• 한국산학기술학회논문지
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• 제15권6호
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• pp.3827-3831
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• 2014

본 논문은 변압기 1차측에 설치된 전력퓨즈의 열화현상을 진단하고 문제점을 해결하고자 한다. 전력퓨즈의 열화현상은 퓨즈 엘리멘트에 반복하여 흐르는 평상전류에 의해 오동작하는 주된 원인이 된다. 따라서 전력퓨즈 전, 후단과 옥내 변전실내 전력기기의 온도변화와 전력퓨즈 열화현상의 관계를 규명하여, 열화현상의 원인을 제거하여 부하설비의 증설을 조사하여 전력퓨즈를 재산정하였다. 변압기는 개선전과 비교하여 평균 $6[^{\circ}C]$가량 하락하였고, 전선로의 온도는 $7{\sim}8[^{\circ}C]$가량 개선되었다. 전력용 콘덴서와 직렬리액터는 실내온도 및 기기동조화와 관계되어 $2{\sim}3[^{\circ}C]$ 높은 상태 유지됨을 알수 있었다. 연구대상인 전력퓨즈 3상간 온도차는 $0.5{\sim}1.0[^{\circ}C]$로 안정화 됨을 보였다. 이에 따라 옥내 변전실내의 환경적인 전력기기간의 온도발생요인을 제거하여 전력퓨즈의 열화 및 온도상승을 억제할 수 있음을 제안 하였다.

• 한국지반공학회논문집
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• 제30권4호
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• pp.21-34
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• 2014

본 연구는 터널 열화 특성과 이와 관련된 각종 문헌 및 사례조사를 통하여 비교 분석하고 정량적인 해석을 위한 영향인자를 도출하여 입력변수를 결정하고 국내 고속철도 터널의 대표단면(풍화암)에 대하여 수치해석을 실시하였다. 해석 결과는 공용 후 30년 경과 시 열화로 인하여 천단침하량은 7.0%, 지표침하량은 30.2%이 증가하고 내공변위는 9.0mm가 수축 한 이후 점차 수렴되는 경향을 보였다. 또한 이완하중고는 공사 완료 후 50년 경과 시 터널고의 2.55배까지 증가하여 극한상태에서의 Terzaghi의 제안값 보다 상당히 큰 값을 나타내었으며, 이러한 소성영역의 확장으로 인하여 터널 라이닝에 3.20~3.66MPa의 축응력이 추가로 작용하게 되는 경향을 확인하였다. 따라서 이로부터 설계에 반영할 수 있는 정량적인 예측기법을 제안하였다.

• 한국자동차공학회논문집
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• 제25권1호
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• pp.60-65
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• 2017

We designed and fabricated the engine oil monitoring sensor to measure engine oil deterioration through increased vehicle mileage. Since the condition of the engine oil can be affected by the state of the vehicle and its operating conditions, it should be directly measured and determined in every vehicle. The fabricated sensor has an aluminum parallel capacitor structure that measures capacitance related with the dielectric constant, which is one of the indices of oil deterioration. The size of the capacitor is small enough that it could be easily adapted on the oil level gauge without introducing any change in the design. The fabricated device is installed in the diesel engine to measure the change in capacitance accurately as the vehicle moved from 0 km (new engine oil state) to 11,364 km. The results showed the maximum value at around 5,000 km, and the values plateaued as mileage increased, corresponding with the measurement result of the TAN (Total Acid Number). Based on the results, the condition of the oil must be monitored regularly though oil change is recommended once the vehicle has traveled the distance of around 10,000 km.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1990년도 봄 학술발표회 논문집
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• pp.37-43
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• 1990

This paper develops practical models and methods for the assessment of safety and rating of damaged and/or deteriorated bridges by incorporating a system identification technique for the explicit inclusion of the degree of deterioration or damage and of the actual bridge response. And, based on the proposed model, reliability-based rating methods are proposed as LRFR(Load and Resistance Factor Rating) and system reliability-index rating criteria. The proposed limit state model explicitly accounts for the degree of deterioration or damage in terms of the damage and response factors. The damage factor in the paper is proposed as the ratio of the current stiffness to the intact stiffness. Based on the observation and the results of applications to existing bridges, it may be concluded that the proposed rating models, which explicitly account for the uncertainties and the effects of degree of deterioration or damage based on the system identification technique, provide more realistic and consistent safety-assessment and capacity-rating.

• Computers and Concrete
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• 제14권6호
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• pp.727-743
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• 2014

The management of existing concrete bridges has become a major social concern in many developed countries due to the large number of bridges exhibiting signs of significant deterioration. This problem has increased the demand for effective maintenance and renewal planning. In order to implement an appropriate management procedure for a structure, a wide array of corrective strategies must be evaluated with respect to not only the condition state of each defect but also safety, economy and sustainability. This paper describes a new performance evaluation system for existing concrete bridges. The system evaluates performance based on load carrying capability and durability from the results of a visual inspection and specification data, and describes the necessity of maintenance. It categorizes all girders and slabs as either unsafe, severe deterioration, moderate deterioration, mild deterioration, or safe. The technique employs an expert system with an appropriate knowledge base in the evaluation. A characteristic feature of the system is the use of neural networks to evaluate the performance and facilitate refinement of the knowledge base. The neural network proposed in the present study has the capability to prevent an inference process and knowledge base from becoming a black box. It is very important that the system is capable of detailing how the performance is calculated since the road network represents a huge investment. The effectiveness of the neural network and machine learning method is verified by comparing diagnostic results by bridge experts.

