• International Journal of Fluid Machinery and Systems
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• 제4권1호
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• pp.179-190
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• 2011

The swirling flow developing in Francis turbine draft tube under part load operation leads to pressure fluctuations usually in the range of 0.2 to 0.4 times the runner rotational frequency resulting from the so-called vortex breakdown. For low cavitation number, the flow features a cavitation vortex rope animated with precession motion. Under given conditions, these pressure fluctuations may lead to undesirable pressure fluctuations in the entire hydraulic system and also produce active power oscillations. For the upper part load range, between 0.7 and 0.85 times the best efficiency discharge, pressure fluctuations may appear in a higher frequency range of 2 to 4 times the runner rotational speed and feature modulations with vortex rope precession. It has been pointed out that for this particular operating point, the vortex rope features elliptical cross section and is animated of a self-rotation. This paper presents an experimental investigation focusing on this peculiar phenomenon, defined as the upper part load vortex rope. The experimental investigation is carried out on a high specific speed Francis turbine scale model installed on a test rig of the EPFL Laboratory for Hydraulic Machines. The selected operating point corresponds to a discharge of 0.83 times the best efficiency discharge. Observations of the cavitation vortex carried out with high speed camera have been recorded and synchronized with pressure fluctuations measurements at the draft tube cone. First, the vortex rope self rotation frequency is evidenced and the related frequency is deduced. Then, the influence of the sigma cavitation number on vortex rope shape and pressure fluctuations is presented. The waterfall diagram of the pressure fluctuations evidences resonance effects with the hydraulic circuit. The influence of outlet bubble cavitation and air injection is also investigated for low cavitation number. The time evolution of the vortex rope volume is compared with pressure fluctuations time evolution using image processing. Finally, the influence of the Froude number on the vortex rope shape and the associated pressure fluctuations is analyzed by varying the rotational speed.

• 한국안광학회지
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• 제10권1호
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• pp.35-40
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• 2005

각막교정 수술이나 안질환이 없고 콘택트렌즈를 착용하지 않는 20대(평균 21세) 남녀 63명 126안의 근시안을 대상으로 자각적 시력과 타각적 굴절력을 측정하였다. 본 연구는 자각적과 타각적 검사를 통해 하루 동안의 시력변동에 관하여 알아보고자 하였다. 자각적 시력검사는 하루 동안 오전(8:00 AM-10:00 AM), 정오(12:00 PM-2:00 PM) 및 오후(4:00 PM-6:00 PM)로 세 차례 나누어 5 m 거리에서 측정하였고, 시력검사 직 후 측정한 굴절력은 Nvision-K 5001(shin-nippon)을 사용하여 시야가 개방된 자연시 상태에서 세 차례 측정한 값의 평균으로 하였다. 연구 결과 시력의 평균은 오전 0.256(${\pm}0.263$), 정오 0.266(${\pm}0.276$), 오후 0.242(${\pm}0.249$)로 나타났다. 우안의 등가구면굴절력의 평균값은 오전 -3.416 D(${\pm}2.907$), 정오 -3.359 D(${\pm}2.735$), 그리고 오후 -3.297 D(${\pm}2.709$)로 나타났으며 시간이 지나면서 굴절력이 감소되었다. 자각적 방법으로 측정한 시력과 타각적 방법으로 측정한 굴절력은 모두 일일변동을 보였으나 통계학적으로 유의하지는 않았으므로 하루 중 시력이나 굴절검사의 시간은 문제가 되지 않을 것으로 판단된다.

• 한국실내디자인학회논문집
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• 제24권4호
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• pp.91-98
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• 2015

Double skin façade is known that several features affected the building energy and daylighting performance. That is why the envelope is able to consist of all architectural materials such as glass, aluminum, wood and insulation for vision of residents and workers in buildings. Its specifications is very diverse according to the building designers and building owners. In recent times, visual environment became a major focus and resulted in the development of cutting edge engineering of diverse glazing systems and shading devices by growing interests of friendly environment. Thus this research has evaluated the fluctuations of interior lighting and atmospheric conditions based on double skin facade systems. Especially in terms of daylighting environment as dependent on solar variations, this research provides quantitative analysis of interior lighting conditions and how it affects the living conditions as well as improve the design of interior spaces.

