bluuebunny/crossref_metadata_2025 huggingface dataset:
TURBULENCE APPEARANCE AT THE BOTTOM OF A SOLITARY WAVE
Authors: Blondeaux Paolo , Pralits Jan , Vittori Giovanna
Published: December 2012

The conditions leading to transition and turbulence appearance at the bottom of a solitary wave are determined by means of a linear stability analysis of the laminar flow in the bottom boundary layer. The ratio between the wave amplitude and the thickness of the viscous bottom boundary layer is assumed to be large and a 'momentary' criterion of instability is used. The results obtained show that the laminar regime becomes unstable, during the decelerating phase, if the height of the wave is larger than a threshold value which depends on the ratio between the boundary layer thickness and the local water depth. A comparison of the theoretical results with the experimental measurements of Sumer et al. (2010) seems to support the stability analysis.
BORE-INDUCED MACROVORTICES OVER A PLANAR BEACH: THE CROSS-SEA CONDITION CASE
Authors: Postacchini Matteo , Brocchini Maurizio , Soldini Luciano
Published: December 2012

Wave breaking over submerged topographic obstacles leads to vorticity generation and, at times, to the generation of strong offshore-directed rip currents. The generation of finite-length breakers may also be induced by the positive interaction of wave trains propagating to shore with a relative angle. Such an interaction gives rise to a short-crested system, this, in turn, generating both breakers of finite crossflow length and an intense associated vorticity. We here analyze such a vorticity generation mechanism specifically focusing on the location where wave breaking occurs. To this purpose we use both a simple theoretical approach, based on the well-known theory of wave ray propagation, and ad-hoc numerical simulations, by means of a NSWE (Nonlinear Shallow Water Equations) solver. A fair comparison between such preliminary theoretical and numerical results suggests that the present work can be used as the basis for future analyses of vorticity generation by cross seas.
NONLINEAR OBLIQUE INTERACTION OF LARGE AMPLITUDE INTERNAL SOLITARY WAVES
Authors: Nakayama Keisuke , Kakinuma Taro , Tsuji Hidekazu , Oikawa Masayuki
Published: December 2012

Solitary waves are typical nonlinear long waves in the ocean. The two-dimensional interaction of solitary waves has been shown to be essentially different from the one-dimensional case and can be related to generation of large amplitude waves (including 'freak waves'). Concerning surface-water waves, Miles (1977) theoretically analyzed interaction of three solitary waves, which is called "resonant interaction† because of the relation among parameters of each wave. Weakly-nonlinear numerical study (Funakoshi, 1980) and fully-nonlinear one (Tanaka, 1993) both clarified the formation of large amplitude wave due to the interaction ("stem† wave) at the wall and its dependency of incident angle. For the case of internal waves, analyses using weakly nonlinear model equation (ex. Tsuji and Oikawa, 2006) suggest also qualitatively similar result. Therefore, the aim of this study is to investigate the strongly nonlinear interaction of internal solitary waves; especially whether the resonant behavior is found or not. As a result, it is found that the amplified internal wave amplitude becomes about three times as much as the original amplitude. In contrast, a "stem" was not found to occur when the incident wave angle was more than the critical angle, which has been demonstrated in the previous studies.
MEASUREMENT AND MODELING OF SOLITARY WAVE INDUCED BED SHEAR STRESS OVER A ROUGH BED
Authors: Seelam Jaya Kumar , Baldock Tom E
Published: December 2012

Bed shear stresses generated by solitary waves were measured using a shear cell apparatus over a rough bed in laminar and transitional flow regimes (~7600 < Re < ~60200). Modeling of bed shear stress was carried out using analytical models employing convolution integration methods forced with the free stream velocity and three eddy viscosity models. The measured wave height to water depth (h/d) ratio varied between 0.13 and 0.65; maximum near- bed velocity varied between 0.16 and 0.47 m/s and the maximum total shear stress (sum of form drag and bed shear) varied between 0.565 and 3.29 Pa. Wave friction factors estimated from the bed shear stresses at the maximum bed shear stress using both maximum and instantaneous velocities showed that there is an increase in friction factors estimated using instantaneous velocities, for non-breaking waves. Maximum positive total stress was approximately 2.2 times larger than maximum negative total stress for non-breaking waves. Modeled and measured positive total stresses are well correlated using the convolution model with an eddy viscosity model analogous to steady flow conditions (nu_t=0.45u* z1; where nu_t is eddy viscosity, u* is shear velocity and z1 is the elevation parameter related to relative roughness). The bed shear stress leads the free stream fluid velocity by approximately 30° for non-breaking waves and by 48° for breaking waves, which is under-predicted by 27% by the convolution model with above mentioned eddy viscosity model.
CHARACTERIZATION OF TRANSITION TO TURBULENCE IN SOLITARY WAVE BOUNDARY LAYER
Authors: Winarta Bambang , Tanaka Hitoshi , Yamaji Hiroto
Published: December 2012

