• Journal of The Korean Society of Agricultural Engineers
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• v.57 no.5
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• pp.19-27
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• 2015

The results of Saemangeum seadike field inspection and material testing of armor stones in order to analyze causes of abrasion according to material characteristics of seaside armor stones in Saemangeum seadike are in the following: 1. The armor stones in Saemangeum seadike have been constructed by using internal stones (mainly, sinsi stones) and external stones, which had less strength (77.3 %) and more abrasion rate (133.3 %) compared with sinsi stones. 2. The compressive strength and abrasion rate were compared between ordinary wave section and high wave section for the purpose of analyzing the influence of waves. In compressive strength, sinsi stones were 4.0 % stronger and external stones were 0.6 % stronger in ordinary wave section than those of high wave section in average. In the case of abrasion rate, sinsi stones were 3.0 % higher and external stones were 8.2 % higher in the high wave section than those in the ordinary section. 3. The result of comparing compressive strength according to a zone is that the compressive strength in the Intertidal area was less strong in most of the zones. 4. Considering that deviated stones are moving around over the surface of armor stones in situ, it is important to compare material characteristics. So the comparison test about this factor showed that deviated sinsi stones were stronger than armor stones in situ in terms of compressive strength and resistance to abrasion. Based on these results, abraded armor stones may have resulted from their durability. Therefore it is assumed that armor stones are likely to be abraded when deviated stones which are more durable are moving around over armor stones which are less durable.

• Journal of The Korean Society of Agricultural Engineers
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• v.55 no.6
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• pp.187-196
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• 2013

This study is focused on analyzing the deformation types of seaside armor stones based of field survey in order to establish the cause of abrasion following the deformation of seaside armor stones. 1. The deformation of seaside armor stone in saemangeum sea dike was classified as three different types: floating, deviation, and abrasion. 2. It was discovered that the stones floated to the extent of maximum 50 m, as the result of inspecting floating stones which were situated on different ten places. 3. The average number of deviation in the high ocean wave section was four times more than that in the ordinary ocean wave section, as a result of comparing the deviation number of the ordinary ocean wave section and that of the high ocean wave section for the purpose of inspecting the relation between the deviation of armor stones and the effects of ocean wave. 4. The angular shape of armor stones seen in the initial construction period has been abraded smoothly, as result of comparing of the shape change of armor stones for the purpose of inspecting abrasion state of seaside armor stones. 5. It was discovered that the abrasion of armor stone was severe in the section of many floating stones, as a result of analyzing the levels of abrasion and the cumulative sections of floating stones for the purpose of investigating the cause of abrasion.

• Journal of The Korean Society of Agricultural Engineers
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• v.58 no.4
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• pp.47-55
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• 2016

This study is on the stability re-evaluation of armor stones in saemangum seadike according to recently increased sea-level and frequent high wave incoming and the results are in the following. The field inspection of armor stones in the seadike revealed that damages of armor stones have been caused by higher waves than designed waves and that the reconstruction of armor stones and concrete grouting method have been used as the reinforcement work. The result of numerical simulation of wave channel conducted to estimate the safety weight of armor stones influenced by flows revealed that the safety weight of armor stones in the seadike No.4 was estimated as 5.47 tons by using the Isbash method, which is about 122 % more than 4.49 tons estimated by using Van der Meer method. Therefore, in designing armor stones which can be influenced by high waves such as the case of Saemangum seadike, it is necessary to apply the safety weight method of armor stones, based on the Isbash method, which produced the significant figures among the safety weight methods using flows as well as the safety weight method using high waves based on the Hudson method.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.3
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• pp.300-309
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• 2008

The partial safety factors of armor stones have been calculated on the assumption that all random variables are independent one another. However, wave height and wave steepness are not independent in the van der Meer's formula of armor stones but they are correlated. In the present study, we calculated the partial safety factors considering the correlation and compared them with those of other researchers who did not consider the correlation. The correlation between wave height and steepness is closely related to the variability of wave period. As the variability of wave period decreases, the correlation between wave height and steepness becomes strong, and hence the calculation results with and without consideration of the correlation show more difference. Therefore, the correlation should be taken into account in the calculation of partial safety factors in the area where the variability of wave period is small.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.15 no.3
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• pp.186-189
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• 2003

Various empirical formulas have been developed to describe the stability of breakwater armor stones. The Hudson formula is known to have needs to be refined in many ways. but it is most widely used because of its simplicity. The van der Meer formula is sometimes used for the cross-check, but it is not very popularly used due to its complexity and the uncertainty of the relevant parameters. Recently, on the other hand, Yoo(2003) proposed a formula of a simple form using a new non-dimensional number which is called 'action slope' (abbreviated as Yoo formula hereinafter). In this study, in order to provide coastal engineers with some idea of the use of these formulas, their accuracies were estimated by comparing with the experimental data reported by van der Meer in 1987 and 1988. It was found that the van der Meer formula showed the highest accuracy, while the Hudson formula of very low accuracy needed considered judgment on its use. On the other hand, the Yoo formula of slightly lower accuracy but simpler expression than the van der Meer formula seems to be able to be used in engineering practice if a slightly higher safety factor is taken.