• Tribology and Lubricants
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• 제30권3호
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• pp.156-167
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• 2014

This paper presents the test results of small dipstick-gage-type engine-oil-deterioration-detection sensor. The measured sensor signal characteristics for the capacitance and temperature are analyzed. The engine oil deterioration condition correlates with the electrical property of the dielectric constant that comprised with physical properties such as TAN (Total Acid Number), TBN (Total Base Number) and viscosity. Several problems encontered during the test of the sensor system are improved. The results of vehicle tests show that the capacitance signal is stable after the engine stops. Therefore, the sensor should start measuring the parameters for monitoring the engine oil condition after the engine stops. The engine is considered to be in a stopped state if the difference between the maximum and minimum values of the oil capacitance measured every 1 min is below 0.02 pF. The key test results in this paper will help in the development of an engine oil change warning algorithm.

• Nuclear Engineering and Technology
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• 제49권1호
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• pp.103-112
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• 2017

Application of the supercritical condition in reactor core cooling needs to be properly justified based on the extreme level of parameters involved. Therefore, a numerical study is presented to compare the thermalhydraulic performance of supercritical and single-phase natural circulation loops under low-to-intermediate power levels. Carbon dioxide and water are selected as respective working fluids, operating under an identical set of conditions. Accordingly, a three-dimensional computational model was developed, and solved with an appropriate turbulence model and equations of state. Large asymmetry in velocity and temperature profiles was observed in a single cross section due to local buoyancy effect, which is more prominent for supercritical fluids. Mass flow rate in a supercritical loop increases with power until a maximum is reached, which subsequently corresponds to a rapid deterioration in heat transfer coefficient. That can be identified as the limit of operation for such loops to avoid a high temperature, and therefore, the use of a supercritical loop is suggested only until the appearance of such maxima. Flow-induced heat transfer deterioration can be delayed by increasing system pressure or lowering sink temperature. Bulk temperature level throughout the loop with water as working fluid is higher than supercritical carbon dioxide. This is until the heat transfer deterioration, and hence the use of a single-phase loop is prescribed beyond that limit.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2011년도 춘계 학술논문 발표대회 1부
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• pp.27-30
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• 2011

Analysis data of basics which are used for LCC(Life Cycle Cost) analysis of buildings and maintenance plan, are demanded to secure according as replacement cycle of repairs of apartment houses has come. However, investigation techniques and systems for investigating condition of deterioration of apartment houses, have not been made yet in Korea. For this reason, this study was wanted to make investigation techniques and systems, so the process for maintenance of apartment houses was researched and the required quality and deterioration factors of interior/exterior materials were investigated. As a result Check-List for investigating condition of deterioration, was made. if this is used during a nonscheduled, a routine, a regular and a urgency check, the methodical investigation will be achieved. Furthermore, if this is used for maintenance of apartment houses, it will be helped to select the repair cycle and the long-term repair plan.

• 한국화재소방학회논문지
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• 제28권3호
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• pp.87-91
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• 2014

본 논문은 선풍기 모터의 회전을 정상 및 고정상태로 구분하여 주권선에서의 전압 및 전류, 모터 전체의 온도특성을 분석하여 전기화재 위험성을 제시하는 것을 목표로 하고 있다. 전압과 전류 신호에 대하여, 전압의 경우 정상상태와 고정상태에 대하여 큰 차이점은 없었으며, 전류의 경우는 비정상상태(최대 203 mA)보다 정상상태(최대 309 mA)가 상당히 높았다. 온도신호의 경우, 모터 전반에 있어서 온도 분포도가 다르게 나타났으며, 정상상태의 경우는 $4^{\circ}C$, 고정상태는 $18^{\circ}C$ 차를 보였다. 특히 대부분의 선풍기의 전기배선이 모터의 고정자철심에 부착되어 있었으며 해당전선의 허용온도가 $60^{\circ}C$를 감안했을 때에 절연열화가 가속될 수 있다. 또한 본 데이터는 선풍기 안전장치개발의 기초자료나 전기화재에 대한 조사 자료로 활용할 수 있다.

• 한국산학기술학회논문지
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• 제15권1호
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• pp.482-487
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• 2014

본 연구(I)의 목적은 현재 K-water에서 실시하는 대구경 노후관로 개량사업시 매설관의 노후도를 판단할 수 있는 방법을 제시하였다. 대구경 관로의 노후도 평가모형을 개발하기 위해 국내의 대표적 평가기법 중 1995년 평가법, 2002년 평가법, 상태평가법 등 3개를 분석하였다. 대구경 관로의 노후도를 평가하기 위하여 기존의 3가지 평가방법별 인자의 우선순위를 바탕으로 공통 인자와 대구경 관로의 특성을 고려할 수 있는 인자를 함께 고려하여 10개 인자를 선정하였다. 또한 개발모형의 인자별 가중치는 국내의 대구경 관로의 실험 및 분석 값을 바탕으로 한 회귀식과 전문가 의견과 관리경험 등을 고려하여 산정하였다. 따라서 기존의 3가지 모형의 특성을 고려하여 개발된 평가모형은 대구경 관로의 노후도를 평가하기에 보다 신뢰성 있는 모형으로 판단된다.