• 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.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.4
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• pp.947-964
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• 2014

Rubble mound breakwaters protect the coastal line against severe erosion caused by wave action. This study examined the performance of different sizes and properties (i.e. height of vertical wall and tetrapod size) of rubble mound breakwaters on reducing the overtopping discharge. The physical model used in this study was derived based on an actual rubble mound in Busan Yacht Harbor. This research attempts to fill the gap in practical knowledge on the combined effect of the armor roughness and vertical wall on wave overtopping in rubble mound breakwaters. The main governing parameters used in this study were the vertical wall height, variation of the tetrapod weights, initial water level elevation, and the volume of overtopping under constant wave properties. The experimental results showed that the roughness factor differed according to the tetrapod size. Furthermore, the overtopping discharge with no vertical wall was similar to that with relatively short vertical walls (${\gamma}_v=1$). Therefore, the experimental results highlight the importance of the height of the vertical wall in reducing overtopping discharge. Moreover, a large tetrapod size may allow coastal engineers to choose a shorter vertical wall to save cost, while obtaining better performance.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.6
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• pp.335-343
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• 2019

Overtopping discharge for sea dike having low mound and high wave wall (LMHW sea dike) is investigated with hydraulic experiments in this study. Vertical, Flare and Bullnose type wave walls are selected and Tetrapods (double layer) and Accropode (one layer) are adopted for armour layers of the front slope. The results of the hydraulic experiments are compared to the overtopping formulas for armoured rubble slopes and vertical sea dikes suggested by EurOtop Manual. Predicted overtopping discharges are underestimated as the roughness efficiency factors (γ_f) of armour blocks suggested by EurOtop are adopted when the overtopping formula for armoured rubble slopes sea dike is used. Meanwhile the predicted overtopping discharges agree well with the hydraulic experiments when the modified roughness efficiency factors redefined by multiplying efficiency factor of the heights of armoured crest berm and wave wall (γ_AR) are adopted. Return wall effects on a vertical wall (Kortenhaus et al., 2003; Pearson et al., 2004a) and the effects on a smooth dike slope (Van Doorslaer et al., 2015) in EurOtop Manual are investigated for Flare and Bullnose type wave walls. As a results of the comparison between experimental results and 2 formulas, return wall effect on a smooth dike was more valid for LMHW sea dike.