• Journal of the Korean Geographical Society
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• v.46 no.2
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• pp.197-211
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• 2011

Due to the complexity of spatial interaction and the necessity of spatial representation and modeling, aggregation of spatial interaction data is indispensible. Given this, the purpose of this paper is to evaluate the effects of modifiable areal unit problem (MAUP) on a spatial interaction model. Four aggregation schemes are utilized at eight different scales: 1) randomly select seeds of district and then allocate basic spatial units to them, 2) minimize the sum of population weighted distance within a district, 3) maximize the proportion of flow within a district, and 4) minimize the proportion of flow within a district. A simple Poisson regression model with origin and destination constraints is utilized. Analysis results demonstrate that spatial characteristics of residuals, parameter values, and goodness-of-fit of the model were influenced by aggregation scale and schemes. Overall, the model responded more sensitively to aggregation scale than aggregation schemes and the scale effect on the model was varied according to aggregation schemes.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.6
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• pp.537-544
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• 2009

This paper concerns analysis technique on determining of attitude control gain in the low frequency region using stability area. The stability area is defined by the D-Decomposition method, which was designed by Neimark. In this paper, it is introduced D-Decomposition method from reference paper and design attitude control gain of generic launch vehicle during first stage flight phase. For selecting PD control gain, it is considered the system parameter uncertainty about whole first-stage flight phase, represented the stability area boundary on each case. After deciding the PD control gain using stability area method, it is applied to launch vehicle linear model, and checking the stability margin requirement, frequency response characteristics.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.6 no.2
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• pp.147-154
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• 2008

It is expected that the temporary storage facilities at the nuclear power plants will be full of the spent fuels within 10 years. Provided that a centralized interim storage facility is constructed along the coast of the Korean peninsula to solve this problem, a substantial amount of spent fuels should be transported by sea or by land every year. In this paper we developed a computer program for the analysis of transportation logistics of the spent fuels from 4 different nuclear power plant sites to the hypothetical centralized interim storage facility and the final repository. Mass balance equations were used to analyze the logistics between the nuclear power plants and the interim storage facility. To this end a computer program, CASK, was developed by using the VISUAL BASIC language. The annual transportation rates of spent fuels from the four nuclear power plant sites were determined by using the CASK program. The parameter study with the program illustrated the easiness of logistics analysis. The program could be used for the cost analysis of the spent fuel transportation as well.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.645-652
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• 2016

The statistical modeling of input random variables is necessary in reliability analysis, reliability-based design optimization, and statistical validation and calibration of analysis models of mechanical systems. In statistical modeling methods, there are the Akaike Information Criterion (AIC), AIC correction (AICc), Bayesian Information Criterion, Maximum Likelihood Estimation (MLE), and Bayesian method. Those methods basically select the best fitted distribution among candidate models by calculating their likelihood function values from a given data set. The number of data or parameters in some methods are considered to identify the distribution types. On the other hand, the engineers in a real field have difficulties in selecting the statistical modeling method to obtain a statistical model of the experimental data because of a lack of knowledge of those methods. In this study, commonly used statistical modeling methods were compared using statistical simulation tests. Their advantages and disadvantages were then analyzed. In the simulation tests, various types of distribution were assumed as populations and the samples were generated randomly from them with different sample sizes. Real engineering data were used to verify each statistical modeling method.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.2
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• pp.660-665
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• 2014

Optimization of process parameters in polymer extrusion is an important task to reduce manufacturing cost. To determine the optimum values of the process parameters, it is essential to find their influence on the elongation of polymer breathable thin film. The significance of six important process parameters namely, extruder cylinder temperature, extruder speed, extruder dies temperature, cooling roll temperature, stretching ratio, stretching roll temperature on breathable film elongation of polymer extrusion was determined. Moreover, this paper presents the application of Taguchi method and analysis of variance(ANOVA) for maximization of the breathable film elongation influenced by extrusion parameters. The optimum parameter combination of extrusion process was obtained by using the analysis of signal-to-noise ratio. The conclusion revealed that stretching ratio were the most influential factor on the film elongation. The best results of film elongation were obtained at lower stretching ratio.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.9A
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• pp.1313-1321
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• 2000

