• Korean Chemical Engineering Research
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• v.47 no.4
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• pp.481-487
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• 2009

In this of study, effects of input air velocity(0.05~0.22 m/sec) and molten carbonate salt temperature ($870{\sim}970^{\circ}C$) on flow regime transition have been studied by adopting a drift-flux model of air holdup and a stochastic analysis of differential pressure fluctuations in an air-molten sodium carbonate salt two-phase system(molten salt oxidation process). Air holdup where the flow regime transition begins was determined by air holdup-drift flux plot. The air holdup value which the flow regime transition begins was increased with increasing molten carbonate salt temperature due to the decrease of viscosity and surface tension of molten carbonate salt. To characterize the flow regime transition more quantitatively, differential pressure fluctuation signals have been analyzed by adopting the stochastic method such as phase space portraits and Kolmogorov entropy, The Kolmogorov entropy decreased with an increasing of molten carbonate salt temperature but increased gradually with an increase in an air velocity, however, it exhibited different tendency with the flow regime and the air velocity value which flow regime transition begins was same to the results of drift-flux analysis.

• Economic and Environmental Geology
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• v.53 no.3
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• pp.271-285
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• 2020

In this study, a numerical experiment related to the stress-strain analysis was performed on 3-D discrete fracture network(DFN) systems based on the distinct element method to evaluate the effect of joint geometry on deformability of jointed rock masses. Using one or two joint sets with deterministic orientation, a total of 12 3-D DFN blocks having 10m cube domain were generated with different joint density and size distribution. Directional deformation modulus of the DFN cube blocks were estimated along the axis directions of 3-D cartesian coordinate. In addition, deviatoric stress directions were chosen at every 30° of trend and plunge in 3-D for some DFN blocks to examine the variability of directional deformation modulus with respect to joint geometry. The directional deformation modulus of the DFN block were found to reduce with the increase of joint size distribution. The increase in joint density was less likely to have a significant effect on directional deformation modulus of the DFN block in case of the effect of rock bridges was relatively large because of short joint size distribution. It, however, was evaluated that the longer the joint size, the increase in the joint density had a more significant effect on the anisotropic deformation modulus of the DFN block. The variation of the anisotropic deformation modulus according to the variations in joint density and size distribution was highly dependent on the number of joint sets and their orientation in the DFN block. Finally, this study addressed a numerical procedure for stress-strain analysis of jointed rock masses considering joint geometry and discussed a methodology for practical application at the field scale.

• Journal of Korea Water Resources Association
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• v.42 no.8
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• pp.591-605
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• 2009

In this study the risk integrated erosion and seepage failure factor and combined risk of the levee embankment were assessed. For the research of the reliability, the risk assessment of erosion, seepage and both of them combined for the levee embankment were conducted using discharge curve and stage hydrograph generated by stochastic rainfall variation method during typhoon and monsoon season. The risk of erosion was evaluated using tractive force and the seepage analysis was performed by selecting representative cross sections for SEEP/W model analysis. And the probability of seepage failure was assessed with MFOSM analysis using critical hydraulic gradient method. Unlike deterministic analysis method, quantitative risk could be obtained and the characteristics of realistic rainfall variation patterns as well as a variety of factors contributing to levee failure could be reflected in this research. The results of this study show significantly enhanced applicability for the combined risk. As this model can be employed to determine dangerous spots for levee failure and to establish flood insurance linked with flood risk map, it will dramatically contribute to the establishment of both efficient and systematic measures for integrated flood management on a watershed.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.294-294
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• 2012