This paper reports on continues an experimental investigation of characterizing transition to turbulence for solitary wave boundary layer in a smooth bed condition. A series of experiments have been carried out by means of a closed conduit solitary wave generation system over the Reynolds number (Re) range 5.64 x 105 - 7.34 x 105. Additionally, the instantaneous velocities were measured by using a Laser Doppler Veloci-meter (LDV) over 50 wave numbers and at 17 to 22 points in the vertical direction. The turbulence intermittency has been analyzed based on experimental data. Moreover, momentum method has been employed for calculating bottom shear stress for all cases. And then, the turbulence intensity is plotted to give clearly description how turbulence generated in the various values of Re. The phase difference and wave friction factor obtained from the present experiment has an excellent agreement with the result of previous studies. Inconsistency critical Reynolds number (Recr) can be found in solitary wave case in terms of phase difference and wave friction factor, this observable fact is difference with sinusoidal wave case which has consistency in Recr.
WAVE INTERACTION WITH LARGE ROUGHNESS ELEMENTS ON AN IMPERMEABLE SLOPING BED
Authors: Jensen Bjarne , Christensen Erik Damgaard , Sumer B. Mutlu
Published: December 2012

The present paper presents the results of an experimental and numerical investigation of the flow between large roughness elements on a steep sloping impermeable bed during wave action. The setup is designed to resemble a breakwater structure. The work is part of a study where the focus is on the details in the porous core flow and the armour layer flow i.e. the interaction between the two flow domains and the effect on the armour layer stability. In order to isolate the processes involved with the flow in the porous core the investigations are first carried out with a completely impermeable bed and successively repeated with a porous bed. In this paper the focus is on the impermeable bed. Results are obtained experimentally for flow and turbulence between the roughness elements on the sloping bed. Numerical simulations have reproduced the experimental results with good agreements and can hereby add more details to the understanding of the fluid-structure interaction.
EXPERIMENTAL STUDY OF TURBULENT OSCILLATORY BOUNDARY LAYERS IN A NEW OSCILLATORY WATER TUNNEL
Authors: Yuan Jing , Madsen Ole , Chan Eng Soon
Published: December 2012

A new oscillatory water tunnel has been built in the Civil and Environmental Engineering Department's Hydraulic Laboratory at the National University of Singapore. It can accurately produce oscillatory flows that correspond to full-scale sea waves. Tests including pure sinusoidal waves and combined wave-current flows over smooth and rough bottoms have been performed. High quality measurements of the boundary layer flow fields are obtained using a PIV system. The PIV measured flow field is phase and spatially averaged to give a mean vertical velocity profile. It is found that the logarithmic profile can accurately approximate the near-bottom first-harmonic amplitude of sinusoidal waves and give highly accurate determinations of the hydrodynamic roughness and the theoretical bottom location. The bottom shear stress obtained from momentum integral is in general agreement with results from log-profile fitting. The current profiles of combined wave-current flows indicate a two-log-profile structure as suggested by simple combined wave-current flow theory. The difference between the two current shear velocities obtained from combined wave-current flows, as well as a small but meaningful third harmonic embedded in a pure sinusoidal wave, suggest the existence of a time-varying turbulent eddy viscosity.
ASYMMETRY AND SKEWNESS IN THE BOTTOM BOUNDARY LAYER : SMALL SCALE EXPERIMENTS AND NUMERICAL MODEL
Authors: Berni Céline , Suarez Leandro , Michallet Hervé , Barthélemy Eric
Published: December 2012

This study investigates the non-linearities of wave boundary layers in the surf zone. It mainly focuses on the acceleration skewness or asymmetry. Experiments [e.g. Grasso et al., 2011] show that asymmetry influences the sediment transport. Its influence lies in the fact that asymmetry in velocity (acceleration skewness) tends to transform into velocity skewness within the boundary layer. Analysis by Henderson et al. [2004] predicts a linear relation between Skb/Skâˆž and Asâˆž/Skâˆž where Skb is the dimensionless skewness near the bed, Skâˆž the free-stream dimensionless skewness and Asâˆž the free-stream dimensionless asymmetry. Numerous experiments were carried out in the LEGI wave flume over a mobile bed composed of lightweight sediments. The quasi-random forcing is a repetition of 2 concatenated bichromatic wave packets. Vertical profiles of velocity are measured in the surf zone. A clear linear relation is shown between these two ratios. The experimental results are compared with the numerical results. A linear relation between skewness and asymmetry is also obtained.
INTEGRATED STUDY ON THE VELOCITY FIELD INDUCED BY PLUNGING BREAKERS
Authors: Rivillas Germán Daniel , Pedrozo-Acuña Adrián , Silva Rodolfo , Torres-Freyermuth Alec , Gutierrez Cesar
Published: December 2012

In this investigation we employ a technique called Bubble Image Velocimeter (BIV) to obtain measurements of flow fields in the surf-zone. This technique allows measurements of flow velocity in the aerated breaking zone, where other techniques are ineffective. The technique has been widely used to study flow propagation in front of vertical structures, it is employed in this study to estimate the velocity field induced by the propagation of a plunging wave travelling over an impermeable slope. The BIV measurements were compared to those obtained with an Acoustic Doppler Velocimeter (ADV) showing that the BIV technique is more suitable when the velocity field is estimated under the presence of an aerated flow. Moreover, the phase-averaged velocity fields obtained from the numerical model were compared against those evaluated from the BIV measurements. A reliable estimation of the VOF-type numerical derivations in the surf zone was established. In the swash zone, an over prediction of the offshore flow was identified.
MEASUREMENTS OF VORTEX GENERATION AND MOTION AT WIND WAVE SURFACES
Authors: Takano Yasuhide , Etoh Goji T. , Tsujimoto Gozo
Published: December 2012

