• 한국항행학회논문지
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• 제20권4호
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• pp.361-366
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• 2016

본 논문은 S-파라미터를 어드미턴스 파라미터로 변환하는 것을 바탕으로 비대칭 분배되면서 동시에 임의의 임피던스로 변환시킬 수 있는 임피던스 변환기를 나타내었다. 회로 해석 방법을 우수/ 기수 모드 방법과 비교하면 본 논문의 파라미터 변환을 통한 방법은 위상 지연 정보와 임의의 포트 임피던스 값을 포함시키고 그리고 비대칭 구조등을 해석하는데 간단함을 알 수 있다. 이 설계 방법의 타당성을 확인하기 위해서 중심주파수 1 GHz에서 3:1의 비대칭 분배비율을 갖고 있고 $50{\Omega}$을 $12.5{\Omega}$ 비율로 변환되는 임피던스 변환기를 설계하였다. 임피던스 변환기를 구현하는 방법은 유도된 수식으로부터 계산된 작은 임피던스 선로를 병렬 오픈스터브가 연결된 전송선로를 사용하여 구현하였고, 이것의 실험 결과는 시뮬레이션 결과와 동일하게 나옴을 확인하였다.

• Journal of Communications and Networks
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• 제13권2호
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• pp.187-200
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• 2011

We present the design and implementation of a novel anti-malware system called SplitScreen. SplitScreen performs an additional screening step prior to the signature matching phase found in existing approaches. The screening step filters out most non-infected files (90%) and also identifiesmalware signatures that are not of interest (99%). The screening step significantly improves end-to-end performance because safe files are quickly identified and are not processed further, and malware files can subsequently be scanned using only the signatures that are necessary. Our approach naturally leads to a network-based anti-malware solution in which clients only receive signatures they needed, not every malware signature ever created as with current approaches. We have implemented SplitScreen as an extension to ClamAV, the most popular open source anti-malware software. For the current number of signatures, our implementation is $2{\times}$ faster and requires $2{\times}$ less memory than the original ClamAV. These gaps widen as the number of signatures grows.

• 한국광학회지
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• 제35권2호
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• pp.49-60
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• 2024

본 연구에서는 킬로와트 급 고출력 레이저의 대기 전파 시뮬레이션에 필요한 위상판의 개수를 분석하였다. 킬로와트 급 레이저가 대기 중에 전파될 때, 주로 대기 난류와 열적 블루밍 효과에 영향을 받는다. 이에 따라 split step 방법을 사용하여 대기의 흡수 및 산란에 의한 손실, 그리고 난류와 열적 블루밍으로 인한 빔의 왜곡 현상을 구현할 때, 위상판의 개수는 시뮬레이션의 정확성 및 소요 시간을 결정짓는 중요한 요소이다. 본 연구에서는 광범위한 대기 난류 조건에서 많은 수의 위상판(예: 150개)을 사용하여 시뮬레이션을 진행하고, 레이저 출력 밀도 2.5×10⁶ W/m² (50 cm 직경 레이저 빔의 경우 500 kW 출력) 미만의 고출력 레이저 빔 전파 시뮬레이션에 필요한 위상판 개수에 대한 새로운 가이드 라인을 제시한다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 추계 학술대회논문집
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• pp.215-220
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• 2004

A mathematical formulation based on two-phase, two-fluid hyperbolic conservation laws is developed to investigate propagation of shock waves in one- and two-dimensions. We used a high resolution upwind scheme called the split-coefficient matrix method. Two extreme cases are computed for validation of the computer code: the states of a pure gas and a pure liquid. Computed results agreed well with the previous experimental and numerical results. It is studied how the shock wave propagation pattern is affected by the void fraction in the two-phase flow. The shock structure in a two-phase flow turned out, in fact, much deviated from the shape well known in the gas only phase.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2013년도 추계학술대회 논문집
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• pp.111-112
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• 2013

The three-phase four-leg voltage source inverter (VSI) topology can be an interesting option for the three phase-four wire system. With an additional leg, this topology can handle the neutral current, hence the DC link capacitance can be reduced significantly. In this paper the three dimensional space vector modulation (3D SVM) in ${\alpha}{\beta}{\gamma}$ coordinates for the three-phase four-leg VSI is presented. By using the 3D SVM method, the DC link voltage can be reduced by 16% compared with the split DC link capacitor topology and the output distortion can also be reduced under the unbalanced load condition.

