• Journal of The Korean Society of Agricultural Engineers
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• v.48 no.4
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• pp.67-74
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• 2006

This study was carried out to investigate the liquefaction behaviour of saturated silty sand under monotonic loading conditions. The undrained soil tests were conducted using a modified triaxial cell and specimens were prepared using the moisture tamping method. Undrained triaxial compression tests were performed at different confining pressures, void ratios and overconsolidation ratios and the samples were sheared to axial strains of about 20% to obtain monotonic loading conditions. It is shown that increasing confining pressures, void ratios and overconsoildation ratios increases the deviator stress, but it has no effect on increasing the dilatant tendencies. It is shown that complete static liquefaction was observed regardless of increases in the confining pressure, void ratio and overconsolidation ratio. Therefore, the confining pressure, void ratio and overconsoildation ratio does not provide significant effects on the liquefaction resistance of the silty sand. The presence of fines in the soil was shown to greatly increase the potential for static liquefaction and creates a particle structure with high compressibility for all cases.

• Structural Engineering and Mechanics
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• v.37 no.6
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• pp.633-648
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• 2011

This paper investigates the aspect-ratio locking of the isoparametric 8-node quadrilateral (QUAD8) element. An important finding is that, if finite element solution is carried out with in exact arithmetic (i.e., with no truncation and round off errors), the locking tendency of the element is completely avoided even for aspect-ratios as high as 100000. The current finite element codes mostly use floating point arithmetic. Thus, they can only avoid this locking for aspect-ratios up to 100 or 1000. A novel method is proposed in the paper to avoid aspect-ratio locking in floating point computations. In this method, the offending terms of the strain-displacement matrix (i.e., $\mathbf{B}$-matrix) are multiplied by suitable scaling factors to avoid ill-conditioning of stiffness matrix. Numerical examples are presented to demonstrate the efficacy of the method. The examples reveal that aspect-ratio locking is avoided even for aspect-ratios as high as 100000.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.93-100
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• 2008

Recently, due to the advanced measurement techniques, long-term health monitoring systems have been frequently applied to existing bridges. It is known that damping ratios as one of dynamic properties would be an important parameter for evaluating the bridge condition. However, damping ratios may be normally varied depending on the external loading effects on bridges. In general, both the logarithmic decrement and the half-power band width method as a conventional method can be simply used for evaluating the damping ratios accurately when bridge response signals are measured under free vibration conditions. In this study, the Hilbert-Huang transform and the extended Kalman filter were applied to evaluate the damping ratio by using the bridge acceleration signals measured under ambient vibration condition. From the results under ambient vibration condition of bridges, it was examined that the damping ratios evaluated from both the Hilbert-Huang transform and the extended Kalman filter could be more reliable than those from conventional methods.

• Journal of Korean Society for Atmospheric Environment
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• v.13 no.3
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• pp.231-241
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• 1997

A tracer model was applied in the Far East Asia to investigate the dry deposition rates of air pollutants on Korean Peninsula originated from different countries including China and Japan. Wind direction was chosen to predict the maximum deposition rates and SO$_2$ was chosen as a tracer to estimate the source strength. Model simulation shows that inflow, deposition and airborne ratios of China-originated SO$_2$ were 50%, 8% and 30%, respectively, at most. Also it was found that deposition, outbounded and airborne ratios of Korea-originated SO$_2$ were 15~77%, 8~75%, and 3~30%, respectively Model simulation also shows that inflow, deposition and airborne ratios of Kyushu-originated SO$_2$ were, 30~45%, 8~14％ and 20~25%, respectively. This study shows that tracer model can be applied on the estimation of air pollutants partitioning in regional scale and that more sophisticated modules and schemes can be developed and applied to better predict the transboundary amounts of air pollutants in this region.

