• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2012년도 추계학술대회 논문집
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• pp.458-463
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• 2012

This case study refers to resonance with vertical pumps. Vibration problem occurring after the inverter was installed for speed control. Its problem was appeared any revolution under rated speed. Vibration data was acquired during normal operation and transient state. We examined FRF on its resonance in field and also analyzed a result by finite element method. There was carried out the retrofit in field which was based on these results for solving problem.

• 유공압시스템학회논문집
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• 제6권2호
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• pp.22-30
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• 2009

An in-process method of diagnosing the spool wear of hydraulic servovalves was explored. The diagnostic method discussed in this paper is for force-control hydraulic servo systems. The key principle used is that pressure sensitivity of a servovalve drops as the valve spool wears out so that it is possible to determine the spool condition by monitoring pressure sensitivity. A diagnostic algorithm was developed and evaluated through numerical simulation and experiments. Two major steps of diagnosis are the evaluation of null bias of the servovalve and the approximation of pressure sensitivity, both of which could be successfully done during normal operation of a servo system. The difference between a new servovalve and a worn valve could be clearly detected in-process, and the diagnostic test was found to be repeatable.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 B
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• pp.1286-1288
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• 2000

Commutation failure can be considered as the severest abnormal operation of thyristor HVDC converter. During the failure, power conversion from DC to AC is stopped until the AC voltage get recovered. The process of thyristor converter is subscribed at normal and abnormal state, respectively. The detection and the protection for Cheju HVDC are explained by computer simulation results.

• 한국정보처리학회논문지
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• 제6권5호
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• pp.1263-1271
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• 1999

This paper designs the performance analysis layer for the various performance analysis of parallel programs using event expressions are similar to the normal program language to analyze the events which display a dynamic state exchange of a program. The event expressions suggest operations for overloading and functions which are needed in performance analysis, such as a filtering operation, data format translation functions, performance analysis, static functions, and etc. By using the event expressions, the programmer can modify the event trace data to analyze the performance and analyze more easily and variously than the pre-developed tools.

• Restorative Dentistry and Endodontics
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• 제12권2호
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• pp.27-32
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• 1987

After a vital pulpotomy in human permanent teeth, the responses of the remaining pulp tissue under formocresol was studied histologically. The class I cavity was prepared on the teeth and the pulp was amputated. Formocresol was placed over the amputated tissue and the cavity was sealed with zinc phosphate cement and amalgam. The teeth were extracted after 1, and 3 weeks following the operation and were decalcified, sectioned and stained with hematoxylin and losin. Microscopic examination reveals as follows; I. Healing of the pulp at the amputated site did not occur in the pulps treated with formocresol. 2. At one week the pulps were normal except only slight inflammatory reaction. 3. At three weeks, the pulps showed the most serious inflammation, bleeding and necrotic state.

• Nuclear Engineering and Technology
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• 제51권1호
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• pp.54-59
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• 2019

The main objective of nuclear reactor safety is to maintain the nuclear fuel in a thermally safe condition with enough safety margins during normal operation and anticipated operational occurrences. In this research, core flow bypass is studied under the conditions of the unavailability of safety systems. As core bypass occurs, the core flow rate is assumed to decrease exponentially with a time constant of 25 s to new steady state values of 20, 40, 60, and 80% of the nominal core flow rate. The thermal hydraulic code PARET is used through these calculations. Reactor thermal hydraulic stability is reported for all cases of core flow bypass.

• 설비공학논문집
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• 제9권4호
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• pp.552-560
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• 1997

Analysis is performed to determine the optimal lengths or cross-sectional areas of refrigerator-cooled current leads that can be applied to the conduction-cooled superconducting systems. The binary current lead is composed of the series combination of a normal metal at the upper(warm) part and a high $T_c$ superconductor(HTS) at the lower(cold) part. The heat conduction toward the cold end of HTS part constitutes a major refrigeration load. In addition, the joint between the parts should be cooled by a refrigerator in order to reduce the load at the low end and maintain the HTS part in a superconducting state. The sum of the work inputs required for the two refrigeration loads needs to be minimized for an optimal operation. In this design, three simple models that depict the refrigeration performance as functions of cooling temperature are developed based on some of the existing refrigerators. By solving one-dimensional conduction equation that take into account the temperature-dependent properties of the materials, the refrigeration works are numerically calculated for various values of the joint temperature and the sizes of two parts. The results show that for given size of HTS, there exist the optimal values for the joint temperature and the size of the normal metal. It is also found that the refrigeration work decreases as the length of HTS increases and that the optimal size of normal metal is quite independent of the size of HTS. For a given length of HTS, there is an optimal cross-sectional area and it increases as the length increases. The dependence of the optimal sizes on the refrigerator models employed are presented for 1kA leads.