Vortices generated at water surface under wind wave condition are most important phenomena for mass exchange between atmosphere and ocean. To extract vortices from randomly distributed velocity vectors obtained by a PTV, a new method to accurately estimate vorticity is proposed. The proposed method uses the Moving Least Square method which has been developed for grid-less numerical simulation. The optimal size of fitting area is derived theoretically and is confirmed by Monte Carlo simulation. Comparison of the accuracy between the proposed method and the commonly used method shows the advantage of the proposed method. The developed method is applied to the measurements of vorticity near the wind wave interfaces. The results show the generation and movements of the vortices at water surfaces.
APPLYING PIV MEASUREMENTS ON FLOW FIELD OF WAVES PROPAGATING OVER A SINGLE SUBMERGED POROUS ELASTIC BREAKWATER
Authors: Hsu Tai-Wen , Lan Yuan-Jyh , Lai Jian-Wu , Cheng Yung-Han , Ou Shan-Hwei
Published: December 2012

The objective of the present study is to investigate the flow field for waves propagating over a submerged poro-elastic breakwater. Particle Image Velocimetry (PIV) measurements were performed in wave conditions with breakwaters made of different materials. The experimental results were compared for various rigid and impermeable, elastic and impermeable, as well as poro-elastic cases. Measurements of wave reflection and transmission induced by soft and permeable submerged breakwaters are both carried out. The results show that the oscillatory motion of elastic submerged breakwater can induce extra reflective waves and result in a larger reflection coefficient. Positive (counterclockwise) and negative (clockwise) vortices are generated due to corner separation and pressure gradients. The negative vortex obtained in a poro-elastic breakwater is generated by the surface friction at the top of the structure. Because of the permeability, it is found that the negative vortex at the upstream side of the elastic and permeable case is smaller than that of the rigid and impermeable one. In contrast, the positive vortex at the downstream side of the poro-elastic case is larger than that seen with the other two cases. It is concluded that a poro-elastic breakwater would induce different wave reflections and flow patterns from those seen with the other cases due to its particular wave and structure interactions.
WKB APPROXIMATION TO THE MODIFIED MILD-SLOPE EQUATION
Authors: Seo Seung-Nam
Published: December 2012

WKB approximation for water wave scattering by rapidly varying topography is obtained from a modified mild-slope equation of the general form by Porter (2003). The present WKB solution is reduced to the previous study where shallow water conditions are present. WKB models from the transformed mild-slope equation, without the described bottom curvature modification, show better performance than those by the original developed mild-slope equation. The underlying significance of the present equation is discussed in the context of linear wave scattering. The selected figures representing our results further characterize main feature of this study.
LABORATORY MEASUREMENTS OF A STEADY BREAKER USING PIV AND BIV
Authors: Lin Chang , Hsieh Shih-Chun , Lin I-Ju , Chang Kuang-An , Raikar Rajkumar
Published: December 2012

Image-based particle image velocimetry (PIV) and bubble image velocimetry (BIV) techniques were employed to measure the flow field in both the non-aerated and aerated regions in a steady hydraulic jump. The jump has a Froude number of 4.62 with a large amount of air entrainment. The mean velocities and turbulence properties were obtained by ensemble averaging the repeated measurements. The spatial variations of mean velocity profiles, turbulent intensity, and Reynolds stress were discussed in details. The results show that the ratio between the maximum bubble velocity and the maximum water velocity is almost constant with a value about 0.6. The turbulence intensity of bubbles is very high in the aerated region and reaches about 0.4, while the turbulence velocity of water below the roller is significantly lower. The Reynolds stress is mostly negative and increases as elevation increases. The maximum Reynolds stress occurs at the free surface.
BIOLUMINESCENCE IMAGING FOR MEASURING FLUID SHEAR DISTRUBUTIONS
Authors: Watanabe Yasunori , Sakai Jun , Mitobe Yuta , Niida Yasuo
Published: December 2012

The dinoflagellate Pyrocystis lunula emits light in response to water motion. The statistical features of the bioluminescence, emitted by P. lunula, owing to shear stress in oscillatory boundary layer flows over ripped bed were studied in this paper with the aim to develop a new imaging technique for measuring fluid strain rate and shear using plankton that emit light in response to mechanical stimulation. The flash intensity has been found to correlate with fluid strain rate estimated from fluid velocity over ripples. Thus the instantaneous planar distribution of the fluid shear can be estimated from video images of the bioluminescence in a fluid region by using the empirical relation determined in this study.
FLOW VISUALISATION AROUND A SOLID SPHERE ON A ROUGH BED UNDER REGULAR WAVES
Authors: Vithana Hela Vidura , Simons Richard Robert , Hyde Martin
Published: December 2012

Flow visualization using Volumetric Three-component Velocimetry (V3V) was carried out during laboratory tests to determine threshold shear stress and forces on idealized spherical stones. Incipient motion tests consisted of light weight spherical particles of specific gravity=1.19-2.65 and diameter=9.6mm-31.8mm. In-line and uplift forces on a 50mm sphere sitting on a rough bed of similar spheres were measured using pressure transducers linked to tappings on the sphere surface. It was found that the Shields critical shear stress and stone protrusion has an exponential relationship. At an exposure of 0.2d and less, bed protection is remarkably stable. Incipient motion data for currents are applicable for waves when the flow is fully developed.
NONLINEAR WAVE PRESSURES GIVEN BY EXTREME WAVES ON AN UPRIGHT BREAKWATER: THEORY AND EXPERIMENTAL VALIDATION
Authors: Romolo Alessandra , Arena Felice
Published: December 2012

