• Journal of Mechanical Science and Technology
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• 제17권10호
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• pp.1507-1519
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• 2003

The two-phase flow patterns for both non-loop and loop type oscillating capillary tube heat pipes (OCHPs) were presented in this study. The detailed flow patterns were recorded by a high-speed digital camera for each experimental condition to understand exactly the operation mechanism of the OCHP. The design and operation conditions of the OCHP such as turn number, working fluid, and heat flux were varied. The experimental results showed that the representative flow pattern in the evaporating section of the OCHP was the oscillation of liquid slugs and vapor plugs based on the generation and growth of bubbles by nucleate boiling. As the oscillation of liquid slugs and vapor plugs was very speedy, the flow pattern changed from the capillary slug flow to a pseudo slug flow near the annular flow. The flow of short vapor-liquid slug-train units was the flow pattern in the adiabatic section. In the condensing section, it was the oscillation of liquid slugs and vapor plugs and the circulation of working fluid. The oscillation flow in the loop type OCHP was more active than that in the non-loop type OCHP due to the circulation of working fluid in the OCHP. When the turn number of the OCHP was increased, the oscillation and circulation of working fluid was more active as well as forming the oscillation wave of long liquid slugs and vapor plugs in the OCHP. The oscillation flow of R-142b as the working fluid was more active than that of ethanol and the high efficiency of the heat transfer performance of R -142b was achieved.

• 대한물리의학회지
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• 제5권4호
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• pp.577-585
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• 2010

Purpose : This study was to evaluate gait velocity and stance time on 5 conditions in elderly women and elderly women with LBP. The subjects were 70's generation. Methods : The subjects are 20 divided into 2 groups. They measured gait velocity, stance-time. The 5 conditions were normal gait, 10cm obstacle gait, 25cm obstacle gait, dual 10cm obstacle gait, dual 25cm obstacle gait. The experimental period was between 2008/12 and 2009/2. Statistical analysis was used Repeated measurement for difference between conditions, independent t-test for difference in two groups. Subjects were countdown from 50 during dual task gait. Results : The results were as follow: there were significantly difference 10cm obstacle velocity, dual 10cm obstacle velocity in two group. The others were not significantly differences. Velocity and stance-time were significantly difference in control group. In dual 25cm obstacle gait, velocity was difference of normal gait. Stance-time was difference in 25cm obstacle gait, and dual 25cm obstacle gait. In Experimental group, velocity and stance-time were not significantly difference. But measured value of velocity was gradually decreased and stance time was increased. Conclusion : These results indicate that elderly people with LBP women are reduced gait ability in dual task, and obstacle condition. So they need to prevent falling in dual task, and obstacle gait and to train obstacle/dual tak gait.

• 한국항해항만학회지
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• 제35권3호
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• pp.187-195
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• 2011

선박운항자의 인적사고 방지 및 운항 훈련을 위한 방안으로 선박 운항 시뮬레이터가 사용된다. 선박운항 시뮬레이터에서 실시간 3D 가시화 기술은 현실감 있는 직관적인 영상을 제공하여 피교육자에 인지력을 향상시켜 시뮬레이터의 교육 효과를 높이는 중요한 요소이다. 본 연구에서는 공개형 3D 그래픽 엔진을 기반으로 선박 운항 시뮬레이터용 실시간 3D 가시화 시스템을 설계하고 구현한 결과에 대해서 설명한다. 실시간 3D 가시화 시스템은 요소 기능, 기존 그래픽 데이터 활용, 타 시스템과의 연동 측면에서 도출된 운용 요구사항들을 만족하며 추가적인 기능의 확장이 용이한 구조로 설계되었다.

