• Proceedings of the KIPE Conference
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• 2008.06a
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• pp.466-468
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• 2008

본 논문에서는 불평형, 고조파, 잡음 등에 의해 왜곡된 3상 전원으로부터 정확한 위상각을 검출하는 PLL(Phase Locked Loop) 방법을 제안한다. 역상분과 고조파를 포함하는 왜곡된 3상 전원을 동기좌표계 d-q축 전압으로 변환하면 기본파 성분에 의한 일정한 d-q축 전압에 역상분과 고조파에 의한 맥동이 포함된 형태의 전압이 된다. 상태관측기는 이러한 전압에서 맥동성분을 제거하고 기본파 전압만 추출하여 이를 동기좌표계 PLL의 입력으로 사용함으로써 왜곡된 전원조건에서도 정확한 위상각을 검출할 수 있다. 시뮬레이션을 통해 제안된 방법의 성능을 검증하였다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2012.07a
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• pp.104-106
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• 2012

본 논문에서는 단일 반송파 MIMO 시스템 기반의 PN 시퀀스를 이용한 반송파 주파수 오차 추정 방법을 제안한다. 제안하는 방법은 송신되는 각각의 PN 시퀀스들의 위상을 회전시켜 전송하여, 일부 PN 시퀀스들이 서로 상쇄되어 버리는 것을 방지한다. 수신한 PN 시퀀스와 수신기에서 자체 생성한 PN 시퀀스의 공액곱셈 연산을 통해 변조를 제거한 뒤, 다수의 자기 상관기를 이용한 ML 알고리듬 계열의 L&R[3]을 이용하여 반송파 주파수 오차를 추정한다. 컴퓨터 모의실험을 통해, 송신 및 수신 안테나가 두 개인 $2{\times}2$ MIMO 시스템에 제안하는 기법을 적용하고 L&R 알고리듬을 이용하여 AWGN (Additive White Gaussian Noise) 채널에서의 분산 성능을 측정하였다. 그 결과 MIMO 시스템에서의 분산 성능이 SISO 시스템에서의 성능과거의 동일함을 보였다.

• The Journal of the Society of Korean Medicine Diagnostics
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• v.12 no.1
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• pp.42-62
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• 2008

Objectives: It is well known that some parameters of the photoplethysmogram (PPG) acquired by time domain contour analysis can be used as markers of vascular aging. But the previous studies that have been performed for frequency domain analysis of the PPG to date have provided only restrictive and fragmentary information. The aim of the present investigation was to determine whether the harmonics extracted from the PPG using a fast Fourier transformation could be used as an index of vascular aging. Methods: The PPG was measured in 600 recruited subjects for 30 second durations, To grasp the gross age-related change of the PPG waveform, we grouped subjects according to gender and age and averaged the PPG signal of one pulse cycle. To calculate the conventional indices of vascular aging, we selected the 5-6 cycles of pulse that the baseline was relatively stable and then acquired the coordinates of the inflection points. For the frequency domain analysis we performed a power spectral analysis on the PPG signals for 30 seconds using a fast Fourier transformation and dissociated the harmonic components from the PPG signals. Results: A final number of 390 subjects (174 males and 216 females) were included in the statistical analysis. The normalized power of the harmonics decreased with age and on a logarithmic scale reduction of the normalized power in the third (r=-0.492, P<0.0001), fourth (r=-0.621, P<0.0001) and fifth harmonic (r=-0.487, P<0.0001) was prominent. From a multiple linear regression analysis, Stiffness index, reflection index and corrected up-stroke time influenced the normalized power of the harmonics on a logarithmic scale. Conclusions: The normalized harmonic power decreased with age in healthy subjects and may be less error prone due to the essential attributes of frequency domain analysis. Therefore, we expect that the normalized harmonic power density can be useful as a vascular aging marker.

• YAKHAK HOEJI
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• v.40 no.3
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• pp.293-299
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• 1996

The $^1H$- and $^{13}C$-NMR signals of (20R)-panaxadiol and (20R)-panaxatriol were completely assigned by the extensive application of modern 2D-NMR techniques, $^1H-^1H$ COSY, HMQC and HMBC.

• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.174-175
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• 2000

1946년 S M MacNeille에 의해 연구된 유전체 다층 박막을 이용한 편광광속분리기는 브르스터 각 편광광속분리기(Brewster angle polarizing beam splitter) 혹은 맥닐 프리즘(MacNeille prism)으로 알려져 있으며 지금도 많은 광학계에서 사용되고 있다. 맥닐 프리즘은 두 개의 프리즘 사이의 빗면에 높은 굴절률( $n_{H}$ )을 갖는 물질과 낮은 굴절률( $n_{L}$ )을 갖는 물질을 λ/4 광학두께로 교번으로 한 고반사 다층박막 구조를 갖는다. 각 층의 경계면에서 브르스터 각으로 입사할 경우 p-편광파는 투과하고 s-편광파는 부분적으로 반사한다. 편광광속분리 정도는 p-편광파와 s-편광파의 투과율( $T_{p}$, $T_{s}$ ) 혹은 반사율( $R_{p}$, $R_{s}$ )의 비로 나타내며 이를 소광비(extinction ratio)라 한다. (중략)(중략)략)

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.1C
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• pp.45-51
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• 2010

In urban area, design and construction of civil engineering structures such as subway tunnel, underground space and deep excavation is impeded by unreliable site investigation. Variety of embedded objects, electric noises and traffic vibrations degrades the quality of site investigation, whatever the site-investigation technique would be. In this research, a preliminary research was performed to develop a dedicated site investigation technique for urban geotechnical sites, which can overcome the limitations of urban sites. HiRAS (Hybrid Integration of Surface Waves and Resistivity) technique which is the first outcome of the preliminary research was proposed in this paper. The technique combines surface wave as well as electrical resistivity. CapSASW method for surface-wave technique and PDC-R technique for electrical resistivity survey were incorporated to develop HiRAS technique. CapSASW method is a good method for evaluating material stiffness and PDC-R technique is a reliable method for determination of underground stratification even in a site with electrical noise. For the inversion analysis of HiRAS techniuqe, a site-specific relationship between stress-wave velocity and resistivity was employed. As for outgrowth of this research, the 2-D distribution of Poisson's ratio could be also determined.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.4
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• pp.308-315
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• 2009

Wave-current interaction due to strong ambient currents causes to alter wave properties such as wave height, wave profile and wave spectrum. In this study we first examined the SWAN model's applicability by comparing with an analytical solution of Suh et al. (1994) for wave-current interaction in finite water-depth. Numerical experiments using SWAN model have been conducted for Garolim Bay to estimate the design waveheights influenced by strong tidal currents. For the design wave periods of 8~10 sec, the design wave height of 3 m in NNW direction was increased by up to 40% when the incident waves encounter the opposing currents of 1.4 m/s while the wave height was reduced by 26% due to the following currents of 1.1 m at the bay mouth. This result indicates that the effect of wave-current interaction must be included to determine the design wave height if there exists a strong current.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.6
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• pp.332-349
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• 2016

OLAFOAM is the powerful CFD code and is an expanded version of $OpenFOAM^{(R)}$, for wave mechanics simulation. The $OpenFOAM^{(R)}$ does provide many solvers to correspond to each object of the numerical calculation in a variety of fields. OLAFOAM's governing equation bases on VARANS (Volume-Averaged Reynolds-Averaged Navier-Stokes) equation, and the finite volume method is applied to numerical techniques. The program is coded in C++ and run on the Linux operating system. First of all, in this study, OLAFOAM was validated for 1) wave transformation inside porous structure under bore and regular wave conditions, 2) wave transformation by submerged breakwater under regular wave condition, and 3) regular wave transformation and resultant vertical velocity distribution under current by comparison with existing laboratory measurements. Hereafter, this study, which is almost no examination carried out until now, analyzed closely variation characteristics of water surface level, wave height, frequency spectrum, breaking waves, averaged velocity and turbulent kinetic energy around porous submerged breakwater in the wave and current coexisting field for the case of permeable or impermeable rear beach. It was revealed that the wave height fluctuation according to current direction(following or opposing) was closely related to the turbulent kinetic energy, and others.

• Proceedings of the KIPE Conference
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• 2007.07a
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• pp.524-526
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• 2007

국내의 태양광발전용 계통 연계형 삼상 인버터는 대부분 저주파(60Hz) 변압기를 사용하는 절연형 인버터이다. 이 인버터의 경우 무변압기 또는 고주파 변압기 인버터에 비해 회로 및 제어가 간단하다. 하지만 무게나 부피가 상당히 크고, 소형화 하기 어려운 단점이 있다. 무변압기형 인버터의 경우 저주파 절연형 인버터에 비해 무게나 부피가 작고, 소형화 할 수 있으나, 계통과의 전기적 절연이 되지 않는 단점이 있다. 본 논문에서는 이러한 문제점을 해결하기 위하여 태양광발전용 고주파링크 계통 연계형 삼상 인버터 시스템을 개발 하였다.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.4
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• pp.295-300
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• 2016

This paper presents a numerical analysis of the delivery pressure wave in a 210-kW/cyl fuel injection pump (P. Corporation, Changwon-si, Korea) for medium-speed diesel engines using Ansys Fluent R15.0. Results obtained from experiment and from numerical analysis of the fuel delivery pressure wave were compared and found to be similar, thereby confirming the reliability of the numerical analysis of the delivery pressure wave in the fuel injection pump.