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        검색결과 113

        1.
        2024.12 KCI 등재 구독 인증기관 무료, 개인회원 유료
        With technological and social development, high-rise atypical buildings have emerged. In order to take into account the structural vulnerability due to their high-rise atypical shape, systems such as vibration control system and seismic isolation can be applied. In this study, dynamic behavior characteristics analysis was conducted based on the location of the seismic isolation system installation of the atypical facade shape Tapered and reverse shell structure models. With the installation of Lead Rubber Bearing(LRB), the maximum story drift ratio showed a decrease, but the maximum absolute acceleration showed a phenomenon in which the response was amplified in the middle and low story. LRB1(base isolation system) is the most effective for simultaneous control of the two dynamic responses, but the 46th floor of ‘Nor’ and’ RS’ and the 41st floor of ‘TA’ are considered the most effective installation location of the seismic isolation system in consideration of the burden of the seismic isolation system and the structure stability.
        4,000원
        2.
        2024.10 KCI 등재 구독 인증기관 무료, 개인회원 유료
        본 논문에서는 다중 연결 NURBS 패치 모델에 대한 등기하해석방법을 제시하고 이를 기하학적으로 엄밀한 쉘의 해석에 적용하였 다. 서로 다른 NURBS 패치를 연결할 떼 조정점 망(control point meshes)의 밀도와 패치간의 불연속성으로 인해 등기하해석이 부정확 해질 수 있다. 이러한 문제를 해결하기 위해 니셰(Nitsche) 방법을 등기하해석법에 적용하여 두 패치 사이의 변위와 견인력(traction) 의 정합성(compatibility)을 확보하였고, 최종 유도된 해석 방정식이 대칭성을 유지하도록 하였다. 추가되는 경계 조건은 패치간 경계 의 적분으로 표현되기 때문에 계산비용이 크게 증가되지 않는다. 시스템 방정식이 양정 행렬(positive definite matrix)이 되도록 안정 성 매개변수(stability parameters)를 도입하였으며 일반화된 고유치 해석을 통해 두 패치사이의 조정점 밀도에 따른 안정성 매개변수 의 값과 응력장의 해의 정확성을 분석하였다. 이 다중 패치 등기하해석법을 1차 전단변형을 고려한 기하학적으로 엄밀한 쉘요소의 해석에 적용하였으며, 니셰 방법을 사용함으로써 패치간의 변위 및 응력 연속성이 향상된 결과를 확인 할 수 있었다.
        4,000원
        3.
        2024.10 KCI 등재 구독 인증기관 무료, 개인회원 유료
        본 논문에서는 다중 연결 NURBS 패치 모델에 대한 등기하해석방법을 제시하고 이를 기하학적으로 엄밀한 쉘의 해석에 적용하였 다. 서로 다른 NURBS 패치를 연결할 떼 조정점 망(control point meshes)의 밀도와 패치간의 불연속성으로 인해 등기하해석이 부정확 해질 수 있다. 이러한 문제를 해결하기 위해 니셰(Nitsche) 방법을 등기하해석법에 적용하여 두 패치 사이의 변위와 견인력(traction) 의 정합성(compatibility)을 확보하였고, 최종 유도된 해석 방정식이 대칭성을 유지하도록 하였다. 추가되는 경계 조건은 패치간 경계 의 적분으로 표현되기 때문에 계산비용이 크게 증가되지 않는다. 시스템 방정식이 양정 행렬(positive definite matrix)이 되도록 안정 성 매개변수(stability parameters)를 도입하였으며 일반화된 고유치 해석을 통해 두 패치사이의 조정점 밀도에 따른 안정성 매개변수 의 값과 응력장의 해의 정확성을 분석하였다. 이 다중 패치 등기하해석법을 1차 전단변형을 고려한 기하학적으로 엄밀한 쉘요소의 해석에 적용하였으며, 니셰 방법을 사용함으로써 패치간의 변위 및 응력 연속성이 향상된 결과를 확인 할 수 있었다.
        4,000원
        4.
        2024.07 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        In this study, we report significant improvements in lithium-ion battery anodes cost and performance, by fabricating nano porous silicon (Si) particles from Si wafer sludge using the metal-assisted chemical etching (MACE) process. To solve the problem of volume expansion of Si during alloying/de-alloying with lithium ions, a layer was formed through nitric acid treatment, and Ag particles were removed at the same time. This layer acts as a core-shell structure that suppresses Si volume expansion. Additionally, the specific surface area of Si increased by controlling the etching time, which corresponds to the volume expansion of Si, showing a synergistic effect with the core-shell. This development not only contributes to the development of high-capacity anode materials, but also highlights the possibility of reducing manufacturing costs by utilizing waste Si wafer sludge. In addition, this method enhances the capacity retention rate of lithium-ion batteries by up to 38 %, marking a significant step forward in performance improvements.
