• Journal of Power Electronics
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• 제19권2호
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• pp.580-590
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• 2019

The concept of virtual synchronous generators (VSGs) is a valuable means for improving the frequency stability of microgrids (MGs). However, a great virtual inertia in a VSG's controller may cause power oscillation, thereby deteriorating system stability. In this study, a small-signal model of an MG with two paralleled VSGs is established, and a control strategy for maintaining a constant inertial time with an increasing active-frequency droop coefficient (m) is proposed on the basis of a root locus analysis. The power oscillation is suppressed by adjusting virtual synchronous reactance, damping coefficient, and load frequency coefficient under the same inertial time constant. In addition, the dynamic load distribution is sensitive to the controller parameters, especially under the parallel operation of VSGs with different capacities. Therefore, an active power increment method is introduced to improve the precision of active power sharing in dynamic response. Simulation and experimental is used to verify the theoretical analysis findings.

• 수산경영론집
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• 제36권2호
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• pp.71-95
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• 2005

As one of the most popular outdoor leisure activities in the world, recreational fishing has a lof of significant meaning in terms of social, economic, and cultural views. However, both not considering an indiscreet fishing activity and environment and not thinking our next generation, fishing circumstance has been deteriorating more and more. Unlike Korea, most advanced countries enact various recreational fishing management and support policies in order to keep sustainable recreational fishing and develop eco-tourism through cooperation with government, fishing industries and civil organizations. This paper consist of the following contents. First, the study attempted to investigate how to operate management system of the recreational fishing dividing into in - land fishing and sea fishing respectively. And it exhibits issues and troubles of the realities of recreational fishing management and related fishing laws and ordinances in Korea. And then, it examines various fishing management schemes in representative advanced nations; U.S., Germany, and Japan. Also, it analyzes the advantages and disadvantages of respective recreational fishing management systems; market - based license system, qualification - based management system, and self- regulatory based management system. In addition, after these three systems are adopted to Korea's recreational fishing condition, we analyzes whether respective management systems fit or not. As a result of this, the optimal management for recreational fishing is the participatory self - management scheme in Korea. Finally, in order to support recreational fishing promotion and encouragement, issues and complementary policies with respect to recreational fishing are introduced.

• Industrial Engineering and Management Systems
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• 제13권3호
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• pp.252-257
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• 2014

Global economic recession, global market reduction, and the deteriorating economic recession are forcing the industry to reconsider the business plan and strategy related to supply chain regardless of the size of the companies. During the economic recession caused by financial anxiety, development of international collaborative producer is the key theme for a manufacturing industry to get over the situation. Especially, development of high-skilled people who are capable of handling global manufacturing management is the key factor in China which shifted from a world factory to a world market. In this background, we started the international project of global manufacturing education and training for Chinese company managers from 2009. In this paper, based on the research conducted by the universities and companies in China, a design of global manufacturing education and training is proposed. This presented design is based on the theory of Japanese production strategy and investigation of actual conditions for Chinese companies and the research methodology of business management practice with efficiency and productive for international level management organization. The effectiveness of the education design is evaluated by applying the international education and training project of Aoyama Gakuin Human Innovation Consulting Inc. and Vigor Management Technology Association.

• Journal of Advanced Marine Engineering and Technology
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• 제25권3호
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• pp.471-486
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• 2001

The principal trends in the course of emission control legislation are reviewed in this paper. In order to keep such a regulation, moreover, an inquiry ito the concrete technical possibility is conducted through review articles, Also, the composition of exhaust gases emitted from a marine diesel engine are investigated as several samples and the measures that can satisfy the value of regulation are handled with laying stress on the control methods discussed to date. It was concluded that various combined systems can be made to reduce NOx emissions without deteriorating substantially navigation costs since many technologies for reducing NOx emissions are being developed. All heat engines suffer from SOx emissions. There are two methods for reducing SOx emissions: desulfurization from exhaust gas and removal of sulfur composition from fuel oil. However it is necessary to watch the development of these technologies to evaluate which method is more favorable. Heat engines have a big problem in the regulation of environmental pollution from exhaust emissions. In the near future, however, diesel engines may be superior to other heat engines, owing to the high thermal efficiency, although the sales of individual models in dises engines may be prosperous and declining.

• Structural Engineering and Mechanics
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• 제59권6호
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• pp.1121-1137
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• 2016

A large number of structure in the world were build with poor seismic details, with or without any lateral load resisting system like concentrically braced frames and steel plate shear walls. These structures can reveal deteriorating hysteretic behaviors with stiffness and strength degradation. Therefore, seismic retrofitting of such structures for drift control has vital importance. In this study a retrofit methodology has been developed, which involves diagonal bracing of steel frames with different cable arrangements. In the experimental and numerical program 5 different lateral load resisting system were tested and results compared with each other. The results indicated that multi-cable arrangements suggested in this study showed stable ductile behavior without any sudden decrease in strength. Due to the usage of more than one diagonal cable, fracture of any cable did not significantly affect the overall strength and deformation capacity of the system. In cable braced systems damages concentrated in the boundary zones of the cables and beams. That is why boundary zone must have enough stiffness and strength to resist tension field action of cables.

