• Journal of Ship and Ocean Technology
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• v.8 no.2
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• pp.41-60
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• 2004

Ship design process requires lots of complicated analyses for determining a large number of design variables. Due to its complexity, the process is divided into several tractable designs or analysis problems. The interdependent relationship requires repetitive works. This paper employs collaborative optimization (CO), one of the multidisciplinary design optimization (MDO) techniques, for treating such complex relationship. CO guarantees disciplinary autonomy while maintaining interdisciplinary compatibility due to its bi-level optimization structure. However, the considerably increased computational time and the slow convergence have been reported as its drawbacks. This paper proposes the use of an approximation model in place of the disciplinary optimization in the system-level optimization. Neural network classification is employed as a classifier to determine whether a design point is feasible or not. Kriging is also combined with the classification to make up for the weakness that the classification cannot estimate the degree of infeasibility. For the purpose of enhancing the accuracy of a predicted optimum and reducing the required number of disciplinary optimizations, an approximation management framework is also employed in the system-level optimization.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.6
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• pp.468-476
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• 2016

In this study, the conic winglet which is made by rotating wing tip airfoil by each 3 axis is applied to the dual type combined fan to reduce the wing tip leakage loss. Computational Fluid Dynamics is used to calculate the loss and optimum technique is used to get minimum loss. Optimization results shows that total pressure loss coefficient was reduced by 3.4 %, and optimization model was a bended shape at the end of wing forward to pressure side.

• Journal of The Korean Society of Agricultural Engineers
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• v.51 no.2
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• pp.35-41
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• 2009

The impacts of climate change on paddy irrigation requirements for Nakdong river basin in Korea have been analyzed. The HadCM3 model outputs for SRES A2 and B2 scenarios and International Water Management Institute $10'{\times}10'$ pixels observed data were used with kriging method. Maps showing the predicted spatial variations of changes in climate parameters and paddy irrigation requirements have been produced using the GIS. The results showed that the average growing season temperature was projected to increase by $2.2^{\circ}C$ (2050s A2), $0.0^{\circ}C$ (2050s B2), $3.7^{\circ}C$ (2080s A2) and $2.9^{\circ}C$ (2080s B2) from the baseline (1961-1990) value of $21{\circ}C$. The average growing season rainfall was projected to increase by 15.2% (2050s A2), 24.2% (2050s B2), 41.4% (2080s A2) and 16.7% (2080s B2) from the baseline value of 900 mm. Average volumetric irrigation demands were projected to decrease by 3.7% (2050s A2), 7.0% (2050s B2), 10.2% (2080s A2) and 1.4% (2080s B2) from the baseline value of $1.25{\times}10^9\;m^3$. These results can be used for the agricultural water resources development planning in the Nakdong river basin for the future.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.6
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• pp.831-838
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• 2018

This paper presents a method to estimate the flow discharge in a backwater affected river junction. First, unsteady HEC-RAS model was simulated and calibrated using 2 recent real flood and then HPG (Hydraulic Performance Graph) was created by plotting the relationship between upstream and downstream stages and discharge in the reach and performing kriging interpolation. During a flood, the discharge through the reach can be estimated based on the stages at its ends and the developed HPG. These discharge data were in good agreement with the automatic discharge measurements such as ADVM. This study could provide an economical and practical method for estimating discharge in a junction with a high hysteresis of stage-discharge relationships.

• Journal of the Korea Institute of Military Science and Technology
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• v.22 no.4
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• pp.527-535
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• 2019

Hanger in a rail-launched missile protrudes in general and causes to increase significant drag force. One method to avoid the significant increase of drag force is to apply fairings on the hanger. In this paper, sloping shaped fairing parameters of height, width, and length are optimized to minimize the drag force under subsonic speed region by examining three configurations of fairings : front-fairing only, rear-faring only, and the both front and rear fairing. We use Latin Hypercube Sampling method to determine the experimental points, and computational fluid dynamics with incompressible RANS solver was applied to acquire the data at sampling points. Then, we construct a meta model by kriging method. We find the best choice among three configurations examined : both front and rear fairing reduce the drag force by 63 % without the constraint of fairing mass, and front fairing reduced the drag force by 52 % with the constraint of hanger mass.

