• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.10
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• pp.41-48
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• 2008

This paper proposes a three-phase Z-source dynamic voltage restorer (Z-DVR) to mitigate the voltage sag for the critical loads. The proposed system is composed of passive filter and Z-source topology inverter. As an ESS(Energy Storage System) of the proposed system is employed the Proton Exchange Membrane Fuel Cells (PEMFC). To calculate and control the harmonics and compensation voltage, $i_{d}-i_{q}$ theory in dq rotating reference frame and PI controller are used. In case that three-phase voltage sags occurred, a PSIM simulation was done for the performance comparison of the conventional method employed battery stacks and proposed method. As a result, considering the voltage compensation performance, each method was nearly similar. Also, the compensation performance and the %THD(%Total Harmonic Distortion) result under the various source voltage conditions (sag or swell) were presented and discussed to show the performance of the proposed system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.641-646
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• 2016

Soot particles generated by fossil fuel combustion normally have fractal morphology with aggregates consisting of small spherical particles. Thus, Rayleigh or Mie elastic light scattering theory is not feasible for determining the fractal properties of soot aggregates. This paper describes a detailed process for applying Rayleigh-Debye Gans (RDG) scattering theory to effectively extract the morphological properties of any nano-scale particles. The fractal geometry of soot aggregates produced from an isooctane diffusion flame was observed using ex situ transmission electron microscopy (TEM) after thermophoretic sampling. RDG scattering theory was then used to analyze their fractal morphology, and various properties were calculated, such as the diameter of individual soot particles, number density, and volume fraction. The results show indiscernible changes during the soot growth process, but a distinct decreasing trend was observed in the soot oxidation process. The fractal dimension of the soot aggregates was determined to be around 1.82, which is in good agreement with that produced for other types of fuel. Thus, it can be concluded that the value of the fractal dimension is independent of the fuel type.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.10
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• pp.720-727
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• 2019

Resonating thermal lags of solid fuel with heat transfer oscillations generated by boundary layer oscillation is the primary mechanism of the occurrence of the LFI (Low Frequency Combustion Instability) in hybrid rocket combustion. This study was experimentally attempted to confirm that how the boundary layer was perturbed and led to the LFI. Special attention was also made on oxidizer swirl injection to investigate the contribution to combustion stabilization. Also the overall behavior of fluctuating boundary layer flow and the occurrence of the LFI was monitored as swirl intensity increased. Fluctuating boundary layer was successfully monitored by the captured image and POD (Proper Orthogonal Decomposition) analysis. In the results, oscillating boundary layer became stabilized as the swirl intensity increases. And the coupling strength between high frequency p', q' diminished and periodical amplification of RI (Rayleigh Index) with similar frequency band of thermal lag was also decreased. Thus, results confirmed that oscillating axial boundary layer triggered by periodic coupling of high frequency p', q' is the primary mechanism to excite thermal resonance with thermal lag characteristics of solid fuel.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.5
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• pp.627-633
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• 2019

This study aimed to predict the resistance and propulsion performance of a ship using computational fluid dynamics (CFD) and a database as well as establish an assessment method for the energy efficiency design index (EEDI) using the results. First, the total resistance of the studied ship is obtained using CFD. A flow analysis is conducted with the free surface and trim and sinkage using a commercial CFD code (STAR-CCM+). The effective power of the ship is assessed based on the CFD results. The quasi-propulsive efficiency is calculated from an empirical prediction equation using experimental data and similar material. Finally, a general calculation program for the EEDI is established based on the hydrodynamic results, ship information for principal particulars, conversion factor of $CO_2$ for fuels, and fuel consumption.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2019.10a
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• pp.6-6
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• 2019

