common coastal slopes. This paper presents an experimental study of 2-D regular and irregular wave transformations on a simplified coral reef with a steep slope of 1:5 and a horizontal reef flat, focusing on the characteristics of the waves that break on the reef flat. The analyzed results show that the estimates of the wave breaking made by using the well-known previous formulae do not agree completely with the experimental results. When the waves break on a reef flat, the relative breaking wave height (H/d)b is related to the incident deep-water wave steepness and the relative water depth db/L0. Hence, a new criterion for breaking waves on a reef flat is proposed. Furthermore, in view of the fact that the local Ursell number is commonly used to parameterize the wave nonlinearity, the relationships among the skewness, the asymmetry, and the local Ursell number are also presented. Experimental data confirm that when the Ursell number is greater than 30, the absolute values of the skewness and the asymmetry on a reef flat are greater than those on a steep slope.

Nearshore Wave Transformation Domains from Video Imagery

Within the nearshore area, three wave transformation domains can be distinguished based on the wave properties: shoaling, surf, and swash zones. The identification of these distinct areas is relevant for understanding nearshore wave propagation properties and physical processes, as these zones can be related, for instance, to different types of sediment transport. This work presents a technique to automatically retrieve the nearshore wave transformation domains from images taken by coastal video monitoring stations. The technique exploits the pixel intensity variation of image acquisitions, and relates the pixel properties to the distinct wave characteristics. This allows the automated description of spatial and temporal extent of shoaling, surf, and swash zones. The methodology was proven to be robust, and capable of spotting the three distinct zones within the nearshore, both cross-shore and along-shore dimensions. The method can support a wide range of coastal studies, such as nearshore hydrodynamics and sediment transport. It can also allow a faster and improved application of existing video-based techniques for wave breaking height and depth-inversion, among others.

Numerical investigation of wave propagation and transformation over a submerged reef

ABSTRACTIn this paper, wave transformation over a submerged reef has been numerically studied based on the OpenFOAM model. This numerical model solves the Reynolds-Averaged Navier-Stokes equations for two-phase flow and employs the volume of fluids (VOF) method for the free surface. The k-ω SST turbulence model is used to simulate wave breaking, and the wave generation library waves2Foam is adopted to generate waves in the model. The numerical model is first validated against the physical experimental data, and it is shown that the model is capable of simulating the key processes of wave shoaling, breaking and transmission over the submerged reef. Then, a series of numerical tests are conducted considering different incident wave heights, submergences and slopes of the reef. The influences of reef slope and submergence on the wave properties over the reef are discussed, which include the wave reflection and transmission coefficients, breaking wave height, wave-induced setup, and energy dissipation.

Experimental study of runup for sandy beaches under waves and tide

This paper describes an experimental investigation of runup for intermediate sandy beaches from a physical modelling in a wave flume with tide simulation. Shoreline elevation measurements are acquired over a wide range of conditions using an optical method. Simultaneous morphological and hydrodynamic changes are considered to determine the best parameters to predict the maximum wave runup. The tidal level significantly affects the breaking conditions (position, height and type), and the slopes of the beach. Present data show that the surf zone slope and the wave breaking height should be used to estimate the maximum runup. The results are compared with previous formulations issued from the literature. A new formula is proposed for the runup estimation for intermediate beaches.

Wave farm impacts on coastal flooding under sea-level rise: A case study in southern Spain

