• 한국전산유체공학회:학술대회논문집
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• 1998.05a
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• pp.168-173
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• 1998

A numerical analysis of axisymetric backward facing step main nozzle flow in air jet loom has been accomplished. To obtain basic design data for an optimum main nozzle for an air-jet loom and to predict the transonic/supersonic flow, a characteristic based upwind flux difference splitting compressible Navier-Stokes method has been used. The wall static pressure of the main nozzle and the flow velocity changes in the nozzle tube were analyzed by changing air tank pressures and acceleration tube lengths. The flow inside the nozzle experiences double choking one at the needle tip and the other at the acceleration tube exit at tank pressures over $4kg_f/cm^2$. The tank pressure $P_t$ leading to the critical condition depends on the acceleration tube length; i.e, $P_t$ is higher for longer acceleration tubes. The $P_t$ value required to bring the acceleration tube exit to the critical condition is nearly constant regardless of acceleration tube length. The round needle tip shape might lead to less total pressure loss when compared with step shape.

• 한국전산유체공학회:학술대회논문집
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• 2007.04a
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• pp.103-107
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• 2007

Computational Fluid Dynamics (CFD in short) approach is now playing an important role in the engineering process recently. Generating proper grid system for the region of interest in time is prerequisite for the efficient numerical calculation of flow physics using CFD approach. Grid generation is, however, usually considered as a major obstacle for a routine and successful application of numerical approaches in the engineering process. CFD approach based on the unstructured grid system is gaining popularity due to its simplicity and efficiency for generating grid system compared to the structured grid approaches. In this paper an automated triangular surface grid generation using CAD surface data is proposed According to the present method, the CAD surface data imported in the STL format is processed to identify feature edges defining the topology and geometry of the surface shape first. When the feature edges are identified, node points along the edges are distributed. The initial fronts which connect those feature edge nodes are constructed and then they are advanced along the CAD surface data inward until the surface is fully covered by triangular surface grid cells using Advancing Front Method. It is found that this approach can be implemented in an automated way successfully saving man-hours and reducing human-errors in generating triangular surface grid system.

• Journal of Power System Engineering
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• v.16 no.4
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• pp.51-59
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• 2012

The computational flow analysis using LES technique was carried out to investigate the flow characteristics of a sirocco fan under the maximum flowrate condition. The commercial SC/Tetra software was used for this unsteady and three-dimensional numerical analysis. In consequence, because a flow is unstable within the range of about 50% of a housing depth from a bellmouth around the cutoff region, the passing flow through the blade cascade occurred on the X-Y plane is a slow or a reverse with approaching to the housing inlet. Also, the secondary flow shows on the radial plane of a housing, and its vortex center exists within about 33% of a housing depth from a bellmouth except the cutoff region. Moreover, the flow occurring on the exit plane of a sirocco fan shows a complex secondary flow.

• Journal of Sensor Science and Technology
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• v.1 no.2
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• pp.165-172
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• 1992

To determine the effect of additions of trivalent and pentavalent ions on the electrical conductivity and sensing behaviour, indium and antimony were incorporated in tin oxide by the coprecipitation method. Antimony may be considered to enter the cassiterite structure as pentavalent ions, thermal energy could excite electrons from these ions into the conduction band. Similarly the indium ions would enter the lattice as $In^{3+}$ but could accept electrons from the valence band, thereby becoming monovalent or divalent. These phenomena, however, how the potential barrier existing $SnO_{2}$ by addition of two kinds of ions could influence on the sensing behaviour in comparison with their influence on the resistivity were observed.

• Journal of Institute of Control, Robotics and Systems
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• v.16 no.1
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• pp.48-52
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• 2010

In this paper, we introduce a new path planning algorithm which combines the merits of a visibility graph algorithm and an adaptive cell decomposition. We quantize a given map with empty cells, blocked cells, and mixed cells, then find the optimal path on the quantized map using a visibility graph algorithm. For reducing the number of the quantized cells we use the quad-tree technique which is used in an adaptive cell decomposition, and for improving the performance of the visibility checking in making a visibility graph we propose a new visibility checking method which uses the property of the quad-tree instead of the well-known rotational sweep-line algorithm. For the more efficient visibility checking, we propose two additional improvements for our suggested method. Both of them are used for reducing the visited cells in the quad-tree. The experiments for a performance comparison of our algorithm with other well-known algorithms show that our proposed method is superior to others.

• Bulletin of the Society of Naval Architects of Korea
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• v.25 no.1
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• pp.11-20
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• 1988

From the engineering point of view, a synthesis as well as an analysis technique is explored to search for the improved design of grillage which is common in ship structure. As an approximate analysis method for the grillage, an interaction reaction method is developed and compared with the finite element method. It is found that the discrepancy between these two methods is so negligible that the percent method could be used effectively for the grillage analysis. As an optimization technique, a feasible direction method could be used is combined with the intersection reaction method in order to design a minimum weight optimal grillage. The feasible direction method shows a good numerical performance although it requires more calculation times compared with the direct search method. Finally, the application of multiple objective optimization method to grillage is investigated in order to resolve conflicts existed between the multiple objectives which is a common characteristic of structure design problem. Goal programming method is extended to handle a nonlinear property of constraints and objective functions. It seems that the nonlinear goal programming could help not only to establish a relative importance of each objective, but also enable the designer to choose the best combination of design variables.

