• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.137-138
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• 2017

한반도의 근해는 다양한 해양변화가 있으며, 작전을 수행하는 해군함정, 함재기, 해상운용 비행기, 공군의 전투기, 해안에 위치한 공항 및 비행장 등이 영향을 받는다. 특히 해양환경의 직접적인 영향인 염분은 가스터빈엔진과 같이 고온/고속으로 운용되는 장비에 연료의 황성분과 화학적 변화로 고온부식(Hot Corrosion)이 발생시킨다. 한계값으로 정의 할 수 없지만 염분에 의한 부식은 디미스터(공기흡입구) 높이가 7m 이하일 경우 해상에서 유입되는 염분이 증가하여 부식이 급격하게 증가하였다. 또한 서해보다 동해에서 작전임무를 수행하는 무기체계는 염분도, 풍량, 파고에 의해 비산되는 염분이 상대적으로 많아 부식율이 17% 증가함을 확인하였다. 해상에서 가스터빈엔진을 운용하는 해상무기체계는 염분유입을 최소화하기 위해 해상으로부터 13m이상에서 운용되어야 급격한 고온부식을 최소화 될 것으로 본다.

• 대한인간공학회지
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• 제36권3호
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• pp.169-181
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• 2017

Objective: The aim of this study was to explore the influence of outdoor weather conditions on subjective responses during physical activity. Background: The largest difference between indoor and outdoor conditions is the existence of the sun. The heat load from the sun has an influence on the heat gain of the human body and the intense degree of solar radiation affected thermal comfort. Method: Thirty eight people were exposed to a range of climatic conditions in the UK. Weather in England does not have extremely hot and cold temperature, and the current study was conducted under warm (summer and autumn) and cool (spring and summer) climates. Measurements of the climate included air temperature, radiant temperature (including solar load), humidity and wind around the subjects. Subjective responses were taken and physiological measurements included internal body temperature, heart rate and sweat loss. Results: This study was conducted under four kinds of environmental conditions and the environmental measurement was performed in September, December, March, and June. The values for sensation, comfort, preference, and pleasantness about four conditions were from 'neutral' to 'warm', from 'not uncomfortable' to 'slightly comfortable', from 'slightly cooler' to 'slightly warmer', and from 'neither pleasant nor unpleasant' and 'slightly unpleasant', respectively. All subjective responses showed differences depending on air temperature and wind speed, and had correlations with air temperature and wind speed (p<0.05). However, subjective responses showed no differences depending on the radiant temperature. The combined effects of environmental parameters were showed on some subjective responses. The combined effects of air temperature and radiant temperature on thermal sensation and pleasantness were significant. The combined effects of metabolic rate with air temperature, wind speed and solar radiation respectively have influences on some subjective responses. In the case of the relationships among subjective responses, thermal sensation had significant correlations with all subjective responses. The largest relationship was shown between preference and thermal sensation but acceptance showed the lowest relationship with the other subjective responses. Conclusion: The ranges of air temperature, radiant temperature, wind speed and solar radiation were $6.7^{\circ}C$ to $24.7^{\circ}C$, $17.9^{\circ}C$ to $56.6^{\circ}C$, $0.84ms^{-1}$ to $2.4ms^{-1}$, and $123Wm^{-2}$ to $876Wm^{-2}$ respectively. Each of air temperature and wind speed had significant relationships with subjective responses. The combined effects of environmental parameters on subjective responses were shown. Each radiant temperature and solar radiation did not show any relationships with subjective responses but the combinations of each radiant temperature and solar radiation with other environmental parameters had influences on subjective responses. The combinations of metabolic rate with air temperature, wind speed and solar radiation respectively have influences on subjective responses although metabolic rate alone hardly made influences on them. There were also significant relationships among subjective responses, and pleasantness generally showed relatively high relationships with comfort, preference, acceptance and satisfaction. Application: Subjective responses might be utilized to predict thermal stress of human and the application products reflecting human subjective responses might apply to the different fields such as fashion technology, wearable devices, and environmental design considering human's response etc.

