• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.243-246
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• 2009

본 연구에서는 분자동역학 전산모사와 미시역학 모델을 이용하여 나노입자의 크기와 체적분율 변화가 나노복합재의 물성변화에 미치는 영향을 효과적으로 묘사할 수 있는 순차적 브리징 해석기법을 개발하였다. 나노 입자의 크기변화와 체적분율 변화에 따른 영률과 전단계수를 분자동역학 전산모사를 통해 예측한 후, 이를 연속체 모델에서 구현하기 위해 다중입자 모델을 적용하였다. 나노입자의 크기효과를 반영하기 위해 입자와 기지 사이에 유효계면을 추가적인 상으로 도입하였고, 체적분율 효과는 나노복합재를 둘러싸는 무한영역의 물성값을 통해 조절되도록 하였다. 유효계면과 무한영역의 물성을 입자의 반경과 체적분율의 함수로 근사한 후, 다양한 입자의 크기와 체적분율에서 나타나는 나노복합재의 물성변화를 예측하였다. 제안된 해석기법의 적용을 통해 분자동역학 전산모사 결과와 잘 일치하는 예측해를 효과적으로 얻을 수 있었다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.4
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• pp.495-503
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• 2001

In a functionally graded materials(FGM), two constituent material particles are mixed up according to a specific volume fraction distribution so that its thermoelastic behavior is definitely characterized by such a material composition distribution. Therefore, the designer should determine the most suitable volume fraction distribution in order to design a FGM that optimally meets the desired performance against the given constraints. In this paper, we address a numerical optimization procedure, with employing interior penalty function method(IPFM) and FDM, for optimizing 2D volume fractions of heat-resisting FGMs composed of metal and ceramic. We discretize a FGM domain into finite number of homogenized rectangular cells of single design variable in order for the optimization efficiency. However, after the optimization process, we interpolate the discontinuous volume fraction with globally continuous bilinear function in order to enforce the continuity of volume fraction distributions.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.558-561
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• 2010

본 연구에서는 나노복합재의 탄소성 거동과 항복응력을 예측하기 위해 분자동역학 전산모사를 수행하였다. 나일론 기지와 실리카 나노입자가 포함된 단위 셀 구조로부터 나노입자의 체적분율 변화에 따른 응력-변형률 선도를 등변형률을 적용한 등온등압 앙상블 전산모사로부터 도출하였다. 4%의 변형률 범위에서 나노복합재의 탄성계수를 도출하였고, 이를 이용하여 2% 오프셋 방법으로 항복응력을 예측하였다. 나노입자의 유무에 따른 항복평면의 변화와 고분자 재료에서 나타나는 정수압 효과가 항복평면에 미치는 영향을 확인하기 위해 일축 인장/압축 그리고 이축 인장/압축을 수행하였고, 각각의 경우에 나타나는 나노복합재 내부의 자유체적 변화에 대한 분석을 통해 나노입자의 강화효과를 고찰하였다. 또한 고분자 기지로 인해 발생하는 정수압 효과를 반영한 von-Miss 항복평면을 도출하고, 입자의 체적분율 변화에 따른 항복응력의 예측이 가능하도록 정수압효과에 대한 파라메터를 체적분율의 함수로 근사하였다.

• Journal of the Korean Society of Marine Environment & Safety
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• v.15 no.1
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• pp.63-69
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• 2009

Gas volumetric fractions and pressure loss are very important parameters in understanding and predicting gas-liquid two-phase flows. They are also essential to design large heat exchanging system in many industries, boiler and refrigerating systems mounted at ships. This paper therefore presents a theoretical method of predicting the pressure loss and gas volumetric fractions in gas-liquid two-phase flows for the whole range of pipe inclinations. The theoretical analysis is based on the two-fluid stratified flow model. It also provides the results of the comparisons between this theoretical analysis results and previous experimental results.

• Journal of the Korean Society for Nondestructive Testing
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• v.17 no.3
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• pp.151-155
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• 1997

In this research, nondestructive test using a radioisotope, $^{241}Am$ gamma-ray, was accomplished in order to evaluate the fiber volume fraction of the accumulated composite layers such as glass fiber/epoxy and carbon fiber/epoxy. Attenuation coefficients of the fiber and resin were measured respectively by NaI(T1) detector The fibers volume fraction was measured for various thickness of composite layers between 2 and 20mm. Fiber volume fraction of the composite layers were also measured for various amount of fibers. The experimental errors from nondestructive test using gamma-ray were in the range of ${\pm}1{\sim}2.5%$ in comparison with those from observation by optical microscopy. By selecting the optimum energy and activity of radioisotope, this method can provide a new means for the evaluation of the fiber volume fraction.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.1
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• pp.11-19
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• 2001

