• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1994.04a
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• pp.23-26
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• 1994

130mm D.B. 추진기관의 고온 시험에서 나타난 극심한 이상 연소 현상을 해결하기 위해 미세한 고체 입자들을 연소 가스에 분산시켜 불안정 연소를 억제하는 particulate damping 효과를 연구하였다. 고체 입자로서 효과적인 것으로 알려진 $K_2$$SO_4$. ZrC, Graphite를 CTPB, HTPB 고분자 물질에 충진시켜 epoxide, isocyanate 반응기와 가교 반응을 일으킴으로써 고무상의 탄성체 성질을 갖게 하는 $K_2$$SO_4$/CTPB, ZrC/Graphite/HTPB, ZrC/Graphite/AP/HTPB, ZrC/AP/HTPB 조성의 연소 안정제를 개발하였다. 이 연소 안정제는 외경 17mm, 길이 1000mm의 안정봉 형태로 제작하여 모타의 중심 cavity에 조립한 후 지상 연소 시험을 통하여 성능을 확인하였다. 시험 결과, 조성에 AP를 포함시켜 연소 안정제에 일정한 연소 속도를 부여하여 추진제 grain 연소 동안 고체 입자를 연소 가스에 분산되게 설계한 ZrC/Graphite/AP/HTPB, ZrC/AP/HTPB 조성의 연소 안정제가 불안정 연소 억제에 효과적인 것으로 나타났다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.636-640
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• 2002

Acoustic coupled combustion instability, which is one of the most undesirable phenomena in the development of liquid propellant rocket engine, can cause serious damage to a rocket itself, and must be avoided by all means. Unfortunately, KSR-III rocket went through combustion instability during engine start at the propulsion test article No.2. To resolve the problem, time sequence (cyclogram) has been changed, and baffle system has been applied. In consequence of change, stable combustion was achieved.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.415-418
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• 2011

It is critical to assess the characteristics of flame response to pressure perturbations for the understanding of nonlinear combustion instabilities. Previous studies can be grouped into flame response upon perturbed, fresh air and fuel mixture, and flame response directly perturbed from longitudinal waves. The present study presents experimental methodology for the understanding of the flame response exposed to transverse acoustic waves generated by loud speakers.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.141-144
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• 2009

This paper presents an achieving method of highly progressive pressure gradient to enhance the missile ejection system's performance by using a gas generator. To obtain a stable burning, the decrease of a grain's L/D is proposed except making radial holes through the grain. New approach by applying adjustment of a grain's L/D reduces the maximum acceleration level by about 33% than that of reference model.

• The KSFM Journal of Fluid Machinery
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• v.10 no.4
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• pp.21-28
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• 2007

The ratio of disk friction loss in a centrifugal pump is very large for the total pump loss in the range of very low specific speed. Therefore, impeller radius should be shortened to increase the pump efficiency because the disk friction loss is proportional to the fifth power of impeller radius. In order to compensate the decreased head by the shortened impeller radius, vane angle at impeller outlet should be increased. However, as the vane angle at impeller outlet becomes larger, performance instability occurs at low flow rate regions. In this study, J-Groove is adopted to suppress the performance instability and detailed examination is performed for the influence of the J-Groove on the pump performance. The results show that J-Groove gives good effect on the suppression of performance instability. Moreover, as J-Groove increases pump head considerably, the pump size can be smaller for head requirements.

• Membrane Journal
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• v.27 no.5
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• pp.434-440
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• 2017

Electrical impedance spectroscopy is used to detect membrane fouling in-situ in reverse electrodialysis. The impedance data for the AMX membrane being fouled in the reverse electrodialysis are plotted and analyzed by Nyquist and admittance method. The meaningful graphical analyses for the fouling phenomena could be done by both Nyquist and admittance method. In addition, the unstable initial fouling stage was identified by the admittance data with high standard deviation, and the structural change of the fouling layer formed at the surface of anion-exchange membranes with the operation time of reverse electrodialysis was also detected.

• The Korean Journal of Nuclear Medicine Technology
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• v.12 no.1
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• pp.78-81
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• 2008

Purpose: In this study, we evaluated unstable serum data of HBe antigen (HBeAg) or HBe antibody (HBeAb) in patients who experienced HBeAg seroconversion. This study have been performed to assist a medical technologist in the recognition of patients who were chronically infected with the hepatitis B virus (HBV). Materials and Methods: A total number of 3 patients were enrolled in this study. All patients experienced HBeAg seroconversion. Serum data of HBeAg and HBeAb were measured by radioimmunoassay. Results: The data of HBeAg or HBeAb showed an unstable change during seroconversion from HBeAg to HBeAb in chronic type B hepatitis (CBH). Conclusions: Serum data of HBeAg or HBeAb can change during HBe seroconversion. These data suggest that patients with HBe seroconversion can experience an unstable oscillation of HBeAg or HBeAb value from positive to negative. Unstable data can appear naturally due to the seroconversion process.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.4
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• pp.28-37
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• 2002

Acoustic behavior in combustion chamber with acoustoc cavity is numerically investigated by adopting linear acoustic analysis. Helmholtz-type resonator is employed as a cavity model to suppress acoustic instability passively. The tuning frequency of acoustic cavity is adjusted by varying the sound speed in acoustic cavity. Through harmonic analysis, acoustic pressure responses of chamber to acoustic oscillating excitation are shown and the resonant acoustic modes are identified. Acoustic damping effect of acoustic cavity is quantified by damping factor. As the tuning frequency approaches the target frequency of the resonant mode to be suppressed, mode split from the original resonant mode to lower and upper modes appears and thereby damping effect is degraded significantly. Considering mode split and damping effect as a function of tuning frequency, it is desirable to make acoustic cavity tuned to maximum frequency of those of the possible splitted upper modes.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.4
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• pp.52-58
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• 2007

The irregular fuel surface was observed by the visualization of hybrid rocket combustion. Even though the test condition maintained oxidizer rich environment, the irregular dark fuel surface was formed as the result of incomplete combustion. In order to investigate the correlation of the characteristics of oxidizer flow and the irregular fuel surface, various flow conditions were imposed such as swirl flow, induced swirl flow by helical fuel configuration and straight flow. Test results revealed no correlation was found between oxidizer flow condition and irregular fuel surface. And this can be a commonly observed phenomena in the tests with different fuel/oxidizer combination. Thus, the irregular fuel surface can be a result of the interaction of blowing flow of vaporized fuel and the boundary layer of oxidizer flow. A further study will be required to confirm the assumption for the formation of irregular fuel surface.

• The Journal of the Convergence on Culture Technology
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• v.8 no.5
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• pp.341-349
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• 2022

This study explored in-depth emotional experiences influenced by childhood trauma of adult female survivors. For this purpose, in-depth interviews were conducted with married adult women who experienced trauma in their childhood. The collected data were analyzed using Colaizzi phenomenological research method. As a result of the study, 7 categories were derived: 'children who cannot protect themselves', 'childhood trauma,' 'insecure attachment and good child syndrome,' 'difficulties in interpersonal relationships,' 'difficulties in raising children,' 'somatization symptoms,' 'finding myself who is lost.' In addition, this study aims to understand the psychological experience of children in the family and the relationship between parents and children and the growth experience of healing them by comparing and contrasting the two cases of trauma. The foundation for healthy ego-resilience and emotional well-being has been laid through the research results on negative and maladaptive emotional experiences reflected throughout the life of adult women who suffered childhood trauma.