• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.2A
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• pp.79-87
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• 2011

The parameter study of buckling behavior of steel built-up column under compression force is presented in this study. The shear deformation effects due to the bending moment and shear forces are considered for the H-shaped main members along the entire built-up column and batten member connecting double H-shaped main members. The parametric study is performed according to the length of the built-up column, the distance of the H-shaped main members and the number and type of cover plate for battens, respectively. The applicability of AISC design specification of normal and high tension bolted built-up column is investigated. The buckling loads for built-up columns are compared with those obtained from the analytic solution developed in this study, AISC specification, and finite element method based on the beam and plate element, respectively.

• Journal of KIISE:Computer Systems and Theory
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• v.32 no.4
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• pp.177-185
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• 2005

NAND-type flash memory is becoming increasingly popular as a large data storage for mobile computing devices. Since flash memory is an order of magnitude more expensive than magnetic disks, data compression can be effectively used in managing flash memory based storage systems. However, compressed data management in NAND-type flash memory is challenging because it supports only page-based I/Os. For example, when the size of compressed data is smaller than the page size. internal fragmentation occurs and this degrades the effectiveness of compression seriously. In this paper, we present an efficient flash compression layer (FCL) for NAND-type flash memory which stores several small compressed pages into one physical page by using a write buffer Based on prototype implementation and simulation studies, we show that the proposed scheme offers the storage of flash memory more than $140\%$ of its original size and expands the write bandwidth significantly.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.6
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• pp.16-27
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• 2020

For the operation of the scramjet engine in the wide flight range, the design of the inlet must show stable performance in various flight conditions. In this study, the design methods of a 2D fixed inlet for stable performance in wide flight ranges of Mach number 4 to 6 and angle -6° to 6°, is performed. After proposing the design method and design focus, performance prediction and analysis were performed by various initial compression angles and design Mach numbers, which are essential design factors in total pressure recovery and inlet capture area ratio in the wide flight range. Based on the analysis results, we present the selection criteria for the two main design elements to represent stable performance in the wide flight range.

• Journal of the Society of Disaster Information
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• v.17 no.4
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• pp.829-838
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• 2021

Purpose: The Air Spring Damper System (ASDS) is proposed when existing concrete structures that have not been seismic resistant for economic and technical reasons or low-rise concrete structures that are difficult to earthquake. Method: To conduct a study on the damping force antigen in the kinetic equation of free vibration, we analyze whether this device has damping ability as a damper experimentally and theoretically, and examine the possibility of field application. Result: The air damper system is considered to be more economical than steel hysteresis dampers even if the number of dampers increases due to its easy manufacture and construction and low restrictions on shape, size, material, etc. Conclusion: In an air spring damper system, it is essential to reduce the diameter of the air inlet/outlet hole to improve the damping ratio, and in this case, if the diameter exceeds a certain lower limit, consideration of the compressibility of air is required, so further research is needed.

• Journal of the Korean GEO-environmental Society
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• v.5 no.3
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• pp.31-39
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• 2004

The bored pile is widely used as a low noise and vibration piling method in Korea. However, there is design tendency to minimize the friction capacity of the bored pile because of uncertainty and the quality control specification is not set up. This research analysed the strength characteristics of cement paste after the uniaxial compression test with various condition. Test results show that the compressive strength of cement paste with w/c=0.83 was up to $156.0kgf/cm^2$, and the lower w/c ratio and the longer age, the strength of cement paste increased. Also the higher soil mixing ratio, the strength of soil cement decreased, and too high soil mixing ratio caused the malfuction of soil cement. Also this research analysed the 188 dynamic pile test results which were performed before and after hardening of cement paste. Analysis result showed that the average ultimate unit friction capacity was $9.1tf/m^2$ and this result surpassed the common design criteria of the bored pile.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1993.04a
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• pp.80-84
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• 1993

공기베어링은 기체으 압축성에 의한 평균화 효과로 운전정밀도가 우수하고 기체의 낮은 점도에 의한 효과로 마찰력과 열발생량이 매우 적으며, 사용가능 온도구간이 저온에서 고온까지 넓고 프로세스 계통내의 기체를 윤활제로 사용할 수 있기 때문에 그 경우 불순물에 의한 오염이 문제되지 않는 장점등이 있다. 이와 같은 특성과 더불어 공기베어링은 지지 물체를 완전히 부상시켜 운전하므로써 마찰$\cdot$마모와 온도변화에 다른 열변형이 문제되지 않는다. 이러한 장점으로 인해서 공기베어링은 현재 정밀기기의 미끄럼면, 각종 측정장치의 테이블지지 기구로 많이 사용되고 있다. 반면 공기베어링의 단점으로는 기체의 낮은 점성계수로 인해서 부하능력이 적고 강성, 감쇄계수 또한 적다. 그리고 기체의 압축성으로 인해 뉴메틱 헤머라는 불안정 현상이 생기기도 한다. 본 연구에서는 스퀴즈 효과를 이용한 능동 공기베어링을 설계, 제작하여 실험하였다. 본 연구의 목적은 강성과 감쇄 계수가 작은 공기 베어링의 단점을 보완하기 위해 드러스트베어링을 대상으로 능동베어링을 설계, 제작하여 그 특성을 연구하고 기초 설계자료를 축적하는데 있다.

