• 자원환경지질
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• 제40권2호
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• pp.209-221
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• 2007

본 연구에서는 중금속으로 오염된 토양이나 자갈을 댐 축조 재료로 사용할 경우 주변 환경에 미치는 영향을 파악하기 위하여 댐 침투수와 오염물 거동에 대한 수치 모의를 실시하였다 두 가지 상용 프로그램(SEEP2D 와 FEMWATER)을 이용하여 침투수 분석을 수행하였으며, 결과를 상호 비교 분석함으로써 수치 모의의 신뢰성을 획득하였다. 특히 오염된 댐 축조재료로 인한 환경적 안정성을 검토하기 위하여 세 가지 시나리오, 즉 댐체에 균열이 없는 경우(시나리오 1), 댐의 차수벽 역할을 하는 표면 콘크리트 슬래브 상부에 균열이 발생하는 경우(시나리오 2), 댐체 하부 즉 프린스와 콘크리트 슬래브와 접촉부에 균열이 발생하는 경우(시나리오 3)에 대하여 각각 수치 모의를 실시하였다. 침투수 해석 결과, 슬래브 상부에 균열이 있는 경우, 즉 시나리오 2에서 계산된 단위폭당 침투수량은 $14.311\sim14.924m^3/day$으로 다른 경우에 비해 약 1,000배 큰 값을 보였다. 또한 FEMWATER프로그램을 사용하여 오염물 거동을 수치모의하였다. 오염물질이 지속적으로 침출되어 나오는 상황을 고려하여 주축조구역은 농도 13ppb가 지속적으로 유지되도록 초기조건을 설정하였다. 오염물 거동분석 결과 시나리오 1에서 2ppb 정도의 오염물이 댐체 하류 부분에 도달하는데 걸리는 시간은 최소 55,000년이었으며, 시나리오 2의 경우 약 50년 정도, 마지막으로 시나리오 3의 경우 27,000년이였다. 댐체 상부에 균열이 발생한 경우는 댐에 균열이 발생하지 않은 경우보다 약 500배 이상 빠른 유속이 나타나기 때문에 오염물도 균열이 발생하지 않은 경우에 비해 상당히 빠르게 퍼져나가는 것을 확인할 수 있었다. 결론적으로 슬래브 상부에 균열이 발생한 경우 100년 이내에 댐체 하부천 2ppb 이상의 오염물이 전달될 가능성이 있음을 확인하였지만, 균열이 없거나 슬래브 하부에 균열이 발생한 경우에는 오염물이 외부로 이동될 가능성이 거의 없었다. 따라서 콘크리트 슬래브에 대한 지속적인 유지 관리로 균열 발생을 적절히 제어할 수 있다면, 본 연구에서 제안한 오염된 사력재의 CFRD 내부 축조재료로의 활용은 고려 가능한 대안이 될 수 있을 것으로 판단된다.

• Restorative Dentistry and Endodontics
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• 제39권4호
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• pp.276-281
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• 2014

Objectives: The purpose of this study was to compare the cutting efficiency of a newly developed microprojection tip and a diamond-coated tip under two different engine powers. Materials and Methods: The apical 3 mm of each root was resected, and root-end preparation was performed with upward and downward pressure using one of the ultrasonic tips, KIS-1D (Obtura Spartan) or JT-5B (B&L Biotech Ltd.). The ultrasonic engine was set to power-1 or -4. Forty teeth were randomly divided into four groups: K1 (KIS-1D / Power-1), J1 (JT-5B / Power-1), K4 (KIS-1D / Power-4), and J4 (JT-5B / Power-4). The total time required for root-end preparation was recorded. All teeth were resected and the apical parts were evaluated for the number and length of cracks using a confocal scanning micrscope. The size of the root-end cavity and the width of the remaining dentin were recorded. The data were statistically analyzed using two-way analysis of variance and a Mann-Whitney test. Results: There was no significant difference in the time required between the instrument groups, but the power-4 groups showed reduced preparation time for both instrument groups (p < 0.05). The K4 and J4 groups with a power-4 showed a significantly higher crack formation and a longer crack irrespective of the instruments. There was no significant difference in the remaining dentin thickness or any of the parameters after preparation. Conclusions: Ultrasonic tips with microprojections would be an option to substitute for the conventional ultrasonic tips with a diamond coating with the same clinical efficiency.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.143-148
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• 2003

