• Ocean and Polar Research
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• 제39권1호
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• pp.61-71
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• 2017

This study estimates the cost function through offshore fishery cost data and analyzed the economies of scale of Korea's offshore fishery. For the estimation of the cost function, translog cost function was used, and the analysis implemented the panel analysis of the panel data. Also, annual economies of scale of the offshore fishery and economies of scale of 14 offshore fisheries in 2015 were analyzed using translog cost function coefficient estimation. The analysis result of economies of scale of Korea's offshore fishery showed that with the exception of 2003, economies of scale exist in all periods of time. However, as it almost reaches the minimum efficient scale, it was revealed that further scale expansion will bring inefficiency. Thus, according to the analysis result, Korea's offshore fishery requires a scale reduction policy rather than scale expansion policy, and this seems to coincide with the current government's fishery reconstruction policy and its practice such as the fishing vessel buyback program. The analysis result of economies of scale of each offshore fishery in 2015 showed that economies of scale of each offshore fishery exists with the exception of five trawl fisheries such as large pair-trawl and large otter trawl and large purse seines. This strongly suggests that the five fisheries and Large Purse Seines with non performing economies of scale need urgent scale reduction and should be the first target for the government's fishery reconstruction policy.

• 한국해양공학회지
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• 제34권1호
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• pp.26-36
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• 2020

An extreme value analysis of metocean data which include wave, wind, and current data is a prerequisite for the operation and survival of offshore structures. The purpose of this study was to provide information about the return wave, wind, and current values for the Barents Sea using extreme value analysis. Hindcast datasets of the Global Reanalysis of Ocean Waves 2012 (GROW2012) for a waves, winds and currents were obtained from the Oceanweather Inc. The Gumbel distribution, 2 and 3 parameters Weibull distributions and log-normal distribution were used for the extreme value analysis. The least square method was used to estimate the parameters for the extreme value distribution. The return values, including the significant wave height, spectral peak wave period, wind speed and current speed at surface, were calculated and it will be utilized to design offshore structures to be operated in the Barents Sea.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2013년도 전력전자학술대회 논문집
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• pp.244-245
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• 2013

This paper proposes a control algorithm for permanent magnet synchronous generator with a back-to-back three-level neutral-point clamped voltage source converter in a medium-voltage offshore wind power system under unbalanced grid conditions. The proposed control algorithm particularly compensates for the unbalanced grid voltage at the point of common coupling in a collector bus of offshore wind power system. This control algorithm has been formulated based on the symmetrical components in positive and negative rotating synchronous reference frames under generalized unbalanced operating conditions. Instantaneous active and reactive power are described in terms of symmetrical components of measured grid input voltages and currents. Negative sequential component of ac input current is injected to the point of common coupling in the proposed control strategy. The amplitude of negative sequential component is calculated to minimize the negative sequential component of grid voltage under the limitation of current capability in a voltage source converter. The proposed control algorithm makes it possible to provide a balanced voltage at the point of common coupling resulting in the generated power of high quality from offshore wind power system under unbalanced network conditions.

• 전기학회논문지
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• 제65권10호
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• pp.1639-1647
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• 2016

This paper deals with eddy current loss analysis of Slotless Double sided Cored type permanent magnet linear generator by using analytical method, space harmonic method. In order to calculate eddy current, this paper derives analytical solution by the Maxwell equation, magnetic vector potential, Faraday's law and a two-dimensional(2-D) cartesian coordinate system. First, we derived the armature reaction field distribution produced by armature wingding current. Second, by using derived armature reaction field solution, the analytical solution for eddy current density distribution are also obtained. Finally, the analytical solution for eddy current loss induced in permanent magnets(PMs) are derived by using equivalent, electrical resistance calculated from PMs volume and eddy current density distribution solution. The analytical result from space harmonic method are validated extensively by comparing with finite element method(FEM).

• 해양환경안전학회지
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• 제18권4호
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• pp.295-307
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• 2012

한국 남해에서 조류와 취송류, 밀도류 그리고 잔차류의 특성을 이해하기 위하여 3차원유동모델(POM; Princeton Ocean Model)을 이용하였다. 조석 잔차류의 분포를 보면, 대조기에는 동쪽 방향으로의 흐름이, 소조기에는 서쪽으로의 흐름이 우세하였다. 잔차류는 연안에서 지형의 효과로 인하여 불규칙하게 나타났다. 연안역에서의 밀도류는 비교적 약하고 계절적인 차이는 작다. 외해에서는 특별한 유동현상을 주목해야 한다. 즉, 외양역에서의 흐름은 쓰시마 해류와 유사한 결과를 보이고 있다. 연안역에서의 취송류는 외해역에서 보다 매우 강하게 나타났다. 또한 표층의 해류가 저층의 해류보다 강하게 나타났다. 이상의 결과를 통하여 남해안에서의 물질 이동 확산을 예측하기 위한 기초자료로 활용 가능 할 것으로 판단된다.

