• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.9
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• pp.859-866
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• 2010

Nonlinear dynamics of pulsating instability-diffusional-thermal instability with Lewis numbers sufficiently higher than unity-in counterflow diffusion flames, is numerically investigated by imposing a Damkohler number perturbation. The flame evolution exhibits three types of nonlinear behaviors, namely, decaying pulsating behavior, diverging behavior (which leads to extinction), and stable limit-cycle behavior. The stable limit-cycle behavior is observed in counterflow diffusion flames, but not in diffusion flames with a stagnant mixing layer. The critical value of the perturbed Damkohler number, which indicates the region where the three different flame behaviors can be observed, is obtained. A stable simple limit cycle, in which two supercritical Hopf bifurcations exist, is found in a narrow range of Damkohler numbers. As the flame temperature is increased, the stable simple limit cycle disappears and an unstable limit cycle corresponding to subcritical Hopf bifurcation appears. The period-doubling bifurcation is found to occur in a certain range of Damkohler numbers and temperatures, which leads to extend the lower boundary of supercritical Hopf bifurcation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.200-214
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• 1993

This paper presents the results of fluidelastic instability analysis performed for the U-tube bundle of a Westinghouse model 51 steam generator, one of the recirculating types designed at an early stage, in which the principal region of external cross-flow is associated with the U-bend portion of tube. The prerequisites for this analysis are detailed informations of the secondary side flow conditions in the steam generator and the free vibration behaviours of the U-tubes. In this study, the three-dimensional two-phase flow field in the steam generator has been calculated employing the ATHOS3 steam generator two-phase flow code and the ANSYS engineering analysis code has been used to calculate the free vibration responses of specific U tubes under consideration. The assessment of the potential instability for the suspect U-tubes, which is the final analysis process of the present work, has been accomplished by combining the secondary side velocity and density distributions obtained from the ATHOS3 prediction with the relative modal displacement and natural frequency data calculated using the ANSYS code. The damping of tubes in two-phase flow has been deduced from the existing experimental data by taking into account the secondary side void fraction effect. In operation of the steam generator, the tube support conditions at the tube-to-tube support plate intersections due to either tube denting degradation or deposition of tube support plate corrosion products or ingression of dregs. Thus, various hypothetical cases regarding the tube support conditions at the tube-to-tube support plate intersections have been considered to investigate the clamped support effects on the forced vibration response of the tube. Also, the effect of anti-vibration bars support in the curved portion of tube has been examined.

• Korean Journal of Crystallography
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• v.2 no.1
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• pp.1-11
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• 1991

When GaAs single crystals are grown by LEC method, a serious problem is that longitudinal twins are often generated. the growth axis is changed from (100) to (221) direction by logitudinal twin. In this experiment, 3 inch GaAs single crystals, slaving (100) uonh axis, were von by LEC method. Striations and edge facets generated during crystal growth, were observed by SPW photo-etching. Relationship between striations and edge facets was studied. Instability of their generation was the cause of goneration of longitudinal twins. The shape of striations was changed with the growth conditions such as crystal diameter and melt volume. In the region of crystal edge: there was the microscopic fluctuation by the instability of melt convection. Edge facets consisting of {111} plane developed well in the region which striation were convex to the melt. Because the angle between striation and {111} edge facet decreased in that region. Longitudinal twins were generated on the crystal surface at the <111> direction which is perpendicular to the growth axis. These were generated by unstable melt convection and propagated in the crystal as crystal grew. Longitudinal twins were generated when regrowth rate was very fast after {111} edge facets were remelted. So, in order to supress the generation of longitudinal twin, abrupt change of melt convection must be prohibited.

• Genomics & Informatics
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• v.1 no.2
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• pp.101-107
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• 2003

Loss of heterozygosity (LOH) has been used to detect deleted regions of a specific chromosome in cancer cells. LOH on chromosome 16q has been reported to occur frequently in progressed hepatocellular carcinoma (HCC). Liver tissues from 37 Korean HCC patients were analyzed for LOH by using 25 polymorphic microsatellite markers distributed along 16q. Out of the 37 HCC patients studied, 21 patients (56.8%) showed LOH in various regions of 16q with at least one polymorphic marker. Puring the analysis of these 21 LOH cases, 6 patients showed interstitial LOHs in which the boundary of the LOH region was defined. With two rounds of LOH analysis, five commonly occurring interstitial LOH regions were identified; 16q21-22.1, 16q22.2 - 22.3, 16q22.3, 16q23.2 and 16q23.3 - 24.1. Among the five LOH regions the 16q23.3 - 24.1 region has been reported to be related with chromosome instability. A complete physical map, which covers the 3.2 Mb region of 16q23.3 - 24.1 (D16S402 and D16S486), was constructed to identify novel candidate tumor suppressor genes. We provide the minimally tiling path map consisting of 28 BAC clones. There was one gap between NT_10422.11 and NT_019609.9 of the human genome sequence contig (NCBI sequence build 33, April 29, 2003). This gap can be filled by sequencing the R-1425M20 clone which bridges these sequence contigs.