• Journal of the Korean Applied Science and Technology
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• v.9 no.1
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• pp.55-61
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• 1992

This study was performed observe the effect of edible oil on the serum lipid of 0.5% cholesterol-fed rats. In this experiment, male rats of Sprague-Dawley strain were used. The rats were divided into 5groups which were fed differently eigher for 8 weeks : basal diet, 20% sunflower oil diet, 20% soybean oil diet, 20% rapeseed oil diet, 20% coconut oil diet. The followings are the results of this experiment. 1. The total chol., free chol., TG, PL level in the serum were showed tendency of decrease with in creasing of P/S ratios. 2. HDL-chol. level was increased with increasing of P/S ratios but LDL-chol. level was decreased. 3. GOT, GPT, TBA level in the serum were increased with increasing of P/S ratios.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.1
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• pp.52-62
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• 1995

The purpose of this study is to determine the wind pressure coefficients around prismatic structures with different aspect ratios. Air flows around a model of prismatic shape are investigated experimentally in the wind tunnel and simulated using finite volume method. Pressure distributions and the corresponding pressure coefficients are calculated from the experimental and numerical results. The effects of aspect ratios on the pressure coefficients are discussed extensively. The numerical results are compared with those of experiments. The simulated and experimental results for average wind pressure coefficients are considerably lower than those defined in the Korean Architectural Standard Code.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.89-92
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• 2005

An experimental study was conducted to study the mechanical properties of recycled aggregate concrete in accordance with the different replacement ratios of recycled fine and coarse aggregate, ranging from 0$\%$ to 30$\%$ and 0$\%$ to 50$\%$, respectively. According to increase of these replacement ratios, compressive strengths and elastic modulus are reduced down to $10\∼20\%$ and $15\∼30\%$, respectively. The reducing ratios of elastic modulus are more distinct than that of compressive strength. For the selection of replacement ratios of recycled aggregate for structural concrete properly, it is necessary to evaluate the elastic modulus carefully.

• East Asian mathematical journal
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• v.32 no.1
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• pp.129-138
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• 2016

In this paper, we propose an efficient regularization technique (The Method of Regularized Ratios) for the reconstruction of the shape of a rigid elastic scatterer from far field measurements. The approach used is based on the factorization method and creates via Picard's condition ratios, baptized Regularized Ratios, that serve to effectively remove unwanted singular values that may lead to poor reconstructions. This is achieved through the use of a sophisticated algorithm that progressively adjusts an initially set moderate tolerance. In comparison with the well established Tikhonov-Morozov regularization techniques our new algorithm appears to be more computationally efficient as it doesn't require computation of the regularization parameter for each point in the grid.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.5
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• pp.615-623
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• 1999

The objective of present study is to analyze a hot steel-tube cooling system as a kind of concentric triple-passage heat exchanger, whose inner tube is moving with a constant speed. Velocities and temperatures of an antioxidant gas flowing between inner and outer tubes are calculated theoretically for both laminar and turbulent flow regimes and used to give Nusselt numbers and friction factors with respect to various radius ratios and velocity ratios. In addition, it is shown that heat transfer coefficients based on ratios of average heat fluxes from inner and outer tubes might result in great errors for the temperature distributions of the flows, since the local heat transfer coefficients are dependent on the local heat flux ratios.

• Structural Engineering and Mechanics
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• v.71 no.6
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• pp.657-668
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• 2019

The numerical thermal frequency responses of the skew sandwich shell panels structure are investigated via a higher-order polynomial shear deformation theory including the thickness stretching effect. A customized MATLAB code is developed using the current mathematical model for the computational purpose. The finite element solution accuracy and consistency have been checked via solving different kinds of numerical benchmark examples taken from the literature. After confirming the standardization of the model, it is further extended to show the effect of different important geometrical parameters such as span-to-thickness ratios, aspect ratios, curvature ratios, core-to-face thickness ratios, skew angles, and support conditions on the frequencies of the sandwich composite flat/curved panel structure under elevated temperature environment.