Wave Overtopping Simulator Research Articles

Numerical Evaluation of Wave Dissipation on a Breakwater Slope Covered by Precast Blocks with Different Geometrical Characteristics

Slopes suffer damage from waves in coastal environments. Precast blocks with well-designed geometrical characteristics can benefit the construction of revetments by mitigating the issue of wave overtopping and dissipating wave energy. In this study, we numerically studied the effect of the geometrical characteristics of precast blocks on wave overtopping by carrying out a numerical simulation of wave overtopping on a slope covered with precast blocks. A total of three different types of blocks were considered in this study to determine the optimal geometric shape using a validated numerical model. Our numerical investigation demonstrated that the roughness of the precast block plays an important role in lessening the height of the wave run-up. Concave and embedded regular hexagons could reduce the wave run-up height by 44.6% compared with smooth slopes within a 2 s wave period. Herein, we evaluate and discuss the influence of the geometrical characteristics of a given precast block, such as thickness, aperture, and wave dissipation notch, on wave run-up. We also present an empirical formula for predicting wave run-up on a slope covered by a concave and embedded regular hexagon-type prefabricated block. This study provides valuable insights into the design of prefabricated revetment blocks.

Combined Pullout Tests And Wave Overtopping Simulations On Three Species-Rich Grass Covered Dikes In The Netherlands

Grass cover erosion by wave overtopping is a major failure mechanism for earthen dikes. Grass cover erosion resistance (represented by the critical velocity, Uc) can be assessed using full-scale, destructive tests with the wave overtopping simulator (WOS) in combination with the erosion model ‘cumulative overload method’ (COM). Although these tests provide valuable information, they are relatively expensive and time consuming. Therefore, a small-scale grass pullout test (GPT), which translates the vertical pullout force of a grass sod to a Uc, may be an attractive alternative. In this paper, based on comparative testing with the WOS and GPT on three species-rich grass covers on dikes in the Netherlands, we assess the correspondence between the Uc obtained with the WOS and GPT for species-rich grass covers. Ultimately, by also including historical tests, we aim to get more insight into the suitability of the GPT for quantitative erodibility assessment of grass covers in general. During testing with the WOS, no failure was observed for the tested grass cover sections. Therefore only a lower bound of the Uc could be derived. Results indicate that the estimated Uc with the GPT is around the lower bound values obtained with the WOS. This is in line with previous tests on conventional grass covers, for which the GPT provides a more conservative estimate of the Uc than the WOS. Adaptations in the translation from pullout force to Uc may correct for the negative bias and hence improve the reliability of the GPT for quantitative erodibility assessment. Several suggestions to adapt the GPT in future work are provided in this paper. These adaptations should be tested and validated for conventional as well as species-rich grass covers to guarantee the general applicability of the method.

GRASS SOD PULLING TESTS TO DETERMINE RESISTANCE AGAINST EROSION BY WAVE OVERTOPPING

From 2007 wave overtopping tests with the Wave Overtopping Simulator (Van der Meer et al, 2008) have been performed on real dikes in order to determine the strength of grass covers against loads from wave overtopping. Over 15 different locations and over 50 different test sections have been tested. Most of these large scale tests have been performed on grass covers on a clay subsoil. As part of the tests since 2014, grass pull tests with a grass sod pulling device have been performed in order to estimate the critical velocity, the strength of the grass cover, on a specific subsoil with a small and easy to perform test. The critical velocity is derived from the critical normal stresses which are calculated from the force needed to pull out the grass sod and the dimensions of the pulled sod. The method of determining the critical velocity from grass pull tests has been validated with the results of tests with the Wave Overtopping Simulator. The practical, mobile and easy to perform grass pull tests can be used to evaluate the strength of grass covers over time after seeding and for an estimation of strength of existing grass covers on different subsoils.

