• 한국정밀공학회지
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• 제12권3호
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• pp.32-41
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• 1995

In the analysis of metal forming processes by the finite element method, there are many numerical instabilities such as element locking, hourglass mode and shear locking. These instabilities may have a bad effect upon accuracy and convergence. The present work is concerned with improvement of stability and efficiency in two-dimensional rigid-plastic finite element method using various type of elemenmts and numerical intergration schemes. As metal forming examples, upsetting and backward extrusion are taken for comparison among the methods: various element types and numerical integration schemes. Comparison is made in terms of stability and efficiency in element behavior and computational efficiency and a new scheme of adaptive directional reduced integration is introduced. As a result, the finite element computation has been stabilized from the viewpoint of computational time, convergency, and numerical instability.

• 한국광학회:학술대회논문집
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• 한국광학회 1991년도 제6회 파동 및 레이저 학술발표회 Prodeedings of 6th Conference on Waves and Lasers
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• pp.126-130
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• 1991

다이오드 레이저의 능동형 모드락킹 구조로부터 극초단 광펄스를 발생시켰다. 모드락킹된 광펄스를 얻기 위해 다이오드 레이저의 한쪽 면을 무반사 코팅했으며, 얻어진 광펄스의 폭(FWHM)은 22psec였다.

• Journal of the Optical Society of Korea
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• 제17권2호
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• pp.117-129
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• 2013

We briefly review the recent progress in passively mode-locked fiber lasers (PMLFLs) based on semiconductor saturable absorber mirrors (SESAMs) and discuss the detailed characterization of a SESAM-based, passively mode-locked erbium-doped fiber (EDF) laser operating in the 1.5-${\mu}m$ spectral range for various configurations. A simple and compact design of the laser cavity enables the PMLFL to generate either femtosecond or wavelength-tunable picosecond pulses with high stability as the intra-cavity filtering method is altered. All the cavities investigated in our experiments present self-starting, continuous-wave mode-locking with no Q-switching instabilities. The excellent stability of the source eventually enables the wavelength-tunable PMLFL to be used as a master oscillator for a power-amplifier source based on a large-core EDF, generating picosecond pulses of >10-kW peak power and >100-nJ pulse energy.

• 대한기계학회논문집A
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• 제25권4호
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• pp.582-591
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• 2001

It is known that the reduced integration, modified shape function, anisoparametric and non-conforming element can reduce the error induced by stiffness locking phenomenon in the finite element analysis. In this study, we propose new anisoparametric curved beam element. The new element based on reduced minimization theory is composed of different shape functions in each displacement field. By the substitution of this modified shape function, the unmatched coefficient that cause stiffness locking in the constraint energy is eliminated. To confirm the availability of this new model, we performed numerical tests for a simple model. As a result of numerical test, the undulate stress patterns are disappeared in static analysis, and displacements and stresses are close to exact solution. Not only in the static analysis but also in the eigen analysis of free vibrated curved beam model, this element shows successful convergent results.

• Steel and Composite Structures
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• 제48권5호
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• pp.599-610
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• 2023

To avoid debonding failure, a novel type of hybrid anchorage (HA) is proposed in this study that uses a slotted plate to lock the ends of the fiber-reinforced polymer (FRP) sheet in addition to the usual bonding over the substrate of the strengthened member. An experimental investigation was performed on three groups of RC beams, which differed from one another in either concrete strength or steel reinforcement ratio. The test results indicate that the end self-locking of the CFRP sheet can improve the failure ductility, ultimate capacity of the beams and its utilization ratio. Although intermediate debonding occurred in all the strengthened beams, it was not a fatal mode of failure for the three specimens with end anchorage. Among them, FRP rupture occurred in the beam with higher concrete strength and lower steel reinforcement ratio, whereas the other two failed by concrete crushing. The beam strengthened by HA obtained a relatively high percentage of increase in ultimate capacity when the rebar ratio or concrete strength decreased. The expressions in the literature were inspected to calculate the critical loads at intermediate debonding, FRP rupturing and concrete crushing after debonding for the strengthened beam. Then, the necessity of further research is addressed.

• 한국통신학회논문지
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• 제28권8A호
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• pp.644-649
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• 2003

새로운 구조의 622Mbps급 버스트 모드 클럭/데이터 복원 회로를 구현하였다. 회로는 2개의 muxed oscillator (MO)와 위상 동기 회로 등으로 구성되어 있으며, passive optical network(PON) 시스템에 사용될 수 있도록 instantaneous locking 특성을 갖는다. 또한. 지터가 내재된 데이터가 인가되어도 데이터에 따라 클럭이 연동되어 항상 최적의 샘플링 포인트를 갖는다. 이 회로는 0.35$\mu\textrm{m}$ CMOS 공정을 이용하여 제작되었다. 측정 결과 제안된 클럭/데이터 복원 회로는 400Mbps 680MbPs 까지의 버스트 모드 입력 데이터를 에러없이 복원하였다.

• 한국광학회지
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• 제26권6호
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• pp.312-317
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• 2015

레이저 공진기 모드 크기가 반도체 포화 흡수체 거울(SESAM)을 이용하여 모드 잠금된 Yb:YAG 레이저의 출력에 주는 영향을 조사하였다. SESAM과 Yb:YAG 매질 위치에서 공진 모드들 크기를 곱한 값이 작을수록 모드 잠금이 안정적으로 발생함을 실험적으로 보였다. 수치적으로 레이저 매질의 열 렌즈 효과와 무관하게 모드 잠금이 이루어지는 공진기 길이 조건이 있음을 확인하였다.

• 대한기계학회논문집
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• 제18권3호
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• pp.540-547
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• 1994

Contact and frictional locking conditions and the effect of shielding due to contact at the facet, which could be represented by the difference in energy release rate, as a function of phase angle of loading are analyzed in this study for the case of interfacial cracks by assuming single crack-kink model. The analysis of contact effects on interfacial fracture resistance shows that relative shielding increases as the shear component was increased, which indicates a qualitative agreement with the previous experimental results.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1993년도 추계학술대회 논문집
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• pp.195-199
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• 1993

In the analysis of metal forming processes by the finite element method, there are many numerical instabilities such as element locking, hourglass mode, shear locking. These instabilities may have a bad effect upon accuracy and convergence. The present work is concerned with improvement of stability and efficiency in two dimensional rigid-plastic finite element method using various type of elements and numerical integration schemes. AS metal forming examples, upsetting and backward extrusion are taken for comparison among the methods : various element types and numerical integration schemes. comparison is made in terms of stability and efficiency. As a result, it has been shown that the finite element computation is stabilized from the viewpoint of computational time, convergency, and numerical instability.

• ETRI Journal
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• 제29권4호
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• pp.463-469
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• 2007

A phase-locked loop (PLL) is described which is operable from 0.4 GHz to 1.2 GHz. The PLL has basically the same architecture as the conventional analog PLL except the locking information is stored as digital code. An analog-to-digital converter is embedded in the PLL, converting the analog loop filter output to digital code. Because the locking information is stored as digital code, the PLL can be turned off during power-down mode while avoiding long wake-up time. The PLL implemented in a 0.18 ${\mu}m$ CMOS process occupies 0.35 $mm^2$ active area. From a 1.8 V supply, it consumes 59 mW and 984 ${\mu}W$ during the normal and power-down modes, respectively. The measured rms jitter of the output clock is 16.8 ps at 1.2 GHz.