Coastal flooding, already an acute problem in many parts of the world, will be exacerbated in the near future by the sea level rise induced by climate change. The influence of wave farms, i.e., arrays of wave energy converters, on coastal processes, in particular sediment transport patterns, has been analysed in recent works; however, their influence on coastal flooding has not been addressed so far. The objective of this work is to investigate whether a wave farm can provide some protection from flooding on the coast in its lee through a case study: a gravel-dominated beach in southern Spain (Playa Granada). We consider three sea-level rise (SLR) scenarios: the present situation (SLR0), an optimistic projection (SLR1) and a pessimistic projection (SLR2). Two state-of-the-art numerical models, SWAN and XBeach-G, are applied to determine the wave propagation patterns, total run-up and flooded dry beach area. The results indicate that the absorption of wave power by the wave farm affects wave propagation in its lee and, in particular, wave heights, with alongshore-averaged reductions in breaking wave heights about 10% (25%) under westerly (easterly) storms. These lower significant wave heights, in turn, result in alongshore-averaged run-up reductions for the three scenarios, which decreases with increasing SLR values from 5.9% (6.8%) to 1.5% (5.1%) for western (eastern) storms. Importantly, the dry beach area flooded under westerly (easterly) storms is also reduced by 5.7% (3.2%), 3.3% (4.9%) and 1.99% (4.5%) in scenarios SLR0, SLR1 and SLR2, respectively. These findings prove that a wave farm can actually reduce coastal flooding on its leeward coast.

HARMONIC WAVES ON AN ABRUPT TRANSITION

A simple long-wave reflection and transmission over an abrupt depth change with constant channel width are presented. Firstly, the wave propagation is modeled on a two-step abrupt transition, and the waves are reflected and transmitted only once. The model is extended to include more than one re-reflection and retransmission as well as depth-limited breaking-wave height criteria. The Dean beach profile is also modeled. The profile is a function of the median grain size of the beach material. It is found that the wave energy is conserved when the waves are re-reflected and retransmitted more than five times. The breaking waves reduce the reflection coefficient by 30%. The results are compared with other research on the reflection coefficient occurring in a smooth sloping beach model. On a small sloping beach, an abrupt depth change gives a significant difference in the value of the reflection coefficient. The reflection coefficient on the smooth small sloping beach is close to zero, while the abrupt depth change can increase the reflectioncoefficient to about 60% in this case.

The Competing Effects of Breaking Waves on Surfzone Heat Fluxes: Albedo Versus Wave Heating

AbstractDepth‐limited wave breaking modifies the heat flux in the surfzone relative to the inner‐shelf (where waves are not breaking). Surfzone wave breaking generates heat through viscous dissipation (wave heating), but also increases surface foam coverage and albedo, thereby reducing solar heating, that is, cooling relative to the inner‐shelf. These two competing breaking wave effects are quantified with a yearlong experiment at the Scripps Institution of Oceanography Pier. Cross‐shore averaged surfzone albedo estimates were more than three times higher than inner‐shelf albedo, reducing the yearly averaged surfzone water‐entering shortwave radiation by 41 W/m2 relative to the inner‐shelf. Surfzone breaking wave dissipation added an additional yearly averaged 28 W/m2 relative to the inner‐shelf. The albedo‐induced solar heating reduction in spring, summer, and fall was usually greater than the wave heating. However, in winter, large waves and relatively weak shortwave solar radiation (due to both lower top of the atmosphere solar radiation and clouds) resulted in a nearly equal number of days of breaking wave‐induced heating or cooling. These two heat flux terms are coupled via wave breaking dissipation. Averaged over the surfzone, the albedo‐induced solar radiation reduction is linearly related to the downwelling solar radiation and is independent of wave height. Consequently, the albedo‐induced cooling to wave heating ratio is a function of breaking wave height to the −3/2 power, allowing evaluation of the relative importance of these terms in other geographic regions.

