• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.467-474
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• 2002

이 연구에서는 점탄성감쇠기가 설치된 구조시스템의 통합최적설계 방법을 제시하였다. 최적화를 위한 목적함수로는 구조시스템이 유발하는 사회적 비용을 의미하는 총 생애주기비용을 사용함으로써, 구조제어 시스템의 성능에 기반한 경제적 유익을 극대화하도록 하였다. 구조물의 층별 기둥 강성 및 점탄성감쇠기의 사용량 등을 설계변수로 하여 생애주기비용함수를 정의하였으며, 통합시스템을 동시에 최적화하기위한 방법으로 유전자 알고리즘을 적용하였다. 동일한 초기비용을 사용하며 통합최적설계를 수행하지 않은 설계를 통해 얻어진 지진응답과 비교한 결과, 제안하는 통합 설계방법은 보다 우수한 진동제어효과를 발휘하는 것으로 나타났다.

• Proceedings of the Korean Information Science Society Conference
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• 1999.10a
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• pp.258-260
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• 1999

주기억 데이터베이스를 위한 색인 구조는 기존의 디스크 기반 데이터베이스의 색인 구조와는 고려되어야 할 사항이 다르다. 최근까지 연구된 색인 구조 중 대표적인 것은 T-트리와 T*-트리이다. 비록 T*-트리가 T-트리의 단점인 범위 질의의 비효율성을 해결하고 있지만 데이터의 삽입과 삭제가 많은 시스템에서 트리 균형을 맞추기 위한 오버헤드, 회전 연산의 수행과 후위 포인터(successor pointer)의 추가적인 오버헤드가 있다. 따라서 본 논문에서는 삽입과 삭제가 빈번한 동적 주기억 데이터베이스를 위해서 억제된 노드 생성 및 삭제 기법과 스레드 이진 트리의 특성을 이용한 보다 효율적인 색인 구조인 T2-트리를 제안한다.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.426.2-426.2
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• 2014

Wavefront control은 렌즈, 거울 등을 포함한 많은 광학소자를 대체할 수 있는 기술이며, 이는 광 직접 소자 개발에 매우 유용하다. 기존의 Distributed bragg reflector (DBR) 구조의 경우 lattice mismatch, 낮은 효율, 작은 굴절률 차이의 물질만을 사용해야 하는 문제 등으로 광 직접 소자에의 적용에는 한계가 있다. 본 연구에서는 이러한 한계점을 극복하고, 더 나아가 광학소자 구조 내에서의 빛의 거동을 조절하기 위해서 High-index contrast grating (HCG), 즉, 큰 굴절률 차이가 나는 물질로 이루어진 격자 구조 내의 빛이 가지는 waveguide 특성에 대한 연구가 수행되었다. 굴절률 차이가 큰 물질을 sub-wavelength의 주기적인 혹은 비주기적인 격자 구조로 만듦으로써 투과된 빛의 투과도와 위상 등을 조절할 수 있고 이를 통해 빛의 초점 거리, 휘어짐을 조절 할 수 있다. HCG 구조 내의 빛의 거동을 Rigorous coupled wave analysis (RCWA) 및 Finite element method (FEM) 계산을 이용하여 시뮬레이션 하였다. RCWA 계산을 통해 주기 격자구조의 투과도 및 반사도, 빛의 위상을 계산하여 비주기를 갖는 전체적인 HCG 구조를 결정하였고, FEM 계산을 통하여 그 구조 내에서 빛의 거동을 시뮬레이션 하였다. 1,300 nm 파장의 빛이 광원으로 사용되었고 시뮬레이션을 위해 낮은 굴절률의 물질로 ITO, 높은 굴절률의 물질로는 Si이 사용되었다. $15{\mu}m$ 포커싱, $7.91^{\circ}$의 휘어짐을 시뮬레이션 하였고, 실제 소자 공정을 하여 제작한 후, 광 측정 결과 포커싱은 $15{\mu}m$, 휘어짐은 $4.5{\sim}6.5^{\circ}$를 확인하였다. 이러한 결과를 바탕으로 HCG구조체를 통하여 빛의 엔지니어링이 가능함을 알 수 있었다. HCG구조체는 빛이 투과하는 광학 소자의 전반에 적용이 가능하며 더 나아가 인위적인 빛의 엔지니어링이 가능함을 시사한다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.4
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• pp.235-242
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• 2022

Compared with buildings that have already been constructed, buildings under construction may be more vulnerable to such natural disasters as earthquakes because the concrete strength is not yet sufficient. Currently, Korean design standards present minimum performance targets for each seismic grade of buildings, but the seismic load for design is based on a return period of 2400 years. However, because the construction period of the building is much shorter than the period of use of the building, the application of the earthquake return period of 2400 years to buildings under construction may be excessive. Therefore, in this study, a construction stage model of buildings with 5, 15, 25, and 60 floors was created to analyze earthquake loads during construction of residential reinforced concrete (RC) buildings. The structural stability was confirmed by applying reduced seismic loads according to the return period. As a result, the structural stability was checked for an earthquake of the return period selected according to the construction period, and the earthquake return period that can secure structural safety according to the size of the building was confirmed.

