Search

Longshore and cross-shore currents in the surf zone were observed on a dissipative barred beach for 20 days using a horizontally mounted acoustic-Doppler current profiler (H-ADCP). This novel deployment strategy allowed for the synoptic measurement of the longshore current at approximately mid-depth at several cross-shore locations. The longshore current data were analyzed with wave and tide level data to show the effect of tidal range on the variation of the longshore current with respect to cross-shore location. The longshore current was higher near the outer bar area than that observed near the inner bar. Moreover, the current became higher during the low tide and lower during the high tide. A longshore current model was proposed using the spring and neap tide data sets and then applied to the remaining observation period during large events of incident wave energy flux. The model with the relative water level luded provided sufficient accuracy to account for the tide effects. [ABSTRACT FROM AUTHOR]

Field observations were conducted during relatively mild wave conditions at a dissipative barred sandy beach to investigate the cross-shore sediment dynamics from the inner surf zone to the offshore side of the outer bar. Fluorescent sand tracers of five different colors were placed on the seabed at different cross-shore locations, and sand core samples were extracted respectively 11 and 20 days after the placement of tracers. Moreover, nine cross-shore bathymetric/topographic beach surveys were conducted, and the water level, wave, and wind conditions were observed. The objective of this research was to investigate the mechanisms of the on- and offshore-directed sediment transport during the inner- and outer-bar accretion events. The analyzed results revealed that at the inner surf zone, the sediment was dominantly transported in the onshore direction. The sediment was also transported offshore-ward due to the undertow; however, this occurred until the offshore end of the trough region. Overall, the outer bar shape affected the on-offshore sediment transport rate. The sediment movements in the onshore region and offshore region of the outer bar were not related; however, the outer bar was formed with the sediments from both the inner- and outer-bar regions. [ABSTRACT FROM AUTHOR]

Observations of the cross-shore variations of pressure gradients measured on a fixed barred beach in a large-scale laboratory wave flume are presented in this paper. The wave-induced components (0.1-1.0 Hz) of the free surface elevation, near-bottom vertical and cross-shore velocities, and pressure gradient are used in the analysis. The cross-shore variation of the pressure gradient showed the maximum value in the area of wave breaking over the bar, and the pressure gradients were considered to be influenced by the fluctuation of the water surface elevation, which are shown to be a rough proxy for the water surface slope. The cross correlation related to the vertical velocity showed no correlation in the wave breaking area. Surprisingly, although several measuring points were located in the wave breaking area or in the inner surf zone, the spatial variation of the pressure gradient and water surface elevation had a correlation coefficient greater than 0.8 with time lags approximately 0.1 of the wave period from offshore to onshore in both regular and irregular wave cases. This indicates that the near-bottom pressure gradient can be estimated using the water surface elevation over a complex barred bathymetry and through the inner surf zone. [ABSTRACT FROM AUTHOR]

The wave-induced pressure gradient, ∂p/∂x, at the bottom is related to fluid acceleration and sediment movement in the surf zone. Following similar large-scale laboratory work by Suzuki et al. [2008a], this paper deals with the observations and analysis of bottom pressure gradients on a natural sandy beach. The cross-correlation coefficients between ∂p/∂x and the water surface elevation are high even in the surf zone, and the coefficients are higher than the coefficients between ∂p/∂x and the vertical velocity component or ∂p/∂x and du/dt. The observed nonlinear characteristics of ∂p/∂x are weaker than the laboratory experimental data but extreme values of ∂p/∂x are larger than the experiments. The distributions of exceedance probability of ∂p/∂x are evaluated using the two-parameter Weibull distribution. The modulus of the Weibull distribution is evaluated as a function of local significant wave height normalized by the offshore significant wave height. The exceedance probability distributions of ∂p/∂x show a broader distribution for the field data compared to the laboratory, but are, nevertheless, predicted reasonably well with the Weibull distribution. [ABSTRACT FROM AUTHOR]

This paper describes the hydrodynamic characteristics of a pile-supported vertical wall breakwater, the upper part of which is a vertical wall, and the lower part consisting of an array of vertical piles. For regular waves, using the eigenfunction expansion method, a numerical model has been developed that can compute wave transmission, reflection, and run-up, and wave force acting on the breakwater. For irregular waves, the regular wave model is repeatedly used for each frequency component of the irregular wave spectrum. The wave period is determined according to the frequency of the component wave, while the root-mean-squared wave height is used for all the component waves to compute the energy dissipation between piles. To examine the validity of the developed models, large-scale laboratory experiments have been conducted for pile-supported vertical wall breakwaters with a constant spacing between piles but various drafts of the upper vertical wall. Comparisons between measurement and prediction show that the numerical model adequately reproduces most of the important features of the experimental results for both regular and irregular waves. The pile-supported vertical wall breakwater always gives smaller transmission and larger reflection than a curtain wall breakwater with the same draft as that of the upper wall, or a pile breakwater with the same porosity as that of the lower part, of the pile-supported vertical wall breakwater. [ABSTRACT FROM AUTHOR]

