• The KSFM Journal of Fluid Machinery
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• v.15 no.5
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• pp.11-19
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• 2012

The main function of fuel cell manifold is to render reactants distribution as uniform as possible into a fuel cell stack. The purpose of this study is to numerically investigate the effects of stack manifold design on reactants distribution within a fuel cell stack. Four manifold designs with different manifold entrance shapes (expansion or diffuser) and different values of the extra width between the cell outer channel and manifold side wall are considered and applied to the fuel cell stack consisting of 50 cells. Since the fuel cell stack geometry involves several millions of grid points for numerical calculations, a parallel computing methodology is employed to substantially reduce the computational time and overcome the memory requirement. The numerical simulations are carried out and calculated results clearly demonstrate that both the manifold entrance shape and extra width have a substantial influence on manifold performance, controlling the degree of flow separation and entrance length for fully developed flow in the manifold channel. Finally, we suggest the optimum design of fuel cell manifold based on the simulation results.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.11
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• pp.718-725
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• 2011

Characteristics of flow boiling heat transfer in microchannels were investigated experimentally. The microchannels consisted of 9 parallel trapezoidal channels with each channel having 205 ${\mu}m$ of bottom width, 800 ${\mu}m$ of depth, $3.6^{\circ}$ of sidewall angle, and 7 cm of length. Tests were performed with R113 over a mass velocity range of 150~920 $kg/m^2s$, heat flux of 10~100 $kW/m^2$ and inlet pressures of 105~195 kPa. Flow boiling heat transfer coefficient in microchannels was found to be dominated by heat-flux. However the effect of mass velocity was not significant. Contrary to macrochannel trends, the heat transfer coefficient was shown to decrease with increasing thermodynamic equilibrium quality. A new correlation suitable for predicting flow boiling heat transfer coefficient was developed based on the laminar single-phase heat transfer coefficient and the nucleate boiling dominant equation. Comparison with the experimental data showed good agreement.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.10 s.340
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• pp.25-30
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• 2005

This paper generalizes the concept of the signal space detection to construct a fixed delay tree search (FDTS) detector which estimates a block of n channel symbols at a time. This technique is applicable to high speed implementation. Two approaches are discussed both of which are based on efficient signal space partitioning. In the first approach, symbol detection is performed based on a multi-class partitioning of the signal space. This approach is a generalization of binary symbol detection based on a two-class pattern classification. In the second approach, binary signal detection is combined with a look-ahead technique, resulting in a highly parallel detector architecture.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.7A
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• pp.659-667
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• 2002

In this dissertation, in the Turbo Code used for error correction coding of the recent digital communication systems, we propose a new S-R interleaver that has the better performance than the existing block interleaver, and the Turbo Decoder that has the parallel concatenated New structure using the MAP algorithm. For real-time voice and video services over the third generation mobile communications, the performance of two proposed methods is analyzed by the reduced decoding delay using the variable decoding method by computer simulation over multipath channels of DS-CDMA system. Also, a Modified NCMA based on conventional NCMA is proposed to improve the channel efficiency in the mobile communication system, and is investigated over the multi-user environment of DS-CDMA system through computer simulation.

• Steel and Composite Structures
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• v.12 no.1
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• pp.73-92
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• 2012

The effect of element interaction and material nonlinearity on the ultimate capacity of stainless steel plated cross-sections is investigated in this paper. The focus of the research lies in cross-sections failing by local buckling; member instabilities, distortional buckling and interactions thereof with local buckling are not considered. The cross-sections investigated include rectangular hollow sections (RHS), I sections and parallel flange channels (PFC). Based on previous finite element investigations of structural stainless steel stub columns, parametric studies were conducted and the ultimate capacity of the aforementioned cross-sections with a range of element slendernesses and aspect ratios has been obtained. Various design methods, including the effective width approach, the direct strength method (DSM), the continuous strength method (CSM) and a design method based on regression analysis, which accounts for element interaction, were assessed on the basis of the numerical results, and the relative merits and weaknesses of each design approach have been highlighted. Element interaction has been shown to be significant for slender cross-sections, whilst the behaviour of stocky cross-sections is more strongly influenced by the material strain-hardening characteristics. A modification to the continuous strength method has been proposed to allow for the effect of element interaction, which leads to more reliable ultimate capacity predictions. Comparisons with available test data have also been made to demonstrate the enhanced accuracy of the proposed method and its suitability for the treatment of local buckling in stainless steel cross-sections.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.9
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• pp.781-786
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• 2013

