• Journal of Korean Society of Coastal and Ocean Engineers
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• v.18 no.4
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• pp.383-389
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• 2006

In three dimensional wave field, a direct numerical simulation model, which is able to handle free-fall and slope-fall of a waterdrop due to overtopping, is proposed to evaluate the overtopping rate on the coastal structures like an absorbing revetment. A comparison between the numerical model and existing experimental results for overtopping rate was made to validate the proposed numerical model's accuracy, and showed fairly good agreement between them. It is confirmed in numerical and hydraulic(existing) model test that the overtopping quantity on a absorbing revetment becomes larger with an increase in Ursell number. Also, the overtopping rate estimated by 3-D numerical model is compared with it obtained by 2-D numerical model.

• Korean Journal of Agricultural Science
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• v.47 no.1
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• pp.163-171
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• 2020

In this study, a large laboratory model experiment was conducted with the aim of developing an embankment reinforcement method to prevent overtopping, which is the main cause for the failure of agricultural reservoirs. The model experiment was carried out with concrete and asphalt as a permanent reinforcement method and with geomembrane as the emergency method at a deteriorated homogeneous reservoir. Under the non-reinforced conditions, the pattern of the failure appeared in several scour directions from the downstream slope as the overtopping began, and the width and depth of the erosion were magnified as it gradually moved to the dam crest. Under the conditions reinforced with asphalt and concrete, the overtopping was stabilized. In the case of the concrete reinforcement, it was found that the slope of the riprap boundary exhibited downward erosion by the current; thus, it was necessary to construct an extension up to the riprap joint of the upstream and downstream sides to prevent the expansion of the failure. Under the conditions reinforced with the geomembrane sheet, the overtopping was stabilized, and no seepage was found that required the emergency reinforcement method. Asphalt, concrete, and geomembrane sheet reinforcements have been shown to be capable of delaying failure for about 1 hour and 40 minutes compared to the non-reinforcement conditions. The reinforcement method is considered to be a very effective method to prevent disasters during overtopping. The pore water pressure can be used as useful data to predict the risk of failure at an embankment.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.3
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• pp.115-126
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• 1990

In the past, seawall and sea dike very higher than sea-water elevation had been constructed mainly to prevent the wave overtopping volume. However, the coastal zone is recently developed for the multipurpose of not only preventing from the coastal disaster but conserving the coastal environment and utilizing the coastal space. In this sense, this paper deals with the artificial reef being able to reduce the overtopping volume. Relations of the overtopping volume to the breaking wave are briefly reviewed theoretically, and fundamental factor affecting it are also obtained experimentally form the artificial reef with the irregular waves, In addition, the numerical simulation is developed to investigate the effects of spectral band width for the overtopping volume. The most effective artificial reef section to reduce the overtopping volume is proposed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.3
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• pp.228-234
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• 2012

Two-dimensional hydraulic experiments for wave overtopping under non-breaking wave condition are conducted. The wave overtopping formula for vertical structure is suggested and the results are compared with EurOtop (2007). The relative water depth coefficient (${\gamma}_{kh}$) shows that almost the same coefficient is obtained for certain range (kh > 1.55) regardless of relative water depth, that is, although the relative water depth becomes larger, the relative water depth coefficient is almost same. When the wave steepness becomes larger the wave steepness coefficient decreases. The overtopping formula are expressed by relative freeboard(R) and non-dimensional wave overtopping rate(Q) and this formula has the form of exponential function. In this formula, the effects of wave period on wave overtopping are quantitatively investigated and suggested through the relative water depth coefficient(${\gamma}_{kh}$) and wave steepness coefficient(${\gamma}_s$).

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.2
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• pp.157-167
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• 2008

The aeration of an overtopping wave on a vertical structure generated by a plunging wave was investigated through laboratory measurements of void fraction. The overtopping wave occurring after wave breaking becomes multi-phased and turbulent with significant aeration, so that the void fraction of the flow is of importance. In this study, fiber optic reflectometer and bubble image velocimetry were employed to measure the void fraction, velocity, and layer thickness of the overtopping flow. Mean properties were obtained by ensembleand time-averaging the repeated instantaneous void fractions and velocities. The mean void fractions show that the overtopping wave is very high-aerated near the overtopping wave front and relatively low-aerated near the deck surface and rear free surface of the wave. The flow rate and momentum of the overtopping flow estimated using the measured data show that the void ratio is an important parameter to consider in the multiphase flow. From the similarity profiles of the depth-averaged void fraction, velocity, and layer thickness, one-dimensional empirical equations were obtained and used to estimate the flow rate and momentum of the overtopping flow.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.18 no.4
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• pp.372-382
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• 2006

