• Journal of the Korean Geotechnical Society
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• v.32 no.12
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• pp.23-32
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• 2016

A single particle crushing test was carried out for recycled aggregates from waste concrete while demolishing various structures. When the recycled aggregates were used for backfill or road subbase materials, load-displacement and crushing characteristics were analyzed. The recycled aggregates with hydrates and aggregates were sorted into 40 mm size (75-40 mm) and 20 mm size (40-20 mm). At initial loading, their irregular surface was closed to and then crushed by loading plate. Such first crushing stage was called 'Surface crushing'. Further loading, some hydrate was crushed and detached from aggregate, and such process repeated several times. This state is called 'hydrate crushing'. The final state is called 'aggregate crushing' in which aggregate crushed and following load suddenly dropped down. As the load increased, such crushing cycle is repeated several times. The shapes of aggregates are round or square, and triangle or long shaped. Depending on their shapes and surface conditions, they crushed in different ways. The 63% of aggregates showed more than 50% load reduction due to aggregate crushing. The 90% load reduction occurred at 15% of aggregates. The 40 mm aggregate crushed at maximum load between 3.05-4.38 kN and 70% of crushed aggregates were less than 20 mm.

• Applied Chemistry for Engineering
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• v.25 no.3
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• pp.274-280
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• 2014

Polysulfone (PSf) hollow fiber membranes were prepared via the nonsolvent induced phase separation technique. The cosolvent of ${\gamma}$-butyrolactone (GBL) was added to the polymer solution containing a mixture of PSf and N,N-dimethylacetamide (DMAc). Water was utilized as a precipitation nonsolvent. The morphology of prepared membranes was investigated using a field emission scanning electron microscopy. The fabricated membrane showed a typical asymmetric structure such as the dense layer on the porous support layer by the addition of GBL to the polymer solution. As the concentration of GBL increased, the asymmetric porous structure was shown to be more intensified. It was thought that the added GBL played a role of enhancing the liquid-liquid phase separation of the polymer solution, since the cosolvent of GBL might change the thermodynamic solubility parameter of the doping solution. Permeation properties through the prepared hollow fiber membranes were characterized by measuring the pure water flux and the solute rejection using $0.05{\mu}m$ polystyrene latex (PSL) beads. Experimental results revealed that the use of PEG as the internal coagulant enhanced the pure water flux up to 130 times compared to the use of EG while the rejection of the PSL beads decreased only 5%.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.3
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• pp.121-125
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• 2018

In this study, finite element analyses of crack propagation along a sinusoidal interface are performed by using cohesive elements. BK law is used for cohesive zone to consider mixed mode traction-separation relation at the crack tip on a sinusoidal interface of a double cantilever beam specimen. The shape of a sinusoidal interface crack and the cohesive strength and the cohesive energies in mixed mode cohesive laws are varied in numerical experiments, and load-displacement curves at the ends of a double cantilever beam specimen are obtained to investigate the crack propagation behavior along a sinusoidal interface.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.6
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• pp.53-59
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• 2010

This research aims in finding a more optimal ejector size for evacuating engine exhaust gasses and 20% of the cell cooling air. The remaining 80% of cell cooling air pumped into the test chamber is separately exhausted from the test chamber via a discharge port fitted with flow control valves and vacuum pump. Unlike its predecessor this configuration utilizes a smaller capture area to improve pressure recovery. The modified ejector size has a diameter of 1100mm enough to evacuate 66kg/s jet engine exhaust in addition to about 20%, 24kg/s of the cell cooling air tapped from the sterling chamber. This configurations has an area ratio of the engine exit and ejector inlet of about 1.2. Simulation results of the proposed ejector configuration, indicates improved pressure recovery.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.149-152
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• 2008

Effects of chamber configuration on combustion characteristic velocity of full-scale combustion chamber for 30-tonf-class liquid rocket engine were studied. The configurations of combustion chamber are ablative and channel cooling chamber (${\varepsilon}$=3.2) which have detachable mixing head, and single body regenerative cooling chamber which has nozzle expansion ratio of 3.5 and 12, respectively. The combustion chambers have chamber pressure of 53${\sim}$60 bar and propellant mass flow rate of 89 kg/s, and the injectors of all combustion chamber have recess number 1.0 and double-swirl characteristics. The hot firing test results at design point show that the combustion characteristic velocity of the regenerative cooling chamber which has nozzle expansion ratio of 12 is higher than that of other combustion chambers. The reasons for the above result are the increases of combustion pressure and enthalpy of kerosene which is heated due to cooling of the chamber wall before injection into the combustion field.