An analytical nonlinear theory is presented for the interaction between three-dimensional sea wave groups and a seawall during the occurrence of an exceptionally high crest or deep trough of the water elevation. The solution to the second order of the free surface displacement and of the velocity potential is derived by considering an irrotational, inviscid, incompressible flow bounded by a horizontal seabed and a vertical impermeable seawall. The analytical expression of the nonlinear wave pressure is derived. The resulting theory is able to fully describe the mechanics at the seawall and in front of it, which represents a strongly nonhomogeneous wave field, then demonstrating that it is influenced by characteristic parameters and wave conditions. The theoretical results are in good agreement with measurements carried out during a small-scale field experiment at the Natural Ocean Engineering Laboratory in Reggio Calabria (Italy). The theoretical and experimental comparisons show that some distinctive phenomena regarding wave pressures of very high standing wave groups at a seawall, in the absence of either overturning or breaking waves, may be associated with nonlinear effects.
PHYSICAL MODEL TESTS ON WAVE OVERTOPPING AND FLOW PROCESSES ON DIKE CRESTS INFLUENCED BY WAVE-CURRENT INTERACTION
Authors: Lorke Stefanie , Scheres Babette , Schuttrumpf Holger , Bornschein Antje , Pohl Reinhard
Published: December 2012

Flow processes like flow depths and flow velocities give important information about erosion and infiltration processes, which can lead to an unstable dike structure and consequently to dike failure. Up to now several physical model tests on wave run-up and wave overtopping are available to adjust and improve design formula for different dike structures. This kind of physical model tests have been performed in the here presented project FlowDike. Its main purpose is to consider two new aspects that could influence the assessment of wave run-up and wave overtopping as well as the flow processes on dikes which have not been investigated yet: longshore current and wind. Especially in estuaries and along coasts, the effect of tidal and storm induced currents combined with local wind fields can influence the incoming wave parameters at the dike toe as well as the wave run-up height, the wave overtopping rate and the flow processes on dikes. This paper will focus on these flow processes on dike slopes and dike crests on an 1:6 sloped dike influenced by oblique wave attack and longshore current.
IMPROVEMENTS IN DESCRIBING WAVE OVERTOPPING PROCESSES
Authors: Hughes Steven A , Thornton Christopher I , Van der Meer Jentsje W , Scholl Bryan N
Published: December 2012

This paper presents a new empirical relation for the shape factor in the Weibull distribution that describes the distribution of overtopping wave volumes. This improvement increases the applicable range of the Weibull distribution from very low average overtopping discharges to large discharges resulting from combined wave overtopping and steady surge overflow at negative freeboards. The effect this improvement has on wave overtopping simulation is also discussed. Measured maximum flow thicknesses, velocities, and discharges from experiments of combined wave and surge overtopping are examined to learn more about the variability of these key parameters as a function of individual overtopping wave volumes. A key finding is that wave volumes containing the 2%-exceedance value of maximum velocity typically have maximum flow thicknesses well below the 2%-exceedance level, and vice-versa. Furthermore, the 2%-exceedance hydrodynamic parameters do not occur in the 2%-exceedance wave volumes. Finally, empirical relationships are developed for several parameters that showed strong trends.
DESIGN OPTIMIZATION FOR A PASSIVE MESH SCREEN WAVE ABSORBER FOR THE CCOB
Authors: Klinghammer Christian , Lomonaco Tonda Pedro , Higuera Caubilla Pablo
Published: December 2012

A new passive wave absorber, consisting of multiple mesh screens, for the Cantabria Coastal and Ocean Basin (CCOB) was optimized regarding its overall length and performance. Physical model wave flume tests were conducted to calibrate and verify a 2D-RANS model utilizing different combinations of vertical and horizontal mesh screens. The final design of the main wave absorber at the back wall of the new CCOB was obtained by simulating different mesh screen configurations at full scale using the IH-2VOF model. Very good wave absorption over the entire working range of the wave basin could be achieved with a relatively short passive mesh screen wave absorber.
A DEMOUNTABLE WAVE ABSORBER FOR WAVE FLUMES AND BASINS
Authors: Tiedeman Simon Alexander , Allsop William , Russo Viviana , Brown Andy
Published: December 2012

Passive wave absorption is an integral component of the physical modeling environment, used to minimise unwanted reflections of wave energy that compromise test results. This paper reviews data for methods of passive absorbers and then extends this knowledge through the design and implementation of a device that can be removed from the working water surface. The modeling tests that were carried out in this paper demonstrate that a parabolic spending beach can perform by absorbing waves with coefficients of reflection Cr(energy) significantly
A LABORATORY AND FIELD STUDY ON 2DH SPECTRAL WAVE TRANSFORMATION IN MUDDY ENVIRONMENTS
Authors: Soltanpour Mohsen , Haghshenas S. Abbas , Shibayama Tomoya
Published: December 2012

