• Journal of the Korean Geotechnical Society
• /
• v.29 no.11
• /
• pp.85-97
• /
• 2013

Electric pole foundations for overhead catenary system of railroad should be designed so that they may resist significant overturning moment but relatively small vertical forces. Also they should have proper shapes to be installed at restricted narrow areas adjacent to railroad track. In this paper the moment responses of rectangular pole foundations according to their shapes were investigated numerically. A three-dimensional finite element method was developed and verified so that the numerical behaviors of the foundation resisting the overturning moments were compared reasonably well with those from an existing real-scale load test. The influences of aspect ratio, varying section with depth and loading directions for rectangular section were investigated using the developed numerical method. From the numerical results, the optimized shapes of pole foundation for more effective and economic installation adjacent to railroad track are proposed.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.17 no.8
• /
• pp.1790-1795
• /
• 2013

The current velocity and turbulence information in each range cell can be obtained from the first and second Doppler spectrum moment estimates. However, the very widely used correlation method often called as the pulse-pair method has the inherent restrictions under the highly turbulent conditions since it does not satisfy the assumptions that the return Doppler spectrum should be symmetric and have a single peak value. Therefore, in this paper, the quality of pulse-pair estimates were compared with that of FFT estimates for problem analysis using various shapes of simulated Doppler spectra. It can be known that the pulse-pair method often yields meaningless results if the received signals are severely biased or multi-peak Doppler spectra in the Doppler frequency domain.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.15 no.6
• /
• pp.1037-1044
• /
• 2020

Since radar wind profiler (RWP) provides wind field data with high time and space resolution in all weather conditions, their verification of the accuracy and quality is essential. The simultaneous wind measurement from rawinsonde is commonly used to evaluate wind vectors from RWP. In this study, the simulation algorithm which produces the spectrum and raw time series (I/Q) data from the average values of moments is presented as a step-by-step verification method for the signal processing algorithm. The possibility of the simulation algorithm was also confirmed through comparison with the raw data of LAP-3000. The Doppler power spectrum was generated by assuming the density function of the skew-normal distribution and by using the moment values as the parameter. The simulated spectrum was generated through random numbers. In addition, the coherent averaged I/Q data was generated by random phase and inverse discrete Fourier transform, and raw I/Q data was generated through the Dirichlet distribution.

• Journal of Aerospace System Engineering
• /
• v.16 no.6
• /
• pp.114-122
• /
• 2022

This paper explores three-dimensional unsteady computational fluid dynamic (CFD) analyses with an overset grid technique to analyse the wake effect created by a rotating propeller on a hand-launched unmanned aerial vehicle (UAV). Additionally, the influence of actual aileron deflection on the equilibrium condition of the rolling moment is examined in various hand-launched take-off conditions. The results of this study demonstrate the importance of initial aileron deflection in increasing the initial rolling stability during the hand-launched take-off process. Furthermore, an aerodynamic database is constructed to rapidly predict the aileron set values required for different take-off speeds and angle-of-attacks.

• Journal of Korea Water Resources Association
• /
• v.42 no.10
• /
• pp.857-866
• /
• 2009

In this study, basic data is consisted annual maximum rainfall at 56 stations that has the rainfall records more than 30years in Korea. The 14 probability distributions which has been widely used in hydrologic frequency analysis are applied to the basic data. The method of moments, method of maximum likelihood and probability weighted moments method are used to estimate the parameters. And 4-tests (chi-square test, Kolmogorov-Smirnov test, Cramer von Mises test, probability plot correlation coefficient (PPCC) test) are used to determine the goodness of fit of probability distributions. This study emphasizes the necessity for considering the variability of the estimate of T-year event in hydrologic frequency analysis and proposes a framework for evaluating probability distribution models. The variability (or estimation error) of T-year event is used as a criterion for model evaluation as well as three goodness of fit criteria (SLSC, MLL, and AIC) in the framework. The Jackknife method plays a important role in estimating the variability. For the annual maxima of rainfall at 56 stations, the Gumble distribution is regarded as the best one among probability distribution models with two or three parameters.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.3B
• /
• pp.277-284
• /
• 2011