대마는 인류가 이용해 온 가장 오래된 약제 중 하나로 그 원산지는 중앙아시아와 남아시아이다. 식물분류학적으로 대마속 일년생 식물로서 Cannabis sativa, Cannabis indica, Cannabis ruderalis 3종이 있으며, 우리나라에서 재배되고 있는 종은 Cannabis sativa이다. 대마 재배의 역사는 인류의 시작과 그 궤를 같이하며, 동 서양을 막론하고 고대 문명에서 대마에 대한 기록을 쉽게 찾아볼 수 있다. 기록에 의하면 병의 치료나 심리적 치유 및 신에게 제사를 올릴 때 제사장이 사용한 것으로 알려져 있다. 대마의 약효에 대하여는 B.C. 2737년 중국의 신농황제시대의 기록에 관절염과 통증등 의료목적으로 사용했던 최초의 기록이 있으며 본초강목과 동의보감에 저술되어 있다. 우리나라의 대마에 관한 문헌 기록은 삼국지 '위지동이전', 삼국사기 '동성왕편'과 삼국유사에 삼베를 사용한 기록이 있는 것으로 미루어 봤을 때 대마재배의 역사는 삼국시대 이전으로 볼 수 있다. 우리 민족은 생활 속에서 대마를 즐겨 사용하였으며 삼베로 의복과 멍석, 행주 그리고 칠공예품이나 신발등을 만들어 사용하였으며, 죽음에 이르러 삼베옷을 수의로 사용하였다. 대마의 용도는 뿌리, 줄기, 잎, 꽃대 그리고 씨앗까지 다양하게 이용된다. 전통적으로 줄기의 껍질을 이용한 섬유제품이 있으며 실, 의복 및 밧줄등이 있다. 대마 줄기의 속대는 종이, 건축자재, 연료로 사용된다. 씨앗의 경우 식품과 조류의 먹이, 생약으로 이용되고 씨앗의 기름은 연료, 화장품, 맛사지 오일등으로 사용되고 있다. 환각성분이 있어 마리화나 원료로 사용되는 꽃대와 잎은 의약품의 원료로 주목받고 있다. 대마에 관한 최초의 논문은 1843년에 Cannabis indica의 약효에 관한 것으로 보고되었다. 1850년부터 1937년까지 미국의 약전은 대마를 100가지 이상의 질병에 효과가 있는 주요 의약품으로 기재하고 있다. 세계적으로 여러 가지 이유로 대마를 의료 응용과 연구 및 사용을 제한하여 대마에 관한 연구가 침체되었다. 대마의 의학연구는 대마의 약효성분인 칸나비노이드의 발견과 그 구조 및 약효에 관한 연구가 시작되면서 1960년대부터 증가하였으며 2000년 이후에는 칸나비노이드 및 칸나비디올의 다양한 의학적 효과가 밝혀지면서 급격히 증가하고 있다. 대마에 포함된 성분의 의학적 효과가 입증되면서 대마 사용을 합법화한 국가가 증가하면서 대마 산업이 급부상하고 있으며, 의료용뿐만 아니라 기호용, 식품용, 그리고 주류 및 음료시장까지 확대되고 있다. 우리나라도 2019년 3월 질병 치료 목적 대마성분 의약품을 제한적으로 허용하는 마약류 관리에 관한 법률 일부 개정안이 시행되면서 의료용 대마에 관한 연구와 산업화에 관심이 증가하는 추세이다.

• Journal of the Korean Institute of Gas
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• v.19 no.3
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• pp.44-48
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• 2015

The equations of hydrocarbon dew points(DT) of the fuel gas mixtures have been derived using the multiple regression analysis. In QSDR(Quantitative Structure Dew-point Relationship), the principal descriptors are CN(average carbon number) and BI(the ratio of the branched isomers). QSDRs studied by changing the pressures of the fuel gas mixtures in the range of 100 kPa ~ 500 kPa are as follows; $$DT(^{\circ}C)=-683.1+1224.98CN-898.01CN^2+308.58CN^3-49.56CN^4+3.02CN^5-12.42BI$$ (at 100 kPa, $$R_{adj}{^2}=0.99$$) (1) $$DT(^{\circ}C)=-745.2+1351.66CN-978.1CN^2+332.7CN^3-52.96CN^4+3.20CN^5-12.84BI$$ (at 200 kPa, $$R_{adj}{^2}=0.99$$) (2) $$DT(^{\circ}C)=-795.4+1457.1CN-1051.1CN^2+357.53CN^3-57.07CN^4+3.46CN^5-13.10BI$$ (at 300 kPa, $$R_{adj}{^2}=0.99$$) (3) $$DT(^{\circ}C)=-868.1+1608.4CN-1156.0CN^2+393.38CN^3-63.06CN^4+3.85CN^5-13.39BI$$ (at 500 kPa, $$R_{adj}{^2}=0.99$$) (4) As the average carbon numbers in the mixed fuel being reduced or the ratio of the branched isomers having a boiling point lower increase, The hydrocarbon dew point becomes lower, The differences between the hydrocarbon-dew points determined by the multiple regression and those calculated by the commercial program, VMGSim are negligible.

• Microbiology and Biotechnology Letters
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• v.38 no.4
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• pp.461-466
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• 2010

In this study the feasibility of simultaneous electricity generation and treatment of swine farm wastewater using microbial fuel cells (MFCs) was examined. Two single-chamber MFCs containing an anode filled with different ratio of graphite felt and stainless-steel cross strip was used in all tests. The proportion of stainless-steel cross strip to graphite felt in the anode of control microbial fuel cell (CMFC) was higher than that of swine microbial fuel cell (SMFC) to reduce construction costs. SMFCs produced a stable current of 18 mA by swine wastewater with chemical oxygen demand (COD) of $3.167{\pm}80\;mg/L$ after enriched. The maximum power density and current density of SMFCs were $680\;mW/m^3$ and $3,770\;mA/m^3$, respectively. In the CMFC, power density and current density was lower than that of SMFC. CODs decreased by the SMFC and CMFC from $3.167{\pm}80$ to $865{\pm}21$ and $930{\pm}14\;mg/L$, achieving 72.7% and 70.6% COD removal, respectively. The suspended solid (SS) of both fuel cells was also reduced over 99% ($4,533{\pm}67$ to $24.0{\pm}6.0\;mg/L$). The concentration of nutritive salts, ${NH_4}^+$, ${NO_3}^-$, and ${PO_4}^{3-}$, dropped by 65.4%, 57.5%, and 73.7% by the SMFC, respectively. These results were similar with those of CMFC. These results show that the microbial fuel cells using electrode with mix stainless-steel cross strip and graphite felt can treat the swine wastewater simultaneously with an electricity generation from swine wastewater.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.12
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• pp.1129-1135
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• 2013

