• Proceedings of the Korean Society for Emotion and Sensibility Conference
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• 2001.05a
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• pp.109-113
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• 2001

The purpose of this paper is to propose an analytical method for evaluating user satisfaction of Internet websites using the structural equation model(SEM). This paper is intended to identify critical evaluation factors of user satisfaction for websites to determine criteria for evaluating the websites, and use the criteria to develop a SEM model for quantitatively evaluation of each factors' effects of user satisfaction. The SEM model used 2 variables of usability and good-looks for the evaluation factors of websites user satisfaction and each factors have 4 sub evaluation criteria, 3 portal sites were evaluated to construct the SEM model, and 155 subjects participated the website evaluation using the walk-through and face-to-face survey method. Analysis results showed that the SEM model was statistically significant for all the 3 websites evaluated. Both the usability and good-looks two factors also showed significant effects to user satisfaction of websites and have positive correlation. The user satisfaction was more effected by the usability factor than good-looks, and the simplification and harmonization were the most critical sub-factors of the usability and good-looks.

• Geophysics and Geophysical Exploration
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• v.15 no.2
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• pp.57-65
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• 2012

Various numerical methods in simulation of seismic wave propagation have been developed. Recently an innovative numerical method called as the Spectral Element Method (SEM) has been developed and used in wave propagation in 3-D elastic media. The SEM that easily implements the free surface of topography combines the flexibility of a finite element method with the accuracy of a spectral method. It is generally used a weak formulation of the equation of motion which are solved on a mesh of hexahedral elements based on the Gauss-Lobatto-Legendre integration rule. Variational formulations of velocity-stress motion are newly modified in order to implement ADE-PML (Auxiliary Differential Equation of Perfectly Matched Layer) in wave propagation in 3-D elastic media, because a general weak formulation has a difficulty in adapting CFS (Complex Frequency Shifted) PML (Perfectly Matched Layer). SEM of Velocity-Stress motion having ADE-PML that is very efficient in absorbing waves reflected from finite boundary is verified with simulation of 1-D and 3-D wave propagation.

• Geomechanics and Engineering
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• v.18 no.6
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• pp.651-659
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• 2019

The IB-SEM numerical method combines the spectral/hp element method and the rigid immersed boundary method. This method avoids the problems of low computational efficiency and errors that are caused by the re-division of the grid when the solids move. Based on the Fourier transformation and the 3D immersed boundary method, the 3D IB-SEM system was established. Then, using the open MPI and the Hamilton HPC service, the computational efficiency was increased substantially. The flows around a cylinder and a sphere were simulated by the system. The surface of the cylinder generates vortices with alternating shedding, and these vortices result in a periodic force acting on the surface of the cylinder. When the shedding vortices enter the flow field behind the cylinder, a recirculation zone is formed. Finally, the three-dimensional pore flow was successfully investigated.

• Structural Engineering and Mechanics
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• v.65 no.3
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• pp.263-274
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• 2018

In this study, we propose a frequency domain spectral element method (SEM) for the vibration analysis of a multi-span beam subjected to a moving point force. This study is an extension of the authors' previous study for a single-span beam subjected to a moving point force, where the two-element model-based SEM was applied. In this study, each span of a multi-span beam is represented by the Timoshenko beam model and the moving point force is transformed into the frequency domain as a series of each stationary point force distributed on the multi-span beam. The span at which a stationary point force is located is represented by two-element model, but all other spans are represented by one-element models. The vibration responses to a moving point force are obtained by superposing all individual vibration responses generated by each stationary point force. The high accuracy and computational efficiency of the proposed SEM are verified by comparing the solutions by SEM with exact analytical solutions by the integral transform method (ITM) as well as the solutions by the finite element method (FEM).

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.3
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• pp.543-560
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• 2018

