• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1737-1741
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• 2008

하천 개수나 치수를 위한 기초 연구의 일환으로 수치모형을 이용한 검증 및 예측 과정이 요구되어 왔고, 고전적인 수치모의 방법으로 결과 산출이 용이한 1차원 모형을 적용시켜 왔다. 1차원 모형의 경우 모의영역을 쉽게 넓힐 수 있고, 입력 자료가 간단하다는 장점이 있지만, 수직적이고 수평적인 흐름특성 변화 및 난류 구조를 보이는 3차원적인 자연하천 흐름을 종방향의 1차원적인 모의 결과를 이용하여 평가한다는 점에서 비현실적이다. 하천을 가로질러 교각이나 보와 같은 구조물이 위치하고 있거나, 좌우 비대칭적인 형상의 수로를 모의할 경우 흐름특성의 공간적인 분포는 단순한 단면 평균적인 개념으로는 설명되기 힘들다. 최근에야 비로소 수공학 관련 실무자들에 의해서 최소한 2차원 수치모형을 기본적인 평가법으로 도입해야 한다는 분위기가 감지되고 있으며, 일반적으로 한강과 같은 대하천을 모의할 경우, 대다수의 실무자들과 연구자들이 축척을 문제 삼아 수로 내부에 위치한 교각을 생략하여 2차원 모의를 수행하기도 한다. 따라서 본 연구에서는 수로 내부에 위치한 교각을 2차원 모의하는 방법에 대한 비교 평가를 수행하고자 한다. 동일한 격자를 이용하여 교각을 고려하지 않았을 경우와 교각 형상을 모의 영역에서 삭제하여 경계처리를 하였을 경우, 마지막으로 교각이 위치하고 있는 영역에 항력을 적용하였을 경우에 대해서 비교 평가한다. 이를 위하여 2차원 천수방정식을 흐름방정식으로 하는 유한요소모형을 구축하였으며, 모형의 검증을 위해 교각이 수로에 위치할 경우에 대한 실내 실험 자료와 비교한다. 또한 검증된 모형을 이용하여 교각이 포함된 한강의 일부 구간을 선정하여, 교각 모의 방법에 대한 비교 평가를 수행한다. 본 연구에서 구축된 자료 및 제시된 수치모형은 하천복원, 치수관리 측면에서 매우 유용하게 사용될 것으로 기대된다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.10
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• pp.882-887
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• 2012

This paper describes on the aerodynamic characteristics of the first domestically manufactured aircraft, Buhwalho, in Korea. The computational fluid dynamics(CFD) calculations and wind tunnel test were utilized to investigate the basic aerodynamic characteristics of aircraft with control surface deflections and attitude changes. Variations of lift, drag and pitching moment due to angles of attack and control surface deflections were analyzed and also flight stability due to side force, yawing and rolling moments caused by the change of sideslip angles, rudder and aileron deflections were discussed. Through this study, the meaningful aerodynamic data by CFD calculations and wind tunnel tests were obtained and the flight characteristics based on these data were confirmed accordingly by the flight tests.

• Conservation Science in Museum
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• v.25
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• pp.85-94
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• 2021

Conservation treatment of metallic artifacts contaminated with corrosion and foreign substances requires changes in the shape, characteristics, weight and thickness of the artifacts. Thus far, recording the changes after conservation treatment has mainly been performed through visual observation and photography, which lacks any quantitative description of the changes. In this study, the processes of removing foreign substances, joining cracks, and restoring an affected area were recorded using 3D scanning and then quantitatively analyzed to identify changes in form due to conservation treatment. The volume change after the conservation process was calculated based on the results of the 3D scanning, and numerical data on the changes to the form was analyzed. It was revealed that the foreign or corroded substances removed after the conservation accounted for 18.1 cm³, which is approximately 52% of the total volume of the ring pommel, and those substances were removed from about 98% of the surface of the ring pommel. This study confirmed that 3D form analysis was useful for recording the processes of conservation treatment and analyzing the results. It is therefore believed that this methodology can be applicable to not only metal artifacts, but to cultural heritage items in a range of materials.

