• 동력기계공학회지
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• 제3권3호
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• pp.22-28
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• 1999

The injected liquid does not break-up instantly after injection for diesel engine. There is some unbroken portion, which is the liquid core(The length of liquid core is called the break-up length) in the spray. If the liquid core is longer than the depth of the bowl in the small DI diesel engine, the liquid core impinges on the surface of the piston. Once the liquid core impinges on the surface, it cannot ignite or burn rapidly and thus prolongs burning time with a degradation in thermal efficiency. The break-up length of a diesel spray in a compressure vessel was measured by an electric resistance method, A voltage was applied between the nozzle and screen, bar, needle electrode inserted at various axial and radial positions into atomizing sprays. As a result, a current flows not only in the region of liquid core but also through the droplets of the spray. It is found that the break-up length measured with screen electrode is overestimated. The break-up length of the spray is found to be proportional to the square root of the density ratio of fuel and surrounding gas. The break-up length of the spray decreases as the injection pressure and the back pressure increase.

• 한국압력기기공학회 논문집
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• 제15권2호
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• pp.58-63
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• 2019

This paper presents preliminary analysis and results on IASCC sensitivity of a core shroud in the reactor pressure vessel. First, neutron irradiation flux distribution of the reactor internals was calculated by using the Monte Carlo simulation code, MCNP6.1 and the nuclear data library, ENDF/B-VII.1. Second, based on the neutron irradiation flux distribution, temperature and stress distributions of the core shroud during normal operation were determined by performing finite element analysis using the commercial finite element analysis program, ABAQUS, considering irradiation aging-related degradation mechanisms. Last, IASCC sensitivity of the core shroud was assessed by using the IASCC sensitivity definition of EPRI MRP-211 and the finite element analysis results. As a result of the preliminary analysis, it was found that the point at which the maximum IASCC sensitivity is derived varies over operating time, initially moving from the shroud plate located in the center of the core to the top shroud plate-ring connection brace over operating time. In addition, it was concluded that IASCC will not occur on the core shroud even after 60 years of operation (40EFPYs) because the maximum IASCC sensitivity is less than 0.5.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2008년도 하계종합학술대회
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• pp.797-798
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• 2008

Visual quality of video telephony over 3G networks is not satisfactory due to limited bandwidths. Therefore, it is worthwhile to enhance subjective visual quality based on ROI coding. In this paper, we propose a rate-control algorithm for video telephony with ROI based H.264|AVC coding. The QP values are increasingly assigned in non-ROI away from the ROI so that graceful degradation of visual quality can be achieved, which is more visually pleasant.

• 한국분말재료학회지
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• 제24권4호
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• pp.279-284
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• 2017

The formation mechanism and photocatalytic properties of a multiwalled carbon nanotube (MWCNT)/$TiO_2$-based nanotube (TNTs) composite are investigated. The CNT/TNT composite is synthesized via a solution chemical route. It is confirmed that this 1-D nanotube composite has a core-shell nanotubular structure, where the TNT surrounds the CNT core. The photocatalytic activity investigated based on the methylene blue degradation test is superior to that of with pure TNT. The CNTs play two important roles in enhancing the photocatalytic activity. One is to act as a template to form the core-shell structure while titanate nanosheets are converted into nanotubes. The other is to act as an electron reservoir that facilitates charge separation and electron transfer from the TNT, thus decreasing the electron-hole recombination efficiency.

• 한국지진공학회논문집
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• 제20권5호
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• pp.311-318
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• 2016

The lead-rubber bearing (LRB) dissipates seismic energy through plastic deformation of lead core. Under large-displacement cyclic motion, the temperature increases in the lead core. The shear strength of a lead-rubber bearing is reduced due to the heating effect of the lead core. In this study, the seismic responses such as displacement increasing, shear strength and vertical stiffness degradations of LRB due to the heating effect are evaluated for design basis earthquake (DBE) and beyond design basis earthquake (150% DBE, 167% DBE, 200% DBE).

• Nuclear Engineering and Technology
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• 제55권12호
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• pp.4583-4590
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• 2023

This study aims at modeling the beryllium reflector poisoning under neutron irradiation conditions and calculating the impact of beryllium poisoning on the core parameters of ETRR-2 research reactor. The CITVAP code was used to calculate the neutron flux and parameters of ETRR-2 core with beryllium reflector elements. The neutron flux in each reflector element was calculated to solve the modeling equations for the atomic densities of lithium-6 (⁶Li), tritium-3 (³H), and helium-3 (³He) using the BERYL program. The results are discussed based on CITVAP calculations of the core excess reactivity and cycle length Full Power Days (FPD). Possible solutions to minimize the degradation due to beryllium poisoning are also discussed and compared based on calculations.