Numerical Simulation of Wave Overtopping of an Ecologically Honeycomb-Type Revetment with Rigid Vegetation

Traditional concrete revetments can destroy the ecological environment and the water landscape. An increasing number of ecological revetment structures have been applied in coastal, lake, and river regulation projects. It has been found that honeycomb-type revetments display a better performance in the attenuation of wave overtopping when compared to experimental data collected using the Eurotop and Muttray’s formula; recording a 40% decrease in the wave run-up in comparison to the latter. To further investigate the wave run-up and overtopping of the ecologically vegetated honeycomb-type revetment, based on OpenFOAM, an open source computational fluid dynamics software, a three-dimensional numerical wave tank was established. The Discrete Particle Method (DPM) was used to simulate gravel movement, and the flexible plant move boundary model was developed to simulate vegetation. The results of wave run-up calculated by the numerical model and those obtained by the experiments were in good agreement, with errors less than 20%. The modeled results of wave overtopping were within the same order of magnitude as those from the experiments; however, critical limitations were noticed due to effects of plant generalization and grid restrictions imposed by DPM methods. The results showed that wave overtopping increased with increasing wave period and wave height. However, with an increase in the wave overtopping, the influence of the wave period on wave overtopping decreased. The increase in vegetation density effectively reduced wave overtopping. Furthermore, an empirical formula for wave overtopping, considering the effects of vegetation density, was proposed.

Experimental analysis and numerical simulation of wave overtopping on a fixed vertical cylinder under regular waves

Wave overtopping phenomenon affects relatively narrow offshore marine structures different from shoreline linear structures, where there is not defined a precise prediction methodology as it is the case of the behaviour at long coastal defences. In the present study a combined experimental and numerical approach has been followed to obtain an empirical relation that represents the relative overtopping discharge over a fixed vertical cylinder exposed to non-impulsive wave conditions. The phenomenon follows a Weibull type dependence on the relative freeboard in a similar way as the case of vertical walls but reporting a decreasing overtopping rate at higher freeboards. In addition, a direct linear relationship between the relative mean flow thickness computed at the centre of the circular crest of the cylinder and the relative overtopping discharge has been observed. This methodology may be used as an indirect cost-effective method to characterize experimentally the wave overtopping phenomenon in cylindrical structures of full-scale prototypes without the need of accumulating and characterising huge amounts of overtopped water volumes. The present study contains a systematic analysis of the dispersion obtained in the experimental and computational results to evaluate the performance attributed to the proposed empirical expressions. • Overtopping has been characterized in a fixed vertical cylinder and compared with the behaviour of long shoreline defences. • A RANS-VOF Eulerian numerical model has been validated experimentally with a physical scaled model in a wave flume. • A new Weibull type expression predicts the overtopping discharge in a vertical cylinder for non-impulsive wave conditions. • The flow thickness measured at the crest has been proposed to determine the mean overtopping discharge over the structure.

Simulation of random wave overtopping by a WCSPH model

In this work the Weakly Compressible SPH-based (WCSPH) model DualSPHysics has been validated and applied to study the random wave overtopping of dike-promenade layout in shallow water conditions. Data from physical model tests carried out in a small-scale wave flume have been used for model validation. The results have been compared in terms of water surface elevation, mean discharges and individual overtopping volumes distribution. The selected geometrical layout is representative of the coastal area of Premià de Mar, in Catalonia (Spain). This stretch of the coast presents both railways and a bike path very close to the shore and therefore exposed to possible sea storms. For the first time an SPH-based model has been employed to reproduce long-lasting wave overtopping tests, made of time series of 1000 irregular waves, which are representative of real sea states. The density diffusion scheme and the modified Dynamic Boundary Conditions have been applied in the present simulations. By employing standard setup for SPH modelling of wave-structure interaction problems of a very long duration, stable simulations and accurate results have been attained.

Numerical Simulation of Random Wave Overtopping of Rubble Mound Breakwater with Armor Units

Based on the open source code OpenFOAM, a three-dimensional model is presented for simulation of the interaction between waves and rubble mound breakwater with armor units. The armor units with their real geometries are depicted through computational grids. The volume-averaged RANS equation and the seepage equation containing nonlinear term are used to describe the percolation in the core and underlayer of the breakwater. Grids independence analysis are carried out, the horizontal and vertical grid size are recommended to take as one-fifteenth of the mean nominal diameter D50 of the armor units and one-fifteenth of the wave height respectively. Random wave overtopping of rubble mound breakwater with armor units is simulated through the proposed model. The results show good agreement between the simulated and measured overtopping discharge rates for different types of armor units. The developed numerical model can be used to evaluate the random wave overtopping in design of rubble mound breakwater with artificial armor blocs.

