• Title/Summary/Keyword: stratification

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COMPUTATIONAL FLUID DYNAMICS ANALYSIS OF THERMAL STRATIFICATION IN THE UPPER PLENUM OF THE MONJU FAST BREEDER REACTOR (몬주 고속증식로 상부플레넘에서의 열성층에 관한 전산유체역학 해석)

  • Choi, S.K.;Lee, T.H.
    • Journal of computational fluids engineering
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    • v.17 no.4
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    • pp.41-48
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    • 2012
  • A numerical analysis of thermal stratification in the upper plenum of the MONJU fast breeder reactor was performed. Calculations were performed for a 1/6 simplified model of the MONJU reactor using the commercial code, CFX-13. To better resolve the geometrically complex upper core structure of the MONJU reactor, the porous media approach was adopted for the simulation. First, a steady state solution was obtained and the transient solutions were then obtained for the turbine trip test conducted in December 1995. The time dependent inlet conditions for the mass flow rate and temperature were provided by JAEA. Good agreement with the experimental data was observed for steady state solution. The numerical solution of the transient analysis shows the formation of thermal stratification within the upper plenum of the reactor vessel during the turbine trip test. The temporal variations of temperature were predicted accurately by the present method in the initial rapid coastdown period (~300 seconds). However, transient numerical solutions show a faster thermal mixing than that observed in the experiment after the initial coastdown period. A nearly homogenization of the temperature field in the upper plenum is predicted after about 900 seconds, which is a much shorter-term thermal stratification than the experimental data indicates. This discrepancy is due to the shortcoming of the turbulence models available in the CFX-13 code for a natural convection flow with thermal stratification.

Estimation of Proper EFDC Parameters to Improve the Reproductability of Thermal Stratification in Korea Reservoir (저수지 수온성층 해석능력 제고를 위한 적정 EFDC 매개변수 선정)

  • Kim, Seon-Joo;Seo, Dong-Il;Ahn, Ki-Hong
    • Journal of Korea Water Resources Association
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    • v.44 no.9
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    • pp.741-751
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    • 2011
  • In this study, a methodology was devised to overcome that difficulty for thermal stratification modeling using EFDC. For the increase of reproductability for thermal stratification analysis, the effect of parameter such as distribution of solar radiation, depth of active bed temperature layer, heat transfer coefficients were analyzed. The simulation period was from June to December in 2005 and statistical index is used to analyze the model results. The results showed that distribution of solar radiation is zero and depth of active bed temperature layer is 10 m are suitable for simulation of thermal stratification in Yongdam Dam reservoir. This study results can be used for guideline to analyze the thermal stratification of large dam reservoir in Korea.

Characteristics of Surface and Internal Wave Propagation through Density Stratification (밀도성층을 통과하는 수면파 및 내부파의 전파특성)

  • Lee, Woo-Dong;Hur, Dong-Soo
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.36 no.5
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    • pp.819-830
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    • 2016
  • Hydrodynamic characteristics of wave propagation through density stratification have not been identified in details. So this study conducted a numerical simulation using LES-WASS-3D ver. 2.0 for analysis of density current due to water temperature and salinity in order to analyze hydraulic characteristics under wave action in a two-layer density stratified fluid. For the validity and effectiveness of numerical wave tank used, it was compared and analyzed with the experiment to show waveform based on $3^{rd}$-order Stoke wave theory at the internal of a density stratification. Using the results obtained from numerical simulation, the surface and internal wave heights are reduced as the wave propagates in a two-layer density stratified water. And the surface or internal wave attenuation became more serious as the vorticities were increased by the velocity difference of wave propagation due to the upper-lower density difference around the interface of a density stratification. As well, the surface and internal wave attenuations became more serious with higher density difference and depth ratio between upper and lower layers when the wave propagates through a density stratification.

Study on the Effect of Thermal Stratification on DME/n-Butane HCCI Combustion (열적성층화가 DME/n-Butane 예혼합압축자기착화연소에 미치는 영향에 관한 연구)

  • Lim, Ock-Taeck
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.34 no.12
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    • pp.1035-1042
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    • 2010
  • The thermal stratification effect has been thought as one of the way to avoid dramatically generating the heat from HCCI combustion. We investigate the effect of thermal stratification on HCCI combustion fueled by DME and n-Butane. The thermal stratification occurs in a combustion chamber of a rapid compression machine with premixture by buoyancy effect that is made of fuel and air. The premixture is then adiabatically compressed, and during the process, the in-cylinder gas pressure is measured and two-dimensional chemiluminescence images are prepared and analyzed. Under the thermal stratification, the LTR starting time and the HTR starting time are advanced than that of homogeneous case. Further, the LTR period and the luminosity duration under homogeneous conditions are shorter than the corresponding quantities under stratified conditions. Additionally, under stratified conditions, the brightest luminosity intensity is delayed longer than that of homogeneous condition.