• Journal of Ocean Engineering and Technology
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• v.35 no.6
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• pp.403-413
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• 2021

As the size of ships increases, the size and output power of their thrusters also increase. When a large ship berths or unberths, the jet flow produced from its thruster has an adverse effect on the stability of quay walls. In this study, we conducted a numerical analysis to examine the impact of the thruster jet flow of a 30,000 TEU container ship, which is expected to be built in the near future, on the stability of a quay wall. In the numerical simulation, we used the fluid-structure interaction analysis technique of LS-DYNA, which is calculated by the overlapping capability using an arbitrary Lagrangian Eulerian formulation and Euler-Lagrange coupling algorithm with an explicit finite element method. As the ship approached the quay wall and the vertical position of the thruster approached the mound of the quay wall, the jet flow directly affected the foot-protection blocks and armor stones. The movement and separation of the foot-protection blocks and armor stones were confirmed in the area affected directly by the thruster jet flow of the container ship. Therefore, the thruster jet flows of ultra-large ships must be considered when planning and designing ports. In addition, the stability of existing port structures must be evaluated.

• 제어로봇시스템학회:학술대회논문집
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• 2002.10a
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• pp.81.1-81
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• 2002

$\textbullet$ This paper presents a study on the development of a walking robot for an armor-stone work of the breakwater construction. The armor-stone work is putting stones about 0.3 ∼ 2m3 on the surface of the breakwater to prevent it from waving. $\textbullet$ This work has been done manually, and its process plan is uncertain by effects of the weather, wave and tide of sea. Therefore the constructional cost is considered to be wasteful $\textbullet$ Working in underwater as well as on land for human workers causes the accident and caisson disease, so it is necessary to replace the process to be mechanized. $\textbullet$ The basic requirements of the robot for mechanizing are as follows : 1) To have a large...

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.121-127
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• 2003

Wave overtopping is one of the most important hydraulic responses of breakwater because it significantly affects its functional efficiency, the safety of transit and mooring on the rear side, wave transmission in the sheltered area, rear side armor stones and to some extent, the structural safety itself. In this study, hydraulic model tests has been carried out to investigate the influence of berm's size on overtopping rate by maximum overtopping rate and mean overtopping rate. The hydrodynamic characteristics of berm breakwater by the overtopping rate can be summarized as follows: 1. It is better to use maximum overtopping rate than to use mean overtopping rate for design of coastal structures in the point of view of stability. 2. When construct berm to decrease energy of waves that it was needed to make breaking conditions of wave on the berm. 3. Under the relative length of berm was over 0.13 overtopping rate was significantly decreased. 4. Overtopping rate affected significantly by the relative length of yhe berm than height of the berm.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.113-118
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• 2002

Wave overtopping is one of the most important hydraulic responses of breakwater because it significantly affects its functional efficiency, the safety of transit and mooring on the rear side, wave transmission in the sheltered area, rear side armor stones and to some extent, the structural safety itself. The hydrodynamic characteristics of low crest breakwater by the overtopping rate can be summarized as follows: 1. It is better to use maximum overtopping rate than to use mean overtopping rate for design of coastal structures. 2. Maximum overtopping rate was increase with wave steepness (between 0.01 and 0.02). 3. Overtopping rate is decreased when relation length of berm was over wave length.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.4
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• pp.191-201
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• 2016

A stochastic process has been used to develop a condition-based model for preventive maintenance of armor units of rubble-mound breakwaters that can make a decision the optimal interval at which some repair actions should be performed under the perfect maintenance. The proposed cost model in this paper based on renewal reward process can take account of the interest rate, also consider the unplanned maintenance cost which has been treated like a constant in the previous studies to be a time-dependent random variable. A function for the unplanned maintenance cost has been mathematically proposed so that the cumulative damage, serviceability limit and importance of structure can be taken into account, by which a age-based maintenance can be extended to a condition-based maintenance straightforwardly. The coefficients involved in the function can also be properly estimated using a method expressed in this paper. Two stochastic processes, Wiener process and gamma process have been applied to armor stones of rubble-mound breakwaters. By evaluating the expected total cost rate as a function of time for various serviceability limits, interest rates and importances of structure, the optimal period of preventive maintenance can easily determined through the minimization of the expected total cost rate. For a fixed serviceability limit, it shows that the optimal period has been delayed while the interest rate increases, so that the expected total cost rate has become lower. In addition, the gamma process tends to estimate the optimal period more conservatively than the Wiener process. Finally, it is found that the more crucial the level of importance of structure becomes, the more often preventive maintenances should be carried out.