• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.3
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• pp.29-34
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• 2007

Numerical analyses are carried out to evaluate the cumulative impact damage of an automotive front end bumper under the low speed crash events(CMVSS215) by using explicit code. Results of first impact simulation, which are deformed shape, thickness, stress tensors and strain tensors, are used as the initial conditions for a next impact simulation. Between the events, the residual vibration is damped out by using nodal damping, and then recovery after each event is evaluated by several methods, one of which is a springback analysis with implicite finite element analysis code. The coupled analysis scheme for the evaluation of cumulative impact damage is verified through the comparison with test results.

• Journal of Korea Foundry Society
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• v.15 no.5
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• pp.514-522
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• 1995

The microstructural evolution with isothermal stirring during semi-solid state processing of hypoeutectic Al-6.2wt%Si alloy was studied. Substructure of the individual primary solid particle in the slurry was investigated through transmission electron microscopy(TEM). Formation of subgrain boundaries on the rheocast Al-6.2wt%Si alloy is observed and the misorientation between the grains is shown typically under 2 degrees by analyzing selected area diffraction (SAD) and convergent beam electron diffraction (CBED) patterns. The existence of high angle grain boundaries are also observed in the alloy. Based upon these observations, mechanisms for the primary particles fragmentation are considered. With isothermal stirring, the dislocation density increases, and the evolution of dislocation cell structure takes place, which is interpreted as a process of achieving uniform deformation by dynamic recovery under applied shear stress.

• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2302-2304
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• 1999

The application of polymeric insulators for outdoor use has been increasing as a new replacement of overhead line in abroad. In domestic case, it is actively going on the research of polymeric insulators. The Silicone rubber among polymeric insulators have a good electrical properties, due to surface hydrophobicity. This paper is concentrated on the recovery of surface hydrophobicity and the change of surface construction after electrical stress. The feature of silicone rubber, a good hydrophobicity, is demanded the improvement method as the estimation of the non-ceramic insulators like it.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.4
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• pp.485-500
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• 2000

In this paper the adaptive crack propagation analysis based on the estimated local and global error in the element-free Galerkin (EFG) method is presented. It is possible to keep consistency and accuracy of analysis in each propagation step by adaptive analysis. The adaptivity analysis in crack propagation is achieved by adding and removing the node along the background integration cell that are refined or recovered as estimated error. These errors are obtained by calculating the difference between the values of the projected stresses and original EFG stresses. To evaluate the performance of proposed adaptive procedure, the convergence behavior is investigated lot several examples. The results of these examples show the efficiency of proposed scheme in crack propagation analysis.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.376-379
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• 2005

High efficiency and low cost sustain driver for plasma display panel (PDP) with current fed is proposed. Main concept of the proposed circuit is using the current source to charge and discharge panel. As a result, all power switches can achieve the zero voltage switching (ZVS) and every auxiliary switch can also do the zero current switching (ZCS). Moreover, since the inductor current can compensate the discharge current, the current stress of all power switches can be reduced considerably. Furthermore, it has features as a simpler structure, less mass, less cost, and lower electromagnetic interference than prior circuit.

• Journal of Power Electronics
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• v.14 no.5
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• pp.882-889
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• 2014

This paper presents a zero voltage switching (ZVS) converter with three resonant tanks. The main advantages of the proposed converter are its ability to reduce the switching losses on the power semiconductors, decrease the current stress of the passive components at the primary side, and reduce the transformer secondary windings. Three resonant converters with the same power switches are adopted at the low voltage side to reduce the current rating on the transformer windings. Using a series-connection of the transformer secondary windings, the primary side currents of the three resonant circuits are balanced to share the load power. As a result, the size of both the transformer core and the bobbin are reduced. Based on the circuit characteristics of the resonant converter, the power switches are turned on at ZVS. The rectifier diodes can be turned off at zero current switching (ZCS) if the switching frequency is less than the series resonant frequency. Therefore, the reverse recovery losses on the rectifier diodes are overcome. Experiments with a 1.6kW prototype are presented to verify the effectiveness of the proposed converter.