The present paper offers a set of wave basin experiments on muddy beds together with field measurements data at Hendijan Mud Coast in the north-west corner of the Persian Gulf in order to investigate the 2DH spectral wave transformation over muddy beds. A dissipation model was added to REF/DIF S wave model to develop a numerical wave spectrum transformation model for muddy beaches. The proposed model was utilized to analyze the experimental and field measurements data on muddy beds. The simulated wave spectra over-mud bed are in fair agreement with the measurements.
NEW BOUSSINESQ SYSTEM FOR NONLINEAR WATER WAVES
Authors: Zhang Yao , Kennedy Andrew Brian , Westerink Joannes , Panda Nishant , Dawson Client
Published: December 2012

In this paper, a new Boussinesq water wave theory is derived which can simulate highly dispersive nonlinear waves, their depth-varying velocities, and wave-induced currents, from very deep, but still finite, depths through the surf zone to the shoreline.. Boussinesq scaling is employed. We removed the irrotationality assumption by using polynomial basis functions for velocity profile which are inserted into basic equations of motion. Keep terms up to the desired approximation level and solve the coupled weighted residual system together with vertically integrated mass equation. The computational cost is similar to normal Boussinesq theories although there are more unknown variables to be solved than that in normal Boussinesq models. Because we can reduce the number of the coupled equations by multiplying some coefficients and subtracting from each other which means the matix to be solved is in similar size as normal Boussinesq models. The models show rapid convergence to exact solutions for linear dispersion, shoaling, and orbital velocities; however, properties may be simultaneously and substantially improved for a given order of approximation using asymptotic rearrangements. This improvement is accomplished using the large numbers of degrees of freedom inherent in the definitions of the polynomial basis functions either to match additional terms in a Taylor series, or to minimize errors over a range. Future work will be focused on rotational performance in 2D model by including viscosity,breaking and turbulence.
WAVE ATTENUATION IN MANGROVE FORESTS; FIELD DATA OBTAINED IN TRANG, THAILAND
Authors: Horstman Erik , Dohmen-Janssen Marjolein , Narra Pedro , Van den Berg Niels-Jasper , Siemerink Martijn , Balke Thorsten , Bouma Tjeerd , Hulscher Suzanne
Published: December 2012

Mangroves thrive in sheltered intertidal areas in the tropics and sub-tropics. Due to this position at the interface between land and sea, mangroves play an important role in the attenuation of waves. Dissipation of wave energy in mangrove forests is an interesting feature from the viewpoint of coastal protection. Nevertheless, field data are sparse and modeling attempts reveal the need for additional data. This paper presents the results of an extensive field campaign, lasting 6 months, in mangroves along the Andaman coast of Trang Province in southern Thailand. Wave attenuation has been studied along two contrasting transects with different elevation and vegetation characteristics and different orientations towards the Andaman Sea. Along the Kantang transect, which is mostly exposed to swell waves, vegetation densities increased from 4.5 to 9.3 volume-†° along the transect and on average 63% of the incident wave energy was attenuated over a distance of 246 m. Along the Palian transect, mostly exposed to sea waves instead, vegetation increased from 4.3 to 19 volume-†° and 72% of the incident wave energy was attenuated over this 98 m transect. It was found that standardized wave attenuation correlates well with incident wave energy, when attenuation is analyzed per vegetation zone. Energy reduction rates of these zones, defined by the gradient of the correlations between the standardized wave attenuation and incident wave energy, are found to increase significantly with vegetation density. Consistently, wave reduction rates, expressing the gradient of the correlation between wave height reduction and incident wave heights, are found to be 0.001-0.014 for the study sites and also show a significant and increasing trend with vegetation densities.
FIELD INVESTIGATION OF WAVE DISSIPATION OVER SALT MARSH VEGETATION DURING TROPICAL CYCLONE
Authors: Jadhav Ranjit S , Chen Qin
Published: December 2012

Wave data were measured along a 28 m transect using 3 pressure transducers over a 2-day period during a tropical storm. The tropical storm force winds produced waves up to 0.4 m high (zero-moment) that propagated over vegetation of Spartina alterniflora submerged under a surge of over 1 m above the marsh floor. Measured wave heights, energy losses between gages and spectral energy dissipation models of rigid vegetation were utilized to estimate wave height decay rates, integral and frequency-dependent bulk drag coefficients, and frequency distribution of energy dissipation induced by the vegetation. Measurements showed that incident waves attenuated exponentially over the vegetation. The exponential wave height decay rate decreased as Reynolds number increased. The swell was observed to decay at a slower rate than the wind sea regardless of the wave height. The linear spatial wave height reduction rate increased from 1.5% to 4% /m as incident wave height decreased. The bulk drag coefficient estimated from the field measurement decreased with increasing Reynolds and Keulegan-Carpenter numbers. The energy dissipation varied across the frequency scales with the largest magnitude observed near the spectral peaks, above which the dissipation gradually decreased. The wave energy dissipation did not linearly follow the incident energy, and the degree of non-linearity varied with the frequency. For a given spectrum, the frequency-distributed drag coefficient increased gradually up to the peak frequency and remained approximately at a stable value at the higher frequencies. This spectral variation was parameterized by introducing a frequency-dependent velocity attenuation parameter inside the canopy. The spectral drag coefficient is shown to predict the distribution of energy dissipation with more accuracy than the integral coefficients, which results in a more accurate prediction of the mean wave period and spectral width of a wave field with vegetation.
THE USE OF SPATIAL RADAR OBSERVATIONS IN WAVE HINDCASTS
Authors: Gautier Caroline , Groeneweg Jacco
Published: December 2012

