• Journal of Korea Water Resources Association
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• v.46 no.11
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• pp.1041-1052
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• 2013

In this study, we estimate parameters of a distributed hydrologic model, GRM (grid based rainfall-runoff model), using a model-independent parameter estimation tool, PEST. We implement auto calibration of model parameters such as initial soil moisture, multipliers of overland roughness and soil hydraulic conductivity in the Geumho River Catchment and the Gamcheon Catchment using radar rainfall estimates and ground-observed rainfall represented by Thiessen interpolation. Automatic calibration is performed by GRM-MP (multiple projects), a modified version of GRM without GUI (graphic user interface) implementation, and "Parallel PEST" to improve estimation efficiency. Although ground rainfall shows similar or higher cumulative amount compared to radar rainfall in the areal average, high spatial variation is found only in radar rainfall. In terms of accuracy of hydrologic simulations, radar rainfall is equivalent or superior to ground rainfall. In the case of radar rainfall, the estimated multiplier of soil hydraulic conductivity is lower than 1, which may be affected by high rainfall intensity of radar rainfall. Other parameters such as initial soil moisture and the multiplier of overland roughness do not show consistent trends in the calibration results. Overall, calibrated parameters show different patterns in radar and ground rainfall, which should be carefully considered in the rainfall-runoff modelling applications using radar rainfall.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.2
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• pp.123-130
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• 2004

The automobile suspension system is composed of parts that affect performances of a vehicle such as ride quality, handling characteristics, straight performance and steering effort, etc. Moreover, by using the finite element analysis the cost for the initial design step can be decreased. In the design of a suspension system, usually system vibration and structural rigidity must be considered simultaneously to satisfy dynamic and static requirements simultaneously. In this paper, we consider the weight reduction and the increase of the first eigen-frequency of a suspension part, the upper control arm, especially using topology optimization and size optimization. Firstly, we obtain the initial design to maximize the first eigen-frequency using topology optimization. Then, we apply the multi-objective parameter optimization method to satisfy both the weight reduction and the increase of the first eigen-frequency. The design variables are varying during the optimization process for the multi-objective. Therefore, we can obtain the deterministic values of the design variables not only to satisfy the terms of variation limits but also to optimize the two design objectives at the same time. Finally, we have executed reliability based optimal design on the upper control arm using the Monte-Carlo method with importance sampling method for the optimal design result with 98％ reliability.

• Steel and Composite Structures
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• v.23 no.5
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• pp.585-596
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• 2017

Tubular joints have been widely used in offshore platforms and space structures due to their merits such as easy fabrication, aesthetic appearance and better static strength. For existing tubular joints, a grouted sleeve reinforced method was proposed in this paper. Experimental tests on five tubular T-joints reinforced with the grouted sleeve and two conventional tubular T-joints were conducted to investigate their mechanical behaviour. A constant axial compressive force was applied to the chord end to simulate the compressive state of the chord member during the tests. Then an axial compressive force was applied to the top end of the brace member until the collapse of the joint specimens occurred. The parameters investigated herein were the grout thickness, the sleeve length coefficient and the sleeve construction method. The failure mode, ultimate load, initial stiffness and deformability of these joint specimens were discussed. It was found that: (1) The grouted sleeve could change the failure mode of tubular T-joints. (2) The grouted sleeve was observed to provide strength enhancement up to 154.3%~172.7% for the corresponding un-reinforced joint. (3) The initial stiffness and deformability were also greatly improved by the grouted sleeve. (4) The sleeve length coefficient was a key parameter for the improved effect of the grouted sleeve reinforced method.

• International Journal of Highway Engineering
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• v.17 no.4
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• pp.33-40
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• 2015

PURPOSES: Evaluation of the wind speed effect on the temperature drop of an asphalt mixture during construction, by using the transient heat transfer theory and dominant convective heat transfer coefficient model. METHODS: Finite difference method (FDM) is used to solve the transient heat transfer difference equation numerically for various wind speeds and initial temperature conditions. The Blasius convective heat transfer coefficient model is adapted to account for the effect of wind speed in the temperature predictions of the asphalt mixture, and the Beaufort number is used to select a reasonable wind speed for the analysis. As a function of time and depth, the temperature of the pavement structure is predicted and analyzed for the given initial conditions. RESULTS : The effect of wind speed on the temperature drop of asphalt mixture is found to be significant. It seems that wind speed is another parameter to be accounted for in the construction specifications for obtaining a better quality of the asphalt mixture. CONCLUSIONS: It is concluded that wind speed has a significant effect on the temperature drop of the asphalt layer. Although additional field observations have to be made to reflect the effect of wind speed on the construction specifications, it appears that wind speed is a dominant variable to be considered, in addition to the atmospheric temperature.

