• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.3
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• pp.156-162
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• 2010

When eccentric or inclined load acts on foundation of the port & harbor structures, partial safety factors of bearing capacity limit state were estimated using reliability analysis. Current Korean technical standards of port and harbor structures recommend to estimate the geotechnical bearing capacity using the simplified Bishop method. In practice, however, simple method of comparing ground reaction resistance with allowable bearing capacity has been mostly used by design engineers. While the simple method gives just one number fixed but somewhat convenient, it could not consider the uncertainty of soil properties depending on site by site. Thus, in this paper, partial safety factors for each design variable were determined so that designers do perform reliability-based level 1 design for bearing capacity limit state. For these, reliability index and their sensitivities were gained throughout the first order reliability method(FORM), and the variability of the random variables was also considered. In order to verify partial safety factors determined here, a comparison with foreign design codes was carried out and were found to be reasonable in practical design.

• Journal of the Korean Society of Marine Environment & Safety
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• v.19 no.6
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• pp.612-620
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• 2013

In this study, time series analysis was tried, which is widely applied to demand forecast of diverse fields such as finance, economy, trade, and so on, different from previous regression analysis. Future marine traffic volume was forecasted on the basis of data of the number of ships entering Incheon port from January 1996 to June 2013, through courses of stationarity verification, model identification, coefficient estimation, and diagnostic checking. As a result of prediction January 2014 to December 2015, February has less traffic volume than other months, but January has more traffic volume than other months. Also, it was found out that Incheon port was more proper to ARIMA model than exponential smoothing method and there was a difference of monthly traffic volume according to seasons. The study has a meaning in that future traffic volume was forecasted per month with time series model. Also, it is judged that forecast of future marine traffic volume through time series model will be the more suitable model than prediction of marine traffic volume with previous regression analysis.

• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.1
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• pp.129-137
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• 2016

In the present study we verified performance of feed-forward control algorithm using short term prediction of ship motion information by taking advantage of developed numerical simulation model of FPSO motion. Up until now, various studies have been conducted about thrust control and allocation for dynamic positioning systems maintaining positions of ships or marine structures in diverse sea environmental conditions. In the existing studies, however, the dynamic positioning systems consist of only feedback control gains using a motion of vessel derived from environmental loads such as current, wind and wave. This study addresses dynamic positioning systems which have feedforward control gain derived from forecasted value of a motion of vessel occurred by current, wind and wave force. In this study, the future motion of vessel is forecasted via Brown's Exponential Smoothing after calculating the vessel motion via a selected mathematical model, and the control force for maintaining the position and heading angle of a vessel is decided by the feedback controller and the feedforward controller using PID theory and forecasted vessel motion respectively. For the allocation of thrusts, the Lagrange Multiplier Method is exploited. By constructing a simulation code for a dynamic positioning system of FPSO, the performance of feedforward control system which has feedback controller and feedforward controller was assessed. According to the result of this study, in case of using feedforward control system, it shows smaller maximum thrust power than using conventional feedback control system.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.6
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• pp.882-889
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• 2022

In this study, to understand the factors influencing the flow change the Tsushima Warm Current (TWC), the correlation between the volume transport the TWC, El Niño Southern Oscillation (ENSO), and Pacific Decadal Oscillation (PDO) was analyzed. A calculation of the monthly volume transport of TWC for 25 years (1993-2018) revealed that the seasonal fluctuation cycle was the largest in summer and smallest in winter. Power spectrum analysis to determine the periodicity of the TWC volume transport, Oceanic Niño Undex (ONI), and PDO indicated that the TWC volume transport peaked at a one year cycle, but ONI and PDO showed no clear cycle. Further, to understand the correlation between the TWC transport volume and ONI and PDO, the coherence estimation method was used for analysis. The coherence of ONI and PDO had a high mutual contribution in long-period fluctuations of three years or more but had low mutual contribution in short-period fluctuations within one year. However, the coherence value between the two factors of the TWC volume transport and PDO was 0.7 in the 0.8-1.2 year cycle, which had a high mutual contribution. Meanwhile, the TWC volume transport and PDO have an inverse correlation between period I (1993-2002) and period III (2010-2018). When the TWC maximum transport volume (2.2 Sv or more) was high, the PDO index showed a negative value below -1.0, and the PDO index showed a positive value when the TWC maximum transport volume was (below 2.2 Sv). Therefore, using long-term PDO index data, changes in the TWC transport volume and water temperature in the East Sea coastal area could be predicted.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.4
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• pp.419-428
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• 2020

The flow past a wall mounted square cylinder, a typical and basic shape of building, bridge or offshore structure, was simulated using URANS computation through adoption of three turbulence models, namely, the k-ε model, k-ω model, and the v²-f model. It is well known that this flow is naturally unstable due to the Karman vortex shedding and exhibits a complex flow structure in the wake region. The mean flow field including velocity profiles and the dominant frequency of flow oscillation that was from the simulations discussed earlier were compared with the experimental data observed by Wang et al. (2004; 2006). Based on these comparisons it was found that the v²-f model is most accurate for the URANS simulation; moreover, the k-ω model is also acceptable. However, the k-ε model was found to be unsuitable in this case. Therefore, v²-f model is proved to be an excellent choice for the analysis of flow with massive separation. Therefore, it is expected to be used in future by studies aiming to control the flow separation.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.4
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• pp.316-325
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• 2009

