• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.173-178
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• 2011

Nowadays, SELENE-2 is under development for the moon explorer rover in Japan. AXS(Active X-ray Spectrometer) sensor development among the candidated payloads will be on going by the world-wide co-operation. The thermal design, analysis and test will be specially performed by Korean institutes. CFD techniques are used for the conceptual design and analysis. Thin-shell plate meshes being applied by Monte-Carlo Ray Tracing Method are generated for the thermal radiation analysis. Lumped capacity model is employed for the thermal conduction simulation of the AXS payload itself. Various shapes of the payload configuration with thermal boundary conditions are proposed and selected on the purpose of the analysis of the initial design. The results of the analysis are supposed to be used as the baseline for the further detailed design of the AXS payload in the future.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.67-67
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• 2004

다공성 물질을 건조하거나 습한 환경에 노출시키면 열과 수분이 외부로 전달된다. 열 및 수분 전달로 인한 은도 및 습도의 변화는 물질 체적을 변화시켜 습열 응력을 유발시킨다 즉 다공성 제품의 품질은 외양뿐만 아니라 건조 공정 시의 온도, 수분함유량, 응력, 변형률 등의 공정변수에 크게 영향을 받는다. 최근까지도 다공성 물질의 생산 공정은 다수의 공정변수를 갖는 복합공정이기 때문에 이들의 영향을 정량적으로 평가하는 것은 매우 까다로워 현장 경험에 기초한 기술자의 노하우에 의존해 왔다.(중략)

• Tunnel and Underground Space
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• v.32 no.6
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• pp.568-585
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• 2022

In the present study, we proposed a numerical method for simulating thermally induced fracture slip using a grain-based distinct element model (GBDEM). As a part of DECOVALEX-2023, the thermo-mechanical loading test on a saw-cut rock fracture conducted at the Korea Institute of Civil Engineering and Building Technology was simulated. In the numerical model, the rock sample including a saw-cut fracture was represented as a group of random Voronoi polyhedra. Then, the coupled thermo-mechanical behavior of grains and their interfaces was calculated using 3DEC. The key concerns focused on the temperature evolution, thermally induced principal stress increment, and fracture normal and shear displacements under thermo-mechanical loading. The comparisons between laboratory experimental results and the numerical results revealed that the numerical model reasonably captured the heat transfer and heat loss characteristics of the rock specimen, the horizontal stress increment due to constrained displacement, and the progressive shear failure of the fracture. However, the onset of the fracture slip and the magnitudes of stress increment and fracture displacement showed discrepancies between the numerical and experimental results. We expect the numerical model to be enhanced by continuing collaboration and interaction with other research teams of DECOVALEX-2023 Task G and validated in further study.

• Journal of Korean Society of Steel Construction
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• v.20 no.3
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• pp.377-387
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• 2008

The post-buckling behavior of slender members, such as the chord of truss structures generally implies extreme strength degradation. The buckling strength is usually determined as the performance of the compressed steel members, so it is important to understand the exact buckling behavior of a member in order to design the entire structure. A target analytical model is usually divided by beam or shell element when we simulate the buckling behavior of a compressed steel member such as atruss member. In this case, it is possible to accurately obtain the behavior, but such would be expensive and would require experience inanalysis even in monotonic loading. In this paper, we propose a consistent and convenient method to analyze the post-buckling behavior of elastoplastic compression members. The present methods are formulated to satisfy the second law of thermodynamics. Three numerical examples were tested to determine the validity of the proposed model in cyclic loading with comparable F.E.M results.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.2
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• pp.19-25
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• 2004

The linear analysis for the balance of linear momentum of a structure is relatively easy to perform, but the error becomes large when the structure experiences large deformation. Therefore, the material and geometric nonlinearity need to be considered for the precise calculations in that case. The plastic flow of a ductile steel-like metal mainly transforms its dissipated mechanical energy into heat, which transfers under the first and second law of thermodynamics. This heat increases the temperature of the material and the strength of the material decreases accordingly, which affects mechanical behavior of the given structure. This paper presents a finite-strain thermo-elasto-plastic steel model. This model can handle large deformation and thermal load simultaneously, which is common during earthquake periods. Two 3-dimensional finite element analyses verify this formulation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.11
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• pp.2008-2013
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• 2006

In numerical analysis on evaluating the thermal performance of the thermal equipment, numerical values of thermodynamic properties such as temperature, pressure, specific volume, enthalpy and entropy are required. But the steam table itself cannot be used without modelling. In this study applicability of neural networks in modelling the wide temperature range of wet saturated vapor region was examined. the multi-layer neural network consists of a input layer with 1 node, two hidden layers with 10 and 20 nodes respectively and a output layer with 6 nodes. Quadratic and cubic spline interpoations methods were also applied for comparison. Neural network model revealed similar percentage error to spline interpolation. From these results, it is confirmed that the neural networks could be powerful method in modelling the wide range of the steam table.

