• International Journal of Automotive Technology
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• 제7권1호
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• pp.1-7
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• 2006

The ignition delay of a dual fuel system has been numerically investigated by adopting a constant volume chamber as a model problem simulating diesel engine relevant conditions. A detailed chemical kinetic mechanism, consisting of 28 species and 135 elementary reactions, of dimethyl ether (DME) with methane ($CH_{4}$) sub-mechanism has been used in conjunction with the multi-dimensional reactive flow KIVA-3V code to simulate the autoignition process. The start of ignition was defined as the moment when the maximum temperature in the combustion vessel reached to 1900 K with which a best agreement with existing experiment was achieved. Ignition delays of liquid DME injected into air at various high pressures and temperatures compared well with the existing experimental results in a combustion bomb. When a small quantity of liquid DME was injected into premixtures of $CH_{4}$/air, the ignition delay times of the dual fuel system are longer than that observed with DME only, especially at higher initial temperatures. The variation in the ignition delay between DME only and dual fuel case tend to be constant for lower initial temperatures. It was also found that the predicted values of the ignition delay in dual fuel operation are dependent on the concentration of the gaseous $CH_{4}$ in the chamber charge and less dependent on the injected mass of DME. Temperature and equivalence ratio contours of the combustion process showed that the ignition commonly starts in the boundary at which near stoichiometric mixtures could exists. Parametric studies are also conducted to show the effect of additive such as hydrogen peroxide in the ignition delay. Apart from accurate predictions of ignition delay, the coupling between multi-dimensional flow and multi-step chemistry is essential to reveal detailed features of the ignition process.

• 한국통신학회논문지
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• 제18권4호
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• pp.549-560
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• 1993

접지면이 있는 무한 평판의 유전체상에 놓인 점 전기전류원 문제에서 야기되는 마이크로스트립 표면 dyadic Green 함수에 대한 간단하면서도 정확한 근사표현식이 본 논문에서 개발된다. 이 근사표현식은 본 논문에서 소개하는 새로운 방법에 의해서 유도된 공간파와 표면파 그리고 전이지역에서 이들간의 결합을 나타내는 전이함수를 모두 포함하고 있으며, 유전체 두께가 $0.04\pi$($\pi$는 자유공간파장)나 되는 두꺼운 경우에도 점원에서 $0.1\pi$ 떨어진 가까운 위치에서까지 유용하므로 실제 마이크로스트립 안테나 어레이설계시 안테나 소자간 전자기적 결합에 의한 어레이 안테나의 특성저하나 마이크로웨이브회로 또는 초고속의 디지탈 프린트 회로기판 설계시 연결선 특성임피던스와 연결선간의 crosstalk에 의한 회로성능 저하 문제를 해석하는데 아주 유효하다. 이 근사식에 의한 상호임피던스 수치해석 결과와 함께 계산에 소요되는 CPU 시간을 예시함으로써 본 근사식의 정확성 및 효율성을 입증하여 보았다.

• 대한전기학회논문지
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• 제41권8호
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• pp.858-868
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• 1992

0.085Ba(LaS11/2TNbS11/2T)OS13T-0.915Pb(ZrS1yTTiS11-yT)OS13T (0.45$\leq$y$\leq$0.65) transparent electrooptic ceramics were fabricated by two-stage sintering method. The structural, ferroelectric and electrooptic properties were investigated varying composition and second sintering time. Also the possibility of application to electrooptic device was studied. If we increase the PbZrOS13T contents, dielectric constants were increased and Curie temperature was decreased. In the composition of 0.55[mol] PbZrOS13T, electromechanical coupling factor and piezoelectric charge constant were the highest values of 43[%] and 173x10S0-12T[C/N], respectively. Mechanical quality factors were decreased with the increasing PbZrOS13T contents. Light transmittance was increased with wavelength when measured from 300[nm] to 900[nm], and with PbZrOS13T contents in the range of 0.50[mol]-0.65[mol], and had the highest value of 67[%] in the composition of 0.65[mol] PbZrOS13T. From the results of ferroelectric hysteresis loop and transmitted light intensity with electric field, the specimens with compositions of 0.65,0.60,0.55[mol] PbZrOS13T were applicable to electrooptic memory device and those with compositions of 0.50,0.45[mol] PbZrOS13T were applicable to linear electrooptic device.

