• Computers and Concrete
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• 제31권2호
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• pp.111-121
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• 2023

The influence of material composition such as aggregate types, addition of supplementary cementitious materials as well as exposed temperature levels have significant impacts on concrete residual mechanical strength properties when exposed to elevated temperature. This study is based on data obtained from literature for fly ash blended concrete produced with natural and recycled concrete aggregates to efficiently develop prediction models for estimating its residual compressive strength after exposure to high temperatures. To achieve this, an extensive database that contains different mix proportions of fly ash blended concrete was gathered from published articles. The specific design variables considered were percentage replacement level of Recycled Concrete Aggregate (RCA) in the mix, fly ash content (FA), Water to Binder Ratio (W/B), and exposed Temperature level. Thereafter, a simplified mathematical equation for the prediction of concrete's residual compressive strength using Gene Expression Programming (GEP) was developed. The relative importance of each variable on the model outputs was also determined through global sensitivity analysis. The GEP model performance was validated using different statistical fitness formulas including R², MSE, RMSE, RAE, and MAE in which high R² values above 0.9 are obtained in both the training and validation phase. The low measured errors (e.g., mean square error and mean absolute error are in the range of 0.0160 - 0.0327 and 0.0912 - 0.1281 MPa, respectively) in the developed model also indicate high efficiency and accuracy of the model in predicting the residual compressive strength of fly ash blended concrete exposed to elevated temperatures.

• 한국물환경학회지
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• 제32권3호
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• pp.243-252
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• 2016

In cases of water pollution accidents, accurate prediction for arrival time and concentration of contaminants in a river is essential to take proper measures and minimize their impact on downstream water intake facilities. It is critical to fully understand the behavior characteristics of contaminants on river surface, especially in case of oil spill accidents. Therefore, in this study, the effects of main parameters of advection and diffusion of contaminants were analyzed and validated by comparing the results of Lagrangian particle tracking (LPT) simulation of Environmental Fluid Dynamic Code (EFDC) model with those of Global Position System (GPS)-equipped drifter experiment. Prevention scenario modeling was accomplished by taking cases of movable weir operation into account. The simulated water level and flow velocity fluctuations agreed well with observations. There was no significant difference in the speed of surface particle movement between 5 and 10 layer modeling. Therefore, 5 layer modeling could be chosen to reduce computational time. It was found that full three dimensional modeling simulated wind effects on surface particle movements more sensitively than depth-averaged two dimensional modeling. The diffusion range of particles was linearly proportional to horizontal diffusivity by sensitivity analysis. Horizontal diffusivity estimated from the results of GPS-equipped drifter experiment was 0.096 m²/sec, which was considered to be valid for applying the LPT module in this area. Finally, the scenario analysis results showed that particle movements could be stagnant when discharge from the upstream weir was reduced, implying the possibility of securing time for mitigation actions such as oil boom installation and wiping oil contaminants. The outcomes of this study can help improve the prediction accuracy of particle tracking simulation to establish the most suitable mitigation plan considering the combination of movable weir operation.

• 물과 미래
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• 제26권2호
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• pp.99-105
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• 1993

호우발생전의 기상상태, 유역의 저류상태 그리고 과거의 패턴을 반영한 실용성 있는 홍수 예보모형을 제안하였다. 호우 예보는 구름 물리학을 토대로한 지점 호우 예보 모형을, 유출예측은 저류함수모형을 채택하였다. 홍수 예보 모형의 입력 변수는 예보 발령 시점의 지상 기온, 지상 기압, 지상 이슬점 온도 그리고 유출점의 초기 유량이다. 홍수 예보 모형의 매개 상수는 과거의 홍수 사상이 갖는 최적 상수들의 산술평균값으로 하였다. 유출률은 홍수 초기 유량을 지표로 하여 예측될 수 있게 하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.1172-1177
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• 2010

