• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.3
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• pp.506-513
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• 1992

본 연구에서는 복합재 구조물에 대하여 유한요소해석법에 현상학적 모델인 전 단지연해석을 도입하여 강성저하와 모재파손을 예측하고 변형률을 매개변수로 한 Wei- bull 함수를 섬유파손해석에 도입하여 초기파손후의 거동을 묘사하고자 한다. 그리 고 면내전단하중이 작용하는 경우에 대해 전단지연해석을 수행할 수 있도록 모델링을 확장했다. 모재균열의 존재로 인한 단층의 강성변화는 실험으로 측정이 불가능하므 로 유한요소해석을 수행하여 비교하였다. 이 모델로부터 전단강성의 저하를 평가하 는 방법을 사용하였으며, 모재파손의 밀도 예측도 평균변형률 개념으로 전단효과를 고 려할 수 있도록 수정하였다. 그리고 초기파손후의 거동을 점진적으로 해석하기 위해 비선형 유한요소프그램을 작성하고, 상기의 모델을 도입하여 초기파손후의 거동을 보 다 정확히 묘사할 수 있는 방법을 제시하고 예로서 평시편에 대해 해석하고 실험치 및 타방법의 결과와 비교하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.6 s.165
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• pp.1001-1010
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• 1999

Thermo-mechanical behavior of discontinuous shape memory alloy(SMA) reinforced polymeric composite has been studied using modified shear lag theory and finite element(FE) analysis with 2-D multi-fiber model. The aligned and staggered models of short-fiber arrangement are employed. The effects of fiber overlap and aspect ratio on the thermomechanical responses such as the thermal expansion coefficient are investigated. It is found that the increase of both tensile stress(resistance stress) in SMA fiber and compressive stress in polymer matrix with increasing aspect ratio is the main cause of low thermal deformation of the composite.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.2 s.233
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• pp.318-324
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• 2005

Theoretical efforts are performed to extend the formulation of NSLT(New Shear Lag Theory) for the prediction of the elastic modulus in short fiber composite. The formulation is based on the elastic stress transfer considering the stress concentration effects influenced by elastic modulus ratio between fiber and matrix. The composite modulus, thus far, is calculated by changing the fiber aspect ratio and volume fraction. It is found that the comparison with FEA(Finite Element Analysis) results gives a good agreement with the present theory (NSLT). It is also found that the NSLT is more accurate than the SLT(Shear Lag Theory) in short fiber regime when compared by FEA results. However, The modulus predicted by NSLT becomes similar values that of SLT when the fiber aspect ratio increases. Finally, It is shown that the present model has the capability to predict the composite modulus correctly in elastic regime.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.8
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• pp.1464-1474
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• 1994

GPS(Global Positioning System)is a satellite-based navigation system that we can survey where we are, anywhere and anytime. In this paper, delay-lock loop of the receiver which detects the navigation data is theoretically analyzed, and designed using the digital logic circuit. Also logic operations for the synchronization are analyzed. The designed system consists of the correlator which correlates the received C/A code and the generated C/A code in the receiver, the C/A code generator which generates C/A code of selected satellite, and the direct digital clock syntheizer which generates the clock of the C/A code generator to control the C/A code phase and clock rate. From the analyses results of the proposed digital delay-lock loop system, the system has the detection propertied over 90% when its input signal power is above-113.98dB. The influence of input signal variation of digital delay loop, which is the input of A/D converter, is investigated and the performance is analyzed with the variation of threshold level via the computer simulation. The logic simulation results show that the designed system detects precisely the GPS navigation data.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.3
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• pp.58-64
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• 1997

A micromechanics model to describe the elastic behavior of fiber or whisker reinforced metal matrix composites was developed and the stress concentrations between reinforcements were investigated using the modified shear lag model with the comparison of finite element analysis (FEA). The rationale is based on the replacement of the matrix between fiber ends with the fictitious fiber to maintain the compatibility of displacement and traction. It was found that the new model gives a good agreement with FEA results in the small fiber aspect ratio regime as well as that in the large fiber aspect ratio regime. By the calculation of the present model, stress concentration factor in the matrix and the composite elastic modulus were predicted accurately. Some important factors affecting stress concentrations, such as fiber volume fraction, fiber aspect ratio, end gap size, and modulus ratio, were also discussed.

• Korean Journal of Optics and Photonics
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• v.15 no.4
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• pp.385-390
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• 2004

In this paper, we designed a 4-bit optical true time-delay(TTD) for phased array antennas(PAAs), which is composed of a wavelength-fixed optical source, 2 ${\times}$ 2 optical MEMS switches, and fiber-optic delay lines. A 4-bit TTD with a unit time delay difference of 6 ps for 10-GHz PAAs has been implemented. Measurement results on time delay show an error of -0.4 ps at maximum, corresponding to a radiation angle error of less than 1.63$^{\circ}$. Thus, the TTD implemented in this research performs in excellent agreement with theory. Each TTD line, composed of MEMS switches and fiber-optic delay lines, connected to the corresponding antenna element has insertion loss in between 1.36 ㏈ and 2.40 ㏈ depending upon the setup of the switches. On the other hand, the insertion loss difference between TTD lines was 0.32 ㏈ at maximum for a fixed radiation angle. The TTD structure proposed in this paper might be more reliable and economical than those previously proposed using tunable wavelength sources if proper power equalization either with gain control of RF amplifiers or variable attenuators is achieved.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.167-175
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• 2018

This research deals, The characteristics of mechanics and behavior of the tube structural systems, It has been investigated and considered conventional theory and case models, It has shown the suitability, The best location, And optimal shape of the unit module system, Considered variables materials of stiffness increase and decrease in hybrid tube structural systems this study carried out adapting analysis of statistical concepts. In a concrete way, This study exams the effect of reducing horizontal displacement and the shear lag phenomenon, Also, The purpose of this study is to utilize the basic data on the design and study of future high-rise hybrid structural system using this research. As a result, The framed- tube structural system does not effectively cope with horizontal behavior of high-rise buildings, The results of using varying material tested resistance factors and lateral loads in hybrid tube structural system, When each material is compared Bracing material is identified as a key factor in lateral behavior. In a ratio of material quantity framed-tube structural system, The level of sensitivity affecting the horizontal displacement is greater then the beam's column, In case of braced tube structural system, Braced appeared to be most sensitive in comparison of material quantity ratio in columns and beams.