• 대한기계학회논문집A
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• 제34권8호
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• pp.1059-1065
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• 2010

본 연구에서는 SMART 원자로의 사류형 원자로냉각재펌프의 축소모형에 대한 수력성능을 예측하기 위하여 설계점을 포함한 다양한 탈설계점에서의 해석을 수행하였다. 계산시간의 효율성을 위하여 임펠러와 디퓨저 각 1개 유로로 이루어진 계산영역을 해석대상으로 선정하였다. 임펠러와 디퓨저간의 정보교환을 위하여 스테이지 기법을 사용하였다. 정상상태 비압축성 유동조건에서 축소모형의 수력성능특성을 파악하기 위하여 해석영역의 입구와 출구에서 압력차를 측정하여 양정, 효율과 축동력을 산출하였다. 수력성능 곡선은 일반적인 사류펌프의 성능특성을 잘 모사하는 것으로 나타났다. 저유량에서의 펌프 내부유동의 복잡한 흐름을 확인 하였다.

• Nuclear Engineering and Technology
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• 제43권3호
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• pp.301-308
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• 2011

The diametral creep of pressure tubes (PTs) in CANDU (CANada Deuterium Uranium) reactors is one of the principal aging mechanisms governing the heat transfer and hydraulic degradation of the heat transport system (HTS). PT diametral creep leads to diametral expansion, which affects the thermal hydraulic characteristics of the coolant channels and the critical heat flux (CHF). The CHF is a major parameter determining the critical channel power (CCP), which is used in the trip setpoint calculations of regional overpower protection (ROP) systems. Therefore, it is essential to predict PT diametral creep in CANDU reactors. PT diametral creep is caused mainly by fast neutron irradiation, temperature and applied stress. The objective of this study was to develop a bundle position-wise linear model (BPLM) to predict PT diametral creep employing previously measured PT diameters and HTS operating conditions. The linear model was optimized using a genetic algorithm and was devised based on a bundle position because it is expected that each bundle position in a PT channel has inherent characteristics. The proposed BPLM for predicting PT diametral creep was confirmed using the operating data of the Wolsung nuclear power plant in Korea. The linear model was able to predict PT diametral creep accurately.

• 항공우주시스템공학회지
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• 제11권5호
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• pp.1-5
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• 2017

본 논문은 실 궤도면 누적량 계산법을 활용한 원자산소의 저궤도위성의 태양전지판 코팅재료 침식량에 대한 예측 연구로써, 기존 프로젝트에서 활용하던 최악 경우 추정법과 상호 비교를 통해 원자산소 영향성의 차이가 있음을 확인하였으며, 이렇게 예측된 결과를 바탕으로 해외 제작사의 설계입증 자료 확인시 활용할 예정이다. 가상으로 설정한 궤도정보를 바탕으로 한 계산은 유럽우주기구(ESA)가 제공하고 있는 우주환경정보시스템을 이용하였고, 실제 궤도상에서의 태양전지판에 충돌되는 원자산소 플럭스를 계산하기 위해서 궤도 계산 소프트웨어를 활용하였다.

• Nuclear Engineering and Technology
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• 제26권4호
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• pp.526-535
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• 1994

KMRR(다목적 연구용원자로) 핵연료의 알루미늄 피복재의 부식거동을 평가하기 위해, 부식 예측치와 노내 부식 실측치의 비교를 통해 유도된 열속인자를 도입한 수정된 Griess 경험식을 유도하였다. KMRR 핵연료의 건전성이 유지되는 부식의 설계기준으로써는 산화층의 박리 방지가 보수적으로 설정되었으며, 산화층의 박리는 산화층에서의 온도차이가 114$^{\circ}C$ 이상에서 일어난다고 보수적으로 가정하였다. KMRR 핵연료의 출력이력을 첫 주기부터 평형주기까지 분석하여, 한계출력이력을 결정하였다. 한계출력이력을 가진 KMRR 핵연료의 부식량 예측계산 결과, 최대 산화층의 두께는 50$\mu\textrm{m}$ 이하였으며, 산화층 박리의 설계기준은 2배의 여유도를 가지고 만족하였다. 따라서, KMRR 핵연료는 피복재의 부식으로 인해 손상되지 않을 것으로 판단된다. 그러나, 수정된 Griess 부식경험식의 KMRR에의 적용 타당성은 KMRR 핵연료의 부식 감시를 통해 추가로 검증될 필요성이 있다.

