• The Bulletin of The Korean Astronomical Society
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• 제41권1호
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• pp.47.2-47.2
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• 2016

The protons and helium ions in the solar wind are observed to possess anisotropic temperature profiles. The anisotropy appears to be limited by various marginal instability conditions. One of the efficient methods to investigate the global dynamics and distribution of various temperature anisotropies in the large-scale solar wind models may be that based upon the macroscopic quasi-linear approach. The present paper investigates the proton and helium ion anisotropy instabilities on the basis of comparison between the quasi-linear theory versus particle-in-cell simulation. It is found that the overall dynamical development of the particle temperatures is quite accurately reproduced by the macroscopic quasi-linear scheme. The wave energy development in time, however, shows somewhat less restrictive comparisons, indicating that while the quasi-linear method is acceptable for the particle dynamics, the wave analysis probably requires higher-order physics, such as wave-wave coupling or nonlinear wave-particle interaction. We carried out comparative studies of proton firehose instability, aperiodic ordinary mode instability, and helium ion anisotropy instability. It was found that the agreement between QL theory and PIC simulation is rather good. It means that the quasilinear approximation enjoys only a limited range of validity, especially for the wave dynamics and for the relatively high-beta regime.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• 제16권2호
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• pp.165-170
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• 2016

Nano-scale power splitter based on curved plasmonic waveguides are designed by utilizing the multimode interference (MMI) coupler. To analyze easily the adaptive properties of plasmonic curverd multimode interference coupler(PC-MMIC), the curved form transforms equivalently into a planar form by using conformal transformation method. Also, effective dielectric method and longitudinal modal transmission-line theory are used for simulating the light propagation and optimizing the structural parameters at 3-D guiding geometry. The designed $2{\times}2$ PC-MMIC does not work well for quasi-TM mode case due to the bending structure, and it does not exist 3dB coupling property, in which the power splitting ratio is 50%:50%, for quasi-TE mode case. Further, the coupling efficiency is better when the signal is incident at channel with large curvature radius than small curvature radius.

• Proceedings of the KIPE Conference
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• 전력전자학회 2011년도 추계학술대회
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• pp.223-224
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• 2011

This paper presents the method to design the inductor and capacitor value considering the ripple component that may be generated by three operating states of the Quasi Z source inverter at the impedance network. Based on the analysis of each operation mode, the equations of the capacitor voltage and inductor current are derived. In order to simplify the design processing, design equations of the impedance network are derived where the capacitor voltage and inductor current are lineared. The validity of the design method is verified with the simulation result using PSIM.

• The Transactions of the Korean Institute of Power Electronics
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• 제5권2호
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• pp.170-175
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• 2000

A new quasi-parallel resonant DC link inverter is proposed for three phase soft switching application. By i inserting only one additional switch, the proposed inverter excludes both voltage stresses and restricted PWM p problems, which are demerits of the conventional resonant inverter. In this paper, the circuit operations are e explained in detail using the operational mode analysis of the proposed inverter and design methods of the r resonant components are suggest('x:l. Lastly, the applicable possibility of the proposed inverter is vel예fied t through the experimental results.

• Transactions of the Korean Society of Mechanical Engineers
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• 제17권10호
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• pp.2555-2562
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• 1993

In this paper, the axial crush of the rectangular STS304 tube is analyzed using DYNA3D, and 10 models are tested under quasi-static load. The deformed shapes of analysis and test are present, and the analysis results are compared with the results of quasi-static test. This paper describes that free rotational boundary condition causes a very similar deformed shapes to expermental results, and using the elastic buclking modes as initial imperfecion shapes, the deformed shapes are very close to the experimental shapes.

• Bulletin of the Korean Space Science Society
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• 한국우주과학회 2009년도 한국우주과학회보 제18권2호
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• pp.44.1-44.1
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• 2009

Identification of wave characteristics during current disruption events in the near-Earth geomagnetic tail region (~ 10 RE) is important to understand the substorm onset mechanism. In this paper, linear stability analysis in the ion-cyclotron grequency range, considering temperature anisotropy and cross-field flow is presented. It is found that the ion-cyclotron drift waves propagating in a quasi-perpendicular direction with respect to the ambient magnetic field are characterized by low frequencies ($\omega$ < $0.5{\Omega}ci$), while quasi-parallel waves have frequencies close to the ion-cyclotron frequency ($\omega{\sim}{\Omega}ci$). This finding is consistent with the observation by THEMIS spacecraft of a current disruption event in which a similar high- and low-frequency band structure is also present [A. T. Y. Lui, et al., J. Geophys. Res. 113, A00C06 (2008)]. It is also found that the quasi-perpendicular mode is excited by the ion cross-field flow.