Studi Hindcasting Dalam Menentukan Karakteristik Gelombang dan Klasifikasi Zona Surf Di Pantai Uluwatu, Bali

Bali is one of the islands where there are many surf zones with various characteristics. In addition, Bali is also a heaven with a classy wave for the surfers of the world. One of the most challenging places to surf in Bali is Uluwatu Beach. Uluwatu Beach is ranked the 3rd best surf spot in the world version of CNN Travel in 2012. Wind causes sea waves, therefore wind data can be used to estimate the height and direction of the waves. Wave Hindcasting with Sverdrup, Munk and Bretschneider (SMB) method is calculated based on wind data for 10 years (2001 - 2010) from BMKG Ngurah Rai Station - Denpasar to obtain a significant wave height and period. In this research, it is necessary to approach through Hindcasting procedure, wave transformation analysis and surfing Terminology in determining the type of breaking wave and classification of surf zone in Uluwatu Beach area. Wave calculation result in Uluwatu Beach dominated by wave that coming from west side with significant wave height (Hs) of 0.98 m and significant wave period (Ts) of 5.21 s. The wave height due to the influence of wave refraction and shoaling is 0.976 m. The breaking wave height obtained from the calculation is 1.04 m at a depth of 0.849 m. From the result in this research, it can be concluded that the breaking wave type that occurred at Uluwatu Beach is plunging type according to the calculation result from its Irribaren number (0.4 <Ni <2.3). The classification of the surf zone at Uluwatu Beach based on its breakup type of wave is thought to be a good zone for surfers on intermediate level.

Four-dimensional wave refraction from Sentinel-1A satellite data

This investigation has incontestable a replacement technique for the modelling of wave refraction configuration from synthetic aperture radar data. To this end, the nonlinear of bunching rate exploited to exhibit the wave spectral peaks braced the novel progress of the 4-D B-spline algorithmic program. The study shows that convergence zone is conquered by breaking wave height of 4.5 m. The study also indicates that wave diversion array could be modelled from Sentinel-1A satellite in both divergence and convergence spectra energy arrays. This can impact the society through causing a coastal erosion. Lastly, 4-D wave refraction pattern in spite of nonlinearity between actual ocean wave spectra and Sentinel-1A data is simulated by 4-D B-spline algorithmic program supported Pareto optimization.

Wave breaking in the KdV equation on a flow with constant vorticity

The paper describes the critical breaking waveheight for long surface water waves on a flow with constant vorticity in the KdV approximation. Given a background linear shear flow, a KdV equation can be found with coefficients depending on the strength of the shear flow. The derivation also shows that the velocity field under the wave can be constructed approximately from the free surface excursion.A convective breaking criterion is put forward and used to detect incipient wave breaking in periodic traveling waves and solitary waves. It is shown that for both the solitary wave and the cnoidal waves, there are limiting waveheights where the horizontal component of the particle velocity equals the phase velocity of the wave. It is found that the strength of the vorticity has a considerable influence on the critical waveheight.

Machine learning based prediction of wave breaking over a fringing reef

The characteristics of wave breaking in shallow waters that are of interest include whether a wave will break, the type of breaking that will occur, the breaking wave height, breaking depth, the position of breaking, the wave setup, and the transformation of the broken wave for given offshore wave characteristics and given bottom profile. Various methods have been proposed in the literature to estimate these wave-breaking characteristics. Deo et al. (2003) used a neural network approach to predict the breaking wave height and breaking depth for waves transforming over a range of simply sloped bottoms. The Deo et al. approach is extended here to predict other characteristics of wave breaking, including the type of wave breaking, the position of breaking, the wave setup, and the rate of dissipation of wave energy, in the case of waves impinging on a fringing reef. Observations from a series of specially conducted laboratory experiments involving monochromatic waves impinging on an idealized reef are used to develop and train respective models. The input parameters to the neural network models are the ratio of offshore wave height to the shallow-water depth of the flat section of the reef, H1/hs and the wave frequency parameter fH1/g. The breaker type classification model developed predicts the type of breaker with a success rate of 96%, outperforming previously used criteria for classifying breaker types. The numeric prediction models for the dimensionless position of wave breaking for plunging and spilling breakers, for wave setup, and for the reduction in energy flux across the reef have performance ratings characterized by respective correlation coefficients of 0.99, 0.82, 0.89, and 0.94. The modest value for the correlation between prediction and the actual result for the position of breaking of spilling breakers is believed to be associated with inaccuracies in determination of the exact position of breaking and to difficulty in visually capturing spilling breakers in observations. High correlation between predicted and actual values of the reduction in energy flux across the reef is achieved in spite of the fact the model was trained using data from a wave tank that included partial reflection (characterized by 7% mean deviation among non-breaking waves) from the downstream end of the tank. The method can be extended to provide predictive models for consideration of a range of natural coastal conditions, random waves, and various bottom profiles and complex geometry, based on training and testing of the models using representative laboratory, field, and/or flow simulation, in support of accurate prediction of near-shore wave phenomena.

