• 대한전기학회논문지:전력기술부문A
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• 제54권4호
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• pp.165-171
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• 2005

Electromagnetic transient simulation can be used to model complex non-linearities that very difficult to represent adequately in the frequency domain. This problem is greatly reduced with the use of frequency dependent network equivalents for the linear part of the system. S-domain rational function fitting techniques for representing frequency dependent equivalents have been developed using Least Squares Fitting(LSF). However it does not suffer the implementation error that exited in this work as it ignored the instantaneous term. This paper presents the formulation for developing 2 port Frequency Dependent AC System Equivalent(FDACSE) with the instantaneous term in S-domain and illustrates its use. This 2 port FDNE have been applied to the New Zealand AC system. The electromagnetic transient package PSCAD/EMTDC is used to assess the transient response of the 2 port (FDACSE) developed with Norton Equivalent network. The study results have indicated the robustness and accuracy of 2 port FDACSE for electromagnetic transient studies.

• 한국전산구조공학회논문집
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• 제21권4호
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• pp.401-410
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• 2008

보의 고유진동수는 진동해석 뿐만 아니라 구조물의 동적특성을 파악하는데 중요한 역할을 한다 보의 단면이 불연속적으로 변하는 계단형 보의 고유진동수 해석은 복잡하다. 이런 계단형 보의 진동해석은 Rayleigh-Ritz법, FEM 등과 같은 근사해석법이 흔히 사용되는데 이들 해석의 정확성은 분할요소의 수, 계산의 반복수, 가정처짐곡선의 형상에 따라 좌우된다. 본 연구에서는 계단형 외팔보의 등가보 변환 방법을 이용한 기본고유진동수의 근사해석방법을 제시하고자 하였으며 여러 예제에 대하여 제안방법과 유한요소해석 결과를 비교하여 그 적용성과 신뢰성을 검증하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.1218-1223
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• 2007

In this study, we experimentally investigate the equivalent ring theory for a slightly asymmetric ring. The slightly asymmetric ring has mode pair and frequency pair due to the small asymmetry and this mode pair generates beat in vibration and sound. In this paper, a slightly asymmetric ring is modeled as the equivalent ring, i.e., the assemblage of a symmetric ring and imperfect point masses. The equivalent ring has the same mode pair condition as that of the original asymmetric ring. Effect of the additional mass attachment is investigated by the equivalent ring theory and the result is compared with those of the measurement and the finite element analysis. It is confirmed that the original ring and the equivalent ring show the same change in frequency and mode under the various additional imperfection mass conditions. The equivalent ring theory explains how the asymmetric elements influence the mode characteristics and provides useful information to tune the beat property.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 A
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• pp.283-285
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• 2004

Modern power systems are very complex and to model them completely is impractical for electromagnetic transient studies. Therefore areas outside the immediate area of interest must be represented by some form of frequency dependent equivalent. This paper presents the formulation for developing 1 & 2 port Frequency Dependent Network Equivalent (FDNE) with the instantaneous term in S-domain and illustrates its use. This 1 & 2 Port FDNE have been applied to the CIGRE Benchmark Rectifier test AC system. The electromagnetic transient package PSCAD/EMTDC is used to assess the transient response of the 1 & 2 port (FDNE) developed with Norton Equivalent network.

• ETRI Journal
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• 제46권2호
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• pp.238-249
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• 2024

Equivalent-time sampling can improve measurement or sensing systems because it enables a broader frequency band and higher delay resolution for periodic signals with lower sampling rates than a Nyquist receiver. Meanwhile, a digital down-conversion (DDC) technique can be implemented using a straightforward radio frequency (RF) circuit. It avoids timing skew and in-phase/quadrature gain imbalance instead of requiring a high-speed analog-to-digital converter to sample an intermediate frequency (IF) signal. Therefore, when equivalent-time sampling and DDC techniques are combined, a significant synergy can be achieved. This study provides a parameter design methodology for optimal equivalent-time sampling using DDC.

• 한국정밀공학회지
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• 제16권6호
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• pp.108-113
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• 1999

For cylindrical shells, the closed-form solutions are confined to the specific boundary and/or loading conditions. Though the finite element method is certainly a powerful solution approach for the structural dynamics problems, it has been well known to provide the solution reliable only in the low frequency region due to the inherent high sensitivities of structual and numerical modeling errors. Instead, the spectral element method has been proved to provide accurate dynamic characteristics of a structure even at the ultrasonic frequency region. Since the wave characteristic of a cylindrical shell becomes identical to that fo a flat plate as the frequency increases, an equivalent plate model (EPM) representing the high-frequency dynamic characteristics of the cylindrical shell is introduced herein. The EPM-based spectral element analysis solutions are compared with the known analytical solutions for the cylindrical shells to confirm the validity of the present modeling approach.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.273-276
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• 2008

Equivalent linear method indirectly reflects a variation of shear modulus(G/Gmax) and damping ratio $(\xi)$ by selects mean value of every response analysis. Existing equivalent linear method does not properly consider variation of shear strain along frequencies and uses mean value. Real dynamic soil behavior is affected by shear stiffness and damping ratio. Modified equivalent linear method is developed to consider variation. Modified equivalent linear method can reflects high strain at low frequency and low strain at high frequency by using an easement curve. This study presents propriety of method by case study.