• 제어로봇시스템학회논문지
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• 제7권8호
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• pp.689-696
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• 2001

Large-scale Multi-disciplinary Systems(LMS) such as transportation, aerospace, defense etc. are complex systems in which there are many subsystems, interfaces, functions and demanding performance requirements. Because many contractors participate in the development, it is necessary to apply methods of sharing common objectives and communicating design status effectively among all of the stakeholders. The processes and methods of systems engineering which includes system requirement analysis; functional analysis; architecting; system analysis; interface control; and system specification development provide a success-oriented disciplined approach to the project. This paper shows not only the methodology and the results of model-based systems engineering to Automated Guided Transit(AGT) system as one of LMS systems, but also propose the extension of the model-based tool to help manage a project by linking WBS (Work Breakdown Structure), work organization, and PBS (Product Breakdown Structure). In performing the model-based functional analysis, the focus was on the operation concept of an example rail system at the top-level and the propulsion/braking function, a key function of the modern automated rail system. The model-based behavior analysis approach that applies a discrete-event simulation method facilitates the system functional definition and the test and verification activities. The first application of computer-aided tool, RDD-100, in the railway industry demonstrates the capability to model product design knowledge and decisions concerning key issues such as the rationale for architecting the top-level system. The model-based product design knowledge will be essential in integrating the follow-on life-cycle phase activities. production through operation and support, over the life of the AGT system. Additionally, when a new generation train system is required, the reuse of the model-based database can increase the system design productivity and effectiveness significantly.

• 대한기계학회논문집A
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• 제35권1호
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• pp.11-15
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• 2011

본 논문은 풍력터빈의 출력 제어 방법에 관한 논문이다. MW급 풍력 터빈 출력제어의 기본 제어 구조는 가변속도 가변피치 방식을 사용한다. 가변속도 가변피치 제어는 파워 커브를 추종하기 위한 방법으로서, 풍속변화에 따라 이 제어방식이 어떻게 적용되는지 논의한다. 제어 시스템 설계를 위하여 단순화된 드라이브 트레인 모델이 사용되었다. 제어 시스템은 토크제어와 피치제어로 구성되고, 제시된 동적 모델을 사용하여 설계된 제어 시스템의 시뮬레이션 결과에 대하여 논의한다.

• 대한의용생체공학회:의공학회지
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• 제30권4호
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• pp.347-354
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• 2009

For the reliable transmission of meaningful visual information using prosthetic electrical stimulation, it is required to develop an effective stimulation strategy for the generation of electrical pulse trains based on input visual information. The characteristics of neuronal activities of retinal ganglion cells (RGCs) evoked by electrical stimulation should be understood for this purpose. In this study, for the development of an optimal stimulation strategy for visual prosthesis, we analyzed the neuronal responses of RGCs in rd1 mouse, photoreceptor-degenerated retina of animal model of retinal diseases (retinitis pigmentosa). Based on the in-vitro model of epiretinal prosthesis which consists of planar multielectrode array (MEA) and retinal patch, we recorded and analyzed multiunit RGC activities evoked by amplitude-modulated electrical pulse trains. Two modes of responses were observed. Short-latency responses occurring at 3 ms after the stimulation were estimated to be from direct stimulation of RGCs. Long-latency responses were also observed mainly at 2 - 100 ms after stimulation and showed rhythmic firing with same frequency as the oscillatory background field potential. The long-latency responses could be modulated by pulse amplitude and duration. From the results, we expect that optimal stimulation conditions such as pulse amplitude and pulse duration can be determined for the successful transmission of visual information by electrical stimulation.

• 한국산학기술학회논문지
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• 제18권1호
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• pp.609-617
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• 2017

