• Journal of Ocean Engineering and Technology
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• v.29 no.1
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• pp.62-69
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• 2015

Coastlines are protected by breakwater structures against the erosion of sand or other materials along beaches due to wave action. This research examined the use of physical modeling to determine the effects of the tetrapod size and vertical walls of a rubble mound on the volume of wave overtopping under irregular wave conditions in coastal areas in Busan Yacht Harbor. In this analysis model, the structures were studied using irregular waves and the JONSWAP wave energy spectrum. To understand the effects of the tetrapod size and heights of the vertical wall, the study considered vertical walls of 0, 1.78, 6.83, and 9.33 cm with armor double layered material tetrapods of 8, 12, 16, and 20 tons. An extensive number of experiments covering a relatively large range of variables enabled a comprehensive discussion. First, in the presence of a short vertical wall, the water level played a key role in the overtopping discharge. In such circumstances, the values of the wave overtopping discharge decreased with increasing freeboard size. In the presence of a tall freeboard and middle, the value of the wave overtopping discharge was equally influenced by the vertical wall factor. Moreover, the tetrapod size decreased by an increase in the vertical wall factor, and relationship between them resulted in a short wall height. From an engineering point of view, considering a small water level may allow the choice of a shorter vertical wall, which would ultimately provide a more economical design.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.6
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• pp.389-398
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• 2017

The re-analysis on the stable weight of the concrete armor unit (CAU) at the roundhead and the suggestion of the covering range at the roundhead with the increased weight of CAU were conducted. Tetrapods were applied to the tests and the three dimensional hydraulic tests were performed. The test results for the stable weight at the roundhead area were similar to the guides from Korean Design Standard for Harbour and Fishery Port (MOF, 2014) and Coastal Engineering Manual (USACE, 2005). The investigation of covering range at the roundhead of rubble mound structures armoured with Tetrapods was suggested that the length of five times of the design wave height from the tip of the superstructure was needed and appropriate. Both sides of the superstructure should be covered with increasing weighted CAU to satisfy the stability at roundhead area.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.5
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• pp.1051-1059
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• 2015

Wave runup is one of the most important factors affecting the design of coastal structure exposed to wave attack. In this study, two dimensional laboratory tests were conducted under the different random wave conditions and structure configurations to develop a formula to predict runup heights. Rubble-mound structure consisted of tetrapod armour blocks with 1:1.5 and 1:2 slopes. The relative water depths (the ratio of the significant wave height to water depth at the toe) ranged from 0.14 to 0.56. The formula proposed here is applicable to surf similarity parameter ranging from 2 to 6. Runup heights on 1:2 slope were higher than those on 1:1.5 slope. Runup heights were reduced by 5% when the armour layer thickness increased two times.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.6
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• pp.3074-3080
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• 2013

Amplification of wave height at concave corner was investigated by three dimensional hydraulic tests. A typical rubble mound structure was tested with two-layer Tetrapod and the slope of 1:1.5. The irregular waves with Bretschneider-Mitsuyasu spectrum were applied to the tests. The center angles of concave corner were 120 degree, 140 degree and 160 degree. According to the test results, the maximum wave height amplification ratio at concave corner was about 1.5 times of incident wave height among the all test conditions, and the W-shaped wave height distribution was shown.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.2A
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• pp.117-122
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• 2012

Coastal structures, constructed for preventing coastal slope erosion, often causes the scour on the boundary between the coastal structure and the sea-bed, which might lead to collapse of coastal structures. To prevent the collapse, the usual upright block type coastal structures can be modified to other forms or systems of coastal structures. To validate the performance of the proposed systems, it is necessary to conduct high cost hydraulic experiments. If numerical modeling can be performed prior to the hydraulic experiments and the performance of the proposed systems is analyzed numerically in advance, the expenses can be reduced significantly by optimizing the number of cases for conducting the experiments. In this study, a fluid-structure interaction analysis procedure is proposed for modeling the hydraulic experiments of costal structures using the finite element package, LS-DYNA. As can be found in the usual hydraulic experiments, fluid velocities of potential scour locations are monitored and analyzed in detail for four types of coastal structures, block, step, trapezoid and rubble mound.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.4
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• pp.181-190
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• 2013