• Journal of Urban Science
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• v.9 no.2
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• pp.31-44
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• 2020

This study aims to analyze the relations among greenbelt, air pollution empirically in order to assess the environmental effects of the greenbelt in the Seoul metropolitan area, objectively. For this purpose, this study conducts an empirical analysis of impacts of greenbelt on urban air pollution using a multiple-regression model. The major findings are summarized as follows. As a result of an empirical analysis of the impacts of greenbelt on air pollution, it is found that the characteristics of the city have impacts on air pollution concentration. It is found that the population and employment are the causes of increases in CO and NO2 concentrations, and the number of employees in the manufacturers has impacts on increases of O3 and SO2, while power plants have impacts on PM10, CO and NO2. Intersections have impacts on O3 and SO2, while the areas of the roads have impacts on CO and NO2. In addition, as for the spatial distribution of air pollutants, it is found that CO and NO2 concentrations are relatively higher in the center of the Seoul metropolitan area, while PM10, O3 and SO2 concentrations are relatively higher in the suburbs. It is found that air pollution concentration is low in greenbelt zone. In the greenbelt zone, PM10, CO and SO2 concentrations are low.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.347-347
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• 2023

홍수 예·경보 시에는 시간-단위 또는 그 이하의 시간 척도에서 작용하는 강우에 대한 고도의 영향이 중요하게 되며, 특히 상대적으로 더 드문 관측 밀도가 있는 산악지역에서 강우의 공간분포에 대한 산악 효과의 중요도가 더 높아지게 된다. 일반적으로 1시간 시간스케일에서 강우-고도의 관계를 살펴보기 위해서는 대략 5km 내외의 관측 밀도를 가져야 하는 것으로 알려져 있으나 이러한 지역은 매우 드물다. 최근 기상 예측 수치모델로부터 모의된 강우량의 품질이 눈에 띄게 향상됨에 따라 국내에도 다양한 연구가 수행된 바 있다. 본 연구에서는 WRF를 이용하여 남강댐 지역의 과거 호우 사상을 재현한 후, 이로부터 생산된 공간적인 강우장을 이용하여 시간-단위의 시간 척도에서 강우량과 고도 사이의 관계를 고려할 수 있는 WREPN(WRF Rainfall-Elevation Parameterized Nowcasting) 모형을 제안한다. 홍수량 분석을 위해 WREPN 모형을 이용하였으며, 비교군으로 실무적으로 많이 사용되는 IDW, Kriging 기반 격자강우가 사용되었다. 격자기반 분포형 강우자료로부터 홍수량을 분석하기 위해 Mod-Clark 모형이 적용되었으며, 입력된 강우자료별매개변수의 불확실성을 분석하기 위해 베이지안 기법이 적용되었다. 매개변수의 불확실성 분석으로부터 강우-고도 관계가 고려된 WREPN 모형의 강우자료가 상대적으로 불확실성이 낮다는 것을 확인할 수 있었다.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.135-135
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• 2020

