• Journal of the Society of Naval Architects of Korea
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• v.33 no.1
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• pp.98-108
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• 1996

In the reliability analysis of general structures, the limit state equations are implicit and cannot be described in closed form. Thus, sampling methods such as the Crude Monte-Carlo simulation, and probabilistic FEM are often used, but these methods are not so effective in view of computational cost, because a number of structural analysis are required and the derivatives must be calculated for probabilistic FEM. Alternatively the response surface approach, which approximates the limit state surface by using several results of structural analysis in the region adjacent to MPFP, could be applied effectively. In this paper, the central composite design, Bucher-Bourgund method and the approximation method using artificial neural network are studied for the calculation of probability of failure by the response surface method. Through the example comparisons, it is found that Bucher-Bourgund method is very effective and Neural network method for the reliability analysis is comparable with other methods. Specially, the central composite design method is found to be rational and useful in terms of mathematical consistency and accuracy.

• Journal of the Korean Data and Information Science Society
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• v.21 no.2
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• pp.251-262
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• 2010

While outsourcing has become a basic strategy of the information system adoption, there is an emerging needs to analyze the gap between the required data and the existing data for the new system from an adopting company's perspective. In CRM adoption failure cases, the first reason is adopting company pay no attention to the data that will support investment and systems. So far, there is no attempt to consider data driven approach in information system adoption field. Hence, we propose Information System Adoption Model based on Data (ISAMD) and show how to use in real world by simulation. By using ISAMD, information system adoption decision maker can simulate the needed data and related cost with various information system alternatives in short term, and long term planning. ISAMD can prevent the possible threat of unexpected data cost in adopting new system at the adopting decision stage.

• Journal of the Korean Geotechnical Society
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• v.20 no.9
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• pp.65-75
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• 2004

In this paper, a mechanism of the soil structure reinforced by geosynthetics is discussed. The reinforcing mechanism is interpreted as an effect arising from the reinforcement works preventing the dilative deformation (negative dilatancy) of soil under shearing. A full-scale in-situ model test was carried out in Kanazawa of Japan (1994), and in the laboratory test the strength and the characteristics of deformation conducting a constant volume shear test are examined. The parameters needed in the FEM are also applied by using the experimental data. The elasto-plastic finite element simulation is carried out, and the results are quantitatively compared with that of experiment. As a results, it is known that the theoretical predictions could explain effectively the experimental results which are obtained by a full-scale in-situ model test.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.3
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• pp.45-52
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• 2006

In this paper, we analyze on the effect of LCR filter to mitigate transient overvoltage on the high voltage induction motor fed by H-bridge cascaded 7-level inverter. The switching surge voltage that it was occurred in inverter appears transient overvoltage at the motor input terminal. the transient overvoltage becomes the major cause to occur the insulation failure by serious voltage stress in the stator winding of high voltage induction motor. The effect of transient overvoltage appears more serious in high voltage induction motor than low voltage induction motor. We selected LCR filter for reduction of the transient overvoltage. Consequently, we demonstrated that the LCR filter connected to the invertor output terminals greatly reduces the transient voltage stress and ringing. The results of simulation show the suppression of transient overvoltage at the motor end of a long cable. using EMTP

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.10a
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• pp.808-811
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• 2015

Cognitive radio has been proposed as a promising dynamic spectrum allocation paradigm. In cognitive radio, spectrum sensing is a fundamental procedure that enables secondary users (unlicensed) employing unused portion of spectrum of primary users (licensed) without causing harmful interference. However, the performance of single-user spectrum-sensing scheme was limited by fading, noise uncertainty shadowing and hidden node problem. Cooperative spectrum sensing was proposed to mitigate these problem. In this paper, we observe cooperative sensing scheme with energy detection using three adaptive thresholds for local decision, which can mitigate sensing failure problem and improve sensing performance at local node. In cooperative scheme we employed OR rules as decision combining at fusion center. We evaluate our scheme through computer simulation, and the results show that with OR combination rule our scheme can achieve best performance than other schemes.

