• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.5
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• pp.539-546
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• 2010

In this paper, lattice Boltzmann method(LBM) results for a laminar flow in a microchannel with rough surface are presented. The surface roughness is modeled as an array of rectangular modules placed on the top and bottom surface of a parallel-plate channel. The effects of relative surface roughness, roughness distribution, and roughness size are presented in terms of the Poiseuille number. The roughness distribution characterized by the ratio of the roughness height to the spacing between the modules has a negligible effect on the flow and friction factors. Finally, a significant increase in the Poiseuille number is observed when the surface roughness is considered, and the effects of roughness on the microflow field mainly depend on the surface roughness.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.6
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• pp.704-709
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• 2014

Plate heat exchanger is being applied in the field of marine plants and chemical industry, such as OTEC and SWAC equipment. The study aims to interpret the heat transfer and pressure drop characteristics of plate heat exchangers to determine the geometric design parameters such as the channel space. In this study, heat transfer performance was numerically studied with respect to the variation of channel spaces. The results from numerical analysis indicated that the j factor was linearly decreased with the flowrate of seawater over every cases. As the flowrate of water increased with respect to channel spaces, the j factor decreased linearly. And the f factor decreased linearly with the increase of flowrate. When the channel space is 2.8~3.2 mm and 3.2~3.2 mm, respectively, the area goodness factor of plate heat exchanger showed the highest performance.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.1
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• pp.1-8
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• 2014

Two-dimensional laminar numerical analyses were carried out for investigating the thermo-hydraulic characteristics of wavy channels with different shape parameters ($0.5{\leq}{\in}{\leq}1.5$, $0.1{\leq}{\gamma}{\leq}0.4$). PAO (polyalphaolefin), which is used for electronics cooling, is considered as the working fluid. In addition, constant properties, periodically developed flow, and uniform channel wall temperature conditions are assumed. Streamline and temperature fields, isothermal Fanning friction factors, and Colburn factors are presented for different Reynolds numbers in the laminar region ($1{\leq}Re{\leq}1000$). The results show that heat transfer is enhanced when the channel corrugation ratio (${\gamma}$) is large and channel spacing ratio (${\in}$) is small in the low Reynolds number region (Re < 50) and when ${\in}$ and ${\gamma}$ are large in the high Reynolds number region ($Re{\geq}50$).

• The Journal of the Acoustical Society of Korea
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• v.31 no.2
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• pp.107-113
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• 2012

In this paper, we have analyzed the performance of space diversity technologies using experimental data in order to analyze the usability of space diversity techniques in underwater channel environments. After analyzing the experimental data we found out that high diversity gain should not be expected when using a stationary transmitter with a stationary receivers in swallow underwater channel. And we also find out that the distance between sensors should be at least 8 wavelengths apart to take advantage of diversity gain in underwater moving channel environments.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.8
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• pp.748-757
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• 2015

MIMO systems utilizing multiple antenna transmission and reception is one of the key technologies to enhance the capacity of 5G wireless communications. In order to obtain an appropriate performance evaluation of MIMO techniques, the usage of wireless channel model reflecting spatial channel characteristics is required, such as the 3-dimensional spatial channel model(3D SCM) proposed by 3GPP TR36.873 documentation. In this paper, we implement and verify the channel simulation environment based on 3D SCM, to present and compare the characteristics of UMi and UMa environments. We also apply MIMO transmission to the UMa scenario to investigate the channel correlation among antenna elements with different array distances and to identify the corresponding throughput changes. By evaluating the channel power correlations for randomly distributed users within the sector for different horizontal and vertical antenna distances, we present the statistical characteristics which determine the transmission performance under the SCM environment.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.12
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• pp.2805-2812
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• 2015

For the purpose of estimation of time variant frequency selective transmission channels, reference symbols are usually employed. The bit error performance of LTE OFDM systems is analyzed in the case of LTE standard reference symbol arrangement. Results show that LTE OFDM system with this LTE reference symbol arrangement is robust against Doppler time variant fading. However, the performance of that system is degraded due to channel estimation error in frequency domain. An equidistant arrangement with a diamond shape structure of reference symbols, however having 4 subcarriers distance in frequency domain, is suggested for the optimal channel estimation.

