• 한국화재소방학회논문지
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• 제18권1호
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• pp.24-30
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• 2004

본 논문은 원자력발전소 방화벽에 설치된 케이블관통부 충전시스템(CPFS: Cable Penetration Fire Stop)안에서 일어나는 동적 열 전달 현상을 해석하기 위해 수행된 실험을 다루고 있다. Dow Corning사의 내화성 충전물에 대해서 내화실험이 수행되었으며, 본 실험을 통해 준비된 CPFS 시험체가 성능위주 시험방법인 ASTM E-814의 F-rating과 T-rating을 동시에 만족시킬 수 있는지를 알아보았다. 그리고 여기서 얻어진 실험결과는 CPFS시스템 내화성능 평가용 소프트웨어를 개발하기 위해 사용되었다. CPFS 시스템 내에서의 열전도 현상은 주어진 초기조건과 경계조건 하에서 Parabolic PDE(Partial differential equation)로 수식화 되었으며, 이렇게 수식화된 PDE는 다시 연속과완화법(SOR: Sequential over-relaxation)과 Galerkin 유한요소법(FEM: Finite element method)로 구성된 혼합알고리즘에 따라 풀 수 있었다. PDE을 풀기 위해 널리 사용되고 있는 상용소프트웨어 Femlab을 이용하여 방화시스템 내에서의 온도분포를 계산하여 3차원 그래픽으로 나타내었다. 특히 CPFS시스템 내에서의 시간의 경과에 따른 온도분포의 변화에 대한 실험과 수치해석을 병행함으로써 결과에 대한 신뢰성을 높일 수 있었다.

• Wind and Structures
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• 제15권6호
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• pp.481-494
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• 2012

The greenhouse type metal structures are increasingly used in modern construction of livestock farms because they are less laborious to construct and they provide a more favorable microclimate for the growth of animals compared to conventional livestock structures. A key stress factor for metal structures is the wind. The external pressure coefficient ($c_{pe}$) is used for the calculation of the wind effect on the structures. A high pressure coefficient value leads to an increase of the construction weight and subsequently to an increase in the construction cost. The EC1 in conjunction with EN 13031-1:2001, which is specialized for greenhouses, gives values for this coefficient. This value must satisfy two requirements: the safety of the structure and a reduced construction cost. In this paper, the Navier - Stokes and continuity equations are solved numerically with the finite element method (Galerkin Method) in order to simulate the two dimensional, incompressible, viscous air flow over the vaulted roofs of single span and twin-span with eaves livestock greenhouses' structures, with a height of 4.5 meters and with length of span of 9.6 and 14 m. The simulation was carried out in a wind tunnel. The numerical results of pressure coefficients, as well as, the distribution of them are presented and compared with data from Eurocodes for wind actions (EC1, EN 13031-1:2001). The results of the numerical experiment were close to the values given by the Eurocodes mainly on the leeward area of the roof while on the windward area a further segmentation is suggested.

• 설비공학논문집
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• 제6권3호
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• pp.302-314
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• 1994

The effects of the inclination of enclosure and partition on natural convective flow and heat transfer were investigated numerically. The enclosure was composed of the lower hot and the upper cold horizontal walls and the adiabatic vertical walls, and a partition was positioned perpendicularly at the mid-height of one vertical insulated wall. The governing equations are solved by using the finite element method with Galerkin method. The computations were performed with the variations of the partition length and Rayleigh number based on the temperature difference between two horizontal walls and the enclosure height with water(Pr=4.95). The effects of the inclination angle of enclosure and partition on the heat transfer within an enclosure were also studied. As the results, the increase of the inclination angle of enclosure rapidly raised the heat transfer rate, while the inclination angle for the maximum Nusselt number was retarded with the increase of the partition length and the decrease of the heat transfer rate became larger in proportion to the increase of the partition length. The Nusselt number obtained by the inclination of partition was smaller than that of the inclination of enclosure. However, the difference of the heat transfer rates was considerably decreased at the longer partition lengths and the trends for the variation of the average Nusselt number were more similar with that of the inclination of enclosure. The upward oriented partition increases the convective heat transfer distinctly in contrast to that of the inclination of enclosure as the partition length increases.

