• Journal of the Earthquake Engineering Society of Korea
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• v.22 no.6
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• pp.323-332
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• 2018

Recent two moderate earthquakes (2016 $M_w=5.4$ Gyeongju and 2017 $M_w=5.5$ Pohang) in Korea provided the unique chance of developing a set of relations to estimate instrumental seismic intensity in Korea by augmenting the time-history data from MMI seismic intensity regions above V to the insufficient data previously accumulated from the MMI regions limited up to IV. The MMI intensity regions of V and VI was identified by delineating the epicentral distance from the reference intensity statistics in distance derived by using the integrated MMI data obtained by combining the intensity survey results of KMA (Korea Meteorological Administration) and 'DYFI (Did You Feel It)' MMIs of USGS. The time-histories of the seismic stations from the MMI intensity regions above V were then preprocessed by applying the previously developed site-correction filters to be converted to a site-equivalent condition in a manner consistent with the previous study. The average values of the ground-motion parameters for the three ground motion parameters of PGA, PGV and BSPGA (Bracketed Summation of PGA per second for 30 seconds) were calculated for the MMI=V and VI and used to generate the dataset of the average values of the ground-motion parameters for the individual MMIs from I to VI. Based on this dataset, the linear regression analysis resulted in the following relations with proposed valid ranges of MMI. $MMI=2.36{\times}log_{10}(PGA(gal))+1.44$ ($I{\leq}MMI$$MMI=2.44{\times}log_{10}(PGV(kine))+4.86$ ($I{\leq}MMI$$MMI=2.59{\times}log_{10}(BSPGA(gal{\cdot}sec))-1.02$ ($I{\leq}MMI$

• Journal of Korean Tunnelling and Underground Space Association
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• v.6 no.4
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• pp.327-343
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• 2004

During tunnel construction, ground failures often occur due to existence of weak zones, such as faults, joints, and cavities, ahead of tunnel face. It is hard to detect effectively weak zones, which can lead underground structure to fail after excavation and before supporting, by using conventional characterization methods. In this study, an enhanced analytical method of predicting weak zones ahead of tunnel face is developed to overcome some problems in the conventional geophysical exploration methods. The analytical method is based on Coulomb's and Gauss' laws with considering the characteristics of electric fields subjected to rock mass. Using the developed method, closed form solutions are obtained to detect a spherical shaped zone and an oriented fault ahead of tunnel face respectively. The analytical results suggest that the presence of weak zones and their sizes, location, and states can be accurately predicted by combining a proper inversion process with resistance measured from several electrodes on the tunnel face. It appears that the skin depth or resistivity in rock mass is affected by the diameter of tunnel face, natural electric potential and noises induced by experimental measurement and spatial distribution of uncertain properties. The developed analytical solution is verified through experimental tests. About 1800 concrete blocks of 5cm by 5cm by 5cm in size are prepared and used to model a joint rock mass around tunnel face. Weak zones are simulated ahead of tunnel face with a material which has relatively higher conductivity than concrete blocks. Experimental results on the model test show a good agreement with analytical results.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.338-341
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• 2018

Wireless Power Transfer(WPT) of array antenna applied to beam-forming techniques enables highly efficient WPT when transmitters and receivers are not contacting and even when they are separated. However, this WPT method is possible to use only when human safety restriction by distance between the transmitters and the receivers is satisfied. In the paper, a $4{\times}8$ array antenna for 2.4 GHz is modeled by simulation, then electric field intensity and 10 gram average head SAR(Specific Absorption Rate) by distance away from the array antenna inputted 1 W of 2.4 GHz sinusoidal wave at each single antenna of the array antenna for 2.4 GHz were obtained. And they were compared with human safety restriction of draft of 2018 ICNIRP(International Commission on Non-Ionizing Radiation Protection) guidelines. As the result, power density of far field derived from the electric field intensity was $33.257W/m^2$, which satisfied with occupational human safety restriction but exceeded public's. In addition, the 10 gram average head SAR exceeded the human safety restriction.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.4
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• pp.34-42
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• 2017

Since existing nonintrusive appliance load monitoring (NIALM) studies assume that voltage fluctuations are negligible for load identification, and do not affect the identification results, the power factor or harmonic signals associated with voltage are generally not considered parameters for load identification, which limits the application of NIALM in the Smart Home sector. Experiments in this paper indicate that the parameters related to voltage and the characteristics of harmonics should be used to improve the accuracy and reliability of the load monitoring system. Therefore, in this paper, we propose an improved NIALM method that can efficiently analyze the types of household appliances and electrical energy usage in a home network environment. The proposed method is able to analyze the energy usage pattern by analyzing operation characteristics inherent to household appliances using harmonic characteristics of some household appliances as recognition parameters. Through the proposed method, we expect to be able to provide services to the smart grid electric power demand management market and increase the energy efficiency of home appliances actually operating in a home network.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.6
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• pp.566-572
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• 2021