• Advances in materials Research
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• 제8권2호
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• pp.117-135
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• 2019

The lifetime of a gas turbine combustor is typically limited by the durability of its liner, the structure that encloses the high-temperature combustion products. The primary objective of the combustor thermal design process is to ensure that the liner temperatures do not exceed a maximum value set by material limits. Liner temperatures exceeding these limits hasten the onset of cracking which increase the frequency of unscheduled engine removals and cause the maintenance and repair costs of the engine to increase. Hot gas temperature prediction can be considered a preliminary step for combustor liner temperature prediction which can make a suitable view of combustion chamber conditions. In this study, the temperature distribution of ceramic panels for a V94.2 gas turbine combustor subjected to realistic operation conditions is presented using three-dimensional finite difference method. A simplified model of alumina ceramic is used to obtain the temperature distribution. The external thermal loads consist of convection and radiation heat transfers are considered that these loads are applied to flat segmented panel on hot side and forced convection cooling on the other side. First the temperatures of hot and cold sides of ceramic are calculated. Then, the thermal boundary conditions of all other ceramic sides are estimated by the field observations. Finally, the temperature distributions of ceramic panels for a V94.2 gas turbine combustor are computed by MATLAB software. The results show that the gas emissivity for diffusion mode is more than premix therefore the radiation heat flux and temperature will be more. The results of this work are validated by ANSYS and ABAQUS softwares. It is showed that there is a good agreement between all results.

• 대기
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• 제33권3호
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• pp.307-317
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• 2023

This study investigates the physical mechanisms that contributed to the 2022 European record-breaking heatwave throughout May-August (MJJA). The European climate has experienced surface warming and drying in the recent decade (1979~2022) which influences the development of the 2022 European heatwave. Since its spatial pattern resembles the 2003 European heatwave which is a well-known case developed by the strong coupling of near-surface conditions to land surface processes, the 2022 heatwave is compared with the 2003 case. Understanding heatwave development is carried out by the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis version 5 (ERA5) and daily maximum surface temperature released by NCEP (National Centers for Environmental Prediction) CPC (Climate Prediction Center). The results suggest that the persistent high pressure along with clear sky tends to increase the downward shortwave radiation which leads to enhanced sensible heat flux with the land surface dryness. Terrestrial Coupling Index (TCI), a process-based multivariate metric, is employed to quantitatively measure segmented feedback processes, separately for the land, atmosphere, and two-legged couplings, which appears to the development of the 2022 heatwave, can be viewed as an expression of the recent trends, amplified by internal land-atmosphere interactions.

• 한국물환경학회지
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• 제35권4호
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• pp.316-331
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• 2019

Carbon dioxide($CO_2$) emission from rivers to the atmosphere is a key component in the global carbon cycle. Most of the rivers are supersaturated with $CO_2$. At a global scale, the amount of $CO_2$ emission from rivers is reported to be five-fold greater than that from lakes and reservoirs, but relevant data are rare in Korea. The objectives of this study is to estimate the $CO_2$ net atmospheric flux(NAF) from the upstream of Gangjeong-Goryeong Weir(GGW), Dalseong Weir(DSW), Hapcheon-Changnyeong Weir(HCW), and Changnyeong-Haman Weir(CHW) located in Nakdong River South Korea) using field and laboratory experiments and to apply data mining techniques to develop parsimonious prediction models that can be used to estimate $CO_2$ NAF with physical and water quality variables that can be collected easily. As a result, the study sites were all heterotrophic systems that often released $CO_2$ to the atmosphere, except when the algal photosynthesis was active.The median $CO_2$ NAF was minimum $391.5mg-CO_2/m^2$ day at GGW and maximum $1472.7mg-CO_2/m^2$ day at DSW. The $CO_2$ NAF showed a negative correlation with pH and Chl-a since the overgrowth of the algae consumed $CO_2$ in the water and increased the pH. As the parsimonious multiple regression model and random forest model developed, this study showed an excellent performance with the $Adj.R^2$ value higher than 0.77 in all weirs. Thus, these methods can be used to estimate $CO_2$ NAF in the river even if there is no $pCO_2$ measurement data.

