• 대한전기학회:학술대회논문집
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• 대한전기학회 2011년도 제42회 하계학술대회
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• pp.374-375
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• 2011

This paper presents a method to determine parameters of BTB (back-to-back) converters in terms of the enhancement of interface flow margins. Interface flow margin is by definition a measure of how much active power can be transferred from the external areas to the study area with the fixed load demand, and it is mainly constrained by system voltage stability. BTB converters are controllable equipments with the active power flow through them, and its DC link in fact can divide the AC systems at the location and hence can reduce the fault current level. This paper first cals margin sensitivities at the nose point of F-V curves and formulates an optimization problem to update the BTB parameters to improve the margins. This procedure is repeated performed until the required margin enhancement is achieved.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2001년도 유체기계 연구개발 발표회 논문집
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• pp.235-242
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• 2001

Hydraulic performance of LCH4 fuel inducer in turbopump system was predicted by 3-D Wavier-stokes calculation. The inducer was designed initially using 1-D method. Different parameters with blade angle and flow coefficient were set from the initial design one, md computation was fulfilled to assess the redesigned models. Especially, influence of inlet back flow on inducer performance and its effective control were explored. The numerical results showed that through reducing inlet back flow strength., the hydraulic efficiency of inducer could be improved up to about $20\%$ compared to that of the initial design one.

• 연구논문집
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• 통권24호
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• pp.107-117
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• 1994

In aerodynamic design of centrifugal compressors, impellers are designed through preliminary design and blade profile generation. In order to find out faults of the initially designed impellers, the detailed informations about internal flow phenomena such as pressure distribution, flow separation, blade loading, etc are essential. These informations can be acquired with flow measurements or computational flow analyses. In this study, we calculated 3-D viscous flow in 4 back-swept impellers which were designed in our laboratory, and analyzed the flow characteristics which influence the performance of impellers.

• 한국콘텐츠학회논문지
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• 제20권6호
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• pp.439-444
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• 2020

이 연구는 자기공명영상검사 시 조영제 주입용으로 사용되는 자동주입기에서 조영제 역류에 의한 생리식염수의 오탁 현상을 방지할 수 있는 대안을 모색하고자 하였다. 연구방법은 실린지 내에서 조영제 역류를 차단할 대안으로 밸브를 자체 제작한 다음, 임상적용의 유용성을 알아보기 위해 생리식염수의 상태를 세 그룹으로 나누고 조영제 주입을 실험하여 각각 채취한 생리식염수의 지방소거 T1 강조영상으로 신호강도를 비교하였다. 연구결과, 그룹 1의 조영제 주입 전 생리식염수와 그룹 3의 역류방지용 밸브를 적용한 조영제 주입 후 생리식염수가 통계적으로 유의한 차이가 없었다(p>0.05). 이는 자체 제작한 역류방지용 밸브가 조영제 주입 시 생리식염수로 역류하는 조영제를 완벽히 차단한 것으로 분석된다. 결론적으로 조영제 자동주입기를 활용한 자기공명영상 동적검사 시 본 연구에서 제시한 역류방지밸브를 적용한다면 조영제 역류로 인한 생리식염수의 오탁 현상을 예방할 수 있으리라 본다.

• Environmental Engineering Research
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• 제24권3호
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• pp.521-528
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• 2019

Electrochemical method was used for the fracturing flow-back fluid treatment in Guangyuan oilfield. After performing electrolysis, we found that the amount of $H_2$ gas produced by electrode was closely related to the combination mode of electrodes and electrode materials. Using an aluminium electrode resulted in a large $H_2$ production of each electrode combination, whereas inert anode and cathode materials resulted in low $H_2$ production. Then, the relationship between the gas production of $H_2$ and the treatment efficiency of fracturing flow-back fluid in Guangyuan oilfield was studied. Results showed that the turbidity removal and decolourisation rates of fracturing flow-back fluid were high when $H_2$ production was high. If the $H_2$ production of inert electrode was large, the energy consumption of this inert electrode was also high. However, energy consumption when an aluminium anode material was used was lower than that when the inert electrode was used, whereas the corresponding electrode combination production of $H_2$ was larger than that of the inert electrode combination. When the inert electrode was used as anode, the gas production type was mainly $O_2$, and $Cl_2$ was also produced and dissolved in water to form $ClO^-$. $H_2$ production at the cathode was reduced because $ClO^-$ obtained electrons.