A methodology for the identification and coordinates estimation of air cavities under urban ground or sandy soil using its natural poles and natural resonant frequencies is presented. The potential of this methodology was analyzed. Simulation models of PEC (Perfect Electric Conductor)s with various shapes and dimensions were developed using an EM (Electromagnetic) simulator. The Cauchy method was applied to the obtained EM scattering response of various objects from EM simulation models. The natural poles of objects corresponding to its instinct characterization were then extracted. Thus, a library of poles can be generated using their natural poles. The generated library of poles provided the possibility of identifying a target by comparing them with the computed natural poles from a target. The simulation models were made assuming that there is an air cavity under urban ground or sandy soil. The response of the desired target was extracted from the electromagnetic wave scattering data from its simulation model. The coordinates of the target were estimated using the time delay of the impulse response (peak of the impulse response) in the time domain. The MP (Matrix Pencil) method was applied to extract the natural poles of a target. Finally, a 0.2-m-diameter spherical air cavity underground could be estimated by comparing both the pole library of the objects and the calculated natural poles and the natural resonant frequency of the target. The computed location (depth) of a target showed an accuracy of approximately 84 to 93%.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6D
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• pp.871-879
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• 2008

Recently, as there are a rise in the standard of living and higher concerns of an electromagnetic wave and environment, undergrounding the aerial cables which are supported by large pylons and generally considered as the least attractive feature of an urban area is on an increasing trend to improve aesthetic benefits and electric reliability. This study applied Contingent Valuation Method (CVM) which is expected to become an effective tool to measure indirect benefit to estimate the substantial benefits of undergrounding overhead power line projects in an urban area. The tunneling construction project of the 345kV Shinsungnam electric power cable in Seongnam city was selected and a hypothetical scenario was given to respondents to determine their levels of Willingness to Pay (WTP) for undergrounding overhead power lines. The result from the estimation of the WTP of undergrounding overhead power lines in Seongnam city was calculated as approximately 17.1 billion won. Placing existing overhead lines underground is difficult to justify economically. Most undergrounding costs appear to be justified by aesthetic and public policy considerations. Therefore, considering the result of this study, undergrounding overhead power lines is of great benefit to public.

• Korean Chemical Engineering Research
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• v.52 no.5
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• pp.558-563
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• 2014

To study the effects of fabrication methods on the performance and durability of polymer electrolyte membrane fuel cells (PEMFCs), membrane-electrode assemblies (MEAs) were fabricated using a Dr blade method, a spray method, screen print method and screen print + spray method. The performance of single cells assembled with the prepared MEAs were initially measured and compared. Electrode accelerated stress testing (AST) involving a potentiostatic step-wave with 10 s at 0.6 V followed by 30 s at 0.9 V was applied to test durability of MEAs. Before and after 6,000cycles of the AST, I-V curves, impedance spectra, cyclic voltammograms, linear sweep voltammetry (LSV) and transmission electron microscope (TEM) were measured. Under the operating conditions, the Dr Blde MEA exhibited the highest initial performance. After electrode accelerated stress testing, screen print + spray MEA showed lowest degradation rate.

• 전자공학회논문지 IE
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• v.43 no.4
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• pp.122-127
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• 2006

A series of conductive filler were prepared with electroless plating method. Base conductive materials of the filler were nickel and copper. The cores were prepared with Nylon 6 and rayon in different aspect ratio. Also, various complexes were made with ABS resin and conductive filler with different filler feed ratio. The conductivity of the filler was measured with conductivity analyzer and the size distributions of fillers was measured with laser particle size analyzer. Electromagnetic wave shielding efficiency of each complex film was measured with flange circular coaxial transmission line sample holder within the 1MHz$\sim$1GHz bandwidth range. From this study, the conductivity of filers surpass that of other carbon films. It is available that the filler made of fibrous materials can be applied in plastic molding industry of electric appliances as a EMI filler.

• Transactions of the KSME C: Technology and Education
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• v.4 no.1
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• pp.63-71
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• 2016

Although mechatronics education in a mechanical engineering curriculum is recently recognized as important, its experimental education has been done generally in the laboratory equipped with all the apparatus and could not be done at home by students. This paper introduces experimental educations on mechatronics, e.g., digital logic circuits, 7-segment LED drive, square wave generation, microcontroller programming using assembly and C languages, timer interrupt, and step motor drive using a small 5 V power supply, a breadboard, various electronic and electric components, a microcontroller and its programmer, a step motor, and a student's PC. In the developed mechatronics course, experimental educations are scheduled in parallel with content's lectures together, and cheap and economic experimental environment is prepared for students in which students can easily practice experimental works in advance or later at home by themselves.

• Journal of the Korean Society of Groundwater Environment
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• v.2 no.1
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• pp.30-37
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• 1995

In the tidal compartment, the hydraulic head is affected by the stage of tidal rivers. For groundwater or construct works, head variation of groundwater should be considered in zone of this aquifer. A numerical analysis is performed which has an 1-dimemsional explicit finite difference scheme to show the head variation of groundwater with tidal stage and hydraulic conductivity, etc. The stability of the numerical scheme is validated by using the analytic solution. The head variation of groundwater is observed for various tidal amplititude and hydraulic conductivity, mean hydraulic gradient and pumping at any point. The range of influence corresponding to the parameters used in this study is about 60m. This value is not beyond a wave length (equation omitted). There was a pumping at a constant rate out of aquifers affected by tide and not affected by tide. Because pumping head in aquifer affected by tide is short, the expense of electric power is economized in this zone. These results are applicable to trace of contaminant transport, efficient operation of groundwater, and examination of the safety and stability of works in the tidal compartment.