• 천문학회보
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• 제42권1호
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• pp.51.1-51.1
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• 2017

The galaxy cluster Abell 115 shows ongoing merger features, which suggest that it might be in an intermediate phase of dynamical evolution. As merging clusters often show, the characteristic hints of A115's merging activities include radio relics, double X-ray peaks, and large offsets between the cluster member galaxies and the X-ray distributions. To constrain the exact stage of the merger, it is necessary to obtain its dark matter distribution. In this study, we carry out a precision weak lensing study of this interesting system based on Subaru images. We present our mass reconstruction together with descriptions on our core procedure of the analysis: Subaru data reduction, galaxy shape measurement, and source selection. We find that Abell 115 consists of two massive dark matter clumps, which closely follow the cluster galaxies. Our weak lensing mass estimate is a few factors lower than the published dynamical mass obtained from velocity dispersion. This large mass discrepancy may be attributed to a significant departure from dynamical equilibrium.

• Ocean Systems Engineering
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• 제10권3호
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• pp.289-316
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• 2020

In the present paper, the effect of the location of stern planes on the flow entering the submarine propeller is studied numerically. These planes are mounted on three longitudinal positions on the submarine stern. The results are presented considering the flow field characteristics such as non-dimensional pressure coefficient, effective drag and lift forces on the stern plane, and the wake flow formed at the rear of the submarine where the propeller is located. In the present study, the submarine is studied at fully immersed condition without considering the free surface effects. The numerical results are verified with the experimental data. It is concluded that as the number of planes installed at the end of the stern section along the submarine model increases, the average velocity, width of the wake flow and its turbulence intensity formed at the end of the submarine enhance. This leads to a reduction in the non-uniformity of the inlet flow to the propulsion system.

• 한국생산제조학회지
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• 제25권6호
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• pp.479-485
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• 2016

A 40 mm medium caliber gun to be equipped with ventilation holes is designed and manufactured in this study. The muffler used is composed of holes, blades, and several spaces in the tube. Accordingly, a numerical analysis is performed with computational fluid dynamics (CFD) before testing the muffler. The validity of the numerical analysis is examined by analyzing the differences between the measured data of the firing test and the results of the CFD analysis. The CFD analysis showed that the numerical analysis can be used positively in the muffler design because no difference exists between the results of the field test and the CFD analysis. The test result also indicated a noise reduction of approximately 10 dB. Moreover, the muzzle velocity is almost equivalent, regardless of the muffler.

• 한국산업융합학회 논문집
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• 제7권2호
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• pp.161-166
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• 2004

The impact factor of bridges is analyzed based on experimental data to examine the characteristics of the dynamic responses of bridges. The experimental impact factors are compared with the impact factor of Korean Highway Design Specification and Japan T-load in terms of the span length. According to the superstructural types of bridges, the variation of the impact factor is analyzed. When vehicles are passing on a bridge, the dynamic effect acts on the bridge impact factor more than at the time of design because of the velocity of vehicles, the surface roughness reduction due to the deterioration of the bridge deck pavement, and the disconnection of the bridge entrance and the expansion joint. Because the actual value is greater than the expected value at the time of design, the dynamic response of the bridge accelerates the deterioration of the bridge due to the accumulation of fatigue, and the bridge's life-time is shortened and can have an influence on the serviceability and safety of the bridge.

• 한국전산유체공학회지
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• 제14권2호
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• pp.39-45
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• 2009

In engine room, proper enclosure system is preferable for reducing noise level but the enclosure system in the engine room causes bad influence on cooling performance due to poor ventilation. Cooling efficiency of the enclosure system can be improved by varying fan speed and proper flow path for ventilation. In this study, numerical analysis is performed to assess cooling effect of the enclosure system using finite volume method. The RNG k-$\varepsilon$ model is adopted for turbulence model along with heat exchanger model and porous media model for heat exchanger analysis, and moving reference frame model for rotational fan. Verification result shows reasonable agreement with experimental data. Analysis results show direct effect of velocity and temperature distribution on cooling ability in the enclosure system. Enclosure system of case B shows high heat transfer coefficient and has the smallest area ratio of opened flow passages which is good for noise level reduction.

• 지질공학
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• 제12권1호
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• pp.53-61
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• 2002

국내의 경우는 국토의 70%이상이 산지로 구성되어 있어 도로 개설에 따라 필연적으로 절개면이 발생된다. 더욱이 여름철에 집중적으로 발생하는 태풍, 장마에 의해 절개면의 붕괴가 많이 발생하고 있다. 국내 도로절개면 붕괴 중 낙석이 차지하는 비중이 40.8%이며, 토사붕괴는 29.5%를 차지한다. 낙석의 경우, 절개면 상부 암석의 자유운동에 의해 빠른 시간 내에 발생하고, 토사붕괴의 경우, 집중강우와 관련 쇄설성 유동형태로 도로이용에 많은 인명 및 재산피해를 유발한다. 특히 자동차 운행속도와 토사 붕괴 및 낙석이 떨어지는 속도와의 관계를 고려할 대 불과 몇 초의 짧은 시간에 인명피해를 발생시키게 된다. 본 연구는 최근 국도 주변 붕괴 현장 자료를 분석하고 국내 도로절개면의 특성과 붕괴유형을 근거로 낙석 및 쇄설성 유동에 대한 인명피해를 최소화하기 위한 방안으로 낙석 및 쇄설성 유동 발생시 이동시간, 절개면 통과 차량의 속도와 정지거리의 상관성을 검토하여 도로 경보시스템의 설치기준을 제시하는데 있다. 경보시스템은 낙석발생과 동시에 작동하여 운전자로 하여금 붕괴위치로의 이동을 사전에 차단시킴으로 피해를 최소화한다.