• Atmosphere
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• v.22 no.2
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• pp.209-219
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• 2012

Extreme heavy snowfall episodes have been investigated in case of accumulated snowfall amount larger than 50 cm during the past ten years, in order to understand the association of low-level stability with heavy snowfall in the Yeongdong region. In general, the selected 4 events have similar synoptic setting such as the Siberian High extended to East Sea along with the Low passing by the southern Korean Peninsula, eventually inducing easterly in the Yeongdong region. Specifically moist-adiabatically neutral layer has been observed during the heavy snowfall period, which was easily identified using vertical profiles of equivalent potential temperature observed at Sokcho, whereas convective unstable layer has been formed over the East sea due to relatively warm sea surface temperature (SST) about $8{\sim}10^{\circ}C$ and lower temperature around 1~2 km above the surface, obtained from RDAPS. Difference of equivalent potential temperature between 850 hPa and surface as well as difference between air and sea temperatures altogether gradually increased before the snowfall period. Instability-induced moisture supply to the atmosphere from the East sea, being cooled and saturated by the upper cold surge, would make low-level ice cloud, and eventually move inland by the easterly flow. Heavy snowfall will be enhanced in association with low-level convergence by surface friction and upslope wind against Taebaek mountains. This study emphasizes the importance of low level stability in the Yeongdong region using the radiosonde sounding and RDAPS data, which should quantitatively be examined through numerical model as well as heat and moisture supply from the ocean.

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.183-190
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• 2002

In order to reduce NOx emissions in the 20kw class microturbines under development, the low NOx characteristics, as being an application to the lean premixed combustion technology, have been investigated. The study has been conducted at the conditions of high temperature and pressure. Air from a compressor with the temperature of 500K to 650K and the pressure of 0.3bar gauge to 0.7bar gauge, was supplied to the combustor through an air preheat-treatment. Sampling exhaust gases were measured at the immediate exit of the combustor. for the effect of temperature on NO and CO emissions. though NOx was increased, CO was decreased with increasing inlet air temperature. With increasing inlet air pressure, NOx and CO were increased also. NOx was decreased, but CO was increased with increasing inlet air mass flow rate. The test has been performed on the equivalent ratios of 0.10 to 0.25 in a lean region. NOx was increased with increasing equivalent ratios, but CO was decreased as an influence of flame temperature. In the very lean region of the equivalent ratio below 0.12, CO was increased suddenly, due to instability. As the results of this study, NOx and CO are found to be reduced to the similar level at the same time when operated at optimal conditions.

• International Journal of Quality Innovation
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• v.1 no.1
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• pp.89-96
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• 2000

Evolutionary operation (EVOP) is a continuous improvement system which explores a region of process operating conditions by deliberately creating some systematic changes to the process variable levels without jeopardizing the product. It is aimed at securing a satisfactory operating condition in full-scale manufacturing processes, which is generally different from that obtained in laboratory or pilot plant experiments. Information on how to improve the process is generated from a simple experimental design. Traditional EVOP procedures are established on the assumption that the variance of the response variable should be small and stable in the region of the process operation. However, it is often the case that process noises have an influence on the stability of the process. This process instability is due to many factors such as raw materials, ambient temperature, and equipment wear. Therefore, process variables should be optimized continuously not only to meet the target value but also to keep the variance of the response variables as low as possible. We propose a scheme to achieve robust process improvement. As a process performance measure, we adopted the mean square error (MSE) of the replicate response values on a specific operating condition, and used the Kruskal-Wallis test to identify significant differences between the process operating conditions.

• Tribology and Lubricants
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• v.22 no.2
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• pp.105-111
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• 2006

The floating ring seal which is used in the high pressure turbo pump is frequently used in the oxidizer pump and the fuel pump of the turbo pump of the liquid propulsion rocket, because it is able to minimize clearance to decrease the leakage flow rate. Compared with contact seal, the floating ring seal has advantage of minimizing clearance without rubbing phenomenon. But, the floating ring seal has a tendency to increase instability in operating condition in the high speed region. In this research, we devised floating ring seal which is inserted bump in the outer surface in order to improve the stability in the high speed region. Through this work, we expect to improve stability of floating ring seal with increasing the direct damping coefficient of seal and decreasing the eccentricity ratio.

• Journal of Distribution Science
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• v.20 no.7
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• pp.23-33
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• 2022

Purpose: Although foreign capital flows have played a vital role in fostering the economic growth in recipient countries, there are some concerns about the adverse impact of international capital flows on the banking stability. Hence, the study revisits this issue to explore the relationship between the different types of foreign investments and banking stability in ASEAN region. Research design, data and methodology: Based on the bank-level data of 96 commercial banks and country-level in six ASEAN countries from 2008 to 2019, we perform the multivariate regression analysis and provide a variety of robustness tests. Results: Our empirical evidence shows the volatility of foreign portfolio investments has significantly negative effect on the banking stability, besides that of foreign other investments has the similar influence but the result is relatively less pronounced in some robustness tests. Additionally, increasing trade cooperation and international distribution may lead countries to face higher risk of banking instability driven from these international investments. Meanwhile, the impact of foreign direct investments is positive, but the evidence is the least obvious. Conclusions: Our findings suggest policy-makers in ASEAN and emerging nations as a whole should carefully consider when building policies-related to mitigate the adverse impact of foreign capital flows.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.04a
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• pp.290-297
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• 2000

A new form of construction utilizing structural steel as the boundary elements in ductile flexural concrete walls is proposed to solve the bar congestion problems associated with such a heavily reinforced region. Two wall specimens containing rectangular hollow structural sections(HSS) and channels at their ends respectively were constructed rectangular hollow structural sections(HSS) and channels ar their ends respectively were constructed and tested under reversed cyclic loading to evaluate the construction process as well as the structural performance. One companion standard reinforced concrete wall specimen was also tested for the comparison purpose At an Initial stage all three specimens were carefully detailed to have the approximately same flexural capacity. Analysis and comparison of test results indicated that the reversed cyclic responses of the three walls showed similar hysteretic properties but in those with steel boundaries local bucking of the corresponding steel elements following significant yielding of structural steel was prominent. Design procedures considering local instability of the structural steel elements and the interaction between steel chord and concrete web members in such composite walls are presented.