• Journal of Industrial and Engineering Chemistry
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• 제68권
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• pp.14-23
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• 2018

$TiO_2-coated$ cubic ${\alpha}-Fe_2O_3$ with mostly exposed (012) and (101) facets (${\alpha}-Fe_2O_3@TiO_2$) was fabricated using a hydrothermal route for the photo-Fenton degradation of tetracycline under visible light irradiation. $TiO_2$ coating could greatly affect the photocatalytic activity of ${\alpha}-Fe_2O_3@TiO_2$. Compared with cubic ${\alpha}-Fe_2O_3$ alone for photodegradation of tetracycline, ${\alpha}-Fe_2O_3@TiO_2$ with $TiO_2$ shell of around 15 nm exhibited higher removal efficiency of tetracycline in photo-Fenton system, and its durability was slightly affected after five cycle times under same conditions. It is ascribed to the well-matched interface between cubic ${\alpha}-Fe_2O_3$ core and $TiO_2$ shell, leading to the broadened light-absorption and the efficient separation of photo-generated electon-hole pairs. The $^{\bullet}OH$ radicals were main responsible for the advanced photocatalytic performance of ${\alpha}-Fe_2O_3@TiO_2$ in visible-light driven degradation of tetracycline.

• 한국전기전자재료학회논문지
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• 제28권10호
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• pp.636-641
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• 2015

In this study, the partial discharge degradation properties for 2-core PVC cable($2cores{\times}1.5mm^2$ cross section, length of 10 cm, 20 cm, 30 cm) following immersion with the salt water that the 2%, 4%, 8% of NaCl is dissolved in 100 g of distilled water for 48 and 96 hours has been measured. The results of this study are as follows. When the degradation time in salt water of 2% NaCl is 48 hours, it found that the number of partial discharge increased as about 40 pps, 50 pps, 90 pps with increasing the length of cable to 10 cm, 20 cm, 30 cm. In case the concentration and degradation time is same, the inception and extinction voltage decreased with increasing the length of cable. When the degradation time in salt water is 96 hours and the length of cable is 20 cm, it found that the number of partial discharge decreased as 3,000 pps, 500 pps, 100 pps with increasing the concentration of NaCl to 2%, 4%, 8%.

• Earthquakes and Structures
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• 제6권1호
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• pp.89-110
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• 2014

Nonlinear dynamic analyses are carried out to investigate the influence of the pinching hysteretic response of the exterior RC beam-column joints on the seismic behavior of multistory RC frame structures. The effect of the pinching on the local and global mechanisms of an 8-storey bare frame and an 8-storey pilotis type frame structure is evaluated. Further, an experimental data bank extracted from literature is used to acquire experimental experience of the range of the real levels that have to be considered for the pinching effect on the hysteretic response of the joints. Thus, three different cases for the hysteretic response of the joints are considered: (a) joints with strength and stiffness degradation characteristics but without pinching effect, (b) joints with strength degradation, stiffness degradation and low pinching effect and (c) joints with strength degradation, stiffness degradation and high pinching effect. For the simulation of the beam-column joints a special-purpose rotational spring element that incorporates the examined hysteretic options developed by the authors and implemented in a well-known nonlinear dynamic analysis program is employed for the analysis of the structural systems. The results of this study indicate that the effect of pinching on the local and global responses of the examined cases is not really significant at early stages of the seismic loading and especially in the cases when strength degradation in the core of exterior joint has occurred. Nevertheless in the cases when strength degradation does not occur in the joints the pinching may increase the demands for ductility and become critical for the columns at the base floor of the frame structures. Finally, as it was expected the ability for energy absorption was reduced due to pinching effect.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 춘계학술발표회논문집(2)
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• pp.637-642
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• 1996

This paper presents the analysis results for the core degradation processes and the fission product release of the PHEBUS FPT0 experiment using MELCOR1.8.3. The objective of this study is to assess models associated with the core damage and fission product behavior in MELCOR. The calculation results were much improved through sensitivity studies. Thermal/hydraulic behavior in the core and the circuit was well predicted under the intact core geometry. In non-eutectic model case. the UO$_2$ dissolution model in the MELCOR always showed such a tendency that the resulting dissolved UO$_2$ mass was small at the highly oxidized condition due to the model logic. Total H$_2$ generation mass was underpredicted because the stiffner was not modeled and the liner in the shroud was not allowed to be oxidized in MELCOR. Some difficulties were found in modeling the activation product were solved by manipulating the RN input associated with the initial fission product inventory. These problem were occurred because there are no control rod model in MELCOR. Generally the fission product release ratio showed a similar trend compared with the measured data except the activation product. which have no model to simulate in MELCOR.