Effects Of Wave Breaking Research Articles

Retrieval of whitecap coverage with the ERS-1 scatterometer data

In this paper, the whitecap coverage is retrieved from the ERS-1 data and the KHCC03 scattering model which takes into account the effect of wave breaking, and a new whitecap coverage formula is obtained based on the retrieval results. The results calculated from this new formula of whitecap coverage have better agreement with the measured whitecap coverage than those obtained by some famous previous formula in the range of wind speed at 10 m height from 7 m/s to 16 m/s. This shows that it is feasible to retrieve whitecap coverage from scatterometer data and the scattering model including the effect of wave breaking. Moreover, this approach is different from those methods usually used in passive remote sensing.

Smoothed particle hydrodynamics (SPH) simulation of a tuned liquid damper

The roll motion response of a single degree of freedom (SDOF) structural system to which a rigid rectangular partially filled liquid tank has been attached is considered. The SDOF structural system with the empty tank is first described with a mathematical model and this model is validated by performing decay experiments as well as experiments in which periodic excitations are applied to the system. The responses are accurately predicted by the model. The accuracy of these predictions allows us to study both experimentally and numerically, with weakly compressible SPH, the performance of the partially filled tank as a tuned liquid damper (TLD). The sloshing flows inside the tank comprise the onset of breaking waves which make the TLDs devices extremely difficult to model, especially for the potential flow multimodal approaches commonly used to simulate these sorts of coupled systems. In order to characterise the wave breaking effects on the response curves, tests have been performed with liquids of different viscosity, the increasing viscosity preventing the onset of breaking waves. The capabilities of SPH to treat this coupling problem are assessed and the results show that SPH is able to capture a substantial part of the physics involved in the addressed phenomena but further work remains still to be done relating to a more accurate treatment of the laminar viscosity and turbulence effects.

Wave and Flow Response to an Artificial Surf Reef: Laboratory Measurements

Waves and currents are essential elements in the design of an artificial surfing reef (ASR). ASRs are primarily designed to optimize the surfing conditions (i.e., increase the surfability of the incoming waves) possibly in combination with the shoreline protection from erosion. The currents generated by waves breaking on the ASR play an important role in the surfability through the wave-current interaction (WCI). Depending on the design, the WCI may negatively affect the surfability by causing the waves to break prematurely due to the current-induced wave steepening. In addition, wave breaking tends to become more irregular due to the temporal variability of the underlying currents. To mitigate the negative effects of wave breaking induced currents on the surfability, three ASR layouts are examined through detailed laboratory experiments. The layouts differ in the alongshore separation distance between two symmetrical reef sides. The ensuing flow circulations are examined in detail with both in situ current meters and video observations of surface drifters. This is done for regular incident waves, bichromatic incident waves, and irregular incident waves, all with equal energy. A data analysis shows that for a given layout the mean flow patterns for regular, bichromatic, and irregular waves are qualitatively similar, with oblique rip currents exiting at either side of the reef and strong flow circulations onshore of the gap in between the two reef sides. Increasing the separation distance leads to a significant reduction of the obliquely exiting rip currents at the outer sides of the reef, but an increase in the flow circulation onshore of the gap. This has a positive effect on the surfability by reducing the negative effects associated with the WCI on the wave breaking, thus, providing longer rides.

Reliability Analysis of Failure Probability of Wave-Dissipating Blocks

The probability of failure due to armour layer instability was estimated using a reliability software package which employs the Level II First Order Reliability Method (FORM). The stability of concrete blocks was investigated and the stability formulae taking into account the effects of wave steepness and wave breaking were used in the realibility analysis. The sensitivity of the performance function to external random variables was examined in order to establish the relative importance of variables influencing the failure probabilities.

Modeling Near-Shore Currents Induced by Irregular Breaking Wave

Abstract Near-shore surface water waves and wave-induced currents are important hydrodynamic factors in coastal zones. Propagation of irregular water waves and irregular breaking-wave induced near-shore currents have been numerical studied based on parabolic mild slope equation and near-shore currents model. Based on the JOSNWAP wave spectrum, the parabolic mild slope equation incorporating irregular and wave-breaking effects have been applied to model water waves. The wave radiation stresses exerted on currents have been calculated based on variables in the parabolic mild slope equation, and near-shore wave-induced currents have been numerically simulated based on these. The numerical results have also been validated and analyzed. It is believed that the presented numerical models are capable of adaptation to numerical simulating wave-induced near-shore circulation.