Ten years ago, an extensive measurement has been set up in the tidal inlet of Ameland, to obtain validation data in tidal inlets. Then the focus was on buoy measurements. In addition to these scarce point measurements wave radar data became available two years ago. The aim of this paper is to gain insight in the use and reliability of the wave radar data by comparing the radar data with SWAN model results in a storm hindcast in the Wadden Sea. In order to use the SWAN results as a benchmark the SWAN model performance was assessed first by comparing the model results with buoy measurements. In the comparison between radar and SWAN, the wave direction is considered, as well as the spectral distribution. Consistent results give confidence in both radar data and SWAN results. In general, the radar data seems to be reliable. An exception on this are regions with large bed gradients and small wave heights. At many locations, the wave spectra turn out to be bimodal. This makes it difficult to catch the wave direction in one value. In these cases, it is better to consider the full 2d spectra. The study has given insight into the quality and usefulness of the radar data. The radar observations provide an interesting data source, in addition to buoy data. Based on the first experiences with the radar data we believe that in the future the radar will be a reliable source for spatial wave data, providing proper insight in the wave models being applied in a complex area like the tidal inlet of Ameland. This will improve the prediction of extreme current and wave conditions in the Wadden Sea and thus decrease uncertainties in the safety assessments of our flood defense structures.
FIELD OBSERVATIONS AND MODEL PREDICTIONS OF WAVE TRANSFORMATION ON A MACRO-TIDAL BEACH, KOREA
Authors: Yoo Jeseon , Shin Sungwon , Jun Ki-Cheon , Shim Jae-Seol
Published: December 2012

Macro-tidal beach processes are influenced by complicated interactions of tide actions, coastal waves and morphological changes. Tidal cycles may be a primary forcing responsible for specific characteristics of hydrodynamic and morphological processes complicated on the intertidal flat in space and time. Macro-tidal sandy beaches are frequently developed in the west coast of Korea, experiencing seasonal variations of inter-tidal processes caused by a monsoonal climate in the Yellow Sea. Large winter waves tend to excite active beach morphological processes, inducing beach erosion and seaward-directed sediment transports. This study is intended to investigate and characterize intertidal hydrodynamics including wave dynamics in a macro-tide environment in Korea, by using a numerical model named COBRAS. The measured water surface elevation data are divided into wave and tidal components, in order to be used as inputs of the model. Tidal components in terms of water level change are implemented in the model by adding constant currents at the offshore boundary. Comparisons of the measurements and the predictions show a good performance of the model for wave height transformation and wave set-up across the macro-tidal beach
REMOTELY SENSED DATA FOR WAVE PROFILE ANALYSIS
Authors: Harry Matthew , Zhang Hong , Colleter Gildas
Published: December 2012

Laser scanning technology (LiDAR) is a form of remote sensing from which a water surface can be measured rapidly and accurately without in-situ sensors. An experimental setup for the measurement of waves in a wave flume is detailed with an analysis of various wave parameters. The experiments function as a source of reliable laboratory controlled data while the data analysis presents the range of research fields that the data can be applied to.
MODELLING EXTREME WAVE EVENTS (PRESENT AND FUTURE SCENARIOS) IN SOUTHWEST ENGLAND
Authors: Horrillo-Caraballo Jose M , Pan Shunqi , Reeve Dominic E , Simmonds Dave , Greaves Deborah , Fox Andrew
Published: December 2012

Coastal areas are vital part of the local economies in terms of population, tourism, trade, industry only to mention a few sectors. As the economy in these coastal areas develops, the risk in which the assets are based will increase as well as the likelihood of extreme events. The European project THESEUS "Innovative coastal technologies for safer European coasts in a changing climate† was conceived with the idea of tackle these and to reduce coastal risks. In this paper we will present a detailed study of the results obtained with the model and how this can affect the area of the Teign estuary under the future climate scenarios and the sea level rise expected. In particular the importance (or otherwise) of the joint extreme occurrence of large waves and high surge.
WAVE MODELING WITH SWAN+ADCIRC FOR THE SOUTH CAROLINA COASTAL STORM SURGE STUDY
Authors: Bender Christopher , Miller William , Naimaster Ashley , Mahoney Tucker
Published: December 2012

The South Carolina Surge Study (SCSS) used the tightly coupled SWAN+ADCIRC model to simulate tropical storm surge events. The tightly coupled model allowed calculation of wave-induced water level changes within the storm surge simulations. Inclusion of the wave-induced water level changes represents a more physics-based approach than previous methods that added wave setup after model simulations ended. Development of the SWAN+ADCIRC model included validation of water levels to local tidal forcing and for three historical hurricanes - Hazel (1954), Hugo (1989), and Ophelia (2005). The validation for waves did not include Hurricane Hazel because measured data was unavailable. Additional comparisons with WAM model results provided supplemental support to the SWAN model results. Model output applied in comparisons included contour plots of maximum wave parameters, time series of wave parameters at selected locations, and wave spectra.
A NUMERICAL SIMULATION OF THE WOS AND THE WAVE PROPAGATION ALONG A COASTAL DIKE
Authors: Prinos Panayotis , Tsakiri Maria , Souliotis Dimitris
Published: December 2012

