• Wind and Structures
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• 제13권2호
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• pp.109-125
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• 2010

This work presents some analytical and numerical results of a dynamic analysis of the dimensionless 2-D sheet flight equations. Two empirical models for aerodynamic forces and moments are used and compared. Results show that the initial condition of rest is always unstable, and for long times three distinct flight regimes are possible, depending on the initial angle of attack, the Tachikawa number, Ta (in fact, the parameter chosen was its inverse, ${\Omega}$), and a mass ratio ${\Phi}$. The final orbits in the velocity space and their maximum kinetic energy are compared with a theoretical asymptotic state of the motion equations, and some design considerations are proposed.

• Ocean and Polar Research
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• 제23권2호
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• pp.97-107
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• 2001

The Sejong Formation of Late Paleocene to Eocene is a lower volcaniclastic sequence unconformably overlain by upper volcanic sequence, and distributed along the southern and southeastern cliffs of the Barton Peninsula. The Sejong Formation is divided into five sedimentary facies; disorganized matrix-supported conglomerate (Facies A), disorganized clast-supported conglomerate (Facies B), stratified clast-supported conglomerate (Facies C), thin-bedded sandstone (Facies D), and lapilli tuff (Facies E), based on sedimentary textures, primary sedimentary structures and bed geometries. Individual sedimentary facies is characterized by distinct sedimentary process such as gravel-bearing mudflows or muddy debris flows (Facies A), cohesionless debris flows (Facies B),unconfined or poorly confined hyperconcentrated flood flows and sheet floods (Facies C), subordinate streamflows (Facies D), and pyroclastic flows (Facies E). Deposition of the Sejong Formation was closely related to volcanic activity which occurred around the sedimentary basin. Four different phases of sediment filling were identified from constituting sedimentary facies. Thick conglomerate and sandstone were deposited during inter-eruptive phases (stages 1, 3 and 4), whereas lapilli tuff was formed by pyroclastic flows during active volcanism (stage 2). These records indicate that active volcanism occurred around the Barton Peninsula during Late Paleocene to Eocene.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2019년도 학술발표회
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• pp.158-158
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• 2019

Recent studies show the possibility of more frequent extreme events as a result of the changing climate. These weather extremes, such as excessive rainfall, result to debris flow, river overflow and urban flooding, which post a substantial threat to the community. Therefore, an effective flood model is a crucial tool in flood disaster mitigation. In recent years, a number of flood models has been established; however, the major challenge in developing effective and accurate inundation models is the inconvenience of running multiple models for separate conditions. Among the solutions in recent researches is the development of the combined 1D-2D flood modeling. The coupled 1D-2D river flood modeling allows channel flows to be represented in 1D and the overbank flow to be modeled over two-dimension. To test the efficiency of this approach, this research aims to assess the capability of HEC-RAS model's implementation of the combined 1D-2D hydraulic simulation of river overflow inundation, and compare with the results of GERIS and FLUMENS 2D flood model. Results show similar output to the flood models that had used different methods. This proves the applicability of the HEC-RAS 1D-2D coupling method as a powerful tool in simulating accurate inundation for flood events.

• 한국항공우주학회지
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• 제42권2호
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• pp.158-164
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• 2014

IADC의 '25년 규정'에 의해 미션종료 된 저궤도 인공위성은 25년 이내에 지구로 재진입, 소각 폐기되도록 권고하고 있다. 이때 인공위성의 부품일부 또는 다수가 살아남아 지상에 충돌할 경우 인명 및 재산피해를 낼 수 있다. 우리나라의 경우 저궤도 위성으로서 아리랑 인공위성과 과학기술위성을 운용 중에 있으며 임무종료 후에는 모두 대기권 재진입을 통한 폐기처리가 필수이다. 따라서 본 논문에서는 ESA의 DRAMA내부의 SARA(Re-entry Survival and Risk Analysis)모듈을 이용하여 지상피해가 예측되는 크기인 가상위성의 추락궤적 및 생존부품을 분석하고 그에 따른 지상충돌확률, 피해확률을 분석하였다. 분석결과 198.831kg이 생존할 것으로 예상되며 추락지점이 한반도일 경우 전체 피해면적은 $15.2742m^2$, 피해확률은 5.9614E-03(2D)일 것으로 예상된다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2015년도 학술발표회
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• pp.112-112
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• 2015

우리나라는 산지가 국토의 64%이상으로 토석류 등 지반재해의 위험성에 노출되어 있다. 2011년 7월 우면산 토석류, 춘천시 펜션 토석류 등 규모가 큰 토석류 재해가 일어나며 문제가 되고 있다. 이에 본 연구에서는 토석류 피해지역을 연구지역으로 선정하고 지상 LiDAR스캔을 통한 현장조사로 연구지역과 유사한 매개변수 값을 산정하고 정밀도가 높은 지형자료를 생성하여 토석류 해석에 대한 정확도를 높혔다. 토석류 해석프로그램은 국내에서 토석류 해석에 많이 사용되는 FLO-2D와 아직 국내에서는 사용 빈도가 높지는 않지만 국외 연구사례에서 사용 빈도가 높은 모델 중 RAMMS 모형을 선정하여 토석류 피해가 발생한 동일 지역에 두 모형을 적용하고 그 적용성을 검토하였다.