기능경사재(FGM)는 구성 물질의 체적분율(volume fraction)이 복합재 전체에 걸쳐 연속적 그리고 기능적으로 분포되어 있어, 기존의 이종물질 접합식(bi-material-type) 복합재보다 현저히 우수한 열기계적 특성을 가진다. 하지만, 기능경사 내열복합재의 열-탄소성 거동은 체적분율의 분포형태와 경사층이 차지하는 상대두께비에 따라 절대적으로 좌우된다. 본 연구는 기능경사 내열복합재의 열-탄소성 특성의 이들 두 설계인자에 대한 파라메트릭 FEM해석을 다룬 것이다. 열-탄소성 이론과 유한요소 근사화에 따라 연구용 2차원 FEM 프로그램을 개발하고, 대표적인 3층 구조의 2차원 기능경사 내열복합재의 열-탄소성 특성을 설계변수의 다양한 조합에 따라 분석하였다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.4
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• pp.343-348
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• 2009

In this study, an efficient sequential bridging method to characterize both the particle size effect and concentration effect on the mechanical properties of nanocomposites at high volume fraction is suggested through a molecular dynamics(MD) simulations and micromechanics of composites materials. The Young's modulus and the shear modulus of the nanocomposites at various particle radius and at 12% volume fraction were obtained from MD simulations and multi-inclusion model was adopted to describe both modulus in continuum model. In order to describe the particle size effect, an additional phase, effective interface, was adopted as characteristic phase and the non-dilute concentration effect which appears at 12% volume fraction was describe via the variation of the elastic modulus of the infinite medium. Both the elastic modulus of the interface and infinite medium were fitted into functions of particle radius for the applicability of the present bridging method at various particle radii. Using the present bridging method the elastic modulus of the nanocomposites was efficiently obtained with accuracy. In addition, the effect of the interface thickness and modulus on the elastic modulus of the nanocomposite was investigated.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.11a
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• pp.421-426
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• 1996

본 논문에서는 고압분출 사고시 격납용기 하중 완화를 위해 국내 원전에서 채택하고 있는 캐비티내 나포체적이 용융물 방출 분율에 미치는 효과를 분석하기 위한 방법을 제시하고, 이를 울진 3,4호기 캐비티 모형에 적용하였다. 이를 위해 용융물 방출을 예측을 위해 이미 개발된 Kim's 상관식에 고온 상사물을 모의하기 위한 방정식을 도출하여 고온 실험에 적용하였다. 또한, SNL에서 실험자료를 정리하면서 얻은 결과와 나포체적을 가진 캐비티를 대상으로 국내에서 수행된 실험결과를 이용하여 나포체적 해석을 위한 방안을 제시하였다. Kim's 상관식에 고온 상사물 모델을 위한 방정식과 나포체적 해석 방안을 적용. 개선하여 울진 3,4호기와 이와 유사한 캐비티모형에서 용융물 방출 분율을 예측하였다.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.5
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• pp.611-618
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• 2018

In this study, numerical analysis of solid-liquid two-phase flow was conducted as a preliminary step to analyze the flow characteristics of drilling fluid using the commercial CFD code, ANSYS CFX 14.5. The homogeneous model and separated flow model were used to simulate solid-liquid two-phase flow phenomena. In the separated flow model, Gidaspow's drag force model was applied with the kinetic theory model was applied for solid particles. The validity of the numerical model used in this study was verified based on the published experimental results. Numerical analysis was carried out for volume fractions of 0.1 to 0.5 and velocities of 1 to 5 m/s in a horizontal tube with a diameter of 54.9 mm and a length of 3 m. The Pressure drop and volume fraction distribution of solid particles were confirmed. The pressure drop was predicted using the homogeneous model and separated flow model within the MAE of 17.04 % and 8.98 %, respectively. A high volume fraction was observed in the lower part of the tube, and the volume fraction decreased toward the upper part. As velocity increased, variations in volume fraction distribution at varying heights were decreased, and the numerical results predicted these flow characteristics well.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.6
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• pp.988-995
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• 2001

Functionally graded materials(FGMs) are highlighted to be suitable for high temperature engineering due to their continuous distribution of material properties. In this paper, an optimal design is executed for determining the optimal material volume distribution pattern that minimizes the steady-state thermal stress of FGM heat-resisting composites. The interior penalty function method and the golden section method are employed as optimization techniques while the finite element method is used for thermal stress analysis. Through numerical simulations we suggest the volume fraction distributions that considerably improve initial thermal stress distributions.