Demonstration of detuning and wavebreaking effects on Raman amplification efficiency in plasma

A plasma-based resonant backward Raman amplifier/compressor for high power amplification of short laser pulses might, under ideal conditions, convert as much as 90% of the pump energy to the seed pulse. While the theoretical highest possible efficiency of this scheme has not yet been achieved, larger efficiencies than ever before obtained experimentally (6.4%) are now being reported, and these efficiencies are accompanied by strong pulse compression. Based on these recent extensive experiments, it is now possible to deduce that the experimentally realized efficiency of the amplifier is likely constrained by two factors, namely the pump chirp and the plasma wavebreaking, and that these experimental observations may likely involve favorable compensation between the chirp of the laser and the density variation of the mediating plasma. Several methods for further improvement of the amplifier efficiency in current experiments are suggested.

Sea-Surface Polarization Ratio From Envisat ASAR AP Data

The polarization ratio (VV/HH) of normalized radar cross section over ocean surface is processed from Envisat Advanced Synthetic Aperture Radar (ASAR) alternating polarization (AP) data and compared with existing electromagnetic (EM) scattering models. The processing of the AP data is based on Level0 (raw data) product that enables us to accurately compute the contribution from additive noise separately from each burst. This is important in estimating the correct polarization ratio, particularly at higher incidence angles where the relative contribution from noise becomes severe. A recently published EM scattering model, general curvature method (GCM), is extended here to incorporate scattering from breaking waves. The performance of this model with and without breaking waves is compared with AP data and with other models for the polarization ratio. The extended GCM model is furthermore used to assess the performance of wind speed retrieval in HH polarization. The inclusion of wave breaking in the GCM model reduces the polarization ratio standard deviation from 0.64 to 0.50 and the bias from -0.34 to 0.16, as compared to the measured ASAR AP polarization ratio. The best semiempirical model from literature gives 0.51 and 0.63 for the standard deviation and bias, respectively. The difference in performance is shown to be caused by the wind speed dependence not accounted for in the semiempirical model. Validation of the new polarization ratio model in combination with C-band Model Function (CMOD) for wind speed retrieval at HH polarization shows similar performance as at VV polarization. We conclude that the GCM polarization ratio model incorporating wave-breaking effects is found to reproduce well polarization ratio measurements (ASAR AP) versus wind vector and incidence angle.

On the Vertical Structure of Wind-Driven Sea Currents

Abstract The vertical structure of wind-driven sea surface currents and the role of wind-wave breaking in its formation are investigated by means of both field experiments and modeling. Analysis of drifter measurements of surface currents in the uppermost 5-m layer at wind speeds from 3 to 15 m s−1 is the experimental starting point of this study. The velocity gradients beneath the surface are found to be 2 to 5 times weaker than in the “wall” boundary layer. Surface wind drift (identified via drift of an artificial slick) with respect to 0.5-m depths is about 0.7%, which is even less than the velocity defect over the molecular sublayer in the wall boundary layer at a smooth surface. To interpret the data, a semiempirical model describing the effect of wave breaking on wind-driven surface currents and subsurface turbulence is proposed. The model elaborates on the idea of direct injection of momentum and energy from wave breaking (including microscale breaking) into the water body. Momentum and energy transported by breaking waves into the water significantly enhance the turbulent mixing and considerably decrease velocity shears as compared to the wall boundary layer. No “artificial” surface roughness scale is needed in the model. From the experimental fact of the existence of cool temperature skin at the sea surface, it is deduced that there is a molecular sublayer at the water side of the sea surface with a thickness that depends on turbulence intensity just beneath the surface. The model predictions are consistent with the reported and other available experimental data.

