• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.2
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• pp.179-187
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• 2018

In order to understand the flow of currents around Aphae Island and the surrounding Archipelago, the numerical model experiments on tidal currents and tide-induced residual currents were carried out. Dominant semidiurnal tidal currents have a reversing form and flow along the narrow channels of the archipelago. During periods of flood, currents flow from the west of Hwawon Peninsula to the archipelago to the northwest together with the currents flowing from the channels at Palgeum Island to Amtae Island and Amtae Island to Jeung Island. Ebb currents flow from the northwest archipelago to the channel of Amtae Island and Jeung Island as well as Amtae Island to Palgeum Island, further flowing south between Palgeum Island and Hwawon Peninsula. Flood currents are separated from east and west at the southern coast of Aphae Island, but flow south from both the west and east of Aphae Island to the channel found between Palgeum Island and Hwawon Peninsula at ebb. Flow speed is high between Amtae Island and Aphae Island where the flows meet and join. Lee wakes or topographical eddies are formed around the islands due to the high speed of the currents flowing along the narrow channel in the archipelago, manifesting as a tide-induced residual current. A weak cyclonic wake and anti-cyclonic eddy both exist at the west and northwestern coast of Aphae Island individually. The speed of the tide-induced residual current become slow on account of the wide littoral zone at exists around Aphae Island.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.12
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• pp.1279-1284
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• 2012

Micro structures which are widely used at various fields are commonly fabricated by lithograph, etching and laser methods. Recently, with the emergence of micro tools and ultra-precision machine tools, fabrication of the micro structures obtained using end-milling are studied. However, there are some problems due to the diameter of the micro end-mill getting smaller below $100{\mu}m$. The micro run-out resulted from miniaturization of end-mills have influence seriously on accuracy of micro structures. The error of run-out with a tooling jig showed a decrease of about $9.3{\mu}m$. Furthermore, micro structures with width of $30{\mu}m$ could be applied through experiments of slot machining obtained using 30 and $50{\mu}m$ end-mill. Also, narrow angle structures with $30^{\circ}$ angle could be applied through analysis of machining acute angle structures. Based on basic experiments, micro fluidics channels and spiral patterns for air bearing were machined.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.1749-1753
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• 2003

We proposed several systems for 1Giga bit Modem. The first, Binary ASK(Amplitude Shift Keying) system has a high speed shutter transmitter and no IF(Intermediate Frequency) receiver only by symbol synchronization. The advantage of proposed system is that circuitry is very simple without IF process. The disadvantage of proposed system are that line spectrum occurs interference to other channels, and enhancement to 4-level system is impossible due to its large SNR degradation. The second, Binary phase modulation system has a high speed shutter transmitter and IF-VCO(IF-Voltage Controlled Oscillator) control by base-band phase rotation. Polarity of shutter window is changed by the binary data. The window should be narrow same as above ASK. The advantage of proposed system is which error rate performance is superior. The disadvantage of proposed system are that Circuitry is more complex, narrow pull-in range of receiver caused by VCO and spectrum divergence by the non-linear amplifier. The third, 4-QAM(Quadrature Amplitude Modulation)system has a nyquist pulse transmitter and IF-VCO control by symbol clock. The advantage of proposed system are that signal frequency band is a half of 1GHz, reliable pull-in of VCO and possibility of double speed transmission(2Gbps) by keeping 1GHz frequency-band. The disadvantage of proposed system are that circuit complexity of pulse shaping and spectrum divergence by the non-linear amplifier.

• Proceedings of KOSOMES biannual meeting
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• 2003.11a
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• pp.75-83
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• 2003

The navigation area approach to Mokpo port consists of narrow channels with 30mile section, and the route is crossed with many fairways. Specially, except Mokpo-Gu fairway routeing is not assigned and there are many threatening factors against the safe operation of vessel because fishing and mining areas are designated Therefore, this paper proposed a plan for safe passage through a maritime transportation environmental assessment with the analysis of surrounding environment, danger element of navigation, traffic observation and marine accidents.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.10
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• pp.1030-1035
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• 2003

In this paper, we compare the performance of IS-OFDM(interference suppressing orthogonal frequency division multiplexing) system with that of the conventional OFDM system. Each parallel branch symbol of IS-OFDM is multiplied by the orthogonal sequence and distributed into all sub-carriers. Then, each sub-carrier transmits information composed of the symbol components of all parallel branches in the given frame. The structure of IS-OFDM shows the frequency diversity characteristic. Therefore, IS-OFDM can be robust to the narrowband interference. BER performances are found in the narrow-band interference and a harmonic noise channels. When JSR(Jamming to signal ratio) increases from -10 dB to +10 dB in the constant interference bandwidth, IS-OFDM outperforms the conventional OFDM and the BER difference between IS-OFDM and OFDM is reduced as JSR increases. Also, the similar properly can be shown when interference bandwidth increases at the constant JSR. In the harmonic noise channel, we can find the good performance of IS-OFDM when the h-rate(harmonic noise bandwidth to signal bandwidth ratio) increases from 0.01 to 0.8. So, simulation results show that the IS-OFDM is more robust to the interference than the conventional OFDM.