• 전산구조공학
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• 제2권1호
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• pp.65-70
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• 1989

우리는 생활주변에서 파이프의 사용을 흔히 볼 수 있다. 그 만큼 파이프의 소요량은 우리 생활에서 엄청난 양이라 할 수 있는데 그것이 기존 재료로는 콘크리트나 철강제품이 대부분을 차지하고 있다. 요즈음 대체 재료로써 복합재료가 여러 산업분야에서 각광을 받고 있다. 처음 항공분야에서 사용이 시작되어 제품의 우수성 뿐 아니라, 그 값이 점차 낮아짐에 따라 여러 분야에서 사용되고 있다. 복합재료는 내구성, 내열성, 내부식성 등 다른 어느 재료보다 좋은 성질을 가지고 있으며 특히 중량이 가볍다. 파이프 매설 공사에 있어서 운반비의 비중은 전체 공사비에 약 20-40%에 달할 만큼 크다. 따라서 복합재료의 선택은 그 비용을 감소시킬 수 있을 뿐 아니라 내구성, 내열성 등 복합재료의 여러가지 우수성을 동시에 가질 수 있다. 그리고 재료의 발달이 가속되고 있어 앞으로 유용성은 더욱 커질 것이다. 지하매설 파이프로써 반경에 비해 두께가 얇은 관인 경우 큰 변형이 발생할 것이다. 따라서 기하학적 비선형성을 고려하여야 한다. 이를 위해 변형 후의 형상에 대해 평형방정식을 세웠으며, 이를 Galerkin's method에 의해 풀었다. 하중조건은 파이프가 땅속에 묻히게 되므로 수직하중은 매설깊이에 비례하며 수평하중은 수평변위에 비례하게 가정하였다. 복합재료로 만들어진 파이프는 층(layer)수와 fiber 방향 등에 따라 강성이 틀려지며 또한 흙의 종류와 발생되는 변위에 따라 파이프-흙간의 상호작용이 달라진다. 본 연구에서는 복합재료로 만들어진 파이프가 지하에 매설된 경우 기하학적 비선형을 고려한 해석방법을 제시하며 파이프 강성에 미치는 여러 인자에 대해 고찰해 보았다. 결과가 유한요소법에 의해 검증되었다. 기술고도화를 위한 과감한 측정관련 투자 결과가 제품의 불량감소에 크게 영향을 준다는 사실이 밝혀졌다. 연구결과에 따른 주요내용과 평가분석 모형을 제시한다.을 나타냄으로써 누에소화액 protease에 의하여 용해되지 않았음을 보여 주었다. 4. 결정성독소의 amino산 조성은 subsp. israelensis에서는 aspartic산이 14.5%로 가장 많은 비율을 차지하였고 그외 4개의 subsp.에서는 glutamic산이 13.9-14.6%로 가장 많았다. 5. 결정성독소의 면역학적 특성을 보면 subsp. israelensis의 항체는 그것의 항원과만 반응하고 그외 4개의 subsp.의 항체는 각각의 항원과 그리고 서로 다른 항원과 교호하여 반응하였다.화지방산을 다량으로 함유한 칠성장어유 및 옥수수유는 동맥경화증 랫트에 있어 생체내 지질대사에 영향을 미침으로써 혈청지질치를 저하시키고 동맥벽내에 지방침착을 억제시켰으며, 이러한 효과는 n-6계 다불포화지방산을 많이 함유하고 있는 옥수수유보다 n-3rP 다불포화지방산을 다량으로 함유한 칠성장어유에 더욱 크게 나타났다isozyme but not with p. esocinus B4 isogyme, reflecting that subunit B is less conservative in its evolution.e bands (fractions) with 290 Kd to 23 Kd molecular weight, and 8 bands of these detected bands developed strongly by silver stain. In serological test, ELISA, we recognized the cross-reaction

• Steel and Composite Structures
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• 제18권1호
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• pp.1-28
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• 2015