홍수위험도 추정에 있어서 불확실성은 수리, 수문, 구조, 환경 및 사회경제적인 불확실성과 관련 있으며, 수리 수문학적 불확실성은 주로 수리 수문학적 현상과 그 과정에 대한 불완전한 지식, 그리고 그 과정에 포함된 매개변수들에 대한 불완전한 지식과 관련이 있다. 이러한 여러 가지 불확실성은 홍수위험도 추정에 있어서의 불확실성에 중요한 요인으로 작용하므로 불확실성을 설명하기 위한 통계적 정보는 신뢰성 있는 홍수위험도 추정에 있어서 선행조건이라 할 수 있다. 이러한 불확실성 요인중 강우의 공간분포에 대한 신뢰성 있는 추정은 수자원 해석 및 설계에 있어서 필수적인 요소이다. 강우장의 공간변동성에 대한 고해상도 추정은 홍수, 특히 돌발홍수의 원인이 되는 국지성 호우의 확인 및 분석에 있어서 중요하다. 또한 강우의 공간 변동성에 대한 고려는 면적평균강우량 추정의 정확도를 향상시키는데 있어서 중요하며, 강우-유출모델의 모의결과에 대한 신뢰도를 향상시키는데 큰 영향을 미친다. 최근 공간자료에 대한 공간분포예측에 있어서 공간상관성을 고려할 수 있는 공간통계학적 기법의 적용이 증가하고 있으며, 이러한 공간통계학적 기법의 적용에 있어서 신뢰성 있는 모델 매개변수의 추정 및 불확실성 평가는 공간분포 예측결과에 대한 신뢰성을 향상시키는데 중요한 역할을 한다. 외국의 경우 공간분포예측 및 모의, 매개변수의 불확실성 평가 등과 관련하여 활발한 연구가 이루어지고 있는 반면 국내 수자원 분야에서는 아직까지 활발한 연구가 이루어지고 있지 않은 실정이다. 국내의 수문설계실무에서와 같이 확률홍수량을 강우빈도분석과 강우-유출모델을 이용하여 추정할 경우 확률홍수량 추정에 있어서 확률강우량 및 공간분포에 대한 불확실성과 강우-유출모델에서의 불확실성이 확률홍수량 추정에서의 불확실성에 영향을 미치며, 이후 연피해기대치 추정과 같은 홍수위험도 추정의 불확실성에도 영향을 미치게 된다. 따라서 본 연구에서는 강우공간분포의 불확실성을 고려한 홍수량 추정을 위하여 공간추계모의 기법인 CEM을 적용하여 강우공간분포의 불확실성을 정량화하고 강우-유출모델의 입력 강우량에 대한 확률분포를 추정하였다. 강우-유출해석의 경우 유효우량 및 홍수수문곡선 산정을 위하여 국내 수자원 실무에서 가장 많이 적용되고 있는 NRCS CN 기법, Clark 및 Muskingum 모델을 적용하였다. 이로부터 강우공간분포의 불확실성 추정, 소유역별 입력 강우량에 대한 확률분포의 추정 및 재현기간별 확률홍수량의 불확실성 정량화 방안을 제시하였다. 이러한 결과들은 풍수해저감대책, 유역종합치수대책 등 각종 수자원 계획 및 설계실무에서 확률홍수량 및 홍수 또는 재해위험도 추정의 신뢰성을 향상시킬 수 있는 방법론적 대안으로 활용될 수 있을 것으로 판단된다.

• Tunnel and Underground Space
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• v.30 no.1
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• pp.15-28
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• 2020

In this study, a procedure was introduced to estimate strength and deformation modulus of the 3-D discrete fracture network(DFN) systems using the distinct element method(DEM). Fracture entities were treated as non-persistent square planes in the DFN systems. Systematically generated fictitious fractures having similar mechanical characteristics of intact rock were combined with non-persistent real fractures to create polyhedral blocks in the analysis domain. Strength and deformation modulus for 10 m cube domain of various deterministic and stochastic 3-D DFN systems were estimated using the DEM to explore the applicability of suggested method and to examine the effect of fracture geometry on strength and deformability of DFN systems. The suggested procedures were found to effective in estimating anisotropic strength and deformability of the 3-D DFN systems.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.6 no.3
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• pp.63-74
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• 1986

A methodology for the probabilistic determination of active storage capacity of an impounding reservoir is proposed with due considerations to the durations and return periods of the low flow series at the reservoir site. For more reliable probabilistic analysis the best-fit stochastic generation model of Monte Carlo type was first selected for the generation of monthly flow series, the models tested being the Month Carlo Model based on the month-by-month flow series (Monte Carlo-A Type), Monte Carlo Model based on the standardized sequential monthly flow series (Monte Carlo-B Type), and the Thomas-Fiering Model. Monte Carlo-B Model was final1y selected and synthetic monthly flows of 200 years at Hong Cheon dam site were generated. With so generated 200 years' monthly flows partial duration series of low flows were developed for various durations. Each low flow series was further processed by a nonsequential mass analysis for specified draft rates. This mass analysis furnished the storage-draft-recurrence interval relationship which gives the reservoir storage requirement for a specified water demand from the reservoir during a drought of given return period. Illustrations are given on the application of these results in analyzing the water supply capacity of a particlar reservoir, existing or proposed.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.1
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• pp.81-88
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• 2010

The analysis and synthesis of various types of hydrologic variables such as precipitation, surface runoff, and discharge are usually required in planning and management of water resources. These hydrologic variables are mostly represented using stochastic models. One of which is the autoregressive model, that gives promising results in time series modeling. This study is an application of this model, which aimed to determine the AR model that best represents the historical monthly streamflow of the two gauging stations, namely Andong Dam and Imha Dam, both located in the upper Nakdong River Basin. AR(3) model was found to be the best model for both gauging stations. Parameters of the determined order of AR model ($\phi_1$, $\phi_2$ and $\phi_3$) were also estimated. Using several diagnostic tests, the efficiency of the determined AR(3) model was tested. These tests indicated the accuracy of the determined AR(3) model.