Large-Eddy Simulation of Langmuir Turbulence in Pure Wind Seas

Abstract The scaling of turbulent kinetic energy (TKE) and its vertical component (VKE) in the upper ocean boundary layer, forced by realistic wind stress and surface waves including the effects of Langmuir circulations, is investigated using large-eddy simulations (LESs). The interaction of waves and turbulence is modeled by the Craik–Leibovich vortex force. Horizontally uniform surface stress τ0 and Stokes drift profiles uS(z) are specified from the 10-m wind speed U10 and the surface wave age CP/U10, where CP is the spectral peak phase speed, using an empirical surface wave spectra and an associated wave age–dependent neutral drag coefficient CD. Wave-breaking effects are not otherwise included. Mixed layer depths HML vary from 30 to 120 m, with 0.6 ≤ CP/U10 ≤ 1.2 and 8 m s−1 < U10 < 70 m s−1, thereby addressing most possible oceanic conditions where TKE production is dominated by wind and wave forcing. The mixed layer–averaged “bulk” VKE 〈w2〉/u*2 is equally sensitive to the nondimensional Stokes e-folding depth D*S/HML and to the turbulent Langmuir number Lat = u*/US, where u* = |τ0|/ρw in water density ρw and US = |uS|z=0. Use of a D*S scale-equivalent monochromatic wave does not accurately reproduce the results using a full-surface wave spectrum with the same e-folding depth. The bulk VKE for both monochromatic and broadband spectra is accurately predicted using a surface layer (SL) Langmuir number LaSL = u*/〈uS〉SL, where 〈uS〉SL is the average Stokes drift in a surface layer 0 > z > − 0.2HML relative to that near the bottom of the mixed layer. In the wave-dominated limit LaSL → 0, turbulent vertical velocity scales as wrms ∼ u*La−2/3SL. The mean profile (z) of VKE is characterized by a subsurface peak, the depth of which increases with D*S/HML to a maximum near 0.22HML as its relative magnitude /〈w2〉 decreases. Modestly accurate scalings for these variations are presented. The magnitude of the crosswind velocity convergence scales differently from VKE. These results predict that for pure wind seas and HML ≅ 50 m, 〈w2〉/u*2 varies from less than 1 for young waves at U10 = 10 m s−1 to about 2 for mature seas at winds greater than U10 = 30 m s−1. Preliminary comparisons with Lagrangian float data account for invariance in 〈w2〉/u*2 measurements as resulting from an inverse relationship between U10 and CP/U10 in observed regimes.

Numerical Modeling of Wave Transformation on Muddy Coasts

The present study offers a two-dimensional horizontal wave transformation model that can be applied on a general three-dimensional bathymetry of soft muddy coasts. The wave transformation model is based on time-dependent mild slope equations including the high energy dissipation of bottom mud layers as well as the combined effects of wave refraction, diffraction and breaking. The constitutive equations of visco-elastic-plastic model are adopted for rheological behavior of fluid mud. The results of the numerical model are compared with a series of the conducted wave-basin experiments. The performance of the application of the numerical model on a real field condition, i.e. Kumamoto Port of Japan, is also examined. Comparison between the simulated results and measured values in both laboratory and field conditions reveal the capability of the proposed wave transformation model to consider the wave attenuation on fluid mud layers.

Energy dissipation in non-uniform mangrove forests of arbitrary depth

This study aims to develop a predictive model of wave propagation through non-uniform forest in water of arbitrary depth. The theoretical model solves a full boundary value problem for wave propagation with dissipation for non-uniform mangrove forest and arbitrary water depth. In particular, wave−trunk interaction and wave breaking were found to be the dominant dissipation mechanisms. A modified mild-slope equation including dissipation is applied for wave model over changing water depth within the mangrove forest. The non-linear governing equations for wave−trunk interactions are linearised using the concept of stochastic minimalisation. The numerical results of the model are verified and compared with the experimental wave data in Can Gio Mangrove Biosphere Reserve, Southern Vietnam. The results for wave height, wave spectrum and wave-induced velocities as well as for the coefficients of transmission and reflection suggest that most of the energy is dissipated within the mangrove forest even at relatively small distance. The effect of wave breaking plays a more important role on wave attenuation in sparse forest, however, it is smaller compared to the effect of wave–trunk interactions in the denser forest.

