• Composites Research
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• v.26 no.6
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• pp.363-372
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• 2013

Numerical simulation for Resin Transfer Molding manufacturing process is attempted by using the eXtended Finite Element Method (XFEM) combined with the level set method. XFEM allows to obtaining a good numerical precision of the pressure near the resin flow front, where its gradient is discontinuous. The enriched shape functions of XFEM are derived by using the level set values so as to correctly describe the interpolation with the resin flow front. In addition, the level set method is used to transport the resin flow front at each time step during the mold filling. The level set values are calculated by an implicit characteristic Galerkin FEM. The multi-frontal solver of IPSAP is adopted to solve the system. This work is validated by comparing the obtained results with analytic solutions. Moreover, a localization method of XFEM and level set method is proposed to increase the computing efficiency. The computation domain is reduced to the small region near the resin flow front. Therefore, the total computing time is strongly reduced by it. The efficiency test is made with a simple channel flow model. Several application examples are analyzed to demonstrate ability of this method.

• Journal of the Korean Vacuum Society
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• v.2 no.2
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• pp.236-245
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• 1993

Single crystals, SbSI : V, SbSeI : V, BiSI : V, BiSeI : V, SbSI : Cr, SbSeI : Cr, BiSI : Cr, BiSeI : Cr, SbSI : Ni, SbSeI : Ni, BiSI : Ni, and BiSeI : Ni were grown by the vertical Bridgman method. It is found that the grown single crystals have an orthorhombic structure and the indirect optical transitions. The temperature dependence of energy gap shows the two reflection point related with the phase transitions and is well fitted with Varshni equation in the continuous region. The optical absorption peaks due to the doped impurities (V, Cr and Ni) are respectively attributed to the electron transitions between the split energy levels of $V^{+2}$, $Cr^{+2}$ and $Ni^{+2}$ ions sited at $T_d$ symmetry of the host lattice.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.234-234
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• 2012

Saddle field ion source는 구조가 간단하고 영구자석을 사용하지 않아 소형화에 유리하고 구조가 간단한 DC 파워서플라이를 이용하기 때문에 장치 가격이 저렴하여 다양한 분야에서 응용되고 있으며 특히 이온빔 밀링 분야에 많이 사용된다. 초기 saddle field ion source 는 대칭형의 구형이었으나 지속적인 연구 개발로 와이어형, 원판형, 원통형 등 다양한 형태의 saddle field ion source가 개발되었다. 본 연구에서는 비교적 제작이 용이하고, 구조적으로 외부간섭에 대하여 덜 민감한 원통형 saddle field ion source를 제작하였다. 초기 saddle field ion source는 이온원 내부에 saddle field를 형성하기 위하여 대칭 구조를 가지 형태로 제작되었으나, 비대칭 구조에서도 saddle field가 형성될 수 있고 비대칭 구조를 채택할 경우 한쪽으로 더 많은 이온빔을 인출할 수 있기 때문에 실제 응용면에서는 비대칭 구조가 더 유리하다. 따라서 본 연구에서는 원통형 비대칭 saddle field ion source를 제작하였으며, 제작된 이온소스는 높이가 62 mm 지름이 55 mm의 소형 이온소스였다. 제작된 원통형 saddle field ion source는 진공도와 가속전압에 따라 방전 모드 변화하였다. Saddle field ion source는 전극과 extractor의 구조에 따라 조금씩 다르지만 대체로 5x10-5 Torr ~ 5x10-4 Torr 영역에서 안정적으로 작동하였다. 이온소스 내부의 압력이 높을 경우 수십 mA 의 방전 전류가 흐르는 고전류 방전 모드로 작동하였으며 압력이 낮을 경우에는 동일한 전압에서 수 mA 의 방전 전류만 흐르는 저전류 방전 모드로 작동하였다. 압력이 더 높아질 경우 아크 방전이 발생하여 이온소스의 작동이 불안정하여 연속적인 작동이 어려웠다. 고전류 방전 모드에서는 이온빔 전류가 Child-Langmuir 방정식에 따라 Vi3/2에 비례하여 증가하는 경향을 보여주었으며 저전류 방전 모드에서는 Vi에 선형적으로 증가하였다. 가속 전압이 동일한 경우 고전류 방전 모드가 저전류 방전 모드에 비하여 더 많은 이온빔 인출이 가능하지만, 고전류 방전 모드의 경우 이온의 방출 각도가 매우 넓은 반면 저전류 방전 모드에서는 이온빔의 퍼짐이 현저히 줄어듦을 관찰할 수 있었다. 원통형 saddle field ion source는 내부 구조가 간단하기 때문에 내부 전극의 구조 변화에 따라 방전 특성 및 이온빔 인출 특성이 심하게 변동하였다. Saddle field ion source에서는 Anode에 인가되는 방전 전압이 가속 전압과 같은 역할을 하는데 가속 전압은 2~10 kV 사이에서 인가가 가능하였다. 일반적으로 동일한 방전 모드에서 진공도가 높아질수록 방전 전류의 양과 인출되는 이온의 양이 증가하는 것이 관찰되었다. 제작된 이온소스는 최적 조건에서 5 mm 인출구를 통하여 0.7 mA의 이온빔 인출이 가능하였으며, 9 mm 인출구를 사용한 경우 1 mA까지 이온빔 인출이 가능하였다.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.7
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• pp.719-725
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• 2005

