• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.2
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• pp.75-81
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• 2006

Thermal effect of finite-rate chemistry on linear combustion stability and film-cooling effect are investigated in sample rocket engines. The flow variables required to evaluate stability limits are obtained from CFD data with finite-rate chemistry adopted in three dimensional chamber. Major flow variables are affected appreciably by finite--rate chemistry and thereby, the calculated stability limits are modified. It is found that finite-rate chemistry contributes to stability enhancement in thermal point of view. And film cooling also has the effect of combustion stabilization.

• 전기의세계
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• v.12
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• pp.30-34
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• 1963

비선형자기철심을 사용한 inductance를 그 비선형영역까지 동작하게 할때와 직렬형가포화 reactor에 R-C부하를 직렬로 연결하여 동작시킬 때 어떠한 동작범위에서는 회로의 전류진폭이 불안정한 경우가 있다. 특히 직렬형가포화 reactor에 R-C부하를 연결한 경우는 J.T.Salihi씨 및 H.C.Bourne씨에 의하여 그 동작현상이 설명되었다. 그러나 안정조건은 충분한것이 아니라고 생각되며 이와같은 R-L-C 직렬회로는 정량적으로 해석하는데 수학적인 난점이 있어서 곤란하지만 정성적인 방법 즉 근사계산에 의하여 안정성문제와 그 회로동작상태 등을 고찰할 수 있다. 본 고는 이러한 안정조건을 계산하여 제시코져 한다.

• 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.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.6
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• pp.32-40
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• 2012

For predicting eigenfrequency and initial growth rate of combustion instabilities in lean premixed gas turbine combustor, linear thermoacoustic analysis model was developed in the current paper. A model combustor was selected for the model validation, which has well-defined inlet and outlet conditions and a relatively simple geometry, compared to the combustor in the previous works. Analytical linear equations for thermoacoustic waves were derived for a given combustion system. It was found that the prediction results showed a good agreement with the measurements, even though there was underestimation for instability frequencies. This underestimation was more obvious for a longer flame (i.e. wider temperature distribution) than for a shorter flame.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2004.10a
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• pp.453-456
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• 2004

퍼지논리제어기는 제어 대상 플랜트에 관한 완전한 정보를 필요로하지 않으면서도 우수한 제어 성능을 발휘하는 비선형 제어기이다. 그러나 퍼지논리제어기는 많은 장점에도 불구하고 엄격한 수학적 해석을 요구하는 안정성 분석의 관점에서는 다소의 문제점을 가지고 있다. 본 논문에서는 퍼지논리제어기를 가지는 전체 폐루프 시스템을 섭동의 성분을 가지는 Lur'e 시스템으로 변형하고, 이를 통하여 퍼지논리제어기의 절대 안정성을 입증하고자 한다. 여기서는 이미 기존의 논문에서 제시한 간단구조 퍼지논리제어기를 대상으로 절대 안정성 해석을 제시한다.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.3
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• pp.71-82
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• 1999

Irregular motions of nonlinear dynamic system are the result of an intrinsic characteristics that the system have, and sometimes occur unpredictable large motion. For a ship in a regular seaway, the capsizing occur because of this unexpectable motion. So, from the safety's point of view, nonlinear ship motions should be treated carefully. In this study, stable and unstable regions are investigated firstly under the variation of a control external force. Secondly, we consider the attractors to know how ship motions of the stable region that does not undergo capsizing change. Thirdly, bifurcation diagram is considered to study the range in detail where nonlinear chaotic motions are occurred.

• Korean Journal of Optics and Photonics
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• v.12 no.6
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• pp.507-510
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• 2001

A numerical analysis based on the nonlinear Schroedinger equation is presented to analyze the propagation stability of the average soliton in a simple nonlinear amplifying loop mirror. The ratio of amplification period to soliton period and the length fraction of the erbium-doped fiber in the loop are varied to investigate their effects on the soliton stability. It is observed that stable soliton propagation is obtained even when the amplification period is only slightly shorter than the soliton period when the length fraction of the erbium-doped fiber in the loop is small, which is different from the previously published condition for stable average soliton propagation.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 1997.11a
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• pp.189-195
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• 1997

S-box의 암호학적 성질이 블록 암호 알고리즘의 안정성을 좌우한다. 여기서 말하는 암호학적 성질이란 선형 공격법에 안전한 높은 비선형성과 입출력 변화공격법에 안전한 입출력 변환의 낮은 균등성을 말한다. 본 논문에서는 갈로아 체의 원시원을 밑으로 하는 멱승 순환 함수를 이용한 S-box의 입출력 변환의 균등성에 관하여 서술한다.

• Journal of Korean Society of Steel Construction
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• v.23 no.1
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• pp.13-27
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• 2011

This paper presents an investigation of the structural stability of cable-stayed bridges, using geometric nonlinear finite-element analysis and considering various geometric nonlinearities, such as the sag effect of the cables, the beam-column effect of the girder and mast, and the large displacement effect. In this analytic research, a nonlinear frame element and a nonlinear equivalent truss element were used to model the girder, mast, and cable member. The live-load cases that were considered in this research were assumed based on the traffic loads. To perform reasonable analytic research, initial shape analyses in the dead-load case were performed before live-load analysis. In this study, the geometric nonlinear responses of the cable-stayed bridges with different cable arrangement types were compared. After that, parametric studies on the characteristics of the structural stability in critical live-load cases were performed considering various geometric parameters, such as the cable arrangement type, the stiffness ratios of the girder and mast, the area of the cables, and the number of cables. Through this parametric study, the effect of geometric shapes on the structural stability of cable-stayed bridges was investigated.

• Journal of Advanced Navigation Technology
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• v.26 no.6
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• pp.504-509
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• 2022

In this paper, we deal with the stability condition of linear time-varying interval discrete systems with time-varying delays and unstructured uncertainty. For the time-varying interval discrete system which has interval matrix as its system matrices, time-varying delay time within some interval value and unstructured uncertainty which can include non-linearity and be expressed by only its magnitude, the stability condition is proposed. Compared with the previous result derived by using a upper bound solution of the Lyapunov equation, the new result is derived by the form of simple inequality based on Lyapunov stability condition and has the advantage of being more effective in checking stability. Furthermore, the proposed condition is very comprehensive, powerful and inclusive the previously published conditions of various linear discrete systems, and can be expressed by the terms of magnitudes of the time-varying delay time and uncertainty, and bounds of interval matrices. The superiority of the new condition is shown in the derivation, and the usefulness and advantage of the proposed condition are examined through numerical example.