• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.4
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• pp.230-241
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• 2020

Since the construction of Pohang New Port, the problems of the low harbor tranquility caused by decreasing port operation rate has been continuously reported. In order to improve the harbor tranquility, a detached breakwater (DB) has been constructed outside the outer breakwater of Pohang New Port in 2018~2020. In this study, the effectiveness of the DB was proved by comparing the reduction rates of wave heights that were observed before and after the construction of the DB. First, the observed data were compared with the numerical model results available from a previous study, and the model data showed reasonable agreement with measured data at 3 out of 4 locations inside the port. The discrepancy in one of the locations was because the model could not accurately calculated the effect of wave interference in the inner corner of the port. The observation data showed excellent results that the number of waves that exceeded 0.3 m, the critical value to reach desired harbor tranquility, was significantly reduced after the construction of the DB. In addition, the reduction rate, the ratio of wave heights between outside and inside of the port, was decreased after the DB construction, which proved that properly designed coastal structures such as DB in this study could be effective in improving the port tranquility. The results of this study can be usefully applied for solving problems in similar cases.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.5
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• pp.343-351
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• 2012

In this study, shallow-water design waves are calculated for the return period of 10, 20, 30, and 50 years, based on the extreme value analysis of the wave measurement data at Gangneung beach. These values are compared with the results of SWAN simulation with the boundary condition of the deep-water design waves of the corresponding return periods at the Gangneung sea area provided by the Fisheries Agency (FA, 1988) and Korea Ocean Research & Development Institute (KORDI, 2005). It is found that the shallow-water wave heights at Gangneung beach calculated by the deep-water design waves were significantly less than the observation data. As the return period becomes higher, the significant wave heights obtained by the extreme value analysis becomes higher than those computed by SWAN with the deep-water design waves of the corresponding return periods. KORDI computed the hindcast wave data from January 2004 to August 2008 by WAM with a finer-grid mesh system than those of previous studies. Comparisons of the wave hindcast results with the wave observation show that the reproducibility of the winter-season storm wave was considerably improved compared to the hindcast data from 1979 to 2003. Hereafter, it is necessary to carry out hindcast wave data for the years before 2004 using WAM with the finer-grid mesh system and to supplement the deep-water design wave.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.6
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• pp.713-719
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• 2001

The aim of this study is to check the application criteria of the conventional techniques and clarify the effects of breaker depth, seabed conditions on the stability in relation to the effects of uncertainty of storm duration and directional irregular waves. The typical damage modes were divided by the direct wave force on the armor unit and by the local scouring around the toe of a breakwater head by the model experiments. The destruction modes are defined, and some criteria on the damage modes and scouring/deposition at the toe of a breakwater head in relating the wave-bottom-structural conditions can be checked using the multi-directonal irregular wave generator system. According to the results, it is emphasized that the 3-D effects on the stability should be analyzed in the design of multi-purpose/function coastal structures in consideration of the evaluation of spatial variation of damage modes and hydraulic characteristics as well as the wave distribution along the structures.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.6
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• pp.374-386
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• 2010

Recently, the theoretical and experimental research is being made actively in control character of waves of perforated-wall caisson breakwater like the slit caisson. This study showed that the character of reflection coefficient and the wave pressure acting on the front and inner of slit caisson were estimated in two and three dimensional numerical wave flume and compared each other. The numerical experiment was set and conducted by various cases as to a variety of wave steepness under 7 sec, 9 sec, 11sec and 13 sec period condition. In this study using a 2 and 3 dimensional numerical wave flume, it applied the Model for the immiscible two-phase flow based on the Naveir-Stokes Equations. This technique can easily reproduce a complicated physical phenomenon more than others and organize the program simply. According to the results of the experiment, the reflection coefficient was estimated high in short-period waves. However, 2-dimensional numerical experiment and 3-dimensional numerical experiment were the same in case of the long-period waves and high wave steepness. And to conclude in case of short-period waves the pressures were a relatively small difference between the two, but there was a big gap in longperiod waves and high wave steepness.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.368-368
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• 2020

