• Journal of Korean Society of Steel Construction
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• v.22 no.5
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• pp.487-496
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• 2010

The structural damping ratios for seismic design of nuclear power plant structures are specified in Regulatory guide 1.61 of the United States NRC for RC structures of 4%(OBE) and 7%(SSE), and for steel structures of 3%(OBE) and 4%(SSE), but not for steel-plate concrete (SC) structures that have been developed recently. The objective of this study is to investigate the damping ratios of SC structures by identifying the relative differences in the damping ratios between RC and SC structures. An experimental study was performed on four specimens, RC-S, RC-M, SC-S and SC-M, where S stands for shear-governed and M for moment-governed. The conducted method was free vibration testing by rupturing a brittle steel plate that linked the actuator and the mass center. The test results were analyzed to determine fundamental frequencies and damping ratios at various load levels. By examining the relative differences in damping ratios of four specimens, it is proposed for SC structures to use the same damping ratio of 4% as RC one at OBE, but 1% less damping ratio than RC one resulting in 6% at SSE.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.2A
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• pp.75-83
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• 2012

In this study, an analytical studies were carried out for the buoyancy preflexion method to improve structural performance of concrete floating structures. The buoyancy preflexion means that the preflexion effects were induced to the floating structure due to the difference in buoyancy between the pontoon modules composing the floating structures. In order to verify the buoyancy preflexion effects, an analytical studies were carried out for the floating structures. The size and dimensions of FE model were determined through the structural design process. The parameter of this analytical study was length ratios of central module part, which induces buoyancy preflexion effects, to the total length. The analysis results were pre-compression on the bottom concrete slab and displacement of freeboard due to buoyancy preflexion effects. These results were processed according to the loading step, buoyancy preflexion loads on the bottom and live loads on the topside. Then, the buoyancy preflexion effects on structural performance was analyzed. As the results of this study, it was found that the buoyancy preflexion significantly influence on structural performance of floating structures. According to the length ratio, the buoyancy preflexion effects have a tendency of parabolic form and maximized at the length ratio of 40~60%. The buoyancy preflexion method is simple in principle and easy in application. Also, it can effectively induce pre-compression on the bottom concrete slab. Therefore, it can be concluded that the buoyancy preflexion method contribute to the improvement of structural performance and decreasing of the cross-sectional depth of floating structures.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.150.2-150.2
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• 2012

로켓 엔진용 짐벌 마운트는 발사체 발사 후 자세 제어를 위해 발사체와 엔진사이에 장착된 TVC(Thrust Vector Control) 구동기의 작동으로 짐벌 운동을 수행하며 기구학적으로 자세 제어를 하는데 있어 매우 중요한 역할을 하는 요소이다. 이러한 짐벌 마운트는 엔진 추력을 발사체에 전달하는 기능 이외에 지정된 위치에 엔진을 고정시키는 역할과 위치 고정 후 발사체 단과 엔진의 정확한 추력 전달을 위한 기계적 불일치 보정 기능, 짐벌 구동에 대한 피봇 기능을 동시에 수행하여야 하는 복합적인 기능을 가지고 있다. 특히, 이중에서도 물리적으로 고 추력의 하중을 전달하는 요소로서 충분한 강도와 강성을 지녀야 하므로 본 연구에서는 이와 관련된 초기 설계 요구도 분석을 바탕으로 설계 규격에 부합하는 짐벌 마운트의 구조적 검토를 통해 로켓 엔진용 짐벌 마운트 설계 형상을 개념적으로 제시하였다.

• International Journal of Highway Engineering
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• v.12 no.2
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• pp.99-106
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• 2010

Until now, the thickness design of anti-freezing layer has been empirically conducted using the frost depth determined from the freezing index. This approach cannot consider the structural properties of anti-freezing layer, which can cause the over-design of pavement structure. This paper presents results of structural evaluation of anti-freezing layer using the Falling Weight Deflectormeter (FWD) deflections. The FWD testing was directly conducted on top of the subbase layer located at the embankment, cutting, and boundary area of each section. It is observed from this testing that the center deflections of pavement structure with anti-freezing layer are smaller than those without anti-freezing layer. The deflection reduction rates are 15~55% in the embankment, 11~64% in the cutting, and 2~38% in the boundary, respectively. It was also found that the use of antifree zing layer enables to reduce the Surface Curvature Index (SCI) values up to 24 percent. Fatigue lives show that pavement structure with antifreezing layer are about two times higher than the those without anti-freezing layer. This fact indicates that the anti-freezing layer should be considered as a structural layer in the asphalt pavement system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.3
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• pp.311-316
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• 2015

This paper presents a design method for thin but wideband absorbers using resistive sheets. Its equivalent circuit consists of a series RLC resonant circuit and a short-terminated transmission line. Based on this equivalent circuit, we presented the three conditions for an electromagnetic absorber which has a thickness less than a quarter wavelength and wide absorption bandwidth at center frequency. By using an root-finding algorithm, the equivalent resistance, capacitance, and inductance of the absorbers are obtained. These equivalent circuit values for the absorber surface can be realized by a 2D periodic cross-shaped structure which has required surface resistance. Using the design method, we have designed the absorber which has 18.75 mm($67.5^{\circ}$ electrical length) thickness and 90 % absorption bandwidth of 116 % bandwidth at 3 GHz.

