• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2004년도 봄 학술발표회 논문집
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• pp.301-308
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• 2004

The present study mainly focuses on the inelastic stress analysis of the 1/4 scale prestressed concrete containment vessel model(PCCV) under internal pressure and evaluates not only failure mode but also ultimate pressure capacity of the PCCV. Inelastic analysis is carried out 2D axisymmertic FE model and 3D FE model using four concrete material models which are Drucker-Prager Model, Chen-Chen Model, Damaged Plasticity Model and Menetrey-Willam Model. The uplift phenomenon of the basemat is considered in the 2D axisymmetric FE models. It is found from the 2D axisymmetric analysis results that both of Drucker-Prager model and Damaged Plasticity Model have a good performance and the uplift of the basemat is too small to influence on the global behavior of the PCCV. The FE analysis results on the ultimate pressure and failure mode have a good agreement with experimental results.

• Advances in aircraft and spacecraft science
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• 제6권2호
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• pp.169-187
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• 2019

This work presents a practical detailed finite element (FE) approach for the three-dimensional (3D) free-vibration analysis of actual aircraft and spacecraft-type lightweight and thin honeycomb sandwich panels. It consists of calling successively in $MATLAB^{(R)}$, via a developed user-friendly GUI, a detailed 3D meshing tool, a macrocommands language translator and a commercial FE solver($ABAQUS^{(R)}$ or $ANSYS^{(R)}$). In contrary to the common practice of meshing finely the faces and core cells, the proposed meshing tool represents each wall of the actual hexagonal core cells as a single two-dimensional (2D) 4 nodes quadrangularshell element or two 3 nodes triangular ones, while the faces meshes are obtained simply using the nodes at the core-faces interfaces. Moreover, as the same 2D FE interpolation type is used for meshing the core and faces, this leads to an automatic handling of their required FE compatibility relations. This proposed approach is applied to a sample made of very thin glass fiber reinforced polymer woven composite faces and a thin aluminum alloy hexagonal honeycomb core. The unknown or incomplete geometric and materials properties are first collected through direct measurements, reverse engineering techniques and experimental-FE modal analysis-based inverse identification. Then, the free-vibrations of the actual honeycomb sandwich panel are analyzed experimentally under different boundary conditions and numerically using different mesh basic cell shapes. It is found that this approach is accurate for the first few modes used for pre-design purpose.

• Journal of Magnetics
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• 제11권4호
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• pp.151-155
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• 2006

The electromagnetic engine valve actuator is a key technology to achieve variable valve timing in internal combustion engine and the steel core and clapper of the electromagnetic engine valve actuator are laminated to reduce the eddy current loss. To design and characterize the performance of the electromagnetic engine valve actuator, FE (finite element) analysis is the most effective way, but FE (finite element) 3-D modeling of real lamination needs very fine meshes resulting in countless meshes for modeling and numerous computations. In this paper, the equivalent FE 2-D model of electromagnetic engine valve actuator is introduced and FE analysis is performed using the equivalent FE 2-D model.

• 한국자기학회지
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• 제21권2호
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• pp.43-47
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• 2011

Fe-Al 계의 전이금속 화합물은 구조적 안정성과 자성에 대한 이견이 많은 것으로 알려져 있다. 본 연구에서는 B2, $L1_2$, 및 $D0_3$ 구조를 갖는 Fe-Al 계 화합물의 자성과 원자구조의 상관관계를 논의하기 위해 전전자 총퍼텐셜선형보강평면파(all-electron fullpotential linearized augmented plane wave; FLAPW) 방법을 이용하여 일반기울기 근사(generalized gradient approximation; GGA) 하에서 계산하였다. 고려한 모든 구조에서 강자성이 비자성에 비해 안정한 것으로 계산되었다. Fe 원자의 계산된 스핀 자기모멘트는 B2, $L1_2$ 구조에서 각각 0.771 ${\mu}_B$, 2.373 ${\mu}_B$의 값을 얻었고, $D0_3$ 구조의 Fe(I) 및 Fe(II) 원자들은 각각 2.409 ${\mu}_B$, 1.911 ${\mu}_B$로 계산 되었다. $Fe_3Al$의 같은 조성을 갖는 $L1_2$와 $D0_3$ 구조간의 안정성을 조사하기 위하여 형성 엔탈피 계산을 통해 강자성 상태에서 16 meV/atom의 에너지 차이로 $D0_3$ 구조가 $L1_2$ 구조보다 더 안정함을 확인하였다. 이 결과는 실험연구와 잘 일치하며, 원자구조와 전자구조의 분석을 통해 구조적 안정성과 자성에 대해 이해하였다.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제49권2호
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• pp.85-92
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• 2000

