• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.6
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• pp.569-577
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• 2010

A multiscale particle simulation technique that can be applied to a multiphase fluid system has been developed. In the boundary region where the macroscopic- and microscopic-scale models overlap each other, three distinctive features are introduced in the simulation. First, a wall is set up between the gas and liquid phases to separate them and match the phases respectively to the macroscopic conditions stably. Secondly, the interfacial profile is obtained near the matching region and the wall translates and rotates to accommodate the change in the liquid-vapor interfacial position in the molecular model. The contact angle thus obtained can be sent to the macroscopic model. Finally, a state of mass and temperature in the region is maintained by inserting and deleting the particles. Good matching results are observed in the cases of the complete and partial wetting fluid systems.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.1
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• pp.105-114
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• 1993

The ciculation due to bottom density current produced by a dense inflow into a small reservoir is analysed by numerical scheme. Before the front of the density current arrives at the downstream end, the mixing in the reservoir is mainly caused by the anticlockwise vortex formed at the downstream of plunging point along the movement of bottom density current. Upon the arrival of the front of the density current at the downstream end an internal surge is created through an internal hydraulic jump. With repeated propagation of the internal surge back and forth the mixing in the reservoir is progressed and the thickness of dense layer is increased upward. The dilution of the overflow at downstream end is found to depend on inflow densimetric Froude number, reservoir length and elapsed time. The time required for the overflow to attain a specified dilution increases as reservoir length increases and Fre decreases.

• The Journal of the Korea Contents Association
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• v.4 no.4
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• pp.133-139
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• 2004

This paper proposes a Korean sentence boundary detection system which employs k-nearest neighbor algorithm. We proposed three scoring functions to classify sentence boundary and performed comparative analysis. We uses domain independent linguistic features in order to make a general and robust system. The proposed system was trained and evaluated on the two kinds of corpus; ETRI corpus and KAIST corpus. As experimental results, the proposed system shows about $98.82\%$ precision and $99.09\%$ recall rate even though it was trained on relatively small corpus.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.199-203
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• 2008

수위관측지점의 수위-유량관계는 하천단면 형태와 경사에 따라 1개의 유량곡선이 형성될 수도 있으나, 저수위, 평수위, 고수위 등 여러 개 구간의 곡선이 각각 다른 형태로 구성될 수 있다. 또한 이러한 곡선의 연결접점에서 연결이 연속적이어야 하고 부드러워야 한다고 알려져 있다. 각 수위구간에서 유도된 수위-유량관계곡선이 수위구간을 나눈 경계수위에서 곡선식이 일치하지는 경우가 종종 나타난다. 본 연구에서는 경계수위와 곡선접점이 일치하는지 여부를 판단하고 오차의 크기를 확인하기 위하여 할선법을 적용하여 Excel의 VBA로 프로그램을 작성하여 사용하였다. 한편, 수위유량곡선의 연결부에서 부드럽게 연결되는 것이 바람직 하지만, 지금까지 실무에서는 경계수위에서 기울기가 급변하는 형태의 수위-유량관계곡선을 사용하고 있다. 왜냐하면 최소자승회귀분석을 통하여 유도되는 과정에서 경계수위지점의 1차 도함수를 일치시키는 것은 현실적으로 불가능하기 때문이다. 본 연구에서는 이러한 문제를 해결하기 위하여, 회귀분석으로 지수함수의 형태로 유도된 수위-유량관계곡선으로부터 수위와 유량의 대표 값을 계산하고 이들 대표 값들을 3차 스플라인 보간법을 이용하여 1차 도함수를 접점에서 일치시키는 부드러운 연결과 함께 수위-유량관계곡선과도 잘 일치하는 새로운 대안을 제시하였다. 2006년도 한국수문조사연보(유량편)의 자료를 검토하여 문제점들을 도출하고, 본 연구에서 제안한 방법들을 적용하여 보았다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.664-671
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• 2017

This paper presents a numerical analysis of behaviors of rear closer of vertical launch system under rocket plume based on fluid structure interaction analysis. The rocket plume loading is modeled by fully Eulerian method and elasto-plastic behavior of rear cover is calculated by total Lagrangian method based on a 9-node planar element. The interface motion and boundary conditions are described by a hybrid particle level-set method within the ghost fluid framework. We compare the fluid flow pattern between different rear closer models which are elast-plastic and rigid deformation.

