• Smart Structures and Systems
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• 제14권5호
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• pp.811-830
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• 2014

A numerical study has been carried out to simulate an innovative monitoring procedure to detect and localize damage in reinforced concrete beams retrofitted with carbon fiber reinforced polymer (CFRP) unidirectional laminates. The main novelty of the present simulation is its ability to conduct the electromechanical admittance monitoring technique by considerably compressing the amount of data required for damage detection and localization. A FEM simulation of electromechanical admittance-based sensing technique was employed by applying lead zirconate titanate (PZT) transducers to acquire impedance spectrum signatures. Response surface methodology (RSM) is finally adopted as a tool for solving inverse problems to estimate the location and size of damaged areas from the relationship between damage and electromechanical admittance changes computed at PZT transducer surfaces. This statistical metamodel technique allows polynomial models to be produced without requiring complicated modeling or numerous data sets after the generation of damage, leading to considerably lower cost of creating diagnostic database. Finally, a numerical example is carried out regarding a steel-reinforced concrete (RC) beam model monotonically loaded up to its failure which is also retrofitted by a CFRP laminate to verify the validity of the present metamodeling monitoring technique. The load-carrying capacity of concrete is predicted in the present paper by utilizing an Ottosen-type failure surface in order to better take into account the passive confinement behavior of retrofitted concrete material under the application of FRP laminate.

• 분석과학
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• 제24권2호
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• pp.85-93
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• 2011

국내에서는 건물의 화재 방지를 위하여 인증된 내화뿜칠재를 사용하도록 규정되어 있다. 하지만 일부 현장에서는 성능이 없는 흡음뿜칠재을 사용함으로 해서 내화구조 부실시공의 원인이 되고 있다. 따라서 성능이 인정된 내화 뿜칠재와 일반 흡음뿜칠재를 현장에서 분석하여 적정 시공 여부를 확인하는 방법을 제시하고자 한다. 이에 본 연구에서는 성능이 인정된 내화 뿜칠재 9종과 정상 내화 뿜칠재 및 내화성능이 없는 일반 흡음뿜칠재 3종을 비교 측정하였다. 측정하기 전에 분석시료를 대상으로 mill을 사용하여 powder로 전처리를 하였으며 현장에 접근성이 용이한 NIR을 사용하였다. 측정은 NIR중에서 FTNIR을 사용하였으며, 측정 모듈은 적분구(integrating sphere)를 사용하여 측정하였다. 이 측정된 흡수 스펙트럼은 통계 처리 방법 중에서 주성분 분석법인 PCA 기법으로 분석함으로 해서 정상과 비정상 내화뿜칠재를 판별이 가능 함을 확인하였다.

• 한국철도학회논문집
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• 제17권1호
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• pp.79-85
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• 2014

본 논문은 도시형 신교통시스템 도입 계획단계에서 적정 신교통시스템을 용이하게 선정하기 위해 대중교통수단의 다양한 특성들에 대한 중요도를 고려하는 평가기법을 제시하고 있다. 이 기법은 대중교통수단의 특성을 이용자 영향요인, 지역사회 영향요인, 정부 및 운영자 영향요인으로 구분하여 총 12개의 평가항목을 설정하고, 이에 대한 중요도를 분석하여 신교통시스템을 평가하는 기법이다. 실증적 분석을 위해 AHP 기법을 이용하여 중소도시의 간선형 신교통시스템에 대한 가중치를 조사하여 평가를 시행한 결과, 중요도는 안전성, 신속 및 정시성, 편리성, 지역활성화 순으로, 우선순위는 철재차륜 AGT, LIM, 고무차륜 AGT 순으로 분석되었다.