30 kVA rotating-field type Super-Conducting Generator is built and tested with intensive FE(Finite Element) analysis. The generator is driven by VVVF inverter-fed induction motor. Open Circuit Characteristic(OCC) and Short Circuit Characteristic(SCC) are presented in this paper. Also, the test result under the light load(up to 3.6 kW) are given. From the design stage, 2-D FE analysis coupled with the external circuit has been performed. The external circuit includes the end winding resistance and reactance as well as two dampers. When compared with the test data, the FE analysis results show a very good agreement.

• 한국자기학회지
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• 제21권2호
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• pp.56-60
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• 2011

준강자성체(ferrimagnet) $Fe_3O_4$를 기반 물질로 하여 주기율표 상에서 Fe와 인접한 전이금속 원소 T(= V, Cr, Mn)가 도핑된 삼원화합물($T_{0.2}Fe_{2.8}O_4$) 박막 시료들을 제작하여 그 광학적 성질을 1~8 eV 범위 내에서 분광타원해석법(spectroscopic ellipsometry)을 이용하여 측정하고 $Fe_3O_4$에서의 결과와 비교하였다. V, Cr, Mn 도핑 시 선호되는 스피넬(spinel) 구조 상의 양이온 자리(site) 및 이온수(ionicity)와 연관된 전자구조 상의 변화에 근거하여 삼원화합물과 $Fe_3O_4$의 흡수 스펙트럼 차이의 원인을 분석하였다. $Fe_3O_4$ 및 전이금속 도핑된 화합물들에서 관측된 광학적 흡수 스펙트럼은 주로 Fe 이온의 d 전자가 관련된 이온 간의 전하이동전이(charge-transfer transition)에 의하여 발생하는 에너지 폭이 넓은 흡수구조들의 기여에 의한 것으로 해석된다. 또한, 흡수 스펙트럼에서 관측된 좁은 에너지 폭의 구조들은 사면체 자리에 존재하는 $Fe^{3+}(d^5)$ 이온 내의 d 전자들에 의한 결정장 전이(crystal-field transition)에 기인한 것으로 해석된다. 이와 같은 전이들과 관련된 전자상태들을 스핀편극된 $Fe_3O_4$ 전자구조를 토대로 기술하였다.

• 소성∙가공
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• 제15권4호
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• pp.319-325
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• 2006

The laser forming process is a new flexible forming process without forming tools and external force, which is applied to various fields of industry. Especially, applications of the laser forming process focused on cutting, welding and marking process. In this paper, the laser bending process of sheet metal which is heated by laser beam and formed by internal stress is simulated by using thermo elastic-plastic analysis model. Based on the result of FE-analysis, the laser bending machine is made to obtain reliable data for sheet bending. Under the same condition as FE-analysis, the laser bending experiment has been performed to ver 펴 the result of FE-analysis and good agreement has been obtained between FE-analysis and experiments. Additional laser bending experiments have been performed to evaluate the laser bending machine.

• Corrosion Science and Technology
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• 제11권1호
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• pp.9-14
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• 2012