In this, three types of natural gas were employed to investigate the effect of low-calorific natural gas on the performance of and emissions from a heavy-duty CNG engine. The performance and emission characteristics were analyzed by conducting a full-load test, WHSC mode test, and WHTC mode test. The results showed that the torque of low-calorific natural gas with $9,800kcal/Nm^3$ of higher heating value decreased by 4.4 compared to that of the current natural gas with $10,400kcal/Nm^3$ of heating value. With low-calorific fuels, CO, $CO_2$, and $NO_x$ emissions decreased. However, THC emissions increased. According to the WHSC and WHTC mode test results, the thermal efficiency increased and the emission characteristics showed a similar trend to the full-load test results. Low-calorific natural gases cause a decrease in torque at full-load operation conditions and an increase in hydrocarbon emissions.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.5 no.1
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• pp.79-84
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• 2007

Inventories of soluble elements in the gap and grain boundaries of domestic used PWR fuel pellets were measured to estimate the quantities of radionuclides that are liable to be rapidly released into the groundwater of a disposal site. The gap inventory of cesium for the pellets in the used fuel with a burn-up range of 45 to 66 GWD/MTU showed 0.85 to 1.7% of its total inventory, which was close to 1/6 to 1/3 of the fission gas release fraction (FGRF). However, the amounts of cesium released from the gaps of the pellets below 40 GWD/MTU of a burn-up and less than 1% FGRF were so erratic that the gap inventory could not be defined by ie FGRF. Strontium inventories in the gap and grain boundaries of the pellets in the same rod were not significantly varied, and the iodine inventory in the gap of the used PWR fuels was estimated to be less than or the same as the FGRF.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.174-174
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• 2008

초음파를 이용하여 액체 연료를 분사하면 균일한 입경과 미립화가 우수하며 에너지 절약과 공해방지등을 할 수 있다. 또한 유속과 유량에 관계없이 이용할 수 있어 반도체 분야의 웨이퍼와 평판 표시기상에 사진 석판용 화학물질의 균일도포 컴퓨터 하드 디스크의 광택제 도포등에 사용할 수 있다. 이처럼 초저의 유출 용량을 요구하는 모든 공정 및 액체연료의 분사가 요구되는 모든 산업에 적용할 수 있는 장점을 가지고 있다. 하지만 현제까지 주로 사용되고 있는 초음파노즐의 액츄에이터는 단판액츄에이터형로 높은 교류전압을 인가해주어야 하는 단점을 가지고 있다. 이 단점을 해결하기 위해 적층액츄에이터형을 사용하여 초음파 노즐 구동하면 낮은 교류 입력전압에서도 단판액츄에이터형 초음파 노즐과 같은 특성을 가질 수 있다. 또한 초음파 노즐의 구동시 기계적인 진동을 이용하므로 많은 열을 발생시켜 노즐의 온도가 상승하여 세라믹 액츄에이터에도 그 영향을 미치게 되어 열적 열화 현상이 일어날 수 있기에 높은 큐리온도를 가지는 액츄에이터가 필요하다. 본 실험에서는 $Pb(Mn_{1/3}Nb_{2/3})_{0.02}(Ni_{1/3}Nb_{2/3})_{0.12}(Zr_{0.50}Ti_{0.50})_{0.86}O_3$ 조성을 사용하여 $900^{\circ}C$의 저온에서 액상 소결하여 적층혈액츄에이터를 제작하였으며 압전 및 유전 특성을 조사하였다. 제작된 초음파노즐을 구동하기 위해서는 약 36kHz의 30V이상의 교류입력전압 할 수 있는 구동회로가 필요로 한다. 압전액츄에이터의 구동을 위해서는 정확한 정현파 입력이 필요 없다. 압전액츄에이터의 특성상 유사 정현파 입력 만으로도 임피던스 매칭이 이루어지기 때문에 설계가 쉽고 간편한 Push-Pull 방식을 이용한 PWM인버터를 사용하였고 인버터의 출력 주파수를 34~38kHz까지 가변 할 수 있게 설계하였다. 제작된 적층액츄에이터형 초음파 노즐을 PWM인버터로 실제 액체 연료인 경유를 분사하였을 때의 액츄에이터의 온도 변화에 따른 공진주파수와 온도 의존성, 전기적 특성을 조사하고 미립화 분사되는 경유의 미립자 크기 및 최대 분사량을 조사 하였다.