Anaerobic fill time and feeding pattern in SBR operation were investigated to find way of minimizing poor nitrogen removal efficiency in BNR process without external carbon addition. The three types of the modified SBR operations that were CO-SBR, IA-SBR, and SF-SBR were tested by lab-scale and pilot-scale SBR processes($2\;m^3/day$). In addition, practical equation for biological nitrogen removal was suggested and the equation considered the effect of ratio of fill volume over whole SBR volume and the ratio of step-feed in SBR. The denitrification efficiency of the SF-SBR was best among the three SBRs and followed by IA-SBR, and CO-SBR. The efficiency was 95%, 61%, and 19%, respectively. Looking at the change of sludge floc density by the length of anaerobic fill time, the density of sludge floc at 1 hour and 2 hours of anaerobic fill time were greater than 3 hours of one. The floc size distributions were $100{\sim}300\;{\mu}m$ and $200{\sim}400\;{\mu}m$ with respect to anaerobic fill time 2 hours and 3 hours, respectively.

• Journal of Korea Game Society
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• v.9 no.3
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• pp.107-119
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• 2009

Online games belong to a technology-oriented service industry that has emerged from the assimilation of game contents and communication networks in the respective realms of culture technology (CT) and information technology (IT). This study examines the individual acceptance of online games as entertainment-oriented technology based on the belief-attitude-intention paradigm and the underlying hedonic and utilitarian motivations. To measure the latent variables influencing the acceptance process, a structured questionnaire was developed based on the existing Technology Acceptance Model. Research model analysis and hypothesis testing were carried out using a structural equation model. Results indicated that latent variables reflecting hedonic and utilitarian characteristics had a significant influence on user behavior in the acceptance of online games. By uncovering the core factors in! fluencing the acceptance of online games and thereby theoretically verifying the latent variables influencing the acceptance of entertainment-oriented technology, this study provides strategic implications for business models by game companies aimed at attracting a large user base and dominating the market.

• Journal of Service Research and Studies
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• v.7 no.2
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• pp.17-41
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• 2017

The purpose of this research is to investigate the factors that impact customer satisfaction and loyalty in mobile payment services. Specifically, this research (1) studies the influence of company reputation on customer satisfaction and loyalty, (2) examines service quality dimensions that increase customer satisfaction, and (3) assesses switching barriers as moderators in influencing customer loyalty. Findings of this empirical research reconfirm the point of view that company reputation, service quality, and switching barriers are crucial for customer satisfaction in mobile payment services. The research methodologies that were used to verify the hypothesis in this study included customized surveys and structural equation modeling. The results demonstrated that company reputation significantly affects customer satisfaction and loyalty. Additionally, the results indicated that only two of the five total service qualities, ease of use and the security/privacy qualities, have positive influences on customer satisfaction. Customer satisfaction has also proven to be a significant influence on loyalty. Lastly, the results showed that among the factors of switching barriers, the factors of lost performance costs, sunk costs, setup costs, the attractiveness of alternatives, and service recovery have moderating effects on the relationships between customer satisfaction and loyalty. Base on the results, this research recommends that firms aim at devising integrated strategies that make switching barriers act as complements to customer satisfaction.