Wave overtopping and the propagation of the waves on the crest and the landward slope of a coastal dike is investigated numerically. Wave overtopping conditions are simulated using the concept of the Wave Overtopping Simulator (WOS). Two numerical models of the WOS are constructed using the FLUENT 6.0.12 (FLUENT Inc. 2001) and the FLOW 3D 9.4 (FLOW 3D 2010) CFD codes. The former simulates the WOS without accounting for air entrainment while the latter accounts for air entrainment. The unsteady RANS equations, the RNG k-Îµ turbulence model and the VOF method are solved numerically, for "tracking" the free surface and the head of the "current" from the dike crest to the landward dike slope. The computed results from the two models are compared with each other and also against field measurements and proposed empirical relationships (Van der Meer et al. 2010).
BOUSSINESQ-TYPE EQUATIONS WITH VARIABLE COEFFICIENTS FOR NARROW-BANDED WAVE PROPAGATION FROM ARBITRARY DEPTHS TO SHALLOW WATERS
Authors: Simarro Gonzalo , Galan Alvaro , Orfila Alejandro
Published: December 2012

A fully nonlinear Boussinessq-type model with 7 Nwogu's Î±-like coefficients is considered. The model is one-layer and low-order to simplify the numerical solvability. The coefficients of the model are here considered functions of the local water depth so as to allow an improvement of the dispersive properties for narrow banded trains in very deep waters. The proposed model is fully nonlinear in weakly dispersive conditions, so that nonlinear wave decomposition in shallower waters is well reproduced.
A NUMERICAL STUDY ON THE EFFECT OF BEACH NOURISHMENT ON WAVE OVERTOPPING IN SHALLOW FORESHORES
Authors: Suzuki Tomohiro , Verwaest Toon , Veale William , Trouw Koen , Zijlema Marcel
Published: December 2012

In this paper, the effect of beach nourishment on wave overtopping in shallow foreshores is investigated with the non-hydrostatic wave-flow model SWASH. Firstly, the applicability of SWASH to model wave overtopping is tested by comparing results with a physical model setup with different storm wall heights on top of an impermeable sea dike. The numerical results show good agreement with the physical model. After validation, sensitivity analysis of the effect of beach nourishment on wave overtopping is conducted by changing bottom configurations with the SWASH model. From the sensitivity analysis, it becomes clear that wave overtopping discharge in shallow foreshores is characterized by the bores generated in surf zone due to wave breaking. To reduce wave overtopping discharge in shallow foreshore, it is important to reduce the horizontal momentum of the bores.
EVALUATION OF A PARAMETRIC-TYPE WAVE TRANSFORMATION MODEL AGAINST FIELD AND LABORATORY DATA
Authors: Jafari Alireza , Cartwright Nick
Published: December 2012

Predicting wave properties via parametric wave propagation models are broadly used in many coastal engineering applications. Numerous researchers have refined these types of models to increase their accuracy including; Battjes and Janssen (1978), Thornton and Guza (1983), Baldock et al. (1998), and Alsina and Baldock (2007). Alsina and Baldock (2007), proposed an improved parametric wave propagation models for a non-saturated surfzone which returns relatively more accuracy in comparison to others. In this paper, the Alsina and Baldock (2007) model along with Baldock et al. (1998) and Thornton and Guza (1983), are applied to data collected in South-East Queensland under stormy and calm conditions as well as laboratory data. Some of the comparisons indicate the need to incorporate some additional energy loss at the break point to account for plunging type breakers where the existing bore dissipation model is insufficient.
NEARSHORE WAVE PREDICTIONS ALONG THE OREGON AND SOUTHWEST WASHINGTON COAST
Authors: García-Medina Gabriel , Özkan-Haller H. Tuba , Ruggiero Peter
Published: December 2012

A nearshore wave forecasting system was implemented to elevate the ocean information resources in the US Pacific Northwest region. This implementation brings the US State of Oregon and the Southwest region of the state of Washington to the same level of prediction as the neighboring state of California and other regions of the country. It was achieved using the Wavewatch III numerical wave model, which was validated in intermediate to shallow waters. The forecasting system provides data at a 30 arc-second resolution from the shelf break up to a depth of 20 meters. The data is distributed to the public at no cost as part of a greater initiative put together by the Networked Association of Ocean Observing Systems. Information generated by this implementation is presently being used to provide boundary conditions to localized applications in the region as well as to beach users.
FORECASTING THE WAVE-CURRENT INTERACTIONS AT THE MOUTH OF THE COLUMBIA RIVER, OR, USA
Authors: Kassem Sarah , Ozkan-Haller H. Tuba
Published: December 2012

An operational wave forecast of the area near the mouth of the Columbia River is presented. This region is known for its large waves and strong tidal currents. The forecast is forced with full directional spectra obtained from a refined WaveWatchIII forecast of the Pacific Northwest, and tidal current inputs are obtained from an estuarine circulation forecast of the Columbia River. The forecast has been operational since August 2011 providing short-term predictive wave information at the mouth of the Columbia River. Results from a 6-month period are promising, with a normalized root-mean-squared error (NRMSE) of 16% at the location of an inshore buoy, which is located outside the zone of tidal influence in 25 m water depth. Near the river mouth and in the channel, wave heights are heavily dominated by the tidal currents which significantly increase wave heights on ebb tides. Hindcast results shows that the model is able to predict the general effect of the tidal currents with a NRMSE of 30% in wave heights at the river mouth. Despite some of the model limitations, it still provides valuable information to navigators and bar pilots since it includes the effects of the tidal currents.
NUMERICAL VALIDATION OF WAVE PROPAGATION, TRANSFORMATION AND DISSIPATION TOWARDS A HARBOUR FACILITY: A NEW BECHMARK CASE
Authors: Diaz-Hernandez Gabriel , Lomonaco Pedro , Armesto Jose Antonio , Mendoza Andrés Patricio
Published: December 2012

