• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.2
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• pp.139-148
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• 2001

Phenomena induced by waves, such as overtopping, sediment transport, vibration/fluctuation and destruction of structures are highly influenced by the directionality of wave propagation. These phenomena are often dominated by non-linearity, and so hydraulic model experiments are widely adopted for stability analysis rather than numerical modeling, Thus, stability ofrubblc mound breakwaters(RMB) due to wavc directionality was experimentally investigated in this study. The incident wave angle $30^{\circ}$ was found more risky on the damage rate of RMB under directional regular waves, and the incident wave angle $40^{\circ}$ was found relatively risky under directional irregular waves. These results clarified the wave directionality effect on the stability ofRMB, These facts were found correspondent to the occurrence of the peak between $20^{\circ}$-$40^{\circ}$ with the directional frequency distribution of lIlO maximum water particle velocity.

• Journal of the Korean Institute of Intelligent Systems
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• v.14 no.4
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• pp.481-486
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• 2004

The biped robot has the better mobility than the conventional wheeled robot. Since a biped robot tends to tip over easily, it is necessary to take stability into account when determining a walking pattern. To ensure the dynamic stability of the biped robot, we have to adapt the ground conditions with a foot motion and maintain motion, and ensure its stability through the kinematics and dynamics analysis. But its mathematic model is not too easy. In this paper, in order to ensure the dynamic stability of a biped robot, we design the fuzzy model and confirm the realization possibility of the proposed method through some simulations.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.47 no.2
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• pp.8-15
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• 2010

This paper proposes a robust high-gain observer design scheme for nonlinear systems and its stability is analyzed based on Lyapunov theory. It is assumed that their states are unmeasurable. The proposed high-gain observer has the integrator of the estimation error in dynamics. It improves the performance of high-gain observers and makes the proposed observer robust to noisy measurements, uncertainties and peaking phenomenon as well. Its stability is analyzed by the Lyapunov approach. In order to verify the effectiveness of the proposed scheme, it is applied to output feedback controllers and some comparative simulation result with the existed observer based output feedback controllers and state feedback controllers is given.

• 한국정보통신설비학회:학술대회논문집
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• 2007.08a
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• pp.11-14
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• 2007

CMOS technology 기반의 고주파 직접회로에서는 충분한 이득과 안정성을 얻기 위하여 inductor, capacitor와 같은 수동 소자를 적절히 사용하여 설계하여야 한다. 이와 같은 수동 소자는 CMOS 집적회로에서 넓은 면적을 차지하는 단점이 있다. 고주파 증폭기의 부하를 능동 소자로 대체하게 되면 작은 크기로 회로의 제작이 가능하게 되나, 능동 소자는 수동 소자에 비하여 선형 특성이 좋지 않기 때문에 실제로 고주파 증폭기 설계에 사용하지 않는다. 본 논문에서는 이와 같은 능동 소자의 비선형성을 억제하면서, 동시에 회로의 크기를 줄일 수 있는 기능성 능동 부하를 적용한 고주파 증폭기를 설계하였다. 기능성 능동 부하는 2개의 MOSFET은 대칭으로 연결된 구조를 가지며, 하나의 MOSFET은 일반적인 load로 동작하며, 다른 MOSFET은 gate에 가변 전압을 인가함으로써, 증폭기의 전달함수를 변화시킬 수 있다. 이와 같은 특성을 이용하여 고주파 증폭기의 선형성을 보상할 수가 있다.

• The Korean Journal of Food And Nutrition
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• v.9 no.4
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• pp.504-508
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• 1996

This study was performed to investigate the browning intensity and electron donating ability of browning material in perilla oils from seeds roasted at 150~21$0^{\circ}C$ for 10~30 min. It was also investigated the oxidative stability of the blended perilla oil on the basis of sensory property and oxidative stability. The browning intensity in perilla oil increased with the roasting temperature and time increased. The browning intensity of perilla oil from seed roasted at 21$0^{\circ}C$ for 30 min indicated 13 times higher than that of perilla oil from seed at 15$0^{\circ}C$ for 10 min. Electron donating ability on DPPH of browning materials presented in perilla oils increased with the roasting temperature and time increased. The electron donating ability of browning materials in perilla oil from seed reasted at 21$0^{\circ}C$ for 30 min indicated 3 times higher than those of perilla oil from seed at 15$0^{\circ}C$ for 10 min. In conclusion, for the improvement of oxidative stability of perilla oil, perilla seed should be roasted at 21$0^{\circ}C$ for 30 min. These results suggest that browning materials formed between sugars and amino acids attribute to improve quality of oil such as sensory properties and oxidative stabilities. For the improvement of sensory property and oxidative stability of oil, perilla oil from seed roasted at 19$0^{\circ}C$ for 20 min was blended with the oil from seed roasted at 21$0^{\circ}C$ for 30 min as ratio of 85 : 15.