This paper provides two types of engineering J estimation equations for cylinders with finite internal axial surface cracks under internal pressure. The first type is the so-called GE/EPRI type J estimation equation based on Ramberg-Osgood materials. Based on detailed 3-D FE results the GE/EPRI-type J estimation equation along the crack front is proposed and validated for Ramberg-Osgood materials. For more general application, the developed GE/EPRI-type solutions are then re-formulated based on the reference stress concept. The proposed reference stress based J estimation equation has good agreement between the FE results and the proposed reference stress based J estimation provides confidence in the use of the proposed method for elastic-plastic fracture mechanics of pressurised piping

• Computers and Concrete
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• 제12권4호
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• pp.443-498
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• 2013

A detailed finite element modeling is presented for the simulation of the nonlinear behavior of reinforced concrete structures which manages to predict the nonlinear behavior of four different experimental setups with computational efficiency, robustness and accuracy. The proposed modeling method uses 8-node hexahedral isoparametric elements for the discretization of concrete. Steel rebars may have any orientation inside the solid concrete elements allowing the simulation of longitudinal as well as transverse reinforcement. Concrete cracking is treated with the smeared crack approach, while steel reinforcement is modeled with the natural beam-column flexibility-based element that takes into consideration shear and bending stiffness. The performance of the proposed modeling is demonstrated by comparing the numerical predictions with existing experimental and numerical results in the literature as well as with those of a commercial code. The results show that the proposed refined simulation predicts accurately the nonlinear inelastic behavior of reinforced concrete structures achieving numerical robustness and computational efficiency.

• 한국컴퓨터정보학회:학술대회논문집
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• 한국컴퓨터정보학회 2021년도 제64차 하계학술대회논문집 29권2호
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• pp.363-366
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• 2021

본 연구에서는 콘크리트의 균열을 추출하여 추출한 균열을 분석하고 시각화하여 나타내는 방법을 제안한다. 추출한 균열을 분석하여 길이, 넓이, 평균 폭 등의 주요 지표를 측정하여 균열 부위에 대한 세부 정보를 파악할 수 있게 하였다. 특히 균열 분석 과정에서 기존의 균열 중심부와 에지 간의 직선 최단 거리 계산을 통한 균열 폭 측정 방식이 아닌 내접원 탐색 방식을 적용하여 다각형의 균열에 대한 폭 측정 방식을 제안하고 있다. 또한 분석 결과를 Wavefront 3D OBJ 모델과 CAD 파일로 생성하였고, 이를 웹 브라우저를 통해 입체적으로 볼 수 있도록 시각화 하였다.

• Design & Manufacturing
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• 제6권2호
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• pp.64-69
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• 2012

This study looks at plastic mold design for robots and mold manufacture, which is an injection mold branch at The Korea-China-Japan University Grand Prize Contest. Product analysis and layout, molding analysis, and upper and lower core design are carried out to design molds in 2D and 3D. After the design of the cores, NC machining software is used for simulation before actual manufacture. Before the production of end-product, test injection is done to troubleshoot problems like bad dimensions, burr, cracks and stepped pulley.

• 한국환경과학회지
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• 제16권10호
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• pp.1169-1177
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• 2007