• 소성∙가공
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• 제15권2호
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• pp.112-117
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• 2006

Sliding wear mechanism of a high nitrogen austenitic 18Cr-18Mn-2Mo-0.9N steel has been investigated. Dry sliding wear tests of the steel were carried out at various loads of IN-10N under a constant sliding speed condition of 0.15m/s against AISI 52100 bearing steel balls. Solution ($1050^{\circ}C$) and isothermal aging ($900^{\circ}C$) heat treatments were performed on the steel and the effect of the heat treatments on the wear was investigated. Wear rates of the solution-treated steel specimen remained low until 5N load, and then increased abruptly at loads above 5N. The rates of isothermally aged specimens were low and increased gradually with the applied load. Worn surfaces, their cross sections, and wear debris of the steel specimens were examined with a scanning electron microscopy. Phases of the heat-treated specimen and the wear debris were identified using XRD. The transformed phase underneath a sliding track was investigated and analyzed using a TEM. Effects of the phase transformation during the wear and $Cr_{2}N$ precipitates formed during the isothermal aging on the wear of the austenitic steel were discussed.

• 한국터널지하공간학회 논문집
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• 제15권4호
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• pp.387-400
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• 2013

본 연구에서는 터널 갱구사면을 대상으로 사면안정성 및 산사태 위험도를 평가하였다. 먼저 사면안정성 해석을 통해 붕괴위험도가 가장 높은 구간을 선정하고 구체적인 붕괴규모를 파악하였다. 해석결과 해발고도 485~495 m인 구간은 강우시 안전율이 0.99로 불안정한 상태로 나타났다. 이 때 붕괴심도는 최대 2.1 m이며 붕괴 길이는 사면의 경사방향으로 18.6 m로 분석되었다. 해당구간에서 사면붕괴 시 파생되는 사태물질의 이동특성을 실시간으로 분석하고 터널 갱구부에 미치는 영향을 파악하고자 산사태 시뮬레이션 해석을 수행하였다. 해석결과 사태물질은 7.74 m/sec의 평균속도를 보이며 주로 계곡부를 따라 산 하부로 이동하는 것으로 분석되었다. 사태물질은 산 하부로 갈수록 점차 확산되며 10초 후에 터널 갱구부 위를 지나고 20.2초 후에 산하부에 도달하는 것으로 분석되었다. 특히 터널 갱구부는 사태물질 이동경로의 중심부에 위치하고 있어 산사태 발생 시 직접적인 피해를 받는 것으로 나타났다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.105-108
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• 2005

Sliding wear mechanism of a high nitrogen austenitic 18Cr-18Mn-2Mo-0.9N steel has been investigated. Dry sliding wear tests of the steel were carried out at various loads of 1N-10N under a constant sliding speed condition of 0.15m/s against AISI 52100 bearing steel balls. Solution $(1050^{\circ}C)$ and isothermal aging $(900^{\circ}C)$ heat treatments were performed on the steel and the effect of the heat treatments on the wear were investigated. Wear rates of the solution-treated steel specimen remained low until 5N, and then increased abruptly at loads above 5N. The rates of isothermally aged specimens were low and increased gradually with the applied load. Worn surfaces, their cross sections, and wear debris of the steel specimens were examined with a scanning electron microscopy. Phases of the heat-treated specimen and the wear debris were identified using XRD. Phases transformed underneath the sliding track during the wear were investigated and analyzed using TEM. Effects of the phase transformation during the wear and $Cr_2N$ precipitates formed during the isothermal aging on the wear of the austenitic steel were discussed.

• Spatial Information Research
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• 제23권2호
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• pp.39-48
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• 2015

본 연구에서는 2차원 범람해석을 통해 도출된 침수해석정보에 현실적인 위험도를 고려한 산정식을 적용하여 홍수위험도를 평가하였고, 이를 표준화된 정보체계로 제공하는 방안을 제시하였다. 일반적으로 침수심과 침수구역을 기반으로 하는 현재의 홍수위험도 평가방법은 홍수발생시 사람에게 미치는 실질적인 위험도를 충분히 반영하지 못 할 것으로 판단되어 침수심, 유속, Debris Factor와 Flood Hazard Rating 관계식을 이용하여 외수범람이 사람에게 미치는 홍수위험도를 평가하고 4개로 등급화하였다. 이를 위해 2차원 외수범람해석 모형인 Flumen을 이용하여 대구의 금호강유역 대하여 500년 빈도 홍수로 인한 월류와 200년 빈도 홍수로 인한 파제 시나리오에 따라 외수범람을 모의하였다. 이러한 연구결과를 통해 외수범람시 침수가 예상되는 지역에 위치한 사람들에게 더 현실적인 위험도정보를 제공하고, 표준화된 정보체계 기반에서 위험도정보 제공이 가능해짐으로써 재해관련분야의 정보분석, 평가, 계획수립 등 다양한 분야에서 활용성을 증대시킬 수 있을 것으로 판단된다.

• Wind and Structures
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• 제14권2호
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• pp.167-186
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• 2011

This paper presents the results of measurements relating to the aerodynamic forces on flat square plates which were allowed to rotate at different speeds about their horizontal axis, by modifying the velocity of the incoming flow. A 1 m square test-sheet and a 0.3 m square test-sheet were fitted with a number of pressure sensors in order to obtain information relating to the instantaneous pressure distribution acting on the test-sheet; a compact gyroscope to record the angular velocity during the rotational motion was also implemented. Previous work on autorotation has illustrated that the angular velocity varies with respect to the torque induced by the wind, the thickness and aspect ratio of the test-sheet, any frictional effects present at the bearings, and the vorticity generated through the interaction between the plate and the wind flow. The current paper sets out a method based on the solution of the equation of motion of a rotating plate which enables the determination of angular velocities on autorotating elements to be predicted. This approach is then used in conjunction with the experimental data in order to evaluate the damping introduced by the frictional effects at the bearings during steady autorotation.