• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1125-1128
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• 2008

본 연구에서는 Bayesian MCMC 방법과 2차 근사식을 이용한 최우추정(Maximum Likelihood Estimation, MLE)방법 방법을 이용하여 낙동강 유역의 본류지점인 낙동, 왜관, 고령교, 진동지점에 대한 점 빈도분석을 수행하고 그 결과로써 불확실성을 포함한 빈도곡선을 작성하였다. 통계적 실험을 통한 두 가지 추정방법의 분석을 위하여 먼저 자료의 길이가 100인 8개의 합성 유량자료 셋을 생성하여 비교 연구를 수행하였으며, 이를 자료길이 36인 실측 유량자료의 추정결과와 비교하였다. Bayesian MCMC 방법에 의한 평균값과 2차 근사식을 이용한 취우추정방법에 의한 모드에서의 2모수 Weibull 분포의 모수 추정값은 비슷한 결과를 보였으나, 불확실성을 나타내는 하한값과 상한값의 차이는 Bayesian MCMC 방법이 2차 근사식을 이용한 취우추정방법보다 불확실성을 감소시켜 나타내는 것을 알 수 있었다. 또한 실측 유량자료를 이용한 결과, 2차 근사식을 이용한 최우추정방법의 경우 자료의 길이가 감소됨에 따라 불확실성의 범위가 합성 유량자료를 사용한 경우에 비해 상대적으로 증가되지만, Bayesian MCMC 방법의 경우에는 자료의 길이에 대한 영향이 거의 없다는 결론을 얻을 수 있었다. 그러므로 저수량 빈도분석을 수행하기 위해 충분한 자료를 확보할 수 없는 국내의 상황을 감안할 때, 위와 같은 결론으로부터 Bayesian MCMC 방법이 불확실성을 표현하는데 있어서 2차 근사식을 이용한 최우추정방법에 비해 합리적일 수 있다는 결론을 얻을 수 있었다.

• Journal of Korea Water Resources Association
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• v.41 no.1
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• pp.49-63
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• 2008

The Bayesian MCMC(Bayesian Markov Chain Monte Carlo) and the MLE(Maximum Likelihood Estimation) methods using a quadratic approximation are applied to perform the at-site low flow frequency analysis at the 4 stage stations (Nakdong, Waegwan, Goryeonggyo, and Jindong). Using the results of two types of the estimation method, the frequency curves including uncertainty are plotted. Eight case studies using the synthetic flow data with a sample size of 100, generated from 2-parmeter Weibull distribution are performed to compare with the results of analysis using the MLE and the Bayesian MCMC. The Bayesian MCMC and the MLE are applied to 36 years of gauged data to validate the efficiency of the developed scheme. These examples illustrate the advantages of the Bayesian MCMC and the limitations of the MLE based on a quadratic approximation. From the point of view of uncertainty analysis, the Bayesian MCMC is more effective than the MLE using a quadratic approximation when the sample size is small. In particular, the Bayesian MCMC is a more attractive method than MLE based on a quadratic approximation because the sample size of low flow at the site of interest is mostly not enough to perform the low flow frequency analysis.

• Korean Institute of Interior Design Journal
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• no.10
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• pp.3-10
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• 1997

The purpose of this study was to identify and categorize the space use characteristics of the university professor's office. The data were recorded and collected through the physical trace method. Acture Measurement. Photograph, sketch and CAD drawings were used to trace 118 professors offices at Yonse-University. The analysed features were the user characteristics, the size, characteristics of space (such as composition, layout and furniture arrangement), the appliance and the instrument characteristics. To categorize the 'space use' characteristics. 6 variables were used: 1) the territorial characteristics, 2) the spatial relationship between professor's territory and entrance, 3) the layout type of work area, 4) the spatial relationship between professor's and assistant's work area, 5) the arrangement of table, and 6) the completion of sofa set. The results of this study are expected to be used as a basis for the development of design alternatives for the most typical university professors' office.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.1159-1163
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• 2005

자연하천에서의 유량측정은 직$\cdot$간접유속측정을 통하여 이루어진다. 홍수기는 주로 봉부자에 의한 방법을 이용하고 평$\cdot$갈수기에는 파샬플룸이나 유속계에 의한 방법을 이용한다. 이 방법은 측정지점의 상태 또는 기술자의 숙련도에 따라 많은 오차를 발생시키고 연속적인 관측의 어려움을 가진다. 본 연구는 자연하천의 기본적인 수리학적 정보와 하천의 수리특성을 나타내는 조도계수를 유량규모별로 추정하여 유량을 산정하는 기법을 활용하여 자연하천 유량자료의 연속적인 획득이 가능한 프로그램을 개발하였다. 대상지점으로 금강 대청댐 하류 공주지점을 선정하여 2003년$\~$2004년의 유량실측 자료를 바탕으로 유량 측정하고, 단면의 적절한 조도계수를 추정하여 유량을 산정하였다. 이를 통하여 기존 수위-유량관계곡선식의 신뢰성을 평가하고, 실측값에 근사한 유량을 연속적으로 산정할 수 있도록 하였으며, 이를 적용하여 향후 수문해석, 유출분석등에 활용하고자 한다.