WAVE OVERTOPPING TESTS TO DETERMINE TROPICAL GRASS SPECIES AND TOPSOILS FOR POLDER DIKES IN A TROPICAL COUNTRY

A dike or levee will protect a polder to build in a tropical country against coastal flooding. To ensure that the performance of the dike is in accordance with the safety standard, wave overtopping tests with a wave overtopping simulator have been performed on a mock-up dike. These wave overtopping tests will guide the selection of the grass species and topsoil for the grass cover of the landward side of the dike. The paper describes the design of a new dedicated wave overtopping simulator, the construction of the mock-up dike, the results of the eight tests on the mock-up dike and the critical velocities (strength indicator of the grass cover) established with the cumulative overload method.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/MCuKojNyNyQ

Numerical simulation of wave overtopping above perforated caisson breakwaters

A two-dimensional numerical model was used to study the wave overtopping performance above perforated caisson breakwaters under regular waves. The turbulent flow was simulated by solving the Reynolds Averaged Navier–Stokes (RANS) equations and the k–ε turbulence model equations. In the numerical wave flume, the free surface was tracked by the Volume of Fluid (VOF) method, and a relaxation zone was added to avoid the unwanted re-reflection from the inflow boundary. Based on the ideal gas equation at a constant temperature, the pressure change caused by the compressed air inside the wave chamber was incorporated into the numerical model for accurately simulating the wave motion inside the wave chamber. The numerical results of the free surface elevations inside and outside the wave chamber, the wave overtopping discharges and the reflection coefficients of perforated caisson breakwaters were in good agreement with the experimental data. This means that the numerical model is valid in estimating wave action and overtopping on complicated coastal structures with perforated thin walls. The distributions of flow velocity and turbulence kinetic energy (TKE) around the perforated caissons were clarified, which gave a better understanding of the wave overtopping mechanism above the perforated caisson breakwaters. Numerical results showed that the wave energy transferred by the overtopping flows is much smaller than that dissipated by the perforated caisson breakwater. When the relative freeboard (the ratio of the crest freeboard to the incident wave height) of the perforated caisson breakwater was larger than 0.58, the existence of the overtopping flow has no significant influence on the reflection coefficient. Besides, avoiding the air compression inside the wave chamber can effectively reduce the overtopping discharge. Increasing the caisson porosity or the wave chamber width can also reduce the overtopping discharge above the perforated caisson breakwaters.

Numerical Simulation of Wave Runup and Overtopping for Short and Long Waves Using Staggered Grid Variational Boussinesq

In designing a numerical tool for simulating a wide variety of water waves, i.e. short to long waves, an accurate and robust wave model and numerical implementation are needed. Dispersion and nonlinearity are the two most important physical aspects that should be modeled accurately. To be applicable to simulate many coastal engineering applications, the numerical scheme should be capable of simulating wave runup and overtopping. In this paper, we extend the capability of a Boussinesq-type model called Variational Boussinesq (VB) model for simulating the runup and overtopping of water waves. To that end, the vertical layer of the fluid is modeled continuously by a linear combination of three functions. If two of these three functions have been incorporated in the previous numerical approximation called the SVB model, this paper discusses the improvement of SVB model by incorporating all the three functions. This approach improve the dispersive property of the SVB model due to its ability to simulate short waves up to kd = 20, compared to the previous model which was only up to kd = 7, where k denotes wave number and d water depth. Furthermore, the model is implemented numerically by using the staggered conservative scheme. In the new implementation, the model is switched to the non-dispersive Shallow Water Equations (SWE) when dealing with a dry area for runup and overtopping phenomena. The new implementation is tested against analytical solutions of soliton propagation and standing wave phenomenon; moreover, it is also tested against experimental data from hydrodynamic laboratories for simulating solitary wave breaking above a sloping bottom, composite beach, and in a structure for simulating overtopping phenomenon. The implementation is also tested against experimental data for simulating irregular wave propagation and runup above a fringing reef. The results of numerical simulation agree quite well with experimental data.

Numerical Simulation of Wave Overtopping on Breakwater with an Armor Layer of Accropode Using SWASH Model

In this paper, a new method for predicting wave overtopping discharges of Accropode armored breakwaters using the non-hydrostatic wave model Simulating WAves till SHore (SWASH) is presented. The apparent friction coefficient concept is proposed to allow the bottom shear stress term calculated in the momentum equation to reasonably represent the effect of comprehensive energy dissipation caused by the roughness and seepage during the wave overtopping process. A large number of wave overtopping cases are simulated with a calibrated SWASH model to determine the values of equivalent roughness coefficients so that the apparent friction coefficients can be estimated to achieve the conditions with good agreement between numerical overtopping discharges and those from the EurOtop neural network model. The relative crest freeboard and the wave steepness are found to be the two main factors affecting the equivalent roughness coefficient. A derived empirical formula for the estimation of an equivalent roughness coefficient is presented. The simulated overtopping discharges by the SWASH model using the values of the equivalent roughness coefficient estimated from the empirical formula are compared with the physical model test results. It is found that the mean error rate from the present model predictions is 0.24, which is slightly better than the mean error rate of 0.26 from the EurOtop neural network model.