In this study, a total of 51 cases of hydraulic model tests has been conducted for various wave conditions and slope angles of breakwater to develop a stability formula for Rakuna-IV armoring a rubble-mound breakwater. The stability number of the formula is expressed as a function of relative damage, number of waves, structural slope, and surf similarity parameter. The stability formula is derived separately for plunging and surging waves, the greater of which is used. The transitional surf similarity parameter from plunging waves to surging waves is also presented. Lastly, to explain the stability of Rakuna-IV to the engineers who are familiar with the stability coefficient in the Hudson formula, the required weight of Rakuna-IV is calculated for varying significant wave height for typical plunging and surging wave conditions, which is then compared with those of the Hudson formula using several different stability coefficients.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.14 no.1
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• pp.19-33
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• 2002

A numerical method to efficiently secure necessary design informations of the hydraulic characteristics of rubble mound breakwater was attempted here. The method combines the exterior wave field with the interior wave field which is formulated incorporating porous media flow inside the breakwaters. An approximate method based on the long wave assumption was used for the exterior wave field while a boundary element method was used for the interior wave field. A hydraulic experiment was also performed to verify the validity of the numerical analysis. The numerical results were compared with experimental data and results from existing formulae. They generally agreed in both reflection and transmission coefficients. The calculated pore pressures also showed a similar pattern with experimental data, even if they gave some significant differences in their values fur some cases. The main cause of such differences can be attributed to the strongly nonlinear wave field occurring on the frontal slope of the breakwater. The direct input of dynamic pressures(measured from hydraulic experiment) into the numerical method was suggested as a promising method to enhance the predictability of pore pressures.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.6
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• pp.397-404
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• 2010

Laboratory tests of wave overtopping rates for a rubble mound breakwaters armoured Tetrapod were carried out, with varying design waves, crest berm widths and crest freeboards. The objective of this study is to investigate overtopping performance and to examine the characteristics of the widely used overtopping prediction models through the results of laboratory tests. Laboratory tests show that structure slope and wave periods have a considerable influence on overtopping rates, but the difference of overtopping rates related to crest berm widths is slight. Owen(1980)'s prediction considerably overestimates compared to the measured valued. Prediction of Van der Meer et al.(1998) underestimates only for steep slope($cot{\alpha}$=1.5). Besley(1999)'s and Pedersen(1996)'s predictions have a relatively good agreement with the measured results for slopes with a broader crest berm width. In general, best agreement between measured and predicted overtopping rates is observed using modified Pedersen(1996)'s formula for all test conditions.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.6
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• pp.516-523
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• 2020

Since the aging of coastal structures have been increased, the researches about the reinforcements of the existing aged structures are needed. Especially, the existing armor units placed on rubble mound structures should satisfy the stability against the increased design wave conditions. However the researches about these design problems have not been performed. In this study, the hydraulic model tests to investigate the stability number about the additionally placed armor unit were conducted. The main armor unit is a Tetrapod. The test results showed that the stability number (Kd) for additionally placed armor units(Tetrapod) increased up to maximum 10% comparing with that for 2 layers tetrapod (Kd = 8) within these test conditions with the pattern placing for existing armor layers and the stable armor layer slope for the non overtopping condition.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.6
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• pp.663-673
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• 2021

Normally, allowable mean overtopping discharge is used as a design parameter for coastal structures. The crest elevation of a structure must ensure wave overtopping discharge within acceptable limits for structural safety and the safety of pedestrians, vehicles, operations, and so on. Some researchers have alternatively proposed using the maximum individual wave overtopping volumes as design criteria during a design storm, since these can provide a better design measure than the mean overtopping rate. This study contributes to the knowledge on maximum individual overtopping volumes in Rayleigh-distributed wave conditions. Two-dimensional physical model tests on typical rubble mound structure geometries were performed, and the new measurement method for individual overtopping was adopted. An empirical formula was proposed to predict the maximum individual overtopping volumes based on the mean overtopping rate, and the reduction effects by the armor crest width on the mean wave overtopping discharge were assessed.