Multiplexing information over parallel data channels based on RF MIMO concept is possible to achieve considerable data rates over large transmission ranges with just a single transmitting element. Visual multiplexing MIMO techniques will send independent streams of bits using the multiple elements of the light transmitter array and recording over a group of camera pixels can further enhance the data rates. The proposed system is a combination of the reliance on computer vision algorithms for tracking and OOK cell frame modulation. LED array are controlled to transmit message in the form of digital information using ON-OFF signaling with ON-OFF pulses (ON = bit 1, OFF = bit 0). A camera captures image frames of the array which are then individually processed and sequentially decoded to retrieve data. To demodulated data transmission, a motion tracking algorithm is implemented in OpenCV (Open source Computer Vision library) to classify the transmission pattern. One of the most advantages of proposed architecture is Computer Vision (CV) based image analysis techniques which can be used to spatially separate signals and remove interferences from ambient light. It will be the future challenges and opportunities for mobile communication networking research.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.1
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• pp.51-59
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• 2004

We design multilevel coding(MLC) with a semi bit-interleaved coded modulation(BICM) scheme based on low density parity check(LDPC) codes. Different from traditional designs, we joint the MLC and BICM together by using the Gray mapping, which can transmit the multimedia data over several equivalent channels with different code rates. To get a good performance from signal-to-noise ratio(SNR) very close to the capacity of the additive white Gaussian noise(AWGN) channel, random regular LDPC code and a simple semi-algebra LDPC(SA-LDPC) code are discussed in MLC with parallel independent decoding(PID). Finally, the numerical results demonstrate that the proposed scheme could achieve both power and bandwidth efficiency for multimedia communication system.

• 한국정보통신설비학회:학술대회논문집
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• 2005.08a
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• pp.417-421
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• 2005

In the recent digital communication systems, the performance of Turbo Code using the error correction coding depends on the interleaver influencing the free distance determination and the recursive decoding algorithms that is executed in the turbo decoder. However, performance depends on the interleaver depth that needs many delays over the reception process. Moreover, turbo code has been known as the robust coding methods with the confidence over the fading channel. International Telecommunication Union(ITU) has recently adopted it as the standardization of the channel coding over the third generation mobile communications(IMT-2000). Therefore, in this paper, we proposed the interleaver that has the better performance than existing block interleaver, and modified turbo decoder that has the parallel concatenated structure using MAP algorithm. In the real-time voice and video service over third generation mobile communications, the performance of the proposed two methods was analyzed and compared with the existing methods by computer simulation in terms of reduced decoding delay using the variable decoding method over AWGN and fading channels for CDMA environments.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.16 no.6
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• pp.102-108
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• 2002

This paper handles the design of a real time traffic data acquisition system using loop detector and piezo-electric sensor to acquire the vehicle information EISA compatible parallel I/O interface card is designed to sample 30 I/O channels at variable rates for raw traffic data acquisition. The control software is designed to generate the traffic data informations from the raw data. The traffic data information provides vehicle length, speed, number of axles, etc. Vehicle types are detected and categorized into eleven types from the vehicle length, axles positions and axle counts information. The traffic information is formed into packet and transferred to the remote hosts through serial communications for ITS applications.

• Convergence Security Journal
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• v.21 no.1
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• pp.209-219
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• 2021

The problem of congestion in the licensed radio channels spectrum can be solved by Cognitive Radio Networks (CRN). Several algorithms exist to ensure the rendezvous between Secondary Users (SUs), they are increasingly efficient, allowing faster rendezvous under multiple scenarios. In parallel, several jamming algorithms are developed to counter rendezvous which are also improving. The goal in CRN is to ensure the rendezvous by warding such jammers with robust algorithms. In this paper, we classify various jamming techniques and analyze the performance of various well-known rendezvous algorithms under jamming attacks.