• Proceedings of the KIEE Conference
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• 2000.07b
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• pp.1165-1167
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• 2000

This paper describes a current fed high frequency resonant inverter used as the power supply for sealing-wax. The proposed inverter can reduce switching losses, noise and voltage stress at turn-on and turn-off. The analysis of proposed circuit uses normalized parameter and characteristic estimation which is needed in each step before design is generally described according to normalized frequency ($\mu$), coefficient of coupling($\kappa$) and all parameters. The theoretical analysis is proved through experiment and this circuit shows that it can be used practically as the power supply system for sealing wax and DC-DC converter.

• Smart Structures and Systems
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• v.1 no.2
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• pp.217-233
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• 2005

Elastic and electromagnetic waves can be used to gather important information about particulate materials. To facilitate smart geophysical characterization of particulate materials, their fundamental properties are discussed and experimental procedures are presented for both elastic and electromagnetic waves. The first application is related to the characterization of particulate materials using shear waves, concentrating on changes in effective stress during consolidation, multi-phase phenomena with relation to capillarity, and microscale characteristics of particles. The second application involves electromagnetic waves, focusing on stratigraphy detection in layered soils, estimation of void ratio and its spatial distribution, and conduction in unsaturated soils. Experimental results suggest that shear waves allow studying particle contact phenomena and the evolution of interparticle forces, while electromagnetic waves give insight into the characteristics of the fluid phase and its spatial distribution.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.397-404
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• 2002

The bearing capacity of open-ended piles is affected by the degree of soil plugging, which is quantified by the IFR. There is not at present a design criterion for open-ended piles that explicitly considers the effect of IFR on pile load capacity In order to investigate this effect, model pile load tests using a calibration chamber were conducted on instrumented open-ended piles. The results of these tests show that the IFR increases with increasing relative density and increasing horizontal stress of soils. The unit base and shaft resistances decrease with increasing IFR. Based on the results of the model pile tests, new empirical relations for base load capacity and shaft load capacity of open-ended piles are proposed. In order to check the accuracy of predictions made with the proposed equations, the equations were applied to the full-scale pile load test preformed in this study, Based on the comparisons with the pile load test results, the proposed equations appear to produce satisfactory predictions.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.1
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• pp.93-101
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• 2002

In this study, the stator form-winding sample coils based on silicone resin and polyimide were made for fault prediction and reliability estimation on the C-Class(200$\^{C}$ ) insulation system of traction motors. The complex accelerative degradation was periodically performed during 10 cycles, which was composed of thermal stress, fast rising surge voltage, vibration, water immersion and overvoltage applying. After aging of 10 cycles, the condition diagnosis test such as insulation resistance '||'&'||' polarization index, capacitance '||'&'||' dielectric loss and partial discharge properties were investigated in the temperature range of 20 ∼ 160$\^{C}$. Relationship among condition diagnosis tests was analyzed to find a dominative degradation factor and an insulation state at end-life point.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.53 no.8
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• pp.517-524
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• 2004

In this paper, a novel zero-voltage-switching(ZVS) resonant DC-DC converter is proposed. It is composed of two symmetrical active-clamped circuits, the converter can be achieve ZVS in each switches. Also, active clamp capacitor ratios($\alpha$) of proposed circuit can be reduce a peak stress of switching voltage for each main switch. Simulation results using Pspice 9.2 ver and $C^{++}$ characteristic analysis show a provement for the validity of theoretical analysis. The analysis of the proposed Current-Fed Push Pull type DC-DC converter is generally described by using normalized parameter, and achieved an evaluated characteristic values which is needed to design a circuit. We confirm a rightfulness theoretical analysis by comparing a theoretical values and experimental values obtained from experiment using MOSFET as switching devices.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.20-25
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• 2002

