• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.12
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• pp.1828-1835
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• 2012

In this paper, a conceptual design and a detailed design of novel cylindrical magnetic levitation stage is introduced. This is came from planar-typed magnetic levitation stage. The proposed stage is composed of cylinder-typed permanent magnet array and semi-cylinder-typed 3 phase winding module. When a proper current is induced at winding module, a magnetic levitation force between the permanent magnet array and winding module is generated. The proposed stage can precisely move the cylinder to rotations and translations as well as levitations with the magnetic levitation force. This advantage is useful to make a nano patterning on the surface of cylindrical specimen by using electron beam lithography under vacuum. Two methods are used to calculate required magnetic levitation forces. The one is 2D FEM analysis, the other is mathematical modeling. This paper shown that results of two methods are similar. An assistant plate is introduced to reduce required currents of winding module for levitations in vacuum. The mathematical model of cylindrical magnetic levitation stage is used for dynamic simulation of magnetic levitations. A lead-lag compensator is used for control of the model. Simulation results shown that the detail designed model of the cylindrical magnetic levitation stage with the assistant plate can be controlled very well.

• Restorative Dentistry and Endodontics
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• v.20 no.2
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• pp.432-461
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• 1995

The basic principles in the design of Class II amalgam cavity preparations have been modified but not changed in essence over the last 90 years. The early essential principle was "extension for prevention". Most of the modifications have served to reduce the extent of preparation and, thus, increase the conservation of sound tooth structure. A more recent concept relating to conservative Class II cavity preparations involves elimination of occlusal preparation if no carious lesion exists in this area. To evaluate the ideal ClassII cavity preparation design, if carious lesion exists only in the interproximal area, three cavity design conditions were studied: Rodda's conventional cavity, simple proximal box cavity and proximal box cavity with retention grooves. In this study, MO amalgam cavity was prepared on maxillary first premolar. Three dimensional finite element models were made by serial photographic method. Linear, eight and six-nodal, isoparametric brick elements were used for the three dimensional finite element model. The periodontal ligament and alveolar bone surrounding the tooth were excluded in these models. Three types model(B option, Gap option and R option model) were developed. B option model was assumed perfect bonding between the restoration and cavty wall. Gap option model(Gap distance: $2{\mu}m$) was assumed the possibility of play at the interface simulated the lack of real bonding between the amalgam and cavity wall (enamel and dentin). R option model was assumed non-connection between the restoration and cavty wall. A load of 500N was applied vertically at the first node from the lingual slope of the buccal cusp tip. This study analysed the displacement, 1 and 2 direction normal stress and strain with FEM software ABAQUS Version 5.2 and hardware IRIS 4D/310 VGX Work-station. The results were as followed. 1. Rodda's cavity form model showed greater amount of displacement with other two models. 2. The stress and strain were increased on the distal marginal ridge and buccopulpal line angle in Rodda's cavity form model. 3. The stress and strain were increased on the central groove and a part of distal marginal ridge in simple proximal box model and proximal box model with retention grooves. 4. With Gap option, Rodda's cavity form model showed the greatest amount of the stress on distal marginal ridge followed by proximal box model with retention grooves and simple proximal box model in descending order. 5. With Gap option, simple proximal box model showed greater amount of stress on the central groove with proximal box model with retention grooves. 6. Retention grooves in the proximal box played the role of supporting the restorations opposing to loads.

• Proceedings of the Technology Innovation Conference
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• 1996.12a
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• pp.265-295
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• 1996

