• Steel and Composite Structures
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• 제27권5호
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• pp.555-566
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• 2018

A 1/3 composite cylindrical shell with a central rectangular opening was axially compressed experimentally, and its critical buckling load and displacement, and strains were measured. A finite element model (FEM) of the shell with Hashin failure criteria was established to analyze its buckling and post-buckling behaviors by nonlinear Newton-Raphson method. The geometric imperfection sensitivity and the effect of side supported conditions of the shell were investigated. It was found that the Newton-Raphson method can be used to analyze the buckling and post-buckling behaviors of the shell. The shell is not sensitive to initial geometric imperfection. And the support design of the shell by side stiffeners is a good way to obtain the critical buckling load and simplify the experimental fixture.

• Nuclear Engineering and Technology
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• 제33권5호
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• pp.468-482
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• 2001

As a process of Direct Containment Heating (DCH) issue resolution for Korean Standard Nuclear Power Plants (KSNPs), a containment load/strength assessment with two different approaches, the probabilistic and the deterministic, was performed with all plant-specific and phenomena-specific data. In case of the probabilistic approach, the framework developed to support the Zion DCH study, Two-Cell Equilibrium (TCE) coupled with Latin Hypercubic Sampling (LHS), provided a very efficient tool to resolve DCH issue. In case of the deterministic approach, the evaluation methodology using the sophisticated mechanistic computer code, CONTAIN 2.0 was developed, based on findings from DCH-related experiments or analyses. For three bounding scenarios designated as Scenarios V, Va, and VI, the calculation results of TCE/LHS and CONTAIN 2.0 with the conservatism or typical estimation for uncertain parameters, showed that the containment failure resulted from DCH loads was not likely to occur. To verify that these two approaches might be conservative , the containment loads resulting from typical high-pressure accident scenarios (SBO and SBLOCA) for KSNPs were also predicted. The CONTAIN 2.0 calculations with boundary and initial conditions from the MAAP4 predictions, including the sensitivity calculations for DCH phenomenological parameters, have confirmed that the predicted containment pressure and temperature were much below those from these two approaches, and, therefore, DCH issue for KSNPS might be not a problem.

• Nuclear Engineering and Technology
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• 제32권4호
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• pp.410-423
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• 2000

A two-dimensional numerical model is developed and applied to the LAVA-EXV tests performed at the Korea Atomic Energy Research Institute (KAERI) to investigate the external cooling effect on the thermal margin to failure of a reactor pressure vessel (RPV) during a severe accident. The computational program was written to predict the temperature profile of a two-dimensional spherical vessel segment accounting for the conjugate heat transfer mechanisms of conduction through the debris and the vessel, natural convection within the molten debris pool, and the possible ablation of the vessel wall in contact with the high temperature melt. Results of the sensitivity analysis and comparison with the LAVA-EXV test data indicated that the developed computational tool carries a high potential for simulating the thermal behavior of the RPV during a core melt relocation accident. It is concluded that the main factors affecting the RPV failure are the natural convection within the debris pool and the ablation of the metal vessel, The simplistic natural convection model adopted in the computational program partly made up for the absence of the mechanistic momentum consideration in this study. Uncertainties in the prediction will be reduced when the natural convection and ablation phenomena are more rigorously dealt with in the code, and if more accurate initial and time-dependent conditions are supplied from the test in terms of material composition and its associated thermophysical properties.

• 천문학논총
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• 제30권2호
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• pp.113-114
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• 2015

Recent high-resolution, high-sensitivity observations of protostellar jets have shown many to possess an underlying 'wiggle' structure. HH 211 is one such example where recent sub-mm observations revealed a clear reflection-symmetric wiggle. An explanation for this is that the HH211 jet source is moving as part of a protobinary system. Here we test this assumption by simulating HH211 through 3D hydrodynamic simulations using the pluto code with a molecular chemistry and cooling module, and initial conditions based on an analytical model derived from SMA observations. Molecular chemistry allows us to accurately plot synthetic molecular emission maps and position-velocity diagrams for direct comparison to observations, enabling us to test the observational assumptions and put constraints on the physical parameters of HH211. Our preliminary results show that the reflection-symmetric wiggle can be recreated through the assumption of a jet source being part of a binary system.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 춘계학술대회 특별세미나.특별세션
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• pp.27-41
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• 2008

Construction of metro transportation infra is a large-scale project requiring tremendous financial resources. This study suggests operation method to use for rapid transit line existing infra such as Gyeongbu line and spare line capacity following second phase KTX construction. Reviewing various constraints of metro rapid transit operation, we found that the conditions for metro rapid transit operation are already satisfied in Daegu area, just like the case of Gyeongbu line in Seoul Metro area. Also, the evaluation of the economic feasibility of metro rapid transit operation in Daegu area shows that B/C is about 2.4, which implies that there is sufficient economic feasibility. According to the result of sensitivity analysis, the project is economically feasible unless the passenger demand decreases 15% and construction costs increases more than 70%. B/C is evaluated large because the utilization of already exiting infra lowers the initial cost. As one of mass transportation system of large capacity, metro rapid transit can generate significant spillover effect: It will strengthen competitiveness of metro area by connecting cities within the area and by extending one-day life zone of the area, to say nothing of the benefit of improving traffic condition. The construction of metro rapid transit network is necessary for the mass transportation system of Yeongnam area as well as Daegu area, and it may work as a starting point for uniting Daegu and Gyeongbuk and strengthening regional competitiveness.

