• Journal of Power Electronics
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• v.6 no.1
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• pp.83-93
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• 2006

A new high efficiency and low profile on-board DC/DC converter for digital car audio amplifiers is proposed. The proposed converter shows low conduction loss due to the low voltage stress of the secondary diodes, a lack of DC magnetizing current for the transformer, and a lack of stored energy in the transformer. Moreover, since the primary MOSFETs are turned-on under zero-voltage-switching (ZVS) conditions and the secondary diodes are turned-off under zero-current-switching (ZCS) conditions, the proposed converter has minimized switching losses. In addition, the input filter can be minimized due to a continuous input current, and an output inductor is absent in the proposed converter. Therefore, the proposed converter has the desired features, high efficiency and low profile, for a viable power supply for digital car audio amplifiers. A 60W industrial sample of the proposed converter has been implemented for digital car audio amplifiers with a measured efficiency of $88.3\%$ at nominal input voltage.

• Structural Engineering and Mechanics
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• v.87 no.2
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• pp.107-116
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• 2023

The three-dimensional Hashin criterion and user subroutine VUMAT were used to simulate the damage in the composite layer, and the secondary stress criterion was used to simulate the interlayer failure of the cohesive element of the bonding layer and the propagation characteristics under the layer. The results showed that when the shear stress wave (shear wave) propagates on the surface of the laminate, the stress wave attenuation along the fiber strength direction is small, and thus producing a large stress profile. When the compressive stress wave (longitudinal wave) is transmitted between the layers, it is reflected immediately instead of being transmitted immediately. This phenomenon occurs only when the energy has accumulated to a certain degree between the layers. The transmission of longitudinal waves is related to the thickness and the layer orientation. Along the symmetry across the thickness direction, the greater is the stress amplitude along the layer direction. Based on the detailed investigation on the impact on various laminated composites carried out in this paper, the propagation characteristics of stress waves, the damage and the destruction of laminates can be explained from the perspective of stress waves and a reasonable layering sequence of the composite can be designed against damage and failure from low velocity impact.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.11a
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• pp.123-124
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• 2010

• Journal of the Optical Society of Korea
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• v.7 no.1
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• pp.13-19
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• 2003

The effects of strain distribution in quantum wire arrays have been analyzed using a finite-element method including both the hydrostatic and shear strain components. Their effects on the optical properties of the quantum wire arrays are assessed for various types of stress profiles by calculating the optical gain and the polarization dependence. The results show unique polarization dependency, which can be exploited either for the single polarization or the polarization-independent operation in quantum wire photonic devices.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.2
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• pp.115-119
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• 2016

Winding is one of the major processes in roll-to-roll systems. Taper tension profile in a winding determines the distribution of stress in the radial direction, i.e., the radial stress in the wound rolls. Maximum radial stress is major cause of material defect, and this study has been actively proceeded. Traditional models of radial stress model were focused on flexible and light substrate. In this study, we developed an advanced radial stress model including effects of both these parameters(weight and stiffness) on the radial stress. The accuracy of the developed model was verified through FEM(Finite Element Method) analysis. FEM result of maximum radial stress value corresponds to 99 % in comparison to result with the model. From this study, the material defects does not occur when the steel winding. And steel industry can be applied to improve the winding process.

• Journal of Welding and Joining
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• v.16 no.2
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• pp.111-121
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• 1998

It is well recognized that a excessive temperature gradient from the junction of head to skirt in axial direction in a hot pressure vessel can cause unpredicted high thermal stress at the junction and/or in axial direction of a skirt. this thermal stress resulting from axial thermal gradient may be a major cause of unsoundness of structural integrity. In case of cyclic operation of hot pressure vessels, the thermal stress becomes one of the primary design consideration because of the possibility of fracture as a result of cyclic thermal fatigue and progressively incremental plastic deformation. To perform thermal stress analysis of the junction and cylindrical skirt of a vessel, or, at least, to inspect quantitatively the magnitude and effect of thermal stress, the temperature profile of the vessel and skirt must be known. This paper demonstrated the temperature distribution and thermal stress analysis for the junction of skirt to head using F.E. analysis. Effect of air pocket in crotch space was quantitatively investigated to minimize the temperature gradient causing the thermal stress in axial direction. Effect of the skirt height on thermal stresses was also studied. Analysis results were compared with theoretical formulas to verify th applicability to the strength calculation in design field.

• Journal of Korean Academy of Nursing
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• v.29 no.4
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• pp.855-869
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• 1999

