• Journal of the Korean Association of Geographic Information Studies
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• v.11 no.3
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• pp.174-182
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• 2008

As the survey and the analysis the research can offer the characteristic methods for regeneration in the city of Busan. To figure out the functional regions of city center the research has analyzed 15 Dongs in city center and 12 Dongs in sub centers to find out the donut phenomenon and the regeneration of city center. The survey has chosen 22 variation factors using factor analysis. Major factors in each year are shown 4 factors, presenting 80.4% of the accumulated explanation rate. These factors explain residental centered, commercial centered, management centered, and development centered factor. The donut phenomenon emerges in the city centers as a residential function, and the phenomenon occurs in the sub centers as commercial or managerial function. So it is necessary to plan the regeneration of the total city center owing to the total donut phenomenon regarding the functions. And the methods to regenerate city centers should be established according to the various regional characterizations.

• Journal of the Korean Association of Geographic Information Studies
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• v.10 no.1
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• pp.205-217
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• 2007

Donut phenomenon of city centers has resulted from the decreasing residential population and the fluid population with curved commercial function, but the analysis can bring other problems owing to the simplified method. And As the survey and the analysis the research can offer the characteristic methods for regeneration in the city of Busan. To figure out the functional regions of city center the research has analyzed 15 Dongs in city center of the three years of 1996, 2000 and 2004 to find out the donut phenomenon and the regeneration of city center. The survey has chosen 20 variation factors using factor analysis and cluster analysis. Major factors in each year are shown 3 factors, presenting 84.2%, 87.1% and 85.5% of the accumulated explanation rate. These factors explain residential centered, commercial centered, and management centered factor. The results are as following. First, it is necessary to plan the regeneration of the total city center owing to the total donut phenomenon regarding the functions. Second, the methods to regenerate city centers should be established according to the various regional characterizations.

• Korean Chemical Engineering Research
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• v.59 no.1
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• pp.94-99
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• 2021

It was found that mixing patterns suddenly changed at an impeller rotation speed in a dished bottom vessel with dual Rushton turbines. Two isolated mixing regions like doughnuts rings generated at a low rotational speed and three isolated mixing regions generated at a higher speed. This phenomenon was observed at the mixing condition in transition area, where the power number with baffle was the same as that without baffle. We found a phenomenon in which the flow state in a dish-bottom agitation tank equipped with a two-stage Rushton turbine blade changes at a certain rotational speed. In the laminar flow region, the isolated stable donut rings were formed even when the rotational speed was changed, and no specific variation in the mixing pattern was observed. In the transition region, the two isolated thick unmixed donut rings do not change even if the rotation speed is changed in the flat bottom vessel, whereas in the dished bottom vessel, when the rotation speed is 450 rpm, the two isolated thick unmixed donut rings are changed to three isolated thin donut rings and then improved mixing. In the dished bottom vessel, in the range of Re=138~178, the isolated ring-shaped unmixed region appeared in three places and the size was also large. But in the flat bottom vessel, the isolated thick ring-shaped unmixed region appeared in two places in Re=116~176 and the size was also small. It appeared in two places, and the size was also small. The condition in which this phenomenon is observed is a transition region, and it was found that when the baffle plate is attached, the power number starts to increase compared to when the baffle plate is not present. In addition, when the mixing Reynolds number exceeded 300 and a slight turbulence was mixed in the flow state, the disconnection of these flow pattern was resolved and the mixture was completely mixed.

• Nuclear Engineering and Technology
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• v.37 no.2
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• pp.201-206
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• 2005

Fretting, which is a special type of wear, is defined as small amplitude relative motion along the contacting interface between two materials. The structural integrity of steam generators in nuclear power plants is very much dependent upon the fretting wear characteristics of Inconel 690 U-tubes. In this study, a finite element model that can simulate fretting wear on the secondary side of the steam generator was developed and used for a quantitative investigation of the fretting wear phenomenon. Finite element modeling of elastic contact wear problems was performed to demonstrate the feasibility of applying the finite element method to fretting wear problems. The elastic beam problem, with existing solutions, is treated as a numerical example. By introducing a control parameter s, which scaled up the wear constant and scaled down the cycle numbers, the algorithm was shown to greatly reduce the time required for the analysis. The work rate model was adopted in the wear model. In the three-dimensional finite element analysis, a quarterly symmetric model was used to simulate cross tubes contacting at right angles. The wear constant of Inconel 690 in the work rate model was taken as $K=26.7{\times}10^{-15}\;Pa^{-1}$ from experimental data obtained using a fretting wear test rig with a piezoelectric actuator. The analyses revealed donut-shaped wear along the contacting boundary, which is a typical feature of fretting wear.