• Smart Structures and Systems
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• 제4권5호
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• pp.641-653
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• 2008

This paper proposes a practical and realistic method to establish an optimal lifetime maintenance strategy for deteriorating bridges by considering the life-cycle performance as well as the life-cycle cost. The proposed method offers a set of optimal tradeoff maintenance scenarios among other conflicting objectives, such as minimizing cost and maximizing performance. A genetic algorithm is used to generate a set of maintenance scenarios that is a multi-objective combinatorial optimization problem related to the lifetime performance and the life-cycle cost as separate objective functions. A computer program, which generates optimal maintenance scenarios, was developed based on the proposed method using the life-cycle costs and the performance of bridges. The subordinate relation between bridge members has been considered to decide optimal maintenance sequence and a corresponding algorithm has been implemented into the program. The developed program has been used to present a procedure for finding an optimal maintenance scenario for steel-girder bridges on the Korean National Road. Through this bridge maintenance scenario analysis, it is expected that the developed method and program can be effectively used to allow bridge managers an optimal maintenance strategy satisfying various constraints and requirements.

• 한국국방경영분석학회지
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• 제17권1호
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• pp.61-83
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• 1991

There has been a great deal of research dealing with the optimal replacement of stochastically deteriorating equipment and research in queueing systems with a finite calling population. However. there has been a lack of research which combines these two areas to deal with optimal replacement for a fixed number of machines and a limited number of repairmen. In this research, an optimal control policy for replacement involving two machines and one repairman is developed by investigating a class of age replacement policies in the context of controlling a G/M/1 queueing system with a finite calling population. The control policy to be imposed on this problem is an age-dependent control policy, described by the control limit $t^{\ast}$. The control limit is operational only when the repairman is idle; that is. if both machines are working, as soon as a machine reaches the age $t^{\ast}$ it is taken out of service for replacememt. We obtain the ${\epsilon}$-optimal control age which will minimize the long-run average system cost. An algorithm is developed that is applicable to general failure time distributions and cost functions. The algorithm does not require the condition of unimodality for implementation.

• Structural Engineering and Mechanics
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• 제20권5호
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• pp.589-608
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• 2005

There is a growing need for the development and implementation of new methods for the rapid and cost-effective rehabilitation of deteriorating steel structural components to offset the drawbacks related to welding and/or bolting in the field. Carbon fiber reinforced polymer (CFRP) composites provide a potential alternative as externally bonded patches for strengthening and repair of metallic structural members for building and bridge systems. This paper describes results of an investigation of tensile and fatigue response of steel/CFRP joints simulating scenarios of strengthening and crack-patching. It is shown that appropriately designed schemes, even when fabricated with levels of inaccuracy as could be expected in the field, can provide significant strain relief and load transfer capability. A simplified elasto-plastic closed form solution for stress analysis is presented, and validated experimentally. It is shown that the bond development length remains constant in the linear range, whereas it increases as the adhesive is deformed plastically. Fatigue resistance is shown to be at least comparable with the requirements for welded cover plates without attendant decreases in stiffness and strength.

• 한국인터넷방송통신학회논문지
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• 제17권2호
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• pp.245-250
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• 2017

케이블은 설치하여 동작함과 동시에 열화과정이 진행된다. 고압전력케이블 시스템에 있어, 케이블의 절연층 및 방식층의 절연상태뿐만 아니라 케이블을 연결하는 단말부 및 접속부의 절연상태도 함께 감시하여야 케이블 시스템의 절연상태를 종합 관리할 수 있다. 케이블 시스템(케이블 자체 및 접속재)의 상태가 계속 나빠지는 경우, XLPE의 절연 파괴현상으로 인한 화재가 발생한다. 우리는 케이블시스템의 절연 상태를 감시하기 위한 장비를 개발하여 충남 태안의 한국 서부발전주식회사(Korea Western Power Co. Ltd.)에 설치하였다. 이 논문에서, 이 장비를 사용하여 케이블에 흐르는 누설전류를 추출하여 누설전류의 표준편차를 계산하여 분석한 결과를 제시한다. 정해진 누설 전류의 표준 편차값이 기준값 미만이면 안전하지만. 그 이상이면 케이블시스템의 단말부 및 접속부의 절연상태가 나쁜 것으로 판단하고, 새로운 케이블시스템의 단말부 및 접속부로 대체함으로써 전력공급 중단으로 인한 전력설비의 중단사고를 미연에 방지할 수 있다.

• 정보처리학회논문지:소프트웨어 및 데이터공학
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• 제3권4호
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• pp.139-148
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• 2014

IT의 발전과 더불어 금융권의 비대면 채널 역시 폭발적으로 증가되어왔다. 하지만 금융 시스템의 특성을 명확하게 반영한 규모 산정에 대한 모델의 부재로 인하여 예산 수립의 신뢰성 저하, 그리고 이에 따른 저가 수주 경쟁 등이 빈번하게 발생하였다. 이러한 규모 예측의 신뢰성 저하는 인터넷 뱅킹 시스템의 품질 저하로 이어져 금융 상품을 이용하는 고객에게 피해가 전해지고 있다. 따라서 본 논문에서는 기존 금융권에서 사용하는 규모 산정 기법의 두 종류인 FP 기반 규모 산정과 전문가 유추 기반의 규모 산정을 토대로 규모 산정 기법을 개선하여 보다 간편하고, 실제 금융 비대면 채널 수행 규모에 근접한 규모 예측 기법을 구축하고 이의 효용성을 회귀분석을 통하여 검증하였다. 그 결과, 기존 규모 산정 기법보다 실제 수행 규모와 상관관계 및 정확도가 증가된 인터넷 뱅킹 시스템을 위한 개선된 FP 기반 초기 규모예측 모델과 도구를 구축하였다.