Simulation of Wave Overtopping and Inundation over a Dike Caused by Typhoon Chaba at Marine City, Busan, Korea

Suh, S.-W. and Kim, H.-J., 2018. Simulation of wave overtopping and inundation over a dike caused by Typhoon Chaba at Marine city, Busan, Korea. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 711–715. Coconut Creek (Florida), ISSN 0749-0208.This study follows up previous research on simulating the wave-induced overtopping of coastal dikes by incorporating the empirical formulas of EurOtop version 2007 into the storm surge model ADCIRC SWAN. Hindcasting simulations were performed for the wave overtopping and inundation induced by Typhoon Chaba along the dike of Marine City, South Korea, in 2016. The simulation results showed that the wave overtopping and inundation lasted for at least three hours and were spread over the dike. Normal storm surge inundation was not seen because the dike crest height of 4.40 m was higher than the peak water surface elevation (WSE) of 1.13 m and significant wave height of 3.09 m. Near the dike, the wave overtopped maximum inundation height was ~0.7 m and decreased along the overland road to the upper zone, which agrees with the field survey results. This tendency was almost the same as that reported previously regardless of the dike dimensions and incoming wave heights. The reduction factor in EurOtop is an important influence in generating the inundation. Sensitivity tests indicated that a value of 0.63 is appropriate for combining a rising WSE with storm waves and filling gap effects on two-layer tetrapod slopes. This kind of approach to inundation vulnerability is more applicable than the prevailing storm surge inundation for natural or low-lying coastal areas because more than 50% of the South Korean coast is artificial and should help in developing early warning systems and/or vulnerability analyses of mitigation projects at other artificial coasts.

DETERMINING THE CRITICAL VELOCITY OF GRASS SODS FOR WAVE OVERTOPPING BY A GRASS PULLING DEVICE

DETERMINING THE CRITICAL VELOCITY OF GRASS SODS FOR
 WAVE OVERTOPPING BY A GRASS PULLING DEVICE
 Roel Bijlard, Delft University of Technology, roelbijlard@gmail.com
 Gosse Jan Steendam, INFRAM International, gosse.jan.steendam@infram.nl
 Henk Jan Verhagen, Delft University of Technology, h.j.verhagen@tudelft.nl
 Jentsje van der Meer, Van der Meer Consulting bv, jm@vandermeerconsulting.nl
 
 INTRODUCTION
 There is a shift in the approach for designing coastal
 structures in the Netherlands, such as dikes or levees.
 In the past dikes were designed on the probability of
 exceedance of the water level during specific incoming
 (wave) storm conditions. In the near future the design
 criterion will be the probability of flooding of the
 hinterland. In order to determine this flood probability,
 the strength of the dike has to be known at which
 failure occurs. During extreme storm conditions waves
 will overtop the crest which can lead to erosion of the
 grass sod on the landward slope. This can finally result
 in instability of the dike and flooding of the hinterland.
 Past research focused on the erosion of the grass sod
 during different wave overtopping conditions, see
 Steendam 2014. The last few years many tests have
 been performed with the Wave Overtopping Simulator.
 During these tests the Cumulative Hydraulic Overload
 Method has been developed, see Van der Meer 2010
 and Steendam 2014. With this method an estimation
 of the critical velocity of the grass sod has to be made.
 The critical velocity is a strength parameter for a grass
 sod on a dike during loads induced by overtopping
 wave volumes.
 