Wind-wave transformations in an elongated bay

In order to determine wave transformations in an elongated bay, a numerical solution was used to interpret yearlong records of bottom pressure and wind velocity obtained at the mouth and head of Concepción Bay, on the Gulf of California side of the Baja California peninsula. Observed wind waves were predominantly produced by southeastward winds in the winter and north–northwestward winds in the summer. Typical mean wave periods at the bay entrance were between 3 and 5 s. In contrast, the waves at the head of the bay had predominant periods <3 s. The energetic long-period swell waves were dissipated somewhere in the bay as they were not observed at the head of the bay. This study centered in identifying the effects that caused swell waves to attenuate in the bay. The ‘Simulating WAves Nearshore (SWAN)’ model was used to determine the cause for such wave attenuation. Model results showed that swell waves were attenuated because of the combined effects of bottom friction, wave breaking, whitecapping, refraction and wave blocking by the coastline. Most of the attenuation (close to 90%), however, was caused by wave blocking owing to the change of coastline orientation of the bay. This wave blocking mechanism should therefore be explored further in embayments of complex coastline morphology.

Fundamental Numerical Study of Rip Current Generation Affected by Coastal Terrain

The formation of rip currents affected by regularly arranged beach cusps has been investigated quantitatively using 2-dimensional Boussinesq type numerical wave simulation. The numerical model has nonlinearity, dispersion, wave runup on the beach and wave breaking effects. The rip currents are generated regularly at the edge of the each cusp. Shape of the beach cusp enhances the formation of rip currents. The rip current takes its maximum velocity at H/Lo=0.013 and corresponding surf zone similarity parameter 0.7-1.0. We found the constantly low water level point at the edge of the beach cusp.

消しい消波ブロックの安定数算定実験および波形勾配と砕波の効果に関する一考察

A set of experiments was conducted to examine the stability of new type of wave dissipating blocks. It was confirmed from the experimental results that offshore wave steepness influences the stability of blocks. The parameters of stability number formula were derived with classification of wave steepness. Required weight of new block against a design wave can be reduced to 90 percent compared to a typical standard block because the stability is being improved. The wave steepness relates deeply to the breaker type, and wave steepness' effect should not be neglected in the stability estimation of blocks. In order to separate the effects of wave steepness and wave breaking, it had better to conduct the experiments with flat bottom condition for further investigation of blocks' stability.

Estimation of Shallow Water Representative Wave Heights

If the Rayleigh distribution of wave heights is valid, the representative wave heights can all be converted one to another through the known relationships. In shallow water, it has been pointed out by many researchers that the wave height distribution deviates from the Rayleigh distribution. However, it is not clear whether this deviation can lead to significant errors on the estimation of representative wave heights or not. Experimental data from small-scale, large-scale, and field experiments were used to examine the errors of the relationships derived from the Rayleigh distribution on estimating representative wave heights. The examination indicates that if Hrms is given, the relationships give overall very good estimations on H̄ and H 1/3, good estimation on H 1/10 but fair estimation on H max. The effect of wave breaking was empirically incorporated into the relationships. The new relationships give better estimation than the relationships derived from the Rayleigh distribution.

Gravity Wave Turbulence in a Laboratory Flume

We present an experimental study of the statistics of surface gravity wave turbulence in a flume of a horizontal size 12 x 6 m. For a wide range of amplitudes the wave energy spectrum was found to scale as Eomega approximately omega(-nu) in a frequency range of up to one decade. However, nu appears to be nonuniversal: it depends on the wave intensity and ranges from about 6 to 4. We discuss our results in the context of existing theories and argue that at low wave amplitudes the wave statistics is affected by the flume finite size, and at high amplitudes the wave breaking effect dominates.

An Irregular Wave Propagation Model Application to an Open Coastal Area

Abstract In this paper the DREAMS_CR_S model for propagation and deformation of random waves (characterized by a directional spectrum) over regions of variable depth is described. It is based on the linear superposition of the wave fields obtained from a monochromatic wave model for several frequency–direction components in which the incident directional spectrum is discretized. The model predicts the effects of refraction, diffraction, shoaling, reflection, and wave breaking. The model was applied to a real case—the Ancao Inlet at Ria Formosa, in Algarve (Portugal). Incident wave model conditions were chosen from measurements by a directional buoy, deployed over the seabed at −25 m depth below chart datum. The results illustrate that the model without breaking is working well and can be applied to areas with complex bathymetry. When breaking is taken into account, the results are not very accurate. The wave-breaking iterative process and the estimation of the breaking point used in the model have to be i...