Laboratory measurements of the instantaneous free surface, horizontal velocity, and void fraction fluctuations were made simultaneously for three cases of regular waves breaking on a plane slope. The data were reduced by ensemble averaging to quantify the temporal variation of the turbulence intensity and void fraction above trough level in the aeration region of the breaking waves. The cross-shore location of the measurements was restricted to the transition region marked by a rapid decrease in wave height. The study showed that the maximum ensemble-averaged void fractions were between 15 and 20% and that the temporal variation of the normalized void fraction above the still water level could be modeled by linear growth followed by exponential decay. The temporal variation of void fraction above the still water normalized by the wave period and average void fraction appears to be self-similar. [ABSTRACT FROM AUTHOR]

A small-scale laboratory experiment was conducted to quantify a transient wave overtopping a horizontal, deck fixed above the free surface. Detailed free surface and velocity measurements were made for two cases with and without the deck structure to quantify the effect of the deck on the wave kinematics. The study showed that the structure increased the free surface above the leading edge of the deck by 20%. The velocity profile at the leading edge was fairly uniform, and the maximum horizontal velocity was similar to the maximum crest velocity measured without the deck. Immediately below the deck, the maximum velocity was 2.5 times greater than the corresponding velocity without the deck and 2.1 times greater than the maximum crest velocity without the deck. On the deck, the wave collapsed into a thin bore with velocities that exceeded 2.4 times the maximum crest velocity measured without the deck. [Copyright &y& Elsevier]

This research employs a Computational Fluid Dynamics (CFD) model utilizing the olaFlow solver to investigate the efficacy of flooding mitigation structures, such as a seawall (SW) and submerged breakwater (SB), in safeguarding an idealized coastal community against tsunami-like waves-induced overland flows. The numerical model results were validated through a series of large-scale laboratory experiment. A range of surges and wave conditions, encompassing non-breaking, impulsive breaking, and broken waves interacting with the beachfront berm, were examined. The outcomes reveal excellent consistency between simulated and measured wave hydrodynamic and loading parameters, including free surface displacements, velocities, forces, and pressures. Beyond the scope of the laboratory experiment, the numerical simulations shed light on the intricacies of overland flow patterns around macro-roughness elements. These simulations highlight that the overland flow passes the macro-roughness elements, generating the jet-type channelized flow with stronger velocity and lower water elevation in the middle of the landward area. The study also elucidates the impact of tsunami-like waves on the first row of buildings, with maximum runup heights ranging from two to four times the incident wave heights. Moreover, the combined installation of seawall and submerged breakwater (SWSB) mitigated baseline runup heights by 10% and 45% for breaking and broken wave conditions, respectively. Conversely, a 20% runup amplification was observed in the non-breaking wave condition compared to the baseline configuration. Additionally, the research explores the vertical distribution of wave-induced pressures on the seaward-most building row, strongly influenced by water level variations. Maximum pressures exhibited a linear decrease from low to high pressure transducer elevations in low-water-level conditions, contrasting with a significant increase in high-water-level conditions. These findings provide valuable insights for coastal community planning and resilience strategies, emphasizing the importance of tailored mitigation measures in coastal regions vulnerable to tsunami-like wave events. • OpenFOAM-based model was employed to investigate flow hydrodynamics and the efficacy of flooding mitigation structures. • Characterize three wave-breaking patterns through building elements and formation mechanisms of jet-type channelized flows. • Evaluation of maximum wave runup on the first row, with significant reductions achieved in combined SWSB configuration. • Analysis of pressure distribution on the first array during different wave phases, revealing insights into pressure dynamics. [ABSTRACT FROM AUTHOR]

Quantitative CFD model validation and inter-model comparisons between IHFOAM and ANSYS-FLUENT were performed for pressures and forces on an elevated structure using a 1:10 physical model. Non-breaking, impulsive breaking, and broken wave conditions at the structure's location were simulated in IHFOAM and FLUENT. The calculated time series of water surface elevation and horizontal and vertical pressures and forces were compared with the measured data. We introduced the impulse of residual to quantify the variation of the force and pressure time series. Results indicated that the numerical models performed differently depending on the wave conditions, even for the same initial set up. Non-breaking wave simulations showed the best agreement with experimental data for both models, while broken wave trials showed the largest deviations. Bottom pressures and vertical forces were less sensitive to wave breaking conditions. Results indicate that future benchmarking tests for an elevated structure must consider both horizontal and vertical forces due to various wave breaking conditions. The accuracy of simulated wave shoaling and breaking processes played a key role in precisely calculating the forces and pressures on the structure, and it was difficult for the CFD models to simulate the exact wave breaking conditions as the measurements. [ABSTRACT FROM AUTHOR]