 SOD PULLING TESTS
 For safety assessments it would be beneficial if there
 is also an easier way to determine the critical velocity
 of the grass sod. However, it is important to measure
 the actual strength of the grass cover, so a visual
 inspection cannot be satisfactory. The sod pulling
 test is developed in order to investigate the
 resistance of the grass cover. It lifts the grass sod
 perpendicular to the slope out of the sod and
 measures the force as a function of the deformation.
 In order to lift the sod, a pull frame is anchored into
 the top layer with pins. This frame then is lifted out of
 the grass sod by a hydraulic cylinder.
 In order to insert the pins into the sod, the soil has to
 be excavated on two sides (condition 2 test) or on all
 4 sides (condition 4 test). This has the disadvantage
 that the strength of an intact sod cannot be
 measured directly. So a methodology is developed to
 estimate the strength of an intact grass sod from the
 measured data. A further introduction on the sod
 pulling tests is given in Steendam 2014. The goal is
 to rewrite the measured forces from the sod pulling
 test into a critical velocity so that the Cumulative
 Hydraulic Overload Method can be used for
 determining the flooding probability of a dike.
 Some of the locations tested with the wave
 overtopping simulator have also been tested for the
 strength of the grass cover with the sod pulling tests.
 The two methods use the same failure mechanism of
 the grass, erosion of the grass sod.
 The top layer of a dike consists of soil and roots
 growing in multiple directions. The roots anchor the
 grass into the soil and can deform centimeters
 without tearing. Pressures acting on the grass cover
 will first break the weakest roots, but the forces will
 be redistributed to other roots. Only when a critical
 amount of roots are broken, the redistribution stops
 and the grass cover will fail.
 
 CONCLUSION
 It is possible to rewrite the measured forces with the
 sod pulling tests into a critical grass normal stress
 (σgrass.c), which is one of the input parameters for
 determining the critical velocity of a grass sod, see
 Hoffmans 2012.
 
 The equation also uses the pore water pressure (pw),
 the relative turbulence intensity (r0) and the density of
 the water (ρ). When the critical velocity resulting from
 this equation is compared with the determined critical
 velocity during the wave overtopping simulations,
 there is good correspondence between the values for
 the five tested locations. So the sod
 pulling test could provide results that are reliable
 enough to determine the critical velocity of a dike
 section. Further elaboration and scientific background
 will follow in the paper after the conference.
 
 REFERENCES
 Hoffmans (2012): The influence of turbulence on soil
 erosion. Eburon, Delft.
 Steendam, van Hoven, van der Meer, Hoffmans
 (2014): Wave Overtopping Simulator tests on
 transitions and obstacles at grass covered slopes of
 dikes, proc. ICCE 2014 Seoul.
 Van der Meer, Hardeman, Steendam, Schüttrumpf,
 Verheij (2010): Flow depths and velocities at crest
 and inner slope of a dike, in theory and with the Wave
 Overtopping Simulator, Proc. ICCE 2010, Shanghai.

WAVE RUN-UP SIMULATIONS ON REAL DIKES

A new Wave Run-up Simulator has been designed, constructed, calibrated and used for testing of the seaward face of dikes. The upper part of dikes or levees often have a clay layer with a grass cover. The new device is able to test the strength of the grass cover under simulation of up-rushing waves for pre-defined storm conditions. The cumulative overload method has been developed to describe the strength of grass covers on the crest and landward side of dikes, for overtopping wave volumes. In essence there is not a lot of difference between the hydraulic load from an overtopping wave volume or from an up-rushing wave. Therefore the hypothesis has been evaluated that the cumulative overload method should also be applicable for up-rushing waves. Tests on a real dike have been used to validate this hypothesis. The main conclusions are that the new Wave Overtopping Simulator works really well, but that the results on testing till so far has not yet been sufficient for a full validation of the method. More research is required. Furthermore, a new technique has been developed to measure the strength of a grass sod on a dike: the grass pulling device. Tests with this device showed that it is possible to measure the critical velocity (= strength) of a grass cover, which is much easier than performing tests with a Wave Run-up or Overtopping Simulator.

Simulation of wave overtopping using an improved SPH method

An improved Smoothed Particle Hydrodynamics (SPH) method is used to study wave overtopping for different coastal structures. Simulated wave overtopping is too sensitive to the particle movements near the free surface boundary; however, the calculated flow acceleration by means of common SPH methods is not free of errors at this boundary due to the truncation of kernel function and contribution of fewer particles in solving the governing equations. In this paper, this problem is solved by modifying the viscosity of surface particles based on the concept of surface viscosity originally introduced by Xu (2010). By means of the introduced modification, unrealistic particle fluctuation at free surface boundary can be decreased significantly while keeping the model accuracy. This improvement can be used for both Incompressible and Weakly Compressible SPH methods and its implementation is easy and computationally efficient too. Different cases including dam break, solitary wave breaking and wave overtopping at vertical and sloping seawalls are simulated with the modified model and the new model is validated via comparing the results with several experimental and numerical data. Based on this study, free surface boundary can be simulated more accurately by means of the introduced modification and as a result, the predicted values particularly the calculated wave-overtopping rate become more reliable.