• Proceedings of the KIPE Conference
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• 전력전자학회 2012년도 전력전자학술대회 논문집
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• pp.203-204
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• 2012

This paper presents the method to design the inductor and capacitor value considering the ripple component that may be generated by three operating states of the Quasi Z-source inverter at the impedance network. Based on the analysis of each operation mode, the equations of the capacitor voltage and inductor current are derived. In order to simplify the design processing, design equations of the impedance network are derived where the capacitor voltage and inductor current are lineared. The validity of the design method is verified with the simulation result using PSIM and experimental result using 32-bit DSP.

• Journal of Power Electronics
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• 제17권4호
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• pp.860-873
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• 2017

The present article reports an analysis and investigation of a direct AC-AC quasi-resonant converter. A bidirectional power device, whose switching frequency is lower than the frequency of the current passing through the load, is used for its realization. The zero voltage switching mode is described when zero voltage on the power device is available by measuring it with the control system. The continuous current in the resonant inductance by switching the power device at zero voltage is considered, and it is characterized by two sub-modes. A mathematical analysis of the processes has been made and comparative results from the computer simulation and experimental study have been brought. The converter can be used in a wide areas of power electronics: induction heating, wireless power transfer, AC-DC converters, etc.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• 제14권3호
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• pp.171-176
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• 2014

The polarization characteristics of ultracompact polarization-insensitive directional coupler (PIDC) based on double sandwiched rib-type waveguide are explored in detail by using longitudinal modal transmission-line theory (L-MTLT). To obtain the polarization-insensitive condition of ultracompact directional coupler, the coupling length and coupling efficiency as functions of the refractive index and thickness of sandwiched rib-type waveguide are analyzed for quasi-TE and quasi-TM modes. The numerical results show that the ultracompact polarization-insensitive coupler with hundreds of micrometer scales is realized by properly choosing structural and material parameters of double sandwiched layers. Furthermore, the influence of fundamental mode profile, which is distributed in lateral waveguide of coupler, on the coupler performance has been investigated.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 한국전산구조공학회 2011년도 정기 학술대회
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• pp.685-688
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• 2011

본 논문에서는 다양한 음향 가진에 따른 음향 응답을 유한 요소법을 통하여 효과적으로 계산하기 위한 새로운 모델 축소법을 제안한다. 일반적인 유한 요소법을 통한 기계구조물의 응답을 구하기 위해서는 음향 방정식의 강성 및 행렬을 구한 뒤 이들의 조합을 통한 동적 강성행렬을 구한 뒤 역행렬을 구하여 다양한 주파수 응답을 구하게 된다. 현재 컴퓨터 하드웨어의 발전과 소프트 웨어의 발전에 의하여 더 많은 유한 요소를 사용할 수 있게 되었고 이로 인하여 더욱 정확하고 넓은 대역의 음향 응답을 구할 수 있게 되었다. 그러나, 아직까지도 아주 복잡한 구조물의 음향 응답을 구하기 위하여 유한 요소를 무한정으로 증가할 수 없는 경우가 많다. 이를 해결하기 위하여 일반적으로 모델 축소법(Model order reduction) 기법을 사용한다. 이 모델 축소법은 기본적으로 전체 행렬을 아주 작지만 효율적인 작은 행렬로 바꾸어 응답을 예측하는 기법으로 mode superposition method, ritz vector method, quasi-static ritz vector method등이 있다. 기존의 모델 축소법은 기본적으로 질량 및 강성행렬이 가진 주파수에 영향을 받지 않는 행렬이라 가정한다. 그렇기 때문에 경계조건이나 다공성 재료를 모델링할 경우 가진 주파수에 영향을 받는 강성행렬과 질량행렬이 만들어지게 되어 기존의 모델 축소법은 효과적이지 못하게 된다. 이런 문제점을 해결하기 위하여 이 논문에서는 Quasi-static ritz vector method의 기본적인 개념을 확장하여 여러 개의 중심 주파수(Center frequency)에서 기저를 계산하고 이를 동시에 이용하는 Multi-frequency quasi-static ritz vector method를 제안한다.