• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.397-397
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• 2013

The electrical, electronic, optical properties and the local structure of Nickel Oxide (NiO) thin film have been investigated by X-ray photoelectron spectroscopy (XPS), Reflection Electron Energy Loss Spectroscopy (REELS), UV-spectrometer,Hall Effect measurement and X-ray absorption spectroscopy (XAS). The XPS results show that the Ni 2p spectra for all films consist of $Ni2p_{3/2}$ at around 854.5 eV which indicate the presence of Ni-O bond from NiO phase and for the annealed film at temperature above $200^{\circ}C$ shows the coexist Ni oxide and Ni metal phase. The REELS spectra showed that the band gaps of the NiO thin films were abruptly decreased with increasing temperature. The values of the band gaps are consistent with the optical band gaps estimated by UV-Spectrometer. The optical transmittance spectra shows that the transparency of NiO thin films in the visible light region was deteriorated with higher temperature due to existence of $Ni^0$. Hall Effect measurement suggest that the NiO thin films prepared at relatively low temperatures (RT and $100^{\circ}C$) are suitable for fabricating p-type semiconductor which showed that the best properties was achieved at $100^{\circ}C$, such as a low resistivity of $7.49{\Omega}.cm$. It can be concluded that the annealing process plays a crucial role in converting from p type to n type semiconductor which leads to reducing electrical resistivity of NiO thin films. Furthermore, the extended X-ray absorption fine structure (EXAFS) spectrum at the Ni K-edge was used to address the local structure of NiO thin films. It was found that the thermal treatments increase the order in the vicinity of Ni atom and lead the NiO thin films to bunsenite crystal structure. Moreover, EXAFS spectra show in increasing of coordination number for the first Ni-O shell and the bond distance of Ni-O with the increase of substrate temperature.

• 한국항공우주학회지
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• 제39권11호
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• pp.1005-1012
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• 2011

본 연구에서는 기하학적 비선형 후좌굴해석 및 전역-국지해석을 통하여 얇은 막재에서 주름이 파괴거동에 미치는 영향을 연구하였다. 해석에서 양단노치 및 일단노치를 가지는 사각형 인장시험 시편형상을 고려하였으며 주름이 발생한 경우와 억제된 경우에 대해 각각 해석을 수행하여 그 결과를 비교하였다. 해석결과의 분석을 통하여 주름의 발달에 따라 J-적분값의 변화에 미치는 영향을 조사하였고, 컷 길이에 따른 영향 및 시편형상의 길이 효과에 대해 체계적으로 연구하였다.

• 한국항공우주학회지
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• 제40권5호
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• pp.423-430
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• 2012

본 논문에서는 기하학적 비선형 후좌굴 유한요소 해석을 통하여 얇은 멤브레인에서 주름 발생이 컷의 진전방향에 미치는 영향을 연구하였다. 해석에는 양단에 인장을 받고 있고 중앙에 기울어진 컷을 가진 직사각형 멤브레인을 고려하였다. 주름이 발생한 경우와 주름이 발생하지 않은 경우에 대해 각각 해석을 수행하여 컷의 진전각도 및 $J$-적분값을 비교하였다. 컷의 진전각도는 에너지 방출률이 최대인 방향, $K_{II}$의 값이 0이 되는 방향을 구하는 방법 및 접선응력이 최대인 방향을 구하는 방법을 사용하여 계산하였다. 또한 다양한 컷의 초기방향각을 고려하여 각도에 따른 주름의 영향을 조사하였으며 가상의 미소크기의 컷을 반복적으로 진전시켜 컷이 전파되는 경향도 알아보았다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2005년도 추계학술대회 논문집
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• pp.229-234
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• 2005

Thin-walled multicell box girders subjected to an eccentric load can he produced the three global behaviors of flexure, torsion, and distortion. Specially in railway bridges subjected to much eccentric load, it is quite important to evaluate influences of torsion and distortion. But it is very difficult to evaluate each influences of major behaviors numerically. If we can decompose an eccentric load P into flexural, torsional, and distortional forces. we can execute quantitative analysis each influences of major behaviors. Decomposition of Applied Load for Thin-walled Rectangular multi-cell box girders is reserched by Park, Nam- Hoi(Development of a multicell Box Beam Element Including Distortional Degrees of Freedom, 2003). But researches about trapezoidal multi-cell section is insufficient. So, this paper deals with multi-cell trapezoidal box girders. An expanded method, which is based on the force decomposition method for a single cell box girder given by Nakai and Yoo, is developed herein to decompose eccentric load Pinto flexural, torsional, and distortional forces. Derive formulas by decomposition of eccentric load is verified by 3D shell-modelling numerical analysis.

• 한국공간구조학회논문집
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• 제10권4호
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• pp.123-132
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• 2010

본 연구에서는 비대칭 단면을 갖는 박벽 곡선보의 자유진동 및 처짐해석을 위하여 박벽단면을 갖는 기존의 곡선보 이론의 단점을 보완하고자 도심-전단중심 정식화에 근거한 개선된 곡선보 이론을 제시한다. 변위장은 각각 도심과 전단중심에서 정의한 변위파라미터를 도입하여 나타내었으며 곡선보의 두께-곡률 효과와 회전관성효과를 고려한 개선된 변형에너지와 운동에너지를 엄밀하게 유도하였다. 본 연구의 타당성과 정확성을 증명하기 위하여 Hermitian 곡선보요소를 사용한 유한요소해석을 수행하였으며 해석 결과들을 도심 정식화에 의하여 산정한 결과, 선행 연구자 결과 및 ABAQUS의 쉘요소를 이용한 결과와 비교하였다.