The Spatial Characteristics of Stratification in Deukryang Bay, Korea (밀도류 효과에 으히나 득령만의 성층변동 특성)

  • Byung-Gul Lee;Kyu-Dae Cho
    • Journal of Environmental Science International
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    • v.7 no.2
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    • pp.223-232
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    • 1998
  • The spatial characteristics of stratification In Deukryang Bay were studded using observed data and analytical models. From the description of the density structure and its the potential energy anomaly (PEA) from observed data along longitudinal direction (from the mouth to head of the bays, we found that the stratification Intensity could be changed strongly by density current effect during the spring-neap tidal cycle, and depth variation. To find out density current effect for the formation of the stratification In detail, we Implemented a diagnostic approach by using the modified analytical model including density current, tidal current, surface heating and wind stirring. The model allowed for the observed similarities for the whole domain in the bay and increased tidal mixing efficiency value s up to 0.006-0.007 as compared to the results without density current effect. We found that the density current effect was also an important key factor In determining the formation of the spatial distribution of stratification.

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Gibberellic Acid and Cold Stratification Promotes Seed Germination and Seedling Growth in Kadsura coccinea (GA3처리와 저온습윤처리에 의한 흑노호(Kadsura coccinea)의 종자발아 및 유묘생장 촉진)

  • Byoung Il Je;Joonng Suk Jeon;Jum-Soon Kang;Young Whan choi
    • Journal of Environmental Science International
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    • v.32 no.1
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    • pp.77-88
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    • 2023
  • Kadsura coccinea (Lem.) A.C. Smith is used as a medicinal plant and cosmetic material in China and Southeast Asia. To mass-produce Kadsura coccinea seedlings, the effects of gibberellic acid (GA3) and cold stratification treatments on seed germination were investigated. Seed germination rate with GA3 treatment was most effective at concentrations of 250 or 500 mg/L. With respect to mean germination time (MGT), mean daily germination, and T50 (days to reach 50% seed germination), the germination-promoting effect was improved as the concentration of GA3 increased. Stem growth of seedlings was the highest following GA3 treatments of 250 and 500 mg/L, and the growth promoting effect gradually decreased as the concentration of GA3 decreased. Root growth was stimulated at GA3 concentrations of 250-1,000 mg/L. Examination of the effect of stratification treatment for 15, 30 and 60 days at temperatures of 0, 5 and 10℃ on the germination rate revealed that the most stratification treatment temperature was 10℃, and the results improved with longer treatment periods. Altogether, GA3 and stratification treatments improved the seed germination rate, shortened the MGT, improved germination uniformity, and produced healthy seedlings.

Dormancy-breaking and Germination of Chelidonium majus L. subsp. asiaticum H. Hara Seeds by Stratification and Gibberellins

  • Boran Ji;Hayan Lee;Kyungtae Park;Sang Yeob Lee;Bo-Kook Jang;In Hwan Chae;Chung Youl Park;Sung Pil Kwon;Deug-Chan Lee;Ju-Sung Cho
    • Korean Journal of Plant Resources
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    • v.35 no.6
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    • pp.796-804
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    • 2022
  • The demand for Chelidonium majus L. subsp. asiaticum H. Hara is expected to increase due to its pharmacological properties such as antibacterial, antioxidant, and anti-inflammatory effects. However, an effective propagation system for this species has not yet been established. This study was conducted to analyze the seed dormancy and germination characteristics of C. majus L. subsp. asiaticum H. Hara native to Korea and establish a mass propagation system. The dormancy type was primarily classified by analyzing the general information of the collected seeds. The seed dormancy breaking was investigated by comparing the effects of cold stratification (0, 2, 4, 8, 10, or 12 weeks) with warm stratification (S, summer temperature, 25/15℃) and intermediate temperature stratification (A, autumn temperature, 15/10℃) of alternating temperature stratification (S12-A4 or S12-A8 weeks). After dormancy break, 500 mg/L GA3 and GA4+7 treatment replaced cold stratification and improved seed germination. The results of this study are expected to provide basic data for future seed propagation and mass propagation by analyzing the dormancy and germination characteristics of C. majus L. subsp. asiaticum H. Hara seeds.

