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Park, Y.H.; Oh, Y.-M.; Ahn, S.M.; Han, T.H.; Kim, Y.-T.; Suh, K.-D., and Won, D., 2019. Development of a new concrete armor unit for high waves. Journal of Coastal Research, 35(3), 719–728. Coconut Creek (Florida), ISSN 0749-0208. Hundreds of new concrete armor units (CAUs) have been developed since 1950, but only a few have been used because of their low price and familiarity. Because the design wave height has been increasing as a result of climate change, the Korean government decided to develop a new CAU for protection against high waves. Therefore, a new research project to develop a new CAU that considers stability, structural strength, economic feasibility, casting efficiency, and constructability was started. The new CAU was called Chi Block. The hydraulic stability achieved a Hudson stability coefficient of more than 13 at a significant wave height of 10 m by adopting a conservative approach. Chi Block can be installed in both uniform and random placements and can be used as an overlay for repair. A new placement for Chi Block was invented, and it features the advantage of functioning like a 1.5 layer. Although a single layer generally has a higher overtopping rate than a double layer, Chi Block, on uniform placement, has a performance near that of the Tetrapod. [ABSTRACT FROM AUTHOR]

The present study assesses the climate change impact on local storm surges along the coasts of the Korean Peninsula and Tottori Prefecture, Japan. A series of storm surge simulations are conducted on a physical process-based storm surge model using direct forcing from general circulation model output data in the two periods of 1979-2008 and 2075-2099. It is found that the typhoon intensity is enhanced and its number increases under the future climate condition in the area of the Korean Peninsula (32 to 40 N and 120 to 138 E). In addition, the typhoon approach course moves by 0.523 westward in the future climate. From a series of storm surge simulations, the statistical analysis showed that the climate change influences the storm surge height regionally and locally; it decreases on the west coast of the Korean Peninsula in the future, whereas it increases on the south coast of the Korean Peninsula and on the coast of Tottori Prefecture, Japan. [ABSTRACT FROM AUTHOR]

Abstract: During the last decade, partial safety factor systems have been adopted in the design standards of coastal structures, which are based on probabilistic theories but have a format similar to the traditional safety factor system. Tetrapod is one of the widely used breakwater armor units in the world. The previous partial safety factor system was developed based on limited wave and structure data in several locations. In this paper, a partial safety factor system for Tetrapod armor units is developed by performing reliability analysis and optimal code calibration for 116 breakwater cross-sections and wave conditions in 31 harbors in Korea. The partial safety factors associated with different ranges of the shape parameter of the Weibull extreme wave height distribution for different target probabilities of failure are proposed. For other types of extreme distributions, the skewness of the distribution should be calculated and the partial safety factors of the Weibull distribution of the same skewness could be used (the skewness of the Weibull distribution changes with the shape parameter). The developed system is applied to existing breakwaters to examine its applicability. [Copyright &y& Elsevier]

In Korea, Tetrapods have been widely used to protect rubble mound breakwaters against erosion due to wave action. The deterministic design method has been used based on Hudson or van der Meer formula. In this study, we have performed reliability analyses for thus designed Tetrapod armors of 12 trade harbors and 8 coastal harbors in Korea. It is found that there is a linear relationship between the safety factor and the probability of failure; the larger the safety factor, the smaller the probability of failure. It is also found that the probability of failure during 50-year service lifetime is about 60% for the Tetrapod armors designed by the deterministic design method with the safety factor of 1.0. This finding seems to be natural since the encounter probability that a breakwater will experience storm waves greater than the design wave during its lifetime is 63% if the lifetime is set equal to the design return period. The results of this study could provide a guideline for determining the target probability of failure of Tetrapod armors in the future. A similar approach could be used for armor units other than Tetrapods. [ABSTRACT FROM AUTHOR]

Abstract: The relationship between significant wave height and period, the variability of significant wave period, the spectral peak enhancement factor, and the directional spreading parameter of large deepwater waves around the Korean Peninsula have been investigated using various sources of wave measurement and hindcasting data. For very large waves comparable to design waves, it is recommended to use the average value of the empirical formulas proposed by Shore Protection Manual in 1977 and by Goda in 2003 for the relationship between significant wave height and period. The standard deviation of significant wave periods non-dimensionalized with respect to the mean value for a certain significant wave height varies between 0.04 and 0.21 with a typical value of 0.1 depending upon different regions and different ranges of significant wave heights. The probability density function of the peak enhancement factor is expressed as a lognormal distribution, with its mean value of 2.14, which is somewhat smaller than the value in the North Sea. For relatively large waves, the probability density function of the directional spreading parameter at peak frequency is also expressed as a lognormal distribution. [Copyright &y& Elsevier]

Reliability design methods have been developed for breakwater designs since the mid-1980s. The reliability design method is classified into three categories depending on the level of probabilistic concepts being employed, i.e. Level 1, 2, and 3 methods. Each method gives results in different forms, but all of them can be expressed in terms of probability of failure so that the difference can be compared among the different methods. In this study, we apply the reliability design methods to the stability of armor blocks and sliding of caissons of the breakwater of Donghae Harbor located in the east coast of Korea, which was constructed by traditional deterministic design methods to be damaged in 1987 and reinforced in 1991. Analyses are made for the breakwaters before the damage and after the reinforcement. The allowable probability of failure of a Tetrapod armor layer of 50 year's lifetime is proposed as 40% for existing stability formulas, whilst that for caisson sliding as 20% with the failure criterion for the cumulative sliding distance over the lifetime of 0.1 m. The probability of failure before the damage is much higher than the allowable value for both stability of armor blocks and sliding of caissons, indicating that the breakwater was under-designed. The probability of failure for the reinforced breakwater is lower than the allowable value, indicating that the breakwater became stable after the reinforcement. On the other hand, the results of different reliability design methods were in fairly good agreement, confirming that there is not much difference among the different methods. [ABSTRACT FROM AUTHOR]

This paper presents empirical formulas for calculating the maximum wave height and period in a numerical wave hindcasting model in terms of significant wave height, mean wave period, and peakedness parameter. The formulas are developed by applying the least-square method to the wave data measured at KOGA-E1 and KOGA-S2, which are located in the Japan/East Sea and on the southeast coast of the Korean Peninsula, respectively. The developed formulas are validated by comparing with the wave measurements around the Korean Peninsula. The formulas are shown to concur well with the measurements even in the Yellow Sea where the tide is very strong. To examine the applicability of the formulas in a wave hindcasting model, numerical simulation has been performed for wind wave generation around the Korean Peninsula. The maximum wave height and period have been calculated using the wave parameters computed in the numerical simulation. The calculated maximum wave height and period are then compared with the measurements to show that the developed formulas can be used for long-term prediction of the maximum wave height and period in a numerical wave hindcasting model. This comparison shows that the predicted maximum wave height and period agree well with the measured ones. Image 10768 • This paper presents formulas on the maximum wave height and period in terms of spectral wave parameters. • The formulas were developed using the wave measurements in the Japan/East Sea and on the southeast of Korean peninsula. • The applicability of the present formulas was examined by the wave hindcasting around the Korean peninsula. [ABSTRACT FROM AUTHOR]