• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.10a
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• pp.273-279
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• 1995

본 연구에서는 증기발생기 튜브의 마모마손에 대한 평가 방법을 열수력해석, 자유진동해석, 비선형해석, 마모량예측 등의 과정을 통해 증기발생기튜브의 마모량과 수명을 예측하는 방법에 대해 알아보았다. 본 연구를 통해 얻어진 결론은 다음과 같다. 1) 증기발생기 비선형충격해석에서 사용되는 정확한 난류 여기진동가진 가진력의 확보가 정확한 마모치를 예측할 수 있고, 2) 마모치예상을 위한 수식의 사용시 튜브의 미끌림거리 over bar L값이 매우 주요한 변수임을 알 수 있었다. 3) 충격력과 마모치의 연관관계에 대한 정확한 정의가 본 연구에 사용된 Archard의 마모방정식 이외에 여러 가지가 있으나, 아직 이들에 대한 정보부족으로 더 많은 검토가 필요하다.

• Proceedings of the KIEE Conference
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• 1998.07g
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• pp.2433-2435
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• 1998

원자력발전소의 증기발생기는 기능상으로도 중요한 역할을 하지만 증기발생기 내의 전열관 손상이나 누설은 바로 방사능 누출의 원인이 되므로 원자력 발전소의 안전성 측면에서 보면 매우 중요한 설비이다. 따라서, 증기발생기 전열관은 정기보수시 마다 전열관 각각에 대해 비파괴검사의 일종인 와전류검사(Eddy Current Testing, ECT)를 통해 건전성을 평가하고 있다. 현재는 신호를 취득하고 평가하는 업무가 별개의 기관에서 수행하고 있으며 이를 위해 현장에 관련 인력과 장비가 이동되어야 한다. 그러나, 취득한 신호를 평가자가 on-line으로 받을 수 있고 그 결과를 이용하여 즉시 피드백이 가능하다면 평가기관의 인력은 현장에 있지 않더라도 평가가 가능하다. 그러므로, 원격 평가 환경을 구축한다는 것은 평가자가 굳이 현장에 가지 않더라도 지역에 상관없이 LAN을 활용하여 전국 어디서든 평가가 가능하도록 하고자 함에 있다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.84-91
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• 2003

Flow-Induced Vibration of steam generator tubes may result in fretting wear damage at the tube-to-support locations. KSNP(Korean Standard Nuclear Power plant) steam generators experienced fretting wear in the upper part of U-bend above the central cavity region of steam generators. This region has conditions susceptible to the flow-induced vibration, such as high flow velocity, high void fraction, and longer unsupported span. To improve its performance, APR1400 steam generator is designed with additional supports in this region to reduce unsupported span and to reduce peak velocity in the central cavity region. In this paper, we examined its performance improvement using ATHOS code. The thermal-hydraulic condition in the region of secondary side of APR1400 steam generator is obtained using the ATHOS3 code. The effective mass for modal analysis is calculated using the void fraction, enthalpy, and operating pressure information from ATHOS3 code result. With the effective mass distribution along the tube, natural frequency and mode shape is obtained using ANSYS code. Finally, stability ratios and real mean squared displacements for selected tubes of the APR1400 steam generator are computed. From these results, the current design of the APR1400 steam generator are examined.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.148-154
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• 2005

Ground-source (Geothermal) heat pump (GSHP) systems can achieve a higher coefficient of performance than conventional air-source heat pump (ASHP) systems. However, GSHP systems are not widespread in Japan because of their expensive boring costs. The authors have developed a GSHP system that employs the cast-in-place concrete pile foundations of a building as heat exchangers in order to reduce the initial boring cost. In this system, eight U-tubes are arranged around the surface of a cast-in-place concrete pile foundation. The heat exchange capability of this system, subterranean temperature changes and heat pump performance were investigated in a foil-scale experiment. As a result, the average values for heat rejection were 186${\sim}$201 W/m (for pile, 25 W/m per Pair of tubes) while cooling. The average COP of this system was 4.6 while cooling; rendering this system more effective in energy saving terms than the typical ASHP systems. The initial cost of construction per unit for heat extraction and rejection is ${\yen}$72/W for this system, whereas it is f300/W for existing standard borehole systems.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.12
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• pp.858-866
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• 2012

A numerical study was performed to predict the performance of a fin-and-tube condenser. A condenser model was developed and verified by comparing the simulation results with experimental data for a R410A condenser in a residential air-conditioning system. The prediction error was 0.07% and -5.77% for the condenser capacity and pressure drop, respectively. In simulation results, the capacity and pressure drop of the condenser with even air velocity distribution were 0.67% and 12.93% higher than those with uneven distribution of air velocity. It was predicted by the model that the refrigerant distribution at the condenser inlet to the two first passes was not significantly influenced by the air distribution. The simulation results presented that the 1.49% of capacity and 64.6% of pressure drop were reduced by replacing helical microfin tubes with smooth tubes for the condenser.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.9
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• pp.641-647
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• 2010

Ground-source(Geothermal) heat pump(GSHP) systems can achieve a higher coefficient of performance than conventional air-source heat pump(ASHP) systems. However, GSHP systems are not widespread because of their expensive installation costs. The authors have developed a GSHP system that employs the cast-in-place concrete pile foundations of a building as heat exchangers in order to reduce the initial cost. In this system, eight U-tubes are arranged around the surface of a cast-in-place concrete pile foundation. The heat exchange capability of this system, subterranean temperature changes and heat pump performance were investigated in a full-scale experiment. As a result, the average values for heat rejection were 186~201 W/m(per pile, 25 W/m per pair of tubes) while cooling. The average COP of this system was 4.6 while cooling; rendering this system more effective in energy saving terms than the typical ASHP systems.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.312-317
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• 2005

