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결함유형에 따른 소프트웨어 신뢰도와 소프트웨어 상품화 최적 시기 전략
김영휘,이완형,Kim Yeong-Hwi,Lee Wan-Hyeong 한국국방경영분석학회 1990 한국국방경영분석학회지 Vol.16 No.2
This paper classifies faults into three types : simple, degenerated, and regenerated faults. This paper also deals with the characteristics of each type of fault to determine the software reliability based on the assumption; i. e., a system consisting of several subsystems (modules) which may be debugged simultaneously. For each type of fault, several formulas are developed to obtain the failure rate and the expected number of failures found during debugging. A model is developed based on the formulas of the failure rate and the expected number of failures to decide the optimal release time of a new software: minimizing the total cost with constraints restricting to the failure rate of each module in the software. By using this model, optimal release times are found for some cases; the eliminated faults are assumed simple faults only, regenerated faults only, simple and degenerated faults, and so on.
김영휘,하석태,Kim Yeong-Hwi,Ha Seok-Tae 한국국방경영분석학회 1989 한국국방경영분석학회지 Vol.15 No.1
This paper deals with the mission effectiveness of an airfleet, Airfleet operating system consists of a finite number of units performing the several mission types. Earlier works for the mission effectiveness of a fleet is limited to only one mission type and computer simulation approaches. The mission effectiveness. model of a fleet is constructed by three attributes - the mission readiness of the units, the mission reliability and capability of units. The environmental conditions and human factors affecting the mission success are considered together. The solution of the model is obtained by analytical technique. Especially, AOS is considered a closed queueing network with a finite number of units and a single job class. And then, the mission readiness of the units is found by the mean value analysis. The model would be a useful tool to readily evaluate mission effectiveness of a airfleet as it is and provide a criterion for determining the optimal operating policy.
Distributed Lag Non-linear Model을 이용한 Baltic Dry Index 예측 및 요인 별 시차 영향도 도출에 관한 연구
김영휘(Younghwi Kim),심성현(Sunghyun Sim) 한국자료분석학회 2024 Journal of the Korean Data Analysis Society Vol.26 No.2
Baltic Dry Index(BDI)는 해운 물류 산업에서 시장의 현황을 파악하기 위한 중요한 대표적인 지표로써, 전 세계 무역 및 제조 활동의 흐름을 파악할 수 있는 지표이다. BDI는 변동성이 큰 지표로 알려져 있어, 이를 정확히 예측하기 위해 다양한 머신러닝 및 딥러닝 기반의 연구들이 활발히 진행되고 있다. 하지만 이러한 접근 방식들은 예측 결과에 대한 해석이 어렵다는 한계점이 존재한다. 본 논문에서는 BDI 예측을 위해 시계열 데이터의 시간과 값 범위 두 차원에서의 종속성을 포착해 이를 설명하는 Distributed Lag Non-linear Model(DLNM)을 이용한다. DLNM을 통해 BDI 예측력을 향상시키고, 예측 결과에 대해서 요인별 시차 영향도를 제공함으로써 예측에 대한 설명을 제공할 수 있는 모형 프레임워크를 제안한다. 제안된 모형의 성능을 평가하기 위해 선행 연구에서 주로 활용된 다양한 머신러닝 및 딥러닝 모형과의 비교실험을 위해 4가지 성능비교 지표를 이용하여 비교 실험을 수행하였고, 기존 접근 방식에 비해 개선된 예측 성능을 보여주었다. 학습된 DLNM 모형을 활용하여 시차에 따른 요인별 영향도를 분석하였으며, 기존 선행연구와의 비교를 통해 분석된 결과가 기존 선행 연구의 결과들과 일관성이 있음을 확인하였다. 본 연구를 통해 해운 물류 산업에서 데이터를 기반으로 한 의사 결정을 이루기 위한 방향을 제시할 것으로 기대된다. The Baltic Dry Index (BDI) is a crucial and representative indicator in the shipping logistics industry sector for evaluating the market conditions, providing valuable information on the movement of global trade and production operations. The BDI, known for its significant volatility, has been the focus of several research initiatives utilizing machine learning and deep learning approaches to improve accuracy. Nevertheless, these approaches frequently encounter difficulties in understanding the results of the predictions. This study provides a framework that utilizes the Distributed Lag Non-linear Model to enhance the predictive accuracy of the BDI. The proposed model has the capability of capturing lag effects based on different factors to improve the prediction results. To evaluate the efficacy of the suggested approach, we carried out comparison experiments utilizing four performance metrics that have been widely utilized in previous studies to compare with different machine learning and deep learning models. The results showed enhanced prediction accuracy in comparison with existing methodologies. The lag effects by factor have been examined using the trained DLNM model, and we verified that the analyzed results are in good agreement with prior research by comparing them with previous research
김영휘(Young-Hwi Kim) 산업기술교육훈련학회 2014 산업기술연구논문지 (JITR) Vol.19 No.1
It has been known that the value of soil resistance drops when a high impulse curennt is injected into a grounding electrode. In this paper, impulse generator is used to investigate the dry soil and wet soil characteristics in cylinderical test cell. The impulse resistances and breakdown characteristics were discussed based on its voltage and current traces. As a result, sand resistances are decreased with increasing the applied currents. It was thought that a decrease in resistance of dry sand with increasing current is due to both thermal and ionization processes. On the other hand, in case there is no water presence in the soil, the reduction in resistance as the currents are of dry sand increased is mainly due to the ionization process.