• Tunnel and Underground Space
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• v.28 no.2
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• pp.170-185
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• 2018

The effect of fault on the stability of the closely-spaced twin tunnels located in fault zones was investigated by numerical analyses and scaled model tests on condition of varying widths, inclinations and material properties of fault. When obtaining the strength/stress ratios of pillar between twin tunnels, three different stresses were used which were measured at the middle point of pillar, calculated to whole average along the pillar section and measured at the left/right edges of pillar. Among them, the method by use of the left/right edges turned out to be the most conservative stability estimation regardless of the presence of fault and reflected the excavating procedures of tunnel in real time. It was also found that the strength/stress ratios of pillar were decreased as the widths and inclinations of fault were increased and as the material properties of fault were decreased on condition using the stresses measured at the left/right edges of pillar. As a result of scaled model tests, it was found that the model with fault showed less crack initiating pressure than the model without fault. As the width of fault was larger, tunnel stability was decreased. The fault had also a great influence on the failure behavior of tunnels, such as the model without fault showed failure cracks generated horizontally at the left/right edges of pillar and at the sidewalls of twin tunnels, whereas the model with fault showed failure cracks directionally generated at the center of pillar located in the fault zone.

• Proceedings of the Korean Fiber Society Conference
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• 1998.04a
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• pp.67-70
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• 1998

지방족 폴리에스테르계 고분자인 Poly(lactic acid)(PLA)는 생분해성, 생체적합성, 분해물의 비독성, 가공성 등이 우수하여 부러진 뼈의 접합 재료, 약물 조절 방출 재료 및 흡수성 봉합사 등과 같은 의료용 소재로 널리 이용되고 있다[1]. 그러나 PLA는 높은 결정화도로 인해 물성이 brittle하고 분해속도가 느릴 뿐만 아니라 낮은 열 안정성으로 인해 용융 가공할 경우 급격한 분자량의 감소를 유발하여 기계적 특성이 좋지 않은 단점이 있다.(중략)

• Proceedings of the Korean Fiber Society Conference
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• 2001.10a
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• pp.37-40
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• 2001

Aromatic polyimides는 다른 고분자 재료에 비해 고온에서의 열 안정성 및 기계적 물성, 내화학성, 전기 절연성, 난연성 등이 매우 탁월하기 때문에, 최근 들어서 고성능 구조재료, 전자재료(microelectronics devices, electrical insulators of semiconduntor packages), 내열성 접착제, 코팅제 등 그 응용 범위가 점차 확대되고 있는 추세이다. (중략)

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1995.05a
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• pp.3-8
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• 1995

추진기관 적용에 따른 복합재연소관의 일반적 사항들을 논하였다. 추진기관의 효율에 주요인자인 경량화에 있어서 복합재 연소관의 무게가 철금속 연소관에 비해 약 50%의 감소효과가 있으며 단가의 측면에서도 부가가치가 있는 것으로 평가된다. 그러나 추진기관 체계적(추진제 공정 및 구조안정성) 관점에서 추진제 내면변형율(Inner Bore Strain)의 증가, 제작공차, 공정의 재현성, EPDM의 접착기밀성 및 외부습도 유입 문제 등의 앞으로 해결되어야 할 사항들이 제시되었다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.8
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• pp.1910-1919
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• 1994

The nonlinear behavior of continuous structural systems which possess external resonances as well as internal resonances are found be exhibit interesting reponses, arising because of the exhange of energy between the coupled modes. In this paper, the undamped forced vibrations was studied on the effect of primary resonance based on the concept of normal modes. By using the concept of normal mode the stability relation between free and forced vibrations was investigated in case of small exciting force. Numerical results show that the excitation of one unstable mode has a great influence on the response of the other mode but that of one stable mode does not.