• International Journal of Aeronautical and Space Sciences
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• 제17권3호
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• pp.285-295
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• 2016

A contact strip shape of a high speed train pantograph system was optimized with CFD to increase the aerodynamic performance and stability of contact force, and the results were validated by a wind tunnel test. For design of the optimal contact strip shape, a Kriging model and genetic algorithm were used to ensure the global search of the optimal point and reduce the computational cost. To enhance the performance and robustness of the contact strip for high speed pantograph, the drag coefficient and the fluctuation of the lift coefficient along the angle of attack were selected as design objectives. Aerodynamic forces were measured by a load cell and HWA (Hot Wire Anemometer) was used to measure the Strouhal number of wake flow. PIV (Particle Image Velocimetry) was adopted to visualize the flow fields. The optimized contact strip shape was shown a lower drag with smaller fluctuation of vertical lift force than the general shaped contact strip. And the acoustic noise source strength of the optimized contact strip was also reduced. Finally, the reduction amount of drag and noise was assessed when the optimized contact strip was applied to three dimensional pantograph system.

• Advances in Energy Research
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• 제5권2호
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• pp.129-145
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• 2017

In this study, the use of a micro gas turbine system using biogas to supply heating, cooling and electricity loads of a rural building located in rural area around Tehran has been studied. Initially, the amount of energy needed by the farmhouse was calculated and then the number of needed microturbines was determined. Accordingly, the amount of substances entering biogas digester as well as tank volume were determined. The results of this study showed that village house loads including electrical, heating and cooling and hot water loads can be supplied by using a microturbine with a nominal power of 30 kW and $33.5m^3/day$ of biogas. Digester tank and reservoir tank volumes are $67m^3$ and $31.2m^3$, respectively. The cost of electricity produced by this system is 0.446 US$/kWh. For rural area in Iran, this system is not compatible with micro gas turbine and IC engine system use urban natural gas due to low price of natural gas in Iran, but it can be compatible by wind turbine, photovoltaic and hybrid system (wind turbine& photovoltaic) systems.

• 대한조선학회논문집
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• 제36권3호
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• pp.15-21
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• 1999

KRISO 300K VLCC 이중모형선 주위의 유동특성을 풍동실험을 통해 연구하였다. 선체 선미 주위유동과 후류유동의 평균속도 성분, 난류강도, 레이놀즈 전단응력 및 난류 운동에너지 분포를 열선풍속계를 이용하여 측정하였다. 실험은 선미와 후류의 횡단면에서 수행하였으며, 선체 표면에서의 유동 패턴을 정성적으로 조사하기 위하여 유막법을 이용한 유동가시화도 수행하였다. 선미와 근접 후류영역은 매우 복잡한 3차원의 유동특성을 가지고 있으며, 특히 종방향 와류영역에서 고리 모양의 후류 구조를 볼 수 있었다. 그리고 중앙평행부에서의 얇은 경계층은 선미 영역을 지나며 점차 두꺼워지고 복잡한 3차원 난류후류로 발전하였다.

• 대한기계학회논문집B
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• 제23권2호
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• pp.218-225
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• 1999

Flow visualization study has been conducted to simulate the turbulent dispersion behavior of a crossflow jet physically under the conditions of various thermal stratification in a wind tunnel. A smoke jet with the constant ratio of the jet to freestream velocity is injected normally to the cross flow of the thermally stratified wind tunnel(TSWT) for flow visualization. The typical natures of the smoke dispersion under different thermal stratifications such as neutral, weakly stable, strongly stable, weakly unstable, strongly unstable and inversion layer are successfully reproduced in the TSWT. The Instantaneous velocity and temperature fluctuations are measured by using a cold and hot-wire combination probe. The time averaged dispersion behaviors, the centerline trajectories, the spreading angles and the virtual origins of the cross jet are deduced from the edge detected images with respect to the stability parameter. All the general characteristics of the turbulent dispersion behavior reveal that the definitely different dispersion mechanisms are inherent in both stable and unstable conditions. It is conjectured that the turbulent statistics obtained in the various stability conditions quantitatively demonstrate the vertical scalar flux plays a key role in the turbulent dispersion behavior.

