• Composites Research
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• v.21 no.6
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• pp.23-30
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• 2008

In this paper, the effect of the natural aging on the strength distribution and structural service life of a Filament Wound (FW) composite pressure vessel was studied. The fiber failure strain, which is varied significantly, was considered as the design random variable and the strength analysis was carried out by probabilistic numerical approach. The progressive failure analysis technique and the First Order Reliability Method (FORM) were embedded in this numerical model. As the calculation results, the probability of failure was obtained for each aging time steps and it is found that the strength degradation in FW composite pressure vessel, due to the natural aging, appears within 10 year-aging-time. As an example of the life prediction under natural aging using arbitrary laminated model, the service lifetime of 13 years was predicted based on the probability of failure of 2.5% and the design pressure of 3,250 psi.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.14 no.1
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• pp.98-103
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• 2021

In this study, we propose a group communication technique that guarantees security and expandability by configuring a network consisting of IoT terminals equipped with security functions. As the number of devices participating in the network increases, network resources are proportionally reduced, and adding a security function to the IoT device increases the delay time due to encryption in the IoT device. If the error rate that occurs in the network increases, network resources are quickly consumed due to retransmission. Therefore, IoT terminals are grouped to ensure scalability while supporting security, reducing the consumption of network resources even when the number of participating nodes increases, thus ensuring scalability. For the future implementation, the encryption method used in IoT terminals considered the standard of IEEE802.5.4, and the standardization trend was investigated and classified. The proposed method applies IoT devices that provide security functions of the IEEE802.5.4 standard to the group communication base to ensure reliability and scalability. In the performance evaluation, the effectiveness of the proposed method was confirmed by comparing the delay times when grouping IoT devices with security functions through simulation.

• Clean Technology
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• v.18 no.3
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• pp.287-294
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• 2012

In this study, performances of two cleaning methods were analyzed and a cleaning system was designed to develop a cleaning process of electronic components to remanufacture old laser copy machine. First, plasma cleaning as a dry cleaning method was executed to test cleaning ability. In cleaning of printed circuit board (PCB) by plasma, some damages were found near the metal parts, and considering the productivity, this method was not adequate for the cleaning of electronic components. With 4 different cleaning agents, ultrasonic cleaning tests were executed to select an optimal cleaning agent, aqueous agents showed superior cleaning performance compared to semi-aqueous and non-aqueous agents. Cleaning with aqueous cleaning agent A and 28 kHz ultrasonic frequency can be completed in 30 sec to 1 min. Finally, an ultrasonic cleaning system was constructed based on the pre-test results. Optimal cleaning conditions of 40 kHz and $50^{\circ}C$ were found in the field test. The productivity and economic efficiency in remanufacturing of laser copy machine are expected to increase by adapting developed ultrasonic cleaning system.

• Journal of Korea Water Resources Association
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• v.53 no.8
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• pp.627-636
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• 2020

Debris flow disasters primarily occur in mountainous terrains far from cities. As such, they have been underestimated to cause relatively less damage compared with other natural disasters. However, owing to urbanization, several residential areas and major facilities have been built in mountainous regions, and the frequency of debris flow disasters is steadily increasing owing to the increase in rainfall with environmental and climate changes. Thus, the risk of debris flow is on the rise. However, only a few studies have explored the characteristics of flooding and reduction measures for debris flow in areas designated as steep slopes. In this regard, it is necessary to conduct research on securing independent disaster prevention technology, suitable for the environment in South Korea and reflective of the topographical characteristics thereof, and update and improve disaster prevention information. Accordingly, this study aimed to calculate the amount of debris flow, depending on disaster prevention performance targets for regions designated as steep slopes in South Korea, and develop an independent model to not only evaluate the impact of debris flow but also identify debris barriers that are optimal for mitigating damage. To validate the reliability of the two-dimensional debris flow model developed for the evaluation of debris barriers, the model's performance was compared with that of the hydraulic model. Furthermore, a 2-D debris model was constructed in consideration of the regional characteristics around the steep slopes to analyze the flow characteristics of the debris that directly reaches the damaged area. The flow characteristics of the debris delivered downstream were further analyzed, depending on the specifications (height) and installation locations of the debris barriers employed to reduce the damage. The experimental results showed that the reliability of the developed model is satisfactory; further, this study confirmed significant performance degradation of debris barriers in areas where the barriers were installed at a slope of 20° or more, which is the slope at which debris flows occur.