Study on the Effects of Stratification and Sediment Organic Matter Characteristics on Methane Production in Asan Lake (아산호의 성층과 퇴적층 유기물 특성이 메탄 발생에 미치는 영향에 관한 연구)

  • Sun Ryeol Lee;Haeseong Oh;Jung Hyun Choi
    • Journal of Korean Society on Water Environment
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    • v.40 no.5
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    • pp.215-228
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    • 2024
  • Lakes are one of major sources of methane gas due to anaerobic decomposition of organic matter in sediments. Since methane released from lakes is a greenhouse gas, it is necessary to investigate factors affecting methane production of lakes. This study conducted field and incubation experiments in Lake Asan in August and October to determine effects of thermal stratification and sediment organic matter characteristics on methane production. Field experiments measured temperature and dissolved oxygen to determine the formation of thermal stratification of lakes. Methane and organic matter characteristics were analyzed using gas chromatography, Total Organic Carbon (TOC) analyzers, and fluorescence spectroscopy. Incubation experiments under anaerobic conditions used sediment and water samples from the same site. Field results showed higher methane fluxes in August and increased Dissolved Organic Carbon (DOC) concentration closer to Asan Bay seawall. Elevated methane fluxes and DOC concentration resulted from intensified anaerobic decomposition formed by thermal stratification. Incubation results indicated that sediment organic matter characteristics influenced methane flux between sites. Statistical analysis revealed that thermal stratification could be a primary factor affecting methane production of lakes. Characteristics of sediment organic matter with respect to quantity and quality could be factors influencing methane production of lakes. Results of this study can serve as fundamental data for predicting methane emissions from lakes due to climate change and for mitigating lake's contributions to global warming.

Application of Judgement Post-Stratification to Extended Producer Responsibility System (생산자 책임재활용 제도를 위한 혼입비율 조사에서 Judgement Post-Stratification의 활용)

  • Choi, Wan-Suk;Lim, Jo-Han;Lim, Jong-Ho;Kim, Hyun-Joong
    • Communications for Statistical Applications and Methods
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    • v.15 no.1
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    • pp.105-115
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    • 2008
  • Judgement post-stratification is a new sampling method developed by MacEachern et al. (2004). This article suggests that the judgement post-stratification method can be a good alternative for the simple random sampling when analyzing real-world environmental data. It becomes an important task to accurately measure the output of a recycling facility since the EPR (Extended Producer Responsibility) system takes effect on 2003. However, the total weight of materials processed in the recycling facility may not be a proper measure because the materials are frequently mingled with other non-recycling materials. Therefore, it is necessary to estimate the mixture ratio of non-recycling materials among the total materials admitted in the facility. Unfortunately, the size of sample in a recycling facility is restricted due to the inconvenience of sampling procedure such as safety, odor, time and classification of non-recycling materials. In this article, we showed the relative efficiency of the judgement post-stratification method over the simple random sampling method for equal sample sizes using Monte Carlo simulation. Furthermore, we applied the judgement post-stratification method on the 2004 recycling data and showed that it can replace the simple random sampling even with smaller observations.

Consideration on Changes of Density Stratification in Saemangeum Reservoir (새만금호 내 밀도 성층 변화 고찰)

  • Oh, Chan-Sung;Choi, Jung-Hoon
    • Journal of the Korean Society for Marine Environment & Energy
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    • v.18 no.2
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    • pp.81-93
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    • 2015
  • The comprehensive master plan in November 2010 on Saemangeum internal development has been released, and there is a need for complementary measures related to in-situ monitoring methods in order to acquire water temperature (T) and salinity (S) data. Thus, these data are monitored and analyzed by Korea Rural Community Corporation continuously. The purposes of current study are to evaluate the distributions of seasonal T and S, sigma-t, and stratification parameter and to compare annual stratification system in 2011 and 2012. To achieve these objectives, monthly vertical changes of T, S, and sigma-t, which are reproduced by a kriging technique, have been analyzed. In summer, the temperature difference between surface and bottom layers varies from 2 to $3^{\circ}C$, and the stratification of T is considerably weak. The stratification of S occurs abruptly within depth of EL. (-)5 to EL. (-)10 m. Therefore, stratification is induced by sudden increasing of water inflow amount due to a localized downpour during the rainy season, and these stratification processes are strongly influenced by inflowing a fresh water from watersheds in estuary environment.