• 한국전문물리치료학회지
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• 제16권1호
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• pp.10-17
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• 2009

The aim of this study was to investigate the effect of abdominal drawing-in maneuver (ADIM) on peak exploratory flow (PEF), forced exploratory volume in 1 second ($FEV_1$), and low back pain during forced expiration. Twenty-two subjects (14 subjects in experimental group, 8 subjects in control group) participated in this study. The stabilizer was used for ADIM training for five consecutive days. Vitalograph PEF/$FEV_1$ DIARY and visual analogue scale (VAS) were used to determine forced expiratory pulmonary function and low back pain, respectively. Independent t-test and analysis of covariance were used for statistical analysis with a significance level of .05. The findings of this study were as follows: 1) There were no significant differences of ADIM effect on PEF and $FEV_1$ between experimental group and control group. 2) There was a significant pain reduction in experimental group with ADIM. 3) PEF and $FEV_1$ increased significantly in the fifth day compared with the first day pre-exercise baseline. Therefore, it is concluded that ADIM was effective in improving PEF and $FEV_1$, and reducing VAS during forced expiration in patients with chronic low back pain.

• 대한전기학회논문지:전력기술부문A
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• 제51권1호
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• pp.15-22
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• 2002

This paper proposes a new power flow method for distribution system analysis by modifying the conventional back/forward sweep method using symmetrical components. Since the proposed method backward and forward sweeps with the variables expressed by symmetrical components, this method reduces computation time for matrix calculations; therefore, it is able to reduce the computational burden for real-time distribution network analysis. The proposed method was also developed to effectively analyze the unbalanced distribution system installing AVR(Auto Voltage Regulator), shunt capacitors. The proposed algorithm was compared with the conventional Back/forward Sweep method by applying both methods to three phase unbalanced distribution system of IEEE 123-bus model, and the test results showed that the proposed method would outperformed the conventional method in real-time distribution system analysis.

• 한국생산제조학회지
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• 제21권3호
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• pp.362-367
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• 2012

Though a micro pump is a crucial element in miniaturized bio-fluidic systems or drug delivery systems, most of the conventional micro pumps still have some limitations to miniaturize their controller system and to obtain the sufficient back pressure which can rise over the inner pressure of human body or experimental animals. In this paper, to overcome these limitation, a new PZT disc and its controller were designed and fabricated to get the sufficient flowrate and the back pressure with guaranteeing embeddability of the controller into pumping body. The amplitudes of the disc deflections were as large as 40 ${\mu}m$ at 200 V - 100 Hz condition. As results of experiments, the flow rate and the back pressure increase when the frequency increases. The obtainable maximum flow rate and back pressure are 5.2 ml/min at 95 Hz and 13.14 kPa at 90 Hz respectively.

• 멤브레인
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• 제12권1호
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• pp.8-20
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• 2002

본 연구에서는 분리막의 일반적 역세척 방법이 아닌 질소 역세척을 하면서, 4종의 탄소계 관형 세라믹 한오여곽막으로 제지공장의 방류수를 처리하였을 때 역세척 주기 및 막간압력차 (TMP), 유량의 영향과 최적운 전조건을 규명하였다. 역세척시간 (BT)을 40초로 고정하였고, 정상운전시간 (FT)은 4~32분, TMP는 $1.0~3.0kg_f/cm^2$ 유속은 0.53~1.09cm/s로 변화시켰다. 또한 최적조건은 무차원 투과선속 ($J/J_0$) 및 총과여부부피 ($V_T$) 막오염에 의한 저항 ($R_f$)의 측면에서 고찰하였다. 그 결과 최적 역세척주기는 BT/FT=0.083 (FT=8분)으로 가장 빈번한 역세척 BT/FT=0.167 (FT=4분) 보다 오히려 많은 총여과부피를 얻을수 있었다. 한편, TMP가 증가할수록 구동력의 증가로 보다 많은 $V_T$를 얻을 수 있었고, 유량이 증가할수록 발생한 난류의 영향으로 막오염은 감소되고 투과유속은 증가하여 많은 $V_T$를 얻을수 있었다. 오염물질 제거율은 탁도 95% 이상, 호학적 산소요구량 ($COD_{Cr}$)45~83%로 높았으나 총용존고형물 (TDS)의 경우 10% 이하로 낮았다.

• 한국추진공학회지
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• 제1권1호
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• pp.73-81
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• 1997

질량가중평균의 완전 Wavier-Stokes 방정식, 압축성 난류유동에 대한 Morkovin의 가설, $\textsc{k}$-$\varepsilon$ 난류모델, 압력구배와 벽열전달과 압축성의 효과를 고려한 벽함수 모델, Karki의 수치해석기법 등을 사용하여 로켓노즐 내의 난류유동 및 열 전달을 수치해석하고 Back 등의 실험 결과와 비교하였다.