This paper investigates empirically the relationship between various business portfolio properties (particularly technological properties) and chaebol′s performance using data on the 50 largest chaebols in Korea. In addition to the traditional indexes to measure diversification such as entropy index we calculated inter-industry technological similarity using R&D expenditure data by industry and 1990 Input-output Table in Korea, and obtained chaebol-level technological relatedness and internal transaction proportion from chaebols′business profile, inter-industry technological similarity and 1990 input-output table. We applied factor analysis on 13 business portfolio property indexes and showed that they could be grouped into 3 dimensions, diversification scope, inter-business relatedness and degree of vertical integration. In this paper, using 50 largest chaebols′financial data (1989-1994), we analyzed empirically the effect of business portfolio properties on ROS (Return On Sales) which is conventional index for firm performance and on TFP(Total Factor Productivity) growth which is a pure measure of firm performance. To utilize the advantage of panel data, FEM(Fixed Effect Model) and REM(Random Effect Model) were used. The empirical result shows that the entropy index as a measurement of inter-business relatedness is not significant but technological relatedness index is significant. OLS estimates on pooled data were considerably different from FEM or REM estimates on panel data. By introducing interaction effect among the three variables for business portfolio properties, we obtained three findings. First, only VI (Vertical integration) has a significant positive correlation with ROS. Second, when using TFP growth as an dependent variable, both TR(Technological Relatedness) and f[ are significant and positively related to the deepened variable. Third, the interaction term between TR and VI is significant and negatively affects TFP growth, meaning that TR and VI are substitutes. These results suggest strategic directions on restructuring business portfolio. As VI is increased, chaebols will get more profit. A higher level of either TR or W will increase TFP growth rate. but increase in both TR and VI will have a negative effect on TFP growth. To summarize, certain business portfolio properties such as VI and TR can be considered "resources" themselves since they can affect profit rate and productivity growth. VI and TR have a synergy effect of change in profit rate and productivity growth. VI increases ROS and productivity growth, while TR increases productivity growth representing a technological synergy effect.

• Journal of Biosystems Engineering
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• v.28 no.4
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• pp.305-314
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• 2003

The ROPS of an agricultural tractor is designed to protect its driver when the tractor overturns. Although the current OECD tests to determine whether the ROPS meets the requirements of the OECD regulation are desirable, they need long time to test. We experimental time and effort by using CAE. We conducted a finite element analysis for the ROPS design of a Dae-Dong tractor cabin in an attempt to reduce the design and manufacturing time. This study shows the interpretative skill using MARC(v.2000) for designing ROPS and difference between the results of testing and FEA. Design process is generally divided into two phases: a concept and a detail design. The concept design uses simple analysis to predict structural behavior, whereas the detail design involves a finite element analysis performed by the results of the concept design. This study focused on the detail design and used Patran(v.2000r2) and MARC(v.2000) of the MSC software corporation. The model consisted of 4812 elements and 4582 nodes. Four tests. specified in the OECD standards, were performed: (1) longitudinal loading test (2) rear crushing test (3) side loading test (4), and front crushing test. Independent analyses were also performed for each test, along with a sequential analysis. When compared, the results of the independent and sequential analyses were found to be similar to the test results.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.4
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• pp.325-334
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• 2008

Statement of problem & Purpose: The purpose of this study was to investigate the effect of a mouth guard material properties on the skull and brain when they were under impact loads on mandible. Material and methods: Two customized mouth protectors having different material propeerst ieach other were made for a female Korean who had no history of brain trauma, no cerebral diseases, nomal occlusion and natural dentition. The 3D finite element model of human skull and brain scanned by means of computed tomography was constructed. The FEM model of head was composed of 407,825 elements and 82,138 nodes, including skull, brain, maxilla, mandible, articular disc, teeth and mouth guard. The stress concentrations on maxillary teeth, maxilla and skull with two mouth guards were evaluated under oblique impact load of 800N onto mandibular 3 loading points for 0.1sec. And the brain relative displacement was compared in two different mouth guard materials under same condition. Result and Conclusion: The results were as follows; 1. In comparison of von Mises stress on maxillary teeth, a soft mouth guard material had significantly lower stress values on measuring point than a hard mouth protector materials (P < .05). 2. In comparison of von Mises stress on maxilla and skull, A soft mouth protector material had significantly lower stress values on measuring point than a hard mouth protector materials (P < .05). 3. For impact loads on mandible, there were more stress concentrated area on maxilla and skull with hard mouth guard than soft with mouth protector. 4. For impact loads on mandible, brain relative displacement had little relation with mouth guard material properties. In results of this study, soft mouth guard materials were superior to hard mouth guard materials for mandible impact loads for prevention of sports injuries. Although the results of this study were not enough to figure out the roles of needed mouth guard material properties for a human head, we got some knowledge of the pattern about stress concentration and distribution on maxilla and skull for impact loads with soft or hard mouth protector. More studies are needed to substantiate the relationship between the mouth guard materials and sports injuries.