• 로봇학회논문지
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• 제6권1호
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• pp.18-26
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• 2011

This paper presents a method, Exposure Controlled Temporal Filtering (ECF), applied to visual motion tracking, that can cancel the temporal aliasing of periodic vibrations of cameras and fluctuations in illumination through the control of exposure time. We first present a theoretical analysis of the exposure induced image time integration process and how it samples sensor impingent light that is periodically fluctuating. Based on this analysis we develop a simple method to cancel high frequency vibrations that are temporally aliased onto sampled image sequences and thus to subsequent motion tracking measurements. Simulations and experiments using the 'Center of Gravity' and Normalized Cross-Correlation motion tracking methods were performed on a microscopic motion tracking system to validate the analytical predictions.

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.324-333
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• 2009

This paper presents a numerical simulation study of the transient behavior of a $2{\times}340MW$ pump-turbine power plant, where the results show an unstable behavior at runaway. First, the modeling of hydraulic components based on equivalent schemes is presented. Then, the 2 pump-turbine test case is presented. The transient behavior of the power plant is simulated for a case of emergency shutdown with servomotor failure on Unit 1. Unstable operation at runaway with a period of 15 seconds is properly simulated using a 1-dimensional approach. The simulation results points out a switch after 200 seconds of the unstable behavior between a period of oscillations initially of 15 seconds to a period of oscillation of 2.16 seconds corresponding to the hydraulic circuit first natural period. The pressure fluctuations related to both the rigid and elastic water column mode are presented for oscillation mode characterization. This phenomenon is described as a switch between a rigid and an elastic water column oscillation mode. The influence of the rotating inertia on the switch phenomenon is investigated through a parametric study.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 춘계학술대회 논문집
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• pp.1487-1501
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• 2011

Recently, fast-growing up railway transportations. Because, regional traffic congestion problem solving and a period of rapid expansion to meet the demand of industries. In addition the government also suggest to new paradigm for the future 'Low Carbon, Green Growth' is presented as a new national vision. To meet the social needs and the time demands, Last of the railway increase very long tunnels and huge deep tunnels. Especially this trend accelerated high speed up in the tunnel, the revision of design criteria and research challenges are being actively improved. Mainly in the tunnel cross-section was under the control of the vehicle train speed 150km/hr by the construction of the vehicle cross-section of the tunnel. More than 200km/hr rail tunnel depending on the vehicle's speed caused the tunnel to the pressure fluctuations will be governed by the aerodynamic changes. Considering the economy to ensure the optimum cross-section of the railway tunnel to the description scheme is selected cross-section of the railway tunnel to determine the size domestic or international railway tunnel for the elements((based on fast Algorithm design criteria, the center line spacing, streetcar line, cross-sectional shape, sectoral issues, such as interface and aerodynamics) based on design practices and to review results. In this study, to propose guidelines depending on the size of a railway tunnel cross section for the size of the determining reasonable factors when designing the railway tunnel and cost-effective standards guidelines.

• Journal of Preventive Medicine and Public Health
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• 제34권4호
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• pp.399-407
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• 2001

Objectives : To investigate the current status of hospital-based health promotion programs in Korea and to elucidate the factors which affect to the process of implementation. Methods : We conducted a mail survey of all 875 hospitals in Korea from March to May 2001. In reference to 12 specific kinds of health promotion programs, hospital CEOs were asked whether their hospital have such programs, whether they are fully staffed and whether the program is paid for by the patients. Contextual factors(location, hospital type, number of beds, length of operation, public/private status, economic level of the community, the level of competition) and organizational factors (the extent of market, compatibility with vision, formalization), strategic types of the CEOs (defender/analyser/prospector) were also surveyed. The relationships between each variable and the implementation of health promotion services, activation of services, and the target groups(patient/community resident) were analyzed by univariate analysis and the independent effects of these variables were examined with multiple logistic regression. Results : 100 of 125 hospitals responding (84.8%) had mere than one health promotion program. However, they showed fluctuations in the adoption rate of each programs, meaning that comprehensive health promotion services were not provided. Many programs were not fully staffed and few hospitals had paid programs. In factors affecting health promotion service implementation, private hospitals showed a higher rate in implementation than public hospitals. In contrast, when the competition among nearby hospitals was intense, the level of implementation of service lowered. In the strategic type of the CEOs, the prospectors were shown to have instituted more health promotion programs in their hospitals and the analysers had a greater tendency to have programs for community residents than the defenders. Conclusion . Considering the above results, contextual factors may contribute greatly to the introduction of health promotion services in Korean hospital, although the CEO's personal preference and organizational factors play a larger role in the activation of services. Additionally, the CEO's personal preference may be the major influencing factor in the introduction of programs for community residents.