A new set of experimental data is used in the numerical validation (2DH) of waves propagating towards a scaled harbour facility. The Laredo marina-harbour located at the North coast of Cantabria (Spain), which has lately improved by the extension of its main breakwater, was modelled in the 28 m long and 8.6 m wide directional wave basin of the Environmental Hydraulic Institute, at the University of Cantabria. For two months, different 3D tests were simulated for this harbour configuration, starting with the detailed construction of the real bathymetry contour data, and followed by the construction of the 450 m (trunk and head), of a curved rubble-mound, 1:2 slope breakwater, capped with a variable height L-shaped crownwall and the armour layer is composed of 60 ton (trunk) and 70 ton (roundhead) cubic units.
NEARSHORE WAVE DAMPING DUE TO THE EFFECT ON WINDS IN RESPONSE TO OFFSHORE WIND FARMS
Authors: Rodriguez Gandara Ruben , Harris John
Published: December 2012

Despite the progress that has been made in modeling wind wake interaction between turbines in offshore wind farms, only a handful of studies have quantified the impact of wind turbines or wave farms upon surface waves, and there are even less articles about the wave blockage induced by the whole array of turbines upon wind waves. This hypothetical case study proposes a methodology that takes into account the combined effect of wind wake and wave blockage on wind waves when transforming offshore waves to nearshore in an offshore wind farm scenario.
SPH MODEL TO SIMULATE MOVEMENT OF GRASS MEADOW OF POSIDONIA UNDER WAVES
Authors: Larroude Philippe , Oudart Thibault
Published: December 2012

The objective of this paper is to try a new approach to simulate the interactions between waves and algae. The chosen method is to simulate waves and plants through SPH (Smoothed Particle Hydrodynamics, SPH). In this model, the algae are defined as a solid that respects Hook's law, which is in direct interaction with the fluid part. Given the properties of this method especially in terms of computation time, the dimensions of the simulations are limited. A successful representation of the movement of algae under waves or/and current by SPH will permit the determination of coefficient of friction corresponding to a type of algae, that can be used in a different larger scale code.
THE NUMERICAL INVESTIGATION OF WAVE GENERATION BY LOW SPEED WINDS
Authors: Liao Ying-Po , Kaihatu James M.
Published: December 2012

In this study we investigate the process of wind-wave generation by using direct numerical simulation (DNS). Air and water domains are respectively solved by Navier-Stokes equations in 3D Cartesian coordinates in which air-water coupled boundary conditions are specified at interface. A shear wind on the top of the air domain is specified, and air and water domains are subsequently driven to fully-developed turbulence, allowing wave growth at interface. In this paper we improve the work published by Lin et al. (2008). Instead of simplified linear boundary conditions (BCs), we derive and impose the non-linear BCs for normal stress at interface, as well as non-linear curvature terms used to balance the discontinuity. The results show that at the linear (initial) stage, faster wave growth is seen with non-linear BCs than with linearized BCs. This is reversed during the exponential (developed) stage.
VORTICAL VLF MOTIONS UNDER SHORE-NORMAL INCIDENT WAVES
Authors: De Schipper Matthieu Andreas , Reniers Ad , MacMahan Jamie , Ranasinghe Roshanka
Published: December 2012

Field observations and numerical model simulations are examined to investigate the magnitude of vortical very low frequency (VLF) velocity fluctuations (i.e. large scale surfzone eddies) under different offshore wave forcing. Observations of vortical VLF motions under shore -normal wave incidence at Duck, NC, USA are re-analyzed and compared with the characteristics of the incident wave spectrum. Long wave periods and narrow frequency spread incident waves were found to coincide with stronger vortical VLF motions. Numerical model simulations investigating the effect of the incident wave parameters in a more isolated way confirm the observed effect of frequency spread and wave period on the magnitude of VLF motions. Variations in incident wave spectrum resulted in changes in the vortical VLF magnitude of the same order as the magnitude of the vortical VLF velocity fluctuations themselves. These results imply that under shore-normal incident waves strong vortical VLF velocity fluctuations in the surfzone are more likely under swell conditions and at swell dominated coasts.
NUMERICAL SIMULATIONS OF BREAKING SOLITARY WAVES
Authors: Lubin Pierre , Glockner Stéphane
Published: December 2012

This paper presents the application of a parallel numerical code to breaking solitary waves impacting a seawall structure. The three-dimensional Navier-Stokes equations are solved in air and water, coupled with a subgrid-scale model to take turbulence into account. We compared three numerical methods for the free-surface description, using the classical VOF-PLIC and VOF-TVD methods, and an original VOF-SM method recently developed in our numerical tool (Vincent et al., 2010). Some experimental data for solitary waves impinging and overtopping coastal structures are available in literature (Hsiao et al., 2010). Solitary waves are often used to model tsunami behaviors because of their hydrodynamic similarities. From a numerical point of view, it allows shorter CPU time simulations, as only one wave breaks. Here we apply the model to simulate three-dimensional solitary waves and compare qualitatively our results with the experimental data. We investigate three configurations of solitary waves impinging and overtopping an impermeable seawall on a 1:20 sloping beach.