• Steel and Composite Structures
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• 제35권3호
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• pp.439-447
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• 2020

This paper presents two sets of full three-dimensional thermoelastic finite element analyses of superimposed thermo-mechanically loaded Spar Wingskin Joints made with laminated Graphite Fiber Reinforced Plastic composites. The study emphasizes the influence of residual thermal stresses and material anisotropy on the inter-laminar delamination behavior of the joint structure. The delamination has been pre-embedded at the most likely location, i.e., in resin layer between the top and next ply of the fiber reinforced plastic laminated wingskin and near the spar overlap end. Multi-Point Constraint finite elements have been made use of at the vicinity of the delamination fronts. This helps in simulating the growth of the embedded delamination at both ends. The inter-laminar thermoelastic peel and shear stresses responsible for causing delamination damage due to a combined thermal and a static loading have been evaluated. Strain energy release rate components corresponding to the Mode I (opening), Mode II (sliding) and Mode III (tearing) of delamination are determined using the principle of Virtual Crack Closure Technique. These are seen to be different and non-self-similar at the two fronts of the embedded delamination. Residual stresses developed due to the thermoelastic anisotropy of the laminae are found to strongly influence the delamination onset and propagation characteristics, which have been reflected by the asymmetries in the nature of energy release rate plots and their significant variation along the delamination front.

• Nuclear Engineering and Technology
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• 제27권1호
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• pp.74-83
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• 1995

원자로 압력용기에서의 정화한 속중성자 조사량의 계산은 발전소 압력용기 surveillance program의 핵심적인 부문이다. 최근 기존의 ENDF /B-III~V에 있는 철의 핵단면적 자료가 압력용기와 같은 철이 포함된 구조물에서 속중성자속을 낮게 평가하는 것으로 알려지고 있다. 본 논문에서는 ENDF /B-IV와 VI의 철(Fe) 자료의 비교를 위해 영광3/4호기 모델과 2개의 ENDF/B 파일에 있는 각각의 철자료를 이용하여 47-에너지그룹 핵단면적집 (CXFe-IV와 CXFe-VI )을 만들었다. CXFe-IV와 CXFe-VI를 사용하여 수행한 DOT4.3 계산결과에 의하면 압력용기 취화해석에 중요한 속중성자속(E 〉 1.0 MeV) 계산에서 ENDF /B-VI의 철자료를 사용한 경우가 ENDF /B-IV의 철자료를 사용한 경우보다 압력용기 내부표면에서 7.6%, 외부표면에서 20% 높게 나타났다.

• 한국건설관리학회논문집
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• 제15권4호
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• pp.30-38
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• 2014

시공성에 대한 연구는 활발히 진행되어 왔으며 시공성이 공기, 원가, 품질, 생산성을 높인다고 다양한 연구에서 언급하고 있다. 그러나 실제 시공성이 생산성에 미치는 영향을 정량적으로 분석한 연구는 사례조사나 설문을 통한 결과가 대부분이여서 미흡한 실정이다. 또한 시공성에 관한 연구가 세부 특정 공정의 시공성을 높이기 위한 것들이 대부분이여서 다양한 공종에 적용하기에는 다소 hard하다고 할 수 있다. 따라서 본 논문은 시공성에 영향을 주는 인자들을 도출하고 이 요인들이 각 공종의 시공성에 미치는 영향도를 분석한 후 실제 공사 데이터를 가지고 시공성 요인이 생산성에 미치는 영향을 검증하여 기존 연구에 대한 뒷받침이 되고자 한다.

• Nuclear Engineering and Technology
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• 제31권5호
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• pp.486-497
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• 1999

