• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 추계학술대회 논문집
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• pp.206-213
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• 2013

본 논문에서는 적분변환법을 이용하여 면외전단 충격하중이 작용하는 두 개의 서로 다른 압전재료층 사이의 기능경사압전재료 접합층 내부 균열에 대한 과도응답 해석 을 수행한다. 기능경사압전재료의 물성치는 두께 방향을 따라 연속적으로 변하는 것으로 가정한다. 라플라스 변환과 푸리에 변환을 이용하여 문제를 복합적분방정식으로 구성하고, 수치해석을 위해 복합적 분방정식을 제 2 종 프레드홀름 적분방정식으로 표현한다. 전기적 하중, 재료물성 치의 변화율, 각 접합층의 두께가 균열의 과도응답에 미치는 영향을 보기 위해 동에너지 해방률에 대한 수치해석 결과를 제시한다.

• 조명전기설비학회논문지
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• 제19권6호
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• pp.67-74
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• 2005

접지 시스템은 전기설비의 기준 전위점을 확보할 뿐만 아니라, 대지에 낮은 저항으로 고장 전류를 흐르게 한다. 고장전류는 넓은 범위의 주파수를 포함하기 때문에 접지의 성능을 평가하기 위해선 주파수에 대한 함수로 접지임피던스에 대한 특성의 분석이 필요하다. 본 논문에서는 상용화된 접지봉(매직봉)의 접지임피던스를 0[Hz]에서 100[kHz] 범위까지 측정하였고, 접지임피던스를 회로 모델과 전달함수 모델로 구하여 측정된 값과 비교 검토하였다.

• Progress in Superconductivity
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• 제10권2호
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• pp.103-107
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• 2009

$Bi_2Sr_2Ca_1Cu_2O_x$(BSCCO 2212) superconductors for current lead were fabricated by centrifugal melting process(CMP). BSCCO 2212 powder was melted at $1200^{\circ}\C$ in a resistance furnace using a Pt crucible and poured in a rotating cylindrical mold preheated at $550^{\circ}\C$ for 2 hour. The solidified BSCCO-2212 samples were heat-treated by partial melting process in oxygen atmosphere. The current-voltage curves at 77 K of the samples were obtained by transport measurement, and the microstructure was investigated by scanning electron microscope. The $J_c$ values at 77 K of the tubes partially melted at $840^{\circ}C,\;860^{\circ}C\;and\;880^{\circ}C$ were 492, 430 and 398 $A/cm^2$, respectively. It was observed that the plate-like grains in BSCCO 2212 tube was more developed in the sample heat-treated at $840^{\circ}C$. It was found that the critical current of the BSCCO 2212 samples was dependent on the partial melting schedule regarding the grain shape and size of the BSCCO 2212.

• 공업화학
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• 제8권6호
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• pp.1034-1040
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• 1997

전기자동차의 동력원으로 사용되는 90Ah급 Nickel/Metal hydride 전지 11개로 구성된 module의 온도특성을 상용 software인 NISA II를 사용하여 해석하였다. 전지 module에 대한 element수를 감축하기 위하여 열전도도가 다른 여러 층을 통하여 전달되는 열흐름에 대한 해석을 전기저항 등가식을 사용하여 단순화하였으며, Cartesian coordinate의 축별로 다른 열전도도를 삽입하는 orthotropic model을 사용하였다. 전지 module의 온도를 낮추기 위하여 알루미늄 재질의 cooling fin을 전지와 전지사이에 삽입하여 실험을 수행하였고, 전지 module 최외곽에 위치한 fin에 의한 최고온도의 강하 효과는 미미하다는 결과를 얻었다. 전지 module내 전지별 온도차이를 극소화하기 위하여 cooling fin의 개수와 두께 그리고 측면 fin의 복합적인 영향에 대한 실험을 수행하였으며, 1mm 두께의 알루미늄 fin을 4개 사용하여 module내 전지별 최고온도의 차이를 $3^{\circ}C$ 이내로 줄일 수 있었다.

• 한국전기전자재료학회논문지
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• 제16권12S호
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• pp.1286-1291
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• 2003

Quench behavior of resistive superconducting fault current limiters (SFCLS) with various pattern shapes was investigated. The pattern shapes employed were meander, bi-spiral, and spital shapes of identical line width, gap and margin. SFCLS were fabricated from YBCO thin films grown on two-inch diameter Al$_2$O$_3$ substrates under the same conditions. The total length of current limiting paths was the shortest at the spital shape due to its larger useless space. Inductance component of SFCLs with the spiral shape was around two times as high as those of other two shapes. This is not desirable since impedance characteristics of existing power systems can be changed. Resistance rise of current limiting elements was low at a spiral shape before the whole quench completion, which may act as a disadvantage for simultaneous quench in serial connection between current limiting elements, but the temperature tended to have similar values at higher voltages. On the other hand, hi-spital shape was severe at insulation level between current limiting lines. When these aspects were considered, we concluded that a meander shape was appropriate to design for a resistive SFCL based on thin films except the concentration of electric field at edge areas of strip lines.