• The Journal of Engineering Geology
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• v.14 no.1
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• pp.29-46
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• 2004

It is important to identify geometries of fracture that act as a conduit of fluid flow for characterization of ground water flow in fractured rock. Fracture geometries control hydraulic conductivity and stream lines in a rock mass. However, we have difficulties to acquire whole geometric data of fractures in a field scale because of discontinuous distribution of outcrops and impossibility of continuous collecting of subsurface data. Therefore, it is needed to develop a method to describe whole feature of a target fracture geometry. This study suggests a new approach to develop a method to characterize on the whole feature of a target fracture geometry based on the Fourier transform. After sampling of specimens along a target fracture from borehole cores, effective frequencies among roughness components were selected by the Fourier transform on each specimen. Then, the selected effective frequencies were averaged on each frequency. Because the averaged spectrum includes all the frequency profiles of each specimen, it shows the representative components of the fracture roughness of the target fracture. The inverse Fourier transform is conducted to reconstruct an averaged whole roughness feature after low pass filtering. The reconstructed roughness feature also shows the representative roughness of the target subsurface fracture including the geometrical characteristics of each specimen. It also means that overall roughness feature by scaling up of a fracture. In order to identify the characteristics of permeability coefficients along the target fracture, fracture models were constructed based on the reconstructed roughness feature. The computation of permeability coefficient was performed by the homogenization analysis that can calculate accurate permeability coefficients with full consideration of fracture geometry. The results show a range between $10^{-4}{\;}and{\;}10^{-3}{\;}cm/sec$, indicating reasonable values of permeability coefficient along a large fracture. This approach will be effectively applied to the analysis of permeability characteristics along a large fracture as well as identification of the whole feature of a fracture in a field scale.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.1
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• pp.63-70
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• 2017

In this paper, we design and fabricate a de-orbiter using drag-sail and evaluate deployment characteristics. Without employing an actuator to deploy, the de-orbiter is activated by the SMA wire based the release mechanism and driven by the restoring force of the tape-spring. For efficient storage and deployment of drag-sail, an origami method of original ISO flasher is chosen and low priced mylar film is used as the material of the drag-sail. In addition, through the fault tree analysis method which is one of the one-shot device reliability evaluation methods, we confirm the reliability of the de-orbiter(0.997572) and the Roller failure has the highest criticality. Finally, we find feasibility of the proposed de-orbiter through the deployment demonstration of drag-sail.

• Journal of the Mineralogical Society of Korea
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• v.31 no.4
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• pp.267-275
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• 2018

The purposes of this study were to analyze the mineralogical characteristics of slaked lime used for wall repair of traditional buildings in Bagan, Myanmar and to evaluate the physical properties of lime plaster produced by the same method as Bagan region. In the X-ray diffraction and thermal analysis of the Myanmar slaked lime, portlandite ($Ca(OH)_2$) and brucite ($Mg(OH)_2$) were detected as main constituent minerals, and a carbonate rock mainly composed of dolomite ($CaMg(CO_3)_2$) minerals may be used as a raw material to make slaked lime. The field-emission scanning electron microscope analysis showed that the Myanmar slaked lime was composed of irregularly shaped crystals of $0.5{\mu}m$ or larger and a small amount of $0.1{\mu}m$ of plate - like crystals. The size and uniformity of crystals in Myanmar lime is different from that of Korea slaked lime. This may be attributed to the effect of the mineral composition and the lime hydration method of Myanmar, which produces slurry by immersing the burnt lime in excess water for a long period of time. The compressive strength of the lime plaster in Myanmar resulted in a mean value of $1.13N/mm^2$ for the specimens cured for 28 days. The strength of the specimens with Bale juice was $1.03N/mm^2$, respectively. The lime is an air setting material that exhibits strength through long carbonation process. Therefore, it is necessary to evaluate physical properties according to curing period through long-term curing over 28 days in the future.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.3
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• pp.1585-1593
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• 2015

3D-structured (embossed) aluminum sheets have been used in the heat insulation purpose for automative exhaust parts because of increasing their surface areas and stiffness reinforcement imposed in making the embossing pattern. However, there are many restrictions in press forming of the embossed sheet compared with the flat sheet (non-embossed one) because of its difference in the mechanical properties and the geometrical 3-dimensional shape. In this paper we investigated the deformation characteristic of embossed aluminum sheet in the incremental sheet forming process which has frequently used in the design verification and the trial manufacturing of sheet products. The single point incremental forming (SPIF) experiments for the rectangular cone forming using the CNC machine with a chemical wood-machined die and a circular tool shape showed that the formability of the embossed sheet are better than that of the flat sheet in view of the maximum angle of cone forming. This comes from the fact that the embossed sheet between the tool and the elastic die wall is plastically compressed and the flatted area contributes to increase the plastic deformation. Also the tool path along the outward movement from the center showed a better formability than that of the inward movement from the edge. However the surface quality for the tool path along the outward movement evaluated from the surface deflection is inferior than that of the tool path along the inward movement.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.7
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• pp.539-547
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• 2021

