• Proceedings of the Korea Water Resources Association Conference
• /
• 2008.05a
• /
• pp.1770-1773
• /
• 2008

수위-유량 관계 곡선식에 포함되어져 있는 매개변수를 추정하기 위해 많이 사용되는 로그선형 회귀분석은 잔차의 비등분산성(heterocesdascity)을 고려하지 못하므로 본 연구에서는 의사우도추정법(Pseudo-likelihood Estimation, P-LE)에 의해 분산함수를 추정하고 이와 함께 회귀계수를 추정할 수 있는 방법을 제시하였다. 이 과정에서 제시된 회귀잔차를 최소화하기 위하여 SA(simulated annealing)이라는 전역 최적화 알고리즘을 적용하였다. 또한 수위-유량 관계 곡선식은 단면 등의 영향으로 인해 구간에 따라 각각 다르게 구축되어져야 하므로 이를 보다 객관적으로 판단하고 분리 위치를 정확히 추정하기 위하여 Heaviside 함수를 의사우도함수에 포함시켜 결과를 추정하도록 하였으며, 2개의 구간을 가지는 유량자료를 이용하여 제시된 방법의 합리성을 통계적으로 실험하였다. 이와 같이 통계적 실험을 통해 제시된 방법들이 기존 방법과 비교하여 가질 수 있는 장점을 파악하였으며, 제시된 방법들을 금강유역 5개 지점에서 대해 수행하여 효율성을 검증하였다.

• Journal of Korea Water Resources Association
• /
• v.41 no.9
• /
• pp.943-958
• /
• 2008

This study employs Bayesian regression analysis for fitting discharge rating curves. The parameter estimates using the Bayesian regression analysis were compared to ordinary least square method using the t-distribution. In these comparisons, the mean values from the t-distribution and the Bayesian regression are not significantly different. However, the difference between upper and lower limits are remarkably reduced with the Bayesian regression. Therefore, from the point of view of uncertainty analysis, the Bayesian regression is more attractive than the conventional method based on a t-distribution because the data size at the site of interest is typically insufficient to estimate the parameters in rating curve. The merits and demerits of the two types of estimation methods are analyzed through the statistical simulation considering heteroscedasticity. The validation of the Bayesian regression is also performed using real stage-discharge data which were observed at 5 gauges on the Anyangcheon basin. Because the true parameters at 5 gauges are unknown, the quantitative accuracy of the Bayesian regression can not be assessed. However, it can be suggested that the uncertainty in rating curves at 5 gauges be reduced by Bayesian regression.

• Journal of Korea Water Resources Association
• /
• v.41 no.8
• /
• pp.807-823
• /
• 2008

This paper presents a technique for estimating discharge rating curve parameters. In typical practical applications, the original non-linear rating curve is transformed into a simple linear regression model by log-transforming the measurement without examining the effect of log transformation. The model of pseudo-likelihood estimation is developed in this study to deal with heteroscedasticity of residuals in the original non-linear model. The parameters of rating curves and variance functions of errors are simultaneously estimated by the pseudo-likelihood estimation(P-LE) method. Simulated annealing, a global optimization technique, is adapted to minimize the log likelihood of the weighted residuals. The P-LE model was then applied to a hypothetical site where stage-discharge data were generated by incorporating various errors. Results of the P-LE model show reduced error values and narrower confidence intervals than those of the common log-transform linear least squares(LT-LR) model. Also, the limit of water levels for segmentation of discharge rating curve is estimated in the process of P-LE using the Heaviside function. Finally, model performance of the conventional log-transformed linear regression and the developed model, P-LE are computed and compared. After statistical simulation, the developed method is then applied to the real data sets from 5 gauge stations in the Geum River basin. It can be suggested that this developed strategy is applied to real sites to successfully determine weights taking into account error distributions from the observed discharge data.

• Journal of Industrial Technology
• /
• v.16
• /
• pp.277-284
• /
• 1996

암석의 파괴인성계수는 암석이 갖는 불균질성 및 비등방성에 의하여 시험조건에 따른 측정자료의 분산이 심하다. 즉, 시험편의 형태나 크기에 따른 변화가 심하여 기존의 선형탄성 파괴역학 이론의 적용에 문제점이 있는 것으로 지적되고 있다. 이러한 자료의 분산을 최소화하기 위한 방법의 하나로 균열감응도를 적용한 해석을 제시하고 있다. 균열감응도란 파괴역학 실험 당시 시험편에 가해진 인공 균열의 감응도를 말하며 이는 3점 하중에 의한 파괴가 균열의 성장에 의한 파괴인지, 혹은 단순히 인장파괴에 의한 것인지를 판명함으로써 측정자료의 선택을 명확하게 하기 위한 방법의 하나로 적용될 수 있다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.17 no.2 s.105
• /
• pp.165-170
• /
• 2006

A two dimensional(2-D) finite-difference time-domain(FDTD) method based on a novel finite difference scheme is developed to eliminate the numerical dispersion errors. In this paper, numerical dispersion and stability analysis of the new scheme are given, which show that the proposed method is nearly dispersionless, and stable for a larger time step than the standard FDTD method.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.15 no.10 s.89
• /
• pp.977-982
• /
• 2004