• Proceedings of the KIEE Conference
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• 2007.11a
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• pp.242-243
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• 2007

본 논문은 1310nm 단일모드 광섬유를 이용하여 온도센서로 활용하기 위한 연구이다. 기존광섬유센서의 연구는 복잡한 여러 가지 기기를 이용하여 구성된 시스템이었다. 그리고 산란 변화를 주기 위하여 Bragg 격자나 Pulse generator를 이용하여 광주파수의 변화를 측정하거나, YAG 레이저를 이용 벌크형 시스템을 택하여 구성하였는데 실험 환경을 구성하는 어려움과 측정된 데이터의 정확도에 대한 문제점이 있었다. 본 연구에서 제안한 유도 브릴루앙 산란(sBs: stimulated Brillouin scattering)광을 이용한 온도센서 시스템은 기존의 측정방식 보다 간소화된 직렬방식의 시스템이다. 광주파수에서 발생하는 노이즈와 애매한 결과에 대해서 신뢰성과 정확도를 확보하기 위하여 지능형인 뉴로-퍼지 알고리즘을 이용하여 분석함으로써 기존 시스템 보다 정확한 데이터를 얻고자 하였다. 본 연구에서 sBs는 빛의 산란 특성 중 광주파수가 온도에 변화에 대해 각각의 온도 변화당 천이가 이루어졌음을 측정하였다. 시스템에서 출력된 데이터를 뉴로-퍼지로 분석한 변화율은 1.1MHz/의 결과를 얻었다.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.123-123
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• 2019

최근 기후변화로 인해 중국, 한국, 일본, 몽골 등을 포함한 동아시아 지역은 태풍, 가뭄, 홍수와 같은 자연재해의 발생 빈도가 증가하고 있는 추세이다. 중국의 경우 2017년 극심한 가뭄으로 1,850만 (ha)의 농작물 피해가 발생하였으며, 몽골 또한 2017년 4월 이후 극심한 가뭄으로 사막화가 급속도로 진행되고 있다. 위성 기반의 강우 자료는 공간과 시간 해상도가 높아짐에 따라 지상관측소 강수량 자료의 대체 수단으로 이용되고 있다. 본 연구에서는 Climate Hazards Groups InfraRed Precipitation with Station (CHIRPS), Precipitation Estimation From Remotely Sensed Information Using Artificial Neural Networks-Climate Data Record (PERSIANN-CDR), Global Precipitation Climatology Centre (GPCC) 강우 위성 자료를 활용하여 기상학적 가뭄지수인 표준강수지수 (Standardized Precipitation Index, SPI)를 산정하였다. 시간 해상도는 월별 영상을 기준으로 2008년부터 2017년까지 지난 10년간의 데이터를 이용하였으며, 각각 격자가 다른 위성영상을 기존 기상관측소와 비교하였다. 피어슨 상관계수 (Pearson Correlation Coefficient, R)를 활용하여 강우 위성 영상과 지상관측소의 상관관계를 분석하고, 평균절대오차 (Mean Absolute Error, MAE), 평균제곱근오차 (Root Mean Square Error, RMSE)를 통해 통계적으로 정확도를 분석하였다. 인공위성 강수량 자료는 미계측 지역이 많은 곳이나 측정이 불가능한 지역에 효율성 측면에서 중요한 이점을 제공할 것으로 판단된다.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.4
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• pp.109-118
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• 1994

In this study, an optimization method to design the hull structure of the surface effect ships with twin hulls is proposed for the purpose of minimization of weight based on the regulations of DnV class, and computer programs following the method are developed. The method uses simple formulas as to bending and buckling strength of beams and plates to design local structures, and considers the effect of interaction between longitudinal girders and transverse web frames by grillage analysis and calculates torsional strength of the cross structure by the simplified method. Global optimization of the midship section is attained by integration of optimized substructures. According to optimized results by applying the method to the designed ship, reduction of 20 percent of hull weight can be shown, and optimum transverse frame space can be obtained.

• Journal of Sensor Science and Technology
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• v.4 no.1
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• pp.51-63
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• 1995

Polycrystalline $CdS_{1-x}Se_{x}$ thin films were grown on ceramic substrate using a chemical bath deposition method. They were annealed at various temperature and X-ray diffraction patterns were measured by X-ray diffractometer in order to study $CdS_{1-x}Se_{x}$ polycrystal structure using extrapolation method of X-ray diffraction patterns for the CdS, CdSe samples annealed in $N_{2}$ gas at $550^{\circ}C$ it was found hexagonal structure which had the lattice constant $a_{0}=4.1364{\AA}$, $c_{0}=6.7129{\AA}$ in CdS and $a_{0}=4.3021{\AA}$, $c_{0}=7.0142{\AA}$ in CdSe, respectively. Hall effect on these samples was measured by Van der Pauw method and then studied on carrier density and mobility depending on temperature. We measured also spectral response, sensitivity(${\gamma}$), maximum allowable power dissipation and response time on these samples.