최근 초대형화 되어 나타나고 있는 이상홍수와 지진 등에 의한 저수지 붕괴와 같은 대규모 비상상황 발생으로 하류지역 주민의 생명과 재산의 피해가 발생하고 있다. 국내의 경우 1996년 이후로 지속적으로 발생하고 있는 이상홍수로 인해 1998년에는 40개,1999년에는 5개의 소규모 저수지가 붕괴되었으며 최근 2013년과 2014년에도 저수지가 붕괴되는 상황이 발생했다. 댐붕괴의 원인은 구조물의 자연적 노화, 극심한 강우나 홍수, 지진, 제체전도, 파이핑, 침윤발생, 월류 및 파랑 등에 의한 자연적 상황 등이 요인이 될 수 있으며, 시공결함, 사고 또는 전쟁과 같은 인위적인 요인으로 발생할 수도 있다. 과거에 설계 및 시공기술이 부족하였거나 경제적인 이유로 부실하게 건설되어 있는 댐이 세계적으로 산재되어 있어 잠재적인 위험을 상당수 내재하고 있는 실정이다. 본연구는 댐의 점진적인 파괴에 의해 발생하는 유출수문곡선을 구하고 파괴의 성질을 예측 및 홍수파를 수리학적으로 추적하기위해 BREACH 모형과 DAMBRK 모형을 사용했으며 극한홍수(PMF)조건과와 최대지진발생(MCE)조건을 적용하여 원주시 관내 저수지 붕괴 모의 시나리오를 구축했다. 저수지 붕괴에 따른 유출수문곡선을 유도하기 위해서 본 연구에서는 기존의 EAP보고서 자료를 참고하여 붕괴지속시간, 붕괴부 평균폭, 붕괴부 측벽면 경사의 변화에 따라 다양한 모의를 수행함으로써 발생되는 붕괴부 유량 수문곡선을 도출하여 각각의 조건들이 붕괴파 형성에 미치는 영향에 대한 분석을 실시하였다. 그 결과 저수지의 붕괴시 첨두유출량에 민감한 영향을 주는 인자는 붕괴지속시간과, 붕괴부 평균폭으로서 이들 값이 붕괴유출량 변화에 많은 영향을 주는 것으로 나타났다. 최대지진발생(MCE)조건 해석결과 홍수류의 범람으로 인해 홍수파가 하류측으로 진행할수록 완만히 감소하며, 하천 중·상류부 인근 제내지로 홍수류의 범람이 발생하는 것으로 검토되었으며, 극한홍수(PMF)조건 해석결과 최대지진발생(MCE)조건과 같이 홍수파가 하류측으로 진행할수록 완만히 감소하는 특성을 보이며, 하천 전체 구간에서 인근제내지로 홍수류의 범람이 발생하는 것으로 검토되었다. 본 연구는 침수구역 피해규모 산정 및 비상대처계획도를 작성시 기초데이터가 되어 상황별 피해예상지역에 대해 응급행동요령, 주민대피계획비상대처계획을 수립하여 지역 주민생활에 안정을 기여하고자 한다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.17 no.2
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• pp.106-118
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• 2005

It is well-known that when pipelines are positioned on a sandy seabed, they have a tendency to bury themselves. This paper presents the results of an experimental investigation on the characteristics of the local scour around the submarine imbeded pipelines exposed to waves. Scour depths were measured according to the imbedment ratios of the pipelines. The results indicated that the effect of lee-wake of the pipe is the key element in the scour process of the submarine imbeded pipelines. In general, scour depths are smaller as the imbedment ratios are larger. Using the experimental results, the relative scour depths are related to Keulegan -Carpenter number and modified Ursell number, and the empirical equations are established. These equations show that the relative scour depths are proportional to above two parameters and the scour region is extended as Keulegan-Carpenter number and modified Ursell number are larger.

• Computational Structural Engineering
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• v.5 no.3
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• pp.119-126
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• 1992

Most civil engineering structures such as bridges, power plants, and offshore platforms are apt to suffer structural damages over their service lives caused by adverse loadings, such as earthquakes, wind and wave forces. Accumulation of structural damages over a long period of time might cause catastrophic structural failure. Therefore, a methodology for monitoring the structural integrity is essential for assuring the safety of the existing structures. A method for the damage assessment of structures by the second order inverse modal perturbation technique is presented in this paper. Perturbation equation consists of a matrix equation involving matrices of structural changes(stiffness and mass matrix changes) and matrices of modal property changes(natural frequency and mode shape changes). The damages of a structure are represented as changes in the stiffness matrix. In this study, a second order perturbation equation is formulated for the damage assessment of structures, and solved by an iterative procedure. The effectiveness of the proposed method has been investigated through a series of example analysis. The estimated results for the structural damage indicated that the present method yields resonable estimates for the structural changes.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.15 no.3
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• pp.151-158
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• 2003

The study of velocity fields and vortex generation around the submerged breakwater can be utilized as materials related to understanding of wave dissipation mechanism, sediment transport, and stability of structure. In the present study, two-dimensional numerical wave flume, based on the VOF method to trace free surface, developed by Kim et al.(2001, 2002) was used to numerically simulate velocity fields and vortex generation around the impermeable submerged breakwater installed at the uniform bottom. Especially, the characteristics of vortex generation due to the geometry of the structure and incident wave conditions are examined through the analysis of averaged-velocity fields around the impermeable submerged breakwater. From the numerical simulations, it is confirmed that a counter clockwise vortex is formed in front of the structure and a clockwise vortex develops behind the structure. Also, incident wave height and period have an sensitive effect on the strength of vortex.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.6
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• pp.547-556
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• 2007

The sediment transport by waves, wave-induced current and tidal current was calculated using the TRANSPOR2004, then the seasonal sediment budget was analyzed. Also, annual sediment budget was calculated, and sediment circulation patterns was deduced in the broad area including Haeundae beach. A sediment mainly inflows from the east coast of the beach and then moves to the eastward to the Dongback Is, where the 80% of inflow sediment transported to the eastward as a longshore sediment while 20% of them going out to the offshore at the center of the beach. Above results shows a good agreement with the sediment transport trend analysis results by the Gao model.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.8
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• pp.5327-5332
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• 2014

In Korea, the quantitative growth rate of artificial reef construction is supposed to reach the peak point. Therefore, new approach is needed to the point of artificial reefs business. Functional reefs, such as shellfish reefs, recreational reefs, seaweed reefs, and fish reefs, are beneficial alternatives. This study conducted hydraulic testing to assess the stability of corrugated artificial reefs (ARs) that were constructed to promote the growth of shellfish and seaweed. The results of this study showed that some dimensionless design parameters affected the stability of corrugated artificial reefs under a range of wave and water depth conditions in a fixed bed condition. The findings also highlight the importance of hydraulic experiments in solving the problems that have emerged in the design and construction of artificial reefs.