Most of the conventional breakwaters impermeable breakwaters which block seawater exchange between the outside and inside of the harbors. The blocking of seawater exchange may cause pollution of water in harbors. To solve the water pollution problem, various kinds of seawater exchange breakwaters have been proposed. Their types can be classified into the current type which uses tidal current, and the overtopping type which uses the wave energy. The overtopping type breakwaters require a discharge coefficient to calculate the rate of overtopping into the harbor. The present study is to compute the rate of overtopping with introduction of a correct discharge coefficient and to evaluate the effect of the overtopping type breakwater on the water qualify inside a harbor. The rate of overtopping was computed by using Forchheimer formula with time dependent mild-slope equation for various wave conditions. The formula has been generally used to calculate the overflow discharge in steady state river flows. The discharge coefficient, which is the key parameter of the calculation, was determined by a series of hydraulic model tests. The present scheme was applied to the seawater exchange section of the western breakwater of Jeju New Harbor's and the efficiency of that section was examined. The calculated results showed that the rate of overtopping into the harbor reached about $27.5m^3/s$ in the wave condition (wave height 3.7 m, wave period 8.5s, and wave direction NNW).

• Journal of the Korean Society for Marine Environment & Energy
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• v.11 no.1
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• pp.35-41
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• 2008

Overtopping wave energy convertor is an offshore wave energy convertor for collecting the overtopping waves converting the water pressure head into electric power through the hydro turbines. This paper presents a numerical wave tank based on the commercial CFD code Fluent. The Reynolds Averaged Naiver-Stokes and VOF model is utilized to generate the 2D numerical linear propagating waves, which has been validated by the analytical solutions. Several incident wave conditions and shape parameters are calculated in the optimal designing investigation of the overtopping characteristics and discharge for the overtopping wave energy convertor.

• Journal of Korea Water Resources Association
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• v.38 no.11
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• pp.947-954
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• 2005

In this study, laboratory measurements are presented for run-up heights and overtopping of water waves on slopes of rubble-mound breakwaters armored with tetrapods. The effects of wave steepness, surf similarity and wave period on the run-up height and overtopping are investigated in detail. A measurements. A very reasonable agreement is observed. A slopes of breakwaters become milder, run-up heights become smaller. The overtopping rate also is considerably rate also is considerably affected by wave steepness and period.

• Journal of Navigation and Port Research
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• v.36 no.2
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• pp.97-103
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• 2012

Overtopping Wave Energy Convertor (OWEC) is an offshore wave energy convertor, which comprises the circular ramp and reservoir. It collects the overtopped waves and converting water pressure head into electric power through the hydro-turbines installed in the vertical duct, which is fixed in the sea bed. The performance of OWEC can be represented by the operating water heads of the device, which depends on the amount of the wave water overtopping into the reservoir. In the present paper, the reservoir with the duct connecting to the sea water are studied in the 3D numerical wave tank, which has been developed based on the computational fluid dynamics software Fluent 6.3. Both the overtopping motion and the discharges of the reservoir are investigated together, and several shape parameters and incident wave conditions are varied to demonstrate their effects on the performance of OWEC.

• Structural Monitoring and Maintenance
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• v.2 no.1
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• pp.49-64
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• 2015

This paper presents a method for assessing the risk of wave run-up and overtopping of existing coastal defences and for analysing the probability of failure of the structures under future hydraulic conditions. The recent UK climate projections are employed in the investigations of the influence of changing environments on the long-term performance of sea defences. In order to reduce the risk of wave run-up and overtopping caused by rising sea level and to maintain the present-day allowances for wave run-up height and overtopping discharge, the future necessary increase in crest level of existing structures is investigated. Various critical failure mechanisms are considered for reliability analysis, i.e., erosion of crest by wave overtopping, failure of seaside revetment, and internal erosions within earth sea dykes. The time-dependent reliability of sea dykes is analysed to give probability of failure with time. The results for an example earth dyke section show that the necessary increase in crest level is approximately double of sea level rise to maintain the current allowances. The probability of failure for various failure modes of the earth dyke has a significant increase with time under future hydraulic conditions.