• Journal of the Korea Concrete Institute
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• v.22 no.4
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• pp.595-603
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• 2010

Monte-Carlo simulation technique is often used in order to predict service life of concrete structure subjected to chloride penetration in marine environment based on probability theory. Monte-Carlo simulation method, however, the method gives different results every time that the simulation is run. On the other hand, moment method, which is frequently used in reliability analysis, needs negligible computational cost compared with simulation technique and gives a constant result for the same problem. Thus, in this study, moment method was applied to the calculation of corrosion-initiation probability. For this purpose, computer programs to calculate failure probabilities are developed using first-order second moment (FOSM) and second-order second moment (SOSM) methods, respectively. From the analysis examples with the developed programs, SOSM was found to give a more accurate result than FOSM does. The sensitivity analysis has shown that the factor affecting the corrosion-initiation probability the most was the cover depth, and the corrosion-initiation probability was influenced more by its coefficient of variation than its mean value.

• Journal of the Korea Concrete Institute
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• v.20 no.2
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• pp.185-191
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• 2008

To fundamentally solve the problem of deterioration of concrete structures, it has been researched that the high durable concrete structure reinforced with the FRP rebar can be one of major solution to the newly-developed concrete structure. FRP rebar has lots of advantages such as non-corrosive, high performance and light weight against the conventional steel rebar. Among these kinds of FRP rebars, GFRP rebar has usually been considered as the best reinforcement because of its economic point of view. Even though the material capacity of the GFRP rebar was already investigated, there are some problems such as low modulus of elastic that will be cause for degrade of the serviceability of flexural concrete member reinforced with the GFRP rebar. Thus, the deflection characteristics of the GFRP rebar reinforced concrete structure should be considered then investigated. In this study, ACI 440 guideline (2003), ISIS Canada Design Manual (2001) and Toutanji et al. (2000) was considered for predicting the moment of inertia of the concrete beam reinforced with the GFRP rebar. And it was also evaluated that load-deflection relationship had a good accordance with the test and analysis result. In the result of this study, it could be estimated that the load-deflection relationship using the suggested equation of moment of inertia in this study indicated better accordance with the test result than that of the others until failure.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.3
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• pp.447-453
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• 2010

Response-based approach is getting more preferred in determining the design sea-state for offshore structures because traditional environment-based approach is known to yield a much conservative design condition. This paper introduces the inverse first-order second-moment (IFOSM) method as a response-based approach, which is expected to give a more feasible design condition at the cost of reasonable number of motion analyses. The IFOSM method is based on the theory of probability and adopts an optimization scheme to determine the design point. Both the design maximum response and design sea state can be obtained straightforwardly from the optimum. The IFOSM method has been applied to a turret-moored FPSO's design problem and showed its effectiveness in practical use.

• Journal of computational fluids engineering
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• v.12 no.3
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• pp.55-61
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• 2007

A computational study on a strongly stratified natural convection is performed with the elliptic blending second-moment closure. The turbulent heat flux is treated by both the algebraic flux model (AFM) and the differential flux model (DFM). Calculations are performed for a turbulent natural convection in a square cavity with conducting top and bottom walls and the calculated results are compared with the available experimental data. The results show that both the AFM and DFM models produce very accurate solutions with the elliptic-blending second-moment closure without invoking any numerical stability problems. These results show that the AFM and DFM models for treating the turbulent heat flux are sufficient for this strongly stratified flow. However, a slight difference between two models is observed for some variables.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.20 no.3
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• pp.51-56
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• 2012

The wing is a framework composed chiefly of skin, spars, ribs and can be simplified by matrix structure. In this paper, a displacement reliability of matrix structure is analysed by AFORM(Advanced First Order Reliability Method) and applicability is assessed.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.04a
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• pp.269-277
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• 2001