• Journal of the Korean Society of Marine Environment & Safety
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• v.10 no.1 s.20
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• pp.15-22
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• 2004

The navigation area approach to Mokpo port consists of narrow channels with 30mile section, and the route is crossed with many fairways. In particular, fairway routeing except Mokpogu is not assigned and there are many threatening factors against the safe operation of vessel because fishing and mining areas are designated. Therefore, this paper proposed elements for safe passage through a marine traffic environmental assessment with the analysis of surrounding environment, dangerous elements, traffic survey and marine casualty.

• 한국해양학회지
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• v.17 no.1
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• pp.12-18
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• 1982

Tidal exchanges of sea water are studied by using drogue experiments and tidal current measurement data in Gamag Bay which has two channels. At the spring tide, the volume of tidal transport in the bay was estimated to be 46∼52% of the total volume of sea water in Gamag Bay, 7.1 10$\^$8/㎥. The tidal transport through the wide channel occupies 87% of the total tide transport of the bay. Residual current was deduced to flow north-northeastward at the rate of 3.254 10$\^$5/㎥ per tidal cycle. the tidal exchange of the sea water during the flood flow was estimated to be approximately 26% of the tidal transport, while that during the ebb flow was 41%. The tidal exchange through the wide channel during the flood flow occupies 77% of total tidal exchange of the bay through both channels, whereas that during the ebb flow does 88%. The diffusion coefficient of 2.08∼ 2.30 10$\^$7/$\textrm{cm}^2$/sec at the narrow channel was greater than that at the wide channel which was 1.2∼2.8 10$\^$6/$\textrm{cm}^2$/sec.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.4
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• pp.202-216
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• 2015

In the narrow water channel, which has been frequently deployed in the artificial canal in the South Korea due to the lack of available land, solitary wave type ship induced waves can occur. In order to test this hypothetical view, we carried out the numerical simulation. Numerical model consists of Navier-Stokes Equations and VOF, and the verification is implemented using the data by PIANC (1987) and the analytical model derived in this study. It was shown that numerically simulated front wave height are much larger than the one by PIANC (1987), and the fluctuation of free surface near the channel bank persists much longer (around 20s). For the case of stern waves, numerically simulated wave height are somewhat smaller than the data by PIANC (1987). These results seriously deviates from the general characteristics of ship induced waves observed in the wide water channels, and leads us to conclude that ship induced waves is severely affected by the width of water channel. It was also shown that the currents from the channel banks toward a ship, and currents from the ship toward the channel banks are alternatively occurring due to reflection at the channel banks. The velocity of currents reaches its maximum at 0.90 m/s, and these values are sustained through the entire depth. which implies that severe scourings at the channel bottom can be underway.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.2
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• pp.91-100
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• 2004

Plate heat exchangers (PHE) have been widely used in different industrial applications, because of high heat transfer efficiency per unit volume. Basic study is performed for PHE to the application of intercooler in automobile. In order to understand the flow phenomena in the plate heat exchanger, a channel which was formed by the upper and lower plate in single plate was considered as calculation domains. Because chevrons attached on the upper plate are brazed with chevrons attached on the lower plate, the flow channel has very complex configuration. This complex geometry was analyzed by Fluent. In order to validate this methodology the proper experimental and theoretical data are collected and compared with numerical results. Finally, due to the lack of experimental values for PHE to the application of intercooler, various chevron angles and air velocities at inlet were tested in terms of physical phenomena. From this point of view, results of velocity vector, path lines, static pressure, heat flux, heat transfer coefficient, and Nusselt number are physically reasonable and accepted for the solutions. From these results, the correlations for pressure drop and Nusselt number with respect to chevron angle and Reynolds number in specific PHE are obtained for the design purpose. Thus, the methodology of the flow analysis in the full geometry of the channel was established for the predictions of performance in plate heat exchanger.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.40 no.2
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• pp.144-148
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• 2004

Generally a ship in a port or canal is guided by tugboat(s), while the ship engine(s) and steering mechanism idle. The shortcomings of this method are insufficient in course keeping ability, danger of collision with waterside structures, time-consuming preparation for tugging, as well as the need to maintain tugboats. A new technology for ship guiding, based on the physical principle of interaction of a solid body with aerated liquids has been developed [1]. Model tests were carried out for the verification of system at slow speed by engine operating conditions and with an idle steering. The developed device has been proved to keep the ship on course safely.