• Steel and Composite Structures
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• 제6권5호
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• pp.401-415
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• 2006

Based on a non-linear model taking into account flexural-torsional couplings, analytical solutions are derived for lateral buckling of simply supported I beams under some representative load cases. A closed form is established for lateral buckling moments. It accounts for bending distribution, load height application and pre-buckling deflections. Coefficients $C_1$ and $C_2$ affected to these parameters are then derived. Regard to well known linear stability solutions, these coefficients are not constant but depend on another coefficient $k_1$ that represents the pre-buckling deflection effects. In numerical simulations, shell elements are used in mesh process. The buckling loads are achieved from solutions of eigenvalue problem and by bifurcations observed on non linear equilibrium paths. It is proved that both the buckling loads derived from linear stability and eigenvalue problem lead to poor results, especially for I sections with large flanges for which the behaviour is predominated by pre-buckling deflection and the coefficient $k_1$ is large. The proposed solutions are in good agreement with numerical bifurcations observed on non linear equilibrium paths.

• 한국자동차공학회논문집
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• 제14권5호
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• pp.100-106
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• 2006

NiTi alloy known as its shape memory effect also has superelastic characteristic, which makes it possible to be elastic under large deformation. Since the tensile strength of the alloy is very high and density is low compared to carbon steel, it can be applied to lightweight structural design. In order to design structures with shape memory alloy, finite element analysis is used and a constitutive algorithm based on Aurrichio's model is added to LS-DYNA as a user subroutine. Explicit time integration and shell element formulation are used to simulate thin-walled structures. The algorithm uses Drucker-Prager type loading condition to calculate martensite volume fraction during the transformation. The implemented algorithm is verified in uni-axial loading condition and martensite phase transformation can be detected well with the algorithm. In this study, as a energy absorbing structure, thin-walled tube is modeled with finite elements and the deformation behavior is studied. Simulation results has shown that the martensite transformation was generated in loading condition. After plastic deformation reached, the load decreases linearly without reverse martensite transformation.

• Structural Engineering and Mechanics
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• 제41권3호
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• pp.313-337
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• 2012

A three-dimensional formulation is proposed to analyze the lateral loading distribution of external actions in high-rise buildings. The method is extended to encompass any combination of bracings, including bracings with open thin-walled cross-sections, which are analyzed in the framework of Timoshenko-Vlasov's theory of sectorial areas. More in detail, the proposed unified approach is a tool for the preliminary stages of structural design. It considers infinitely rigid floors in their own planes, and allows to better understand stress and strain distributions in the different bearing elements if compared to a finite element analysis. Numerical examples, describing the structural response of tall buildings characterized by bracings with different cross-section and height, show the effectiveness and flexibility of the proposed method. The accuracy of the results is investigated by a comparison with finite element solutions, in which the bracings are modelled as three-dimensional structures by means of shell elements.

• Advances in materials Research
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• 제11권1호
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• pp.59-73
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• 2022

In the construction industry, thin-walled frame elements with very slender open cross-sections and low torsional stiffness are often subjected to a complex loading condition where axial, bending, shear and torsional stresses are present simultaneously. Hence, these often fail in instability even before the yield capacity is reached. One of the most common instability conditions associated with thin-walled structures is Lateral Torsional Buckling (LTB). In this study, a first order Generalized Beam Theory (GBT) formulation and numerical analysis of cold-formed steel lipped channel beams (C80×40×10×1, C90×40×10×1, C100×40×10×1, C80×40×10×1.6, C90×40×10×1.6 and C100×40×10×1.6) subjected to uniform moment is carried out to predict pure Lateral Torsional Buckling (LTB). These results are compared with the Finite Element Analysis of the beams modelled with shell elements using ABAQUS and analytical results based on Euler's buckling formula. The mode wise deformed shape and modal participation factors are obtained for comparison of the responses along with the effect of varying the length of the beam from 2.5 m to 10 m. The deformed shapes of the beam for different modes and GBTUL plots are analyzed for comparative conclusions.

• 로봇학회논문지
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• 제16권4호
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• pp.327-335
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• 2021

In this paper, we propose an embedded robot system based on "ROS2 on Yocto" that can support various robots. We developed a lightweight OS based on the Yocto Project as a next-generation robot platform targeting cloud robotics. Yocto Project was adopted for portability and scalability in both software and hardware, and ROS2 was adopted and optimized considering a low specification embedded hardware system. We developed SLAM, navigation, path planning, and motion for the proposed robot system validation. For verification of software packages, we applied it to home cleaning robot and indoor delivery robot that were already commercialized by LG Electronics and verified they can do autonomous driving, obstacle recognition, and avoidance driving. Memory usage and network I/O have been improved by applying the binary launch method based on shell and mmap application as opposed to the conventional Python method. Finally, we verified the possibility of mass production and commercialization of the proposed system through performance evaluation from CPU and memory perspective.