• 환경영향평가
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• 제28권6호
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• pp.507-524
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• 2019

본 연구의 목적은 낙동강 내에 위치한 강정고령보 구간을 대상으로 EFDC 모델을 검정하고, 보 구간의 유량에 따른 체류시간과 유입수 인 농도 변화가 수질 및 조류 그룹별(규조류, 녹조류, 남조류) 생체량에 미치는 영향을 평가하는데 있다. 2018년 실험자료를 이용하여 모델을 검정한 결과, 보 구간의 수위와 수온의 수직 분포, DO, 유기물, 질소, 인 계열의 시계열 변화를 적절히 모의하였다. 조류 그룹별 생체량 예측에 있어서는 계절별 변동 특성은 적절히 재현하였으나, 일부기간에 실측값과 편차가 크게 나타났다. 보의 관리수위와 유량을 조절하는 시나리오 모의결과, 보의 운영 수위를 낮출수록 유량을 증가시킬수록 수온성층이 완화 또는 해소되는 것으로 분석되었다. 강정고령보에서 수온성층이 해소된 유속은 약 0.1 m/s였으며, 이는 금강의 백제보에서 연구결과와 일치한다. 2Q 유량 시나리오 모의결과, Chl-a는 8.7% 감소하였고 규조류와 녹조류 세포수 밀도도 감소하였다. 하지만 남조류 세포수는 오히려 증가하였는데, 그 이유는 유량이 증가함에 따라 유속이 빨라져 상류경계조건의 높은 남조류 농도가 하류에 직접 영향을 끼친 것으로 나타났다. 유입수 인 부하 농도(평균 0.056mg/L)를 50% 수준으로 저감하는 시나리오 모의결과, Chl-a는 13.6 % 감소하였다. 연구결과는 강정고령보의 조류 과잉성장을 억제하기 위해서는 수리학적 제어와 함께 상류 유입 조류 농도와 인 부하량 저감이 동시에 고려되어야 함을 시사한다.

• 대한기계학회논문집B
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• 제39권7호
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• pp.567-578
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• 2015

Leidenfrost 온도 이상으로 가열된 벽면과 충돌하는 액적의 속도가 열전달 특성에 미치는 영향에 관한 실험 연구를 수행하였다. 동기화된 초고속 가시화 카메라와 적외선 카메라를 이용하여 벽면과 충돌하는 액적의 충돌 특성과 충돌면의 온도 분포를 측정하였다. 획득한 표면온도 분포를 충돌면의 경계 조건으로 이용하여 가열 벽면의 3차원 비정상 열전도 수치해석을 통해 표면 열유속 분포를 얻었다. 수직방향 충돌속도가 증가할수록 최대 액막 직경이 증가하고 가열 벽면과 액막 사이에 존재하는 증기막의 두께가 감소하여 열전달 효율이 증가하였다. 액적은 웨버수가 30보다 작은 경우 되튐현상이 발생하였으며, 큰 경우 작은 액적들로 분쇄되어졌다. 충돌속도에 의한 열전달량의 증가 경향이 되튐영역에서 분쇄영역에서 가면서 약화되었으며, 이는 분쇄현상에 의해 유효 열전달 면적의 확대 효과가 저감되었기 때문으로 해석된다.

• 대한기계학회논문집A
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• 제26권8호
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• pp.1506-1511
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• 2002

A computer aided expert system fur spur, helical, bevel and worm gears was newly developed by using AutoiCAD system and its AutoLISP computer language in the present study. Two methods are available for a designer to draw a gear. The first method needs the gear design parameters such as pressure, module, number of tooth, shaft angle, velocity, materials, etc. When the gear design parameters are inputted, a gear is drawn in AutoCAD system and maximum allowable power and shaft diameter are calculated additionally. The second method calculates all dimensions and gear design parameters to draw a gear when the information such as transmission, reduction ratio, nm, materials and pressure are inputted. The system includes four programs. Each program is composed of a data input module, a database module, a strength calculation module, a drawing module, a text module and a drawing edit module. In conclusion, the CAD system would be widely used in companies to find the geometric data and manufacturing course.

• 한국분무공학회지
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• 제21권2호
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• pp.78-87
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• 2016

This study experimentally investigated the effects of droplet temperature on the heat transfer characteristics during collision of a single droplet on a heated wall above the Leidenfrost temperature. Experiments were performed by varying temperature from 40 to $100^{\circ}C$ while the collision velocity and wall temperature were maintained constant at 0.7 m/s at $500^{\circ}C$, respectively. Evolution of temperature distribution at the droplet-wall interface as well as collision dynamics of the droplet were simultaneously recorded using synchronized high-speed video and infrared cameras. The local heat flux distribution at the collision surface was deduced using the measured temperature distribution data. Various physical parameters, including residence time, local heat flux distribution, heat transfer rate, heat transfer effectiveness and vapor film thickness, were measured from the visualization data. The results showed that increase in droplet temperature reduces the residence time and increases the vapor film thickness. This ultimately results in reduction in the total heat transfer by conduction through the vapor film during droplet-wall collision.