        4,000원
        5.
        2024.07 KCI 등재 구독 인증기관 무료, 개인회원 유료
        For the OPR1000, a standard power plant in Korea, an analytical model of the containment building considering voids and deterioration was built with multilayer shell elements. Voids were placed in the vulnerable parts of the analysis model, and the deterioration effects of concrete and rebar were reflected in the material model. To check the impact of voids and deterioration on the seismic performance of the containment building, iterative push-over analysis was performed on four cases of the analytical model with and without voids and deterioration. It was found that the effect of voids with a volume ratio of 0.6% on the seismic performance of the containment building was insignificant. The effect of strength reduction and cross-sectional area loss of reinforcement due to deterioration and the impact of strength increase of concrete due to long-term hardening offset each other, resulting in a slight increase in the lateral resistance of the containment building. To determine the limit state that adequately represents the seismic performance of the containment building considering voids and deterioration, the Ogaki shear strength equation, ASCE 43-05 low shear wall allowable lateral displacement ratio, and JEAC 4601 shear strain limit were compared and examined with the analytically derived failure point (ultimate point) in this study.
        4,000원
        6.
        2024.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        This study aims to investigate the seismic response of a large span thin shell structures and assess their displacement under seismic loads. The study employs finite element analysis to model a thin shell structure subjected to seismic excitation. The analysis includes eigenvalue analysis and time history analysis to evaluate the natural frequencies and displacement response of the structure under seismic loads. The findings show that the seismic response of the large span thin shell structure is highly dependent on the frequency content of the seismic excitation. The eigenvalue analysis reveals that the tenth mode of vibration of the structure corresponds to a large-span mode. The time history analysis further demonstrates, with 5% damping, that the displacement response of the structure at the critical node number 4920 increases with increasing seismic intensity, reaching a maximum displacement of 49.87mm at 3.615 seconds. Nevertheless, the maximum displacement is well below the allowable limit of the thin shell. The results of this study provide insight into the behaviour of complex large span thin shell structures as elevated foundations for buildings under seismic excitation, based on the displacement contours on different modes of eigenvalues. The findings suggest that the displacement response of the structure is significant for this new application of thin shell, and it is recommended to enhance the critical displacement area in the next design phase to align with the findings of this study to resist the seismic impact.
        4,200원
        7.
        2024.04 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        To fabricate intermetallic nanoparticles with high oxygen reduction reaction activity, a high-temperature heat treatment of 700 to 1,000 °C is required. This heat treatment provides energy sufficient to induce an atomic rearrangement inside the alloy nanoparticles, increasing the mobility of particles, making them structurally unstable and causing a sintering phenomenon where they agglomerate together naturally. These problems cannot be avoided using a typical heat treatment process that only controls the gas atmosphere and temperature. In this study, as a strategy to overcome the limitations of the existing heat treatment process for the fabrication of intermetallic nanoparticles, we propose an interesting approach, to design a catalyst material structure for heat treatment rather than the process itself. In particular, we introduce a technology that first creates an intermetallic compound structure through a primary high-temperature heat treatment using random alloy particles coated with a carbon shell, and then establishes catalytic active sites by etching the carbon shell using a secondary heat treatment process. By using a carbon shell as a template, nanoparticles with an intermetallic structure can be kept very small while effectively controlling the catalytically active area, thereby creating an optimal alloy catalyst structure for fuel cells.
        4,000원
        8.
        2024.02 KCI 등재 구독 인증기관 무료, 개인회원 유료
        In this study, a core-shell powder and sintered specimens using a mechanically alloyed (MAed) Ti-Mo powder fabricated through high-energy ball-milling are prepared. Analysis of sintering, microstructure, and mechanical properties confirms the applicability of the powder as a sputtering target material. To optimize the MAed Ti-Mo powder milling process, phase and elemental analyses of the powders are performed according to milling time. The results reveal that 20 h of milling time is the most suitable for the manufacturing process. Subsequently, the MAed Ti-Mo powder and MoO3 powder are milled using a 3-D mixer and heat-treated for hydrogen reduction to manufacture the core-shell powder. The reduced core-shell powder is transformed to sintered specimens through molding and sintering at 1300 and 1400oC. The sintering properties are analyzed through X-ray diffraction and scanning electron microscopy for phase and porosity analyses. Moreover, the microstructure of the powder is investigated through optical microscopy and electron probe microstructure analysis. The Ti-Mo core-shell sintered specimen is found to possess high density, uniform microstructure, and excellent hardness properties. These results indicate that the Ti-Mo core-shell sintered specimen has excellent sintering properties and is suitable as a sputtering target material.
