• Tribology and Lubricants
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• v.25 no.5
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• pp.335-341
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• 2009

Elastohydrodynamic lubrication (EHL) analysis shows that film thickness is very flat in the contact area and pressure distribution is somehow similar to that of Hertzian contact pressure except the outlet region with pressure spike. These typical patterns of EHL film thickness and pressure are the cases under the steady contact conditions of applied loads and speeds. However, many engineering contacts are rather under the conditions of varying loads and contact speeds, and therefore the predictions for endurance life and performance of machine elements with steady EHL analysis are not suitable in many occasions. This study shows the differences in film thickness formation and pressure distribution between steady and transient contact conditions in several contact cases.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.12
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• pp.67-74
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• 2006

An unsteady blockage-correction method utilizing wall pressure distribution on the test section has been developed for the wall interference correction of a closed test-section subsonic wind tunnel. The pressure distribution along the test section wall was decomposed into Fourier series and a quasi-steady method based on a measured-boundary-condition method was applied to each Fourier coefficient. The unsteady correction for a complete test period was accomplished by recombining each corrected terms. The present method was validated by appling computed unsteady flows over a cylinder and an oscillating airfoil in the test sections. The corrected results by the present method agreed well with free-air condition.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.341-341
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• 2009

초전도 케이블의 대용량 전력수송능력을 실계통에 적용하기 위해서는 정상상태 뿐 아니라 계통운용상 발생하는 비정상 상태에 대해서도 안정된 성능을 나타내야 한다. 계통운영시 가장 일반적으로 발생하는 비정상 상태의 하나인 계통불평형부하 상태에서의 초전도 케이블의 특성을 실증적으로 확인하기 위해 한전 고창전력시험센터에서 신뢰성시험을 실시하였다. 삼상 송전계통에서 각 상 도체전류는 각 상의 부하량에 의해 결정이 되므로 과도상태라 해도 상당한 시간동안 도체전류가 불평형일 경우 자기적으로 결합된 차폐층전류의 불평형상태가 발생한다. 차폐층전류는 삼상 순환회로의 중성도체가 존재하지 않는 경우 도체전류와의 차이가 발생하게 되어 자기차폐 실패의 원인이 됨으로서 AC손실 증가요인으로서 영향이 커진다. 본 논문에서는 도체전류의 불평형 상태를 실증적으로 모의 발생시켜 연관된 차폐층 순환전류의 형태 및 특성을 검토함으로서 삼상 초전도 케이블의 불평형 부하특성에 대한 연구 진행경과를 요약한다.

• Journal of Satellite, Information and Communications
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• v.12 no.3
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• pp.35-40
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• 2017

Out-of-limit (OOL) alarm method that is threshold checking of telemetry value is widely used for the satellites fault diagnosis and health monitoring. However, it requires engineering knowledge and effort to define delicate threshold value and has limitations that anomalous behaviors within the defined limits can't be detected. In this paper, we propose a satellite anomalous behavior detection system through fuzzy model that is composed by important statistical feature selected by rough-set theory. Not pre-defined anomaly is detected because only normal state data is used for fuzzy model. Also, anomalous behavior within the threshold limit is detected by using statistic feature that can be collected without engineering knowledge. The proposed system successfully detected non-ordinary state for battery temperature telemetry.

• Journal of the Institute of Convergence Signal Processing
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• v.19 no.3
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• pp.97-103
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• 2018

This paper addresses an improved naval combat UPS(Uninterruptable Power Supply) system under abnormal transients. Previously, thermistor and varistor elements were used to cope with transient overvoltage and overcurrent, however the UPS was frequently unavailable because it was vulnerable to abnormal transient voltage generated during system operation. In order to overcome this problem and protect UPS system, this paper proposes an input power cut-off circuit that detects the initial input power and abnormal transient voltage generated during operation, improvement of power control sequence, and a method to prevent malfunction of an inverter and CPU. The UPS system implementing the proposed method was simulated by input power variable test using programmable AC/DC generator, and finally validated its reliability and stability through field tests by mounting on multifunctional console of naval combat system.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.3
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• pp.29-40
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• 1999

A numerical method in frequency domain for the analysis of the acoustic wave equation governing the sound field generated by a non-cavitating propeller under a steady of unsteady loading condition is developed. Theory shows that only multiples of the blade passage frequency exist and that the wave number consists of the frequency component due to the nonuniformity of the wake and the Doppler effect originated from the rotation of the blades. Correlation with experiments for a two bladed propeller, designed to be load-free at a particular advance speed, indicate that the thickness effect can be significant in steady case, but can be negligible compared to the unsteady loading effect.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.9
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• pp.724-733
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• 2017

Accidents caused by upset condition leads to fatal damage to both manned and unmanned aircraft. This paper deals with real-time detection of these aircraft upset situations to prevent further severe situations. Firstly, the difference between sensor measurement and predicted measurement from Extended Kalman filter is monitored to determine whether a target aircraft goes into an upset condition or not. In addition, repeating the time update stage of the Extended Kalman filter for a specific length of time can enable future upset situation prediction. The results of aforementioned both the approaches will build a bridge to upset prevention for future generation of manned/unmanned aircraft.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1998.10a
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• pp.4-4
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• 1998

고체 추진제의 비정상적인 연소 현상을 해석하여 연소 불안정을 예측하는 것은 추진시스템의 설계 시 매우 중요하다. 로켓의 비정상 연소 현상을 해석하기 위하여 많은 이론적 연구가 진행되어 왔다. 이론적인 해는 주로 선형 해석의 결과들로 정상 상태에서 발생하는 불안정 현상을 예측하는 데에는 적합하지만 비정상 현상을 설명하기에는 부족하다. 따라서 수치 기법을 이용한 비선형 해석이 수행되어 졌다. 기존의 비정상 연소에 관한 연구들은 일정한 물성치를 사용하고 추진제 내에서의 화학 반응과 복사 열전달 등을 무시하여 추진제의 특성을 단순화 시켜 비정상 해석을 수행하였다. 본 연구에서는 비정상 연소 현상에 대한 비선형 수치 해석을 하려한다. 실험에서 밝혀진 것과 같이 추진제의 물성치를 온도의 함수로 사용하고 응축영역으로의 복사 열전달을 고려하였다.

• Journal of the Korean Institute of Intelligent Systems
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• v.13 no.3
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• pp.266-274
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• 2003

This paper considers an incremental support vector learning for the abnormality detection problems. One of the most well-known support vector learning methods for abnormality detection is the so-called SVDD(support vector data description), which seeks the strategy of utilizing balls defined on the kernel feature space in order to distinguish a set of normal data from all other possible abnormal objects. The major concern of this paper is to modify the SVDD into the direction of utilizing the relation between the optimal solution and incrementally given training data. After a thorough review about the original SVDD method, this paper establishes an incremental method for finding the optimal solution based on certain observations on the Lagrange dual problems. The applicability of the presented incremental method is illustrated via a design example.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2006.05a
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• pp.306-309
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• 2006

SVDD(support vector data description)는 one-class 서포트 벡터 학습 방법론 중 하나로 비정상 물체에서 정상 데이터를 구분하기 위해서 특징 공간에서 정의된 구를 이용하는 전략을 쓰는 방법론이다. 본 논문에서는 SVDD를 이용해서 노이즈가 섞인 비정상 데이터를 노이즈가 제거된 정상 데이터로 복원하는 방법에 대해서 논한다. 그리고 저해상도의 이미지를 고해상도의 이미지로 복원함으로써 본 논문의 방법론이 어떻게 실용적으로 적용되는지에 대해서 다룬다.