• 한국HCI학회:학술대회논문집
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• 2007.02a
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• pp.897-902
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• 2007

인간과 컴퓨터간의 전통적인 인터페이스는 인간이 요구하는 다양한 인터페이스를 제공하지 못한다는 점에서 점차 사용하기 불편하게 되었고 이는 새로운 형태의 인터페이스에 대한 요구로 이어지게 되었다. 본 논문에서는 이러한 추세에 맞추어 카메라를 통해 인간의 손 제스처를 인식하는 새로운 인터페이스를 연구하였다. 손은 자유도가 높고 3차원의 view direction에 의해 형상이 매우 심하게 변한다. 따라서 윤곽선 기반방법과 같은 2차원으로 투영된 영상에서 contour나 edge의 정보로 손 제스처를 인식하는 데는 한계가 있다. 그러나 모델기반 방법은 3차원 정보를 이용하기 때문에 손 제스처를 인식하는데 좋으나 계산량이 많아 실시간으로 처리하기가 쉽지 않다. 이러한 문제점을 해결하기 위해 손 형상에 대한 대규모 데이터베이스를 구성하고 정규화된 공간에서 Feature 간의 연관성을 파악하여 훈련 데이터 모델을 구성하여 비교함으로써 실시간으로 손 포즈를 구별할 수 있다. 이러한 통계적 학습 기반의 알고리즘은 다양한 데이터와 좋은 feature의 검출이 최적의 성능을 구현하는 것과 연관된다. 따라서 배경으로부터 노이즈를 최대한 줄이기 위해 피부의 색상 정보를 이용하여 손 후보 영역을 검출하고 검출된 후보 영역으로부터 HLF(Haar-like Feature)를 이용하여 손 영역을 검출한다. 검출된 손 영역으로부터 패턴 분류 과정을 거쳐 손 포즈를 인식 하게 된다. 패턴 분류 과정은 HLF를 이용하여 손 포즈를 인식하게 되는데 미리 학습된 각 포즈에 대한 HLF를 이용하여 손 포즈를 인식하게 된다. HLF는 Violar가 얼굴 검출에 적용한 것으로 얼굴 검출에 좋은 결과를 보여 주었으며, 이는 적분 이미지로부터 추출한 HLF를 이용한 Adaboost 학습 알고리즘을 사용하였다. 본 논문에서는 피부색의 색상 정보를 이용 배경과 손 영상을 최대한 분리하여 배경의 대부분이 Adaboost-Haar Classifier의 첫 번째 스테이지에서 제거되는 방법을 이용하여 그 성능을 더 향상 시켜 손 형상 인식에 적용하였다.

• Korean Chemical Engineering Research
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• v.54 no.6
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• pp.847-853
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• 2016

Here has been examined a 3-dimensional computational fluid dynamics (CFD) modeling in order to investigate the performance analysis of proton exchange membrane (PEM) fuel cells with serpentine flow fields. The present CFD model considers the isothermal transport phenomena in a fuel cell involving mass, momentum transport, electrode kinetics, and potential fields. Co-current flow patterns for a PEMFC are considered for various geometries in the single straight cell. Current density distribution from the calculated distribution of oxygen and hydrogen mass fractions has been determined, where the activation overpotential has been also calculated within anode and cathode. CFD results showed that profiles differ from those simulations subjected to each the calculated activation overpotential. It is interesting that the present serpentine flow field shows the specific distribution of current density with respect to the aspect ratio of depth to width and the ratio of reaction area for various serpentine geometries. Simulation results were considered reasonable with the other CFD results reported in literature and global comparisons of the PEMFC model.