For the deep excavation in urban area, the braced-cut method is mainly adopted. In this case, inadequate consideration of ground water level may result in wrong prediction of structural behavior. In this study, the effects of hydraulic interaction between wall and grout were investigated using the finite element method. The maximum stress in case of confined ground water condition is obtained at the final excavation stage in the range of 70~80% of excavation depth. The stress of impermeable case is about 50% larger than that of permeable case. When the relative permeabililty of wall-grout become smaller, the stress is getting bigger. And the stress tends to converge in case of 1/100 or less of the relative permeability.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2016년도 학술발표회
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• pp.562-562
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• 2016

신경망 모형에서 학습이란 주어진 입출력시스템에 대하여 원하는 동작을 수행할 수 있도록 연결 강도를 최적의 상태로 적응(adaptation)시키는 과정을 의미한다. 따라서 강수와 지하수위의 관계를 연계시킨 인공신경망기법은 선택적으로 예측 지하수위에 영향을 미치는 변수들을 학습에 의하여 택함으로써 예측모형을 구성할 수 있다. 즉, 예측 지하수위와의 상관관계에 의하여 입력되는 변수와의 연결강도를 조정하여 매개변수 조정 및 모형의 최적화를 자동화할 수 있다. 본 연구에서는 지하수위에 영향을 주는 요소는 지하수위와 강우량이라고 가정하고, 지하수위의 입출력과정을 시계열 분석에 의하여 모형화하였으며 예측지하수위는 강우 및 지하수위의 선행조건과 매우 밀접한 관계를 갖는다. 따라서 선행강우 및 지하수위의 상태에 따라 이를 입력하여 미래의 지하수위를 예측하게 된다. 이 모형을 제주지역의 관측소에 적용한 결과 관측소별로 타당한 예측결과를 도출하였다.

• Nuclear Engineering and Technology
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• 제50권8호
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• pp.1412-1420
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• 2018

An experiment was performed using the large-scale test facility (LSTF), which simulated a 1% vessel upper head small-break loss-of-coolant accident with an accident management (AM) measure under an assumption of total-failure of high-pressure injection (HPI) system in a pressurized water reactor (PWR). In the LSTF test, liquid level in the upper head affected break flow rate. Coolant was manually injected from the HPI system into cold legs as the AM measure when the maximum core exit temperature reached 623 K. The cladding surface temperature largely increased due to late and slow response of the core exit thermocouples. The AM measure was confirmed to be effective for the core cooling. The RELAP5/MOD3.3 code indicated insufficient prediction of primary coolant distribution. The author conducted uncertainty analysis for the LSTF test employing created phenomena identification and ranking table for each component. The author clarified that peak cladding temperature was largely dependent on the combination of multiple uncertain parameters within the defined uncertain ranges.

• 환경영향평가
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• 제26권6호
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• pp.470-478
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• 2017

본 연구는 SPSS(18 version)를 사용하여 남한강 보를 완공한 후에 해당되는 2012년부터 2015년까지의 기상, 수질 자료로 군집분석한 결과에 의해 평수기그룹과 가뭄기그룹으로 분류하고, 각 기간 그룹별로 강천보, 여주보 및 이포보로 공간적 그룹으로 분류하였다. 이와 같은 6개의 그룹에 대해서 조류 주의보 이상의 Chl-a 농도에 해당된 월별 자료로 다중회귀분석을 실시하였다. 시 공간적으로 분류된 6개 그룹을 Chl-a 농도와 3개의 기상요인, 11개의 수질 요인 및 유량 요인과의 상관분석을 수행하여, 상관분석결과를 회귀분석의 독립변수로 적용하고. 각 6개의 그룹 별로 Chl-a 농도 예측식을 도출하고자하였다. 위 연구방법으로 수행한 연구 결과는 아래와 같다. 군집분석을 실시한 결과 연 총강수량이 평년수준이었던 평수기그룹(2012~2013년)과 연 총강수량이 1,000mm/hr 미만으로 극심한 가뭄특성을 보였던 가뭄기그룹(2014~2015년)으로 시간적으로 분류되었다. 평수기그룹과 가뭄기그룹 별로 각 3개의 보 지점에서 조류 주의보 이상의 Chl-a 농도에 해당된 월은 평수기그룹은 3~8월이었고, 가뭄기그룹은 3월, 6~10월이었다. 각 6개의 그룹 별로 Chl-a 농도와 기상, 수질 및 유량 등의 요인과의 상관분석을 수행한 결과, 3개의 보 모두에서 평수기그룹보다 가뭄기그룹의 수온 및 유량이 Chl-a 농도와의 상관성이 증가하였다. 이는 극심한 가뭄에 의한 하천 내 유속 감소와 체류시간 증가로 인한 영향으로 판단된다. 6개의 그룹에 대한 상관분석을 수행한 결과에 따라 Chl-a 농도와의 상관성이 큰 기상, 수질 및 유량 요인들을 Chl-a 농도 예측식의 독립변수로 적용하여 다중회귀분석을 수행한 결과에 의하면, 남한강의 하류에 위치하고, 팔당댐과 직접적으로 연결되어 있는 이포보에 대한 Chl-a 농도 예측식의 $Ad.R^2$ 값은 평수기그룹에서 0.920, 가뭄기그룹 0.818로 우수한 선형성을 나타내었다.