• 조명전기설비학회논문지
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• 제28권1호
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• pp.16-28
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• 2014

This paper presents a novel high-power-factor circuit topology of AC to AC current-fed type high frequency resonant inverter which includes the function of power factor correction(PFC) in the proposed inverter to operate the AC input block with high power factor. The proposed circuit topology of AC to AC current fed type high resonant inverter removes DC link electrolytic capacitor and has also the one of power factor correction(PFC) in the inverter circuit without an additional PFC circuit since the input current by constituting it in parallel as an unit inverter, which assumes the class-E high frequency resonant inverter of conventional current-fed type, flows in the form of the resultant current flowing through each constant current reactor($L_{d1}$, $L_{d2}$). The circuit analysis of proposed inverter is generally described by adopting the normalized parameters and the evaluation of its operating characteristics are conducted by using the parameters such as the ratio of switching and resonant frequency(${\mu}$), coupling coefficient(k) and so on. An example of procedure for circuit design based on the characteristic values obtained from the theoretical analysis is presented. To confirm the validity of the theoretical analysis, the experimental results are also presented. In the future, the proposed inverter shows it can be practically used as power supply system for induction heating application, DC-DC converter etc.

• 한국정보통신학회논문지
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• 제6권1호
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• pp.89-98
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• 2002

본 연구에서는 광계측 기술을 이용하여 배전자동화 개폐기 내에서 발생하는 전자 계측장치의 절연문제 및 측정오차의 문제점을 개선하기 위하여 배선자동화개폐기 내장형 광전류 및 광전압센서를 연구하였다. 자기광학 효과(magneto optic effect)인 페러데이효과(Faraday effect)를 이용하여 최적의 광전류 센서를 설계 제작하여 높은 전류까지 선형성을 유지시키고 다른 상의 전류에 대한 유도현상을 최소로 하기 위해 순철 코아를 사용하여 광전류 센서를 일체화시켜 설계 제작하였다. 설계내에서 결정의 굴절률 및 방위각의 변화에 의해 생기는 전기광학효과(electrooptic effect)인 포켈스 효과(pockels effect)를 이용하여 광전압센서를 구성하였으며 배전 자동화용 개폐기의 협소한 내부구조를 고려하여 공간전계방식을 채택하였다. 또한 다심의 광섬유를 개폐기와 외부의 신호처리 단말기와 연결하기 위하여 기밀형 멀티 광커넥터를 설계 자작하여 접속 손실 및 가스 누설 시험을 하였다. 전기적 특성시험에서 광 전류센서에서는 인가 전류에 대한 선형 특성은 20A 에서 700A까지 변동 오차 2.5% 이내의 선형성을 유지하였으며, 광전압센서에 있어서 인가 전압에 대한 선형 특성은 6.6kV에서 19.8kV까지 거의 변동 오차가 1% 이내로 우수한 선형 특성을 나타냈다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.403-406
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• 2000

The piezoelectric properties and the doping effect of N $b_2$ $O_{5}$ and Mn $O_2$for 0.95PbZ $r_{x}$ $Ti_{x}$ $O_3$+0.05Pb(M $n_{0.42}$ $W_{0.26}$S $b_{0.32}$) $O_3$ compositions have been investigated. In the composition of 0.95PbZ $r_{0.54}$ $Ti_{0.46}$ $O_3$+0.05Pb(M $n_{0.42}$ $W_{0.26}$S $b_{0.32}$) $O_3$the Values Of $k_{p}$ find and $\varepsilon$$_{33}$ $^{T}$ are maximized, but $Q_{m}$ Was minimized ( $k_{p}$ =0.51, $Q_{m}$ =1750). The grain size was suppressed and the uniformity of grain was improved with doping concentration of N $b_2$ $O_{5}$ for 0.95PbZ $r_{0.54}$ $Ti_{0.46}$ $O_3$+0.005Pb(M $n_{0.42}$ $W_{0.26}$S $b_{0.32}$) $O_3$sample. The values of $k_{p}$ increased and the values of $Q_{m}$ slightly decreased when 0.5 wt% of N $b_2$ $O_{5}$ is doped. And the values of $k_{p}$ was the same formation of the N $b_2$ $O_{5}$ dopant when 0.5 wt% of M $n_2$ $O_{5}$ is doped. But the values of $Q_{m}$ was deeply decreased when 0.5 wt% of Mn $O_2$is doped. As a experiment results under high electric field driving, this piezoelectric ceramics are very stable. Conclusively, piezoelectric ceramic compsiton investigated at this paper is suitable for application to high power piezoelectric devices.. devices..ices.. devices..

