• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.12 no.2
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• pp.142-149
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• 2019

The coils to transmit the electric energy are necessary to charge an electric vehicle wirelessly. There are several types of coils, from basic circular coils to DD-type coils for enhancing the coupling effect between two coils. However, DD-type coils with a good coupling effect between coils have a disadvantage in use because of the structure complexity of the power conversion device of transmitting and receiving side. In this paper, we propose a method to calculate the inductance value and to design the size of the spiral inductor which is convenient to fabricate when the power is transmitted wirelessly by using two coils in free space. Since the bifurcation phenomenon occurs when the XLm value is similar to the load resistance value in the resonator the XLm value was selected to be equal to the minimum load resistance value to minimize this phenomenon, and the inductance value required for the resonator was calculated. In order to realize the calculated inductance value by the spiral inductor, the relationship between the inductance value and the size, the number of turns, the total coil length of a spiral inductor was investigated. In addition, the change of coupling coefficient k according to the horizontal separation of two coils was examined and an appropriate inductor was selected.

• Journal of Mechanical Science and Technology
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• v.18 no.8
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• pp.1435-1450
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• 2004

Experimental data are presented which describe the effects of a combustor-level high free-stream turbulence on the near-wall flow structure and heat/mass transfer on the endwall of a linear high-turning turbine rotor cascade. The end wall flow structure is visualized by employing the partial- and total-coverage oil-film technique, and heat/mass transfer rate is measured by the naphthalene sublimation method. A turbulence generator is designed to provide a highly-turbulent flow which has free-stream turbulence intensity and integral length scale of 14.7% and 80mm, respectively, at the cascade entrance. The surface flow visualizations show that the high free-stream turbulence has little effect on the attachment line, but alters the separation line noticeably. Under high free-stream turbulence, the incoming near-wall flow upstream of the adjacent separation lines collides more obliquely with the suction surface. A weaker lift-up force arising from this more oblique collision results in the narrower suction-side corner vortex area in the high turbulence case. The high free-stream turbulence enhances the heat/mass transfer in the central area of the turbine passage, but only a slight augmentation is found in the end wall regions adjacent to the leading and trailing edges. Therefore, the high free-stream turbulence makes the end wall heat load more uniform. It is also observed that the heat/mass transfers along the locus of the pressure-side leg of the leading-edge horseshoe vortex and along the suction-side corner are influenced most strongly by the high free-stream turbulence. In this study, the end wall surface is classified into seven different regions based on the local heat/mass transfer distribution, and the effects of the high free-stream turbulence on the local heat/mass transfer in each region are discussed in detail.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.7
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• pp.628-633
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• 2008

Cruciform parachute has advantage in manufacture and expanse compare with circular parachute. But it has disadvantage in stability. Wind tunnel test were conducted to investigate the effects of reefing-line on the cruciform parachutes with the purpose of finding aerodynamics characteristics of the parachute such as drag coefficient, normal force coefficient. Aerodynamics characteristics are measured accurately with 6-components pyramidal balance and load cells which were installed in the fixed-body. Four different models were tested and the test results were compared with each other. The aerodynamics characteristics were changed with reefing-line length. Separation edge was developed due to reefing-line also it made increasing of the stability. The cruciform parachute which improve stability is supposed to be used in variety purpose.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.3
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• pp.307-313
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• 2009

In general, pyroshock is generated from the actuation of separation devices for several stage, fairing, and satellite separation in the flight of a launch vehicle. During these events, transient vibration phenomenon called pyroshock, which shows large acceleration in the high frequency range, occurs and it can result in the malfunction of electronic components which is equipped inside the launch vehicle or satellite. In this paper, mesh washer isolators made out of SMA were introduced for the isolation of pyroshock. One type of isolator primarily used pseudoelastic characteristics of SMA and the other type of isolator used shape memory effect of SMA. For the study of basic load-displacement relationship of each SMA isolator, compressive loading tests were performed and the results showed the capability of the isolator itself. Pyroshock isolation tests were followed and verified the outstanding isolation performance of isolator. In addition, random vibration tests were also performed and checked the dynamic characteristics of each SMA isolator.

• Coupled systems mechanics
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• v.6 no.3
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• pp.229-249
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• 2017

A new technique to mitigate irregular buildings with soil structure interaction (SSI) effect subjected to critical seismic waves is presented. The L-shape in plan irregular building for various reasons was selected, subjected to seismic a load which is a big problem for structural design especially without separation gap. The L-shape in plan building with different dimensions was chosen to study, with different rectangularity ratios and various soil kinds, to show the effect of the irregular building on the seismic response. A 3D building subjected to critical earthquake was analyzed by structural analysis program (SAP2000) fixed and with SSI (three types of soils were analyzed, soft, medium and hard soils) to find their effect on top displacement, base shear, and base torsion. The straining actions were appointed and the treatment of the effect of irregular shape under critical earthquake was made by using tuned mass damper (TMD) with different configurations with SSI and without. The study improve the success of using TMDs to mitigate the effect of critical earthquake on irregular building for both cases of study as fixed base and raft foundation (SSI) with different TMDs parameters and configurations. Torsion occurs when the L-shape in plan building subjected to earthquake which may be caused harmful damage. TMDs parameters which give the most effective efficiency in the earthquake duration must be defined, that will mitigate these effects. The parameters of TMDs were studied with structure for different rectangularity ratios and soil types, with different TMD configurations. Nonlinear time history analysis is carried out by SAP2000 with El Centro earthquake wave. The numerical results of the parametric study help in understanding the seismic behavior of L-shape in plan building with TMDs mitigation system.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.9
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• pp.937-942
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• 2008