Effects of the deep-water wave breaking dissipation on the wind-wave modelling in the Irish Sea

A numerical study of the effect of the deep-water wave breaking on the simulation of wind-waves in the Irish Sea region during some North Hemisphere winter months (January–February 2003) was carried out. A new formulation that takes into account the nonlinear effect of wave groups on the onset of wave breaking [Alves, J.H.G.M., Banner, M.L., 2003. Performance of a saturated-based dissipation-rate source term in modeling the fetch-limited evolution of wind waves. J. Phys. Oceanogr. 33, 1274–1298.] has been implemented and tested in a third-generation wave model. Its effect is assessed against the standard WAM Cycle 4 formulation and observations in the Irish Sea. The integrated spectral parameters computed by the new implementation of wave breaking tend to be larger (between 10% and 15% for significant wave height and mean period) than those computed by the standard formulation of WAM, especially on the eastern coast of the Irish Sea. It is found that, in the Liverpool Bay area, the only possibility for the waves to resuspend sediment is the occurrence of northwesterly wind conditions. In these situations fetch-limited growth is observed and both standard and new implementations provide similar results. In the southern Irish Sea, stronger mixed sea-swell conditions are predicted by the new formulation, which may have an impact in the description of the areas susceptible to sediment resuspension.

Vertical distribution of wave shear stress in variable water depth: Theory and field observations

A generalized analytical model is developed to describe the vertical distribution of wave‐induced shear stress in the presence of bottom slope, bottom friction and depth‐induced wave breaking in the shoaling region and surf zone. The theory is compared to data obtained on an unbarred beach in 3.7‐m mean water depth over a 2° bottom slope. Bottom slope and bottom friction are incorporated in the theory by including the wave energy dissipation by bottom friction in a potential wave theory for variable water depth, and coupling the wave theory with a wave bottom boundary layer (WBBL) theory over a sloping bottom. The effect of wave breaking is included through a periodic bore dissipation model. Previous studies have considered some, but not all, of these effects. Each of the three components, sloping bottom, bottom friction and wave breaking, exhibits a different vertical structure. The contributions due to bottom slope and bottom friction attain maximum strength in the WBBL, and decay with distance above the bed, approaching smaller but nonzero values at the surface. In contrast, the contribution from wave breaking is maximal at the surface, and decays linearly with depth, becoming zero at the bed. The vertical structure of the cross‐shore (u) and vertical (w) components of wave orbital velocity was measured using a coherent Doppler acoustic profiler. The measured velocity fields were used to obtain the ensemble averaged wave shear stress profiles that extend across the WBBL to a height of 30 cm above the bed. Close to the seabed, the observed and predicted 〈uw〉 profiles are similar, confirming the sensitivity of wave stress to frictional and bottom slope effects within the WBBL. Farther from the bed, however, the observed profiles fall off more rapidly with height, as w approaches quadrature with u faster than predicted. Wave breaking induced shear stresses were not observed.

The effect of wave breaking on surface wave imaging by Synthetic Aperture Radar

The effect of ocean wave breaking as a non-Bragg mechanism on backscattering cross-section and modulation transfer functions (MTF) of radar was investigated based on Bragg resonance theory and parametric method. The result showed that the additional effect of wave breaking on backscattering cross-section is not more than 20% except for the small incident angle of VV polarized electromagnetic (e.m.) wave but is significant for HH polarized e.m. wave. Breaking waves lead to increase in the modulus of tilt modulation MTF and the larger the wind speed, the faster the increase. For large incident angle, the modulus of tilt modulation MTF with wave breaking decreases quickly with incident angle of HH polarization and approach to that without wave breaking for VV polarization. The hydrodynamic MTF increases 30%–60% when considering wave breaking and the increase is larger for HH polarization than for VV polarization.