• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.149-150
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• 2015

소규모 분산전원 및 에너지 저장장치로 구성된 마이크로그리드는 에너지 자급자족이 가능한 특징을 가지며 계통연계 혹은 독립운전 모드로 운전이 가능하다. 마이크로그리드를 계통연계 모드로 운전하는 경우, 상위 계통에서 사고 발생 시 마이크로그리드 내 동기기의 과도안정도 문제가 발생할 수 있다. 이 때 인버터 기반 분산전원의 빠른 응답 속도를 활용하면 인접 동기기의 유효출력을 효과적으로 제어하여 계통연계 모드를 유지하면서도 과도안정도를 유지할 수 있다. 본 연구에서는 인버터 기반 분산전원의 P-w 제어를 통해, 정상 운전시에는 정해진 전력을 공급하면서 사고 시에는 인접 동기기의 과도안정도를 향상시킬 수 있는 제어 방법을 제안하였다. 또한 실제 적용 가능성을 확인하기 위해 ATP/EMTP프로그램을 이용하여 계통을 구성하고 해석하였다.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.4
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• pp.307-314
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• 2004

A circumferential guided wave method was developed to detect the axial crack on the bent feeder pipe. Dispersion curves of circumferential guided waves were calculated as a function of curvature of the pipe. In the case of thin plate, i.e. infinite curvature, as the frequency increases, the $S_0$ and $A_0$ mode coincide and eventually become Rayleigh wave mode. In the case of pipe, however, as the curvature increases, the lowest modes do not coincide even in the high frequencies. Based on the analysis, a rocking technique using angle beam transducer was applied to detect an axial defect in the bent region of PHWR feeder pipe. Based on the analysis of experimenal data for artificial notches, the vibration modes of each signal were identified. It was found that the notches with the depth of )0% of wall thickness can be detected with the method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.6A
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• pp.825-832
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• 2000

광섬유 통신 시스템이 고속화되고 장거리를 전송하게 될 수록 편광모드 분산의 중요성은 더욱 부각되어 있다. 따라서 본 논문에서는 복굴절 광섬유에서 비선형 광펄스의 전파특성을 편광 모드 분산의 영향을 고려하여 시뮬레이션하였으며 이러한 현상이 발생되는 것을 알 수 있었다. 그리고 광섬유 비션형성에 의해서 GVD(Group Velocity Dispersion)와 마찬가기로 PMD(Polarization Mode Dispersion)에서도 부분적인 보상 현상이 나타남을 수치 결과를 통해 알 수 있었다. 이러한 광 전송 시뮬레이션을 구현하기 위해서 기존의 단계분할 푸리에 방식 (SS-FM, Split-Step Fourier Method)보다 장거리 전송시 오차의 발생이 적은 단계 분할 유한 요소법)SS-FEM, Split-Step Finite Element Method)을 적용하였으며, 또한 그 단점인 수행 속도를 개선한 희귀 행렬 근사 단계 분할 유한 요소법을 제안하였다. 그 결과 제안된 방법이 기존의 푸리에 연산법이나 일반적인 유한 요소법과 비교하여 더 빠른 수행 속도를 나타내는 것을 알 수 있었다.

• The Journal of the Acoustical Society of Korea
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• v.28 no.3
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• pp.208-212
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• 2009

Ground wave is an acoustic wave propagating at a sediment sound speed in the case that sediment sound speed is constant with depth, which is explained by modal dispersion effects. In this paper, the ground wave in time domain is simulated using the ray-based approach, which is possible because the modal dispersion can be explained by the guiding of energy caused by reflection and refraction in the waveguide geometry. For a Pekeris waveguide, the ground wave can be interpreted as a sequence of head waves, called a head wave sequence [Choi and Dahl, J. Acoust. Soc. Am. 119, 3660-3668 (2006)]. The ground wave is simulated by convolution of the source signal with a channel impulse response of the head wave sequence, which is compared with simulated signals obtained via a Fourier synthesis of a complex parabolic equation (PE) field.

