• Journal of Electrical Engineering and Technology
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• 제8권5호
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• pp.1002-1011
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• 2013

This paper proposes the new adaptive protection algorithm for inverse-time overcurrent relays (OCRs) to ensure their proper operating time and protective coordination. The application of the proposed algorithm requires digital protection relays with microcontroller and memory. The operating parameters of digital OCRs are adjusted based on the available data whenever system conditions (system with distributed generation (DG)) vary. Moreover, it can reduce the calculation time required to determine the operating parameters for achieving its purpose. To verify its effectiveness, several case studies are performed in time-domain simulation. The results show that the proposed adaptive protection algorithm can keep the proper operating time and provide the protective coordination time interval with fast response.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.725-730
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• 2006

The purpose of this study is on the performance evaluation of horizontally installed GHEX(Geothermal Heat Exchanger, HGHEX) which has been operated for 5 years successfully. Followings are the results. Firstly, in summer season, on Aug. 2000, $33^{\circ}C$ water was flowing out from HGHEX with continuous operating method, and $27{\sim}29^{\circ}C$ with interval operating method on Jul. 2005. But $2.5{\sim}3.0^{\circ}C$ temperature differences are gained from HGHEX. Secondly, in winter season, on Nov. 2000, $25^{\circ}C$ water was flowing out from HGHEX with continuous operating method, and $13{\sim}15^{\circ}C$ with interval operating method on Jan. 2006. But with each operating method, only $0.1^{\circ}C$ and $0.7^{\circ}C$ temperature differences are gained from HGHEX respectively. As the conclusion of this study, at the point of continuos operating method, seasonal balance of heating and cooling loads, and at the point of interval operating method, balance for geothermal restoring time respectively must be considered for better system performances.

• 산업경영시스템학회지
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• 제18권34호
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• pp.139-146
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• 1995

This study is concerned with cost analysis in periodic maintenance policy. Generally periodic maintenance policy in which item is repaired periodic interval times. And in the article minimal repair is considered. Minimal repair means that if a unit fails, unit is instantaneously restored to same hazard rate curve as before failure. In the paper periodic maintenance policy with minimal repair is as follows; Operating unit is periodically replaced in periodic maintenance time, if a failure occurs between minimal repair and periodic maintenance time, unit is replaced by a spate until the periodic time comes. Also unit undergoes minimal repair at failures in minimal-repair-for-failure interval. Then total expected cost per unit time is calculated according to maintenance period and scale parameter of failure distribution. Total cost factors ate included operating, fixed, minimal repair, periodic maintenance and replacement cost Numerical example is shown in which failure time of system has erlang distribution.

• 산업경영시스템학회지
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• 제18권36호
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• pp.287-295
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• 1995

This paper is concerned with cost analysis model in periodic maintenance policy. Generally periodic maintenance policy in which item is repaired periodic interval times. And in the article minimal repair is considered. Mimimal repair means that if a unit fails, unit is instantaneously restored to same hazard rate curve as before failure. In the paper periodic maintenance policy with minimal repair is as follows; Operating unit is periodically replaced in periodic maintenance time, if a failure occurs between minimal repair and periodic maintenance time, unit is replaced by a new item until tile periodic maintenance time comes. Also unit undergoes minimal repair at failures in minimal-repair-for-failure interval. Then total expected cost per unit time is calculated according to scale parameter of failure distribution. Maintenance cost factors are included operating, fixed, minimal repair, periodic maintenance and new item replacement cost. Numerical example is shown in which failure time of system has weibull distribution.

• 전자공학회논문지CI
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• 제45권1호
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• pp.78-85
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• 2008

대부분의 전력 관리 기법에 대한 연구는 동작 주파수나 동작 전압을 변화 시켜 시스템의 가용성을 증가시키는데 집중되었다. 이 방법은 전력소모를 줄이기 위해 구동 주파수를 수시로 변경하므로 실 시스템의 성능을 저하 시킨다. 소비 전력을 줄이기 위한 다른 방법은 구동 주파수의 개수를 제한하거나 실행 시간 동안 전체 주파수를 완만하게 관리하여 시스템의 성능을 높이는 것이다. 허나 기존 연구는 실시간 응용 프로그램에는 적합하지 않다. 본 논문에서는 실시간 시스템에서 소비 전력의 손실을 줄이고 시스템의 성능을 향상시키기 위해 구동 주파수 레벨의 할당 방법과 주파수 평활화 기법을 이용한 전력 관리 기법을 제안한다. 이 기법은 연속적인 주파수 간격에서 알고리즘이 예측한 주파수를 양자화된 주파수로 매핑한다. 이러한 주파수 평활화 기법은 좁은 주파수 대역에서 잦은 주파수 변경으로 발생한 시스템의 오버헤드를 줄일 수 있다. 매핑된 주파수는 넓은 주파수 간격에서 주파수 불일치로 발생하는 전력소모를 줄일 수 있다. 모의실험을 통하여 제안한 알고리즘이 기존의 CC RT-DVS 기법에 비해 최대 40%, 평균 15% 정도 소비 전력을 줄일 수 있었다.