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.147-147
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• 2013

Multiferroic material $BiFeO_3$ (BFO) is a typical multiferroic material with a room-temperature magnetoelectric coupling in view of high magnetic- and ferroelectric-ordering temperatures (Neel temperature $T_N$ ~ 647 K and Curie temperature TC ~1,103 K). Rare-earth ion substitution at the Bi sites is very interesting, which induces suppressed volatility of the Bi ion and improved ferroelectric properties. At the same time, the Fe-site substitution with magnetic ions is also attracting, since the enhanced ferromagnetism was reported. In this study, BFO, $Bi_{0.9}Dy_{0.1}FeO_3$ (BDFO), $BiFe_{0.97}Co_{0.03}O_3$ (BFCO) and $Bi_{0.9}Dy_{0.1}Fe_{0.97}Co_{0.03}O_3 $ (BDFCO) compounds were prepared by conventional solid-state reaction and wet-mixing method. High-purity $Bi_2O_3$, $Dy_2O_3$, $Fe_2O_3$ and $Co_3O_4$ powders with the stoichiometric proportions were mixed, and calcined at $500^{\circ}C$ for 24 h. The samples were immediately put into an oven, which was heated up to 800oC and sintered in air for 1 h. The crystalline structure of samples was investigated at room temperature by using a Rigaku Miniflex powder diffractometer. The field-dependent magnetization measurements were performed with a vibrating-sample magnetometer. The electric polarization was measured at room temperature by using a standard ferroelectric tester (RT66B, Radiant Technologies). Dy and Co co-doping at the Bi and the Fe sites induce the enhancement of both magnetic and ferroelectric properties of $BiFeO_3$.

• Advances in nano research
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• 제8권1호
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• pp.83-94
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• 2020

An analytical formulation and solution process for the buckling analysis of porous magneto-electro-elastic functionally graded (MEE-FG) beam via different thermal loadings and various boundary conditions is suggested in this paper. Magneto electro mechanical coupling properties of FGM beam are taken to vary via the thickness direction of beam. The rule of power-law is changed to consider inclusion of porosity according to even and uneven distribution. Pores possibly occur inside FGMs due the result of technical problems that lead to creation of micro-voids in these materials. Change in pores along the thickness direction stimulates the mechanical and physical properties. Four-variable tangential-exponential refined theory is employed to derive the governing equations and boundary conditions of porous FGM beam under magneto-electrical field via Hamilton's principle. An analytical model procedure is adopted to achieve the non-dimensional buckling load of porous FG beam exposed to magneto-electrical field with various boundary conditions. In order to evaluate the influence of thermal loadings, material graduation exponent, coefficient of porosity, porosity distribution, magnetic potential, electric voltage and boundary conditions on the critical buckling temperature of the beam made of magneto electro elastic FG materials with porosities a parametric study is presented. It is concluded that these parameters play remarkable roles on the buckling behavior of porous MEE-FG beam. The results for simpler states are proved for exactness with known data in the literature. The proposed numerical results can serve as benchmarks for future analyses of MEE-FG beam with porosity phases.

• 한국태양에너지학회 논문집
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• 제33권4호
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• pp.39-45
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• 2013

This paper presents the estimation of minimum BESS capacity for regulating the output of wind farms considering power grid operating condition in Jeju Island. To analyze the characteristics of wind farm outputs with a BESS, the real data of wind farms, Sung-San, Sam-dal and Hang-Won wind farm, located in the eastern part of Jeju island is considered. The wind farms are connected to Sung-san substation to transfer the electric power to Jeju power grid. Consequently, at PCC (Point of Common Coupling), it can see a huge wind farm connected to the substation and thus it can be expected that the smoothing effect is affected by not only the different wind speeds for each area but also the different mechanical inertia of wind turbines. In this paper, two kinds of simulation have been carried out. One is to analyze the real data of wind farm outputs during a winter season, and the other is to connect a virtual BESS to eliminate the unintended generating power changes by the uncontrolled wind farm outputs as shown in the former data. In the conclusion, two kinds of simulation results show that BESS installed in the substation is more efficient than each wind farms with BESS, respectively.

• 대한기계학회논문집A
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• 제38권10호
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• pp.1101-1107
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• 2014

중이온 입자가속기는 중이온을 radio frequency (RF) 주파수로 가속하는 장치이다. RF 공동부에 인가된 전기장은 입력된 RF 파에 의해 전자기파의 위상에 맞춰 중이온을 연속적으로 가속한다. 이를 위해서는 안정적으로 RF 파를 공동부 내부에 전달할 수 있는 커플러의 형상설계가 요구된다. 중이온 가속기에서의 RF 커플러는 입력부와 RF 주파수의 파를 방출하는 커플러 양 끝단 간의 온도차이가 매우 크다. 이 온도차를 극복하기 위해선 초저온(약 0K)부터 상온 간(약 300K)의 열 변형을 고려한 해석 및 설계기술이 필요하다. 본 연구는 RF 커플러의 구조에 따른 출력 전기장의 세기와 온도 분포, 열 손실과 열 변형을 고려한 내구도 분석을 통해 성능 향상을 위한 방안들을 도출하는 것을 목적으로 하였다.