This paper presents a case history on failures of impeller and shaft due to pressure pulsation at single stage feed water pumps in 700 MW nuclear power plant during commissioning operation. The pumps had been service and had run for approximately $40{\sim}50$ hours. For the most part, the failures of impeller occurred with the presence of a number of fatigue cracks. All cracks were associated with the deleterious surface layer of impeller by visual and metallurgical examination. On-site testing and analytical approach was performed on the systems to diagnose the problem and develop a solution to reduce the effect of exciting sources. A major concern at high-energy centrifugal pump is the pressure pulsation created from trailing edge of the Impeller blade, flow separation and recirculation at centrifugal pumps of partial load. Pressure pulsation due to the interaction generating between impeller and casing coincided with natural frequencies of the impeller and shaft system during 1ow load operation. It was identified that dynamic stress exceeding the fatigue strength of the material at the thin shroud section due to the hydraulic instability at running condition below BEP.

• Wind and Structures
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• v.20 no.2
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• pp.327-347
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• 2015

This paper investigates the effects of Reynolds number (Re) on the aerodynamic characteristics of a twin-deck bridge. A 1:36 scale sectional model of a twin girder bridge was tested using the Wall of Wind (WOW) open jet wind tunnel facility at Florida International University (FIU). Static tests were performed on the model, instrumented with pressure taps and load cells, at high wind speeds with Re ranging from $1.3{\times}10^6$ to $6.1{\times}10^6$ based on the section width. Results show that the section was almost insensitive to Re when pitched to negative angles of attack. However, mean and fluctuating pressure distributions changed noticeably for zero and positive wind angles of attack while testing at different Re regimes. The pressure results suggested that with the Re increase, a larger separation bubble formed on the bottom surface of the upstream girder accompanied with a narrower wake region. As a result, drag coefficient decreased mildly and negative lift coefficient increased. Flow modification due to the Re increase also helped in distributing forces more equally between the two girders. The bare deck section was found to be prone to vortex shedding with limited dependence on the Re. Based on the observations, vortex mitigation devices attached to the bottom surface were effective in inhibiting vortex shedding, particularly at lower Re regime.

• Proceedings of the KIEE Conference
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• 2001.11b
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• pp.421-423
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• 2001

Restructuring of electricity industry is going on for the purpose of introducing competition and after separation of generation and retail business and introduction of competition, substantial change is expected in overall electric power system. In other words, DSM projects are divided with public projects and private projects. Particularly for public project, it is essential to evaluate the DSM volumes by program. This paper tries to derive the ways for achieving the necessary DSM goal in the electricity industry in Korea. First of all, by analyzing the load in Korea, we forecast the standard demand and estimate the technological potentials of each program in considering DSM technological indicators. Moreover, by using economic analysis by program, we estimate economic potentials and finally, we estimate the potentials by program in considering the DSM policy. We estimate the potentials by using random method because application methodology and procedures by program are not established until now, which leads to not obtaining transparency for implementation effect by program. Therefore, this paper estimates the future potentials of DSM projects by using the logical and systematic analytic method and establishing database for DSM basic indicator. The DSM goals estimated by this method will be reflected to mid/long term nation-wide resource planning, which will mitigate anticipated power supply shortage and be applied to derive desirable energy demand/supply structure.

• Structural Engineering and Mechanics
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• v.78 no.2
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• pp.135-143
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• 2021

In this study, continuous contact problem in the functionally graded (FG) layer loaded with a FG flat punch resting on the elastic semi-infinite plane was analyzed by the finite element method (FEM). It was assumed that the shear modulus and density of the layer and punch varied according to exponentially throughout their depth. FG layer's weight was included to the problem and additionally all surfaces were considered as frictionless. Analysis of FG materials was performed with a special macro which was added to the ANSYS program. Firstly, the shear modulus of the punch was considered to be very rigid and the results of initial separation load (λcr) and distance (xcr) were compared with the analytical solution. Afterwards, results obtained from the contact analysis made according to the inhomogeneity parameters (β, γ) between FG punch-FG layer which had been unprecedented in the literature were discussed. As a result, FG punch's stress values at the punch edges where stress accumulations occurred were found to be smaller than the rigid punch. The security of the structure, longer life of the material and ease of production are directly related to the reduction of the stress values. The results obtained in this study are important in this respect. Also this work is the first study that investigates the effect of FG punch on the FG layer.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.5
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• pp.368-375
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• 2018

In the present study, aerodynamic load analysis for a floating off-shore wind turbine was conducted to examine the effect of periodic platform motion in the direction of 6-DOF on rotor aerodynamic performance. Blade-element momentum method(BEM) was used for a numerical simulation, the unsteady airload effects due to the flow separation and the shed wake were considered by adopting a dynamic stall model based on the indicial response method. Rotor induced downwash was estimated using the momentum theory, coupled with empirical corrections for the turbulent wake states. The periodic platform motions including the translational motion in the heave, sway and surge directions and the rotational motion in the roll, pitch and yaw directions were considered, and each platform motion was applied as a sinusoidal function. For the numerical simulation, NREL 5MW reference wind turbine was used as the target wind turbine. The results showed that among the translation modes, the surge motion has the largest influence on changing the rotor airloads, while the effect of pitch motion is predominant for the rotations.