In this paper, a dispersive anisotropic perfectly matched layer(APML) is proposed using piecewise linear recursive convolution(PLRC) for finite difference time domain(FDTD) methods. This proposed APML can be utilized for the analysis of a nonlinear dispersive medium as absorbing boundary condition(ABC). The formulation is simple modification to the original AMPL and can be easily implemented. Also it has some advantages of the PLRC approach-fast speed, low memory cost, and easy formulation of multiple pole susceptibility. We applied this APML to 2-D propagation problems in dispersive media such as Debye and Lorentz media The results showed good absorption at boundaries.

• Applied Chemistry for Engineering
• /
• v.23 no.1
• /
• pp.65-70
• /
• 2012

Structural changing materials which can induce the physical deformation of materials are interesting research topics with various potential applications. Particularly, light among many driving mechanisms is a non-contact energy source, hence the light-responsive system can be used where non-destructive, local irradiation, and remote control is needed. Here, a mainchain azobenzene polymer is synthesized and its physical and optical properties are observed and compared to that of a polymer having a light-responsive azobenzene moiety on its side chain. Further dispersion onto polyvinylalcohol hydrogel is made and its dual stability and actuation are observed upon UV-visible light irradiation. Extended azobenzene polymer blend films show an anisotropic light-actuation with non-polarized UV light at room temperature. This physical shape change is quite reversible and occurs at lower temperature than that of any other reported systems including liquid crystalline elastomers. It is successfully demonstrated that the simple physical azobenzene/polymer blending has a very good actuation compared to that of LCEs which need an elaborate chemical design and it can be further used in the areas requiring a dimensional shape change.

• Journal of Korea Water Resources Association
• /
• v.43 no.10
• /
• pp.893-909
• /
• 2010

The purpose of this study is to consider the interaction between surface water and groundwater in basin scale by developing TANK_GS model. The soil moisture structure of tank model with 3 tanks is improved to simulate the appropriate stream-aquifer interactions. Maximum likelihood method is applied to calibrate parameters with variance functions to deal with heteroscedasticity of residuals. The parameters of improved TANK_GS model and variance function are simultaneously estimated by Simulated Annealing method, a global optimization technique. The results of TANK-GE are compared to those of the SWMM-GE model which had been developed to consider the stream-aquifer interactions. The new TANK_GS model and SWMM-GE model are applied to Gapcheon basin, which belongs to Geum River basin. TANK_GS model showed better model performance compared to the original TANK model and characterized the relationship of stream-aquifer interactions as satisfactorily as the SWMM-GE model. The sustainable groundwater yield can be estimated for the regional water resources planning using the TANK_GS model

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.3 no.3
• /
• pp.3-13
• /
• 2001

The behavior of the masonry lining is studied to gain basic information on how to reinforce the masonry tunnels. Apart from the previous works on the masonry structures, the multi-course masonry structure, realistic in field condition, is considered and the constitutive relationship of the masonry is, therefore, established. The design charts of the orthotropic material properties are proposed according to the stiffness ratio and the crack initiation and subsequent propagation model is also considered to model the brittle nature of the masonry. A numerical analysis on the masonry panel is investigated to verify the proposed model and future works of the masonry lining are briefly explained.

• Journal of Industrial Technology
• /
• v.16
• /
• pp.267-275
• /
• 1996

금속과 같은 균질한 재료의 균열파괴의 특성을 설명하기 위하여 도입된 파괴역학의 이론들은 1960년대 이후 콘크리트나 암석 등에 대하여 적용되기 시작하였다. 파괴인성계수(fracture toughness)는 균열의 성장에 대한 재료의 저항을 나타낸다. 그러나, 암석의 파괴역학적 특성은 암석이 갖는 불균질성이나 비등방성에 의하여 영향을 받는다. 즉, 암석의 파괴역학적 특성의 측정은 시험편의 크기나 초기균열의 길이, 시험편의 형상 등에 의하여 측정자료의 분산이 심하며 따라서 다른 기본 물성들의 경우에서와 마찬가지로 일정한 시험기준의 도입이 요구되었다. 1988년에 국제암반공학회(ISRM)에서 제시한 표준시험방법은 시험편의 제작이나 시험방법에 있어서 복잡한 과정을 요구하고 있다. 본 논문에서는 표준시험방법에서 사용되는 시험편의 형태에 비하여 비교적 간단한 시험방법들에 의하여 얻어진 파괴적인성계수들을 서로 비교하여 제시하고 시험편의 크기와 기타 시험조건에 따른 파괴인성계수 측정치의 변화를 나타내고 있다. 또한, 암석에 포함되어있는 자연균열들의 특성과 파괴역학실험 중 유발되는 인공균열들의 형태를 비교하여 실험실에서 얻은 파괴역학적 계수들의 현장적용에 대한 문제점들을 지적하고 있다.