우리나라의 기후 자료는 일반적으로 기상청에서 발표하는 종관기상관측(ASOS)과 방재기상관측(AWS), 그리고 북한이 세계기상기구(WMO, World Meteorogical Organization)의 기상통신망(GTS)을 통해 보낸 북한기상관측(NKO)을 사용 할 수 있다. 그러나 이 중 40년 이상의 완전한 관측 자료를 얻을 수 있는 건 ASOS가 유일하지만 공간적인 표현에 한계를 갖고 있다. AWS는 관측소가 많다는 장점이 있지만 관측 기간이 길지 않고 이용 가능한 기간에도 관측이 연속적이지 못한 경우가 많다. NKO는 비록 27개의 관측소가 있지만 많은 데이터가 누락되어 일별 기후자료의 사용에 한계를 갖고 있다. 이러한 미관측 기간이나 관측 자료의 누락은 연속적인 시계열 자료분석을 기반으로 하는 수자원 모델링에 있어서 문제를 야기한다. 본 연구는 1973년부터 2019년까지 47년의 신뢰도 높은 한반도 일일 기후 자료를 구축하기 위해 다양한 방법론을 비교하였다. 추정에 사용한 방법은 총 7개로 EM algorithm for probabilistic principal components (PPCA-EM), Inverse distance weight method (IDWM), Nearest neighbor method (NNM), Multivariate normal copulas (Copula), Elastic net model (Elastic), Ordinary kriging (OK), Regularized principal components with EM algorithm (RPCA-EM)를 살펴보았다. 다양한 형태의 결측치를 가정하여 그 결과값을 비교하였고 이는 Root mean squared error(RMSE), Kling-Gupta efficiency(KGE), Nash-Sutcliffe efficiency(NSE)를 통해 평가하였다. 최종 선택된 방법론을 통하여 한반도 전역을 그리드 기반의 강수 및 최저온도/최고온도의 일별자료로 생성하였다.

• Journal of Korean Society for Atmospheric Environment
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• v.34 no.1
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• pp.101-119
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• 2018

In this study, we analyzed long-term measurements and air quality simulation results of four criteria air pollutants ($PM_{10}$, $O_3$, $NO_2$, and $SO_2$) for 10 years, from 2006 to 2015, with emphasis on trends of annual variabilities. With the observation data, we conducted spatial interpolation using the Kriging method to estimate spatial distribution of pollutant concentrations. We also performed air quality simulations using the CMAQ model to consider the nonlinearity of the secondary air pollutants such as $O_3$ and the influence of long-range transport. In addition, these simulations are used to deduce the effect of long-term meteorological variations on trends of air quality changes because we fixed the emissions inventory while changing meteorological inputs. The nation-wide inter-annual variability of modeled $PM_{10}$ concentrations was $-0.11{\mu}g/m^3/yr$, while that of observed concentrations was $-0.84{\mu}g/m^3/yr$. For the Seoul Metropolitan Area, the inter-annual variability of observed $PM_{10}$ concentrations was $-1.64{\mu}g/m^3/yr$ that is two times rapid improvement compared to other regions. On the other hand, the inter-annual variability of observed $O_3$ concentrations is 0.62 ppb/yr which is larger than the simulated result of 0.13 ppb/yr. Magnitudes of differences between the modeled and observed inter-annual variabilities indicated that decreasing trend of $PM_{10}$ and increasing trend of $O_3$ are more influenced by emissions and oxidation states than meteorological conditions. We also found similar patterns in $NO_2$. However, $NO_2$ trends showed greater regional and seasonal differences than other pollutants. The analytic approach used in this study can be applicable to estimate changes in factors determining air quality such as emissions, weather, and surrounding conditions over a long term. Then analysis results can be used as important data for air quality management planning and evaluation of the chronic impact of air quality.

• The Journal of Engineering Geology
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• v.16 no.4 s.50
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• pp.393-402
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• 2006

The contamination characteristics of BTEX and TPH components in silty soils with the oil leakage event from point source were studied. The over ratios of three soil pollution standard for TPH component were $1.5{\sim}1.7$ times higher than that of BTEX component. The mean and maximum values of BTEX and TPH components with sample points were B-zone > A-zone > C-zone, and the highest concentrations were measured at $1{\sim}2m$ depth below surface. BTEX and TPH components were increased with linear distance in zone within 120 m and 80 m from point source. For the zone more than 120 m, BTEX and TPH concentrations were under soil pollution standard. The cutoff values of indicator kriging using BTEX and TPH components were defined as confirmative limit, warn- ing limit and counterplan limit. The variograms of indicator-transformed data were selected linear model. The contamination ranges of BTEX and TPH components using confirmative limit and warning limit were estimated similar, but the contamination range of those using counterplan limit was much reduced. The maximum contamination probabilities were estimated by probability maps usinB confirmative limit, warning limit and counterplan limit. The maximum contamination probabilities with three soil pollution standard were estimated 26%, 26% and 13% for BTEX component, and 44%, 38% and 26% for TPH component.