• Journal of Electrical Engineering and Technology
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• v.11 no.3
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• pp.675-682
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• 2016

Sudden voltage drops and outages frequently disturb the operation of sensitive loads for domestic, commercial, and industrial use. In some cases, these events may even impair the functioning of relevant equipment. To maintain power under such conditions, a UPS system is usually installed. Once a disturbance happens at the grid side, the line-interactive UPS system takes over the load to prevent an interruption. But, due to magnetic saturation of the transformer, a significant inrush current may occur for the transformer-coupled loads during this transition. The generation of such transient currents may in turn decrease the line voltage and activates over-current protecting devices of the system. In this work, a cost-effective, line-interactive UPS system is proposed that eliminates the inrush current phenomenon associated with transformer-coupled loads. The strategy was implemented by connecting a standard current-regulated voltage source inverter (CRVSI) to the secondary winding of the load transformer. During any transient condition at the grid side, the load current is monitored and regulated to achieve either seamless compensation of the load current or complete transferal of load from grid to the inverter. Experimental results were obtained for a prototype under all possible operating conditions so as to validate the performance of the proposed topology.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.38 no.2
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• pp.96-100
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• 2012

Objectives: This study sought to evaluate trabecular changes in the mandible using fractal analysis and to explain the transient osteopenia related to rapid orthodontic tooth movement after orthognathic surgery. Materials and Methods: Panoramic radiographs were taken of 26 patients who underwent bilateral sagittal split ramus osteotomy. Radiographs taken before the surgery and 1 month after surgery were overlapped, and $40{\times}40$ pixel square regions of interest were selected near the mandibular canines and 1st molars. After the image processing procedure, the fractal dimension was calculated using the box-counting method. Results: Fractal dimension after orthognathic surgery decreased in a statistically significant manner (P<0.05). The change in fractal dimension on the canine side had greater statistical significance as compared to that seen on the 1st molar side. Conclusion: This study found that bone density decreases after orthognathic surgery due to transient osteopenia related to the regional acceleratory phenomenon. This result can provide a guide to evaluating orthodontic tooth movement after orthognathic surgery.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.821-826
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• 2011

The turbopump+gas generator (TP+GG) coupled test for the liquid rocket engine development was performed. By comparing the results of a engine startup transient analysis with this test results, the verification of the analysis model was performed. From this, as to the analysis of the engine startup, the method calculating the pressure ratio of the turbine during the initial stage of startup was improved. And a fact that the transient heat transfer phenomenon between the working fluid and the solid parts of turbine effects to the calculation of turbine pressure ratio and consequentially to the startup analysis was revealed.

• Journal of Advanced Marine Engineering and Technology
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• v.11 no.1
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• pp.72-79
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• 1987

When the wall temperature is very high, a stable vapor film covers the heat transfer surface. The vapor film creates a strong thermal resistance when heat is transferred to the liquid though it. This phenomenon, called "film boiling" is very important in the heat treatment of metals, the design of cryogenic heat exchangers, and the emergency cooling of nuclear reactors. In the practical engineering problems of the transient cooling process of a high temperature wall, the wall temperature history, the variation of the heat transfer coefficients, and the wall superheat at the rewetting points, are the main areas of concern. These three areas are influenced in a complex fashion such factors as the initial wall temperature, the physical properties of both the wall and the coolant, the fluid temperature, and the flow state. Therefore many kinds of specialized experiments are necessary in the creation of precise thermal design. The object of this study is to investigate the heat transfer characteristics in the transient cooling process of a high temperature wall. The slow transient cooling experiment was carried out with a copper block of high thermal capacity. The block was 240 mm high and 79 mm O.D.. The coolant flowed throuogh the center of a 10 mm diameter channel in the copper block. In the copper block, three sheathed thermocouples were placed in a line perpendicular to the flow. These thermocouples were used to take measurements of the temperature histories of the copper block.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.5
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• pp.581-588
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• 2014

Extensive researches toward pool boiling characteristics have been widely investigated. However, the correct understanding of its boiling crisis by Critical Heat Flux (CHF) phenomenon during steady and transient heat transfer as a fundamental database for designing heat generation systems is still need to be clarified. The pool boiling CHFs were investigated to clarify the generalized phenomena of transition to film boiling at transient condition. The CHFs were measured on 1.0 mm diameter horizontal cylinder of platinum for exponential heat generation rates with various periods for saturated liquids at atmospheric pressure. The incipience of boiling processes was completely different depending on pre-pressurization. Also, the dependence of pre-pressure in transient CHFs changed due to the wettability of boiling liquids. The trend of typical CHFs were clearly divided into the first, second and third groups for long, short and intermediate periods, respectively. By the effect of pre-pressurization, the boiling incipience mechanism was replaced from that by active cavities entraining vapor to that by the HSN in originally flooded cavies.