철도는 전 세계적으로 매우 안전하고 중요한 운송 수단 중 하나이다. 그러나 철도시스템이 복잡도가 높아지고 주행거리 증가 등으로 인해 매년 사고가 지속적으로 발생하고 있다. 특히, 고속열차와 화물열차의 경우, 차축베어링 비정상 과열로 인하여 차축베어링의 기능이 소실되면 차축의 불균등한 하중을 초래한다. 따라서, 차축베어링의 비정상 과열은 심각한 사고 또는 차량 탈선의 원인이 될 수 있다. 이에 따라서 현재 고속열차 운행 중 차축의 비정상적인 발열을 검지하기 위하여 차축온도검지장치(Hot Box Detector, HBD)가 설치되어 운영되고 있다. 본 연구에서는 비정상 차축 과열 발생시, 이를 빠르고 효율적으로 검지하기 위하여 지수가중이동평균(EWMA) 기법을 적용한 차축온도 모니터링 방법을 제안하였다. 또한 제안한 방법에 대하여 통계적으로 설계하였다. 본 연구에서 제안하는 방법은 현재의 차축온도검지 모니터링 방법과 비교하여 비정상 과열의 발생에 대하여 더 좋은 성능으로 평가되었으며 그 수행도는 최대 170% 향상되었다.

• 한국철도학회논문집
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• 제16권6호
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• pp.510-518
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• 2013

현재 국내외적으로 차세대 철도 무선망에 대한 관심이 높아지고 있으며, 지금까지 열차제어신호 중심의 철도무선망에서 영상 및 대용량 데이터를 전송하기 위한 철도통합 무선망에 대한 연구가 진행 중이다. 본 논문에서는 철도통합 무선망 구축을 위한 무선통신방식과 우리나라에서 사용하고 있는 주파수대역에서 철도 전용주파수 대역으로 할당이 가능한 후보 주파수대역을 제안한다. 본 연구내용은 국내 철도의 열차 운행효율 향상은 물론 철도의 안전성과 편의성 최적화에 기여할 것이며, 세계 기술시장 변화에 대응하는 무선통신기반의 한국형 철도 통합무선망 구축을 실현 할 수 있을 것으로 예상된다.

• 한국철도학회논문집
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• 제15권5호
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• pp.429-435
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• 2012

차세대 고속철도(HEMU-430X)는 최고 속도 430km/h, 운영 속도 370km/h를 목표로 개발 중인 세계적 수준의 철도 차량이다. 시속 300km 이상의 운영 속도를 유지하기 위하여 충족해야 할 요건들은 다양하지만 주행 중 안정적인 전력 공급 여부는 상용화를 결정짓는 핵심기술 중 하나이다. 따라서 고속에서의 가선과 판토그래프의 동적 상호작용은 사전 평가를 통하여 충분히 검토되어야 한다. 본 논문에서는 다물체 동역학 해석 기법을 기반으로 한 집전성능 해석 프로그램을 이용하여 차세대 고속철도의 집전성능을 평가하였다. 국제 규정을 기반으로 기존 사양에 대한 성능 평가를 실시하고, 추가적으로 장력 및 경간 길이 변화에 따른 평가 결과를 토대로 집전성능 향상 방안에 대하여 고찰하였다.

• Asian Journal of Atmospheric Environment
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• 제7권1호
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• pp.38-47
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• 2013

$PM_{10}$ concentrations were measured at four monitoring sites at the Daechaung station of the Seoul subway. The four locations included two tunnels, a platform, and a waiting room. The outside site of the subway was also monitored for comparison purposes. In addition, the effect of the platform screen doors (PSDs) recently installed to isolate the $PM_{10}$ in a platform from a tunnel were evaluated, and a comparison between $PM_{10}$ levels during rush and non-rush hours was performed. It was observed that $PM_{10}$ levels in the tunnels were generally higher than those in the other locations. This might be associated with the generation of $PM_{10}$ within the tunnel due to the train braking and wear of the subway lines with the motion of the trains, which promotes the mixing and suspension of particulate matter. During this tunnel study, it was observed that the particle size of $PM_{10}$ ranged from 1.8 to 5.6 ${\mu}m$. It was revealed that the $PM_{10}$ levels in the tunnels were significantly increased by the PSDs, while those in the platform and waiting room decreased. As a result, in order to estimate the effect of ventilation system on $PM_{10}$ levels in the tunnels, fans with inverters were operated. It was found that the concentration of $PM_{10}$ was below 150 ${\mu}g/m^3$ when the air flow rate into a tunnel was approximately 210,000-216,000 CMH.