• Proceedings of the KIEE Conference
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• 2011.07a
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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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• 2001.11a
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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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• s.24
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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.

• The Journal of the Korea Contents Association
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• v.20 no.6
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• pp.439-444
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• 2020

The purpose of this study is to seek an alternative method to prevent the contamination of normal saline caused by the back-flow of Gadolinium Based Contrast Agent(GBCA) by the use of auto-injector for dynamic MRI. The research method is to manufacture the non-return valve as an alternative to the existing, and to examine the usefulness of the normal saline by dividing the state of normal saline into three groups. The signal intensity were compared. As a result, there was no statistically significant difference between normal saline before injection of group 1 and group 3 non-return valve (p> 0.05). It is analyzed that the self-produced non-return valve completely blocked the GBCA back to normal saline when the GBCA was injected. In conclusion, the application of the non-return valve presented in this study for dynamic MRI imaging using the auto injector can prevent normal saline contamination due to GBCA back-flow.

• Environmental Engineering Research
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• v.24 no.3
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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.

• Physical Therapy Korea
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• v.16 no.1
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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.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.51 no.1
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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.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.3
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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.

• Membrane Journal
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• v.12 no.1
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• pp.8-20
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• 2002

In this study using $N_2$-back flushing, which wwas not the general back-flushing method of membranes, the discharged wastewater from a paper plant was filtrated by 4 kinds of tubular carbon ceramic ultrafiltration membranes. We could in vestigate effects of $N_2$-back flushing period, transmembrane pressure (TMP)and flow rate and find optimal operating conditions. The $N_2$-back flushing time (BT) was fixed at 40 sec, filtration times (FT) were changed in 4~32 min, TNP in $1.0~3.0kg_f/cm^2$ the flow celocities in 0.53~1.09cm/s. The optimal conditions were discussed in the viewpoints of dimensionless permeate flux ($J/J_0$), toal permeate volume ($V_T$) and resistance of membrane fouling ($R_f$). Optimal back-flushing period was BT/FT=0.167 (FT=8 min ), in which more $V_T$ was obtained than that in BT/FT=0.083 (FT=4 min) which was the most friquent back-flushing condition. Then rising TMP should increase the driving force, and more $V_T$ could be accumulated. And rising flow rate should decrease membrane fouling increase permeate flux, and more $V_T$could be produced. Average rejection rates of pollutants were higher than 95% for turbidity and 45~83% for $COD_{Cr}$, but rejection rates of total dissolved solid (TDS) were lower than 10%.

• Journal of the Korean Society of Propulsion Engineers
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• v.1 no.1
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• pp.73-81
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• 1997

Numerical analysis on turbulent flow and heat transfer in the rocket nozzle has been studied using the mass-weighted-averaged full Navier-Stokes equations, the Morkovin hypothesis on turbulent flow, the $\textsc{k}$-$\varepsilon$ turbulence model with the wall function specially designed to be able to consider the effects of pressure gradients, heat transfer and compressibility, and the numerical scheme of Karki. The present results are in good agreement with the experiments of Back et al.