• Journal of Korea Water Resources Association
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• v.40 no.10
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• pp.755-768
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• 2007

The purpose of this study is to analyse the characteristics of Manning's roughness coefficient according to change of discharge by using observed data obtained from a stable gravel-bed river and to investigate the applicability of the relevant existing empirical methods to it. Observed water level and discharge data are used as input data for the USGS computer program NCALC model for calculation of the roughness coefficient. Calculated values are compared with roughness values which are estimated with four widely used methods. The results show that though the empirical methods are able to give similar roughness values only for flood flow, they seem to have rather high uncertainty because of necessity of subjective judgement and differences of resultant values. Roughness coefficients for normal-low flow cannot be estimated from the existing empirical formulae. Especially, using the Manning equation for calculating them should be careful as this provides a wide range of estimated values in normal-low flow. The relations between the roughness coefficient and characteristic size of bed materials are different from them in flood flow even though they have a close relations.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.335-338
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• 2001

잔향음은 시변동성이 존재하는 유동성 경계면 잔향음(해수면, 체적)과 시변동성이 존재하지 않는 고정 경계면 잔향음(해저면)으로 분류된다. 그러나 고정 경계면 잔향음으로 알려진 해저면 잔향음에서도 단주기적 시변동성이 존재하고 있음이 여러 실측자료에서 관측되고 있다. 본 연구는 시변동성의 원인을 파악하고자 실험실에서 부유성 퇴적물의 농토에 따른 후방산란 신호를 측정하였다. 또한 동해에서 측정된 시간에 따른 잔향음신호(80kHz)와 ADCP(4.2MHz) 자료를 비교하여 천해에서의 체적 산란체의 변동이 잔향음 신호에 영향을 미칠 수 있음을 확인하였다. 아울러 본 논문에서는 잔향음 신호의 단주기적 시변동성에 의한 잡음 성분을 제거하여 표준화된 잔향음 신호를 획득하기 위한 방법으로 Low Rank Approximation(LRA)을 제안하였다. 이 기법은 특이해 분해(Singular Value Decomposition, SVD)를 수행하여 실측 자료 행렬로부터 고유치(Eigenvalue)과 고유벡터(Eigenvector)를 추출한 후, 추출된 고유치를 제한적으로 사용하여 근사화 하는 기법으로 시변동성 신호를 제거하는데 효율적인 방법이다.

• The Journal of Engineering Geology
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• v.29 no.4
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• pp.417-425
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• 2019

Agricultural groundwater use accounts for 51.8% of total groundwater use, so accurate estimation of groundwater use is important for efficient groundwater management. The purpose of this study is to develop a method for estimating the groundwater use of agricultural (rice farming and dry-field farming) wells using regression tree model based on the measured data of 370 wells. Three input variables of the model were evaluated as being significant: well depth, pipe diameter, and pump capacity, and the importance of each variable was 75% for well depth, 17% for pipe diameter, and 8% for pumping capacity. The daily usage of agricultural (rice farming and dry-field farming) wells by the regression tree model was estimated to be very similar to the actual usage, compared to the previous estimation method proposed by the Ministry of Construction and Transportation. In the future, it is expected that the reliability of the usage statistics will be improved if additional observed data is secured and this classification method is modified.

• Journal of the Korea Society for Simulation
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• v.23 no.3
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• pp.19-25
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• 2014

Demand forecasting is the basis of management activities including marketing strategy. Especially, the demand of a part is remarkably important in supply chain management (SCM). In the fields of various industries, the part demand usually has the intermittent characteristic. The intermittent characteristic implies a phenomenon that there frequently occurs zero demands. In the intermittent demands, non-zero demands have large variance and their appearances also have stochastic nature. Accordingly, in the intermittent demand forecasting, it is inappropriate to apply the traditional time series models and/or cause-effect methods such as linear regression; they cannot describe the behaviors of intermittent demand. Markov bootstrap method was developed to forecast the intermittent demand. It assumes that first-order autocorrelation and independence of lead time demands. To release the assumption of independent lead time demands, this paper proposes a modified bootstrap method. The method produces the pseudo data having the characteristics of historical data approximately. A numerical example for real data will be provided as a case study.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.2 no.2
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• pp.19-28
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• 1982

The development of unsteady, depth-averaged two dimensional sediment transport prediction model in estuaries and harbors by the Galerkin finite element technique is presented. The model consists of two submodels, flow induced circulation model and sediment transport model. The sediment transport submodel is formulated by incorporating sediment continuity equation and sediment diffusion equation. Numerical experiments of the model, which were carried out in one dimensional channel under different conditions for circulation and sediment transport, show the adaptability of the formulation for predicting the migration of both cohesive and noncohesive sediments. The model was applied to Busan harbor to simulate circulation and sediment transport for simplified conditions. Of the results by the model the flow pattern are shown to be similar to observed data.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4C
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• pp.137-145
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• 2011

The amount of material upheaved owing to the installation of a granular compaction pile (GCP) in the seabed was analyzed by a field execution. The amount of material upheaved was predicted by existing equations, proposed by the Korea Construction New-Technology Association (KCNET; 2003) and Shiomi and Kawamoto (1986), and compared with the amount measured by bathymetry in the field. As a result, the upheaval heights were found to show a clear increase with increasing replacement ratio. The measured amount was larger than the amount predicted by the equations, but the amount predicted from the equation proposed by KCNET (2003) was relatively close to the measured amount. The upheaval heights were found to be more sensitive to the replacement ratio than the installation depth. The increasing trends of the upheaval heights with the installation depth as predicted by the equation of KCNET (2003) were in agreement with the measured trends at a replacement ratio of 25%. As a result of comparing the coefficients of upheaval by the equations, the coefficients of upheaval determined by the equation of KCNET (2003) were larger than those determined by the equation proposed by Shiomi and Kawamoto (1986), which were relatively close to the measured trends. Specifically, the difference between results obtained by both these equations was large when the replacement ratio was relatively low.