Detailed Study on Breaking Wave Interactions With a Jacket Structure Based on Experimental Investigations

Wave breaking is one of the major concerns for offshore structures installed in shallow waters. Impulsive breaking wave forces sometimes govern the design of such structures, particularly in areas with a sloping sea bottom. Most of the existing offshore wind turbines were installed in shallow water regions. Among fixed-type support structures for offshore wind turbines, jacket structures have become popular in recent times as the water depth for fixed offshore wind structures increases. However, there are many uncertainties in estimating breaking wave forces on a jacket structure, as only a limited number of past studies have estimated these forces. Present study is based on the WaveSlam experiment carried out in 2013, in which a jacket structure of 1:8 scale was tested for several breaking wave conditions. The total and local wave slamming forces are obtained from the experimental measured forces, using two different filtering methods. The total wave slamming forces are filtered from the measured forces using the empirical mode decomposition (EMD) method, and local slamming forces are obtained by the frequency response function (FRF) method. From these results, the peak slamming forces and slamming coefficients on the jacket members are estimated. The breaking wave forces are found to be dependent on various breaking wave parameters such as breaking wave height, wave period, wave front asymmetry, and wave-breaking positions. These wave parameters are estimated from the wave gauge measurements taken during the experiment. The dependency of the wave slamming forces on these estimated wave parameters is also investigated.

Parameterization of nearshore wave front slope

This study presents an empirical parameterization of wave front slope angle used in the characterization of shoaling and breaking waves in nearshore environment. A large amount of experimental datasets is analyzed for determining possible values of the wave front slope angles. Results indicate that the slope angle increases with wave shoaling and decreases when wave breaks. For the data used here, the maximum slope angle is around 0.8 rad at the breakpoint. Two empirical formulas developed based on data analysis establish relationships between the wave front slope angle and other parameters of engineering interest. Specifically, the first formula expresses the local wave front slope angle as a function of the local wave parameters. The applicability of this formula to regular and random shoaling and breaking waves is verified using extensive datasets. The second formula defines the critical wave front slope angle for wave breaking as a function of the relative water depth and bed slope. This formula is shown applicable to both the first and second breakpoints for regular wave breaking over sloping and barred beaches. A combination of these two formulas provides estimates of the incipient breaking wave heights which are in good agreement with independent experimental data.

Nearshore Current Pattern and Rip Current Occurrence at Jungmun Beach, Jeju by Numerical Computation

A nearshore current or a wave-induced current is an important phenomenon in a nearshore zone, which is composed of longshore, cross-shore, and rip currents. The nearshore current is closely related to the occurrence of coastal accidents by beachgoers. A considerable number of coastal accidents by beachgoers involving the rip current have been reported at Jungmun Beach. However, in studies and observations of the nearshore current of Jungmun Beach, understanding of the rip current pattern remains unclear. In this study, a scientific approach is taken to understand the nearshore current and the rip current patterns at Jungmun Beach by numerical computation for year of 2015. From results of numerical computation, the occurrence and spatial characteristics of the rip current, and the similarities between the rip current and incident wave conditions are analyzed. The primary results of this study reveal that the rip currents are frequently generated at Jungmun Beach, especially in the western parts of the beach, and that the rip currents often occur with a wave breaking height of around 0.5 ~ 0.7 m, a wave period of around 6 ~ 8 seconds, and a breaking angle of around 0 ~ 15 degrees.