• 한국해안해양공학회지
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• 제3권1호
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• pp.14-20
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• 1991

심해에서 발생한 다방향불규칙 파랑이 수심변화에 의해서 어떠한 형태로 변형할 것인가를 명확히 파악하는 것은 연안구조물의 설계, 연안침식대책 공법의 확립에 있어서 중요한 과제이다. 본 연구는 선형파동이론을 적용할 수 있는 수심영역을 대상으로 에너지 평행방정식에 의해 방향 스펙트럼을 천수변형시킴으로써 얻어지는 제원을 입력조건으로서 파고, 주기, 파향의 결합확률분포를 수치적으로 구했고, 추정된 결합확률분포로부터 에너지 평형방정식의 천수변형예측에 대한 적용성을 수치적으로 검토했다. 또한 수심이 다른 2지점의 3성분 행렬배치에 의해 동시 측정되어진 방향 스펙트럼을 입력조건으로서, 천해역에 있어서의 방향 스펙트럼의 천수변형예측에 대한 에너지 평형방정식의 적용성 및 문제점에 대해서 검토한 것이다.

• 한국추진공학회지
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• 제16권2호
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• pp.42-50
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• 2012

열전달 연구의 목적은 온도와 열유속 분포를 보다 정확하게 예측하는 것이다. 이를 위해 상용 CFD 코드인 FLUENT를 사용하여 2종류의 노즐에 대해 질량유속비와 압력비를 계산하였으며, 실험결과와 잘 일치하였다. 또한 1종류의 노즐에 대해 FLUENT를 사용한 노즐 벽면에서의 열전달계수 계산결과는 노즐 축소부에서 실험결과 보다 약간 크게 예측되었으나 확대부에서는 잘 일치하고 있다. Bartz식을 이용한 열전달계수 계산결과는 전체적으로 실험결과 보다 크게 예측되었다. 계산결과가 실험결과와 차이를 보이는 원인은 노즐 내 급가속 유동에 의한 층류화, 난류모델 및 격자구성 등을 고려해 볼 수 있다.

• 설비공학논문집
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• 제7권2호
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• pp.225-233
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• 1995

Experiments were performed to investigate the heat transfer characteristics of nonazeotropic mixture R-22+R-114 in a heat pump system. The ranges of parameter, such as heat flux, mass flow rate, and quality were $8,141{\sim}32,564W/m^2$, 24~58kg/h, and 0~1, respectively. The overall compositions of the mixtures were 50 and 100 per-cent of R-22 by weight for R-22+R-114 mixture. The results indicated that there were distinct different heat transfer phenomena between the pure substance and the mixture. In case of pure refrigerant the heat transfer rates for cooling were strongly dependent upon quality of the refrigerant. Overall evaporating heat transfer coefficients for the mixture were somewhat lower than pure R-22 values in the forced convective boiling region. For a given flow rate, the heat transfer coefficient at the circumferential tube wall(top, side, and bottom of the test tube) for R-22/R-114(50/50wt%)mixture, however, was higher than for pure R-22 at side and bottom of the tube. Furthermore, a prediction for the evaporating heat transfer coefficient of the mixtures was developed based on the method of Yoshida et.al.'s. The resulting correlation yielded a good agreement with the data for the refrigerant mixtures.