• Journal of the Korea Institute of Building Construction
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• v.16 no.6
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• pp.579-585
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• 2016

3D laser scanning can be used for scanning the freeform surface and building a model from which the measurements could be taken, in order to solve the difficulty with getting access to the exact freeform shape and position data of the complex building envelope. The shape making process using 3D scanning is as follows: point cloud, mesh surface segmentation, NURBS(Non-Uniform Rational B-spline) surface generation, and parametric solid model generation. In this research, we review previous studies, reverse engineering notion, importance of reverse engineering usage for freeform envelope, and previous cases in order to identify the detail reverse engineering process for prefabrication and construction of freeform panels using 3D laser scanning technology. Therefore, the purpose of this research is to present a basic information which should be considered during design and construction phase and improve quality and constructibility of freeform building by analyzing the reverse engineering process and case study for prefabrication and construction of freeform panels using 3D laser scanning. The research results will enable 3D shape engineering and design parameterization using reverse engineering to be used in various construction projects.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.1
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• pp.66-72
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• 2007

an approach to air-vehicle design, an application of the radio-controlled model flight test techniques has been presented. The approach presented in this study is to validate the air-vehicle design configuration by analyzing the flight test results of scale model with dynamic similarities, and then to apply the analyzed results to the aerodynamic design process in early stage of the air-vehicle development. To develop practically applicable similarity laws for the subscale flying model design, the air-vehicle motions are decoupled into rotational motions for stability & control similarities and translational motions for flight performance similarities. Also, detail techniques for radio-controlled model flight test have been developed. Based on the results obtained from the radio-controlled flight test, the present approach for air-vehicle design has shown to be useful to validate the air-vehicle design configuration.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.445.2-445.2
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• 2014

표면 조직화의 목적은 태양전지 표면에서의 입사되는 빛의 반사율을 감소 시키고, 웨이퍼 내에서 빛의 통과 길이를 길게 하며, 흡수되는 빛의 양을 증가시키는 것이다. 본 연구에서는 여러 가지 표면 조직화 공정 기술을 이용하여 표면 형상에 따른 광 변환 효율에 대해 연구하였으며, 셀을 제작하여 전기적 특성과 광학적 특성의 상관관계를 분석하였다. KOH를 이용한 표면 조직화, 산 증기를 이용한 표면 조직화, 반응성 이온 식각을 이용한 표면 조직화, 금속 촉매 반응을 이용한 표면 조직화 공정 기술을 이용하여 표면 조직화 공정을 진행하였다. 셀 제작 결과, 반사도 결과와는 상반되는 결과를 얻을 수 있었다. 표면 조직화 형상에 따른 셀 효율의 변화는 도핑 프로파일과 표면 재결합 속도의 변화 때문이라 생각되며 더 명확한 분석을 위해 양자 효율을 측정하여 분석을 시도하였다. 표면 조직화 공정 기술별 도핑 프로파일을 보면 KOH를 이용한 표면 조직화 공정을 제외한 나머지 표면 조직화 공정들의 도핑 프로파일은 불균일하게 형성되어 있는 것을 확인 할 수 있다. 양자 효율 측정 결과 단파장 대역에서 낮은 응답특성을 가지는 것을 확인 할 수 있었다. 그 이유는 낮은 반사도를 가지는 표면 조직화 공정의 경우 나노사이즈의 구조를 갖기 때문에 균일한 도핑 프로파일을 얻지 못해 전자, 정공의 분리가 제대로 이루어지지 못하였고 표면 재결합 속도증가의 원인으로 단락전류와 개방전압이 낮아져 효율이 떨어진 것으로 판단된다. 결과적으로 낮은 반사율을 갖는 표면 조직화 공정도 중요하지만 표면 조직화 공정 기술에 따른 균일한 도핑 프로파일을 갖는 공정을 개발한다면 단파장 응답도가 향상되어 단락전류밀도와 개방전압 상승효과를 얻을 수 있을 것이라 판단된다.