        4,000원
        9.
        2023.10 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Transition metal chalcogenides are promising cathode materials for next-generation battery systems, particularly sodium-ion batteries. Ni3Co6S8-pitch-derived carbon composite microspheres with a yolk-shell structure (Ni3Co6S8@C-YS) were synthesized through a three-step process: spray pyrolysis, pitch coating, and post-heat treatment process. Ni3Co6S8@C-YS exhibited an impressive reversible capacity of 525.2 mA h g-1 at a current density of 0.5 A g-1 over 50 cycles when employed as an anode material for sodium-ion batteries. However, Ni3Co6S8 yolk shell nanopowder (Ni3Co6S8-YS) without pitch-derived carbon demonstrated a continuous decrease in capacity during charging and discharging. The superior sodium-ion storage properties of Ni3Co6S8@C-YS were attributed to the pitchderived carbon, which effectively adjusted the size and distribution of nanocrystals. The carbon-coated yolk-shell microspheres proposed here hold potential for various metal chalcogenide compounds and can be applied to various fields, including the energy storage field.
        4,000원
        10.
        2023.09 KCI 등재 구독 인증기관 무료, 개인회원 유료
        BNKT Ceramics, one of the representative Pb free based piezoelectric ceramics, constitutes a perovskite(ABO3) structure. At this time, the perovskite structure (ABO3) is in the form where the corners of the octahedrons are connected, and in the unit cell, two ions, A and B, are cations, A ion is located at the body center, B ion is located at each corner, and an anion O is located at the center of each side. Since Bi, Na, and K sources constituting the A site are highly volatile at a sintering temperature of 1100℃ or higher, it is difficult to maintain uniformity of the composition. In order to solve this problem, there should be suppression of volatilization of the A site material or additional compensation of the volatilized. In this study, the basic composition of BNKT Ceramics was set to Bi0.5(Na0.78K0.22)0.5TiO3 (= BNKT), and volatile site (Bi, Na, and K sources) were coated in the form of a shell to compensate additionally for the A site ions. In addition, the physical and electrical properties of BNKT and its coated with shell additives(= @BNK) were compared and analyzed, respectively. As a result of analyzing the crystal structure through XRD, both BNKT(Core) and @BNK(Shell) had perovskite phases, and the crystallinity was almost similar. Although the Curie temperature of the two sintered bodies was almost the same (TC = 290 ~ 300 ℃), it was confirmed that the d33 (piezoelectric coefficient) and Pr (residual polarization) values were different. The experimental results indicated that the additional compensation for a shell additive causes the coarsening, resulting in a decrease in sintering density and Pr(remanent polarization). However, coating shell additives to compensate for A site ion is an effective way to suppress volatilization. Based on these experimental results, it would be the biggest advantage to develop an eco-friendly material (Lead-free) that replaced lead (Pb), which is harmful to the human body. This lead-free piezoelectric material can be applied to a biomedical device or products(ex. earphones (hearing aids), heart rate monitors, ultrasonic vibrators, etc.) and skin beauty improvement products (mask packs for whitening and wrinkle improvement).
        4,000원
        11.
        2023.02 KCI 등재 구독 인증기관 무료, 개인회원 유료
        The shell & tube-type heat exchanger has been frequently used because it shows simple structure, easy manufacturing and wide operation conditions among many heat exchangers. This study aims to investigate the characteristics for thermal flow of coolant and the possibility of damage for tube equipped with shell due to thermal stress. For these purposes, The thermal flow of coolant in tube was simulated using ANSYS-CFX program and thus the behaviors of coolant were evaluated with standard k-ε turbulence model. As the results, as the flow rate of coolant in tube was increased, the mean relative pressure was also increased with quadratic curve, however, as the surface temperature of tube was increased, mean temperature difference was linearly increased. Finally it showed that the damage of tube could be predicted, that is, which tube was the most weak due to thermal stress.
        4,000원
        12.