The main objective of this research was to evaluate the effects of process variables which were forming ability, flow displacement, effective stress, effective strain, fluid vector and products defects on manufactured artificial lightweight aggregate made of both incinerated sewage sludge ash and clay by means of the numerical analysis of a rigid-plastic finite element method. CATIA (3D CAD program) was used for an extrusion metal mold design that was widely used in designing aircraft, automobile and metallic molds. A metal forming analysis program (ATES Co.) had a function of a rigid-plastic finite element method was used to analyze the program. The result of extrusion forming analysis indicated clearly that a shape retention of the manufactured artificial light-weight aggregate could be maintained by increasing the extrusion ratio (increasing compressive strength inside of extrusion die) and decreasing the die angle. The stress concentration of metal mold was increased by increasing an extrusion ratio, and it was higher in a junction of punch and materials, friction parts between a bottom of the punch and inside of a container, a place of die angle and a place of die of metal mold. Therefore, a heat treatment as well as a rounding treatment for stress distribution in the higher stress concentration regions were necessary to extend a lifetime of the metallic mold. A deformity of the products could have made from several factors which were a surface crack, a lack of the shape retention and a crack of inside of the products. Specially, the surface crack in the products was the most notably affected by the extrusion ratio.

• 한국산학기술학회논문지
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• 제14권8호
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• pp.4048-4057
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• 2013

부모멘트를 받는 합성보 슬래브에서 인장균열 발생과 균열의 진행에 따른 슬래브의 강성저하가 전단연결부의 합성거동에 미치는 영향을 실험적으로 분석하기는 매우 어렵다. 본 논문에서는 부모멘트를 받는 합성보에서 콘크리트 슬래브 및 강재 보, 스터드를 포함한 전단연결부 등의 형상과 물성을 최대한 실제와 유사하게 모델링하는 기법을 이용함으로써, 부재 간 합성작용을 해석할 수 있는 3차원 유한요소모델을 개발하였다. 개발된 3차원 유한요소모델을 이용하여 부모멘트 구간에 설치되는 합성보의 전체 휨거동 및 기존의 1차원 또는 2차원 모델로는 해석이 어려운 전단합성작용을 분석할 수 있었다. 해석결과에 따르면 부모멘트를 받는 합성보에서의 전단연결부 거동은 철근콘크리트 슬래브의 철근비 및 인장 균열거동에 지배를 받게 됨을 알 수 있었다. 전단연결부의 하중-슬립 관계를 검토해 본 결과, 전단연결부의 슬립강성은 슬래브의 초기균열 및 철근의 항복이 발생한 시점을 기준으로 변화됨을 알 수 있었다. 또한, 구간별로 합성율이 100% 미만으로 설계되는 부분합성 설계가 합성설계의 효율성 측면에서 더 유리할 수 있다는 기존의 실험적 연구결과를 간접적으로 확인할 수 있었다.

• 한국정밀공학회지
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• 제28권6호
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• pp.738-744
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• 2011

The reliability of blade root fixing section is required to endure the centrifugal force and vibration stress for the last stage blade of steam turbine in thermal power plant. Most of the domestic steam turbine last stage blades have finger type roots. The finger type blade is very complex, so the inspection had been performed only on the exposed fixing pin cross-section area due to the difficulty of inspection. But the centrifugal force and vibration stress are also applied at the blade root finger and the crack generates, so the inspection method for finger section is necessary. For the inspection of root finger, inspection points were decided by simulating ultra-sonic path with 3D modeling, curve-shape probe and fixing jig were invented, and the characteristics analysis method of ultrasonic reflection signal and defect signal disposition method were invented. This invented method was actually executed at site and prevented the blade liberation failure by detecting the cracks at the fingers. Also, the same type blades of the other turbines were inspected periodically and the reliability of the turbine increased.

• 대한기계학회논문집A
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• 제26권1호
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• pp.139-146
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• 2002

This paper provides validations of the reference stress based J and $C^{*}$ estimations, proposed in Part I, for inner, circumferential surface cracked pipes under internal pressure and global bending against detailed 3-D elastic-plastic and elastic-creep FE results. For this purpose, actual tensile properties of two typical stainless steels (TP304 and TP316) are used for elastic-plastic FE analyses and two realistic creep laws are used for elastic-creep FE analyses. For a total of twenty cases considered in this paper, agreements between the proposed reference stress based J and $C^{*}$ estimations and the FE results are excellent. More important aspect of the proposed estimations is that they can be used to estimate J and $C^{*}$ not only at the deepest point of the surface crack but also at an arbitrary point along the crack front.front.