• Journal of Adhesion and Interface
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• v.23 no.2
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• pp.39-43
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• 2022

In optoelectronic devices including displays and solar cells that convert electricity into light or light into electricity, it is important to control optical behavior of light to improve device efficiency. Specifically, the control of internal emitting light in the OLEDs can induce more light to go out, improving luminous efficiency. In addition, the control of optical behavior of incident light in solar cells can increase optical path in the light absorption layer, increasing power-conversion efficiency. In this study, we generated wrinkles as a physical structure to control optical behavior of light and independently controlled their wavelength and height by changing stress relaxation time. To explore the effect of wavelength and height on optical behavior, we conducted UV/Vis spectroscopy analysis of wrinkles with various heights at a constant wavelength or various wavelengths at a comparable height, figuring out a wrinkle with high aspect ratio has more dispersive light and less straight light. It indicates that high aspect ratio is required to change the optical behavior and increase the optical path.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.3
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• pp.87-94
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• 2007

A structural dynamic analysis can be divided into a time domain analysis and a frequency domain analysis. The time domain analysis makes use of a direct integration method or a mode superposition method and the frequency domain analysis applies a DFT method. Generally the DFT method is more effective method in case of calculating response of periodic excitation. But in case of transient excitation exact solution can not be acquired. So, by modifying the response or increasing the period accuracy of solution can be enhanced. Accordingly this study analyzed dynamic responses of structures under aperiodic moving load in time domain and frequence domain. Consequently it is concluded that exact solution would be get enough using DFT method by increasing the duration of free vibration or modifying the dynamic response.

• Journal of IKEEE
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• v.24 no.1
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• pp.1-8
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• 2020

In this paper, a semi-infinite array analysis method is proposed to analyze the defects that may occur during the fabrication of the frequency selective radome. In the analysis of N×N finite array structure using 3D analysis software, much analysis time and memory are required, whereas the semi-infinite array structure analysis proposed in this paper can predict relatively accurate electromagnetic performance while reducing the analysis time. In comparison with the results of the periodic simulation, the simulation of the semi-infinite array structure confirmed the error within ±3%. To verify the results of the simulation, the results were compared with the measured results, and the same tendency at the point of performance change and similar performance degradation at the band of interest were investigated. Using the proposed semi infinite array structure analysis, it is confirmed that the analysis of defects in the electromagnetic periodic structure is possible.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.3
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• pp.65-74
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• 2019

This study presents the optimal isolation period according to the number of vertically expended stories in order to provide the basic data for the application of the seismic isolation system in the vertically expended remodeling of the aged apartment. As a result of the structural analysis, the isolation period should be at least twice the primary structure in three-story vertical expansion, three times in two-story expansion, and four times in one-story expansion for the effective application of the isolation system. On the basis of the result, the efficacy of an isolation system for the actual apartment structure, which is three-story vertically expended, was analytically verified. The maximal acceleration response on the top floor reduced by 70% and 65% of the non-isolated structure in the X and Y directions respectively. Additionally, the base shear force decreased by 30% in the both directions, compared to the non-isolated structure.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.4
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• pp.239-245
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• 2014

Finite element modeling of composite structures may be cumbersome due to complex distributions of reinforcements. In this paper, an efficient scheme is proposed that can generate periodic meshes for the composite structures. Regular meshes with hexahedral finite elements are first prepared, and the elements are then trimmed to fit external surfaces of reinforcements in the composite structures. The trimmed hexahedral finite elements located at interfaces between the matrix and the reinforcements correspond to polyhedral finite elements, which allow an arbitrary number of nodes and faces in the elements. Because the trimming process is consistently conducted by means of consistent algorithms, the elements of the reinforcements are automatically compatible with those of the matrices. With the additional consideration of periodicity of reinforcements in a representative volume element(RVE), the proposed scheme provides periodic meshes in an efficient manner, which are compatible for each pair of periodic boundaries of the RVE. Therefore, periodic boundary conditions for the RVE are enforced straightforwardly. Numerical examples demonstrate the effectiveness of the proposed scheme for finite element modeling of complex composite structures.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6A
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• pp.965-976
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• 2006

A realistic lifetime seismic-reliability based approach is unavoidable to perform Life-Cycle Cost (LCC)-effective optimum design, maintenance, and retrofitting of structures against seismic risk. So far, though a number of researchers have proposed the LCC-based seismic design and retrofitting methodologies, most researchers have only focused on the methodological point. Accordingly, in most works, they have not been quantitatively considered critical factors such as the effects of seismic retrofit, maintenance, and environmental stressors on lifetime seismic reliability assessment of deteriorating structures. Thus, in this study, a systemic lifetime seismic reliability analysis methodology is proposed and a program HPYER-DRAIN2DX-DS is developed to perform the desired lifetime seismic reliability analysis. To demonstrate the applicability of the program, it is applied to an example bridge with or without seismic retrofit and maintenance strategies. From the numerical investigation, it may be positively stated that HYPER-DRAIN2DX-DS can be utilized as a useful numerical tool for LCC-effective optimum seismic design, maintenance, and retrofitting of bridges.