• Polymer(Korea)
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• v.29 no.2
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• pp.122-126
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• 2005

The effect of Al-MCM-41 preparation methods on the catalytic degradation of linear low density polyethylene (LLDPE) was investigated. Al-MCM-41 catalysts were synthesized by direct method (Al-MCM-41-D) and post treatment method (Al-MCM-41-P) and their characteristics were elucidated by XRD, BET, $NH_3\;TPD,\;^{27}Al$ MAS NMR. TGA kinetic analysis showed that the catalytic activation energies of Al-MCM-41-D and Al-MCM-41-P were 191.54 and 114.26 kJ/mol, respectively. The higher catalytic activity of Al-MCM-41-P would be attributed to its smaller pore size as well as higher number of acid sites that are accessible.

• Journal of the Korean Geotechnical Society
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• v.36 no.12
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• pp.125-132
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• 2020

Embedded joints in the rock mass are a major constituent influencing its mechanical behavior. Numerical analysis requires a rigorous modeling methodology for the rock mass with detailed information regarding joint properties, orientation, spacing, and persistence. This paper provides a mechanical model for a jointed rock mass based on the implicit joint-continuum approach. Stiffness tensors for rock mass are evaluated for an assemblage of intact rock separated by sets of joint planes. It is a linear summation of compliance of each joint sets and intact rock in the serial stiffness system. In the application example, kinematic analysis for a planar failure of rock slope is comparable with empirical daylight envelope and its lateral limits. Since the developed implicit joint-continuity model is formulated on a continuum basis, it will be a major tool for the numerical simulations adopting published plenteous thermal-hydro-chemical experimental results.

• Journal of the Korea Institute of Building Construction
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• v.20 no.1
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• pp.11-18
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• 2020

Carbon nanotubes are used in various industries with their excellent mechanical properties and electrical conductivity. In the construction industry, research is being conducted to give self-sensing capabilities to structures, but the results of experiments vary among researchers, and the analysis is insufficient. Therefore, in this study, the hydration and electrical properties of MWCNT-added cement pastes were measured. The electrical resistance values of hydration heat, porosity, Rietveld quantitative analysis, compressive strength, and distance were measured.. The heat resistance, porosity, Rietvelt quantitative analysis, compressive strength and distance were measured according to electrical resistance. Experimental results showed that the heat of hydration decreased with increasing MWCNT. XRD Rietveld quantitative analysis showed that there was no significant difference in the amount of hydration products with increasing addition rate of MWCNT. As a result of SEM analysis, the MWCNT is agglomerated by van der Waals forces, and this area is considered to be caused by voids and weak areas. The electrical resistance value decreases as the addition rate is increased, and thus may play a role for magnetic sensing in the future.

• Journal of the Korean Geographical Society
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• v.34 no.5
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• pp.473-491
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• 1999

세균성 이질은 국내 제1종 법정 전염병으로 분류되어 관리되고 있는 질환으로서 1998년 이후 그 발병 사례가 급속히 증가하고 있다. 본 연구는 1999년 3월 부산시 사상구에서 집단 발병한 세균성 이질을 대상으로 하여, 각 환자들의 발병 시점과 장소의 분포패턴에 대한 지리학적 고찰을 목적으로 한다. 환자분포의 특징적 공간패턴과 그들의 시계열적 확산 양상 등을 탐색하기 위한 방법론은 보건지리학과 지도학 및 공간통계학에 기반을 둔 공간분석기법을 중심으로 설정하였다. 분석자료는 해당 지역의 수치지형도, 지적도, 인구 센서스 자료를 포함한 GIS 데이터베이스로 구축되었다. 인구분포를 감안한 밀도구분도를 바탕으로 개별환자의 위치자료와 동 단위로 집계된 자료를 자료의 형태에 따라 분석기법을 달리하였으며, 환자 발생 밀도, 상대적 위험지수 등을 지도화하여 역학자료의 시각적 통계적 분석을 수행하였다. 환자분포의 공간적 중심위치와 분산의 변화 등 기술적 통계분석과 함께 제1차 공간속성을 커널추정법으로 찾아보았다. 이와 더불어 ‘공간적 의존성’과 관련된 제2차 공간속성은 K-함수와 시뮬레이션을 통해 분석하여 군집성 등이 통계적으로 확인되었다. 본 연구를 통해 역학조사시 GIS의 활용사례가 제시되었으며, 모집단 인구를 고려한 확률지도 작성 기법과 다양한 데이터 가시화 방법, 그리고 시계열별 발생 환자들의 지리적 변이를 분석 하는데 따르는 문제들이 논의되었다.