본 논문은 대 변형 굽힘에 의한 소성 모멘트의 계산시 ovality를 고려한 파이프의 중립축에 대한 모멘트에 관해 논한다. 기존의 계산방법에 의한 중립축에 대한 모멘트 계산결과와 새로운 방법에 의한 계산결과를 비교해 보았다. 파이프가 길이방향의 모멘트에 의하여 굽어질 때, 증가하는 모멘트에 따른 ovality 변화를 고려하여 중립축에 대한 모멘트 계산에 적용해 보았다. 모멘트 계산은 타원형의 파이프 단면을 미세한 단면으로 나누어서 각 단면에 대한 응력을 비선형 strain-stress 식을 이용하여 구한 다음 중립축에 대해 계산을 수행하였다. 대 변형 굽힘에서 일어나는 실제현상 중 하나인 ovality를 파이프의 계산에 적용함으로써 좀 더 정확한 중립축에 대한 모멘트를 계산할 수 있었다. 이 방법을 reel에 의한 해저배관의 설치 공법에서 사용되는 reverse bending radius 계산에 적용해 보았다.

• IE interfaces
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• v.16 no.1
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• pp.85-93
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• 2003

The purposes of this study are to investigate perceived discomfort for static joint motions, and to propose rankings for the joint motions based on the perceived discomfort. The perceived discomfort was measured through an experiment using the free modulus method of the magnitude estimation, in which ten healthy college-age female students participated. The results showed that joints, joint motions and their levels significantly affected the perceived discomfort at $\alpha$=0.01, and that the interaction of joints and joint motion levels was also significant. Based on the experimental results, three rankings were proposed by joint and joint motions, by joints and by joint motions, which were very different from the existing ones. Especially, the proposed rankings were different from the males' published before in their order and magnitude. These rankings can be used as a valuable tool for better understanding potentially adverse effects of poor working postures in industrial sites, and as basic data for developing the postural classification scheme.

• Tribology and Lubricants
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• v.21 no.3
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• pp.136-141
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• 2005

Analytical model to calculate the contact fatigue life of rough surface is presented in this paper. The effect of surface roughness can be calculated by this model. Computational method and the theoretical basis are also discussed. Contact stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions; the subsurface stress field is obtained using rectangular patch solutions. Mesoscopic multiaxial fatigue criterion which can yield satisfactory results for non-proportional loading is then applied to predict fatigue damage. Suitable counting method and damage rule were used to calculate the fatigue life of random loading caused by rough surface. As a result of analysis the relationship between the life and the roughness as well as the most probable depth of the crack initiation is calculated.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.29 no.2
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• pp.152-161
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• 1993

This paper deals with the effect of spatial distribution of material properties on its statistical characteristics and numerical estimation method of reliability of fatigue sensitive structures with respect to the fatigue crack growth. A method is proposed to determine experimentally the probability distribution functions of material parameters of Paris law. da/dN=C(ΔK/K sub(0) ) super(m), using stress intensity factor controlled fatigue tests. The result with a high tensile strength steel shows that the distribution of the parameter m is approximately normal and that of 1/C, is a 3-parameter Weibull. The main result obtained are : (1) The theoretical autocorrelation of the resistance, 1/C, to fatigue crack growth are almost same for different lengths. (2) The variance decreases with the increasing a averaging length. When spatial correlation length is very small. the variane decreases significantly were the averaging length. (3) The probability distribution of load cycles or the number for a crack to reach a certain length can be estimated using these functions by simulation of non-Gaussian(expecially Weibull) Stochastic Process.

• East Asian Economic Review
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• v.23 no.1
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• pp.3-26
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• 2019

This study investigates the effect of high-skilled inventor emigration rate on growth rate of the country of origin (COO). Inventor emigrants represent the human capital that can generate highly innovative work. The social network they form spurs knowledge diffusion and technology transfer back to their COOs, which in turn affects innovation and growth in their home countries. We run dynamic panel estimation for 154 countries during 1990-2011, and empirically show that a positive and statistically significant effect exists for the interaction of inventor emigration and trade. The result indicates that the direct negative impact of the brain drain can be mitigated by the positive feedback effect generated by the high-skilled inventor emigrants abroad. When coupled with an active trade policy that reinforces growth, countries can partially recoup the direct effect of the human capital loss. We stress the importance of international trade for successful technology transfer to occur, and offer insights for policies that can utilize the benefits of the rich social network of their high-skilled emigrants.