• 전력전자학회논문지
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• 제3권3호
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• pp.214-221
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• 1998

직접 구동용 브러시 없는 직류전동기(BRUSHLESS direct drive motor : BLDD motor)의 강인한 위치제어를 위해 신경망을 사용하여 접근하는 새로운 제어방식이 소개된다. 전향 신경망이 추가된 선형 2차 제어기는 AC서보의 객체지향 방법을 사용함으로서 대략적으로 선형화 되어지는 강인한 BLDD 모터 시스템을 얻기 위해 사용된다. 구동 상태의 온-라인 위상에서 학습되는 이 신경망은 전향신호와 오차 역 전파법(Back-Propagation Method)에 의해 구성된다. 총 노드의 수가 8개이기 때문에 이 시스템은 일반적인 마이크로 프로세서에 의해 쉽게 실현될 수 있다. 일반적인 작동중, 입출력 응답은 표본화되어지고 가중치는 매개변수 또는 부하 토크의 능한 변이를 적용하기 위해 각 표본주기에서 오차 역 전파법에 의해 학습된다. 그리고, 상태공간에서 시스템 분석은 상태 궤환 이득을 얻기 위해 체계적으로 실행했다. 또한, 강인성은 전반적인 시스템응답에 영향력을 주지 않고 얻어진다.

• 비파괴검사학회지
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• 제33권4호
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• pp.355-360
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• 2013

본 연구에서는 적외선 열화상 카메라를 통하여 베어링의 온도변화를 분석하고, FEM 수치해석을 통하여 모델러에 대한 정상상태에서의 시뮬레이션을 통해 베어링의 열적분포를 해석하였다. 전산 열해석을 위한 유한요소 해석과 열화상 실험을 서로 비교분석하였고 유한요소 전산해석을 통하여 열화상 실험의 정확도를 확인하였다. 본 연구를 통하여 적외선 열화상 실험은 실시간으로 베어링의 상태를 감시할 수 있어 다른 진단방식보다 많은 장점을 가지고 있다. 또한 작업 현장에서 베어링 파손 상태 유무 확인과 파손 방지를 위해서 현장 작업조건을 적용한 유한요소 해석 결과를 비롯하여, 하중조건 회전속도조건, 볼 손상조건, 내외륜 손상조건 등에 따라, 열화상 카메라로 실시간으로 베어링을 감시하면 베어링의 파손을 진단 검출할 수 있다.

• 대한기계학회논문집B
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• 제35권12호
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• pp.1351-1358
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• 2011

열펌프의 고장감지 및 진단을 위하여 측정값에 대한 분석은 필수적이다. 열펌프의 고장감지는 열전대 등의 온도센서로 수행되는데, 재연성과 센서자체의 오차에 의해 시스템의 정상상태 측정값들은 통상 백색 노이즈의 형태로 존재한다. 고장감지 및 진단시스템을 구축하기 위하여 이상적인 정상상태를 정의하는 기준모델을 추출하게 되는데, 실제 측정값과 모델에 의한 기대값은 수학적 편차, 즉 잔차가 필연적으로 존재하게 된다. 이러한 잔차는 운전조건에 따라 변화하며, 다양한 불확실도를 포함한 확률분포를 갖게 된다. 본 연구에서는 온도센서를 활용하여 정상상태 진단을 수행하고 이를 기반으로 기준모델을 도출하였다. 이후 실측값과 기준모델과의 잔차를 통계적으로 분석하여 고장여부를 판단하는 경계값을 산출하였다. 본 분석에 의하여 열펌프의 고장감지 및 진단시스템의 개발을 위한 불확실도와 경계값을 통계적으로 계산함으로써 진단결과의 확률적 신뢰성을 보장할 수 있는 방법론을 제공하였다.