The local heat transfer coefficient is experimentally investigated for the reflux condensation in a countercurrent flow between the steam-air mixture and the condensate, A single vertical tube has a geometry which is a length of 2.4m, inner diameter of 16.56mm and outer diameter of 19.05mm and is made of stainless steel. Air is used as a noncondensible gas. The secondary side has a shape of annulus around vertical tube and the lost heat by primary condensation is transferred to the coolant water. The local temperatures are measured at 11 locations in the vertical direction and each location has 3 measurement points in the radial direction, which are installed at the tube center, at the outer wall and at the coolant side. In three different pressures, the 27 sets of data are obtained in the range of inlet steam flow rate 1.348∼3.282kg/hr, of inlet air mass fraction 11.8∼55.0%. The investigation of the flooding is preceded to find the upper limit of the reflux condensation. Onset of flooding is lower than that of Wallis' correlation. The local heat transfer coefficient increases as the increase of inlet steam flow rate and decreases as the increase of inlet air mass fraction. As an increase of the system pressure, the active condensing region is contracted and the heat transfer capability in this region is magnified. The empirical correlation is developed by 165 data of the local heat transfer. As a result, the Jacob number and film Reynolds number are dominant parameters to govern the local heat transfer coefficient. The rms error is 17.7% between the results by the experiment and by the correlation.

• 대한기계학회논문집
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• 제12권5호
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• pp.935-943
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• 1988

본 연구에서는 유압벌지시험기를 이용한 저속 벌지시험과 낙하해머(drop hammer)를 응용한 충격벌지시험기를 제작, 사용하여 충격벌지시험을 하여 저속변형과 충격변형에서 판재금속의 성형한계선도를 구하고 변형율속도가 판재의 불안정 및 성형 성에 미치는 영향을 조사하고 다이의 형상비(단축/장축)를 0.5, 0.75, 1.0 등으로 달 리하여 실험하므로써 변형경로에 따른 한계변형율의 변화를 관찰하고 아울러 기존의 성형한계이론과 비교, 검토하였다.

• Nuclear Engineering and Technology
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• 제54권10호
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• pp.3855-3863
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• 2022

An evaluation of the radiation shielding performance of high-Z-particle-loaded polylactic acid (PLA) composite materials was pursued. Specimens were produced via fused deposition modeling (FDM) using copper-PLA, steel-PLA, and BaSO₄-PLA composite filaments containing 82.7, 75.2, and 44.6 wt% particulate phase contents, respectively, and were tested under broad-band flash x-ray conditions at the Sandia National Laboratories HERMES III facility. The experimental results for the mass attenuation coefficients of the composites were found to be in good agreement with GEANT4 simulations carried out using the same exposure conditions and an atomistic mixture as a model for the composite materials. Further simulation studies, focusing on the Cu-PLA composite system, were used to explore a shield design parameter space (in this case, defined by Cu-particle loading and shield areal density) to assess performance under both high-energy photon and electron fluxes over an incident energy range of 0.5-15 MeV. Based on these results, a method is proposed that can assist in the visualization and isolation of shield parameter coordinate sets that optimize performance under targeted radiation characteristics (type, energy). For electron flux shielding, an empirical relationship was found between areal density (AD), electron energy (E), composition and performance. In cases where ${\frac{E}{AD}}{\geq}2MeV{\bullet}cm{\bullet}g^{-1}$, a shield composed of >85 wt% Cu results in optimal performance. In contrast, a shield composed of <10 wt% Cu is anticipated to perform best against electron irradiation when ${\frac{E}{AD}}<2MeV{\bullet}cm{\bullet}g^{-1}$.

• Steel and Composite Structures
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• 제42권6호
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• pp.779-789
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• 2022

This work presents a non-linear cylindrical bending analysis of functionally graded plate reinforced by single-walled carbon nanotubes (SWCNTs) in thermal environment using a simple integral higher-order shear deformation theory (HSDT). This theory does not require shear correction factors and the transverse shear stresses vary parabolically through the thickness. The material properties of SWCNTs are assumed to be temperature-dependent and are obtained from molecular dynamics simulations. The material properties of functionally graded carbon nanotube-reinforced composites (FG-CNTCRs) are considered to be graded in the thickness direction, and are estimated through a micromechanical model. The non-linear strain-displacement relations in the Von Karman sense are used to study the effect of geometric non-linearity and the solution is obtained by minimization of the total potential energy. The numerical illustrations concern the nonlinear bending response of FG-CNTRC plates under different sets of thermal environmental conditions, from which results for uniformly distributed CNTRC plates are obtained as benchmarks.