The formation of the Fe-Al inhibition layer in hot-dip galvanizing is a confusing issue for a long time. This study presents a characterization result on the inhibition layer formed on C-Mn-Cr and C-Mn-Si dual-phase steels after a short time galvanizing. The samples were annealed at $800^{\circ}C$ for 60 s in $N_{2}$-10% $H_{2}$ atmosphere with a dew point of $-30^{\circ}C$, and were then galvanized in a bath containing 0.2 %Al. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) was employed for characterization. The TEM electron diffraction shows that only $Fe_{2}Al_{5}$ intermetallic phase was formed. No orientation relationship between the $Fe_{2}Al_{5}$ phase and the steel substrate could be identified. Two peaks of Al 2p photoelectrons, one from metallic aluminum and the other from $Al^{3+}$ ions, were detected in the inhibition layer, indicating that the layer is in fact a mixture of $Fe_{2}Al_{5}$ and $Al_{2}O_{3}$. TEM/EDS analysis verifies the existence of $Al_{2}O_{3}$ in the boundaries of $Fe_{2}Al_{5}$ grains. The nucleation of $Fe_{2}Al_{5}$ and the reduction of the surface oxide probably proceeded concurrently on galvanizing, and the residual oxides prohibited the heteroepitaxial growth of $Fe_{2}Al_{5}$.

• 소성∙가공
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• 제16권2호
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• pp.126-131
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• 2007

Voids in a large rotor are formed in solidification process of a cast ingot. The voids have to be eliminated from the rotor by a forming process, because they would became stress-intensity factors which suddenly fracture the rotor in the operation. Previous studies on void-elimination of a large rotor have mainly focused on finding the process variables affecting the void-closure. But the study on the amount of void closure in a large rotor has been very rare. This study was performed to obtain an equation which predicts the amount of void-closure in a forging process of a large rotor and to evaluate the availability of the void-closure equation through finite element analyses. Firstly, 2D FE analysis was carried out to find effects of time integral of hydrostatic stress and effective strain on void volume rate of a large rotor in the upsetting process for various diameters and shapes of void, and material temperature. From the 2D FE analysis, we found that effective strain was suitable for predicting the void-closure of a large rotor, because there was a constant relationship between void volume rate and effective strain. And a void-closure equation was proposed fur predicting void-closure of a large rotor in the upsetting process. Finally, ken the 3D FE analysis, the proposed void-closure equation was verified to be useful for upsetting and cogging processes.

• 박물관보존과학
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• 제23권
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• pp.71-90
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• 2020

전쟁기념관에서 소장하고 있는 등록문화재 제666호 F-51D 무스탕 전투기의 과학적 분석을 진행하였다. F-51D 무스탕 전투기는 1950년 6월 25일 전쟁이 발발하자, 7월 2일 우리 공군이 미국으로부터 인수해 최초로 운용한 전투기이다. 전쟁기간 동안 북한군을 상대하여 괄목할 만한 작전을 펼친 한국 공군의 주력기이다. 본 연구 대상은 6·25전쟁 당시 직접 사용된 기체로 현재까지 과학적 조사·분석이 이루어지지 않았으며 차후 해체 및 복원을 계획하고 있다. 지속적인 옥외 전시로 인해 도료층 및 캐노피가 변색되었으며 도료의 박락 및 균열 또한 확인되었다. 비파괴 과학적 분석을 통해 대형유물의 해체 및 복원의 기초 자료로 활용하고자 한다. P-XRF를 사용하여 적색, 청색, 황색, 백색, 흑색, 회색을 중심으로 안료 성분 분석을 진행하였고, 전투기에 사용된 도료의 수지 성분을 확인하기 위해 적외선 분광 분석(FT-IR-ATR)을 하였다. 몸체, 날개, 꼬리날개에 사용된 금속의 성분 분석도 함께 진행하였다. 안료 성분 분석은 적색 산화철인 벵가(Fe₂O₃), 프탈로시아닌 블루계 등의 유기안료, 황색의 황연(PbCrO₄), 백색의 티타늄화이트(TiO₂), 흑색의 철흑(Fe₃O₄), 회색의 철흑(Fe₃O₄)+티타늄화이트(TiO₂)가 확인되었다. 전투기 외부 도장에 사용된 수지는 주로 Alkyd 수지를 사용한 것으로 확인되었으며 청색의 경우 Acryl 수지를 이용하여 도장 한 것으로 추정된다. 전투기 캐노피는 투명성과 내광성이 우수한 Poly methyl methacrylate(PMMA)로 확인되었다. 전투기 몸체, 날개, 꼬리날개에서 모두 알루미늄(Al)이 주성분으로 검출되었다. 꼬리날개부 후면부의 경우 철-아연 도금(함석)이 사용된 것을 보아 과거 복원부인 것으로 판단되었다.