        2022.04 KCI 등재 SCOPUS 구독 인증기관 무료, 개인회원 유료
        The capacity of high nickel Li(NixCoyMn1-x-y)O2 (NCM, x ≥ 0.8) cathodes is known to rapidly decline, a serious problem that needs to be solved in a timely manner. It was reported that cathode materials with the {010} plane exposed toward the outside, i.e., a radial structure, can provide facile Li+ diffusion paths and stress buffer during repeated cycles. In addition, cathodes with a core-shell composition gradient are of great interest. For example, a stable surface structure can be achieved using relatively low nickel content on the surface. In this study, precursors of the high-nickel NCM were synthesized by coprecipitation in ambient atmosphere. Then, a transition metal solution for coprecipitation was replaced with a low nickel content and the coprecipitation reaction proceeded for the desired time. The electrochemical analysis of the core-shell cathode showed a capacity retention of 94 % after 100 cycles, compared to the initial discharge capacity of 184.74 mA h/g. The rate capability test also confirmed that the core-shell cathode had enhanced kinetics during charging and discharging at 1 A/g.
        4,000원
        15.
        2019.12 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Fe3O4/SiO2/YVO4:Eu3+ multifunctional nanoparticles are successfully synthesized by facile stepwise sol-gel processes. The multifunctional nanoparticles show a spherical shape with narrow size distribution (approximately 40 nm) and the phosphor shells are well crystallized. The Eu3+ shows strong photoluminescence (red emission at 619 nm, absorbance at 290 nm) due to an effective energy transfer from the vanadate group to Eu. Core-shell structured multifunctional nanoparticles have superparamagnetic properties at 300 K. Furthermore, the core-shell nanoparticles have a quick response time for the external magnetic field. These results suggest that the photoluminescence and magnetic properties could be easily tuned by either varying the number of coating processes or changing the phosphor elements. The nanoparticles may have potential applications for appropriate fields such as laser systems, optical amplifiers, security systems, and drug delivery materials.
        4,000원
        16.
        2019.12 KCI 등재 구독 인증기관 무료, 개인회원 유료
        본 연구는 탄소나노튜브/보강섬유/폴리머 복합 쉘에 대한 동적응답을 다루었다. 단일벽 탄소나노튜브, 유리섬유 및 에폭시 레진으로 구성된 3단계 복합구조이며, 유효 물성값은 멀티스케일 해석을 통하여 산정하였다. 유한요소 프로그램인 ABAQUS를 적용하여 다양한 탄소나노튜브 함유비율, 적층각도, 곡률 및 중앙 개구부의 다양한 변화에 대한 동적응답 및 상호 작용을 분석하였다. 본 연구는 원통형 복합쉘의 동적 하중에 의한 처짐을 감소시킬 수 있는 변수들의 중요성을 보여주었다.
        4,000원
        18.
        2019.06 KCI 등재 구독 인증기관 무료, 개인회원 유료
        본 연구에서는 중앙 개구부를 갖는 카본나노튜브/유리섬유/폴리머 합성 복합 적층쉘을 다루었다. 수정된 Halpin-Tsai 모델과 마이크로 역학적 접근방법은 단일벽 탄소나노튜브의 합성 비율에 따른 탄성적 물성변화를 추정하기 위하여 적용되었다. 유한요소 해석을 통하여 쉘의 고유진동 및 모드 특성을 분석하였다. 탄소나노튜브의 무게 비율, 보강섬유 각도, 개구부 크기, 고 유진동수 및 고유모드의 상관관계를 규명하였다. 개구부를 갖는 경우와 갖지 않는 경우에 대하여 곡률 변화에 따른 기존 문헌 과의 비교를 통하여 본 연구결과를 검증하였다. 본 연구결과는 고유진동 특성에 영향을 미치는 탄소나노튜브 보강의 중요성을 보여준다.
        4,000원
        20.
        2018.10 KCI 등재 구독 인증기관 무료, 개인회원 유료
        Core-shell structured nanoparticles are garnering attention because these nanoparticles are expected to have a wide range of applications. The objective of the present study is to improve the coating efficiency of gold shell formed on the surface of silica nanoparticles for SiO2@Au core-shell structure. For the efficient coating of gold shell, we attempt an in-situ synthesis method such that the nuclei of the gold nanoparticles are generated and grown on the surface of silica nanoparticles. This method can effectively form a gold shell as compared to the conventional method of attaching gold nanoparticles to silica particles. It is considered possible to form a dense gold shell because the problems caused by electrostatic repulsion between the gold nanoparticles in the conventional method are eliminated.
        4,000원
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