• 한국재료학회지
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• 제13권12호
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• pp.796-800
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• 2003

The polypyrrole prepared with pyrrole monomer, APS and DBSA was synthesized by chemical Polymerization at $V^{\circ}C$ under atmosphere conditions. After dissolving polypyrrole powder to the chloroform including DBSA, polypyrrole film was prepared on the alumina substrate with an interdigitated electrode by using the dip-coating method. This film was soaked in methanol solvent for 1 h at room temperature and heated to $70^{\circ}C$ for 4 h in $N_2$. Initial resistance was increased with the increasing humidity and decreasing temperature. The sensitivity was increased with lower humidity and decreasing temperature. The best linearity was achieved at $25^{\circ}C$ and low humidity of 0%.

• 한국생산제조학회지
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• 제18권4호
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• pp.337-347
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• 2009

Generally, finite element models used in structural analysis have some uncertainties of the geometric dimensions, applied loads and boundary conditions, as well as in material properties due to the manufacturability of aluminum intensive body. Therefore, it is very important to refine or update a finite element model by correlating it with dynamic and static tests. The structural optimization problems of automotive body are considered for mechanical structures with initial stiffness due to preloading and in operation condition or manufacturing. As the mean compliance and deflection under preloading are chosen as the objective function and constraints, their sensitivities must be derived. The optimization problem is iteratively solved by a sequential convex approximation method in the commercial software. The design variables are corrected by the strain energy scale factor in the element levels. This paper presents an updated method based on the sensitivities of structural responses and the residual error vectors between experimental and simulation models.

• Advances in aircraft and spacecraft science
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• 제7권2호
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• pp.135-149
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• 2020

In the current paper, a generalization of the results of Zhao et al. (2008) on a new design of C/C composite multidisc brake system is presented. The purpose of this paper is to study the effect of thermal sensitivity of Carbon/Carbon (C/C) composite material on the temperature distributions, deformation, and stress during braking. In this regard, a transient temperature-displacement coupled analysis for C/C composite brake discs with frictional heat generation under simulated operating conditions is performed. An axisymmetric model for brake system is used for the finite element analysis according to the theory of energy transformation and transportation. The transient temperature distributions on the friction surfaces, deformation, and stress are obtained. To check the validity, the results are corroborated with other solutions available in the literature, wherever possible. The current study could be used as a guide in the initial design of a high performance multidisc brake system.

• 해양환경안전학회지
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• 제26권5호
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• pp.514-522
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• 2020

해양생태독성시험의 국제표준시험종 중 생산자에 속하는 대표적인 Skeletonema sp.와 Dunaliella tertiolecta의 생태독성학적 차이점을 알아보기 위해 각 표준시험법(규격)을 비교하였고 환경에 대한 종 적합성과 다양한 시험물질에 대한 민감도를 비교 분석하였다. 그 결과, 시험법의 경우 대부분 동일하였으나 시험 유효성의 기준에서 pH 변화 제한과 초기접종밀도에서 차이가 나타났으며 이는 D. tertiolecta의 낮은 성장률에 기인된 것으로 추정된다. 적합성에서는 두 종 모두 규격에서 요구하는 유효성의 기준을 연속 만족하여 시험수행의 일관성을 보였고 시험한계 염분범위는 Skeletonema sp.와 D. tertiolecta 각각 20 및 10 psu로 나타났다. 마지막으로 민감도의 경우, 시험규격에서 제시하는 참조물질, 실제 오염 배출수(선박평형수) 및 기타 다양한 화학물질에서 모두 Skeletonema sp.가 D. tertiolecta에 비해 독성 민감도가 상대적으로 높음을 확인하였으며 이는 해양생태독성시험 수행에 있어 생산자를 이용한 시험의 경우 최소 2종 이상의 다른 분류군의 미세조류를 이용하는 것이 시험결과의 신뢰성과 객관성을 높일 수 있는 방법임을 시사한다.

• 한국전자통신학회논문지
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• 제15권1호
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• pp.179-184
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• 2020

랜덤성이 우수한 의사난수열 생성기로 알려진 셀룰라 오토마타(Cellular automata, CA)는 그 응용분야가 매우 다양하다. Cho 등은 긴 주기의 비선형 수열을 생성하기 위하여 CA기반의 수축수열 생성기를 설계하였다. 또한, 카오스 캣맵은 초기 조건에 대한 민감성과 예측 불가능한 특성을 가지는 복잡한 비선형 동역학계로 많은 연구자들에 의하여 연구되어 왔다. 본 논문에서는 높은 보안성을 위하여 최대 주기를 갖는 CA기반의 수축 생성기로 생성한 비선형 수열과 3차원 카오스 캣맵을 이용한 새로운 영상 암호화 방법을 제안한다.