• 암석학회지
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• 제20권4호
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• pp.243-250
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• 2011

백두산 화산으로부터 분화된 것으로 추정되는 1702년의 역사기록을 화산학적 견지에서 고찰하였다. 분화지점인 백두산으로부터 140 km 떨어진 2 장소에서의 강하화산재의 등층후선을 설정하여 경험식에 의하여 계산된 분출물의 최소량은 $1.2km^3$로 1702년의 백두산 분화 사건은 화산폭발지수 5에 해당하는 대규모 분화였다. 플리니안 분화에 의한, 열기를 가진 화산재구름이 바람의 영향 하에 지면 가까이 낮은 고도로 이동하면서 강하화산재가 발생 퇴적된 것을 잘 묘사하고 있다. 향후 분화에 대비하여 역사기록에 대한 철저한 분석을 통한 화산의 특성 이해가 절실하다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.705-706
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• 2008

When heat generated inside a large factory building is not discharged due to a stagnant flow, the working environment of workers becomes worse and the cooling of high-temperature products such as hot-rolling coils is delayed. To investigate the natural ventilation inside a large factory building, experimental studies were carried out using wind-tunnel tests. The scale-down factory building models were placed in an atmospheric boundary layer (ABL) and the mean and fluctuating velocity fields were measured using a particle image velocimetry (PIV) technique. For the prototype factory model, the outdoor air is only entrained into the factory building through the one-third open windward wall, and stagnant flow is formed in the rear part of the target area. In order to improve the indoor ventilation environment of the factory building, three different louver-type ventilators were attached at the upper one-third open windward wall of the factory model. Among the three louver ventilators tested in this study, the ventilator model #3 with the outer louver (${\theta}_o$ = 90$^{\circ}$) and the inner louver (${\theta}_i$ = -70$^{\circ}$) was found to improve the natural ventilation inside the factory building model effectively. The flow rate of the entrained air was increased with aligning the outer louver blades with the oncoming wind and guiding the entrained air down to the ground surface with elongated inner louver blades.

• 동력기계공학회지
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• 제1권1호
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• pp.51-60
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• 1997

In this paper, we investigated the heating performance and the basic characteristics required for normal combustion of kerosene fan heater. And also the iso-velocity contours and the iso-temperature contours of hot gas discharged from the exit of kerosene fan heater were analyzed. The experiment was carried out with kerosene fan heater attached to the blow-down-type subsonic wind tunnel with a test section of $240mm{\times}240mm{\times}1200mm$. The purpose of this paper was to obtain the basic data for new design from conventional kerosene fan heater. Consequently it was found that (i) the pressure ratio $P_2/P_1$ had a comparatively constant value of 0.844 according to the increase of the revolution of turbo fan, (ii) the primary excess air ratio had a range of $0.84{\sim}1.11$ during normal combustion, and (iii) the heating performance of kerosene fan heater had a range of $1,494{\sim}3,852kcal/hr$.

• 천문학회보
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• 제44권1호
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• pp.46.3-46.3
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• 2019

We present our observational and theoretical investigation of Raman-scattered features in symbiotic stars (SySts). SySts are long interacting binaries, consisting of a hot compact star and an evolved giant, whose interaction via accretion process is at the origin of a tangled network of gas and dust nebulae. These systems are ideal objects to study a variety of important astrophysical problems, and have also been proposed as possible progenitors of type Ia supernova. In this talk, we emphasize that Raman-scattered features are exclusive spectroscopic tools to probe the stellar wind accretion processes in SySts. We studied mass transfer and mass loss processes in SySts using high resolution spectra obtained with 1.8m telescope at Mt. Bohyun and the 6.5m Magellan-Clay telescope combining with the theoretical modeling of radiative transfer of Raman-scattered features. We also note that there are a much smaller number of SySts known in our Galaxy, implying the necessity of systematic search programs. In view of the fact that Raman O VI features at $6830{\AA}$ are found in only bona fide SySts, we will carry out a photometric search of objects with Raman O VI features using a narrow band filter centered at $6830{\AA}$ in Local group galaxies.