• Proceedings of the KIEE Conference
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• 2008.10c
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• pp.182-184
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• 2008

수소리니어 동력/발전시스템은 기존의 인프라를 이용한 개발이 가능한 이점과 고압축비, 초회박연소 실현에 의한 고효율, 저배기 달성이 가능한 장점을 가지고 있다. 또한 엔진 혹은 발전기의 구조변경 없이 다양한 연료를 사용이 가능하기 때문에 차세대 수소이용 기관으로 연구가 이루어지고 있다. 본 연구에서는 기존에 설계한 5kW급 리니어발전기의 성능향상을 위해 공극구조의 개선과 디텐트력 감소 설계를 했다. SPM 타입의 자석을 적용한 내충격 구조의 이동자 설계과 디텐트력 감소를 위한 치 형상설계가 이루어졌다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.75-82
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• 2021

The objective of this study is to examine the loss of prestressing stress in the developed prestressing reinforcing units using steel bar and pipe (SP). The main parameters were the reinforcing bar type, the magnitude of prestressed force, and prestressing method. The test results showed that the loss of prestressing stress for SP was highest in the initial prestressing step, which was higher for the compression introduction typed specimens than tension introduction typed specimens. The loss of prestressing stress of SP made with P800 was 1.6% for the compression introduction typed specimen with 0.8f_y, which was lowest than the other specimens. Meanwhile, the relaxation of SP with the respect to the time ranged between 0.4 and 1.9%, irrespective of SP material type, the magnitude of prestressed force, and prestressing method. These values were less than 2.5%, which is the maximum value for the relaxation of prestressed reinforcing steel bars in design codes. Consequently, considering the loss of stress developed in the initial prestressing step, the developed SP material type, prestressing introduction method, and magnitude are recommended to be P800, compression introduction type, and 0.8f_y.

• Journal of Korean Society of Steel Construction
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• v.29 no.2
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• pp.123-134
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• 2017

Ultimate axial strength of longitudinally stiffened cylindrical steel shells for wind turbine tower was investigated by applying the geometrically and materially nonlinear finite element method. The effects of radius to thickness ratio of shell, shape and amplitude of initial imperfections, area ratio between effective shell and stiffener, and stiffener spacing on the ultimate axial strength of cylindrical shells were analyzed. The ultimate axial strengths of stiffened cylindrical shells by FEA were compared with design buckling strengths specified in DNV-RP-C202. The shell buckling modes obtained from a linear elastic bifurcation FE analysis as well as the weld depression during fabrication specified in Eurocode 3 were introduced in the nonlinear FE analysis as initial geometric imperfections. The radius to thickness ratio of cylindrical shell models was selected to be in the range of 50 to 200. The longitudinal stiffeners were designed according to DNV-RP-C202 to prevent the lateral torsional buckling and local buckling of stiffeners.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.383-386
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• 2005

철근콘크리트 부재가 하중을 받을 때, 응력교란구역에서의 힘의 흐름은 스트럿-타이 모델을 이용하여 효과적으로 표현할 수 있다. 그러나 스트럿-타이 모델을 이용하여 철근콘크리트 부재의 해석과 설계를 하기 위해서는 큰크리트 압축스트럿이 가지는 유효강도를 정확히 산정하여야 한다. 본 연구는 철근콘크리트 부재에 휨과 전단력이 동시에 작용할 때 발생하는 대각선 균열이 콘크리트 압축스트럿에 미치는 영향에 대해 설명하고 있다. 대각선 균열의 발생 메커니즘과 이로 인한 콘크리트 압축스트럿의 강도 저하를 이론적으로 설명하였으며, 그 결과를 철근콘크리트 보의 강도 산정에 적용하였다. 최종적으로 철근콘크리트 보의 강도 예측값을 기존 연구자들의 실험결과와 비교하여 제안된 이론의 합리성을 검증하였다.