The limitations of existing Markov chain model for reproducing extreme rainfalls are a known problem, and the problems have increased the uncertainties in establishing water resources plans. Especially, it is very difficult to secure reliability of water resources structures because the design rainfall through the existing Markov chain model are significantly underestimated. In this regard, aims of this study were to develop a new daily rainfall simulation model which is able to reproduce both mean and high order moments such as variance and skewness using a piecewise Kernel-Pareto distribution. The proposed methods were applied to summer and fall season rainfall at three stations in Han river watershed in Korea. The proposed Kernel-Pareto distribution based Markov chain model has been shown to perform well at reproducing most of statistics such as mean, standard deviation and skewness while the existing Gamma distribution based Markov chain model generally fails to reproduce high order moments. It was also confirmed that the proposed model can more effectively reproduce low order moments such as mean and median as well as underlying distribution of daily rainfall series by modeling extreme rainfall separately.

• Journal of Korea Water Resources Association
• /
• v.46 no.1
• /
• pp.13-24
• /
• 2013

The main objective of this study was to develop a new regional frequency analysis model based on hierarchical Bayesian model that allows us to better estimate and quantify model parameters as well as their associated uncertainties. A Monte-carlo experiment procedure has been set up to verify the proposed regional frequency analysis. It was found that the proposed hierarchical Bayesian model based regional frequency analysis outperformed the existing L-moment based regional frequency analysis in terms of reducing biases associated with the model parameters. Especially, the bias is remarkably decreased with increasing return period. The proposed model was applied to six weather stations in Jeollabuk-do, and compared with the existing L-moment approach. This study also provided shrinkage process of the model parameters that is a typical behavior in hierarchical Bayes models. The results of case study show that the proposed model has the potential to obtain reliable estimates of the parameters and quantitatively provide their uncertainties.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.25 no.5
• /
• pp.585-591
• /
• 2014

An improved numerical scattering model with the 2-dimensional moment method including roof-top basis and a modified window-function to reduce edge-effect is presented in this study. The roof-top basis function is used to depict randomly positioned surface currents and increase an efficiency of the moment method. To reduce the edge-effect which occurs at the end of numerically generated surfaces, an enhanced window-function which is weighted by incident angle variable is proposed. To validate an proposed 2-dimensional scattering model and numerical analysis techniques for randomly rough surfaces, computational results are compared and analyzed to SPM(Small Perturbation Model) as well.

• Journal of the Korea Concrete Institute
• /
• v.27 no.3
• /
• pp.283-290
• /
• 2015

This paper proposes a method for predicting flexural strength of hybrid steel fiber-reinforced ultra-high strength concrete beams. It includes an experimental test framework and associated numerical analyses. The experimental program includes flexural test results of hybrid steel fiber-reinforced ultra-high strength concrete beams with steel fiber content of 1.5% by volume. Tensile softening characteristics play an important role in the structural behavior of steel fiber-reinforced ultra high performance concrete. Tension softening modeling is carried out by using crack equation based on fictitious crack and inverse analysis in which load-crack mouth opening displacement relationship is considered. The comparison of moment-curvature curves of the numerical analysis results with the test results shows a reasonable agreement. Therefore, the numerical results confirms that good prediction of flexural behavior of steel fiber-reinforced ultra high strength concrete beams can be achieved by employing the proposed method.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.25 no.10
• /
• pp.1087-1094
• /
• 2014

An numerical technique of impedance boundary condition to improve an efficiency in the process of moment method with CFIE(Combined Field Integral Equation), which is widely used to analyze the scattering property of dielectric scatterers, and results of its cross-validations are presented in this study. Application of the impedance boundary allows to represent the equivalent surface currents of dielectric scatterer depicted by both kinds of electric/magnetic surface currents(Js, Ms) to the single surface current by Js or Ms only. Accuracy of this technique is validated by the existing CFIE and theoretical values such as Mie-series solution and small perturbation scattering model. The computational difference of less than 1 dB was verified within an imaginary part of dielectric constant more than 12, as well.