• 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 KIISE:Information Networking
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• v.36 no.2
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• pp.108-117
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• 2009

Data aggregation is one of the well-known techniques to reduce the energy consumption for information transmission over wireless sensor networks (WSN). As the WSNs are deployed in untrusted or even hostile environments, the data aggregation becomes problematic when end-to-end data privacy including data confidentiality and integrity between sensor nodes and base station, is required. Meanwhile, data homomorphic cryptoschemes have been investigated recently and recommended to provide the end-to-end privacy in the hostile environments. In order to assure both data confidentiality and integrity for data aggregation, this paper analyzes the existing homomorphic cryptoschemes and digital signature schemes, proposes possible combinations, and evaluates their performance in terms of CPU overheads and communication costs.

• Proceedings of the Korea Information Processing Society Conference
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• 2002.11c
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• pp.2133-2136
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• 2002

인터넷 특성상 방대한 양의 정보와 상품 등으로 사용자들이 원하는 정보를 찾기 위해서 많은 시간을 낭비하고 있는 실정이다. 이러한 사용자의 시간 소모를 중이기 위해서 추천 시스템이 개발되었다. 현재 인터넷 상의 추천 기술 중에서 가장 많이 사용하는 기법으로는 협력적 여과(Collaborative filtering) 방법이다. 그러나, 협력적 추천 방법으로 추천 받기 위해서는 특정수 이상의 아이템에 대한 평가가 필요하며, 또한 비슷한 성향을 가지는 일부 사용자 정보에 근거하여 추천함으로써 나머지 사용자 정보를 무시하는 경향이 있다. 이러한 문제점이 발생되므로 최근에는 데이터 마이닝(Data Mining) 기법 중 연관 규칙(Association Rule)을 이용한 추천 시스템이 개발되고 있다[1,10]. 그러나, 연관 규칙 기법은 개인별 사용자의 성향을 반영하지 못하는 단점이 있다[4]. 연관 규칙은 단지 대용량 데이터 베이스에서 아이템간의 지지도(Support)와 신뢰도(Confidence)에 근거하여 규칙을 발견하는 특징을 가지고 있기 때문이다. 즉 개인성향을 무시하고 아이템간의 연관성만을 근거로 하여 아이템을 추천하기 때문이다. 본 논문에서는 효율적인 연관 규칙을 이용한 개인화 추천 시스템을 구현하기 위해서 연관 규칙과 여과 방법을 통합한 시스템을 제안한다. 본 시스템에 대하여 성능 비교 실험을 수행함으로써 제안한 방법의 타당성을 제시한다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.2
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• pp.34-40
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• 2003

This paper gives an assessment criteria and reliability improvement for high frequency power supply of high efficacy electrodeless fluorescent lamp. The electrodeless fluorescent lamp system consist of electrodeless fluorescent lamp, high frequency power supply and lighting fixtures. The high frequency power supply has a shortest life at the system. Therefore It is need th assess the Failure Rate or mean Time To Failure(MTTF) for the high frequency power supply of electrodeless fluorescent lamp system and improve the reliability at design. We suggest the assessment criteria and improve methods of the reliability on the design basis for the electodeless fluorescent system.

• Journal of Korean Society for Quality Management
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• v.41 no.1
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• pp.135-148
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• 2013

Purpose: This paper presents a method to evaluate the stockpile reliability of propelling charge for performance and storage safety with storage time. Methods: We consider a performance failure level is the amount of muzzle velocity drop which is the maximum allowed standard deviation multiplied by 6. The lifetime for performance is estimated by non-linear regression analysis. The state failure level is assumed that the content of stabilizer is below 0.2%. Because the degradation of stabilizer with storage time has both distribution of state and distribution of lifetime, it must be evaluated by stochastic process method such as gamma process. Results: It is estimated that the lifetime for performance is 59 years. The state distribution at each storage time can be shown from probability density function of degradation. It is estimated that the average lifetime as $B_{50}$ life is 33 years from cumulative failure distribution function curve. Conclusion: The lifetime for storage safety is shorter than for performance and we must consider both the lifetime for storage safety and the lifetime performance because of variation of degradation rate.

• Journal of the Korean Society of Safety
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• v.27 no.6
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• pp.115-121
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• 2012

This paper, being the second in a two-part series, presents the robust performance of the proposed design method which can enhance a reliability-based design optimization(RBDO) under the uncertainties of probabilistic models. The robust performances of the solutions obtained by the proposed method, described in the Part 1, are investigated through the parametric studies. A 10-bar truss example is considered, and the uncertain parameters include the number of data observed, and the variations of applied loadings and allowable stresses. The numerical results show that the proposed method can produce a consistent result despite of the large variations in the parameters. Especially, even with the relatively small data set, the analysis results show that the exact probabilistic model can be successfully predicted with optimized design sections. This consistency of estimating appropriate probability model is also observed in the case of the variations of other parameters, which verifies the robustness of the proposed method.