• Journal of the Korean Geotechnical Society
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• v.20 no.4
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• pp.29-38
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• 2004

A finite element nonlinear stress-deformation model with multi-interface element is applied to the stability analysis of waste landfill slope. Strength parameters of waste and geosynthetic materials are obtained from the triaxial test of waste and the direct shear test of geosynthetics, respectively. The landfill models used for the numerical models are fit to regulations of the Korean waste management law. The results of the strength tests showed linear behavior for the waste and nonlinear behavior for the eosynthectic materials. The stability analysis with multi-interface element for the geosynthetic materials in the liner system showed large shear stress and slippage at the boundary of the foundation and the slope of the waste fill. This analysis verified the necessity of multi-interface analysis for waste landfills with composite liners.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1263-1264
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• 2007

자계 유도 고상결정화(FESPC)를 이용하여 제작한 다결정실리콘(poly-Si) 박막 트랜지스터(TFT)는 비정질 실리콘 박막 트랜지스터(a-Si:H TFT)보다 뛰어난 전기적 특성과 우수한 안정성을 지닌다. $V_{DS}$ = -0.1 V에서 채널 폭과 길이가 각각 $5\;{\mu}m$, $7\;{\mu}m$인 P형 TFT의 이동도(${\mu}$)와 문턱 전압($V_{TH}$)은 각각 $31.98\;cm^2$/Vs, -6.14 V 이다. FESPC TFT는 일반 poly-Si TFT에 비해 채널 내 결정 경계 숫자가 많아서 상대적으로 열악한 특성을 가진다. 채널 길이 $5\;{\mu}m$인 TFT의 $V_{TH}$는 채널 길이 $18\;{\mu}m$ 소자의 $V_{TH}$보다 1.36V 작지만, 일반적으로 큰 값이다. 이 현상은 채널에 다수의 결정 경계가 존재하고, 수평 전계가 크기 때문이다. 수평 전계가 증가하면, 결정 경계의 전위 장벽 높이가 감소하게 되는데, 이는 DIGBL 효과이다. ${\mu}$의 증가에 따라서, 드레인 전류가 증가하고 $V_{TH}$은 감소한다. 활성화 에너지($E_a$)는 드레인 전압과 결정 경계의 수에 따라 변하는데, 드레인 전압이 크거나 결정 경계의 수가 감소하면 $E_a$는 감소한다. $E_a$가 감소하면 $V_{TH}$가 감소한다. 유리기판 위의 FESPC를 이용한 P형 poly-Si TFT의 $V_{TH}$는 채널의 길이와 $V_{DS}$에 영향을 받는다. 증가한 수평 전계가 결정 경계에서 에너지 장벽을 낮추는 효과를 일으키기 때문이다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.1
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• pp.17-25
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• 2019

An intake of Aircraft becomes S-shaped geometry due to spatial limitation or procuring survivability. But curvature of the S-shaped geometry makes secondary flow or flow separation which is the cause of non-uniform pressure distribution. In this study, boundary layer suction is applied to RAE M 2129 S-Duct by attaching sub duct. Design variable is suction location and angle. A mass flow rate drawn out by suction at the sub duct outlet is constant over every model. A grid dependency test was conducted to verify validity of computation. The comparison among the CFD (Computation Fluid Dynamics), ARA experimental result, and ARA computation result of non-dimensional pressure distribution on the Port side and Starboard Side confirmed the validity of CFD. In this study, Distortion Coefficient was used for evaluating aerodynamic performance of S-Duct. The analysis, which was about flow separation, vortex, mass flow rate distribution, and pressure distribution were also investigated. Maximum 26.14% reduction in Distortion Coefficient was verified.

• Journal of the Korean Geotechnical Society
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• v.27 no.10
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• pp.105-116
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• 2011

No analytical solution exists for evaluating in-situ hydraulic conductivity of vertical cutoff walls by analyzing slug test results. Recently, an analytical solution to interpret slug tests has been proposed for a partially penetrated well in an aquifer. However, this analytical solution cannot be directly applied to the cutoff wall because the solution has been developed exclusively for an infinite aquifer instead of a narrow cutoff wall. To consider the cutoff wall boundary conditions, the analytical solution has been modified in this study to take into account the narrow boundaries by introducing the imaginary well theory. Two boundary conditions are considered according to the existence of filter cakes: constant head boundary and no flux boundary. Generalized steady-state shape factors are presented for each geometric condition, which can be used for evaluating the in-situ hydraulic conductivity of cutoff walls. The constant head boundary condition provides higher shape factors and no flux boundary condition provides lower shape factors than the infinite aquifer, which enables to adjust the in-situ hydraulic conductivity of the cutoff wall. The hydraulic conductivities calculated from the analytical solution in this paper give about 1.2~1.7 times higher than those from the Bouwer and Rice method, one of the semi-empirical formulas. Considering the compressibility of the backfill material, the analytical solution developed in this study was proved to correspond to the case of incompressible backfill materials.

• Journal of Navigation and Port Research
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• v.29 no.3 s.99
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• pp.269-274
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• 2005

Geodetic surveying using precise GPS equipment are used without analysis with a statistical verification of GPS observed value and it was preformed by necessity to integration projection of digital topographic map and nautical Chart for integration geographic information system construction. The purpose of this study proposes method that improve accuracy of GPS observed value and direction that integrally manage digital topographic map and electronic nautical chart in analyzing the boundary line error between digital topographic map and nautical Chart. For improvement of the precision of GPS observed value, the author studied precision-analysis of GPS observed value by geometric strength and variance factor in 3 control points used in GPS network adjustment. And like this, produce EDM measurement using this GPS observation results and compare the whole boundary point error when set digital topographic map and nautical chart by these boundary.