In this paper, the dynamic response of functionally gradient steel (FGS) composite cylindrical panels in steady-state thermal environments subjected to impulsive loads is investigated for the first time. FGSs composed of graded ferritic and austenitic regions together with bainite and martensite intermediate layers are analyzed. Thermo-mechanical material properties of FGS composites are predicted according to the microhardness profile of FGS composites and approximated with appropriate functions. Based on the three-dimensional theory of thermo-elasticity, the governing equations of motionare derived in spatial and time domains. These equations are solved using the hybrid Fourier series expansion-Galerkin finite element method-Newmark approach for simply supported boundary conditions. The present solution is then applied to the thermo-elastic dynamic analysis of cylindrical panels with three different arrangements of material compositions of FGSs including ${\alpha}{\beta}{\gamma}M{\gamma}$, ${\alpha}{\beta}{\gamma}{\beta}{\alpha}$ and ${\gamma}{\beta}{\alpha}{\beta}{\gamma}$ composites. Benchmark results on the displacement and stress time-histories of FGS cylindrical panels in thermal environments under various pulse loads are presented and discussed in detail. Due to the absence of similar results in the specialized literature, this paper is likely to fill a gap in the state of the art of this problem, and provide pertinent results that are instrumental in the design of FGS structures under time-dependent mechanical loadings.

• 한국전산응용수학회:학술대회논문집
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• 한국전산응용수학회 2003년도 KSCAM 학술발표회 프로그램 및 초록집
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• pp.1-1
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• 2003

In this talk, a reduced-order modeling methodology based on centroidal Voronoi tessellations (CVT's)is introduced. CVT's are special Voronoi tessellations for which the generators of the Voronoi diagram are also the centers of mass (means) of the corresponding Voronoi cells. The discrete data sets, CVT's are closely related to the h-means clustering techniques. Even with the use of good mesh generators, discretization schemes, and solution algorithms, the computational simulation of complex, turbulent, or chaotic systems still remains a formidable endeavor. For example, typical finite element codes may require many thousands of degrees of freedom for the accurate simulation of fluid flows. The situation is even worse for optimization problems for which multiple solutions of the complex state system are usually required or in feedback control problems for which real-time solutions of the complex state system are needed. There hava been many studies devoted to the development, testing, and use of reduced-order models for complex systems such as unsteady fluid flows. The types of reduced-ordered models that we study are those attempt to determine accurate approximate solutions of a complex system using very few degrees of freedom. To do so, such models have to use basis functions that are in some way intimately connected to the problem being approximated. Once a very low-dimensional reduced basis has been determined, one can employ it to solve the complex system by applying, e.g., a Galerkin method. In general, reduced bases are globally supported so that the discrete systems are dense; however, if the reduced basis is of very low dimension, one does not care about the lack of sparsity in the discrete system. A discussion of reduced-ordering modeling for complex systems such as fluid flows is given to provide a context for the application of reduced-order bases. Then, detailed descriptions of CVT-based reduced-order bases and how they can be constructed of complex systems are given. Subsequently, some concrete incompressible flow examples are used to illustrate the construction and use of CVT-based reduced-order bases. The CVT-based reduced-order modeling methodology is shown to be effective for these examples and is also shown to be inexpensive to apply compared to other reduced-order methods.

• International Journal of Vascular Biomedical Engineering
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• 제2권1호
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• pp.17-24
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• 2004

Tumor angiogenesis was simulated using a two-dimensional computational model. The equation that governed angiogenesis comprised a tumor angiogenesis factor (TAF) conservation equation in time and space, which was solved numerically using the Galerkin finite element method. The time derivative in the equation was approximated by a forward Euler scheme. A stochastic process model was used to simulate vessel formation and vessel elongation towards a paracrine site, i.e., tumor-secreted basic fibroblast growth factor (bFGF). In this study, we assumed a two-dimensional model that represented a thin (1.0 mm) slice of the tumor. The growth of the tumor over time was modeled according to the dynamic value of bFGF secreted within the tumor. The data used for the model were based on a previously reported model of a brain tumor in which four distinct stages (namely multicellular spherical, first detectable lesion, diagnosis, and death of the virtual patient) were modeled. In our study, computation was not continued beyond the 'diagnosis' time point to avoid the computational complexity of analyzing numerous vascular branches. The numerical solutions revealed that no bFGF remained within the region in which vessels developed, owing to the uptake of bFGF by endothelial cells. Consequently, a sharp, declining gradient of bFGF existed near the surface of the tumor. The vascular architecture developed numerous branches close to the tumor surface (the brush-border effect). Asymmetrical tumor growth was associated with a greater degree of branching at the tumor surface.