• Structural Engineering and Mechanics
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• 제60권1호
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• pp.91-110
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• 2016

Tube hydroforming (THF) under pulsating hydraulic pressures is a novel technique that applies pulsating hydraulic pressures that are periodically increased to deform tubular materials. The deformation behaviours of tubes in pulsating THF may differ compared to those in conventional non-pulsating THF due to the pulsating hydraulic pressures. The equivalent stress-strain relationship of metal materials is an ideal way to describe the deformation behaviours of the materials in plastic deformation. In this paper, the equivalent stress-strain relationships of SS304 tubes in pulsating hydroforming are determined based on experiments and simulation of free hydraulic bulging (FHB), and compared with those of SS304 tubes in non-pulsating THF and uniaxial tensile tests (UTT). The effect of the pulsation parameters, including amplitude and frequency, on the equivalent stress-strain relationships is investigated to reveal the plastic deformation behaviours of tubes in pulsating hydroforming. The results show that the deformation behaviours of tubes in pulsating hydroforming can be well described by the equivalent stress-stain relationship obtained by the proposed method. The amplitude and frequency of pulsating hydraulic pressure have distinct effects on the equivalent stress-strain relationships-the equivalent stress becomes augmented and the formability is enhanced with the increase of the pulsation amplitude and frequency.

• 한국지반공학회논문집
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• 제24권12호
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• pp.113-120
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• 2008

1차원 지반응답해석은 지반에 의한 지진동의 증폭현상을 모사하는 데 널리 사용되고 있다. 가장 널리 사용되고 있는 등가선형 지반응답해석기법은 유효변형률에 상응하는 전단탄성계수와 감쇠비를 전 주파수 영역에 일률적으로 적용하며, 진동주파수에 대한 지반 응답의 영향을 고려하지 않는다. 지반의 비선형 거동을 주파수영역에서 보다 정확하게 모사하기 위하여 진동주파수와 지반거동의 상관관계를 주파수-변형률 곡선으로써 모의하는 등가선형해석기법이 개발되었으며, 이 방법은 기존의 등가선형해석기법에 비하여 정확성을 향상시킨다고 알려져 있다. 이제까지 다양한 형상의 주파수변형률 곡선이 제안되었으며, 이들은 한결같이 해석의 정확성을 증가시킨다고 주장된 바 있다. 본 연구에서는 기존의 연구에서 제안되었건 두 개의 주파수-변형률 관계 완화곡선과 본 연구에서 새롭게 제안된 세 개의 곡선을 이용하여 주파수 의존성을 고려한 등가선형해석기법의 정확성을 검증하였다. 검증에는 세 개의 부지에서 기록된 6개의 지진파가 사용되었다. 해석결과, 완화곡선은 지반응답에 지배적인 영향을 미치는 것으로 나타났으며, 주파수 의존성을 고려한 해석은 정확성을 향상시킬수 있는 것으로 나타났다. 하지만, 모든 사례에서 가장 정확하게 응답을 예측하는 완화곡선은 없는 것으로 나타났으며, 해석사례별로 최적의 완화곡선이 다른 것으로 나타났다. 따라서, FDEL 해석 수행 시, 다양한 완화곡선을 사용해야 할 것으로 판단되며 등가선형해석과 병행해서 수행되어야 한다고 판단된다.

• 전기학회논문지
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• 제56권12호
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• pp.2166-2172
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• 2007

In this study a low-signal equivalent circuit based on the Double Schottky Barrier model is proposed for ZnO-based varistor. Since pin-lead inductance and stray capacitance are considered in pin-lead type ZnO varistor these inductance and capacitance could be removed from the experimental dielectric data of the varistor. According to the equivalent circuit simulation results the higher the varistor-voltage of varistor sample the capacitance of dielectric layer is larger, and the capacitances of semiconducting layer and depletion layer are smaller, while the parallel resistances of semiconducting layer and depletion layer are more larger values. Spectra of the dielectric loss factor $tan{\delta}$ show 2 peaks in low frequency and high frequency regions respectively. The low-frequency peak is due to the relaxation by deep donors and the high-frequency peak is due to the relaxation by shallow donors. Above results are well consistent with the theoretical mechanism of ZnO varistor.