• 한국산업정보학회논문지
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• 제28권6호
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• pp.99-105
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• 2023

고도의 생존성이 요구되는 잠수함은 군의 전략자산에서 가장 중요한 전투 무기체계 중 하나이다. 일반적인 재래식 잠수함은 추진시스템을 작동하기 위해 공기가 필요해 필연적으로 스노클 항해를 하며 잠수함 내부로 공기를 공급해야 한다. 그리고 스노클 항해 시 수중으로 배출된 폐기 가스는 주변 유체를 가열해 온도 항적을 형성하고 결과적으로 잠수함의 생존성을 감소시킨다. 본 연구에서는 수중 잠수함의 폐기로 인해 형성된 수면의 온도 항적에 관한 기초 실험 연구를 수행하였다. 이를 위해 국내 도입된 잠수함의 추진시스템과 항해 조건 자료를 수집하였으며, 온도 항적을 계측하기 위한 실험 시스템을 구현하였다. 실험 결과 수조로 주입된 고온 기포는 작은 크기로 부서져 주위를 둘러싼 유체와 유사한 수준으로 온도가 감소하였으며, 이를 열전대 센서로 확인하였다. 그리고 수면의 온도 항적을 계측하기 위한 열화상 시스템의 결과에서도 온도 항적은 계측되지 않았다.

• 대한기계학회논문집
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• 제9권5호
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• pp.555-563
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• 1985

본 논문에서는 원주(circular cylinder)가 균일속도장에 놓였을 때의 2차원적 인 난류후류유동 특성을 실험에 의해 조사하고, 근접후류에서의 주기적인 대규모 운동 에 의한 코히어런트구조가 하류에서 자체유사(selfpreserving)로 되어 가는 데 있어서 의 난류변동성분에 관한 해석을 위해 확률밀도함수, 자기상관계수, 파워스펙트럼 등과 같은 통계적 처리기법을 도입하고자 한다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.428-433
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• 2000

The characteristics of unsteady heat transfer and boundary layer flow in the SSME turbine rotor passage are investigated with LRN $k-{\varepsilon}$ turbulence model. The unsteady flow and heat transfer in a rotor blade passage as a result of wake/blade interaction is modeled by the inviscid/boundary-layer flow approach. The relevant governing equations are discretized to a system of finite different equations by means of a BTBCS implicit method. These equations have been solved numerically, for the velocity and temperature fields using TDMA method. Heat flux on the blade surface and flow parameters in the rotor passage are calculated with wake interaction. Numerical results show that velocity, pressure, turbulent kinetic energy and heat flux on the blade surface are varied periodically by wake passing.

• 설비공학논문집
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• 제18권1호
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• pp.73-80
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• 2006

Present study is concerned with an experimental study on the cooling characteristics of heat-generating components arranged in channels which are made by printed circuit boards. To assess the thermal performance of the heat-generating components arranged by $5\times11$ in flow channel, three variables are used: the velocity of the fluid at the entrance, the height of channel, and row number of the component. The cooling characteristics of the heat-generating components such as the surface temperature rise, the adiabatic temperature rise, the adiabatic heat transfer coefficient, and the effect of thermal wake are compared with the result of the experiment and the numerical analysis. Based on the experiment analysis, some conclusions can be drawn: First of all, the experiment and numerical analysis are identical comparatively; the heat transfer coefficient increases as H/B decreases. Howeve., when H/B is over 7.2, the effect of H/B is rather trivial. The effect is the biggest at the first component from the entrance, and it decreases until the fully developed flow, where it becomes very consistent. The thermal wake function calculated for each row decreases as H/B increases.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.36-41
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• 2001

In order to simulate wake of stator and a gas turbine engine's balde row, acryl cylinder and a linear turbine cascade were used respectively in this study. Experimental of heat transfer distributions was done on the passage endwall and blade suction surface. Temperature distributions on the experimental regions were obtained through image processing system by using the cholesteric type liquid crystal which has chain structure of metyl$(CH_3)$. To represent the degree of heat transfer, dimensionless St number was used. The results show that heat transfer on the blade suction surface was increased due to the wake from the cylinder and was decreased as the distance between cylinder row and blade row increases. Because of groth of passage vortex, heat transfer distributions on the trailing edge area showed triangular shape which was little changed with wake. On the other hand, heat transfer on the passage endwall was decreased due to the wake from cylinder. As the distance between cylinder row and blade row increases, heat transfer was more decreased.