• Composites Research
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• v.15 no.6
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• pp.24-29
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• 2002

For the development of all composite unmanned aerial vehicle(UAV), the consideration for manufacturing in design phase and events in composite parts fabrication, subassembly and final assembly are summarized. In design phase, to maximize the advantages of composite material such as cocuring, cobonding and secondary bonding for manufacturing, the advanced structural concept is introduced. For the curing of designed parts, the manufacturing tools for composite parts are designed and manufactured. The assembly jigs are designed to meet dimensional tolerance requirements of the vehicle structure. And the inspection criteria are established and applied for the manufacturing. Technical data for inspection items and methodologies are summarized to utilize for the exclusive specifications of the manufacturing sequence.

• Aerospace Engineering and Technology
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• v.10 no.1
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• pp.98-106
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• 2011

This paper is summarized for designing launch vehicle autopilot structure with attitude angle command from guidance algorithm and for evaluating performance of autopilot using launch vehicle six-degree of freedom simulation program. The suggested autopilot has heritage from KSR-III/KSLV-I upper stage autopilot designing experience, and it has two design point. The one is, it must have same performance with KSR-III/KSLV-I upper stage autopilot, the other is, it must be simple autopilot structure and use low number of variable to apply on-board system. It is evaluated the performance using launch vehicle six-degree of freedom simulation program in case of roll maneuvering and no roll control flight condition.

• Nuclear Engineering and Technology
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• v.26 no.3
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• pp.433-439
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• 1994

영광 3, 4호기는 ABB-CE 사의 System 80 원자로와 비교해서 원자로 내부 구조물의 수력학적 설계 목적과 방법 이 동일하고, 단지 원자로의 크기와 출력이 상대적으로 작아진 내부 구조물이 축소된 형태이다. 따라서 System 80 유동 모델 시험에서 측정된 실험 결과로부터 영광 3, 4호기 연료 집합체 수에 맞게 보간법을 사용하여 보수적으로 유량 분포를 구하고 영광 3, 4호기 유동 모델 시험에서 얻어진 유량 분포와 비교하여 원자로의 수력학적 특성을 검토하고 자각에 대해 열적 여유도를 구하여 이런 경우에 원자로 유동 모델 시험을 수행하지 않고 이전의 실험 결과를 설계에 사용할 수 있는 가에 대해 연구하였다.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.192.2-192.2
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• 2012

위성시스템 소형화, 탑재체 수용증대, 발사비용절감, 탐사임무 효율화 등의 요구로 인하여, 위성 설계에 있어 경량화는 오랜 기간 진행되어온 연구 주제였다. 이러한 연구결과로서, 위성 구조체를 복합재료로 대신하기 위한 구조 경량화 연구와 적용이 성과를 거두었으며, 현재 위성체 프레임이나 전개형 안테나, 광학구조물 등에 경량 탄소섬유 강화 복합재료의 적용은 보편화되어 있다. 한편, 위성시스템에서 전력, 통신, 명령/데이터처리, 자세제어 및 관측기기의 각종 전자장비를 보호하는 하우징 구조물에는 여전히 금속재료가 광범하게 적용되고 있다. 특히, 알루미늄 합금은 하우징 재료로 널리 사용되는데, 강도, 강성, 열전달, 우주방사, 전기전도도 및 EMI 차폐특성과 더불어 가공성이 우수하다는 장점을 지닌 반면에, 금속재료로서 중량이 상당하여 위성 경량화 관점에서는 한계를 갖게 하는 단점이 있다. 전자장비에 부여된 전자기능 측면에서 보면, 하우징은 기생 구조물로서, 경량으로 제공될수록 전자장비 전체 무게에서 전자유닛만의 무게가 차지하는 전기전자기능비가 향상되고 위성 경량화에 크게 기여할 수 있다. 구조 경량화를 위하여 전자장비 하우징을 경량 복합재로 대체하여 설계 및 제작하였으며, 복합재 하우징의 강도, 강성, 열전달, 우주방사, 전기전도도 및 EMI 차폐를 검증할 수 있는 방법에 대하여 검토하였다.

• Journal of Astronomy and Space Sciences
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• v.25 no.4
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• pp.445-458
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• 2008

Image chain analysis of synthetic aperture radar (SAR) satellite is one of the primary activities for satellite design because SAR image quality depends on spacecraft bus performance as well as SAR payload. Especially, satellite pointing and stability error make worst effect on the original SAR image quality which is implemented by SAR payload design. In this research, Image chain analysis S/W was developed in order to analyze the SAR image quality degradation due to satellite pointing and stability error. This S/W consists of orbit model, attitude control model, SAR payload model, clutter model, and SAR processor. SAR raw data, which includes total 25 point targets in the scene of $5km{\times}5km$ swath width, was generated and then processed for analysis. High resolution mode (spotlight), of which resolution is 1m, was applied. The results of image chain analysis show that radiometric accuracy is the most degraded due to the pointing error. Therefore, the successful design of attitude control subsystem in spacecraft bus for enhancing the pointing accuracy is most important for image quality.