• Journal of the Society of Naval Architects of Korea
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• v.36 no.2
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• pp.40-49
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• 1999

A Finite Volume Method for the two-dimensional incompressible, two-fluids Navies-Stokes equation and level-set scheme are used to analyse the interface of two fluids, free-surface flow. The numerical characteristics and the applicability of level-set scheme are brief1y investigated and appraised by solving oscillating small surface wave in a water tank and dam break problems. In the numerical results, a method for improving the convergence of the solution is presented.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.198-201
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• 2010

지형이 불규칙한 자연하천에 대해 2차원 격자를 구성할 경우, 사각형 격자만을 사용한다면 지류와 본류의 합류부분에서 격자의 처리가 어려운 문제가 발생할 수 있으며, 삼각형 격자만을 사용하여 지형을 처리한다면 격자수가 많아져 계산시간이 다소 많이 소요되는 어려움이 존재할 수 있다. 혼합격자의 적용이 가능하다면 이러한 어려움은 어느정도 극복할 수 있다. 본 연구에서는 1차정확도 기법인 HLLC 기법을 적용하고, 지형이 복잡한 자연하천에 대한 격자처리의 유연성을 위해 삼각형 및 사각형 격자 그리고 이 두 격자가 혼용된 혼합격자의 적용이 가능한 2차원 유한체적모형을 개발하였다. 그리고 개발모형을 수리모형 실험을 통해 얻어진 실험자료가 존재하는 실험하도 및 실제 자연하천에서의 댐 붕괴에 대해 적용하여 결과를 비교하였다.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1677-1678
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• 2006

전력계통의 과도현상 분석용으로 개발된 수치계산 프로그램인 EMTP (Electromagnetic Transient Program)를 사용하여 건물내에 낙뢰에 의한 뇌서지가 침입했을 때 건물 전체에 surge current가 어떻게 확산되어 가는지를 분석해 본다. 이러한 현상을 분석하기 위해서 건물의 등가회로를 $\pi$-회로로 구현하고, ANSI 규격에 맞는 뇌서지를 건물에 유입시켜서 그에 따른 건물 내부의 torrent 분포를 알아본다. 그리고, 건물 체적을 변화시켜 가면서 뇌 서지가 건물 내부의 전기기기에 미치는 영향을 해석해 본다.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.2
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• pp.1-12
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• 1990

Interactions between a propeller and vortex system contained in a ship stern flow is treated theoretically. A new formulation to determine the effective velocity distributions is developed, which may be immediately applicable to the design and analysis of compound propulsors under the influence of severe vortical cross-flows around ship stern. An axisymmetric shear flow is represented by a system of ring vortices and the axial variation of the stream lines due to the action of propeller is represented by a cubic function. The strengths of ring vortices, which are varying along the stream lines, are determined by the conservation of angular momentum. Two simplified effective velocity models are proposed to confirm the theory. Sample calculations using the simplified models are made to compare with the results by other investigators.

• Composites Research
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• v.31 no.5
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• pp.276-281
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• 2018

In this paper, elastic behavior of woven fabric composites with various fiber yarn structure were predicted through a theoretical calculation model. A representative volume elements (RVE) that can represent the mechanical properties of the woven composites were selected and crimp angle of the weave yarn was defined by several sinusoidal functions. The effective material properties of the woven composite such as young's modulus, shear modulus and poisson's ratio was predicted by classical laminate theory (CLT). The fiber volume fractions were calculated according to the shape and pattern (plain, twill weave) of the fiber yarn, and the elastic behavior of each woven composite was obtained through a theoretical calculation model. Also, to verify the theoretical predictions, woven composite specimens of plain and twill weave were fabricated by vacuum assisted resin transfer molding (VARTM) process and then mechanical test was conducted. As a results, a good correlation between theoretical and experimental results for the elastic behavior of woven composites could be achieved.