• Journal of Advanced Marine Engineering and Technology
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• v.12 no.1
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• pp.53-61
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• 1988

Most of the recent for the flow field hydrofoil in partially cavitating condition are the ones which are linearized, and the problem of cavity end region for hydrofoil is not verified. This paper deals with a study on characteristics of end region flow field for partially cavitating hydrofoil by using a characteristics of shear turbulence flow and nonlinear cavity flow theory. The results obtained as follows : 1) Shear layer thickness is decreased gradually going to the end section of hydrofoil. When attack angle is large, it is appeared largely at the region of partial cavitation after its collapsing. 2) The fluctuation velocity of a second-degree relative direction have minimum value at the front of hydrofoil or at the end of hydrofoil. The difference for the validity of attack angle is appeared largely at the surrounding of .chi.$_{e}$ point. 3) The fluctuation velocity of transverse direction decrease from the maximum thickness of cavitation to the end of hydrofoil, but it undergoes largely the effect of pressure recovery. The difference is larger at the region of partial cavitation after its collapsing than at the of hydrofoil. 4) The distribution of Reynolds stress have maximum values at the region of partial cavitation after its collapsing and the end of foil, and the larger attack angle, the larger the distribution of value.e.

• Journal of Korean Academy of Fundamentals of Nursing
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• v.16 no.1
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• pp.92-102
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• 2009

Purpose: Relocation stress is a common phenomenon in patients discharged from an intensive care unit(ICU) to a ward. Therefore, nurses need to be aware of the problems that can arise during the transfer process. The aim of this study was to identify nurses' experiences in transferring critically ill patients from the ICU to a ward. Method: Focus group interviews were done with 13 nurses from wards and ICU, which participated in receiving and sending of ICU patients. The debriefing notes and field notes were analyzed using the consistent comparative data analysis method. Result: Seven major categories were identified in the analysis of the data. These were 'mixed feeling about transfer', 'lack of transfer readiness', 'increase in family burden', 'uncertainty with unfamiliar environment', 'difficulty in decision making', 'difference of perception of the relationships between patients and health care providers', 'need for continuity of nursing care'. Conclusion: Transferring out of the critical care area should be presented to the patient and family as a positive step in the recovery process. However, a more universal method of passing information from nurse to nurse is needed to assist in a smooth transition.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.1
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• pp.99-107
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• 2008

There are being a lot of studies for achievement of high speed Dehydration, high-strength and Lightweight of washing machine in the latest washing machine business. It is essential that strength of mechanical press-Joining (MPJ) for spin drum is improved to attain that target. MPJ of spin drum is composed of seaming and caulking process. Because Seaming process of MPJ has various design factors such as thickness, bending radius, seaming width, caulking press width and the dynamic factor such as multistage plastic working, elastic recovery, residual stress, the optimum conditions can't be easily determined. Using a design of experiment (DOE) based on the FEM (Finite Element Method), which has several advantages such as less computing, high accuracy performance and usefulness, this study was performed investigating the interaction effect between the various design factor as well as the main effect of the each design factor during drum MPJ and proposed optimum condition using center composition method among response surface derived from regression equation of simulation-based DOE.

• Journal of Power Electronics
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• v.17 no.3
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• pp.579-589
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• 2017

In this study a new high step-up dc-dc converter is presented. The operation of the proposed converter is based on the capacitor switching and coupled inductor with a single active power switch in its structure. A passive voltage clamp circuit with two capacitors and two diodes is used in the proposed converter for elevating the converter's voltage gain with the recovered energy of the leakage inductor, and for lowering the voltage stress on the power switch. A switch with a low $R_{DS}$ (on) can be adopted to reduce conduction losses. In the generalized mode of the proposed converter, to reach a desired voltage gain, capacitor stages with parallel charge and series discharge techniques are extended from both sides of secondary side of the coupled inductor. The proposed converter has the ability to alleviate the reverse recovery problem of diodes with circuit parameters. The operating principle and steady-states analyses are discussed in detail. A 40W prototype of the proposed converter is implemented in the laboratory to verify its operation.