In recent years LEO(Low Earth Orbit) satellite communication systems have gained a lot of interest as high speed multimedia services by satellite are about to be provided. It is mandatory to use very efficient ECC(Error Correcting Code) to support high speed multimedia services over LEO satellite channel. Turbo codes developed by Berrou et al. in 1993 have been actively researched since it can achieve a performance close to the Shannon limit. In this paper, a LEO satellite channel model is adopted and the fading characteristics of LEO satellite channel are analyzed for the change of elevation angle in various propagation environments. The performance of turbo code is analyzed and compared to that of conventional convolutional code using the satellite channel model. In the simulation results using the Globalstar orbit constellations, performance of turbo codes shows 1.0~2.0dB coding gain compared to that of convolutional codes over all elevation angle and propagation environment ranges we have investigated. The performance difference resulting from the change of elevation angle in various propagation environments and the performance of different ECC are analyzed in detail, so that the results can be applied to choose an appropriate ECC scheme for various system environment.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.5
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• pp.2603-2609
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• 2014

Reliability analysis of mechanical systems requires statistical modeling of input random variables such as distribution function types and statistical parameters that affect the performance of the mechanical systems. Some random variables are correlated, but considered as independent variables or wrong assumptions on input random variables have been used. In this paper, joint distributions were modeled using copulas and Bayesian method from limited number of data. To verify the proposed method, statistical simulation tests were carried out for various number of samples and correlation coefficients. As a result, the Bayesian method selected the most probable copula types among candidate copulas even though the candidate copula shapes are similar for low correlations or the number of data is limited. The most probable copulas also yielded similar reliabilities with the true reliability obtained from a true copula, so that it can be concluded that the Bayesian method provides accurate statistical modeling for the reliability analysis.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.4
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• pp.56-62
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• 2013

The system analysis and design program of the liquid rocket engine has been developed for preliminary conceptual design process. The program analyzes the engine system and obtains optimal design variables by optimization methods such as genetic algorithm for the higher specific impulse and thrust to weight ratio using given input parameters and requirements. For the users' convenience, the GUI has been offered. The 3-dimensional model for the visualization of results has been interconnected with the CATIA program. The results are expected to be applied to the design process of the space launch vehicle for the analysis and selection of the propulsion system.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.6
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• pp.973-987
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• 2018

Most of the previous seismic analyses have been carried out by separating the ground and structures, and there is a lack of comparative study on the dynamic behavior of high-rise and low-rise buildings. Therefore, in this study, the sensitivity analysis was performed with selected parameters by using a finite element analysis program in order to grasp the dynamic behavior of high-rise and low-rise buildings. As a result, it was turned out that the horizontal displacement, the interstory drift ratio, and the bending stress of a high-rise building were more affected by a long seismic wave than a low-rise buildings. Also, the weak parts of a high-rise and low-rise building were more affected by type of seismic wave than the ground conditions. Therefore, it is inferred that it will be helpful for seismic designs to consider the influence of ground conditions and seismic wave type on buildings.

• Journal of the Korean GEO-environmental Society
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• v.20 no.10
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• pp.5-14
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• 2019

Recently, earthquakes have occurred in our country and seismic stability of high-rise buildings in large cities is being a growing interest and thus the related studies have been increased. Also the grounds are considered indirectly in most of seismic designs and analyses and seismic researches based on 3D dynamic analysis are insufficient. In this study, therefore, 2D and 3D dynamic analyses were performed based on the SSI complete model including grounds and the behavior was compared and analyzed. For dynamic modeling, linear time history analyses were performed by using MIDAS GTS NX. For this purpose, a high-rise building was assumed to be constructed on top of the bedrock and surrounded by a surface layer. A sensitivity analysis was performed with the selected parameters. The dynamic behavior was compared and analyzed in terms of horizontal displacements, drift ratios, bending stresses, and weak parts. In most cases, 2D dynamic behavior was calculated to be larger than 3D's and thus it shows more conservative results with increasing number and size of weak parts.