• 조명전기설비학회논문지
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• 제24권8호
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• pp.94-100
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• 2010

접지시스템은 전기설비의 기준 전위점을 확보할뿐만 아니라 낮은 대지저항으로 고장전류나 과도 전류를 흐르게 한다. 접지임피던스는 주파수에 대한 함수로 고장이나 과도전류가 넓은 범위의 주파수 성분을 포함하기 때문에 접지성능을 평가하는데 중요한 역할을 한다. 본 논문에서는 스테인리스강판 접지전극의 접지특성을 파악하기 위하여 3점 전위강하법으로 접지저항, 접지임피던스와 과도접지임피던스를 측정하였다. 측정된 데이터를 이용하여 접지임피던스와 과도접지임피던스의 등가 전달함수 모델은 ARMA 기법으로 모델링 되었고, 규약접지임피던스로 비교하여 평가하였다.

• 대한기계학회논문집B
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• 제31권2호
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• pp.141-150
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• 2007

This paper presents a lumped model to predict crosstalk characteristics of thermally driven inkjet print heads. Using the lumped R-C model, heating characteristics of the head are predicted to be in agreement with IR temperature measurements. The inter-channel crosstalk is simulated using the lumped R-L network. The values of viscous flow resistance, R and flow inertance, L of connecting channels are adjusted to accord with the 3-D numerical simulation results of three adjacent jets. The crosstalk behaviors of a back shooter head as well as a top shooter head have been investigated. Predictions of the proposed lumped model on the meniscus oscillations are consistent with numerical simulation results. Comparison of the lumped model with experimental results identifies that abnormal two-drop ejection phenomena are related to the increased meniscus oscillations because of the more severe crosstalk effects at higher printing speeds. The degree of crosstalk has been quantified using cross-correlations between neighboring channels and a critical channel dimension for acceptable crosstalk has been proposed and validated with the numerical simulations. Our model can be used as a design tool for a better design of thermal inkjet print heads to minimize crosstalk effects.

• Journal of the Korean Wood Science and Technology
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• 제47권6호
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• pp.700-708
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• 2019

To verify the possibility of using resistograph to estimate the age of big old living trees, we selected three Zelkova serrata and seven Pinus densiflora in Goesan. The mean diameters at breast height of Z. serrata and P. densiflora were 102 (92-116) cm and 80 (65-110) cm, respectively. The heights measured from the ground using a resistograph ranged at 1.2-4.3 m and 0.6-1.1 m for Z. serrata and P. Densiflora, respectively. The most appropriate needle speed to determine tree-ring boundaries for measuring ring width was 1500 r/min for both tree species. Alternatively, the suitable feed speeds for Z. serrata and P. densiflora were 50 cm/min and 150 cm/min, respectively. From the measured data, the mean numbers of tree rings of Z. serrata and P. densiflora were 57 (43-68) and 104 (93-124), respectively, and the mean tree-ring widths were 4.27 mm (3.18-5.09 mm) and 2.93 mm (2.32-3.34 mm), respectively. A comparison between the time series of tree-ring widths by resistograph and that from the local master chronologies tallied for the heartwood part. Finally, this study showed that resistograph can be used to estimate tree ages when a local master chronology is available.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.147-162
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• 2021

The problem of predicting a ship's form factor and associated scale effects has been subject to many investigations in recent years. In this study, an attempt is made to investigate whether the form factor is influenced by a change in the ship's speed by numerically modelling a geosim series of the KCS hull form by means of a RANS solver. The turbulence dependence of the problem is also studied by altering the closure model among three widely used approaches (the k-𝜔, k-𝜔 SST, and k-𝜀 models). The results show that at very low speeds (Froude numbers in the range of 0.02-0.06) the numerical model predicts changes in the form factor of a ship between 10% and 20%, depending on the turbulence model and scale factor choices. As the speed is increased further, the form factor exhibits little change, usually in the range of 1% or less. Simulations where the Reynolds number is changed by approximately two orders of magnitude, achieved by altering the value of viscosity, confirmed that the form factor can be considered Froude-dependent only for low speeds, predicting essentially identical values when high speed cases are considered.

• 한국정보통신학회논문지
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• 제26권11호
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• pp.1686-1696
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• 2022

본 논문에서 소개하는 페이저도에 의한 임피던스 정합회로 설계는 회로이론의 임피던스 삼각도에 기초한다. 정합회로 설계에 주어진 값들을 이용하여 페이저 도형의 작도를 통하여 설계하는 기법이다. 설계 패턴은 L형, 역L형, T형, 𝜋형을 기본으로, 미지의 리액턴스 소자를 페이저 도형을 통하여 결정한다. 본 논문에서는 입력과 출력포트가 순저항인 경우와 리액턴스를 갖는 경우의 몇 가지 사례에 대하여 설계하고 이를 직병렬 등가변환에 의하여 설계값을 검증하여 정합이 이루어짐을 확인하였다. 본 설계 기법은 입출력 위상이나 크기를 바로 파악할 수 있어 설계의 변경과 적용이 신속하여 주로 낮은 주파수 대역에서 적용이 기대된다.