• 대한조선학회논문집
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• 제35권1호
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• pp.1-14
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• 1998

2차원 천수방정식에 기초한 조류계산 수치모델을 개발하였다. 복잡한 해안선의 입력을 단순화할 수 있는 직각격자를 사용하였으며, 방정식은 효율이 뛰어난 것으로 알려져 있는 인수분해음해법(Implicit Factorization Method)에 의하여 수치적으로 풀었다. 대류항은 상류차분법으로 처리하여 수치소산이 자동적으로 들어가도록 하였으며, 따라서 수치불안정에 의한 발산을 억제할 수 있었다. 모델의 검증을 위하여 선형화된 천수방정식을 풀고 계산결과를 해석해와 비교하였으며 잘 일치하고 있음을 확인하였다. 수치모델의 응용 예로서 인천항부근의 경인운하 개발예정인 수로에서의 조류 계산결과를 보였다.

• Journal of Communications and Networks
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• 제18권3호
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• pp.340-350
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• 2016

The performance of large-scale cognitive radio (CR) networks with secondary users sustained by opportunistically harvesting radio-frequency (RF) energy from nearby primary transmissions is investigated. Using an advanced RF energy harvester, a secondary user is assumed to be able to collect ambient primary RF energy as long as it lies inside the harvesting zone of an active primary transmitter (PT). A variable power (VP) transmission mode is proposed, and an energy-based opportunistic spectrum access (OSA) strategy is considered, under which a secondary transmitter (ST) is allowed to transmit only if its harvested energy is larger than a predefined transmission threshold and it is outside the guard zones of all active PTs. The transmission probability of the STs is derived. The outage probabilities and the throughputs of the primary and the secondary networks, respectively, are characterized. Compared with prior work, the throughput can be increased by as much as 29%. The energy-based OSA strategy can be generally applied to a non-CR setup, where distributed power beacons (PBs) are deployed to power coexisting wireless signal transmitters (WSTs) in a wireless powered sensor network.

• 전력전자학회논문지
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• 제10권1호
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• pp.38-44
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• 2005

전압형 인버터에서 데드 타임은 직류단 단락을 방지하기 위하여 필요하다. 데드 타임 효과는 출력 전압, 출력 전류의 왜곡으로 나타난다. 최근 많은 논문에서 데드 타임 보상 방법에 대한 연구가 이루어졌다. 본 논문에서는 데드타임을 보상하는 것이 아니라 데드 타임이 없는 인버터를 제안한다. 부하전류를 측정할 필요도 없으며 데드 타임보상을 위한 계산도 필요 없다. 이는 인버터의 각 레그에 트랜스포머를 추가함으로써 가능하다. 제안된 방법의 각 모드 해석이 선행되고 타당성을 위한 시뮬레이션 결과가 제시된다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2017년도 전력전자학술대회
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• pp.231-232
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• 2017

This paper describes the design and implementation of a 2.5kW (500V, 5A) simmer circuit that maintains the ionization of xenon gas inside the lamp. The design is based on a LCC resonant converter in continuous conduction mode (CCM) with above resonant frequency to take advantage of high power density from using parasitic elements such as the leakage inductance in a power transformer. In addition, since the converter has current source output characteristics, it is suitable for maintaining ionization of the lamp having the negative resistance load characteristic. To verify this converter design, PSpice modeling was performed. Finally, the developed simmer circuit is verified by a resistive load of rated performance and the Ionization maintenance operation of the xenon flash lamp.

• 한국전기전자재료학회논문지
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• 제21권5호
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• pp.434-439
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• 2008

Silver pastes as the outer electrodes have been prepared using Pb-free glass frits with different content of $Bi_2O_3$ and the effects of glass composition on the degradation behaviors of the Ag electrodes were investigated using the change of adhesion between Ag electrode and alumina substrate with thermal cycle stress. Low adhesion and high surface resistance were observed in Ag electrode using glass frit with a $Bi_2O_3$ content of 60 wt%, owing to the open microstructure formed at the firing temperature of $600^{\circ}C$. When the $Bi_2O_3$ was increased to 80 wt% in the glass frit, the Ag electrodes had a dense microstructure with high adhesion and a low surface resistance. Delamination of the Ag electrodes was a major failure mode under thermal cycle stress and this was attributed to residual stress due to the thermal expansion mismatch between the Ag electrode and the alumina substrate.