Fluid-elastic instability and turbulence excitation for an under developing steam generator are investigated numerically. The stability ratio and the amplitude of turbulence excitation are obtained by using the PIAT (Program for Integrity Assessment of Steam Generator Tube) code from the information on the thermal-hydraulic data of the steam generator. The aspect ratio, the ratio between the height of U-tube from the upper most tube support plate (h) and the width of two vertical portion of U-tube (w), is defined for geometric parameter study. Several aspect ratios with relocation of tube support plates are adopted to study the effects on the mode shapes and characteristics of flow-induced vibration. When the aspect ratio exceeds value of 1, most of the mode shapes at low frequency are generated at the top of U-tube. It makes very high value of the stability ratio and the amplitude of turbulent excitation as well. We can consider that the local mode shape at the upper side of U-tube will develop the wear phenomena between the tube and the anti-vibration bars such as vertical, horizontal, and diagonal strips. It turns out that the aspect ratio reveals very important parameter for the design stage of the steam generator. The appropriate value of the aspect ratio should be specified and applied.

• 한국균학회소식:학술대회논문집
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• 2015.05a
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• pp.60-60
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• 2015

Hybrid histidine kinase is a part of two-component system that is required for various stress responses and pathogenesis of pathogenic fungi. In the present study, Tco1, a homologue of human pathogen Cryptococcus neoformans Tco1 encoding a hybrid histidine kinase, was identified in corn smut pathogen Ustilago maydis by bioinformatic analysis. To explore the role of Tco1 in the virulence of U. maydis, mutants in which the tco1 gene was partially deleted were constructed by allelic exchange. The U. maydis tco1 mutants did show unaltered growth rate on axenic medium but were unable to produce conjugation tubes and develop fuzzy filaments, resulting in impaired mating of compatible strains. The expression levels of prf1, pra1, and mfa1 which are involved in the pheromone pathway significantly decreased in the tco1 mutants. In inoculation tests to host, the tco1 mutants showed significantly reduced ability in the production of anthocyanin pigments and tumor development on maize leaves. Overall, the combined results indicated that Tco1 plays important roles in sexual development and virulence of U. maydis by regulating the expression of the genes involved in the pheromone pathway.

• Journal of the speleological society of Korea
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• no.4
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• pp.41-50
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• 1996

The coastal plains of the Puna and Ka' u Districts of the island of Hawaii are a contradiction to the popular view that the island of Hawaii is a tropical rain forest or a vegetated landscape with abundant water sour This section of the island lies in the rain shadow of Mauna Loa a Kilauea Volcanoes and receives less than 30 inches of annual precipita When rain does come. it is in the form of sudden down pours. givi residents of the area little time to collect and conserve water. Due to porous nature of the rock. there is no standing surface water. In spite of these harsh climatic conditions. archeological evidence indic that an extensive agriculture complex existed not only along the coast. into the most remote parts of what is called the Ka'u Desert. Pass through these agricultural areas are historic and pre - historic t systems. These trail systems apparently played a significant suppor role for exchange between the ahupua's (classic land divisions of Haw and the geopolitical districts. The question arises as to how could vast agricultural complexes a heavy foot travel over miles of arid land exist without dependable wa sources\ulcorner While planting - pits and mounds were designed to make most efficient use of available water and conserve moisture(Carter 19 9). people involved in planting also needed potable water for surv Most publications and research papers dealing with the early population this area make only oblique reference to springs and wells which t populations depended upon. The Federal Cave Resource Protection Act(1988) has served as imprtus for the National Park Service to look closer at the lava tu caves and fault cracks within Hawaii Volcanoes National Park. P visitors to these underground areas found large volumes of standing wa in fault cracks. and abundant drip areas with the lava tubes. Re observes noted that in most cases. where the cracks and caves we located in the arid sections of the park. there has been extens modifiacation or utilization of these water sources by the early Hawaii and others. The variety of western containers used for collection indica that these water sources were used during historic times. William E described similar water sources in his narrative of his trip around island in 1823(Eills 1979), This report is directed at documenting recent observations and a stimulating further research into early Hawaiian water collection syst It also explores the implications that power and political influence of e chiefs in the arid portions of Hawaii could have been linked to the con of the water resources.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.9 s.102
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• pp.1009-1015
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• 2005

Fluid-elastic instability and turbulence excitation for an under developing steam generator are investigated numerically. The stability ratio and the amplitude of turbulence excitation are obtained by using the $PIAT^{(R)}$ (program for integrity assessment of steam generator tube) code from the information on the thermal-hydraulic data of the steam generator. The aspect ratio, the ratio between the height of U-tube from the upper most tube support Plate (h) and the width of two vertical portion of U-tube (w), is defined for geometric parameter study. Several aspect ratios with relocation of tube support plates are adopted to study the effects on the mode shapes and characteristics of flow-induced vibration. When the aspect ratio exceeds value of 1, most of the mode shapes at low frequency are generated at the top of U-tube. It makes very high value of the stability ratio and the amplitude of turbulent excitation as well. We can consider that the local mode shape at the upper side of U-tube will develop the wear phenomena between the tube and the anti-nitration bars such as vortical, horizontal, and diagonal strips. It turns out that the aspect ratio reveals very important parameter for the design stage of the steam generator. The appropriate value of the aspect ratio should be specified and applied.