With the increased development in downtown underground space facilities that vertically cross under a railway at a shallow depth, the demand for non-open cut method is increasing. However, most construction sites still adopt the pipe roof method, where medium and large diameter steel pipes are pressed in to form a roof, enabling excavation of the inside space. Among the many factors that influence the loosening region and loads that occur while pressing in steel pipes, the size of the pipe has the largest impact, and this factor may correspond to the magnitude of load applied to the underground structure inside the steel pipe roof. The super equilibrium method (SEM) has been developed to minimize ground disturbance and loosening load, and uses small diameter pipes of approximately 114 mm instead of conventional medium and large diameter pipes. This small diameter steel pipe is called an SEM pile. After SEM piles are pressed in and the grouting reinforcement is constructed, a crossing structure is pressed in by using a hydraulic jack without ground subsidence or heaving. The SEM pile, which plays the role of timbering, is a fore-poling pile of approximately 5 m length that prevents ground collapse and supports surface load during excavation of toe part. The loosening region should be adequately calculated to estimate the spacing and construction length of the piles and stiffness of members. In this paper, we conducted a comparative analysis of calculations of loosening load that occurs during the press-in of SEM pile to obtain an optimal design of SEM. We analyzed the influence of factors in main theoretical and empirical formulas applied for calculating loosening regions, and carried out FEM analysis to see an appropriate loosening load to the SEM pile. In order to estimate the soil loosening caused by actual SEM-pile indentation and excavation, a steel pipe indentation reduction model test was conducted. Soil subsidence and soil loosening were investigated quantitatively according to soil/steel pipe (H/D).

• Journal of the Ergonomics Society of Korea
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• v.22 no.2
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• pp.45-56
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• 2003

The purpose of this study is to develop the model including multiple causal relationship between factors to evaluate overall user satisfaction and develop an objective method to quantify the impacts and scores of each qualitative factors on overall user satisfaction using Structural Equation Model(SEM) and also test the feasibility to construct a comprehensive website evaluation model including qualitative and quantitative factors. The SEM model used 2 qualitative factors of usability and esthetic factors for the evaluation factors of user satisfaction and select 4 attributes of each factors using factor analysis. 3 shopping mall sites were evaluated to construct the SEM model, and 155 subjects participated the website evaluation using the walk-through and face-to-face survey method. Analysis results showed that the SEM model was statistically significant for all the 3 websites evaluated. Both the usability and esthetic factors showed significant effects to user satisfaction of websites and have positive correlation. The user satisfaction was more effected by the usability factor than esthetic factors, and the simplification and harmonization were the most critical attributes of the usability and esthetic factors.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2003.04a
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• pp.151-159
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• 2003

This study presents method for self-calibration of the SEM(Scanning Electron Microscope) stereo image using the standard microprobe with same grid pattern and using parallel and central perspective projection equation. Result showed that parallel projection method is more suitable for standard microprobe. The maximum error of 3D coordinates acquired by this method did not exceed 5 $\mu\textrm{m}$, and DSM(Digital Surface Model) for three dimensional measurement of the rock sample was generated by the digital photogrammetry. This result can be used for quantification of micro scale change of shape and analysis of the micro morphology of rock due to weathering.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.210-216
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• 1996

Spectral element method(SEM) has been recognized to provide accurate structural dynamic responses even at high frequency. The Duhamel's integral based SEM developed by the authors for the structures under dynamic distributed loads does not take into account the zero frequency effect and requires significant computational time due to the integration procedure of Duhamel's integral. Hence, in this paper, a new SEM algorithm is proposed. This new algorithm is based on the FEM-type procedure for the distributed loads and includes the zero frequency correction to improve the accuracy. Some numerical results are illustrated to prove the accuracy of present new SEM algorithm.

• Journal of the Ergonomics Society of Korea
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• v.20 no.3
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• pp.47-60
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• 2001

The purpose of this paper is propose an analytical method for evaluating user satisfaction of Internet website and identifying casual relationships between user satisfaction of Internet website and performance measures as like revisit intention and complaints using the structural equation model (SEM). This paper is intended to identify critical evaluation factors of user satisfaction for Internet website to determine criteria for evaluating the website. and use the criteria to develop a SEM model for quantitatively evaluation of each factors effects of user preference. The SEM model used 5 latent variables for the evaluation factors of website user satisfaction and 2 latent variables for performance evaluation. 2 portal sites were evaluated to construct the SEM model. and 74 subjects participated the website evaluation using the walk-through and face-to face survey method. Analysis results showed that the SEM model was statistically significant for all the 2 websites evaluated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.04a
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• pp.328-334
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• 1996

Finite Element Method(FEM) is the most popularly used method in analyzing the dynamic behaviors of structures. But unless the number of finite elements is large enough, the results from FEM are somewhat different from exact analytical solutions, especially at high frequency range. On the other hand, as the Spectral Element Method(SEM) deals directly with the governing equations of structures, the results from this method cannot but be exact regardless of any frequency range. However, despite two dimensional structures are more general, the SEM has been applied only to the analysis of one dimensional structures so far. In this paper, therefore, new methodologies are introduced to analyze the two dimensional plate using SEM. The results from this new method are compared with the exact analytical solutions by letting the two dimensional plate be one dimensional one and showed the dynamic responses of two dimensional plate by including various waves propagated into x-direction.