• Journal of The Korean Astronomical Society
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• v.17 no.1
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• pp.1-14
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• 1984

Analyses of an integrated form $N(\tau)={\int}_{\tau}^{\infty}n(\tau)d{\tau}$ of the distribution of cluster ages, rather than its differential form $n(\tau)$, demonstrate that the observed distribution has clusters older than about 500 million years in a significant excess over theoretical model distributions. Considerations on cluster disruption processes show that a single disruption time-scale, frequently employed by current theoretical models, is no longer an adequate parameter for describing survival probability of clusters over wide age range, because different initial conditions of these clusters produce corresponding spreads in their lifetimes. To take into account for the spread in initial conditions, we have introduced an age-dependent disruption time, and deduced its age-dependence from the present-day age distribution of clusters. Results show a distinct two-stage variation: The newly introduced disruption time stays constant at about 50 million years for clusters younger than about 100 million years, while for clusters older than that it increases monotonically with the cluster age. This leads us to conclude that clusters experience different types of disrupting causes as they get old.

• Journal of the Korean Institute of Intelligent Systems
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• v.17 no.6
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• pp.807-812
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• 2007

Recently, Extreme learning machine(ELM), a novel learning algorithm which is much faster than conventional gradient-based learning algorithm, was proposed for single-hidden-layer feedforward neural networks. The initial input weights and hidden biases of ELM are usually randomly chosen, and the output weights are analytically determined by using Moore-Penrose(MP) generalized inverse. But it has the difficulties to choose initial input weights and hidden biases. In this paper, an advanced method using the bacterial foraging algorithm to adjust the input weights and hidden biases is proposed. Experiment at results show that this method can achieve better performance for problems having higher dimension than others.

• Advanced Composite Materials
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• v.18 no.4
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• pp.381-394
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• 2009

The kinetics of centrifugal infiltration of fibrous tubular preform is built theoretically, and simulations are conducted to study the effects of various casting conditions on infiltration kinetics and macrosegregation by combining with the energy, mass and kinetic equations. A similarity way is used to simplify the one-dimensional model and the parameter is ascertained by an iterative method. The results indicate that the increase of superheat, initial preform temperature, porosity tends to enlarge the remelting region and decrease copper solute concentration at the infiltration front. Higher angular velocity leads to smaller remelting region and solute concentration at the tip. The pressure in the infiltrated region increase significantly when the angular velocity is much higher, which requires a stronger preform. It is observed that the pressure distribution is mainly determined by the angular velocity, and the macrosegregation in the centrifugal casting is greatly dependent on the superheat of inlet metal matrix, initial temperature and porosity of the preform, and the angular velocity.

• Journal of Ocean Engineering and Technology
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• v.25 no.2
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• pp.67-72
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• 2011

This study had the goal of investigating the effect of the curvature along the heating line on the transverse angular distortion of plates having an initial curvature from line heating. A thermo-elasto-plastic analysis was carried out using 54 models with various radii of curvature, plate thicknesses, and heating speeds. The results show the effect of the curvature along the heating line on the angular distortion in relation to changes in the magnitudes of the curvature, heating speed, and plate thickness. The present numerical results show that the time history of the angular distortion after cooling and reaching the final deformed shape for a plate having an initial curvature is quite different from that of a flat plate. This emphasized the importance of considering the curvature effect on the transverse angular distortion. From the viewpoint of the curvature effect on the deformation, it has been seen that the curvature does not affect the transverse shrinkage. In this study the predicting formula for the transverse angular distortion was derived through a regression analysis. It showed that as the curvature increased, the angular distortion was reduced because of the higher bending rigidity at the same heat input parameter, and the peak points moved toward the origin as the curvature increased.

• Phonetics and Speech Sciences
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• v.2 no.3
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• pp.47-63
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• 2010

This study provides a description of the glottal characteristics of the word-initial low vowels /a, $\ae$/ in terms of a set of acoustic parameters and discusses glottal configuration as their acoustic correlates. Furthermore, it examines the effect of prosodic boundary on the glottal properties of the vowels, seeking an account of the possible role of prosodic structure based on prosodic theory. Acoustic parameters reported to indicate glottal characteristics were obtained from the measurements made directly from the speech spectrum on recordings of Korean and English collected from 45 speakers. They consist of two separate groups of native Korean and native English speakers, each including both male and female speakers. Based on the three acoustic parameters of open quotient (OQ), first-formant bandwidth (B1), and spectral tilt (ST), comparisons were made between the speech of males and females, between the speech of native Korean and native English speakers, and between Korean and English produced by native Korean speakers. Acoustic analysis of the experimental data indicates that some or all glottal parameters play a crucial role in differentiating the speech groups, despite substantial interspeaker variations. Statistical analysis of the Korean data indicates prosodic strengthening with respect to the acoustic parameters B1 and OQ, suggesting acoustic enhancement in terms of the degree of glottal abduction and the glottal closure during a vibratory cycle.

• The Journal of Information Technology
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• v.4 no.1
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• pp.71-79
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• 2001

This paper presents an adaptive back propagation algorithm that update the learning parameter by the generated error, adaptively and configuration of the range for the initial connecting weight according to the different maximum target value from minimum target value. This algorithm is expected to escaping from the local minimum and make the best environment for the convergence. On the simulation tested this algorithm on three learning pattern. The first was 3-parity problem learning, the second was $7{\times}5$ dot alphabetic font learning and the third was handwritten primitive strokes learning. In three examples, the probability of becoming trapped in local minimum was reduce. Furthermore, in the alphabetic font and handwritten primitive strokes learning, the neural network enhanced to loaming efficient about 27%~57.2% for the standard back propagation(SBP).