• Progress in Superconductivity and Cryogenics
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• v.19 no.3
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• pp.44-48
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• 2017

Current lead is a device that connects the power supply and superconducting magnets. High temperature superconductor (HTS) has lower thermal conductivity and higher current density than normal metal. For these reasons, the heat load can be reduced by replacing the normal metal of the current lead with the HTS. Conventional HTS current lead has same cross-sectional area in the axial direction. However, this is over-designed at the cold-end (4.2 K) in terms of current. The heat load can be reduced by reducing this part because the heat load is proportional to the cross-sectional area. Therefore, in this paper, heat load was calculated from the heat diffusion equation of HTS current leads with uniform and non-uniform cross-sectional areas. The cross-sectional area of the warm-end (65K) is designed considering burnout time when cooling system failure occurs. In cold-end, Joule heat and heat load due to current conduction occurs at the same time, so the cross-sectional area where the sum of the two heat is minimum is obtained. As a result of simulation, current leads for KSTAR TF coils with uniform and non-uniform cross-sectional areas were designed, and it was confirmed that the non-uniform cross-sectional areas could further reduce the heat load.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.2
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• pp.87-94
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• 2014

In solid mechanics, the peridynamics theory has provided a suitable framework for material failure and damage propagation simulation. Peridynamics is computationally expensive since it is required to solve enormous nonlocal interactions based upon integro-differential equations. Thus, multiscale coupling methods with other local models are of interest for efficient and accurate implementations of peridynamics. In this study, peridynamic models are restricted to regions where discontinuities or stress concentrations are present. In the domains characterized by smooth displacements, classical local models can be employed. We introduce a recently developed blending scheme to concurrently couple bond-based peridynamic models and the Navier equation of classical elasticity. We demonstrate numerically that the proposed blended model is suitable for point loads and static fracture, suggesting an alternative framework for cases where peridynamic models are too expensive, while classical local models are not accurate enough.

• Structural Engineering and Mechanics
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• v.75 no.6
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• pp.643-657
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• 2020

This study presents experimental and numerical investigations on circular steel tube confined ultra high performance concrete (UHPC) columns under axial compression. The plain UHPC without fibers was designed to achieve a compressive strength ranged between 150 MPa and 200 MPa. Test results revealed that loading on only the UHPC core can generate a significant confinement effect for the UHPC core, thus leading to an increase in both strength and ductility of columns, and restricting the inherent brittleness of unconfined UHPC. All tested columns failed by shear plane failure of the UHPC core, this causes a softening stage in the axial load versus axial strain curves. In addition, an increase in the steel tube thickness or the confinement index was found to increase the strength and ductility enhancement and to reduce the magnitude of the loss of load capacity. Besides, steel tube with higher yield strength can improve the post-peak behavior. Based on the test results, the load contribution of the steel tube and the concrete core to the total load was examined. It was found that no significant confinement effect can be developed before the peak load, while the ductility of post-peak stage is mainly affected by the degree of the confinement effect. A finite element model (FEM) was also constructed in ABAQUS software to validate the test results. The effect of bond strength between the steel tube and the UHPC core was also investigated through the change of friction coefficient in FEM. Furthermore, the mechanism of circular steel tube confined UHPC columns was examined using the established FEM. Based on the results of FEM, the confining pressures along the height of each modeled column were shown. Furthermore, the interaction between the steel tube and the UHPC core was displayed through the slip length and shear stresses between two surfaces of two materials.

• Journal of Aerospace System Engineering
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• v.11 no.5
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• pp.28-35
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• 2017

Magnetic Suspension and Balance System (MSBS) demonstrates the capacity to levitate an experimental model absent any mechanical contact using magnetic forces and moments. It allows precise control of position and attitude of the model, and measures external forces and moments acting on the model. For the purpose of acquisition of reliable experimental results under stable and safe conditions, the performance and robustness of the position and attitude control system of MSBS needs to be improved. To this end, Iterative Feedback Tuning (IFT) and L1 adaptive output feedback algorithm were employed to automatically increase command following performance and to ensure robust operation of MSBS with failure of electric power supply. The applicability was validated using computational simulation.

• Journal of Institute of Control, Robotics and Systems
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• v.15 no.9
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• pp.877-880
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• 2009

A curing process in post-printing section of R2R process is required for an electrical property of the printed pattern when devices such as RFID, Solar cell are printed. PEN as well as heat-stabilized PET which is used as a plastic substrate would be deformed at high temperature due to change of its elastic modulus. And crack in the printed pattern, which is on the plastic substrate is occurred due to the deformation of the substrate. The occurrence of crack causes electrical resistance to increase and the quality of the device to deteriorate. In case of RFID antenna, the range of reading distance is shortened as the electrical resistance of the antenna is increased. Therefore, the deformation of the plastic substrate, which causes the occurrence of crack, should be minimized by setting up low operating tension in R2R process. In low tension, slippage between a moving substrate and a roller would be generated when the operating speed is increased. And scratch would be occurred when slippage is generated due to an air entrainment, which is related to the thickness of the air film. The thickness of the air film is increased when operating speed is increased as shown by simulation based on mathematical model. The occurrence of scratch in conductive pattern printed by roll to roll process is a critical damage because it causes degradation or failure of electrical property of it.