• Proceedings of the Korea Information Processing Society Conference
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• 2024.05a
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• pp.147-148
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• 2024

WAVE 표준의 채널 구조는 하나의 제어 채널(CCH)과 여러 개의 서비스 채널(SCH)로 나뉜다. SCH 는 비안전 데이터 전송을 위해 사용되며 CCH 는 비콘 및 제어 메시지(즉, 서비스 광고 메시지)의 브로드캐스팅을 위해 사용된다. 두 간격 모두 표준에서 고정된 값(50ms)으로 설정되어 있다. 그러나 고정 길이 간격은 동적으로 변화하는 트래픽 부하에 대해 효과적으로 대응할 수 없다. 또한, 많은 차량이 동시에 제한된 채널 자원을 사용하여 데이터를 전송할 때 수많은 패킷 충돌로 인해 통신 성능이 크게 저하된다. 본 논문에서는 네트워크 성능을 향상하기 위한 적응적 자원 할당 기법을 제안한다.

• Korean Chemical Engineering Research
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• v.53 no.6
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• pp.818-823
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• 2015

In this study, FT reaction in a microchannel was simulated using computational fluid dynamics(CFD), and sensitivity analyses conducted to see effects of channel geometry variables, namely, process channel width, height, gap between process channel and cooling channel, and gap between process channels on the channel temperature profile. Microchannel reactor considered in the study is composed of five reaction channels with height and width ranging from 0.5 mm to 5.0 mm. Cooling surfaces is assumed to be in isothermal condition to account for the heat exchange between the surface and process channels. A gas mixture of $H_2$ and CO($H_2/CO$ molar ratio = 2) is used as a reactant and operating conditions are the following: GHSV(gas hourly space velocity) = $10000h^{-1}$, pressure = 20 bar, and temperature = 483 K. From the simulation study, it was confirmed that heat removal in an FT microchannel reactor is affected channel geometry variables. Of the channel geometry variables considered, channel height and width have significant effect on the channel temperature profile. However, gap between cooling surface and process channel, and gap between process channels have little effect. Maximum temperature in the reaction channel was found to be proportional to channel height, and not affected by the width over a particular channel width size. Therefore, microchannels with smaller channel height(about less than 2 mm) and bigger channel width (about more than 4 mm), can be attractive design for better heat removal and higher production.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.4
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• pp.747-752
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• 2009

In this paper, the MIMO(Multi-Input Multi-Output) channel characteristics for Rx antenna spacing are described in the real environment, which has LOS(Ling of Sight) and NLOS (Won-Line of Sight). We developed $2\times2$ MIMO channel measurement system at 2.3GHz Wibro Band. MIMO antenna evaluation parameters such as received power, channel capacity and spatial correlation are evaluated for standard dipole antenna with 0.25, 0.5, 0.75 and 1.0 wavelength spacing at 2-position for LOS and 4-position for NLOS. The spatial correlation is distributed more than 0.9 in most LOS case which might be intricate to operate MIMO communication. MIMO antenna design need to be focused on getting spatial diversity and reducing spatial correlation in LOS case.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.12
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• pp.1023-1030
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• 2012

The diversity techniques can benefit underwater acoustic communications when the distance between sensors is sufficiently apart, and this leads to the increases in the physical size of the communication system: thus it is very hard to practically use such systems in real-environments. Therefore, in this paper, we have collected data from real underwater cannel environments in order to analyze the usability of diversity combined with beamforming techniques. And we have estimated the fading characteristics from the measurement data, and analyzed the correlation coefficients using the estimated fading characteristics. After analyzing the estimated fading characteristics from the measurements data, we found out that by applying diversity techniques on the output signals from beamformers that perform beamforming from different multipath directions, we can reduce the distance between sensors and at the same time benefit from the diversity gain.