• Journal of Electrical Engineering and Technology
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• 제12권5호
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• pp.1945-1954
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• 2017

In recent years, several LCL filter design methods for different converter topologies have been published, many of which use analytical expressions to calculate the ideal converter AC voltage harmonic spectrum. This paper presents the LCL filter design methodology but the focus is on presentation and validation of the non-iterative filter design method for a grid-connected three-phase two-level PWM-VSC. The developed method can be adapted for different converter topologies and PWM algorithms. Furthermore, as a starting point for the design procedure, only the range of PWM carrier frequencies is required instead of an exact value. System nonlinearities, usually omitted from analysis have a significant influence on VSC AC voltage harmonic spectrum. In order to achieve better accuracy of the proposed procedure, the system nonlinear model is incorporated into the method. Optimal filter parameters are determined using the novel cost function based on higher frequency losses of the filter. An example of LCL filter design for a 40 kVA grid-connected PWM-VSC has been presented. Obtained results have been used to construct the corresponding laboratory setup and measurements have been performed to verify the proposed method.

• 대한기계학회논문집A
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• 제25권7호
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• pp.1073-1081
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• 2001

Many researches have published numerous papers about the high-strain-rate obtained from Split Hopkinson Pressure Bar(SHPB) tests. And 6.5wt%Si steel is widely known as an excellent magnetic material because its magnetostriction is nearly zero. Single crystals are prepared by the Floating Zone(FZ) method, which melts the alloy by the use of a high temperature electron beam in a pure argon gas condition. In this paper, the fracture behavior of the poly crystals and single crystals (DO$_3$phase) of Fe-6.5wt%Si alloy by SHPB test is observed. The comparison of high-strain-rate results with static results was done. Obtained main results are as follows: (1) Fe-6.5wt%Si alloy has higher strength at high-strain-rate tensile. SHPB results of polycrystal are twice as high as static results. (2) From the fractography, the cleavage steps are remarkably reduced in the SHPB test compared with the static test.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1998년도 Proceedings ICPE 98 1998 International Conference on Power Electronics
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• pp.871-875
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• 1998

A DSP-based source current control for power conditioner is presented to compensate current harmonics and asymmetries of three-phase four-wire emergency generators caused by nonlinear and/or unbalanced loads. There-phase voltage type converter with split-dc-capacitor is adopted as the power circuit and a new direct source current control method is suggested, which simplifies the controller. The proposed control method shapes the generator current sinusoidally inphase with the voltage and allows the generator to supply maximum power even to single phase loads. An IGBT base lookVA prototype with the controller realized with a DSP (TMS320C32) is built and tested to verify the performance of the power conditioner.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2016년도 전력전자학술대회 논문집
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• pp.235-236
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• 2016

본 논문에서는 400Hz 항공기용 3상 4선식 인버터의 전압 제어에 대해 연구하였다. 시스템에서 불평형이 발생하면 중성선 전류가 증가하며 이에 따라 출력전압 불균형 및 왜곡 증가 등 시스템에 심각한 문제를 발생시킨다. 전압의 크기를 제어해주는 RMS 제어의 경우 불평형 발생 시 전압의 크기는 정상적으로 제어가 가능하지만, THD가 상승하여 전력의 품질이 저하될 수 있다. 다른 제어 방식인 비례 공진(PR) 제어는 순시적으로 제어를 함으로써 전압의 크기뿐만 아니라 위상차 및 THD 감소 등의 향상된 전력 품질을 기대할 수 있다. 두 제어방법의 비교는 시뮬레이션 및 실험을 통해 수행하였으며, 두 제어방법 불평형 발생 시 모두 전압의 크기 오차가 3% 이하로 정상적으로 제어하는 것을 확인하였고, THD는 RMS 제어에 비하여 PR 제어의 결과가 2% 감소하는 것을 확인하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 하계학술대회 논문집 A
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• pp.459-461
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• 1994

This paper proposed a new converter topology improving the split source type converter. In this converter. two switches and six diodes add to the split source type converter. The proposed converter has a performance minimized a negative torqe, putting a phase current off by double impressed voltage 2Vdc. Hence, a new converter results in increase of the average output power and improves converter efficiency in heavy load and high speed. Theoretical prediction is verified by experimental results got with a new proposed converter and 8/6 poles SRM.