• 한국전기전자재료학회논문지
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• 제21권5호
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• pp.458-462
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• 2008

In this paper, we investigated the (002) preferred orientation and morphology characteristics of AlN thin film by using reactive rf sputtering. Additionally, AlN thin films grown in the range from 150 to 300 W were studied under room temperature without substrate heating and post annealing. Sputtered AlN thin films were well grown on Si substrates and the (002) main peak in XRD patterns showed the highest intensity at 300 W with $0.25^{\circ}$ degree of full width at half-maximum (FWHM). As increased RF power, the surface roughness was increased from 1.0 to 3.4 nm. In Fourier transformation infrared spectroscopy (FTIR), $A_1$ (TO) and $E_1$ (TO) mode closed to AlN thin film confirmed the changes with increasing the intensity rate. From these results, we could confirm a chance of the growth of AlN thin film by only low temperature.

• 한국자동차공학회논문집
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• 제12권1호
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• pp.91-98
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• 2004

This paper is concerned with crash analysis for an auto-body member with the forming effect. Auto-body members such as a front frame assembly are fabricated with sheet metal forming processes that induce forming histories such as the plastic work hardening and non-uniform thickness distribution. Numerical simulation is carried out with LS-DYNA3D in order to identify the forming effect on the crashworthiness. The crash analysis of the front frame assembly with the forming effect leads to a different result from that without the forming effect. Crashworthiness such as the load-carrying capacity, the crash mode and the energy absorption are calculated to investigate and identify the forming effect. It is fully demonstrated that the design of auto-body members needs to consider the forming effect for accurate assessment of the load-carrying capacity and the deformation mechanism of the formed members.

• Journal of Electrical Engineering and Technology
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• 제6권5호
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• pp.671-676
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• 2011

A multilayer square-type piezoelectric transformer with a hole at the center was investigated in this paper. Temperature distribution at the center was improved by using this construction, therefore increasing input voltage and output power. This model was simulated and investigated successfully by applying a finite element method (FEM) in ATILA software. An optimized structure was then fabricated, examined, and compared to the simulation results. Electrical characteristics, including output voltage and output power, were measured at different load resistances. The temperature distribution was also monitored using an infrared camera. The piezoelectric transformer operated at first radial vibration mode and a frequency area of 70 kHz. The 16 W output power was achieved in a three-layer transformer with 96% efficiency and $20^{\circ}C$ temperature rise from room temperature under 115 V driving voltage, 100 ${\Omega}$ matching load, $28{\times}28{\times}1.8mm$ size, and 2 mm hole diameter. With these square-type multilayer piezoelectric transformers, the temperature was concentrated around the hole and lower than in piezoelectric transformers without a hole.

• 한국전기전자재료학회논문지
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• 제33권4호
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• pp.276-280
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• 2020

A linear piezoelectric actuator that utilizes the elliptical motion of the two tips of the actuator is proposed. This device is easy to fabricate owing to its simple structure, consisting of three piezo ceramic benders and is suitable for use in micro robotic applications. A π-shaped structure, which was composed of four piezo ceramic benders, was constructed. Two of the benders were positioned on the center of the actuator, and the joints were attached at the ends of the cantilever. The other two benders were positioned on the side of the actuator and were attached between the joint and the tips. The actuator structure was designed to obtain the first bending mode of the horizontal vibration and the vertical vibration at the same frequency, resulting in elliptical motions at the tips. When two sinusoidal wave voltages with a 90-degree phase difference were applied to the two pairs of the actuator benders, elliptical motions were obtained at the tips. The driving characteristics of the prototype actuator were then measured using a laser doppler vibrometer.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.3-4
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• 2007

본 논문은 전력계통의 보다 합리적인 신뢰도 운영을 실시하고자 근래 V&R Energy System Research에서 개발한 신뢰도 평가 프로그램인 POM과 EPRI에서 개발한 PRA를 이용하여 우리나라계통에 적용하여 성공적으로 얻은 다양한 사례연구 결과를 소개한다. 여기서는 PRA 프로그램을 우리나라 전력계통의 계획측면에서 활용방안을 모색하기로 하고 다음과 같은 몇 가지 사례연구에 주안점을 두고 실시하였다. 2008년도 우리나라 계통의 병입되는 당진화력 7,8호기의 신설에 따란 계통영향에 대한 신뢰도 지수 비교 순석과 2007년부터 2012년까지의 향후 6년간에 걸친 장기계통계획에 대한 우리나라계통의 신뢰도 지수의 변화를 비교 분석하는 등 계통계획측면에서의 활용방안의 타당성에 관하여 검토하였다.