• 수면정신생리
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• 제5권1호
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• pp.12-17
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• 1998

Circadian rhythms in subjective alertness, mood, and performance can be classified as psychological rhythm, compared with physiological rhythm such as body temperature and hormonal change. While in normal condition entrained by 24hr zeitgeber, subjective alertness would reach its maximum value around midday, subjective alertness would parallel body temperature rhythm with its peak at evening in non-entrained, free-running state. With desynchronization technique, subjective alertness rhythm is thought to be controlled by both temperature and sleep-wake rhythm oscillator. Circadian performance rhythms depend on the kind of task tested. It shows parallelism with body temperature rhythm when subjects are tested with simple, repetitive task. But when tested with tasks requiring complex verbal reasoning or immediate memory, subjects would perform them best at early morning, with performance decreasing as time of day advances. The desynchronization technique shows that circadian performance rhythm of simple, repetitive task is dependent on temperature oscillator but circadian performance rhythm of complex verbal reasoning is influenced by both temperature and sleep-wake rhythm oscillator or another independent oscillator. It would be worthwhile to compare psychological rhythm with hormonal change such as cortisol and melatonin. And more simple and time-saving method than desynchronization technique may facilitate the study of the mechanism underlying psychological rhythm.

• 한국동물학회:학술대회논문집
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• 한국동물학회 1999년도 공동 춘계학술대회
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• pp.66.2-66
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• 1999

No Abstract, See Full Text

• 기본간호학회지
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• 제1권1호
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• pp.77-97
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• 1994

The circadian system represents a temporal order which is mediated by the mutual coupling of oscillators and by the synchronizing effects of zeitgebers. It is known that well-being of man depends partly on the maintenance of this order, and that repeated or long lasting disturbances to it such as shift work will Cause harmful effects. This study was a quasi-experimental study to test the effect of shift directions for the clinical nurses on the circadian rhythm. Fourteen nurses working at the general units of Y hospital were selected according to the established criteria. Fourteen subjects were assigned to a weekly shift but the directions of shift work were phase delay first and then phase advance or vice versa. Oral temperature, total sleeping time, frequency of sleep-wake cycle, fatigue, mental performance, and physical symptom were measured during these days except holidays. The data collection period was from April 26, 1993 to July 3, 1993. MANOVA and Wilcoxon signed rank test were used for statistical analysis. The results are summarized as follows. 1. Having worked on evening and night shifts in either phase delay or phase advance schedules, temperature rhythms of shift workers were gradually adapted to the new sleep-wake cycles. A complete adaptation to work on the night shift was achieved the sixth day of the night shift in the phase delay schedule compared to the partial adaptation to the work on the night shift in the phase advance schedule. Accordingly, by putting evening shift between day and night shifts, it will be possible for circadian rhythm to adapt easily to the night shift. 2. There were differences in the total sleeping time, frequency of steep-wake cycle, fatigue, and physical symptom except for mental performance between night shift and day, evening shift. This indicates further that shift workers working on the night shift have a hard time adapting to the shift work compared to the other shifts. 3. Evaluating all the acrophases of temperature rhythm either in phase delay or phase ad-vance schedules, it was shown that night to evening shift in the phase ad-vance schedule revealed the smallest phase move. Also phase advance schedule showed poorer adaptation to shift work than phase delay schedule in connection with total sleeping time, frequency of sleep-wake cycle, fatigue, mental performance, and physical symptom. It is suggested, taken together, these findings reflect that phase delay schedule facilitated the degree of adjustment to the shift work compared to the phase advance schedule.

• 수면정신생리
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• 제21권2호
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• pp.51-60
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• 2014

A 'circadian rhythm' is a self-sustained biological rhythm (cycle) that repeats itself approximately every 24 hours. Circadian rhythms are generated by an internal clock, or pacemaker, and persist even in the absence of environmental time cues, collectively termed 'zeitgebers.' Although organisms generate circadian rhythms internally, they are entrained by environmental stimuli, particularly the light-dark cycle. Measurement of the endogenous melatonin rhythm provides relatively reliable surrogate way of assessing the timing of the internal circadian clock. Also, core body temperature and cortisol can be used as markers of circadian rhythms. The sleep-wake cycle, body temperature, and melatonin rhythm have a stable internal phase relationship in humans and other diurnal species. They play an important role in controlling daily behavioral rhythms including task performance, blood pressure, and synthesis and secretion of several hormones. In this review, we address not only the properties, methods of measurement, and markers of circadian rhythms, but also the physiological and psychological importance of human circadian rhythms.

• 대한기계학회논문집B
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• 제22권6호
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• pp.849-859
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• 1998

The heat generated in an induction motor is mostly dissipated through the frame. The study on the heat transfer characteristics of a newly manufactured finless TEFC(Totally Enclosed Fan Cooled) induction motor showed/that it had an unsuitable structure in view of the heat transfer. The angle of the cooling air flow was very large and the ribs disturbed the air flow and partially generated the wake region on the frame. In the wake region the temperature was very high. Thus the heat transfer coefficients were lower than those of the frame with fins. Also was investigated the heat transfer characteristics of the motor frame by installing various guide vanes in the fan-side end cap. An optimum heat transfer case was found and the average heat transfer coefficient of the frame was 70% higher and the average coil temperature measured by the resistance method was 9 deg. C lower than that of the frame which had no guide vanes.