• The Magazine of the IEIE
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• v.29 no.4
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• pp.98-98
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• 2002

• Proceedings of the Korea Contents Association Conference
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• 2013.05a
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• pp.29-30
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• 2013

차세대 전자 소자용 전송 선로로 사용될 수 있는 나노 원기둥 배열의 분산 관계 특성을 모드 정합법을 사용하여 계산하였다. 서로 떨어진 나노 원기둥 배열에도 배열이 놓인 방향으로 전자파 모드가 형성되는 것을 수치 해석 결과로 제시한다. 또한 나노 원기둥 배열에 생기는 전기장의 분포 특성도 제시한다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.2
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• pp.90-96
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• 2018

Tracer experiments were carried out on two laboratory modes, "without media mode" and "with media mode", to examine the hydraulic characteristics of the anaerobic fluidized bed bioreactor (AFBR). For both configurations, a formula was derived for the hydraulics and data interpretation to obtain the actual characteristics of the reactor. The dispersion model is based on the assumption that carriers are non-reacting and the dispersion coefficient is constant. The model represents the one-dimensional unsteady-state concentration distribution of the non-reacting tracer in the reactors. The experimental results showed that the media increased the mixing conditions in the reactor considerably. For the reactor without media, in the range tested, the dispersion coefficient was at least an order of magnitude smaller than that of the reactor with media. Advective transport dominates and the flow pattern approaches the plug flow reactor (PFR) regime. The dispersion coefficient increased significantly as us, the superficial liquid velocity, was increased proportionally to 0.82cm/s. On the other hand, for the reactor with media, the flow pattern was in between a PFR and a completely mixed flow reactor (CMFR) regime, and the dispersion coefficient was saturated at us=0.41cm/s, remaining relatively constant, even at us=0.82cm/s. The dispersion coefficient depends strongly on the liquid Reynolds number (Re) or the particle Reynolds number (Rep) over the range tested.

• Korean Journal of Optics and Photonics
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• v.8 no.2
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• pp.134-141
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• 1997

We design the single mode dispersion-compensating fibers (DCF) which may be necessary for upgrading the previously installed 1.31 ${\mu}{\textrm}{m}$ optical communication system to the 1.55 ${\mu}{\textrm}{m}$ system. To obtain the optimum index profile that allows large negative dispersion at 1.55 ${\mu}{\textrm}{m}$, parabolic-index, double-clad fibers are analyzed by applying the 1-D FEM to the scalar wave equation of optical fibers. In constideration of macro-bending loss, the fibers are designed so that the cutoff wavelength of the $LP_{01}$ mode is greateer than 1.80 ${\mu}{\textrm}{m}$. The computer simulations show that the lower bound of the dispersion at 1.55 ${\mu}{\textrm}{m}$ is limited to about -120 ps/nm . km for the fiber index profiles satisfying the $LP_{01}$'s cutoff condition.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.12
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• pp.2963-2967
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• 2015

The pump-probe scheme is used to analyze the cross-phase modulation penalty of a single-mode fiber in a WDM system. The pump signal is assumed to be a periodically modulated input like a raised sinusoidal. The periodic signal models an alternating bit sequence, and leads to an analytical expression of CPM penalty which is measured by EOP. The derived expression shows good agreement with numerical results in conventional single-mode fiber systems over a wide range of channel spacing, ${\Delta}f$. In dispersion-shifted fiber systems when ${\Delta}f$ < 100GHz, the derived expression shows increased discrepancy with the numerical results due to the increased FWM. This is not a surprising because the pump-probe scheme is used to analyze system performance degradation due to CPM.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.6
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• pp.761-767
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• 1998

The Perfectly Matched Layer(PML) provide good performance in absorption over a wide frequency range and is an appropriate ABC for waveguides with high dispersion. In this paper, a novel algorithm is proposed to improve the computational efficiency of the PML. In the input and output ports, the fields are decomposed into a series of modes, and then an appropriate ABC is applied to each mode. CPU time and memory storage requirements are greatly reduced, since the computational region is analyzed in one dimension. A WG-90 rectangular waveguide with a thick asymmetric iris is analyzed by Finite-Difference Time-Domain(FDTD) simulations with the conventional PML and the proposed one-dimensional (1-D) PML. Numerical results show that the computational efficiency is significantly improved by the proposed method.