Technical design codes of slope stability for port structures were studied by comparing local Korean code with international codes; Japanese, EC and China codes. Three international design codes are based on limit state design method. Although Chinese code was based on the modified Fellenius method in slope stability analyses, it is currently changing to the simplified Bishop method. In Eurocode, the Morgenstern & Price method or the Bishop method is recommended. In Japanese code, however, the modified Fellenius method is preferentially recommended, but the simplified Bishop method could be alternatively used in case of thick sandy ground conditions. As for design parameter determination, Eurocode has stipulated comprehensive partial factors and partial material factors, however Japanese code has clarified empirical partial material factors for each port structure. Chinese code, the minimum ranges of the comprehensive partial factors are stipulated, and the use of the strength index by specific tests is concretely clarified with the safety condition. Case study of slope stability analyses showed the safety factors were higher in order of Chinese, Japanese and Eurocode, respectively.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.1533-1536
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• 2009

기후변화에 따른 빈번한 태풍과 집중호우로 인해 지속적으로 피해규모가 증가하고 있으며 점차 다양한 지역에서 피해가 나타나고 있다. 과거 태풍 루사나 매미의 경우 도시유역에서 주요 피해가 발생하여 대규모 피해를 야기하였으나 2006년 발생한 태풍 에위니아의 경우 집중호우로 인한 배수문제, 산사태로 인한 토석류 발생과 이에 따른 도로 및 하천 유입으로 피해가 나타났다. 이러한 피해는 남해안 및 영남지방, 강원 영서지방에서 주로 발생한 것으로 과거 피해 유형과 차이가 난다. 기존 하천 중심의 치수대책만으로는 다양한 지역특성을 고려한 치수계획을 종합적으로 수립할 수 있는 한계가 발생하며 이에 따라 국토해양부(2001)는 수자원 장기종합계획에서 하도와 유역 시스템을 함께 고려하는 유역종합치수정책을 제안하였다. 홍수피해잠재능은 수자원장기종합계획(2001)에서 처음 제시된 개념으로 면 개념을 도입하여 공간적 비교가 가능하고, 단위구역의 치수특성 및 사회경제적 가치를 평가할 수 있도록 개발된 지수(이승종, 2006)이며, 치수안전도 설정을 위한 가장 중요한 개념으로 활용되고 있다. 그러나 최근에 제시된 개념으로 아직 이론적 기반이 미흡하며 지속적인 연구를 통해 수정된 개념이 제시되고 있는 실정이다. 본 연구에서는 유역종합치수계획 등 국가 치수정책을 수립하기 위해 중요한 개념인 홍수피해잠재능과 치수안전도의 치수계획 활용 사례를 조사하여 지역특성별로 유역분할기법을 조사 정리하였으며 국외 사례를 분석하여 유역분할기법의 발전 방향을 제시함으로써 유역단위 맞춤형 치수계획 수립을 위한 기초 자료를 제공하고자 한다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.1
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• pp.23-33
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• 1994

Liquefaction characteristics of the reclaimed marine sand deposits is studied by means of the dynamic response analysis and the cyclic triaxial compression test. 1) From the result of the dynamic response analysis. it was found that the amplification of ground surface maximum acceleration varied with input earthquake motions and soil data, and earthquake coefficients were proposed to be applicable in evaluating liquefaction potential by simplified prediction methods. 2) For upper and soft sand deposits with small N-value, liquefaction strengths estimated by Seed and Idriss's simplified method were lower than those by the cyclic triaxial test while those by Iwasaki & Tatsuoka's or Vs-method were not lower. 3) Simplified methods were inclined to overestimate liquefaction potential in comparison with the dynamic response analysis and the cyclic triaxial compression test Allowable depths of liquefaction(safety factor 1) were estimated to be 7-14m for 0.1 -0.2g of input maximum acceleration.

• Journal of Navigation and Port Research
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• v.39 no.3
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• pp.179-184
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• 2015

The purpose of this study is to provide appropriate methodology to ensure the safety and integrity of the production riser in offshore structure. In order to select integrity estimation methodology for production riser, level I and II Non-destructive Damage Evaluation (NDE) methods that were applied to existing structures are classified and reviewed. Numerical analysis is performed to verify the applicability and capability on damage detection of reviewed methods. As a result, the damage detection methodology using modal strain energy is more sensitive in detection of the damage than other methods. In practice, the number of sensors is limited due to the environmental and financial conditions. The impact on damage detection performance by reducing the number of sensors is systematically investigated through a series of numerical analyses and the results are discussed. The optimal number of sensor for the integrity estimation of production riser is recommended.

• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.4
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• pp.358-371
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• 2014

For the systematic scientific management in Cheonsu Bay of Korea, this study was conducedt to survey the particle composition, organic matter(I.L.) and heavy metals in farming and non-farming areas. The sediment of study area showed feature mixed property by sand, silt and clay. The farming area showed superior by fine-grained sediment, non-farming area showed superior by coarse-grained sediment. The organic pollution of farming area were appeared to be heavily polluted more than non-farming area. The concentration of total nitorgen in sediment was higher farming area than non-farming area. Also, in the case of heavy metals pollution in sediments, farming area was higher than non-farming area. The correlation analysis among to heavy metals, organic matter and particle size was found to have a good interrelationship. For evaluation of heavy metals pollution of sediments, three criteria are applied, Enrichment Factor(EF), Geoaccumulation index(Igeo) and NOAA criteria for sediment. In the case of EF, Heavy metals pollution was appeared to artificial effect all heavy metals if except Cu. In the case of Geoaccumulation index, Cu, Al, Pb was shown zero grade, that is non polluted group, and Cd, Hg, Cr was shown to 0~1 grade, that is mid polluted group, As was shown to 2 grade, that is moderately polluted group. In the case of NOAA, pollution levels of heavy metals except Cd belonged to a group of ERL(Effect range low)~ERM(Effect range median).