본 연구에서는 리브로 보강된 내진 철골 모멘트 접합부의 응력전달 메커니즘을 검토하였다. 리브보강 접합부의 응력전달 메커니즘은 고전 휨이론에 의한 예측과 전혀 다르다. 일반적으로 구조 기술자가 리브를 사용할 경우 단면이차모멘트의 증가에 따른 휨응력의 감소효과를 기대하는 것이 보통이다. 그러나 리브는 구조기술자들이 통상 가정하는 휨응력 전달요소라기 보다는 리브 구배 방향의 스트럿 요소로 기능하여 휨응력 외에도 전달응력을 전달한다. 리브를 스트럿 요소로 파악할 때 응력전달 메커니즘을 올바로 파악할 수 있으며 이를 기초로 합리적 설계법의 정립이 가능하다.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.111-117
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• 2008

This paper reports briefly on the computational results of a turbulent Rayleigh-Benard convection with the elliptic-blending second-moment closure (EBM). The primary emphasis of the study is placed on an investigation of accuracy and numerical stability of the elliptic-blending second-moment closure for the turbulent Rayleigh-Benard convection. The turbulent heat fluxes in this study are treated by the algebraic flux model with the temperature variance and molecular dissipation rate of turbulent heat flux. The model is applied to the prediction of the turbulent Rayleigh-Benard convection for Rayleigh numbers ranging from $Ra=2{\times}10^6$ to $Ra=10^9$, and the computed results are compared with the previous experimental correlations, T-RANS and LES results. The predicted cell-averaged Nusselt number follows the correlation by Peng et al.(2006) ($Nu=0.162Ra^{0.286}$) in the 'soft' convective turbulence region ($2{\times}10^6{\leq}Ra{\leq}4{\times}10^7$) and it follows the experimental correlation by Niemela et al. (2000) ($Nu=0.124Ra^{0.309}$) in the 'hard' convective tubulence region ($10^8{\leq}Ra{\leq}10^9$) within 5% accuracy. This results show that the elliptic-blending second-moment closure with an algebraic flux model predicts very accurately the Rayleigh Benard convection.

• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.554-559
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• 2016

본 논문은 EDISON CFD를 사용하여 스포일러가 장착된 무미익 BWB UCAV에 대하여 이차원 유동해석을 수행하였다. 무미익 형상은 일반적인 항공기보다 롤과 요 방향의 안정성과 조성성에 있어 불리한 특징을 갖는데 특히 이 착륙 시 고 받음각의 영역에서 발생하는 Pitch-up 현상이 항공기 안정성에 문제를 야기한다. 수직 미익 부재와 pitch-up 현상으로 인한 BWB형상의 UCAV가 지니는 단점을 보완하기 위해서 스포일러가 장착된 형상이 적용되기도 한다 본 연구에서는 윗면과 아랫면에 스포일러가 장착된 경우에 대해 전산유동해석을 수행하였다. 해석결과 윗면의 스포일러는 양력의 감소와 항력의 증가를 야기했으며, 아랫면의 스포일러는 양력과 항력을 모두 증가시켰다. 피칭모멘트의 경우 아랫면의 스포일러가 저받음각에서 안정성을 증가시켰다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.3
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• pp.337-344
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• 2000

The wavelet analysis technique is applied in the spectral domain to efficiently represent the multi-scale features of the impedance matrices. In this scheme, the 2-D quadtree decomposition (applying the wavelet transform to only the part of the matrix) method often used in image processing area is applied for a sparse moment matrix. CG(Conjugate-Gradient) method is also applied for saving memory and computation time of wavelet transformed moment matrix. Numerical examples show that for rectangular cylinder case the non-zero elements of the transformed moment matrix grows only as O($N^{1.6}$).

• Journal of Korean Society of Steel Construction
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• v.18 no.3
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• pp.373-383
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• 2006

In a steel structural system, noncomposite form deck one-way slab is the plate element supported by four-edged steel beams with unequaled stiffness. However, design criterion has analyzed the one-way slab as the continuous beam. Because the end beams that support the one-way slab have elastic supports t hat cause different deflections according to the support conditions and locations, the bending moments corresponding to the support ic support effect is not considered in the design criterion. Accordingly, to conduct a reasonable estimation of approximate moment coefficients considering the unequaled elastic support conditions, this study analyzes and estimates various models with varia bles for the ratios of live load to dead load and pattern arangements of live loads and span lengths. The analytical methods considering the finite three-dimensional plate element, the two-dimensional elastic support and the infinite stifnes suport are performed.