• The Journal of Engineering Geology
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• v.18 no.4
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• pp.381-391
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• 2008

The eigenvalue technique is introduced to overcome the problem of truncation errors caused by temporal discretization of numerical analysis. The eigenvalue technique is different from simulation in that only the space is discretized. The spatially discretized equation is diagonized and the linear dynamic system is then decoupled. The time integration can be done independently and continuously for any nodal point at any time. The results of eigenvalue technique are compared with the exact solution and FEM numerical solution. The eigenvalue technique is more efficient than the FEM to the computation time and the computer storage in the same conditions. This technique is applied to the solute transport analysis in nonuniform flow fields around underground storage caverns. This method can be very useful for time consuming simulations. So, a sensitivity analysis is carried out by using this method to analyze the safety of caverns from nearly located contaminant sources. According to the simulations, the reaching time from source to the nearest cavern may takes 50 years with longitudinal dispersivity of 50 m and transversal dispersivity of 5 m, respectively.

• Economic and Environmental Geology
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• v.43 no.6
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• pp.603-613
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• 2010

The Domi Basin in the South Sea of Korea is located between the Jeju Basin and Ulleung Basins, and is characterized by several sediment sags that are interested to have formed by crustal extension. This paper aims to derive an optimized seismic data processing procedure which helps stratigraphic interpretation of the Domi Basin. In particular, our data processing flow incorporated horizon velocity analysis (HVA) and surface-relative wave equation multiple rejection (SRWEMR) to improve the quality of stack section by enhancing the continuity of reflection events and suppressing peg-leg multiples respectively. As a result of processing procedures in this study, unconformities were recognized in the stack section that defines the early and middle Miocene, Eocene-Oligocene sequences. In addition, the overall quality of the stack section was increased as essential data to investigate the evolution of the basin. The suppression of multiple resulted in the identification of the Cretaceous basement. The data processing scheme evaluated through this study is expected to improve the standardization of processing sequences for seismic data from the Domi and adjacent Sora and north-Sora Basins.

• Journal of Korean Society of Steel Construction
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• v.23 no.4
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• pp.429-438
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• 2011

In this study, the explicit numerical algorithm was proposed to simulate the stress erection process and ultimate-load analysis of the strarch (stressed arch) system. The strarch system is a unique and innovative structural system and member prestress comprising prefabricated plane truss frames erected through a post-tensioning stress erection procedure. The flexible bottom chord, which has sleeve and gap details, is closed by the reaction force of the prestressing tendon. The prestress imposed on the tendon will enable the strarch system to be erected. This post-tensioning process is called "stress erection process." During this process, plastic rigid-body rotation occurs to the flexible top chord due to the excessive amount of plastic strain, and the structural characteristic is unstable. In this study, the dynamic relaxation method (DRM) was adopted to calculate the nonlinear equilibrium equation of the system, and a displacement-based finite-element-formulated filament beam element was used to simulate the nonlinear behavior of the top chord sections of the strarch system. The section of the filament beam element was composed by the amount of filaments, which can be modeled by various material models. The Ramberg-Osgood and bilinear kinematic elastic plastic material models were formulated for the nonlinear material behaviors of the filaments. The numerical results that were obtained in the present study were compared with the experiment results of the stress erection and with the results of the ultimate-load analysis of the strarch unit frame. The results of the present studies are in good agreement with the previous experiment results, and the explicit DRM enabled the analysis of the post-buckling behaviors of the strarch unit frame.

• Journal of the Korean Geotechnical Society
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• v.29 no.12
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• pp.35-44
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• 2013

In this study, a particle method without using grid was applied for analysing large deformation problems in soil flows instead of using ordinary finite element or finite difference methods. In the particle method, a continuum equation was discretized by various particle interaction models corresponding to differential operators such as gradient, divergence, and Laplacian. Soil behavior changes from solid to liquid state with increasing water content or external load. The Mohr-Coulomb failure criterion was incorporated into the particle method to analyze such three-dimensional soil behavior. The yielding and hardening behavior of soil before failure was analyzed by treating soil as a viscous liquid. First of all, a sand column test without confining pressure and strength was carried out and then a self-standing clay column test with cohesion was carried out. Large deformation from such column tests due to soil yielding or failure was used for verifying the developed particle method. The developed particle method was able to simulate the three-dimensional plastic deformation of soils due to yielding before failure and calculate the variation of normal and shear stresses both in sand and clay columns.