• 한국농공학회지
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• 제39권3호
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• pp.128-137
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• 1997

In this study, examined influence of consolidation effect that had affected by location of pump inlet that was set collection well for drainage of pore water discharged by embankment on soft ground through the field test. The results of this study are summarized as follows; 1 Initial consolidation curve value were larger than theoritic value, the cause of these phenomena were thought influence of secondary consolidation and three dimensional strain of soft clay. 2. The settlement value of Hosino method was larger than that of Hyperbolic method, but settlement value of Hyperbolic method was accurate more than that of Hosino method in the prediction of settlement. 3. When pump inlet in collection well came down from GL+O.3m to GL-1.5m, settlement value increased about 10cm and when the ground water level was made insitu after pumping had completed , settlement was expanded about 7~8cm. So it is found that location change of pump inlet bad an influence on settlement remarkably. 4. If location of pump inlet in collection well for large scale estate or wide road site is lowered than original ground level, the settlement will be accelerated effectively, and at this stage automatic pump must be used in pumping.

• Journal of Magnetics
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• 제22권1호
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• pp.34-42
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• 2017

Material defects in the Steam Generator Tubes (SGT) of sodium cooled fast breeder reactor (PFBR) can lead to leakage of water into sodium. The water and sodium reaction will lead to major accidents. Therefore, the examination of steam generator tubes for the early detection of defects is an important requirement for safety and economic considerations. In this work, the Magnetic Flux Leakage (MFL) based Non Destructive Testing (NDT) technique is used to perform the defect detection process. The rectangular notch defects on the outer surface of steam generator tubes are modeled using COMSOL multiphysics 4.3a software. The obtained MFL images are de-noised to improve the integrity of flaw related information. Grey Level Co-occurrence Matrix (GLCM) features are extracted from MFL images and taken as input parameter to train the neural network. A comparative study on characterization have been carried out using feed-forward back propagation (FFBP) and cascade-forward back propagation (CFBP) algorithms. The results of both algorithms are evaluated with Mean Square Error (MSE) as a prediction performance measure. The average percentage error for length, depth and width are also computed. The result shows that the feed-forward back propagation network model performs better in characterizing the defects.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.405-408
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• 2008

Up to now, a lot of houses, roads and other urban facilities have been damaged by natural disasters such as flash floods and landslides. It is reported that the size and frequency of disasters are growing greatly due to global warming. In order to mitigate such disaster, flood forecasting and alerting systems have been developed for the Han river, Geum river, Nak-dong river and Young-san river. These systems, however, do not help small municipal departments cope with the threat of flood. In this study, a real-time urban flood forecasting service (U-FFS) is developed for ubiquitous computing city which includes small river basins. A test bed is deployed at Tan-cheon in Gyeonggido to verify U-FFS. It is found that U-FFS can forecast the water level of outlet of river basin and provide real-time data through internet during heavy rain. Furthermore, it is expected that U-FFS presented in this study can be applied to ubiquitous computing city (u-City) and/or other cities which have suffered from flood damage for a long time.