Comparing overflow and wave-overtopping induced breach initiation mechanisms in an embankment breach experiment

As part of the SAFElevee project Delft University of Technology collabored with Flanders Hydraulics Research, and Infram B.V. in the preperation and execution of a full scale embankment breach experiment in November 2015. This breach experiment was performed on an 3.5m high embankment with a sand core and clay outer layer situated along the tidal river Scheldt in Belgium near Schellebelle. During the experiment a wave overtopping simulator and overflow simulator were used to initiate a breach. Both simulators were placed near the top of the waterside slope. The use of the simulators facilitated comparison between the effects of continueous overflow and the effects of intermittent wave overtopping. This paper presents the data collected during the experiment, describe the development of hypotheses on the failure processes using the latest insights, and comment on the failure initiation process of a grass covered flood embankment with a clay outer layer and a sandy core.

WAVE OVERTOPPING SIMULATOR TESTS ON TRANSITIONS AND OBSTACLES AT GRASS COVERED SLOPES OF DIKES

Previous tests performed with the Wave Overtopping Simulator showed that objects on dikes may impose a weak spot. To investigate this conclusion further in 2013, within the Dutch program SBW (Strength and Loads on Water Defences), new wave overtopping tests have been performed. These tests were particularly aimed at the influence of transitions between the soft cover layer of clay and grass on dikes with hard structures like asphalt and concrete. In these tests research was performed on the behaviour of the grass cover by wave overtopping at the direct interaction between grass cover and the hard obstacle or cover. Specific tests were performed to determine the critical velocity of the grass covered slope, which is used in the cumulative overload method, and the influence of objects on that. Grass pull tests were also performed with a new developed device and further analysis may give a relationship with the critical velocity.

Wave Overtopping Simulator Tests on Vietnamese Sea Dikes

Little is known about the strength of the land-side slopes of the Vietnamese sea dikes under overtopping attack. Some grass-covered slopes were tested by a wave overtopping simulator. The paper describes the simulator and presents the test results. The tested grass covers could withstand overtopping rates varying from 20 1/s to 100 1/s per meter of dike length in some hours. Damage usually started at bare spots, at the transition between the slope and the toe, at the transition between different materials, and around objects (e.g. big trees). These features reduce the strength of a grass cover and therefore should be avoided.

Application of Grass Cover Failure Models Following in Situ Wave Overtopping Experiments in Belgium

In situ wave overtopping tests were performed on typical dike structures along the Schelde in Flanders (Belgium) with the Dutch Wave Overtopping Simulator. For a storm duration of 2 hours, wave overtopping characteristics were derived for significant wave heights ranging from 0,75 to 1 m and peak periods between 3 and 4 s. Prior to the in situ experiments, soil investigations were executed together with a detailed study of the quality of the grass cover. During the tests, video recordings were made and detailed pictures of the damage were taken. Water content and evolution of the grass cover were monitored. At one location, no failure was experienced up to 50 l/s per m, even after applying initial damage to the surface protection. Other locations failed after facing 30 l/s per m. Besides the cumulative overload method, available failure models are derived for steady overtopping conditions. Assuming erosion equivalence with unsteady overtopping conditions, different erosion resistance as well as (superficial) slip models are applied. Outcomes of the models are compared to the results of the in situ wave overtopping tests in Flanders (Belgium). Different approaches for describing the load term are discussed. Whether for unsteady overtopping conditions, erosion is predominant determined by the front velocity or an approximation of the average velocity of consecutive waves still needs further investigation. However, this discussion is maybe rather philosophical, because one's choice has a direct influence on the threshold values under which waves are not accounted for. For all methods, the determination of threshold values given different qualities of covering is at-the-time still questionable.

Numerical Simulation of Wave Overtopping Based on DualSPHysics

To obtain a more detailed description of wave overtopping, a 2-D numerical wave tank is presented based on an open-source SPH platform named DualSPHysics, using a source generation and absorption technology suited for SPH methods with analytical relaxation approach. Numerical simulation of regular wave run-up and overtopping on typical sloping dikes is carried out and satisfactory agreements are shown between numerical results and experimental data. Another overtopping simulation of regular wave is conducted against six different types of seawalls (vertical wall, curved wall, recurved wall, 1:3 slope with smooth face, 1:1.5 slope with smooth face and 1:1.5 slope with stepped-face), which represents the details of various breaking waves interacting with different seawalls, and the average deviation of wave overtopping rate is 6.8%.