• Journal of Chest Surgery
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• 제45권4호
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• pp.230-235
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• 2012

Background: Although patients with a ruptured abdominal aortic aneurysm (RAAA) often reach the hospital alive, the perioperative mortality is still very high. We retrospectively reviewed thirty patients who underwent repair of RAAA to identify the factors affecting postoperative mortality in a single hospital. Materials and Methods: Between September 2007 and May 2011, thirty patients with RAAA underwent emergent surgery (n=27) or endovascular aneurysm repair (n=3). Their medical records were retrospectively reviewed regarding three categories: 1) preoperative patient status: age, gender, vital signs, serum creatinine, blood urea nitrogen, hematocrit, and hemoglobin level: 2) aneurysmal status: size, type, and rupture status; and 3) operative factors: interval time to operating room, operative duration, and amount of perioperative transfusion. Results: The 30-day postoperative mortality rate was 13.3% (4/30); later mortality was 3.3% (1/30). On multivariate analysis, the initial diastolic blood pressure (BP), interval time to operating room and amount of preoperative packed cell transfusion were statistically significantly linked with postoperative mortality (p<0.05). Conclusion: In this study, preoperative diastolic BP, preoperative packed cell transfusion amount and interval time between arrival and entry to operating room were significantly associated with postoperative mortality. It is important to prevent hemorrhage as quickly as possible.

• 항공우주시스템공학회지
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• 제15권1호
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• pp.63-71
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• 2021

한국해군은 1978년에 하푼 유도탄을 최초 도입 후 단계적인 획득을 통하여 현재까지 운용하고 있다. 하푼 유도탄을 장기 운용함에 따라 성능보장을 위한 적극적인 후속 군수지원이 필요하며, 유도탄 검사는 유도탄 상태를 확인하기 위한 기본 활동이다. 본 연구는 장기간 운용 중인 하푼 유도탄의 기존 검사주기가 적절한지 확인하기 위하여 수행되었으며, 연구 방법은 해군의 야전운용자료를 바탕으로 Martinez 이론과 비모수적 MCF 기법을 활용하여 운용 기간에 따른 구간별 검사주기를 분석하여 제시하였다.

• 대한안전경영과학회지
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• 제19권3호
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• pp.89-95
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• 2017

This paper presents another maintenance policy for a group of units under finite operating horizon. A group of identical units are subject to random failures. Group maintenances are performed to all units together at specified intervals, and the failed units during operation are remained idle until the next group maintenance set-up. Unlike the traditional assumption of infinite operating horizon, we adopt the assumption of the finite operating horizon which reflect the rapid industrial advance and short life cycle of modern times. The units are under operation until the end of the operating horizon. Further, the operation of units are extended to the first group maintenance time after the end of the horizon. The total cost under the proposed maintenance policy is derived. The optimal group maintenance interval and the expected number of group maintenances during the horizon are found. It is shown that the proposed policy is better than the classical group maintenance policy in terms of total cost over the operating horizon. Numerical examples are presented for illustrations.

• Journal of Biosystems Engineering
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• 제23권3호
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• pp.211-218
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• 1998

A variable flow-controlled boom sprayer was developed and evaluated. Field tests were conducted to evaluate the adoptability of the sprayerr with optimal conditions. Negative response time was obtained from the field test because pump and PTO were interlocked with the speed of sprayer. Another reason for the negative value was due to the definition of the response time. With constant on-time control, the system was unstable at the conditions of small tolerance and long control interval. The performances of the spray system were stable and accurate. The stable and synchronous responses were achieved with a variable on-time control. The flow control system with an optimal condition (1.0 sec of control interval, 2 of damping ratio, 1% of tolerance) provided the proper performance for uniform spraying. A standard operating procedure of the flow compensating boom sprayer for the ground speed variation was presented and recommended.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 1999년도 춘계 학술발표회 논문집
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• pp.171-176
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• 1999

Nondestructive inspection and accompanying life analysis based on fracture mechanics were the major conventional methods for evaluating remaining life of critical high temperature components in power plants. By using these conventional methods, it has been difficult to perform in-service inspection for life prediction. Also, quantitative damage evaluation due to unexpected abrupt changes in operating temperature was almost impossible. Thus, many efforts have been made for evaluating remaining life during operation of the plants and predicting real-time life usage values based on the shape of structures, operating history, and material properties. In this study, a core software for on-line life monitoring system which carries out real-time life evaluation of a critical component in power boiler(high temperature steam headers) is developed. The software is capable of evaluating creep and fatigue life usage from the real-time stress data calculated by using temperature/stress transfer Green functions derived for the specific headers and by counting transient cycles. The major benefits of the developed software lie in determining future operating schedule, inspection interval, and replacement plan by monitoring real-time life usage based on prior operating history.