• Composites Research
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• v.34 no.5
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• pp.305-310
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• 2021

Mechanical properties of fiber reinforced composites were affected to fiber volume fractions (FVF) and interfacial property by sizing agent conditions. An optimum interface can relieve stress concentration by transferring the mechanical stress from the matrix resin to the reinforcements effectively, and thus can result in the performance of the composites. The interfacial properties and wettability between the epoxy resin and glass fiber (GF) were evaluated for different sizing agent conditions and FVFs. The surface energies of epoxy resin and different sizing agent treated GFs were calculated using dynamic and static contact angle measurements. The work of adhesion, W_a was calculated by using surface energies of epoxy matrix and GFs. The wettability was evaluated via the GF tow capillary test. The interfacial shear strength (IFSS) was evaluated by microdroplet pull-out test. Finally, the optimized GFRP manufacturing conditions could be obtained by using wettability and interfacial property.

• Journal of the Korean Geotechnical Society
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• v.25 no.5
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• pp.47-52
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• 2009

A sand replacement method is commonly used to determine the density of the compacted soils. The density of the test or compacted soil is computed on the assumption that the calibration container has approximately the same size or volume and allows the sand to deposit approximately in the same way as a test hole in the field. The sand filling process is simulated in the laboratory and its effect on the determination of density is investigated. Artificially-made holes with different heights and bottom shapes are prepared to simulate various shapes of the test hole in the field. Three sands with different gradations are used in the testing to examine how sand grain size influences the determination of density in the field. As the height of a test hole increases, the error between known density and calculated density decreases, regardless of the types of test hole and sand used. The results of this study can be used to reevaluate and revise the test method for soil density by the sand replacement method.

• 한국전산유체공학회:학술대회논문집
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• 2000.05a
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• pp.107-112
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• 2000

연소실 안으로 분출되는 스월 유동의 vortex breakdown mechanism 에 대한 연구를 하였다. 3 차원 유한 체적기법과 Runge-Kutta 시간 적분법이 적용되었으며, 난류모델은 dynamic large eddy simulation (DLES)이 적용되었다. 계산 시간의 효율성과 기억용량을 효과적으로 사용하기 위하여 message passing interface (MPI) 병렬계산 기법이 적용되었다. 스월 난류 유동에 있어서 vortex breakdown 거동을 가시적으로 표착 하였는데. 이는 스월 유동에 의한 난류 응력 증대, 난류 생성/소산율 증대 및 혼합율 증대에 대한 실험적 근거를 뒷받침하는 매우 중요한 결과이다. 또한 평균 속도와 레이놀스 응력에 대한 계산 결과도 실험 결과와 비교하였다.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.1258-1262
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• 2007

수치해석분야에서 가장 난해한 부분은 복잡한 지형을 표현할 수 있는 격자망을 쉽고 간편하게 생성하고 수치모형에 적용하는 것이다. 가장 쉽고 널리 적용되던 직사각형격자망의 한계를 극복하기 위하여 곡선좌표계를 이용하거나, 삼각형 또는 사각형의 불규칙 격자망을 적용하여 복잡한 지형을 표현하는 연구들이 시도되었다. 그러나, 곡선좌표계를 이용하여 지배방정식을 변환하는 방법은 지배방정식이 매우 복잡하고 수치모형의 구성이 난해하며, 불규칙 격자망을 이용한 방법은 계산영역을 적절히 표현하는 격자망을 구성하기 위해서 상당한 노력과 시간이 소요되는 단점이 있다. 이에, 직사각형의 격자망과 비구조 격자망의 장단점을 보완하여 수치격자 구성이 간편하고 지형을 정확히 표현할 수 있는 기법에 대한 연구가 필요한 단계에 이르게 되었다. 본 연구에서는 직사각형 격자를 기본으로 지형을 따라 계산격자를 분할하는 기법인 cut-cell기법을 이용하여 계산격자망을 구성하고, 그 적용성을 검토하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.179-188
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• 1990

The characteristic of volumetric efficiency considering gas exchange process in a reciprocating engine is presented in this paper. The characteristic method is used for solving gas exchange problems of engine system in theoretical studies. The validity of the simulation is investigated by a comparison with the results obtained by the experiment which have been performed on the practical 4-cycle, 4-cylinder gasoline engine. The relationship between the volumetric efficiency and the intake pressure variation according to configuration of intake pipe, position of branch point, valve timing, compression ratio is clarified through simulation and experiment. The results predicted by the simulation are found to be in approximate agreement with those obtained by the experiment.