• Economic and Environmental Geology
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• v.50 no.1
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• pp.61-71
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• 2017

The effects of joint density and size distribution on the hydrogeologic characteristics of jointed rock masses are addressed through numerical experiments based on the 2-D DFN (discrete fracture network) fluid flow analysis. Using two joint sets, a total of 51 2-D joint network system were generated with various joint density and size distribution. Twelve fluid flow directions were chosen every $30^{\circ}$ starting at $0^{\circ}$, and total of 612 $20m{\times}20m$ DFN blocks were prepared to calculate the directional block conductivity. Also, the theoretical block conductivity, principal conductivity tensor and average block conductivity for each generated joint network system were determined. The directional block conductivity and chance for the equivalent continuum behavior of the 2-D DFN system were found to increase with the increase of joint density or size distribution. However, the anisotropy of block hydraulic conductivity increases with the increase of density discrepancy between the joint sets, and the chance for the equivalent continuum behavior were found to decrease. The smaller the intersection angle of the two joint sets, the more the equivalent continuum behavior were affected by the change of joint density and size distribution. Even though the intersection angle is small enough that it is difficult to have equivalent continuum behavior, the chance for anisotropic equivalent continuum behavior increases as joint density or size distribution increases.

• The Korean Journal of Ecology
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• v.22 no.3
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• pp.169-179
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• 1999

The present study was undertaken to classify and describe the spring naturalized plant communities in old-Andong city by the methodology of the ZM school of phytosociology. As a result, the vegetation was classified into the six communities and two subcommunities: A. Bromus tectorum community A-a. Bromus japonicus subcommunity, A-b. Melica onoei subcommunity; B. Poa pratensis community; C. Rumex crispus community; D. Oenothera lamarckiana community; E. Ambrosia artemisiifolia var. eiatior community; F. Rumex conglomeratus community. The total taxa of the naturalized plant communities consisted of 31 families, 86 genera, 114 species and 13 varieties. Of which the taxa of the naturalized plant species consisted of 8 families, 21 genera, 25 species and 1 variety. The result of Bray-Curtis ordination revealed that the plots suveyed were arranged according largely to the vegetation units of' the communities. Also the interspecific affinity was examined by an analysis of interspecific association and the main component species in the communities were divided into two groups. The naturalized rate was higher in the communitise affected by strong human impacts, while was lower in the communities affected relatively less by human impacts. On the other hand the seasonal changes of the communities and the naturalized rate between the spring and the autumn were investigated. Many naturalized communities present in Spring were replaced by the other native ruderal communitues in the Autumn. The naturalized rate based on the dominance was largely decreased over from the spring to the Autumn.

• Economic and Environmental Geology
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• v.46 no.4
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• pp.313-327
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• 2013

In the study, three-dimensional geostatistical simulations on McMurray Formation which is the largest oil sand reservoir in Athabasca area, Canada were performed, and the optimal site for steam assisted gravity drainage (SAGD) was selected based on the predictions. In the selection, the factors related to the vertical extendibility of steam chamber were considered as the criteria for an optimal site. For the predictions, 110 borehole data acquired from the study area were analyzed in the Markovian transition probability (TP) framework and three-dimensional distributions of the composing media were predicted stochastically through an existing TP based geostatistical model. The potential of a specific medium at a position within the prediction domain was estimated from the ensemble probability based on the multiple realizations. From the ensemble map, the cumulative thickness of the permeable media (i.e. Breccia and Sand) was analyzed and the locations with the highest potential for SAGD applications were delineated. As a supportive criterion for an optimal SAGD site, mean vertical extension of a unit permeable media was also delineated through transition rate based computations. The mean vertical extension of a permeable media show rough agreement with the cumulative thickness in their general distribution. However, the distributions show distinctive disagreement at a few locations where the cumulative thickness was higher due to highly alternating juxtaposition of the permeable and the less permeable media. This observation implies that the cumulative thickness alone may not be a sufficient criterion for an optimal SAGD site and the mean vertical extension of the permeable media needs to be jointly considered for the sound selections.