The purpose of this study was to test the effectiveness of self-management relaxation training through biofeedback and progressive muscle relaxation methods. The effectiveness of the experimental methods was tested by measuring the degree of symptoms of stress (SOS), the McNair's profile of Mood States (POMS), the levels of ephinephrine, norepinephrine, pulse rate, blood pressure and natural killer cells. The subjects of this study were sixty six nursing students divided into four groups : two groups were the biofeedback and progressive muscle relaxation groups, the other two groups served as control groups. One was a group of sophomores with no experience at all, the other a junior group without self -management or relaxation training. This study was conducted for eight weeks of clinical practice from April, 26th 1998 to June, 20th 1998. Biofeedback training was done with software developed by J&J company (1-410 form for abdominal respiration training). Progressive muscle relaxation training was done with u audiotape recorded according to Jacobson's Theory. The data were analyzed with frequencies, means, and analysis of covariance using the SPSS program and the significance level of statistics was 5%. The results of the study are : 1) The importance of clinical practice stress reduction is shown in that the level of symptoms of stress in the experimental groups in clinical practice was higher than in the group receiving only a lecture. 2) The relaxation training methods of biofeedback and progressive muscle relaxation were effective in reducing the symptoms of stress under the clinical practice stress conditions. 3) The effectiveness of the biofeedback training relaxation method to reduce symptoms of stress was higher than that of progressive muscle relaxation. 4) The relaxation training methods of biofeedback and progressive muscle relaxation were effective in reducing stressful mood states. 5) The relaxation training methods of biofeedback and progressive muscle relaxation were not effective in reducing epinephrine and norepinephrine levels. 6) The relaxation training methods of biofeedback and progressive muscle relaxation were effective in increaing the number of natural killer cells. 7) The relaxation training methods of biofeedback and progressive muscle relaxation were effective in decreasing high systolic and diastolic values of blood pressure and high pulse rates. In summary, the relaxation methods of biofeedback and progressive muscle relaxation in reducing clinical practice stress were effective in lowering the level of symptoms of stress and the profile of stressful mood states. They were also effective in lowering high blood pressure and pulse rates. The relaxation methods were effective in increasing the number of natural killer cells as part of the immune function. However, relaxation methods were not effective in reducing the catecholamine level. The biofeedback training method for reduction of symptoms of stress was more effective than the progressive muscle relaxation method.

• Advances in concrete construction
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• v.8 no.4
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• pp.335-349
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• 2019

To investigate the axial compressive performance of the recycled aggregate concrete (RAC) filled glass fiber reinforced polymer (GFRP) tube and profile steel composite columns, static loading tests were carried out on 18 specimens under axial loads in this study, including 7 RAC filled GFRP tube columns and 11 RAC filled GFRP tube-profile steel composite columns. The design parameters include recycled coarse aggregate (RCA) replacement percentage, profile steel ratio, slenderness ratio and RAC strength. The failure process, failure modes, axial stress-strain curves, strain development and axial bearing capacity of all specimens were mainly analyzed in detail. The experimental results show that the GFRP tube had strong restraint ability to RAC material and the profile steel could improve the axial compressive performance of the columns. The failure modes of the columns can be summarized as follow: the profile steel in the composite columns yielded first, then the internal RAC material was crushed, and finally the fiberglass of the external GFRP tube was seriously torn, resulting in the final failure of columns. The axial bearing capacity of the columns decreased with the increase of RCA replacement percentage and the maximum decreasing amplitude was 11.10%. In addition, the slenderness ratio had an adverse effect on the axial bearing capacity of the columns. However, the strength of the RAC material could effectively improve the axial bearing capacity of the columns, but their deformability decreased. In addition, the increasing profile steel ratio contributed to the axial compressive capacity of the composite columns. Based on the above analysis, a formula for calculating the bearing capacity of composite columns under axial compression load is proposed, and the adverse effects of slenderness ratio and RCA replacement percentage are considered.

• The Journal of Korean Academy of Prosthodontics
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• v.52 no.4
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• pp.279-286
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• 2014

Purpose: The aim of this study was to investigate the effect of implant thread profile on the marginal bone stresses which develop during implant insertion. Materials and methods: Four experimental implants were created by placing four different thread systems on the body ($4.1mm{\times}10mm$) of the ITI standard implant. The thread types studied in this study included the buttress, v-shape, reverse buttress, and square shape threads. In order to examine the insertion stress generation, 3D dynamic finite element analysis was performed which simulated the insertion process of implants into a 1.2 mm thick cortical bone plate (containing 3.5 mm pilot hole) using a PC-based DEFORM 3D (ver 6.1, SFTC, Columbus, OH, USA) program. Results: Insertion stresses higher than human cortical bone developed around the implants. The level of insertion stresses was much different depending on the thread. Stress level was lowest near the v-shape thread, and highest near the square shaped thread. Difference in the interfacial bone stress level was more noticeable near the valley than the tip of the threads. Conclusion: Among the four threads, the v-shape thread was turned out to minimize the insertion stress level and thereby create better conditions for implant osseointegration.

• Journal of Welding and Joining
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• v.35 no.1
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• pp.55-60
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• 2017

There are many Industry Code and Standard (ICS) for Structural Integrity Assessment (SIA) on welded structure with defect. The general ICSs, such as R6, BS 7910 and API 579-1/ASME FFS-1, provide equations to determine the upper bound residual stress profiles based on collections from many literatures. However, these residual stress profiles used in the SIA cause the conservative design for welded structures. In this study, the structural integrity assessment for girth weld in pipeline has been conducted based on fracture mechanics. In addition, thermo-elastic plastic FE analysis was performed for evaluating the residual stress of girth weld in pipeline. The weight function solution is used to determine the stress intensity factor using the residual stress profile obtained by the FE analysis. This approach can account for redistribution and relaxation of residual stress as the defects grow. In order to the evaluate quantitative comparison between BS 7910 and weight function solution, structural integrity assessment determining allowable crack size on cracked pipe was performed with failure assessment diagram.