• Journal of the Society of Disaster Information
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• v.14 no.3
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• pp.379-386
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• 2018

Purpose: This study was to the fragility evaluation of I-shape curved beam structure subjected to strong ground motions including Gyeongju and Pohang earthquakes Method: In particular, to conduct the analytical model, ABAQUS and ANSYS platform was used in this study. Furthermore, the analytical model using 3D Finite Element Model (FEM) was validated, in comparison to the theoretical solutions at the location of 025L, 05L, and 0.75L in static loading condition. In addition, in order to evaluate the seismic fragility of the curved beam structure, 20 seismic ground motions were selected and Monte-Carlo Simulation was used for the empirical fragility evaluation from 0.2g to 1.5g. Result: It was interesting to find that the probability of the system failure was found at 0.2g, as using 190 MPa limit state and the probability of the failure using 390 MPa limit state was starting from 0.6g. Conclusion: This study showed the comparison of the theoretical solution with analytical solution on I-shaped curved beam structures and it was interesting to note that the system subjected to strong ground motions was sensitive to high frequency earthquake. Further, the seismic fragility corresponding to the curved beam shapes must be evaluated.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.1
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• pp.205-215
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• 2006

In this study 3-D shell FEM model was applied to analyze the behavior of curved steel box girders stiffened by diaphragms. The reliability of the analytical method has been proved by comparing with the existing results. It was also found from this analysis that main factors affecting a distortional stress are length of a girder, curvature of the girder, and spacing of diaphragms. A modelled bridge with 30m of span length and 40m of radius was analyzed to find an optimum spacing of diaphragm, and as a result of applying different spacings, 5m was found to be most appropriate to control the stress ratio regulated by specifications. In the effect of diaphragm shape, the rhamen-typed diaphragm is found to be more effective than the fully filled-up one in the range of opening ratio of 0.4 to 0.6. But, the fully filled-up diaphragm had more efficiency in terms of reducing the distortional stress than X-truss typed diaphragm.

• Journal of the Korean Institute of Gas
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• v.20 no.5
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• pp.82-88
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• 2016

Resource development is needed in order to develop the industry. However, because resources are running out, there is a growing interest in the arctic regions. If you want to develop resources in cold regions, it is necessary to understand the environment there and it should be a priority to secure proper technology for construction. In particular, thaw settlement, which frequently occur in Arctic regions, have a fatal effect on essential pipeline needed to transport resources. Therefore, it is important to analyze how piping will be impacted by thaw settlement. In this study, we developed 3-D FEM model in order to analyze the influence of the buried depth of the pipe at the time of thaw settlement. We analyzed a displaced pipe which is subjected to stress and considered Elasto-plastic, using the finite element analysis according to these Arctic environments.

• 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 Korea Concrete Institute
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• v.24 no.3
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• pp.285-292
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• 2012

Fixed connection is generally used for beam and column connections of concrete structures, but significant damages at the connection due to severe earthquakes have been reported. In order to reduce damages of the connection and improve seismic performance of the connection, several innovative connections have been suggested. One newly proposed connection type allows a rotation of the connection for applications in rotating or rocking beams, columns, and shear walls. Such structural elements would provide a nonlinear lateral force-displacement response since their contact depth developed during rotation is gradually reduced and the stress across the sections of the elements is non-linearly distributed around a contact area, which is called an elastic hinge region in the present study. The purpose of the present study is to define the elastic hinge region or length for the rocking columns, through investigating the cross-sectional stress distribution during their lateral behavior. Performing a finite element analysis (FEA), several parameters are considered including axial load levels (5% and 10% of nominal strength), different boundary conditions (confined-ends and cantilever types), and slenderness ratios (length/depth = 5, 7, 10). The FEA results showed that the elastic hinge length does not directly depend on the parameters considered, but it is governed by a contact depth only. The elastic hinge length started to develop after an opening state and increased non-linearly until a rocking point(pre-rocking). However, the length did not increase any more after the rocking point (post-rocking) and remained as a constant value. Half space model predicting the elastic hinge length is adapted and the results are compared with the numerical results.