Helicopter rotor blade is required to be designed by considering the interacting effects among aerodynamics, flexibility, and controllability. The reverse design allows the structural components to have common characteristics by using the configuration numerics and experimental results. This paper aims to design the composite rotor blade which will feature common characteristics with that of BO-105. The present engineering design procedure is done by dividing the rotor blade into a few sections and composite laminates across the cross section. For each section, variational asymptotic beam sectional analysis (VABS) program is used to evaluate its flapwise, lagwise, and torsion stiffnesses to have discrepancy smaller than certain tolerance. Finally, CAMRAD II is used to predict the stress acting on the rotor blade during the specific flight condition and to check whether the present deign is structurally valid.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.367-367
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• 2016

우리나라는 하상계수가 큰 하천의 특성 때문에 콘크리트 구조의 고정보를 설치하여 하천수위를 유지하고, 취수용으로 사용하여 왔다. 그러나 고정보는 유수방해, 토사퇴적으로 인한 홍수위 상승 등의 다양한 문제를 야기시키고 있다. 이에 따라 4대강에는 다양한 형상과 운영방식이 적용된 가동보가 설치되었으며, 소하천과 중규모 하천 역시 하천기능의 복원을 위한 정비사업이 진행되고 있다. 하천관리의 목표는 하천의 이수, 치수 및 생태환경 기능의 종합적이며, 유기적인 관계를 조화롭게 유지하면서 각 기능을 극대화시키는 것이다. 우선, 토사의 퇴적을 사전에 예방하고, 퇴적된 토사는 유수에 따라 배출될 수 있도록 하단방류 형식으로 개선되어야 한다. 또한 홍수기에는 통수가 원활하도록 보의 기능을 해제할 수 있어야 하는 한편, 하류구간이 범람하지 않도록 상류구간에서의 완충기능을 가져야 한다. 이러한 요구조건을 충족하기 위해서 다단형태의 하단방류형 가동보 수문 시스템을 고려할 수 있다. 다단형태의 하단방류형 가동보 수문시스템은 경사 하천에 가동보에 의해 물을 저수하고, 저수된 물을 보 상류에서 유입되는 유입수량 만큼만을 수문 하단 개도부를 통하여 방류하도록 하여, 일정량이 항상 저류되면서 퇴적토사가 배출되도록 하여 수질을 개선하는 방식이다. 본 연구에서는 금강의 지류인 치성천 9Km 구간을 대상으로 HEC-RAS 4.1 모형을 적용하여 하단방류형 가동보를 하류부터 상류구간까지 다단형태로 설치하였을 경우, 하천의 저류와 분배기능 회복에 따른 홍수위 저감 효과를 고정보 설치의 경우와 비교 분석하였다. 홍수소통 능력을 검토하기 위해서 연구대상 구간을 200년 빈도의 확률홍수량 별로 10개 구간으로 나누어 검토한 결과, 고정보 설치의 경우에는 여유고 기준을 초과하는 부분이 나타났으나, 다단식 하단방류형 가동보를 설치하고, 수문개도를 조작하여 운영할 경우에는 여유고 기준을 초과하는 부분이 없어, 홍수위 저감 효과를 기대할 수 있는 것으로 나타났을 뿐만 아니라, 홍수기이후에도 하천유지용수 기준을 만족하는 것으로 나타났다. 또한 설치 및 유지관리의 비용측면과 용수확보 및 홍수피해 절감의 편익측면에서도 50년 운영주기의 비용편익성은 양호한 것으로 나타났으며, 생태환경보전과 친수공간 확보측면의 편익성을 추가로 고려할 경우, 경제성은 충분히 확보될 것으로 판단되었다.

• Journal of Convergence for Information Technology
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• v.11 no.6
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• pp.146-153
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• 2021

Recently, research on perovskite semiconductor materials has been performed, and the evaluation of properties using surface treatment for this material is the basis for subsequent studies. We studied the results of surface treatment of perovskite thin films exposed to air for about 6 months by generating oxygen plasma with an atmospheric pressure plasma equipment. The reason for exposure for 6 months is that the perovskite thin film is made of organic and inorganic substances, so when exposed to air, the surface changes through reaction with oxygen or water vapor. Therefore, this change is to investigate whether it is possible to restore the original film. The surface shape and the ratio of elements were analyzed by varying the process time from 1 s to 1200 s in an oxygen plasma atmosphere. It was found that the crystal grains change over a process time of 5 s or more. In order to maintain the properties of the deposited film, it is the optimal process condition between 2 s and 5 s.