• 한국연안방재학회지
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• 제4권spc호
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• pp.245-253
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• 2017

In this study, surface currents measured by small lagrangian GPS drifters (Aquadrifter) in Anmok coastal waters were analysed to account for the variability of nearshore surface current and wave-induced current to understand sediment transport mechanism near the crescentic bars in the surf-zone and near Kangneung breakwater and submerged breakwater in Anmok. The 8 times lagrangian drifter experiments were conducted mostly during in 2nd, 3rd, 4th intensive measurements in winter, summer, and spring seasons with long-term wave observation at the station W1. The analysed surface currents near the breakwaters in Anmok show that wave-induced currents at the middle of the submerged breakwater were separated and flowed toward the shoreline but offshore currents were dominant through the channels between the breakwaters. The longshore currents near the shoreline were flowed to the northwest (southeast) depending on the incoming waves from ENE (NNE). The surface nearshore offshore currents were generated mostly by waves and winds in case of high and low wave energy environments. Using the small-size lagrangian surface drifter experiments, we successfully measured longshore and offshore wave-induced currents in the surf-zone and near submerged breakwater close to Kangneung breakwater. The drifter experiment results show the availability of direct observation of nearshore surface currents to understand the mechanism of sediment transport analysing observed wave-induced current and ebb-current in the surf-zone generated by incoming waves and local winds.

• 한국환경과학회지
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• 제18권8호
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• pp.877-883
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• 2009

This study has analyzed the scale, location, resource potential and feasibility of offshore wind farm scientifically and systematically based on the national wind map and GIS. For long-term wind power development, this study pursues siting strategy building, selection of target area and deciding development priority as well as the presenting a basis for assessment that are necessary for policy decision making by making theme layers under GIS environment. According to the analysis after organizing technological development by stages, even if only the most suitable sites are developed among the area of offshore wind farm candidates that can be developed under the current technological standard, it has been evaluated as being able to develop about 3 times of the wind power dissemination target until 2012. It is expected that about 5% of territorial water area can be developed in a short-term future while the southern offshore area possessing relatively favorable wind resource than the western offshore has been identified as the most feasible site. While about 23% of territorial water area has been classified as potential area for offshore wind farm development in a long-term future, even Jeju Island and offshore of Ulsan possessing excellent wind resource have been analyzed as feasible sites. The feasibility assessment of offshore wind lam development established by this study is expected to assist national strategy building for accomplishing the wind power dissemination target.

• 한국해양공학회지
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• 제34권3호
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• pp.208-216
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• 2020

The Integrated Offshore Standard Specification (IOSS) involves Korean shipyards, classification societies, research institutes, the Korean industrial society, engineering companies, and oil companies with the objective of reducing costs and risks without compromising safety in international offshore engineering procurement construction (EPC) projects using new standardized bulk components and qualification procedures. The activities of the IOSS include the analysis of the existing rules and regulations to achieve the best standardization, which is reflected in the best practices, and minimize the variables in regulations and rules. In addition, a standard inventory of shapes and dimensions, referred to as specifications, is proposed in the IOSS. In this paper, the aluminum tertiary standardization part (IOSS S102-1/2 S104: Specification for Structural Tertiary Design) is presented with the details of the procedures, background reviews, and cost-benefit analyses of the design and verification methods for standard designs in the IOSS standardization items. Based on the cost-benefit analysis, the application of standardized aluminum tertiary items to offshore projects has significant advantages in terms of maintenance and repair compared to the carbon steel tertiary items utilized in current industrial practices.

• 수산경영론집
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• 제54권3호
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• pp.45-67
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• 2023

The purpose of this study is to construct a regional-sector-fishery-offshore and inshore fishery competitiveness index, examine the types and changes of competitiveness, and derive implications by processing data of the Survey on the Current Status of Offshore and Inshore Fishery from 2013 to 2020 for this study. The main results of this study can be summarized as follows. First, considering the competitiveness of offshore and inshore fishery by region and year, Jeonnam, Jeju, and Incheon were relatively competitive. Second, considering the competitiveness of inshore fishery by region and year, we found that Jeonnam, Chungnam, Jeonbuk, and Jeju were relatively competitive. Third, looking at the types of competitiveness based on the competitiveness index in the management sector of offshore and inshore fisheries by region and year, Ulsan, Jeonnam, and Gyeongbuk were relatively competitive between 2014 and 2020. Fourth, Jeonnam and Jeju were relatively competitive between 2014 and 2020 based on the competitiveness index in the fishing sector of offshore and inshore fisheries by region and year. Fifth, we found that Jeonnam, Jeju, and Chungnam were relatively strong in the competitiveness of offshore and inshore fishery, combining the offshore and inshore fishery indexes by region and year. The results of this study have some limitation on outlier treatment, grade assignment, and weight for aggregation, so research considering these needs to be done in the future. In conclusion, the results of this study which were derived objectively and scientifically in the era of the 4th industrial revolution, when evidence-based decision-making was becoming critical, are expected to help the central or local governments determine the priority of support projects or investments.

• Wind and Structures
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• 제18권2호
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• pp.117-134
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• 2014

It is believed that offshore wind farms may satisfy an increasing portion of the energy demand in the next years. This paper presents a comparative study of the fatigue performances of tripod and jacket steel support structures for offshore wind turbines in waters of intermediate depth (20-50 m). A reference site at a water depth of 45 m in the North Atlantic Ocean is considered. The tripod and jacket support structures are conceived according to typical current design. The fatigue behavior is assessed in the time domain under combined stochastic wind and wave loading and the results are compared in terms of a lifetime damage equivalent load.