• Journal of Welding and Joining
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• v.25 no.3
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• pp.64-71
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• 2007

The dissolution phenomenon of the solid phase powder and base metal by liquid phase insert metal during Transient Liquid Phase bonding using the mixed powder composed of the modified GTD111(base metal) powder and the GNi3 (Ni-l4Cr-9.5Co-3.5Al-2.5B) powder was investigated. In case of the mixed powder contains modified GTD111 powder 50wt%, all of the powder was melted by liquid phase at 1423K. At the temperature between solidus and liquidus of GNi3, liquid phase penetrated into the boundary of the modified GTD111 powder and solid particle separated from powder was melted easily because area of reaction was increased. With increasing mixing ratio of the modified GTD111, it needed the higher temperature to melt all of the modified GTD111 powder. During Transient Liquid Phase bonding using the mixed powder composed of the modified GTD111 50wt% and GNi3 50wt% as insert metal, width of the bonded interlayer was increased with increasing bonding temperature by reaction of the base metal and liquid phase in insert metal. Dissolution of the base metal and modified powder by liquid phase progressed all together and after all of the powder was melted nearly, the dissolution of the base metal occurred quickly.

• Magazine of the Korea Concrete Institute
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• v.10 no.4
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• pp.145-151
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• 1998

The vertical tensile stress, ${\sigma}_y$, in the contact zone between the overlay (mortar layer) and substratum (base concrete) can be the main cause of the failure phenomenon of overlaid concrete structures. The development of tensile stress, ${\sigma}_y$, due to external rainy condition was analytically investigated using finite element method. Rainfall intensity $(n_R\;=\;1/a,\;t_R\;=\;10min,\;60min)$, thickness of overlay (do=1,2,4,10 cm) and overlay material (CM,ECM,EM) were the main variables in the analyses. An equation was suggested with which the development of vertical tensile stress, ${\sigma}_y$, in the rainy condition could be determined. Using this equation, it is possible to select proper material properties and overlay thicknesses to prevent failure in the contact zone due to thermally transient condition caused by rainfall.

• Korean Journal of Metals and Materials
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• v.47 no.4
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• pp.242-247
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• 2009

On the Transient Liquid Phase Bonding (TLPB) phenomenon with the MBF-50 insert metal at narrow gap (under 100), it takes long time for the bonding and the homogenizing. Typically, isothermal solidification is controlled by the diffusion of depressed element of B and Si. However, the amount of B and Si in the MBF-50 filler metal is large. This is reason of the long bonding time. Also, the MBF-50 filler metal did not contained Al and Ti which are ${\gamma}^{\prime}$ phases former. This is reason of the long homogenizing time. From the bonding phenomenon with the MBF-50 insert metal, we search main factors on the bonding mechanism and select several insert-metals for using the wide-gap TLPB. New insert-metals contained Al and Ti which are ${\gamma}^{\prime}$ phases former and decrease the B then the MBF-50. When the new insert-metal was used on the TLPB, the bonding time was decreased about 1/10 times and homogenizing heat treatment was no needed. In spite of the without homogenizing, the volume fraction of ${\gamma}^{\prime}$ phases in the boned interlayer was equal to homogenizing heat treated specimen which was TLPB with the MBF-50. Finally, the new insert metal named WG1 for the wide-gap TLPB is more efficient then the MBF-50 filler metal without decreasing the bonding characteristic.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.2
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• pp.58-64
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• 2012

Hysteresis phenomena in fluid flow systems are frequently encountered in many industrial and engineering applications and mainly appear during the transient processes of change of the pressure ratio. Shock-containing flow field in supersonic nozzles is typically subject to such hysteresis phenomena, but associated flow physics is not yet understood well. In the present study, experimental work has been carried out to investigate supersonic nozzle flows during the transient processes of change in the nozzle pressure ratio. Time-dependent surface wall pressures were measured by a multiple of pressure transducers and the flow field was visualized using a nano-spark Schlieren optical method. The results obtained show that the hysteresis phenomenon is strongly dependent on the nozzle geometry as well as the time scale of the change of pressure ratio.

• Journal of the Korean Society of Costume
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• v.59 no.3
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• pp.27-41
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• 2009

Interpreting the phenomenon of Fast fashion that is prevalent these days, this research is meaningful in that it prepares the frame which suggests the vision to read the trend of 2000s and analyzes the property of phenomenon of Fast Fashion in the connection with society and culture. The so[io-cultural property can be largely characterized by consumption orientation, change orientation, efficiency, moment and multiculturism. Analyzing the phenomenon of fast fashion that emerged after 2000 on the basis of such sociocultural background, it is largely classified into imitation, fashionability, disposability, portability, transformation and convergence. Due to the hi-polarization of consumption, people tend to select imitated goods, and people accustomed to speed get interested in the fashionability of all Phenomena. Further, society that is transient and changing rapidly makes the habit of purchasing in disposability. The property of nomad society encourages to keep the habit of portability. Such change-oriented society and rapidly changing life pattern make them adapt in diverse transformation modes of Fast Fashion. Further, multi-cultural world integrates enterprises through combination of all cultures and the convergence of all factors.